The $Ba_{1-x}Sr_xTiO_3$ thin films was deposited on ITO-coated glass substrate at various substrate temperatures from the five different $Ba_{1-x}Sr_xTiO_3$ (X=0, 0.25, 0.5, 0.75, 1) targets by means of rf magnetron sputtering for their application to the insulating layer of an thin film electroluminescent (TFEL) flat panel display. The $Ba_{1-x}Sr_xTiO_3$ thin films deposited at 550℃ have individual preferential orientations as a function of composition (X=0, 0.25, 0.5, 0.75, 1) due to the stress relief interactions among the intrinsic compressive stress, thermal tensile stress and extrinsic compressive stress (compressive stress in case of $BaTiO_3$ ($T_c$=120℃) and $Ba_{0.75}Sr_{0.25}TiO_3$ ($T_c$=57℃)). This behavior also appears on the (BaSr)$TiO_3$ thin films (X=0.5) deposited on ITO-coated glass substrate at deposition temperature between 350℃ and 550℃. The composition of $Ba_{1-x}Sr_xTiO_3$ thin films deposited on ITO-coated glass substrate at 550℃ is close to stoichiometry (1.009~1.089 in A/B ratio), but the compositional deviation from a stoichiometry is larger as $SrTiO_3$ is added. The drastic decrease of dielectric constant ($\varepsilon^\prime$) and increase of dielectric loss (tan δ) in $Ba_{1-x}Sr_xTiO_3$ thin films is observed above 100 kHz. There are also diffuse transitions in $Ba_{1-x}Sr_xTio_3$ thin films as a result of the measurements of dielectric constant with the variation of measuring temperature (-25~200℃). I-V characteristics of $Ba_{1-x}Sr_xTiO_3$ thin films show the decrease of leakage currents with the increase of $SrTiO_3$ contents. Breakdown field is 2.3 MV/cm at X=0, 1.7 MV/cm X=0.5, and 2.7 MV/cm at X=1. Optically, transparent (BaSr) $TiO_3$ thin films are deposited on ITO-coated glass substrate.
The influence of the ITO layer on the properties of (BaSr)$TiO_3$ thin films deposited on the ITO-coated substrate was also investigated. The ITO layer does not affect the crystallographic orientation of (BaSr)$TiO_3$ thin film, but enhance the grain growth. Another effect of the ITO layer on (BaSr)$TiO_3$ thin films is the interdiffusion phenomenon, which is studied by means of secondary ion mass spectrometry (SIMS). As the substrate temperature increase, interdiffusion intensifies at the interface not only between the grown film and ITO layer but also between the ITO layer and base glass substrate. The refractive index ($n_f$) of (BaSr)$TiO_3$ thin film deposited on a bare glass subsrtrate is 2.138 - 2.286, as a function of substrate temperature. Dielectric constant and loss of (BaSr)$TiO_3$ thin films deposited on ITO-coated glass substrate are larger with the increase of deposition temperature. As the deposition temperature increases, leakage current increases and the breakdown field decreases from 2.5 MV/cm to 1.97 MV/cm.
In order to exempt the propagating breakdown mode of (BaSr)$TiO_3$ thin three kinds of buffer layer (thickness : 500~600Å), i.e., $Y_2O_3$, $Al_2O_3$ and $Si_3N_4$ are adopted between ITO layer and (BaSr)$TiO_3$ thin film by using rf magnetron sputtering method. The existence of buffer layer results in the drop of dielectric constant, but the uniformity of dielectric constant over all frequency. There is also much decreasing effect in the case of dielectric loss. I-V characteristics of buffered (BaSr)$TiO_3$ thin films show the decrease of leakage currents with the increase of (BaSr)$TiO_3$ thin film thickness. Especially, $Si_3N_4$ layer is the most effective for the decrease of leakage currents and increase of breakdown field.
