Dual Free Layer Read Head Rear Hard Bias Coercivity
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Solution Overview
Problem
There is a need for an improved dual free layer (DFL) read head with a strong rear hard bias (RHB) magnetic field and enhanced coercivity to enhance robustness against longitudinal fields when integrated with a writer.
Innovation Solution
The DFL read head incorporates a rear hard bias structure with a seed layer and two bulk layers of different densities, where the second bulk layer thickness is about 4 to 15 times that of the first, and is deposited using a dual gas process of argon and xenon sputtering, providing enhanced coercivity and robustness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a traditional antiferromagnetic (AFM) layer is used in the read head, then thermal stability is improved, but the spacing between shields increases and head instabilities occur due to thermal fluctuations in AFM grains
Solution Approach 1:
The patent removes the traditional antiferromagnetic (AFM) layer from the read head structure and replaces it with a dual free layer (DFL) sensor configuration. This extraction eliminates the source of thermal fluctuations in AFM grains while maintaining thermal stability through the DFL's inherent design, and simultaneously reduces the spacing between shields by eliminating the AFM layer requirement
2Length of stationary object
If the spacing between shields is reduced to eliminate AFM layer, then shield distance is improved, but thermal stability deteriorates due to removal of AFM layer
Solution Approach 1:
The patent employs a composite structure consisting of two free layers (first free layer and second free layer) with different magnetic properties, stabilized by antiferromagnetically coupled soft bias structures. This composite DFL configuration provides thermal stability through the combined magnetic properties of the layers while maintaining reduced shield spacing, replacing the function previously provided by a single AFM layer
3Device complexity
If a standard RHB structure is used in DFL read head, then device complexity is maintained, but coercivity and robustness against longitudinal fields are insufficient
Solution Approach 1:
The patent segments the RHB structure into multiple distinct layers: a seed layer, a first bulk layer, and a second bulk layer with different magnetic properties. This segmentation allows each layer to contribute specific magnetic characteristics, achieving high coercivity (Hcr greater than 3100 Oe) and improved robustness against longitudinal fields while maintaining manageable device complexity through systematic layering
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 results in a read head with increased coercivity, improved thermal stability, and expanded design space, enabling higher throughput and robustness against longitudinal fields.
Implementation Method 1
deposited using a dual gas process of argon and xenon sputtering
Data Source
AI summary
The present disclosure generally relates to read heads having dual free layer (DFL) sensors. The read head has a sensor disposed between two shields. The sensor is a DFL sensor and has a surface at the media facing surface (MFS). Recessed from the DFL sensor, and from the MFS, is a rear hard bias (RHB) structure. The RHB structure is disposed between the shields as well. In between the DFL sensor and the RHB structure is insulating material. The RHB is disposed on the insulating material. The RHB includes a RHB seed layer as well as a RHB bulk layer. The RHB bulk layer includes a first bulk layer and a second bulk layer, the first bulk layer having a different density relative to the second bulk layer.