Compensating Layer in TMR Reader for Signal Noise
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Solution Overview
Problem
The reduction of HDD areal density capability leads to increased electronic noise and degradation of the signal-to-noise ratio in tunnel magnetoresistive readers due to higher resistance-area product, causing canting of the free layer magnetization and reduced amplitude and increased asymmetry of the transfer curve.
Innovation Solution
Incorporation of a compensating layer behind the free layer, magnetized towards the air bearing surface, to bias the free layer and reduce exchange coupling with the reference layer, thereby improving the signal-to-noise ratio and linear resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the tunnel barrier layer thickness is reduced to lower resistance-area product, then electronic noise increases and signal-to-noise ratio degrades, but if thickness is increased, then resistance-area product increases and reading capability worsens
Solution Approach 1:
A compensating layer is introduced as an intermediary magnetic layer between the free layer and the substrate. This compensating layer generates a magnetic field that compensates for the canting effect caused by the tunnel barrier, thereby improving the signal-to-noise ratio without requiring changes to the tunnel barrier thickness that would affect resistance-area product
Solution Approach 2:
The magnetic properties of the free layer are modified by introducing the compensating layer, which changes the effective magnetic field and magnetization orientation. This parameter change allows optimization of the signal-to-noise ratio independently of the resistance-area product of the tunnel barrier
2Device complexity
If the free layer magnetization is allowed to cant naturally, then the structure remains simple, but the transfer curve amplitude decreases and asymmetry increases
Solution Approach 1:
The compensating layer serves as a mediator that corrects the magnetization orientation of the free layer. By placing this layer behind the free layer, the patent achieves improved transfer curve characteristics (amplitude and asymmetry) without significantly complicating the overall device structure
Solution Approach 2:
The compensating layer is designed to preemptively counteract the unwanted canting of the free layer magnetization. By applying a compensating magnetic field in advance, the patent prevents the degradation of transfer curve characteristics before they occur during operation
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 compensating layer mitigates the losses in signal-to-noise ratio and linear resolution by aligning the free layer magnetization, achieving a 0.5 dB gain and restoring amplitude and asymmetry values comparable to standard readers.
Implementation Method 1
a compensating layer behind the rear surface of the free layer
Implementation Method 2
reduce exchange coupling with the reference layer
Implementation Method 3
tunnel magnetoresistive readers due to higher resistance-area product
Data Source
AI summary
A reader includes a bearing surface and a free layer having a front surface and a rear surface. The front surface of the free layer forms a portion of the bearing surface. The reader also includes a compensating layer behind the rear surface of the free layer. The reader further includes a tunnel barrier layer below the free layer.