The simultaneous maximization of a MEMS pressure sensor diaphragm’s deflection and resonance frequency are two essential but entirely contradictory objectives for maximum performance. Selection of proper material which has optimum diaphragm deflection and resonating frequency by using Ashby’s technology is the main objective of this paper. By using Ashby’s technique three materials are found which shows optimum performance for diaphragm deflection and resonating frequency. They are Single crystal Silicon, Polycrystalline Silicon and Silicon carbon Nitride. After selecting the material, a piezoresistive pressure sensor is designed and the performances are analyzed for Single crystal Silicon, Polycrystalline Silicon type piezoresistor material and Single crystal Silicon, Polycrystalline Silicon and Silicon carbon Nitride diaphragm material. The purpose of this study is to select optimized material for piezoresistive pressure sensor diaphragm and piezoresistor material to achieve maximum output voltage.
A diaphragm of size 3,000 um * 2,400 um * 50 um is constructed using different ceramic materials and it is simulated for deflection and resonance frequency determination using COMSOL Multiphysics software. As per Ashby’s method the deflection ratio of different material to standard material (Silicon) and Eigen frequency ratio of different material to standard material is calculated and a graph is plotted. Three material lies in the first quadrant of the graph which become optimum for pressure sensor material. They are Single crystal Silicon, Polycrystalline Silicon and Silicon carbon Nitride. Then a pressure sensor is designed by using these materials and the performances are compared. The performance and sensitivity of the piezoresistive pressure sensor can be improved by using a < 110> piezoresistor on a < 100> diaphragm. But Polycrystalline Silicon is a cheap and abundant material. In this proposed model, the performance of the pressure sensor is improved by using polycrystalline silicon as a piezoresistor on a single-crystal N-silicon diaphragm.
By applying Ashby’s material selection technique three materials (Single crystal Silicon, Polycrystalline Silicon and Silicon carbon Nitride) are found suitable for pressure sensor design which has optimum diaphragm deflection and resonating frequency. Then a piezoresistive pressure sensor is designed and the performance like output voltage, diaphragm deflection and maximum Von Misses stress is analyzed and compared for two piezoresistor material (Single crystal Silicon, Polycrystalline Silicon) and the same parameters are analyzed and compared for three different types of diaphragm material (Single crystal Silicon, Polycrystalline Silicon, Silicon Carbon Nitride).
In this work at first by Ashby’s material selection technology proper material for piezoresistor and sensor diaphragm is selected. Then a MEMS pressure sensor is designed using those selected materials. The performance of the sensor for different material is analyzed and compared. It is clear from the proposed work that the output voltage response of the sensor can be improved by using Polysilicon piezoresistor and Silicon Carbon Nitride diaphragm. The sensor is suitable in harsh condition also for using Silicon Carbon Nitride diaphragm and it will be cost effective also for the use of polysilicon.
