U.S. patent application number 13/664721 was filed with the patent office on 2013-06-27 for nano electromechanical integrated-circuit filter.
This patent application is currently assigned to Trustees of Boston University. The applicant listed for this patent is Trustees of Boston University. Invention is credited to Robert L. Badzey, Alexei Gaidarzhy, Pritiraj Mohanty.
Application Number | 20130162373 13/664721 |
Document ID | / |
Family ID | 39201278 |
Filed Date | 2013-06-27 |
United States Patent
Application |
20130162373 |
Kind Code |
A1 |
Mohanty; Pritiraj ; et
al. |
June 27, 2013 |
NANO ELECTROMECHANICAL INTEGRATED-CIRCUIT FILTER
Abstract
A nano electromechanical integrated circuit filter and method of
making. The filter comprises a silicon substrate; a sacrificial
layer; a device layer including at least one resonator, wherein the
resonator includes sub-micron excitable elements and wherein the at
least one resonator possess a fundamental mode frequency as well as
a collective mode frequency and wherein the collective mode
frequency of the at least one resonator is determined by the
fundamental frequency of the sub-micron elements.
Inventors: |
Mohanty; Pritiraj; (Los
Angeles, CA) ; Badzey; Robert L.; (Quincy, MA)
; Gaidarzhy; Alexei; (Brighton, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Trustees of Boston University; |
Boston |
MA |
US |
|
|
Assignee: |
Trustees of Boston
University
Boston
MA
|
Family ID: |
39201278 |
Appl. No.: |
13/664721 |
Filed: |
October 31, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12311141 |
Sep 22, 2009 |
8314665 |
|
|
PCT/US07/79059 |
Sep 20, 2007 |
|
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13664721 |
|
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60846129 |
Sep 20, 2006 |
|
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Current U.S.
Class: |
333/186 |
Current CPC
Class: |
H03H 9/485 20130101;
H03H 9/525 20130101 |
Class at
Publication: |
333/186 |
International
Class: |
H03H 9/46 20060101
H03H009/46 |
Goverment Interests
GOVERNMENT SPONSORSHIP
[0002] This invention was sponsored by National Science Foundation
Grant Nos. ECS-0404206 and DMR-0449670 and Army Research Office
Grant No. DAAD19-00-2-0004 The government has certain rights in the
invention.
Claims
1. An integrated circuit filter, the filter comprising: a silicon
substrate; a sacrificial layer; a device layer including at least
one resonator, wherein the resonator includes sub-micron excitable
elements and wherein the at least one resonator possesses a
fundamental mode frequency as well as a collective mode frequency
and wherein the collective mode frequency of the at least one
resonator is determined by the fundamental frequency of the
submicron elements.
2. The filter of claim 1 further including a second resonator
connected to the at least one resonator by a connector.
3. The filter of claim 2, wherein the connection is electrical in
characteristic.
4. The filter of claim 2, wherein a collective mode frequency of
the second resonator is different than the collective mode
frequency of the at least one resonator.
5. The filter of claim 2, wherein the second resonator is selected
from the group consisting of mechanical, electrical, magnetic,
optical and piezo.
6. The filter of claim 2, wherein at least one resonator and second
resonator create a filter with the operational frequency between 10
MHz-100 GHz.
7. The filter of claim 1, wherein the sub-micron excitable elements
vary in size and fundamental mode frequency to determine more than
one collective mode frequency.
8. The filter of claim 1, wherein the sub-micron excitable elements
vibrate in a mode selected from the group consisting of flexural,
torsional shear, and longitudinal.
9. The filter of claim 7, wherein the more than one collective mode
frequency can be combined to generate a desired filter
response.
10. The filter of claim 1, wherein the filter is combined with more
than filter to form a bank of filters of similar frequency
response.
11. The filter of claim 1, wherein the filter is combined with more
than filter operating at multiple frequency bands.
12. The filter of claim 1, wherein the filter is combined with more
than filter operating at the similar frequency bands.
13. The filter of claim 1, wherein the operational frequency
response is selected from the group consisting of high, low, band,
notch, and arbitrary.
14. The filter of claim 1, wherein the filter's bandwidth is
tunable.
15. The filter of claim 1, wherein the sub-micron elements are
excited by a transduction mechanism selected from the group
consisting of piezoelectric, magnetomotive, magnetostatic,
electrostatic capacitive transduction, optical, thermoelastic,
thermomechanical, and piezoresistive.
16. The filter of claim 1, wherein the connection between the at
least one resonator and the second resonator is selected from the
group consisting of capacitive, electrostatic, optical,
thermomechanical, magnetic, piezoelectric/resistive, and
electrodynamic.
17. The filter of claim 1, wherein the filter is combined with
other electronic elements within an integrated circuit.
18. The filter of claim 1, wherein the filter is tunable by causing
an effective change in the stiffness of the at least one resonator
by applying one selected from one of the group consisting of
mechanical strain, electrical spring softening, thermal expansion
and thermal contraction.
19. The filter of claim 17, wherein the at least one resonator is
tuned according to operating temperature.
20. The filter of claim 1 wherein the sub-micron elements consist
of a curvature of a spring structure.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/311,141, filed Sep. 22, 2009, which is a U.S. National Stage
application based on International Application No. PCT/US07/79059,
Sep. 20, 2007, which claims priority to U.S. Provisional
Application Serial No. 60/846,129, Sep. 20, 2006, which are
incorporated herein by reference in their entireties.
TECHNICAL FIELD OF THE INVENTION
[0003] The present invention relates generally to electromechanical
integrated circuit filters at the nanometer scale.
BACKGROUND OF THE INVENTION
[0004] Current telecommunications platforms (such as cell phones)
rely on a series of radiofrequency (RF) and intermediate frequency
(IF) filters in order to isolate the desired communications channel
from the crowded and noisy background. Currently, surface acoustic
wave (SAW), bulk acoustical wave (BAW), film bulk acoustic
resonator (FBAR) and ceramic filters are the devices of choice.
However, in general, these filters are large, bulky, and expensive
discretely packaged components that cannot be integrated with the
rest of the transceiver architecture. While the front-end module of
the transceiver can and does continue to miniaturize with improving
lithographic processes and designs, the filter stands as the
bottleneck to a truly integrated radio package. More and more, a
greater number of communications standards (GSM, CDMA, PCS,
European/US, UMTS) and features (WiFi, cameras) are being
incorporated into a single handset. While this allows for truly
global communications, it comes at the cost of a larger and more
power-hungry device. Adding more bands and modes means that more
and more discrete packages are added onboard, with corresponding
increases in overall board size and power consumption due to
package-to-package signal losses.
[0005] Therefore, a need exists for a type of filter that is small
in size, utilizes minimal power and can be integrated with other
discrete electrical elements.
BRIEF SUMMARY OF THE INVENTION
[0006] The present invention discloses a novel electromechanical
integrated circuit filter at the nanometer scale. A nano
electromechanical integrated circuit (IC) filter, including: a
silicon substrate; a sacrificial layer; a device layer including at
least one resonator, wherein the resonator includes sub-micron
excitable elements and wherein the at least one resonator possess a
fundamental mode frequency as well as a collective mode frequency
and wherein the collective mode frequency of the at least one
resonator is determined by the fundamental frequency of the
sub-micron elements. The use of a nano electromechanical filter of
the present invention allows for several advantages, including the
ability to integrate such a filter on a semiconductor chip with the
rest of the transceiver architecture. Removing the 10-20 discrete
filter packages in a typical multimode phone and replacing them
with a single IC package is obviously a huge advantage.
Additionally, the ability to integrate the filters onto the same
chip as the RFIC allows for even more space and power savings. It
will also allow for a single device to be sensitive to all relevant
communications bands. Additionally, such a filter's small size
allows for the replacement of the RF/IF heterodyning structure of
the modern architecture with a tunable direct-channel-select
filtering scheme, encompassing hundreds or thousands of individual
filters. This type of filter would necessitate a massive redesign
of the RF transceiver, but the dividends would be enormous. Among
the advantages would be a fully integrated RF transceiver chip,
drastically reducing production costs, RF board space, and power
consumption. Additionally, a single RF transceiver would be capable
of communicating on any band, in any channel, from 10 MHz up to 100
GHz or more. The transceiver could work in all of the cellular
communications bands (GSM, CDMA, PCS, UMTS), wireless data bands
(WiFi, EDGE, etc.), peripherals bands (Bluetooth), satellite radio,
and GPS.
[0007] The following description and drawings set forth in detail a
number of illustrative embodiments of the invention. These
embodiments are indicative of but a few of the various ways in
which the present invention may be utilized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] For a more complete understanding of the present disclosure
and its advantages, reference is now made to the following
description taken in conjunction with the accompanying drawings, in
which like reference numerals represent like parts:
[0009] FIG. 1 illustrates an example frequency response graph of a
nano electromechanical resonator;
[0010] FIG. 2 illustrates an example frequency response graph of a
bandpass filter;
[0011] FIG. 3 illustrates an example used to explain creating a
mechanical filter out of two masses;
[0012] FIG. 4 illustrates one embodiment of two resonators with
minor elements;
[0013] FIGS. 5-10 illustrate one method of fabricating a single
beam resonator;
[0014] FIGS. 11-14 illustrate alternate designs of a spring like
resonator;
[0015] FIG. 15 illustrates an alternate circuit design for
utilizing an embodiment of the resonators described herein;
[0016] FIG. 16 illustrates yet another circuit design;
[0017] FIG. 17 illustrates a single beam resonator;
[0018] FIG. 18 illustrates a resonator with minor elements; and
FIG. 19 illustrates two alternate filter designs.
DETAILED DESCRIPTION OF THE INVENTION
[0019] The following discussion is presented to enable a person
skilled in the art to make and use the invention. The general
principles described herein may be applied to embodiments and
applications other than those detailed below without departing from
the spirit and scope of the present invention as defined herein.
The present invention is not intended to be limited to the
embodiments shown, but is to be accorded the widest scope
consistent with the principles and features disclosed herein.
[0020] The present invention is a radiofrequency (RF) filter based
on electromechanical resonator at the nanometer scale. Because of
the specific characteristics of design and construction, these nano
electromechanical resonators have natural frequencies of
oscillation from about 10 MHz to about 100 GHz or more, including
all of the best-known analog and digital communications bands. The
fabrication and perfection of such a nano scale electromechanical
filter is of great significance to the telecommunications industry,
yielding benefits in the size, cost, and power dissipation of radio
frequency transceivers used in cellular phones, pagers, PDAs,
personal computers, and any manner of wireless communications
device. The construction of the resonator is such that the filter
is able to cover every relevant communications frequency
standard.
[0021] An element of the present invention is the compound nano
electromechanical resonator described in U.S. application Ser. No.
11/813,342 with a filing date of Jul. 3, 2007, entitled
"Nanomechanical Oscillator" filed by Assignee. The resonator
consists of a number of submicron excitable elements coupled to a
larger element in such a way as to possess a number of collective
frequency modes of vibration. Such collective modes are
characterized by all of the smaller elements moving in-phase with
each other, generating a corresponding displacement in the larger
element. The advantage of this configuration is an important
feature of the nano electromechanical resonator. In general, it is
possible to increase the natural resonant frequency of a mechanical
structure by reducing its dimensions. Unfortunately, doing so also
results in a much larger stiffness for the structure, which makes
its oscillations much smaller in amplitude and correspondingly
harder to detect. By coupling a number of these smaller,
highstiffness structures into a larger, lower-stiffness resonator,
the collective modes of vibration have the frequency of the smaller
elements, but the stiffness (and thus amplitude response) of a
larger one. With the dimensions of the smaller elements being less
than one micron (10.sup.-6 m), the collective modes have natural
frequencies from 300 MHz to 10 GHz. The dimensions of the various
elements, the material composition, method of coupling, number and
location of the smaller elements with respect to the larger, and
type of vibration (flexural, torsional, etc.) work together to
determine the exact value of the resonant frequency.
[0022] Now referring to FIG. 1, the shape of the resonance of this
damped, driven nano electromechanical resonator is shown as a
Lorentzian lineshape. However, while useful in some applications,
the Lorentzian is too selective to be used as a bandpass
filter.
[0023] FIG. 2 illustrates a good bandpass filter characterized by a
relatively flat passband surrounded by deep and sharp sideskirts.
One method of achieving such a filter is to couple two or more of
these resonators together to create a suitable filter.
[0024] Passband operation of a filter has been described with
respect to FIG. 3. It should be appreciated that an operational
frequency response of a filter is not limited to being a passband.
Alternatives include high pass filters, low pass filters, notch
filters, and filters with arbitrary operation frequency
response.
[0025] Alteration of a passband of a filter has been described with
respect to FIG. 3 by coupling resonators together. The frequency
response of a filter is also tunable by causing an effective change
in the stiffness of the resonator by applying one selected from one
of the group consisting of mechanical strain, electrical spring
softening, thermal expansion and thermal contraction. A resonator
may be tuned according to operating temperature.
[0026] The creation of a mechanical filter out of discrete
resonating structures is illustrated in FIG. 3. Two masses
connected together by a single spring will exhibit both symmetric
and anti-symmetric modes of vibration. When the two masses move in
the same direction 300, their motion is symmetric. When they move
in opposite directions 302, the spring between them is
compressed/extended and the motion is anti-symmetric. The
difference between the symmetric and anti-symmetric modal
frequencies is determined by the stiffness of the coupling spring.
Under the right conditions, the two frequencies overlap, creating a
passband 304 near the resonant frequencies of the two modes.
Coupling more and more resonators to this network increases this
effective passband 304.
[0027] E-beam or photolithography steps are used to create one or
more resonators to create a filter. The steps of one embodiment are
shown in FIGS. 5-10. In general, the processing steps are similar
to standard CMOS procedures used to create semiconductor integrated
circuits. However, the fabrication of the filter of the present
invention alters the fabrication and design process slightly. FIG.
4 illustrates one embodiment of a filter 400. This embodiment of a
filter 400 includes two resonators 404, 412, and each resonator
includes numerous paddles, or minor elements 406, 410. Both
resonators 404, 412 are suspended over a substrate (shown in FIG.
10) and attached to the substrate by coupling elements 402,
408.
[0028] One complication of the fabrication process is due to the
inclusion of the coupling beam or beams 402, 408. The coupling
elements 402, 408 add extra difficulty to the fabrication of the
filter 400, as these coupling elements 402, 408 need to be free of
electrical contacts in order to preserve each resonators' 404, 412
independence. Additionally, the structure of the coupling elements
cannot interrupt the array of minor elements 406, 410, as it is the
strain coupling between these elements 406, 410 which allows for
the generation of the high-frequency collective modes. One
implementation of the coupling elements 402, 408 can be at the
clamping points of the individual resonators 404, 412 (where the
suspended resonator meets the unsuspended support structure shown
in detail in FIG. 10). The coupling elements 402, 408 can be
modified by changing the depth of the undercut and the separation
between the participating resonators 404, 412. Alternatively, the
coupling elements 402, 408 between the resonators 404, 412 need not
be mechanical in nature--it can be capacitive, electrostatic,
optical, thermomechanical, magnetic, piezoelectric/resistive, or
electrodynamic.
[0029] Now, the process to create a simplified resonator will be
described as illustrated in FIGS. 5-10. In this embodiment, a
resonator is fabricated from silicon on a silicon-on-insulator
(SOI) wafer, using a single lithography layer. The method in this
embodiment of fabrication, a nano electromechanical structure
includes a series of pattern/mask definitions, material deposition
and etching processes. Now referring to
[0030] FIG. 5, creating a silicon nano electromechanical resonator
starts with an epitaxially-grown wafer 508 with required thickness
of silicon 504 on top of a certain thickness of silicon oxide 506,
used as the sacrificial layer. The wafer is then spin-coated with a
trilayer PMMA 502. Then, the structure patterning is created by
e-beam 500 lithography.
[0031] The wafer and pattern is then developed to create the
patterned PMMA 502 as shown in FIG. 6.
[0032] After e-beam exposure and development, a selective metal
mask 700 is evaporated as shown in FIG. 7.
[0033] The process then includes a liftoff technique to create the
structure shown in FIG. 8, which includes a single beam 800.
[0034] As shown in FIG. 9, a directional anisotropic etch is then
done by a reactive ion etch (RIE) process with positive 902 as well
negative 900 particles, until the sacrificial layer 506 is
completely etched out from under the beam 800. In this embodiment,
the undercut is obtained by a second isotropic RIE etch (with a
different gas) or by a wet acid etch. In case of a wet acid etch, a
critical-point drying process allows suspension and release of the
structure without buckling. In addition, the fabrication process is
designed to accommodate additional electrical lines.
[0035] The final structure is shown in FIG. 10 with the beam 500
suspended over the silicon substrate 508.
[0036] While the embodiment of FIGS. 5-10 utilize lithographically
with an electron-beam source, photolithography can also be used as
the device dimensions are well within the feature size designated
by the new deep-UV sources and masks, as well as nano imprint
lithography, self assembled techniques, bottom up chemical
techniques and other similar nano fabrication techniques. In
general however, the fabrication steps for this embodiment were
accomplished with well-established methods in the semiconductor
industry. However, other embodiments can be fabricated from pure
metals, metallic alloys, alternative semiconductor compositions
such as silicon carbide (SiC), GaAs, lithium tantalite, lithium
niobate, diamond, metal/semiconductor or other similar compounds or
any combination of the above. Quartz, aluminum nitride or other
related materials may also be used for piezoelectric actuation and
detection.
[0037] FIG. 11 illustrates an alternate design 1100 of the beam
like structure of the previous embodiment. However, instead of
being a straight beam (element 800 shown in FIG. 8), this
embodiment is a wavelike structure when viewed from its side.
[0038] FIG. 12 illustrates the alternate design 1100 of the
wavelike structure, but from a top view point. Now, the structure
1202 appears to be spring-like in shape. However, this spring
structure 1202 exhibits longitudinal in-plane modes, rather than
transverse modes. In addition, this spring structure design can
accommodate more power than the single beam structure of the
previous embodiment. However, this spring structure 1202 is
attached to coupling elements 1200, 1204 similar to the coupling
elements in the previous embodiment.
[0039] FIG. 13 illustrates the spring structure 1202, with coupling
elements 1200, 1204 and actuators 1302, 1304 that can be used to
excite the spring structure 1202.
[0040] FIG. 14 illustrates another embodiment with multiple spring
structures 1202.
[0041] In an embodiment, a filter may include sub-micron elements
consisting of a curvature of a spring structure.
[0042] FIG. 15 illustrates a circuit architectural design that can
be used with the filter of the present invention. This circuit
design lessens the power levels to half by using two filters 1504,
1506 in parallel. This design includes a 0-90 degree splitter 1502
with an input termination 1500 and a power in port 1512. The 0-90
degree splitter 1502 splits the power into a 0 degree and a 90
degree phase. Thus half the power is inputted to the top filter
1504 and half the power is inputted at 90 degrees to the bottom
filter 1506. The power from both filters 1504, 1506 are then
combined in phase through 0-90 degree splitter 1508 and exit
through the power out port 1514.
[0043] FIG. 16 illustrates another embodiment of the circuit
architectural design. In this embodiment, a set of eight filters
1606 are within the innermost level 1604. These filters 1606 are
fed power by the four 0-90 degree splitters 1502 directly connected
to the filters 1606. In turn, the four 0-90 degree splitters in the
innermost level 1604, are fed power by the two 0-90 degree
splitters 1502 in the middle level 1602. Moreover, the two 0-90
degree splitters 1502 are fed power by the one 0-90 degree splitter
1502 at the outmost level 1600. The same scheme is used to combine
the power in phase in the output power process. While this
embodiment only has three levels of combination, the invention
could utilize more levels to increase the power capacity of the
circuit.
[0044] FIG. 17 illustrates one embodiment of a beam resonator 1700.
This resonator is on silicon and has a thickness 1704 of 100
nanometers, and length 1702 of 10 microns. At these dimensions,
this resonator can produce a 10 MHz response. However, if the
length 1702 is decreased to 1 micron, the resonator can produce a 1
GHz response.
[0045] FIG. 18 illustrates one embodiment similar to the one
depicted in FIG. 4. This resonator has a beam with minor elements.
The top portion 1802 consists of Au sits on 185 nanometer silicon
layer 1804. The silicon layer 1804 in turn is on a 200 nanometer
silicon dioxide layer 1806, which in turn is on a silicon substrate
1808. The length 1814 between element 1808 and element 1810 is 300
nanometers in this embodiment. However, the length 1816 of element
1810 is 200 nanometers, while the length 1818 between element 1810
and coupling element 1812 is 500 nanometers. In addition, in this
embodiment, the length 1820 of the beam 1822 is 400 nanometers.
Moreover, the length 1824 of the element 1826 is 500 nanometers and
is similar to the length of elements 1808 and 1810.
[0046] FIG. 19 illustrates two more embodiments of beam resonators.
A first embodiment 1900 has two doubly clamped beams 1904 joined
with a flexible bridge 1906. A second embodiment 1902 has three
doubly clamped beams 1908 joined with two flexible bridges
1910.
[0047] While staying within the restrictions of the nature of the
resonator of the present invention, there are still many different
variations possible. These include choice of material. While
silicon is still the material of choice for most integrated
circuits today, other materials might also be more commercially
expedient. Piezoelectrics such as Aluminum Nitride (AlN) has in
particular shown much promise because of its intrinsically high
stiffness (yielding high frequencies), low-temperature deposition
methods, and ease of actuation/detection. Other materials include,
but are not limited to, metals, other piezoelectrics (quartz, ZnO),
CVD diamond, semiconductors (GaAs, SiGe, Si), superconducting
materials, and heterostructures of all kinds
(piezoelectric/semiconductor, semiconductor/metal, bimetal, etc.).
While the filter described in the embodiments is a bandpass filter,
the width of that passband is dependent on the quality factor (Q)
of the resonator. By altering the Q so that each filter covers only
an individual communications channel, rather than an entire band,
one can realize the channelselection architecture described above.
Filters can be operated singly or in massively parallel arrays.
These arrays can have at least two different configurations--ones
in which every filter is the same, or one in which every filter is
different. The first configuration yields benefits in the areas of
redundancy and power handling, while the second allows for
frequency selectivity via a single contact. In addition, an array
incorporating both concepts is also possible. The filters can be
operated in a variety of ways, including piezoelectric,
magnetomotive, magnetostatic, electrostatic capacitive
transduction, optical, thermoelastic, thermomechanical, and
piezoresistive. These methods can be used both in actuation and
detection.
[0048] The resonator of the present invention can be used in sets
to produce a filter. In addition, the resonator can be used in a
duplexer consisting of two sets of filters (receive and transmit),
switches and for receive/transmit isolation. The invention can also
be used for timing oscillators with a resonator and a phase locked
loop element. Moreover, the invention can be used to create mixing
element with coupled resonators of different frequencies.
Furthermore, the invention can be used to create a switch with a
resonator in a non-linear regime.
[0049] Additionally, the nano electromechanical filter can be used
many types of devices. For example, the filter may be used in, but
limited to, cellular phones, PDAs, personal computers, RFID
tracking devices, GPS receivers, wireless-enabled appliances and
peripherals (printers, digital cameras, household appliances),
satellite communications, radar communications, miniaturized
communications platforms, satellite radio receivers (Sirius/XM),
military communications platforms, interplanetary space probes,
encrypted safety identification, MEMS device communication/control
(e.g. biocompatible medical micro/nanobots controlled via
integrated RF transceivers).
[0050] The previous description of the disclosed embodiments is
provided to enable those skilled in the art to make or use the
present invention. Various modifications to these embodiments will
be readily apparent to those skilled in the art and generic
principles defined herein may be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the present invention is not intended to be limited to the
embodiments shown herein but is to be accorded the widest scope
consistent with the principles and novel features disclosed
herein.
* * * * *