Effects of Conductor Stress on Bubble Propagation in Contiguous Disk Devices

Stress gradients associated with overlay conductors significantly degrade the propagation margins in ion-implanted contiguous-disk bubble devices. A study has been made of the influence of various conductor metallurgies, including Au, AlCu, and Cr deposited by vacuum evaporation and electroplating, on the bias margins of 1 μm bubble propagation along tracks with 5 μm circuit period. The conductors were 2.5 μm wide by 0.5 μm thick and were spaced 0.2 μm from the garnet surface. Annealing the devices at 250° and 350°C for 30 min in a helium atmosphere generally resulted in an increase in conductor stress and a further reduction in propagation margin. The bias margin loss due to the presence of the overlays depended upon track orientation, but for the so-called “good” tracks was typically 20% for evaporated Au and 27% for AlCu after the final anneal. A correlation between margin loss and the stress level in sheet films of the conductor metals was established and reveals a monotonic loss of margin with increasing stress. The results imply that for a margin reduction of no more than 10%, the conductor stress should not exceed ~108 dynes/cm2. © 1980, The Electrochemical Society, Inc. All rights reserved.