STRUCTURE AND ELECTRICAL PROPERTIES OF ELECTRON-BEAM EVAPORATED ZIRCONIA THIN FILMS

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Department of Engineering

ABSTRACT
In the past 25 years, there has been much interest in dielectric films of Zr02 for several applications such as an alternative insulator material in microelectronics, resistance switching and an oxygen anion conductor. Only recently have thin film anion conductors, especially the cubic Zr02 form, been investigated. However, these films will probably find future uses such as solid electrolytes for thermodynamic and kinetic purposes, for purification and preparation of gases, and in oxygen monitoring suysterns. Zirconia films have been prepared by a variety of methods but electron-beam (E-beam) evaporation has had limited characterization. The objective of this investigation was to study the structure and electrical properties of E-beam evaporated Mo-Zr02-Ho capacitors as a function of deposition temperature. In addition, Y2O3 stabilized Zr02 films were prepared by a new method, E-beam multilayer deposition, and characterized in terms of structure and electrical properties. Zirconia films deposited on molybdenum electrodes were polycrystalline. The raonoclinic phase was the major phase detected in the films deposited at temperatures between 300°C and 600°C. At lower deposition temperatures (190o -200o C), however, the cubic phase was the major crystalline phase formed. The average crystallite size increased from 118 A to 484 A for the (111) and 175 A to 265 A for the (111) crystallites as deposition temperature increased from 200°C to 600°C. Ac conduction in Mo-Zr02-Ho structures at fields < 0.0 5 MV/cm was dominated by electron hop with a frequency independent loss behavior between 25°C and 150°C. Between 150°C and 325°C, a od « fY dependence was observed where y depended on measurement and deposition temperatures. The remanance of interfacial polarization is suggested as an additional mechanism in this temperature range and for frequencies of 60-105 Hz. The admittance plots of the samples showed a single semicircle with a small semicircle depression that was ascribed to bulk conduction. Both ohmic and space-charge-limited-currents (SCLC) dc conduction were obtained for the Mo-Zr02-Ho samples. The charge storage in these films increased linearly with voltage and depended on measurement and deposition temperatures, but was probably polarity independent. Y2O3 stabilized Zr02 films could be formed by multilayer deposition followed by heat treatment at 1200°C for at least seven hours. Heat treated Au/Pd-Y203,Zr02 Pt/Rd capacitors exhibited a SCLC behavior at a field of 0.03 MV/cm and room temperature. The admittance plot of this sample had a large semicircle depression of about 45°.