DFL TDMR Middle Shield Geometry for Magnetization Stability
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Solution Overview
Problem
The middle shield in dual free layer two-dimensional magnetic recording (TDMR) read heads experiences magnetization state flipping due to magnetic domain movement, leading to biasing changes, signal profile fluctuations, and position error signals, which can cause HDD failures.
Innovation Solution
The read head design incorporates a middle shield with a U-like shape and a width-to-throat height ratio of 6:1, a throat height of less than or equal to 2 μm, and RHB structures with stripe heights three times greater than the middle shield, enhancing stability by reducing magnetization domain movement and interaction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the middle shield has a conventional shape and size, then the fabrication process is simpler, but the magnetization state becomes unstable and flips due to domain movement
Solution Approach 1:
The patent changes the geometric parameters of the middle shield by defining a specific width-to-throat-height ratio (6:1 or greater) and limiting the throat height to less than or equal to 2 μm. This parameter optimization stabilizes the magnetization state by reducing domain movement while maintaining manufacturability through standardized fabrication processes.
Solution Approach 2:
The middle shield is designed with a U-like shape that segments the magnetic field distribution, creating distinct regions that prevent unwanted magnetization flipping. The segmented structure separates the functional regions while maintaining overall structural integrity and stability.
2Reliability
If the middle shield throat height is reduced to stabilize magnetization, then magnetization flipping is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent establishes a specific parameter range for the throat height (less than or equal to 2 μm) and width-to-throat-height ratio (6:1 or greater). These parameter specifications balance the stability benefit of reduced throat height with manufacturability by defining clear design targets that can be achieved through standard fabrication tolerances.
3Reliability
If the RHB structure stripe height is increased to reduce interaction with middle shield, then magnetization domain interaction is reduced, but the overall device size increases
Solution Approach 1:
The patent specifies that the RHB structure stripe height should be approximately three times greater than the middle shield throat height. This parameter relationship ensures sufficient separation to minimize domain interaction while maintaining proportional scaling that prevents excessive overall device size.
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 improved design stabilizes the middle shield, reducing magnetization fluctuations and position error signals, thereby enhancing the reliability and performance of TDMR read heads.
Implementation Method 1
the middle shield has a U-like shape and a ratio of a width to a throat height of 6:1, where the throat height is less than or equal to about 2 μm
Implementation Method 2
the two free layers of each reader are individually stabilized longitudinally by an anti-ferromagnetically coupled (AFC) soft bias (SB)
Implementation Method 3
biased transversally by a permanent magnet or a rear hard bias (RHB) structure from the stripe back edge of the sensor
Data Source
AI summary
The present disclosure generally relates to a dual free layer two dimensional magnetic recording read head. The read head comprises a lower shield, a first sensor disposed over the first lower shield, a first rear hard bias (RHB) structure recessed from a media facing surface (MFS), a first upper shield disposed over the first sensor, a middle shield disposed over the first sensor at the MFS, a second sensor disposed over the middle shield, a second RHB structure recessed from the MFS, and an upper shield disposed over the second sensor. The middle shield has a U-like shape and a ratio of a width to a throat height of 6:1, where the throat height is less than or equal to about 2 μm. The first and second RHB structures each individually has a stripe height about 3 times greater than a stripe height of the middle shield.