Fly Height Control for HAMR Data Storage Devices

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Solution Overview

Problem

Existing data storage devices face challenges in maintaining a consistent fly height of the head over the disk surface during write operations, especially due to thermal protrusion caused by heat-assisted magnetic recording (HAMR), which affects data recording accuracy and reliability.

Innovation Solution

The implementation of a control circuitry that adjusts the fly height actuator settings based on measured fly height profiles, using a laser to heat the disk and subsequently read a fly height pattern to compensate for thermal protrusion, ensuring a target fly height is maintained throughout the write operation by adjusting the laser power and fly height actuator settings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If laser power is increased to heat the disk for HAMR write operations, then data recording quality is improved, but thermal protrusion causes fly height to deviate from target

Engineering Contradiction:

Improvedata recording qualityVSAvoidfly height consistency

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The system performs preliminary fly height measurements during disk rotation to predict thermal protrusion effects before they occur during write operations. Based on these measurements, the fly height actuator settings are pre-adjusted to compensate for expected thermal expansion, ensuring the head maintains proper fly height even when laser heating causes thermal protrusion during subsequent write operations.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system implements a feedback mechanism where fly height measurements taken during disk rotation are fed back to adjust fly height actuator settings. The control circuitry continuously monitors fly height deviations and modifies actuator settings in real-time to maintain target fly height, creating a closed-loop control system that compensates for thermal protrusion effects.

Inventive Principle:

Principle #23Feedback

2Reliability

If fly height actuator settings are adjusted to compensate for thermal protrusion, then fly height consistency is improved, but additional control complexity is introduced

Engineering Contradiction:

Improvefly height consistencyVSAvoidcontrol circuitry complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system uses the disk's own rotation and the existing read channel to perform fly height measurements, rather than requiring separate measurement apparatus. The fly height actuator settings are self-adjusted based on measurements taken during normal disk operation, allowing the system to compensate for thermal protrusion using its existing operational cycles without adding significant external complexity.

Inventive Principle:

Principle #25Self-service

3Measurement precision

If fly height measurements are taken during disk rotation, then measurement of thermal protrusion is enabled, but measurement timing and synchronization become more difficult

Engineering Contradiction:

Improvefly height measurement capabilityVSAvoidmeasurement synchronization difficulty

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

Fly height measurements are taken during dedicated measurement revolutions before actual write operations begin. This preliminary measurement approach allows the system to capture fly height data under controlled conditions, establish baseline values, and predict thermal protrusion characteristics before the disk enters write mode, simplifying the synchronization requirements.

Inventive Principle:

Principle #10Preliminary action

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 ensures a consistent fly height is maintained, enhancing data recording accuracy and reliability by compensating for thermal effects, thereby improving the overall performance of data storage devices.

Implementation Method 1

heating the disk surface with a laser during write operations in order to decrease the coercivity of the magnetic medium

Methodology Applied

Scientific EffectHeating: Heating

Implementation Method 2

decrease the coercivity of the magnetic medium, thereby enabling the magnetic field generated by the write coil to more readily magnetize the disk surface

Methodology Applied

Scientific EffectCurie Point (ferromagnetic): Curie Point (ferromagnetic)

Implementation Method 3

thermal protrusion caused by heat-assisted magnetic recording (HAMR)

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS9153266B1Data storage device measuring laser protrusion fly height profile

Publication Date: 2015.10.06 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A data storage device is disclosed comprising a disk comprising a plurality of tracks, where each track comprises a plurality of servo sectors and at least one data segment between consecutive servo sectors. The data storage device further comprises a head actuated over the disk, the head comprising a laser configured to heat the disk during write operations based on a laser power. During a first revolution of the disk, the laser power is first increased over a first interval to cause at least part of the head to protrude toward a first data segment of the disk. After the first interval, the laser power is decreased and a fly height pattern is read from the first data segment to first measure a fly height of the head.