CPP GMR Read Head Minimizing Shunting Loss
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Solution Overview
Problem
CPP GMR devices face challenges in achieving longitudinal magnetic bias stability due to current shunting by abutted hard magnets, which is impractical and affects read width, unlike CIP devices.
Innovation Solution
A novel structure where a pair of hard magnets is abutted to the CPP sensing film with a significantly greater distance than the intended read-width, using a narrow conductor above the free layer to minimize current divergence and allow longitudinal magnetic bias, similar to CIP devices, while maintaining conventional manufacturing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If hard magnets are abutted to the CPP sensing film for longitudinal magnetic bias, then magnetic bias stability is improved, but current shunting occurs which worsens measurement precision
Solution Approach 1:
A non-conductive spacer layer is introduced between the hard magnets and the CPP sensing film. This intermediary layer prevents direct electrical contact that causes current shunting, while still allowing the hard magnets to provide longitudinal magnetic bias to the free layer through magnetic field penetration.
Solution Approach 2:
The device structure is segmented into distinct functional layers: the sensing region (CPP stack), the biasing region (hard magnets), and the isolating region (non-conductive spacer). This segmentation allows each component to perform its function independently without interfering with others, particularly preventing current shunting while maintaining magnetic bias.
2Length of moving object
If hard magnets are placed close together to define narrow read width, then device density is improved, but current shunting into magnets increases which worsens signal detection
Solution Approach 1:
The non-conductive spacer layer acts as an intermediary that blocks current flow into the hard magnets while allowing magnetic field transmission. This enables the hard magnets to be positioned close together for narrow read width without suffering from current shunting losses.
3Stability of the object's composition
If abutted hard magnets are used for longitudinal bias in CPP devices, then magnetic bias is achieved, but manufacturing complexity increases compared to CIP devices
Solution Approach 1:
The device is segmented into modular layers that can be fabricated using sequential deposition processes. The non-conductive spacer layer is deposited as a distinct layer between the CPP stack and hard magnets, making the structure manageable and compatible with existing manufacturing techniques.
Solution Approach 2:
The non-conductive spacer layer serves multiple functions: electrical isolation to prevent current shunting, mechanical support for the hard magnets, and potential magnetic field guidance. This multi-functionality reduces the need for additional specialized components, simplifying the overall device structure.
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 enables stable and precise longitudinal magnetic bias with minimal side-reading, improving read-back signal quality and maintaining low lead-resistance, allowing for narrow read-widths with minimal modifications to existing CPP device manufacturing.
Implementation Method 1
The principle governing the operation of most magnetic read heads is the change of resistivity of certain materials in the presence of a magnetic field (magneto-resistance or MR). Magneto-resistance can be significantly increased by means of a structure known as a spin valve or SV. The resulting increase (known as Giant Magneto-Resistance or GMR)
Implementation Method 2
A pair of hard magnets is abutted to opposite sides of the CPP sensing film... enables stable and precise longitudinal magnetic bias
Implementation Method 3
The hard magnets are separated from the CPP stack by a non-conductive spacer layer... minimal current divergence
Data Source
AI summary
Biasing schemes used for CIP GMR devices were previously thought to be impractical for CPP devices due to current shunting by the abutted hard magnets. In the present invention the CPP stripe is a narrow conductor directly above the free layer. The resistivity of the latter is made to be relatively high so the sensing current diverges very little as it passes through it. This makes it possible to use abutted hard magnets for longitudinal bias with virtually no loss of sensing current due to shunting by the magnets.