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

ABSTRACT

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 La₃Ga_5.5Ta_0.5O₁₄ (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.

KEYWORDS:

• LGT crystal
• bulk acoustic wave resonator
• resonator quality factor
• crystal quality

Acknowledgements

Dr B. Gauthier-Manuel (from FEMTO-ST) is gratefully acknowledged for his help and advice for IR and UV–VIS spectra. Our thanks also go to Dr C. Klemenz Rivenbark for very profitable talks about crystal growth of LGT.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was funded by the ‘Agence Nationale de la Recherche’ in the framework of a French research program ASTRID (ANR-12-ASTR-0030-02, supported by French MOD through DGA) with the project entitled ‘ECLATEMPS2012’.