Transcript Carbon-MEMS Architectures for 3

Carbon-MEMS Architectures for 3D
Micro-batteries
Marc Madou
Department of Mechanical and Aerospace Engineering, UCI
ECS, Orlando, October 14, 2003
Madou group/UCI:
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C.L.Wang
L.Taherabadi
G.Y.Jia
S.Kassegne
A.Randhawa
Dunn group/UCLA:
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C.W.Kwon
George Baure
Tim Yeh
Organization of this Talk
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Intro
Earlier Results
Advantages of C-MEMS
Batteries
Recent Results
Conclusions
Intro: Batteries in Our Daily Life
Miniature portable
electronic devices
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Cardiac pacemakers
Hearing aids
Smart cards
Personal gas
monitors
MEMS devices
Embedded monitors
Remote sensors with
RF capability
Advanced Microbattery
Availability of new materials : photoresists
Development of micromachined battery designs : C- MEMS
Intro: Current State of Art and
Problem Definition
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Lithium-based secondary batteries - high values of
practical specific energies(150 Whkg-1) and energy
densities (220 WhL-1)-- vs. gasoline (3000 Whkg-1)
Highly ordered graphite, hard carbon and soft carbon
serve as host materials for lithium storage in
commercial Li batteries (anode).
Reported values of energy density are generally based
on the performance of larger cells with capacities of
up to several ampere-hours. For small microbatteries
the achievable power and energy densities are
diminished because the packaging and internal hardware
will determine the size and mass of battery  New
manufacturing methods and new materials are needed.
Intro: Our Approach
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Carbon-microelectromechanical system (C-MEMS)
technology provides both the material and
manufacturing solution to this battery
miniaturization problem.
We overcome the size and energy density deficiencies
of 2D batteries by creating three dimensional (3D)
microelectrode arrays by patterning photoresists and
converting those patterns into new battery and
battery array designs.
Earlier Results: What is CMEMS?
Vacuum
Ceramic tube
(a) WEBB #40 vacuum furnace
N2 or forming gas
Exhaust gas
Quartz tube
(b) Inert gas furnace
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Earlier Results: What is CMEMS?
Photoresists are patterned
by (e.g, using
photolithography) and
pyrolyzed in an inert
environment (e.g., vacuum)
to yield carbon films and
microstructures.
In earlier work we
demonstrated that
photoresist derived carbon
electrodes exhibit
kinetics comparable to
glassy carbon for selected
electrochemical reactions
in aqueous and nonaqueous
electrolytes (Madou et al,
JECS).
Earlier Results: Sheet Resistance and
TEM Photos of Pyrolyzed Photoresist
Sheet Resistance (Ohm/square)
450
m
l
400
m
l
AZ-4330
m
OCG-825
350
300
250
Positive
photoresist
200
150
l
100
l
50
m
Negative
photoresist
l
m
0
600 C
700 C
800 C
l
m
l
m
900 C 1000C 1100C
Temperature (°C)
Sheet resistance vs temperature of heat treatment for AZ-4330 and OCG-825 resists
S.Rnaganathan, M.Madou et.al, ”Photoresist derived carbon for microelectromechanical systems”
Earlier Results: 3D Structure-Micro
Patterning of Conductive Polymers (e.g.,
PAN and PPY)
M.Madou. ,”Fundamentals of Microfabrication”
Earlier Results: Electric Field and
Current modeling for 3D carbon
electrodes of microbatteries
(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 q)
( Dunn et al.)  make as high an aspect
ratio electrodes as possible!!!!
Advantages of C-MEMS Batteries
 High current density on a
CMOS
small foot-print,
 Anodes and cathodes in
Battery
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  Smart switchable battery arrays:
baxels are addressable just like pixels:
in a serial arrangement, voltages add up;
in a parallel arrangement, currents add up
unit
Advantages of C-MEMS Batteries
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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 C-MEMS Batteries
Interdigitated fields of anode and
cathode poles,
One planar substrate with
electrolyte in between poles,
Any voltage/current combination
can be achieved on demand.
Recent Results
 Microfabrication
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 We
developed high aspect ratio 3D carbon posts
( >> 10 (> 40 is possible)) in different types of
array configurations
 C-MEMS interconnects --- an all C design, , C
and Au and a C and SiO2 design
 Electrochemical
tests-- Li charge/discharge
processes in pyrolyzed arrays of photoresist
posts
How to Build High Aspect-ratio3D
Carbon Posts?
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Build 3D photoresist structure by photolithography
Positive photoresist (AZ4620, SP 1827)
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Multi-exposure and multi-developing for multilayer photoresist
Embedded masks for multilayer photoresist
Molds
Negative photoresist (SU-8 100)
Pyrolysis of photoresist
Vacuum or forming gas (95% N2 and 5% H2) atmosphere, 9000C
Positive Photoresist (1) :
Multi-exposure and multi-developing
Si
SiO2
PR
Au
Problem:
• bottom layer: over baked
• surface layer: over
exposed and developed
• Difficult to get high
aspect ratio straight
posts
Positive Photoresist (2):
Embedded masks
UV
mask
developing
UV + developing
Si
PR
Au
Ti or Si or Cr
wet etching
wet etching
repeat exposure/
developing/etching
Positive Photoresist (2):
Embedded masks
PR/Au/PR/Si(200Å)/PR
PR/Cr(1000Å)/PR
Problem:
Before pyrolysis: a lot of bubbles on surface
After pyrolysis: peeling
Positive Photoresist (3): Molds
Before spin coating PR
after spin coating PR
PR
High Aspect-ratio Carbon Posts Derived
from SU-8 : Direct pyrolysis
SU-8/Au(3000Å)/Ti(200Å)/SiO2/Si
before
SU-8/SiO2 or SiN/Si
before
SU-8/Au(3000Å)/Ti(200Å)/SiO2/Si
after
SU-8/SiO2/Si
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after
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Current distribution on a
section of electrode array
Electrochemical Tests
Teflon
Li
1M LiClO4
in DMC
sample
Electrochemical Tests
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Flat C-MEMS
Two-electrode configuration
(reference /counter electrode is a
lithium metal foil (Aldrich 99.99 %).
The WE is C-MEMS. Electrolyte was
1M LiClO4 in dimethyl carbonate
(DMC). Carbon sample area
measured was ~ 0.4 cm2, and a
constant current of 5 mA was applied
between 0.005 ~ 3 V vs. Li+/Li.
Graph from UCLA microbattery group
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.
Electrochemical Tests
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Graph from UCLA microbattery group
3.0
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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.
Voltage vs. Li /Li (V)
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2.5
2.0
1.5
1.0
0.5
0.0
0
200
400
600
800
1000
1200
Capacity (uAh)
carbon
Si/ SiO2
Electrochemical Tests
Positive PR, 90x90 arrays: Ø 100µm, thickness: 4µm
Before
Voltage vs. Li+/Li (V)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.02 0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
Capacity (mAh)
After
1st capacity: 0.138mAh(294mAh/g)
2nd capacity: 0.0104mAh (22.3mAh/g)
Electrochemical Tests
3.0
Voltage vs. Li+/Li (V)
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
0
1
2
3
4
Capacity (mAh)
1st capacity: 3.122mAh(153.3mAh/g)
2nd capacity: 0.190mAh(9.33mAh/g)
Conclusions
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We successfully made high aspect ratio (> 10:1)
carbon posts by pyrolysis from negative
photoresists in a simple one-step process
We can make baxel arrays in any type of
configuration
Electrochemical tests demonstrate that these CMEMS 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