Magnetic Tunnel Junction Perpendicular Anisotropy for Low Switching Current
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Solution Overview
Problem
Current magnetic memory technologies, such as STT-MRAM, face challenges in reducing the critical switching current while maintaining thermal stability and magnetoresistive ratio, especially as device sizes shrink, leading to issues with electrical breakdown and compatibility with CMOS transistors.
Innovation Solution
A magnetic element with a free layer interfacing a tunnel barrier layer and a thin out-of-plane Hk enhancing layer is designed to enhance perpendicular surface anisotropy, reducing switching current and increasing thermal stability without degrading the MR ratio, using materials like MgO for the tunnel barrier and Hk enhancing layer, and optimizing their thickness and oxidation states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the size of MRAM cells is decreased to increase storage density, then storage capacity is improved, but the critical switching current increases and electrical breakdown becomes more likely
Solution Approach 1:
The patent changes the magnetization orientation parameter from in-plane to perpendicular-to-plane, which fundamentally alters the switching mechanism. This parameter change enables lower switching currents in scaled devices while maintaining thermal stability, as the perpendicular anisotropy provides a more favorable energy landscape for spin-transfer torque switching in nanoscale devices.
Solution Approach 2:
The patent employs composite magnetic tunnel junction structures with multiple layers including CoFeB, MgO, and other magnetic and non-magnetic materials. This composite structure enables simultaneous optimization of TMR ratio, thermal stability, and switching current characteristics, allowing high-density storage with improved reliability.
2Use of energy by moving object
If the critical switching current is reduced to enable lower power operation, then energy consumption is improved, but thermal stability deteriorates
Solution Approach 1:
The patent utilizes perpendicular-to-plane magnetization as a key parameter change that decouples the relationship between switching current and thermal stability. The perpendicular magnetic anisotropy enables independent optimization: thermal stability is maintained through the anisotropy energy barrier while switching current is reduced through spin-transfer torque efficiency in the perpendicular configuration.
Solution Approach 2:
The patent introduces localized interfacial perpendicular magnetic anisotropy at specific interfaces within the magnetic tunnel junction, particularly at the CoFeB/MgO interfaces. This local quality enhancement provides the necessary thermal stability barrier while keeping the overall switching current low, as the anisotropy is concentrated at critical interfaces rather than distributed throughout the entire structure.
3Device complexity
If conventional in-plane magnetization is used, then device structure is simpler, but switching current is too high for scaled devices
Solution Approach 1:
The patent fundamentally changes the magnetization configuration parameter from in-plane to perpendicular-to-plane orientation. This parameter change, while introducing additional structural considerations, enables dramatically reduced switching currents in scaled devices through the perpendicular spin-transfer torque mechanism, making it essential for continued scaling.
Solution Approach 2:
The patent introduces MgO tunnel barrier layers and specific interface structures as intermediaries that facilitate perpendicular magnetization and enhance the spin-transfer torque effect. These intermediary layers mediate between the magnetic layers and enable the perpendicular anisotropy necessary for low-current switching while maintaining structural integrity.
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 and enhances thermal stability, ensuring compatibility with CMOS transistors and maintaining high MR ratios, crucial for high-density magnetic memory devices.
Implementation Method 1
The spin-transfer effect arises from the spin dependent electron transport properties of ferromagnetic-spacer-ferromagnetic multilayers. When a spin-polarized current transverses a magnetic multilayer in a current perpendicular to plane (CPP) configuration, the spin angular moment of electrons incident on a ferromagnetic layer interacts with magnetic moments of the ferromagnetic layer near the interface between the ferromagnetic layer and non-magnetic spacer. Through this interaction, the electrons transfer a portion of their angular momentum to the ferromagnetic free layer.
Implementation Method 2
Both field-MRAM and STT-MRAM have a MTJ element based on a tunneling magneto-resistance (TMR) effect wherein a stack of layers has a configuration in which two ferromagnetic layers are separated by a thin non-magnetic dielectric layer.
Implementation Method 3
a free layer that interfaces with a tunnel barrier layer and a thin out-of-plane Hk enhancing layer thereby providing enhanced surface perpendicular anisotropy to reduce the perpendicular anisotropy field therein
Data Source
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AI summary
A magnetic element is disclosed wherein first and second interfaces of a free layer with a Hk enhancing layer and tunnel barrier, respectively, produce enhanced surface perpendicular anisotropy to lower switching current or increase thermal stability in a magnetic tunnel junction (MTJ). In a MTJ with a bottom spin valve configuration where the Hk enhancing layer is an oxide, the capping layer contacting the Hk enhancing layer is selected to have a free energy of oxide formation substantially greater than that of the oxide. The free layer may be a single layer or composite comprised of an Fe rich alloy such as Co2oFe6oB2o- With a thin free layer, the interfacial perpendicular anisotropy may dominate the shape anisotropy to generate a magnetization perpendicular to the planes of the layers. The magnetic element may be part of a spintronic device or serve as a propagation medium in a domain wall motion device.