Low-Power Silicon Microheaters for Gas Sensors

Silicon-based SnO2 gas sensors are commonly operated at relatively high temperatures (up to 400 °C and even beyond for specific applications), thus necessitating suitable heating modules to guarantee high temperature uniformity over the sensitive surface area with minimal power consumption. Silicon micromachining allows low-power microheaters to be fabricated, with a low-cost (for mass production) technology, which is potentially suitable for the integration of the sensor, the heating element, as well as the required electronics into the same battery-operated microsystem. In this paper, we report on the development of a microheater structure consisting of a dielectric stacked membrane micromachined from bulk silicon, with an embedded polysilicon resistor acting as the heating element, Different technological solutions in the fabrication process for the micromachined structures have been investigated. In particular, hoth uniform membranes and suspeded microbeam structures have been realized to characterize the different thermal behavior toward the ambient. The microheaters have been designed to enable temperatures in the excess of 500 °C to be reached on the hotplate with a power consumption lower than 50 mW. Extensive thermoelectric and thermomechanical finite-element numerical simulations have been carried out, to predict microheater temperature vs. electric-power characteristics and mechanical stability, respectively. Simulations have also provided helpful hints in view of the optimization of the proposed structures.