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

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.