Investigation on recent quartz like materials for SAW applications

Recent progress on growing and characterizing quartz like materials of the trigonal system class 32 has been reported by several groups. The promising perspective for bulk acoustic wave frequency control applications indicates the potentiality of employing these materials for SAW applications as well. This paper reports results of investigations focused on SAW orientations of langasite (LGS), gallium phosphate (GaPO₄), and langanite (LGN), both single and doubly rotated cuts. Among the characteristics explored, major attention is paid to the temperature coefficient of delay (TCD), the electromechanical coupling coefficient (K²), and the power flow angle (PFA). Three-dimensional graphics and contour graphics are plotted based on our calculated results, showing the regions in space where low TCD and high K² can be obtained, also exhibiting the associated PFA and phase velocity characteristics. The influence of different sets of material constants is addressed where appropriate. The spatial investigation performed shows that there are promising orientation regions in these materials where zero or reduced TCD (<10 ppm/°C) and PFA are obtained. Additional attractive characteristics for SAW applications have been observed like: values of K² a few times higher than the K² of quartz ST-X, thus finding applications in larger bandwidth devices; variation of the TCD with respect to temperature which is comparable to the variation found for quartz ST-X and less than that for zero TCD Li₂B₄O ₇ cuts like 45°X-Z and (0°78°90°); and phase velocity values circa 13 to 25% smaller than the phase velocity of quartz ST-X, thus allowing a reduction in size for intermediate frequency device applications