Nondestructive-readout coupled film memory device

Abstract

By magnetostatically coupling a soft film and a hard film with their easy axes orthogonal to each other, an NDRO (nondestructive readout) memory device with fast read cycle speed has been achieved. This device differes from the previously investigated NDRO devices as follows: (1) The partially magnetized state of the hard film is utilized for information storage. (2) Since the device is read and sensed along the transverse axis of the soft film, low read current can be used. The calculated results of possible combination of the soft and hard film characteristics that will result in a device with this mode of operation are presented. A 10-kÅ NiFe (80-20) film and a 10-kÅ CoFe film (50-50) each evaporated on a DuPont polymer substrate are used, respectively, as the soft and hard films of the device. The insensitivity of this device to bit disturb pulses is established by measuring the pulse hysteresis of the CoFe film's partially magnetized state. It is interesting to note that as long as the CoFe film is switched into these partially magnetized states not by time-limited process, these are stable states. Finally, the feasibility of this device for memory operation is evaluated experimentally in terms of driver current tolerances and signal to noise ratio. © 1966 The American Institute of Physics.