Carbon-MEMS Carbon-MEMS Architectures for 3D Micro-Architectures for 3D Micro-

batteriesbatteries

Marc MadouMarc Madou

Department of Mechanical and Aerospace Engineering, UCIDepartment of Mechanical and Aerospace Engineering, UCI

ECS, Orlando, October 14, 2003ECS, Orlando, October 14, 2003

Madou group/UCI:Madou group/UCI: C.L.WangC.L.Wang L.Taherabadi L.Taherabadi G.Y.JiaG.Y.Jia S.Kassegne S.Kassegne A.RandhawaA.Randhawa

Dunn group/UCLADunn group/UCLA::

C.W.KwonC.W.Kwon George BaureGeorge Baure Tim YehTim Yeh

Organization of this TalkOrganization of this Talk

IntroIntro Earlier ResultsEarlier Results Advantages of C-Advantages of C-

MEMS BatteriesMEMS Batteries Recent ResultsRecent Results ConclusionsConclusions

Intro: Batteries in Our Intro: Batteries in Our Daily LifeDaily Life

Miniature portable Miniature portable electronic deviceselectronic devices

Cardiac pacemakers Hearing aids Smart cards Personal gas

monitors MEMS devices Embedded monitors Remote sensors with

RF capability

Availability of new materials : photoresists Development of micromachined battery designs : C- MEMS

Advanced MicrobatteryAdvanced Microbattery

Intro: Current State of Intro: Current State of Art and Problem Art and Problem

Definition Definition Lithium-based secondary batteriesLithium-based secondary batteries - high values of - high values of

practical specific energies(150 Whkgpractical specific energies(150 Whkg-1-1) and energy ) and energy densities (220 WhLdensities (220 WhL-1-1)-- vs. gasoline (3000 Whkg)-- vs. gasoline (3000 Whkg-1-1) )

Highly ordered graphite, hard carbon and soft carbonHighly ordered graphite, hard carbon and soft carbon serve as host materials for lithium storage in serve as host materials for lithium storage in commercial Li batteries (anode). commercial Li batteries (anode).

Reported values of energy density are generally based Reported values of energy density are generally based on the performance of larger cells with capacities of on the performance of larger cells with capacities of up to several ampere-hours. For small microbatteries up to several ampere-hours. For small microbatteries the achievable power and energy densities are the achievable power and energy densities are diminisheddiminished because the because the packaging and internal hardwarepackaging and internal hardware will determine the size and mass of battery will determine the size and mass of battery New New manufacturing methods and new materials are needed. manufacturing methods and new materials are needed.

Intro: Our ApproachIntro: Our Approach Carbon-microelectromechanical system (C-MEMS) Carbon-microelectromechanical system (C-MEMS)

technology provides both the technology provides both the material and material and manufacturing solutionmanufacturing solution to this battery to this battery miniaturization problemminiaturization problem..

We overcome the size and energy density deficiencies We overcome the size and energy density deficiencies of 2D batteries by creating of 2D batteries by creating three dimensionalthree dimensional (3D)(3D) microelectrode arrays by patterning photoresists and microelectrode arrays by patterning photoresists and converting those patterns into new battery and converting those patterns into new battery and battery array designs. battery array designs.

Exhaust gas

N2 or forming gas

Quartz tube

Ceramic tube

Vacuum

(a) WEBB #40 vacuum furnace

(b) Inert gas furnace

Earlier Results: What is Earlier Results: What is C-MEMS?C-MEMS?

Earlier Results: What is Earlier Results: What is C-MEMS?C-MEMS?

PhotoresistsPhotoresists are patterned are patterned by (e.g, using by (e.g, using photolithography) and photolithography) and pyrolyzedpyrolyzed in an inert in an inert environment (e.g., vacuum) environment (e.g., vacuum) to yield carbon films and to yield carbon films and microstructures.microstructures.

In earlier work we In earlier work we demonstrated that demonstrated that photoresist derived carbon photoresist derived carbon electrodes exhibit electrodes exhibit kinetics comparable to kinetics comparable to glassy carbon for selected glassy carbon for selected electrochemical reactions electrochemical reactions in aqueous and nonaqueous in aqueous and nonaqueous electrolytes (Madou et al, electrolytes (Madou et al, JECS).JECS).

Earlier Results: Sheet Earlier Results: Sheet Resistance and TEM Photos of Resistance and TEM Photos of

Pyrolyzed PhotoresistPyrolyzed Photoresist

S.Rnaganathan, M.Madou et.al, ”Photoresist derived carbon for microelectromechanical systems”

Positive photoresist

Negative photoresist

l

l

l

ll l

m

m

mm m m

600 C 700 C 800 C 900 C 1000C 1100C

0

50

100

150

200

250

300

350

400

450l AZ-4330

m OCG-825

Sheet Resistance (Ohm/square)

Temperature (°C)

Sheet resistance vs temperature of heat treatment for AZ-4330 and OCG-825 resists

Earlier Results: 3D Structure-Earlier Results: 3D Structure-Micro Patterning of Micro Patterning of

Conductive Polymers (e.g., Conductive Polymers (e.g., PAN and PPY) PAN and PPY)

M.Madou. ,”Fundamentals of Microfabrication”

Earlier Results: Earlier Results: Electric Field Electric Field and Current modeling for 3D and Current modeling for 3D

carbon electrodes of carbon electrodes of microbatteriesmicrobatteries

(Top panels) Schematic diagram of 3-D cylindrical battery arrays in parallel row (left) and alternating anode/cathode (right) configurations. (Middle panels) Isopotential lines between cathode (C) and anode (A) for unit battery cells. (Bottom panel) Current densities (in arbitrary units, a.u.) at the electrode surfaces as a function of the angle (see middle panel for definition of )( Dunn et al.) make as high an aspect ratio electrodes as possible!!!!

Advantages of Advantages of C-MEMS C-MEMS BatteriesBatteries

CMOS

Smart switchable battery arrays:baxels are addressable just like pixels: in a serial arrangement, voltages add up; in a parallel arrangement, currents add up

Battery unit

High current density on a small foot-print, Anodes and cathodes in the same plane (easier to manufacture), The current collectors and electrode posts are all fabricated in the same simple one -step process, Si substrate is compatible with further CMOS integration

High repeatability of batch microfabrication and the C-MEMS material,

Customized design possible, Battery arrays may be stacked using the latest space efficient IC packaging techniques (e.g., double sided alignement).

Advantages of Advantages of C-MEMS C-MEMS BatteriesBatteries

Interdigitated fields of anode and cathode poles,One planar substrate with electrolyte in between poles,Any voltage/current combination can be achieved on demand.

Advantages of Advantages of C-MEMS C-MEMS BatteriesBatteries

Recent ResultsRecent Results Microfabrication Microfabrication ------

We developed high aspect ratio 3D We developed high aspect ratio 3D carbon posts ( >> 10 (> 40 is carbon posts ( >> 10 (> 40 is possible)) in different types of array possible)) in different types of array configurationsconfigurations

C-MEMS interconnects --- an all C C-MEMS interconnects --- an all C design, , C and Au and a C and SiOdesign, , C and Au and a C and SiO22 designdesign

Electrochemical testsElectrochemical tests-- Li -- Li charge/discharge processes in charge/discharge processes in pyrolyzed arrays of photoresist pyrolyzed arrays of photoresist postsposts

How to Build High Aspect-How to Build High Aspect-ratio3D Carbon Posts?ratio3D Carbon Posts?Build 3D photoresist structure by Build 3D photoresist structure by

photolithographyphotolithography Positive photoresist (AZ4620, SP 1827)Positive photoresist (AZ4620, SP 1827)

1.1. Multi-exposure and multi-developing for Multi-exposure and multi-developing for multilayer photoresistmultilayer photoresist

2.2. Embedded masks for multilayer photoresist Embedded masks for multilayer photoresist

3.3. MoldsMolds Negative photoresist (SU-8 100)Negative photoresist (SU-8 100)

Pyrolysis of photoresistPyrolysis of photoresistVacuum or forming gas (95% NVacuum or forming gas (95% N22 and 5% H and 5% H22) ) atmosphere, 900atmosphere, 90000C C

Positive Photoresist (1) :Positive Photoresist (1) :Multi-exposure and multi-Multi-exposure and multi-

developingdeveloping

PR AuSi SiO2

Problem: • bottom layer: over baked• surface layer: over exposed and developed

• Difficult to get high aspect ratio straight posts

Positive Photoresist (2): Positive Photoresist (2): Embedded masks Embedded masks

AuPR Ti or Si or CrSi

UVmask

wet etching

wet etchingrepeat exposure/developing/etching

developing

UV + developing

Positive Photoresist (2): Positive Photoresist (2): Embedded masks Embedded masks

PR/Au/PR/Si(200Å)/PR PR/Cr(1000Å)/PR

Problem: Before pyrolysis: a lot of bubbles on surfaceAfter pyrolysis: peeling

Positive Photoresist (3): Positive Photoresist (3): MoldsMolds

PR

Before spin coating PR after spin coating PR

High Aspect-ratio Carbon High Aspect-ratio Carbon Posts Derived from SU-8 : Posts Derived from SU-8 :

Direct pyrolysisDirect pyrolysis

SU-8/Au(3000Å)/Ti(200Å)/SiO2/Si

before

SU-8/SiO2 or SiN/Si

before

after

SU-8/Au(3000Å)/Ti(200Å)/SiO2/Si

after

SU-8/SiO2/Si

Current distribution on a Current distribution on a section of electrode arraysection of electrode array

+

-

-

-

-

+

+

Electrochemical TestsElectrochemical Tests

sample

Li1M LiClO4

in DMC

Teflon

Flat C-MEMSFlat C-MEMS Two-electrode configuration Two-electrode configuration

(reference /counter (reference /counter electrode is a lithium metal electrode is a lithium metal foil (Aldrich 99.99 %). The foil (Aldrich 99.99 %). The WE is C-MEMS. Electrolyte WE is C-MEMS. Electrolyte was 1M LiClOwas 1M LiClO44 in dimethyl in dimethyl carbonate (DMC). Carbon carbonate (DMC). Carbon sample area measured was ~ sample area measured was ~ 0.4 cm0.4 cm22, and a constant , and a constant current of 5 mA was applied current of 5 mA was applied between 0.005 ~ 3 V vs. between 0.005 ~ 3 V vs. LiLi++/Li./Li.

The first capacity is ~ 8.5µAh and the second is ~ 5.5 µAh. The process is quite reversible.Assuming the density of carbon is 2 g/cm3, the estimated specific reversible and irreversible capacities are 49 and 27 mAh/g, respectively.

Graph from UCLA microbattery group

Electrochemical TestsElectrochemical Tests

First five cycles of discharge/charge experiments. The first discharge capacity is ~ 233 Ah and the second is ~ 110 Ah. The process is quite reversible after the first cycle.

The sample is composed of columnar posts with a diameter of 50 um and spacing of 50 um.

If the second discharge capacity is taken as a reversible capacity, the specific reversible and irreversible capacities are 1410 and 1577 mAh/g, respectively. The reversible capacity is too large compared to those of say soft carbon (~ 150 mAh/g), therefore there must be huge contribution of carbon underneath the micropattern and/or outside the measuring window. Anyway, this type of micropatterned sample seems electrochemically active and reversible, which proves the validity of the approach.

Electrochemical TestsElectrochemical Tests

0 200 400 600 800 1000 1200

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Vol

tage

vs.

Li+

/Li (

V)

Capacity (uAh)

Si/ SiO2

carbon

Graph from UCLA microbattery group

Electrochemical TestsElectrochemical Tests

Before

After

-0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Vo

ltag

e v

s. L

i+/L

i (V

)

Capacity (mAh)

1st capacity: 0.138mAh(294mAh/g)2nd capacity: 0.0104mAh (22.3mAh/g)

Positive PR, 90x90 arrays: Ø 100µm, thickness: 4µm

Electrochemical TestsElectrochemical Tests

0 1 2 3 4-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Capacity (mAh)V

olta

ge

vs.

Li+

/Li (

V)

1st capacity: 3.122mAh(153.3mAh/g)2nd capacity: 0.190mAh(9.33mAh/g)

ConclusionsConclusions We successfully made high aspect We successfully made high aspect

ratio (> 10:1) carbon posts by ratio (> 10:1) carbon posts by pyrolysis from negative photoresists pyrolysis from negative photoresists in a simple one-step processin a simple one-step process

We can make baxel arrays in any type of configuration

Electrochemical tests demonstrate that these C-MEMS electrodes can be charged/discharged with Li

A C-MEMS battery approach has the potential to solve both manufacturing and materials problems all at once