Yield analysis of large capacity magnetic bubble circuits with redundancy design

As the capacity of magnetic bubble circuit designs is increased the processing yield decreases due to the finite number of defects in the epitaxial garnet film and the overlay circuit. A model is presented to examine the effect on the fabrication yield of an on-chip modifiable redundant circuit design for a 10⁵bit serial shift register. The yield model is based on a conceptual design which consists of a primary loop and a set of secondary loops which may be eliminated from or made part of the memory storage loop without introducing blanks in the data stream. The ability to enable and disable the secondary loops has a finite yield which is included in the calculation of overall yield. Other factors which contribute to the overall yield include the contribution of the garnet film and the processed circuit, which take the form of a sum of binomial terms, each with a Poisson density probability. The results show that the yield of the enable and disable operation must be greater than 0.9 to achieve fabrication costs which are equal to or less than the nonredundant simple serial shift register.