Smooth Contact Capacitive Pressure Sensors in Touch- and Peeling-Mode Operation

Capacitive (C) pressure sensors typically sense quadratic changes in C as a pressure difference (P) deflects a flexible conducting diaphragm near a rigid ground plane. Touch-mode capacitive pressure (C-P) sensors, where the conducting diaphragm touches a dielectric coated ground plane, often show a more linear response, but with less sensitivity, particularly at low-P. Initial contact of the diaphragm often occurs at a critical P. Until P,,it is reached, the sensitivity is typically too low for accurate measurements. In this work, two different types of electrodes with "parabolic" and "donut" cavity-shapes have been designed, fabricated, and tested to achieve high-sensitivity at low-pressures. A flexible conducting diaphragm touches the bottom electrode smoothly, and both cavity shapes permit initial contact at a zero-pressure differential. This type of C-P sensors can have touch-mode and peeling-mode operations. The sensitivities of these sensors in two operation modes were measured, and their resolutions were smaller than 0.1 Pa at a mean pressure of 10(5) Pa. Both sensors in two modes have the resolution over total-pressure less than 10(-6), which is difficult to achieve at atmospheric pressure.