Angular dependence of surface acoustic wave characteristics in AlN thin films on a-plane sapphire substrates |
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Authors: | J Xu JS Thakur G Hu Q Wang Y Danylyuk H Ying GW Auner |
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Institution: | (1) Department of Electrical and Computer Engineering, Wayne State University, Detroit, Michigan 48202, USA |
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Abstract: | AlN thin films have been grown on a-plane sapphire (Al2O3(112̄0)) substrates. X-ray diffraction measurements indicate the films are fully c-plane (0001) oriented with a full width at half maximum of the AlN(0002) rocking curves of 0.92. The epitaxial growth relationships
have been determined by the reflection high energy electron diffraction analysis as AlN11̄00]//Al2O30001] and AlN112̄0]//Al2O311̄00]. Angular dependence of important surface acoustic wave (SAW) characteristics, such as the phase velocity and electromechanical
coupling coefficient, has been investigated on the AlN(0001)/Al2O3(112̄0) structure. While the SAW is excited at all propagation angles with an angular dispersion of the phase velocity in
the range of 5503–6045 m/s, a higher velocity shear-horizontal (SH) mode is observed only at 0°, 105° and 180° off the reference
Al2O311̄00] over a 180° angular period. The phase velocity of the SH mode shows dispersion (6089–6132 m/s) as a function of the
SAW wavelength. Temperature coefficients of frequency are also demonstrated for both modes.
PACS 81.15.Hi; 77.84.-s; 77.65.Dq |
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