Optical-Coupling Multilayer for HAMR Thermal Gradient Control
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Solution Overview
Problem
Conventional heat-assisted magnetic recording (HAMR) media face challenges in achieving thermal stability and optical coupling due to the thermal and optical properties of plasmonic heat-sink layers like Au, Ag, and Cu, which roughen at high temperatures and require intermediate layers that compromise performance.
Innovation Solution
An optical-coupling multilayer of alternating plasmonic and non-plasmonic materials is introduced between the seed-thermal barrier layer and the heat-sink layer, or within the seed-thermal barrier layer, to enhance thermal and optical coupling without functioning as a heat sink, thereby improving the thermal gradient to laser power ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a plasmonic heat-sink layer (Au, Ag, Cu) is used to improve thermal conductivity and optical coupling, then thermal management and optical coupling are improved, but the layer roughens at high temperatures requiring intermediate layers that compromise performance
Solution Approach 1:
The patent segments the heat-sink layer into a multilayer structure with alternating plasmonic and non-plasmonic materials. Each layer has a thickness of 0.5-2 nm, creating multiple interfaces that reduce lateral thermal conductivity while maintaining optical coupling benefits. This segmentation prevents the roughening problem of single-layer plasmonic materials at high temperatures.
Solution Approach 2:
The patent uses composite materials by combining plasmonic materials (Au, Ag, Cu) with non-plasmonic materials in a multilayer structure. This composite approach maintains the optical coupling advantages of plasmonic materials while the non-plasmonic layers provide thermal barrier properties and structural stability at high temperatures.
2Reliability
If an intermediate layer is added to prevent roughening of plasmonic heat-sink layer, then layer stability is improved, but optical coupling performance deteriorates
Solution Approach 1:
The patent uses thin non-plasmonic layers as intermediaries between plasmonic layers. These intermediary layers have thicknesses of 0.5-2 nm, which is sufficient to provide structural stability and prevent roughening, yet thin enough to maintain effective optical coupling across the multilayer structure.
3Temperature
If a multilayer of alternating plasmonic and non-plasmonic materials is used to reduce lateral thermal conductivity, then thermal gradient is improved, but device complexity increases
Solution Approach 1:
The patent applies local quality by creating alternating regions of high and low thermal conductivity at the nanoscale. The plasmonic layers provide high thermal conductivity for vertical heat transfer, while the non-plasmonic layers provide low thermal conductivity to prevent lateral heat spread. This local differentiation of thermal properties achieves superior thermal gradient control.
Solution Approach 2:
The patent transitions from a single-layer approach to a multilayer vertical structure, adding the dimension of layering. This vertical stacking of alternating materials creates controlled thermal pathways in the vertical dimension while blocking lateral heat flow, achieving thermal gradient improvement without significant horizontal space increase.
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 configuration stabilizes the HAMR medium by maintaining optical benefits while minimizing laser power requirements, extending the life of the near-field transducer and improving the thermal gradient to laser power ratio, thus enhancing recording performance.
Implementation Method 1
An optical-coupling multilayer of alternating plasmonic and non-plasmonic materials is introduced between the seed-thermal barrier layer and the heat-sink layer
Implementation Method 2
Heat-sink layers selected from Au, Ag and Cu provide good thermal and optical properties for HAMR media. The high lateral (in-plane) thermal conductivity of Au, Ag and Cu allows for the heat to be moved laterally and then down vertically very quickly to the substrate
Implementation Method 3
The most common type of proposed HAMR disk drive uses a laser source and an optical waveguide with a near-field transducer (NFT). A 'near-field' transducer refers to 'near-field optics', wherein the passage of light is through an element with sub-wavelength features and the light is coupled to a second element
Implementation Method 4
The thermal stability of a magnetic grain is to a large extent determined by KuV, where V is the volume of the magnetic grain. Thus, a recording layer with a high Ku is important for thermal stability. The c-axis of the L10 phase is the easy axis of magnetization and is oriented perpendicular to the disk substrate
Implementation Method 5
As the areal data density (the number of bits that can be recorded on a unit surface area of the disk) increases, the magnetic grains that make up the data bits can be so small that they can be demagnetized simply from thermal instability or agitation within the magnetized bit
Data Source
AI summary
A heat-assisted magnetic recording (HAMR) disk has a magnetic recording layer (typically a FePt chemically-ordered alloy), a seed-thermal barrier layer (typically MgO) below the recording layer, a heat-sink layer, and an optical-coupling multilayer of alternating plasmonic and non-plasmonic materials between the heat-sink layer and the seed-thermal barrier layer. Unlike a heat sink layer, the multilayer has very low in-plane and out-of-plane thermal conductivity and thus does not function as a heat sink layer. The multilayer's low thermal conductivity allows the multilayer to also function as a thermal barrier. Due to the plasmonic materials in the multilayer it provides excellent optical coupling with the near-field transducer (NFT) of the HAMR disk drive.