Dual Magnetoresistance Element for MRAM Write-Read Trade-off

Solution Overview

Problem

In magnetic random access memory (MRAM) based on the spin transfer magnetization switching method, there is a conflict between reducing the write threshold current density and achieving a high magnetoresistance ratio, as perpendicular magnetization films with appropriate material characteristics for low write current density struggle to provide high spin polarization, and in-plane magnetization films with high spin polarization face challenges in reducing write threshold current density.

Innovation Solution

A magnetoresistance effect element is designed with a first magnetization free layer having perpendicular magnetic anisotropy and a second magnetization free layer with in-plane magnetic anisotropy, where the first and second magnetization free layers are magnetically coupled, allowing for independent optimization of write and read characteristics by using perpendicular magnetization films for writing and in-plane magnetization films for reading.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If perpendicular magnetization films with appropriate material characteristics are used, then write threshold current density is reduced, but spin polarization becomes low resulting in low magnetoresistance ratio

Engineering Contradiction:

Improvewrite threshold current densityVSAvoidmagnetoresistance ratio

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The invention divides the magnetic memory cell into two separate magnetoresistance effect elements: the first element uses perpendicular magnetization films optimized for low write current density, while the second element uses in-plane magnetization films optimized for high magnetoresistance ratio. This segmentation allows each element to be independently optimized for its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention transitions from a single-element approach to a dual-element stacked configuration, adding a vertical dimension to the device architecture. The first magnetoresistance effect element is stacked with the second element, allowing independent optimization in different dimensional orientations (perpendicular vs. in-plane magnetization).

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If in-plane magnetization films with high spin polarization are used, then magnetoresistance ratio is high, but write threshold current density cannot be reduced

Engineering Contradiction:

Improvemagnetoresistance ratioVSAvoidwrite threshold current density

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The invention divides the magnetic memory cell into two separate magnetoresistance effect elements: the first element uses perpendicular magnetization films optimized for low write current density, while the second element uses in-plane magnetization films optimized for high magnetoresistance ratio. This segmentation allows each element to be independently optimized for its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the magnetic memory cell are assigned different magnetic anisotropy characteristics: the first element region has perpendicular magnetic anisotropy for efficient writing, while the second element region has in-plane magnetic anisotropy for high read signal. Each local region has optimized quality for its specific operation.

Inventive Principle:

Principle #3Local quality

3Device complexity

If a single magnetization free layer is used, then device complexity is low, but both write and read characteristics cannot be independently optimized

Engineering Contradiction:

Improvenumber of magnetic layersVSAvoidindependent optimization capability

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The invention divides the magnetic memory cell into two separate magnetoresistance effect elements: the first element uses perpendicular magnetization films optimized for low write current density, while the second element uses in-plane magnetization films optimized for high magnetoresistance ratio. This segmentation allows each element to be independently optimized for its specific function without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The magnetic memory cell achieves multi-functionality by combining two different magnetoresistance effect elements with different magnetic anisotropy characteristics. The first element primarily handles write operations while the second element handles read operations, allowing the single device to perform both functions with independently optimized characteristics.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 enables improved write and read characteristics independently, reducing write threshold current density while maintaining a high magnetoresistance ratio, thus enhancing both data writing and reading efficiency in MRAM.

Implementation Method 1

a first magnetization free layer and a second magnetization free layer which are magnetically coupled to each other

Methodology Applied

Scientific EffectMagnetic coupling: Ferromagnetism

Implementation Method 2

interaction between spin-polarized conduction electrons of the write current and local electrons in the first magnetic layer causes switching of the magnetization of the first magnetic layer

Methodology Applied

Scientific EffectSpin transfer magnetization switching:

Implementation Method 3

a giant MR ratio (about 500% at room temperature) can be obtained in the Co—Fe—B/Mg—O/Co—Fe—B MTJ

Methodology Applied

Scientific EffectMagnetoresistance effect: Magnetoresistance

Implementation Method 4

(001)-oriented polycrystalline MgO that exhibits high spin filtering effect is formed by annealing Mg—O sandwiched between amorphous Co—Fe—B at high temperature

Methodology Applied

Scientific EffectSpin filtering effect:

Data Source

PatentUS8154913B2Magnetoresistance effect element and magnetic random access memory

Publication Date: 2012.04.10 NEC CORP

AI summary

A magnetoresistance effect element comprising: a first magnetization fixed layer whose magnetization direction is fixed; a first magnetization free layer whose magnetization direction is variable; a first nonmagnetic layer sandwiched between the first magnetization fixed layer and the first magnetization free layer; a second magnetization fixed layer whose magnetization direction is fixed; a second magnetization free layer whose magnetization direction is variable; and a second nonmagnetic layer sandwiched between the second magnetization fixed layer and the second magnetization free layer. The first magnetization fixed layer and the first magnetization free layer have perpendicular magnetic anisotropy, while the second magnetization fixed layer and the second magnetization free layer have in-plane magnetic anisotropy. The first magnetization free layer and the second magnetization free layer are magnetically coupled to each other. In a plane parallel to each layer, center of the second magnetization free layer is displaced from center of the first magnetization free layer.