Homogeneity of Langasite and Langatate wafers for acoustic wave applications
ABSTRACT Variations in the concentration of the chemical constituents of Langasite (La3Ga5SiO14) and its homeotype Langatate (La3Ta0.5Ga5.5O14) have been found by the means of X-ray methods and selective crystal etching. To determine their influence on the acoustic properties SAW resonators have been designed and processed on 3" wafers from Langasite and Langatate crystal boules of different suppliers. Compositional changes on a short range scale according to growth striations and on a long range scale as well could be distinguished leading to variations of the SAW velocity up to 1000 ppm within a wafer. If a device covers several growth striations a superposition of different propagation characteristics occurs leading to a multimode behavior and thereby degrading the effective Q-value of the SAW resonators. Wafers from recently grown boules, however, reveal frequency shifts with a standard deviation of 50 ppm only and maximum Q-values of up to 15000, thus demonstrating the progress in crystal growing.
Conference Proceeding: Properties of radio frequency Rayleigh waves on langasite at elevated temperatures[show abstract] [hide abstract]
ABSTRACT: The properties of Rayleigh waves operating both at radio frequency (RF) and at high temperatures (HT) on langasite crystal cuts with Euler angles of (0°, 138.5°, 26.6°) and (0°, 30.1°, 26.6°) are investigated. By evaluating the frequency response of surface acoustic wave (SAW) test devices the SAW velocity, the coupling factor, and the propagation attenuation have been determined experimentally in a temperature range from 20°C to 500°C. The SAW devices could be operated up to frequencies of 3 GHz. However, considering a future sensor application a limiting factor is a strong increase of the acoustic losses in conjunction with frequency and temperature.Ultrasonics Symposium, 2004 IEEE; 09/2004