Fabrication of thin film microheater for gas sensors on polyimide membrane

The work presented here describes the fabrication and characterisation of a microheater on a polyimide membrane for metal oxide (tin oxide) gas sensors. Four such heaters for an array of 4 sensors have been developed on a polyimide membrane of 3.5 × 3.5mm² size. The sensing area for each sensor can be heated as high as 350 °C. The polyimide membrane (PI) is fabricated on a bulk etched silicon <100> wafer. This type of membrane is more rugged than silicon dioxide or silicon nitride membranes currently being used as substrates for gas sensors. The main challenge in the fabrication of metal oxide gas sensors is low power consumption and high thermal uniformity of temperature (Dermane, 1988, Faglia et al., 1999 and Lee, 1996). The silicon frame surrounding the membrane is almost at ambient temperature, so when a heater array is operated, the thermal cross talk between sensors is minimised. In this paper, the design and fabrication of a microheater on a thermally isolated polyimide membrane is described.