Narrow-Linewidth Yttrium Iron Garnet Films for Heterogeneous Integration
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ABSTRACT We report on the fabrication and characterization of single-crystal films of yttrium iron garnet (YIG) for heterogeneous integration onto growth-incompatible substrates. The process entails the implantation of energetic helium ions into the material, resulting in the formation of a fast etching sacrificial layer. Separation from the growth substrate is followed by an annealing step, yielding a ferromagnetic resonance (FMR) linewidth of 0.70 Oe from a virgin sample of linewidth 0.55 Oe. Magnetization measurements show a distinct softening of the in-plane response to an applied field. INTRODUCTION Narrow-linewidth magnetic garnets are of interest in microwave systems because of their use as tunable low-loss filters. Of particular importance is the development of low-cost integrated technologies for microwave resonators and phased-array systems. Recently epitaxial liftoff techniques, entailing the separation of liquid-phase-epitaxy grown single-crystal ferrite films, have been applied to the problem of integrating ferrites onto semiconductor platforms. Other interesting platforms to which this technology may be applied are high-temperature superconductors, such as yttrium barium copper oxides, where YIG films may be used as tunable filters in monolithic microwave integrated circuit (MMIC) devices.
To achieve separation of the ferrite film, a sacrificial layer is created in a single-crystal magnetic garnet by means of energetic He ion implantation.' Most of the lattice damage from the implantation occurs towards the end of the ionic trajectories,' resulting in the formation of a deeply buried and strongly localized one-to-two micrometer-thick sacrificial layer. This process generates a high etch selectivity between the implantation layer and the rest of the sample, leading to layer detachment. Since the quality factor (Q) of a ferrite filter is inversely proportional to the ferromagnetic resonance (FMR) linewidth of the ferrite, we investigated the X-band FMR and the dc magnetization of narrow linewidth GaYIG samples in various stages of the separation process. A 10.8 jim-thick epitaxial Y 3Fe 4.6Ga0 .4012 film was employed in this study, grown on oriented gadolinium gallium garnet (GGG) single-crystal substrate by liquid phase epitaxy. At this Ga doping level, GaYIG has a 4ntMs that is nominally 1070 G reduced from 1750 G for pure YIG. The samples were implanted with 3.8-MeV singly charged helium ions impinging normal to the surface without masking. The implant dose in all cases was 5 x 1016 ions/cm 2 . Other details of the implantation procedure are discussed in Ref. 1. At the above energy, the implantation damage is concentrated approximately 9 gim beneath the surface, in a I ýim spread. The crystal ion slicing occurred entirely in the GaYIG film. Implanted but unseparated samples contain a -2 gim thick region of GaYIG shielded from direct exposure to the He ions. 650 'C 119 Mat. Res. Soc. Symp. Proc. Vol. 603 © 2000 Materials Research Society
and 720 'C postimplantation rapid thermal anneals (RTA) were
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