Magnetic Tunnel Junction Spacer Layer for STT MRAM Read Reliability

Solution Overview

Problem

Spin torque switched (STT) MRAM faces challenges in read operations due to relatively low tunnel magnetoresistance (TMR) in magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA) materials, resulting from structural and chemical incompatibility between material layers, which complicates the resistance difference between high and low resistance states.

Innovation Solution

Incorporating a spacer layer made of non-magnetic materials, such as chromium (Cr), ruthenium (Ru), or magnesium oxide (MgO), between the interfacial and magnetic layers or within the magnetic layers to promote crystallization and prevent diffusion of TMR-degrading substances, thereby enhancing the TMR of PMA MTJs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If PMA materials are used in MTJs to reduce write current, then write current is reduced, but TMR becomes relatively low resulting in difficulty with read operations

Engineering Contradiction:

Improvewrite currentVSAvoidread operation reliability

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

A non-magnetic spacer layer is introduced as an intermediary between the tunnel barrier and the magnetic layers. This spacer layer promotes crystallization and prevents diffusion of TMR-degrading substances, thereby enhancing the TMR ratio without affecting the perpendicular magnetic anisotropy that enables low write current operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The MTJ structure is designed as a composite material system combining the tunnel barrier, non-magnetic spacer layer, and PMA magnetic layers. This composite structure leverages the beneficial properties of each material: the PMA layers provide perpendicular anisotropy for low write current, while the spacer layer enhances TMR through crystallization promotion and diffusion prevention.

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If MTJ size is reduced to lower write current, then write current is reduced, but read operation difficulty increases due to low TMR

Engineering Contradiction:

Improvewrite currentVSAvoidread operation difficulty

Core Design Contradiction:

Use of energy by moving objectVSDifficulty of detecting and measuring

Solution Approach 1:

The non-magnetic spacer layer serves as a mediator that enhances the TMR ratio by promoting crystallization at the interface and preventing diffusion of substances that would degrade TMR. This allows smaller MTJ sizes to maintain sufficient TMR for reliable read operations while still benefiting from reduced write current due to the perpendicular anisotropy of the PMA materials.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 spacer layers increase the TMR of PMA MTJs, improving the resistance difference between states and facilitating better read operations in STT MRAM by maintaining strong magnetic coupling and blocking substance diffusion.

Implementation Method 1

Incorporating a spacer layer made of non-magnetic materials, such as chromium (Cr), ruthenium (Ru), or magnesium oxide (MgO), between the interfacial and magnetic layers or within the magnetic layers to promote crystallization

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Implementation Method 2

Incorporating a spacer layer made of non-magnetic materials, such as chromium (Cr), ruthenium (Ru), or magnesium oxide (MgO), between the interfacial and magnetic layers or within the magnetic layers to promote crystallization and prevent diffusion of TMR-degrading substances

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS8492859B2Magnetic tunnel junction with spacer layer for spin torque switched MRAM

Publication Date: 2013.07.23 GLOBALFOUNDRIES US INC

AI summary

A magnetic tunnel junction (MTJ) includes first and second magnetic layers; a tunnel barrier located between the first and second magnetic layers; a first spacer layer located between the first magnetic layer and the tunnel barrier, the first spacer layer comprising a non-magnetic material; and a first interfacial layer located between the first spacer layer and the tunnel barrier.