Perpendicular Magnetoresistive Element Buffer Layer Design
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Solution Overview
Problem
Conventional perpendicular magnetoresistive memory devices face challenges in achieving thermal stability and low write current due to insufficient magnetic crystalline anisotropy, leading to increased damping constants and higher write currents, which complicates device miniaturization and power efficiency.
Innovation Solution
A bottom-pinned perpendicular magnetoresistive element is designed with a reference layer, a recording layer, a spacing layer, and a buffer layer, where the buffer layer features a rocksalt crystal structure to induce perpendicular anisotropy and magnetization, and the recording layer is thermally annealed to form bcc CoFe grains, reducing the damping constant and enhancing spin polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional perpendicular magnetization layers (such as TbCoFe, CoPt, or multilayer (Co/Pt)n) are added to obtain enough perpendicular anisotropy, then thermal stability is improved, but damping constant increases leading to higher write current
Solution Approach 1:
The invention extracts and removes the additional perpendicular magnetization layers (TbCoFe, CoPt, or multilayer (Co/Pt)n) that were previously necessary to achieve sufficient perpendicular anisotropy. By eliminating these extra layers, the damping constant is reduced, enabling lower write current while maintaining thermal stability through the optimized CoFeB layer thickness (0.5-1.5 nm) and interface engineering with the MgO tunnel barrier.
Solution Approach 2:
The invention changes critical parameters of the recording layer, specifically optimizing the CoFeB layer thickness to 0.5-1.5 nm and controlling the interface quality with the MgO tunnel barrier. These parameter changes enhance the perpendicular magnetic anisotropy density and reduce damping constant, allowing thermal stability to be maintained without requiring additional magnetization layers, thus reducing write current.
2Volume of moving object
If the volume of the magnetic layer is reduced to achieve device miniaturization, then device size is reduced, but the injected spin-polarized current required for writing increases
Solution Approach 1:
The invention changes the material composition and thickness parameters of the magnetic layers, specifically using CoFeB with optimized thickness (0.5-1.5 nm) and controlling the interface quality with MgO. These parameter changes increase the perpendicular magnetic anisotropy density, allowing smaller device volumes to maintain sufficient thermal stability and achieve lower write currents through enhanced spin polarization efficiency.
Solution Approach 2:
The invention employs composite material structures, specifically the CoFeB/MgO/CoFeB sandwich structure with optimized layer thicknesses and interface engineering. This composite structure enhances spin polarization and perpendicular magnetic anisotropy, enabling miniaturization while maintaining low write current through improved magnetic properties at the interfaces.
3Measurement precision
If conventional in-plane magnetization MTJ materials are used in perpendicular MTJ, then high MR ratio is achieved, but insufficient magnetic crystalline anisotropy prevents thermal stable perpendicular magnetization
Solution Approach 1:
The invention changes the thickness parameter of the CoFeB recording layer to 0.5-1.5 nm and optimizes the interface quality with the MgO tunnel barrier. These parameter changes induce strong perpendicular magnetic anisotropy through interface effects, enabling thermal stable perpendicular magnetization while preserving the high MR ratio achieved with CoFeB materials.
Solution Approach 2:
The invention uses the composite CoFeB/MgO structure where the interface between the CoFeB recording layer and MgO tunnel barrier generates strong perpendicular magnetic anisotropy. This composite material approach maintains the high MR ratio of CoFeB while achieving thermal stable perpendicular magnetization through interface-induced anisotropy, eliminating the need for additional perpendicular magnetization layers.
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 configuration reduces the write current while maintaining thermal stability and enabling miniaturization of the device, achieving efficient power usage and improved thermal energy stability in perpendicular spin-transfer-torque MRAM.
Implementation Method 1
both two magnetization films have easy axis of magnetization in a direction perpendicular to the film plane due to their strong magnetic crystalline anisotropy
Implementation Method 2
the recording layer is thermally annealed to form bcc CoFe grains
Implementation Method 3
the recording layer is thermally annealed
Implementation Method 4
the magnetization direction of a recording layer is reversed by applying a spin-polarized current to the magnetoresistive element
Implementation Method 5
magnetic random access memories (hereinafter referred to as MRAMs) using the magnetoresistive effect of ferromagnetic tunnel junctions
Data Source
AI summary
A perpendicular magnetoresistive element includes a novel buffer layer having rocksalt crystal structure interfacing to a CoFeB-based recording tri-layer has (100) plane parallel to the substrate plane and with {110} lattice parameter being slightly larger than the bcc CoFe lattice parameter along {100} direction, and crystallization process of amorphous CoFeB material in the recording layer during thermal annealing leads to form bcc CoFe grains having epitaxial growth with in-plane expansion and out-of-plane contraction. Accordingly, a perpendicular anisotropy, as well as a perpendicular magnetization, is induced in the recording layer. The invention preferably includes materials, configurations and processes of perpendicular magnetoresistive elements suitable for perpendicular spin-transfer torque MRAM applications.