THIN FILM CERAMIC GAS/TEMPERATURE MICRO-

SENSORS

Paul JooYoung LeeJoo.Y.Lee@colorado.eduAdvisor: Prof. Rishi Raj

Department of Mechanical EngineeringUniversity of Colorado at Boulder

Acknowledgement: U.S. Department of Energy

Project Outline

• Developing thin film ceramic gas-temperature sensor

– A ceramic micro-sensor to detect gas and temperature

– Fabrication of thin conducting SiCN micro-patterns on insulating substrates

– Establish electrical properties of the SiCN thin film sensor at high temperatures (1000 deg. C)

Polymer Derived SiCN Conducting Ceramic

• Made from monomer liquid precursor, CerasetTM plus photo-initiator mixture

• Silicon CarboNitride amorphous ceramic • Excellent oxidation resistance• Electrically semi-conducting

– Resistance of the film changes with the surrounding temperature and gas environment

Ceramic Micro-sensor?

Micro-electronics/MEMS Fabrication Technology

Many identical chips on one wafer/substrate

Polymer Derived Ceramics(PDC)Technology

Conducting Ceramic - SiCN

+

Conducting ceramic micro-

sensors on substrate

(Batch processing capability leads to cheap production)

Fabrication

Photo-sensitive precursor and

insulating, refractory substrate

Array of polymer micro-patterns on

the substrate

Spin-coat precursor

onto substrate and pattern using UV

lithography

Non-conducting ceramic patterns on the substrate

Microelectronics Technology

Heat treat the whole substrate(polymer ceramic)

Many conducting ceramic devices on

one substrate

Annealing heat

treatment to conducting

ceramic

Polymer Derived Ceramics

Electrical Properties

• Ceramic refractory, oxidation resistant

Working temperature = 1000 deg. C

Cyclic Resistance Response of SiCN Thin Film in Air and Hydrogen Flow (300°C)

0

5

10

15

20

25

30

35

40

0 20 40 60

Time (min)

Res

ista

nce

(kΩ

)

Air H 2 H 2 H 2AirAir

CYCLE I CYCLE II CYCLE III

• Establish the relationship, conductivity vs temperature/gas type gas/temperature sensor

Methodology

• Increase sensitivity Reduce resistivity of the thin film– Doping with boron or other dopants– Annealing condition changes

• Electrical property measurement– Four point probe test – resistivity measurement of thin films

(Commercially available = 300 deg. C max)– Build Four point probe testing unit for high temperature

environment– Sealed testing unit can readily change the gas environment– Measure the resistance response vs temperature and

surrounding gas type