Preparation And Characterization Of ZnSnO₃ Ferroelectric Thin Films

Ferroelectric thin films have been widely used in semiconductor device due to their properties include piezetlectriy, ferroelectricity, dielectricity, pyroelectricity, photoelectric effect and nonlinear optical effect. People use these propertie to fabricate functional device such as memory, transducer, phototube etc. But,traditional perovskite ferroelectric thin films like PZT have a lot of defect, for emaxple size effect, interface issues, compatibility issues and the Pb element brings about environmental pollution. These defect effect the useful life and reliability of device, which limit the development of ferroelectric thin films.Recently, a LiNbO₃-type ZnSnO₃ had been synthesized with a high pressure synthesis which had ferroelectricity. LiNbO₃ is a ferroelectric which has max spontaneous polarization（） and R3c-type space group. ZnSnO₃ is a new type functional materials, which is uesd as TCO glass and gas sensor due to it’s ferroelectricity, gas sensitivity, photocatalysis property.ZnSnO₃ has well applied value and widely prospect.In this thesis we use LiNbO₃-type ZnSnO₃ as research object. We deposit ZnSnO₃ at Pt/Si substrate and Al2O₃ substrate respectively by PLD. The main research is looking for optimum condition, and we both analyze electrical properties of ZnSnO₃ thin films. The main conclusions are as follows.1. Firstly we deposit ZnSnO₃ at Pt/Si substrate by PLD so as to find optimum condition. Researches have shown that oxygen partial pressure, growth temperature, laser energy and buffer layer effect the properties of ZnSnO₃ thin film. Film’s crystal quality is best and leakage current density is least in 30 Pa oxygen partial pressure. Thin films show only（006） phase which is same to ZnSnO₃ single crystal in 600℃. When laser energy is 120 mJ, film’s crystal quality is best and surface is smooth.We use ZnO as buffer layer, resluts show that film’s electrical properties and crystal quality has been improved, the leakage current density has declined one order of magnitudes.2. We direct deposit ZnSnO₃ at Al2O₃ substrate. thin films show only（006） phase, We use ZAO as bottom electrode, RMS is 2.23 nm. We also study the relationship between leakage current and annealing. With increasing the annealing temperature, grain size and RMS increase. Stepped annealing make leakage current density smaller than only annealing once. Leakage current mechanism of films are analyzed. Results show that the conducive mechanism of ZnSnO₃ thin films is Schottky emission mechanism. Film’s hysteresis loop is tested and the result shows that polarization increase first and then decrease with increasing the annealing temperature. Film’s leakage current density and polarization have a linear relation with the thickness of film. Fatigue tests show that after 2×109 inversion, the reversible polarization of ZnSnO₃ films declined 27.5%.