Electrical properties of thin film zirconia grown by ultraviolet ozone oxidation

Abstract

Zirconia films of varying thickness (ranging from 20–55 Å) have been grown by the method of UV ozone oxidation at room temperature. The electrical properties of these films have been studied in detail by capacitance–voltage (C–V) and I–V measurements. Capacitors were subjected to various anneals in differing ambient to study their effects on C–V hysteresis, dispersion and charge trapping. It was found that annealing in nitrogen followed by forming gas resulted in C–V curves with negligible hysteresis. The effects of different underlayers on the electrical properties of zirconia films have also been studied and are briefly discussed. It was found that zirconia films grown on UV-ozone grown SiO2 had lower hysteresis and lower interface trap density compared to zirconia films grown on chemical oxide. The effect of oxidation time and oxygen pressure have been investigated; in particular, detailed electrical studies have been performed on partially oxidized zirconia. Defective oxides are shown to have significant frequency dispersion in both the accumulation and depletion regions of the C–V curves along with very high loss tangent factor compared to stoichiometric oxides. A physical mechanism based on Maxwell–Wagner interfacial polarization is presented here for a model system of ZrO2–Zr to explain the experimental data qualitatively. Finally, we have attempted to correlate the C–V hysteresis to the presence of traps in the zirconia film using temperature-dependent current–voltage measurements. The leakage current was found to be nearly independent of temperature at low voltages, suggesting a tunneling mechanism, while at higher voltages the data can be modeled using the Poole–Frenkel conduction mechanism. It is suggested that C–V hysteresis in zirconia films possibly arises from electrical traps in the film and can be identified by modeling their I–V characteristics.