Effects of the Langatate crystal quality on the resonance frequency stability of bulk acoustic wave resonators

In the time and frequency domain, we need ultrastable crystal resonators embedded in Ultra Stable Oscillators (USO), working at 10 MHz and exhibiting excellent short-term stabilities. Up to now, the quartz crystal fulfils its function. But, Langatate La3Ga5.5Ta0.5O14 (LGT) piezoelectric crystal seems to allow better performances with high quality material. The applications of this domain require high-quality material with reproducible properties. The LGT crystal is grown by the Czochralski method. Its physical and chemical properties and specificities of this growth process induce defects. They can react as ionic and electronic charge carriers and generate conductive losses. To assess the quality of the LGT crystal, we recorded the UV-VIS and IR transmission spectra and measured the electrical resistivity. At least, Y-cut resonators have been designed and manufactured to study the quality of the 10 MHz resonance, particularly its Q-factor, directly linked to the stability of the USO. We studied the effect of air annealing on the resonance frequency quality.