An Assessment of Lithium Tetraborate for SAW Applications

Abstract

X-cut 2-propagating lithium tetraborate (Li2B407) has a SAW coupling factor of 1.02X and parabolic delay/temperatur e b ehaviour with ~60 ppm variation between 0’ and 4OoC. Further measurements have now been made to assess this material for SAW device applications. The SAW response has a lower untuned insertion loss than quartz, with comparable temperature stability. Shear and longitudinal bulk waves are generated by interdigital transducers at significant levels. Modes propagating into the crystal can be suppressed by back-grooving. However, near its low frequency cut-off, t he shear vertical mode is beam steered parallel to the surface as a surface skimming bulk wave (SSBW). The SSBW response attenuates s trongly with t ransducer separation and is reduced by beam steering in devices w ith SAW propagation 7O off 2. Encouraging results have also been obtained with a three-transducer b ulk wave cancellation scheme, showing promise that the spurious responses may be reduced to acceptable levels for bandpass filter applications.