Preparation And Properties Of BST Thin Films

In recent years, the electronic device is increasingly miniaturized and integrated with the development of microelectronic integration and optoelectronic technology. Thin film is lighter, smaller and easier to be integrated with semiconductor in comparison with the bulk ceramics. Barium strontium titanate (Ba1-xSrxTiO3) ferroelectric thin film is one of ABO3 complex perovskite materials. It has been widely applied in dielectric phase shifter, dynamic random access memories (DRAMs), pyroelectric infrared detectors because of its high dielectric constant, low dielectric loss, high tenability, low leakage current and high breakdown voltage. This research focuses on improving the technology of thin film preparation and enhancing the performance of the thin films.In this thesis, Ba0.6Sr0.4TiO3 (BST) thin films were deposited on Pt/Ti/SiO2/Si substrates by a RF-magnetron sputtering. This research improved the preparation conditions for the thin films and analyzed the dielectric, ferroelectric and piezoelectric properties of the BST thin films. The following major research results were achieved:1. The factors impacting the microstructure and property of BST thin films are substrate temperature, sputtering power, argon and oxygen ratio and sputtering pressure. The optimum conditions of RF-magnetron sputtering have been obtained through a series of experiments:substrate temperature of 400℃, sputtering power of 200-220 W, argon oxygen proportion of 5:1 and sputtering pressure of 0.5 Pa.2. The BST thin films present different orientational growth dependent on the substrate characteristics because the substrate orientation can significantly induce the growth of the films.3. XPS survey spectra and narrow spectra of BST thin films deposited at different sputtering pressures were researched. The results show that the chemical composition in the BST thin films is close to that in the target. But oxygen vacancy appears in thin films.4. The crystal structure and crystallization of BST thin films were researched by XRD. The results show that high temperature is helpful for crystallization. The BST thin films exhibits a tetragonal ferroelectric phase after crystallization.5. The BST thin films present a typical ferroelectric behavior with a remanent polarization of 3.11 μC/cm2 and coercive field of 106 kV/cm. The low remanent polarization is attributed to the small grain size and low Ba/Sr ratio. The hysteresis loops shift to right hand relative to the horizontal axis.6. The C-V characteristics of BST thin film exhibit an asymmetric "double butterfly" behaviour. The dielectric constant decreases from 320 to 200 under a bias voltage of 10 V, exhibiting a high dielectric tunability of 37.5%. The curve is also asymmetric about the axis, keeping consistent with the hysteresis loops.7. We researched the PFM images and the piezoelectric response switching as a function of bias voltage of the BST thin films with different thicknesses. The results show that more ferroelectric domains appear in the films with high thickness. The amplitude and phase have clear change in the films with different thicknesses.