CPP Magnetoresistive Head Antiparallel Free Layer Noise Reduction

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Solution Overview

Problem

Modern magnetoresistive sensors experience instability due to operating conditions, which degrades read operations by increasing noise in read signals, and increasing stability reduces sensitivity, necessitating a solution that enhances magnetic stability without compromising sensitivity.

Innovation Solution

The implementation of an antiparallel free layer structure with ferromagnetic and antiferromagnetic coupling layers in magnetoresistive sensors, which includes a first and second free layer with ferromagnetic coupling layers to enhance coupling with antiferromagnetic coupling layers, improving magnetic stability while maintaining sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the magnetic stability of the magnetoresistive sensor is increased, then the noise in read signals is reduced, but the sensitivity of the sensor to magnetized areas is reduced

Engineering Contradiction:

Improvemagnetic stabilityVSAvoidsensitivity

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The free layer is segmented into multiple sub-layers (first free layer, second free layer, third free layer) with different thicknesses, allowing each segment to contribute differently to the overall magnetic properties. This segmentation enables the sensor to achieve both stability and sensitivity by optimizing the magnetic characteristics of individual layers while maintaining their collective functionality.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the free layer are assigned different thicknesses to achieve local optimization of magnetic properties. The first free layer has a greater thickness than the second and third free layers, creating local variations in magnetic moment that enhance both stability and sensitivity in different operational aspects.

Inventive Principle:

Principle #3Local quality

2Measurement precision

If the thickness of the free layer is increased to improve sensitivity, then the magnetic stability is reduced

Engineering Contradiction:

ImprovesensitivityVSAvoidmagnetic stability

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The free layer is divided into multiple sub-layers with varying thicknesses, where the first free layer has greater thickness for sensitivity while the second and third free layers have smaller thicknesses for stability. This segmentation allows the sensor to achieve both high sensitivity and magnetic stability simultaneously.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The sensor employs a composite structure with multiple ferromagnetic layers (pinned layer, first free layer, second free layer, third free layer) separated by non-magnetic spacer layers. This composite architecture combines materials and structures with different magnetic properties to achieve both sensitivity and stability that cannot be obtained with a single uniform layer.

Inventive Principle:

Principle #40Composite materials

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 configuration increases magnetic stability while preserving sensitivity, allowing for effective reading of magnetic fields from hard drive disks with reduced noise in read signals.

Implementation Method 1

The first ferromagnetic coupling layer is configured to provide increased coupling between the first free layer and an antiferromagnetic coupling layer

Methodology Applied

Scientific EffectFerromagnetic coupling: Ferromagnetism

Implementation Method 2

providing the antiferromagnetic coupling layer formed on the first ferromagnetic coupling free layer

Methodology Applied

Scientific EffectAntiferromagnetic coupling: Magnetism

Implementation Method 3

a magnetoresistive sensor which senses the magnetic fields from the magnetized areas

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS7746603B2CPP Magnetoresistive head with different thickness free layers for improved signal to noise ratio

Publication Date: 2010.06.29 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A magnetoresistive sensor and method for forming the magnetoresistive sensor. The magnetoresistive sensor includes a first layer and an antiparallel free layer disposed on the first layer. The antiparallel free layer includes a first free layer disposed on the first layer and a first ferromagnetic coupling free layer disposed on the first free layer. The first ferromagnetic coupling layer is configured to provide increased coupling between the first free layer and an antiferromagnetic coupling layer. The antiparallel free layer also includes the antiferromagnetic coupling layer disposed on the first ferromagnetic coupling free layer, a second ferromagnetic coupling free layer disposed on the antiferromagnetic coupling layer, and a second free layer disposed on the second ferromagnetic coupling free layer. The second ferromagnetic coupling layer is configured to provide increased coupling between the second free layer and the antiferromagnetic coupling layer.