Magnetically tunable SAW-resonator

At present different tuning methods for acoustic devices exist. Established technologies are the integration of strictive materials or semiconductor structures in the cavity of a delay-line or resonator. Common to all these devices is the tuning of delay time or phase by changing the electrical or mechanical surface boundary condition for the propagating surface acoustic wave (SAW). This paper presents a completely new approach for frequency tuning. The resonance frequency of a SAW resonator is shifted by directly changing the propagation velocity of the SAW. This is achieved by altering the corresponding elastic stiffness by an external magnetic field, using a multilayer structure exhibiting Giant DeltaE effect. A sacrificial layer technique is used to realize a first experimental device, basically consisting of a piezoelectric ZnO-layer on an amorphous magnetostrictive layer of FeCoSiB. All layers have been deposited by RF-sputtering on a 4" quartz carrier-wafer. Aluminum electrode structures were deposited subsequently in order to excite SAWs. In the measurement setup an external magnetic field between 0 to 50 Oe has been applied to the device. A tuning range of about -1.2% and -0.9% at center frequencies of 1.2 and 1.6 GHz could be demonstrated, respectively.