Modeling and Optimization of Bubble Memory Field Access Propagation Circuits

Abstract

<p> The work presented in this thesis relates to one of the most important problems in the design of high-density, high-speed bubble memory systems. A new approach for the analysis, design and optimization of bubble circuits is developed. This formulation is suited to computer-aided methods of solution.</p> <p> A micromagnetic approach to the modeling of permalloy bubble circuits is examined. Basic to the approach is the discretization of the circuit into very small regions to simulate the ferromagnetic essence of the permalloy. This method of analysis is very useful in studying submicron bubble circuits. However, the numerical difficulties as well as the excessive computer time required for such analysis led to careful consideration of possible approximations. A continuum model for analyzing field access bubble circuits has, thus, been developed and used to characterize arbitrary shaped permalloy structures. Various propagation circuits, including gap tolerant circuits, and bubble replicators are analyzed and the results compared to experimentally available data.</p> <p> A model for studying bubble size and position fluctuations is introduced. The model assumes that the bubble domain is circular. However, with slight modifications it can accept general elliptical shapes. For various propagation circuits, the model results are in excellent agreement with experimental measurements in the literature.</p> <p> An algorithm for bubble circuit optimization is developed and discussed in detail. The problem is formulated as a constrained minimax objective which is suited to nonlinear programming methods of solution. Typical examples of T-I propagation circuits are furnished to illustrate the approach.</p>