A surface acoustic wave tag utilizing a multilayer structure of SiO2/Pt/128°YX-LiNbO3 for operation at 600 °C

This study addresses the issue of traditional surface acoustic wave (SAW) tag failure under high-temperature conditions by proposing a SAW tag based on a multilayer structure of SiO₂/Pt/128°YX-LiNbO₃. The structure has been simulated using the finite element method/wave-number domain analysis (FEM/WDA) approach, which reveal the effects of reflector topological parameters on the scattering characteristics of SAWs. Compared with Pt/128°YX-LiNbO₃, the bulk wave scattering in the multilayer structure is reduced by 50%. In the micro-nanofabrication of the tag, a low-roughness, high-density SiO₂ film is prepared using physical vapor deposition (PVD). Test results indicate that the tag exhibits a temperature coefficient of frequency (TCF) of -32.38 ppm/°C over a wide temperature range of 30-600°C. After undergoing thermal shock at 600 °C for 336 h, the time-domain reflection amplitude decreases by less than 1%, demonstrating that the SiO₂ protective layer effectively suppresses the high-temperature decomposition of LiNbO₃ and reduces the agglomeration rate of Pt electrodes. Experimental results confirm that the proposed high-temperature-resistant SAW tag maintains stable performance under prolonged exposure to 600 °C environments. The tag has been installed on the surface of a steel ladle in a steel plant, demonstrating excellent reliability in a vacuum degassing environment.