Development of a High-k Pr $_{2}$ O $_{3}$ Sensing Membrane for pH-ISFET Application

In order to develop a pH sensor having a good pH-sensing characteristic, electrolyte-insulator-semiconductor capacitors using a high-k P₂O₃ thin film as the sensing membrane were fabricated on silicon substrates by reactive radio frequency sputtering. The structural and morphological features of these films with annealing at various temperatures were studied by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. The Pr₂O₃ sensing film after annealing at 900degC is suggested to the increase in the interfacial SiO₂ and silicate formation, and the high surface roughness. Therefore, a physical vapor deposition Pr₂O₃ film is adopted as a new pH-sensing layer. The result produces a pH response of 52.9 mV/pH (pH=2-12), a hysteresis voltage of 17.5 mV (pH=7 rarr 4 rarr 7rarr 10 rarr 7), and a drift rate of 2.15 mV/h (pH=7 buffer solution).