MRAM Keeper Layer Reduces Switching Current
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Solution Overview
Problem
Conventional MRAM devices face challenges in scaling bit cells to smaller dimensions due to susceptibility to bit disturbs and reduced magnetic stability, particularly when using traditional switching techniques, and the implementation of spin-transfer switching is hindered by the need for high currents and specific materials that affect reliability and read signals.
Innovation Solution
Incorporating a magnetic 'keeper' layer with perpendicular anisotropy to cancel the surface anisotropy of the free layer, reducing the spin torque switching current, and using standard materials for the free layer, thereby enhancing thermal stability and selectivity while maintaining reliability and read signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional MRAM switching techniques are used to scale bit cells to smaller dimensions, then device density is improved, but magnetic stability and susceptibility to bit disturbs deteriorate
Solution Approach 1:
The patent introduces a magnetic keeper layer as an intermediary element between the free magnetic layer and the underlying structure. This keeper layer acts as a mediator that provides localized magnetic field support to the free layer, enhancing its thermal stability without requiring increased cell size. The keeper layer's magnetization is coupled to the free layer's magnetization, creating a stabilizing effect that prevents unwanted switching while maintaining small dimensions.
2Stability of the object's composition
If materials with large magnetic anisotropy are used in the free layer to enhance stability, then thermal stability is improved, but the switching current becomes impractically high
Solution Approach 1:
The magnetic keeper layer serves as a mediator that reduces the switching current requirement by providing a stabilizing magnetic field. Instead of relying solely on high anisotropy materials in the free layer, the keeper layer's magnetization couples to the free layer, creating an effective reduction in the energy barrier for switching. This allows the use of materials with moderate anisotropy while achieving both stability and practical switching currents.
Solution Approach 2:
The patent changes the magnetic configuration parameters by introducing the keeper layer with perpendicular magnetic anisotropy. This creates a magnetostatic coupling effect that modifies the effective anisotropy energy landscape, allowing for lower switching currents while maintaining thermal stability. The parameter change involves transitioning from a single-layer free magnetic layer to a coupled free layer-keeper layer system.
3Use of energy by moving object
If transmission mode spin-transfer switching is used to reduce switching current, then switching current is reduced, but write current must flow through the tunnel junction which affects reliability
Solution Approach 1:
The patent segments the current path from the magnetization switching path. The write current flows through the keeper layer rather than through the tunnel junction, separating the high-current switching function from the sensitive tunnel junction. This segmentation protects the tunnel junction from degradation caused by high current densities while still achieving effective magnetization switching in the free layer through the magnetic coupling with the keeper layer.
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 reduced switching currents, improved thermal stability, and enhanced selectivity in MRAM cells, making it suitable for high-density applications without compromising reliability or read signal quality.
Implementation Method 1
a magnetic 'keeper' layer with perpendicular anisotropy to cancel the surface anisotropy of the free layer
Implementation Method 2
magnetic 'keeper' layer with perpendicular anisotropy
Implementation Method 3
the electrons in the write current become spin-polarized after they pass through the fixed magnetic layer. In this technique, the write current actually flows through the tunnel junction in the cell. According to the spin-transfer effect, the electrons in the write current become spin-polarized after they pass through the fixed magnetic layer
Implementation Method 4
The spin-polarized electrons cross the nonmagnetic layer and, through conservation of angular momentum, impart a torque on free magnetic layer
Implementation Method 5
the fixed layer functions as a polarizer. The spin-polarized electrons cross the nonmagnetic layer
Data Source
AI summary
A magnetic random access memory device include a spin torque MRAM cell (100) having a reduced switching current (Ic) wherein standard materials may be used for a free layer (108). A fixed magnetic element (112) polarizes electrons passing therethrough, and the free magnetic element (108) having a first plane anisotropy comprises a first magnetization (130) whose direction is varied by the spin torque of the polarized electrons. An insulator (110) is positioned between the fixed magnetic element (112) and the free magnetic element (108), and a keeper layer (104) positioned contiguous to the free magnetic element (108) and having a second plane anisotropy orthogonal to the first plane anisotropy, reduces the first plane anisotropy and hence reduces the spin torque switching current (Ic). The keeper layer (104) may include alternating synthetic antiferromagnetic layers (132, 134) of magnetization approximately equal in magnitude and opposite in direction.