Domain Wall MRAM Element with Perpendicular Anisotropy
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Solution Overview
Problem
Current domain wall motion MRAMs face challenges in reducing the absolute value of the write current, which increases with miniaturization, and struggle with initializing magnetization fixed areas and domain wall pinning sites, especially when using perpendicular magnetic anisotropy materials.
Innovation Solution
A magnetic memory element with a magnetization recording layer featuring perpendicular magnetic anisotropy, including two domain wall moving areas and three magnetization fixed areas, where the sensor layer has in-plane magnetic anisotropy and is coupled with a reference layer to facilitate easy initialization and pinning of domain walls, reducing the write current through spin transfer methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the size of the memory cell is miniaturized to increase integration density, then the chip area is reduced, but the write current increases significantly making the technique non-scalable
Solution Approach 1:
The magnetization recording layer is divided into multiple magnetic domains separated by domain walls. Instead of switching the entire layer's magnetization, only local domain wall motion is required, enabling scalable miniaturization without proportional increase in write current.
Solution Approach 2:
The patent replaces the conventional current-induced magnetic field method with spin transfer torque mechanism. Spin-polarized current directly interacts with magnetic moments through quantum mechanical spin transfer, eliminating the need for large circulating currents and enabling efficient scaling.
2Reliability
If a large write current is used to generate sufficient magnetic field for switching, then the magnetization switching is reliable, but the power consumption increases and chip area must be larger
Solution Approach 1:
The patent changes the fundamental parameter from current magnitude to current density. By utilizing spin transfer torque, the switching reliability is achieved through sufficient spin polarization and current density rather than large absolute current, enabling low-power operation.
Solution Approach 2:
A spin-polarized current acts as an intermediary between the electrical current and the magnetic moment. The spin angular momentum of conduction electrons mediates the transfer of angular momentum to the magnetic moments, enabling efficient switching with minimal power consumption.
3Use of energy by moving object
If the spin transfer method is used to reduce write current for better scaling, then the write current decreases enabling higher integration, but the write time period increases becoming slower
Solution Approach 1:
The patent optimizes the dynamic characteristics by adjusting the thickness and material composition of the ferromagnetic layer to achieve perpendicular magnetic anisotropy. This creates a more favorable energy landscape for domain wall motion, enabling faster switching speeds while maintaining low write currents.
Solution Approach 2:
The magnetization recording layer uses composite material structures (e.g., CoFeB, CoFe) with specific thicknesses to achieve perpendicular magnetic anisotropy. These composite structures provide both the low switching current density required for scaling and the fast switching speed needed for high-performance memory operation.
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 allows for efficient and scalable domain wall motion-based data writing with reduced write currents, enabling easier formation of magnetization fixed areas and domain wall pinning sites, thereby enhancing the integration density and stability of the magnetic memory.
Implementation Method 1
a spin-polarized current is injected into a ferromagnetic conductor and magnetization is switched due to a direct interaction between spin of conduction electrons that bear the current and the magnetic moment of the conductor (hereinafter referred to as 'spin transfer magnetization switching')
Implementation Method 2
a magnetization direction cf a ferromagnetic layer in the magneto-resistance effect element is switched by a current-induced magnetic field that is generated by the write current passing by
Implementation Method 3
In the magnetic material having multiple areas (magnetic domains), a current is introduced to pass through the domain wall thereby moving the domain wall. The magnetization direction of each of the areas is treated as a recorded data.
Data Source
AI summary
A magnetic memory cell includes: a magnetization recording layer; and a magnetic tunneling junction section. The magnetization recording layer includes a ferromagnetic layer with perpendicular magnetic anisotropy. The magnetic tunneling junction section is used for reading information in the magnetization recording layer. The magnetization recording layer includes two domain wall moving areas.