Magnetic Disk Protective Layer Thickness Variation

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Solution Overview

Problem

Magnetic disks using the Load/Unload method face issues with fly-stiction and particle formation due to the roughness of the side surface portion and the thin protective layer, leading to instability and contamination, especially at low flying heights of 10 nm or less, which affects recording density and durability.

Innovation Solution

A magnetic disk with a protective layer that is thinner on the side surface portion than on the principal surface, and a manufacturing method involving plasma CVD to form the protective layer with varying thicknesses, including a chamfered surface with an amorphous carbonaceous protective layer, to prevent particle formation and improve durability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the protective layer is made thicker to improve abrasion resistance, then durability is improved, but spacing losses increase and recording density decreases

Engineering Contradiction:

Improveabrasion resistanceVSAvoidrecording density

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The patent applies different thicknesses of protective layers to different regions of the magnetic disk. The principal surface has a protective layer thickness of 3-8 nm optimized for recording density, while the side surface portion has a protective layer thickness of 1-3 nm that prevents particle formation. This local differentiation resolves the contradiction by providing sufficient protection where needed without compromising recording performance in data zones.

Inventive Principle:

Principle #3Local quality

2Reliability

If the protective layer on the side surface portion is made thicker to prevent particle formation, then reliability is improved, but spacing losses increase and recording density decreases

Engineering Contradiction:

Improveparticle formation preventionVSAvoidrecording density

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent specifically addresses the side surface portion by applying a thinner protective layer (1-3 nm) compared to the principal surface (3-8 nm). This local quality approach prevents particle formation at the side surface where roughness causes adhesion issues, while maintaining sufficient thickness on the principal surface for recording density requirements.

Inventive Principle:

Principle #3Local quality

3Manufacturing precision

If the magnetic head flies at extremely low height (10 nm or less) to improve recording density, then recording capacity increases, but fly-stiction occurs causing instability

Engineering Contradiction:

Improverecording densityVSAvoidflying stability

Core Design Contradiction:

Manufacturing precisionVSStability of the object's composition

Solution Approach 1:

The patent creates a locally optimized surface by applying a protective layer with specific thickness (3-8 nm) on the principal surface where data is recorded. This localized treatment maintains extremely low flying height for high recording density while the protective layer prevents direct contact between the magnetic head and disk surface, avoiding fly-stiction.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The protective layer is applied in advance to the principal surface before the magnetic head operates. This preliminary action creates a protective barrier that prevents fly-stiction from occurring during low-height flying operations, enabling stable recording at 10 nm or less flying height.

Inventive Principle:

Principle #10Preliminary action

4Reliability

If the side surface portion is highly polished to reduce roughness, then particle formation is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improveparticle formation preventionVSAvoidmanufacturing process complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies a protective layer specifically to the side surface portion with a thickness of 1-3 nm, which is thinner than on the principal surface. This local application reduces particle formation caused by surface roughness without requiring extensive polishing or other complex manufacturing processes for the entire disk surface.

Inventive Principle:

Principle #3Local quality

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

The solution effectively reduces particle occurrence and fly-stiction, enhancing the magnetic disk's stability and recording density while improving durability, especially under harsh conditions like those in mobile HDDs.

Implementation Method 1

a manufacturing method involving plasma CVD to form the protective layer with varying thicknesses

Methodology Applied

Scientific EffectPlasma CVD: Plasma Enhanced Chemical Vapour Deposition

Data Source

PatentUS7736768B2Magnetic disk and manufacturing method thereof

Publication Date: 2010.06.15 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A magnetic disk comprises a magnetic layer and a protective layer sequentially formed on a disk-shaped substrate and has a principal surface to which data is recorded, and a side surface portion both of which are coated with the protective layer. The protective layer on the side surface portion is thinner than the protective layer on the principal surface. Preferably, the side surface portion includes a side wall surface, and a chamfered surface lying between the side wall surface and the principal surface, and at least the protective layer on the chamfered surface is thinner than the protective layer on the principal surface.