Lithium tetraborate as a promising material for BAW filters

At present Li tetraborate, a new piezoelectric material, is created. This crystal displays high electromechanical coupling and has the cuts with zero temperature-frequency coefficient. These properties have attracted attention of scientists developing the bulk acoustic wave (BAW) filters. For using this crystal it is very important to know and to predict theoretically the effect of temperature on the piezoelement resonant frequency. We have calculated resonant frequencies of rotated Y cut thin plate with metal electrodes and have determined temperature-frequency dependencies for above cut under various rotation angles and various electrode dimensions. The obtained data are in a good agreement with theoretically calculated ones. The temperature-frequency curves of the studied resonators have parabolic shape with the turnover point appearing in the room temperature region. The second order temperature coefficient is found to be 0.30.10^-6°C^-2 . Q values range from 2000 to 9000, the dynamic resistance is in range of 25 to 100 Ω. Using acoustically coupled resonators as the base, we have manufactured monolithic filters with the bandwidth of 0.2 to 1.5%