Sensing and Impedance Characteristics of YbTaO₄ Sensing Membranes

In this study we developed ytterbium tantalum oxide (YbTaO₄) sensing membranes for use in electrolyte-insulator-semiconductor (EIS) pH sensors. The influence of rapid thermal annealing (RTA) treatment on the sensing and impedance properties of the YbTaO₄ sensing membranes deposited through reactive co-sputtering onto Si substrates was explored. X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy revealed the structural, morphological, and chemical features, respectively, of these YbTaO₄ films annealed at 700, 800 and 900 °C. The YbTaO₄ EIS device annealed at the 800 °C exhibited a super-Nernstian response of 71.17 mV/pH within the pH range of 2-12. It also showed the lowest hysteresis voltage ( < 1 mV) and the lowest drift rate (0.22 mV/h) among the tested systems. Presumably, the optimal annealing temperature improved the stoichiometry of YbTaO₄ film and increased its (-131)-oriented nanograin size. Moreover, the impedance properties of YbTaO₄ EIS sensors were investigated by using the capacitance-voltage method. The resistance and capacitance of YbTaO₄ sensing films annealed at three various temperatures were evaluated by using different frequency ranges in accumulation, depletion, and inversion regions. The semicircle diameter of the YbTaO₄ EIS sensor became smaller, due to a gradual decrease in the bulk resistance of the EIS device, as the RTA temperature was increased.