Disk Drive Laser Destabilization for Defect Detection
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Solution Overview
Problem
Current disk drive defect scanning methods are inadequate in detecting and characterizing defects on magnetic media, particularly in identifying and mapping out defective data sectors effectively during manufacturing and in-field usage.
Innovation Solution
The method involves writing a test pattern to the disk using a write element and a laser, followed by destabilizing the magnetization using a lower laser power to detect defects by evaluating changes in the read signal, allowing for the identification and characterization of different types of defects and their growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional defect scanning methods are used to detect defects on the disk, then the defect detection process is simple and fast, but the detection precision and ability to characterize defects is insufficient
Solution Approach 1:
A test pattern is written to the disk before defect scanning to establish a reference pattern. This preliminary action enables subsequent comparison between the written pattern and the readback signal, significantly improving defect detection precision by allowing identification of deviations that indicate defects.
Solution Approach 2:
The magnetization stability of the test pattern is deliberately modified by controlling laser power during writing. By adjusting laser power parameters, the test pattern's magnetization is optimized to be sufficiently stable for storage but susceptible to destabilization by defects, enhancing the sensitivity and precision of defect detection.
2Stability of the object's composition
If high laser power is used to write the test pattern, then the magnetization is stable for storage, but defects cannot be effectively detected because the magnetization is too stable
Solution Approach 1:
The laser is applied in two distinct periodic phases: first at high power to write and stabilize the test pattern magnetization, then at reduced power during the scanning phase to allow defect-induced destabilization. This periodic variation in laser power enables both stable storage and sensitive defect detection.
Solution Approach 2:
Laser power is dynamically adjusted between two states: a first power level for writing that ensures stable magnetization storage, and a second reduced power level for scanning that allows defects to destabilize the magnetization. This parameter change enables the system to achieve both stability for storage and sensitivity for detection.
3Measurement precision
If low laser power is used to write the test pattern, then defects can be detected, but the magnetization is not stable enough for reliable data storage
Solution Approach 1:
The system uses periodic laser application with different power levels at different stages: high power during the writing phase to ensure stable magnetization, and reduced power during the scanning phase to enable defect detection. This temporal separation resolves the contradiction between stability and detectability.
Solution Approach 2:
The test pattern is first written with high laser power to establish stable magnetization. Only after this preliminary stabilization is complete does the system switch to reduced power for defect scanning, ensuring that the magnetization is sufficiently stable before attempting to detect defects.
4Measurement precision
If comprehensive defect characterization is performed using multiple test patterns and laser powers, then defect detection accuracy is improved, but the scanning time and productivity are reduced
Solution Approach 1:
Different laser power levels are applied locally to target different types of defects. By adjusting the laser power during scanning, the system can selectively enhance detection sensitivity for specific defect types (e.g., stuck bits, inverted bits, partial defects) without requiring comprehensive scanning at all power levels, thus maintaining productivity while improving characterization accuracy.
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 enhances the detection and characterization of defects, enabling more accurate defect mapping and improving the reliability and longevity of recorded data by identifying and remapping defective sectors effectively.
Implementation Method 1
heating the disk using a second, lower power applied to the laser
Data Source
AI summary
A disk drive is disclosed comprising a head actuated over a disk, wherein the head comprises a write element, a read element, and a laser operable to heat the disk while writing data to the disk. The disk is magnetized by writing a first test pattern to the disk using the write element and a first power applied to the laser. The magnetization of the first test pattern is destabilized by heating the disk using a second power applied to the laser, wherein the second power is less than the first power. After destabilizing the magnetization of the first test pattern, the first test pattern is read with the read element to generate a read signal, and the read signal is evaluated to detect a defect on the disk.