Sensing and Impedance Characteristics of YbTaO(4) Sensing Membranes

In this study we developed ytterbium tantalum oxide (YbTaO(4)) 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 YbTaO(4) 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 YbTaO(4) films annealed at 700, 800 and 900 °C. The YbTaO(4) 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 YbTaO(4) film and increased its (−131)-oriented nanograin size. Moreover, the impedance properties of YbTaO(4) EIS sensors were investigated by using the capacitance–voltage method. The resistance and capacitance of YbTaO(4) 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 YbTaO(4) EIS sensor became smaller, due to a gradual decrease in the bulk resistance of the EIS device, as the RTA temperature was increased.