TMR Reader Soft Bias Thickness Control via Patterned Spacer
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Solution Overview
Problem
The incorporation of an extended pin layer with a soft bias layer in tunnel magnetoresistance (TMR) sensors degrades sensor performance due to extra layer volume, affecting thermal stability and stripe height, track width, and resistance changes.
Innovation Solution
A patterned spacer layer is used to control the thickness of the soft bias layer, ensuring preferred vertical positioning and substantial elimination of the soft bias layer from rear areas, thereby improving TMR reader performance by optimizing the separation between the soft bias and free layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an extended pin layer is incorporated with a soft bias layer to enhance pinning thermal stability, then device stability at smaller stripe heights is improved, but sensor performance is degraded due to extra layer volume affecting thermal stability, stripe height, track width, and resistance changes
Solution Approach 1:
The patent divides the extended pin layer into two functionally distinct regions: a first region with full soft bias layer coverage for thermal stability, and a second region without soft bias layer for optimal sensor performance. This segmentation allows each region to serve its specific function without the negative effects of combining both features in a single continuous layer.
Solution Approach 2:
The patent applies different structural configurations to different portions of the extended pin layer. The first portion has the soft bias layer deposited on it to provide thermal stability, while the second portion excludes the soft bias layer to maintain sensor performance. This local differentiation of structure and properties resolves the contradiction between needing thermal stability and maintaining sensor performance.
2Force
If the soft bias layer thickness is increased to provide sufficient bias field, then magnetic benefits are improved, but thermal stability and stripe height control are degraded
Solution Approach 1:
The patent segments the soft bias layer function by providing it only in the first region of the extended pin layer where thermal stability is needed, while excluding it from the second region where sensor performance is critical. This spatial segmentation allows the bias field to be provided where needed without compromising thermal stability or stripe height control in the sensor region.
Solution Approach 2:
The patent extracts the soft bias layer from portions of the extended pin layer where it would be harmful to sensor performance. By removing the soft bias layer from the second region, the patent eliminates the negative effects on thermal stability and stripe height while retaining the bias field benefits in the first region.
3Reliability
If the soft bias layer is present on the extended pin layer to enhance pinning, then pinning thermal stability is improved, but stripe height and track width control are degraded
Solution Approach 1:
The patent segments the extended pin layer into a first region with soft bias layer for thermal stability and a second region without soft bias layer for stripe height control. This segmentation allows the soft bias layer to provide pinning stability where needed while preventing degradation of stripe height and track width in the sensor region.
Solution Approach 2:
The patent applies the soft bias layer locally only to the first portion of the extended pin layer, creating a local quality difference that provides thermal stability where needed while maintaining proper stripe height and track width control in the second portion where the sensor structure is located.
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 approach enhances the stability and performance of TMR readers by reducing soft bias layer thickness without compromising the spacing, leading to improved magnetic benefits, reduced corrosion, and better track width control, while maintaining the magnetic benefits of an extended pin layer.
Implementation Method 1
depositing a spacer layer on the insulating layer
Implementation Method 2
performing an angled milling sub-process to remove preselected portions of the spacer layer
Implementation Method 3
The hard or soft bias layer can include a permanent or soft magnetic material and can provide a bias field along a direction perpendicular to layers of the TMR stack
Implementation Method 4
The soft bias layer on the spacer layer can include a soft magnetic material
Implementation Method 5
The resistance of the device is dependent on the relative orientation between the two ferromagnetic layers. In a TMR read head, a sense current passes perpendicularly through layers of the TMR stack. The magnetic transitions between adjacent oppositely-directed magnetized regions cause changes in electrical resistance that are detected by the TMR sensor.
Data Source
AI summary
Systems and methods for controlling a thickness of a soft bias layer in a tunnel magnetoresistance (TMR) reader are provided. One such method involves providing a magnetoresistive sensor stack including a free layer and a bottom shield layer, performing contiguous junction milling on the sensor stack, depositing an insulating layer on the sensor stack, depositing a spacer layer on the insulating layer, performing an angled milling sub-process to remove preselected portions of the spacer layer, depositing a soft bias layer on the sensor stack, and depositing a top shield layer on the sensor stack and the soft bias layer. The method can further involve adjusting an alignment of a top surface of the spacer layer with respect to the free layer. In one such case, the top surface of the spacer layer is adjusted to be below the free layer.