CPP TMR Sensor Multiple Reference Layers Magnetic Field Balance
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Solution Overview
Problem
Current CPP TMR read sensors face challenges in achieving robust operation due to limitations in the reference layer, which affects the balance of magnetic fields and the TMR coefficient, necessitating further improvements for enhanced performance.
Innovation Solution
The implementation of multiple reference layers, comprising a ferromagnetic polycrystalline Co—Fe film, a ferromagnetic substitute-type amorphous Co—Fe—X film, and a ferromagnetic interstitial-type amorphous Co—Fe—B film, to facilitate high exchange and antiparallel-coupling fields, low ferromagnetic-coupling fields, and high TMR coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single reference layer is used in the CPP TMR read sensor, then the device structure is simple and manufacturing is easier, but the TMR coefficient is insufficient and thermal stability is poor
Solution Approach 1:
The reference layer is segmented into multiple distinct layers (first reference layer, second reference layer, and third reference layer) with different material compositions and magnetic properties. Each layer contributes differently to the overall magnetic field balance and spin-dependent scattering, enabling improved TMR coefficient and thermal stability while distributing the functional requirements across multiple components.
Solution Approach 2:
The patent employs composite material structure by combining different ferromagnetic materials in the reference layers. The first reference layer uses Co-Fe alloy, the second reference layer uses Co-Fe-B alloy, and the third reference layer uses Co-Fe-Si-B alloy. This composite approach leverages the complementary properties of different materials to achieve both high TMR coefficient and thermal stability.
2Reliability
If the reference layer is optimized for high TMR coefficient, then the TMR effect is enhanced, but the balance of magnetic fields (exchange coupling, antiparallel coupling, and ferromagnetic coupling) becomes difficult to maintain
Solution Approach 1:
Different regions of the reference layer structure are assigned different material qualities and magnetic properties. The first reference layer (Co-Fe) provides strong exchange coupling, the second reference layer (Co-Fe-B) enhances spin-dependent scattering for high TMR coefficient, and the third reference layer (Co-Fe-Si-B) contributes to antiparallel coupling. This local differentiation of material properties enables simultaneous optimization of multiple magnetic field parameters.
Solution Approach 2:
The patent systematically varies material composition parameters across the reference layers. By adjusting the concentration of alloying elements (Fe, B, Si) and controlling layer thicknesses, the magnetic properties (magnetization, anisotropy, coupling strength) are tuned to achieve the desired balance between exchange coupling field, antiparallel coupling field, and ferromagnetic coupling field while maintaining high TMR coefficient.
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
The multiple reference layers enhance the CPP TMR sensor's performance by inducing spin-dependent scattering, resulting in improved TMR coefficients and thermal stability, thereby enhancing the sensor's robustness and data reading capabilities.
Implementation Method 1
The multiple reference layers induce spin-dependent scattering, thus facilitating the CPP TMR sensor to exhibit a high TMR coefficient
Implementation Method 2
a unidirectional anisotropy field (HUA) is induced by exchange coupling between the antiferromagnetic pinning layer and the keeper layer
Implementation Method 3
an antiparallel-coupling field (HAPC) is induced by antiparallel coupling between the keeper layer and the reference layer across the antiparallel-coupling layer
Implementation Method 4
When the sense current 'quantum-jumps' across the Mg—O or MgOX barrier layer, changes in the resistance of the CPP GMR read sensor is detected through a TMR effect
Data Source
AI summary
A current-to-perpendicular-to-plane (CPP) read sensor with multiple reference layers and associated fabrication methods are disclosed. According to one embodiment of the invention, the multiple reference layers of a CPP tunneling magnetoresistance (TMR) read sensor includes a first reference layer formed by a ferromagnetic polycrystalline Co—Fe film, a second reference layer formed by a ferromagnetic substitute-type amorphous Co—Fe—X film where X is Hf, Zr or Y, and a third reference layer formed by a ferromagnetic interstitial-type amorphous Co—Fe—B film. The first reference layer facilitates the CPP TMR read sensor to exhibit high exchange and antiparallel-coupling fields. The second reference layer provides a thermally stable flat surface, thus facilitating the CPP TMR read sensor to exhibit a low ferromagnetic-coupling field. The multiple reference layers may induce spin-dependent scattering, thus facilitating the CPP TMR sensor to exhibit a high TMR coefficient.