HAMR Write-Induced Protrusion Calibration via Thermal Feedback
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Solution Overview
Problem
Current methods for measuring write-induced protrusion in heat-assisted magnetic recording (HAMR) systems are difficult due to the highly localized nature of the protrusion and require significant setup or risk damaging the near-field transducer, making it challenging to determine the optimized laser current and maintain desired write clearance.
Innovation Solution
A method involving iterations of laser powers, where the read/write head is written to at a selected power to achieve thermal equilibrium, with temperature measurements and adjustments to the steady-state write power to determine write-induced protrusion, allowing for calibration without contact detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contact-based measurement methods are used to measure write-induced protrusion, then measurement precision may be improved, but the near-field transducer is damaged
Solution Approach 1:
The patent uses an intermediary measurement approach by monitoring temperature changes of the read/write head during writing operations. Instead of direct contact measurement that would damage the transducer, the system measures temperature variations caused by write-induced protrusion, which serve as an indirect indicator. This intermediary temperature measurement allows accurate protrusion assessment without physical contact that could harm the near-field transducer.
Solution Approach 2:
The patent replaces mechanical contact-based measurement systems with a thermal measurement system. By substituting mechanical probes with temperature sensing, the system eliminates the need for physical contact between measurement devices and the near-field transducer, thereby preventing damage while maintaining measurement capability through thermal field interactions.
2Measurement precision
If traditional measurement setup is used for write-induced protrusion, then measurement accuracy may be improved, but device complexity and setup time increase significantly
Solution Approach 1:
The patent implements self-service measurement by utilizing the read/write head's own temperature characteristics to measure write-induced protrusion. The system leverages the inherent thermal response of the read/write head during normal writing operations, eliminating the need for external measurement apparatus or complex setup procedures. The read/write head essentially measures its own protrusion effects through temperature monitoring.
Solution Approach 2:
The patent makes the temperature measurement system multi-functional by using it for both thermal management during writing operations and for measuring write-induced protrusion. This universal approach allows the same temperature sensing mechanism to serve dual purposes: controlling write head temperature and quantifying protrusion, thereby reducing overall system complexity and eliminating dedicated measurement hardware.
3Productivity
If laser power is increased to improve write performance, then writing speed is improved, but write-induced protrusion increases reducing write clearance
Solution Approach 1:
The patent implements feedback control by continuously monitoring temperature changes that indicate write-induced protrusion and using this information to dynamically adjust laser power. The system measures temperature variations during writing, determines the resulting protrusion, and feeds this information back to modulate laser power levels, thereby maintaining optimal write clearance even at high writing speeds.
Solution Approach 2:
The patent applies dynamic control to laser power levels based on real-time temperature measurements. Instead of using fixed laser power, the system continuously adapts power levels according to the measured thermal state and resulting protrusion, allowing the write clearance to be maintained dynamically throughout the writing process regardless of writing speed variations.
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
Enables simultaneous determination of write-induced protrusion slope and initial laser calibration, maintaining consistent write clearance across varying laser currents without damaging the near-field transducer, thus improving the control and efficiency of HAMR systems.
Implementation Method 1
heat-assisted magnetic recording (HAMR) systems use a laser to create a small hotspot on a magnetic disk during recording. The heat lowers magnetic coercivity at the hotspot
Implementation Method 2
measuring a temperature of the read/write head during the write and adjusting the steady-state write power to achieve a predefined difference between the temperature at the start of the write and the end of the write
Data Source
AI summary
A test involves iterations over a series of laser powers of a heat-assisted read/write head. The iterations involve writing to a recording medium at the selected laser power for a sufficient duration to ensure thermal equilibrium of the read/write head at an end of the write. A clearance-control heater of the read/write head is transitioned from a pre-write power before a start of the write to a steady-state write power. The iterations further involve measuring a temperature of the read/write head during the write and adjusting the steady-state write power to achieve a predefined difference between the temperature at the start of the write and the end of the write. The adjusted steady state write power is stored for each iteration. A write-induced protrusion is determined based on the iterations and used for calibration of the read/write head.