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The growth, dielectric and lattice dynamical properties of strontium titanate and barium strontium titanate thin films.

机译：钛酸锶和钛酸锶钡薄膜的生长，介电和晶格动力学性质。

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摘要

Ferroelectric materials have become increasingly important in microelectronic applications, such as dynamic random access memory, ferroelectric random access memory, and tunable microwave devices. This requires the growth of high quality ferroelectric thin films, as well as fundamental understanding of their structural and dielectric properties, which often differ from those in respective bulk materials. The present thesis focuses on the investigation of the perovskite type ferroelectrics strontium titanate, SrTiO3 (STO) and barium strontium titanate, BaxSr1− xTiO3 (BST). Pulsed laser deposition is considered as one of the most advantageous methods for the growth of thin ferroelectric films, and was used to produce STO films of high quality for this thesis. Influence of several deposition conditions, such as type of substrate, deposition temperature and chemical treatments of the substrate were investigated to determine their effects on the structural and electrical properties of STO films and to optimize deposition process and improve film quality.; The surface morphology of films was studied by atomic force microscopy. X-ray diffraction was used to study their crystalline structure. It is shown in this thesis that the substrate has a pronounced effect on the crystalline quality and surface morphology of the film. Temperature and electric field dependencies of dielectric constant and loss tangent in STO films were studied by low frequency electric measurements. Improvements of the measured dielectric properties are correlated to the film deposition parameters.; Raman spectroscopy was used to characterize the film structure and study the lattice dynamics of the thin films. Raman spectra show the STO films grown on STO single crystal substrates have a structural phase transition near the phase transition temperature in bulk STO. The soft TO1 phonon, related to the ferroelectric state, was observed in the STO thin films. Raman results of the soft-mode study show a strong correlation between the measured soft-mode and the dielectric properties, demonstrating the Lyddane-Sachs-Teller relation is obeyed in STO thin films. The TO1 phonon in thin films is observed at a higher frequencies than in bulk STO, which is consistent with the reduction of the measured dielectric constant in thin films compared to bulk.; Growth and characterization techniques developed for STO thin films were extended to BST. The soft-mode is observed in Raman spectra of BST thin films of Ba compositions x = 0.05, 0.2 and 0.5 deposited on STO substrates. Dielectric properties were correlated to the Raman spectroscopy data. According to results of Raman spectroscopy and dielectric measurements, the ferroelectric phase transition occurs over a broad range of temperatures in thin films, which is different from bulk behaviour.
机译：铁电材料在微电子应用中已变得越来越重要，例如动态随机存取存储器，铁电随机存取存储器和可调微波设备。这就要求高质量铁电薄膜的生长，以及对它们的结构和介电性能的基本了解，而这通常不同于各自的块状材料。本文主要研究钙钛矿型铁电体钛酸锶锶SrTiO 3 （STO）和钛酸锶钡钡Ba x Sr < sub> 1- x TiO 3 （BST）。脉冲激光沉积被认为是最薄的铁电薄膜生长方法之一，并被用于生产高质量的STO薄膜。研究了几种沉积条件的影响，例如衬底的类型，沉积温度和衬底的化学处理，以确定它们对STO膜的结构和电性能的影响，并优化沉积过程并提高膜质量。通过原子力显微镜研究了膜的表面形态。 X射线衍射用于研究其晶体结构。本论文表明，基材对薄膜的晶体质量和表面形态具有明显的影响。通过低频电测量研究了STO薄膜中介电常数和损耗角正切的温度和电场依赖性。所测量的介电性能的改善与膜沉积参数相关。拉曼光谱法用于表征薄膜结构并研究薄膜的晶格动力学。拉曼光谱表明，在STO单晶衬底上生长的STO膜在本体STO中的相变温度附近具有结构相变。在STO薄膜中观察到与铁电态有关的柔软的TO 1 声子。软模研究的拉曼结果表明，所测得的软模与介电性能之间具有很强的相关性，这表明STO薄膜符合Lyddane-Sachs-Teller关系。薄膜中的TO 1 声子的频率要高于体STO中的频率，这与薄膜中所测量的介电常数相比于体中STO的降低是一致的。为STO薄膜开发的生长和表征技术已扩展到BST。在沉积在STO基板上的Ba组成x = 0.05、0.2和0.5的BST薄膜的拉曼光谱中观察到了软模。介电性能与拉曼光谱数据相关。根据拉曼光谱和介电测量的结果，铁电相变发生在薄膜的较宽温度范围内，这与整体行为不同。

著录项

  • 作者

    Clark, Anna Maria.;

  • 作者单位

    The Pennsylvania State University.;

  • 授予单位 The Pennsylvania State University.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2001
  • 页码 128 p.
  • 总页数 128
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

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