Patent ID: 7222538

Claim:
A pressure sensor for sensing a fluid pressure, the pressure sensor comprising: a first wafer having a front side and an opposing back side, a recess etched into the front side and at least one hole etched from the recess to the back side a chamber at least partially defined by a flexible membrane and the recess on the front side of the wafer, the flexible membrane at least partially formed from conductive material, and the chamber containing fluid at a reference pressure, such that the flexible membrane deflects from any pressure difference between the reference pressure and the fluid pressure; a conductive layer within the chamber spaced from the flexible membrane; associated circuitry incorporating the flexible membrane and the conductive layer; such that, the conductive layer and the flexible membrane form capacitor electrodes and the deflection of the flexible membrane changes the capacitance which the associated circuitry converts into an output signal indicative of the fluid pressure, and the conductive layer being arranged such that deflection of the membrane towards the conductive layer can displace the fluid from between the membrane and the conductive layer; and a second wafer on the back side of the first wafer to seal the at least one hole; wherein, the second wafer is wafer bonded to the first wafer substrate.