Study of high-k Er₂O₃ thin layers as ISFET sensitive insulator surface for pH detection

This paper describes the structural and sensing properties of high-k Er₂O₃ sensing membranes deposited on Si substrates through reactive sputtering. X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy were employed to analyze the structural and morphological features of these films after annealing at various temperatures. Electrolyte-insulator-semiconductor (EIS) devices with a high-k Er₂O₃ sensing film annealed at 700 °C exhibit good sensing characteristics, including a high sensitivity of 57.58 mV/pH in the solutions from pH 1 to pH 13, a small hysteresis voltage of 6.23 mV in the pH loop 7 → 4 → 7 → 10 → 7, a low drift rate of 1.75 mV/h in the pH 7 buffer solution, and a high selective responses towards H⁺. This improvement is attributed to the formation of a thinner silicate layer and the large surface roughness.