Gallium phosphate, GaPO 4: a new piezoelectric crystal material for high-temperature sensorics

Abstract

Single-crystalline GaPO 4, gallium phosphate (more precisely gallium orthophosphate), is a new piezoelectric material which is very similar to quartz in its crystal structure but has a much higher thermal stability, a higher piezoelectric effect, larger electromechanical coupling constants and temperature-compensated cuts for bulk acoustic wave (BAW) and surface acoustic wave (SAW) applications. It is thus a promising material for sensor applications in the temperature range up to 900°C. The first products are already on the market: uncooled pressure sensors for combustion engines, with sensitivity and stability surpassing those attainable with quartz. As the crystal growth process is reaching larger quantity and higher quality, gallium phosphate will be the material for further new applications exceeding the possibilities of conventional materials.