Bulk acoustic wave attenuation in langatate

Abstract

The report is devoted to the study of the attenuation of bulk acoustic waves in crystals of LGT (La/sub 3/Ga/sub 5/ /sub .5/TaO/sub 0.5/O/sub 14/) - one of the most perspective materials for bulk acoustic wave piezoelectric resonators. Two methods of the experimental study and measurements of attenuation coefficient were used. The first method used was a modified bulk acoustic wave composite resonator spectroscopy method previously applied to the study of langasite. A composite resonator structure is a multifrequency bulk acoustic wave resonator. The resonances in the structure were spaced in frequency domain by few MHz and were observed in a wide frequency region from half up to a few GHz. So it was possible to find total acoustic losses in the structure from the data on resonant peaks width in a wide frequency domain. The new modified version of HBAR spectroscopy is based on the measurements of only parallel resonance bandwidth of composite resonator structures at each resonance frequency. Losses in transducers and those due to surface roughness were evaluated and either neglected or (if necessary) subtracted from the total losses. It was found that the frequency dependences in the whole band for most BAW polarizations are not ideally square (as it is required in Akhiezer theory), but at high frequencies limit their behavior is very close to the square law. The second method used in the work was a traditional echo-pulse method. For most experiments the acoustic losses obtained by two methods at high frequency region were close to each other. Here we concentrate our attention on modified HBAR spectroscopy method and on the discussion of the attenuation in LGT. All the peculiarities observed experimentally are discussed, attenuation constants data and Qf product values for most interesting directions are presented.