CPP Sensor Coplanar ELG Tunnel Barrier Ion Milling
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Solution Overview
Problem
The fabrication of current perpendicular to plane (CPP) tunnel junction read sensors in magnetic heads for hard disk drives faces issues with ion milling damaging the tunnel barrier layer edges, leading to electrical shorts and resistance reduction, and variations in electronic lapping guides (ELGs) due to non-coplanar layer fabrication, resulting in inconsistent air bearing surfaces and manufacturing challenges.
Innovation Solution
A partial ion milling process is used to establish the back wall of the sensor stack, where the antiferromagnetic layer is not milled through, and the ELG material is completely milled through in the same step, with photolithographic techniques ensuring accurate optical focusing for ELG mask fabrication, making the ELG layer coplanar with the tunnel barrier layer to minimize damage and variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ion milling is used to mill through the tunnel barrier layer to create the sensor back wall, then the sensor stripe height is defined, but the tunnel barrier layer edges are damaged causing electrical shorts and resistance reduction
Solution Approach 1:
The patent divides the sensor stack into distinct segments with different milling depths. The tunnel barrier layer is partially milled to expose the pinned layer while leaving the antiferromagnetic layer intact, creating a segmented structure where each layer is treated differently to preserve critical interfaces while defining geometric parameters.
Solution Approach 2:
Instead of milling completely through all layers to define the back wall, the patent applies partial action by stopping the milling process at the pinned layer interface. This partial milling achieves the necessary stripe height definition and back wall formation without excessive removal that would damage the tunnel barrier layer edges and cause electrical shorts.
2Productivity
If the ELG material layer is fabricated in the same milling steps as the sensor, then the back edge of ELG is created, but the non-coplanar layers cause optical focusing variations resulting in ELG size variations
Solution Approach 1:
The patent makes the ELG material layer coplanar with the tunnel barrier layer, creating an equipotential surface at the same optical focusing plane. This eliminates focal variations during photolithographic mask fabrication, ensuring consistent ELG dimensions across the wafer while maintaining integrated fabrication productivity.
3Manufacturing precision
If the ELG material layer is made coplanar with the tunnel barrier layer, then optical focusing accuracy is improved for ELG mask fabrication, but the ELG material thickness must be precisely controlled to mill through completely in the partial milling step
Solution Approach 1:
The patent optimizes the ELG material thickness parameter to a specific range (20-50 nm) that enables complete removal during partial ion milling while maintaining coplanarity with the tunnel barrier layer. This parameter optimization achieves both improved optical focusing accuracy and reliable ELG back edge formation without requiring additional process 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 approach reduces electrical shorts and resistance issues, ensures accurate stripe height fabrication, improves manufacturing yield, and maintains consistent properties across magnetic heads, enhancing the quality and consistency of the air bearing surface.
Implementation Method 1
A partial ion milling process is used to establish the back wall of the sensor stack
Implementation Method 2
photolithographic techniques ensuring accurate optical focusing for ELG mask fabrication
Data Source
AI summary
A magnetic head including a CPP read head sensor. The CPP sensor includes a tunnel barrier layer. At least one portion of ELG material is coplanar with the tunnel barrier layer.