p H sensor using AlGaN∕GaN high electron mobility transistors with Sc2O3 in the gate region

Ungated AlGaN∕GaN high electron mobility transistors (HEMTs) exhibit large changes in current upon exposing the gate region to polar liquids. The polar nature of the electrolyte introduced leds to a change of surface charges, producing a change in surface potential at the semiconductor/liquid interface. The use of Sc2O3 gate dielectric produced superior results to either a native oxide or UV ozone-induced oxide in the gate region. The ungated HEMTs with Sc2O3 in the gate region exhibited a linear change in current between pH 3 and 10 of 37μA∕pH. The HEMT pH sensors show stable operation with a resolution of <0.1pH over the entire pH range. The results indicate that the HEMTs may have application in monitoring pH solution changes between 7 and 8, the range of interest for testing human blood.