1. (Pressure measurement under harsh environments)
Micromachined pressure sensor based on sapphire for high temperature applications
(Pressure measurement under harsh environments)

2. Intro What: pressure sensor Pt thin film metallization
Why: harsh environment thus high p
high T
agressive media
Where: gasturbines, dieselengines, …
How: Wheatstone bridge
signal increases with high p
signal decreases with high T

3. Intro Properties: negative drift -30ppm(max) at full p and T
sensitivity ±10µV/V.bar
Problem: monitoring high p and T in combustion engines in presence of harsh environments. This means limited use of Si based MEMS (Micro Electro Mechanical System)
Low stability of Ohmic contacts
Different materials with different temperature dependence

4. Sensor system
Device:
membrane bodies are micromachined using ultrasonic drilling which is less time and costconsuming and has less transfer of mechanical stress
Strain gauge 1µm thick Pt film which is putter deposited
Ar based dry etching technique to create Wheatstone bridge

5. Sensor system Packaging: Package:Ni based superalloy
Substrate(layer of deposition): sapphire (not longer Si based like SiC)
Interconnects:Pt pins kept in position by gold coated Inconel springs
Electrical interconnects implemented in a glass ceramic part
Sealing of the package to the sensor device as to the glass ceramic body by gold coated Wills rings

6. Schematic

7. Sensor characterisation
N2 is fed to an oven
Static pressure measurements measured from room temperature to 300°C
Temperature of the gas is measured by type K thermocouple, the device by thermoresistive thin film element
Pressure from ambient pressure to 100 bar
Reference by digital pressure gauge

8. Results(pressure)

9. Results(temperature)

10. Results(pressure) Outputcharacteristic is linear from 0 to over 100bar
Temperature increase doesn’t change the linearity
At low pressure offset -17ppm
At high pressure offset -29ppm

11. Results (temperature)
At low temperature no offset
At high temperature offset -15ppm
Caused by thermomechanical stress between package and sensor
Asymmetric geometry of the sensor device
Decrease in sensitivity (11.12 to 9.32µV/V.bar) with increasing T

12. Conclusion Succesfull measurements between 100bar and 300°C
Linear dependence on applied pressure over large T-range
Only static measurements, NOT dynamic
Improvements by research on the package