CPP-GMR Sensor Extended Pinned Layer Resistivity Control
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Solution Overview
Problem
The challenge in fabricating Current-Perpendicular-to-Plane (CPP)-Giant Magnetoresistive (GMR) spin-valve sensors with an extended pinned layer is the excessive ion-mill damage to the reference or pinned layer due to the fast milling rates of metal spacer materials, which can lead to electrical shunting and degradation of magnetic properties.
Innovation Solution
A method involving the formation of a device with a reference layer, a free layer, and a spacer layer where the rear portion of the spacer layer has increased resistivity, allowing for partial removal of the free layer while maintaining the spacer layer intact, thereby reducing ion-mill damage and preserving magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the spacer layer is fully milled away to avoid electrical shunting, then electrical shunting is prevented, but the reference or pinned layer suffers excessive ion-mill damage
Solution Approach 1:
The spacer layer is selectively removed only in the region where the reference layer extends beyond the free layer (the extended pinned layer region), while the spacer layer is retained in other regions. This localized removal prevents electrical shunting in the critical extended region while preserving the spacer layer elsewhere to protect the pinned layer from excessive ion-mill damage during fabrication
Solution Approach 2:
The spacer layer removal process is segmented into two distinct regions: (1) the extended pinned layer region where the spacer layer is fully removed to prevent shunting, and (2) the main sensor region where the spacer layer is retained to protect the pinned layer. This segmentation allows different treatments in different locations to resolve the contradiction
2Shape
If ion milling is used to define the extended pinned layer geometry, then the desired shape-enhanced pinning is achieved, but the fast milling rates of metal spacer materials cause excessive damage to the pinned layer
Solution Approach 1:
Ion milling is applied locally only to the extended pinned layer region where the spacer layer needs to be removed, rather than uniformly across the entire structure. This localized application achieves the desired extended geometry while minimizing the total ion-mill exposure and corresponding damage to the pinned layer
Solution Approach 2:
The extended pinned layer geometry is established through selective spacer layer removal before final sensor fabrication steps. By preparing the extended geometry early in the fabrication process, subsequent steps can proceed with minimal additional ion-milling, reducing cumulative damage to the pinned layer
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 minimizes damage to the pinned layer and prevents electrical shunting, enhancing the stability and magnetoresistance of the CPP-GMR read head sensors by controlling the ion milling process and altering the resistivity of the spacer layer.
Implementation Method 1
a rear portion of the spacer layer that extends beyond the rear extent of the free layer has an increased resistivity in comparison with a resistivity of a rest of the spacer layer
Implementation Method 2
The fabrication of such a pinned layer typically involves ion milling to define a free layer at the top of the film stack
Implementation Method 3
CPP-GMR read sensors achieve large magnetoresistive (MR) amplitude, narrow shield-shield spacing, and high magnetic stability
Data Source
AI summary
In one embodiment, a device includes a reference layer, a free layer positioned above the reference layer, and a spacer layer positioned between the reference layer and the free layer, the spacer layer providing a gap between the reference layer and the free layer, wherein the reference layer extends beyond a rear extent of the free layer in an element height direction perpendicular to a media-facing surface of the device, and wherein a rear portion of the spacer layer that extends beyond the rear extent of the free layer has an increased resistivity in comparison with a resistivity of a rest of the spacer layer. In other embodiments, a method for forming the device is presented, along with other device structures having an extended pinned layer (EPL).