Manipulation of 1-μm bubbles with coarse (≳4 μm) overlay patterns

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Abstract
This paper reports on the propagation and transfer of 1‐μm bubbles in ion‐implanted contiguous‐disk devices, made by conventional photolithographic techniques. Bubble‐propagation circuits are made of undulating patterns masked from implantation on a low‐Q garnet film, which is grown on top of and exchange coupled with a medium‐Q garnet film which supports the small bubbles. A double‐garnet composite combines the good features of a medium‐anisotropy storage layer to stabilize bubbles and, more importantly, of a small‐anisotropy driving layer to ensure the creation of a planar magnetization layer by ion implantation. A fundamentally different propagation mechanism employing the charged walls around the implanted pattern edges is explained. The value of the charged walls is that they lend themselves to coarse‐featured devices. Furthermore, they can be substantially lengthened to bridge a large gap between two propagation circuits to assist bubble transfer across that gap. We describe a switching gate employing such a bridging charged wall to transfer 1‐μm bubbles across a 4‐μm gap. Also included is an implantability analysis of several garnet compositions, pointing out why the ability to create a planar magnetization by implanting a single bubble layer diminishes as the bubble size approaches the 1–2‐μm range. An implication is that a double‐garnet composite, such as used in our contiguous‐disk devices, may also be essential to other bubble devices (Permalloy bar and bubble lattice) for bubbles under 1–2 μm in diameter.