Characterization of sputtered yttria-stabilized zirconia thin film and its application to a metal-insulator-semiconductor structure

An rf-sputtered yttria-stabilized zirconia (YSZ) thin film was characterized as to its structural and electrical properties. Then a metal-insulator-semiconductor (MIS) structure incorporating it as a part of a multi-insulator was investigated particularly for use in a field-effect transistor (FET)-type oxygen sensor. The YSZ film deposited on a Si3N4 film was found to be a cubic structure based on x-ray diffraction and reflective high-energy electron diffraction analyses. As cracks were formed at 800 °C, annealing treatment of the film should be carried out below that temperature. The leakage current of the sputtered YSZ film was smaller than 2×10−7 A/cm2 in the applied voltage range 0–5 V, which was comparable to that of the calcia-stabilized zirconia film used for a potentiometric oxygen sensor. The dielectric constant of the sputtered YSZ film was 16±2 at 105 Hz. The minimum loss tangent was 0.01. The frequency dispersion of the dielectric constant and loss tangent were improved by annealing treatment at temperatures lower than 400 °C. The capacitance-voltage (C-V) characteristics of the MIS structure incorporating the YSZ film showed hysteresis and positive shifts of the flatband voltages as compared with those of the MIS structure without the YSZ film. The hysteresis was considered to be due to the movement of charged species such as oxygen ions and/or electrons in the YSZ film, which would cause an unstable response of the FET-type oxygen sensor.