DFL Read Head Shield Tuning for Symmetrical Sidebumps
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Solution Overview
Problem
Magnetic heads in HDDs with dual free layer (DFL) read heads often exhibit asymmetrical sidebumps in the cross-track direction, leading to performance issues during shingle magnetic recording (SMR) due to fabrication and geometrical controllability challenges.
Innovation Solution
Implementing a synthetic antiferromagnetic (SAF) shield, adjusting magnetic moments of soft bias layers, and varying the spacing between free layers and soft bias layers to achieve symmetrical sidebump offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a DFL read head is used to improve areal density, then storage capacity is improved, but sidebump asymmetry occurs due to fabrication and geometrical controllability challenges
Solution Approach 1:
The patent intentionally introduces asymmetry in the form of a notched shield structure to compensate for the inherent asymmetry in sidebump offsets. The notch is positioned and dimensioned specifically to counterbalance the asymmetric magnetic field distribution, thereby achieving symmetrical sidebump characteristics in the output signal despite fabrication variations
Solution Approach 2:
The patent modifies geometric parameters of the shield structure, specifically introducing a notch with controlled depth and position. This parameter change allows tuning of the magnetic field distribution to achieve symmetrical sidebump offsets while maintaining the DFL read head's high areal density capability
2Ease of manufacture
If sidebump asymmetry is present, then fabrication complexity is reduced, but reader performance deteriorates during shingle magnetic recording
Solution Approach 1:
The notched shield introduces a deliberate asymmetric geometric feature that compensates for sidebump asymmetry. This asymmetric structure is designed to create a counterbalancing effect that symmetrizes the sidebump offsets, thereby improving SMR performance without significantly complicating the fabrication process
3Reliability
If symmetrical sidebump offset is achieved through additional structures, then reader performance is improved, but device complexity increases
Solution Approach 1:
Instead of modifying the entire shield structure, the patent applies a localized notch only in the specific region where sidebump asymmetry occurs. This local modification achieves the desired symmetrical sidebump offset while minimizing the increase in overall 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 proposed solution significantly reduces sidebump imbalance, enhancing the performance of DFL read heads by ensuring symmetrical sidebump amplitude and location in the cross-track direction.
Implementation Method 1
a synthetic antiferromagnetic (SAF) shield
Implementation Method 2
magnetic moments of soft bias layers can be adjusted
Data Source
AI summary
A dual free layer (DFL) read head oftentimes has a sidebump in a signal amplitude vs. cross-track profile plot. The sidebump is a magnetic signal of the reader in response to the magnetic field of magnetic media. The sidebump magnitude is far below the main magnetic signal of the reader and is offset from the center of the track in the cross-track direction. The sidebump presence indicates that the magnetic signal of the reader is a little out of phase. When a pair of sidebumps is present, the sidebump should be symmetrically offset in the cross-track direction else there is a negative impact on reader performance. To obtain offset symmetry, a synthetic antiferromagnetic shield may be used, magnetic moments of soft bias layers can be adjusted, and spacing between the free layers of the DFL read head and the layers of the soft bias can also be adjusted.