Integrated capacitive absolute pressure sensor

Although a capacitive sensor has high sensitivity, the sensitivity is degraded by stray capacitance. Therefore, to fabricate a high-performance sensor, the capacitive sensor and capacitance detection circuit must be integrated. This paper describes the integrated capacitive pressure sensor fabricated with integrated circuit technology and micromachining technology. The sensor is composed of a silicon substrate and Pyrex glass. The capacitive sensor is composed of a mesa-type silicon diaphragm and an upper metal electrode. The capacitance of the sensor is converted to frequency using a CMOS C-F converter integrated on a silicon substrate. Since frequency is detected by monitoring the supply current change in the power line, the sensor can be operated with two wires. The temperature compensation is carried out by controlling the supply voltage. The temperature-sensitivity shift is less than a few hundred ppmF.S./°C when the supply voltage is 4.1 V. When pressure applied to the diaphragm is varied from 200 to 1900 mmHg, the frequency changes from 96 to 34 kHz in proportion to the pressure, where the capacitance of the sensor changes about 300 percent. Since in this sensor, glass and silicon form the package for the sensor and circuit sections, the size of the sensor is small (1.7×2.2 mm²) and the cost can be low.