Sub-ppm trace moisture detection with a simple thermally carbonized porous silicon sensor

A simple humidity sensor based on thermally carbonized porous silicon has been used to detect low moisture contents in gaseous atmosphere. Thermal carbonization of porous silicon changes the surface to hydrophilic and improves the sensitivity and the stability of the sensor. The capacitive sensitivity (C/C0 − 1) over 6% in a range of 0–1 RH% was obtained. The resolutions for capacitive and resistive measurements were found to be 0.45 and 0.35 ppm, respectively. The resolution was limited by noise level and with a simple data averaging it was improved down to 0.20 ppm. The response time was observed to be good and it varied from 0.5 to 2.6 min.