Study On The Related Physical Property Of Tungsten Trioxide-Based Thin Film Prepared By Magnetron Sputtering

WO₃ material is an important functional material. It is studied and applied extensively because of its electrochromic property, photochromic property, electrochemistry, etc. In recent years, it has been found that WO₃ show good nonlinear electrical property characterized by low breakdown voltage and low operating current. WO₃ thin films have more advantage of reducing the components thickness than WO₃ ceramic so WO₃ thin films thin films have the potential in empoldering lower power and lower nonlinear voltage varistors. But its instable electrical property must be solved before using WO₃ as a kind of varistor in practice. Previous studies indicated that the electrical behavior of sintered WO₃ thin films was unstable and had serious hysteresis effect, the current under constant voltage decayed with time and current-voltage characteristics depended on the electrical history of the sample. This problem is an obvious blockage for practical application of WO₃ as a varistor material. We want to improve the electrical properties of WO₃ ceramics by doping rare earth elements and understand the related physical mechanism. In this thesis, starting from fabricating WO₃ thin films, the nonlinear electrical properties are mainly investigated to understand the physical mechanism of WO₃ functional materials.In this thesis, WO₃ thin films were prepared by magnetron sputtering method on the glasses and silicon substrates, the influence of the process conditions on the crystallization and orientation of the films were studied for improving the process condition and optimizing the microstructure of WO₃ thin films.The result indicates that the annealed temperature and time affects the microstructure and nonlinear of WO₃ films. The nonlinear voltage of the WO₃ thin film varistors was 1.8V nonlinear coefficient was 14.3and leakage current was 0.072mA when the annealed temperature 500℃and time 20h.In this thesis we changed the adulteration concentration of Co and Ce metal target to carry out an optimization. The results indicate that when at the same process condition the two kind additives power were 50W and 40W repectively, WO₃ thin film varistors have the best voltage-sensitive capacities. WO₃ thin film varistors have the best voltage-sensitive capacities.The nonlinear voltage of the WO₃ thin film varistors was 1.01V;0.93V, nonlinear coefficient were 4.13;7.92 and leakage current was 0.78 mA;0.58mA.Under the condition of appropriate adulterations, Co can promote the formation of crystal boundaries when the films are annealed, Ce can increase barrier potential altitudeand improve the nonlinear coefficient.Based on the analysis of the mentioned experimental data, it is found that the conventional theory of nonlinear electrical transport based on double Schottky barriers at grain boundary is too simple to be used to explain exactly the nonlinear characteristic of tungsten oxide polycrystalline films we must think over that WO₃ is polar material. Its electrical transport mechanism should be polarization coupling.