Stoichiometric Lithium Niobate Crystals: Towards Identifiable Wireless Surface Acoustic Wave Sensors Operable up to 600 °C

Wireless surface acoustic wave (SAW) sensors constitute a promising solution to some unsolved industrial sensing issues taking place at high temperatures. Currently, this technology enables wireless measurements up to 600-700 °C at best. However, the applicability of such sensors remains incomplete since they do not allow identification above 400 °C. The latter would require the use of a piezoelectric substrate providing a large electromechanical coupling coefficient K
²
while being stable at high temperature. In this article, we investigate the potentiality of stoichiometric lithium niobate (sLN) crystals for such purpose. Raman spectroscopy and X-ray diffraction attest to the fact that sLN crystals withstand high temperatures up to 800 °C, at least for several days. In situ measurements of sLN-based SAW resonators conducted up to 600 °C show that the K
²
of these crystals remains high and stable throughout the whole experiment, which is very promising for the future achievement of identifiable wireless high-temperature SAW sensors.