6D-1 Equivalent Circuit Model and Parameter Extraction for HVPSAW

Characterized by phase velocities on the order of 1frac12 to 2 times those of conventional surface acoustic waves (SAWs), high velocity pseudo-SAWs (HVPSAWs) make proportionally higher operating frequencies achievable using present fabrication capabilities. This promise of comparatively higher operating frequencies, using identical fabrication technologies, has focused recent efforts on identifying new HVPSAW orientations of common SAW substrate materials including lithium tantalate (LTO). The authors have previously reported on the existence of low-attenuated, strongly-coupled HVPSAW along the (0deg, 120deg, Psi) orientations of LTO for periodic gratings of thick aluminum, gold (Au), and platinum electrodes. These new HVPSAW orientations were identified using hybrid finite and boundary element method (FEM/BEM) techniques. Rigorous FEM/BEM techniques are well suited to the investigation of HVPSAW mode characteristics but are computationally too intensive to perform rapid simulations needed during device design iterations. In contrast, the transmission line (TL) based equivalent circuit model (ECM) is ideally suited to device and circuit-level simulations. However, along HVPSAW orientations, significant bulk acoustic wave (BAW) leakage and/or scattering may occur, and the traditional ECM does not model these effects. In this paper, a new HVPSAW ECM is proposed that includes attenuation due to leakage and scattering of HVPSAW power into BAWs. Modeling parameters for HVPSAW along the (0deg, 120deg, 45deg) orientation of LTO have been extracted for propagation beneath 4-electrode-per-wavelength gratings comprised of Au electrodes ranging in thickness from 1% to 3.5% of the HVPSAW wavelength, lambda. Open- and short-circuit grating dispersion relationships calculated using extracted ECM parameters agree to within 1.1% of values predicted by FEM/BEM analysis for an infinitely long 4-electrode-per-wavelength grating comprised of Au electrodes of thickness h/lambda = 1.72%.- For this orientation and electrode thickness combination, FEM/BEM calculated and experimentally measured IDT admittance responses show good agreement, with nearly identical admittance responses when variations of metallization ratio and thickness from nominal values are taken into account