Spin Current Injection Capping Layer for MRAM

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Solution Overview

Problem

Conventional MRAM devices face challenges in controlling orthogonal torque transfer and efficiency of spin transfer torque due to the use of metallic spacers between the free layer and the polarizing layer, which results in poor performance and high tunnel magnetoresistance ratio degradation.

Innovation Solution

The introduction of a spin current injection capping layer composed of MgO and ferromagnet between the free layer and the orthogonal polarizer, enabling efficient spin current injection through tunneling, thereby maximizing spin torque and achieving high tunnel magnetoresistance with a desirable resistance area product, lower free layer damping constant, and lower effective magnetization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If metallic spacers are used between the free layer and the polarizing layer, then the device structure is simpler, but the spin transfer torque efficiency deteriorates and tunnel magnetoresistance ratio degradation increases

Engineering Contradiction:

Improvedevice structureVSAvoidspin transfer torque efficiency

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent introduces a spin current injection capping layer as an intermediary component between the free layer and the polarizing layer. This capping layer acts as a mediator that enhances spin current injection efficiency while avoiding the harmful effects of direct metallic spacer contact, thereby resolving the contradiction between structural simplicity and torque efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The spin current injection capping layer is constructed as a composite structure combining non-magnetic insulator material and magnetic conductor material. This composite approach optimizes both the electrical insulation properties and the spin current injection properties, achieving high spin transfer torque efficiency without the degradation issues associated with simple metallic spacers.

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If metallic spacers are used between the free layer and the polarizing layer, then the manufacturing process is easier, but the tunnel magnetoresistance ratio degradation increases

Engineering Contradiction:

Improvemanufacturing processVSAvoidtunnel magnetoresistance ratio

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The composite capping layer structure combines materials with complementary properties: non-magnetic insulator for electrical isolation and magnetic conductor for spin current injection. This composite approach maintains manufacturing feasibility while achieving precise control over tunnel magnetoresistance ratio, avoiding the degradation problems of simple metallic spacers.

Inventive Principle:

Principle #40Composite materials

3Reliability

If a spin current injection capping layer is introduced between the free layer and the orthogonal polarizer, then the spin transfer torque efficiency is improved, but the device structure becomes more complex

Engineering Contradiction:

Improvespin transfer torque efficiencyVSAvoiddevice structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The spin current injection capping layer serves multiple functions simultaneously: it provides electrical insulation, enhances spin current injection efficiency, and contributes to the overall magnetic structure stability. By consolidating these functions into a single composite layer, the patent improves torque efficiency while limiting the increase in structural complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

4Use of energy by moving object

If a spin current injection capping layer is introduced between the free layer and the orthogonal polarizer, then the switching current is reduced, but the device structure becomes more complex

Engineering Contradiction:

Improveswitching currentVSAvoiddevice structure

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The composite capping layer combines non-magnetic insulator and magnetic conductor materials in a configuration that optimizes spin current injection. This material combination achieves lower switching current requirements while maintaining a manageable structural complexity through the integrated design of the capping layer.

Inventive Principle:

Principle #40Composite materials

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

This configuration enhances the control of spin transfer torque, achieving high efficiency in spin transfer torque and low critical current switching, while maintaining high tunnel magnetoresistance and reducing the switching current required for magnetic direction changes.

Implementation Method 1

Spin transfer torque uses spin-aligned ('polarized') electrons to change the magnetization orientation of the free layer in the magnetic tunnel junction

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

Due to the spin-polarized electron tunneling effect, the electrical resistance of the cell changes due to the orientation of the magnetization of the two layers

Methodology Applied

Scientific EffectSpin-polarized electron tunneling:

Implementation Method 3

The spin current injection capping layer injects spin polarized current into the magnetic tunnel junction through tunneling

Methodology Applied

Scientific EffectTunneling:

Implementation Method 4

Passing a current though a magnetic layer polarizes electrons with the spin orientation corresponding to the magnetization direction of the magnetic layer (i.e., polarizer), thus produces a spin-polarized current

Methodology Applied

Scientific EffectSpin polarization:

Implementation Method 5

If a spin-polarized current is passed to the magnetic region of a free layer in the magnetic tunnel junction device, the electrons will transfer a portion of their spin-angular momentum to the magnetization layer to produce a torque on the magnetization of the free layer

Methodology Applied

Scientific EffectSpin-angular momentum transfer:

Data Source

PatentUS10615335B2Spin transfer torque structure for MRAM devices having a spin current injection capping layer

Publication Date: 2020.04.07 INTEGRATED SILICON SOLUTION CAYMAN INC

AI summary

A magnetoresistive random-access memory (MRAM) device is disclosed. The device described herein has a spin current injection capping layer between the free layer of a magnetic tunnel junction and the orthogonal polarizer layer. The spin current injection capping layer maximizes the spin torque through very efficient spin current injection from the polarizer. The spin current injection capping layer can be comprised of a layer of MgO and a layer of a ferromagnetic material.