Magnetic Reader Sensor Shield Spacing Control via Reversed Film Stack
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Solution Overview
Problem
Current hard disk drive (HDD) designs face challenges in achieving consistent and improved resolution of MR sensors due to variations in shield-to-shield spacing and complex process steps, leading to inconsistent sensor performance and reliability.
Innovation Solution
A reversed film stack design is implemented where the magnetic free layer is deposited before the MgO tunnel barrier layer and pin stack, allowing for precise control of the spacing between the free layer and the closest shield through uniform layer thicknesses, simplifying the process and reducing device-to-device variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If shield-to-shield spacing is reduced to improve resolution, then sensor resolution is improved, but manufacturing complexity increases due to additional photo-lithography, etching and refill steps
Solution Approach 1:
The pin and AFM layers are recessed before the shield layers are deposited, establishing the final shield-to-shield spacing early in the manufacturing process. This preliminary action eliminates the need for subsequent complex photo-lithography, etching and refill steps to achieve the same spacing reduction.
Solution Approach 2:
Instead of reducing shield-to-shield spacing by removing material later in the process (the conventional approach), the invention inverts the sequence by recessing the pin and AFM layers first, then depositing the shield layers to achieve the desired spacing. This reversal simplifies the overall manufacturing process.
2Measurement precision
If FL-to-shield spacing is reduced to improve resolution, then sensor resolution is improved, but dimensional uniformity deteriorates due to large device-to-device and wafer-to-wafer variations in spacer thickness
Solution Approach 1:
The FL-to-shield spacing is established during the initial film deposition sequence rather than being adjusted later through spacer treatments. By depositing the FL, tunnel barrier layer, and pin stack in a controlled sequence with defined thicknesses, the spacing is predetermined with high uniformity across all devices and wafers.
Solution Approach 2:
The invention changes the approach from adjusting spacing through variable spacer thickness treatments to controlling spacing through fixed, defined film deposition parameters. The tunnel barrier layer and pin stack thicknesses are specified as precise values (e.g., 1-3 nm for tunnel barrier, 2-5 nm for pin layers) to ensure consistent FL-to-shield spacing.
3Measurement precision
If pin and AFM layers are recessed to reduce shield-to-shield spacing, then resolution is improved, but alignment complexity increases due to critical alignment between recessed pin layer and sensor back edge
Solution Approach 1:
The pin and AFM layers are recessed to a defined depth before shield deposition, establishing a precise reference surface. This preliminary action creates a stable foundation for subsequent shield layer deposition, eliminating the need for complex alignment operations later in the process.
Solution Approach 2:
The recessed pin and AFM layers serve as their own alignment reference for the shield deposition process. By defining the shield-to-shield spacing through the recess depth, the process becomes self-aligning, where the geometry of the recessed structure automatically provides the reference needed for precise shield placement without requiring external alignment operations.
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 design achieves improved resolution and stability of MR sensors with better shielding and reduced dimensional variations, enhancing the consistency and reliability of sensor performance while simplifying the fabrication process.
Implementation Method 1
MR sensor resolution improvement through controlled spacing of magnetic free layer and shield layers
Implementation Method 2
spacing between the magnetic free layer (FL) and the closest shield
Data Source
AI summary
An MTJ or MR read sensor is formed by depositing a stack in a reverse order with a free layer (FL) deposited on a lower shield, followed by a tunneling barrier layer (for an MTJ) or a conducting spacer layer (for an MR) and, finally, an antiferromagnetically coupled pinning structure and an upper shield. This reverse order permits a series of etching processes to be accurately performed on the lower shield and the stack together with the formation of biasing layers that are coupled to the lower shield and the stack, without adversely affecting the stability of the pinning structure. Further, the distance between the FL and the shield is accurately determined and repeatable even down to the sub-nm regime. An upper shield can then be formed and also coupled to the biasing layers.