Technological Journey Towards Reliable Microheater Development for MEMS Gas Sensors: A Review

Micromachined silicon platforms, owing to some of its inherent advantages including miniaturized dimensions, ultralow power consumption, reduced batch fabrication cost, long-term reliability, and compatibility with standard CMOS fabrication technology, attracted the attention of solid-state gas sensor researchers, particularly since the last decade. As the semiconducting gas sensing thin film on top of micromachined platforms often needs an elevated temperature to activate the sensing mechanism, the suitable electrothermal and structural design of a microheater, i.e., having fast response, uniform temperature distribution over sensing area, and minimal residual/thermal-stress-induced membrane deflection, are of prime concern. In this paper, the technological developments related to the various designs and geometries of microheaters and their fabrication technology employing different suitable heating materials, for closed- and suspended-type silicon membranes have been discussed critically with particular emphasis on the relative merits and demerits with reference to heater parameters such as power consumption, temperature distribution, response time, and mechanical stability/reliability.