Properties of pseudomode surface acoustic waves on ST-cut quartz substrates and the effects of the thicknesses of metallic films

The present study utilized an impedance matrix method to solve the properties of a surface acoustic wave (SAW) in a piezoelectric medium. By introducing complex wavenumbers, pseudo-SAWs (PSAWs) and high-velocity pseudo-SAW (HVPSAWs) with higher phase velocity and lower propagation loss can be achieved for certain propagation directions in ST-cut quartz. It is also found that, when a PSAW is excited on ST-cut 90°X propagation, the quartz substrate exhibits the characteristics of the existence of only the shear horizontal component, no spurious response, and zero-power flow angle (PFA). Combining a heavy-metal electrode such as gold (Au) of suitable thickness, the electromechanical coupling factor of PSAWs can be enhanced. The enhancement is about 2.5 times larger than that of conventional SAWs on an ST-X substrate with an aluminum (Al) electrode. Published in Russian in Akusticheskiĭ Zhurnal, 2006, Vol. 52, No. 3, pp. 401–407. The text was submitted by the authors in English.