Bulk wave propagation and energy trapping in the new thermally compensated materials with trigonal symmetry

In this communication, we compare the properties of the new piezo-electric materials that belong to crystal class 32: the aluminium phosphate, the gallium phosphate and langasite with those of quartz. In a first part, a comparison of the main piezo-electric properties of these crystals is made. Computed and experimental results concerning the Y rotated cuts and particularly the compensated cuts are given. The most important facts observed are the increase of the coupling coefficient from quartz, to berlinite, langasite and gallium phosphate, and the simultaneous shift of the angular position of the most interesting compensated cuts towards the angles of maximum coupling coefficient. New determinations of the angular positions of the corresponding compensated cuts of gallium phosphate and doped langasite are also reported; the former one displays the largest coupling coefficient and an outstanding thermal stability. In the second part, the energy trapping properties of these four materials are compared. It is concluded that filters having more than 4 times the bandwidths obtained with quartz can be made using the new materials. Extremely high Q factors and the ability to withstand large excitation levels were observed in langasite resonators making use of energy trapping by the geometry (plano-convex). They appear very promising for low phase noise applications. The materials were found to possess an unique set of complementary properties, a high crystalline perfection, superior thermal behaviours, and different coupling coefficients adapted to an extremely broad range of filtering and frequency generation applications