An integrated miniature capacitive pressure sensor

A newly designed capacitive pressure sensor which incorporates a CMOS IC on the same silicon chip has been developed. The sensor chip is 3.3 mm × 3.7 mm × 0.5 mm in size, and both the sensing capacitive element and the electronic circuit are hermetically sealed between the silicon substrate and the glass cover using a unique electrical feedthrough structure. The incorporated electronic circuit is the C-F converter whose oscillation frequency changes as a function of the sensing capacitance. By optimizing the circuit supply voltage, the thermally induced baseline (oscillation frequency at atmospheric pressure) drift can be reduced to within 3.1% F.S. between 20 °C and 50 °C. Since the oscillation frequency can be counted by the consumed current pulses, the pressure waveform can be monitored with only two external leads.