A SAW resonator with two-dimensional reflectors

It is known that a part of the loss of Leaky SAW resonators is due to radiation of acoustic energy in the bussbars. A lot of researchers are working on so called ldquoPhononic crystalsrdquo. A 2D grating of very strong reflectors allows these devices to fully reflect, for a given frequency band, any incoming wave. A new device, based on the superposition of a regular SAW resonator and of a 2D periodic grating of reflectors, is proposed. Several arrangements and geometries of the reflectors were studied and compared experimentally on 48 degrees rotated Y cut Lithium Tantalate. In particular, a very narrow aperture (7.5 lambda) resonator was manufactured on 48 deg. LT in the 900 MHz range. Due to its small size, this resonator has a resonance Q of only 575 when using the standard technology while a resonance Q of 1100 was obtained for the new device without degradation of the other characteristics. Due to the narrow aperture, the admittance of the standard resonator showed a very strong parasitic above the resonance frequency while this effect is drastically reduced for the new device. These results demonstrate the feasibility of the new approach.