Abstract
To obtain a high-performance surface acoustic wave (SAW) gyroscope substrate, the propagation characteristics and gyroscopic effect of Rayleigh waves in a 128°Y–X LiNbO3/SiO2/Si (LNOI) functional substrate were investigated with a three-dimensional finite element method. The influence of LNOI structural parameters on Rayleigh wave characteristics, including the phase velocity (vp), electromechanical coupling coefficient (K2) and temperature coefficient of frequency (TCF), were analyzed. The results demonstrate that the SiO2 layer compensates for the negative TCF of 128°Y–X LiNbO3 and enhances the K2 of the LNOI substrate. The Rayleigh wave velocity change of the LNOI substrate after rotations in different directions was studied. The gyroscope gain factor (η) represents the strength of the gyroscopic effect in the differential traveling wave SAW gyroscope and is defined. The ηy and ηz of the LNOI substrate with different structural parameters were investigated. Finally, an LNOI substrate with an hLN/λ of 0.2 and an hSiO2/λ of 0.05 was obtained by balancing the characteristic parameters, with a K2 of 3.96%, TCF of −18.75 ppm/°C and ηy of 0.26. The LNOI substrate has a better gyroscopic effect and temperature stability than the 128°Y–X LiNbO3 crystal. The LNOI substrate meets device miniaturization and integration needs.
Highlights
The surface acoustic wave (SAW) gyroscope is a novel inertial sensor based on the SAW gyroscopic effect in which the Coriolis force causes the SAW velocity to change as the medium rotates [1]
Traveling wave SAW gyroscopes have attracted widespread attention because their output signal is easy to detect and temperature compensation can be achieved with a differential scheme [9,10]
Micromachines 2022, 13, 202 research groups have conducted intensive studies on designing interdigital transducers, placing metallic dot arrays on the surface of piezoelectric crystals, modulating amplitude using one-dimensional phononic crystal, and searching for high-performance piezoelectric substrate materials to further improve the performance of SAW gyroscopes [11–15]
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Smart-cut technology is applied to prepare the LNOI substrate with a nanoscale LN film He ions are injected into the LN wafer, and a SiO2 thin film is deposited on the silicon substrate using plasma-enhanced chemical vapor deposition (PECVD). X-cut LNOI substrate has a K2 value of up to 35% and a TCF value of −0.2 ppm/◦ C for shear-horizontal (SH) waves [31] It is a high-performance substrate for preparing SH-SAW and Lamb wave devices with a wide band and low loss [32,33]. This LNOI substrate can achieve a larger K2 and lower TCF by optimizing the structural parameters, providing a new possibility for obtaining a high-performance substrate for SAW gyroscopes. The thicknesses of various layers were optimized to obtain an LNOI substrate with a high K2 and η and a low TCF
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