Researches Of The Non-stoichiometric And Doped CaCu₃Ti₄O₁₂ Thin Films

CaCu₃Ti₄O₁₂ is perovskite-liked material,which not only has large dielectric constant and high stability,but also has a good nonlinear I-V characteristic.The excellent electrical properties have a wide range of applications in the field of microelectronic devices.Engineers can design new multi-functional electronic devices by the electrical characteristics.In this paper,sol-gel method was used to prepare non-stoichiometric and Al-doped CaCu₃Ti₄O₁₂ films.Magnetron sputtering was used to obtain the certain sizes of top metal electrodes on the surface of CaCu₃Ti₄O₁₂ film.The composition and microstructure of the films were analyzed by means of X-ray diffraction and scanning electron microscopy after the film samples were determined.At the same time,the effects of non-stoichiometric and metal doping on the nonlinear I-V characteristics were investigated by a semiconductor analysis instrument.For the research of Ti non-stoichiometric CCTO films,the CuO and CaCuO₂secondary phases are explored in non-stoichiometric samples.The presence of the second phases have a certain effect on the barrier height and the breakdown voltage.Meanwhile,the deviation of the Ti stoichiometry can increase the breakdown voltage of the thin film.When the current-voltage characteristic curve of the film is tested under the changing temperature environment,the non-stoichiometric films are more sensitive to temperature than the pure CCTO film.For the study of Cu non-stoichiometric CCTO films,the second phases of C uO and Cu₂O are found in C u non-stoichiometric films.The breakdown voltages of the films and the sensitivity to temperature are related to the Cu stoichiometric ratio,which can increase the breakdown voltages of the films and decrease the sensitivity of the films to temperature.For the Al-doped CCTO films,it was found that the doping of metal elements can enhance the breakdown voltage of the films.The results of nonlinear I-V measurements at different temperatures show that the CCTO thin films doped with Al have good temperature stability,and the breakdown voltages of the Al-doped films decrease at high temperature.The breakdown voltages of the Al-doped CCTO films are almost unaffected by the change of voltage rise rate in nonlinear measurement.For studying on the mechanism model of nonlinear I-V characteristics of thin films,the double Schottky barrier model is used to analyze the carrier transport mechanism at grain boundary and the change of barrier height caused by the stoichiometric shift.In addition,considering the possible presence of copper oxide on the surface of the film,the metal-insulator-semiconductor structure is proposed for the gold-plated CC TO films.The thermionic emission is the main mechanism of carrier transport in the low-voltage range.