Shaped Rear Bias Dual Free Layer TMR Reader
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Solution Overview
Problem
Dual free layer (DFL) read heads face performance degradation due to smaller track widths, which limit signal-to-noise ratio and areal recording density, and larger rear hard bias (RHB) structures cause topography issues and unintended signal polarity flips, leading to reliability concerns.
Innovation Solution
A dual free layer read head with a shaped rear bias (RB) is developed, where the RB is recessed from the media facing surface and synthetic antiferromagnetic (SAF) soft bias side shields are used to define track widths, enhancing transverse magnetic anisotropy and maintaining performance at smaller track widths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the track width of DFL read heads is decreased, then the areal recording density is improved, but the signal-to-noise ratio degrades
Solution Approach 1:
The patent changes the geometric parameters of the rear bias structure by introducing a recessed configuration with specific depth and width dimensions. This parameter modification allows the bias structure to generate sufficient transverse bias field while occupying less space, enabling smaller track widths without proportionally degrading signal-to-noise ratio.
Solution Approach 2:
The patent transitions from a planar rear bias structure to a three-dimensional recessed structure. By utilizing the vertical dimension through the recessed configuration, the design achieves compact footprint while maintaining the magnetic bias field strength needed for signal detection, thus supporting smaller track widths.
2Force
If the thickness of RHB structure is increased, then the transverse bias field is improved, but the topography along the stripe direction increases
Solution Approach 1:
Instead of increasing thickness in the vertical dimension, the patent uses a recessed configuration that extends laterally. The rear bias structure is positioned at a lower level with defined width and depth dimensions, generating the required transverse bias field while maintaining a flat top surface profile along the stripe direction.
Solution Approach 2:
The patent applies different geometric characteristics to different parts of the rear bias structure. The recessed regions provide the necessary magnetic field generation volume, while the overall structure maintains a controlled footprint and flat topography where needed, achieving local optimization of both field strength and surface profile.
3Force
If the size of RHB is increased, then the transverse bias field is improved, but the read-out signal polarity flip increases
Solution Approach 1:
The patent modifies the dimensional parameters of the rear bias structure through the recessed configuration. By optimizing the width and depth of the recessed regions, the structure generates sufficient transverse bias field while controlling the overall magnetic moment, thereby preventing unintended polarity flips in the read-out signal.
Solution Approach 2:
The patent uses synthetic antiferromagnetic (SAF) side shields that replicate the magnetic field generation capability of a larger RHB structure but with reduced size. The SAF layers provide the necessary bias field through their magnetic moment, achieving the same functional effect with smaller dimensions that prevent polarity flip.
4Productivity
If the track width is decreased, then the areal recording density is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent divides the rear bias structure into multiple segments including the main RHB structure and separate SAF side shields. This segmentation allows independent optimization and fabrication of each component, making it easier to control the overall track width precision while achieving the required magnetic field distribution.
Solution Approach 2:
The patent introduces SAF side shields as intermediary structures between the DFL sensor and the external environment. These side shields mediate the magnetic field distribution and help define the effective track width, providing an additional degree of freedom for precision control during manufacturing.
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 shaped rear bias increases transverse magnetic anisotropy, ensuring consistent bias fields and improved reliability, allowing for smaller track widths without degrading signal-to-noise ratio or areal recording density.
Implementation Method 1
enhancing transverse magnetic anisotropy and maintaining performance at smaller track widths
Implementation Method 2
ensuring consistent bias fields
Implementation Method 3
biased transversally by a permanent magnet or a rear hard bias (RHB) structure
Data Source
AI summary
The present disclosure generally relates to a dual free layer (DFL) read head and methods of forming thereof. In one embodiment, a method of forming a DFL read head comprises depositing a DFL sensor, defining a stripe height of the DFL sensor, depositing a rear bias (RB) adjacent to the DFL sensor, defining a track width of the DFL sensor and the RB, and depositing synthetic antiferromagnetic (SAF) soft bias (SB) side shields adjacent to the DFL sensor. In another embodiment, a method of forming a DFL read head comprises depositing a DFL sensor, defining a track width of the DFL sensor, depositing SAF SB side shields adjacent to the DFL sensor, defining a stripe height of the DFL sensor and the SAF SB side shield, depositing a RB adjacent to the DFL sensor and the SAF SB side shield, and defining a track width of the RB.