Fabrication of large bubble circuits

Large magnetic bubble circuits, having a capacity of 2 × 10⁴bits and a storage density of 10⁶/in², have been fabricated on-the-chip by conductor-first processing using non-planar and planar processing approaches. Aluminum-copper and Ti/Au conductors have been examined with Al-Cu being preferable since it overcomes two major problems encountered when Ti/Au is used-resistance changes due to subsequent high temperature processing and adhesion of a P-glass dielectric which is used as a separating layer between the conductor and the Permalloy elements. When Ti/Au/Ti is used to improve adhesion of the dielectric layer, it is found that resistance changes are even larger than in Ti/Au. The use of intermediate layers of palladium does not alleviate the problem. High-speed operational testing reported elsewhere has demonstrated that non-planar processing results are equivalent to those obtained from planar processing. This is shown in scanning electron micrographs to be a result of achieving excellent step coverage where Permalloy elements overlap the conductor.