Vertical Junction RHB for Dual Free Layer Read Head Bias
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Solution Overview
Problem
Dual free layer (DFL) read heads face challenges in maintaining a stable transverse bias, which is crucial for operating in scissor mode and reducing magnetic noise, due to the strong and non-uniform rear hard bias (RHB) field required.
Innovation Solution
A magnetic read head assembly with a DFL structure between shields, featuring a recessed RHB structure separated by an insulation layer, comprising a seed layer, bulk layer, and capping layer, where the DFL structure has equal stripe heights and the RHB structure is formed by milling with specific depths and angles to ensure uniform magnetic field application.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a rear hard bias (RHB) structure is used to provide strong transverse bias for DFL read head, then readout amplitude is improved, but magnetic noise increases and bias uniformity deteriorates
Solution Approach 1:
The RHB structure is segmented into multiple magnetic layers (seed layer, first magnetic layer, second magnetic layer, capping layer) with different orientations and functions. The first and second magnetic layers are separated by a nonmagnetic layer, creating distinct magnetic domains that can be independently controlled to reduce noise while maintaining strong bias field for high readout amplitude
Solution Approach 2:
Different layers of the RHB structure are assigned different magnetic properties and orientations. The seed layer provides initial magnetic orientation, the first magnetic layer provides strong transverse bias, the second magnetic layer provides additional bias with different orientation, and the capping layer protects the structure. This local differentiation allows optimization of each layer's contribution to reduce noise while maintaining overall strong bias
2Force
If RHB structure is placed close to DFL structure for strong bias, then transverse bias strength is improved, but manufacturing precision requirements increase due to alignment sensitivity
Solution Approach 1:
The RHB structure extends in the vertical dimension between the first and second shields, creating a three-dimensional bias field distribution. This vertical extension allows the bias field to be applied over a larger volume, reducing sensitivity to lateral alignment errors while maintaining strong transverse bias strength on the media-facing surface
Solution Approach 2:
A nonmagnetic layer is introduced as an intermediary between the first and second magnetic layers of the RHB structure. This intermediary layer provides physical separation and magnetic decoupling, allowing the two magnetic layers to be positioned at different depths without direct interaction, thereby reducing alignment sensitivity while maintaining strong overall bias field
3Area of stationary object
If RHB structure extends to second shield for maximum bias application, then transverse bias coverage is improved, but device complexity increases due to additional isolation layers
Solution Approach 1:
The nonmagnetic layer serves multiple functions simultaneously: it provides magnetic isolation between the first and second magnetic layers, provides physical separation for structural stability, and contributes to the overall vertical extension of the RHB structure to enhance bias field coverage. This multi-functionality reduces the need for additional dedicated isolation structures, thereby limiting the increase in device complexity
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 configuration enhances the stability of the transverse bias, reduces magnetic noise, and improves readout amplitudes by ensuring equal bias to both free layers, thereby improving the operational efficiency of the DFL read head.
Implementation Method 1
The RHB structure comprises a seed layer, a bulk layer, and a capping layer... The RHB provides a strong field... The RHB field needs to not only be strong, but also needs to be uniformly applied
Implementation Method 2
an insulation layer separates the RHB structure from the DFL structure. The insulation layer is disposed perpendicularly between the first shield and the second shield
Implementation Method 3
dual free layer (DFL) tunnel magneto-resistive (TMR) read head... The DFL sensor operates in a scissor mode when transversally biased... with self-noise cancellation
Data Source
AI summary
The present disclosure generally relates to a read head assembly having a dual free layer (DFL) structure disposed between a first shield and a second shield at a media facing surface. The read head assembly further comprises a rear hard bias (RHB) structure disposed adjacent to the DFL structure recessed from the media facing surface, where an insulation layer separates the RHB structure from the DFL structure. The insulation layer is disposed perpendicularly between the first shield and the second shield. The DFL structure comprises a first free layer and a second free layer having equal stripe heights from the media facing surface to the insulation layer. The RHB structure comprises a seed layer, a bulk layer, and a capping layer. The capping layer and the insulation layer prevent the bulk layer from contacting the second shield.