Model parameter extraction for obliquely propagating surface acoustic waves in infinitely long grating structures

Abstract

In this paper, we propose the use of the “longitudinal resonance condition” for the characterization of the two-dimensional propagation of surface acoustic waves (SAWs) in periodic grating structures, and also show a procedure for extracting parameters required in the behavior model from the full-wave analysis. The condition is given by β xp = π, where p is the grating period and β x is the wavenumber of the grating mode in the longitudinal direction (x). This is based on the fact that in conventional SAW resonators, acoustic resonances including transverse ones occur when β x is real but the longitudinal resonance condition is mostly satisfied. The longitudinal resonance condition is applied to a simple model, and the wavenumber β y in the lateral direction (y) is expressed as a simple function of the angular frequency ω. The full-wave analysis is applied for SAWs propagating in an infinite grating on a 128°YX-LiNbO3 substrate, and the anisotropy parameter γ is extracted by the fitting with the derived equation. The fitted result agrees well with the original numerical result. It is also indicated that γ estimated by this technique is significantly different from the value estimated without taking the effects of the grating structure into account.

Thin plate model for transverse mode analysis of surface acoustic wave devices

“…The derivation procedure for γ is given elsewhere. 16) Following these procedures, we determined these parameters for the Al grating (0.1p thickness) on the 128°YX-LiNbO 3 substrate as γ = 1.1364, c 45 = 0, e 34 = 0, ρ e = 0.6721, ρ u = 0.6955, and K 2 = 7.6% when c 44 is set to 1.1364e7.…”

“…The remaining parameter can be determined by a procedure proposed in another paper by the authors. 16) Then, the thin plate model is embedded in the partial differential equation (PDE) mode of COMSOL. By compar-ing the numerical and analytical results, the applicability of this method is verified.…”

Use of periodically slotted SiO2 in a layered surface acoustic wave structure for transverse mode suppression

“…9,[19][20][21] In addition, the flat slowness curve is effective in suppressing in-plane SAW diffraction generating lateral SAW leakage. 22,23) From this, flattening the slowness curve is expected to be also important for achieving a high-quality factor Q of SAW devices. 24) The use of low-cut LT such as 20-LT has also received attention because of its intrinsically larger electro-mechanical coupling factor k 2 .…”

Model parameter extraction of lateral propagating surface acoustic waves with coupling on SiO2/grating/LiNbO3structure

“…Since the main and transverse resonances occur when β x ∼ π=p, we will characterize lateral SAW propagation when β x is fixed at π=p (longitudinal resonance condition). 26) Figure 3 shows, as an example, calculated frequency dispersion of β y for SAWs in the IDT region of the SiO 2 -overlay=Cu-grating=128-LN structure. The calculation is performed with the COMSOL, and the width l Cu and thickness h Cu of grating electrodes are 0.5p and 0.06p, respectively, and the SiO 2 thickness h SiO2 is 0.6p, where p = 2 µm.…”

“…The model is similar to the scalar potential (SP) theory 15,25) however it allows us to take coupling of multiple SAW modes into account in addition to various effects such as SAW reflection and excitation at electrode edges. 26,27) First, it is detailed how to determine parameters appearing in the extended thin plate model. Then it is shown how parameters appearing in the model change with the structural parameters, namely h SiO2 , h Cu , and θ.…”