Parylene-membrane piezoresistive pressure sensors with XeF2-etched cavity

Pressure sensors have been fabricated based on a deformable parylene C membrane over a cavity etched in silicon. The cavity is obtained by XeF₂ etching, using a parylene mask composed of an array of holes. A subsequent parylene deposition fills the holes, thus sealing the cavity and completing the membrane. Gold piezoresistors are used to sense the membrane deformation. Compared to traditional pressure sensor designs, this process is more easily integrated into other processes, as no double-side machining or wet silicon etching is needed. The use of parylene is advantageous under certain points of view. First, it protects the piezoresistors and silicon, due to its well known barrier and chemical inertness properties. Second, contrary to other materials commonly used to fabricate pressure sensor membranes (e.g., polysilicon, silicon nitride), parylene is flexible, and thus more resistant to shocks. These two reasons make the sensor useful in chemically and physically harsh environments.