Studies on hysteresis reduction in thermally carbonized porous silicon humidity sensor

Different ways to reduce hysteresis in a capacitive-type thermally carbonized porous silicon (TC-PS) humidity sensor are studied and compared. Modification of the contact angle of the dielectric surface, enlargement of the pore size of dielectric, and operating the sensor at elevated temperature proved all to be possible ways to reduce hysteresis in a TC-PS humidity sensor. By variation of the carbonization temperature, we produced TC-PS surfaces of different contact angles. Although the hydrophobic surface prevents hysteresis, it also decreases considerably the sensitivity of the sensor. Enlargement of the pore size reduces and tunes the hysteresis loop into the higher relative humidity (RH) values. Also operation of the sensor only few degrees above room temperature was found to be a workable method to prevent hysteresis. However, a constant temperature is crucial for exact humidity measurement using a TC-PS sensor.