Boron Oxide Intermediate Layer for Low-Current MRAM

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Solution Overview

Problem

Conventional magnetoresistive random access memories (MRAMs) face challenges in reducing cell size while maintaining low current requirements for ultrahigh capacity, as the coercive force increases with smaller MTJ element sizes, leading to higher writing currents and lower TMR ratios due to Fe alloy oxidization at interfaces, limiting scalability and read/write performance.

Innovation Solution

A magnetoresistive effect element with a boron-containing oxide intermediate layer between the magnetization pinned and free layers, allowing bidirectional current application to reversibly change the magnetization direction, thereby reducing areal resistance and enhancing the TMR ratio, using a film stack with specific layer structures and boron distribution to prevent oxidization and improve crystallinity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of moving object

If the size of MTJ element is reduced to increase capacity, then the cell size decreases, but the coercive force becomes larger and the writing current becomes higher

Engineering Contradiction:

Improvecell sizeVSAvoidwriting current

Core Design Contradiction:

Area of moving objectVSUse of energy by moving object

Solution Approach 1:

A non-magnetic intermediate layer is introduced between the barrier layer and the magnetic layer. This intermediate layer acts as a mediator that prevents direct contact and oxidization between Fe atoms and oxygen, thereby reducing interface resistance and enabling lower writing currents even in scaled-down cells

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The intermediate layer uses a simple material structure (non-magnetic layer with specific magnetization characteristics) that can be easily formed through standard deposition processes, providing an effective solution without adding significant complexity or cost to the MTJ structure

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Ease of operation

If Fe alloy is used for magnetization layer, then the magnetization reversing function is achieved, but oxidization occurs at the interface and the resistance becomes higher

Engineering Contradiction:

Improvemagnetization reversing functionVSAvoidinterface resistance

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The non-magnetic intermediate layer serves as a protective barrier that prevents oxygen from reaching the Fe alloy magnetic layer. This mediator layer eliminates the harmful oxidization reaction while maintaining the necessary magnetization reversing function through spin injection

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The intermediate layer, while adding an additional interface, actually reduces the overall resistance by preventing the formation of high-resistance Fe oxide layers. The potential harm of adding another interface is converted into the benefit of protecting the magnetic layer from oxidization

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 solution enables magnetization reversal with low current, achieving low areal resistance and high TMR ratios, improving scalability and performance by preventing Fe, Co, and Ni oxidization at interfaces and maintaining effective electric conduction characteristics.

Implementation Method 1

due to oxidization of Fe at the interface between the barrier layer and a magnetic layer (the magnetization free layer or the reference magnetization layer), the resistance R of the MTJ element becomes higher

Methodology Applied

Scientific EffectOxidation prevention: Oxidation

Implementation Method 2

MRAMs utilizing a spin momentum transfer (SMT) writing method (hereinafter referred to as the spin-injection writing method) as the writing method to counter the above problem have been suggested

Methodology Applied

Scientific EffectSpin momentum transfer:

Implementation Method 3

magnetoresistive random access memories (hereinafter referred to also as MRAMs) as solid-state magnetic memories utilizing tunneling magnetoresistive effects (hereinafter referred to also as TMR effects)

Methodology Applied

Scientific EffectTunneling magnetoresistive effect: Magnetoresistance

Data Source

PatentUS7920361B2Magnetoresistive effect element with intermediate oxide layer containing boron and an element selected from Ca, Mg, Sr, Ba, Ti, and Sc

Publication Date: 2011.04.05 KIOXIA CORP

AI summary

It is made possible to provide a magnetoresistive effect element that can reverse magnetization direction with a low current, having low areal resistance (RA) and a high TMR ratio. A magnetoresistive effect element includes: a film stack that includes a magnetization free layer including a magnetic layer in which magnetization direction is changeable, a magnetization pinned layer including a magnetic layer in which magnetization direction is pinned, and an intermediate layer provided between the magnetization free layer and the magnetization pinned layer, the intermediate layer being an oxide containing boron (B) and an element selected from the group consisting of Ca, Mg, Sr, Ba, Ti, and Sc. Current is applied bidirectionally between the magnetization pinned layer and the magnetization free layer through the intermediate layer, so that the magnetization of the magnetization free layer is reversible.