Miniaturised Thermal Flow Sensors for Rough Environments

Two concepts of miniaturised thermoelectric flow sensors for rough pressurized environments are presented, based on our high-temperature thermopile fabrication process. Membrane based thermal flow sensors show high sensitivity and stability against aggressive fluids using a LPCVD silicon nitride (SiN) passivation layer but are weak against high pressure. We realised pressure stable sensors using either quartz as substrate or by stabilising the membrane using polymers. The sensors have been fabricated and characterised. The sensors with the polymer stabilised membrane show good sensitivity and dynamic behaviour while the quartz based sensors have superior stability towards pressure and aggressive media. In comparison the quartz based sensors have a far less complex fabrication process than those with a stabilised membrane.