A Coupled Magnetic Film Device for Associative Memories

Abstract

It is well known that a pair of magnetostatically coupled films with easy axes at 90° to each other exhibit biaxial anisotropy. However, when an external bias magnetic field is applied along the easy direction of one of the films, only two states of the coupled system have minimum energy. It can be shown that these two stable states are not collinear in magnetization orientations and the resulting switching characteristic is quite different from that of a uniaxial coupled film device. A new associative memory device based on the above-mentioned switching characteristics is presented in this paper. Nondestructive content interrogation is feasible on this device by applying a current on the strip line intervening between two magnetic layers. When the polarity of the interrogation current mismatches the state of the device, a signal is induced in a detection strip line orthogonal to the interrogation line and located on top of both magnetic films. On the other hand, when the current polarity matches the device state, none or very little flux change is experienced by the detection line. The mismatch signal is always of one polarity independent of the device state. A device sample with electroplated magnetic and conductive layers and photoetched strip lines has been fabricated. The scheme of two storage cells per bit is adopted to cancel capacitive noise. Two 2-bit (4 cells) words have been successfully operated in a parallel by bit content search mode. The measured mismatch to match ratio for a single bit is better than eight.