Amorphous Alloy Spacer for Perpendicular MTJ TMR

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Solution Overview

Problem

Developing perpendicular magnetic tunnel junctions (MTJs) with high tunnel magneto-resistance (TMR) and thermal stability is challenging due to the tendency of magnetic moments in thin films to reside in the film plane, which is exacerbated by demagnetizing fields and non-ideal crystal structures in MgO-based MTJs, leading to poor (001)-texture and in-plane magnetization.

Innovation Solution

Incorporating a tunnel magnetoresistance (TMR) enhancement buffer layer and an amorphous alloy TMR enhancement spacer between the tunnel barrier and reference layers, along with a perpendicular magnetic anisotropy (PMA) enhancement spacer, to promote perpendicular magnetization and increase exchange coupling and surface anisotropy, thereby enhancing TMR and thermal stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If MgO-based MTJ structure is used, then thermal stability is improved, but in-plane magnetization occurs due to non-ideal crystal structures and demagnetizing fields

Engineering Contradiction:

Improvethermal stabilityVSAvoidperpendicular magnetization

Core Design Contradiction:

Stability of the object's compositionVSEase of operation

Solution Approach 1:

A buffer layer is introduced between the MgO tunnel barrier and the reference layer to mediate the crystal structure relationship. This buffer layer promotes ideal (001) orientation in the MgO layer, reducing demagnetizing fields and enabling perpendicular magnetization while maintaining thermal stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The crystal structure parameters of the MgO layer are optimized by controlling the orientation and texture through the buffer layer. By changing the crystallographic orientation from non-ideal to ideal (001) orientation, the magnetization direction transitions from in-plane to perpendicular while maintaining thermal stability.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If conventional MTJ structure is used, then device complexity is reduced, but TMR ratio is insufficient to achieve high performance

Engineering Contradiction:

Improvestructure complexityVSAvoidTMR ratio

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The MTJ structure uses composite material layers including the buffer layer and amorphous alloy spacer layer in addition to the conventional MgO tunnel barrier. These composite materials work together to enhance the TMR ratio by improving spin polarization and reducing magnetic damping, achieving high performance without excessive complexity.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

An amorphous alloy spacer layer is introduced as an intermediary between magnetic layers to enhance exchange coupling and increase the TMR ratio. This spacer layer mediates the magnetic interaction between adjacent layers, providing higher TMR values while maintaining a relatively simple overall structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If buffer layer and amorphous alloy spacer are added, then TMR and thermal stability are enhanced, but device complexity increases

Engineering Contradiction:

ImproveTMR and thermal stabilityVSAvoidlayer structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The MTJ structure is segmented into distinct functional layers: the buffer layer for crystal orientation control, the amorphous alloy spacer for exchange coupling enhancement, and the conventional MgO tunnel barrier for tunneling. This segmentation allows each layer to perform its specific function optimally while keeping the overall structure manageable and manufacturable.

Inventive Principle:

Principle #1Segmentation

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 proposed structure achieves high TMR up to ~150% and improved thermal stability by ensuring perpendicular magnetization and suppressing template effects, while maintaining strong exchange coupling and surface anisotropy, effectively addressing the challenges of in-plane magnetization and poor textures in MgO-based MTJs.

Implementation Method 1

The electrical resistance of an MTJ depends on whether the free layer magnetization and fixed layer magnetization are parallel or anti-parallel with each other

Methodology Applied

Scientific EffectTunnel magneto-resistance (TMR) effect: Magnetoresistance

Implementation Method 2

an amorphous alloy perpendicular magnetic anisotropy (PMA) enhancement spacer deposited on the bottom free layer

Methodology Applied

Scientific EffectSurface anisotropy: Anisotropy

Implementation Method 3

increasing exchange coupling to a TMR enhancement buffer layer

Methodology Applied

Scientific EffectExchange coupling: Ferromagnetism

Data Source

PatentUS9548445B2Amorphous alloy space for perpendicular MTJs

Publication Date: 2017.01.17 QUALCOMM INC

AI summary

A perpendicular magnetic tunnel junction (MTJ) apparatus includes a tunnel magnetoresistance (TMR) enhancement buffer layer deposited between the tunnel barrier layer and the reference layers. An amorphous alloy spacer is deposited between the TMR enhancement buffer layer and the reference layers to enhance TMR. The amorphous alloy spacer blocks template effects of face centered cubic (fcc) oriented pinned layers and provides strong coupling between the pinned layers and the TMR enhancement buffer layer to ensure full perpendicular magnetization.