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      • Theses - Graduate Program in Materials Science and Nanotechnology
      • Graduate Program in Materials Science and Nanotechnology - Master's degree
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      Low temperature growth, characterization and applications of rf-sputtered SrTiO3 and BaSrTiO3 thin films

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      Author
      Bayrak, Türkan
      Advisor
      Bıyıklı, Necmi
      Date
      2016-03
      Publisher
      Bilkent University
      Language
      English
      Type
      Thesis
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      Please cite this item using this persistent URL
      http://hdl.handle.net/11693/28990
      Abstract
      Among the several perovskite ferroelectric oxides, SrTiO3 (STO) and BaSrTiO3 (BST) thin lms have attracted signi cant attention due to their potential applications in oxide-based electronics. However, reliability and performance of STO and BST thin lms depend usually on the precise knowledge of microstructure, as well as optical and electrical properties. STO and BST thin lms were deposited at room-temperature on Si (100), UVgrade fused silica, quartz substrates and TiO2 nano bers by radio frequency (RF) magnetron sputtering using di erent plasma power, oxygen mixing ratios (OMRs) and deposition pressure levels. As-deposited thin lms showed amorphous-like nanocrystalline microstructure almost independent of the deposition conditions. In uence of post-deposition annealing at various temperatures of RF sputtered STO thin lms were also investigated. All lms were found to be highly transparent (>75%) in the visible region, and both STO and BST lms exhibited well de ned main absorption edges: the calculated indirect and direct band gaps for STO lms were in the range of 2.32 to 4.55 eV. The refractive index of the STO lms increased with OMR and post-deposition annealing for 3 mTorr deposition for STO, BST and STO annealing study. However, there is no correlation for 5 mTorr deposition. The refractive indices of BST lms were in the range of 1.90-2.07 at 550 nm depending on their deposition conditions. The optical band gap of the BST lms were calculated the ranging in 3.60 to 4.30 eV. Electrical dielectric constant values of the STO thin lms were extracted from frequency or voltage dependent capacitance measurements using micro-fabricated Ag/STO/p-Si device structures. High dielectric constant values reaching up to 100 were obtained. All STO samples exhibited more than 2.5 C/cm2 charge storage capacity and low dielectric loss (less than 0.07 at 100 kHz). Post-deposition annealing at 800oC for 1 h resulted in polycrystalline BST thin lms with increased refractive indices and dielectric constants, along with reduced optical transmission values. Frequency dependent dielectric constants were found to be in the range of 46-72, and the observed leakage current was very small,less than 1 A. Our experimental results show that these low temperature grown STO and BST lms have the potential for various electrical applications.
      Embargo Lift Date
      2018-03-17
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