Design and fabrication of a novel low cost hotplate micro gas sensor

We present a novel approach to produce a micromachined low cost hotplate gas sensor with reduced number of technology steps. The basic idea was to realise a simple device on common silicon substrates using conventional photolithography, sputtering and evaporation techniques. Two main performance parameter were targeted: the power consumption should not exceed 200 mW for an operation at 350 degrees C-400 degrees C and the thermal response time should be faster than 1sec. Fast thermal time constants allows the operation of device in temperature pulse mode. The first step of the development was the theoretical determination of the power consumption of the micromachined substrates, even temperature distribution on the sensitive area and sufficient mechanical stability. For this we build models describing the thermal behaviour of the devices by means of the finite element method (FEM) and corresponding resistance- capacitor- networks (RC-network). Then we developed technological processes to fabricate sensor structures according to the optimal geometry resulting from the model calculations. A first prototype is introduced in this publication.