Underlayer Thermal Expansion Control for HAMR Near Field Transducers
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Solution Overview
Problem
Heat-assisted magnetic recording (HAMR) write heads face challenges due to thermo-mechanical issues with near-field transducers (NFTs), leading to undesirable protrusion and increased risk of damage during disk contact and thermal asperities, as previous protection methods have been inefficient in managing thermal expansion.
Innovation Solution
Incorporating an underlayer with a lower coefficient of thermal expansion than the surrounding fill material, positioned behind the NFT, which reduces thermal protrusion by minimizing thermal expansion and preventing the NFT from becoming the minimum fly point over the medium, thus enhancing the reliability of the recording process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the NFT is exposed to high temperatures during HAMR operation, then the heating function is achieved, but thermal protrusion occurs making the NFT the minimum fly point
Solution Approach 1:
The patent applies local quality by creating a recessed region specifically at the NFT location with different material properties (lower coefficient of thermal expansion) compared to the surrounding fill material. This localized structural modification addresses the thermal protrusion problem at the NFT without affecting other components, allowing the NFT to maintain proper clearance during thermal operation.
Solution Approach 2:
The patent directly addresses thermal expansion by selecting materials for the recessed region with a lower coefficient of thermal expansion than the surrounding fill material. This causes the recessed region to expand less during heating, preventing the NFT from protruding and becoming the minimum fly point, thereby resolving the thermal protrusion issue while maintaining heating functionality.
2Power
If the NFT protrudes due to thermal expansion, then heating effectiveness is maintained, but the risk of damage during disk contact increases
Solution Approach 1:
The patent implements beforehand cushioning by pre-configuring a recessed region at the NFT location with materials that have lower thermal expansion. This structural preparation cushions the NFT against thermal protrusion before heating occurs, preventing the NFT from becoming the minimum fly point and reducing damage risk during disk contact while maintaining heating effectiveness.
3Reliability
If protection structures are added to prevent NFT damage, then reliability improves, but device complexity increases
Solution Approach 1:
The patent merges the protection function into the existing head structure by integrating the recessed region with different thermal expansion materials directly into the media-facing surface structure. This combination approach provides NFT protection without adding separate, complex protection mechanisms, thereby improving reliability while minimizing increases in device complexity.
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 thermal protrusion at the NFT, preventing damage and ensuring reliable operation by maintaining optimal clearance between the head and disk, even under varying operating conditions, thereby improving the thermal and mechanical reliability of HAMR systems.
Implementation Method 1
The underlayer has a lower coefficient of thermal expansion than the fill material
Implementation Method 2
The heat used in HAMR is provided by a plasmonic nanostructure, namely an NFT, which locally elevates a limited spot on the medium to its Curie temperature of about 600° C.
Data Source
AI summary
A system, according to one embodiment, includes: a near field transducer, a return pole, a main pole, a waveguide adjacent the near field transducer, wherein the waveguide extends away from the near field transducer along a direction perpendicular to a media facing surface, at least one cladding layer adjacent to the waveguide, an underlayer positioned behind the near field transducer with respect to the media facing surface, the underlayer extending away from the near field transducer along the direction perpendicular to the media facing surface, and a fill material at least partially surrounding the underlayer, the waveguide and the at least one cladding layer. The underlayer has a lower coefficient of thermal expansion than the fill material. Other systems, and methods are described in additional embodiments.