Mode Analysis of Pt/LGS Surface Acoustic Wave Devices

Abstract

Platinum (Pt) gratings on langasite (LGS) substrates are a widely used structures in high temperature surface acoustic wave (SAW) devices. Multiple modes can be excited in Pt/LGS SAW devices owing to the heavy weight of the Pt electrode and leaky waves in the LGS substrate. In this work, we report on a detailed mode analysis of Pt/LGS SAW devices, where three commonly used LGS cuts are considered. A three-dimensional (3D) finite element method (FEM) numerical model was developed, and the simulation and experiment results were compared. The experiment and simulation results showed that there are two modes excited in the Pt/LGS SAW devices with Euler angle (0°, 138.5°, 27°) and (0°, 138.5°, 117°), which are Rayleigh-type SAW and SH-type leaky wave, respectively. Only the Rayleigh-type mode was observed in the Pt/LGS SAW devices with Euler angle (0°, 138.5°, 72°). It was found that the acoustic velocities are dependent on the wavelength, which is attributed to the change of wave penetration depth in interdigital transducers (IDTs) and the velocity dispersion can be modulated by the thickness of the Pt electrode. We also demonstrated that addition of an Al2O3 passivation layer has no effect on the wave modes, but can increase the resonant frequencies. This paper provides a better understanding of the acoustic modes of Pt/LGS SAW devices, as well as useful guidance for device design. It is believed that the Rayleigh-type SAW and SH-type leaky waves are potentially useful for dual-mode sensing applications in harsh environments, to achieve multi-parameter monitoring or temperature-compensation on a single chip.

Investigation of Temperature Sensing Capabilities of GaN/SiC and GaN/Sapphire Surface Acoustic Wave Devices

“…The GaN layer (1.2 µm thin) is placed on top of the substrate (SiC or Sapphire) domain, reduced to 50 µm thick. A perfectly matched layer (PML) of 10λ was introduced below, with the role to retain the wave reflections from the bottom [25]. The Boundary conditions imposed for the mechanical and electrical simulations are presented in Table 2.…”

Rational Design of a Surface Acoustic Wave Device for Wearable Body Temperature Monitoring

“…The IDT metallization ratio η was set to be 0.5. YX quartz was chosen as the piezoelectric substrate, resulting in a phase velocity v of 3159 m/s [21]. According to the following equation, the wavelength λ and the correspondence IDT width can be roughly determined for the FEM model,…”