U.S. patent application number 10/350474 was filed with the patent office on 2004-03-18 for microscopic batteries for mems systems.
Invention is credited to Harb, John N., LaFollette, Rodney M., Salmon, Linton G..
Application Number | 20040053124 10/350474 |
Document ID | / |
Family ID | 27658110 |
Filed Date | 2004-03-18 |
United States Patent
Application |
20040053124 |
Kind Code |
A1 |
LaFollette, Rodney M. ; et
al. |
March 18, 2004 |
Microscopic batteries for MEMS systems
Abstract
Microscopic batteries, integratable or integrated with and
integrated circuit, including a MEMS microcircuit, and methods of
microfabrication of such microscopic batteries are disclosed.
Inventors: |
LaFollette, Rodney M.;
(Provo, UT) ; Salmon, Linton G.; (Shaker Heights,
UT) ; Harb, John N.; (Orem, UT) |
Correspondence
Address: |
Lynn G. Foster
602 East 300 South
Salt Lake City
UT
84102
US
|
Family ID: |
27658110 |
Appl. No.: |
10/350474 |
Filed: |
January 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10350474 |
Jan 24, 2003 |
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09627959 |
Jul 28, 2000 |
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09627959 |
Jul 28, 2000 |
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09037801 |
Mar 10, 1998 |
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Current U.S.
Class: |
429/149 ;
29/623.1; 429/162 |
Current CPC
Class: |
H01M 10/0436 20130101;
H01M 6/40 20130101; H01L 2224/48091 20130101; H01M 10/30 20130101;
H01M 10/425 20130101; Y10T 29/49115 20150115; H01M 10/342 20130101;
Y02E 60/10 20130101; H01M 50/10 20210101; H01M 10/287 20130101;
Y10T 29/49108 20150115; H01M 10/42 20130101; Y02P 70/50 20151101;
H01L 2224/48091 20130101; H01L 2924/00014 20130101 |
Class at
Publication: |
429/149 ;
429/162; 029/623.1 |
International
Class: |
H01M 006/42; H01M
006/46 |
Goverment Interests
[0001] This invention was made with Government support under
contract F20601-96-C-0078 awarded by the United States Department
of the Air Force. The Government has certain rights in the
invention.
Claims
What is claimed and desired to be secured by Letters Patent is:
1. In combination, at least one MEMS (micro-electro-mechanical
system) and a source of electrical energy internal within the MEMS
comprising a microscopic battery.
2. In combination, at least one MEMS, at least one microcircuit and
a microscopic battery integrated with the MEMS and the microcircuit
as an low power loss internal source of electrical energy.
3. In combination, at least one microelectronic circuit and a
microscopic battery integrated with the microelectronic circuit as
an internal low power loss source of electrical energy.
4. In combination, a microscopic circuit, at least one MEMS device
and an aqueous microscopic battery integrated with the microscopic
circuit and the MEMS device as an internal low power loss source of
electrical energy.
5. A combination according to claim 4 wherein the MEMS device is
selected from the group consisting of: (a) a device requiring
pulses of electrical power; (b) a remote sensor; (c) an autonomous
microscopic device; and (d) a relay.
6. A combination according to claim 4 wherein the MEMS device is
selected from the group consisting of: (a) an array of remote
sensors; (b) a pump; (c) an accelerometer; and (d) a portable MEMS
device.
7. A combination according to claim 4 wherein the MEMS device is
selected from the group consisting of: (a) an embedded sensor; (b)
a smart sensor; (c) a flexible sensing surface; and (d) an
integrated fluidic system.
8. A combination according to claim 4 wherein the MEMS device is
selected from the group consisting of: (a) a safing and arming
device; (b) a friend or foe identification device; (c) a system
integrity monitor; and (d) a communication monitor system,
including but not limited to a satellite monitor.
9. A combination according to claim 4 wherein the MEMS device is
selected from the group consisting of: (a) a low power display; and
(b) a microopto mechanical monitor system.
10. A microscopic battery integrated or integratable with a
microelectronic circuit and/or a MEMS device to provide long term
power and to materially limit power losses, the microscopic battery
comprising a body of material having low weight, a microscopic
cathode, a microscopic anode and a microscopic amount of
electrolyte contained within a microscopic space in the body.
11. A microscopic battery according to claim 10 wherein the
microscopic battery is rechargeable.
12. A microscopic battery according to claim 10 wherein the
microscopic battery is primary.
13. A microscopic battery according to claim 10 wherein the
microscopic battery is integrated with an autonomous sensor
system.
14. A microscopic battery according to claim 13 wherein the
autonomous sensor system senses conditions, analyzes data, and
issues RF signals.
15. A microscopic battery according to claim 10 wherein at least
one of the cathode and the anode comprises an ultra thin film of
conductive material.
16. A microscopic battery according to claim 10 wherein the cathode
and the anode are held apart by a separator.
17. A microscopic battery according to claim 10 wherein the cells
are carried on a rigid dielectric substrate.
18. A microscopic battery according to claim 10 wherein the cells
are carried on a flexible sheet.
19. A microscopic battery according to claim 10 wherein the
electrodes are created by metallic deposition, thin layer
lithographic patterning and etching.
20. A microscopic battery according to claim 10 wherein the
electrodes comprise an etched profile.
21. A microscopic rechargeable battery adapted for direct
integration with MEMS and/or microcircuitry to significantly reduce
power losses, the microscopic rechargeable battery comprising
etched spaced electrodes comprising microscopically thin layers
with a microscopic space containing electrolyte interposed between
the spaced electrodes.
22. A microscopic rechargeable battery according to claim 21
wherein a microscopic separator is interposed between the
microscopic electrodes.
23. A microscopic rechargeable battery according to claim 21
wherein the thin electrode layers comprise generally flat
conductive film.
24. A microscopic rechargeable battery according to claim 21
wherein the microscopic battery is sealed.
25. A microscopic rechargeable battery according to claim 21
wherein the battery geometry is selected from the group consisting
of: (a) flat cell; (b) spirally wound; (c) bipolar; and (d)
linear.
26. A microscopic rechargeable battery according to claim 21
wherein the battery geometry is selected from the groups consisting
of: (a) wire-shaped; (b) odd-shaped; (c) wire in a can; and (d) peg
in a block.
27. A microscopic rechargeable battery according to claim 21
wherein at least one electrode comprises a material selected from
the group consisting essentially of materials comprising: (a) lead;
(b) zinc; (c) nickel; and (d) derivatives of (a), (b) and (c).
28. A microscopic rechargeable battery according to claim 21
wherein at least one electrode comprises a material selected from
the group consisting essentially of materials comprising: (a) a
metal hydride; (b) lithium; (c) silver; and (d) copper, and
derivatives thereof.
29. A microscopic rechargeable battery according to claim 21
wherein at least one electrode comprises a material selected from
the group consisting essentially of materials comprising: (a)
platinum; (b) carbon; (c) cadmium; and (d) lanthanum, and
derivatives thereof.
30. A microscopic rechargeable battery according to claim 21
wherein the electrolyte is selected from the group consisting
essentially of: (a) liquid; and (b) solid.
31. A microscopic rechargeable battery according to claim 30
wherein the solid electrolyte is selected from the group consisting
essentially of: (a) an ion-conducting polymer; (b) lithium glass;
and (c) a polymer containing an ionically-conductive material.
32. A microscopic rechargeable battery according to claim 30
wherein the liquid electrolyte comprises an aqueous solution also
comprised of potassium hydroxide and/or sulfuric acid.
33. A microscopic rechargeable battery adapted for direct
integration into a MEMS or non-MEMS microcircuit to significantly
alleviate power losses, the battery comprising at least one cell
comprised of separated microscopic electrodes etched and patterned
in place to define a microscopic electrolyte storage space between
the etched microscopic electrodes.
34. A microscopic rechargeable battery according to claim 33
wherein at least one electrode comprises a thin film of conductive
material.
35. A microscopic rechargeable battery according to claim 33
further comprising a non-conductivity base upon which components of
the microscopic battery are carried.
36. A microscopic rechargeable battery according to claim 35
wherein the base is selected from the group consisting essentially
of: (a) conformal material and (b) rigid material.
37. A microscopic rechargeable battery according to claim 33
further comprising an electrolyte influent flow path extending
through at least one electrode by which liquid electrolyte is
introduced into the storage space.
38. A microscopic rechargeable battery according to claim 33
wherein the storage space comprises an etched cavity.
39. A microscopic rechargeable battery according to claim 33
wherein a separator prevents contact between the electrodes.
40. A microscopic rechargeable battery according to claim 33
wherein the storage space comprises a porous separator carrying
electrolyte.
41. A method comprising the steps of: fabricating a microscopic
battery; integrating the microscopic battery into a MEMS as an
internal source of electrical power.
42. A method comprising the steps of: fabricating a microscopic
battery; integrating the microscopic battery with a MEMS and a
microcircuit as a low power loss long term internal source of
electrical power.
43. A method comprising the steps of: fabricating a microscopic
battery; integrating the microscopic battery into a microscopic
circuit as a low power loss internal source of electrical
power.
44. A method comprising the steps of: fabricating a microscopic
battery by interconnecting a plurality of microscopic battery
cells; directly integrating the microscopic battery into a
microelectronic circuit and/or a MEMS device as an internal source
of electrical power.
45. A method according to claim 44 wherein the microscopic cells
are interconnected so that at least two distinct voltage outputs
are available and are integrated into the circuit and/or
device.
46. A method according to claim 44 wherein the fabricating step
produces a rechargeable microscopic battery.
47. A method according to claim 44 wherein the fabricating step
comprises depositing of spaced thin film microscopic electrode
layers and etching the layers using lithographic patterning
technology.
48. A method according to claim 47 wherein the etching creates
space for electrolyte.
49. A method according to claim 44 wherein components comprising
the microscopic battery are mounted on a rigid substrate.
50. A method according to claim 44 wherein components comprising
the microscopic battery are mounted on a yieldable material.
51. A method of making a microscopic battery comprising the steps
of: forming spaced thin film microscopic electrode layers upon
non-conducting material; etching away undesired portions of at
least one thin film microscopic electrode layer; interposing
electrolyte between the remaining microscopic electrode layers.
52. A method according to claim 51 further comprising the step of
interposing a microscopic separator between the microscopic
electrode layers.
53. A method according to claim 52 wherein the microscopic
separator is etched to provide a cavity for the electrolyte.
54. A method according to claim 51 further comprising the step of
interposing a non-conductive microscopic polymeric separator
between the microscopic electrode layers.
55. A method of making a microscopic battery comprising the steps
of: forming several microscopic battery cells by depositing spaced
thin film microscopic electrode layers on non-conducting material
of each cell; removing undesired portions of at least one thin film
microscopic electrode layer of each cell; interposing electrolyte
between the microscopic electrode layers of each cell; electrically
connecting the cells in a desired arrangement.
56. A method of making a microscopic battery according to claim 55
wherein the electrically connecting step provides sets of output
terminals having different voltage levels.
57. A method of making a microscopic battery according to claim 55
wherein the electrically connecting step provides different output
terminals providing different voltage levels for powering digital
and RF devices.
58. A method of making a microscopic battery according to claim 55
further comprising the step of encapsulating each cell.
59. A method of making a microscopic battery according to claim 55
wherein the forming step comprises several deposition steps and
involves thin film deposition.
60. A method of making a microscopic battery according to claim 55
wherein the removing step is by selective etching.
61. A method of making a microscopic battery according to claim 60
wherein the etching removes an undesired part of the non-conducting
material to form a storage cavity for the electrolyte.
62. A method of making a microscopic battery according to claim 55
wherein the interposing step comprises introducing electrolyte
through a hole in one of the microscopic electrode layers.
63. A method of making a microscopic battery according to claim 55
wherein the interposing step comprises injection of the electrolyte
from a medical needle.
64. A microscopic battery comprising a thin microscopic rod-shaped
electrode surrounded by electrolyte which is enclosed by a
microscopic electrode which surrounds the electrolyte.
65. A multi-cell rechargeable microscopic battery which is energy
efficient and characterized by low power losses for integration
into MEMS and non-MEMS microcircuitry, the microscopic battery
comprising a plurality of interconnected microscopic battery cells,
each cell comprising a microscopic cathode, a microscopic anode and
a microscopic quantity of electrolyte enclosed within a casing.
66. A multi-microscopic cell microscopic battery according to claim
65 wherein at least some of the microscopic cells are connected in
parallel.
67. A multi-microscopic cell microscopic battery according to claim
65 wherein at least some of the microscopic cells are connected in
series.
68. A multi-microscopic cell microscopic battery according to claim
65 wherein at least some of the microscopic cells are
interconnected to comprise at least two sources of electrical
energy each at a different voltage.
69. A multi-microscopic cell microscopic battery according to claim
65 wherein at least some of the microscopic cells are
interconnected to provide power sources for both analog and digital
purposes.
70. A microscopic conformal microscopic battery comprising a
flexible layer for contiguous mounting on a non-flat surface and at
least one microscopic cell mounted on one side of the flexible
layer and comprised of two microscopic electrodes and a microscopic
amount of electrolyte encased within an enclosure.
71. A microscopic conformal microscopic rechargeable battery
according to claim 70 further comprising sensor circuitry mounted
to the one side of the flexible layer directly integrated with the
microbattery and solar cells for recharging the microscopic battery
carried at the one side of the flexible layer.
72. A microscopic conformal microscopic battery according to claim
70 wherein the flexible layer comprises a polymeric membrane.
73. A microscopic conformal microscopic battery according to claim
70 wherein the flexible layer comprises a smart sensing
surface.
74. In combination, at least one MEMS and a rechargeable
microscopic battery comprising an integrated internal source of
electrical energy within the MEMS.
75. In combination, a MEMS, a microcircuit and a rechargeable
microscopic battery comprising a fully integrated internal source
of electrical energy to the MEMS and microcircuit with low power
losses associated therewith.
76. In combination, a microelectronic circuit and a rechargeable
battery comprising an integrated internal source of electrical
energy within the micro electronic circuit having low power losses
associated therewith.
77. In combination, a microcircuit and/or a MEMS and a microscopic
battery fully integrated with the microcircuit and/or MEMS to
internally supply electrical energy to the micro circuit and/or
MEMS.
78. An integrated microelectronics system comprising an internal
microscopic battery formed simultaneously with the microelectronics
system using thin film deposition, sacrificial layer and etching
technology to jointly fabricate electrodes and electrolyte space
for the microscopic battery, the components of the microelectronics
system and integrated conductors spanning between the electrodes
and system.
79. A MEMS circuit and a microscopic battery fully and
simultaneously integrated into the MEMS device as an internal
source of electrical energy, the MEMS and the microscopic battery
being formed in common using thin film deposition, sacrificial
layer removal and etching techniques.
80. A microcircuit and a microscopic battery simultaneously to
comprise common thin film elements which span between the
microscopic battery and the microcircuit, the common thin film
elements being formed using metallic deposition, sacrificial layer
removal and etching techniques.
81. A microscopic battery comprising a pair of microscopic
electrodes, a microscopic amount of electrolyte disposed in a
microscopic site, an area as low as 50 .mu.m.times.50 .mu.m and a
volume as low as 50 .mu.m.times.50 .mu.m.times.50 .mu.m.
82. In stacked combination, a rigid non-conductive base, a
microscopic battery superimposed upon the base and a microcircuit
superimposed upon and integrated with the microscopic battery.
83. A microscopic battery comprising microscopic electrodes and a
microscopic amount of electrolyte having low power loss
characteristics and a power discharge capability within the range
of 10 W/cm.sup.2 of area and 0.01 W/cm.sup.2 of area or less.
84. A microscopic battery according to claim 83 wherein the
electrolyte is liquid and the power discharge capability is on the
order of 1 W/cm.sup.2 of area or less.
85. A microscopic battery according to claim 83 wherein the
electrolyte is solid and the power discharge capability is on the
order of 0.01 W/cm.sup.2 of area or less.
86. A microscopic battery comprising spaced concentric electrodes
with electrolyte concentrically interposed between the
electrodes.
87. A method of making a microscopic battery comprising the steps
of: providing extrudable sources of cathode material, anode
material and electrolyte materially and extruding the three
materials simultaneously in concentric relation with the extruded
electrolyte material interposed between the extruded anode and
cathode materials.
88. A microscopic battery comprising features including spaced
microscopic electrodes and a microscopic cavity containing
electrolyte, at least one feature having a dimension as small as
1/2 micron.
89. A conformable microscopic battery comprising a first
microscopic electrode in the form of a wire, electrolyte
concentrically disposed around the wire and a second hollow tubular
electrode concentrically surrounding the electrolyte.
90. A conformable microscopic battery according to claim 89 wherein
the electrolyte is aqueous.
91. A conformable microscopic battery according to claim 90 wherein
the aqueous electrolyte is disposed in a porous material.
92. A conformable microscopic battery according to claim 89 wherein
the electrolyte is solid.
93. In combination, at least one microelectronic circuit and a
microscopic battery comprising at least three of microscopic
battery cells, at least one interconnection being disposed between
at least some of the cells, the at least one interconnection
comprising a switch by which the configuration of the cells is
changed.
94. A rechargeable small area microscopic battery comprising first
and second thin spaced microscopic electrodes and a microscopic
amount of aqueous electrolyte disposed in a microscopic cavity
between the thin microscopic electrodes.
95. A method of making a microscopic battery comprising seriatim
depositing a as thin films a microscopic first electrode, a spacer
and a microscopic second electrode, etching a part of the spacer to
create a microscopic cavity and filling the microscopic cavity with
aqueous electrolyte through a passageway in one of the thin
films.
96. A method according to claim 95 wherein the filling step is
through a passageway in one of the microscopic electrodes.
97. A method according to claim 95 further comprising the step of
closing the passageway after the filling step.
98. A method of confirming the size of at least one feature of a
microscopic battery comprising the step of: concurrently
fabricating the microscopic battery and a substantially similar
test battery using substantially the same fabrication step and
examining at least one feature of the test battery to ascertain the
at least one feature of the microscopic battery.
99. A method according to claim 98 wherein the fabricating step
comprises forming a substantially identical microscopic electrolyte
cavity in both the microscopic battery and the test battery and
examining step comprises inspecting the microscopic cavity of the
test battery.
100. A method according to claim 99 comprising the step of covering
the microscopic cavity of the test battery with a layer of
transparent material and wherein the examining step comprises
visually inspecting the microscopic cavity of the test battery
through the transparent layer.
101. A method of unitarily fabricating an integrated circuit and
microscopic battery as an internal part of the integrated circuit
comprising seriatim depositing as thin films a first microscopic
electrode layer, a separator layer and a second microscopic
electrode layer while similarly fabricating the integrated circuit
at the same site and electrically interconnecting the microscopic
battery to the integrated circuit.
102. A method according to claim 101 wherein the interconnecting
step comprise at least one of wire bond, flip chip, TAB and
integral metallic ribbon.
Description
FIELD OF THE INVENTION
[0002] This invention relates generally to electrical power sources
and more particularly to microscopic batteries some forms of which
are integrated or integratable with and providing internal power to
MEMS and integrated microcircuits, either on a retrofit or original
manufacture basis. MEMS (microelectromechanical systems) involve
the fabrication and use of miniature devices which comprise
microscopic moving parts (such as motors, relays, pumps, sensors,
accelerometers, etc.). MEMS devices can be combined with integrated
circuits, and can perform numerous functions.
BACKGROUND OF THE INVENTION
[0003] Integrated circuits, including microelectronic circuits,
have been used extensively, and have the advantage of small size
and low production costs particularly when produced on a large
scale. A class of integrated circuits that are of particular
interest comprise microelectronic circuits having at least one MEMS
device. MEMS may comprise complex engineering systems comprising
microscopic mechanical elements, such as motors, pumps, relays,
sensors, accelerometers and other components, which are powered by
electrical energy. MEMS devices make possible controlled physical
movement of tiny parts within miniature circuits.
[0004] MEMS devices have the potential to revolutionize
computational technology. The concept of MEMS fabrication provides
the promise of low cost comparable to the cost effectiveness in
producing integrated electronic circuitry. MEMS can include sensing
and actuating components. In defense systems, MEMS are expected to
revolutionize the gathering, evaluation, and communication of
militarily-significant information. "MEMS will create new military
capabilities, make high-end functionality affordable to low-end
military systems, and extend the operational performance and
lifetimes of existing weapons platforms." (Department of Defense
[DOD], 1995).
[0005] The great strength of MEMS as a technology fundamentally
depends on: 1) the ability of MEMS to obtain increased
functionality in a single, integrated system; 2) the low-cost,
high-volume nature of MEMS fabrication; and 3) the overall
reduction in size and mass of sensor/actuator systems. Heretofore,
MEMS technology has typically focused on the need to fabricate MEMS
and electronic devices that meet these three goals, but has failed
to address the difficult problem of electrical energy availability
and management. The overall goals of many MEMS applications has not
and will not be met unless one or more appropriate MEMS power
sources are developed.
[0006] While power and energy availability and management are
problems for all integrated circuits, they are acute problems for
MEMS. Many MEMS devices require periodic power pulses. Conventional
wisdom has required and still requires that electrical power be
supplied from relatively large, heavy external sources. Moving
electrical current into an integrated circuit from such an external
power source is difficult, and results in high power losses,
particularly for a MEMS circuit where high capacities are required.
Additionally, present MEMS devices must be continuously connected
to the external power source. Thus, autonomous (self-contained),
portable or remote operation of MEMS devices (such as MEMS sensors)
is difficult if not impossible to achieve using an external fixed
power source. It is reported that the 1994 market for MEMS was
$500M. The projections of potential future market, based on
expected growth of existing markets and expansion into anticipated
markets within a decade, are that the production of MEMS will
approach $3 billion per year.
[0007] A large fraction of MEMS production presently occurs in two
areas, sensors and accelerometers ($200M/year). These two markets
are expanding very rapidly at present. In addition, other types of
MEMS applications are rapidly emerging. Presently, none of these
devices are using integrated batteries, because none exist, nor
have they previously been invented and developed.
[0008] One analysis of the MEMS sensor and accelerometers
applications are that nearly 100% of the sensor market, and
approximately 30% of the accelerometer market, would use
microscopic batteries, if they were available. On this basis, it is
estimated that a market for microscopic batteries in these two
fields would be $50M/year, if such a product existed. Other
significant markets would also come into place if a microscopic
battery could be provided, such that within a decade microscopic
batteries, would have a market of over $100M/year.
[0009] While the storage of energy in miniature, rechargeable
devices for MEMS application is contrary to the state-of-the-art, a
long term unsatisfied need for such has existed. If miniature
energy sources were inventively created, significant advantages
would be obtained, which are not presently available. First, more
autonomous MEMS devices could be produced because the present
dependency on continuous supply of power from an external source
would be overcome. Second, significant improvement in energy
efficiency would result. The supply of electrical energy would be
at low power, stored temporarily, and then released at higher power
levels in close proximity to the point of use, thus reducing
overall power losses. Third, the cost of the MEMS system its
integrated power supply would be lowered by reducing the complexity
of electrical connections. Presently, it is difficult if not
impossible to effectively store energy locally within a MEM system.
Miniature capacitors have unacceptable useful discharge times (and
hence unacceptable energy storage capacity). Fourth, cells can
selectively be arrayed in series and in parallel to achieve
different (and variable) combinations of operating voltage and
capacity.
[0010] Further, unitary simultaneous formation, for example, of a
microcircuit, one or more MEMS devices and a microscopic battery
would provide a substantial advantage.
[0011] Presently, batteries for MEMS devices are unsatisfactory
external power sources, which undesirably contributing to both the
overall weight and volume of the MEMS device, and have other
disadvantages. There are two primary reasons for this. The first
primary reason is the size of the batteries. The smallest
commercial batteries are the button-shaped energy cells used in
watches, calculators and hearing aids. These are huge when compared
with the MEMS to which such an external battery heretofore has
supplies power. The second primary reason is that the need for
energy supply in MEMS is at a relatively high power level. High
power is often needed to produce mechanical movement in MEMS
devices. Commercially available batteries typically maximize the
amount of energy they store, as opposed to providing high power
release of stored energy. Consequently, conventional external
batteries must be overly large in order to supply the power levels
required by the circuit.
[0012] A further limitation of present commercially available
external batteries for MEMS is that no small batteries are
rechargeable batteries. Rechargeability is mandated by many MEMS
applications.
[0013] Table 1, below, compares the characteristics of several
power source solutions with respect to size, weight, capacity, and
assembly difficulty. Table 2, below, is a partial list of potential
DOD applications for MEMS taken from the text
"Microelectromechanical Systems: A DOD Dual Use Technology
Industrial Assessment" (DOD, 1995), together with an indication of
the power source requirements for the majority of applications in
the given area. As stated above, a significant portion of MEMS
production presently occurs in two areas, sensors and
accelerometers. Military applications for remote sensors and
accelerometers include: safing and arming of fuses; friend or foe
identification; embedded sensors for system integrity monitoring;
communications systems monitoring, such as with satellites; low
power mobile displays; flexible sensing surfaces; and numerous
others.
[0014] Many of the application areas in Table 2 will require an
integrated or integrable microscopic battery power. In general,
systems that require mobile, autonomous, extensively-integrated
sensors will require microscopic batteries. A requirement for
mobility excludes standard wired power sources. A requirement for
autonomy excludes primary battery systems that cannot provide power
to integrated systems for extended periods. Requirements for small
size, extensive integration and large numbers of units exclude the
use of coin-type or standard format batteries because of the
difficulty of mounting such batteries into the format required by
integrated systems. Microscopic batteries, once available, will
have performance advantages that will prove to be critical to
specific system applications, such as multiple, definable voltage
levels, lower power requirements, and better power
distribution.
1TABLE 1 Qualitative Comparison of Power Source Characteristics
Energy Assembly Power Source Size Weight Capacity Difficulty From a
Wall Very Large N/A High N/A Socket Battery Pack Large Heavy
Moderate Very Difficult Button Cell Small Light Low Difficult
Microscopic Microscopic Very Light Low Expected to be Battery
Simple
[0015]
2TABLE 2 MEMS Applications and Associated Power Source Requirements
Application Remote Flexible Integrated Low- MicroOpto Require-
Sensing Sensing Fluidic Safing and Power Embedded Mechaincal ments
Arrays Surfaces Systems Arming Displays Sensors Systems Size Micro-
Micro- Small Micro- Small/ Micro- Micro- scopic scopic scopic/
Large scopic/ scopic/ Small Small Small Weight Very Very Light/
Light/ Light/ Light/ Heavy/ Light Light Heavy Very Heavy Very Light
Light Light Energy Low Low Moderate Low Moderate Low Low/
Capability Moderate Assembly Expected Expected Moderate Expected
Moderate Expected Expected Difficulty to be to be to be to be to be
Simple Simple Simple/ Simple/ Simple/ Moderate Moderate Moderate
Recharge Required Required Not Not Required Required Not Capability
Always Always Always Required Required Required Applicable Micro-
Micro- Coin/ Coin/ Battery Micro- Coin/ Power scopic scopic Micro-
Micro- Pack/ scopic Micro- Solution Battery Battery scopic scopic
Micro- Battery scopic Battery Battery scopic Battery Battery
[0016] FIG. 17 (adapted from Raistrick, 1992 and Olszewski and
Morris, 1987) contrasts the power and energy capabilities of
several prior energy storage technologies. Traditional
electrostatic capacitors have the highest peak specific power (up
to 10.sup.4 kW/kg) of prior technologies. The two major
disadvantages of electrostatic capacitors are low specific energy
and exponential discharge behavior. Specific energies are 0.01-0.1
J/g. The exponential decay in power output vs. time is not suitable
for applications which require a flatter discharge profile. The
advantage of electrostatic capacitors is that high voltages are
possible, limited only by the ability of the dielectric material to
sustain the voltage. The surface areas of the capacitor plates,
where the charge is stored, are not high. Efforts to improve
specific energy by increasing the plate areas have not achieved the
objective.
[0017] Double layer capacitors, which have existed for decades
(Becker, 1957) are not capable of high potential differences (<3
V, as opposed to >10 V for electrostatic capacitors), but
through the use of high surface area material in the electrodes,
energy densities can be made to be much higher than electrostatic
capacitors. High surface area carbon and sulfuric acid are the most
common electrode material and electrolyte. Specific energies of
0.05-0.8 J/g are considered typical (Boos, 1970; Boos et al., 1971;
Currie et al., 1985; Boos and Metcalf, 1972 and Isley 1972; Selover
et al., 1977; Rose, 1988; Rose, 1989). Peak specific powers are
typically 10-30 W/g. Miniaturization of these very high surface
area materials, however, would be difficult, if not impossible.
[0018] A more thorough treatment of recent advances in capacitor
technology are given by Raistrick (1992) and Oxley (1988). Progress
has been made through the use of improved electrodes and
electrolytes, but attempts to provide a combination of very high
specific power (>50 W/g) and specific energy (>30 J/g) have
failed using capacitor technology.
[0019] A variety of electrochemical capacitors exist, which have
been developed, and which have been substantially improved during
the past decade. These range in their mode of operation from
double-layer capacitors, which strictly use non-faradaic processes,
to devices which are somewhat similar to batteries and which use
faradaic reactions to release energy. Intermediate devices exist
between pure double layer capacitors and batteries in their
operation. During discharge of these devices, the double-layer
releases a charge, but the electrode surfaces themselves also
undergo faradic (charge transfer) reactions. Hence, these
intermediate devices employ both faradaic (bulk) and non-faradaic
(surface) reactions, which increase the energy which can be stored
in the cell.
[0020] In contrast to capacitors, traditional secondary
(rechargeable) batteries, which store energy in chemical form, have
the highest specific energy of the technologies presented in FIG. 5
(i.e. 90-400 J/g for existing Systems, up to 3000 J/g for some
systems under development). Batteries have normally been designed
to maximize the specific energy, at the expense of the specific
power. Typical specific power values are low, i.e. 0.03-0.3 W/g
(Linden, 1984).
[0021] Of the available electrical energy storage technologies,
batteries are probably the leading candidate for use in MEMS. As
shown in FIG. 17, batteries can be designed to provide adequate
levels of both power and energy. The major obstacle in using
batteries in MEMS is the size and weight of available batteries. To
date, large external batteries have been used. Internal batteries
must be microscopic, not macro-scopic. Dimensions must be in
micrometers, rather than centimeters, and good specific power and
specific energy must be available. Presently, the smallest external
batteries available commercially are of the order of 0.1 to 1
cm.sup.3 in volume and 1 to 3 g in weight. For example, button
cells employing a variety of electrochemical couples (such as
silver/zinc, zinc/air, and lithium/manganese dioxide), are built
which are approximately 1.06 cm.sup.2 in cross-sectional area, are
0.54 cm in height, and weigh 1 to 3 g (Linden, 1984). The open
circuit potential of these single cells is 1.5 to 3.0 V. The
highest capacity batteries in this class can deliver 1440 C of
energy, with a specific energy of 100-1000 J/g (400-3200
J/cm.sup.3). The biggest difficulty in their use to power MEMS,
along with their size and weight, is the fact that all such
batteries are primary and are not secondary or rechargeable
batteries.
[0022] Batteries for internal MEMS applications would need to have
several important characteristics. First, many MEMS applications
require the capability of large numbers of repeated
charge/discharge cycles. Second, they must have a minimum of
internal resistance to limit energy losses during battery
operation. Third, they must be robust, so that changes in
temperature, pressure, and other conditions do not damage
performance. Fourth, MEMS batteries must be produced in large
quantities, at low cost, and low rejection rate.
[0023] Recently, efforts have been made to provide smaller
secondary (rechargeable) batteries which can operate at very high
efficiency. Such smaller secondary batteries are far larger than
microscopic circuits. Smaller bipolar lead acid batteries have been
built and demonstrated, which had open circuit potentials of 2-8 V
(1-4 V per individual cell). (LaFollette 1988; LaFollette and
Bennion, 1990). These batteries were designed for high efficiency
to produce very short bursts (0.1-100 ms) of very high levels of
power. These batteries produced up to 5 A for 1-2 ms, for a power
output of 35 W during that time. Their specific energy was
approximately 70 J/g which, though modest by battery standards, is
far better than capacitors. Peak specific power was 200-800 W/g
(800-3000 W/cm.sup.3). Typical values for commercially available
batteries are 0.1 W/g or 0.4 W/.sup.3cm ). This specific power was
achieved through the use of an efficient bipolar cell design, and
the use of lightweight, high performance cell components. These
batteries can also deliver multiple, high power discharges without
a significant recharge (LaFollette, 1995).
[0024] While these efforts at building smaller batteries represent
a decrease of two orders of magnitude in battery size from
traditional batteries, the batteries in question are large when
compared to the microscopic size needed to provide internal circuit
power to a MEMS. What is required is an entirely new class of
batteries (i.e. microscopic batteries) with peak specific powers
much higher than present batteries, with specific energies many
times that of capacitors, and which are built on a microscopic
scale suitable for internal integration either into an existing
MEMS, for retrofit purposes, or unitarily fabricated as part of the
MEMS, for original manufacturing purposes.
[0025] The art includes certain thin-film batteries, which are also
large by microelectronics standards. Included in this category are
lithium batteries which may be able to provide high specific energy
(Levasseur et al., 1989). The first totally thin-film rechargeable
lithium battery was a Li/TiS.sub.2 cell built by Kanehori, et al
(1983). Since that time a variety of cells with different
electrolyte and cathode materials have been made. In spite of their
differences, all of these thin-film batteries use an evaporated
layer of metallic lithium as the anode.
[0026] The most common electrolyte used in solid-state lithium
batteries is a lithium glass. For example,
xLi.sub.2O-yB.sub.2O.sub.3 or
xB.sub.2O.sub.3-yLi.sub.2O-zLi.sub.2SO.sub.4 (Jones et al., 1994;
Levasseur et al., 1989; Balkariski et al., 1989) may be used. These
glasses are typically sputter-deposited at a thickness less than 5
.mu.m. The resulting electrolyte layers have room temperature ionic
conductivities ranging from 10.sup.-9 to 10.sup.-5 S/cm, depending
on the composition of the electrolyte (Jones et al., 1994). In
contrast, the ionic conductivity of a 5M KOH electrolyte is
approximately 0.5 S/cm. One of the key problems with the lithium
glass electrolytes has been an absence of long term stability in
contact with metallic lithium (Bates, et al., 1993). This problem
has been pursued by the Eveready Battery Company (EBC). A thin
layer of LiI was deposited by vacuum evaporation between the
lithium electrode and the glassy electrolyte (Jones et al., 1994).
The LiI, however, has a conductivity which is less than {fraction
(1/100)}th of the glassy electrolyte and was, therefore, kept as
thin as possible. An alternate attempt to solve the stability
problem was recently undertaken by Oakridge National Laboratories
(ORNL), which developed a LiPON electrolyte which is stable when in
contact with lithium (Bates, et al. 1993).
[0027] A common characteristic of cathodes used in thin-film
lithium batteries is that they are all lithium intercalation
compounds which have open channels through which Li.sup.+ ions can
diffuse without severely disrupting the surrounding framework
(Bates, et al., 1993). Two cathode materials which have been used
in recent thin-film cells assembled by ORNL and EBC are
V.sub.2O.sub.5 and TiS.sub.2, respectively. While other cells are
also described in the literature, these two cells appear to be
representative of the current state-of-the-art.
[0028] Oakridge National Laboratories has recently assembled
batteries with TiS.sub.2, V.sub.2O, and Mn.sub.2O.sub.4 cathodes
which incorporate a LiPON electrolyte developed at Oakridge (Bates,
et al, 1993). Of these, the Li/V.sub.2O.sub.5 cell exhibited the
best performance with a capacity of 120 .mu.A/cm.sup.2. As with all
intercalation electrodes, the cell voltage decreased steadily
during constant current discharge, owing to insertion of lithium
ions into the cathode. The cell was discharged from an open circuit
voltage of 3.9 V to a cutoff voltage of 1.5 V at current densities
of 100 .mu.A/cm.sup.2. According to the authors, cathode
utilization decreased by only a few tenths of a percent or less per
cycle. The authors also concluded that the cathode was the major
contributor to the battery resistance.
[0029] The battery made by EBC uses sputter-deposited TiS.sub.2 as
a cathode and has an open circuit voltage of 2.5 when the cell is
fully charged. This cell is typically operated in the potential
range from 2.5 to 1.8 V. The cell may vary from 8 to 12 .mu.m in
thickness and have a capacity between 35 and 100 .mu.Ah/cm.sup.2.
This battery has a long cycle life. EBC batteries routinely
complete more than 1000 cycles at current densities as high as 300
.mu.A/cm.sup.2 and have actually cycled more than 10,000 times at a
current density of 100 .mu.A/cm.sup.2. These batteries are also
able to deliver current pulses of two seconds duration at current
densities of approximately 2 mA/cm.sup.2. By comparison, four cell
bipolar lead acid batteries have been constructed with a much
larger total thickness of about 400 microns which discharged at a
current density of 10-25 A/cm.sup.2 for short duration pulses, over
four orders of magnitude greater than the EBC cell. (LaFollette and
Bennion, 1990)
[0030] Because lithium is highly reactive, it is essential that
lithium batteries be sealed with a protective coating that is
impermeable to both gas and water.
[0031] Lithium cells can also be assembled with a solid
ion-conducting polymer as the electrolyte instead of the glass
electrolytes (Owens, 1995). Such cells are not really thin-film
cells since the thickness of the electrolyte (.about.50-100 .mu.m)
is typically much greater than that of a 1 .mu.m thickness used in
the thin-film cells. Polyethylene oxide was the initial polymer
used in lithium polymer electrolyte cells. However, other polymeric
electrolytes with increased room temperature conductivity have
since been developed. The long term stability of the polymer and
the formation of resistive layers at the metallic lithium/polymer
interface are both issues of concern with respect to these
cells.
[0032] Thin-film batteries, other than those based on lithium, have
also been investigated. In particular, silver and copper systems
have been examined because of the high ionic conductivity of
silver- and copper-based solid electrolytes (Julien & Nazri
1994; Levasseur, et al, 1989). By and large, these batteries have
been found to be impractical owing to their relatively high cost
and low energy density. One study of interest was performed by
Takahashi and Yamamoto who fabricated a Ag/A.sub.3SI/I.sub.2,C cell
(Takahashi & Yamamoto, 1971). Six of these cells were stacked
entirely by vacuum evaporation and provided an OCV of 1.2 V at
25.degree. C. The cells were discharged at a high rate of 10
mA/cm.sup.2. Unfortunately, the cells are not without problems as
the iodine oxidizes the solid electrolyte. Reference may be made to
Levesseur, et al (1989) and Julien & Nazri (1994) for
information on other types of nonlithium thin-film batteries.
[0033] Fuel cells are limited in their power output and specific
energy due to the need for manifolding of individual cells to
introduce fuel and oxidant into the cells and remove reaction
products. The complexity of these systems would seem to preclude
their consideration for adaption to microscopic size. Dyer has
reported a proton exchange membrane fuel cell which is only 0.2
cm.sup.2 in area (Dyer. 1990). The fuel cell can be mounted
(according to the Dyer disclosure) directly onto a printed circuit.
It consisted of a thin-film platinum electrode (<0.0001 cm)
mounted on a substrate, a gas-permeable, proton exchange membrane
separator which is only 0.0005 cm thick over this lower electrode,
and a porous platinum electrode on the other side of the membrane.
A mixture of hydrogen and oxygen is introduced into the vessel
containing the fuel cell. Apparently, the membrane allowed hydrogen
gas to move to the inner electrode, but restricted much of the
oxygen mobility, thus allowing the fuel cell to operate. Power
output was low (<0.005 W/cm.sup.2), probably due to the
diffusion resistance of the hydrogen transport to the inner fuel
cell. The energy efficiency was probably also quite low, due to
recombination of hydrogen and oxygen at the outer electrode. Power
output from this fuel cell was low. While this technology is
certainly promising, they can't store or deliver adequate energy
for use as a microscopic source of electrical power for MEMS and
other microcircuits. Fuel cells, of course, are difficult to
recharge.
[0034] Previous efforts have been made to integrate a satisfactory
source of electrical power and a MEMS. A number of different
thin-film (but large area) batteries have been documented in the
literature. Of these, rechargeable lithium batteries have shown the
best performance, as demonstrated by excellent cycle life and shelf
life. At least one notable effort to apply such batteries to use in
conjunction with MEMS has been made by workers at Oak Ridge
National Laboratory (Bates, et. al., 1993).
[0035] The lithium batteries are limited to low discharge rates.
Therefore, the area of these thin-film batteries must be large in
order to increase the power available from the battery to
acceptable levels. Also, lithium is very reactive with water and
O.sub.2 so that such batteries must be completely isolated from the
environment to be useful. It is believed that the lithium batteries
are relatively expensive to build. For example, the EBC battery
uses TiS.sub.2, which is a high cost cathode material.
[0036] It can be seen that if an integratable microscopic battery
were made available it would fill an long existing, unsatisfied
need in the MEMS and microelectronic technologies described
above.
SUMMARY AND OBJECTS OF THE INVENTION
[0037] The present invention involves microscopic batteries, which
comprise a very tiny footprint (area), typically on the order of
0.1 cm.sup.2 down to 0.0001 cm.sup.2, and accommodate direct
integration into microcircuits, and/or MEMS, either on a retrofit
or unitarily with the microcircuit and MEMS at the time of
manufacture. The microscopic batteries of the present invention
provide a solution to long existing MEMS energy and power
management problems of the past, and will significantly enable MEMS
technology for increased utilization. The present invention also
involves novel methods of making microscopic batteries.
[0038] As mentioned above, one of the limiting factors in the
operation of MEMS has been energy transmission and storage. In
conventional practice, electrical energy for a MEMS is supplied
from an external source into the microcircuit, which causes
substantial power losses. The reduction of the power losses is a
profoundly significant aspect of the present invention and is
accomplished by the complete integration of the batteries of the
invention with the MEMS or with a non-MEMS microelectronic circuit,
either on a retrofit or unitary original manufacture basis.
[0039] Microscopic batteries of the invention are adapted to be
located internally within a MEMS or other microcircuitry, in close
proximity to the requirements for power. During periods of high
energy usage, high specific power is immediately available from the
fully integrated internal microscopic battery, without significant
power loss. In typical applications, the battery can be recharged
from an external source at a lower rate, thus reducing power
transmission losses although recharging is not normally required at
frequent intervals. The battery serves as a load-leveling energy
storage device. Thus, features of importance of the microbatteries
of the invention are reduced power loss when integrated into a MEMS
or like microscopic system, higher energy efficiency, remotely
controlled microscopic robotics, and mobility via the autonomy of
the system. The invention also embraces novel methods of
microfabrication of microscopic batteries including unitary
fabrication of the microscopic battery as an integrated part of an
autonomous integrated circuit, such as MEMS. Such circuits,
therefore, are complete with an internal microscopic source of
electrical energy and can operate without any external power supply
or connections thereto.
[0040] Rechargeable microscopic batteries of the present invention
address and solve the power and energy problems heretofore
associated with MEMS. Microscopic batteries of the invention offer
far more energy storage capability than a capacitor, sufficient to
operate MEMS for extended time periods from a single charge.
Portable, remote and autonomous MEMS are thus accommodated by the
invention. Substantial reduction in power losses is achieved in
certain MEMS using an integrated microscopic battery according to
the present invention.
[0041] The form and nature of a microscopic battery according to
the present invention may vary significantly depending upon the
specific intended purposes. Nevertheless, microscopic batteries of
this invention typically will possess one or more of the following
features, among others: (1) is an internal source of energy within
a microcircuit which may also comprise a MEMS device; (2) is
integrated at the time of manufacture or integratable thereafter,
on a retrofit basis, with a MEMS or other microcircuit; (3) is
microscopically small and light weight providing for portability
and autonomy of an integrated system; (4) is highly efficient,
providing high specific power and often high specific energy; power
discharge values within the range of 10 W/cm.sup.2 to 0.001
W/cm.sup.2 being available depending on whether the electrolyte is
liquid or solid, among other things; (5) can be charged and
discharged a large number of times; (6) is most often a secondary
battery but may be primary; (7) has low internal resistance, with
very low power losses; (8) provides a footprint normally within a
range on the order of one square millimeter to one square .mu.m and
a volume on the order of one cubic millimeter to one cubic .mu.m;
(9) comprises most often thin film deposited and etched electrodes;
(10) in some configurations can be of a wire-in-a-can or
peg-in-a-hole species; (11) often will comprise a series of
interconnected cells which can be arranged to provide more than one
output voltage; (12) is formed using film deposition, masking,
spin-coating, sacrificial removal and photolithographic pattern
etching techniques; (13) capable of manufacture using MEMS
microfabricating techniques; (14) often is hermetically sealed;
(15) can be rigid or conformal; (16) accommodate a large range of
materials for use as microscopic electrodes and a microscopic
quantity of electrolyte; (17) can be configured into thin flat
cells, bipolar stacks, linear cells, concentric wire-like or
tubular cells, and/or spirally wound embodiments; (18) the
components of which can be successively layered upon either a rigid
substrate or a flexible conformal base; (19) can be mass produced
on a high quality/low cost basis; (20) is adaptable for recharging
using one or more solar collectors; and (21) is reconfigurable by
the user to change the characteristics of the microscopic battery
where it is being or to be used.
[0042] With the foregoing in mind, it is a prime object of the
invention to overcome or alleviate problems of the past by
providing a microscopic battery.
[0043] Another major object of the present invention is the
provision of microscopic batteries having one or more of the
twenty-one features set forth above.
[0044] It is also an object of the invention to provide microscopic
batteries, which accommodate integration into a microelectronic
integrated circuit, either unitarily at the time of manufacture or
later on a retrofit basis.
[0045] It is a further valuable object to provide an internal
rechargeable battery integrated or integratable into a MEMS or
non-MEMS microcircuit.
[0046] An object of significance is the provision of unique
methodology by which microscopic batteries are made.
[0047] An additional object of dominance is the provision of novel
methodology by which a microscopic battery and a MEMS or non-MEMS
microcircuit are formed simultaneously and unitarily.
[0048] It is further an object of the invention to provide
microscopic batteries with, significantly reduced size and improved
power properties accommodating integration into a MEMS.
[0049] An object of significance is to integrate microscopic
batteries with microscopic integrated circuits and/or MEMS, as
internal low power loss sources of electrical power.
[0050] Yet another object of the invention is to provide
microscopic batteries that can be used to efficiently power
integrated circuits and MEMS circuits.
[0051] An important object of the invention it to provide a
multicell microscopic battery system having at least two distinct
voltage outputs.
[0052] Another object of the invention is to provide a multi-cell
microscopic battery system with matrix of a cell elements supported
on a common substrate.
[0053] It is also an object of the invention to provide a
microscopic battery supported on a flexible conformable
substrate.
[0054] It is further an object of the invention to provide a MEMS
or integrated microcircuit with liquid components in the
circuit.
[0055] An object of significance is to provide a process for the
micro-forming of electrodes and a liquid electrolyte space in a
microscopic battery by the selective application and removal of a
sacrificial layer.
[0056] Yet another object of the invention is to provide
microscopic batteries integrated into a micro-circuit and/or MEMS
to form an autonomous system.
[0057] A further object of the invention is to provide microscopic
batteries that may be connected to existing integrated circuits or
MEMS, as a power source.
[0058] Yet an important object of the invention is to provide
microscopic batteries that are rechargeable.
[0059] Another object of the invention is to provide microscopic
batteries which comprise a liquid or a solid electrolyte.
[0060] It is also an object of the invention to provide new and
modified microfabrication processes for the manufacture of
microscopic batteries.
[0061] It is further an object of the invention to provide a
process wherein microscopic batteries are manufactured
photolithographically.
[0062] An object of significance is to provide various novel
integrable and integrated microscopic battery configurations
applicable to various power requirements in microcircuits.
[0063] Yet another object of the invention is to provide a thin
film deposition and etching process for the manufacture of
microscopic battery electrodes.
[0064] An object is the use of lithographic, thin-film processes to
form microbatteries that are connected through microswitches that
can be used to dynamically reconfigure a collection of microbattery
cells in an arbitrary configuration of parallel and series cells or
arbitrary connection to other MEMS components.
[0065] An object is the use of reconfigurable microbattery cells to
match microbattery charging and/or discharging configurations.
[0066] Further objects of the invention will become evident in the
description below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] FIGS. 1a) through f) show in profile (cross section) thin
film components fabricated during successive micro-fabricating
steps, in accordance with principles of the present invention, by
which a microscopic battery comprising thin film microscopic
electrodes and a microscopic cavity comprising a receptor for a
minute amount of aqueous electrolyte;
[0068] FIG. 2 is a profile of a completed single cell,
lithographically formed, thin film aqueous electrolyte microscopic
battery comprising one form of the present invention;
[0069] FIG. 3 is a profile of a further lithographically formed,
thin film, aqueous electrolyte embodiment of the present invention,
showing microscopic batteries arranged in series and in
parallel;
[0070] FIG. 4 is a profile of a lithographically formed thin film
embodiment of the invention integrated with a MEMS or non-MEMS
microcircuit and including digital/RF capability, the microscopic
battery being rechargeable by a solar cell and all components being
carried on a flexible substrate which can be removed from the rigid
substrate by destruction of a sacrificial layer, to accommodate
placement on a non-flat surface;
[0071] FIG. 5 is a profile substantially similar to FIG. 4, except
the microscopic battery, the system, including digital/RF
capability, and the solar cell are permanently mounted on a rigid
base or substrate, as opposed to a rigid base or substrate;
[0072] FIG. 6 is a profile of another lithographically formed thin
film embodiment of the present invention comprising a MEMS
microswitch/second level interconnect by which the microscopic
cells or batteries of the system can be dynamically reconfigured
for charging and discharging;
[0073] FIG. 7 is a profile of a further embodiment of the present
invention which comprises a support comprising a rigid substrate
coated with silicon dioxide, a first thin film microscopic
electrode, a plurality of microscopic cavities formed in a
separator layer for aqueous electrolyte and a plurality of second
electrodes in the form of microscopic rods or pins, one for each
cavity;
[0074] FIGS. 8 and 9 are diagrammatic representations showing two
stacking arrangements for a microscopic battery and a MEMS or other
microcircuit;
[0075] FIG. 10 is a schematic plan view showing microscopic battery
cells of a microscopic battery system arranged to provide various
voltage and current/capacity outputs;
[0076] FIG. 11 is a schematic of a flat cell microscopic battery
according to the present invention;
[0077] FIG. 12 is a schematic of a plurality of flat cells
connected in series comprising a microscopic battery system
according to the present invention;
[0078] FIG. 13 is a schematic of a parallel wires conformal
microscopic battery according to the present invention;
[0079] FIG. 14 is a schematic of a concentric tubular configuration
of a microscopic battery according to the present invention;
[0080] FIG. 15 is a schematic of a wire-in-the can microscopic
battery configuration according to the present invention;
[0081] FIG. 16 is a schematic of a spirally-wound microscopic
battery according to the present invention;
[0082] FIG. 17 is a Rygone graph representation of the specific
energy and specific power characteristics of various energy storage
technologies;
[0083] FIG. 18 is a perspective with a part broken away for
clarity, of a thin film microscopic battery cell, showing in
particular a microscopic electrolyte cavity;
[0084] FIG. 19 is a perspective of a microscopic battery comprising
a microscopic peg or pin electrode and a hollow receptor
electrode;
[0085] FIG. 20 is a block diagram of a MEMS sensor system
comprising an integrated microscopic battery, among other things;
and
[0086] FIG. 21 is a plan schematic of a remote sensor array for
military purposes.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
Fabrication of Microscopic Batteries
[0087] The microscopic batteries of the invention are fabricated
using techniques parallel to those heretofore used in the formation
of integrated circuits (IC) and MEMS (Microelectromechanical
Systems), but novelly applied to the field of energy storage and
delivery. The new processes are used to form the components of the
microscopic battery, e.g., the microscopic electrodes, the storage
of a microscopic amount of electrolyte in a cavity or space of
microscopic size, an insulating or separator layer in some
configurations, cell seals, etc. In general, these processes can be
described as forming successive thin film patterned layers upon a
substrate to obtain the desired microscopic battery configuration.
A layer may be formed of a sacrificial substance which is
chemically removed to form a microscopic cavity for electrolyte
and/or expose a surface area of a microscopic electrode. The
narrative below describes the application of the novel processes of
this invention by which microscopic batteries of the present
invention are formed.
[0088] In order for a microscopic battery to be optimal for
internal inclusion in an integrated circuit, such as a MEMS, the
batteries must be integrated with the circuit (either on a retrofit
or original manufacture basis). The processes used to make
microscopic batteries are intended for the most part to be
compatible with those used to make components in the circuit,
particularly where integration is obtained at the time of
manufacture.
[0089] Processes applicable to the present invention can typically
be described as the deposition of thin film layers in superimposed
relationship on a dielectric or other suitable substrate, base or
carrier (or over pre-formed layers) and lithographic formation of
patterns in some or all of the layers. A microscopic cavity or
reservoir for electrolyte may be selectively etched in a
sacrificial layer. The composition and pattern of the layers
depends upon its function.
Substrate
[0090] The batteries of the invention are presently most often
formed upon a suitable substrate, either rigid or flexible
(conformal). Commonly a silicon wafer is used as the base or
substrate. Other suitable materials may be used, as will be
apparent to those of skill in the art.
[0091] The substrate may be used not only as a base or carrier upon
which a microscopic battery is formed but a base upon which other
elements of the microcircuit are formed. Thus, a microcircuit with
an internal integrated microscopic battery may be formed
simultaneously or substantially simultaneously on a common base.
Typically, the substrate is first be treated before formation of
the microscopic battery to create an insulating or isolation layer.
Parts of selected layers are removed to form a desired battery
profile.
[0092] The substrate may be rigid where appropriate or formed of a
conformable, yieldable or flexible material, usually of a
dielectric polymeric material. The flexible base may also be
supported by a rigid temporary silicon substrate or other suitable
material. A sacrificial layer, such as SiO.sub.2, can be
superimposed upon the rigid substrate, beneath the flexible
substrate layer. The microscopic battery alone or with the
microcircuit is fabricated on flexible substrate. The sacrificial
layer is then etched away, freeing the flexible conformable
substrate and the microscopic battery and other components mounted
thereon from the rigid substrate for conformal mounting upon a
non-planar surface.
Fabrication of the Electrodes
[0093] A battery comprises two electrodes separated by an
electrolyte. The first battery component applied to the substrate
is usually a deposition-created thin film microscopic electrode
(cathode).
[0094] The microscopic cathode frequently comprises a thin film
metal in an oxidized state. Such materials may be applied by a
suitable deposition technique, such as evaporative sputtering,
chemical vapor deposition (CVD), or electrodeposition. The cathode
is typically a microscopic layer of metal which is modified by
oxidation, diffusion, or ion-implantation. The cathode may be
formed in a charged state or a discharged state, depending upon
process considerations and the nature of the electrochemical couple
of the battery. The cathode may be a metal oxide, such as nickel
hydroxide, which, as such, may be precipitated onto a desired
surface. While such is sometimes called "plating" better terms are
electrodeposition and precipitation.
[0095] The microscopic anode is frequently a thin film metal or a
metal hydride, and can be applied using any method for applying
metal layers, such as sputtering, CVD, vapor deposition or
electrodeposition. Zinc, when used as the active anode material,
can be easily applied using available micro-fabrication techniques,
and has the additional advantage of high operating potential when
used in conjunction with many cathode materials. For example, zinc
cells supply 1.65 V, with a nickel hydroxide cathode, vs. 1.3 V for
a metal hydride with a nickel hydroxide cathode. Multi-component
microscopic anodes, such as metal hydrides, are more difficult to
obtain by such techniques (sputtering, CVD, vapor deposition or
electrodeposition), because of their multi-component composition
and the need for a homogeneous thin film as the microscopic anode.
However, they can be created by spin-coating a slurry containing
powders of the appropriate composition.
The Electrolyte
[0096] The electrolyte has, as its key property, the ability to
conduct ions, while restricting the movement of electronic current.
The electrolyte used in these microscopic batteries may be any
suitable material, the quantity of which is of a microscopic
amount. The electrolyte may be an aqueous liquid disposed in a
microscopic cavity fabricated between the microscopic electrodes,
or an aqueous liquid disposed in a porous separator material
between the microscopic electrodes. Aqueous liquid electrolyte
systems are typically preferred where a higher power density is
required. Novel techniques are available to fill an etched
microscopic cavity with a miniquantity of electrolyte.
[0097] In one embodiment of the invention, a liquid electrolyte is
contained in a microscopic electrolyte cavity. The microscopic
cavity is formed by etching a polyimide layer underneath the anode
through a hole in the anode layer. This same hole in the anode is
used for filling the completed battery cell with a microscopic
amount of aqueous liquid electrolyte. The liquid electrolyte may be
delivered to the microscopic cavity of the battery using a syringe
comprising a thin gauge medical-grade needle, which is positioned
through the hole with the aid of a microscope, or in any other
suitable way. The hole is thereafter sealed. Sealing may comprise
filling and/or covering the hole with sealant or covering the
entire cell.
[0098] In another embodiment a porous separator saturated with
liquid electrolyte is used. The porous separator may obviate the
need to form the electrolyte cavity. Cellulose, polymers (porous
and/or nonporous) and/or fiberglass, each saturated with aqueous
electrolyte may be used. Aqueous solutions of potassium hydroxide
or sulfuric acid are frequently used as liquid electrolyte.
[0099] Solid microscopic electrolytes may, under some circumstances
be used as part of the present invention, and have the advantage of
not requiring a filling process. Solid electrolytes offer
advantages of pliancy for conformal applications where required
power levels are lower.
Fabrication of the Connectors
[0100] The microscopic batteries of the invention can be separately
made and thereafter connected to other circuit components, for
example on a retrofit basis, through use of suitable connectors.
Microscopic wire bond, flip chip or TAB (tape automated bonding)
connections are preferred, although and suitable technique
available to those skilled in the art may be used.
[0101] The microscopic batteries of the invention may also be
integrated (built unitarily and simultaneously) with an IC or MEMS,
for example, to provide an autonomous system. Interconnection
between the battery and the other components of the integrated
circuit may be made by common thin film deposition, overlapping
thin film deposition, wire bond, flip chip, TAB and/or in any other
suitable way.
Seals
[0102] A minute amount of liquid electrolyte is sealed within the
microscopic cavity or within the microscopic pores of a separator
layer. The entire cell may be encapsulated by a suitable polymeric
or other dielectric layer. Riston.TM. or polypropylene are examples
of suitable sealants.
Choice of Electrochemical Couple
[0103] Battery couples and electrochemical couples are synonymous.
Each refers to the basic chemistry of the cell. An electrochemical
couple consists of two electrodes and an electrolyte. More commonly
the name of the electrolyte is omitted when specifying a couple,
such that the two electrode materials define the couple.
[0104] Many different kinds of electrochemical couples have been
used. The lead acid battery uses the lead dioxide/sulfuric acid,
water/lead couple. It is typically called the lead dioxide/lead
couple, or the lead/acid couple. Another common electrochemical
couple is the nickel/potassium hydroxide, water/cadmium couple, or
the nickel/cadmium couple (i.e. N.sub.1-Cad batteries). Others are
nickel/zinc, silver oxide/zinc, lithium/ion, and zinc/air. Each
couple has different electrode materials, and has different
characteristics, such as cell voltage, power capability, cost,
life, rechargeability, and so forth. The choice of the optimum
couple depends on the application and other factors.
[0105] The electrochemical couple for the microscopic battery of
the invention must have microscopic electrodes and a microscopic
amount of electrolyte where formation is by microfabrication
processes discussed herein. Ordinarily the selection of the
electrochemical couple will determine the temperature range at
which the microcircuit and battery need to be operated.
[0106] In most applications, microscopic batteries of the invention
will be secondary (rechargeable) batteries, to accommodate a long
useful life. However, primary microscopic batteries of the present
invention may be fabricated for single use purposes, where
recharging is not required. Circuits with secondary microscopic
battery systems of this invention may include microcircuits and
devices for recharging the secondary microscopic batteries. Solar
cells, electromagnetic couples, and other suitable recharging
devices may be used.
[0107] Rechargeable batteries are, of course, batteries which can
be recharged following discharge. Non-rechargeable batteries cannot
accept a charge following discharge, or at least can only do so
with exceeding difficulty and possibly danger. The reasons that
some batteries can be recharged and others cannot, are normally due
to the internal chemistry of the cell, especially the electrode
processes. During discharge, each electrode experiences chemical
reactions, which involve the transfer of electrical charge. As a
result of the reaction processes, reaction products are formed
These products are usually a different chemical compound. An
example is the lead acid cell. During discharge, the following
reactions occur:
Positive Electrode
PbO.sub.2+HSO.sub.4.sup.-+3H.sup.++2e.sup.-.fwdarw.PbSO.sub.4+2H.sub.2O
Negative Electrode
Pb+HSO.sub.4.sup.-.fwdarw.PbSO.sub.4+H.sup.++2e.sup.-
[0108] When electronic contact is made between the two electrodes
(typically by placing a load across the cell), a flow of electrical
charge (e.sup.-) occurs. Internal to the cell, the solid electrode
reactants, PbO.sub.2 and Pb, combine with the sulfuric acid, and,
form the discharge products, PbSO.sub.4 (note: in the case of the
lead acid cell, the discharge product is the same for both
electrodes. In general, this is not the case, however.). The lead
acid cell is rechargeable. The recharge reactions are the reverse
of the discharge reactions:
Positive Electrode
PbO.sub.2+HSO.sub.4.sup.-+3H.sup.++2e.sup.-.rarw.PbSO.sub.4+2H.sub.2O
Negative Electrode
Pb+HSO.sub.4.sup.-.rarw.PbSO.sub.4+H.sup.-+2e.sup.-
[0109] In a rechargeable battery, the electrode reactions can
proceed back and forth, in either direction. In other words, the
cell is reversible. In a non-rechargeable battery, this is not the
case. Electrode reactions are not easily reversible, if at all.
Attempts to do so can result in excessive cell heating or
explosion. Another name for rechargeable batteries is secondary
batteries. Another name for non-rechargeable batteries is primary
batteries.
[0110] There is a large number of materials available for inclusion
in electrochemical couple for microscopic batteries according to
the present invention. By way of example only, microscopic
electrochemical couples of the present invention may comprise,
among other things microscopic electrodes formed of nickel, zinc,
metal hydride, lead, lithium, silver, copper, platinum, carbon,
cadmium and lanthanum, and derivatives thereof, combined into pairs
of microscopic electrodes in a manner known in the art, and
electrolyte, solid or liquid, in microscopic quantities formed of
aqueous potassium hydroxide, aqueous sulfuric acid, lithium glass,
an ion-conducting polymer, a polymer containing an
ionically-conductive material, or a porous separator saturated with
a suitable liquid electrolyte, as is known in the art. The porous
separator may be of porous spun polymer, cellulose or a pervious
fiberglass. A non-porous separator may be used where electrolyte is
otherwise interposed between microscopic electrodes.
[0111] Among the preferred couples for the invention are
nickel/metal hydride and nickel/zinc. Others are lead acid,
lead/zinc, nickel/cadmium, silver/zinc and lithium/carbon. Both
couples are well-known as secondary couples using an aqueous
electrolyte usually potassium hydroxide or sulfuric acid. Typical
operating voltages (1.0-1.3 V for nickel/metal hydride, and 1.3-1.6
V for nickel/zinc) are suitable for MEMS applications. It is of
importance that the invention accommodate connection of cells in
parallel and in series to provide a satisfactory range of output
voltages. The nickel hydroxide electrode is an excellent cathode
for applications requiring long cycle life. This electrode has
several advantages, e.g. it is suitable for at least moderate rates
of discharge and it is dimensionally stable and can be used with a
variety of different anodic materials. It can also be made in both
the charged and discharged states.
[0112] Zinc anodes are attractive because of their low equivalent
weight, high reactivity, and good electronegativity. Sometimes zinc
secondary batteries fail due to zinc dendrite formation and
redistribution of the zinc during cycling. Such is less likely to
occur with the present microscopic batteries due to the small
dimensions and the simplified microscopic cell geometry. The metal
hydride anode has the advantages of dimensional stability and
reasonable good cycle life. Its past disadvantages are high
self-discharge rate and modest electronegativity.
[0113] Silver/zinc cells are suitable using liquid in porous
materials for the electrolyte. The porous materials may comprise
spun polymers containing an electrolyte (5 M KOH/H.sub.2O). This
type of cell may have a lower cycle life (number of
charge/discharge cycles) due to silver migration to the negative
electrode. The use of cellulose as a separator would enhance cycle
life, but may pose fabrication difficulties.
[0114] Lead dioxide/zinc cells are also suitable, but may have a
low cycle life due to the very high solubility of zinc in acid
electrolytes.
[0115] Nickel/cadmium cells perform comparably to
nickel/metal/hydride cells. However, this electrochemical couple
may present some problems because of cadmium toxicity and the
possibility of cadmium contamination of fabrication equipment and
other fabrication problems.
[0116] Lead acid cells are capable of good cycle life and excellent
power output. The lead acid cells may be thermodynamically unstable
because of the thin film nature of the lead dioxide electrode,
which may retain a charge. Lead acid microscopic batteries can
deliver a power discharge per cell of on the order of 10 W/cm.sup.2
for short (ms) discharge times. The power discharge rate per cell
decreases to 1 W/cm.sup.2, 0.1 W/cm.sup.2 and 0.01 W/cm.sup.2 for
discharge times in seconds, minutes and hours respectively.
[0117] Nickel/zinc microscopic batteries have maximum power
discharge rates of 1 W/cm.sup.2, while cells with solid electrolyte
have much lower maximum power discharge rates, e.g. 0.01
W/cm.sup.2.
[0118] A good metal hydride material which is useful in batteries,
is one which can accept, store, and release hydrogen within its
structure. In order to do this, both the composition and structure
of the metal are important.
[0119] A metal mixture used as a hydride is prepared such that the
composition (the relative amounts of the various constituents, such
as nickel and lanthanum) is proper. The metal when it is deposited
consists largely of two distinct phases: nickel metal, and
lanthanum metal. Mixing of the two is normally not adequate.
However, if the deposited material is heated to a proper elevated
temperature, then the mobility of the metal atoms increases, and
the lanthanum and nickel migrate and mix with one another. Thus,
heating improves mixing of the two metals. Heating can also cause
the metal structure to re-organize itself into other crystal
structures. Some crystal structures are better than others with
respect to hydrogen acceptance.
Characteristics of Microscopic Batteries
[0120] With some variation, microscopic batteries according to the
present invention typically comprise the following
characteristics:
3 Characteristic Lower Limit Upper Limit A. Voltage open circuit
1.0 V 4.0 V (i.e. w/o load) during operation 0.0 V 3.5 V B. Current
0 (no load) 100 mA C. Discharge Power Output 0 (no load) 10 W
Recharge Power Input: 0 1 W Energy Storage 0.00005 Joules 4 Joules
Charge/Discharge Cycles 0 (One Millions Discharge) (limit unknown)
Operating Temperatures 40.degree. C. 80.degree. C. Discharging
Time: 0.001 seconds Days-Months Recharge Time: 0.1 seconds
Days-Months D. Internal energy losses: 108 W 10 W E. Current
Density 0 (Open 10 A/cm.sup.2 Circuit) 1 .mu.A/cm.sup.2 (Load) F.
Inter-electrode gap 1 .mu.m 100 .mu.m G. Coulombic Capacity
0.000025 C 1 C (Coulomb)
[0121] Typical specific energy and specific power characteristics
are show in dotted lines in the graph of FIG. 17. The features of
merits shown in FIG. 17, specific power and specific energy are the
most relevant and common features of merit for traditional
batteries. It is most desirable to maximize energy storage per unit
mass, or power per unit mass. It is also common to assess energy
storage and power per unit volume. In other words, it is important
to minimize the mass and/or volume of the battery.
[0122] In integrated circuits, mass and volume are relatively
unimportant, but the area of the battery (the amount of the surface
on the circuit or chip) is very important. As such, a more useful
feature of merit is energy per area (J/cm.sup.2, or
W.multidot.hr/cm.sup.2), and power per area (W/cm.sup.2). The graph
of FIG. 17 is useful for relative comparisons between different
energy storage concepts.
Method of Integration
[0123] A microscopic battery of the present invention may be
integrated with a MEMS or other integrated circuit by concurrent,
simultaneous or unitary formation of both upon a silicon substrate
wafer, or other suitable base. For example, methods for fabrication
of flexible, thin-film interconnections used in multi-chip
packaging and methods involving lithographic, sacrificial release
and etching may be used which parallel the fabrication of MEMS.
These processes provide for integration of the microscopic battery
into an integrated, interconnected microcircuit system, which is
required for autonomous applications. The support base may be
flexible and may comprise a flexible sensing surface.
[0124] Several microscopic batteries or microscopic cells of the
invention may also be integrated, interconnected, arranged and
combined to provide a power system from which different voltage
outputs are available. This allows for matching of the voltage for
the electronic and MEMS components, which often require different
voltages for optimum performance. The systems may comprise
electronic reconfigurating components, i.e., switching devices, for
example, to change or reconfigurate the combination of cells to
achieve a different or changed set of output voltages. More
specifically this allows, for example, a power system to produce
different voltages, as selected manually or by programing, or to
permit a high voltage output, with a low voltage recharging
circuit.
Battery Configurations
[0125] A flat cell microscopic battery configuration, of the type
shown in FIGS. 2 and 11, is the simplest approach from a
fabrication standpoint. The flat cell 60 is arranged somewhat like
a sandwich, i.e. a set of superimposed layers with two ultra thin
space electrodes on either side of a microscopic space containing
electrolyte. See FIG. 2, for example.
[0126] A variation of the flat cell is a linear cell 62. See FIG.
13. The materials used for each electrode are thin film deposited
adjacent to but spaced from one another in parallel lines.
Electrolyte is placed between and around the two lines of electrode
material. The result is a wire-shaped micro battery. The region on
an integrated-circuit board or the like intended to be devoted to a
wire can be replaced by the wire-shaped battery. Connections are
made to either end of the cell (at the opposite electrodes). Such
cells need not be straight, but can conform to any desired
shape.
[0127] Other configurations are also embraced by the invention,
which use the same or similar fabrication procedures. Each has
advantages with respect to capacity, current output, voltage,
convenience and/or cost effective manufacture. The present
invention accommodates an embodiment comprising a bipolar stack
which is normally best for high voltage. The bipolar stack may be
made by superimposing several single flat cells 60 one on top of
the next, which provides high-voltage availability from a small
area on a substrate. The bipolar configuration may have a lower
capacity when compared with other configurations.
[0128] Another way of achieving high voltage is to connect several
flat cells 60 in series with connecting wires interposed between
the electrodes of successive cells. See FIG. 12. This configuration
is simple, but uses a large substrate area and also may have a low
capacity.
[0129] A high capacity configuration is a "wire-in-can" arrangement
64. See FIG. 15. This configuration may be difficult to fabricate.
A small cylindrical container is made from the anodic metal, such
as zinc. A wire or thin plate is made from suitable cathodic
material and placed into the anodic can, in spaced or separated
relationship, along with electrolyte. The cell is then sealed.
[0130] Another configuration is the concentric wire arrangement 66,
which has the advantages of being flexible and conformable, as well
as being of simple construction. See FIG. 14. This configuration is
made by using a wire made from a metal anodic material (such as
zinc), coating the wire with electrolyte (with or without a porous
separator), and concentrically surrounding the electrolyte and wire
with tubular-shaped cathode material. This type of cell is
extrudable and its pliancy accommodates conformability into almost
any shape. Attachment of the cell to a substrate, base or the like
would not require attachment to the base at several points, but the
cell can be attached at one end so as to extend perpendicular to
the base or substrate. This conformal wire-shaped configuration
typically comprises a diameter within the range of 50 to 1000
microns or less, but may comprise a length of several centimeters.
Long rolls of wire microscopic battery 66 can be made and wound
upon a spool. The spool can be rotated to remove a desired length
of battery 66, which is cut and integrated with a desired circuit,
where the length is a function of the amount of energy storage
required.
[0131] Another high-capacity configuration is the spirally-wound
configuration 68, which also occupies only a small area on the
substrate or base. See FIG. 16. Thin, flat ribbons of opposing thin
film electrode materials are superimposed on top of one another
with a thin separator layer between them and an additional
separator layer placed on top. The thin electrodes comprise a
conductive tab or connector. The combination is then rolled into a
spiral and placed in a cylindrical container. After containment,
the spiral is filled with electrolyte, the container is sealed and
the completed microscopic battery is positioned on the
substrate.
[0132] As shown in FIG. 8, a MEMS or other microcircuit 80 may be
stacked upon a substrate-mounted microscopic battery 82 of this
invention. The reverse arrangement is shown in FIG. 9.
[0133] FIG. 7 depicts the stock arrangement of FIG. 8, but with a
somewhat different microscopic battery 90. Microscopic battery 90
is of thin film construction and comprises a support comprising
rigid substrate 32 coated with silicon dioxide 30, first thin film
microscopic electrode 34', a plurality of microscopic cavities 92
formed in a separator layer 94, in which aqueous electrolyte is
contained, and a plurality of second electrodes in the form of
microscopic rods or pins 94, one for each cavity 92. Each pin 94 is
secured in an aperture or bore 96, which may be formed by drilling
or in any other suitable way. MEMS or other microcircuit 80 is
shown as superimposed upon battery 90.
Description of Processes
[0134] The methodology of the invention involves micro-fabrication
techniques parallel to those used to form integrated circuits
generally and MEMS in particular. Heretofore conventional wisdom
has dictated use of large external power sources for MEMS and other
microcircuits. Microcircuits with integrated or internal
microscopic batteries have been viewed as not viable.
Micro-fabrication techniques have not heretofore been employed in
an attempt to invent or provide a cost effective microscopic
battery for internal microcircuit purposes. The micro-fabrication
techniques used in the manufacture of microscopic batteries of the
invention are to a large extent adaptations from IC fabrication
techniques.
[0135] Fabrication of microscopic battery components involves the
lithographic application of superimposed layers carried by a
substrate. Layer deposition techniques include Chemical Vapor
Deposition (CVD), evaporation or vapor deposition, sputtering, spin
coating and electrodeposition. CVD is generally known for the
application of silicon, silicon oxide, refractory ceramic compounds
(e.. Si.sub.3N.sub.4), and refractory metals and metal oxides. CVD
involves the thermal decomposition and/or reaction of gaseous
compounds to form thin films upon a surface. For the present
invention, CVD is used for deposition of one or both thin film
electrodes (anode or cathode) of the microscopic battery.
[0136] Evaporation or vapor deposition involves the heating of a
metal to form a vapor and then redeposition of the metal vapor to
form a thin metallic film upon a desired surface. Evaporation can
be used in microscopic battery construction for the fabrication of
the microscopic thin film electrodes.
[0137] Sputtering is achieved by bombarding a target with energetic
ions, typically Ar.sup.+, and knocking loose atoms from the surface
of the target, which atoms are transported and deposited upon a
substrate. Sputtering can be used in microscopic battery
construction for the fabrication of metal and metal oxide thin film
electrodes.
[0138] Spin coating is accomplished by spinning a substrate in the
plane of its surface and applying a liquid coating material, which
is spread evenly over the surface by centrifugal force. Spin
coating of a suitable polymeric material over a thin film electrode
creates battery separators or spacers, which are insulating layers,
dielectric spacers and passivating layers. A porous polymeric layer
may be created by spin coating between the electrodes and
thereafter saturating the porous polymeric layer with liquid
electrolyte. A completed microscopic battery or microscopic battery
cell can be externally coated or sealed using spin coating
procedures. Spin coating is an important step in the lithographic
patterning process used to custom etch electrodes into the desired
shape and to remove a specific part of a polymeric coating or layer
to create a microscopic cavity for liquid electrolyte, for example.
In one form, a polyimide layer may be used so that selective
removal of a portion thereof creates an electrolyte cavity. Spin
coating may also used for application of certain electrode
materials where the electrode materials are supplied as a slurry
and the slurry stabilized by photolithographic techniques to form
thin electrode layers. For example, a metal hydride powder may be
slurried with an appropriate liquid and then spin coated.
[0139] Electrodeposition is a process heretofore applied to
microfabrication of IC and MEMS, but not to making microscopic
batteries. This process involves application of a conductive film,
such as a metal, to create a first thin film microscopic electrode
on a substrate and, thereafter, immersing the coated substrate in a
current-driven electrodeposition solution to form a thin film
microscopic counter electrode of suitable composition in spaced
relation to the first electrode. This process may be used in the
present invention for the deposition of electrodes, such as nickel
oxide electrodes, for example, PbO.sub.2 and AgO cathodes may also
be formed by electrodeposition.
[0140] Patterning is the shaping or configuring of layers by
masking portions to be retained and removal of undesired portions
to customize various structures or shapes within the microscopic
battery cell. This can involve the selective application of layers
and removal of predetermined segments of a selected layer, or the
masking of the substrate by a sacrificial masking layer, followed
by applying the next layer and etching to remove the mask.
Lithographic processes, including but not limited to
photolithography, are applied in a known manner consistent with the
microscopic battery to be formed; therefore, the processing is a
modification, adaption and/or variation of prior non-battery
technologies.
[0141] After the thin film layers are applied and before or after
they are shaped by patterning, they may be modified by any of
various processes. These include the chemical modification of the
layer, using oxidation, diffusion, and ion-implantation techniques.
These processes are used in conjunction with lithography to modify
only selected parts of patterned portions of the layer being
treated, or to mask other layers.
[0142] Etching is used for the removal of undesired parts, usually
by chemical reaction, and is often used in conjunction with
lithography to pattern a layer or protect other layers. The method
of etching and the etchant composition depend on the material to be
removed. These include, by way of examples only, hydrofluoric acid
for silicon dioxide materials, wet acid etching for suitable metal
oxides and metals, oxygen plasma etching for polymeric or other
organic materials. Etching is used here in conjunction with other
processing techniques to apply surface micro-machining techniques
to microscopic battery construction. Etching of a part of a layer
can be used to form a cavity for a liquid electrolyte.
[0143] The above-described micro fabrication steps lend themselves
well to mass production, which produces low costs of manufacture
and low rejection rates.
EXAMPLE I
Fabrication of Zinc/Nickel Hydroxide Microscopic Batteries with
Aqueous Liquid Electrolyte
[0144] Small area, thin film nickel/zinc aqueous microscopic
batteries of the invention with a footprint of 350 .mu.m by 350
.mu.m were built and tested. The batteries utilized a 5M
KOH/H.sub.2O electrolyte.
[0145] The cathode was made as an ultra thin, continuous film of
nickel hydroxide, without large crystals or rough deposits. Voids
in the film were avoided. The film adhered to its current collector
(in this case, a thin nickel film on a silicon wafer). The
thickness of this layer was about 1-5 .mu.m. The nickel hydroxide
was electrodeposited from an aqueous solution of 0.1 M
Ni(NO.sub.3).sub.2. The substrate was a four-inch silicon wafer
with a thin nickel film vapor deposited on one face. A thin film
nickel counter electrode was used. The two electrodes were held
apart (2.5 cm spacing), and a cathodic current of 50 mA was used
for deposition. In order to prevent the vapor-deposited nickel film
from detaching from the silicon wafer, a layer of titanium was
first vapor-deposited on the silicon wafer before vapor deposition
of the nickel film, and the combination was annealed. Particulate
matter, especially nickel hydroxide, was excluded from the solution
to avoid formation of large particles. Filtering the deposition
solution reduced the number of large particles formed and improves
adhesion. For optimal performance, the films of nickel hydroxide
are made thin and homogeneous in composition.
[0146] The nickel film was then electrochemically oxidized (in
aqueous KOH solution) to form NiOOH for microscopic cells
fabricated in the charged state. The resulting ultra thin layers
may be approximately 5 .mu.m thick and have a capacity of >0.2
C/cm.sup.2.
[0147] The zinc anode electrodes were made by evaporation of zinc
metal onto the targeted surface.
[0148] FIGS. 1a-f are profile schematics illustrative of the
lithographic steps by which a thin film, aqueous electrolyte, small
area microscopic battery of the invention may be formed. The
profiles are illustrated from the vantage point of a cleaved cross
section of the thin film layers being applied and configured at
various times during the process. The scale for the x- and
y-directions is not the same in order to better illustrate the
layers with clarity.
[0149] The process illustrated in FIGS. 1a-f began, for example, by
growing a global, thermal SiO.sub.2 layer 30 on the top of the
silicon substrate or base 32. The SiO.sub.2 layer, in the
alternative, may be CVD deposited and is capable of being etched
when and to the extent appropriate. Oxide growth was followed by
deposition of the NiOOH cathode material 34 as described above. See
FIG. 1a. A photoresist layer 36 was then spin-deposited on the
wafer and sized or patterned as shown in FIG. 1b. Areas of the
photoresist layer 36 were exposed to carefully focused light, which
effects a change in the structure of the resist layer thus exposed,
allowing for its easy removal (while leaving the rest of the resist
in place). Then, metal can be deposited only in the areas not
covered by the resist. Finally, the remainder of the resist is
removed at the appropriate time. The patterned photoresist was thus
used as a conformal mask for a wet metal etch, which reduced and
thereby defined the peripheral dimensions of the bottom electrode
34' and provided for ample separation between individual
microbattery cells, where more than one cell was formed. See FIG.
1c.
[0150] A 10 .mu.m layer 38 of Dupont 2611D polyimide (other
suitable material may be used including silicon dioxide) was
spin-deposited on the top and edges of the bottom electrode 34' and
along the exposed part of the top surface of SiO.sub.2 layer 30.
The polyimide layer 38 was fully cured by using a 400.degree. C.
anneal in a nitrogen atmosphere.
[0151] After the polyimide cure, a thin film microscopic layer 40
of zinc was evaporated onto the top surface of the layer 38. FIG.
1d represents the wafer profile at this point in the process. A
photoresist layer 42 was spin-deposited over the top of all layers
superimposed upon the wafer 32 and patterned to both separate cells
and to create a fill hole etch mask in the zinc layer. The
photoresist pattern was then used as a mask in conjunction with the
wet etch patterning of the zinc electrode layer, to produce the
contoured configuration shown in FIG. 1e.
[0152] Following patterning of the zinc layer 40 to configure the
second microscopic electrode 40' into the desired shape, the
polyimide layer 38 underneath the zinc layer was etched in an
oxygen plasma to create the polyimide spacers 38' shown in FIG. 1f.
The transformation of polyimide layer 38 into spacers 38' also
created a microscopic cavity 42 into which a microscopic amount of
aqueous electrolyte was later placed.
[0153] The size and characteristics of the etched electrolyte
cavity were visually verified with a test wafer. A separate test
wafer was processed identically to the microscopic battery wafer,
except that the zinc electrode layer was replaced with a
transparent SO.sub.x layer. This transparent layer allowed visual
inspection of the electrolyte cavity. The microscopic battery and
test wafers were processed simultaneously, under the same
conditions, and the test wafer was, therefore, a replica used to
accurately predict the size of the electrolyte cavity. FIG. 18 is a
perspective of a microscopic cell showing the underlying NiOOH
microscopic electrode layer 34' and the microscopic electrolyte
cavity 42 in the polyimide layer 38'.
[0154] After formation of the microscopic electrolyte cavity 42,
the cell was filled with KOH/H.sub.2O through aperture 46 (FIG.
18), using a surgical needle mounted on a micromanipulator (used on
a sub-micron probe station). The aperture 46 had a diameter of
about 300 .mu.m. Other suitable ways for placing electrolyte in the
microscopic cavity 42 may be used. After filling the cavity 42, the
hole 46 and/or the entire cell can be sealed using a suitable
material, such as Riston.TM. or vapor deposited Parylene.
[0155] A polyimide sealant 43 was next deposited over the top of
the microscopic assemblage of FIG. 1f for form the completed
microscopic cell or battery 44 shown in FIG. 2. Other suitable
sealants may be used.
[0156] The microscopic battery of FIG. 18 comprised a footprint
approximately 750 .mu.m by 750 .mu.m with an adjoining tab for
electrical connection. Other microscopic cells with side dimensions
or footprints of 250 .mu.m and 500 .mu.m have also been fabricated.
Similar cells with other configurations have been built.
[0157] A microscopic battery was fabricated and tested. The cell
was built in the charged state with electrodes 34' and 40' of
metallic zinc and NiOOH with a separator 38' interposed between.
The initial open circuit potential was approximately one volt. It
is believed that the fabrication procedure may have influenced the
condition of the electrodes, particular, the etching of the
electrolyte cavity may have changed the nature of the electrode
surfaces. The cell further comprised an etched electrolyte cavity
42 and a micro-aperture 46. Etching of the cavity can be through
the aperture 46. Aqueous electrolyte was deposited into the cavity
42 through the aperture 46. The cell was charged and discharged 13
times at current densities ranging from 0.2 to 5.1 mA/cm.sup.2
based on the approximate area of the NiOOH electrode. The current
densities were approximated based upon the estimated extent of
undercut of the electrolyte cavity. These results represent the
first set of current/voltage data taken from a truly microscopic
battery with an active area less than 0.001 cm.sup.2.
[0158] Batteries of this invention may be described as comprising
"features," i.e. a first microscopic electrode, a second
microscopic electrode and a space or spaces in which electrolyte is
placed between the electrodes (with or without an ultra thin
separator). Batteries according to the present invention may
comprise a feature as small as 1/2 of one micron.
EXAMPLE II
Fabrication of a Metal-Hydride/Nickel Hydroxide Microscopic Battery
with Liquid Electrolyte
[0159] A microbattery was constructed, essentially as in Example I,
except that the anode comprised a metal hydride instead of zinc
metal. For the metal-hydride anode electrodes, a two component
hydride of lanthanum/nickel alloy was used. This electrode was
constructed in the discharged state (i.e., not loaded with
hydrogen). Thin films of La--Ni were formed by evaporating from a
La--Ni melt. The composition and temperature of the La--Ni melt was
carefully controlled. Also, the metal was alloyed after deposition
to ensure that the hydride had the best structure for hydrogen
insertion.
EXAMPLE III
Fabrication of Zinc/Nickel Hydroxide Microscopic Battery with
Liquid Electrolyte in Porous Spacer
[0160] A zinc/nickel hydroxide microbattery was constructed. The
cathode is formed essentially as in Example I by forming an oxide
layer and thereafter a NiOOH cathode. After patterning of the
cathode, a layer of porous material for the electrolyte is
formed.
EXAMPLE IV
Fabrication of Solid Electrolyte Microscopic Battery
[0161] Microscopic batteries with a solid-state electrolyte were
made. Despite their lower power performance relative to liquid
electrolyte batteries, solid electrolyte batteries are attractive
for applications which require, for example, batteries to bend or
conform to a particular shape, or to operate over a broad range of
temperatures.
[0162] Two different solid electrolyte materials were used, i.e.
tetramethylammonium hydroxide pentahydrate (TMAOH) and polyethylene
oxide/potassium hydroxide (PEO/KOH). TMAOH is a solid electrolyte
material used heretofore in a solid-state Ni/MH battery which can
provide current densities of 10 mA/cm.sup.2. PEO, widely used in
solid state cells, is a polymer to which a salt can be added to
produce a finite ionic conductivity.
EXAMPLE V
Fabrication of Flat-Cell Chain Microbattery and Construction of an
Array
[0163] Numerous microscopic nickel/zinc cells were made on a single
substrate. Six cells were connected in parallel by appropriately
attaching microscopic wires. These cells were then charged and
discharged together, and suffered no appreciable capacity loss
through over 250 charge/discharge cycles. Specific capacity
(C/cm.sup.2) of the parallel-connected bank of cells was
essentially the same as that of a single cell being discharged by
itself.
EXAMPLE VI
Fabrication of Wire in Can Microbattery
[0164] A "wire in a can" cell was made comprising a high surface
area porous nickel thin film first electrode, wrapped in a thin
porous separator and placed inside a cylindrical container
comprising a thin film of zinc at the inside surface and containing
an electrolyte comprising 5 M KOH/H.sub.2O.
EXAMPLE VII
Fabrication of Concentric Wires Microbattery
[0165] A hole was create down the axis of a zinc wire. A nickel
wire was thinly coated with nickel hydroxide material, and then by
a thin separator soaked in KOH/H2O. This wire, thus coated, was
then inserted into the zinc wire. The open circuit potential of the
cell was 1.65 V, which is expected from zinc/nickel cells. The cell
was operated through numerous charge/discharge cycles without
significant loss of capacity.
[0166] The concentric wires microbattery may be considered a "long"
version of the wire in a can cell (i.e. a very long can). The
concentric wire battery lends itself well to mass-productive
methods, such as extrusion.
THE EMBODIMENTS OF FIGS. 3-6
[0167] FIG. 3 illustrates a plurality of microscopic cells or
batteries 44; formed unitarily and simultaneously in the manner
described above. The parts of the battery or cell 44 of FIG. 2 are
identically numbered in FIG. 3. The part identified prime numerals
of FIG. 3 are substantially similar to the parts of FIG. 2 so
enumerated. The microscopic cells 44' at the left and in the center
are interconnected in parallel, the two sharing a common first
microscopic electrode 34." The common first thin film microscopic
electrode 34" and the first thin film microscopic electrode 34" are
in electrical communication with a thin film first level
interconnect 46. The right microscopic cell 44' is in series with
the other cell 44.' A second level interconnect 47 is in electrical
communication with the second microscopic thin film 40." Note that
electrical interconnections in FIG. 3 comprise thin film or ribbon
interconnection. Connections between one or more microscopic
batteries or cells of the present invention and a MEMS or non-MEMS
integrated circuit can likewise be thin film or ribbon
connectors.
[0168] Various arrangements and combinations of microscopic battery
cells comprising single cells, cells in parallel and cells in
series are embraced by the present invention. One of these
arrangements is show in FIG. 10, wherein some of the cells 44 are
connected anode to cathode and by which several output voltages are
available.
[0169] FIG. 4 illustrates a further combination according to the
present invention, which comprises one microscopic battery 44", of
the type described in conjunction with FIG. 1a through 1f and 2
with modest variations. Microscopic battery 44 of FIG. 4 is
illustrated as comprising a wire bond 51 connection between the
second microscopic thin film electrode 48 and a second level
interconnect 49, and a wire bond 53 connection between a first
level interconnect 55 and a battery recharging solar cell 57. The
first microscopic thin film electrode 34" is in electrical
communication with both the first level interconnect 55 and an IC
or MEMS circuit 59 (via wire bond 61). The circuit 59 is connected
to the solar cell 57 via wire bond 63, conductor 65 and wire bond
67.
[0170] All of the micro components identified above in conjunction
with FIG. 4 are stably carried on a flexible polymeric substrate 69
from which the underlying sacrificial layer 71 is entirely etched
to accommodate placement (mounting) of the flexible polymeric
substrate and the superimposed micro components in conforming
relation upon a non-linear surface.
[0171] The integrated circuit/microscopic battery arrangement of
FIG. 5 is identical to the heretofore described integrated
circuit/microscopic battery arrangement of FIG. 4, and has been
correspondingly enumerated. However, the mounting of the FIG. 5
arrangement differs from mounting of FIG. 4. Specifically the
integrated circuit/microscopic battery arrangement of FIG. 5 is
mounted upon SiO.sub.2 layer 30, which in turn is superimposed upon
rigid silicon substrate 32.
[0172] The left and central portions of FIG. 6 are essentially the
same as the left and portions of FIG. 3, and have been
correspondingly enumerated. The right portion of FIG. 6 is
different. Specifically, the right side of FIG. 6 comprises a MEMS
microswitch/second level interconnect 81, show in an open
condition. When closed, switch 81 is placed in electrical
communication with the common first thin film microscopic electrode
34" across interconnect 46. Microswitch 81 responds to an
externally-applied electrical impulse, and either open or shut a
circuit. It is used to re-configure an array of cells in a variety
of ways. For example, a string of cells can be connected in series,
when switches 81 placed between them are closed. In this manner,
high voltages can be obtained. On the other hand, if the switches
81 are open, each cell can be isolated from the others. Using
microswitches 81, a number of cells can be temporarily connected in
parallel, i.e. all of the negative electrodes from each cell are in
electrical contact one with another, and all of the positive
electrodes from each cell are in electrical contact one with
another. In this manner, a given group of cells can be arranged as
isolated individual cells, as a series-connected string of cells,
as a parallel-connected group of cells, or in some combination
thereof, depending on the location and condition of various
microswitches. One useful application of this concept is the
series-connection of cells used to achieve a high-voltage
discharge, and the subsequent parallel-connection of cells to
achieve a low-voltage charge.
THE EMBODIMENT OF FIG. 19
[0173] FIG. 19 depicts a microscopic battery 90 which comprises a
pin or peg-in-a-block configuration. More specifically, microscopic
battery 90 comprises a pin, peg or rod microscopic electrode 92,
which accommodates wire bond connection at 94 to a MEMS or non-MEMS
integrated circuit. Electrode 92 is of a predetermined microscopic
diameter. Microscopic battery 90 also comprises a block or receptor
microscopic electrode 96, which accommodates wire bond connection
at 98 to the MEMS or non-MEMS integrated circuit. The microscopic
receptor electrode 96 comprises a blind bore 100, the microdiameter
of which is slightly greater than the diameter of microscopic rod
electrode 92. The rod 92 and a suitable electrolyte are
appropriately placed in the receptor 96, with the receptor
vertically erect to complete assembly of the microscopic battery
90. Typically, the assembled battery 90 is sealed.
[0174] By way of example, the rod electrode 92 of the microscopic
battery 90 may comprise nickel foam, while block electrode 96 may
comprise zinc. A separator soaked in KOH/H.sub.2O may be interposed
between the electrodes. The diameter of rod electrode 92 may be on
the order of 1.65 mm, while the blind bore 100 may comprise a
diameter on-the-order of 2.0 mm.
Solid Electrolyte
[0175] In some configurations, the present invention may comprise
ultra thin solid electrolyte interposed between two microscopic
electrodes. Despite their lower power performance relative to
liquid electrolyte microscopic batteries, solid electrolyte
microscopic batteries are attractive for applications which
require, for example, batteries to bend or conform to a particular
shape, or to operate over a broad range of temperatures.
[0176] Two different solid electrolyte materials, TMAOH
(tetramethylammonium hydroxide pentahydrate) and PEO/KOH
(polyethylene oxide/potassium hydroxide) were substantially tested.
TMAOH is a solid electrolyte material which may comprise part of a
solid-state Ni/MH (metal hydride) microscopic battery which
provided current densities of 10 mA/cm2, considerably more than
that of other known solid-state batteries in the literature. PEO is
a polymer to which a salt can be added to produce a finite ionic
conductivity.
[0177] Lithium glass is a solid electrolyte heretofore used in
lithium batteries. Polyethylene oxide containing
ionically-conducting material may also comprise a solid
electrolyte.
Examples of Adaptation of Microscopic Batteries to MEMS
Technology
[0178] An important aspect of the present invention is the
adaptation of the novel microscopic battery technology disclosed
herein to MEMS and like microcircuits. This unique combination
solves long standing power source problems in each of the major
user segments of the MEMS market, i.e. general military, space, and
commercial. The illustrative applications discussed herein are
remote sensing arrays (general military), flexible sensing surfaces
(space), and smart sensors (commercial). Each of these applications
illustrate the importance of an integrated microscopic battery with
the system and the system constraints on the microscopic battery.
It should be emphasized that numerous other MEMS applications exist
for integratable microscopic batteries, in addition to those
mentioned here.
[0179] FIG. 21 illustrates the use of a sensing array for
battlefield context, while FIG. 20 is a block diagram of one way
basic elements of a MEMS sensor system may be assembled and
interconnected. The application typically calls for large numbers
of small, autonomous sensors with the system capability to sense,
analyze data, and communicate through RF. Microscopic batteries are
critical for battlefield sensor purposes because: 1) the system
must be autonomous and, therefore, must have its own, rechargeable
power source which can be moved from place-to-place with the
system; 2) the entire system including the integrated microscopic
battery must be small to facilitate element delivery; and 3)
components must be extensively integrated in order to accommodate
mass production to provide a cost effective end result.
[0180] Two major challenges face a microscopic battery source of
power for MEMS: i.e. (1) an integrated power source solution, and
(2) provision of different operating voltages for the RF and
digital portions of the system. It is desirable to provide a power
dissipation requirement of 10 .mu.W or more for the sensing
element. The present invention achieves this requirement and is
suitable for use with a MEMS as an integrated internal power source
that is small. The present invention also provides a microscopic
battery having two or more power supply voltages. The voltage
supply required for the digital circuitry is approximately 1 volt
while the voltage supply required for the RF communication
circuitry is approximately 4 volts.
[0181] The microscopic batteries of the invention meet the
foregoing needs. The thin film nature of the battery facilitates
inclusion as part of an integrated substrate which also carries
MEMS circuitry. Photolithographic patterning of the electrode
metallization makes possible custom connection of microbattery
cells into partitions with differing output voltages in a single
battery array. FIG. 10 shows a schematic of a microscopic battery
that has been partitioned into a nominal 1.0 cell voltage section
to power digital circuitry; a high-power, low-voltage section to
power the MEMS-sensor; and, among other things, a smaller, lower
current nominal 4.0 voltage section to power the RF circuitry. The
operating voltage of a given cell can be up to 3.5 V. This
thin-film microscopic battery can be integrated onto a single
substrate together with a EMS and/or another integrated circuit,
using the parallel fabricating and mounting techniques. Any desired
low voltage can be provided and the microscopic battery cell can be
arranged or reconfigured into appropriate series and/or parallel
arrangements to achieve one or more desired low voltages.
Remote Sensing Arrays
[0182] FIG. 20 illustrates the use of sensing arrays for
battlefield awareness and FIG. 21 is a schematic indicating how
individual elements might be arranged. The application calls for
large numbers of small, autonomous sensors with the capability to
sense, analyze data, and communicate through RF. Microscopic
batteries are needed for this application because: 1) each element
must be autonomous and therefore must have its own, rechargeable
power source (it is impractical to use a primary battery to last
the lifetime of the device), 2) the entire system must be small to
facilitate element delivery, and 3) components of each element must
be extensively integrated in order to keep costs reasonable for
large arrays of elements.
[0183] In order to demonstrate the need for microbatteries, we will
discuss a specific implementation of remote sensor array. Sensing
systems according to the present invention integrate a motion
sensor with digital logic and RF communication circuitry into a
single small system. The system is intended to provide battlefield
awareness through the distribution of the remote sensing elements
over the battlefield area.
[0184] Two major challenges face a microscopic battery system for
MEMS; an integrated power solution, and different operating
voltages for the RF and digital portions of the system. FIG. 10
illustrates such an arrangement. One of the major limitations to
improving the sensing system to provide a suitable MEMS comprising
a power source that is small and is integrated into the system.
Another challenge is the need for two power supply voltages; one
for digital circuitry (approximately 1 volt) and another for the RF
communication circuitry (approximately 4 volts).
[0185] The microscopic batteries of the invention meet these needs.
The thin film nature of the battery facilitates inclusion in an
integrated substrate with MEMS sensors and digital-analog
circuitry. Photolithographic patterning of the electrode
metallization makes possible custom connection of microbattery
cells into partitions with differing voltages in a single battery
array. FIG. 10 shows a schematic of a microbattery that has been
partitioned into a 1.0 volt section to power digital circuitry; a
high-power, low voltage section to power the MEMS-sensor; and a
smaller, lower current 4.0 volt section to power the RF circuitry.
This thin-film microbattery can be integrated onto a single
substrate together with the MEMS sensor and the integrated circuits
using the same assembly techniques used to mount and connect the
other components.
Flexible Sensing Surfaces (Space)
[0186] Many space sensing systems will be greatly benefited by the
present invention. Specifically, various forms of the present
invention can be conformably mounted to a non-flat satellite or
vehicle surface. Such surfaces require autonomous power sources.
Solar cell recharging is an available option. The sensor,
circuitry, microscopic battery, and solar cell or cells can all be
mounted, for example, on a flexible membrane surface using
conventional integrated circuit mounting techniques such as die
attach/wire bonding, flip chip and/or TAB. Autonomous power sources
are necessary in order to reduce power consumption and improve
reliability.
[0187] A microscopic battery of this invention can be fabricated on
a flexible substrate, such as Riston.TM., or can be fabricated as
part of the flexible membrane substrate on which integrated
circuits and MEMS sensors are mounted. FIG. 4 shows the profile of
an interconnection substrate that is rigid during processing, but
with a flexible substrate that can be released by etching a
sacrificial layer located beneath the flexible substrate. The
sacrificial release process is widely used in surface
micromachining processes.
[0188] This flexible substrate can also be used as a base upon
which other system components are mounted. FIG. 4 illustrates the
microscopic battery fabricated on a polymeric membrane that also
serves as the carrier for a MEMS or other integrated circuit (IC),
as well as a solar cell for recharging the microscopic battery. The
interconnections between components are illustrated as being wire
bond, but may be flip chip or TAB. The rigid substrate serves as a
temporary mounting base until fabrication of the microbattery and
the system is complete. A protective coating, such as
vapor-deposited Parylene, may be used to encapsulate all
components. The sacrificial layer may typically be etched at room
temperature using hydrofluoric acid. The flexible substrate or
membrane itself can be used as part of a smart sensing surface in
certain configurations.
[0189] It should be noted that this flexible base embodiment
requires use of a microscopic battery that can be integrated upon
and to the flexible substrate. The approach can be used to
fabricate relatively large sensing surfaces.
Smart Sensors (Commercial)
[0190] The requirements for smart sensors are very similar to those
for remote sensing arrays. Smart sensor applications exist where
large numbers of autonomous sensors are needed, such as in
inventory control, commercial security systems, and control of
sensitive manufacturing processes. The components are the same
components typically required for commercial smart sensor systems,
although the integrated circuit and sensing elements may different
somewhat. The need for an integrated microscopic battery is just as
stringent for commercial smart sensing systems as for the military
sensing systems. In fact, because the cost requirements are even
more challenging, the need for an integrated microscopic battery
solution for providing power to commercial smart sensing system may
be greater.
[0191] It is anticipated that microscopic batteries will eventually
find use in many other microelectronic circuits.
[0192] While this invention has been described with reference to
certain specific embodiments and examples, it will be recognized by
those skilled in the art that many variations are possible without
departing from the scope and spirit of this invention, and that the
invention, as described by the claims, is intended to cover all
changes and modifications of the invention which do not depart from
the spirit of the invention.
* * * * *