A BALANCED RESONANT PRESSURE SENSOR

A new type of resonant pressure sensor in silicon is described. The pressure sensitive part consists of a square dual-diaphragm cavity structure which vibrates in a balanced torsional mode. The selected torsional mode in combination with a suspension along the two crossing node lines of the electrostatically vibrated part yields a high Q factor of 2400 in air and 80 000 in a vacuum. The pressure sensitivity is a result of a pressure change-induced flexure of the two diaphragms which changes the torsional stiffness and hence the resonance frequency. The pressure sensitivity of the differential and absolute pressure sensor was 19%/bar and 14%/bar respectively. The basic structure showed an inherent uncompensated low temperature sensitivity of - 16 ppm/°C. The fabrication process involving anisotropic silicon etching and silicon thermal bonding is described. The improved design which increased the Q factor in air to 3300 is also presented. © 1990.