Abstract
Previous work on high-performance bulk wave resonators in the frequency range of 5 to 25 MHz has shown that, by cooling to liquid helium temperature, acoustic losses become negligible. Therefore other sources of losses can be precisely measured. A similar approach is followed in the present work for high-frequency surface wave resonators. Experiments have been performed at 416 MHz on quartz devices. It is shown that for surface waves propagating in a good surface acoustic wave (SAW) resonator an important source of acoustic loss is due to intrinsic acoustic losses. By cooling the device to below 30 K, the quality factor Q shows a T−4 dependence characteristic of intrinsic acoustic losses. Below 4–10 K a plateau region is reached. High Q values in the range of 1.5×105 have been obtained at 4.2 K for 416-MHz devices, yielding a Q×f product of 7.5×1013 almost as good as for cooled bulk devices. Another set of measurements on a lithium niobate (LiNbO3) resonator at 847 MHz does not give a significant increase of quality factor Q at low temperature. This is due to the presence of other loss mechanisms not related to intrinsic acoustic losses because the LiNbO3 resonator operates in a leaky mode rather than a Rayleigh mode. The applications of the method to the characterization of new kinds of SAW resonators will be helpful for optimizing high-Q surface wave resonators at high frequencies, based on new modes or new materials.
Published Version
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