Fluid-Solid Interaction and Modal Analysis of a Miniaturized Piezoresistive Pressure Sensor

In the field of MEMS (MicroElectroMechanical System) devices fabrication as for every other field of microelectronics, numerical multiphysics simulation of the electric (and in our case mechanical) behavior of the devices is needed prior to fabrication in order to reduce research and production costs. In the present paper an ANSYS Multiphysics finite element analysis of a miniaturized pressure sensor based on Silicon On Insulator (SOI) technology is presented [ref. 1,2]. Fluid-Solid Interaction algorithms have been used, in order to simulate the sensor's response with the presence of air. The pressure sensor type is a piezoresistive one with special vent channels for having access to the reference pressure. The particularity of this kind of sensor design is that the gauges are made of monocrystalline silicon and are incorporated into the sensor's membrane. That means that the precise calculation of the stresses throughout the membrane's volume and consequently on the gauges is of great importance for estimating their final sensitivity. Stresses all over the gauges' volume are summed and multiplied by the piezoresistive coefficients of silicon in order to calculate the relative change of resistance. Optimization of the gauges' dimensions and placement has been performed having as a goal their maximum sensitivity. The position of the sensor's vent channels has been also studied and optimized to minimize its impact on the gauges sensitivity. Modal analysis of the sensor is also performed in order to determine the different modes of resonance and their corresponding frequency. The results of the analysis are then used to design the masks for the sensors' fabrication using typical microelectronics CAD tools.

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