MR Sensor Flux Guide Reduces Demagnetization Noise
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Solution Overview
Problem
Current magneto-resistive (MR) sensors in hard disk drives face a trade-off between achieving higher spatial resolution and signal sensitivity while maintaining stability and reducing noise, especially at high data densities, where smaller sensor sizes exacerbate magnetic noise and instability.
Innovation Solution
A novel MR sensor design involves partial etching of the free layer to reduce demagnetization fields, incorporating a magnetic flux guide structure and additional hard bias magnets to enhance resolution and signal without increasing noise and instability, and stabilizing the flux guide with its own longitudinal field or exchange structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the sensor size is reduced to achieve higher track density and spatial resolution, then the cross-track resolution is improved, but magnetic noise increases and sensor stability deteriorates
Solution Approach 1:
The free layer is partially etched away to segment it into distinct regions: a sensing region with reduced width and a flux guide region. This segmentation allows the sensor to achieve higher resolution while the flux guide compensates for stability losses by reducing demagnetization fields.
Solution Approach 2:
A flux guide structure is introduced as an intermediary element between the medium and the MR sensor. This flux guide concentrates and directs magnetic flux from the medium to the sensor, enhancing the read-back signal and improving signal-to-noise ratio without requiring larger sensor dimensions.
2Reliability
If the hard bias field strength is increased to reduce magnetic noise and improve stability, then sensor stability is improved, but signal sensitivity decreases
Solution Approach 1:
Different regions of the sensor are given different properties: the free layer width is reduced in the sensing region to enhance sensitivity, while the flux guide structure provides localized magnetic field management to maintain stability. This local differentiation allows simultaneous optimization of both sensitivity and stability.
3Measurement precision
If the free layer width is reduced to enhance signal sensitivity and resolution, then the read-back signal is improved, but the demagnetization field increases causing instability
Solution Approach 1:
The flux guide acts as an intermediary that compensates for the increased demagnetization field caused by the narrower free layer. By concentrating magnetic flux and providing a controlled magnetic environment, the flux guide enables the use of narrower free layers without sacrificing stability.
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 design achieves increased on-track signal, improved stability and sensitivity, and better performance in densely recorded environments with enhanced magneto-resistance ratio and signal-to-noise ratio, while maintaining low noise levels.
Implementation Method 1
incorporating a magnetic flux guide structure that reduces the free layer's demagnetization field
Implementation Method 2
The longitudinal magnetization of HB 5 provides a biasing magnetic field within sensor stack 6 to bias the magnetization 81 of free layer 8 in the cross-track direction
Implementation Method 3
a generic TMR (tunneling-magneto-resistive) head which is the main MR sensor structure used in state-of-the-art HDD
Data Source
AI summary
A method is described to improve performance of a magneto-resistive (MR) sensor under conditions of high areal density. The free layer is partially etched away, the removed material being replaced by a magnetic flux guide structure that reduces the free layer's demagnetization field. This in turn reduces the stripe height of the sensor so that the resolution and the read-back signal are enhanced without increasing noise and instability.