Magnetic Memory Device Spin Polarization Layer
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Solution Overview
Problem
Current magnetic random access memory (MRAM) technologies face challenges in selectivity and high current densities for magnetization reversal, leading to increased power consumption and limitations in memory density due to electromigration and stochastic fluctuations in switching time.
Innovation Solution
A magnetic device with a reference layer, a storage layer, and an electron spin polarization layer, where the spin transfer coefficient between the reference and storage layers is greater than between the spin polarization and storage layers, allowing for efficient magnetization switching with reduced critical current density and improved selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If writing is carried out by spin transfer torque, then selectivity is improved, but the critical current density becomes too high causing electromigration issues
Solution Approach 1:
The patent segments the magnetization reversal process by introducing a storage layer with perpendicular magnetization that acts as an intermediary. The spin-polarized current first switches the storage layer magnetization, which then exerts a magnetic field on the target layer. This segmentation allows the high current density to be applied to a small storage layer area rather than large bit line areas, reducing electromigration while maintaining selectivity.
Solution Approach 2:
The storage layer with perpendicular magnetization serves as an intermediary between the spin-polarized current and the target layer. It receives the spin transfer torque from the current, switches its own magnetization, and then generates a magnetic field that switches the target layer magnetization. This intermediary mechanism enables selective switching at lower current densities in the bit lines.
2Speed
If perpendicular magnetization switching is used, then switching speed is improved, but stochastic fluctuations in switching time increase
Solution Approach 1:
The patent changes the magnetization orientation parameter from in-plane to perpendicular for the storage layer. This parameter change enables faster switching speeds through spin transfer torque while the subsequent magnetic field coupling to the target layer provides a deterministic switching mechanism that reduces stochastic fluctuations in the overall switching time.
3Use of energy by moving object
If bit line current is reduced to lower power consumption, then power efficiency is improved, but magnetic field generation for writing becomes insufficient
Solution Approach 1:
The patent replaces the direct magnetic field generation mechanism (current in bit line producing magnetic field) with a spin transfer torque mechanism. The spin-polarized current switches the storage layer magnetization, which then generates the magnetic field needed for writing. This substitution allows much lower bit line currents (reducing power consumption) while still achieving the necessary magnetic field for magnetization switching.
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 solution significantly lowers the critical switching current density and reduces stochastic fluctuations in magnetization reversal time, enabling faster and more reliable switching with lower power consumption.
Implementation Method 1
writing is carried out by spin transfer... when a spin-polarized current is injected into a magnetic nanostructure, this current exerts a torque on the magnetization of the nanostructure, called spin transfer torque
Implementation Method 2
Different levels of resistance of the tunnel junction can be achieved depending on the angle between the magnetizations of the two storage and reference layers... The variation in resistance as a function of the magnetic configuration is used to reread the information
Implementation Method 3
This trapping is generally achieved by interaction with an adjacent antiferromagnetic layer, not shown (exchange anisotropy mechanism)
Data Source
Figure 1~2
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Figure 5~6
AI summary
The present invention relates to a magnetic device (200) comprising a reference magnetic layer (201) with a fixed magnetisation direction either aligned with the plane of the layer (201) or perpendicular to the plane of the layer (201), a second magnetic storage layer (203), having a variable magnetisation direction, a nonmagnetic spacer (202) separating the reference layer (201) from the storage layer (203), and a third magnetic layer (205) for the electron spin polarisation with a magnetisation perpendicular to that of the layer (201) and out-of-plane of the layer (205) if the magnetisation direction of the reference layer (201) is in the plane of the layer (201) or in the plane of the layer (205) if the magnetisation direction of the reference layer (201) is perpendicular to the plane of the layer (201). The spin transfer coefficient between the reference layer (201) and the storage layer (203) is higher than the spin transfer coefficient between the spin polarisation layer (205) and the storage layer (203).