Magnetic stacks with perpendicular magnetic anisotropy for spin momentum transfer magnetoresistive random access memory

Abstract

A magnetic tunnel junction (MTJ) includes a magnetic free layer, having a variable magnetization direction; an insulating tunnel barrier located adjacent to the free layer; a magnetic fixed layer having an invariable magnetization direction, the fixed layer disposed adjacent the tunnel barrier such that the tunnel barrier is located between the free layer and the fixed layer, wherein the free layer and the fixed layer have perpendicular magnetic anisotropy; and one or more of: a composite fixed layer, the composite fixed layer comprising a dusting layer, a spacer layer, and a reference layer; a synthetic antiferromagnetic (SAF) fixed layer structure, the SAF fixed layer structure comprising a SAF spacer located between the fixed layer and a second fixed magnetic layer; and a dipole layer, wherein the free layer is located between the dipole layer and the tunnel barrier.

Description

BACKGROUND[0001]This disclosure relates generally to the field of magnetoresistive random access memory (MRAM), and more specifically to spin momentum transfer (SMT) MRAM.[0002]MRAM is a type of solid state memory that uses tunneling magnetoresistance (MR) to store information. MRAM is made up of an electrically connected array of magnetoresistive memory elements, referred to as magnetic tunnel junctions (MTJs). Each MTJ includes a magnetic free layer having a magnetization direction that is variable, and a magnetic fixed layer having a magnetization direction that is invariable. The free layer and fixed layer are separated by an insulating non-magnetic tunnel barrier. An MTJ stores information by switching the magnetization state of the free layer. When the magnetization direction of the free layer is parallel to the magnetization direction of the fixed layer, the MTJ is in a low resistance state. When the magnetization direction of the free layer is anti-parallel to the magnetizat...

AI Technical Summary

Benefits of technology

[0006]In one aspect, a magnetic tunnel junction (MTJ) for a magnetic random access memory (MRAM) includes a magnetic free layer, having a variable magnetization direction; an insulating tunnel barrier located adjacent to the free layer; a magnetic fixed layer having an invariable magnetization direction, the fixed layer disposed adjacent the tunnel barrier such that the tunnel barrier is located between the free layer and the fixed layer, wherein the free layer and the fixed layer have perpendicular magnetic anisotropy; and one or more of: a composite fixed layer, the composite fixed layer comprising a dusting layer, a spacer layer, and a reference layer, wherein the spacer layer is located between the reference layer and the tunnel barrier, and wherein the dusting layer is located between the spacer layer and the tunnel barrier; a synthetic antiferromagnetic (SAF) fixed layer structure, the SAF fixed layer structure comprising a SAF spacer located between the fixed layer and a second fixed magnetic layer, wherein the fixed layer and the second fixed magnetic layer are anti-parallely coupled through the SAF spacer; and a dipole layer, wherein the free layer is located between the dipole layer and the

Problems solved by technology

However, MTJs made using PMA materials may have a relatively low MR because of structural and chemical incompatibility between the various material layers that comprise a PMA MTJ.

A relatively low MR may result in difficulty with read operations in the STT MRAM, as the difference in resistance between the high and low resistance states of the MTJs will also be relatively low.

The fixed layer dipolar field creates a number of issues in MTJ devices, including increasing the free layer loop offset and the minimum required free layer Hc needed to ensure bistability of the MTJ.

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