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.