Soft Underlayer for Heat-Assisted Magnetic Recording Media
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Solution Overview
Problem
Conventional soft underlayer (SUL) structures in perpendicular magnetic recording media lose antiparallel coupling and crystallize at high temperatures, leading to increased noise and reduced signal-to-noise ratio when used in heat-assisted magnetic recording (HAMR) media, which limits areal density and thermal stability.
Innovation Solution
Development of a SUL with a high crystallization temperature (above 450°C) and high Curie temperature (above 300°C) that remains amorphous up to 650°C, using materials like Co or CoFe alloys with additives such as Zr, B, Ta, W, or Mo, and employing spacer layers like MgO, Re, or W that resist inter-diffusion at high temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional SUL structures are used in HAMR media, then the media can be manufactured with standard processes, but the SUL loses antiparallel coupling and crystallizes at high temperatures during HAMR writing, leading to increased noise and reduced signal-to-noise ratio
Solution Approach 1:
The patent modifies the compositional parameters of the SUL by incorporating specific alloying elements (Ta, W, Mo, B, Zr) in controlled amounts to shift the crystallization temperature above 450°C. This parameter change allows the SUL to maintain its amorphous state and magnetic properties during HAMR writing operations at temperatures below 450°C, thereby preventing noise generation while remaining compatible with standard manufacturing processes
Solution Approach 2:
The patent creates a composite SUL structure by combining Co or CoFe base alloys with multiple additive elements (Ta, W, Mo, B, Zr) that serve different functions: some elements raise crystallization temperature, others optimize magnetic properties, and some prevent inter-diffusion. This composite approach enables the SUL to simultaneously achieve high thermal stability, maintained antiparallel coupling, and compatibility with HAMR processes
2Reliability
If the SUL crystallization temperature is raised above 450°C to prevent crystallization during HAMR writing, then thermal stability is improved, but the material composition and deposition requirements become more complex
Solution Approach 1:
The patent systematically adjusts compositional parameters (adding specific elements at controlled concentrations) to shift the crystallization temperature parameter above 450°C. This controlled parameter change achieves the thermal stability requirement while maintaining reasonable material complexity through selective addition of elements with specific functions
Solution Approach 2:
The patent applies different additive elements at specific locations within the SUL composition to address different requirements: certain elements are added primarily to raise crystallization temperature, others to optimize magnetic properties, and some to prevent inter-diffusion. This localized functional assignment reduces overall complexity by giving each component a specific purpose
3Reliability
If higher Ku magnetic materials like L10 FePt are used to achieve higher areal density and thermal stability, then grain size can be reduced to 2-5 nm, but deposition temperature must be greater than 400°C and a write assist mechanism like HAMR is required
Solution Approach 1:
The patent introduces a specially designed SUL as an intermediary layer between the write pole and the high-Ku recording layer. This SUL acts as a mediator that manages the interaction between the write field and the high-anisotropy media, enabling effective writing at lower fields by optimizing magnetic flux return and reducing demagnetizing effects, thereby reducing the complexity requirements of the write assist mechanism
Solution Approach 2:
The patent modifies the SUL's magnetic parameters (saturation magnetization, anisotropy, coercivity) through compositional adjustments to create optimal conditions for supporting high-Ku recording layers. By tuning these parameters, the system achieves effective writing of 2-5 nm grains without requiring excessively high deposition temperatures or complex write mechanisms
4Reliability
If the SUL remains amorphous up to 650°C to prevent noise generation during HAMR writing, then signal-to-noise ratio is improved, but the Curie temperature must also be maintained above 300°C to preserve magnetic properties
Solution Approach 1:
The patent simultaneously optimizes multiple temperature parameters (Crystallization Temperature > 450°C, Curie Temperature > 300°C) through compositional adjustments. By carefully selecting and balancing alloying elements, the patent creates a compositional parameter space where both thermal stability and magnetic property stability are achieved together, preventing noise while maintaining functionality
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 new SUL structure maintains a stable saturation magnetization and flat noise profile across a wide temperature range, preventing noise generation and ensuring compatibility with HAMR media growth and writing processes, thereby enhancing areal density and thermal stability.
Implementation Method 1
employing spacer layers like MgO, Re, or W that resist inter-diffusion at high temperatures
Implementation Method 2
a SUL with a high crystallization temperature (above 450°C) and high Curie temperature (above 300°C) that remains amorphous up to 650°C
Implementation Method 3
The new SUL structure maintains a stable saturation magnetization and flat noise profile across a wide temperature range
Implementation Method 4
the HAMR media is temporarily heated to reduce its coercivity below that of an applied magnetic write field from a recording head, i.e., the temperature of the recording location on the HAMR media is increased
Data Source
AI summary
A soft underlayer (SUL) and methods for making an SUL are provided, the SUL having characteristics that make it compatible with the high temperature requirements associated with heat-assisted magnetic recording (HAMR) media growth and writing, e.g., temperatures greater than 500° C. The SUL may have a high crystallization temperature of greater than 450° C. and a high Curie temperature greater than 300° C., for example. Additionally, the SUL can maintain a saturation magnetization value greater than, e.g., 9 kGauss, at such high temperatures, thereby having the ability to remain amorphous at temperatures up to, e.g., 650° C., and exhibiting a relatively flat integrated noise profile from approximately 300° C. to 650° C. Further still, a spacer layer material is chosen such that inter-diffusion does not occur at these high temperatures.