High Piezoelectric Coupling Temperature-Compensated Cuts of Berlinite (AlPO₄) for SAW Applications

Calculations of the surface acoustic wave (SAW) properties of berlinite (AIPO4) show that it is temperature compensated with more than four times the piezoelectric coupling of STcut quartz. High coupling, temperature compensated orientations have been found for doubly rotated cuts as well as for singly rotated cuts. The best singly rotated orientation is the X axis boule 80.4' cut which, because of the structural similiarity between berlinite and quartz, is a direct analog of the ST cut of quartz. This cut has, like ST quartz, a zero electromc- chanical power flow angle, but the distinct advantage of morc than four times the piezoelectric coupling. Even more promising are the results obtained for two doubly rotated cuts which combine all the advantages of the 80.4' singly rotated cut with the added feature of better diffrac- tion properties than ST cut quartz. As good quality berlinite becomes available, it will be attractive for use in broadband, low insertion loss surface acoustic wave devices.