Tianjin Zhang

Structural and optical properties of BST thin films prepared by the sol-gel process

The Ba0.65Sr0.35TiO3 thin films have been prepared by the sol-gel method on fused quartz and (1102)- oriented Al2O3 substrates. The crystallization behavior and structure characterization were studied at different annealing temperatures by XRD and SEM. The as-fired thin films were found to be amorphous, and the films crystallized to a perovskite structure after a post-deposition annealing at 700 °C for 1 h in air. The grain of BST film was evenly distributed, indicating the sol-gel-derived Ba0.65Sr0.35TiO3 thin film has a well-defined microstructure. The refractive index increased from 2.16 to 2.35 as wavelength decreased from near infrared range (1000 nm) to visible range (430 nm). The energy gap of BST films deposited on Al2O3 substrate was found to be around 3.48 eV of indirect-transition type.

Large rectifying leakage current in Pt/BaTiO3/Nb:SrTiO3/Pt structure

20-nm-thickness epitaxial BaTiO3 (BTO) thin films were prepared on the Nb-doped SrTiO3 single-crystal substrates by RF magnetron sputtering technology. The rectifying characteristic current-voltage curves were observed and was discussed using the Schottky barrier model taking into account the movement of oxygen vacancies. The leakage current mechanisms were interpreted by the Schottky emission and Poole-Frenkel emission near the Pt/BTO interface at lower bias and higher bias, respectively.

Preparation and dielectric properties of compositionally graded (Ba,Sr)TiO3 thin film by sol-gel technique

Abstract Compositional graded Ba x Sr 1- x TiO 3 ( x =0.6, 0.7, 0.8, 0.9, 1.0) (BST) thin films (less than 400 nm) were fabricated on Si and Pt/Ti/SiO 2 Si substrates by sol-gel technique. A special heating treatment was employed to form the uniform composition gradients at 700 °C. The microstructures of the films were studied by means of X-ray diffraction, atomic force microscope and field emission scanning electron microscopy. The results show that the films have uniform and crack-free surface morphology with perovskite structure phase. The small signal dielectric constant (ɛ r ) and dielectric loss (tanδ) are found to be 335 and 0.045 at room temperature and 200 kHz. The dielectric properties change significantly with applied dc bias, and the graded thin film show high tunability of 42.3% at an applied field of 250 kV/cm. All the results indicate that the graded BST thin films prepared by sol-gel technique have a promising candidate for microelectronic device.

Effect of Deposition Parameters on Crystallization of RF Magnetron Sputtered BST Thin Films

Ba0.65Sr0.35TiO3 (BST) thin films on p-silicon substrates were deposited by radio frequency magnetron sputtering. The effects of the deposition parameters on the crystallization and microstructure of BST thin films were investigated by X-ray diffraction and filed emission electron microscopy, respectively. The crystallization behavior of these films was apparently affected by the substrate temperature, annealing temperature and sputtering pressure. The improved crystallization can be observed for BST thin films that deposited at higher temperature. The dominant X-ray diffraction peaks became sharper and more intense as the annealing temperature increased. BST thin films deposited at high sputtering pressure of 3.9 Pa exhibited the (110) + (200) preferred orientation. Possible correlations of the crystallization with the sputtering pressure were discussed. The SEM morphology indicated the film was small grains and smooth.