Strontium titanium oxide and barium(1-x) strontium(x) titanium oxide epitaxial thin films grown by plasma-enhanced metalorganic chemical vapor deposition.

摘要

Recently, Strontium titanate (STO) and barium strontium titanate (BST) thin films have attracted increased scientific and technological interest due to their potential applications in multi-layer high temperature superconducting (HTSC) devices, uncooled IR sensing and imaging devices, dynamic random access memories and monolithic microwave integrated circuits. The goal of this dissertation work is to investigate heteroepitaxial growth of STO and BST thin films by using plasma-enhanced metalorganic chemical vapor deposition (PE-MOCVD) and to study microstructural and electrical properties of the films for applications in yttrium barium copper oxide (YBCO) based multi-layer HTSC devices and monolithic uncooled IR array sensors.; MOCVD/PE-MOCVD systems were designed and installed to meet the growth requirements for the BST films, CeO{dollar}sb2{dollar} buffer layer and multi-layer structures. The deposition conditions were optimized for uniform and high quality epitaxial growth on a large scale wafer (up to 5") based on gas flow pattern simulation. A surface smoothing process for YBCO films was developed, which improved the quality of subsequently grown BST films without deteriorating the superconducting properties of the YBCO films. For the first time, high quality STO/YBCO and BST/YBCO structures were epitaxially grown on LaAlO{dollar}sb3{dollar} substrates by PE-MOCVD. Neither impurity phases nor misorientation was found in the heterostructures. Atomically abrupt interfaces were observed and characterized by high resolution transmission electron microscopy.; Two predominant transport mechanisms, ohmic and bulk-limited Poole-Frenkel emissions, were identified in the Pt/STO/YBCO structure. The leakage current density across the SrTiO{dollar}sb3{dollar} films was {dollar}sim1times10sp{lcub}-6{rcub}{dollar} A/cm{dollar}sp2{dollar} at 2V operation. At a signal frequency of 100 KHz, a dielectric constant as high as 315 was achieved for the STO film. The electric property and dielectric behavior of the BST films were studied using I-V and C-V characterization at different temperatures and frequencies. The leakage current density across the BST films was {dollar}sim1times10sp{lcub}-7{rcub}{dollar} A/cm{dollar}sp2{dollar} at 2V operation. In particular, Ba{dollar}sb{lcub}1-rm x{rcub}{dollar}Sr{dollar}sb{lcub}rm x{rcub}{dollar}TiO{dollar}sb3{dollar} films with x = 0.25 exhibited sharp Curie transitions at temperatures around 37{dollar}spcirc{dollar}C, indicating the potential applicability for the fabrication of monolithic uncooled IR focal plane arrays. An epitaxial CeO{dollar}sb2{dollar} thin film was grown on yttria-stabilized zirconia (YSZ) substrate as a buffer layer for YBCO growth. Finally, a multi-layer structure of YBCO/STO/YBCO/CeO/YSZ was demonstrated by MOCVD/PE-MOCVD for potential multi-layer HTSC device applications.