A micromachined polyurethane/stainless-steel capacitive pressure sensor without cavity and diaphragm

This paper reports micromachined capacitive pressure sensor intended for applications that require mechanical robustness. The device is constructed with two micromachined metal electrode plates and an intermediate polymer layer that is soft enough to deform in a target pressure range. The plates are formed of micromachined stainless steel with overall dimensions of 4×2.4 mm² fabricated by batch-compatible micro-electro-discharge machining. A polyurethane RTV liquid rubber is used as the deformable material. This structure eliminates both the vacuum cavity and the associated lead transfer challenges common to micromachined capacitive pressure sensors. For wireless interrogation of the capacitance, an L-C tank is fabricated by combining the capacitive sensor and a 40-turn coil that are formed by winding a copper wire on the sensor. A preliminary measurement test performed by monitoring frequency shift of a reactance peak of the tank with varying pressure shows its response of 2.6-9.6 Hz/Pa measured over a dynamic range of 350 kPa. Temperature dependence of the tank is also experimentally evaluated.