Perpendicular MRAM Free Assisting Layer Switching Current
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Solution Overview
Problem
Conventional spin transfer torque magnetic random access memory (STT-MRAM) devices face challenges in miniaturization due to increased critical current density required for switching, which affects thermal stability and write current, especially when using perpendicular magnetization anisotropy materials.
Innovation Solution
The introduction of a free assisting layer with in-plane magnetic anisotropy and a spacer between the free layer and the free assisting layer reduces the critical current density for switching by minimizing interlayer exchange coupling, while maintaining thermal stability and magnetoresistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the device size is reduced for miniaturization, then the switching field increases, but this is of no avail for miniaturization
Solution Approach 1:
The patent replaces the conventional magnetic field switching mechanism with a spin transfer torque (STT) mechanism. Instead of using external magnetic fields generated by write wires, the invention uses spin-polarized electrons to exert torque on the magnetic moments in the free layer, enabling magnetization switching through spin angular momentum transfer rather than mechanical magnetic field application. This substitution allows miniaturization to proceed without the switching field penalty.
2Volume of moving object
If the device size is reduced, then miniaturization is achieved, but magnetic anisotropy energy stored in the free layer is reduced, influencing thermal stability
Solution Approach 1:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular magnetization anisotropy. By introducing perpendicular magnetic anisotropy (PMA) through specific material compositions and structures (such as CoFeB/MgO interfaces), the magnetic anisotropy energy density increases significantly. This parameter change compensates for the volume reduction, maintaining thermal stability (KuV/kBT > 60) even at scaled-down device dimensions.
Solution Approach 2:
The patent employs composite material structures, specifically combining perpendicular magnetic materials (such as Co/Pt, Co/Ne, Co/Pd) with tunneling insulation layers (MgO) and polarization enhancement insertion layers (CoFeB). These composite structures create strong exchange coupling and perpendicular magnetic anisotropy at the interfaces, increasing the magnetic anisotropy energy density to maintain thermal stability in miniaturized devices.
3Stability of the object's composition
If high saturation magnetization material or increased free layer thickness is used to improve thermal stability, then thermal stability is improved, but the current required for switching is increased
Solution Approach 1:
The patent applies local quality enhancement by introducing polarization enhancement insertion layers (such as CoFeB) at specific interfaces within the magnetic tunnel junction structure. These localized regions with high spin polarization enhance the spin transfer torque efficiency at critical interfaces, increasing the effectiveness of the switching current without requiring increased current magnitude throughout the entire device.
Solution Approach 2:
The patent changes the magnetization configuration from in-plane to perpendicular orientation, which fundamentally alters the switching dynamics. Perpendicular magnetization switching occurs through a different mechanism involving precession and switching at lower current densities compared to in-plane switching, thereby reducing the switching current requirement while maintaining or improving thermal stability.
4Stability of the object's composition
If perpendicular magnetic material is used to form PMA magnetic magnetoresistance device, then thermal stability is maintained, but a suitable polarization enhancement insertion layer is required to form the ordering direction for high MR ratio
Solution Approach 1:
The patent introduces polarization enhancement insertion layers (such as CoFeB) as intermediary structures between the perpendicular magnetic material layers and the MgO tunneling insulation layer. These insertion layers serve as mediators that facilitate the formation of the required (002) ordering direction at the MgO interface through strong exchange coupling, enabling high magnetoresistance ratio while maintaining the perpendicular magnetization structure for thermal stability.
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 effectively lowers the switching current density without compromising thermal stability or magnetoresistance, facilitating the miniaturization and mass production of perpendicular magnetization anisotropy MRAM devices.
Implementation Method 1
a spin transfer torque (STT) mechanism, by which an angular momentum conservation mechanism of spin-polarized electrons and a local magnetic moment is used to switch the magnetization direction of the free layer of the device
Implementation Method 2
By changing a magnetization direction of the free layer to be parallel or antiparallel to a magnetization direction of the pinned layer, a magnetoresistance thereof respectively have a low resistance state and a high resistance state for storing information
Implementation Method 3
PMA MRAM structure... A magnetization direction 120 of the magnetic pinned layer 110 is a fixed direction perpendicular to its horizontal plane. A magnetization direction 122 of the magnetic free layer 114 can also be freely switched between two directions by applying the external magnetic field or current, though it is perpendicular to its horizontal plane
Data Source
AI summary
A magnetic random access memory (MRAM) has a perpendicular magnetization direction. The MRAM includes a first magnetic layer, a second magnetic layer, a first polarization enhancement layer, a second polarization enhancement layer, a barrier layer, a spacer, and a free assisting layer. A pinned layer formed by the first magnetic layer and the first polarization enhancement layer has a first magnetization direction and a first perpendicular magnetic anisotropy. A free layer formed by the second magnetic layer and the second polarization enhancement layer has a second magnetization direction and a second perpendicular magnetic anisotropy. The barrier layer is disposed between the first polarization enhancement layer and the second polarization enhancement layer. The spacer is disposed on the second magnetic layer. The free assisting layer is disposed on the spacer and has an in-plane magnetic anisotropy. The spacer and the barrier layer are on opposite sides of the free layer.