Magnetic Memory Cell Design for Reliable Spin-Orbit Torque Switching
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Solution Overview
Problem
Magnetic memories face challenges with spin transfer torque magnetization switching, which can lead to nonmagnetic insulating layer breakdown during writing and reading, and the complexity of three-terminal configurations in spin-orbit torque MRAMs increases cell size and electromigration risks.
Innovation Solution
A magnetic memory design with a nonmagnetic layer and a magnetoresistive element featuring a stack structure with a nonmagnetic intermediate layer, where a single select transistor enables both write and read operations, reducing the risk of breakdown and electromigration by controlling current flow and using diodes to minimize leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If spin transfer torque (STT) is used for magnetization switching, then writing speed is improved, but the nonmagnetic insulating layer may break down due to high current density
Solution Approach 1:
The patent introduces a nonmagnetic metal layer as an intermediary between the storage layer and the nonmagnetic insulating layer. This intermediary layer receives the spin current from the storage layer and transfers it to the reference layer, thereby reducing the current density through the nonmagnetic insulating layer and preventing breakdown while maintaining STT writing speed
Solution Approach 2:
The patent extracts the function of magnetization switching from the nonmagnetic insulating layer by introducing a separate nonmagnetic metal layer. The nonmagnetic insulating layer is removed from the current path, and its magnetic barrier function is maintained through the new configuration with the nonmagnetic metal layer positioned adjacent to the reference layer
2Ease of operation
If a three-terminal configuration is used for spin-orbit torque MRAM, then magnetization switching is achieved, but cell area increases due to additional transistors
Solution Approach 1:
The patent merges the read and write current paths into a single terminal configuration. The nonmagnetic metal layer serves both as a spin current source for writing and as part of the read current path, eliminating the need for separate write terminals and reducing the number of required transistors from three to one
Solution Approach 2:
The nonmagnetic metal layer performs multiple functions: it generates spin current for magnetization switching during writing, serves as part of the read current path, and provides electrical connection. This multi-functionality reduces the overall cell complexity and area compared to dedicated separate paths
3Productivity
If MTJ elements are integrated on one nonmagnetic layer, then device integration is achieved, but electromigration risk increases due to longer current path
Solution Approach 1:
The patent segments the nonmagnetic layer into discrete nonmagnetic metal layers, each associated with a specific MTJ element. This segmentation shortens the current path length in each nonmagnetic metal layer, reducing electromigration risk while maintaining high integration density through the stacked configuration
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 design allows for efficient and reliable write and read operations with a simpler cell configuration, reducing the risk of nonmagnetic layer breakdown and electromigration, while minimizing cell size and improving readout accuracy.
Implementation Method 1
A spin-orbit interaction is a phenomenon in which current is applied to a nonmagnetic layer so that electrons having spin angular momenta (hereinafter also referred to simply as the spin) of the opposite orientations from each other are scattered in the opposite directions, and a spin current Is is generated
Implementation Method 2
Another one of the known techniques for writing is a technique using a spin Hall effect or a spin-orbit interaction
Implementation Method 3
An MRAM includes a magnetic tunnel junction (MTJ) element as a storage element
Data Source
AI summary
A magnetic memory according to an embodiment includes: a conductive nonmagnetic layer including a first terminal, a second terminal, and a region between the first terminal and the second terminal; a magnetoresistive element including: a first magnetic layer; a second magnetic layer disposed between the region and the first magnetic layer; and a nonmagnetic intermediate layer disposed between the first magnetic layer and the second magnetic layer; a transistor including a third terminal, a fourth terminal, and a control terminal, the third terminal being electrically connected to the first terminal; a first wiring electrically connected to the first magnetic layer and the fourth terminal; a second wiring electrically connected to the control terminal; and a third wiring electrically connected to the second terminal.