Multilayered TMR Reference Layer for AFM Coupling

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Solution Overview

Problem

Tunneling magnetoresistive (TMR) heads face a challenge in increasing antiferromagnetic (AFM) coupling between the reference layer and the keeper layer without degrading ferromagnetic coupling and tunneling magnetoresistance.

Innovation Solution

A method involving the formation of a magnetic head with a keeper layer, an AFM coupling layer, and a reference layer, where the reference layer includes CoFe, CoFeHf, and CoFeB layers, with CoFeHf being 20 atomic % Hf, and the layers of CoFeHf and CoFeB are directly adjacent, maintaining a thickness ratio less than 0.66, to enhance AFM coupling strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the AFM coupling between the reference layer and keeper layer is increased, then the AFM coupling strength is improved, but the ferromagnetic coupling between the reference layer and free layer increases which degrades TMR head performance

Engineering Contradiction:

ImproveAFM coupling strengthVSAvoidTMR head performance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The reference layer is segmented into multiple sub-layers including CoFe, CoFeHf, and CoFeB layers. This segmentation allows independent optimization of each layer's contribution to AFM coupling while controlling ferromagnetic coupling to the free layer, resolving the contradiction between strengthening AFM coupling and maintaining TMR performance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The reference layer employs a composite structure combining CoFe, CoFeHf (with about 20 atomic % Hf), and CoFeB layers in specific thickness ratios. This composite material approach enables tailored magnetic properties that simultaneously enhance AFM coupling strength and preserve acceptable ferromagnetic coupling characteristics for optimal TMR head performance.

Inventive Principle:

Principle #40Composite materials

2Strength

If the AFM coupling between the reference layer and keeper layer is increased, then the AFM coupling strength is improved, but the tunneling magnetoresistance decreases

Engineering Contradiction:

ImproveAFM coupling strengthVSAvoidtunneling magnetoresistance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

Different regions of the reference layer are assigned different material compositions and thicknesses to achieve local optimization. The CoFeHf layer with about 20 atomic % Hf provides enhanced AFM coupling locally, while the overall layer configuration maintains appropriate ferromagnetic coupling properties, thereby improving AFM coupling strength without substantially decreasing tunneling magnetoresistance.

Inventive Principle:

Principle #3Local quality

3Strength

If a typical TMR head structure is used, then the device complexity is low, but the AFM coupling strength is insufficient

Engineering Contradiction:

ImproveAFM coupling strengthVSAvoidreference layer structure

Core Design Contradiction:

StrengthVSDevice complexity

Solution Approach 1:

The reference layer is divided into multiple functional sub-layers (CoFe, CoFeHf, CoFeB) with specific thickness ratios. This segmentation enables enhanced AFM coupling strength while maintaining a structured approach that manages device complexity through systematic layer design rather than random complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention optimizes specific parameters including the Hf concentration (about 20 atomic %) in the CoFeHf layer and the thickness ratio between CoFeHf and CoFeB layers. By carefully controlling these parameters, the patent achieves substantially increased AFM coupling strength while keeping the overall device structure manageable and manufacturable.

Inventive Principle:

Principle #35Parameter changes

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 increases the AFM coupling strength by at least 20% and maintains tunneling magnetoresistance and exchange coupling strength, improving the performance of the TMR head.

Implementation Method 1

there is a weak antiferromagnetic (AFM) coupling between the reference layer and keeper layer through the antiferromagnetic (AFM) coupling layer

Methodology Applied

Scientific EffectAntiferromagnetic coupling: Magnetism

Implementation Method 2

an increase in the AFM coupling between the reference layer and the keeper layer can cause an increase in the ferromagnetic coupling between the reference layer and the free layer

Methodology Applied

Scientific EffectFerromagnetic coupling: Ferromagnetism

Implementation Method 3

tunneling magnetoresistance can decrease when the AFM coupling between the reference layer and the keeper layer increases

Methodology Applied

Scientific EffectTunneling magnetoresistance: Magnetoresistance

Data Source

PatentUS8218271B2TMR sensor with a multilayered reference layer

Publication Date: 2012.07.10 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

According to one embodiment, a method for forming at least a portion of a magnetic head includes forming a keeper layer, forming a reference layer, and forming an AFM coupling layer which is positioned between the keeper layer and the reference layer. In addition, forming the reference layer includes forming a layer of CoFe, depositing a layer of CoFeHf which is about 20 atomic % Hf, and depositing a layer of CoFeB such that the layers of CoFeHf and CoFeB are directly adjacent and a ratio of respective physical thicknesses of CoFeHf to CoFeB is less than about 0.66. Other embodiments are also included such as a magnetic head and additional methods for forming at least a portion of a magnetic head.