GaPO4 resonators with Q factors of some millions in the fundamental mode

Gallium orthophosphate (GaPO₄) is a novel, synthetic piezoelectric crystal which is homeotypic to quartz. Most physical properties are stable until 970°C. New applications are thickness shear resonators (fundamental mode) with a cut angle near Y-84° and very low coupling coefficients which have shown very high Q factors (Reiter et al, Proc. 15th Euro. Freq. and Time Forum, pp. 50-54, 2001), and thus it is called the HiQ cut. The temperature behavior and the electrical equivalent circuits of some new HiQ resonators are investigated with a HP network analyzer and an oscillator. The oscillator had a special design because of the high motional resistances of the HiQ resonators (several kΩ at normal pressure conditions which decrease to several hundreds of Q under vacuum conditions). The highest Q factors (up to 13×10⁶) are obtained with the network analyzer at a pressure of about 0.04 mbar. The next measurements are focused on short term stability to obtain oscillators with very low noise.