Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/2600
Title: Pulsed laser deposition and characterization of LiNbO₃films for application in surface acoustic wave device
Authors: Lam, Hi-ki
Keywords: Acoustic surface wave devices
Pulsed laser deposition
Thin films
Hong Kong Polytechnic University -- Dissertations
Issue Date: 2005
Publisher: The Hong Kong Polytechnic University
Abstract: Lithium niobate (LiNbO₃) is a well-known ferroelectric oxide displaying prominent piezoelectric, pyroelectric, electro-optic, photo-elastic and nonlinear optical effects. LiNbO₃ has been widely used for the fabrication of optical waveguide, optical switch, optical modulator and surface acoustic wave (SAW) devices, and exhibits important technical value and profound developing prospect in the fields of acoustics, optical communications, integrated optics and nonlinear optics. In this project, the study of pulsed laser deposition (PLD) of LiNbO₃ films on sapphire and diamond substrates and the structural characterization were carried out. Application of the synthesised LiNbO₃ films in fabrication of SAW devices was also tackled. For different applications, different orientations of LiNbO₃ epitaxial films may be needed. By controlling oxygen partial pressure during PLD, orientation controllable deposition of epitaxial LiNbO₃ films on sapphire substrates has been achieved. The interfacial structures of LiNbO₃ on sapphire substrates with different orientation relationships grown under different conditions were examined by transmission electron microscopy, and the mechanism for different growth orientations has been discussed. In addition, a two-step growth, i.e., a seed layer deposition at 500 m Torr for 15 s plus 12 min deposition at 100 m Torr oxygen pressure, was developed to grow surface-flat c-oriented LiNbO₃ epitaxial films on sapphire substrates. A two-step growth technique was implemented for LiNbO₃ film growth on polycrystalline diamond substrates, and highly c-oriented LiNbO₃ films have been achieved by introducing a pulsed laser deposited aluminium oxide (Al₂O₃) buffer Layer. The Al₂O₃ buffer layer was used to protect the diamond surface from oxidation during LiNbO₃ film growth at high temperature in oxygen ambient, due to the fact that Al₂O₃ is a good oxygen diffusion barrier. In addition, the nature of amorphous structure of Al₂O₃ layer can eliminate the heritage of polycrystalline structure of diamond and make the growth of highly c-oriented LiNbO₃ films to be possible. The mechanism of highly c-oriented LiNbO₃ film growth on polycrystalline diamond substrate was interpreted. SAW devices utilizing the stacked structure of LiNbO₃/Al₂O₃ on diamond substrates have been fabricated by introducing two aluminium interdigital transducers (IDTs). The IDTs are fabricated by depositing 100 nm A1 film on the surface of the LiNbO₃ film followed by photolithography and wet etching process. The SAW characteristics were characterized by microwave network analyzer, and the measured scattering parameters were used to evaluate the SAW device propagation property. Based on our preliminary results on the growth and characterization of LiNbO₃ films on Al₂O₃ buffered polycrystalline diamond substrate, we conclude that the stacked structure of LiNbO₃/Al₂O₃/diamond may be a potential candidate for the fabrication of high frequency SAW devices.
Description: xii, 85 leaves : ill. ; 30 cm
PolyU Library Call No.: [THS] LG51 .H577M AP 2005 LamH
URI: http://hdl.handle.net/10397/2600
Rights: All rights reserved.
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