Humidity sensors using porous silicon layer with mesa structure

Abstract

A capacitance-type humidity sensor in which a porous silicon layer is used as a humidity-sensing material was developed. This sensor was fabricated monolithically to be compatible with the typical IC process technology except for the formation of porous silicon layer. As the sensor is made as a mesa structure, the correct measurement of capacitance is expected because it can remove the effect of the parasitic capacitance from the bottom layer and other junctions. To do this, the sensor was fabricated using process steps such as the localized formation of porous silicon, oxidation of the porous silicon layer, and etching of the oxidized porous silicon layer. From completed sensors, capacitance response was measured at a relative humidity of 25-95% at room temperature. As a result, the measured capacitance showed an increase over 300% at the low frequency of 120 Hz, and showed little dependence on temperature between 10 and 40 °C.