Dual Free Layer MTJ for TDMR Read Head Density
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Solution Overview
Problem
Two-dimensional magnetic recording (TDMR) read heads face performance degradation due to the unreliability of synthetic antiferromagnetic pinned layers (SAF PL) and increased distance between upper and lower readers, which lowers area density capacity (ADC) and causes atomic inter-diffusion at elevated temperatures.
Innovation Solution
Implementing a dual free layer (DFL) magnetic tunnel junction (MTJ) structure with synthetic antiferromagnetic soft bias (SAF SB) and rear hard bias (RHB) structures, reducing the distance between the upper and lower readers and enhancing the scissor state magnetic moment at the media facing surface, thereby improving ADC without performance degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a synthetic antiferromagnetic pinned layer (SAF PL) is used in TDMR read heads, then the magnetic layer can be pinned, but the structure requires separate annealing for upper and lower readers which increases manufacturing complexity and reduces reliability
Solution Approach 1:
The patent extracts the pinned layer function from the SAF PL structure and implements it through the interaction between the dual free layers and the biasing fields. The DFL structure with upper and lower free layers coupled through the barrier layer eliminates the need for a separate SAF PL, removing the annealing complexity while maintaining the pinning function through magnetic coupling.
Solution Approach 2:
The barrier layer acts as an intermediary between the upper and lower free layers, enabling magnetic coupling that provides the pinning effect. This intermediary structure allows the two free layers to interact and stabilize each other's magnetization without requiring a separate pinned layer, thereby simplifying the manufacturing process.
2Reliability
If a thick SAF PL is used to ensure desired crystallinity, then the pinned layer can be effectively pinned, but the distance between upper and lower readers increases which lowers area density capacity
Solution Approach 1:
The patent merges the functions of the pinned layer and the biasing structure into the dual free layer configuration itself. The upper and lower free layers work together to provide both the pinning effect and the biasing field, eliminating the need for a thick separate SAF PL. This integration reduces the down-track distance between readers while maintaining pinned layer stability.
Solution Approach 2:
The patent changes the fundamental parameters of the magnetic structure by transitioning from a single thick pinned layer to a dual free layer system with coupled magnetization. This parameter change allows achieving the same pinning stability with a much thinner overall structure, thereby improving area density capacity.
3Manufacturing precision
If separate annealing is performed for upper and lower readers to achieve desired SAF PL crystallinity, then the pinned layer crystallinity is improved, but manufacturing time and process complexity increase
Solution Approach 1:
The patent segments the magnetic layer into two separate free layers (upper and lower) that can be independently optimized during deposition. This segmentation allows each layer to be formed with precise control over its magnetic properties, achieving the desired crystallinity and magnetic performance without requiring complex post-deposition annealing processes.
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 DFL MTJ structure with SAF SB and RHB structures effectively reduces the distance between the readers, enhancing area density capacity and maintaining reliability by eliminating the need for separate annealing of SAF PL, thus preventing performance degradation.
Implementation Method 1
a first barrier layer disposed over the first free magnetic layer... a first magnetic tunnel junction comprising the first free magnetic layer, the first barrier layer, and the second free magnetic layer
Implementation Method 2
A synthetic antiferromagnetic (SAF) soft bias (SB) structure bounds the MTJ, and a rear hard bias (RHB) structure is disposed behind the MTJ... cause the DFL MTJ to have a scissor state magnetic moment
Data Source
AI summary
The present disclosure generally related to a two dimensional magnetic recording (TDMR) read head having a magnetic tunnel junction (MTJ). Both the upper reader and the lower reader have a dual free layer (DFL) MTJ structure between two shields. A synthetic antiferromagnetic (SAF) soft bias structure bounds the MTJ, and a rear hard bias (RHB) structure is disposed behind the MTJ. The DFL MTJ decreases the distance between the upper and lower reader and hence, improves the area density capacity (ADC). Additionally, the SAF soft bias structures and the rear head bias structure cause the dual free layer MTJ to have a scissor state magnetic moment at the media facing surface (MFS).