Pulsed laser deposition and characterization of LiNbO3 films for application in surface acoustic wave device

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Pulsed laser deposition and characterization of LiNbO3 films for application in surface acoustic wave device

 

Author: Lam, Hi-ki
Title: Pulsed laser deposition and characterization of LiNbO3 films for application in surface acoustic wave device
Year: 2005
Subject: Acoustic surface wave devices
Pulsed laser deposition
Thin films
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Applied Physics
Pages: xii, 85 leaves : ill. ; 30 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1793805
URI: http://theses.lib.polyu.edu.hk/handle/200/1792
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.

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