Influence of the pressure range on temperature coefficient of resistivity (TCR) for polysilicon piezoresistive MEMS pressure sensor

Sensitivity with respect to physical change of any type of sensor depends upon structure of the sensor and sensing material. If sensor is sensitive with more than single physical change (pressure or temperature etc) than sensitivity will get affected because of conflict in impact due to multiple physical parameters. Depending upon the designer's intuition and experience, a variety of shapes of sensor had been proposed which can bear both the pressure and temperature. To understand the influence of temperature and pressure on the linearity and sensitivity, pressure sensors has been designed having 50 mu m thick square diaphragm is being simulated and analyzed. The effect of pressure on Temperature Coefficient of Resistivity (TCR) of poly-silicon pressure sensor has been investigated in this paper. The stresses tempted in the piezoresistors and dislocation created in diaphragm have been studied using finite element method (FEM). The physical characteristics of sensor have been determined within the temperature range from 10 degrees C to 100 degrees C under the pressure range of 0 to 100 psi. It has been observed that TCR reduces with increasing pressure up to 30 psi, and beyond this pressure, the TCR begins to increase and thus the TCR shows the duality in nature. At 100 psi pressure, the calculated TCR for the diaphragm is found of the order of similar to 7.7 x 10(-3) (/degrees C). Thus, in conclusion, the pressure range similar to 40-100 psi is recommended as the optimal range to achieve the better sensitivity. The temperature sensitivity of designed sensor has been found to be similar to 0.10455 mV degrees C-1 while the pressure sensitivity of the proposed sensors which has been found to be 1.20051 mV psi(-1). Hence, designed sensor can be used as both pressure and temperature sensing device incorporated into a single sensor.