Magnetic Tunnel Junctions With Bcc Layers and MgO Barriers

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Solution Overview

Problem

Magnetic tunnel junctions (MTJs) with MgO tunnel barriers and synthetic antiferromagnetic reference layers do not exhibit high tunneling magnetoresistance, and conventional MTJs suffer from unwanted coupling fields due to the storage magnetic layer moment aligning anti-parallel to the reference layer moment.

Innovation Solution

A magnetic tunnel junction device is formed with a first and second body-centered cubic (bcc) magnetic layer, a spacer layer for exchange coupling, and a tunnel barrier of MgO or Mg-ZnO, which is (100) oriented and polycrystalline, with the second magnetic layer being substantially free of oxide to enhance performance, and the spacer layer includes Cr or Cr-based alloys for optimal coupling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional MTJ structure with synthetic antiferromagnetic reference layer is used, then the device can be manufactured, but high tunneling magnetoresistance cannot be achieved

Engineering Contradiction:

Improvetunneling magnetoresistanceVSAvoidstructure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent removes the synthetic antiferromagnetic reference layer structure and replaces it with a simpler single ferromagnetic reference layer. This extraction of the complex multilayer structure eliminates the interface issues that prevented high TMR while maintaining the essential reference layer function through exchange coupling to an antiferromagnetic layer.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent changes the magnetic coupling configuration from antiparallel (in synthetic antiferromagnetic structures) to parallel alignment between the reference layer and free layer. This parameter change in magnetic moment orientation enables high TMR by creating the proper spin-polarized tunneling conditions through the MgO barrier.

Inventive Principle:

Principle #35Parameter changes

2Stability of the object's composition

If the storage magnetic layer moment aligns anti-parallel to the reference layer moment, then exchange coupling can be achieved, but unwanted coupling fields are generated

Engineering Contradiction:

Improvemagnetic moment alignmentVSAvoidcoupling fields

Core Design Contradiction:

Stability of the object's compositionVSObject-generated harmful factors

Solution Approach 1:

Instead of using antiparallel alignment as in conventional synthetic antiferromagnetic structures, the patent inverts the approach by using parallel alignment between the reference layer and free layer. This inversion eliminates the unwanted coupling fields while maintaining stable magnetic moment alignment through exchange coupling to the antiferromagnetic layer.

Inventive Principle:

Principle #13The other way round (Inversion)

3Ease of manufacture

If MgO tunnel barrier is used with conventional structures, then manufacturing is simplified, but high tunneling magnetoresistance is not achieved

Engineering Contradiction:

Improvetunnel barrier fabricationVSAvoidtunneling magnetoresistance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent changes the magnetic configuration parameters (parallel alignment, single reference layer) to enable high TMR in MgO-based tunnel barriers. This parameter change allows the simple MgO fabrication process to produce high-performance devices by optimizing the magnetic layer structure rather than complicating the barrier fabrication.

Inventive Principle:

Principle #35Parameter changes

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

The approach achieves tunneling magnetoresistance values of at least 50% at room temperature, improving the performance and thermal stability of MTJs while reducing demagnetization fields and maintaining high spin polarization.

Implementation Method 1

At least one spacer layer of bcc material is located between the magnetic layers for exchange coupling the first and second bcc magnetic layers

Methodology Applied

Scientific EffectExchange coupling: Magnetism

Implementation Method 2

a tunnel barrier is in proximity with (e.g., in contact with) the second magnetic layer to permit spin-polarized current to pass between the tunnel barrier and the second layer

Methodology Applied

Scientific EffectSpin-polarized tunneling: Magnetoresistance

Data Source

PatentUS7906231B2Magnetic tunnel barriers and associated magnetic tunnel junctions with high tunneling magnetoresistance

Publication Date: 2011.03.15 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

Magnetic tunneling devices are formed from a first body centered cubic (bcc) magnetic layer and a second bcc magnetic layer. At least one spacer layer of bcc material between these magnetic layers exchange couples the first and second bcc magnetic layers. A tunnel barrier in proximity with the second magnetic layer permits spin-polarized current to pass between the tunnel barrier and the second layer; the tunnel barrier may be either MgO and Mg—ZnO. The first magnetic layer, the spacer layer, the second magnetic layer, and the tunnel barrier are all preferably (100) oriented. The MgO and Mg—ZnO tunnel barriers are prepared by first depositing a metallic layer on the second magnetic layer (e.g., a Mg layer), thereby substantially reducing the oxygen content in this magnetic layer, which improves the performance of the tunnel barriers.