A High-Sensitive Resonant Minute Differential Pressure Sensor Based on Microcap Structure

Compared with differential pressure sensors, the minute differential pressure (−10 to 10 kPa) sensors have a smaller range and require a more sensitive sensor chip. High-precision resonant differential pressure sensors are resonator-diaphragm integrated structures. To improve their sensitivity, it is necessary to increase the area of the pressure-sensitive diaphragm or decrease the thickness of the pressure-sensitive diaphragm, which were limited by the chip size or the difficulty of the fabrication process. In this article, a microcap structure was proposed, which improved the differential pressure sensitivity by 1.79 times compared with the composite diaphragm structure under the same pressure-sensitive diaphragm size. The vacuum encapsulation of the sensor was achieved by wafer-level gold/silicon eutectic bonding (bonding using eutectic alloy formation), while the use of inverted structure fabrication improved the fabrication yield. With a static pressure of 0–120 kPa and an operating temperature range of $- 40~^{\circ }$ C to $80~^{\circ }$ C, the sensor has a differential pressure measurement range of −10 to 10 kPa (20 kPa F.S.), a differential pressure sensitivity of 150 Hz/kPa over the full temperature range and low air pressure range, a fitting error of less than 0.075%, and a measurement error of less than 0.1% F.S.