Design, optimization and fabrication of surface micromachined pressure sensors

Abstract

Surface micromachined pressure sensors have been designed, optimized and fabricated. Polysilicon diaphragms with thickness of 2 μm have been manufactured by means of LPCVD (Low Pressure Chemical Vapor Deposition) and used as the core elements in micro pressure sensors. The diaphragms stand on top of micro vacuum cavities that are constructed by a specially designed, vacuum sealing process [1]. Pressure changes cause the diaphragms to deflect. The magnitudes of pressure are detected by using built-in piezoresistive resistors that are placed on the surface of the thin diaphragms. Both square- and circular-shape diaphragm pressure sensors with nominal widths (diameters) of 100 μm have been fabricated and tested. Optimized designs, including position, orientation and length of the piezoresistive resistors, have been analyzed. The fabrication process is fully compatible with IC (Integrated Circuit) processing. Therefore, micro electronics can be integrated directly with these micro sensors and microscale mechatronics systems can be realized. Prototype pressure sensors which are designed for 100 Psi in full operational scale have a measured sensitivity of 0.15 mV\\V\\Psi and a maximum linearity error of ±0.1% FSS (Full Scale Span).