Modified Double Magnetic Tunnel Junction Structure for Low RA

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Solution Overview

Problem

Double magnetic tunnel junction (DMTJ) structures reduce switching current but compromise tunnel magnetoresistance (TMR), hindering efficient readout in spin-transfer torque (STT) MRAM devices.

Innovation Solution

A modified double magnetic tunnel junction (mDMTJ) structure with a narrow base and a non-magnetic, spin-conducting metallic spin diffusion layer, which reduces the resistance-area product (RA) of the tunnel barrier layer, allowing for efficient switching at low current and high TMR.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If a double magnetic tunnel junction (DMTJ) structure is used to reduce switching current, then switching current is reduced by about 2×, but tunnel magnetoresistance (TMR) is also reduced, hampering efficient readout

Engineering Contradiction:

Improveswitching currentVSAvoidtunnel magnetoresistance (TMR)

Core Design Contradiction:

Use of energy by moving objectVSMeasurement precision

Solution Approach 1:

The patent applies local quality by creating asymmetric tunnel barrier layers with different resistance-area products. The first tunnel barrier layer has a lower RA product optimized for spin injection, while the second tunnel barrier layer has a higher RA product optimized for readout TMR. This local differentiation allows each interface to be optimized for its specific function, resolving the contradiction between low switching current and high TMR.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent changes the resistance-area product parameter of the tunnel barrier layers to resolve the contradiction. By setting the first tunnel barrier layer with RA ≤ 1 Ω·μm² and the second with RA ≥ 5 Ω·μm², the patent optimizes spin injection efficiency for low switching current while maintaining high TMR for efficient readout.

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If the first tunnel barrier layer has a low resistance-area product for efficient spin injection, then switching current is reduced, but the overall device resistance may increase

Engineering Contradiction:

Improveswitching currentVSAvoiddevice resistance

Core Design Contradiction:

Use of energy by moving objectVSQuantity of substance

Solution Approach 1:

The patent applies asymmetry by designing the first tunnel barrier layer with a lower resistance-area product than the second tunnel barrier layer. This asymmetric configuration allows the first interface to be optimized for spin injection (low RA) while the second interface compensates for overall device resistance (higher RA), resolving the contradiction between efficient switching and acceptable device resistance.

Inventive Principle:

Principle #4Asymmetry

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 mDMTJ structure achieves efficient switching and speedy readout with reduced switching current and maintained high TMR, potentially exceeding 100-200%, compared to typical DMTJ devices.

Implementation Method 1

a non-magnetic, spin-conducting metallic spin diffusion layer, which reduces the resistance-area product (RA) of the tunnel barrier layer

Methodology Applied

Scientific EffectSpin diffusion: Diffusion

Implementation Method 2

spin-transfer torque (STT) MRAM

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 3

tunnel magnetoresistance (TMR)

Methodology Applied

Scientific EffectTunnel magnetoresistance: Magnetoresistance

Data Source

PatentUS12063868B2Low RA narrow base modified double magnetic tunnel junction structure

Publication Date: 2024.08.13 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A modified double magnetic tunnel junction (mDMTJ) structure is provided which includes a narrow base and the use of a spin diffusion layer (i.e., non-magnetic, spin-conducting metallic layer) which gives a low resistance-area product (RA) for the tunnel barrier layer that forms an interface with the spin diffusion layer.