Growth and Properties of Li₂B₄O₇ Single Crystal for SAW Device Applications

Abstract

Large Li 2 B 4 O 7 single crystals, up to 45 mm in diameter, have been successfully grown along the X- and Z-axis by Czochralski technique. Fundamental phsyical and chemical properties were determined, and basic SAW properties were studied for the various surface orientations and SAW propagation directions from theoretical and experimental points of view. It was found that there were useful substrate orientations for SAW resonators and narrow bandpass SAW filters around the rotated X-cut, Z-propagation, where SAW propagation delay time was a parabolic function of temperature and SAW coupling factor k 2 was approximately 1%. When a SAW propagates along the Z-direction on the 28° rotated X-cut substrate, the temperature coefficient of delay time (TCD) is zero at 20°C and the second order TCD is 0.27 ppm/°C 2 , k 2 is 0.8% and SAW velocity v s is 3470 m/s. The bulk wave spurious signal response level is lower by -20 dB than the SAW fundamental response level.