Magnetic Tunnel Junction with Parallel Reference Layers to Reduce Write Errors

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Solution Overview

Problem

Conventional dual MTJ STT-MRAM devices suffer from high write error rates due to back-hopping of the reference layers, particularly when the free layer is in a parallel state with the reference layers, as the magnetization direction of the top reference layer is unstable and prone to flipping.

Innovation Solution

A dual MTJ STT-MRAM device with dual reference layers having parallel magnetization directions, where one reference layer is a positive spin polarization material and the other is a negative spin polarization material, stabilizing the magnetization directions of both layers through additive spin-transfer torque, reducing back-hopping by aligning the magnetization directions of the reference layers in parallel.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If dual reference layers with antiparallel magnetization directions are used in conventional STT-MRAM devices, then the spin-transfer torque effect can switch the free layer magnetization, but the reference layer magnetization becomes unstable and prone to back-hopping

Engineering Contradiction:

Improvewrite error rateVSAvoidreference layer magnetization stability

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent inverts the conventional antiparallel magnetization configuration of dual reference layers to a parallel magnetization configuration. This inversion fundamentally changes the magnetic interaction dynamics, preventing the back-hopping phenomenon that occurs in antiparallel configurations while maintaining the ability to achieve stable write operations in STT-MRAM devices.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the magnetization direction parameter of the reference layers from antiparallel to parallel alignment. This parameter change stabilizes the reference layer magnetization by eliminating the destabilizing interactions present in antiparallel configurations, thereby reducing write error rates and improving overall device reliability.

Inventive Principle:

Principle #35Parameter changes

2Ease of operation

If the top reference layer magnetization is aligned antiparallel to the bottom reference layer, then spin-transfer torque can be applied to switch states, but the top reference layer becomes unstable when the free layer is in a parallel state

Engineering Contradiction:

Improvespin-transfer torque switching capabilityVSAvoidtop reference layer magnetization stability

Core Design Contradiction:

Ease of operationVSStability of the object's composition

Solution Approach 1:

The patent inverts the magnetization alignment of the dual reference layers from antiparallel to parallel. This inversion resolves the instability of the top reference layer that occurs in antiparallel configurations when the free layer is in a parallel state, while preserving the spin-transfer torque switching capability through appropriate current application.

Inventive Principle:

Principle #13The other way round (Inversion)

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 parallel alignment of magnetization directions in the reference layers significantly reduces write error rates by stabilizing the magnetization of both reference layers, enhancing the reliability and stability of the memory cell operation.

Implementation Method 1

Spin-transfer torque (STT) refers to an effect in which the orientation of a magnetic layer in a magnetic tunnel junction or spin valve is modified by a spin-polarized current. When the spin-polarized current flows through a free layer of a magnetic tunnel junction or a spin valve, the electrons in the spin-polarized current can transfer at least some of their angular momentum to the free layer, thereby producing a torque on the magnetization of the free layer.

Methodology Applied

Scientific EffectSpin-transfer torque:

Implementation Method 2

A resistance differential of a magnetic tunnel junction between different magnetization states of the free layer can be employed to store data within the magnetoresistive random access memory (MRAM) cell depending on whether the magnetization of the free layer is parallel or antiparallel to the magnetization of the reference layer.

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS20250285669A1Magnetic tunnel junction with dual reference layers having parallel magnetization directions and methods for operating the same

Publication Date: 2025.09.11 SANDISK TECHNOLOGIES LLC

AI summary

A magnetoresistive memory cell includes a first electrode; a second electrode; and a layer stack located between the first electrode and the second electrode and comprising, from one end to another, a first reference layer, a first tunnel barrier layer, a free layer, a second tunnel barrier layer, and a second reference layer. A first one of the first reference layer and the second reference layer comprises a positive spin polarization material. A second one of the first reference layer and the second reference layer comprises a negative spin polarization material. A magnetization direction of the second reference layer is parallel to a magnetization direction of the first reference layer.