The Preparation And Properties Of High-performance ZnO Films, CCTO Films And ZnO/CCTO Composited Films

Sol-gel method was used to prepare ZnO, CCTO and its composite films. The composition, microstructure and electrical characteristics of the samples were investigated by XRD, XPS, SEM, AFM, varistor dc parameter analyser and impedance analyser.Firstly, study the effects of rare earth oxide Sc₂O₃ on the elecric properties of ZnO thin films, and the effects of rare earth oxide Sc₂O₃ graded doping on ZnO thin films. The result shows:（1） when the content of Sc₂O₃ is no more than 0.2 mol%, grain size shows an increase of ZnO phase with Sc₂O₃ doping. When the concent of Sc₂O₃ is more than 0.2 mol%, grain size shows a decrease of ZnO phase with Sc₂O₃ doping. The threshold voltage VT shows the contrast trend to grain size of ZnO phase. Nonlinear coefficient increased with the increase of Sc₂O₃ concentration. The highest non-linearity was obtained for 0.4mol% Sc content with the nonlinear coefficient α=3.7 and 301 μA in leakage current.（2） Sc-doped graded films were prepared. The nonlinear coefficient of the up graded thin films is as high as 6.8, leakage current is only 109 μA, and the potential gradient is 27.32 V/mm.Seconderly the effects of SrO on the dielectric characteristic of CCTO, and the effects of SrO graded doping on the dielectric characteristic of CCTO thin films. Ca1-xSrxCu3Ti4O12（x=0, 0.05, 0.1, 0.15） films were fabricated by sol-gel method. The results show:（1） the dielectric constant increase, when the sample doped with Sr concentration, especially when x = 0.05, the dielectric constant of thin film rose to 4000, higher than the undoped sample, and keep good frequency independence in 102-106 Hz;（2） the dielectric constant of down graded CCTO films up to 3800 at low frequency, dielectric loss was 0.03, and only a slow downswing with the increase of the frequency, the dielectric properties of down graded CCTO films is better than the up graded CCTO films.Lastly, study the characteristic of ZnO/CCTO composite films, and the metallic oxide graded doping on the electric characteristic of ZnO/CCTO composite films. Overlap CCTO films on the ZnO layer to prepare the ZnO/CCTO capacitance-varistor composite films. The study founds:（1） CCTO films can well grown on the ZnO films, and the composite films have higher dielectric constant and nonlinear coefficient than the CCTO films. The dielectric constant rise to 3900 at low frequency, nonlinear coefficient is 2.1, leakage current is 495 μA and the potential gradient is 42.3 V/mm;（2） compared with the undoped composite films, the graded doped composite films, which was combined by Sc doped Zn O up-graded films with Sr doped CCTO down-graded films, showed the optimal electric properties. The nonlinear coefficient is 2.4, dielectric constant is 4000 at low frequency, and leakage current is 447 μA. Accordingly, the capacitor-varistor double function films can be prepared by compositing the ZnO up-graded and CCTO down-graded films.