LiTaO3 single crystals treated by Vapour Transport Equilibration for temperature-compensated SAW devices

Vapor Transport Equilibration was used to control the Li2O concentration in LiTaO3 single crystals. Li concentration was estimated from Curie Temperature and by means of Raman spectroscopy. Temperature coefficient of frequency TCF was determined from the frequency response of SAW devices measured versus temperature and a correlation between the temperature coefficient of frequency and LiTaO3 non-stoichiometry was studied. Experimental results showed that the temperature coefficient of frequency of treated LiTaO3 crystals was strongly dependent on the Li2O concentration. For example, in these case of the 36°Y cut crystals commonly used in SAW industry, it was moved from -35 ppm/°C for the congruent and commercially available crystal with 48.5 mol% of Li2O to -7 ppm/°C for the treated crystals with 49.43 mol% of Li2O. Moreover, experimental results show that the insertion losses were reduced suggesting the enhancement of the crystalline quality of the treated crystals. Note that temperature coefficient of an almost stoichiometric crystal (49.95 mol% of Li2O) was -13 ppm/°C.