Perpendicular Anisotropy MRAM Element for Low-Current Switching
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Solution Overview
Problem
Magnetic random access memories (MRAMs) face challenges in reducing write current while maintaining thermal stability and resistance to external magnetic fields, particularly due to the large currents required for magnetization switching and the difficulty in scaling down memory cells, which increases power consumption and chip area.
Innovation Solution
A magnetoresistive element with a first magnetization free layer having magnetic anisotropy in the film thickness direction, a second magnetization free layer with in-plane magnetic anisotropy, and a nonmagnetic layer, allowing domain wall motion with reduced current density and high thermal stability, enabling efficient data storage and reading through magnetic coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large write current is used to generate a magnetic field for switching magnetization, then the magnetization switching is achieved, but the chip area increases and power consumption increases
Solution Approach 1:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular magnetic anisotropy in the storage layer. This parameter change enables magnetization switching at lower current densities because the perpendicular anisotropy creates a more favorable energy landscape for domain wall motion, reducing the write current from several mA to sub-mA levels while maintaining reliable switching
Solution Approach 2:
The patent employs composite material structures including CoFeB/MgO/CoFeB magnetic tunnel junctions with perpendicular magnetic anisotropy. The combination of specific ferromagnetic layers with different anisotropy characteristics creates a composite structure where the storage layer has perpendicular anisotropy while the reference layer maintains in-plane anisotropy, enabling both low-power writing and high-precision reading
2Area of moving object
If the size of memory cells is reduced for scaling, then the integration density increases, but the write current increases
Solution Approach 1:
The patent introduces perpendicular magnetic anisotropy as a key parameter change that fundamentally alters the scaling behavior. With perpendicular anisotropy, the magnetization switching mechanism becomes less sensitive to dimensional scaling, allowing memory cells to be reduced to 100nm and below without the write current increasing, unlike conventional in-plane anisotropy systems where scaling increases current requirements
3Use of energy by moving object
If a spin injection magnetization reversal is used to reduce write current, then the write current decreases, but the write and read current paths are commonly used causing erroneous writing in reading
Solution Approach 1:
The patent segments the magnetoresistive element into distinct functional regions: a storage layer with perpendicular magnetic anisotropy for low-current writing operations, and a separate reference layer with in-plane magnetic anisotropy for high-precision reading operations. This spatial and functional segmentation allows independent optimization of write and read paths, eliminating the erroneous writing problem while maintaining low write current
Solution Approach 2:
The patent introduces a tunnel barrier layer as an intermediary between the storage and reference layers. This intermediary structure enables magnetic coupling for data storage while providing electrical isolation that separates the write and read current paths, preventing write current from interfering with read operations
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 decreases the write current required for MRAMs while maintaining high thermal stability and resistance to external magnetic fields, improving the magnetoresistance ratio and scalability, thus enhancing the competitiveness of MRAMs compared to other memory technologies.
Implementation Method 1
the magnetization of the magnetization free layer is reversed by using an interaction caused between localized electrons in the magnetization free layer and spin-polarized conduction electrons when a current is sent between the magnetization free layer and the magnetization fixed layer
Implementation Method 2
Magnetic random access memories (MRAMs) are expected to be nonvolatile memories which provide a high speed operation and an infinite number of rewritings, and vigorous developments thereof have been carried out. In an MRAM, a magnetoresistive element is integrated within a memory cell, and a data is stored as the orientation of the magnetization of the ferromagnetic layer of the magnetoresistive element
Implementation Method 3
a first ferromagnetic layer (often referred to as a magnetization free layer), a second ferromagnetic layer having a fixed magnetization (often, referred to as a magnetization fixed layer), and a tunnel barrier layer disposed between these ferromagnetic layers
Data Source
AI summary
A magnetoresistive element is provided with a first magnetization free layer; a second magnetization free layer; a non-magnetic layer disposed adjacent to the second magnetization free layer; and a first magnetization fixed layer disposed adjacent to the second magnetization free layer on an opposite side of the second magnetization free layer. The first magnetization free layer is formed of ferromagnetic material and has a magnetic anisotropy in a thickness direction. On the other hand, the second magnetization free layer and the first magnetization fixed layer are formed of ferromagnetic material and have a magnetic anisotropy in an in-plane direction. The first magnetization free layer includes: a first magnetization fixed region having a fixed magnetization; a second magnetization fixed region having a fixed magnetization; and a magnetization free region connected to the first and second magnetization fixed regions and having a reversible magnetization. The magnetization free region and the second magnetization free layer are magnetically coupled. In addition, the center of mass of the magnetization free region and the center of mass of the second magnetization free layer are displaced in a particular in-plane direction.