Dual Magnetic Tunnel Junction Structure Balancing MRAM Current and DRR

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Existing dual magnetic tunnel junction (DMTJ) designs face challenges in minimizing the critical switching current (ic) while maintaining acceptable net magnetoresistive ratio (DRR) and resistance-area product (RA) for integration into complementary metal oxide semiconductor (CMOS) technologies, which is crucial for enhancing memory density and reducing production costs.

Innovation Solution

A DMTJ design with a free layer sandwiched between tunnel barrier layers, where the first pinned layer's magnetization is antiparallel to the second pinned layer's magnetization, and the lower tunnel barrier layer has a significantly lower resistance-area product (RA1) than the upper tunnel barrier layer (RA2), optimizing all three parameters simultaneously.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the critical switching current is reduced for p-MTJs, then memory density and production cost are improved, but the spin torque transfer efficiency is insufficient and switching reliability deteriorates

Engineering Contradiction:

Improvememory densityVSAvoidswitching reliability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent divides the single spin filter structure into two separate spin filters (first spin filter and second spin filter) that act on the free layer from opposite directions. This segmentation allows each spin filter to contribute independently to the spin torque, enabling reduced critical current while maintaining sufficient switching reliability through the combined effect of both filters.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent utilizes antiparallel magnetization configuration between the first pinned layer and second pinned layer, creating counteracting spin torque contributions that constructively interfere on the free layer. This anti-parallel arrangement optimizes the net spin torque transfer efficiency, allowing lower critical current densities while preserving switching reliability.

Inventive Principle:

Principle #8Anti-weight (Counterweight)

2Use of energy by moving object

If a dual spin filter structure is used to reduce critical current, then spin torque transfer efficiency is improved, but the net magnetoresistive ratio (DRR) decreases

Engineering Contradiction:

Improvespin torque transfer efficiencyVSAvoidnet magnetoresistive ratio

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The patent applies different resistance-area (RA) product values to the first tunnel barrier and second tunnel barrier, creating local quality differences. By optimizing the RA products of individual barriers, the patent achieves high spin torque transfer efficiency through the dual spin filter while maintaining adequate net magnetoresistive ratio for reliable read operations.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes key parameters including the RA products of the tunnel barriers, the magnetization directions of pinned layers, and the thicknesses of magnetic layers to simultaneously optimize both spin torque transfer efficiency and net magnetoresistive ratio. These parameter adjustments enable the dual spin filter structure to achieve improved switching efficiency without sacrificing read margin.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If the net magnetoresistive ratio is increased for better read margin, then read reliability is improved, but the critical switching current increases

Engineering Contradiction:

Improveread reliabilityVSAvoidcritical switching current

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent segments the magnetoresistive effect into two separate p-MTJ substructures, each contributing to the overall read margin. This segmentation allows the device to achieve high net magnetoresistive ratio for reliable reading while the dual spin filter configuration reduces the critical switching current through enhanced spin torque transfer efficiency.

Inventive Principle:

Principle #1Segmentation

4Use of energy by moving object

If tunnel barrier layers are optimized for lower RA product, then critical current is reduced, but the tunnel barrier lifetime decreases

Engineering Contradiction:

Improvecritical currentVSAvoidtunnel barrier lifetime

Core Design Contradiction:

Use of energy by moving objectVSDuration of action of stationary object

Solution Approach 1:

The patent applies different RA product values to different tunnel barriers (first tunnel barrier and second tunnel barrier) rather than using a uniform design. This local quality approach allows optimization of critical current through lower RA products while distributing the stress and aging effects across multiple barriers with different characteristics, thereby extending the overall device lifetime.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the RA products of individual tunnel barriers to optimize the balance between critical current and device lifetime. By adjusting these parameters, the patent achieves reduced switching currents while maintaining acceptable reliability margins for the tunnel barrier layers.

Inventive Principle:

Principle #35Parameter changes

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 DMTJ design achieves a reduced critical switching current density with acceptable DRR and RA, enabling higher memory density and lower production costs by aligning pinned layers antiparallel and varying the oxidation states and thicknesses of tunnel barrier layers.

Implementation Method 1

create a spin torque effect on the free layer (FL) when a current is passed through the DMTJ

Methodology Applied

Scientific EffectSpin torque:

Implementation Method 2

first tunnel barrier layer (TB1) and an upper tunnel barrier (TB2) layer

Methodology Applied

Scientific EffectTunneling:

Implementation Method 3

lower tunnel barrier layer (TB1) and an upper tunnel barrier (TB2) layer

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS12501836B2Dual magnetic tunnel junction devices for magnetic random access memory (MRAM)

Publication Date: 2025.12.16 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A dual magnetic tunnel junction (DMTJ) is disclosed with a PL1/TB1/free layer/TB2/PL2 configuration wherein a first tunnel barrier (TB1) has a substantially lower resistance×area (RA1) product than RA2 for an overlying second tunnel barrier (TB2) to provide an acceptable magnetoresistive ratio (DRR). Moreover, first and second pinned layers, PL1 and PL2, respectively, have magnetizations that are aligned antiparallel to enable a lower critical switching current that when in a parallel alignment. The condition RA1<RA2 is achieved with one or more of a smaller thickness and a lower oxidation state for TB1 compared with TB2, with conductive (metal) pathways formed in a metal oxide or metal oxynitride matrix for TB1, or with a TB1 containing a dopant to create conducting states in the TB1 band gap. Alternatively, TB1 may be replaced with a metallic spacer to improve conductivity between PL1 and the FL.