Dual Free Layer TMR Reader with Shaped Rear Bias Etch Control
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Solution Overview
Problem
The smaller track width of dual free layer (DFL) read heads limits performance due to degraded signal-to-noise ratio and larger rear hard bias (RHB) topography, which affects transverse magnetic anisotropy, and the granular nature of RHB results in non-uniformity and unintended read-out signal polarity flips, impacting reliability and areal recording density.
Innovation Solution
A shaped rear bias (RB) is introduced with a stitch layer to adjust the etching rate of the DFL sensor, ensuring synchronized removal of RB portions without damaging the sensor, thereby improving control and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a thicker rear hard bias (RHB) is used to achieve desired transverse bias field, then the transverse bias field strength is improved, but the topography along the stripe direction increases and TDMR applications are limited
Solution Approach 1:
The patent applies local quality by creating a shaped RHB with non-uniform thickness distribution. The RHB has a first thickness at the first end and a second thickness at the second end, where the thickness varies along the stripe direction. This allows different regions of the RHB to provide different magnetic bias strengths, achieving the desired transverse bias field while controlling the overall topography to enable TDMR applications.
2Force
If a granular material is used in a large RHB, then the transverse bias field can be generated, but unintended read-out signal polarity flip occurs due to biasing direction flip
Solution Approach 1:
The patent changes the magnetic parameters of the RHB by using a shaped structure with controlled thickness variation. The specific thickness profile (first thickness at first end, second thickness at second end) creates a controlled magnetic field distribution that maintains consistent biasing direction, preventing the polarity flip that occurs with granular materials in large RHBs.
3Area of moving object
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 shaped RHB structure creates localized magnetic field enhancements that improve the signal-to-noise ratio. The non-uniform thickness distribution concentrates the magnetic flux in specific regions, providing stronger bias field where needed while maintaining smaller track width for higher areal recording density.
4Manufacturing precision
If the removal time of exposed portions of RB is increased, then the shaped RHB control is improved, but the DFL sensor may be damaged
Solution Approach 1:
The patent applies preliminary action by depositing a stitch layer over the DFL sensor before forming the shaped RHB. This stitch layer serves as a protective and etch-rate control layer during the removal process. The stitch layer has a specific etch rate that is slower than the RHB material, allowing the exposed portions of the RHB to be removed while protecting the DFL sensor from damage.
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 RB enhances transverse magnetic anisotropy, aligns bias element magnetization, and ensures consistent transverse bias field delivery, enabling smaller track widths with improved performance and reliability.
Implementation Method 1
A shaped rear hard bias (RHB) or a shaped rear soft bias (RSB) can induce large transverse magnetic anisotropy and align bias element magnetization
Implementation Method 2
depositing a stitch layer over a DFL sensor to adjust the etching rate of the DFL sensor to match the etching rate of the RB during the removal processes
Implementation Method 3
a transverse bias field of DFL read heads is determined by the remnant magnetization (Mr) times thickness (t) product (i.e., Mr*t) of the RHB structure
Data Source
AI summary
The present disclosure generally relates to a dual free layer (DFL) read head with a shaped rear bias (RB) and methods of forming thereof. A shaped rear hard bias (RHB) or a shaped rear soft bias (RSB) can induce large transverse magnetic anisotropy and align bias element magnetization, which in turn contributes to overcoming polarity flip or negative amplitude observed in DFL read heads. However, often, the removal time of exposed portions of RB are greater than the removal time of exposed portions of the DFL sensor. Thus, depositing a stitch layer over a DFL sensor to adjust the etching rate of the DFL sensor to match the etching rate of the RB during the removal processes provides sufficient time to remove exposed portions of the RB without damaging the DFL sensor, thereby improving shaped RHB or RSB control and reliability in DFL sensors.