Differential type giant magnetoresistive memory using spin-valve film with a NiO pinning layer

Abstract

The giant magnetoresistive (GMR) memory device of differential type is able to perform data readout without a magnetic field, and has many highly efficient properties, such as a nonvolatile, nondestructive readout, high-speed access, large output signal, and low electric power consumption. We have demonstrated data read/write of this memory by means of a spin-valve film with a NiO pinning layer. The spin-valve film was constructed of a multilayered structure [NiO/NiFeCo/Cu/NiFeCo], and exhibited the appropriate properties of a storage element, such as a MR ratio of 5%, a squareness ratio of unity, a writing field of 20 Oe, and a high corrosion resistance. The differential type memory device is constructed of a memory cell including two storage elements, in which the word currents of each element are in opposite directions. The information storage is performed by storing different resistance values in each element. The data readout of this memory is accomplished by sensing the differentiation of each element output, therefore magnetic field is not necessary for the readout process. The data read/write was established by observing a step-shape output signal: [plus or minus] against a three-step input signal: [zero/plus/zero/minus].