Heusler Compound STT-MRAM with Chemical Templating
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Solution Overview
Problem
Current magnetic random access memory (MRAM) devices using spin transfer torque (STT) face challenges in scaling below 20 nm due to weak perpendicular magnetic anisotropy (PMA) in Co-Fe-B layers, which is insufficient to overcome thermal fluctuations and requires new materials with stronger bulk PMA.
Innovation Solution
The use of Heusler compounds with tetragonal distortion, such as Mn3Ge, Mn3Sn, and Mn3Sb, as magnetic electrodes, which exhibit high perpendicular magnetic anisotropy, and the development of a non-magnetic chemical templating layer to grow ultra-thin films on amorphous or polycrystalline substrates, allowing for the formation of high-quality, switchable magnetic layers without thermal annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Co-Fe-B layers are used with perpendicular magnetic anisotropy, then the magnetization can be oriented perpendicular to the layers, but the PMA is too weak to overcome thermal fluctuations when device size is reduced below 20 nm
Solution Approach 1:
The patent changes the material composition from Co-Fe-B to Heusler compounds (Mn3Ge, Mn3Sn, Mn3Sb), fundamentally altering the magnetic properties. These Heusler compounds exhibit much stronger perpendicular magnetic anisotropy arising from their tetragonal crystal structure, providing sufficient thermal stability while enabling scaling to smaller device sizes below 20 nm
Solution Approach 2:
The patent employs composite structures combining Heusler compound magnetic layers with MgO tunnel barriers and chemical templating layers. This composite approach enables the Heusler layers to be grown as ultra-thin films on amorphous or polycrystalline substrates, maintaining strong PMA and thermal stability while achieving the required thinness for small-scale devices
2Use of energy by moving object
If the magnetic layer thickness is reduced to below 1 nm to enable switching by available current, then the switching current magnitude is reduced, but the PMA becomes too weak to maintain perpendicular magnetization and overcome thermal fluctuations
Solution Approach 1:
By changing from Co-Fe-B to Heusler compounds, the patent achieves a material with inherently stronger PMA that does not require thicker layers to maintain stability. This allows ultra-thin films below 1 nm to simultaneously achieve low switching currents and maintain robust perpendicular magnetization against thermal fluctuations
Solution Approach 2:
The patent introduces chemical templating layers as intermediaries that enable the growth of ultra-thin Heusler compound layers with controlled thickness and crystal orientation. These templating layers facilitate the formation of stable perpendicular magnetization in ultra-thin films while maintaining compatibility with standard semiconductor fabrication processes
3Reliability
If single crystalline substrates or MgO seed layers are used to grow ultra-thin Heusler films, then strong perpendicular magnetic anisotropy is achieved, but integration with CMOS technology becomes difficult due to incompatibility with polycrystalline copper wires
Solution Approach 1:
The patent introduces chemical templating layers as intermediaries between the substrate and Heusler compound layers. These templating layers enable epitaxial growth of high-quality Heusler films with strong PMA on amorphous or polycrystalline substrates, eliminating the need for single crystalline substrates and enabling integration with standard CMOS fabrication processes
Solution Approach 2:
The patent changes the substrate requirement from single crystalline to amorphous or polycrystalline materials, fundamentally altering the manufacturing compatibility. This parameter change enables direct integration with CMOS technology while maintaining the ability to grow ultra-thin Heusler films with strong perpendicular magnetic anisotropy through the use of chemical templating 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 approach enables the growth of ultra-thin Heusler films with strong perpendicular magnetic anisotropy, achieving stable magnetic moments and square hysteresis loops, even at thicknesses below 1 nm, and allows for scalable MRAM devices by using MnxN as a conducting seed layer, facilitating integration with CMOS technology.
Implementation Method 1
The current, which is innately spin-polarized, delivers spin angular momentum, that once a threshold current is exceeded results in switching of the direction of the magnetic memory electrode moment. This transfer of spin angular momentum exerts a spin transfer torque (STT)
Implementation Method 2
The perpendicular magnetic anisotropy (PMA) of Co—Fe—B layers arises from the interfaces between these layers and the tunnel barrier and/or the underlayer on which the Co—Fe—B layer is deposited
Implementation Method 3
thin films formed from such materials may exhibit PMA due to a magneto-crystalline anisotropy associated with their tetragonally distorted structure
Data Source
AI summary
A device is disclosed. The device includes a first magnetic layer and a tunnel barrier. The first magnetic layer has a volume uniaxial magnetic crystalline anisotropy. The magnetic moment of the first layer is substantially perpendicular to the first layer. The tunnel barrier is in proximity to the first magnetic layer. The orientation of the magnetic moment of the first magnetic layer is reversed by spin transfer torque induced by current passing between and through the first magnetic layer and the tunnel barrier.