Al-Doped Heusler MTJ Stack for High PMA and Low Switching Current
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Solution Overview
Problem
Current magnetic random access memories (MRAMs) face limitations in scaling down due to the need for magnetic layers with high perpendicular magnetic anisotropy (PMA) and low magnetic moment, which are challenging to achieve with existing ferromagnetic alloys like CoFeB, especially at sizes below 20 nanometers, and result in low tunneling magnetoresistance (TMR) and high switching currents.
Innovation Solution
The use of Al-doped Heusler compounds in a multilayer structure with specific compositions and configurations, such as Al1-xEx and H1-yAl, where H is a Heusler compound like Mn3Z, to create magnetic layers with high PMA and low magnetic moment, enhancing TMR and reducing switching currents, by incorporating layers like MnyN or VzN and a tunnel barrier like MgO.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ferromagnetic alloys like CoFeB are used in magnetic layers, then the magnetic moment can be reduced, but the perpendicular magnetic anisotropy (PMA) becomes difficult to maintain at sizes below 20 nanometers
Solution Approach 1:
The patent employs ferrimagnetic Heusler compounds (e.g., Mn3Ge, Mn3Sn, Mn3Sb) as composite magnetic materials that combine high perpendicular magnetic anisotropy with low net magnetic moment. These compounds consist of multiple elements arranged in specific crystal structures (L12 or D022) that generate strong spin-orbit coupling and interfacial anisotropy, enabling stable PMA at nanoscale dimensions while maintaining low magnetic moments through ferrimagnetic compensation.
Solution Approach 2:
The patent utilizes interfacial engineering and strain effects to modify the magnetic anisotropy parameters of Heusler compounds. By controlling interface quality with adjacent layers (e.g., MgO, CoFeB) and applying epitaxial strain, the perpendicular magnetic anisotropy energy density is enhanced, allowing stable magnetic moment orientation perpendicular to the film plane even at sub-20nm thicknesses.
2Length of moving object
If magnetic layers with high PMA and low magnetic moment are used, then scaling down is enabled, but tunneling magnetoresistance (TMR) decreases
Solution Approach 1:
The patent implements a multilayer structure where different layers perform specialized functions: ferrimagnetic Heusler compound layers provide high PMA and low moment, while adjacent ferromagnetic metal layers (CoFeB, CoFe) provide high spin polarization and TMR. The tunnel barrier (MgO) is engineered with specific thickness and quality to maximize tunneling magnetoresistance. This local optimization of properties in different layers resolves the contradiction between scaling and TMR.
Solution Approach 2:
The magnetic junction employs composite structures combining ferrimagnetic Heusler compounds with ferromagnetic metals and oxide tunnel barriers. This composite approach allows the Heusler layer to provide size-scaling benefits while the ferromagnetic metal layers contribute high spin polarization, and the MgO barrier provides high TMR, achieving all three requirements simultaneously.
3Reliability
If magnetic layers with high PMA are used, then perpendicular magnetic moment stability is improved, but switching current increases
Solution Approach 1:
The patent utilizes spin transfer torque (STT) mechanism where spin-polarized electrons from the ferromagnetic metal layer exert a torque on the ferrimagnetic Heusler layer to switch its magnetization. The high spin polarization of the ferromagnetic metal compensates for the high PMA of the Heusler compound, enabling switching at reduced current densities. The spin torque efficiently overcomes the perpendicular anisotropy energy barrier.
Solution Approach 2:
The patent modifies the magnetic damping parameter and anisotropy energy density through material composition control and interface engineering in the Heusler compounds. By optimizing these parameters, the switching current density is reduced while maintaining stable perpendicular magnetic moments. The ferrimagnetic nature of the Heusler compounds also provides lower damping compared to conventional ferromagnets, facilitating easier 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
This approach allows for the development of magnetic junctions with improved TMR, reduced switching currents, and stable perpendicular magnetic moments at smaller sizes, enhancing the performance and stability of MRAMs and other magnetic devices.
Implementation Method 1
magnetic random access memories (MRAMs) store information utilizing magnetic materials as an information storage medium. For example, a magnetic tunneling junction (MTJ) may be used in an MRAM, such as a spin transfer torque MRAM (STT-MRAM)
Implementation Method 2
MTJs with positive tunnel magnetoresistance (TMR), when a sufficient current is driven in one direction perpendicular-to-plane (e.g. top to bottom), the free layer magnetic moment switches to be parallel to that of the reference layer
Data Source
AI summary
A magnetic device and method for providing the magnetic device are disclosed. The magnetic device includes a multilayer structure and a magnetic layer. The multilayer structure includes alternating layers of A and E. A includes a first material. The first material includes at least one of Co, Ru, or Ir. The first material may include an IrCo alloy. E includes at least one other material that includes Al. The other material(s) may include an alloy selected from AlGa, AlSn, AlGe, AlGaGe, AlGaSn, AlGeSn, and AlGaGeSn. A composition of the multilayer structure is represented by A1-xEx, where x is at least 0.45 and not more than 0.55. The magnetic layer includes an Al-doped Heusler compound. The magnetic layer shares an interface with the multilayer structure.