Effects of residual stress in the membrane on the performance of surface micromachining silicon nitride pressure sensor

In this paper, influences of the initial stress on the surface micromachining silicon nitride pressure sensor was analyzed and discussed. The residual stress in the diaphragm is a major issue that makes significant difference on the performance of surface micro machined pressure sensors, such as warpage, micro-cracking, delamination, debonding, and nonuniform stress profile of the membrane. The pressure was operated at the room temperature 25°C and barometric pressure 101KPa. As the pressure is multiplied by a safety factor, 120KPa is utilized in this paper. The film is 80μm in diameter and 1μm in thickness, deposited by low pressure chemical vapor deposition (LPCVD). Finite Element Method with ANSYS software was processed to obtain the pressure-displacement curves and the stress profiles of the non-stressed diaphragm and prestressed diaphragm with 100MPa. The theoretical solutions were proposed to verify the validity of the FEA model. Subsequently, the mechanical-electrical models were adopted to investigate the input-output characteristics of the silicon nitride pressure sensor under various pressures. It turned out that the simulation results were greatly in accordance with the theoretical values. The FEA models were proved to be effective. And there was great difference between diaphragm with residual stresses and nonprestressed diaphragm in the voltage output. As a results, the residual stresses in the silicon nitride film have a big difference on the mechanical performance and the output of the surface micromachining silicon nitride pressure sensor.