HIGH-FREQUENCY SURFACE-ACOUSTIC-WAVE DEVICES AT VERY-LOW TEMPERATURE - APPLICATION TO LOSS MECHANISMS EVALUATION

Previous work on high-performance bulk wave resonators in the frequenc y range of 5 to 25 MHz has shown that, by cooling to liquid helium tem perature, acoustic losses become negligible. Therefore other sources o f losses can be precisely measured. A similar approach is followed in the present work for high-frequency surface wave resonators. Experimen ts have been performed at 416 MHz on quartz devices. It is shown that for surface waves propagating in a good surface acoustic wave (SAW) re sonator an important source of acoustic loss is due to intrinsic acous tic losses. By cooling the device to below 30 K, the quality factor Q shows a T-4 dependence characteristic of intrinsic acoustic losses. Be low 4-10 K a plateau region is reached. High Q values in the range of 1.5 X 10(5) have been obtained at 4.2 K for 416-MHz devices, yielding a Q X f product of 7.5 X 10(13) almost as good as for cooled bulk devi ces. Another set of measurements on a lithium niobate (LiNbO3) resonat or 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 mechani sms not related to intrinsic acoustic losses because the LiNbO3 resona tor operates in a leaky mode rather than a Rayleigh mode. The applicat ions of the method to the characterization of new kinds of SAW resonat ors will be helpful for optimizing high-Q surface wave resonators at h igh frequencies, based on new modes or new materials. (C) 1996 Acousti cal Society of America.