Homogeneity of Langasite and Langatate wafers

One-port SAW resonators have been designed and processed on various 3"-wafer cuts from different boules and crystal growers to study the homogeneity of Langasite and Langatate crystals. The influence of crystal defects on several SAW properties has been investigated by correlating the resonant frequency or the Q-value of selected resonators to their location on the wafer being subject to X-ray topographic imaging. Frequency shifts of up to 250 ppm between adjacent devices correlate to growth striations, the main defect of the material. Additional gradual shifts of the resonant frequency mainly radial to the growth direction also occur and lead to frequency shifts with a standard deviation (std) of up to 200 ppm on a single wafer. Furthermore identified variations of the Q-value are also linked to the growth banding. Recent investigations on high quality 3" wafers, however, show frequency shifts with a std of 50 ppm only and high Q-values of up to 15000.