Low power Silicon microheaters on a thin dielectric membrane with Thick Film Sensing Layer for gas sensor applications

We report on the design, fabrication, and characterisation of a microheater module for chemoresistive, metal-oxide semiconductor gas sensors. The microheater consists of a dielectric stacked membrane with a polysilicon resistor heater element as well as a polysilicon temperature sensing element. The geometry of both, the membrane and the heater have been optimised by means of finite element computer simulation in order to maximise heating efficiency, these devices complete of the sensing layer require only 30 mW to achieve a temperature in excess of 500°C. At present, the main limitation for the development of a battery operated thick film gas sensing devices, is power consumption. Conventional thick film sensors fabricated on aluminia substrates require typically more than 200 mW to reach their working temperature (300-500°C). The proposed micromachining technology allows low-power microheaters to be fabricated at low cost and compatible with mass production technology. Furthermore silicon micromachining is potentially suitable for the integration of the sensing and the heating element as well as the required electronics into the same battery-operated low-cost portable microsystem. The measured electrothermal characteristics of the devices are in good agreement with the outcomes of 3D numerical simulations. Overmore extensive thermomechanical finite-element numerical simulations have been carried out, to predict mechanical stability, which are confirmed by experimental tests. The electrical response to various gases of the sensor prototypes will be presented and the results, including power consumption, will be compared with the corresponding ones valid for thick film sensors fabricated on conventional ceramic substrates.