The use of yttrium-rare earth aluminium garnet solid solutions for bulk-acoustic-wave (BAW) devices

The isomorphic solid solution of yttrium-rare earth aluminium garnets is suggested as a dielectric material for acoustic waveguides with extremely low acoustic-wave absorption (AWA) at room temperature and for frequencies higher than 10 GHz. The two main mechanisms by which substitutional atoms decrease the bulk AWA are determined. The first one is the decrease in effective lifetime of the thermal phonons resulting in the corresponding reduction of the viscoelastic absorption-this mechanism is important for the shear acoustic waves. The second is more important for longitudinal waves. It is the reduction of Gruneisen constants for solid solution as compared to the crystal matrices.