Investigations of long-term propagation margins in ion-implanted contiguous-disk bubble devices

Plots of bias field margins for propagation in 1-μm bubble contiguous-disk circuits as a function of the logarithm of the number of propagation steps have been found to be nonlinear. Furthermore, the probability of failure per step of propagation was found to be independent of the number of steps propagated. Statistical tests applied to these data indicate that an exponential distribution function should not be used to describe the probability of failure at the margin edge; rather, a normal distribution function gives a much better fit. Use of the exponential distribution function overestimates the error rate. Data on the error rate as a function of the number of start-stop operations indicate that the contiguous-disk error rate is independent of the number of start-stop operations so long as the bubble domains are stopped in stable positions on the propagation tracks. The propagation margins showed minimal deterioration as the temperature was varied from 0°C to +50°C, and the temperature change of the bias field closely followed the bubble collapse field behavior. At 17°C, a bias field margin of at least 50 Oe was maintained for drive fields ranging from 45 Oe to 60 Oe. All data was obtained with a 146-kHz drive field.