CoFeB Magnetoresistive Element Nitrogen Plasma Crystallization

Solution Overview

Problem

Conventional magnetoresistive elements with MTJ films formed by CoFeB/MgO/CoFeB face challenges in achieving high magnetoresistance ratios due to element diffusion and degradation during heat treatment, limiting the temperature to around 350°C, which restricts the attainment of high MR ratios and spin polarizability.

Innovation Solution

The use of nitrogen plasma heat treatment at 300°C to selectively nitride boron in the CoFeB layer, accelerating its crystallization and forming a boron nitride layer, which reduces the crystallization temperature and maintains the integrity of the MTJ film, thereby enhancing the MR ratio and spin polarizability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If heat treatment is performed at high temperature (500°C) to crystallize CoFeB and achieve high MR ratio, then the MR ratio is improved, but element diffusion occurs and the synthetic antiferromagnetic coupling is degraded

Engineering Contradiction:

ImproveMR ratioVSAvoidelement diffusion

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The invention changes the crystallization mechanism by introducing nitrogen plasma treatment, which modifies the chemical composition of the CoFeB layer through selective nitridation of boron. This parameter change (adding nitrogen) enables crystallization at lower temperatures (300°C) while maintaining the high MR ratio, thus resolving the contradiction between achieving high MR ratio and preventing element diffusion

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Nitrogen plasma acts as an intermediary that facilitates the crystallization process. The nitrogen atoms form boron nitride compounds during plasma treatment, which serve as a mediator to enable low-temperature crystallization of the CoFeB layer without requiring high thermal energy that would cause element diffusion

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stability of the object's composition

If heat treatment temperature is limited to 350°C to prevent element diffusion, then element composition stability is maintained, but the MR ratio and spin polarizability cannot be sufficiently improved

Engineering Contradiction:

Improveelement composition stabilityVSAvoidMR ratio

Core Design Contradiction:

Stability of the object's compositionVSManufacturing precision

Solution Approach 1:

The invention changes the crystallization mechanism by introducing nitrogen plasma treatment, which modifies the chemical composition of the CoFeB layer through selective nitridation of boron. This parameter change (adding nitrogen) enables crystallization at lower temperatures (300°C) while maintaining the high MR ratio, thus resolving the contradiction between achieving high MR ratio and preventing element diffusion

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Nitrogen plasma acts as an intermediary that facilitates the crystallization process. The nitrogen atoms form boron nitride compounds during plasma treatment, which serve as a mediator to enable low-temperature crystallization of the CoFeB layer without requiring high thermal energy that would cause element diffusion

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

This approach allows for the achievement of a high MR ratio of 91% while preventing element diffusion and maintaining the structural integrity of the MTJ film, improving read output and reducing write current requirements.

Implementation Method 1

The use of nitrogen plasma heat treatment at 300°C to selectively nitride boron in the CoFeB layer

Methodology Applied

Scientific EffectPlasma: Plasma

Implementation Method 2

selectively nitride boron in the CoFeB layer, accelerating its crystallization and forming a boron nitride layer

Methodology Applied

Scientific EffectNitriding: Nitriding

Implementation Method 3

500°C is the crystallization temperature at which Co40Fe40B20 in an amorphous state is crystallized

Methodology Applied

Scientific EffectCrystallization: Crystallisation

Implementation Method 4

Magnetoresistive elements each having a MTJ (Magnetic Tunnel Junction) film formed by CoFeB/MgO/CoFeB have high magnetoresistance ratios

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS8530887B2Magnetoresistive element, method of manufacturing the same, and magnetic memory

Publication Date: 2013.09.10 KIOXIA CORP

AI summary

A magnetoresistive element according to an embodiment includes: a first magnetic layer; a tunnel barrier layer on the first magnetic layer; a second magnetic layer placed on the tunnel barrier layer and containing CoFe; and a nonmagnetic layer placed on the second magnetic layer, and containing nitrogen and at least one element selected from the group consisting of B, Ta, Zr, Al, and Ce.