MTJ Switching With a Chiral PSM Layer for Lower Current

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Solution Overview

Problem

Existing STT-MRAM technologies face challenges in achieving lower switching currents and providing additional sources of spin-transfer-torque without complicating the fabrication process.

Innovation Solution

The integration of a parallel spin-momentum (PSM) layer with a chiral material adjacent to the free layer of an MTJ device, which provides an additional source of spin-transfer-torque and is compatible with magnetic structures having perpendicular magnetic anisotropy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a dual MTJ structure is used to provide additional spin-transfer-torque, then switching current is reduced, but MTJ stack thickness increases and top reference layer stability deteriorates

Engineering Contradiction:

Improveswitching currentVSAvoidMTJ stack thickness

Core Design Contradiction:

Use of energy by moving objectVSDevice complexity

Solution Approach 1:

The invention separates the spin torque generation function from the MTJ stack by introducing a distinct PSM layer adjacent to the free layer. This segmentation allows the MTJ stack to remain thin while the PSM layer provides the additional spin transfer torque needed for reduced switching current, avoiding the need to increase MTJ stack thickness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The PSM layer acts as an intermediary component that mediates between the current path and the free layer. It converts charge current into spin current that exerts torque on the free layer, providing additional spin transfer torque without requiring changes to the MTJ stack structure or increasing its thickness.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Use of energy by moving object

If SOT material is added adjacent to free layer to provide spin-orbit coupling torque, then switching current is reduced, but fabrication complexity increases

Engineering Contradiction:

Improveswitching currentVSAvoidfabrication process

Core Design Contradiction:

Use of energy by moving objectVSEase of manufacture

Solution Approach 1:

The PSM layer is designed to be compatible with existing MTJ device structures and fabrication processes. It can be integrated into the existing stack without requiring new material systems or complex fabrication steps, making it a universal solution that works with standard perpendicular magnetic anisotropy structures.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The invention changes the physical arrangement and material composition parameters of the device by introducing the PSM layer with specific chiral materials. This parameter change enables spin transfer torque generation while maintaining compatibility with existing fabrication processes, avoiding the need for complex SOT material integration.

Inventive Principle:

Principle #35Parameter changes

3Use of energy by moving object

If perpendicular magnetic anisotropy is used in MTJ, then switching current is reduced, but magnetic layer stability requirements increase

Engineering Contradiction:

Improveswitching currentVSAvoidreference layer stability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The PSM layer is positioned locally adjacent to the free layer, creating a localized interaction region. This local quality approach allows the reference layer to maintain its perpendicular magnetic anisotropy and stability while the PSM layer provides the additional torque needed for switching, separating the stability function from the switching function.

Inventive Principle:

Principle #3Local quality

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 approach allows for lower switching currents and alleviates fabrication challenges associated with previous methods, while maintaining compatibility with existing MTJ device structures.

Implementation Method 1

a parallel spin-momentum (PSM) layer formed over the free layer of the MTJ, the PSM layer including a chiral material

Methodology Applied

Scientific EffectSpin Hall Effect: Hall Effect

Implementation Method 2

STT-MRAM changes the magnetic direction of the free layer by directly passing a spin-polarized current through the MTJ

Methodology Applied

Scientific EffectSpin Transfer Torque:

Implementation Method 3

MTJs with positive tunnel magnetoresistance (TMR), when a sufficient current is driven in one direction perpendicular-to-plane

Methodology Applied

Scientific EffectTunnel Magnetoresistance: Magnetoresistance

Data Source

PatentEP4557931A1Magnetic tunneling junction switching with parallel spin-momentum locked spin current

Publication Date: 2025.05.21 SAMSUNG ELECTRONICS CO LTD

Figure 1A~1B
Figure 2A~2B
Figure 3A~3B

AI summary

A MRAM device utilizing spin transfer torque includes a substrate; an MTJ formed over the substrate, the MTJ including a reference layer, a tunnel barrier layer, and a free layer; and a PSM layer formed over the free layer of the MTJ. The PSM layer, i.e., a chiral material layer, may be formed adjacent to a free layer (or adjacent to a TBL, which is adjacent to the free layer) of the MTJ, providing an additional source of spin-transfer-torque, and providing MTJ devices that are operable with lower switching current.