Properties of Tunable Yig Hbars

Abstract

We have previously reported a frequency tunable HBAR using a YIG substrate t d with an externally a lied magnetic fieldW. Low loss, high Q, buff shear standing waves are excited in the YIG by ZnO film transducers. These transducers are fabricated on opposing faces of the substrate by sputter deposition. This sputtering techni ue provides a 40' crystallite tilt of the ZnO wi?h respect to the transducer contacts and substrate axis. Several axial orientations of YIG have been used includin and . With the magnetic field direction perpendicular to the acoustic propa ation direction, we have investigated the fiefd dependence of the frequency tuning and loaded Q for several magnetic field orientations. At 1.8 GHz, with the magnetic field parallel to the shear wave displacement (0=0°) the loaded Q is found to change from 28,000 to 15,000 for approximately 0.5 UHz change in frequency. THEORY Single crystal YIG has a low acoustic loss and the smallest measured microwave magnetic loss and is therefore the preferred material for an investigation of the magnetic tuning of HBAR resonators. Acoustic waves propagating in YIG are coupled by the mayeto-e astic interaction to spin waves as shown in Figure 1. In general, both longitudinal and shear wave couple to the spin wave, but may be decoupled for specific crystallographic and magnetic bias field orientations. The stren th of the interaction, i.e., the splitting at &e crossover between the elastic and spin wave branches depends upon the magnetoelastic coupling constants B1 and B and the crystallographic orientation. In Y& the branch splittine is typically a few KHz so that strong interactions are only expected close to the crossover.