U.S. patent application number 13/300582 was filed with the patent office on 2012-11-29 for systems and methods to cool semiconductor.
Invention is credited to Bao Tran.
Application Number | 20120299175 13/300582 |
Document ID | / |
Family ID | 46323996 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120299175 |
Kind Code |
A1 |
Tran; Bao |
November 29, 2012 |
SYSTEMS AND METHODS TO COOL SEMICONDUCTOR
Abstract
Systems and methods are disclosed for fabricating a
semiconductor device by forming heat conducting nanowires on a
first side of a wafer; and depositing semiconductor structures on a
second side of the wafer.
Inventors: |
Tran; Bao; (Saratoga,
CA) |
Family ID: |
46323996 |
Appl. No.: |
13/300582 |
Filed: |
November 19, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12715374 |
Mar 1, 2010 |
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13300582 |
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11369103 |
Mar 6, 2006 |
7671398 |
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12715374 |
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Current U.S.
Class: |
257/712 ;
257/E21.505; 257/E23.09; 438/122 |
Current CPC
Class: |
H01L 2224/45164
20130101; H01L 2224/45144 20130101; H01L 2224/45178 20130101; H01L
2924/01011 20130101; H01L 2924/01044 20130101; H01L 2924/12043
20130101; H01L 27/14806 20130101; B82Y 30/00 20130101; G11C 13/0014
20130101; H01L 2924/01051 20130101; H01L 2924/01322 20130101; H01L
2924/01014 20130101; B82Y 10/00 20130101; H01L 2924/01094 20130101;
H01L 2924/3025 20130101; G11C 13/025 20130101; G11C 13/02 20130101;
H01L 2924/01025 20130101; H01L 2224/45169 20130101; H01L 2924/01028
20130101; H01L 2924/01046 20130101; H01L 2924/14 20130101; H01L
51/5012 20130101; H01L 2224/45015 20130101; H01L 2924/01031
20130101; H01L 2924/01045 20130101; H01L 2924/01056 20130101; H01L
2924/01058 20130101; H01L 2924/01076 20130101; H01L 2924/01105
20130101; H01L 2924/19042 20130101; H01L 2924/30107 20130101; H01L
2924/01047 20130101; H01L 2924/01082 20130101; G11C 2213/79
20130101; H01L 2924/01005 20130101; H01L 2924/01019 20130101; H01L
2924/0103 20130101; H01L 2924/1433 20130101; H01L 2924/01327
20130101; H01L 2924/01073 20130101; H01L 2924/19041 20130101; H01L
23/4952 20130101; H01L 2924/01004 20130101; H01L 2924/10253
20130101; H01L 2924/12043 20130101; G11C 23/00 20130101; H01L
2924/12041 20130101; H01L 2924/181 20130101; Y10S 977/734 20130101;
H01L 2924/12032 20130101; H01L 2924/12042 20130101; B82Y 20/00
20130101; H01L 2224/48624 20130101; H01L 2924/01003 20130101; H01L
2924/01006 20130101; H01L 2924/01016 20130101; H01L 24/85 20130101;
H01L 24/45 20130101; H01L 2924/01012 20130101; H01L 2924/0104
20130101; H01L 2924/01072 20130101; H01L 2224/48624 20130101; H01L
2924/01083 20130101; H01L 2924/181 20130101; H01L 2924/01052
20130101; H01L 2224/05624 20130101; G11C 13/0019 20130101; H01L
2924/01047 20130101; H01L 2924/01024 20130101; H01L 2924/10329
20130101; H01L 2224/45015 20130101; H01L 2924/01078 20130101; H01L
2924/01077 20130101; H01L 2924/01074 20130101; H01L 2924/014
20130101; H01L 2924/0102 20130101; H01L 2924/01023 20130101; G11C
2213/17 20130101; H01L 2924/01049 20130101; H01L 2924/01015
20130101; H01L 2924/01033 20130101; H01L 2924/01075 20130101; H01L
2924/30105 20130101; G11C 13/04 20130101; H01L 2924/01013 20130101;
H01L 2924/01079 20130101; H01L 2924/12044 20130101; H01L 2924/1306
20130101; H01L 2924/01027 20130101; H01L 2924/01022 20130101; H01L
2924/1306 20130101; H01L 2924/00 20130101; H01L 2924/00 20130101;
H01L 2924/00014 20130101; H01L 2924/00 20130101; H01L 2924/00
20130101; H01L 2924/00 20130101; H01L 2924/20752 20130101; H01L
2924/0002 20130101; H01L 2924/00 20130101; H01L 2924/01029
20130101; H01L 2224/45173 20130101; Y10S 977/724 20130101; H01L
2224/45144 20130101; H01L 2924/0105 20130101; H01L 2924/13091
20130101; H01L 2924/3011 20130101; H01L 2924/01061 20130101; H01L
2924/01006 20130101; H01L 24/48 20130101; H01L 2924/01007 20130101;
H01L 2924/01038 20130101; H01L 2924/01042 20130101; H01L 2924/01063
20130101; H01L 2924/12032 20130101; H01L 2924/12042 20130101; H01L
2924/19043 20130101 |
Class at
Publication: |
257/712 ;
438/122; 257/E23.09; 257/E21.505 |
International
Class: |
H01L 23/433 20060101
H01L023/433; H01L 21/58 20060101 H01L021/58 |
Claims
1. A method for fabricating a semiconductor device, comprising:
forming heat conducting nanowires on a first side of a wafer;
depositing semiconductor structures on a second side of the
wafer.
2. The method of claim 1, comprising forming 3D heat conducting
nanowires on the first side of the wafer.
3. The method of claim 1, comprising depositing conductive filler
between the nanowires; and planarizing the nanowires and the
conductive filler
4. The method of claim 1, wherein planarizing comprises performing
chemical-mechanical planarization.
5. The method of claim 1, comprising patterning and etching
cavities on the first side; depositing an interface material on the
cavities; forming nanotubes on the cavities; and depositing a
conductive filler between the nanowires.
6. A method for fabricating a heat remover, comprising: forming
heat conducting nanowires on a first side of a substrate; providing
a heat conducting interface layer on a second side of the
substrate; and mounting the bottom of the substrate to an
electronic device.
6. The method of claim 6, comprising forming one or more cooling
fins above heat conducting nanowires.
7. The method of claim 6, comprising attaching an external cooler
to the electronic device.
8. The method of claim 7, wherein the external cooler comprises one
of: a heat spreader, a heat pipe, a heat sink.
9. The method of claim 6, comprising removing the nanowires to form
channels to circulate a heat conducting fluid therein.
10. A semiconductor device, comprising: a die having heat
conducting nanowires on a first side of the die and semiconductor
structures on a second side of the die; and an external cooler to
remove heat from the nanowires.
11. The semiconductor device of claim 10, wherein the nanowires
comprise one of: rod shape, cone shape, spring shape,
three-dimensional shape.
12. The semiconductor device of claim 10, comprising an
encapsulation around the die having microchannels therein.
13. The semiconductor device of claim 12, comprising: a thermal
transport fluid disposed in the microchannels.
14. The semiconductor device of claim 12, comprising a pump that
circulates the thermal transport fluid through the
microchannels.
15. The semiconductor device of claim 12, comprising a heat
exchanger.
16. The semiconductor device of claim 10, wherein the nanotubes are
oriented generally perpendicular to the die.
17. The semiconductor device of claim 10, comprising a heat remover
between the die and the external cooler, the heat remover having
heat conducting nanowires on a first surface and a heat conducting
interface layer on a second surface.
18. The semiconductor device of claim 17, wherein the heat remover
is etched to provide fins.
19. The semiconductor device of claim 10, wherein the die
comprises: patterned cavities etched on the first side; and an
interface material deposited on the cavities;
20. The semiconductor device of claim 10, wherein the die comprises
a conductive filler deposited between the nanowires.
Description
[0001] This application is a continuation of application Ser. No.
12/715,374 filed Mar. 1, 2010 which is a continuation of U.S.
application Ser. No. 11/369,103, which is a continuation of
application Ser. No. 11/690,937, which in turn is a continuation in
part (CIP) application claiming priority to U.S. application Ser.
No. 11/064,363, filed Feb. 23, 2005 and entitled "Nano Electronic
IC Packaging", the content of which is incorporated by
reference.
BACKGROUND
[0002] The present invention relates to arrays of nano-electronic
devices.
[0003] The success of the PC, networking, and
communications-product markets has been driven largely by Moore's
Law, which says that IC density doubles every 18 months. Experts
predict that CMOS scaling will continue to follow Moore's Law for
at least another decade, but potential bottlenecks could derail
market success if not solved by new design or device technology.
One of these bottlenecks is integrating precision analog and
wideband RF circuitry in standard digital CMOS.
[0004] Applying Moore's Law to mixed-signal (analog and digital)
chips is a significant challenge. Higher transistor density and
lower silicon cost allow more complex digital circuitry, but most
wireless or wireline communications products require integrating
RF, analog, and memory with the digital logic. Advancements in
submicron CMOS processing greatly benefit digital logic and memory,
but result in poor analog and RF performance. Transistor matching,
noise, resistors, capacitors, and inductors drive the density of
analog circuits, and these parameters do not necessarily benefit
from transistor scaling.
[0005] To compound the problem, digital-circuit design continues to
benefit from advances in logic synthesis, accelerating the
time-to-market of digital products. Analog circuit design has not
historically benefited significantly from CAD-tool advances, and
remains a hand-crafted art. Consequently, analog circuits will be a
limiting factor for mixed-signal SoC, both in terms of the
increasingly larger percentage of the die these circuits occupy,
and in terms of their design time.
[0006] Due to increasing speed and density of modern integrated
circuits (ICs), the power generated by these ICs also increases,
often in geometric proportion to increasing density and
functionality. To dissipate the heat, semiconductor ICs
conventionally use large and expensive IC packaging having
externally mounted, finned heat sinks coupled to the ceramic or
plastic encapsulated IC. In the current art, relatively large
interface-thermal-resistances are added when the die is "attached"
to a heat spreader, heat pipe or heat sink. These multiple
interfaces have the undesired side effect of increasing total die
to heat sink resistance and making heat transfer more
difficult.
[0007] To improve heat removal, flip-chip mounted processor ICs and
light emitting diodes (LEDs) have been developed. A flip chip is
one type of IC mounting which does not require any wire bonds.
Instead the final wafer processing step deposits solder beads on
the IC pads. After cutting the wafer into individual dice, the
"flip chip" is then mounted upside down in/on the package and the
solder reflowed. Flip chips then normally will undergo an underfill
process which will cover the sides of the die, similar to the
encapsulation process. The upside down (i.e. flipped) mounting of
the die leaves the IC pads and their solder beads facing down onto
the package, while the back side of the die faces up. Heat
generated by the die is extracted through the substrate to the back
surface of the IC. A heat transfer bonding layer may be utilized to
enhance heat conduction by reducing interfacial heat transfer
resistance created by air gaps and surface irregularities.
Typically, this layer may be composed of a thermal grease or
thermally conductive epoxy. These materials, while better that
solid surface/surface contact, still have a relatively poor thermal
conductivity when compared to solid metals. As a result, the
backside IC surface interface still presents a significant thermal
resistance which limits the power that can be extracted from the
IC.
[0008] In the LED flip-chip arrangement, the active light emitting
layers are grown on a transparent substrate, front-side contacts
are fabricated on the light emitting layers, and the die is bonded
front-side down to a lead frame, heat sink, or sub-mount so that
light is emitted through the transparent substrate. The flip-chip
arrangement places the heat generating active layers near the
heat-sinking substrate or sub-mount, and also minimizes contact
shadowing. However, as noted in US Patent Application No.
20050006754, LED flip-chip bonding has certain disadvantages.
Soldering is usually employed in the die-bonding. This involves
substantial heating near the active layers which can degrade the
device. If the die is bonded to a sub-mount, then two soldering
processes are involved (a die-to-sub-mount soldering process and a
sub-mount soldering process). The first soldering process is
preferably performed at higher temperature so that the first solder
bonds remain stable during the second soldering process. Moreover,
relatively thick solder bumps are often employed for reliability.
These thick solder bumps can limit thermal transport out of the
light emitting diode die.
[0009] US Patent Application No. 20030117770 discloses a process of
forming a thermal interface that employs carbon nano-tubes to
reduce thermal resistance between an electronic device and a heat
sink. Carbon nanotubes are commonly prepared by arc discharge
between carbon electrodes in an inert gas atmosphere. The product
is generally a mixture of single-wall and multi-wall nanotubes,
although the formation of single-wall nanotubes can be favored by
the use of transition metal catalysts such as iron or cobalt.
Single-wall nanotubes can also be prepared by laser ablation.
Bundles of aligned nano-tubes receive injected polymeric material
in molten form to produce a composite which is placed between the
electronic device and the heat sink. The nano-tubes are aligned
parallel to the direction of heat energy. However, the polymeric
filler does little to spread heat laterally, potentially creating
localized hot spots on the device surface. The use of bundles of
aligned carbon nano-tubes may result in reduced thermal conduction
as well.
[0010] US Patent Application Publication US2003/231471 discloses an
integrated circuit package that utilizes single wall or double wall
carbon nano-tube arrays grown subsequent to the deposition of CVD
diamond films. Due to the roughness of CVD diamond films, carbon
nano-tubes are utilized to aid in making thermal contact between
the surfaces of the circuit silicon die and of the integrated heat
spreader. The interstitial voids between the nano-tubes are not
filled in order to maintain flexibility.
[0011] US Patent Application No. 20050046017 discloses heat sink
structures employing carbon nanotube or nanowire arrays to reduce
the thermal interface resistance between an integrated circuit IC
and the heat sink. Carbon nanotube arrays are combined with a
thermally conductive metal filler disposed between the nanotubes.
This structure produces a thermal interface with high axial and
lateral thermal conductivities.
SUMMARY
[0012] In one aspect, systems and methods are disclosed for
fabricating a semiconductor device by forming heat conducting
nanowires on a first side of a wafer; and depositing semiconductor
structures on a second side of the wafer.
[0013] In another aspect, a method for fabricating a heat remover
includes forming heat conducting nanowires on a first side of a
substrate; providing a heat conducting interface layer on a second
side of the substrate; and mounting the bottom of the substrate to
an electronic device.
[0014] In yet another aspect, a semiconductor device includes a die
having heat conducting nanowires on a first side of the die and
semiconductor structures on a second side of the die; and an
external cooler to remove heat from the nanowires. The
semiconductor device may optionally include a heat remover between
the die and the external cooler, the heat remover having heat
conducting nanowires on a first surface and a heat conducting
interface layer on a second surface.
[0015] Systems and methods are disclosed to process a semiconductor
substrate by fabricating a first layer on the substrate using
macroscale semiconductor fabrication techniques; fabricating a
second layer above the first layer having one or more nano-bonding
areas; self-assemblying one or more nano-elements; and bonding the
nano-elements to the nano-bonding areas.
[0016] In one aspect, the present application discloses a hybrid
electronic device, comprising:
[0017] a substrate;
[0018] a first layer fabricated using semiconductor fabrication
techniques;
[0019] a second layer formed above the first layer, the second
layer having one or more nano-bonding areas;
[0020] one or more nano-elements self-assembled to the second layer
molecular bonding areas.
[0021] In another aspect, the present application discloses a
reconfigurable electronic device, comprising:
[0022] a substrate;
[0023] a first layer fabricated using semiconductor fabrication
techniques;
[0024] a second layer formed above the first layer, the second
layer having one or more nano-bonding areas;
[0025] one or more reconfigurable nano-elements self-assembled to
the second layer molecular bonding areas.
[0026] In another aspect, the present application discloses a
memory device, comprising
[0027] an array of memory cells disposed in rows and columns and
constructed over a substrate, each memory cell comprising a first
signal electrode, a second signal electrode, and a nano-layer
disposed in the intersecting region between the first signal
electrode and the second signal electrode;
[0028] a plurality of word lines each connecting the first signal
electrodes of a row of memory cells; and
[0029] a plurality of bit lines each connecting the second signal
electrodes of a column of memory cells.
[0030] In another aspect, the present application discloses a data
storage device, comprising
[0031] a platter having a layer of nano-material; and
[0032] a head capable of reading or writing to the nano-material in
the layer of nano material.
[0033] In still another aspect, the present application discloses
an optical data storage device, comprising a first light source;
and
[0034] a substrate disposed with a layer of nano particles, wherein
the energy structure of the nano particles is changed after the
nano particles are illuminated by the light source.
[0035] In yet another aspect, the present application discloses an
optical interconnection system, comprising
[0036] a substrate;
[0037] an input optical signal;
[0038] an output optical signal; and
[0039] an optical circuit disposed over the substrate, wherein the
optical circuit is formed by nano elements in a self-assemble
process.
[0040] In another aspect, the present application relates to a
photon sensing device, comprising:
[0041] a semiconductor layer comprising charge readout circuit;
and
a photon sensitive layer disposed over the semiconductor layer
comprising one or more of photon sensing elements formed by nano
elements, such photo sensitive elements being capable of converting
photons to electric charges, wherein photon induced charges are
adapted to be transferred to the readout circuit in the
semiconductor layer.
[0042] In still another aspect, the present application relates to
a photon sensing device comprising:
[0043] a semiconductor layer comprising a plurality of transistors;
and
[0044] a photon sensitive layer disposed over the semiconductor
layer comprising one or more of photon sensing elements formed by
nano elements, such photo sensitive elements being capable of
converting photons to electric charges, wherein each photo
sensitive element is electrically connected with one or more
transistors in the semiconductor layer.
[0045] In still another aspect, the present application relates to
a nano display device, comprising
[0046] an array of light-emitting cells disposed in rows and
columns and constructed over a substrate, each light emitting cell
comprising a first electrode, a second electrode, and a
light-emitting nano material disposed in the intersecting region
between the first electrode and the second electrode, wherein the
light-emitting nano material is capable of emitting light when a
voltage is applied between the first electrode and the second
electrode.
[0047] In another aspect, the present application provides a
wireless communication device, comprising:
a) a nano antenna having an nano element providing electrical
resonance to transmit and receive wireless signals; b) a
transceivers coupled to the nano antenna; and c) a processor core
coupled to the nano antenna and the transceivers for controlling
the nano antenna and processing the wireless signals transmitted
and received.
[0048] In another aspect, the present application provides a
package for integrated circuit, comprising
[0049] a chip having a plurality of chip pads adapted to receive
the variety of signals from or to output the same to an external
circuit;
[0050] a lead frame having a plurality of contact points each
corresponding to a chip pad; and
[0051] bonding wires electrically connecting the chip pads and the
respective contact points on the lead frame, wherein the bonding
wires comprise a nano material.
[0052] Advantages may include one or more of the following. The
system is compact, power efficient, and dense. The molecular
electronics in the above system extend the miniaturization that has
driven the density and speed advantages of the integrated circuit
in accordance with Moore's Law.
[0053] The present disclosure will show in detail NOR arrays.
Collections of NOR gates are universal, so this substrate is
sufficient to perform any computation. Upon reading of the present
disclosure, the person skilled in the art will be able to realize
arrays based on a different kind of logic, e.g. NAND logic.
[0054] An advantage of the present invention, is it provides a
universal, programmable structure using conventional semiconductor
elements and nano elements which integrates device from nanoscale
to microscale. The disclosed architecture also supports micro- to
nanoscale interfacing for communication with conventional
integrated circuits.
[0055] A further advantage of the present invention is that the
architecture disclosed logic functionality, minimalism, defect
tolerance, and compatibility with emerging, bottom-up, nanoscale
fabrication techniques.
[0056] An additional advantage of the present invention is that the
integrated nano-semiconductor architecture can utilize a wide range
of nano elements such as nano particles, nano tubes, nano wires,
nano bridges, etc. which is greatly beneficial to system
optimization and minimization.
[0057] Another advantage of the present invention is that the
integrated nano-semiconductor architecture provides conversion and
processing of electronic, optical, wireless signals, as well as
data memory, communication, photo and chemical sensing, power
generation, and display capabilities. The invention architecture is
ideally suited for applications having a plurality of
functionalities provided by system-on-chip or system in one module.
Device cost and sizes can therefore be significantly reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] The present system will be better understood when
consideration is given to the following detailed description
thereof. Such description makes reference to the annexed drawings,
wherein:
[0059] FIG. 1 is a block diagram of a programmable analog
nano-array in accordance with the present invention.
[0060] FIG. 2 is a schematic diagram of a first embodiment of a
programmable nano-cell in accordance with the present
invention.
[0061] FIG. 3 is a schematic diagram of a second embodiment of a
programmable nano-cell in accordance with the present
invention.
[0062] FIG. 4 is a block diagram of a wireless communication device
comprising nano antenna in accordance with the present
invention.
[0063] FIG. 5 is a schematic diagram of the architecture of memory
devices comprising nano elements in accordance with the present
invention.
[0064] FIGS. 6A-6B show perspective views of an exemplary single
molecule magnet data storage device, in this case a disk drive in
accordance with the present invention.
[0065] FIG. 7 is a diagram of a system having an array of
nano-based chemical and biological sensors in accordance with the
present invention.
[0066] FIG. 8 is an exemplary diagram of an array of nano-based
image sensors in accordance with the present invention.
[0067] FIG. 9 depicts a cross-sectional view of a flexible
photovoltaic cell.
[0068] FIG. 10 shows an exemplary power generation system.
[0069] FIGS. 11-16 show exemplary processes for fabricating cooling
structures.
DESCRIPTION
Programmable Analog Nano-Array and Nano-Cells
[0070] FIG. 1 is a block diagram of a programmable array using
nano-analog electronics in an integrated circuit configuration.
nano-analog array 10 includes a plurality of programmable analog
cells 12 arranged along a plurality of interconnect channels that
form a switching network which includes bus lines 13 and 14 for
routing analog signals. Input and output signals are transferred
between analog cells 12 and buses 13 and 14 by means of analog
switching devices such as transmission gates through which analog
signals can be transferred with little or no distortion. Control
over the switching devices is provided by digital signals that may
be stored in a memory such as random access memory (RAM) or
read-only memory included in the cell. Alternatively, a centralized
memory array can be used to control the switching devices in all of
the analog cells 12. As a further alternative, external memory can
be used if provision is made for routing the binary control signals
to individual analog cells 12. As yet a further alternative,
control over the switching devices may be directly provided by
other digital circuitry instead of a memory array. Signal routing
between bus 13 and bus 14 is provided by switching devices 19.
[0071] FIG. 2 is a schematic diagram of a programmable analog cell
12 including an active circuit 22, switches 23-32, programmable
nano-elements 33-39, and a static random access memory (SRAM) 40.
Input signals are received on input terminals 15 and 16 and output
signals are produced on output terminals 17 and 18. Output
terminals 17 and 18 are shown as connected together to drive
horizontal and vertical conductors 13 and 14. In an alternative
embodiment, output terminals 17 and 18 could be isolated such that
active circuit 22 drives output terminal 17 and another active
circuit included in programmable analog cell 12 drives output
terminal 18.
Fabrication of Nano Electronic Components and Systems
[0072] As described below, the nano-elements can be formed last in
the fabrication sequence in one embodiment. Conventional
semiconductor structures are formed as is conventional, which for
example includes semiconductor devices produced by photolithography
or E-beam lithography. During the next to the last conventional
step, gold electrodes are formed. Then a resist layer is formed
over the last layer, and selective etching is performed to expose
the gold electrodes. A solution containing the nano-elements are
spin-coated on top, where the nano-elements self-assemble to form
one or more devices such as resistors, capacitors, inductors,
antennas, emitters and sensors, among others. Other coating
techniques compatible with the present invention include hopper
coating, curtain coating. The nano-elements bond to preselected
spots on the gold electrodes and self-assemble to form a regular
array of resistors, capacitors, inductors, acoustic emitters,
acoustic sensors, light emitters, light sensors, among others. In
one embodiment, the nano-elements do not need patterning. In
another embodiment, patterning of the nano-elements is accomplished
by any of the generally available photolithographic techniques
utilized in semiconductor processing. However, depending on the
particular material chosen, other techniques such as laser ablation
or inkjet deposition or electrostatic deposition may also be
utilized to pattern the nano-elements. In particular nanoimprint
lithography can be used to pattern the nano-elements.
[0073] In another embodiment, the substrate may be formed from
silicon, gallium arsenide, indium phosphide, and silicon carbide to
name a few. Active devices will be formed utilizing conventional
semiconductor processing equipment. Other substrate materials can
also be utilized, depending on the particular application in which
the array will be used. For example various glasses, aluminum oxide
and other inorganic dielectrics can be utilized. In addition,
metals such as aluminum and tantalum that electrochemically form
oxides, such as anodized aluminum or tantalum, can be utilized.
Those applications utilizing non-semiconductor substrates, active
devices can also be formed on these materials utilizing techniques
such as amorphous silicon or polysilicon thin film transistor (TFT)
processes or processes used to produce organic or polymer based
active devices. Accordingly, the present system is not intended to
be limited to those devices fabricated in silicon semiconductor
materials, but will include those devices fabricated in one or more
of the available semiconductor materials and technologies known in
the art.
[0074] The process of creating the first layer of electrical
conductors may consist of sputter deposition, electron beam
evaporation, thermal evaporation, or chemical vapor deposition of
either metals or alloys and will depend on the particular material
chosen for the electrical conductors. Conductive materials such as
polyaniline, polypyrrole, pentacene, thiophene compounds, or
conductive inks, may utilize any of the techniques used to create
thin organic films. For example, screen printing, spin coating, dip
coating, spray coating, ink jet deposition and in some cases, as
with PEDOT, thermal evaporation are techniques that may be
used.
[0075] Depending on the particular memory device being fabricated,
the electrical contacts may be created either on a substrate or
directly on the semiconducting polymer film. Patterning of the
electrical conductors is accomplished by any of the generally
available photolithographic techniques utilized in semiconductor
processing. However, depending on the particular material chosen,
other techniques such as laser ablation or inkjet deposition may
also be utilized. In particular one can utilize nanoimprint
lithography or techniques for forming nanowires. For additional
information on nanoimprint lithography see for example, U.S
Application No. 20030230746, the content of which is incorporated
by reference. Combinations of different conductive materials may
also be utilized that might result in very different processes
being utilized. For example it may be desirable to utilize PEDOT as
the material for the lower electrical traces and indium tin oxide
for the upper electrical traces if erasure via light is desired.
Another embodiment may use a typical metal such as tantalum,
tungsten, or even highly doped polysilicon for electrical
conductors deposited on the substrate and an organic conductor such
as PEDOT for electrical conductors deposited on the semiconducting
polymer film. The process of creating a third layer of electrical
conductors on a second semiconducting polymer film, for the
applications utilizing such a layer, can be the same or similar to
that used for the first layer, depending on whether the electrical
conductor is the same as that used for the first layer electrical
conductors. The process of creating a semiconducting polymer film
will depend on the particular binder and organic dopant chosen. The
particular binder and organic dopant chosen will depend, for
example, on the particular electronic properties desired, the
environment in which the device will be used, and whether a thin
dielectric film will be utilized. Depending on the particular
binder chosen the appropriate solvents are utilized that provide
sufficient solubility for both the binder and the organic dopant as
well as providing appropriate viscosity for the particular coating
or casting process chosen. An exemplary process for creating a
semiconducting polymer layer uses HPLC grade tetrahydrofuran as a
solvent to dissolve the binder bisphenol-A-polycarbonate and a
mono-substituted diphenylhydrazone compound (DPH) in appropriate
concentrations to obtain the desired electrical properties. If a
substrate is utilized, the composition and properties of the
substrate are also taken into consideration, in order to obtain
good adhesion between the substrate and the semiconductor polymer
layer, as well as the electrical conductors and the semiconductor
polymer layer. Adhesion promoters or surface modification may also
be utilized. In addition, a planarizing layer may also be utilized,
for example, when electrical conductors are formed on rather than
in the substrate. The process of creating a multilayer
semiconductor polymer film, for those applications utilizing such a
structure, can be the same or similar as the process used to create
the first layer, depending on whether the binder or organic dopant
is the same as that used for the first layer. The process of
forming a dielectric thin film, will depend on the particular
material chosen, and may consist of, for example, sputter
deposition, chemical vapor deposition, spin coating, or
electrochemical oxidation. For example, tantalum electrical
conductors may be deposited using conventional sputtering or
electron beam deposition techniques. After the tantalum is
deposited a thin tantalum oxide layer may be formed
electrochemically. This process may be performed prior to or after
photolithographic processing to define the electrical conductors.
Another embodiment may utilized a thin silicon oxide layer
deposited on the electrical conductors or on the semiconducting
polymer film depending on which electrical conductor is chosen to
have the thin dielectric film. A thin silicon oxide film may be
deposited by any of a wide range of techniques, such as sputter
deposition, chemical vapor deposition, or spin coating of a spin on
glass material, to name a few. Still another embodiment may utilize
a thin non-conducting polymer layer, such as the binder polymer,
deposited on the appropriate electrical conductors. Other
embodiments may utilize self assembled monolayers or silane
coupling agents to produce a thin dielectric film. The process of
creating a second or multilayer dielectric thin film, for those
applications utilizing such a structure, can be the same or similar
as the process used to create the first layer, depending on whether
the thin dielectric film is the same as that used for the first
layer. The process of creating the second layer of electrical
conductors will depend, for example, on the particular binder and
organic materials chosen as well as the presence or absence of the
thin dielectric film and its chemical composition. For example, a
polyimide binder will typically sustain higher temperatures than a
polyethylene binder will. Thus, thermal or electron beam deposition
of tungsten or platinum electrical conductors may be used on a
polyimide binder whereas chemical vapor deposition, spin coating or
thermal evaporation of an organic conductor may be desirable for a
polyethylene binder. The particular deposition process utilized
will also depend on the degree of defects generated in either the
thin dielectric film if used or the semiconducting polymer film. In
addition, the particular process as well as the process parameters
will also be chosen to optimize adhesion between the film or films
to which the electrical conductor material is deposited on. The
process of creating a fourth layer of electrical conductors, for
those applications utilizing such a structure, can be the same or
similar as the processes used to create the first through third
layers, depending on whether the fourth layer is the same as that
used for the first layer. A passivation layer can be used to
protect the semiconducting polymer film from damage and
environmental degradation when appropriate. For example, a
passivation layer providing a barrier to oxygen permeation can be
desirable when utilizing a memory device having an acceptor organic
dopant or functional group because oxygen is a potential electron
trap. In addition, depending on the particular organic dopant and
electrical conductors utilized it may also be desirable to utilize
a passivation layer providing a moisture barrier to reduce
corrosion. Further depending on whether active devices are present
an electrostatically dissipating or shielding film may also be
desirable.
[0076] Due to the nano-structure, the absolute capacitance values
of programmable nano-elements 33-39 are well controlled using
self-assembly processes. Additional degree of matching accuracy can
be attained if programmable elements 33-39 are carefully laid out
on the die. Such matching accuracy results in a given binary
control chemical structure producing substantially equal
capacitances when applied to each of the programmable elements
33-39. For this reason, operations of active circuit 22 can be
controlled using ratios of programmable resistance, capacitance, or
inductance whenever possible. For example, in one embodiment where
the nano-elements 33-39 are capacitors, if it is desired to operate
amplifier 22 with a closed loop gain of 35/32, a binary control
chemical structure "35" is applied to control programmable
capacitor 39 and a binary control chemical structure "32" is
applied to control programmable capacitor 33. The resulting
capacitance ratio is 35/32.
[0077] Active circuit 22 is shown as an amplifier having inverting
and non-inverting inputs and an output. Analog cell 12 can also
include comparators and other types of active circuits, and can
include more than one active circuits of the same type. For
example, a single cell can incorporate several amplifiers
controlled by programmable nano-elements 33-39 that act as
capacitors to operate as an active filter. Active circuit 22
typically includes an output buffer stage (not shown) for driving
the capacitances and the load capacitances of terminals 17 and
18.
[0078] SRAM 40 comprises memory storage for controlling the
operation of switches 23-32 and switches included in programmable
capacitors 33-39. To simplify the figure, such control is indicated
by the dotted line from SRAM 40 to switches 23-26 and programmable
capacitors 33-36. Switches 23-26 and programmable capacitors 33-36
can alternatively be controlled by other types of memory, such as
read only memory, or with combinational logic.
[0079] It should be noted that programmable analog cell 12 can
alternatively be implemented with programmable nano-elements that
include passive elements other than switchable capacitors, such as
programmable nano-resistors or programmable nano-inductors.
Dynamically Reconfigurable Logic-Analog Devices
[0080] In one embodiment, a field programmable array includes a
matrix of configurable logic and/or analog blocks embedded in a
programmable routing mesh. Each configurable logic/analog block
(CLAB) can provide one or more of the functions provided by an AND
gate, flip-flop, latch, inverter, NOR gate, exclusive OR gate,
resistor, capacitor, inductor, LED, light sensor, as well as
combinations of these functions to form more complex functions. The
particular function performed by the CLAB is determined by control
signals that are applied to the CLAB from a control logic circuit.
The control logic circuit is formed integrally with, and as part
of, the integrated circuit on which the CLAB is formed. If desired,
control information can be stored and/or generated outside of this
integrated circuit and transmitted to the CLAB. The actual set of
control bits provided to each CLAB on the integrated circuit
depends upon the functions that the CLAB and, more globally, the
integrated circuit are to perform. Each CLAB typically has a
plurality of input and output pins, and a set of programmable
interconnect points (PIPs) for each input and output pin. The
general interconnect structure of the field programmable array
includes a plurality of interconnect segments and a plurality of
PIPs, wherein each interconnect segment is connected to one or more
other interconnect segments by programing an associated PIP. A
field programmable array also includes an access PIP that either
connects an interconnect segment to an input pin or an output pin
of the CLAB. Because the PIPs are programmable, any given output
pin of a CLAB is connectable to any given input pin of any other
desired CLB. Thus, a specific field programmable array
configuration having a desired function is created by selected
generation of control signals to configure the specific function of
each CLAB, together with selected generation of control signals to
configure the various PIPs that interconnect the CLABs. Each PIP
typically includes a switch such as a single pass transistor. The
state of conduction, i.e. whether the switch is opened or closed,
is controlled by application of the control signals discussed above
to a transistor control terminal, e.g. a gate. The state of the
control signal stored in a latch determines whether a pass
transistor (PIP) is turned on or off, thereby opening or closing a
path in the field programmanble interconnect, as described in U.S.
Pat. No. 5,581,198, the contents of which is incorporated by
reference. In various embodiments, single molecule magnet (SMM)
cells or single molecule optical storage cells as described in this
application are used to implement PIPs to increase number of PIPs
that can be fit onto an integrated circuit. In one embodiment, the
SMMs replace RAMs coupled to switches or pass transistors as
described in the '198 patent. In another embodiment, the SMMs
operate both as storage and switch, namely that as programmed, the
SMMs are positioned in predetermined positions that link various
interconnected segments to program the field programmable array. In
yet another embodiment, the PIP can be a nanobridge. The nanobridge
includes a thin layer of copper sulfide that separates a copper
electrode from a titanium electrode. The copper whisker is grown
and dissolved across a metal-copper sulphide-metal sandwich. When a
sufficient voltage is applied, copper ions migrate up through the
copper sulfide dielectric, forming a nanoscale whisker that
eventually connects the two electrodes part of the interconnect
structure described above. Applying a programming voltage to the
nanobridge structure causes a low-resistance conduction path to
form through a dielectric material, shorting together two
electrodes. Applying a reverse bias causes the ions to migrate away
from the titanium, in effect taking down the bridge. In one
embodiment, the nano-bridge is used as a dynamically reconfigurable
device where programming voltages are used to establish links
between elements of the reconfigurable device. Alternatively, a
solid, silver atomic-laden chalcogenide electrolyte can be used as
the sandwiched layer with silver being deposited on the electrode
to form the bridge when in the on-state.
[0081] Alternatively, in place of SMMs, electric field activated
switches can be used. For example, United States Patent Application
20020114557 provides a molecular system for nanometer-scale
reversible electronic and optical switches, specifically, electric
field-activated molecular switches that have an electric field
induced band gap change that occurs via a molecular conformation
change or a tautomerization. Changing of extended conjugation via
chemical bonding change to change the band gap is accomplished by
providing the molecular system with one rotating portion (rotor)
and two or more stationary portions (stators), between which the
rotor is attached. The molecular system of the present invention
has three branches (first, second, and third branches) with one end
of each branch connected to a junction unit to form a "Y"
configuration. The first and second branches are on one side of the
junction unit and the third branch is on the opposite side of the
junction unit. The first branch contains a first stator unit in its
backbone, the junction unit comprises a second stator unit, and the
first branch further contains a rotor unit in its backbone between
the first stator unit and the second stator unit. The second branch
includes an insulating supporting group in its backbone for
providing a length of the second branch substantially equal to that
of the first branch, wherein the rotor unit rotates between two
states as a function of an externally-applied field. In other
embodiments, a molecule called a rotaxane or a catenane trapped
between two metal electrodes can be switched from an ON state to an
OFF state by the application of a positive bias across the
molecule. The ON and OFF states differed in resistivity by about a
factor of 100 and 5, respectively, for the rotaxane and
catenane.
[0082] In one embodiment, the nano-elements include nanobridge. The
nanobridge includes a thin layer of copper sulfide that separates a
copper electrode from a titanium electrode. The copper whisker is
grown and dissolved across a metal-copper sulphide-metal sandwich.
When a sufficient voltage is applied, copper ions migrate up
through the copper sulfide dielectric, forming a nanoscale whisker
that eventually connects the two electrodes. Applying a programming
voltage between the two electrodes in the nanobridge structure
causes a low-resistance conduction path to form through a
dielectric material, shorting together two electrodes. Applying a
reverse bias voltage between the two electrodes causes the ions to
migrate away from the titanium, in effect taking down the bridge,
that is, the configuration of the nanobridge structure is removed.
In one embodiment, the nano-bridge is used as a dynamically
reconfigurable device where programming voltages are used to
establish links between elements of the reconfigurable device.
Applications include Field Programmable Gate Array (FPGA). The
semiconductor elements in the first layer or the spin-coated
nano-elements in the second layer form a Field Programmable Gate
Array. At least one of the semiconductor elements in the first
layer or the nano-elements are reconfigurable.
[0083] Alternatively, a solid, silver atomic-laden chalcogenide
electrolyte can be used as the sandwiched layer with silver being
deposited on the electrode to form the bridge when in the
on-state.
[0084] FIG. 3 shows another embodiment having a series chain of
molecular or nano-elements 140 and a means for accessing the chain.
In the embodiment shown in FIG. 3, the nano-elements 140 are
resistors. The series chain 140 has a plurality of two terminal
molecular elements connected in series. The series chain 140 has a
first element 113, a last element 115, and one or more intermediate
molecular elements 112. Each of the intermediate molecular elements
112 is connected to the molecular element adjacent to it at a node,
of which node 143 is typical. One terminal 150 of the first
molecular element is connected to a first terminal 114. The other
terminal 151 of the first molecular element 113 is connected to the
first intermediate molecular element at node 142. Similarly, the
last molecular element 115 has one of its terminals 156 connected
to the adjacent intermediate molecular element at node 155. The
other terminal 157 of the last element 115 is connected by the
accessing means to a second terminal 116. At least one of the
terminals 150 and 157 is accessible to an external circuit
connected to the apparatus of the present invention. The accessing
means connects a selected one of the nodes to a third terminal
118.
[0085] In one embodiment, the nano-elements are resistors. Other
embodiments, however, in which the nano-elements are capacitors,
inductors, or a combination of one or more of these three types of
molecular elements or nano-elements will be obvious to those
skilled in the art. In one version, each of the molecular elements
provides the same impedance (for the resistor embodiment),
capacitance (for the capacitor embodiment), or inductance (for the
inductor embodiment). Embodiments in which the molecular elements
are of different values will also be obvious to those skilled in
the art.
[0086] In the resistor embodiment, each element in the series chain
140 has a series combination of two resistive elements. In one
embodiment, the first such element is chosen to have a positive
temperature coefficient, and the second such element is chosen to
have a negative temperature coefficient. The temperature
coefficients in question are selected such that the series or
parallel combination of the two elements is a resistive element
having an essentially zero temperature coefficient.
[0087] A switch 144 is provided for connecting a selected node to
the terminal 118. The switch 144 in turn includes a selector (not
shown) to select which node is to be connected, and a memory device
(not shown) for storing the identity of the selected node connected
to the third terminal 118 and for causing the node to be
reconnected to the third terminal 118 when power is reapplied or
restored to the apparatus.
[0088] The switch 144 has a plurality of electrically controllable
switches, one tied to each node in the chain 140 of which switch
120 is typical. The switch 120 can be a transistor fabricated in
accordance with semiconductor technique or a nano-transistor as
discussed in this case. One terminal of each electrically
controllable switch is connected to a respective one of the nodes.
The other terminal of each switch is connected in common with all
other corresponding switch terminals to the third terminal 118.
Each electrically controllable switch may be closed by applying a
signal to a control terminal of which terminal 137 is typical. When
an electrically controllable switch is closed, the node to which it
is connected is connected to the third terminal 118. Only one of
the electrically controllable switches is closed at a given time.
In the preferred embodiment, each electrically controllable switch
is a conventional MOSFET.
[0089] A selecting means can be a binary shift register in which
all of the bits are set to "0" except for one bit which contains a
"1" could also be used. Each bit in the shift register would be
connected to a corresponding electrically controllable switch
control terminal. In this embodiment, the choice of which node is
connected to the third terminal 118 would be made by shifting the
contents of the register either up or down by signals on
appropriate control lines. The state of the shift register could be
stored in an electrically reprogrammable memory which has one bit
corresponding to each of the bits in the shift register.
[0090] In another embodiment, the nano-elements are transistors or
diode. As discussed in US Patent Publication 20030178617, the
disclosure of which is incorporated hereof by reference, a
self-aligned carbon-nanotube field effect transistor semiconductor
device is fabricated. The device comprises a carbon-nanotube
deposited on a substrate, a source and a drain formed at a first
end and a second end of the carbon-nanotube, respectively, and a
gate formed substantially over a portion of the carbon-nanotube,
separated from the carbon-nanotube by a dielectric film.
Alternatively, a carbon-nanotube field effect transistor
semiconductor device is provided. The device comprises a vertical
carbon-nanotube wrapped in a dielectric material, a source and a
drain formed on a first side and a second side of the
carbon-nanotube, respectively, a bilayer nitride complex through
which a band strap of each of the source and the drain is formed
connecting the carbon-nanotube wrapped in the dielectric material
to the source and the drain, and a gate formed substantially over a
portion of the carbon-nanotube.
[0091] In accordance with another embodiment of the present
invention, the nano-elements such as transistors, capacitors,
inductors and diodes, can be provided using DNA molecules as a
support structure. DNA binding proteins are used to mask regions of
the DNA as a material, such as a metal is coated onto the DNA. The
present invention also provides methods of making integrated
circuits using DNA molecules as a support structure. Methods for
making DNA based transistors, capacitors, inductors and diodes are
discussed in US Patent Publication 20010044114, the disclosure of
which is incorporated hereof by reference.
[0092] In one embodiment, the nano-elements can be a substantially
two-dimensional array made up of single-walled nanotubes
aggregating (e.g., by van der Waals forces) in substantially
parallel orientation to form a monolayer extending in directions
substantially perpendicular to the orientation of the individual
nanotubes. Such monolayer arrays can be formed by conventional
techniques employing "self-assembled monolayers" (SAM) or
Langmiur-Blodgett films. nanotubes are bound to a substrate having
a reactive coating (e.g., gold). Typically, SAMs are created on a
substrate which can be a metal (such as gold, mercury or ITO
(indium-tin-oxide)). The molecules of interest, here the SWNT
molecules, are linked (usually covalently) to the substrate through
a linker moiety. The linker moiety may be bound first to the
substrate layer or first to single-wall nanotubes ("SWNT") molecule
(at an open or closed end) to provide for reactive self-assembly.
Langmiur-Blodgett films are formed at the interface between two
phases, e.g., a hydrocarbon (e.g., benzene or toluene) and water.
Orientation in the film is achieved by employing molecules or
linkers that have hydrophilic and lipophilic moieties at opposite
ends.
[0093] In one embodiment the SAM, or two-dimensional monolayer,
described above may be the starting template for preparing a three
dimensional self-assembling structures. Where the end caps of the
component SWNT molecules have mono-functional derivatives the
three-dimensional structure will tend to assemble in linear
head-to-tail fashion. By employing multi-functional derivatives or
multiple derivatives at separate locations it is possible to create
both symmetrical and non symmetrical structures that are truly
three-dimensional.
[0094] Carbon nanotubes in material obtained according to the
foregoing methods may be modified by ionically or covalently
bonding functionally-specific agents (FSAs) to the nanotube. The
FSAs may be attached at any point or set of points on the fullerene
molecule. The FSA enables self-assembly of groups of nanotubes into
geometric structures. The groups may contain tubes of differing
lengths and use different FSAs. Self-assembly can also occur as a
result of van der waals attractions between derivitized or
underivitized or a combination of derivitized and underivitized
fullerene molecules. The bond selectivity of FSAs allow selected
nanotubes of a particular size or kind to assemble together and
inhibit the assembling of unselected nanotubes that may also be
present. Thus, in one embodiment, the choice of FSA may be
according to tube length. Further, these FSAs can allow the
assembling of two or more carbon nanotubes in a specific
orientation with respect to each other.
[0095] By using FSAs on the carbon nanotubes and/or derivitized
carbon nanotubes to control the orientation and sizes of nanotubes
which are assembled together, a specific three-dimensional
structure can be built up from the nanotube units. The control
provided by the FSAs over the three-dimensional geometry of the
self assembled nanotube structure can allow the synthesis of unique
three-dimensional nanotube materials having useful mechanical,
electrical, chemical and optical properties. The properties are
selectively determined by the FSA and the interaction of and among
FSAs.
[0096] Properties of the self-assembled structure can also be
affected by chemical or physical alteration of the structure after
assembly or by mechanical, chemical, electrical, optical, and/or
biological treatment of the self-assembled fullerene structure. For
example, other molecules can be ionically or covalently attached to
the fullerene structure or FSAs could be removed after assembly or
the structure could be rearranged by, for example, biological or
optical treatment. Such alterations and/or modifications could
alter or enable electrical, mechanical, electromagnetic or chemical
function of the structure, or the structure's communication or
interaction with other devices and structures.
[0097] In yet another embodiment, a nanotube wired OR logic can be
implemented. The upper nanotubes or nanowires IN0, IN1, IN2, IN3
contact lower nanotube, thus forming a plurality of low resistance
PN-type junctions discussed in US Application Serial No.
20030200521, the content is incorporated by reference.
Alternatively, a programmable diode OR array with nanotubes can be
used. The OR devices do not produce gain. Therefore, restoring
logic performing signal restoration is needed to provide gain,
either at the microscale or at the nanoscale level. Signal
restoration allows high signals to be driven higher and low signals
to be driven lower, in order to allow an arbitrary number of
devices to be cascaded together and a logical distinction between a
low logical value and a high logical value to be maintained.
Therefore, signal restoration helps protecting the circuit against
noise and allows arbitrary circuit composition. Restoring logic is
provided at the nanoscale level in order to allow the output of a
first stage to be used as input for a second stage, making it
possible to compute through an arbitrary number of logic stages
without routing the signal to non-nanoscale (e.g., microscale)
wires. Using the FET junctions, NMOS-like inverters, NAND, AND,
NOR, or OR logic can be built. In a first scenario (pull-up), all
inputs IN0, . . . , INM-1 of the FETs are low. As a consequence,
there is conduction through all the FETs formed at the wire
crossings (no evacuation of charge). Since there is conduction
through all the FETs and the top end of the series of FETs is
connected to a power supply driven to a high voltage, the wire can
be pulled up to the high voltage of the power supply. The output is
now high. In a second scenario (pull-down), one of the inputs IN0,
. . . , INM-1 is high. Ideally, there is no conduction through the
portion of the wire under this FET. This breaks the path from the
high voltage supply to the output region of the wire. In absence of
current flow, the output cannot be pulled up to the high voltage.
The static pulldown is always weakly enabled. If it is not pulling
against a strong connection to the high voltage supply, as in the
previous scenario, the weak static pulldown will be able to pull
the output down to a low voltage level. The output of the FET is
now low. Alternatively, restoration at the nanoscale level could
also be obtained by means of precharge logic structures. In the
simplest case, the static pull-down in the NOR is replaced with a
precharge gate. Alternatively, the single pull-down line could be
microscale instead of nanoscale. Additionally, an additional
microscale input to disable the pull-up could be added. Operation
is started by driving the new pull-up line (the additional input)
to a high value (disabling current flow to the power supply), and
enabling the pull-down precharge line by driving it to a low value.
This will allow the output to charge to a low value. After the
output is charged to a low value, the pull-down is disabled. The
output will remain at the low value for which it is now precharged.
Subsequent to this, the new pull-up line is enabled. If all of the
inputs are low, conduction is allowed to the power supply and the
output can be pulled up. If one or more of the inputs are high,
there is no such path and the output remains at a low voltage
level. Thus, the device continues to perform its NOR function.
Alternate stages will use complementary precharge phases, in order
not to release the pull-up enable line while the inputs to a stage
are still precharging and have not been allowed to evaluate.
Nano Antenna
[0098] Examples of useful electric properties of the above
described self-assembled geometric structure include: operation as
an electrical circuit, a specific conductivity tensor, a specific
response to electromagnetic radiation, a diode junction, a
3-terminal memory device that provides controllable flow of
current, a capacitor forming a memory element, a capacitor, an
inductor, a pass element, or a switch.
[0099] The geometric structure may also have electromagnetic
properties that include converting electromagnetic energy to
electrical current, an antenna, an array of antennae, an array that
produces coherent interference of electromagnetic waves to disperse
those of different wavelength, an array that selectively modifies
the propagation of electromagnetic waves, or an element that
interacts with optical fiber.
[0100] In the present invention, such antenna is referred as nano
antenna. A wireless communication device 400 including such an nano
antenna 430 is shown in FIG. 4. The wireless communication device
400 include a processor core 410 that is fabricated using
conventional semiconductor processes such as CMOS. The processor
core 410 more or more processors 411, one or more memories 412, and
one or more controllers 413. The processor 411 can include one or
more central processor units (CPUs), one or more digital signal
processors (DSPs), and Application Specific Integrated Circuits
(ASICs). The memories 412 can include dynamic random access memory
(DRAM), Read Only memory (ROM), and flash memory. The controller
413 controls the transceiver 420 and the nano antenna 430 to enable
it to transmit and receive wireless signals at different
frequencies.
[0101] The processor core 410 can be fabricated using nano elements
such as transistors, diodes, capacitors, resistors, as described
above or using coventional semiconductor processes on a
semiconductor substrate.
[0102] In accordance with the present invention, the
electromagnetic properties of the nano 440 antenna can be
selectively determined by the FSA and the interaction of and among
FSAs. For example, the lengths, location, and orientation of the
molecules can be determined by FSAs so that an electromagnetic
field in the vicinity of the molecules induces electrical currents
with some known phase relationship within two or more molecules.
The spatial, angular and frequency distribution of the
electromagnetic field determines the response of the currents
within the molecules. The currents induced within the molecules
bear a phase relationship determined by the geometry of the array.
In addition, application of the FSAs could be used to facilitate
interaction between individual tubes or groups of tubes and other
entities, which interaction provides any form of communication of
stress, strain, electrical signals, electrical currents, or
electromagnetic interaction. This interaction provides an
"interface" between the self-assembled nanostructure and other
known useful devices.
[0103] Choice of FSAs can also enable self-assembly of compositions
whose geometry imparts useful chemical or electrochemical
properties including operation as a catalyst for chemical or
electrochemical reactions, sorption of specific chemicals, or
resistance to attack by specific chemicals, energy storage or
resistance to corrosion.
[0104] Examples of biological properties of FSA self-assembled
geometric compositions include operation as a catalyst for
biochemical reactions; sorption or reaction site specific
biological chemicals, agents or structures; service as a
pharmaceutical or therapeutic substance; interaction with living
tissue or lack of interaction with living tissue; or as an agent
for enabling any form of growth of biological systems as an agent
for interaction with electrical, chemical, physical or optical
functions of any known biological systems.
[0105] FSA assembled geometric structures can also have useful
mechanical properties which include but are not limited to a high
elastic to modulus weight ratio or a specific elastic stress
tensor. Optical properties of geometric structures can include a
specific optical absorption spectrum, a specific optical
transmission spectrum, a specific optical reflection
characteristic, or a capability for modifying the polarization of
light.
[0106] Self-assembled structures, or fullerene molecules, alone or
in cooperation with one another (the collective set of alternatives
will be referred to as "molecule/structure") can be used to create
devices with useful properties. For example, the molecule/structure
can be attached by physical, chemical, electrostatic, or magnetic
means to another structure causing a communication of information
by physical, chemical, electrical, optical or biological means
between the molecule/structure and other structure to which the
molecule/structure is attached or between entities in the vicinity
of the molecule/structure. Examples include, but are not limited
to, physical communication via magnetic interaction, chemical
communication via action of electrolytes or transmission of
chemical agents through a solution, electrical communication via
transfer of electronic charge, optical communication via
interaction with and passage of any form with biological agents
between the molecule/structure and another entity with which those
agents interact.
[0107] Fullerene nanotubes can be used to replace the more
traditional conductive elements of an antenna. For example, an
(n,n) tube in conjunction with other materials can be used to form
a Schottky barrier which would act as a light harvesting antenna.
In one embodiment, a (10,10) tube can be connected via sulfur
linkages to gold at one end of the tube and lithium at the other
end of the tube forming a natural Schottky barrier. Current is
generated through photo conductivity. As the (10,10) tube acts like
an antenna, it pumps electrons into one electrode, but back flow of
electrons is prevented by the intrinsic rectifying diode nature of
the nanotube/metal contact.
[0108] In forming an antenna, the length of the nanotube can be
varied to achieve any desired resultant electrical length. The
length of the molecule is chosen so that the current flowing within
the molecule interacts with an electromagnetic field within the
vicinity of the molecule, transferring energy from that
electromagnetic field to electrical current in the molecule to
energy in the electromagnetic field. This electrical length can be
chosen to maximize the current induced in the antenna circuit for
any desired frequency range. Or, the electrical length of an
antenna element can be chosen to maximize the voltage in the
antenna circuit for a desired frequency range. Additionally, a
compromise between maximum current and maximum voltage can be
designed. A Fullerene nanotube antenna can also serve as the load
for a circuit. The current to the antenna can be varied to produce
desired electric and magnetic fields. The length of the nanotube
can be varied to provide desired propagation characteristics. Also,
the diameter of the antenna elements can be varied by combining
strands of nanotubes. Further, these individual nanotube antenna
elements can be combined to form an antenna array. The lengths,
location, and orientation of the molecules are chosen so that
electrical currents within two or more of the molecules act
coherently with some known phase relationship, producing or
altering an electromagnetic field in the vicinity of the molecules.
This coherent interaction of the currents within the molecules acts
to define, alter, control, or select the spatial, angular and
frequency distributions of the electromagnetic field intensity
produced by the action of these currents flowing in the molecules.
In another embodiment, the currents induced within the molecules
bear a phase relationship determined by the geometry of the array,
and these currents themselves produce a secondary electromagnetic
field, which is radiated from the array, having a spatial, angular
and frequency distribution that is determined by the geometry of
the array and its elements. One method of forming antenna arrays is
the self-assembly monolayer techniques discussed above.
[0109] In another embodiment of the present invention, nano wires
can be formed to provide the resonant circuit in the nano antenna
430. The orientation of the nano wires can be controlled to
maximize the reception signal strengths of the wireless
communication device 400. Methods of orienting nanowires include
the use of mask based processes alone or in combination with flow
based alignment of the nanowires to provide oriented and positioned
nanowires on surfaces. The populations of nanowires can also be
controlled. Details of the control of nanowire orientation and
population are discussed in US Patent Publication 20030186522, the
disclosure of which is incorporated hereof by reference.
[0110] In accordance with the present invention, a plurality of
equivalent nano circuits at different orientations are provided in
the nano antenna 430. The orientation of the nano circuits are
disposed such that wireless signals can be received at high
strength at any orientation of the wireless communication device
400 relative to the field propagation direction of the incoming
wireless wave.
[0111] In another embodiment, a plurality of nano tubes can be
connected by nano switches 431 in a serial circuit to provide the
nano antenna 430. The electrical lengths of the circuit and thus
the resonant frequencies can be configured by turning on and off
different combinations of the nano switches 431, depending on the
required frequencies of various telecommunication protocols.
Communications standards and protocols supported by the processor
core 410, the transceiver core 420, and nano antenna 430 include
for example Global System for Mobile Communications (GSM), General
Packet Radio Service (GPRS), Bluetooth. IEEE802.11 etc.
[0112] Fullerene molecules can be used to replace traditional
electrically conducting elements. Thus fullerene molecules or
self-assembled fullerene groups can be the basis of electrical
circuits in which the molecule transfers electrical charge between
functional elements of the circuit which alter or control the flow
of that charge or objects in which the flow of electrical current
within the object performs some useful function such as the
redistribution of the electric field around the object or the
electric contact in a switch or a response of the object to
electromagnetic waves. As an example, nanotubes can also be
self-assembled to form a bridge circuit to provide full wave
rectification. This device can include four nanotubes, each forming
an edge of a square, and four buckyballs, one buckyball would be
located at each corner of the square. The buckyballs and nanotubes
can be derivitized to include functionally specific agents. The
functionally specific agents form linkages connecting the
buckyballs to the nanotubes and imparting the required geometry of
the bridge. A fullerene diode can be constructed through the
self-assembly techniques described above. The diode can be composed
of two bucky tubes and a bucky capsule. The bucky capsule can also
be derivitized to form a zwiterrion. For example, the bucky capsule
can include two positive groups, such as the triethyl amine cation
and two negative groups, such as CO.sub.2-anion. In one embodiment,
each end of the bucky capsule is connected to a (10, 10) bucky tube
by a disulfide bridge. Thus, sulfur serves as the
functionally-specific agent.
[0113] Various molecules or nano-elements can be coupled to one or
more electrodes in a layer of an IC substrate using standard
methods well known to those of skill in the art. The coupling can
be a direct attachment of the molecule to the electrode, or an
indirect attachment (e.g. via a linker). The attachment can be a
covalent linkage, an ionic linkage, a linkage driven by hydrogen
bonding or can involve no actual chemical attachment, but simply a
juxtaposition of the electrode to the molecule. In some preferred
embodiments, a "linker" is used to attach the molecule(s) to the
electrode. The linker can be electrically conductive or it can be
short enough that electrons can pass directly or indirectly between
the electrode and a molecule of the storage medium. The manner of
linking a wide variety of compounds to various surfaces is well
known and is amply illustrated in the literature. Means of coupling
the molecules will be recognized by those of skill in the art. The
linkage of the storage medium to a surface can be covalent, or by
ionic or other non-covalent interactions. The surface and/or the
molecule(s) may be specifically derivatized to provide convenient
linking groups (e.g. sulfur, hydroxyl, amino, etc.). In one
embodiment, the molecules or nano-elements self-assemble on the
desired electrode. Thus, for example, where the working electrode
is gold, molecules bearing thiol groups or bearing linkers having
thiol groups will self-assemble on the gold surface. Where there is
more than one gold electrode, the molecules can be drawn to the
desired surface by placing an appropriate (e.g. attractive) charge
on the electrode to which they are to be attached and/or placing a
"repellant" charge on the electrode that is not to be so
coupled.
Nano Memory Devices
[0114] In yet another embodiment shown in FIG. 5, the nano-elements
can be an array of single-molecule magnets (SMMs). In one
embodiment, arrays of SMMs can be used in combination with
semiconductor structures to replace solid state memory systems or
alternatively the SMMs can be deposited on a disk platter to
achieve high density disk drive. The SMM molecules can be used for
spin-based molecular electronics devices as well.
[0115] Single molecule magnets (SMMs) are nanomagnets that consist
of a core of strongly exchange-coupled transition metal ions with a
large magnetic moment per molecule. SMM form crystals that are
monodisperse--every molecule in a crystal has the same spin,
orientation, magnetic anisotropy and atomic structure. Hence
magnetic measurements of a crystal can be used to characterize the
properties of individual magnetic molecules. SMMs have magnetic
anisotropy that favors the magnetic moment to be either up or down
with respect to the easy axis. The energy barrier between up and
down states (the anisotropy barrier) leads to magnetic hysteresis
and to magnetic bistability for magnetic data storage. Transitions
between up and down magnetic states can occur by thermal activation
and quantum tunneling. Due to the discrete energy spectrum,
transitions are favored when up and down energy levels are in
resonance, or, more precisely, have an anticrossing. These
resonances only occur at certain magnetic fields. Each SMM has a
fixed molecular size and shape, and unlike normal magnets, the
properties of the SMM are due to intrinsic molecular properties.
The SMM gains its properties from the large potential energy
barrier between the spin "up" and spin "down" states. One exemplary
SMM is
Mn.sub.12O.sub.12(O.sub.2CMe).sub.16(H.sub.2O).2MeCO.sub.2H.4H.sub.2O,
with S=10, and its related Mn complexes. Other classes of in the Mn
family of molecules, Mn.sub.4O.sub.3 complexes, can also be used as
SMMs.
[0116] The SMMs are made from transition metal clusters exhibiting
magnetic bistability. The SMMs possess a high-spin ground state
(S), which, when combined with a negative axial zero-field
splitting (D<0), leads to an energy barrier for spin reversal.
The SMMs incorporate oxo-based bridging ligands that mediate the
magnetic exchange coupling between metal centers. In another
embodiment having clusters with larger spin reversal barriers,
cluster systems formed by replacing Cr.sup.III with Mo.sup.III in
the linear cluster
[(Me.sub.3tacn).sub.2-(cyclam)NiCr.sub.2(CN).sub.6].sub.2+(Me.sub.3tacn)
N,N',N''-trimethyl-1,4,7-triazacyclononane;
cyclam=1,4,8,11-tetraazacyclotetradecane) or an analogous
substitution in the trigonal prismatic cluster
[(Me.sub.3tacn).sub.6MnCr.sub.6(CN).sub.18].sup.2+,3c bearing a
higher spin ground state of S=3/2 can be used as a cyano-bridged
single-molecule magnet.
[0117] As shown in FIG. 5, an SMM memory device includes a memory
cell array 200 constructed over a substrate such as the substrate
includes a silicon-on-insulator (SOI) wafer. In the memory cell
array 200, first signal electrodes (chemical structure lines or
word lines) 212 for selecting rows and second signal electrodes
(bit lines) 216 for selecting columns are arranged to intersect at
right angles. The first signal electrodes may be the bit lines and
the second signal electrodes may be the chemical structure lines,
differing from this example. An SMM layer 214 is disposed at least
between the first signal electrodes 212 and the second signal
electrodes 216. Therefore, memory cells 220, each of which includes
an SMM, are formed at intersections between the first signal
electrodes 212 and the second signal electrodes 216. A peripheral
circuit section 260 including a peripheral driver circuit for
selectively allowing information to be written into or read from
the memory cells and an amplifier circuit which for reading the
information is also formed. The peripheral circuit section 260
includes a first driver circuit 250 for selectively controlling the
first signal electrodes 212, a second driver circuit 252 for
selectively controlling the second signal electrodes 216, and a
signal detecting circuit (not shown) such as a sense amplifier, for
example.
[0118] As specific examples of the peripheral circuit section 260,
a Y gate, a sense amplifier, an input-output buffer, an X address
decoder, a Y address decoder, and an address buffer can be given. A
write line is formed near the SMM cell 220 and the write line is
used for writing and inverting magnetization of nano-magnetic
material layer of the SMM cell 220 by a current flow, as the
magnetization is magnetic information.
[0119] The peripheral circuit section 260 may be formed by MOS
transistors formed on a substrate (single crystal silicon
substrate, for example). In the case where the substrate is formed
of a single crystal silicon substrate, the peripheral circuit
section 260 can be integrated on the same substrate as the memory
cell array 200. The SMMs are formed last by spin-coating a solution
containing self-assembled SMMs on a wafer after the wafer has been
processed and devices are formed using conventional semiconductor
fabrication techniques. Conventional semiconductor structures are
formed as is conventional. During the next to the last conventional
step, gold electrodes are formed. Then a resist layer is formed
over the last layer, and selective etching is performed to expose
the gold electrodes. A solution containing the SMMs are spin-coated
on top, where the SMMs self-assemble.
[0120] Writing to the bit is accomplished by applying a polarized
voltage pulse through a nanocircuit element. A positive pulse will
pull the SMM and a negative pulse will push the SMM. The bistable
nature of the bit will result in the SMM staying in the positioned
end when the pulse is removed since that is where the energy is
lowest. To read the bit, another nanocircuit element is biased with
a VREAD voltage. If the SMM is present in the detection end, it
supplies the necessary energy levels for current to resonantly
tunnel across the junction to the ground voltage (in a fashion
analogous to a resonant tunneling diode) resulting in a first
stable state being read. If the SMM is not present in the detection
end, the energy levels are shifted out of resonance and the current
does not tunnel across the junction and a second stable state is
read. Other forms of read/write structure (e.g., microactuators)
can be employed as will be recognized by one skilled in the
art.
[0121] A memory device can be constructed using either a two- or
three-dimensional array of the SMMs. Because the SMMs are molecular
in size, a dense memory chip can be fabricated. Further, the wiring
width and the area of each cell is reduced. The switching electric
field can be reduced by using the SMM memory cell and write current
necessary for writing a magnetization invert may be reduced,
whereby power consumption being restrained and switching being
carried out at high speed. The nano coercive force is small and the
switching magnetic field is small. When the nano-device is used as
a memory cell of a magnetic memory, the current of a write wiring
for generating a magnetic field necessary for inverting
magnetization can be reduced. Therefore, according to the magnetic
memory forming the memory cell by nano-magnets, a highly integrated
formation can be performed, the power consumption is reduced, and
the switching speed can be made faster.
[0122] The molecular memory such as SMM memory is used as on-chip
data or off-chip storage device for a processor chip. In one
embodiment, the memory system organization is a multi-level memory
hierarchy. A combination of a small, low-latency level one (L1)
memory backed by a higher capacity, yet slower, L2 memory and
finally by main memory provides the best tradeoff between
optimizing hit time and miss time. Different molecular memory
arrays with differing speed and size requirements can be deployed
in a computer system. For example, a high speed static RAM can be
used as L1 memory, while a high speed high density nano memory
array can be used as L2 memory and low speed nano memory array can
be used as regular memory. In one system on a chip, processor logic
and cache is implemented using traditional semiconductor structure,
and a large main memory array is provided on chip using molecular
memory. Finally, nano-head disk drive can be used as long term data
storage devices.
Nano Disk Drive
[0123] Yet another embodiment is an embodiment in which the SMMs
are applied to a magnetic head. FIG. 6A is a perspective view of a
nano-magnetic head assembly mounted with an SMM head. An actuator
arm 301 is provided with a hole for being fixed to a fixed shaft
inside of a magnetic disk apparatus and is provided with a bobbin
portion for holding a drive coil (not illustrated) and the like. A
suspension 302 is fixed to one end of the actuator 301. A front end
of the suspension 302 is wired with a lead wire 304 for writing and
reading signals, one end of the lead wire 304 is coupled with
respective electrode of a nano-magnetic head 305 mounted on a head
slider 303, and the other end of the lead wire 304 is connected to
an electrode pad 306. The nano-head 305 is fabricated using
thin-film type substrate, with spin-coating of the SMM elements at
the last stages of head manufacture.
[0124] The nano-head 305 has one or more nano sub-heads so that it
can access information serially or in parallel for improved data
throughput. In addition, error correction codes can be encoded and
decoded on the nano-head. Further, each of the sub-heads can be
part of a RAID array. The nano-head 305 provides data used for
standard RAID levels including 1, 3, and 5 or combinations of two
other RAID levels. For example, in RAID 1+0 (also called RAID 10),
multiple RAID 1 pairs are striped for faster access; and in RAID
15, two RAID 5 arrays are mirrored for added reliability.
[0125] FIG. 6B is a perspective view of an inner structure of a
magnetic disk apparatus (magnetic information reproducing
apparatus) mounted with the magnetic head assembly of FIG. 6A. A
nano-magnetic disk 311 is mounted on a spindle 312 and is rotated
by a motor (not illustrated) responding to a control signal from a
control portion of a drive apparatus (not illustrated). The
nano-magnetic disk 311 has a surface that is processed using thin
film deposition with a spin-coat of the self-assembled SMMs late in
fabrication of the disk 311. The actuator arm 301 is fixed to a
fixed shaft 313 for supporting the suspension 302 and the head
slider 303 at the front end thereof. When the magnetic disk 311 is
rotated, a surface of the head slider 303 opposed to the disk 311
is held in a floating state from a surface of the magnetic disk 311
by a predetermined amount, thereby reproducing the magnetic
information of the magnetic disk. At another end of the actuator
arm 301, a chemical coil motor 314 is provided and includes a type
of a linear motor. The chemical coil motor 314 includes a drive
coil (not illustrated) wound up to the bobbin portion of the
actuator arm 301 and a magnetic circuit including a permanent
magnet and an opposed yoke arranged to be opposed to each other to
interpose the coil. The actuator arm 301 is supported by ball
bearings (not illustrated) provided at two upper and lower
locations of the fixed shaft 313 and can freely be slidingly
rotated by the chemical coil motor 314.
Nano-Optical DRAM
[0126] In yet another embodiment, the nano-elements can be an array
of optical storage molecules (OSMs). In one embodiment, arrays of
OSMs can be used in combination with semiconductor structures to
replace solid state memory systems or alternatively the OSMs can be
deposited on a disk platter to achieve high density disk drive. The
OSM molecules can be used for spin-based molecular electronics
devices as well.
[0127] The OSMs convert energy patterns into electronic digital
signals by exposing an image plate having OSMs supported by a
matrix to an energy pattern. The energy pattern can be provided by
a plurality of optical signals output from a bundle of optical
fibers of optical circuitry. The applications include
telecommunication and parallel optical computing. A plurality of
energy patterns recorded by the array of OSMs in electronic signals
can be considered as snapshots of optical signals which can be read
as optical signals or electronic signals.
[0128] In one embodiment, the OSM can be a nanophase storage
luminescence material of the general formula X/Y, wherein X is at
least one guest and Y is a host. The host can be selected from the
group consisting of organic, inorganic, glass, crystalline,
non-crystalline, porous materials or combinations thereof. The host
can be semiconducting nanoparticles such as insulating
nanoparticles, conducting nanoparticles, and combinations thereof.
The semiconductor nanoparticle can be sulfide, telluride, selenide,
or oxide semiconductors. The semiconductor nanoparticle is selected
from the group of Zn.sub.xS.sub.y, Zn.sub.xSe.sub.y,
Zn.sub.xTe.sub.y, Cd.sub.xS.sub.y, Cd.sub.xSe.sub.y,
Cd.sub.xTe.sub.y, Pb.sub.xS.sub.y, Pb.sub.xSe.sub.y,
Pb.sub.xTe.sub.y, Mg.sub.xS.sub.y, Ca.sub.xS.sub.y, Ba.sub.xS.sub.y
and Sr.sub.xS.sub.y, wherein 0<x.ltoreq.1, 0<y.ltoreq.1. The
semiconductor nanoparticle can be ZnS. The semiconductor
nanoparticle can also be represented by the general formula
(M.sub.1-zN.sub.z).sub.xA.sub.1-yB.sub.y, wherein M=Zn, Cd, Pb, Ca,
Ba, Sr, Mg; N=Zn, Cd, Pb, Ca, Ba, Sr, Mg; A=S, Se, Te, O; B=S, Se,
Te, O; 0<x.ltoreq.1, 0<y.ltoreq.1, 0<z.ltoreq.1). The
semiconductor nanoparticle can also be Zn.sub.0.4Cd.sub.0.4S.
[0129] The writing of optical signals involves the conversion of
optical signals to electronic states via photon induced electronic
excitations. As discussed in Application Serial No. 20030064532,
nano particle energy structure can be modified via quantum size
confinement. When electrons and holes are produced in nano
particles by excitation, the electrons and holes may de-excite or
relax to the lowest excited states and recombine to give
luminescence. They also may be trapped by electron or hole traps at
the surfaces, interfaces, or/and in the surrounding matrix. The
electrons or holes at traps are in a metastable state.
[0130] The read-out of the recorded electronic data converted from
optical signals can be achieved by several mechanisms. 1) When
stimulated by light or by heat some electrons or holes may be
released and go back to the nano particles, recombining to provide
luminescence--i.e., photostimulated luminescence (PSL) or
thermoluminescence. Light energy is provided to optically stimulate
the photostimulated luminescence nano particles. The nano particles
release the stored energy and provide luminescence due to
electron-hole recombination; and converting the luminescence into
digital signals indicative of the energy pattern. The stimulating
light or heat energies can be applied uniformly to the array of
OSMs and detecting the PSL and thermoluminescence by a 2D optical
sensor. 2) Alternatively, the recombination and luminescence of the
stored electrons and holes in the energy pattern can also be
stimulated by sweeping electric voltage pulses along the word lines
and bit lines. The detection of the stimulated luminescence signals
include only a single or 1D array of optical detectors. 3) Finally,
the stored electrons and holes from the exposed energy pattern can
be read out electronically as in conventional memory devices using
the electronic circuitry in the memory cell array as described
below. Transistors can be provided to convert the stored charge to
voltage signals. Additional conductive lines connecting to the
collector, the emitters, the gates can be provided to facilitate
the readouts. The invention device is similar to electrically
erasable programmable read-only memory (EEPROM) devices with
additional optical writing (via 2D optical pattern)
capabilities.
[0131] An exemplified architecture of the OSM memory device is
illustrated in FIG. 5. The OSM memory device includes a memory cell
array constructed over a substrate and the substrate includes a
silicon-on-insulator (SOI) wafer. In the memory cell array, first
signal electrodes (word lines) for selecting rows and second signal
electrodes (bit lines) for selecting columns are arranged to
intersect at right angles. The first signal electrodes may be the
bit lines and the second signal electrodes may be the chemical
structure lines, differing from this example. An OSM layer is
disposed at least between the first signal electrodes and the
second signal electrodes. Therefore, memory cells, each of which
includes an OSM, are formed at intersections between the first
signal electrodes and the second signal electrodes. A peripheral
circuit section (including a peripheral driver circuit for
selectively allowing information to be written into or read from
the memory cells) and an amplifier circuit which for reading the
information is also formed. The peripheral circuit section includes
a first driver circuit for selectively controlling the first signal
electrodes, a second driver circuit 252 for selectively controlling
the second signal electrodes, and a signal detecting circuit such
as a sense amplifier, for example.
[0132] The OSMs are formed last by spin-coating a solution
containing self-assembled OSMs on a wafer after the wafer has been
processed and devices are formed using conventional semiconductor
fabrication techniques. Conventional semiconductor structures are
formed as is conventional. During the next to the last conventional
step, gold electrodes are formed. Then a resist layer is formed
over the last layer, and selective etching is performed to expose
the gold electrodes. A solution containing the OSMs are spin-coated
on top, where the OSMs self-assemble. Writing to the bit is
accomplished by applying a tightly focused light emitter that can
be a nanocircuit element. To read the bit, another nanocircuit
element such as a light detector detects whether the optical DRAM
cell is on or off based on the stored light energy. If the OSM is
on, it supplies the necessary energy levels for current to
resonantly tunnel across the junction to the ground voltage (in a
fashion analogous to a resonant tunneling diode) resulting in a
first stable state being read. If the OSM is off, the energy levels
are shifted out of resonance and the current does not tunnel across
the junction and a second stable state is read. Other forms of
read/write structure (e.g., microactuators) can be employed as will
be recognized by one skilled in the art.
[0133] A memory device can be constructed using either a two- or
three-dimensional array of the OSMs. Because the OSMs are molecular
in size, a dense memory chip can be fabricated. Further, the wiring
width and the area of each cell is reduced. The switching light
field can be reduced by using the OSM memory cell and write current
necessary for writing an optical invert may be reduced, whereby
power consumption being restrained and switching being carried out
at high speed. The molecular memory such as OSM memory is used as
on-chip data or off-chip storage device for a processor chip. In
one embodiment, the memory system organization is a multi-level
memory hierarchy. A combination of a small, low-latency level one
(L1) memory backed by a higher capacity, yet slower, L2 memory and
finally by main memory provides the best tradeoff between
optimizing hit time and miss time. Different molecular memory
arrays with differing speed and size requirements can be deployed
in a computer system. For example, a high speed static RAM can be
used as L1 memory, while a high speed high density nano optical
DRAM array can be used as L2 memory and low speed nano memory array
can be used as regular memory. In one system on a chip, processor
logic and cache is implemented using traditional semiconductor
structure, and a large main memory array is provided on chip using
molecular memory. Finally, nano-head disk drive can be used as long
term data storage devices.
Nano Optical Interconnect
[0134] In a high speed multi-chip module (MCM) environment,
chip-to-chip connections are usually made using bond wires, with
microstrip lines on the MCM substrate used to interconnect chips
that are farther apart. Presently, electrical bond wires are used
to interconnect microchips. Using the electrical wires has serious
drawbacks. The electrical wires are sensitive to electromagnetic
interference and themselves create such interference which poses
especially serious problems for distribution of timing signals. The
electrical wires must be located at the edges of chips. Signal
attenuation and phase delay depend upon the length of the
electrical wires. Thus, depending on the lengths of the electrical
wires and their locations in the module, it may be difficult to
achieve equal attenuation and/or equal signal phase delay among
multiple wires, if needed. In addition, in many cases signal
bandwidths of several Gigahertz are desirable but cannot be
achieved if electrical wires are used because electrical bond wires
act as open antennae at high frequencies and introduce noise
coupling among the wires. For example, bond wires of 500
micrometers in length and 1 mil (0.001 inch) diameter carrying 10
milliamperes of current will produce appreciable (100 millivolts or
more) coupling or cross-talk at 10 Gigahertz even when they are
spaced several pitch distances apart, a typical pitch being 100 to
150 micrometers. This effect will substantially limit the maximum
speed of a typical MCM module having hundreds of bond wires from
several chips. The cross-talk is even more severe when the chips
are located farther apart and require longer bond wires.
Previously, optoelectronic devices such as vertical-cavity lasers
and photodetectors have been bonded onto microelectronic chips to
provide free-space optical interconnections. However, such lasers
and detectors are bulky.
[0135] In one embodiment of the invention, nano optical elements
such as OSMs are used with an optical waveguide to interconnect
MCMs to provide an optical interconnection system. In one
embodiment, conventional electronics are deposited using standard
semiconductor processing techniques. Next, OSMs and light detectors
are spin-coated above the semiconductor layer and they self
assemble to form transmitters or receivers at designated locations
on the MCMs. During fabrication, the MCMs are immersed in a
solution that allows nano-optical interconnect (nano-lightpath) to
self-assemble in 3D space between the transmitters and the
receivers. The self-assembly is keyed so that specific
nano-lightpaths bond between specific transmitter and receiver
pairs. One type of keying uses chemical bond key encoding or DNA
encoding. The nano light fibers or other suitable light conductors
to interconnect the OSMs to their respective light detectors.
Lightpaths traverse several physical links but information
traveling on a lightpath is carried optically from end-to-end. The
system is insensitive to electromagnetic interference; needs not be
located at the edges of a chip but rather can be placed for optimal
utility to the circuit function; can be given the same or other
pre-specified lengths regardless of the placement in the module;
and are capable of high signal bandwidths without causing the
cross-talk problem. The optical interconnection system can further
include a semiconductor region over or in the substrate. An
electronic circuit can be formed conventional semiconductor
techniques. The electronic circuit controls or monitors the
interconnection of the optical signals.
[0136] In another embodiment for wide area networking, the system
performs wavelength routing, which is a form of circuit switching.
In wavelength-routed networks, a lightpath, which is an end-to-end
optical communication connection, is established before data can be
sent. Such lightpaths are called "wavelength-routed" because each
uses a dedicated wavelength channel on every link along a physical
path, and hence, once data is transmitted on a specific wavelength
by its source, how the data will be routed (or switched) at the
intermediate nodes will be determined by the "color" of the
wavelength only. Optical packet switching (OPS) is similar to
traditional electronic packet switching, except for that payload
(i.e., data) will remain in optics, while its header may be
processed electronically or optically. In one embodiment, the above
optical random access memory performs optical buffering. Optical
burst switching (OBS) is a technique for transmitting bursts of
traffic through an optical transport network by setting up a
connection and reserving resources end to end for the duration of a
burst. OBS is a way to achieve a balance between the coarse-grained
wavelength routing and fine-grained optical packet switching.
[0137] In another embodiment, the system includes a nano-optical
switch is a nano photonic switch having N full-duplex ports, each
of which can connect to any other without OEO conversion, although
the switch may still be controlled by electronic signals. Broadly
speaking, switches refer to devices that may be called add-drop
multiplexers (ADMs), routers, and crossconnects. An add/drop
multiplexer (ADM) is an optical system that is used to modify the
flow of traffic through a fiber at a routing node. An ADM passes
traffic on certain wavelengths through without interruption or
opto-electronic conversions, while other wavelengths are added or
dropped, carrying traffic originating or terminating at the node. A
wavelength router (WR) is a more powerful system than an ADM. For
each of the wavelengths it takes in a signal at an input port and
routes it to a particular output port, independent of the other
wavelengths. A WR with N input and N output ports capable of
handling k wavelengths can be considered as k independent N.times.N
single wavelength switches. These switches have to be preceded by a
wavelength demultiplexer and followed by a wavelength multiplexer
to implement a WR. They are sometimes also called wavelength
routing switches (WRS) or wavelength crossconnects (WXCs). Equipped
with WCs, a WXC becomes a wavelength interchanging switch, also
known as wavelength interchanging crossconnect (WIXC). (Note that a
wavelength crossconnect (WXC) is commonly called an optical
crossconnect (OXC).
[0138] In a wavelength-routed network embodiment, nano-wavelength
crossconnect (WXC) or nano-optical crossconnect (OXC) nodes are
inter-connected by nano-fiber links. A lightpath is realized by
allocating a wavelength on each link on the path between the two
nodes. Each link can support a certain number of wavelengths. To
avoid wavelength continuity constraint, nano-wavelength converters
(WCs) are used in the network. A wavelength converter is a device
that takes in data at one wavelength and outputs it on a different
wavelength. Wavelength conversion can play a significant role in
improving the utilization of the available wavelength in the
network, or reducing the blocking rate for lightpath requests. The
lightpaths can be set up and taken down upon demand. These are
analogous to setting up and taking down circuits in
circuit-switched networks. The key elements in the network are the
optical crossconnects (OXCs). The major components required to
realize OXCs are passive wavelength multiplexers and
demultiplexers, switches, and/or wavelength converters. Depending
on the functionality available at the nodes, these networks can be
classified as either static or reconfigurable. A static network
does not have any switches or dynamic wavelength converters in it.
A reconfigurable network, on the other hand, contains switches
and/or dynamic wavelength converters. The main difference between
the two types of networks is that the set of lightpaths that can be
established between users is fixed for a static network, whereas it
can be changed, by changing the states of the switches or
wavelength converters at the OXC nodes, for a reconfigurable
network.
Nano Optical Storage Device
[0139] In another embodiment, single molecule light sensors are
used to provide data storage. The nano-elements convert energy
patterns into digital signals by exposing an image plate having a
nano particle array supported by a matrix to an energy pattern. The
nano particle array formed of photostimulated luminescence nano
particles which cooperate to store energy indicative of the energy
pattern. As discussed in Application Serial No. 20030064532, nano
particle energy structure can be modified via quantum size
confinement. When electrons and holes are produced in nano
particles by excitation, the electrons and holes may de-excite or
relax to the lowest excited states and recombine to give
luminescence. They also may be trapped by electron or hole traps at
the surfaces, interfaces, or/and in the surrounding matrix. The
electrons or holes at traps are in a metastable state.
[0140] When stimulated by light or by heat some electrons or holes
may be released and go back to the nano particles, recombining to
provide luminescence--i.e., photostimulated luminescence (PSL) or
thermoluminescence. Light energy is provided to optically stimulate
the photostimulated luminescence nano particles. The nano particles
release the stored energy and provide luminescence due to
electron-hole recombination; and converting the luminescence into
digital signals indicative of the energy pattern. As a data storage
device, the writing light can be either ultra-violet (UV) or blue
or any other light having energy higher than the energy gap of the
host materials (i.e. the writing light is variable and will depend
on the energy gap of the host material). The reading light can be
visible or infrared (IR) light, the choice of reading light is also
variable and depends on the trap depth of the host material.
Semiconductors such as MgS, CaS, SrS, and SrSe doped with rare
earth elements such as Ce, Sm, and Eu have been previously
considered for optical storage and dosimetric applications. The
configuration of the optical writer and optical reader are similar
a CD-R or DVD-R drive and similar to the configurations in FIGS. 6A
and 6B. The layer of nano particles can be spin-coated over a
substrate surface.
Nano Chemical Sensors
[0141] FIG. 7 is an exemplary diagram of a system having an array
of nano-based sensors. The nano-elements can be used as sensors
such as Guided-Optics Intrinsic Chemical Sensors. These sensor
types are based on the fact that chemical species can affect the
waveguide properties. Hence, it is not the absorption or emission
properties of an analyte that are measured, but rather the effect
of the analyte upon the optical properties of the optical
waveguide. More specifically, these sensors are based on one or
more of the following effects of the analyte: (a) An increase in
the strain/stress of the coating, (b) Modification of the waveguide
temperature, (c) Attenuation of the guided light amplitude, (d)
Change of the effective refractive index of the mode, (e)
Modification of the polarization of the light.
[0142] In one embodiment, a sensor includes resonant nanoparticles
embedded in a semipermeable matrix. The nanoscale sensor can
operate with a single molecule to recognize the presence of a
specific short sequence in a mixture of solid molecules, gaseous
molecules or aqueous molecules such as DNA or RNA molecules. The
system selectively detects and identifies a plurality of chemical
species by using an array of nano sensors. When a target molecule
binds to the probes (nanoparticles) in the sensor, the probe
molecule changes shape and alters the reflectivity of the sensor.
In one embodiment, the nanoparticles are embedded in a carrier or
matrix. The matrix is preferably transparent to an optical sampling
wavelength and not Raman active at the Stokes shifts of interest.
The optical sample wavelength may be any suitable laser wavelength.
The matrix may be any suitable inorganic or polymeric material such
as mesoporous silica. The optical sampling geometry can be as a
layer deposited onto a reflective substrate exposed to incident
light. Alternatively, the optical sampling geometry can be as a
cladding layer in a waveguide structure, where the Raman excitation
is a result of the evanescent wave of the guided optical mode
propagating in that structure.
[0143] The analytes of interest are exposed to the semipermeable
layer, diffuse through this layer and are adsorbed onto the
surfaces of the embedded nanoparticles. The scattered light is
modulated by the Stokes modes of the analyte molecules, and
detection consists of spectral analysis of the scattered light
using a standard dispersive geometry and lock-in based
photodetection. The nanoparticles' resonances are tuned to match a
pump laser wavelength. The nanoparticles can be functionalized with
molecules that exhibit a strong Raman response. A variety of
candidate molecules may be used, such as para-mercaptoaniline,
which can be bound to the surface of the nanoparticles and which
yields three strong Stokes modes. Alternatively the nanoparticles
can be embedded in a medium exhibiting a strong Raman response. The
optical sampling geometry can be a layer deposited onto a
reflective substrate exposed to incident light. Alternatively, the
optical sampling geometry can be as a layer in a waveguide
structure, where the Raman excitation is a result of the evanescent
wave of the guided optical mode propagating in that structure.
[0144] According to some embodiments, the resonant nanoparticles
are solid metal nanoparticles. The shape of the metal nanoparticles
may be selected so as to adjust the wavelength of the resonance.
Thus, contemplated shapes include spheroids, ellipsoids, needles,
and the like. Further the metal nanoparticles may be aggregated
into multiparticle aggregates so as to adjust the wavelength of the
resonance. Still further, the metal nanoparticles may be embedded
in a matrix material that is capable of adjusting the wavelength of
the resonance. For example, the matrix may be any dielectric
material suitable to form the core of a metal nanoshell. More
details on the nanoshell sensor is described in Application Serial
No. 20030174384, the content of which is incorporated by
reference.
[0145] In one embodiment, the sensors are incorporated in an
interferometer, and phase-modulated or interferometric optical
sensors offer the highest sensitivity. Interferometric sensor
systems typically employ the MachZehnder interferometer
configuratio. Other configurations such as those of Michelson and
Fabry-Perot can also be used. The interaction with the chemical
substance takes place through the evanescent waves. The physical
shape of the waveguide may change. The waveguide parameter changes
due to a change in the physical dimension as well as to a change in
the refractive index of the waveguide as a function of temperature.
The intensity of the optical field decreases exponentially as it
travels in the waveguide. The Kramers-Kronig relationship relates
the imaginary part of the refractive index to its real part.
Therefore, in attenuation mode chemical sensors, the phase of the
guided mode also changes. The phase of the guided light may change.
The TM and TE mode experience different phase shifts or
attenuation.
[0146] One embodiment uses polarization of the light in sensing
applications. The nano-sensor consists of an integrated difference
(or polarimetric) interferometer that uses only one waveguide. The
waveguide is designed to have only two modes of propagation: the
fundamental TE and TM modes. A small portion of the waveguide's
core where it contacts the measurand (a gas or a liquid) is
exposed. The propagation constant of the TE and TM modes is
sensitive to the refractive index of the sample. The dependence of
each propagation constant on the refractive index of the sample is
different and is dictated according to the equations for a three
layer waveguide. At the output of the interferometer the light
exiting the waveguide is passed through a polarizer at 45.degree.
and into a photodetector. After the polarizer, the waves arising
from the original TE and TM are polarized in the same direction and
may interfere.
[0147] In one embodiment, shape changes in a single DNA molecule
bound to each sensor are detected and the result is compared
against a database of substances (for example pathogens). If a
match is found, the result is displayed.
[0148] In another embodiment, immobilized "probe" molecules of
biological interest can be used. When exposed to an assay sample of
interest, "target" molecules in the sample bind to the probe
molecules to an extent determined by the concentration of the
target molecule and its affinity for a particular probe molecule.
If the target concentrations are known, the affinity of the target
for the different probes can be estimated simultaneously.
Conversely, given the known affinities of the different molecules
in the target, the amounts of observed binding may be used to
estimate simultaneously the concentrations of multiple analytes in
the sample. United States Patent Application 20040002064 entitled
"Toxin detection and compound screening using biological membrane
microarrays" shows examples of the probe molecules of biological
interest, the content of which is incorporated by reference.
[0149] In another embodiment, when a target molecule binds to the
probe in the sensor, the probe molecule changes shape, and in its
new conformation, pulls on the sensor. The motion of the sensor is
detected using evanescent wave scattering, which analyzes light
that leaks out behind a reflecting mirror. This evanescent wave is
used to sense the position of an object "beyond" the mirror. Thus,
conformational changes in a single DNA molecule at the nanometer
scale are detected and the result is compared against a database of
substances (for example pathogens). If a match is found, the result
is displayed.
[0150] In another embodiment, the matrix can include Polymer
Waveguide Chemical Sensors where both intrinsic and extrinsic
sensing mechanisms are present. In this case, the optical waveguide
itself is made of a nano-polymer that interacts with the chemical
substance. The matrix is made from material that are able to absorb
a target chemical onto the polymer surface. By diffusing into the
waveguide the chemical is separated from the mixture. Thus, in this
case, the waveguide is involved in both the separation process and
the quantitative sensing of the target chemical.
[0151] In another embodiment, to increase the probing efficiency,
optical energy inside the matrix is increased by operating the
waveguide near its cut-off, or, more conveniently, by exciting
surface plasmons. Light propagating inside the waveguide interacts
with the charge density waves of a thin layer such as a metal like
silver layer. If the guided wave's wavenumber matches that of the
surface plasmon, the optical energy is absorbed by the plasmons and
is consequently dissipated. The plasmon wavenumber, in turn,
depends on the conductivity and can the surface condition of the
metallic layer. A thin sensitive polymer film is usually deposited
over the metallic film which, upon absorption of chemicals and
gases, changes the plasmon wavenumber of the metallic film.
[0152] FIG. 7 is an exemplary diagram of an array of nano-based
sensors. As shown in FIG. 7, a sensor includes a nano-cell sensor
array 300. In the sensor array 300, first signal electrodes
(chemical structure lines) 312 for selecting rows and second signal
electrodes (bit lines) 316 for selecting columns are arranged to
intersect at right angles. The first signal electrodes may be the
bit lines and the second signal electrodes may be the chemical
structure lines, differing from this example. A nano-sensor layer
314 is disposed at least between the first signal electrodes 312
and the second signal electrodes 316. Therefore, sensor cells 320,
each of which includes a nano-sensor, are formed at intersections
between the first signal electrodes 312 and the second signal
electrodes 316. A peripheral circuit section 360 including a
peripheral driver circuit for selectively allowing information to
be read from the sensor cells and an amplifier circuit which for
reading the information is also formed. The peripheral circuit
section 360 includes a first driver circuit 350 for selectively
controlling the first signal electrodes 312, a second driver
circuit 352 for selectively controlling the second signal
electrodes 316, and a signal detecting circuit (not shown) such as
a sense amplifier, for example. As specific examples of the
peripheral circuit section 360, a Y gate, a sense amplifier, an
input-output buffer, an X address decoder, a Y address decoder, and
an address buffer can be given. The peripheral circuit section 360
may be formed by MOS transistors formed on a substrate (single
crystal silicon substrate, for example). In the case where the
substrate is formed of a single crystal silicon substrate, the
peripheral circuit section 360 can be integrated on the same
substrate as the nano-sensor array 300. The nano-sensors are formed
last by spin-coating a solution containing self-assembled
nano-sensors on a wafer after the wafer has been processed and
devices are formed using conventional semiconductor fabrication
techniques. Conventional semiconductor structures are formed as is
conventional. During the next to the last conventional step, gold
electrodes are formed. Then a resist layer is formed over the last
layer, and selective etching is performed to expose the gold
electrodes. A solution containing the nano-sensors are spin-coated
on top, where the nano-sensors self-assemble. Finally, a permeable
layer is formed above the nano-sensors to protect the nano-elements
and the semiconductor elements while allowing the target chemicals
to pass through to the nano-sensors.
[0153] In one embodiment, the layer is a gas sensitive film
containing or covering nano-elements such as nano-pores. As the
sensitive film is exposed to different gases or chemicals, its
resistance changes. The resistance of the film is measured by
passing a small amount of current and monitoring the voltage drop
across the film. In one device for sensing air quality, the
sensor's film is readily oxidized (by NO.sub.2 or O.sub.2) or
reduced (by CO or NH.sub.3). Upon oxidation or reduction, the
electrical resistivity (or some other physical parameter) of the
matrix film changes and it is detected to infer the gas
concentration. A heater can be provided near the matrix to provide
temperature adjustments to better detect gas.
[0154] In yet another embodiment, the matrix is ultrasonically
activated to detect gases and chemicals. In these embodiments, a
gas or chemical sensitive nano-layer is deposited over an
ultrasonic vibrator. When gases or chemicals are absorbed by the
sensitive layer, they change the layer's mechanical properties.
These mechanical changes influence the vibration amplitude and
phase and can be picked up by monitoring the vibrational
characteristics of the oscillator. In a microbalance embodiment,
bulk wave detection is used to detect very small mass loading that
occurs when minute quantities of materials are deposited over the
surface of the oscillator. This method is the basis of
thickness-monitors used in evaporation systems and can detect
nanogram of materials. The surface acoustic wave embodiment is even
more sensitive than the microbalance embodiment since it directly
detects the surface loading. It can be used to detect simple mass
loading effects and any mechanical changes that may occur in its
gas or chemical sensitive layer. This method can detect changes as
small as one part in billion.
[0155] For example, if desired, the nano-elements can be coated
with a specific coating of interest (e.g., a ligand such as a
peptide or protein, e.g., an enzyme), chosen for its ability to
bind a particular ligand binding partner (e.g., an antibody or
receptor can bind a ligand, or can themselves be the ligand to
which ligand binding partner binds). Common analytes of interest
for which detection is sought include glucose, cholesterol,
warfarin, anthrax, testosterone, erythromycin, metabolites,
pesticides, toxic molecules (e.g., formaldehyde, benzene, toluene,
plutonium, etc.), ethanol (or other alcohols), pyruvate, and/or
drugs.
[0156] For example, biosensors can include nanostructures which
capture or comprise enzymes such as oxidases, reductases,
aldehyde/ketone reductases, alcohol dehdrogenases, aldehyde
oxidases, cytochrome p450s, flavin monooxygenases, monoamine
oxidases, xanthine oxidases, ester/amide hydrolases, epoxide
hydrolases or their substrates or which capture their reaction
products. Signal transduction is optionally facilitated by use of
conductive polymers, to bind compounds to the nanostructure, which
facilitates electron transport to the surface of the structure.
Several such polymers are available, including, e.g., polyaniline.
It will be recognized that many of the biomolecules or other
analytes to be captured (proteins, nucleic acids, lipids,
carbohydrates) in the setting of a biosensor are charged, which can
be used to cause them to "switch" a nanoscale transistor, providing
for detection of binding of an analyte.
[0157] In other embodiments, biomolecules such as enzymes generate
signals that are detected by an array. For example, the array can
include a glucose oxidase and/or a cholesterol oxidase enzyme for
the detection of glucose or cholesterol levels in blood or other
biological fluids. For example, a number of existing glucose
monitoring systems exist, including ferrocene, ferricyanide and
Osmium polymer mediated systems. These systems generally use
glucose oxidases in the process of glucose detection. These systems
are adapted to the present invention by mounting or capturing one
or more analyte detection molecule (e.g., glucose oxidase or the
relevant mediator) on a nanostructure of interest. Similarly, in a
biohazard detector, a p450 or other suitable enzyme can be used to
detect the presence of warfarin or another relevant molecule of
interest.
[0158] The binding of receptors and carbon nanotubes or
biomolecules can be detected by an electrical method or resonance
method or by using an x-y fluorescent laser reader. When the method
of detecting an electrical signal is applied, the binding of
receptors is detected by reading a minor change in voltage level of
the carbon nanotubes occurring when the receptors or biomolecules
are bound to the carbon nanotubes, using an appropriate circuit. In
one environment, the nanotubes or nanostructures can be any
conducting or semiconducting nanostructures. In some embodiments,
the nanostructures can also be nanowires, nanorods, or some other
elongated nanostructures. In particular, the nanostructures can be
carbon nanotubes and may be single-wall, semiconducting, carbon
nanotubes. There can be any number of nanostructures, some of which
may intersect one another as they traverse the device, and some of
which may traverse the device without intersection. A power supply
applies a first voltage across the nanostructure sensing array. A
first current through the nanostructure sensing array is measured
with a meter. The nanostructure sensing array is exposed to an
environment of interest. The electrical supply applies the same
first voltage across the nanostructure sensing array and the gate
voltage source applies the same first gate voltage to the
substrate. A second current through the nanostructure sensing array
is measured with the meter. Differences between the first current
and the second current can be attributed to electrical changes in
the nanostructure sensing array caused by interaction with an
analyte. Electrical changes can be correlated to identification of
particular analytes by comparing the changes with predetermined
electrical changes made in know environments.
[0159] When the resonance detection method is applied, a nanoplate
structure designed to have a resonance frequency of a range from
megaHertzs to low gigaHertzs is irradiated with a laser diode, and
the binding of receptors or biomolecules to the nanoplate structure
is optically measured by detecting a reflection signal using a
position detection photodiode. When the x-y fluorescent laser
reader is used, the target biomolecules bound to receptors are
reacted with, for example, fluorescent molecules or
fluorescence-labeled antibodies, and the entire chip after the
reaction with the target biomolecules is placed on the x-y
fluorescent laser reader to detect fluorescence. a detection system
for detecting the binding of receptors and carbon nanotubes or the
binding of receptors and biomolecules may be further included.
These types of binding can be detected by an electrical method or
resonance method or by using an x-y fluorescent laser reader. When
the method of detecting an electrical signal is applied, the
binding of receptors or biomolecules is detected by reading a minor
change in voltage level of the carbon nanotubes occurring when the
receptors or biomolecules are bound to the carbon nanotubes, using
an appropriate circuit. When the resonance detection method is
applied, a nanoplate structure designed to have a resonance
frequency of a range from megaHertzs to low gigaHertzs is
irradiated with a laser diode, and the binding of receptors or
biomolecules to the nanoplate structure is optically measured by
detecting a reflection signal using a position detection
photodiode. When the x-y fluorescent laser reader is used, the
target biomolecules bound to receptors are reacted with, for
example, fluorescent molecules or fluorescence-labeled antibodies,
and the entire chip after the reaction with the target biomolecules
is placed on the x-y fluorescent laser reader to detect
fluorescence. In particular, the entire chip is scanned with a
laser beam capable of exciting the fluorescence-labeled target
proteins and imaged by using a charge-coupled device (CCD) capable
of scanning the entire chip array. Alternatively, a confocal
microscope, which increases automation and detects data rapidly at
a high resolution, can be applied to collect data from the chip
array.
[0160] Once digitized using the nano-sensors, various algorithms
can be applied to detect a pattern associated with a substance. The
chemical signal is parameterized into chemical features by a
feature extractor. The output of the feature extractor is delivered
to a sub-chemical structure recognizer. A structure preselector
receives the prospective sub-structures from the recognizer and
consults a dictionary to generate structure candidates. A syntax
checker receives the structure candidates and selects the best
candidate as being representative of the detected chemical. In case
the chemical is a pathogen, suitable alarms can be sent.
[0161] With respect to the feature extractor, a wide range of
techniques can be used, including the short time energy, the zero
crossing rates, the level crossing rates, the filter-bank spectrum,
the linear predictive coding (LPC), and the fractal method of
analysis. In addition, vector quantization may be utilized in
combination with any representation techniques. Further, one
skilled in the art may use an auditory signal-processing model in
place of the spectral models to enhance the system's robustness to
noise and reverberation.
[0162] In one embodiment, the digitized chemical signal series s(n)
is put through a low-order filter, typically a first-order finite
impulse response filter, to spectrally flatten the signal and to
make the signal less susceptible to finite precision effects
encountered later in the signal processing. The signal is
pre-emphasized preferably using a fixed pre-emphasis network, or
preemphasizer. The signal can also be passed through a slowly
adaptive pre-emphasizer. The output of the pre-emphasizer is
related to the chemical signal input s(n) by a difference
equation:
{tilde over (s)}(n)=s(n)-0.9375s(n-1)
[0163] The coefficient for the s(n-1) term is 0.9375 for a fixed
point processor. However, it may also be in the range of 0.9 to
1.0.
[0164] The preemphasized chemical signal is next presented to a
frame blocker to be blocked into frames of N samples with adjacent
frames being separated by M samples. In one embodiment, N is in the
range of 400 samples while M is in the range of 100 samples.
Accordingly, frame 1 contains the first 400 samples. The frame 2
also contains 400 samples, but begins at the 300th sample and
continues until the 700th sample. Because the adjacent frames
overlap, the resulting LPC spectral analysis will be correlated
from frame to frame. Accordingly, frame 1 of the chemical signal is
indexed as:
x.sub.l(n)={tilde over (s)}(Ml+n)
where n=0 . . . N-1 and l=0 . . . L-1.
[0165] Each frame must be windowed to minimize signal
discontinuities at the beginning and end of each frame. The window
tapers the signal to zero at the beginning and end of each frame.
Preferably, the window used for the autocorrelation method of LPC
is the Hamming window, computed as:
x ~ l ( n ) = x l ( n ) w ( n ) ##EQU00001## w ( n ) = 0.54 - 0.46
cos ( 2 .pi. n N - 1 ) ##EQU00001.2##
where n=0 . . . N-1. Each frame of windowed signal is next
autocorrelated by an autocorrelator to give:
r ( m ) = n = 0 N - 1 - m x ~ l ( n ) x ~ l ( n + m )
##EQU00002##
where m=0 . . . p. The highest autocorrelation value p is the order
of the LPC analysis.
[0166] A noise canceller operates in conjunction with the
autocorrelator to minimize noise. The output of the autocorrelator
and the noise canceller are presented to one or more
parameterization units, including an LPC parameter unit, an FFT
parameter unit, a chemical model parameter unit 204, a fractal
parameter unit 206, or a wavelet parameter unit 208, among others.
The parameterization units are connected to the parameter weighing
unit, which is further connected to the temporal derivative unit
before it is presented to a vector quantizer.
[0167] The LPC analysis block is one of the parameter blocks
processed by the preferred embodiment. The LPC analysis converts
each frame of p+1 autocorrelation values into an LPC parameter set
as follows:
k i = r ( i ) - ? r ( i - j ) E ( i - 1 ) ##EQU00003## .alpha. j (
i ) = .alpha. j ( i - 1 ) - k i .alpha. i - j ( i - 1 )
##EQU00003.2## E ( i ) = ( 1 - k i 2 ) E ( i - 1 ) ##EQU00003.3## ?
indicates text missing or illegible when filed ##EQU00003.4##
[0168] The final solution is given as:
? ##EQU00004## ? indicates text missing or illegible when filed
##EQU00004.2##
[0169] The LPC parameter is then converted into cepstral
coefficients. The cepstral coefficients are the coefficients of the
Fourier transform representation of the log magnitude spectrum. The
cepstral coefficient c(m) is computed as follows:
c 0 = ln .sigma. 2 ##EQU00005## c m = a m + k = 1 m - 1 ( k m ) c k
a m - k ##EQU00005.2## c m = k = 1 m - 1 ( k m ) c k a m - k
##EQU00005.3##
where sigma represents the gain term in the LPC model.
[0170] Although the LPC analysis is used in the preferred
embodiment, a filter bank spectral analysis, which uses the
short-time Fourier transformer, may also be used alone or in
conjunction with other parameter blocks. FFT is well known in the
art of digital signal processing. Such a transform converts a time
domain signal, measured as amplitude over time, into a frequency
domain spectrum, which expresses the frequency content of the time
domain signal as a number of different frequency bands. The FFT
thus produces a vector of values corresponding to the energy
amplitude in each of the frequency bands. The FFT converts the
energy amplitude values into a logarithmic value which reduces
subsequent computation since the logarithmic values are more simple
to perform calculations on than the longer linear energy amplitude
values produced by the FFT, while representing the same dynamic
range. Ways for improving logarithmic conversions are well known in
the art, one of the simplest being use of a look-up table.
[0171] In addition, the FFT modifies its output to simplify
computations based on the amplitude of a given frame. This
modification is made by deriving an average value of the logarithms
of the amplitudes for all bands. This average value is then
subtracted from each of a predetermined group of logarithms,
representative of a predetermined group of frequencies. The
predetermined group consists of the logarithmic values,
representing each of the frequency bands. Thus, chemical signals
are converted from scanned data to a sequence of vectors of k
dimensions, each sequence of vectors identified as a chemical
frame, each frame represents a portion of the chemical signal.
[0172] Alternatively, the fractal parameter block can further be
used alone or in conjunction with others to represent spectral
information. Fractals have the property of self similarity as the
spatial scale is changed over many orders of magnitude. A fractal
function includes both the basic form inherent in a shape and the
statistical or random properties of the replacement of that shape
in space. As is known in the art, a fractal generator employs
mathematical operations known as local affine transformations.
These transformations are employed in the process of encoding
digital data representing spectral data. The encoded output
constitutes a "fractal transform" of the spectral data and consists
of coefficients of the affine transformations. Different fractal
transforms correspond to different images or sounds. The fractal
transforms are iteratively processed in the decoding operation. As
disclosed in U.S. Pat. No. 5,347,600, issued on Sep. 13, 1994 to
Barnsley, et al., one fractal generation method comprises the steps
of storing the graphical data in the CPU; generating a plurality of
uniquely addressable domain blocks from the stored spectral data,
each of the domain blocks representing a different portion of
information such that all of the stored image information is
contained in at least one of the domain blocks, and at least two of
the domain blocks being unequal in shape; and creating, from the
stored image data, a plurality of uniquely addressable mapped range
blocks corresponding to different subsets of the image data with
each of the subsets having a unique address. The creating step
included the substep of executing, for each of the mapped range
blocks, a corresponding procedure upon the one of the subsets of
the image data which corresponds to the mapped range block. The
method further includes the steps of assigning unique identifiers
to corresponding ones of the mapped range blocks, each of the
identifiers specifying for the corresponding mapped range block an
address of the corresponding subset of image data; selecting, for
each of the domain blocks, the one of the mapped range blocks which
most closely corresponds according to predetermined criteria; and
representing the image information as a set of the identifiers of
the selected mapped range blocks.
[0173] In U.S. Pat. No. 4,694,407, issued to Joan M. Ogden, another
method for generating fractals using their self-similarity
properties is disclosed. The self-similarity property of fractals
are related to the self-similarity existing in inverse pyramid
transforms. As discussed by P. J. Burt and E. H. Adelson in "A
Multiresolution Spline with Application to Image Mosaics", ACM
Transactions on Graphics, Vol. 2, No. 4, October 1983, pp. 217-236,
the pyramid transform is a spectrum analysis model that separates a
signal into a spatial-frequency band-pass components, each
approximately an octave wide in one or more dimensions and a
remnant low-pass component. The band-pass components have
successively lower center frequencies and successively less dense
sampling in each dimension, each being halved from one band-pass
component to the next lower. The remnant low-pass component may be
sampled with the same density as the lowest band-pass component or
may be sampled half so densely in each dimension. Processes that
operate on the transform result components affect, on different
scales, the reconstruction of signals in an inverse transform
process. Processes operating on the lower spatial frequency, more
sparsely sampled transform result components affect the
reconstructed signal over a larger region than do processes
operating on the higher spatial frequency, more densely sampled
transform result components. The more sparsely sampled transform
result components are next expanded through interpolation to be
sampled at the same density as the most densely sampled transform
result. The expanded transform result components, now sampled at
similar sampling density, are linearly combined by a simple matrix
summation which adds the expanded transform result components at
each corresponding sample location in the shared most densely
sampled sample space to generate the fractal. The pyramidal
transformation resembles that of a wavelet parameterization.
[0174] Alternatively, a wavelet parameterization block can be used
alone or in conjunction with others to generate the parameters.
Like the FFT, the discrete wavelet transform (DWT) can be viewed as
a rotation in function space, from the input space, or time domain,
to a different domain. The DWT consists of applying a wavelet
coefficient matrix hierarchically, first to the full data vector of
length N, then to a smooth vector of length N/2, then to the
smooth-smooth vector of length N/4, and so on. Most of the
usefulness of wavelets rests on the fact that wavelet transforms
can usefully be severely truncated, that is, turned into sparse
expansions. In the DWT parameterization block, the wavelet
transform of the chemical signal is performed. The wavelet
coefficients is allocated in a nonuniform, optimized manner. In
general, large wavelet coefficients are quantized accurately, while
small coefficients are quantized coarsely or even truncated
completely to achieve the parameterization.
[0175] Due to the sensitivity of the low-order cepstral
coefficients to the overall spectral slope and the sensitivity of
the high-order cepstral coefficients to noise variations, the
parameters generated by block may be weighted by a parameter
weighing block, which is a tapered window, so as to minimize these
sensitivities.
[0176] Next, a temporal derivator measures the dynamic changes in
the spectra. The regression coefficient, essentially a slope
measurement, is defined as:
R m ( t ) = n = - .delta. .delta. nC m ( t + n ) n = - .delta.
.delta. n 2 ##EQU00006##
where R is the regression coefficient and Cm(t) is the m-th
coefficient of the t-th frame of the utterance. Next, a differenced
LPC cepstrum coefficient set is computed by:
D.sub.m(t)=C.sub.m(t+.delta.)-C.sub.m(t-.delta.)
where the differenced coefficient is computed for every frame, with
delta set to two frames.
[0177] Power features are also generated to enable the system to
distinguish chemical signal from silence. Power can simply computed
from the waveform as:
P = log ( i = 1 M x i 2 ) ##EQU00007##
where P is the power for frame n, which has M discrete time samples
that has been Hamming windowed. Next, a differenced power set is
computed by:
DP.sub.m(t)=P.sub.m(t+.delta.)-P.sub.m(t-.delta.)
where the differenced coefficient is computed for every frame, with
delta set to two frames.
[0178] After the feature extraction has been performed, the
chemical parameters are next assembled into a multidimensional
vector and a large collection of such feature signal vectors can be
used to generate a much smaller set of vector quantized (VQ)
feature signals by a vector quantizer that cover the range of the
larger collection. In addition to reducing the storage space, the
VQ representation simplifies the computation for determining the
similarity of spectral analysis vectors and reduces the similarity
computation to a look-up table of similarities between pairs of
codebook vectors. To reduce the quantization error and to increase
the dynamic range and the precision of the vector quantizer, the
preferred embodiment partitions the feature parameters into
separate codebooks, preferably three. In the preferred embodiment,
the first, second and third codebooks correspond to the cepstral
coefficients, the differenced cepstral coefficients, and the
differenced power coefficients. The construction of one codebook,
which is representative of the others, is described next.
[0179] One embodiment uses a binary split codebook to generate the
codechemical structures in each codebook. In the preferred
embodiment, an M-vector codebook is generated in stages, first with
a 1-vector codebook and then splitting the codechemical structures
into a 2-vector codebook and continuing the process until an
M-vector codebook is obtained, where M is preferably 256.
[0180] The codebook is derived from a set of training vectors X[q]
obtained initially from a range of known chemical structures. The
vector centroid of the entire set of training vectors is computed
by:
W .fwdarw. [ c ] = 1 Q q = 1 Q X .fwdarw. [ q ] ##EQU00008##
[0181] In step 218, the codebook size is doubled by splitting each
current codebook to form a tree as:
{right arrow over (W)}.sub.n.sup.+={right arrow over
(W)}.sub.n(1+.di-elect cons.)
{right arrow over (W)}.sub.n.sup.-={right arrow over
(W)}.sub.n(1-.di-elect cons.)
where n varies from 1 to the current size of the codebook and
epsilon is a relatively small valued splitting parameter.
[0182] The data groups are classified and assigned to the closest
vector using the K-means iterative technique to get the best set of
centroids for the split codebook. For each training chemical
structure, a training vector is assigned to a cell corresponding to
the codechemical structure in the current codebook, as measured in
terms of spectral distance. The codechemical structures are updated
using the centroid of the training vectors assigned to the cell as
follows:
{right arrow over (W)}[A]={right arrow over (W)}[A]+.eta.({right
arrow over (X)}[q]-{right arrow over (W)}[A]),
0.ltoreq..eta..ltoreq.1
[0183] The distortion is computed by summing the distances of all
training vectors in the nearest-neighbor search so as to determine
whether the procedure has converged:
d iq = 1 N n = 1 N ( w ni - x nq ) 2 ##EQU00009##
wherein w and x represent scalar elements of a vector.
[0184] The split vectors in each branch of the tree is compared to
each other to see if they are very similar, as measured by a
threshold. If the difference is lower than the threshold, the split
vectors are recombined. To maintain the tree balance, the most
crowded node in the opposite branch is split into two groups, one
of which is redistributed to take the space made available from the
recombination. Nodes are readjusted to ensure that the tree is
properly pruned and balanced. If the desired number of vectors has
been reach, the process ends; otherwise, the vectors are split once
more.
[0185] The resultant set of codechemical structures form a
well-distributed codebook. During look up using the codebook, an
input vector may be mapped to the nearest codechemical structure in
one embodiment using the formula:
d = 1 N n = 1 N ( W [ a ] n - W [ b ] n ) 2 ##EQU00010##
[0186] Generally, the quantization distortion can be reduced by
using a large codebook. However, a very large codebook is not
practical because of search complexity and memory limitations. To
keep the codebook size reasonable while maintaining the robustness
of the codebook, fuzzy logic can be used in another embodiment of
the vector quantizer.
[0187] With conventional vector quantization, an input vector is
represented by the codechemical structure closest to the input
vector in terms of distortion. In conventional set theory, an
object either belongs to or does not belong to a set. This is in
contrast to fuzzy sets where the membership of an object to a set
is not so clearly defined so that the object can be a part member
of a set. Data are assigned to fuzzy sets based upon the degree of
membership therein, which ranges from 0 (no membership) to 1.0
(full membership). A fuzzy set theory uses membership functions to
determine the fuzzy set or sets to which a particular data value
belongs and its degree of membership therein.
[0188] The fuzzy vector quantization represents the input vector
using the fuzzy relations between the input vector and every
codechemical structure as follows:
where x k ' isafuzzyVQrepresentaionofinputvector x k , x k ' = i =
1 C [ u ik m v i ] i = 1 C u ik m ##EQU00011##
where x'(k) is a fuzzy VQ representation of the input vector x(k)
and v(i) is a codechemical structure, c is the number of
codechemical structures, m is a constant, and u(i,k) is:
u ik = 1 j = 1 C ( d ik d jk ) 1 m - 1 ##EQU00012##
where d(i,k) is the distance of the input vector x(k) and the
codechemical structure v(i).
[0189] To handle the variance of patterns of chemical substances
over time and to perform structure adaptation in an automatic,
self-organizing manner, an adaptive clustering technique called
hierarchical spectral clustering is used. Such changes can result
from temporary or permanent changes from various environmental
effects. Thus, the codebook performance is improved by collecting
chemical patterns over a long period of time to account for natural
variations in the chemical signal. The adaptive clustering system
is defined as:
W .fwdarw. [ A ] = W .fwdarw. [ A ] + ( X .fwdarw. ' - W .fwdarw. [
A ] ) 2 ##EQU00013##
where the vector X' is the chemical signal vector closest in
spectral distance to W[A] after training.
[0190] In the preferred embodiment, a neural network is used to
recognize each codechemical structure in the codebook as the neural
network is quite robust at recognizing codechemical structure
patterns. Once the chemical features have been characterized, the
chemical recognizer then compares the input chemical signals with
the stored templates of the vocabulary known by the recognizer Data
from the vector quantizer is presented to one or more recognition
models, including an HMM model, a dynamic time warping model, a
neural network, a fuzzy logic, or a template matcher, among others.
These models may be used singly or in combination. The output from
the models is presented to an initial N-gram generator which groups
N-number of outputs together and generates a plurality of
confusingly similar candidates as initial N-gram prospects. Next,
an inner N-gram generator generates one or more N-grams from the
next group of outputs and appends the inner trigrams to the outputs
generated from the initial N-gram generator. The combined N-grams
are indexed into a dictionary to determine the most likely
candidates using a candidate preselector. The output from the
candidate preselector is presented to a chemical structure N-gram
model or a chemical grammar model, among others to select the most
likely chemical structure based on the occurrences of other
chemical structures nearby.
[0191] Dynamic programming obtains a relatively optimal time
alignment between the chemical structure to be recognized and the
nodes of each chemical model. In addition, since dynamic
programming scores chemical structures as a function of the fit
between chemical models and the chemical signal over many frames,
it usually gives the correct chemical structure the best score,
even if the chemical structure has been slightly misspoken or
obscured by background sound. This is important, because humans
often mispronounce chemical structures either by deleting or
mispronouncing proper sounds, or by inserting sounds which do not
belong.
[0192] In dynamic time warping, the input chemical signal A,
defined as the sampled time values A=a(1) . . . a(n), and the
vocabulary candidate B, defined as the sampled time values B=b(1) .
. . b(n), are matched up to minimize the discrepancy in each
matched pair of samples. Computing the warping function can be
viewed as the process of finding the minimum cost path from the
beginning to the end of the chemical structures, where the cost is
a function of the discrepancy between the corresponding points of
the two chemical structures to be compared.
[0193] The warping function can be defined to be:
C=c(1),c(2), . . . , c(k), . . . c(K)
[0194] where each c is a pair of pointers to the samples being
matched:
c(k)=[i(k),j(k)]
[0195] In this case, values for A are mapped into i, while B values
are mapped into j. For each c(k), a cost function is computed
between the paired samples. The cost function is defined to be:
d[c(k)]=(a.sub.i(k)-b.sub.j(k)).sup.2
[0196] The warping function minimizes the overall cost
function:
D ( C ) = k = 1 K d [ c ( k ) ] ##EQU00014##
subject to the constraints that the function must be monotonic
i(k).gtoreq.i(k-1) and j(k).gtoreq.j(k-1)
and that the endpoints of A and B must be aligned with each other,
and that the function must not skip any points.
[0197] Dynamic programming considers all possible points within the
permitted domain for each value of i. Because the best path from
the current point to the next point is independent of what happens
beyond that point. Thus, the total cost of [i(k), j(k)] is the cost
of the point itself plus the cost of the minimum path to it.
Preferably, the values of the predecessors can be kept in an
M.times.N array, and the accumulated cost kept in a 2.times.N array
to contain the accumulated costs of the immediately preceding
column and the current column. However, this method requires
significant computing resources.
[0198] The method of whole-chemical structure template matching has
been extended to deal with connected chemical structure
recognition. A two-pass dynamic programming algorithm to find a
sequence of chemical structure templates which best matches the
whole input pattern. In the first pass, a score is generated which
indicates the similarity between every template matched against
every possible portion of the input pattern. In the second pass,
the score is used to find the best sequence of templates
corresponding to the whole input pattern.
[0199] Dynamic programming requires a tremendous amount of
computation. For the chemical signal recognizer to find the optimal
time alignment between a sequence of frames and a sequence of node
models, it must compare most frames against a plurality of node
models. One method of reducing the amount of computation required
for dynamic programming is to use pruning. Pruning terminates the
dynamic programming of a given portion of chemical signal against a
given chemical structure model if the partial probability score for
that comparison drops below a given threshold. This greatly reduces
computation, since the dynamic programming of a given portion of
chemical signal against most chemical structures produces poor
dynamic programming scores rather quickly, enabling most chemical
structures to be pruned after only a small percent of their
comparison has been performed.
[0200] To reduce the computations involved, one embodiment limits
the search to that within a legal path of the warping. Typically,
the band where the legal warp path must lie is usually defined as
|i-j|.ltoreq.r, where r is a constant representing the vertical
window width on the line defined by A & B. To minimize the
points to be computed, the DTW limits its computation to a narrow
band of legal path to:
i - j S .ltoreq. L t 2 ( 1 + S 2 ) ##EQU00015##
where L(t) is the length of the perpendicular vector connecting
L(A) with j=S(i)+r and L(B) with j=S(i)-r, and S=slope as defined
by A/B.
[0201] Considered to be a generalization of dynamic programming, a
hidden Markov model is used in the preferred embodiment to evaluate
the probability of occurrence of a sequence of observations O(1),
O(2), . . . O(t), . . . , O(T), where each observation O(t) may be
either a discrete symbol under the VQ approach or a continuous
vector. The sequence of observations may be modeled as a
probabilistic function of an underlying Markov chain having state
transitions that are not directly observable.
[0202] In the preferred embodiment, the Markov network is used to
model a number of chemical sub-structures. The transitions between
states are represented by a transition matrix A=[a(i,j)]. Each
a(i,j) term of the transition matrix is the probability of making a
transition to state j given that the model is in state i. The
output symbol probability of the model is represented by a set of
functions B=[b(j) (O(t)], where the b(j) (O(t) term of the output
symbol matrix is the probability of outputting observation O(t),
given that the model is in state j. The first state is always
constrained to be the initial state for the first time frame of the
utterance, as only a prescribed set of left-to-right state
transitions are possible. A predetermined final state is defined
from which transitions to other states cannot occur.
[0203] Transitions are restricted to reentry of a state or entry to
one of the next two states. Such transitions are defined in the
model as transition probabilities. For example, a chemical signal
pattern currently having a frame of feature signals in state 2 has
a probability of reentering state 2 of a(2,2), a probability a(2,3)
of entering state 3 and a probability of a(2,4)=1-a(2,1)-a(2,2) of
entering state 4. The probability a(2,1) of entering state 1 or the
probability a(2,5) of entering state 5 is zero and the sum of the
probabilities a(2,1) through a(2,5) is one. Although the preferred
embodiment restricts the flow graphs to the present state or to the
next two states, one skilled in the art can build an HMM model
without any transition restrictions, although the sum of all the
probabilities of transitioning from any state must still add up to
one.
[0204] In each state of the model, the current feature frame may be
identified with one of a set of predefined output symbols or may be
labeled probabilistically. In this case, the output symbol
probability b(j) O(t) corresponds to the probability assigned by
the model that the feature frame symbol is O(t). The model
arrangement is a matrix A=[a(i,j)] of transition probabilities and
a technique of computing B=b(j) O(t), the feature frame symbol
probability in state j.
[0205] The probability density of the feature vector series Y=y(1),
. . . , y(T) given the state series X=x(1), . . . , x(T) is
[ Precise solution ] ##EQU00016## L 1 ( v ) = x P { Y , X | .lamda.
v } [ Approximate solution ] ##EQU00016.2## L 2 ( v ) = max x [ P {
Y , X | .lamda. v } ] [ Log approximate solution ] ##EQU00016.3## L
3 ( v ) = max x [ log P { Y , X | .lamda. v } ] ##EQU00016.4##
[0206] The final recognition result v of the input chemical signal
x is given by: where n is a positive integer.
v = arg max v [ L n ( v ) ] ##EQU00017##
[0207] The Markov model is formed for a reference pattern from a
plurality of sequences of training patterns and the output symbol
probabilities are multivariate Gaussian function probability
densities. The chemical signal traverses through the feature
extractor. During learning, the resulting feature vector series is
processed by a parameter estimator, whose output is provided to the
hidden Markov model. The hidden Markov model is used to derive a
set of reference pattern templates, each template representative of
an identified pattern in a vocabulary set of reference chemical
sub-structure patterns. The Markov model reference templates are
next utilized to classify a sequence of observations into one of
the reference patterns based on the probability of generating the
observations from each Markov model reference pattern template.
During recognition, the unknown pattern can then be identified as
the reference pattern with the highest probability in the
likelihood calculator.
[0208] The HMM template has a number of states, each having a
discrete value. However, because chemical signal features may have
a dynamic pattern in contrast to a single value. The addition of a
neural network at the front end of the HMM in an embodiment
provides the capability of representing states with dynamic values.
The input layer of the neural network comprises input neurons. The
outputs of the input layer are distributed to all neurons in the
middle layer. Similarly, the outputs of the middle layer are
distributed to all output states, which normally would be the
output layer of the neuron. However, each output has transition
probabilities to itself or to the next outputs, thus forming a
modified HMM. Each state of the thus formed HMM is capable of
responding to a particular dynamic signal, resulting in a more
robust HMM. Alternatively, the neural network can be used alone
without resorting to the transition probabilities of the HMM
architecture.
[0209] Although the neural network, fuzzy logic, and HMM structures
described above are software implementations, nano-structures that
provide the same functionality can be used. For instance, the
neural network can be implemented as an array of adjustable
resistors each representing a link to a neuron whose output is
summed by an analog summer or adder.
Nano Image Sensors
[0210] In another embodiment, the various nano devices can be
integrated into image sensors for capture image information. Common
image sensors include Charge Coupled Devices (CCD) and CMOS
sensors. nano devices as described above can be used to act as
photo collection components, charge transfer devices (such as CCD
registers), and signal amplification devices in the image
sensors.
[0211] Taking CCD sensors as an example, CCD image sensors can
exist in different architectures such as Linear CCD array,
Bi-Linear CCD array, Area CCD Sensor Array, and frame Transfer CCD,
etc. The simplest architecture is a linear sensor. As shown in FIG.
8, the linear CCD array 600 consists of a line of photodiodes
601-604, each of which is respectively adjacent to a single CCD
readout register 631-634. The charges collected by the photo diodes
601-604 are transferred (610) to CCD registers 631-634 under the
control of the transfer gate 620. The charges collected are read
out one pixel at a time at output signal 650 after the charge
signals are converted to voltage signal by readout amplifier
640.
[0212] Although CCD architectures may be different, the basic
operations of a CCD sensor all begin with the conversion of photons
into electrons. When light is incident on the active area of the
image sensor it interacts with the atoms that make up the silicon
crystal. The energy transmitted by the light (photons) is used to
enable an electron to excite to the conduction band and leaving a
hole in the valence band. The more photons incident on the sensor,
the more electron-hole pairs that are generated. High energy
photons (short wavelengths) on the other hand are absorbed more
closely to the surface of the sensor and may not reach the active
part of the detector. Hence, there will be a spectrum over which
the sensor will operate, falling off at short and long
wavelengths.
[0213] The number of electrons generated per photon is known as the
"quantum efficiency", or QE. The electrons can be separated from
the holes in the photo collection areas. The amount of charge
collected will depend on the light intensity, its spectrum and the
integration time. By setting out a line or a 2D array of photo
collection areas, it is possible to build up a representation of
the image incident on the sensor.
[0214] In accordance with the present invention, a 1D or 2D array
of image collection areas are patterned by the nano-elements made
up of single-walled nanotubes aggregating (e.g., by van der Waals
forces) in substantially parallel orientation to form a monolayer
extending in directions substantially perpendicular to the
orientation of the individual nanotubes. Such monolayer arrays can
be formed by conventional techniques employing "self-assembled
monolayers" (SAM) or Langmiur-Blodgett films. nanotubes 1 are bound
to a substrate 2 having a reactive coating 3 (e.g., gold).
Typically, SAMs are created on a substrate which can be a metal
(such as gold, mercury or ITO (indium-tin-oxide)). The molecules of
interest, here the SWNT molecules, are linked (usually covalently)
to the substrate through a linker moiety. The linker moiety may be
bound first to the substrate layer or first to single-wall
nanotubes ("SWNT") molecule (at an open or closed end) to provide
for reactive self-assembly. Langmiur-Blodgett films are formed at
the interface between two phases, e.g., a hydrocarbon (e.g.,
benzene or toluene) and water. Orientation in the film is achieved
by employing molecules or linkers that have hydrophilic and
lipophilic moieties at opposite ends.
[0215] The 1D or 2D array of image collection areas can include
photo diodes formed by PN-type junctions discussed in US
Application Serial No. 20030200521, the content of which is
incorporated herein by reference. The 1D or 2D nano sensor array
can include arrays of crossed nanoscale wires having selectively
programmable crosspoints. Nanoscale wires of one array are shared
by other arrays, providing signal propagation between the
arrays.
[0216] The nano elements can be patterned to form a 2D array for
capturing an image-wise energy pattern from photons or energy
particles. Each pattern nano element forms a photo diode with band
gap sensitive to the photon energies the image sensor is designed
to capture. At regular intervals photo induced charges at each
pixel must be emptied and the amount of charge measured to
determine the local light intensity. This is accomplished using a
CCD register. A measuring device sits at the end of the row, known
as the output node.
[0217] In another embodiment, the 1D or 2D array of image
collection areas can include nano wires which are capable of
capture photons and convert them into photoelectrons. The
orientation of the nano wires can be controlled to maximize the
photon detection efficiency. Methods of aligning nanowires are
discussed in US Patent Publication 20030186522, the disclosure of
which is incorporated hereof by reference.
[0218] In accordance with the present invention, the CCD registers
and charge readout circuit, the readout amplifiers (for example,
620, 631-634, 640, 650) are fabricated in one or more layers made
of semiconductor materials such as silicon and silicon oxide using
conventional semiconductor micro-fabrication technologies. The
image sensitive image layer (comprising photo diodes 601-604)
patterned with nano materials is formed over the layers of the
semiconductor materials.
[0219] The charges in an image collection area, or a pixel, is
transferred into a measuring device in the semiconductor layer to
produce a signal that depends on the amount of stored charge. The
charge transfer is controlled by the transfer gate 620 at a
predetermined clock rate. The empty image collection area in the
nano layer is ready for capturing the next image. The downward
charge transfer from the nano photo sensitive layer to the
semiconductor charge measuring layer is similar to the frame
transfer CCD architecture. Detailed operations of photo induced
charge transfers and readout are discussed in U.S. Pat. Nos.
5,946,034 and 6,576,938, the disclosures of which are incorporated
hereof by reference.
[0220] The nano-semiconductor CCD device as described above has the
following advantages. Since the photon sensing pixels occupy the
nano photo sensitive layer on top, no photon receiving area needs
to be wasted for building CCD registers and voltage conversion
devices. The effective spatial fraction of image sensing can be
maximized to 80-95% range. Another advantage of the
nano-semiconductor CCD device in the present invention is the frame
fresh rate is significantly increased because photo induced charges
are transfer directly to the CCD registers, rather than cascade
transferred between photo charge collection areas. These advantages
are critical for fabricating miniature and high speed imaging
devices such as digital cameras, digital video cameras, night
vision devices, telescope cameras, and microscopic cameras for
scientific observations.
[0221] In accordance to another embodiment of the present
invention, the nano-semiconductor imaging device can be sensitive
to different photo spectrum such red, green, blue, infrared, UV
etc. by using color filter arrays (CFA) disposed over the nano
photo sensitive layer. Different CFA patterns include Bayer
pattern, interlaced liner pattern etc. The semiconductor layer can
further include electronic circuit for constructing color planes
from the photo-induced charges filtered by CFA. The electronic
circuit can also perform various image processing operations well
known in the art. Detailed operations of CFA patterns and
improvement are discussed in U.S. Pat. No. 6,366,318, the
disclosures of which are incorporated hereof by reference.
[0222] In another embodiment, nano-elements are fabricated above a
CMOS image sensor where each pixel contains three transistors: a
select transistor, a source follower transistor and a reset
transistor. The source follower transistor is connected to a
photodiode with a nano-element formed above the photodiode. Light
is collected by the photodiode/nano-element causes a change in the
potential on the photodiode which is read out through the action of
the select and source follower transistors. The reset transistor is
used to establish a constant potential on the photodiodes prior to
the start of exposure to light. In one embodiment, the nano-element
is an FSA assembled geometric structure with a specific optical
absorption spectrum, a specific optical transmission spectrum, a
specific optical reflection characteristic, or a capability for
modifying the polarization of light. In another embodiment,
fullerene nanotubes such as an (m,n) tube can be used in
conjunction with other materials can be used to form a Schottky
barrier which would act as a light harvesting sensor or antenna. In
one embodiment, a (10, 10) tube can be connected via sulfur
linkages to gold at one end of the tube and lithium at the other
end of the tube forming a natural Schottky barrier. Current is
generated through photo conductivity. As the (10, 10) tube acts
like an antenna, it pumps electrons into one electrode, but back
flow of electrons is prevented by the intrinsic rectifying diode
nature of the nanotube/metal contact. In forming an antenna, the
length of the nanotube can be varied to achieve any desired
resultant electrical length. The length of the molecule is chosen
so that the current flowing within the molecule interacts with an
electromagnetic field within the vicinity of the molecule,
transferring energy from that electromagnetic field to electrical
current in the molecule to energy in the electromagnetic field.
This electrical length can be chosen to maximize the current
induced in the antenna circuit for any desired frequency range. Or,
the electrical length of antenna element can be chosen to maximize
the voltage in the antenna circuit for a desired frequency range.
Additionally, a compromise between maximum current and maximum
voltage can be designed. More on the fullerene light sensor is
disclosed in Application Serial No. 20020150524, the content of
which is incorporated by reference.
[0223] The nano image sensor is eventually connected to various
other imaging devices such as a stand-alone digital camera (both
still and video cameras), and embedded digital cameras (that may be
used in cellular phones, personal digital assistants (PDA) and the
like). In another example implementation, various imaging devices
may be coupled to image sensor package, including digital still
cameras, tethered PC cameras, imaging enabled mobile devices (e.g.
cell phones, pagers, PDA's and laptop computers), surveillance
cameras, toys, machine vision systems, medical devices and image
sensors for automotive applications.
[0224] In yet another embodiment, an array of electrically
conductive carbon nanotube (CNT) towers are grown directly on the
surface of a silicon chip. The CNT towers allow signals captured
from a charge-coupled device (CCD) to be transmitted directly to
the neural elements of the retina to restore vision. A retinal
electrode array with a remote return electrode is provided outside
of the eye. An array of stimulating nano-electrodes is placed on
the retinal surface (epiretinally) or under the retina
(subretinally) and a relatively large return electrode is placed
outside of the sclera and distant from the array of stimulating
electrodes. The remote return electrode promotes deeper stimulation
of retinal tissue to support vision.
[0225] The structures discussed above to recognize chemical
substances can be applied to recognize images as well. Such
structures include HMMs, neural networks, fuzzy logic, and
statistical recognizers, among others.
Nano Displays
[0226] Turning now to a different embodiment to display images, the
nano-elements can be light-emitting nano particles. The production
of a robust, chemically stable, crystalline, passivated nano
particle and composition containing the same, that emit light with
high efficiencies and size-tunable and excitation energy tunable
color is discussed in Application Serial No. 20030003300, the
content of which is hereby incorporated b reference. The methods
include the thermal degradation of a precursor molecule in the
presence of a capping agent at high temperature and elevated
pressure. A particular composition prepared by the methods is a
passivated silicon nano particle composition displaying discrete
optical transitions. Group IV metals form nano crystalline or
amorphous particles by the thermal degradation of a precursor
molecule in the presence of molecules that bind to the particle
surface, referred to as a capping agent at high temperature and
elevated pressure. In certain embodiments, the reaction may run
under an inert atmosphere. In certain embodiments the reaction may
be run at ambient pressures. The particles may be robust,
chemically stable, crystalline, or amorphous and organic-monolayer
passivated, or chemically coated by a mixture of organic molecules.
In one embodiment, the particles emit light in the ultraviolet
wavelengths. In another embodiment, the particles emit light in the
visible wavelengths. In other embodiments, the particles emit light
in the near-infrared and the infrared wavelengths. The particles
may emit light with high efficiencies. Color of the light emitted
by the particles may be size-tunable and excitation energy tunable.
The light emission may be tuned by particle size, with smaller
particles emitting higher energy than larger particles. The surface
chemistry may also be modified to tune the optical properties of
the particles. In one embodiment, the surfaces may be
well-passivated for light emission at higher energies than
particles with surfaces that are not well-passivated. The average
diameter of the particles may be between 1 and 10 nm. A particular
composition prepared by the methods is a passivated silicon nano
particle composition displaying discrete optical transitions and
photoluminescence.
[0227] In another embodiment, a light may be formed having a broad
size distribution of silicon nano particles. The broad size
distribution may be advantageous in that the combination of
wavelengths emitted by the different size particles may produce a
white light. The silicon nano particles may be embedded in a
polymer matrix. The polymer matrix is not, however, necessary for
the silicon nano particles to function effectively as the emissive
layer. The size distribution of silicon nano particles may allow
the emission of white light. The nano particles themselves may emit
with size-independent quantum yields and lifetimes. Clusters of
nano particles may produce a broad emission band. If energy
transfer occurs between neighboring nanoparticles, it does not
result in the selective emission from only the largest particles
with the lowest energy gap between the highest occupied and lowest
unoccupied molecular orbits (HOMO and LUMO). This situation is
qualitatively different than known technology using CdSe
nanoparticles.
[0228] An embodiment of a basic design for light emitting device
includes a first electrode, second electrode, and emissive layer.
Emissive layer may include the nano particles exhibiting discrete
optical properties as described herein. Emissive layer may include
a polymer wherein the nano particles may be suspended. However,
nano particle based light emitting devices may not require a
polymer to emit, in contrast to many organic LEDs. Polymers may
inflict losses through absorption, scattering, and poor
electron-hole interfaces. Emissive layer may be positioned adjacent
first electrode. First electrode may function as a cathode.
Emissive layer may be positioned adjacent second electrode. Second
electrode may function as an anode. Substrate may include a
transparent conductive oxide layer. Non-limiting examples of the
transparent conductive oxide layer may include indium tin oxide,
tin oxide, or a translucent thin layer of Ni or Au or an alloy of
Ni and Au. The basic design of light emitting devices is described
in further detail in U.S. Pat. No. 5,977,565 which is incorporated
herein by reference. The nanoparticles may emit light by optical
stimulation. In this device, an optical excitation source is used
in place of electrical stimulation. However, in another embodiment,
a combination of optical excitation and electrical stimulation may
be used to enhance device performance, such as overall energy
efficiency or perhaps color tenability.
[0229] The nano display device in the present invention can include
an array of light-emitting cells disposed in rows and columns and
constructed over a substrate. Each light emitting cell comprises a
first electrode, a second electrode, and a light-emitting nano
material disposed in the intersecting region between the first
electrode and the second electrode. The light-emitting nano
material is capable of emitting light when a voltage is applied
between the first electrode and the second electrode. The nano
display device of claim 1, wherein the light-emitting nano material
includes low molecular weight or polymeric organic molecules, and
nano particles formed by semiconductor materials as described
below. The light-emitting nano material can emit photons at one or
more wavelengths for example in the Ultra Violet, visible, and
infrared spectra. A light emitting diode is formed in each
light-emitting cell by the light-emitting nano material, the first
electrode, and the second electrode. A nano diode can be fabricated
using techniques above. The light-emitting cells are insulated by
insulation regions so that each light-emitting cell can be
individually addressed for light emission.
[0230] In another embodiment, a molecule is used as light emitter
with two electrodes at a tunneling distance from each other. Such a
tunneling distance may as well lie in the subnanometer range as
above that range and is the distance which allows a tunneling
current to flow between the electrodes. As discussed in US
Application Serial 20020096633, the content of which is
incorporated by reference, the molecule can have a tertiary-butyl
substituted tetracycline with the tetracycline as the central
entity and the tertiary butyls as the peripheral entities which are
movable with respect to the central entity. The molecule has
several stable or metastable conformations depending on the states
of its entities. These states are determined by the inner binding
forces of the molecule, i.e. between the peripheral entities and
the central entity, and the binding forces between the entities and
the environment. The molecule is situated preferably on a
crystalline substrate which serves as one of the electrodes. Hence,
the inner forces of the molecule and the forces towards the
substrate determine the conformations. In a first conformation the
peripheral entities have a binding force towards tile substrate
which dominates over the force between the central entity and the
substrate. With other words, the central entity is so far away from
the substrate that the force between it and the substrate is weaker
than the force between the substrate and the peripheral entities.
The binding force between the peripheral entities and the substrate
are however sufficiently weak that the molecule is not fixed in its
horizontal position. It therefore floats around on the substrate
surface at room temperature. Another conformation is dominated by
the force between the central entity and the substrate. The central
entity is then near enough at the substrate that the binding force
holds the central entity to the substrate. In this conformation,
the molecule remains in its position, therefore it is also called
the pinned conformation. The peripheral entities in this
conformation are somehow distorted or bent or more generally moved
from their equilibration position, i.e. the position which they had
in the first conformation. The holding force between the central
entity and the substrate is stronger than eventual restoring forces
between the peripheral entities and the central entity which try to
form the molecule back to the first conformation. The molecule is
immobilized by the combined force between the substrate and the
central entity and between the peripheral entities and the
substrate. The molecule can be switched between the two stable
conformations. The switching is induced by electrical voltage but
can also occur through mechanical energy. The switching is
reversible. However, also irreversible switching is possible for
selected molecule types. When an electrical current is allowed to
flow through the substrate, light emission occurs. The substrate
may have a predetermined surface structure, namely for a
crystalline substrate the crystalline plane in which it lies. Light
emission occurs on various planes, such as the {111} and the {100}
plane. Copper, gold or silver are exemplary substrate materials on
which the effect can be seen. Other materials for the substrate,
such as polycrystalline materials or amorphous materials work as
well.
[0231] In another embodiment, the light emitter nano-elements can
be inorganic nanocrystals. The crystal composition includes a
solvent with semiconductor nanoparticles in the solvent, wherein
the solvent and the semiconductor nanoparticles are in an effective
amount in the liquid crystal composition to form a liquid
crystalline phase. The semiconductor nanoparticles can be
rod-shaped or disk-shaped, and has an aspect ratio greater than
about 2:1 or less than about 1:2. As discussed in Application
Serial No. 20030136943, the content of which is incorporated by
reference, the nanocrystals are treated as a conventional polymer
or biological macromolecule from the assembly point of view. This
enables a wide range of chemical macromolecular assembly techniques
to be extended to inorganic solids, which possess a diverse range
of optical, electrical, and magnetic properties. The optical
properties of the semiconductor nanoparticles can depend upon their
diameters and lengths. The photoluminescence wavelengths produced
by the semiconductor nanoparticles can be tuned over the visible
range by variation of the particle size, and the degree of
polarization can be controlled by variation of the aspect ratio.
Accordingly, by tuning the size of the semiconductor nano
particles, the liquid crystal compositions may emit different
colors (i.e., different wavelengths of light). For instance, when
the semiconductor nano particles in the liquid crystal composition
are about 3 nanometers wide and are about 5 nanometers long, the
liquid crystal composition can produce green light. When the
semiconductor nano particles in the liquid crystal composition are
about 3 nanometers wide and are about 60 nanometers long, the
liquid crystal composition can produce orange light. When the
semiconductor nano particles in the liquid crystal composition are
about 4 nanometers wide and about 6 nanometers long, the liquid
crystal composition can produce red light. Accordingly, in
embodiments of the invention, the optical properties of the liquid
crystal composition can be "tuned" by adjusting the size of the
nano particles in the liquid crystal composition. Also, because the
semiconductor nano particles are aligned in embodiments of the
invention, any light that is produced by the aligned semiconductor
nano particles can be polarized. The semiconductor nano particles
may comprise any suitable semiconductor material. For example,
suitable semiconductors include compound semiconductors. Suitable
compound semiconductors include Group II-VI semiconducting
compounds such as MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe,
SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe,
and HgTe. Other suitable compound semiconductors include Group
III-V semiconductors such as GaAs, GaP, GaAs--P, GaSb, InAs, InP,
InSb, AlAs, AlP, and AlSb. The use of Group IV semiconductors such
as germanium or silicon may also be feasible under certain
conditions.
[0232] In another embodiment, a nano-light emitting faceplate
patterned with colored-light-emitting nano pixels having a
predetermined size, pattern and spacing, the nano-light color
emitters eliminates the need for polarizers and color filters in
the Liquid Crystal Displays, which increases the efficiency of
light transmission, and increase brightness and contrast, and
reduces power consumption. The pattern of nano pixels in patterns
for emitting different color light can be achieved a sequence spin
coating steps. For example, a layer of green-photon emitting nano
materials is first spin coated over nano binding areas that is in a
2D pattern as described above. The excess green emitting nano
material is removed. A second pattern of nano binding materials is
formed on the substrate over the areas that is not covered by the
green-photon emitting nano materials. The nano binding materials at
this step may be specific to a blue-photon emitting material that
is subsequently spin coated. The excess blue-photon emitting
material is removed. A red-photon emitting material is coated
finally in similar steps to complete the color emitting pattern for
a full color display.
[0233] In another embodiment, electronic display can be achieved by
modulating reflective index or the orientations of the reflective
axes of the nano-elements on light reflective or refractive
surfaces. The modulation of the reflective index of the nano
materials can be driven by a two dimensional array of electrode
pairs and driver circuits as in the conventional electronic display
system. Each pair of electrodes and the associated nano material
define an image pixel. The reflective index of the nano materials
can be spatially modulated by selectively switching on and off of
the electrode pairs at different pixel locations, therefore
defining an image-wise pattern. An projective electronic nano
display is obtained by illuminating an uniform light beam across
the nano reflective (or refractive) surfaces. In summary, the nano
display device includes an array of light-emitting cells disposed
in rows and columns and constructed over a substrate. Each light
emitting cell comprises a first electrode, a second electrode, and
a light-reflective or light-refractive nano material disposed in
the intersecting region between the first electrode and the second
electrode. The light-reflective or light-refractive nano material
is capable of deflecting light when a voltage is applied between
the first electrode and the second electrode.
[0234] The nano display devices can include driver circuits for
driving rows and columns electrodes, digital signal processing
units, memory, display mode control, power drivers which are
typically found in conventional electronic displays. The nano
display devices can include driver circuits for driving rows and
columns electrodes, digital signal processing units, memory,
display mode control, power drivers which are typically found in
conventional electronic displays. The display component is mounted
on an interconnect substrate, usually flex, and electrical
connections are made from the edge of the CMOS back plane to the
substrate. Finally, the display component is suitably encapsulated,
thus providing environmental protection. Plastic encapsulation is
typically used in consumer products. The resulting display modules
produced in this manner are compact, lightweight, and relatively
inexpensive.
[0235] The magnification of the image can be accomplished using
refractive or reflective lens assemblies that are well known and
widely utilized in standard optical projection systems.
Nano Solar Cells
[0236] The nano-elements can be used as a solar cell as well. FIG.
9 depicts a flexible photovoltaic cell 600, in accordance with the
invention, that includes a photosensitized interconnected
nanoparticle material 603 and a charge carrier material 606
disposed between a first flexible, significantly light transmitting
substrate 609 and a second flexible, significantly light
transmitting substrate 612. In one embodiment, the flexible
photovoltaic cell further includes a catalytic media layer 615
disposed between the first substrate 609 and second substrate 612.
Preferably, the photovoltaic cell 600 also includes an electrical
conductor 618 deposited on one or both of the substrates 609 and
612. The methods of nano particle interconnection provided herein
enable construction of the flexible photovoltaic cell 600 at
temperatures and heating times compatible with such substrates 609
and 612. The flexible, significantly light transmitting substrates
609 and 612 of the photovoltaic cell 600 preferably include
polymeric materials.
[0237] Suitable substrate materials include, but are not limited
to, PET, polyimide, PEN, polymeric hydrocarbons, cellulosics, or
combinations thereof. Further, the substrates 609 and 612 may
include materials that facilitate the fabrication of photovoltaic
cells by a continuous manufacturing process such as, for example, a
roll-to-roll or web process as discussed in US Application Serial
No. 20030189402, the content of which is incorporated by reference.
The substrate 609 and 612 may be colored or colorless. Preferably,
the substrates 609 and 612 are clear and transparent. The
substrates 609 and 612 may have one or more substantially planar
surfaces or may be substantially non-planar. For example, a
non-planar substrate may have a curved or stepped surface (e.g., to
form a Fresnel lens) or be otherwise patterned.
[0238] An electrical conductor 618 is deposited on one or both of
the substrates 609 and 612. Preferably, the electrical conductor
618 is a significantly light transmitting material such as, for
example, ITO, a fluorine-doped tin oxide, tin oxide, zinc oxide, or
the like. In one illustrative embodiment, the electrical conductor
618 is deposited as a layer between about 100 nm and about 500 nm
thick. In another illustrative embodiment, the electrical conductor
618 is between about 150 nm and about 300 nm thick. According to a
further feature of the illustrative embodiment, a wire or lead line
may be connected to the electrical conductor 618 to electrically
connect the photovoltaic cell 600 to an external load.
[0239] As noted in Application Serial No. 20030189402, metal oxide
nanoparticles are interconnected by contacting the nanoparticles
with a suitable polylinker dispersed in a suitable solvent at or
below room temperature or at elevated temperatures below about
300.degree. C. The nanoparticles may be contacted with a polylinker
solution in many ways. For example, a nanoparticle film may be
formed on a substrate and then dipped into a polylinker solution. A
nanoparticle film may be formed on a substrate and the polylinker
solution sprayed on the film. The polylinker and nanoparticles may
be dispersed together in a solution and the solution deposited on a
substrate. To prepare nanoparticle dispersions, techniques such as,
for example, microfluidizing, attritting, and ball milling may be
used. Further, a polylinker solution may be deposited on a
substrate and a nanoparticle film deposited on the polylinker. The
photosensitized interconnected nanoparticle material 603 may
include one or more types of metal oxide nanotubes, as described in
detail above. Preferably, the nanotubes contain titanium dioxide
particles having an average particle size of about 20 nm. A wide
variety of photosensitizing agents may be applied to and/or
associated with the nanotubes to produce the photosensitized
interconnected nanotube material 603. The photosensitizing agent
facilitates conversion of incident visible light into electricity
to produce the desired photovoltaic effect. It is believed that the
photosensitizing agent absorbs incident light resulting in the
excitation of electrons in the photosensitizing agent. The energy
of the excited electrons is then transferred from the excitation
levels of the photosensitizing agent into a conduction band of the
interconnected nanotubes 603. This electron transfer results in an
effective separation of charge and the desired photovoltaic effect.
Accordingly, the electrons in the conduction band of the
interconnected nanotubes are made available to drive an external
load electrically connected to the photovoltaic cell. In one
illustrative embodiment, the photosensitizing agent is sorbed
(e.g., chemisorbed and/or physisorbed) on the interconnected
nanotubes 603. The photosensitizing agent may be sorbed on the
surfaces of the interconnected nanotubes 603, throughout the
interconnected nanotubes 603, or both. The photosensitizing agent
is selected, for example, based on its ability to absorb photons in
a wavelength range of operation, its ability to produce free
electrons (or electron holes) in a conduction band of the
interconnected nanotubes 603, and its effectiveness in complexing
with or sorbing to the interconnected nanotubes 603. The charge
carrier material 606 portion of the photovoltaic cells may form a
layer in the photovoltaic cell, be interspersed with the material
that forms the photosensitized interconnected nanotube material
603, or be a combination of both. The charge carrier material 606
may be any material that facilitates the transfer of electrical
charge from a ground potential or a current source to the
interconnected nanotubes 603 (and/or a photosensitizing agent
associated therewith). A general class of suitable charge carrier
materials can include, but are not limited to solvent based liquid
electrolytes, polyelectrolytes, polymeric electrolytes, solid
electrolytes, n-type and p-type transporting materials (e.g.,
conducting polymers), and gel electrolytes.
[0240] In another embodiment, nanocrystalline TiO.sub.2 is replaced
by a monolayer molecular array of short carbon nanotube molecules.
The photoactive dye need not be employed since the light energy
striking the tubes will be converted into an oscillating electronic
current which travels along the tube length. The ability to provide
a large charge separation (the length of the tubes in the array)
creates a highly efficient cell. A photoactive dye (such as
cis-[bisthiacyanato bis(4,4'-dicarboxy-2,2'-bipyridine Ru (II))]
can be attached to the end of each nanotube in the array to further
enhance the efficiency of the cell. In another embodiment of the
present invention, the TiO.sub.2 nanostructure described by Grtzel
in U.S. Pat. No. 5,084,365 (incorporated herein by reference in its
entirety) can serve as an underlying support for assembling an
array of SWNT molecules. In this embodiment, SWNTs are attached
directly to the TiO.sub.2 (by absorptive forces) or first
derivatized to provide a linking moiety and then bound to the
TiO.sub.2 surface. This structure can be used with or without a
photoactive dye as described above.
[0241] In yet another embodiment, instead of nanotubes,
shape-controlled inorganic nanocrystals can be used.
Shape-controlled inorganic nanocrystals offer controlled synthesis
that allows not only the prediction of a structure based on
computer models, but also the prediction of a precise synthetic
recipe that produces that exact structure in high-purity and
high-yield, with every particle identical to every other particle.
Inorganic semiconductor nanocrystals can control variables such as
length, diameter, crystallinity, doping density, heterojunction
formation and most importantly composition. Inorganic semiconductor
nanocrystals can be fabricated from all of the industrially
important semiconductor materials, including all of the Group
III-V, Group II-VI and Group IV materials and their alloys, as well
as the transition metal oxides. Furthermore, the inorganic
semiconductor nanostructures can be fabricated such that material
characteristics change controllably throughout the nanostructure to
engineer additional functionality (i.e. heterostructures) and
complexity into the nanostructure. As discussed in US Application
Serial No. 20030145779, three dimensional tetrapods may be
important alternatives to nanocrystal fibers and rods as additives
for mechanical reinforcement of polymers (e.g., polymeric binders
including polyethylene, polypropylene, epoxy functional resins,
etc.). Tetrapod shaped nanocrystal particles, for example, can
interlock with each other and can serve as a better reinforcing
filler in a composite material (e.g., with a binder), than for
example, nanospheres. The nanocrystal particles can be mixed with
the binder using any suitable mixing apparatus. After the composite
material is formed, the composite material can be coated on a
substrate, shaped, or further processed in any suitable manner.
[0242] An exemplary photovoltaic device may have nanocrystal
particles in a binder. This combination can then be sandwiched
between two electrodes (e.g., an aluminum electrode and an indium
tin oxide electrode) on a substrate to form a photovoltaic device.
Two separate mixtures can be used: one containing inorganic
semiconductors made of cadmium selenide (CdSe) nanorod molecules
and one containing the organic polymer to be blended with the
nanorods. The mixtures are then combined and spin-cast at room
temperature to produce an even film of nanorods that's
approximately 200 nanometers thick--about a thousandth the
thickness of a human hair. Tetrapods also have independent
tunability of the arm length and the band gap, which is attractive
for nanocrystal based solar cells or other types of photovoltaic
devices. In comparison to nanocrystal particles that are randomly
oriented, the tetrapods are aligned and can provide for a more
unidirectional current path than randomly oriented nanocrystal
particles.
[0243] In one embodiment, each flexible photovoltaic cell further
includes one or more flexible light-transmitting substrates, a
photosensitized interconnected nanoparticle material, and an
electrolyte redox system. In general, the nanotube material and the
electrolyte redox system are both disposed between the first and
second substrates. The flexible base may be the first significantly
light-transmitting substrate of the flexible photovoltaic cell. In
one embodiment, the flexible photovoltaic cell further includes a
photosensitized nanomatrix layer and a charge carrier medium. The
photovoltaic cell may energize the display element directly, or may
instead charge a power source in electrical communication with the
display element. The display apparatus may further include an
addressable processor and/or computer interface, operably connected
to the at least one photovoltaic cell, for controlling (or
facilitating control of) the display element.
[0244] "Semiconductor-nanocrystal" includes semiconducting
crystalline particles of all shapes and sizes. They can have at
least one dimension less than about 100 nanometers, but they are
not so limited. Rods may be of any length. "Nanocrystal", "nanorod"
and "nanoparticle" can and are used interchangeably herein. In some
embodiments of the invention, the nanocrystal particles may have
two or more dimensions that are less than about 100 nanometers. The
nanocrystals may be core/shell type or core type. For example, some
branched nanocrystal particles according to some embodiments of the
invention can have arms that have aspect ratios greater than about
1. In other embodiments, the arms can have aspect ratios greater
than about 5, and in some cases, greater than about 10, etc. The
widths of the arms may be less than about 200, 100, and even 50
nanometers in some embodiments. For instance, in an exemplary
tetrapod with a core and four arms, the core can have a diameter
from about 3 to about 4 nanometers, and each arm can have a length
of from about 4 to about 50, 100, 200, 500, and even greater than
about 1000 nanometers. Of course, the tetrapods and other
nanocrystal particles described herein can have other suitable
dimensions. In embodiments of the invention, the nanocrystal
particles may be single crystalline or polycrystalline in
nature.
IC Packaging
[0245] The foregoing electronic devices are generally housed in a
package including a chip with a plurality of chip pads formed on
the chip as input/output ports for a variety of signals. A lead
frame includes a plurality of contact points which are electrically
connected to the chip pads to receive the variety of signals from
or to output the same to an external circuit. Further, bonding
wires electrically connect each chip pad to its respective contact
points on the lead frame. The bonding wires comprise one or more of
nano material such as Fullerene molecules, nanotubes, nanowires,
nanocomposite material, nanostructured carbon material as described
below.
[0246] The structure of the package is protected by, for example, a
nano-ceramic power compound or resin as described below to remove
heat.
[0247] Fullerene molecular wires are used to replace conventional
bonding wires. In one embodiment, the bonding wires can be FSAs or
selfassembly assisted by binding to FSA or fullerene nano-wires.
Choice of FSAs can also enable self-assembly of compositions whose
geometry imparts useful chemical or electrochemical properties
including operation as a catalyst for chemical or electrochemical
reactions, sorption of specific chemicals, or resistance to attack
by specific chemicals, energy storage or resistance to corrosion.
Examples of biological properties of FSA self-assembled geometric
compositions include operation as a catalyst for biochemical
reactions; sorption or reaction site specific biological chemicals,
agents or structures; service as a pharmaceutical or therapeutic
substance; interaction with living tissue or lack of interaction
with living tissue; or as an agent for enabling any form of growth
of biological systems as an agent for interaction with electrical,
chemical, physical or optical functions of any known biological
systems.
[0248] FSA assembled geometric structures can also have useful
mechanical properties which include but are not limited to a high
elastic to modulus weight ratio or a specific elastic stress
tensor. Self-assembled structures, or fullerene molecules, alone or
in cooperation with one another (the collective set of alternatives
will be referred to as "molecule/structure") can be used to create
devices with useful properties. For example, the molecule/structure
can be attached by physical, chemical, electrostatic, or magnetic
means to another structure causing a communication of information
by physical, chemical, electrical, optical or biological means
between the molecule/structure and other structure to which the
molecule/structure is attached or between entities in the vicinity
of the molecule/structure. Examples include, but are not limited
to, physical communication via magnetic interaction, chemical
communication via action of electrolytes or transmission of
chemical agents through a solution, electrical communication via
transfer of electronic charge, optical communication via
interaction with and passage of any form with biological agents
between the molecule/structure and another entity with which those
agents interact.
[0249] The bonding wires can also act as antennas. For example, the
lengths, location, and orientation of the molecules can be
determined by FSAs so that an electromagnetic field in the vicinity
of the molecules induces electrical currents with some known phase
relationship within two or more molecules. The spatial, angular and
frequency distribution of the electromagnetic field determines the
response of the currents within the molecules. The currents induced
within the molecules bear a phase relationship determined by the
geometry of the array. In addition, application of the FSAs could
be used to facilitate interaction between individual tubes or
groups of tubes and other entities, which interaction provides any
form of communication of stress, strain, electrical signals,
electrical currents, or electromagnetic interaction. This
interaction provides an "interface" between the self-assembled nano
structure and other known useful devices. In forming an antenna,
the length of the nanotube can be varied to achieve any desired
resultant electrical length. The length of the molecule is chosen
so that the current flowing within the molecule interacts with an
electromagnetic field within the vicinity of the molecule,
transferring energy from that electromagnetic field to electrical
current in the molecule to energy in the electromagnetic field.
This electrical length can be chosen to maximize the current
induced in the antenna circuit for any desired frequency range. Or,
the electrical length of an antenna element can be chosen to
maximize the voltage in the antenna circuit for a desired frequency
range. Additionally, a compromise between maximum current and
maximum voltage can be designed. A Fullerene nanotube antenna can
also serve as the load for a circuit. The current to the antenna
can be varied to produce desired electric and magnetic fields. The
length of the nanotube can be varied to provide desired propagation
characteristics. Also, the diameter of the antenna elements can be
varied by combining an optimum number of strands of nanotubes.
Further, these individual nanotube antenna elements can be combined
to form an antenna array. The lengths, location, and orientation of
the molecules are chosen so that electrical currents within two or
more of the molecules act coherently with some known phase
relationship, producing or altering an electromagnetic field in the
vicinity of the molecules. This coherent interaction of the
currents within the molecules acts to define, alter, control, or
select the spatial, angular and frequency distributions of the
electromagnetic field intensity produced by the action of these
currents flowing in the molecules. In another embodiment, the
currents induced within the molecules bear a phase relationship
determined by the geometry of the array, and these currents
themselves produce a secondary electromagnetic field, which is
radiated from the array, having a spatial, angular and frequency
distribution that is determined by the geometry of the array and
its elements. One method of forming antenna arrays is the
self-assembly monolayer techniques discussed above.
[0250] Various molecules or nano-elements can be coupled to one or
more electrodes in a layer of an IC substrate using standard
methods well known to those of skill in the art. The coupling can
be a direct attachment of the molecule to the electrode, or an
indirect attachment (e.g. via a linker). The attachment can be a
covalent linkage, an ionic linkage, a linkage driven by hydrogen
bonding or can involve no actual chemical attachment, but simply a
juxtaposition of the electrode to the molecule. In some preferred
embodiments, a "linker" is used to attach the molecule(s) to the
electrode. The linker can be electrically conductive or it can be
short enough that electrons can pass directly or indirectly between
the electrode and a molecule of the storage medium. The manner of
linking a wide variety of compounds to various surfaces is well
known and is amply illustrated in the literature. Means of coupling
the molecules will be recognized by those of skill in the art. The
linkage of the storage medium to a surface can be covalent, or by
ionic or other non-covalent interactions. The surface and/or the
molecule(s) may be specifically derivatized to provide convenient
linking groups (e.g. sulfur, hydroxyl, amino, etc.). In one
embodiment, the molecules or nano-elements self-assemble on the
desired electrode. Thus, for example, where the working electrode
is gold, molecules bearing thiol groups or bearing linkers having
thiol groups will self-assemble on the gold surface. Where there is
more than one gold electrode, the molecules can be drawn to the
desired surface by placing an appropriate (e.g. attractive) charge
on the electrode to which they are to be attached and/or placing a
"repellant" charge on the electrode that is not to be so
coupled.
[0251] The FSA bonding wires can be used alone or in conjunction
with other elements. A first group of elements includes palladium
(Pd), rhodium (Rh), platinum (Pt), and iridium (Ir). As noted in US
Patent Application Serial No. 20030209810, in certain situations,
the chip pad is formed of aluminum (Al). Accordingly, when a
gold-silver (Au--Ag) alloy bonding wire is attached to the chip
pad, the Au of the bonding wire diffuses into the chip pad, thereby
resulting in a void near the neck. The nano-bonding wire, singly or
in combination with the elements of the first group form a barrier
layer in the interface between a Au-rich region (bonding wire
region) and an Al-rich region (chip pad region) after wire bonding,
to prevent diffusion of Au and Ag atoms, thereby suppressing
intermetallic compound and Kirkendall void formation. As a result,
a reduction in thermal reliability is prevented.
[0252] Nano-bonding wires can also be used singly or in combination
with a second group of elements that includes boron (B), beryllium
(Be), and calcium (Ca). The elements of the second group enhances
tensile strength at room temperature and high temperature and
suppresses bending or deformation of loops, such as sagging or
sweeping, after loop formation. When an ultra low loop is formed,
the elements of the second group increase yield strength near the
ball neck, and thus reduce or prevent a rupture of the ball neck.
Especially, when the bonding wire has a small diameter, a brittle
failure near the ball neck can be suppressed.
[0253] Nano-bonding wires can also be used singly or in combination
with a third group of elements that includes phosphorous (P),
antimony (Sb), and bismuth (Bi). The elements of the third group
are uniformly dispersed in a Au solid solution to generate a stress
field in the gold lattice and thus to enhance the strength of the
gold at room temperature. The elements of the third group enhance
the tensile strength of the bonding wire and effectively stabilize
loop shape and reduce a loop height deviation.
[0254] Nano-bonding wires can also be used singly or in combination
with a fourth group of elements that includes magnesium (Mg),
thallium (TI), zinc (Zn), and tin (Sn). The elements of the fourth
group suppress the grain refinement in a free air ball and soften
the ball, thereby preventing chip cracking, which is a problem of
Au--Ag alloys, and improving thermal reliability.
[0255] The nano-bonding wires provide superior electrical
characteristics as well as mechanical strength in wire bonding
applications. In a wire bonding process, one end of the nano
bonding wire is melted by discharging to form a free air ball of a
predetermined size and pressed on the chip pad to be bound to the
chip pad. A loop of the nano bonding wire having an appropriate
height and length is formed to reach a corresponding lead frame,
and the other end of the bonding wire is bound to the lead frame
with an application of pressure. As a result, the chip and the lead
frame are electrically connected. For low cost production, the chip
can be embedded inside a suitable epoxy. Alternatively, the chip
can be embedded in a plastic flexible substrate that can
interconnect a number of other chips. For example, in a plastic
flexible credit card, a solar cell is mounted, printed or suitably
positioned at a bottom layer to capture photons and convert the
photons into energy to run the credit card operation. Display and
processor electronics are then mounted or on a plastic substrate. A
transceiver chip with nano antennas is also mounted or printed on
the plastic substrate.
[0256] For high performance applications that generate large
amounts of heat such as processor chips, the resulting chip is then
bonding to a nano-ceramic housing to maximize heat radiation and to
control chip temperature.
[0257] As discussed in US Application Serial No 20040029706, the
content of which is incorporated by reference, methods are
disclosed for using ceramic nanocomposites in applications
requiring thermal barrier materials and in applications requiring
material properties selected from the group consisting of thermally
insulating, electrically conducting, mechanically robust, and
combinations thereof. However, for certain electrical applications,
thermal conductance is required.
[0258] In one embodiment of the present system, a heat conducting
ceramic nanocomposite for removing unwanted heat is made with a
ceramic host material and a nanostructured carbon material selected
from the group consisting of carbon nanotubes, single-wall carbon
nanotubes, vapor grown carbon fibers, fullerenes, buckyballs,
carbon fibrils, buckyonions, metallofullerenes, endohedral
fullerenes, and combinations thereof. In some embodiments, the
nanostructured carbon material serves to increase the thermal
conductivity of the ceramic host. In some embodiments, it does this
by serving as a phonon concentrating center. In other embodiments,
it increases the thermal conductivity by altering the structure of
the ceramic host. In some embodiments of the present system, at
least some of the nanostructured carbon material present imparts
greater structural integrity to the ceramic host. A ceramic
nanocomposite, according to the present system, can exist in the
form of coatings, bulk objects, and combinations thereof. The
ceramic host of the nanocomposite of the present system can be any
ceramic which suitably provides for the nanocomposite material of
the present system. Suitable ceramics include, but are not limited
to, zirconia, alumina, silica, titania, yttria, ceria, boron
nitride, carbon nitride, silicon nitride, silicon carbide, tantalum
carbide, tungsten carbide, and combinations thereof. In some
embodiments, the nanostructured carbon material comprises
single-wall carbon nanotubes which may, or may not, be in the form
of short "pipes." In some embodiments, the nanostructured carbon
material is modified by a chemical means to yield derivatized
nanostructured carbon material. Here, "derivatization" is taken to
mean attachement of other chemical entities to the nanostructured
carbon material. This attachement may be by chemical or physical
means including, but not limited to, covalent bonding, van der
Waals forces, electrostatic forces, physical entanglement, and
combinations thereof. In other embodiments, the nanostructured
carbon material is modified by a physical means selected from the
group consisting of plasma treatment, heat treatment, ion
bombardment, attrition by impact, milling and combinations thereof.
In other embodiments, the nanostructured carbon material is
modified by a chemical means selected from the group consisting of
chemical etching by acids either in liquid or gaseous form,
chemical etching by bases either in liquid or gaseous form,
electrochemical treatments, and combinations thereof.
[0259] In another embodiment, the chip substrate can be in contact
with several thin-film thermoelectric elements placed in parallel
to heat or cool a particular area depending on the direction of
current flow in these elements. Each thermoelectric nano-element
has an n-type thermoelectric material, a p-type thermoelectric
material located adjacent to the n-type thermoelectric material, a
Peltier contact connecting the n-type thermoelectric material to
the p-type thermoelectric material. Electrodes contact both a side
of the n-type thermoelectric material opposite the Peltier contact
and a side of the p-type thermoelectric material opposite the
Peltier contact. Appropriately biased electrical current flow
through selected ones of the thermoelectric elements makes the
Peltier contact either a heated junction or a cooled junction. In
another embodiment, only one leg of the thermoelectric element is
required to produce heating or cooling. In this embodiment, a
selected type of thermoelectric material (i.e. n-type or p-type) is
utilized with the Peltier contact. Current flow in a first
direction through an electrode, a thermoelectric material, the
Peltier contact, and a subsequent electrode results in a heated
junction at the Peltier contact. A current flow in a second
direction opposite to the first produces a cooled junction at the
Peltier contact. As disclosed in US Patent Application No.
20020174660, the content of which is incorporated by reference, a
cantilever similar to arrangements known in the art for atomic
force microscopy (AFM) can be used. The integration of a
thermoelectric cooling/heating device or module with a cantilever,
especially the cantilevers similar to those used in AFM, provides
for "nanometer-size temperature control" of bio-tissues, cells, and
perhaps other atomic-scale structures in nano technology such as
for example nano-self-assembly.
[0260] In some embodiments of the present system, a method for
making ceramic nanocomposites comprising a nanostructured carbon
component and a ceramic host component includes preparing a slurry
comprising ceramic particles and solvent; and adding nanostructured
carbon materials such that they become dispersed in the slurry. The
solvent used to prepare the slurry can be selected from the group
consisting of aqueous solvents, non-aqueous solvent, and
combinations thereof. Such solvents include, but are not limited
to, water, toluene, ethyl alcohol, trichloroethylene, methyl ethyl
ketone, and combinations thereof. In some embodiments, the step of
preparing the slurry further comprises adding a dispersal agent.
Such dispersal agents include, but are not limited to, natural
formulations, synthetic formulations, polyelectrolyte dispersants,
surfactants, wrapping polymers, and combinations thereof. In some
embodiments, the step of preparing the slurry further comprises
adding binding agents and/or plasticizers.
[0261] In some embodiments of the present system, the adding the
nanostructured carbon materials (note that this step can be
combined with the step of preparing the slurry) to the slurry
further comprises the utilization of dispersion assistance to
facilitate dispersion. In some embodiments, this step further
comprises a milling operation, and possibly a nanomilling
operation. In some embodiments of the present system, the slurry is
shaped by a casting technique. Suitable casting techniques include,
but are not limited to, tape casting, spin casting, solid casting,
slip casting, robocasting, and combinations thereof. In some
embodiments, the step of shape-forming comprises a gel casting
technique. Here, a "sol-gel" technique is one which provides for a
ceramic component first as a solution or "sol" of precursors which
is hydrolyzed and polymerized into a "gel." Thus, the term,
"sol-gel" represents the material at any stage of its
transformation from a solution to a gel. The method of making
coatings and objects can also include spraying these ceramic
nanocomposite powders with a technique selected from the group
consisting of plasma spraying, thermal spraying, powder spraying,
electrostatically-assisted powder spraying, and combinations
thereof.
[0262] In various embodiments, nano-elements can be formed in
conjunction with nano-sized materials include, but are not limited
to, ceramics, intermetallics, and metals. Other examples of
nano-sized materials according to embodiments of the present
invention include coated and encapsulated materials. Ceramic
materials and intermetallics are often used to enhance, for
example, the high-temperature mechanical strength of the
nanocomposite material. In some embodiments the ceramic comprises
an oxide, such as, for example, an oxide comprising at least one of
aluminum, yttrium, zirconium, and cerium. In other embodiments, the
ceramic comprises at least one of a carbide, a nitride, and a
boride. In still other embodiments, the intermetallic comprises a
silicide. In certain embodiments where the nano-sized material
comprises a metal, the nano-sized metal has a melting temperature
higher than that of the molten material such that the nano-sized
metal remains substantially inert with respect to the molten metal.
Metals with high melting points, for example, tungsten, are
suitable as nano-sized materials for embodiments of this type. It
will be appreciated by those skilled in the art that the choice of
any specific combination of molten material and nano-sized material
is based upon the combination of properties desired for the
resultant nanocomposite material, including, but not limited to,
physical, chemical, mechanical, electrical, magnetic, and thermal
properties.
[0263] In one embodiment, an electronic device is formed with a
nanocomposite material. The method includes providing a molten
material; providing a nano-sized electronic device along with other
nano-material, the nano-sized electronic device/material being
substantially inert with respect to the molten material;
introducing the nano-sized material into the molten material;
dispersing the nano-sized material within the molten material using
at least one dispersion technique selected from the group
consisting of agitating the molten material using ultrasonic energy
to disperse the nano-sized material within the molten material;
introducing at least one active element into the molten material to
enhance wetting of the nano-sized material by the molten material;
and coating the nano-sized material with a wetting agent to promote
wetting of the molten metal on the nano-sized material; and
solidifying the molten material to form a solid nanocomposite
material, the nanocomposite material comprising a dispersion of the
nano-sized material within a solid matrix. Additional materials
include those noted in US Application Serial No. 20040016318, the
content of which is incorporated by reference. The electronic
devices self-assemble inside the matrix after the dispersion. Such
a nano-composite material with built-in transistors, processors,
memories and other electronics forms intelligent articles such as
medical prostheses, smart clothing, smart appliances and smart
vehicles and smart robots, among others. These articles in turn are
powered by nano fuel cells.
[0264] The resulting composite material can be a nanocomposite
magnet, a magnetic refrigerator element, an abrasion resistant
surface coat, a higher-order structure piezoelectric element
composed of a mixture of piezoelectric materials different in
frequency response property, a heating element, a higher-order
structure dielectric displaying the characteristics over a wide
range of temperature, a photocatalyst material and the induction
material thereof, a functional surface coat composed of a mixture
of materials having such properties as the water holding property,
hydrophilicity, and water repellency, a minute machine part, an
abrasion resistant coat for a magnetic head, an electrostatic
chuck, a sliding member material, an abrasion resistant coat of a
die and mending the abraded and chipped parts thereof, an
insulating coat of an electrostatic motor, an artificial bone, an
artificial dental root, a condenser, an electronic circuit part, an
oxygen sensor, an oxygen pump, a sliding part of a valve, a
distortion gauge, a pressure-sensitive sensor, a piezoelectric
actuator, a piezoelectric transformer, a piezoelectric buzzer, a
piezoelectric filter, an optical shutter, an automobile knock
sensor, a supersonic sensor, an infrared sensor, an antivibration
plate, a cutting machining tool, a surface coat of a copying
machine drum, a polycrystalline solar cell, a dye sensitization
type solar cell, a surface coat of a kitchen knife or a knife, the
ball of a ball point pen, a temperature sensor, the insulation coat
of a display, a superconductor thin film, a Josephson element, a
super plastic structure body, a ceramic heating element, a
microwave dielectric, a water-repellent coat, an antireflection
film, a heat ray reflecting film, a UV absorbing film, an
inter-metal dielectric layer (IMD), a shallow trench isolation
(STI), and the like. In various embodiments, nano-elements such as
FSAs are used as fillers in a variety of pure phase materials such
as polymers that are now readily available at low cost. The
nanofiller may be mixed with a monomer, which is then polymerized
to form a polymer matrix composite. In another embodiment, the
nanofiller may be mixed with a matrix powder composition and
compacted to form a solid composite. In yet another embodiment, the
matrix composition may be dissolved in a solvent and mixed with the
nanofiller, and then the solvent may be removed to form a solid
composite. In still another embodiment, the matrix may be a liquid
or have liquid like properties. The nano-fillers improve the
properties of the low cost pure phase materials including, for
example, electrical conductivity, magnetic permeability, dielectric
constant, and thermal conductivity. A matrix is blended with a
filler material with desirable properties that can include
refractive index, transparency to light, reflection
characteristics, resistivity, permittivity, permeability,
coercivity, B--H product, magnetic hysteresis, breakdown voltage,
skin depth, curie temperature, dissipation factor, work function,
band gap, electromagnetic shielding effectiveness, radiation
hardness, chemical reactivity, thermal conductivity, temperature
coefficient of an electrical property, voltage coefficient of an
electrical property, thermal shock resistance, biocompatibility,
and/or wear rate. The desired material property is selected from
the group consisting of refractive index, transparency to light,
reflection characteristics, resistivity, permittivity,
permeability, coercivity, B--H product, magnetic hysteresis,
breakdown voltage, skin depth, curie temperature, dissipation
factor, work function, band gap, electromagnetic shielding
effectiveness, radiation hardness, chemical reactivity, thermal
conductivity, temperature coefficient of an electrical property,
voltage coefficient of an electrical property, thermal shock
resistance, biocompatibility and wear rate. The nanostructured
filler may comprise one or more elements selected from the s, p, d,
and f groups of the periodic table, or it may comprise a compound
of one or more such elements with one or more suitable anions, such
as aluminum, antimony, boron, bromine, carbon, chlorine, fluorine,
germanium, hydrogen, indium, iodine, nickel, nitrogen, oxygen,
phosphorus, selenium, silicon, sulfur, or tellurium. The matrix may
be a polymer (e.g., poly(methyl methacrylate), poly(vinyl alcohol),
polycarbonate, polyalkene, or polyaryl), a ceramic (e.g., zinc
oxide, indium-tin oxide, hafnium carbide, or ferrite), or a metal
(e.g., copper, tin, zinc, or iron). Other filler materials include
those in Application Serial No. 20030207978, the content of which
is incorporated by reference.
Nano Energy Source
[0265] FIG. 10 shows one embodiment of a mobile power unit 1. The
unit 1 has one or more fuel cells 30. The output of the fuel cells
is direct current (DC) which is provided to an inverter 40 for
generating AC voltages to operate mobile equipment. Since the fuel
cell 30 compactly stores large quantity of energy, the entire
mobile power unit 1 is approximately the size of a cigarette pack
and yet can power AC equipment in the field for days. When the fuel
cells 30 are depleted, they can be refueled in situ, thus allowing
the AC equipment to operate without interruption.
[0266] Fuel cells enable the electrochemical conversion of fuel
gases and oxygen into oxidized products and electrical energy. The
difference from traditional chemical processes consists of
performing reduction and oxidation of the components, separately,
at two electrodes. Chemical reaction of the reactants at the
electrodes occurs because ionic conduction is ensured via a
gas-tight electrolyte, and the transport of electrons takes place
only via an external circuit. The hydrogen is obtained from fossil
fuels. Typical representatives of these fuels are natural gas,
methanol and aliphatic or aromatic hydrocarbons, as well as
mixtures thereof, such as, for example, petrol and diesel oil. In
principle, it is also possible to produce the hydrogen-containing
fuel gas biologically and directly as synthesis gas and to work it
up in an appropriate manner for use in a fuel cell. Methanol can
also be produced biologically, for example, with the aid of
methylotrophic yeasts.
[0267] In one embodiment, the cell 30 stores hydrogen which has
previously been produced from electricity and water. The cell 30 is
a cost-effective and pollution-free energy storage device.
Different types of fuel cells including proton exchange membranes,
solid oxides, high temperature fuel cells, and regenerative fuel
cells can be used. In one embodiment, a proton exchange membrane
(PEM) fuel cell includes an anode, a cathode, and a selective
electrolytic membrane disposed between the two electrodes. In a
catalyzed reaction, a fuel such as hydrogen is oxidized at the
anode to form cations (protons) and electrons. The ion exchange
membrane facilitates the migration of protons from the anode to the
cathode. The electrons cannot pass through the membrane and are
forced to flow through an external circuit thus providing an
electrical current. At the cathode, oxygen reacts at the catalyst
layer, with electrons returned from the electrical circuit, to form
anions. The anions formed at the cathode react with the protons
that have crossed the membrane to form liquid water as the reaction
product. Typically, a combustion reaction is not involved.
Accordingly, fuel cells are clean and efficient.
[0268] The hydrogen in the fuel cell 30 can also move through an
active transport membrane (ATM). In the ATM embodiment, the fuel
cell 30 employs molecules used in biological processes to create
fuel cells that operate at moderate temperatures and without the
presence of harsh chemicals maintained at high temperatures, which
can lead to corrosion of the cell components. The compact, inert
energy sources can be used to provide short duration electrical
output. Since the materials retained within the fuel cells are
non-corrosive and typically not otherwise hazardous, it is
practical to recharge the fuel cells with fuel, with the recharging
done by the user. Alternatively, the fuel cells 30 can be
electrically re-charged.
[0269] In one embodiment, the fuel cell includes a first
compartment with an electron carrier in communication with redox
enzymes to deliver electrons to a first electrode; a second
compartment having an electron receiving composition in chemical
communication with a second electrode, and a barrier separating the
first compartment from the second compartment; said barrier having
embedded proton transporting proteins effective to transport
protons from the first compartment to the second compartment.
During operation, an electrical current flows along a conductive
pathway formed between the first electrode and the second
electrode.
[0270] The first compartment can include an electron transfer
mediator that transfers electrons from the redox enzymes to the
first electrode. The proton transporting proteins include redox
enzyme activity. A reservoir can be used for supplying to the
vicinity of at least one of the electrodes a component consumed in
the operation of the fuel cell and a pump for drawing such
component to that vicinity.
[0271] As discussed in U.S. Pat. No. 6,500,571, the content of
which is incorporated by reference, examples of particularly
preferred enzymes providing one or both of the oxidation/reduction
and proton pumping functions include, for example, NADH
dehydrogenase (e.g., from E. coli. Tran et al., "Requirement for
the proton pumping NADH dehydrogenase I of Escherichia coli in
respiration of NADH to fumarate and its bioenergetic implications,"
Eur. J. Biochem. 244: 155, 1997), NADPH transhydrogenase, proton
ATPase, and cytochrome oxidase and its various forms. Methods of
isolating such an NADH dehydrogenase enzyme are described in
detail, for example, in Braun et al., Biochemistry 37: 1861-1867,
1998; and Bergsma et al., "Purification and characterization of
NADH dehydrogenase from Bacillus subtilis," Eur. J. Biochem. 128:
151-157, 1982. The lipid bilayer can be formed across the
perforations 49 and enzyme incorporated therein by, for example,
the methods described in detail in Niki et al., U.S. Pat. No.
4,541,908 (annealing cytochrome C to an electrode) and Persson et
al., J. Electroanalytical Chem. 292: 115, 1990. Such methods can
comprise the steps of: making an appropriate solution of lipid and
enzyme, where the enzyme may be supplied to the mixture in a
solution stabilized with a detergent; and, once an appropriate
solution of lipid and enzyme is made, the perforated dielectric
substrate is dipped into the solution to form the enzyme-containing
lipid bilayers. Sonication or detergent dilution may be required to
facilitate enzyme incorporation into a bilayer. See, for example,
Singer, Biochemical Pharmacology 31: 527-534, 1982; Madden,
"Current concepts in membrane protein reconstitution," Chem. Phys.
Lipids 40: 207-222, 1986; Montal et al., "Functional reassembly of
membrane proteins in planar lipid bilayers," Quart. Rev. Biophys.
14: 1-79, 1981; Helenius et al., "Asymmetric and symmetric membrane
reconstitution by detergent elimination," Eur. J. Biochem. 116:
27-31, 1981; Volumes on biomembranes (e.g., Fleischer and Packer
(eds.)), in Methods in Enzymology series, Academic Press.
[0272] Using enzymes having both the oxidation/reduction and proton
pumping functions, and which consume electron carrier, the
acidification of the fuel side caused by the consumption of
electron carrier is substantially offset by the export of protons.
Net proton pumping in conjunction with reduction of an electron
carrier can exceed 2 protons per electron transfer (e.g., up to 3
to 4 protons per electron transfer). Accordingly, in some
embodiments care must be taken to buffer or accommodate excess
de-acidification on the fuel side or excess acidification of the
product side. Alternatively, the rate of transport is adjusted by
incorporating a mix of redox enzymes, some portion of which enzymes
do not exhibit coordinate proton transport. In some embodiments,
care is taken especially on the fuel side to moderate proton export
to match proton production. Acidification or de-acidification on
one side or another of the fuel cell can also be moderated by
selecting or mixing redox enzymes to provide a desired amount of
proton production. Of course, proton export from the fuel side is
to a certain degree self-limiting, such that in some embodiments
the theoretical concern for excess pumping to the product side is
of, at best, limited consequence. For example, mitochondrial matrix
proteins which oxidize electron carriers and transport protons
operate to create a substantial pH gradient across the inner
mitochondrial membrane, and are designed to operate as pumping
creates a relatively high pH such as pH 8 or higher. (In some
embodiments, however, care is taken to keep the pH in a range
closer to pH 7.4, where many electron carriers such as NADH are
more stable.) Irrespective of how perfectly proton production is
matched to proton consumption, the proton pumping provided by this
embodiment of the invention helps diminish loses in the electron
transfer rate due to a shortfall of protons on the product side. In
some embodiments, proton pumping is provided by a light-driven
proton pump such as bacteriorhodopsin. Recombinant production of
bacteriorhodopsin is described, for example, in Nassal et al., J.
Biol. Chem. 262: 9264-70, 1987. All trans retinal is associated
with bacteriorhodopsin to provide the light-absorbing chromophore.
Light to power this type of proton pump can be provided by
electronic light sources, such as LEDs, incorporated into the fuel
cell and powered by a (i) portion of energy produced from the fuel
cell, or (ii) a translucent portion of the fuel cell casing that
allows light from room lighting or sunlight to impinge the lipid
bilayer.
[0273] The fuel cell operates within a temperature range
appropriate for the operation of the redox enzyme. This temperature
range typically varies with the stability of the enzyme, and the
source of the enzyme. To increase the appropriate temperature
range, one can select the appropriate redox enzyme from a
thermophilic organism, such as a microorganism isolated from a
volcanic vent or hot spring. Nonetheless, preferred temperatures of
operation of at least the first electrode are about 80.degree. C.
or less, preferably 60.degree. C. or less, more preferably
40.degree. C. or 30.degree. C. or less. The porous matrix is, for
example, made up of inert fibers such as asbestos, sintered
materials such as sintered glass or beads of inert material.
[0274] The first electrode (anode) can be coated with an electron
transfer mediator such as an organometallic compound which
functions as a substitute electron recipient for the biological
substrate of the redox enzyme. Similarly, the lipid bilayer of the
embodiment of FIG. 3 or structures adjacent to the bilayer can
incorporate such electron transfer mediators. Such organometallic
compounds can include, without limitation, dicyclopentadienyliron
(C.sub.10 H.sub.10 Fe, ferrocene), available along with analogs
that can be substituted, from Aldrich, Milwaukee, Wis., platinum on
carbon, and palladium on carbon. Further examples include
ferredoxin molecules of appropriate oxidation/reduction potential,
such as the ferredoxin formed of rubredoxin and other ferredoxins
available from Sigma Chemical. Other electron transfer mediators
include organic compounds such as quinone and related compounds.
The electron transfer mediator can be applied, for example, by
screening or masked dip coating or sublimation. The first electrode
can be impregnated with the redox enzyme, which can be applied
before or after the electron transfer mediator. One way to assure
the association of the redox enzyme with the electrode is simply to
incubate a solution of the redox enzyme with electrode for
sufficient time to allow associations between the electrode and the
enzyme, such as Van der Waals associations, to mature. Attentively,
a first binding moiety, such as biotin or its binding complement
avidin/streptavidin, can be attached to the electrode and the
enzyme bound to the first binding moiety through an attached
molecule of the binding complement.
[0275] The redox enzyme can comprise any number of enzymes that use
an electron carrier as a substrate, irrespective of whether the
primary biologically relevant direction of reaction is for the
consumption or production of such reduced electron carrier, since
such reactions can be conducted in the reverse direction. Examples
of redox enzymes further include, without limitation, glucose
oxidase (using NADH, available from several sources, including
number of types of this enzyme available from Sigma Chemical),
glucose-6-phosphate dehydrogenase (NADPH, Boehringer Mannheim,
Indianapolis, Ind.), 6-phosphogluconate dehydrogenase (NADPH,
Boehringer Mannheim), malate dehydrogenase (NADH, Boehringer
Mannheim), glyceraldehyde-3-phosphate dehydrogenase (NADH, Sigma,
Boehringer Mannheim), isocitrate dehydrogenase (NADH, Boehringer
Mannheim; NADPH, Sigma), and .alpha.-ketoglutarate dehydrogenase
complex (NADH, Sigma).
[0276] The redox enzyme can also be a transmembrane pump, such as a
proton pump, that operates using an electron carrier as the energy
source. In this case, enzyme can be associated with the electrode
in the presence of detergent and/or lipid carrier molecules which
stabilize the active conformation of the enzyme. As in other
embodiments, an electron transfer mediator can be used to increase
the efficiency of electron transfer to the electrode.
[0277] Associated electron carriers are readily available from
commercial suppliers such as Sigma and Boehringer Mannheim. The
concentrations at which the reduced form of such electron carriers
can be as high as possible without disrupting the function of the
redox enzyme. The salt and buffer conditions are designed based on,
as a starting point, the ample available knowledge of appropriate
conditions for the redox enzyme. Such enzyme conditions are
typically available, for example, from suppliers of such
enzymes.
[0278] In another embodiment where the fuel cells 30 need to be
physically replaced while the AC equipment is running, the inverter
40 receives a back-up energy source such as a small battery or a
high capacity capacitor. A current sensor is provided to sense
current from the battery unit 30. Once the current is interrupted
during operation indicating that the energy storage units are being
replaced or that it has lost power, the inverter is connected to
the back up energy source by a solid state switch or a relay. In
this manner, the user-replaceable battery units 30 can be
substituted in the field without interrupting power to the
appliance by using the back-up energy source. The inverter 40
receives a low DC voltage input in electrical communication and
provides a source of high DC voltage. The AC voltage to an
appliance may be by an electrical lead directly from the voltage
converter to the appliance or via a switch mechanism or an
electrical plug or socket. In one embodiment, a standard AC wall
plug connected to the inverter 40 operably supplies the high DC
voltage to an appliance.
[0279] The back-up energy storage device can also be a conventional
battery or a supercapacitor, which is a component intermediate
between a capacitor and a battery in terms of energy and power. The
supercapacitor can be any electrochemical system using at least the
surface properties of an ideally polarizable material of high
specific surface area. In other words, the super-capacitor is an
electrochemical capacitor of high capacitance.
[0280] During charging of the supercapacitor, there is a build-up
of ionic species on either side of the two electrodes, at the
ideally polarizable material/electrolyte interface. There may also
be oxidation-reduction reactions in the presence of redox sites,
resulting in a pseudocapacitive system. Supercapacitors based on
the principle of the double layer have been manufactured from a
variety of materials. These supercapacitors are assembled from two
carbon electrodes having a high specific surface area. In general,
the capacitors include current leads, a separator lying between the
electrodes, an electrolyte and a package sealed with respect to the
environment. One component of a supercapacitor consists of the
electrolyte which, typically, comprises a solution of a salt, that
is to say a combination of a salt and a solvent. In general, the
electrolytes are low-viscosity liquids and have a high conductivity
over a wide temperature range. They must also be of low cost,
chemically and electrochemically stable and compatible with carbon
or the other materials of which the electrodes are composed.
[0281] One exemplary super-capacitor is disclosed in U.S. Pat. No.
6,671,166, the content of which is incorporated by reference. As
discussed therein, a high power capacitor ideally polarizable has a
positive electrode and its current collector, a negative electrode
and its current collector, said electrodes comprising a carbon
containing material with high specific surface area, a separator
and a non-aqueous liquid electrolyte impregnating said separator
and said electrodes. The non-aqueous liquid electrolyte is an
organic solution of a sodium or potassium or alkalin-earth metal
salt, on their own or mixed in a solvent containing an acid.
[0282] The inverter 40 can be a step-up transformer capable of
amplifying low DC voltage to high DC voltage. The term "low voltage
DC" generally encompasses voltages within the range from about 5
volts to about 50 volts DC and more preferably from about 6 volts
to about 36 volts DC and even more preferably from about 8 volts to
about 24 volts DC. Particularly preferred low voltages are about 8,
12, 24 or 36 volts with a variation of about 4 volts. High voltage
AC encompasses voltages within the range from about 280 to about
480 volts AC. At high voltage levels power may be supplied over
long distances with a voltage drop with minimal adverse effect on
the system. As a result, the user can effectively power an end
appliance at a great distance from the power source and portable
converter. This is advantageous in a situation where a mobile
appliance is energized by the system. The mobile power unit and the
appliance, singly or in combination, may be moved widely and
freely.
[0283] In one embodiment, the inverter can be pulse-width modulated
inverter. A PWM inverter is controlled by a control circuit, and
the output of the PWM inverter is supplied to a sine wave filter
(LC low-pass filter). The sine filter includes an LC filter
composed of a reactor and a capacitor, and a damping circuit which
is a serial circuit of a resistor and a capacitor. The damping
circuit is connected in parallel with the capacitor in order to
limit oscillation waveforms accompanying the resonance of the
reactor and the capacitor. The control circuit comprises a mean
value circuit, an automatic voltage regulator (AVR), an
instantaneous voltage command value generator, and a PWM signal
generator. First, a voltage detector is connected to the output of
the sine filter to detect the instantaneous output voltage V of the
sine filter. The output voltage V is inputted to the mean value
circuit. The mean value circuit produces the mean value of the
instantaneous output voltage. The mean value is subtracted from a
predetermined voltage reference value by a summing point, and the
difference is supplied to the automatic voltage regulator. The
automatic voltage regulator corrects the voltage reference value so
that the difference becomes zero, and supplies the resultant
corrected voltage reference value to the instantaneous voltage
command value generator. The instantaneous voltage command value
generator, receiving the corrected voltage reference value VA and a
predetermined frequency reference value, generates a sinusoidal
instantaneous voltage command value having amplitude determined by
the corrected voltage reference value VA and a frequency determined
by the frequency reference value. The output voltage V is
subtracted from the instantaneous voltage command value by a
summing point 82, and the difference is provided to a gain
adjuster. The output of the gain adjuster is added to the voltage
command value by a summing point that outputs a corrected voltage
command value to the PWM signal generator. The PWM signal generator
outputs a pulse signal corresponding to the corrected voltage
command value and controls the PWM inverter by the pulse
signal.
[0284] The foregoing describes the control of one PWM inverter in
one embodiment. In another embodiment, a plurality of PWM inverters
can be connected in parallel to supply power to a common load.
[0285] In one embodiment, the fuel cell 30 has a microcontroller
embedded therein. The microcontroller provides the appliance with
various information items such as fuel cell conditions, fuel cell
charge capacity, and a manufacturing company of the fuel cell.
Typically, communications between the fuel cell microcontroller and
the appliance are done over a serial RS-232 protocol. Other
protocols include Universal Serial Bus (USB), SCSI, or Firewire. In
this manner, the smart fuel cell can provide information about its
residual capacity to the appliance so as to display a fuel cell
state relevant to the residual capacity of the fuel cell.
[0286] As described above, while the smart fuel cell has a function
of offering the information on the residual amount of fuel cell
capacity, and it is required to exactly estimate the fuel cell
capacity changeable in accordance with various environmental
elements in order to offer exact fuel cell residual capacity
information. Thus, the smart fuel cell sets up a new reference
capacity in accordance with the changes of fuel cell capacity, and
provides present residual capacity information based on the
reference capacity. For the purpose of establishing the new
reference capacity, the smart fuel cell carries out calibration
when an output voltage becomes lower than a predetermined level.
The calibration is used for re-establishing the reference capacity
of the fuel cell with a measured value of a total charge capacity
of a fuel cell. During the calibration, a discharge starts from a
full-charged state, and the amount discharged until the output
voltage of the smart fuel cell becomes lower than the predetermined
voltage level is established as a reference capacity. In case that
the fuel cell continues to be discharged after the calibration, the
reference capacity is set by performing a re-calibration after the
former discharge is finished.
[0287] In one embodiment where the appliance is a computer, a power
management software detects a state of low fuel cell (LB) in which
the fuel cell residual capacity is reduced less than 10%, and
displays a warning for a user. Then, if the smart fuel cell
continues to discharge, and thus a low low fuel cell voltage is
detected, i.e. if the fuel cell residual capacity is reduced less
than a predetermined amount, e.g., less than 3%, the power
management system stores data by making an operating system (OS)
program to protect current data at work. This case is called a low
low fuel cell (LLB) state. The OS program serves to support a power
management function such as advanced power manager (APM) or
advanced configuration and power interface (ACPI), and for
instance, a WINDOWS type of OS (operating system) of the MICROSOFT
Corporation belongs to the program. The OS program allows the data
being processed of the present system to be stored in a hard disk
drive, and after the operation, the power management system
finishes the system by blocking the power source provided from the
smart fuel cell. FIG. 11 shows an exemplary process to form a
semiconductor device. In this process, the semiconductor processing
equipment forms heat conducting nanowires on first side of wafer
(4) and then deposits semiconductor structures on second side of
wafer (6). In one implementation, the nanowires can be formed using
CVD techniques and are formed first as the nanowire formation is
done at a temperature that can be harmful to semiconductor
structures. In another embodiment, the nanowires can be formed
after the semiconductor structures have been formed.
In one embodiment, the nanotubes can be grown by metal-organic
chemical vapor deposition (MOCVD) or organometallic vapor phase
epitaxy as known to those skilled in the art. Other types of
chemical vapor deposition can also be employed, as well as other
deposition techniques such as thermal evaporation, laser ablation,
sputtering, and the like. Moreover, nanotubes of boron nitride,
silicon, copper, or another suitable material can be employed
instead of carbon nanotubes. Typically, the system is purged with
dry argon gas and a hydrocarbon ambient including a carbon source
and a catalyst is introduced. The hydrocarbon ambient is suitably
produced by pyrolyzing a mixture of a volatile metal species along
with a carbon source. In one suitable deposition arrangement, the
carbon source is an aromatic hydrocarbon such as xylene, and the
catalyzing volatile metal species is ferrocene
(dicyclopentadienyliron, CAS #102-54-5). The catalyst concentration
in the xylene is about 12 milligrams/ml. The solution of ferrocene
in xylene is introduced via a syringe pump at a rate of about 45
microliters/min. After about 5 ml of solution is introduced, the
system is held at temperature for 10 minutes to insure removal of
all volatiles, and then cooled to below 200 C before switching from
the 10% hydrogen to pure argon. When the reactor reaches ambient
temperature with the help of a cooling fan, the tube is opened and
the coated substrates removed. This growth process is exemplary
only and those skilled in the art can readily adapt the described
growth process, or apply another growth process, to generate
suitable nanotube regions for specific applications using available
deposition facilities. For example, a physical vapor deposition
method such as glancing angle deposition (GLAD) can be employed to
produce nanotubes predominantly in the form of nanocolumns,
nanorods or elongated nanosprings. Other approaches to aligned
patterned nanotubes include nano-contact printing and other methods
of applying nanotube growth catalysts on a substrate. The resulting
individually separated, rod-like nano-structures provide very high
thermal conductivity to reduce interface contact resistance. These
structures may be comprised of metallic nano-wires, multi walled
carbon nano-tubes (MWCNT) or multi-wall carbon nano-fibers.
Metallic nanowires (for example Au, Cu, Ni, zinc oxide, and metal
borides) can be used for efficient heat transport characteristics
and thermal contact. In one example, the MWCNTs are oriented (with
their longitudinal axis) approximately perpendicular to the first
surface of the wafer, parallel to the direction of heat flow. They
are preferably grown on the wafer surface as an array of free
standing, vertically aligned, individually separated carbon
nanotubes (or nanofibers) that occupy between about 15 and 40% of
the surface from which they are grown. In some embodiments, the
MWCNT are grown by plasma enhanced CVD (PECVD) growth methods.
Turning now to FIG. 12, another exemplary process for semiconductor
device formation is shown. First, the process forms heat conducting
3D nanowires on first side of wafer (10). Next, the process
deposits semiconductor structures on second side of wafer (12).
Referring now to FIG. 13, a third exemplary process for device
fabrication is shown. In this process, the fabrication equipment
deposits heat conducting nanowires on first side of wafer (20).
Next, conductive fillers are deposited between nanowires (22). To
improve lateral heat conduction, the thermally conductive filler
material is placed within the interstitial voids between the
MWCNTs. The thermally conducting material provides lateral heat
conduction within the nano-tube containing layer. Lateral heat
conduction facilitates the spreading of heat from a relatively
small silicon die surface to the much larger surface area of the IC
body and any heat sink coupled thereto. The thermally conductive
material may be a metal or metal alloy, thermally conductive
ceramics, CVD diamond, thermally conductive polymers, copper,
aluminum, silver, gold, or their alloys. CMP equipment is used to
planarize the nanowires and conductive filler (24). The wafer is
flipped to expose the second side (26), and semiconductor
structures are formed on the second side of the wafer (28). FIG. 14
shows a fourth exemplary process for device fabrication. The
process first patterns and etches cavities on a first side of a
wafer (30). The process then deposits interface materials on
cavities (32) and then grows nanotubes on cavities using CVD (34).
The process then deposits a conductive filler between nanowires
(36). Next, CMP is used to planarize nanowires and conductive
filler (38). The wafer is moved to expose a second side (40), where
the process can continue with a deposition of semiconductor
structure on the second side of the wafer (42). Turning now to FIG.
15, a fifth exemplary process is shown. First, the process patterns
and etches cavities on first side of wafer (50). Next, interface
materials are deposited on cavities (52). The process then forms 3D
nanotubes on cavities using CVD or any suitable nanotube forming
techniques (54). A conductive filler is deposited between 3D
nanowires (56), and the filler/nanowires structure is planarized
(58). The wafer is moved to expose a second side (60). The process
then deposits semiconductor structures on the second side of wafer
(62). Referring now to FIG. 16, a sixth exemplary process is
disclosed. In this process, heat conducting 3D nanowires are formed
on a substrate (70). The process then fills the space between the
nanowires with a metallic filler for example and the process then
planarizes the exposed nanowires/filler surface (72). The process
then patterns and etches cooling fins on surface (74) which can
optionally be attached to an external cooler during electronic
manufacturing (76). The process provides a heat conducting
interface layer on bottom of substrate (77) and mounts the bottom
of substrate to the electronic device (78). The substrate formed
using the process of FIG. 16 can be encapsulated with the die for
heat removal. The encapsulation process uses an encapsulation mold
having a downward-recessed cavity. First, the substrate is dropped
into the cavity of the encapsulation mold and an array of dies is
then placed above the substrate in the cavity of the encapsulation
mold, an encapsulating material, such as resin, is injected into
the cavity of the encapsulation mold to form a single continuous
encapsulation body which encapsulates the array of dies and the
substrate with nanowires for heat removal. The resin may be any
conventional molding or encapsulation compound known in the art,
and may include various polymers (including thermosetting compounds
such as silicones, epoxies, polyimides, and parylenes), adhesives,
B-stage epoxies, and the like. The resin should have little or no
susceptibility to shrinkage so as to ensure maximum coverage of
semiconductor die or wafer as well as optimum strength in the
handling and processing of the device. Cycloaliphatic epoxy resins
with anhydride curing agents are preferred mold compound materials
in light of their favorable viscosity for flow, good chemical
resistance, and low moisture absorption. As the encapsulation
process is completed, the entire encapsulation body is taken out of
the encapsulation mold. Next, a ball-implantation process is
performed to implant a plurality of solder balls on the back
surface of the die. A singulation process is performed to saw
through the encapsulation body so as to cut apart the entire
package body into individual package units to complete the
fabrication of a batch of flip-chip packages. In another
embodiment, nano-composite material can be formed, e.g., by
depositing a layer of a matrix material with a desired thickness on
a substrate, growing nanotubes on the base material, then
depositing a new layer of matrix material on top of the nanotubes
and repeating the process until the desired total thickness of the
material is reached. Alternatively, nanotube films can be grown on
a layer of matrix material; the resulting composite may be cut into
sections that are then stacked. The filler material and the
nanotubes are planarized with CMP (chemical-mechanical
planarization) or electrochemical etching techniques. An additional
(optional) bonding layer can be added if eutectic metal bonding
between the IC and an external cooling fin is desired. In this
case, the exposed nanotube ends would protrude into this layer and
may extend through it. In another embodiment, internal flow
channels or flow passages are provided to remove thermal energy
transferred from an IC. Liquid cooling is preferred due to the high
specific heat capacity of a liquid coolant such as water, but both
liquid and/or gas cooling can be done. A refrigerant is also
possible for use in very high heat removal systems, or where sub
ambient junction temperatures are required for very high speed
electronics. In one embodiment, the packaging material can be
nano-ceramic composites. The ceramic materials include metal oxides
such as alumina, magnesium oxide, titania, cerium oxide, yttria,
and zirconia. Further examples are combinations of two or more of
these metal oxides, and combinations that include other oxides such
as silica and other metal and non-metal oxides. Still further
examples are mixed metallic oxides such as SiAlON, AlON, spinels
such as magnesia spinel, and calcium aluminate. A metal oxide that
is currently of particular interest is alumina, either
.alpha.-alumina, .gamma.-alumina, or a mixture of both. The
composites can also include conductive metals such as iron,
aluminum or copper, dispersed throughout the composite to further
enhance the electrical conductivity of the composite. In one
implementation, powder mixtures of the ceramic material and carbon
nanotubes such as single-wall nanotubes are mixed together. The
relative amounts of ceramic material and single-wall carbon
nanotubes can vary, although the mechanical properties and possibly
the performance characteristics may vary with the proportions of
the single-wall carbon nanotubes. In another implementation, the
packaging material can be nano-plastic composites. In yet another
embodiment, a composite mold having two portions can be used. The
first mold portion covering the die side with semiconductor
structure formed thereon is an electrically non-conductive material
such as conventional resin. The second mold portion covering the
back side of the die is a nano-plastic material that is heat and
electrically conductive to remove heat. In this embodiment, the
substrate is dropped into the cavity of the encapsulation mold and
an array of dies is then placed above the substrate in the cavity
of the encapsulation mold, and an encapsulating material, such as
resin, is injected into the cavity of the encapsulation mold up to
the back side of the die. Next, nanotube material is injected into
molten polymeric material to produce a composite which subsequently
forms a mold compound on the back side of the die. As the
encapsulation process is completed, the entire encapsulation body
is taken out of the encapsulation mold and the ball-implantation
process is performed. A singulation process is performed to saw
through the encapsulation body so as to cut apart the entire
package body into individual package units to complete the
fabrication of a batch of flip-chip packages. The completed IC
package can receive an external heat sink to dissipate heat as
needed. Hereinbefore, various embodiments of methods for cooling a
semiconductor wafer have been described in relation to the appended
drawings. However, the various embodiments are merely exemplary of
the present invention and, thus, the specific features described
herein are merely used to more easily describe such embodiments and
to provide an overall understanding of the present invention.
Accordingly, one skilled in the art will readily recognize that the
present invention is not limited to the specific embodiments
described herein. As such, while the present invention has been
described in terms of certain methods and embodiments, it is not so
limited, and those of ordinary skill in the art will readily
recognize and appreciate that many additions, deletions and
modifications to the embodiments described herein may be made
without departing from the scope of the invention as hereinafter
claimed. For instance, it is also contemplated that the methods of
the present invention could be applied to, or used in adjunct
fashion with, a myriad of semiconductor wafer thinning processes
known in the art. Such processes include, but are not limited to,
plasma etch, wet chemical etch, microblasting, lapping, sputter
removal, or a combination thereof. In addition, the present methods
are not limited to semiconductor wafers made of silicon or gallium
arsenide, but may also encompass any other type of semiconductor
wafer that requires mechanical support and/or active circuitry
protection during back side processing of the semiconductor wafer.
Therefore, it is intended that this invention encompass all such
variations and modifications as fall within the scope of the
appended claims.
[0288] It is understood that the examples and embodiments described
herein are for illustrative purposes only and that various
modifications or changes in light thereof will be suggested to
persons skilled in the art and are to be included within the spirit
and purview of this application and scope of the appended claims.
All publications, patents, and patent applications cited herein are
hereby incorporated by reference in their entirety for all
purposes.
* * * * *