Characteristics of junctions between ion-implanted and permalloy tracks in hybrid bubble devices

The characteristics of junctions between ion-implanted and Permalloy tracks are described for hybrid bubble memory devices. It has been found that the junctions which have a sharply formed edge of the ion-implanted layer have a problem in reproducibility of bias field margins. It is caused by the potential barrier due to the stress change and free poles which appear at the edge as well as the attractive poles in the ion-implanted tracks which tend to keep the bubbles in the ion-implanted tracks. To reduce their influence, we have introduced the tapered edge. A good bias field margin has been obtained for the tapered junctions with the modified pickax Permalloy pattern from the ion-implanted to Permalloy tracks. In the junctions from the Permalloy to ion-implanted tracks, the bias field margin strongly depends on the orientation of the edge of the ion-implanted layer with respect to the easy magnetization directions of the garnet. The edge should not be parallel to the easy magnetization direction, and the Permalloy pattern should be made larger near the edge. The improved junctions have a good bias field margin with reproducibility.