Design, Simulation and Modeling of a Micromachined High Temperature Microhotplate for Application in Trace Gas Detection

Modeling and simulation of a micromachined microhotplate (MHP) designed to achieve low power dissipation and uniform temperature distribution on the sensing area at operating temperatures of up to 700°C is presented in this paper. At the operating temperature of 700°C, it is demonstrated that as the silicon nitride (Si3N4) and silicon carbide (SiC) membrane and heat distributor layer, respectively, is increased from 0.3 μm to 3 μm, the power dissipation of the MHP increases while the mechanical displacement of the MHP membrane decreases. On the other hand, the temperature gradient on the MHP decreases as the thickness of the SiC temperature distributor layer is increased and is a minimum with a value of 0.005°C/μm for SiC thickness of 2 μm and above. However for an increase in the tin dioxide (SnO2) thickness from 0.3 μm to 3 μm, the power dissipation on the MHP is not affected while the mechanical displacement decreases. A comparison between simulation and mathematically modeled results for power dissipation and
current density of the MHP showed close agreement. An
optimized simulated device exhibited low power dissipation of 9.25 mW and minimum mechanical deflection of 1.2 μm at the elevated temperature of 700°C.