High temperature piezoelectric glass-ceramics for SAW sensors
Résumé
During the last ten years, interest in sensors based on surface acoustic waves (SAW) has been growing. Basically, these devices use two set of interdigitate electrodes on a piezoelectric substrate to generate, propagate and receive an acoustic signal (Figure 1). Changes in propagation conditions, by mean of a sensitive zone located between the emitter and the receiver, allow the detection and the quantification of an external solicitation (pressure, temperature, environmental composition.…). Figure 1 Numerous applications for these devices, at room or moderate temperatures, already exist. Extension of these applications at high temperatures is inhibited by a lack of suitable piezoelectric substrate. Indeed, most of conventional piezoelectric are ferroelectric ceramics. Their use in temperature is limited by their Curie point, which is usually well below 400 - 500°C. For the few ferroelectrics exhibiting high Curie temperatures, their stability over time is poor due to depolarization. Alternatively, highly stable non-ferroelectric singles crystals can be used, but they are expensive and not easy to process. This presentation aim at showing the good potential of highly textured piezoelectric non ferroelectric glass ceramics as substrates for SAW sensors able to work up to 800°C. It will focus of the control of their elaboration process, on their properties and applications as temperature, pressure or gas sensors.