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Increased electromechanical coupling in w−ScAlN

Gunilla Wingqvist, Ferenc Tasnádi, Agne Zukauskaite, Jens Birch, Hans Arwin, and Lars Hultman

        

Applied Physics Letters 97, 112902 (2010)

                          

The thin film electroacoustic technology and the use of wurtzite semiconductors (namely AlN) has established a sector within the piezoelectric industry, specifically through the release of the thin film bulk-acoustic resonator duplex filters for the use in mobile phones. AlN has proven to be a superior material due to high acoustic and dielectric quality and compatibility with the electronic circuit fabrication. However, a limiting factor of AlN, and hence the whole thin film electroacoustic technology as such, is its low electromechanical coupling factor of 6%–7%, which is the determining factor for bandwidth in filters.
    We present the promise of superior electromechanical coupling, in w−ScAlN by studying its dielectric properties. w−ScAlN (0<Sc content<0.3) thin films grown by dual reactive magnetron sputtering exhibited low dielectric losses along with minor increased dielectric constant (epsilon). Ellipsometry measurements of the high frequency epsilon; showed good agreement with density function perturbation calculations. Our data show that the electromechanical coupling factor will improve from 7% to 10% by alloying AlN with up to 20 mol % ScN.


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