Properties and applications of singly rotated GaPO4 resonators

The novel piezoelectric crystal gallium orthophosphate (GaPO₄) shows very promising properties for resonator applications. Advantages over quartz are temperature stability up to 970°C, higher electromechanical coupling coefficients and lower damping. Singly rotated Y-cut resonators with different rotating angles are investigated: Y-84° resonators show low electromechanical coupling coefficients and Q factors in the order of millions, but also high drive level dependencies (DLD). Y-15°45´ resonators operating at 10 MHz in the third overtone, mounted in HC-52/U crystal holders show in comparison to quartz resonators in the same crystal holder low motional resistances of about 30 Ω and Q factors around 200000. Because of the high coupling coefficients this resonators can be used for VCXO applications with very high pulling ranges up to 1500 ppm. The DLD of this high coupled resonators are very low. Resonators with a cut angle of about Y+27° show no frequency jumps and a very linear frequency dependence on temperature in a temperature range from room temperature up to 600°C.