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 on 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 combined TMAH and HF sacrificial layer etching technique of a polysilicon/oxide sandwich. Compared to step-type bent, nearly flat structures provide decisive advantages for fabrication and show improved performance. Pressure response, noise behavior as well as the thermal drift of both types of sensors is presented.