Asymmetric Composite Free Layer for Low-Current Stable MTJs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional magnetic tunnel junction (MTJ) devices in spin transfer torque random access memories (STT-MRAMs) face challenges in achieving low switching current and thermal stability of the free layer's magnetization, which affects the performance and endurance of magnetic random access memories (MRAMs).
Innovation Solution
The implementation of an MTJ structure with perpendicular shape anisotropy, featuring a reference layer, a non-magnetic spacer, and a free layer with a coupling layer, where the second layer has a saturation magnetization 2 to 5 times that of the first layer, and a spin-orbit torque line, to enhance switching efficiency and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional MTJ structure is used, then the device complexity is low, but the switching current is high and thermal stability is poor
Solution Approach 1:
The free layer is divided into two distinct magnetic sublayers (first magnetic sublayer and second magnetic sublayer) with different saturation magnetizations. This segmentation allows each sublayer to contribute differently to the overall magnetic stability, with the higher Ms sublayer providing thermal stability and the lower Ms sublayer facilitating switching, thereby resolving the contradiction between thermal stability and switching efficiency.
Solution Approach 2:
Different regions of the free layer are assigned different magnetic properties through the use of sublayers with different saturation magnetizations. The first magnetic sublayer has lower Ms for easier switching in its local region, while the second magnetic sublayer has higher Ms for thermal stability in its local region. This local differentiation allows the system to achieve both low switching current and high thermal stability simultaneously.
2Reliability
If the saturation magnetization of the free layer is increased for thermal stability, then thermal stability improves, but switching current increases
Solution Approach 1:
The free layer is segmented into sublayers with different saturation magnetizations, allowing the system to achieve thermal stability through the higher Ms sublayer while maintaining low switching current through the lower Ms sublayer. The spin transfer torque preferentially switches the lower Ms sublayer first, reducing the overall switching current requirement.
Solution Approach 2:
The free layer employs a composite structure of multiple magnetic sublayers with different material compositions and saturation magnetizations. This composite approach allows the system to combine the thermal stability benefits of high Ms materials with the low switching current benefits of low Ms materials, achieving both goals simultaneously.
3Use of energy by moving object
If the free layer thickness is reduced to lower switching current, then switching current decreases, but thermal stability deteriorates
Solution Approach 1:
The free layer is segmented into sublayers with different thicknesses and saturation magnetizations. The lower Ms sublayer can be thinner to facilitate switching, while the higher Ms sublayer provides thermal stability. This segmentation allows the system to achieve low switching current without sacrificing thermal stability, as each sublayer performs its specialized function.
Solution Approach 2:
Different sublayers are assigned different thicknesses and magnetic properties to optimize their local functions. The first magnetic sublayer with lower Ms can have optimized thickness for low switching current, while the second magnetic sublayer with higher Ms provides thermal stability. This local optimization resolves the contradiction between switching current 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
This configuration reduces the switching current and improves the thermal stability of the free layer, leading to enhanced performance and endurance of MRAMs by increasing the Figure of Merit (FOM) and maintaining a high energy barrier at small critical dimensions.
Implementation Method 1
A spin-polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction
Implementation Method 2
MTJ structure with perpendicular shape anisotropy
Data Source
AI summary
A perpendicular shape anisotropy magnetic tunnel junction structure includes a reference layer, a non-magnetic layer, and a free layer. The reference layer includes a first side and a second side that is opposite the first side. The non-magnetic spacer includes a first side and a second side. The first side of the non-magnetic spacer is on the second side of the first reference layer. The free layer includes a first side and a second side. The first side of the free layer is on the second side of the non-magnetic spacer. The free layer further includes a first layer on the first side of the free layer, a second layer on the second side of the free layer and a coupling layer disposed between the first layer and the second layer. A saturation magnetization of the second layer is between 2-5 times inclusive a saturation magnetization of the first layer.