STTMRAM Switchable Free Layer for Low Current
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Solution Overview
Problem
Current spin-transfer torque magnetic random access memory (STTMRAM) elements require higher electric current for switching, which is not practical for storage systems, especially due to limitations in scalability and thermal stability.
Innovation Solution
A STTMRAM element with a tri-layer structure comprising a fixed layer, a barrier layer, a first and second free layer separated by a non-magnetic separation layer, and a perpendicular reference layer, where the first and second free layers have in-plane magnetizations that couple anti-parallelly, allowing for lower current switching and enhanced thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional STTMRAM element structure is used, then the device can store data through spin transfer torque switching, but the electric current required for switching is too high to be practical for storage systems
Solution Approach 1:
The free layer is segmented into two separate free layers (first free layer and second free layer) with different magnetization orientations. The first free layer has in-plane magnetization and the second free layer has perpendicular magnetization. This segmentation allows each layer to contribute differently to the switching mechanism, enabling lower switching current while maintaining thermal stability through the combined structure.
Solution Approach 2:
The patent employs a composite magnetic layer structure combining ferromagnetic materials with different magnetic anisotropy characteristics. The first free layer uses materials with in-plane magnetic anisotropy while the second free layer uses materials with perpendicular magnetic anisotropy. This composite structure leverages the advantages of both material types to achieve low-power switching and high thermal stability simultaneously.
2Ease of operation
If the magnetization switching threshold is reduced to enable lower current operation, then switching efficiency improves, but thermal stability against agitation deteriorates
Solution Approach 1:
The patent introduces a second dimension of magnetization orientation by incorporating both in-plane and perpendicular magnetization components in the free layers. Instead of relying solely on in-plane switching, the structure utilizes perpendicular magnetization in the second free layer to provide enhanced thermal stability while the in-plane component facilitates easier switching. This dimensional approach allows independent optimization of switching efficiency and 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
The tri-layer structure enables lower current switching while maintaining stability against thermal agitation, improving scalability and reducing the thickness of magnetic layers, thus enhancing data retention and switching efficiency.
Implementation Method 1
ST from electrons transmitted from the RL 3 to the FL 1 can orientate storage layer or free layer magnetization (as shown by the direction of the arrows in FIG. 1) to a direction parallel to that of RL 3
Implementation Method 2
When electrons flow from the FL 1 to the RL 3, ST from electrons reflected from the RL 3 back into the FL 1 can orientate SL magnetization in a direction that is anti-parallel relative to that of RL 3
Implementation Method 3
The exchange coupling layer (ECL) 4 is typically made of ruthenium (Ru)
Data Source
AI summary
A perpendicular spin-transfer torque magnetic random access memory (STTMRAM) element is configured to store a state when electrical current is applied thereto. The perpendicular STTMRAM element includes a magnetization layer having a first free layer and a second free layer, separated by a non-magnetic separation layer (NMSL). The direction of magnetization of the first and second free layers each is in-plane prior to the application of electrical current and after the application of electrical current, the direction of magnetization of the second free layer becomes substantially titled out-of-plane and the direction of magnetization of the first free layer switches. Upon electrical current being discontinued, the direction of magnetization of the second free layer remains in a direction that is substantially opposite to that of the first free layer.