Tunnel Junction Laminated Film With Hafnium for STT-MRAM Thermal Stability

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Solution Overview

Problem

Miniaturizing STT-MRAM elements for high-density magnetic memory leads to decreased thermal stability of the recording layer, compromising data retention and nonvolatility.

Innovation Solution

Incorporating a hafnium layer adjacent to the first ferromagnetic layer in a tunnel junction stacked film, enhancing perpendicular magnetic anisotropy and improving thermal stability of the recording layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the STT-MRAM element is miniaturized to achieve high-density magnetic memory, then the storage density increases, but the thermal stability of the recording layer decreases

Engineering Contradiction:

Improvestorage densityVSAvoidthermal stability

Core Design Contradiction:

Quantity of substanceVSStability of the object's composition

Solution Approach 1:

The invention uses a composite material structure by introducing a hafnium layer adjacent to the CoFeB recording layer. This composite structure (CoFeB + Hf) creates interface magnetic anisotropy that enhances perpendicular magnetic anisotropy energy, thereby improving thermal stability while maintaining the miniaturized high-density configuration. The hafnium layer serves as a non-magnetic metal that modifies the magnetic properties of the adjacent ferromagnetic layer through interface effects.

Inventive Principle:

Principle #40Composite materials

2Volume of moving object

If the recording layer thickness is reduced to enable miniaturization, then the device size decreases, but the thermal stability factor decreases

Engineering Contradiction:

Improvedevice sizeVSAvoidthermal stability factor

Core Design Contradiction:

Volume of moving objectVSStability of the object's composition

Solution Approach 1:

The invention changes the magnetic anisotropy parameter by introducing the hafnium layer, which induces interface magnetic anisotropy. This parameter change compensates for the reduction in thermal stability factor caused by thinner recording layers. The perpendicular magnetic anisotropy energy is enhanced through the interface between CoFeB and Hf, allowing thin recording layers to maintain sufficient thermal stability for data retention.

Inventive Principle:

Principle #35Parameter changes

3Power

If a ferromagnetic layer with high spin orbit interaction is used to increase spin polarizability, then the magnetization reversal efficiency improves, but the damping constant increases

Engineering Contradiction:

Improvemagnetization reversal efficiencyVSAvoiddamping constant

Core Design Contradiction:

PowerVSUse of energy by moving object

Solution Approach 1:

The hafnium layer acts as an intermediary between the CoFeB recording layer and the surrounding structure. It modifies the interface properties to enhance perpendicular magnetic anisotropy while maintaining low damping constant. The Hf layer serves as a mediator that enables efficient spin transfer torque magnetization reversal without the adverse effects of high damping that would result from using heavy metals with strong spin-orbit coupling.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 hafnium layer enhances the thermal stability of the magnetization, allowing for a tunnel junction stacked film and magnetic memory element with high thermal stability and nonvolatility.

Implementation Method 1

the perpendicular magnetic anisotropy of the first ferromagnetic layer is improved, and as a result thereof, a thermal stability of a magnetization of the first ferromagnetic layer adjacent to the hafnium layer is improved

Methodology Applied

Scientific EffectPerpendicular magnetic anisotropy: Anisotropy

Implementation Method 2

when a current flows through the MTJ, polarized electron spins flow into the recording layer, and the magnetization direction of the recording layer is reversed by the spin transfer torque induced by the polarized electron spins

Methodology Applied

Scientific EffectSpin transfer torque:

Data Source

PatentUS12520732B2Tunnel junction laminated film, magnetic memory element, and magnetic memory

Publication Date: 2026.01.06 TOHOKU UNIV

AI summary

Provided are a tunnel junction stacked film having a high thermal stability, and a magnetic memory element and a magnetic memory using the tunnel junction stacked film. A tunnel junction stacked film 1 includes a recording layer 14 including a first ferromagnetic layer 24 containing boron, a tunnel junction layer 13 adjacent to the recording layer 14, and a reference layer 12 adjacent to the tunnel junction layer 13, wherein the first ferromagnetic layer 24 and the reference layer 12 are magnetized in a perpendicular direction with respect to a film surface, and the recording layer 14 includes a hafnium layer 25 adjacent to the first ferromagnetic layer 24.