Perpendicular MTJ Switching-Enhancing Layer for STTMRAM
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Solution Overview
Problem
Magnetic random access memory (MRAM) with perpendicular magnetic tunnel junctions (MTJs) faces challenges in reducing the threshold voltage and current required for switching the free layer magnetization, which limits their practical application due to high effective coercivity fields that are non-uniform across the free layer.
Innovation Solution
A spin transfer torque magnetic random access memory (STTMRAM) element with a perpendicular magnetic orientation, incorporating a switching-enhancing layer (SEL) with in-plane magnetic orientation, which generates magneto-static fields that tilt the magnetic moments of the free layer's outer edges, reducing the switching current and voltage while maintaining thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If perpendicular magnetic tunnel junctions (MTJs) are used to improve density and thermal stability, then storage capacity and reliability are improved, but the threshold voltage and current required for switching increase due to high effective coercivity fields
Solution Approach 1:
The patent segments the free layer into different regions with different magnetic properties - the center region maintains perpendicular magnetization for thermal stability, while the outer edge regions are engineered with in-plane magnetization components that reduce the effective coercivity field. This segmentation allows the device to achieve both high thermal stability and low switching current requirements.
Solution Approach 2:
The patent applies local quality by creating spatially varying magnetic anisotropy within the free layer. The outer edges of the free layer are designed with different magnetic characteristics (reduced perpendicular anisotropy, enhanced in-plane components) compared to the center region. This local modification reduces the effective coercivity field at the edges where switching initiates, thereby reducing the overall switching current while preserving the perpendicular magnetization and thermal stability of the bulk free layer.
2Ease of operation
If the effective coercivity field is reduced to lower switching current, then ease of operation is improved, but thermal stability deteriorates
Solution Approach 1:
The patent creates a spatial gradient in magnetic anisotropy where the outer edge regions have reduced perpendicular anisotropy (enhancing switchability) while the center region maintains strong perpendicular anisotropy (ensuring thermal stability). This local differentiation resolves the contradiction by allowing easy switching at the edges without compromising the overall thermal stability of the perpendicular magnetized free layer.
Solution Approach 2:
The free layer is segmented into functionally distinct regions: edge regions that facilitate low-field switching and a central region that provides thermal stability. This segmentation enables the device to simultaneously achieve ease of operation through edge-mediated switching and reliability through the stable perpendicular magnetization of the bulk free 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
The solution effectively reduces the switching current and voltage by 20-25% compared to prior art structures, facilitating easier switching of the free layer with minimal disturbance to the center's magnetic moment, thereby enhancing the operational efficiency of STTMRAM devices.
Implementation Method 1
The SEL has an in-plane magnetic orientation and generates magneto-static fields onto the free layer, causing the magnetic moments of the outer edges of the free layer to tilt with an in-plane component
Implementation Method 2
An exemplary MTJ uses spin transfer torque to effectuate a change in the direction of magnetization of one or more free layers in the MTJ. That is, writing a bit ('1' or '0' in digital logic) of information is achieved by using a spin polarized current flowing through the MTJ
Data Source
AI summary
An STTMRAM element includes a magnetic tunnel junction (MTJ) having a perpendicular magnetic orientation. The MTJ includes a barrier layer, a free layer formed on top of the barrier layer and having a magnetic orientation that is perpendicular and switchable relative to the magnetic orientation of the fixed layer. The magnetic orientation of the free layer switches when electrical current flows through the STTMRAM element. A switching-enhancing layer (SEL), separated from the free layer by a spacer layer, is formed on top of the free layer and has an in-plane magnetic orientation and generates magneto-static fields onto the free layer, causing the magnetic moments of the outer edges of the free layer to tilt with an in-plane component while minimally disturbing the magnetic moment at the center of the free layer to ease the switching of the free layer and to reduce the threshold voltage/current.