SURF 2003
FABRICATION, TESTING, AND IMPROVEMENT OF
LITHIUM COBALT PHOSPHATE MICRO-BATTERIES
SURF 2003
PRESENTATION OUTLINE
I. Micro Power Sources: Overview
II. Battery Speak
III. Project Starting Point and Goals
IV. Fabricating μ-Batteries
V. Testing Capacity of μ-Batteries
VI. Experimental Data
VII. Project Results and Summary
SURF 2003
MICRO POWER SOURCES: OVERVIEW• Need for highly miniaturized power sources
• Proposed NASA missions calling for small, compact vehicles for exploring a great variety of environments
• Cold, hot, high g, high radiation, sun-obscured• Long life characteristics highly desirable (includes shelf life)
• Will enable/prolong planetary exploration, to permitnovel/more science measurements
• JPL development includes many aspects of micro power: • Generation: Micro thermoelectrics• Storage: Solid state micro batteries• Conversion: Micro inductors for
DC-DC conversion
SURF 2003
BATTERY SPEAK IN ONE MINUTE
•Anode – Positive side (+) of battery• In this project, anode is lithium metal
•Cathode – Negative side (-) of battery• Lithium Cobalt Phosphate (LiCoPO4)
• Current Collector – Connects Anode andCathode to circuit
•Separator – Layer between anode and cathode that prevents cell from shorting (Lithium Phosphorous Oxynitride or Lipon)
• Electrolyte – Material that allows flow of ionsbetween anode and cathode (Lipon)
SURF 2003
PROJECT GOALS
•Research μ-battery capacity (analytical and practical)• Examine Design• Study temperature effects
• Kinetic Limitation• Resistance between layers
• Procedure/Materials• Separator
SURF 2003
LiCoPO4|LiPON|Li/Li+ Cell Performance
•Highest voltage thin film battery reported•Moderately low rate capability tied to poor cathode conductivity
0
1
2
3
4
5
6
0 2 10-6 4 10-6 6 10-6 8 10-6 1 10-5 1.2 10-5
Cel
l Vol
tag
e (V
)
Capacity (A-hr)
3
3.5
4
4.5
5
5.5
0 2 4 6 8 10 12C
ell
Vo
ltag
e (
V)
Discharge Capacity (A-hr/m-cm2)
C/15C/7.5C/1.5 C/3
C/2
SURF 2003
Si
FABRICATING μ-BATTERIES:
PHOTOLITHOGRAPHY AND LAYERS
1.)
Si2.)
Start with silicon nitride wafer
SiN
Spin photoresist
Si3.)
Expose photoresist to uv light
Si4.)
Sputter material
Si5.)
Liftoff Photoresist
SURF 2003
SiN
Si
Ti/Pt
1.)
2.)
3.)
LiCoPO4:Nb
Lipon layer
4.)
Lithium layer
5.)
Cross section diagrams of micro batteries
FABRICATING μ-BATTERIES
SURF 2003
Ti/Pt Contacts on SiN
FABRICATING μ-BATTERIES
SURF 2003
LiCoPO4:Nb After annealing
FABRICATING μ-BATTERIES
SURF 2003
Cathode Material600μ x 600μ active area300 to 500 nm thick
FABRICATING μ-BATTERIES
SURF 2003
DATA ACQUISITION
• Testing of fabricated μ-batteries in a dry room• Temperature Analysis
• Charge and discharge single μ-batteries at
different temperature•Find voltage when current fixed at 10nA/hr • Run test for 24+ hours• Compare current capacity and temperature
SURF 2003
Voltage vs. Time
3.00
3.50
4.00
4.50
5.00
5.50
0 1000 2000 3000 4000 5000 6000
Time (s)
Vo
lta
ge
(V
)
DATA AT 70°C
SURF 2003
CAPACITY DATA
Voltage vs. Time
3.00
3.50
4.00
4.50
5.00
5.50
0 2000 4000 6000 8000 10000
Time (s)
Vo
ltag
e (V
)
RT
40 C
50 C
70 C
80 C
90 C
100 C
SURF 2003
Sealed lithium micro-batteries
PACKAGING μ-BATTERIES
SURF 2003
FINAL GOAL: POWERING S-RAM CHIPS
SURF 2003
• Micro batteries are useful for a host of low power/extreme environment applications.
• LiCoPO4|LiPON|Li cells are highest voltage thin film/micro batteries reported.
• The result of this research begins the verification of the belief that LiCoPO4 thin film batteries are kinetically limited.
• Increasing capacity of thin film batteries can open doors to low cost production of micro power sources integrated with MEMS/IC technology.
PROJECT RESULTS AND SUMMARY
SURF 2003
• Dr. Erik Antonsson
• Dr. William West
• Dr. Jay Whitacre
• Jimmy Lim
THANK YOU
• The Tyson family
• The SFP team
• My family
Without the support of everyone mentioned above, my SURF experience would not have been possible. Thank you for investing in my future.