A low cost batch-sealed capacitive pressure sensor

This paper describes a new design for sealed capacitive pressure sensors by which the sealed lead transfer is eliminated. This allows the devices to be fabricated from p/sup ++/ Si on a glass substrate using the dissolved wafer process with as few as three masking steps. The pick-off capacitance is between a flap or skirt-like extension of the flexible diaphragm that reaches past the sealed cavity, and an electrode patterned on the substrate directly below this extension. The sidewall of the cavity is relatively narrow and flexible. FEA predicts that for a device with 30 /spl mu/m high and 5 /spl mu/m thick sidewalls, 5 /spl mu/m thick diaphragm and skirt, and a nominal pick-off capacitance gap of 5 /spl mu/m, the sensitivity is -11.2 fF/kPa in non-touch mode and -0.52 fF/kPa in touch mode. The devices have a very wide dynamic range, potentially exceeding 1000 kPa, and very low temperature coefficients of 80-100 ppm//spl deg/C TCO and 30-80 ppm//spl deg/C TCS. Preliminary measurements of fabricated structures match FEA models.