Analytical Modeling of Square Microhotplate for Gas Sensing Application

Square microhotplates find their usefulness because of ease of fabrication and high yield compared with bridge or spider membrane. It has been already established that often in microhotplates, an insulation layer is required to separate the thermal domain from other application domains such as gas sensor. However, enhancing the performance of microhotplate by the optimization of insulation layer area, especially in terms of power and uniformity aspects, has not been explored yet. Nevertheless, the improvement in the uniformity was also accompanied by increased power consumption. An analytical model is developed for the optimization of the insulation nitride area. The model is compared with the finite element method simulations and the results are in close agreement with errors within 5%. Because of the modular nature of the developed model, the thermal losses in the insulation layer could be estimated separately. Since power consumption of the microhotplate depends on the thermal mass, an optimized dimensions of heat spreader can bring multiple advantages such as better uniformity, higher temperature, and minimized power overhead. Compared with insulation nitride dimensions of 250 × 250 × 8 μm, for attaining a temperature of 550 K, an optimized insulation nitride dimension of 120 × 120 × 8 μm has improved the thermal uniformity by 40.1%, power consumption by 34.48%, and maximum operating temperature by 28.45% when 2 V input voltage is applied.