DEPOSITED MICROARCHITECTURED BATTERY AND

MANUFACTURING METHOD

Technical Field

[0001] This patent relates to energy storage systems. More particularly,

this patent relates to a deposited microarchitectured battery system and a

design and manufacturing method for the same.

Background

[0002] Many micro-electromechanical systems (MEMS) require a power

source of electrical energy. In some instances electrical power is provided by

a coupled battery or battery system. The size advantage of the MEMS device

is lost if the battery is large. Physical limitations of the electrode materials,

separators, and electrolyte dictate their separate manufacture, and subsequent

coupling of the battery to the MEMS device.

[0003] MEMS technology also has enabled development of fully

implantable medical devices. The power supplies for these devices, however,

can account for up to 85 % of the mass and 35 % of the volume of these

systems. The smallest commercially available batteries are in the millimeter

(mm) range and utilize zinc or lithium chemistries. Stainless steel casing is

typically used to contain the fluid electrolyte and the gaseous reaction

byproducts.

[0004] Further miniaturization of implantable systems requires new

battery technologies with enhanced compatibility with MEMS fabrication

techniques and with MEMS-processing compatible materials and substrates.

Power source selection will also rely on more than the electrochemistry. Form

factor, performance, lifetime, toxicity of the chemistry and the rate of heat

generation must be considered in the design process. This is particularly true

with implantable systems.

Summary of the Invention

[0005] Embodiments of the present invention relate to microarchitectured

batteries. These batteries can be used to create microscopic footprints,

typically on the order of lmm ² , and can be integrated directly into MEMS

devices at the time of manufacture. Microarchitectured batteries have the

potential to overcome the energy and power limitations of the past for MEMS,

and will enable the widespread utilization of MEMS devices for creating

wireless sensor networks for environmental or bio-medical applications; this

is because power sources can be created which are of the same scale as other

components of the system. By using improved fabrication processes to

deposit battery materials, energy losses can be reduced and storage capability

increased, enabling microbatteries with sizes that can be integrated with

MEMS and meet their lifetime requirements.

Brief Description of the Drawings

[0006] Fig. 1 is a schematic illustration of a micro-electromechanical

system including a coupled micromachined battery in accordance with an

embodiment of the invention.

[0007] Fig. 2 section view of a micromachined battery in accordance with

an embodiment of the invention.

[0008] Fig. 3 is a schematic illustration of a multiple cell micromachined

battery.

Detailed Description

[0009] MEMS devices may benefit from a thin-film, microarchitectured,

deposited battery that can be manufactured with or in a manner compatible

with the manufacture of the MEMS device. A microbattery may be

manufactured using processing techniques used for MEMS devices

themselves. In this manner, the microbattery may be manufactured to have a

footprint no larger than the device itself, may be manufactured during the

processing or using the same processing techniques as the MEMS device. The

microbattery may be directly coupled to the MEMS device, eliminating

additional process steps. Other microarchitecturing processes can be applied

to the substrates to create spacing, connections or microchannels for

electrolyte, e.g. laser machining, micro-drilling, micro-cutting or similar

processes. While several embodiments of the invention are described in

connection with battery structures suitable for combination with MEMS

devices, the techniques are scalable to larger dimensions. Therefore, the

present invention can be applied to the design and manufacture of batteries

for integration into much larger format applications, including larger portable

devices such as cell phones, personal digital assistants (PDAs) and laptop

computers, flat photovoltaic arrays, and large format, high power prismatic or

wound cells which power a large variety of devices, including vehicles, or to

provide load-leveling for grid power installations.

[0010] Fig. 1 illustrates a MEMS device 10 and a coupled micromachined

battery 12. The MEMS device may include a glass, silicon-based substrate 14,

e.g., silicon dioxide (SiO2); a transducer 16 formed on the substrate 14 and

circuitry 18, e.g., a processor, formed in the substrate 14. A cover 20 may

enclose the circuit 18 leaving the transducer exposed. The instant invention is

not limited to the particular structure of the MEMS device or its intended

function, including whether the MEMS device is or includes a transducer or

whether or not the MEMS device includes processing circuitry or similar

structures. Thus, the MEMS device may be virtually any type of MEMS

device that has an electrical power requirement.

[0011] The micromachined battery 12 is coupled to the MEMS device 10,

and the micromachined battery 12 may be bonded, for example, to the MEMS

device 10 using polymer adhesive 19, e.g. two parts epoxy resin.

[0012] Fig. 2 illustrates a microbattery, for example the microarchitectured

battery 12, in section. In this realization, the substrate has been machined

using microdiamond drills to create a spacing between electrodes suitable to

contain solid, gel or liquid electrolyte. The microarchitectured battery 12

includes a first section 22 and a second section 24 with a separator 26

positioned between the two sections. The two sections respectively define an

anode and a cathode and therefore differ at least in the electrode material. The

sections may be secured together by adhesive, for example a fast curing epoxy

resin, with the separator 26 being disposed in between. The separator 26 may

be a membrane formed from polymer such as Celgard®, or other polymeric

membranes with nanometer sized pores, and may be approximately 25

micrometer (μm) thick, down to lOOnm.

[0013] Electrolyte may be introduced using microfluidic channels 28

(depicted in phantom as these channels are sealed following introduction of

the electrolyte) formed in one or both of the sections. In a preferred

implementation, introduction of the electrolyte is delayed until the MEMS

device is placed into operation to increase the shelf life and then the usable

life of the device.

[0014] Each section 22 and 24 may be formed by the deposition of

electrode material 30 onto a substrate 32. A suitable current collector structure

34 is also deposited onto the substrate 32 advantageously during the electrode

deposition process or as a follow-on process. The current collector 34 may be

formed to include conductive taps 36 to allow an output of the battery to be

coupled to the MEMS device 10. Deposition of electrode active material may

be accomplished by laser machining, e.g. Nd-YAG laser, or other type of

laser) in combination with pulsed laser deposition (PLD), electron beam

deposition (EBD), chemical vapor deposition (CVD), physical vapor

deposition (PVD), chemical fluid deposition (CFD) or electroplating, or any

combination of the above.

[0015] In one realization, and not to limit the general nature of the

microarchitectured battery 12, substrates 32 for the anode and the cathode,

may be prepared by first forming masks using computer-aided design and

printing techniques. A photoresist may be spin coated onto blank substrate

stock, such as wafer stock, and cured using ultraviolet (UV) light exposure or

other method. The photoresist may be selectively removed by a solvent. The

substrate is then etched to the desired depth using an etchant, such as

fluoridic acid (HF), or other etchant which can uniformly and controllably

remove material.

[0016] As an alternative to wet etching, laser ablation may be used to etch

the substrate. Laser ablation offers potentially fewer processing steps and

faster processing speeds. However, wet etching may potentially provide

better control of the etched depth, and depth of the cavity geometry.

[0017] The first section 22, in this example, a zinc (Zn) anode, may by

formed using three metal deposition steps. A layer of nickel (Ni) (not

depicted), or other metallic or metal oxide materials, for adhesion purposes,

may be deposited onto the etched substrate followed by a gold (Au) or other

conductive current collector, e.g., current collector 34. A layer of zinc is then

deposited for the active material, e.g., electrode material 30. In this

embodiment, zinc (Zn), is deposited via aerosol spray deposition of Zn

nanoparticles suspended in petroleum or other distillate.

[0018] The second section 24, in this example a silver oxide (AgO) cathode,

may be formed using three metal deposition steps. A layer of nickel (Ni) (not

depicted), or other metallic or metal oxide material, for adhesion purposes, is

deposited onto the etched substrate followed by a gold (Au) or other

conductive current collector, e.g., current collector 34. A layer of silver is then

deposited for the active material, e.g., electrode material 30. Following

placement of the silver active material, the silver is oxidized to silver oxide.

The oxidation may be accomplished by immersing the structure in hydrogen

peroxide (H2O2) until the silver material is sufficiently oxidized. Alternatively,

oxidation of the metal may be achieved by exposing the film to UV rays in an

ozone atmosphere (O3). Other oxidative agents or atmospheres can be utilized

for this purpose, e.g. exposing the substrate film to oxygen (O2) during metal

deposition.

[0019] Any suitable metal deposition technique may be employed. PVD

may offer faster deposition of thick (greater than lOμm) metallic layers than

other processes. Electroplating may be alternatively used, if the required

thickness of the active material exceeds the thickness possible via PVD or

sputtering, for the film. The thickness of the current collector is generally less

than the thickness of the active material and may be formed by any suitable

technique. Chemical fluid deposition offers the advantage of being a lower

temperature process and may reduce the number of processing steps. While

sintering may be used to deposit silver powder onto the substrate, this

process may be less desirable because of the required processing

temperatures. The surface finish of the final electrode structure depends

strongly on the temperature of the substrate and on the evaporation technique

used. PVD is conducted at lower substrate temperatures, creating substrates

of higher porosity and rougher surface finishes. The deposited films may be

amorphous, and may require subsequent heating to induce re-crystallization.

The porous structure is beneficial for battery electrodes employing liquid

electrolytes because of the active surface area afforded, and the permeability

to electrolyte, while maintaining electronic conductivity and mechanical

integrity.

[0020] If necessary, multiple substrates may be prepared on a wafer or

other base structure. After etching, metal deposition and oxidization steps

are completed as needed to achieve proper specific and gravimetric energy

and power characteristics. Individual substrates may be separated from the

wafer using standard cutting techniques. Cooling water should not be used

during dicing of anode parts to prevent oxidation of the zinc.

[0021] Sub-millimeter diameter channels or apertures 28, for example, on

the order of 100 μm diameter, are formed in the substrate 32 to allow for the

introduction of electrolyte, for example, potassium hydroxide (KOH), diethyl

carbonate (DEC), dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl

methyl carbonate (EMC), propylene carbonate (PC), or other electrolyte which

conducts ions but is electrically neutral, into a completed microarchitectured

battery structure 12 with simultaneous evacuation of air. Alternatively, gel-

type electrolytes may be used and enclosed within the microbattery structure

during the joining and sealing of the sections, or may be inserted afterward,

using passages formed in the substrate suitable for this purpose.

[0022] Micromachine drilling or chemical drilling may be used to form the

apertures 28. Optional glass channels (not depicted) may be inserted into the

formed holes and secured therein using a fast curing epoxy resin. Following

introduction of the electrolyte, the glass channels, if present, may be cut from

the package and the apertures 28 sealed using epoxy.

[0023] In the foregoing example, individual substrates are separated prior

to assembly into battery structures. Plural batteries may be assembled prior

to separation. After completion of the metal deposition steps, an adhesive, for

example one or more dry adhesive sheets or screen printed wet adhesive, may

be disposed on one or both of the wafers. The wafers may then be brought

together in a wafer-adhesive-separator-adhesive-wafer sandwich, the

adhesive cured and then individual batteries separated.

[0024] Plural processing of the micromachined battery further permits

manufacture of multiple cell micromachined batteries. During the separation

process, multiple cells may be left joined (see battery cells 12' depicted in Fig.

3). During formation of the current collectors 34 and the conductive taps 36,

the conductive taps may be formed to link the multiple cells (see conductive

taps 36') to provide a single output of the multiple cell micromachined

battery.

[0025] The actual electrode, electrolyte and separator materials may be

chosen for the application and may be improved using known optimization

techniques. One such optimization technique is described by Albano, et al.,

Design of an Implantable Power Supply for an Intraocular Sensor, Using POWER

(Power Optimization for Wireless Energy Requirements) and by Cook, et al.,

POWER (power optimization for wireless energy requirements): A MATLAB based

algorithm for design of hybrid energy systems, Journal of Power Sources 159

(2006) 758-780.

[0026] Nickel cell chemistries offer the advantage of being radio frequency

rechargeable. Silver cell chemistries may enhance reliability and provide

discharge current stability. Thin film technologies, including lithium

chemistries, pose potential processing difficulties when combining with a

MEMS device due to potentially high processing temperatures required in the

MEMS processing. However, some cell chemistries may are capable of

withstanding temperatures up to 200 ⁰ C

[0027] The polymer bond to silicon, joining the micromachined battery 12

to the MEMS device 10 may be enhanced by first coating both parts with

evaporated gold. A plasma enhanced chemical vapor deposition (PECVD)

silicon nitride film may also enhance bonding. Gold and silicon are known to

create a eutectic compound that has a much lower melting point than the pure

metals. A liquid film is created in the joining process that bonds the two parts

upon cooling and solidification.

[0028] Embodiments of batteries in accordance with the present invention

may have one or more of the following characteristics:

1) formed and integrated at the same time of manufacturing with a MEMS

device;

2) small and lightweight enabling creation of autonomous and remote sensor

networks;

3) present high gravimetric and volumetric energy and power and Faradic

efficiency superior to commercial batteries with the potential to meet

(~27mWh/em ² );

4) low internal resistance and low power leakage due to high precision

manufacturing;

5) thin film deposited electrodes;

6) stackable and/or layered electrodes to achieve higher voltages;

7) suitable for configuration as thin-film flat cells, prismatic stacks of cells,

cylindrical cells or spirally wound cell

8) amendable to primary or secondary electrochemistries

9) compatible with solid thin-film electrolyte or liquid or gel solutions of

electrolyte

10) capable of hermetic sealing;

11) mass produceable potentially reducing cost;

12) scalable to macroscopic battery size.

[0029] While application of batteries in accordance with the herein

described embodiments in MEMS devices is apparent, the techniques are fully

scalable, and large-scale deposited batteries are possible and desirable.

Demonstration of the inventive technology for a small battery illustrates and

validates the approach. The invention and embodiments of the invention

therefore provide:

A) design and fabrication of optimized power supplies for MEMS with

significantly reduced size and improved energy and power properties that

allow integration at the time of manufacture or after manufacturing of the

device is complete;

B) a fabrication technique based on thin-film deposition, allowing small scale,

low-cost, and integrateable fabrication for CMOS systems;

C) characterization of capacity and lifetime of microbattery stacks,

arrangements and multi-cells configurations; and

D) a process for forming microscopic electrode films on rigid or flexible

substrates and a liquid, gel or solid electrolyte spacing by application of

microarchitecturing techniques to the substrates.

[0030] While the invention is described in terms of several preferred

embodiments of mounting assemblies that may be used in connection with

fault protection devices, it will be appreciated that the invention is not limited

to such devices. The inventive concepts may be employed in connection with

any number of devices and structures. Moreover, while features of various

embodiments are shown and described in combination, the features may be

implemented individually each such single implementation being within the

scope of the invention.

[0031] While the present disclosure is susceptible to various modifications

and alternative forms, certain embodiments are shown by way of example in

the drawings and the herein described embodiments. It will be understood,

however, that this disclosure is not intended to limit the invention to the

particular forms described, but to the contrary, the invention is intended to

cover all modifications, alternatives, and equivalents defined by the

appended claims.

[0032] It should also be understood that, unless a term is expressly defined

in this patent using the sentence "As used herein, the term ' ' is hereby

defined to mean..." or a similar sentence, there is no intent to limit the

meaning of that term, either expressly or by implication, beyond its plain or

ordinary meaning, and such term should not be interpreted to be limited in

scope based on any statement made in any section of this patent (other than

the language of the claims). To the extent that any term recited in the claims

at the end of this patent is referred to in this patent in a manner consistent

with a single meaning, that is done for sake of clarity only so as to not confuse

the reader, and it is not intended that such claim term by limited, by

implication or otherwise, to that single meaning. Unless a claim element is

defined by reciting the word "means" and a function without the recital of

any structure, it is not intended that the scope of any claim element be

interpreted based on the application of 35 U.S.C. §112, sixth paragraph.

We claim: