PSAW and HVPSAW behaviour in layered structures

Abstract

The Pseudo-SAWs (PSAW) have been extensively used since the 80's specially for high frequency SAW applications. The regular PSAW and the recently introduced High Velocity Pseudo-SAWs (HVPSAW), with phase velocities circa 40% (PSAW) and 100% (HVPSAW) higher than the phase velocities of the SAWs, permit the construction of higher frequency devices using the same photolithographic processes used for SAW devices. The resulting high frequency, high performance, and low loss devices have found immediate applications in communication equipment such as: cellular and mobile telephony, pagers, Local Area Networks (LANs), cordless phones, Global Positioning Systems (GPS), and security systems. Metallic layers are essential parts of all SAW devices, playing fundamental roles in the excitation, propagation, and reflection of the SAW signal. The careful analysis of the layered structure allows the understanding of the PSAW and HVPSAW relationship with higher order lossless SAW modes, also known as Generalized SAW modes (GSAW). This original analysis shows details of PSAWs' and HVPSAWs' transitions to GSAWs through some significant examples. The analysis includes original data regarding the different surface acoustic modes which coexist for a certain layer thickness and material, including the pseudo waves. The current study discuss how the field polarization, the estimated power flow angle (PFA), the power distribution with depth, and the electromechanical coupling coefficient behave with layer thickness and layer material for the referred modes. The results presented herein find immediate interest and application in the design of low loss, high performance, high frequency SAW devices for recent wireless applications (communication, remote sensing, security).