Perpendicular Magnetic Recording Medium Interface Roughness Control
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Solution Overview
Problem
The challenge is to increase the recording density of perpendicular magnetic recording media while maintaining the smoothness and flatness of the magnetic recording medium to prevent head crashes and thermal asperity failures, which are exacerbated by the reduction in flying height of magnetic heads.
Innovation Solution
The solution involves optimizing the interface roughness and total thickness of the crystalline layers, specifically setting the interface roughness between the soft magnetic layer and the pre-underlayer to 0.4 nm or less, and the product of interface roughness and SUL-MAG distance to 12 nm or less, to reduce surface roughness and ensure excellent signal-to-noise ratio (SNR).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the flying height of the magnetic head is reduced to increase recording density, then the signal-to-noise ratio is improved, but the risk of head crash and thermal asperity failure increases
Solution Approach 1:
The patent applies preliminary action by forming a smoothness control layer before the magnetic recording layer to prevent surface roughness formation in advance. This layer is specifically designed to suppress roughness that would otherwise develop during subsequent layer formation, thereby preventing head crash and thermal asperity failures before they can occur during operation.
Solution Approach 2:
The smoothness control layer acts as an intermediary between the substrate and the magnetic recording layer. It mediates the interface between these layers, providing a smooth surface that prevents direct contact between rough substrate features and the magnetic recording layer, thereby reducing surface roughness and improving both reliability and signal quality.
2Reliability
If the surface roughness is reduced to prevent head crash, then the flying height can be reduced, but the manufacturing complexity increases
Solution Approach 1:
The patent applies local quality by making the smoothness control layer selectively positioned only where needed - specifically between the substrate and the magnetic recording layer. This localized approach provides surface smoothness control only at the critical interface, rather than requiring smoothness control throughout the entire structure, thereby reducing overall manufacturing complexity.
Solution Approach 2:
The patent changes the material parameters of the smoothness control layer, specifically setting its thickness to 0.5 nm or less and controlling its composition (containing Ru and/or Os). These parameter changes enable the layer to provide effective surface smoothness control while maintaining manufacturability and avoiding excessive complexity.
3Manufacturing precision
If the interface roughness between soft magnetic layer and pre-underlayer is reduced, then the surface roughness is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The smoothness control layer provides self-service by automatically suppressing interface roughness formation through its inherent material properties and structure. Rather than requiring external measurement and adjustment processes, the layer itself performs the function of maintaining smooth interfaces, thereby reducing the need for complex measurement and control systems.
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 allows for a further increase in recording density by reducing the surface roughness of the magnetic recording medium, enabling a lower flying height of the magnetic head while maintaining an excellent SNR, thus addressing the dilemma of improving recording density without compromising smoothness and crystal orientation.
Implementation Method 1
a pre-underlayer made of a nonmagnetic crystalline material for controlling a crystal orientation of the underlayer
Implementation Method 2
the easy magnetization axis of a magnetic recording layer is adjusted so as to be oriented in a direction perpendicular to the surface of a substrate
Implementation Method 3
a magnetic head has also shifted from a thin film head to a magnetoresistive head (MR head) and to a giant magnetoresistive head (GMR head)
Data Source
AI summary
In a perpendicular magnetic recording medium having, over a substrate, a magnetic recording layer, an underlayer made of Ru or a Ru compound and provided below the magnetic recording layer, a pre-underlayer made of a nonmagnetic crystalline material, and a soft magnetic layer provided below the pre-underlayer, when the difference between the highest point and the lowest point of unevenness of the interface between the soft magnetic layer and the pre-underlayer, derived by a cross-sectional TEM image, is given as an interface roughness (nm) and the distance between the soft magnetic layer and the magnetic recording layer, excluding the soft magnetic layer and the magnetic recording layer, is given as a SUL-MAG distance (nm), interface roughness (nm)≦0.4 (nm) and interface roughness×SUL-MAG distance (nm)≦12 (nm) are satisfied.