Langasite, langanite, and langatate bulk-wave Y-cut resonators

Materials in the langasite family are of current interest for both bulk wave and surface wave devices. Piano-convex Y-cut bulk wave resonators have been built and tested on overtones 1 through 9 using LGS (langasite; La/sub 3/Ga/sub 5/SiO/sub 14/), LGN (langanite; La/sub 3/Ga/sub 5.5/Nb/sub 0.5/O/sub 14/), and LGT (langatate; La/sub 3/Ga/sub 5.5/Ta/sub 5.5/O/sub 14/). Frequencies and motional inductances are compared with calculated values, with good agreement except for the motional inductance of LGT. For all three materials, frequency variation is an essentially parabolic function of temperature. For LGN and LGT, reported values of the Q-frequency product are significantly above the classical limit for AT-cut quartz. A maximum 4 f value of 25.6/spl times/10/sup 6/, where frequency is in megahertz;, was observed for an LGT resonator; for an unplated resonator, 29.2/spl times/10/sup 6/ was measured. Still higher values are believed possible.