Dual Free Layer Read Head Planar Design
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The large topography of dual free layer (DFL) two-dimensional magnetic recording (TDMR) read heads due to thicker rear hard bias (RHB) structures limits down-track spacing, causing misalignment and asymmetric performance of the readers, which reduces the accessible disk fraction and reliability in TDMR mode.
Innovation Solution
The DFL TDMR read head design includes recessed rear hard bias structures and optimized shield geometries, with the first RHB structure being recessed further into the lower shield than the second, allowing for a more linear and aligned upper shield and read separation gap, thereby reducing the down-track spacing between sensors to about 75-85 nm.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a thicker RHB structure is used to achieve the desired transverse bias field, then the transverse bias field strength is improved, but the topography along the reader stripe height direction increases
Solution Approach 1:
The patent transitions from a planar RHB structure to a three-dimensional recessed structure that extends into the lower shield. This dimensional change allows the RHB to achieve sufficient transverse bias field strength without increasing the topography along the stripe height direction, as the biasing function is achieved through vertical extension into the shield rather than lateral expansion.
Solution Approach 2:
The RHB structure is nested within the lower shield by recessing it into the shield material. This nesting approach allows the RHB to be positioned deeper in the structure, achieving the required transverse bias field while maintaining a flush or substantially flush surface with the sensor, thereby reducing topography.
2Length of moving object
If the topography is reduced by using a thinner RHB structure, then the down track spacing capacity is improved, but the transverse bias field strength decreases
Solution Approach 1:
The patent achieves sufficient transverse bias field strength not by increasing the lateral dimensions (which would increase down-track spacing), but by extending the RHB structure vertically into the lower shield. This dimensional shift allows reduced down-track spacing while maintaining field strength.
Solution Approach 2:
The patent employs asymmetric positioning of the RHB structure, recessing it into the lower shield by a specific distance that is optimized to achieve both reduced topography and sufficient transverse bias field. This asymmetric placement allows the structure to function effectively with minimal impact on down-track spacing.
3Length of moving object
If the RHB structure is recessed further into the lower shield, then the topography is reduced and down track spacing is improved, but the manufacturing complexity increases
Solution Approach 1:
The RHB structure is recessed into the lower shield during the initial fabrication process, before subsequent assembly steps. This preliminary action integrates the recessing operation into the base fabrication flow, avoiding the need for additional post-assembly machining or complex multi-step manufacturing sequences.
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 design enhances the read head's performance and reliability by improving down-track spacing, allowing a larger fraction of the disk to be accessed in TDMR mode, leading to better areal density capacity and reduced head instability.
Implementation Method 1
A transverse bias field of TDMR read heads is determined by the remnant magnetization (Mr) times thickness (t) product (i.e., Mr*t) of the RHB structure
Implementation Method 2
the two free layers or each reader are individually stabilized longitudinally by an anti-ferromagnetically coupled (AFC) soft bias (SB)
Data Source
AI summary
The present disclosure generally relates to a dual free layer (DFL) two dimensional magnetic recording (TDMR) read head. The read head comprises a first sensor, a first rear hard bias (RHB) structure disposed adjacent to the first sensor, an upper shield disposed over the first sensor and first RHB structure, a lower shield disposed over the upper shield, a second sensor disposed over the lower shield, and a second RHB structure disposed adjacent to the second sensor. A first surface of the first sensor is substantially flush or aligned with a first surface of the first RHB structure. A first surface of the second sensor is substantially flush or aligned with a first surface of the second RHB structure. The upper shield extends linearly from a media facing surface into the read head. The first lower shield is over-milled a greater amount of time than the second lower shield.