Study on the frequency dependence of lateral energy leakage in RF BAW device by fast-scanning laser probe system

This paper describes the application of the developed fast-scanning laser probe system to the diagnosis of frequency dependence of lateral energy leakage occurring in RF BAW devices. According to wavenumber domain analyses, dispersion relation for the device under test is derived, the leakage behaviors at different frequencies are shown as images, and energy of each lateral mode is evaluated quantitatively. The cause of the lateral energy leakage and its frequency dependence are discussed. It is shown that the cause of lateral energy leakage is the higher order transverse modes which are not excited at frequency higher than a cut-off frequency (f_c) for the longitudinal extension mode. It is demonstrated that by using this laser probe system, the lateral energy leakage variation upon frequency can be seen intuitively, and the underlying mechanism for the leakage can be analyzed and explained clearly.