Smooth Contact Mode Capacitive Pressure Sensor with Polyimide Diaphragm

Capacitive (C) pressure sensors typically sense a quadratic change in C as a pressure difference (P) deflects a flexible conducting membrane near a rigid ground plane. Touch-mode capacitive pressure (C-P) sensors, where the conducting membrane touches a dielectric coated ground plane, often show a more linear response, but at the expense of a lower sensitivity, particularly at low-P. Initial contact of the membrane often occurs at a critical P, and until reached, the sensitivity is typically too low for accurate measurements. Two different types of electrode shapes with "parabolic" and "donut" cavities, have been designed, fabricated and tested to achieve high-sensitivity at low pressures, which is critical for many emerging BioMEMS applications. Both cavity shapes permit initial contact at a zero pressure differential. The sensitivity obtained in these sensors is ~25 pF/kPa for pressure less than 1 kPa, and ~3 pF/kpa for pressure larger than 10 kPa, which is several order magnitudes higher than standard C-P sensors.