Spin-Valve Element Design for Hard Disk Head Sensitivity

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Solution Overview

Problem

Current spin-valve elements face challenges in achieving further size reduction and higher sensitivity for magnetic sensing in hard disk drives due to limitations in spin diffusion length and structural complexity, which affects their ability to accurately detect small magnetic bits.

Innovation Solution

A spin-valve element design featuring a nonmagnetic unit with a free magnetic unit that has a changeable magnetization direction, pinned magnetic units, and a configuration where the free magnetic unit is not connected to an external electrode, allowing for spin mixing conductance at the contact surface between the free and nonmagnetic units, enabling efficient spin current transport and resistance sensing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If the spin-valve element size is reduced to detect smaller magnetic bits, then measurement precision is improved, but spin diffusion length becomes insufficient leading to signal loss

Engineering Contradiction:

Improvemagnetic bit detection precisionVSAvoidspin diffusion length

Core Design Contradiction:

Measurement precisionVSLength of stationary object

Solution Approach 1:

The patent introduces a vertical stacking dimension by placing multiple magnetic layers (pinned layer, free layer, separator layer) in the thickness direction. This allows the spin-valve element to maintain sufficient spin diffusion length in the lateral direction for signal transport while reducing the lateral footprint size for high-density bit detection, effectively resolving the contradiction by utilizing the third dimension.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

Solution Approach 2:

The patent employs composite magnetic layer structures including pinned magnetic layers, free magnetic layers, and separator layers with specific magnetic properties. These composite structures enable the element to achieve both small lateral dimensions for high resolution and sufficient vertical spin diffusion paths, maintaining signal integrity while enabling detection of smaller magnetic bits.

Inventive Principle:

Principle #40Composite materials

2Ease of manufacture

If the spin-valve element structure is simplified to reduce manufacturing complexity, then ease of manufacture is improved, but sensitivity and resolution are reduced

Engineering Contradiction:

Improvestructural complexityVSAvoidmagnetic field sensing sensitivity

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent divides the magnetic sensor into distinct functional segments: pinned magnetic layers for reference, free magnetic layers for sensing, and separator layers for isolation. This segmentation allows each layer to be optimized independently for its specific function while maintaining overall manufacturing simplicity through standardized layering processes, achieving both ease of manufacture and high sensitivity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent optimizes specific parameters of each magnetic layer including thickness, magnetization direction, and material composition. By carefully controlling these parameters, the element achieves high sensitivity and resolution without requiring complex structural configurations, enabling manufacturing simplicity to coexist with enhanced performance through parameter optimization rather than structural complexity.

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 design enhances sensitivity and resolution for magnetic field sensing by maintaining spin accumulation over longer distances and reducing structural complexity, enabling compact and high-yield manufacturing of spin-valve elements for hard disk heads.

Implementation Method 1

A maximum length of a contact surface between the first magnetic unit and the nonmagnetic unit is not more than a spin diffusion length of the nonmagnetic unit

Methodology Applied

Scientific EffectSpin diffusion: Diffusion

Implementation Method 2

The voltage sensor senses a voltage between the second magnetic unit and the third magnetic unit

Methodology Applied

Scientific EffectElectrical resistance sensing: Electrical Resistance

Implementation Method 3

The second magnetic unit contacts the nonmagnetic unit. A direction of magnetization of the second magnetic unit is pinned

Methodology Applied

Scientific EffectMagnetization pinning: Magnetism

Data Source

PatentUS20160035377A1Spin-valve element, hard disk head, and hard disk head assembly

Publication Date: 2016.02.04 KK TOSHIBA

AI summary

According to one embodiment, a spin-valve element includes a nonmagnetic unit, a first magnetic unit, a second magnetic unit, a third magnetic unit, a current source, and a voltage sensor. The current source is connected to the second magnetic unit and the third magnetic unit. The current source causes a current to flow between the second magnetic unit and the third magnetic unit via the nonmagnetic unit. The voltage sensor is connected to the second magnetic unit and the third magnetic unit. A maximum length of a contact surface between the first magnetic unit and the nonmagnetic unit is not more than a spin diffusion length of the nonmagnetic unit. A length of the first magnetic unit in a direction orthogonal to the contact surface is not more than 3 times a spin diffusion length of the first magnetic unit. The first magnetic unit does not contact an external electrode.