Mode selection for a piezoelectric layer in a bulk-acoustic-wave composite acoustic resonator

An analysis is made of the mode selection for a thin piezoelectric layer in a bulk-acoustic-wave composite layered acoustic resonator by transformation of the impedance using a set of quarter-wave layers. Depending on the number of layers, the impedance of the substrate on which the piezoelectric layer is deposited may be abruptly increased or sharply reduced. This serves to simulate a “fixed” or “free” surface. As a result, a mechanically strong resonator structure is produced, operating at the natural frequencies of a thin piezoelectric layer. A numerical simulation is made of multilayer structures formed by alternating quarter-wave layers of LiNbO₃ and LiTaO₃. It is shown that if these layers are of micron thickness and there is a sufficiently large number of them, the acoustic properties of the substrate do not influence the frequency characteristics and Q factor of the thin piezoelectric vibrating layer in the microwave range. Pis’ma Zh. Tekh. Fiz. 23, 35–41 (October 12, 1997)