Shear mode coupling and tilted grain growth of AlN thin films in BAW resonators |
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Authors: | Martin F. Jan M.-E. Rey-Mermet S. Belgacem B. Dong Su Cantoni M. Muralt P. |
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Affiliation: | Ceramics Lab., Ecole Polytech. Fed. de Lausanne, Switzerland; |
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Abstract: | Polycrystalline AlN thin films were deposited by RF reactive magnetron sputtering on Pt(111)/Ti electrode films. The substrates were tilted by an angle ranging from 40/spl deg/ to 70/spl deg/ with respect to the target normal. A low deposition temperature and a high sputter gas pressure were found ideal for tilted growth. The resulting grain tilt angle amounts to about half the substrate tilt angle. For coupling evaluation, 5 GHz solidly mounted resonator structures have been realized. The tilted grain AlN films exhibited a permittivity in the 9.5-10.5 range and loss tangent of 0.3%. Two shear modes as well as the longitudinal mode could be clearly identified. The coupling coefficient k/sub eff//sup 2/, of the fundamental thickness shear mode (TSO) was found to be about 0.5%, which is compatible with a c-axis tilt of about 6/spl deg/. |
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