Research On Non-linear Dielectric Properties Of STO Thin Films And Its Microwave Applications

Because of the excellent non-linear dielectric properties at low temperature (nitrogen boiling temperature), and the good compatibility with high temperature superconductors (HTSC), such as Y₁Ba₂Cu₃O_7-x (YBCO), SrTiO₃ (STO) thin films was regarded as a good candidate for high quality microwave tunable components.The STO thin films were prepared by pulsed laser deposition (PLD) method, the effect of growth parameters and substrate treatment, such as, the substrate temperature, the oxygen pressure, the laser energy density, the repetition rate, the in-situ annealing time, the mismatch between substrate and thin films and the step-terrace of substrate surface, on the microstructure of STO thin films were systematically studied in the dissertation. The interval deposition process was proposed. Two dimensional layer-by-layer mode was realized for heteroepitaxial growth of STO thin films on step-terraced substrate by the interval deposition process. STO thin films with atomic flat surface and excellent crystalline quality were prepared on step-terraced LaAlO₃(100) substrate by interval deposition process under optimum growth parameters. The root-mean-square (RMS) roughness of STO thin films with thickness of 300 nm was only 0.25 nm.The relationship between the microstructure and the non-linear dielectric properties of STO thin films was studied in the dissertation. The investigation was focused on the grain size and internal stress. The STO thin films with large grain size have large dielectric tunability. The tensile stress increase the tunability of STO thin films, while the compressive stress decrease the tunability of STO thin films. The experimental results are benefit for the optimization of the non-linear dielectric properties of STO thin films. The effect of oxygen vacancy on the dielectric properties of STO thin films was investigated. Although STO thin films with low oxygen vacancy concentration demonstrated low dielectric tunability, high dielectric dissipation, the STO thin films however, could withstand a large electric field; while the STO thin films with high concentration of oxygen vacancy exhibited reduced dielectric loss, and...