Characterization of a humidity sensor that incorporates a cmos capacitance measuring circuit

An integrated relative humidity sensor that combines a capacitive sensor with CMOS measurment circuitry on the smae 1.4 mm × 5.0 mm silicon chip has been designed, fabricated and tested. The device provides a d.c. voltage output that varies linearly with relative humidity over the entire range 0 to 100%.

When it is compared to discrete capacitive relative humidity sensors, the integrated sensor design offers the advantages of greater adaptability to standard instrumentation, low power consumption and ease in remote location of the sensor. It has the additional advantage of single-point calibration capability.

Measurements of sensor output show the expected linearity and close agreement with theory. The response time has been found to be about 10 s, while repeatability and hysterisis and typically within 1.6% of fullscale output. A thermistor is packaged with the sensor to provide compensation for temperature effects.