Multi-Free Layer MRAM for Thermal Stability and Switching Current

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Solution Overview

Problem

The thermal stability of spin transfer torque magnetic random access memory (STT-MRAM) devices degrades with miniaturization, requiring higher switching currents to maintain long-term data retention.

Innovation Solution

A magnetic random access memory (MRAM) element with multiple magnetic free layers coupled in series, including a first and second magnetic reference layer with fixed magnetization directions and three magnetic free layers with variable magnetization directions, providing improved thermal stability and reduced switching current requirements through anti-ferromagnetic or ferromagnetic coupling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the size of the perpendicular MTJ is reduced for scalability, then device miniaturization is achieved, but thermal stability of the magnetic layers degrades

Engineering Contradiction:

ImproveMTJ sizeVSAvoidthermal stability

Core Design Contradiction:

Volume of moving objectVSStability of the object's composition

Solution Approach 1:

The patent divides the single free layer into multiple free layers (first magnetic free layer and second magnetic free layer) coupled in series between the reference layer and the electrode. This segmentation allows each layer to contribute to thermal stability while maintaining overall device scalability, as the composite structure provides enhanced energy barrier without requiring a single large layer.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs a composite magnetic structure with multiple magnetic layers (reference layer, first free layer, second free layer) with different magnetic properties coupled together. This composite structure achieves superior thermal stability compared to single-layer designs, as the combined magnetic moments and anisotropy energies provide a higher energy barrier against thermal fluctuations while allowing device miniaturization.

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If the anisotropies and magnetic moments of the magnetic layers are increased to improve thermal stability, then thermal stability is improved, but the switching current required increases

Engineering Contradiction:

Improvethermal stabilityVSAvoidswitching current

Core Design Contradiction:

Stability of the object's compositionVSUse of energy by moving object

Solution Approach 1:

By segmenting the free layer into multiple layers with different magnetic moment magnitudes, the patent enables the first free layer to have higher magnetic moment for thermal stability while the second free layer can have lower magnetic moment, reducing the overall switching current requirement. The series coupling allows the spin transfer torque to act on multiple layers sequentially.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies different magnetic moment magnitudes to different free layers, creating local quality variations. The first magnetic free layer can be designed with higher magnetic moment for stability, while the second magnetic free layer uses lower magnetic moment material or thinner thickness to reduce switching current, optimizing the trade-off locally in each layer.

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

The MRAM element achieves enhanced thermal stability and lowers the switching current needed, maintaining data retention while scaling down the device size.

Implementation Method 1

Spin transfer torque magnetic random access memory (STT-MRAM) is a new class of non-volatile memory

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

the electrical resistance of the magnetic memory element would change accordingly, thereby switching the stored logic

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Implementation Method 3

electrons polarized by the magnetic reference layer can tunnel through the insulating tunnel junction layer

Methodology Applied

Scientific EffectQuantum tunneling:

Implementation Method 4

A magnetic random access memory (MRAM) element with multiple magnetic free layers coupled in series

Methodology Applied

Scientific EffectFerromagnetic coupling: Ferromagnetism

Implementation Method 5

providing improved thermal stability and reduced switching current requirements through anti-ferromagnetic or ferromagnetic coupling

Methodology Applied

Scientific EffectAnti-ferromagnetic coupling:

Data Source

PatentUS9166143B1Magnetic random access memory with multiple free layers

Publication Date: 2015.10.20 AVALANCHE TECHNOLOGY INC

AI summary

The present invention is directed to a magnetic random access memory element comprising a first magnetic reference layer, a first insulating tunnel junction layer, a first magnetic free layer, a first coupling layer, a second magnetic free layer, a second coupling layer, a third magnetic free layer, a second insulating tunnel junction layer, and a second magnetic reference layer formed in sequence. The first and second magnetic reference layers have respectively a first and second fixed magnetization directions that are substantially perpendicular to respective layer planes and are substantially opposite to each other. The first, second, and third magnetic free layers have respectively a first, second, and third variable magnetization directions that are substantially perpendicular to respective layer planes. The second variable magnetization direction may be parallel or anti-parallel to the first and third variable magnetization directions.