Investigation of Sc2O3 Based All-Solid-State EIS Structure for AlGaN/GaN HEMT pH Sensor

In this work, an all-solid-state electrolyte-insulator-semiconductor (EIS) device is developed for pH sensing performance evaluation of insulating materials. The EIS capacitor incorporates scandium oxide (Sc2O3) sensing film deposited on undoped gallium nitride (u-GaN) by thermal evaporation. The structural and morphological features of the thin films annealed at different temperatures (650-850°C), were investigated through X-ray diffraction and AFM analysis. A gold wire with diameter of 25 µm was bonded on the device and served as the quasi reference electrode for the C-V measurements and pH sensitivity characterizations. After correction of the measured capacitance regarding the pH dependent variation of the standard potential E⁰(pH) of gold, the Sc2O3 EIS capacitor prepared with an annealing at 650°C exhibited a linear response with a sensitivity of 40 mV/pH while the device with the as-deposited Sc2O3 film showed nonlinear behavior and, those annealed at temperature higher than 650°C were shown to be insensitive to pH variation.