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Title: Preparation and Characterization of Ferroelectric Thin Films for Tunable and Pyroelectric Applications
Keywords: Ferroelectric Thin Films, Pulsed Laser Deposition, Pyroelectric Effect, Tunable Application
Issue Date: 7-Jan-2011
Source: WANG SHIJIE (2011-01-07). Preparation and Characterization of Ferroelectric Thin Films for Tunable and Pyroelectric Applications. ScholarBank@NUS Repository.
Abstract: Ferroelectric thin films have been extensively studied for their wide applications in pyroelectric detectors and tunable devices. In the present work, pulsed laser deposition (PLD) technique has been employed to deposit ferroelectric Ba(Ti0.85Sn0.15)O3 (BTS) thin films and heterostructures. BTS thin films have been successfully deposited on LaNiO3 (LNO)/SiO2/Si substrates by PLD. The role of oxygen pressure and the effect of thickness on the microstructure, electrical and pyroelectric properties of BTS thin films have been systematically studied. BTS thin films deposited at higher oxygen pressures are found to possess better electrical properties. The study on the thickness dependence of dielectric and pyroelectric properties shows that both LNO and BTS thin films are under tensile stress and they decrease with increasing thickness of the BTS films. Larger dielectric constant and higher pyroelectric coefficient are obtained for BTS thin films with higher thickness, and the effect of stress is considered to be the dominant factor. The substrate temperature is also found to play an important role in structural evolution of BTS thin films. In addition, Pt and LNO are used as bottom electrodes to investigate their influences on conduction mechanisms. For the Pt/BTS/LNO structure, the leakage current shows bulk-limited space-charge-limited-current (SCLC) behavior at positive bias while interface-limited Fowler-Nordheim (FN) tunneling at negative bias. For the Pt/BTS/Pt structure, the dominant conduction mechanism is mainly controlled by the bulk-limited SCLC and/or Poole-Frenkel (PF) emission. We have studied Bi1.5Zn1.0Nb1.5O7 (BZN) -buffered BTS heterostructures deposited on Si-based substrates. The BZN layer has been proven to be a high-quality growth template and effective diffusion barrier to reduce the dielectric loss and leakage current of the BTS films. Improved tunable and pyroelectric properties of BTS films have been achieved by controlling the thickness of the BZN layer. The leakage mechanism of the Pt/BTS/BZN/LNO heterostructure has been studied at the temperature range from 303 to 403 K. At positive bias and high electric fields, the conduction mechanism is controlled by SCLC; while at negative bias and high electric fields, FN tunneling is the dominant conduction mechanism. At low electric fields, the leakage is controlled by the Ohmic contact irrespective of the sign of the bias field. La has been selected as a dopant to tailor BTS thin films through the effect of compositional modification. 1 mol % La-doped BTS (BLaTS) thin films have been successfully deposited on LNO/SiO2/Si substrates by PLD. It is found that BLaTS films show highly (h00) textured orientation. Higher crystallization quality is obtained at higher deposition temperature. Sharp interface between as-deposited BLaTS thin films and the bottom LNO layers are confirmed. In addition, BLaTS thin films demonstrate lower loss tangent than that of pure BTS. This is attributed to the reduction in defects. La dopant intensifies the relaxor behavior of BTS thin films as reflected by the more diffused phase transition between the ferroelectric and paraelectric states. The present study is expected to help better understand the potential of BTS thin films. The efforts toward improving the tunable and pyroelectric properties of BTS thin films have demonstrated the appealing prospective applications of BTS thin films in the relevant fields.
Appears in Collections:Ph.D Theses (Open)

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