Design And Research Of The Pressure Detecting Elements Inside The MEMS Silicon Micro Resonant Pressure Sensor

The micro-silicon resonant pressure sensor is one of the major research objects in micro pressure sensors, which uses a pressure sensitive diaphragm and a resonant beam as preliminary sensing unit and final sensing unit. This article analyzes the deformation mechanism of the diaphragm inside the pressure detecting element. The diaphragm and resonant beam are connected by a silicon island which is used to detect the diaphragm deflection and cause the axial stretch displacement of the resonant beam. The external pressure is detected by the natural frequency variation of the resonant beam under axial force. With the combined effects of external pressure and reaction forces caused by bending and tensile stiffness of the resonant beam, the deflection curve along the central axis of the diaphragm is no longer a parabolic curve. Currently, most research focus on the study of the diaphragm deformation under uniform load, and the theoretical analysis mainly focus on the diaphragm deflection without considering the influence of final sensing unit. Diaphragm deformation under combined loads is solved by finite element analysis, which lacks of theoretical basis. This paper deduces a combined loads deformation analytical model for calculating the diaphragm deflection and optimizing the structure parameter of the pressure detecting element. It has a clear physical meaning and easy to implement by programming, which provides an efficient theoretical analysis method for pressure sensor designers.This article includes three major components: Deduce a uniform load deflection analytical model of the diaphragm. The diaphragm deformation in this paper could be considered as a small deflection problem of thin plate with four edges clamped.Therefore, the deflection surface equation could be deduced easily. The clamped plate is equivalent to a simple supported plate with boundary moments distributing on its edges.The deflection of the clamped plate is acquired by superposing the deflections of simple supported plate under uniform load and boundary moments. The calculation result and simulation result gets fine mutual verification. The influence of the diaphragm structure parameter on its deflection and stress distribution is analyzed by the theoretical model.Then the structure optimization of the pressure detecting element is proposed; Deduce a combined loads deflection analytical model of the diaphragm. A full surface uniform load is applied on the bottom of the diaphragm, and a partial uniform load is applied on the central symmetry rectangular area which is on the top of the diaphragm. The partial load is used to simulate the reaction force caused by the resonant beam. By the same equivalent method, the diaphragm deflection analytical model under combined loads is deduced by superposing the deflections under full surface uniform load,partial uniform load and boundary moments. The calculation result agrees well with the simulation result. The combined loads deflection model is used to analyze the influence of partial load on diaphragm deflection, then the optimized structure parameter of the silicon island is presented; Based on above research, this article analyzes the influence among components inside the pressure sensitive element. Many calculation and simulation works have been done to figure out the influence factors of the diaphragm deflection,the resonant beam's natural frequency and sensitivity by varying the structure parameter.Then, a feasible structure design scheme is proposed to improve the performance of the pressure sensors.