Temperature dependence of sensing characteristics of a pH sensor fabricated on AlGaN/GaN heterostructure
The miniaturization of the pH sensor has been improved with the development of the silicon ion-sensitive field-effect transistor (ISFET). Gallium nitride (GaN) is a possible candidate for developing a pH sensor owing to its superior resistance to environmental effects, superior conductivity, wide bandgap and chemical stability compared with silicon. In this study, a pH sensor fabricated on an AlGaN/GaN heterostructure was developed and its sensing characteristics were evaluated at temperature range from room temperature to 80 °C. The sensor shows good pinch-off and transfer characteristics at each temperature point in three standard buffered solutions. The drain current decreased and the threshold voltage showed a positive shift with pH increasing. Drain current decrease and positive threshold voltage shift were also noted with increasing temperature. The pH sensitivities (∆V/pH) are 52.3, 57.2, 64.2, and 69.5 mV/pH at temperatures of 20, 40, 60, and 80 °C, respectively, which are close to the theoretical values at all the temperature points.