Other Bubble Device Forms

Abstract

In the previous chapter we have studied the permalloy-bar (PB) bubble devices which use a gap in the pattern to define bit positions and to create magnetic poles, under the influence of a rotating field, to propagate bubbles. Other forms have been investigated in an attempt to achieve higher density for a given lithography, which is specified by the minimum feature, W₀, that can be realiably defined thereby. In PB devices the minimum feature is the gap, g, so that g = W₀, The density is determined by the pit pattern period, P and P is limited by P = 4−5d where d > g = W₀. Four approaches to decreasing P and increasing density for a given W₀ are:

• 1) “Two-level permalloy bar” where the gap is not defined by W₀, but can be smaller.

• 2) “Charged-wall” devices using a different mechanism for localizing the bubble and for propagating it so that the need for gaps in the propagation pattern is eliminated. In these devices then the bubble size can be smaller then the minimum feature, instead of larger as in PB, so that d < W₀.

• 3) “Lattice” devices where the bubbles are allowed to interact and can thus be closer together so that P ≃ 2d instead of 4−5d.

• 4) “Current Sheet” devices where the bubbles are propagated under the influence of fields from current-carrying conductor sheet(s) and the rotating field and the drive field coils are eliminated.