Body Magneto-acoustic devices, integrating ferri- and ferro-magnetic materials with surface and bulk acoustic wave transducers, are of interest for nonlinear signal processing applications such as frequency selective and tunable filtering, signal correlation and isolation 1-3. Typically, the devices are fabricated by sputter depositing the piezoelectric material needed for acoustic transduction onto the magnetic substrate. Lack of epitaxy as well as thermal budget constraints in the sputtering processes, however, restrict the combinations of piezoelectric and magnetic materials possible for these devices. In this work, we present an alternate fabrication approach based on heterogeneous integration whereby the acoustic transducer is grown on an epitaxially suitable substrate and subsequently transferred to the desired magnetic material 4, allowing for device design and performance to be optimized unhindered by process limitations. A magnetoelastic high overtone bulk acoustic resonator (ME-HBAR) is implemented as an example device, as shown in Fig. 1. A GaN acoustic transducer with a top Al electrode is grown on epitaxially compatible 4H-SiC and released for transfer onto a Cu/YIG substrate by etching a sacrificial NbN layer. Cu serves as the bottom electrode of the acoustic transducer and an acoustic matching layer. The frequency response of the ME-HBAR is measured as a function of magnetic field vector. Two representative responses corresponding to zero field and Bx = 56 mT (in-plane component) and Bz = 180 mT (normal component) are shown in Fig. 2. Around 2.75 GHz, the resonant acoustic modes are strongly attenuated and shifted in frequency due to hybridizing with spin wave modes of similar frequency and wavelength to form coupled magneto-elastic waves 5. Sufficiently far from the crossover region (not shown), the frequency shift is attributed to the ΔE effect, which together with the lossy hybridization region may be used to realize tunable bandpass and notch filters respectively.

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