Abstract
Thin film bulk acoustic wave (BAW) resonators and filters are appropriate for mobile communication systems operating at high frequencies between 0.5 and 10 GHz. c-axis orientated AlN films are used for medium bandwidth applications. Electromechanical coupling factors k/sub t/ of 0.25/spl plusmn/0.03, which are close to the bulk data, have been found in AlN thin films using optimum sputter conditions. The correlation between k/sub t/ and AlN film orientation is discussed. Resonator Q values of approx. 450 are reported at 2.6 GHz and a Q of 250 was realized at 9.2 GHz. A physical model is shown to accurately predict the frequency responses of BAW resonators and band-pass filters. For wide bandwidth applications PbZr/sub x/Ti/sub 1-x/O/sub 3/ (PZT) films are investigated. They exhibit large coupling coefficients.
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