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Abstract

A method of fabricating a pressure sensor (30) for harsh environments such as vehicle tires, formed from a first wafer substrate (32) having first and second opposing planar surfaces. CMOS circuitry (34) is deposited on the first planar surface and a layer of passivation material is deposited on the circuitry. Openings in the passivation layer are etched to expose parts of the circuitry and an aperture is etched into the first wafer from the first planar surface towards the second planar surface. Sacrificial material is deposited in the aperture and then a flexible membrane (50) is deposited on the sacrificial material and the exposed parts of the circuitry. The sacrificial material is subsequently plasma cleaned out of the aperture from the second surface and a second substrate is sealed to the second planar surface of the first wafer substrate to define a chamber (58) containing a fluid at a reference pressure. During use, the flexible membrane deflects due to pressure differentials between the reference pressure and the fluid pressure and the circuitry converts the deflection of the flexible membrane into an output signal indicative of the fluid pressure.

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First Claim