Humidity sensitive field effect transistors

A new device, named humidity sensitive field effect transistors (HUSFETs), for integrated humidity sensors has been fabricated using conventional silicon microtechnology. The insulator structure of this HUSFETs is TiO2/Si3N4/SiO2 and the water molecular permeable electrode is thin porous gold. The fabricated devices showed typical enhancement mode characteristics and the threshold voltage was about 2.7 V in 60% RH. It can be seen that the threshold voltages of HUSFET decreased from 3.0 to 2.4 V and the drain current increased from 208 to 464 mu A according to increasing relative humidities from 30 to 90%. The sensitivity of HUSFET is 3.2 mu A/RH, when the drain and gate voltages are constant.