High-sensitivity silicon capacitive sensors for measuring medium-vacuum gas pressures

Abstract

The design, construction, and preliminary testing of an experimental capacitive silicon pressure sensor are described. The prototype sensor is designed as a robust, precision barometer suitable for measurements on the planet Mars where the mean atmospheric pressure is ~ 6 mbar (600 Pa). Most commercially available silicon pressure sensors tend to operate over pressure ranges ≥ 1 bar, or measure gauge pressure, but this sensor is specifically constructed to measure absolute pressure of 0–10 mbar with a very high sensitivity ~ 1 pF mbar −1. The transductional mechanism is the deflection of a silicon diaphragm under applied pressure across a sealed vacuum cavity. Under storage conditions of 1 bar, the diaphragm displacement is mechanically constrained by an underlying stopping surface. Finite-element analysis shows that typical structures are extremely resistant to overpressure: fracture occurs at many tens of bar. The device is fabricated using a silicon fusion-bonded vacuum cavity which provides for relative insensitivity to temperature changes.