Write Transducer Buffer Layer Spacing for Track Erasure Control
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Solution Overview
Problem
Magnetic hard disk drives face a trade-off between off-track and on-track writing performance due to the presence of side shields, which can cause wide area track erasure (WATER) and affect write field rise time and data rate.
Innovation Solution
A shielded write transducer design with a ferromagnetic side shield and buffer layers, including a non-magnetic gap and decoupling layers, allows for a longer throat height without increasing write field rise time or degrading data rate, effectively shunting off-track write fields and reducing WATER.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the side shield throat height is increased to reduce WATER and off-track writing, then off-track writing performance is improved, but write field rise time increases and on-track data rate degrades
Solution Approach 1:
A non-magnetic buffer layer is introduced between the side shield and the write pole as an intermediary element. This buffer layer has permeability less than 1.0 and is positioned at a distance from the side shield, allowing it to mediate the magnetic field interactions. The buffer layer reduces the harmful off-track write fields and WATER effects while maintaining the write pole's ability to generate fast rise time fields for high data rate on-track writing.
Solution Approach 2:
The side shield structure is modified by creating a localized non-magnetic buffer region between the side shield and write pole. This local modification allows different regions of the transducer to have different magnetic properties - the side shield provides off-track shielding while the buffer layer region allows fast field rise, and the write pole maintains high field strength. This local quality differentiation resolves the contradiction between off-track and on-track performance.
2Object-affected harmful factors
If the side shield throat height is increased to reduce WATER, then off-track writing performance is improved, but device complexity increases
Solution Approach 1:
The non-magnetic buffer layer serves as a simple intermediary between the side shield and write pole, adding only one additional layer to the transducer structure. This buffer layer with permeability less than 1.0 effectively reduces WATER and off-track writing without requiring complex geometric modifications to the side shield throat, thus improving off-track performance while minimizing increases in device complexity.
3Speed
If the side shield throat height is decreased to reduce write field rise time, then on-track data rate is improved, but off-track writing performance deteriorates
Solution Approach 1:
The non-magnetic buffer layer positioned between the side shield and write pole acts as a mediator that allows the side shield to maintain a shorter throat height (improving write field rise time) while still providing effective off-track shielding. The buffer layer's low permeability prevents magnetic field leakage in the off-track direction, thereby reducing off-track writing despite the reduced side shield throat height.
Solution Approach 2:
By creating a localized non-magnetic buffer region, the transducer achieves different magnetic characteristics in different spatial zones. The buffer layer region allows for fast field rise time with shorter side shield throat, while the buffer's low permeability locally suppresses off-track field leakage. This local quality differentiation enables simultaneous optimization of both on-track speed and off-track shielding.
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 improves the engineering trade-off between off-track and on-track writing performance by maintaining high data rates while minimizing wide area track erasure.
Implementation Method 1
a ferromagnetic buffer layer disposed between a write pole and a side shield
Implementation Method 2
a first non-magnetic layer disposed between the side shield and the ferromagnetic buffer layer such that the ferromagnetic buffer layer is spaced from the side shield
Data Source
AI summary
A write transducer for a disk drive magnetic head includes a ferromagnetic write yoke having a write pole protruding towards an air bearing surface. The write transducer also includes a ferromagnetic side shield, and a ferromagnetic buffer layer disposed between the write yoke and the side shield. A first non-magnetic layer is disposed between the side shield and the ferromagnetic buffer layer. A second non-magnetic layer is disposed between the ferromagnetic buffer layer and the write yoke. The ferromagnetic buffer layer extends in a direction normal to the air bearing surface by a buffer layer throat height in the range of 10 nm to 500 nm. In certain embodiments, such a write transducer may advantageously reduce undesired wide area track erasure, without unacceptably degrading write field rise time for acceptable on-track writing data rate.