SURFACE-MICROMACHINED CAPACITIVE DIFFERENTIAL PRESSURE SENSOR WITH LITHOGRAPHICALLY DEFINED SILICON DIAPHRAGM

A capacitive surface-micromachined sensor suitable for the measurement of liquid and gas pressures was fabricated, The structure consists of a polysilicon stationary electrode suspended 0.7 mu m above a 20-mu m -thick lightly doped silicon diaphragm formed by a patterned etch stop , The a priori patterning of the buried etch stop yields diaphragm wid ths independent of wafer thickness variations with excellent alignment , The design described here has a pressure range of 100 PSI, a nominal capacitance of 3.5 pF with a full scale span of 0.8 pF, and a tempera ture coefficient of 100 ppm degrees C-1. Each device, including a matc hed reference capacitor, occupies 2.9 mm(2) yielding approximately 200 0 devices per 100-mm wafer.