SURFACE MICROMACHINED PIEZORESISTIVE PRESSURE SENSORS WITH STEP-TYPE BENT AND FLAT MEMBRANE STRUCTURES

Surface micromachined pressure sensors with step-type bent and nearly flat membranes are compared. The influence of the membrane structure o n the sensor characteristics is investigated. The sensors contain four polysilicon piezoresistors arranged at the underside of a polysilicon membrane. For the step-type bent version of the sensor polysilicon is used as sacrificial layer and aqueous TMAH solution for underetching. Devices with a nearly flat structure are fabricated by applying a com bined TMAH and HF sacrificial layer etching technique of a polysilicon /oxide sandwich. Compared to step-type bent, nearly flat structures pr ovide decisive advantages for fabrication and show improved performanc e. Pressure response, noise behavior as well as the thermal drift of b oth types of sensors is presented.