Abstract
High temperature characteristics of langasite surface acoustic wave (SAW) devices coated with an AlN thin film have been investigated in this work. The AlN films were deposited on the prepared SAW devices by mid-frequency magnetron sputtering. The SAW devices coated with AlN films were measured from room temperature to 600 °C. The results show that the SAW devices can work up to 600 °C. The AlN coating layer can protect and improve the performance of the SAW devices at high temperature. The SAW velocity increases with increasing AlN coating layer thickness. The temperature coefficients of frequency (TCF) of the prepared SAW devices decrease with increasing thickness of AlN coating layers, while the electromechanical coupling coefficient (K2) of the SAW devices increases with increasing AlN film thickness. The K2 of the SAW devices increases by about 20% from room temperature to 600 °C. The results suggest that AlN coating layer can not only protect the SAW devices from environmental contamination, but also improve the K2 of the SAW devices.
Highlights
A wireless and battery-free sensor which can stably operate in harsh environments is in great demand for many industries, in aerospace, automotive, and energy industries
Sensors based on surface acoustic wave (SAW) technology are attractive due to its characteristics of passivity, wireless, high sensitivity, high precision, and good reproducibility
Peng [2] and Thiele [3] fabricated a high temperature SAW gas sensor with LGS materials. Another LGS SAW gas sensor for harsh environments was reported by Greve et al [4]
Summary
A wireless and battery-free sensor which can stably operate in harsh environments is in great demand for many industries, in aerospace, automotive, and energy industries.Sensing of physical properties such as temperature, strain, and vibration are useful for dynamic and static health monitoring and maintenance of the target components. The operation temperature is strongly dependent on the phase transition temperature of the piezoelectric substrate. Lanthanum gallium silicate (La3 Ga5 SiO14 , LGS, langasite) has been thought as one of the most attractive materials in high temperature application due to the absence of a phase transition from room temperature up to its melting temperature (1450 ◦ C), good temperature stability, and large coupling constant K2 (0.34%), which is two times larger than that of ST-quartz (0.14%) [1]. Peng [2] and Thiele [3] fabricated a high temperature SAW gas sensor with LGS materials Another LGS SAW gas sensor for harsh environments was reported by Greve et al [4]. We reported SAW strain sensors based on different cuts of LGS substrate at high temperature [5]
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