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 /spl mu/m above a 20 /spl mu/m-thick lightly-doped silicon diaphragm formed by a patterned etch stop. The a-priori patterning of the buried etch stop yields diaphragm widths 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 temperature coefficient of 100 ppm//spl deg/C. Each device, including a matched reference capacitor, occupies 2.9 mm/sup 2/ yielding approximately 2000 devices per 100 mm wafer.