HAMR Thermal Gradient Measurement Using Stepped Laser Power

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Solution Overview

Problem

Existing methods for measuring thermal gradients in heat-assisted magnetic recording (HAMR) devices are either external and require calibration or rely on high laser power, which can lead to systematic biases and increased perturbation of the head/media system.

Innovation Solution

The use of pseudorandom bit sequences recorded at stepped laser power to determine timing differences, allowing for the estimation of thermal gradients without external calibration and at lower laser currents, reducing systematic biases and perturbation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If external methods are used to measure thermal gradients, then measurement capability is provided, but calibration requirements and system complexity increase

Engineering Contradiction:

Improvethermal gradient measurement capabilityVSAvoidcalibration requirements

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The HAMR device measures its own thermal gradient by recording and reading back pseudorandom bit sequences at stepped laser power levels. The system uses its existing recording and reading functionality to generate timing difference measurements, eliminating the need for external measurement equipment and calibration procedures. The device serves itself by utilizing its own operational characteristics (timing variations at different power levels) to determine thermal gradient.

Inventive Principle:

Principle #25Self-service

2Measurement precision

If high laser power is used for measurement, then thermal gradient signal strength increases, but systematic biases and head/media system perturbation increase

Engineering Contradiction:

Improvethermal gradient measurement signalVSAvoidsystem perturbation and systematic biases

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The system applies periodic modulation to the laser power at known frequencies while recording pseudorandom bit sequences. By stepping through multiple discrete power levels periodically and measuring timing differences at each level, the system extracts thermal gradient information through spectral analysis. This periodic approach allows measurement at lower average power levels while maintaining sufficient signal strength through frequency-domain processing.

Inventive Principle:

Principle #19Periodic 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 enables accurate and reliable measurement of thermal gradients within HAMR devices, improving data quality and reducing bit error rates, while being less sensitive to jitter and requiring lower modulation amplitudes, thus enhancing the performance and reliability of HAMR components.

Implementation Method 1

heat-assisted magnetic recording (HAMR) devices... create a small hotspot on a magnetic disk during recording

Methodology Applied

Scientific EffectLaser heating: Laser

Implementation Method 2

the thermal gradient is the change in temperature over distance at the boundaries of the hotspot

Methodology Applied

Scientific EffectThermal gradient: Temperature Gradient

Implementation Method 3

pseudorandom bit sequences are recorded to a heat-assisted recording medium at a laser power that is stepped

Methodology Applied

Scientific EffectHeat-assisted magnetic recording:

Implementation Method 4

The pseudorandom bit sequences are read from the heat-assisted recording medium to determine timing differences between bits

Methodology Applied

Scientific EffectMagnetic signal detection:

Data Source

PatentUS10339963B1Determining thermal gradient of a HAMR hotspot using pseudo-random bit sequences recorded at a stepped laser power

Publication Date: 2019.07.02 SEAGATE TECH LLC

AI summary

Pseudorandom bit sequences are recorded to a heat-assisted recording medium at a laser power that is stepped while recording the pseudorandom bit sequences. The pseudorandom bit sequences are read from the heat-assisted recording medium to determine timing differences between bits written before and after the laser power is stepped. A thermal gradient of bits written to the heat-assisted recording medium is determined based on the timing differences.