Trilayer Reader Current Constraint at Air Bearing Surface

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Solution Overview

Problem

Magnetoresistive sensors with trilayer stacks face challenges in achieving both sensitivity and stability due to variability in sensor output and magnetically unstable parts, particularly when the stripe height is longer than the reader width, leading to electrical shunting and decreased sensor output.

Innovation Solution

The introduction of an insulator layer that partially covers the trilayer stack, constraining current flow to the vicinity of the air bearing surface, effectively blocking electrical shunting at the back end of the sensor stack and enhancing sensitivity and stability by maintaining the magnetization orientations in a scissor relationship.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the stripe height is made longer than the reader width to increase sensitivity, then the sensor output is improved, but electrical shunting occurs at the back end of the stack which decreases sensor output and stability

Engineering Contradiction:

Improvesensor sensitivityVSAvoidsensor stability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent divides the current path into two distinct regions by introducing an insulator layer: a first region near the air bearing surface where current flows through the trilayer stack, and a second region at the back end where current is blocked. This segmentation prevents electrical shunting while maintaining the long stripe height geometry needed for sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The insulator layer acts as an intermediary element that selectively blocks current flow at the back end of the trilayer stack. This intermediary structure prevents the harmful electrical shunting effect while allowing the beneficial long stripe height configuration to remain in place for enhanced sensitivity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If current flows through the entire trilayer stack including the back end, then the current path is simple, but electrical shunting occurs which decreases sensor output

Engineering Contradiction:

Improvesensor outputVSAvoidelectrical shunting

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent extracts or removes the harmful electrical shunting path from the system by introducing the insulator layer at the back end. This extraction eliminates the energy loss mechanism while preserving the useful current flow path through the sensing region near the air bearing surface.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The insulator layer serves as an intermediary that blocks the harmful current shunt path at the back end of the stack, preventing energy loss while allowing the productive current flow to continue through the trilayer stack in the sensing region.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Stability of the object's composition

If no insulator layer is present, then the device structure is simpler, but magnetization orientations cannot be maintained in a stable scissor relationship

Engineering Contradiction:

Improvemagnetization stabilityVSAvoidlayer structure complexity

Core Design Contradiction:

Stability of the object's compositionVSDevice complexity

Solution Approach 1:

The insulator layer segments the trilayer stack into a stable front region near the air bearing surface where magnetization orientations are maintained, and a blocked back region where electrical shunting is prevented. This segmentation enables stable magnetization configuration without excessive structural complexity.

Inventive Principle:

Principle #1Segmentation

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 sensor output and stability by ensuring that the current flow is confined to the air bearing surface, thereby preventing electrical shunting and improving the robustness and sensitivity of the magnetoresistive sensing signal.

Implementation Method 1

A magnetoresistive sensor has at least a trilayer stack comprising a cap layer, a first ferromagnetic layer, and a second ferromagnetic layer separated by a nonmagnetic layer

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Implementation Method 2

The trilayer sensor is biased by a back biasing magnet positioned at the back end of the stack

Methodology Applied

Scientific EffectMagnetic field: Magnetic Field

Data Source

PatentUS8659855B2Trilayer reader with current constraint at the ABS

Publication Date: 2014.02.25 SEAGATE TECH LLC

AI summary

A magnetoresistive read sensor with improved sensitivity and stability is described. The sensor is a trilayer stack positioned between two electrodes. The trilayer stack has two free layers separated by a nonmagnetic layer and a biasing magnet positioned at the rear of the stack and separated from the air bearing surface. Current in the sensor is confined to regions close to the air bearing surface by an insulator layer to enhance reader sensitivity.