Control function margin degradation in a bubble memory chip

Chip control function and propagation circuit margin degradation due to long-term memory operation, was observed, using the bias field switching technique. 16 kbit major-minor loop organized bubble memory chips with 28 μm bit period, which had an average access time of 2.7 ms for a 100-kHz rotating field, were used. It was seen that degradations in the lower side of the bias field range were independent of chip functional elements. However, at the upper side of the bias field range, degradations in the performance can be classified by dividing the elements into two categories. These were propagation circuits (Permalloy patterns only) such as H-bars, chevrons, etc., and control functions (Permalloy and conductor patterns), such as generators, replicators, etc. Also, it was found that the degradation in the performance of propagation circuits is small compared with that of the control functions. These differences were considered to be caused by a failure in the Permalloy steps over conductors and/or by the magnetic interaction of the bubble and the conductor current.