SAF Coupled Free Layer for p-MTJ Thermal Stability

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Solution Overview

Problem

Current magnetoresistive random access memory (MRAM) technologies face challenges in achieving high-density storage with good thermal stability and low switching current, particularly in maintaining high tunneling magnetoresistance (TMR) and perpendicular magnetic anisotropy (PMA) while ensuring data retention.

Innovation Solution

The implementation of a magnetic tunnel junction (MTJ) device structure comprising a first free ferromagnetic layer, a synthetic antiferromagnetic (SAF) coupling layer, and a second free ferromagnetic layer with opposite magnetic moments, along with specific materials like ruthenium (Ru) and chromium (Cr), to enhance tunneling magnetoresistance, perpendicular magnetic anisotropy, and thermal stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional MTJ structure is used, then the device complexity is low, but the tunneling magnetoresistance (TMR) and perpendicular magnetic anisotropy (PMA) are insufficient

Engineering Contradiction:

Improvetunneling magnetoresistanceVSAvoidMTJ structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The free ferromagnetic layer is segmented into multiple sub-layers (first free ferromagnetic layer and second free ferromagnetic layer) separated by a SAF coupling layer. This segmentation allows each layer to contribute differently to the magnetic properties, enabling enhanced TMR and PMA through the combined effect of multiple magnetic layers with opposite magnetic moments.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite material structures including the SAF coupling layer composed of alternating ferromagnetic and non-magnetic metal layers. This composite structure creates synthetic antiferromagnetic coupling that stabilizes the magnetic moments and enhances the overall TMR and PMA performance of the MTJ device.

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If high-density MRAM is achieved, then the storage capacity increases, but thermal stability and data retention deteriorate

Engineering Contradiction:

Improvestorage densityVSAvoidthermal stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The patent changes the magnetic parameters by introducing the SAF coupling layer that creates opposite magnetic moments in adjacent free layers. This parameter change in magnetic configuration enhances thermal stability through magnetic compensation effects while maintaining high storage density through the multi-layer structure.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The SAF coupling layer acts as an intermediary between the first and second free ferromagnetic layers, mediating their magnetic interactions. This intermediary structure enables stable magnetic coupling that preserves data retention at high densities by preventing unwanted magnetic switching and enhancing thermal stability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Use of energy by moving object

If the switching current is reduced, then the energy consumption decreases, but the magnetic anisotropy and data retention are compromised

Engineering Contradiction:

Improveswitching currentVSAvoiddata retention

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The SAF coupling layer provides a counterweight effect by creating opposite magnetic moments that balance each other. This magnetic compensation reduces the net magnetic field required for switching, thereby reducing switching current and energy consumption while the coupled structure maintains data retention through stable magnetic configurations.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

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 improves tunneling magnetoresistance, perpendicular magnetic anisotropy, and data retention, while maintaining magnetic and electrical properties at high process temperatures, effectively addressing the thermal stability and switching current challenges in MRAM devices.

Implementation Method 1

a synthetic antiferromagnetic (SAF) coupling layer disposed on the first free ferromagnetic layer; and a second free ferromagnetic layer disposed on the SAF coupling layer, the second free ferromagnetic layer having a second magnetic moment opposite to the first magnetic moment

Methodology Applied

Scientific EffectSynthetic antiferromagnetic coupling: Magnetic Field

Implementation Method 2

A STT-MTJ (Spin Torque Transfer MTJ) changes the spin orientation by using a switching current

Methodology Applied

Scientific EffectSpin torque transfer:

Implementation Method 3

the orientation of the magnetic field in the free ferromagnetic layer is perpendicular to the interface between the barrier and ferromagnetic layers

Methodology Applied

Scientific EffectPerpendicular magnetic anisotropy: Anisotropy

Data Source

PatentUS9324939B2Synthetic antiferromagnet (SAF) coupled free layer for perpendicular magnetic tunnel junction (p-MTJ)

Publication Date: 2016.04.26 QUALCOMM INC

AI summary

A magnetic tunnel junction (MTJ) device in a magnetoresistive random access memory (MRAM) and method of making the same are provided to achieve a high tunneling magnetoresistance (TMR), a high perpendicular magnetic anisotropy (PMA), good data retention, and a high level of thermal stability. The MTJ device includes a first free ferromagnetic layer, a synthetic antiferromagnetic (SAF) coupling layer, and a second free ferromagnetic layer, where the first and second free ferromagnetic layers have opposite magnetic moments.