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Capacitive pressure sensors with stainless steel diaphragm and substrate

Much of the cost of commercial micromachined pressure sensors lies in the package that houses the device itself. If a robust material is used for the substrate of the sensors as well as the packaging material, i.e., fabricating the sensor on the package itself, cost savings for the overall system may accrue. In this work, stainless steel has been studied as a potential robust substrate and a diaphragm material for micromachined devices. Lamination process techniques combined with traditional micromachining processes have been investigated as suitable fabrication technologies. To illustrate these principles, capacitive pressure sensors based on a stainless steel diaphragm have been designed, fabricated and characterized. Each sensor uses a stainless steel substrate, a laminated stainless steel film as a suspended movable plate and a fixed, surface micromachined back electrode of electroplated nickel. The sensitivity of the device fabricated using these technologies is 9.03 ppm kPa−1 with a net capacitance change of 0.14 pF over a range 0–178 kPa. Two types of read-out circuitry have been introduced to microfabricated sensors for removing parasitic effects. Finally, a die-type ASIC chip was integrated and measured with this capacitive pressure. The measured value of relative voltage change was 2.85% over the applied pressure range 0–75 kPa. The sensitivity of the sensor was 0.92 mV kPa−1 with a gap of 21 µm.