TMR Device Ferromagnetic Underlayer Crystallinity
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Solution Overview
Problem
TMR devices with MgO tunneling barriers exhibit low magnetoresistance due to inferior crystallinity of the MgO barrier, which is not conducive to high spin-polarization and optimal performance.
Innovation Solution
A ferromagnetic underlayer with a composition of (CoxFe(100-x))(100-y)Gey, where x is between 45 and 55 atomic percent and y is between 26 and 37, is used in contact with the MgO tunneling barrier to improve crystallinity and magnetoresistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional ferromagnetic layers are used with MgO tunneling barriers, then the device structure is simple, but the MgO barrier exhibits inferior crystallinity and low magnetoresistance
Solution Approach 1:
The invention changes the compositional parameters of the ferromagnetic underlayer by introducing a specific alloy formula (CoxFe(100-x))(100-y)Gey with controlled ranges of x (45-55) and y (26-37). This parameter optimization enables the underlayer to promote (001) epitaxial growth of MgO, significantly improving crystallinity and magnetoresistance compared to conventional ferromagnetic layers.
Solution Approach 2:
The invention uses a composite ferromagnetic underlayer combining Co, Fe, and Ge elements in specific proportions. This composite material approach creates synergistic effects where Ge addition promotes MgO crystallization while Co and Fe provide necessary spin-polarization, achieving both improved crystallinity and high magnetoresistance.
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 specific composition of the ferromagnetic underlayer enhances the crystallinity of the MgO barrier and significantly increases the tunneling magnetoresistance of the TMR device, achieving higher spin-polarization and improved performance.
Implementation Method 1
The amorphous CoFeB is known to promote high quality crystallization of the MgO into the (001) direction
Implementation Method 2
The barrier layer is typically made of a metallic oxide that is so sufficiently thin that quantum-mechanical tunneling of charge carriers occurs between the two ferromagnetic layers
Implementation Method 3
The quantum-mechanical tunneling process is electron spin dependent, which means that an electrical resistance measured when applying a sense current across the junction depends on the spin-dependent electronic properties of the ferromagnetic and barrier layers, and is a function of the relative orientation of the magnetizations of the two ferromagnetic layers
Data Source
AI summary
A tunneling magnetoresistance (TMR) device, like a TMR read head for a magnetic recording hard disk drive, has a magnesium oxide (MgO) tunneling barrier layer and a ferromagnetic underlayer beneath and in direct contact with the MgO tunneling barrier layer. The ferromagnetic underlayer comprises a crystalline material according to the formula (CoxFe(100-x))(100-y)Gey, where the subscripts represent atomic percent, x is between about 45 and 55, and y is between about 26 and 37. The ferromagnetic underlayer may be the CoxFe(100-x))(100-y)Gey portion of a bilayer of two ferromagnetic layers, for example a CoFe/(CoxFe(100-x))(100-y)Gey bilayer. The specific composition of the ferromagnetic underlayer improves the crystallinity of the MgO tunneling barrier after annealing and improves the tunneling magnetoresistance of the TMR device.