BAW temperature sensitivity and coupling in langanite

One of the new quartz-like materials belonging to the trigonal 32 class is langanite (LGN, La₃Ga_5.5Nb_0.5O ₁₄). High-quality langanite single crystals have become available, and although similar in composition and structure to langasite (LGS, La₃Ga₅SiO₁₄), LGN has smaller thermal expansion coefficients, and comparable piezoelectric constants to LGS; these are desirable material properties for both SAW and BAW applications that require low dependence on temperature. The present research examines in detail the characteristics for LGN of: phase velocity, temperature coefficient of frequency (TCF), electromechanical coupling coefficient, and power flow angle for both singly and doubly rotated plate cuts. Contour plots for the characteristics are given showing the orientation regions where zero TCF and high coupling are found, suggesting potentially interesting orientations for practical BAW device design. Temperature compensated cut regions with coupling coefficients as high as 0.16 are predicted, which is 100% higher than the value for AT cut quartz. A temperature compensated cut with cubic behavior for Δf/fo around room temperature is also identified. With such desirable properties, LGN is a promising material for BAW applications that require low temperature sensitivity (maybe surpassing LGS) with superior bandwidth characteristics due to its larger values of coupling coefficient. A number of orientations with low temperature coefficients of frequency and high coupling are identified