SOT-MRAM Structure With Decoupled Read/Write Paths
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Solution Overview
Problem
Spin-orbit torque magnetic random access memory (SOT-MRAM) technologies face challenges in memory density and write efficiency due to the need for additional transistors in each unit cell and uncontrollable writing difficulties in dense arrays, while spin-transfer torque MRAM (STT-MRAM) experiences reliability issues like read disturbance and oxide breakdown.
Innovation Solution
A magnetic memory structure incorporating a heavy-metal layer, magnetic tunnel junction (MTJ) layers, a conductive layer with separate conductive portions, and an insulation layer, where the conductive layer has higher electric conductivity than the heavy-metal layer, allowing for decoupled read and write paths and voltage-controlled magnetic anisotropy to improve reliability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If spin-orbit torque (SOT) is used with three-terminal MTJ to decouple read and write paths, then reliability is improved, but device complexity increases due to additional transistors required in each unit cell
Solution Approach 1:
The conductive layer is merged with the heavy-metal layer to form a unified structure that serves both as a current path for spin-orbit torque switching and as an electrode for voltage-controlled magnetic anisotropy, eliminating the need for separate transistor control structures while maintaining decoupled read/write paths
Solution Approach 2:
The conductive layer performs multiple functions: it acts as a current injection path for SOT switching, provides voltage control for magnetic anisotropy modulation, and serves as an electrode for read operations, thereby reducing the need for additional dedicated components
2Use of energy by moving object
If voltage-controlled magnetic anisotropy is used to modulate interfacial magnetic anisotropy, then power dissipation is reduced, but writing control becomes uncontrollable in dense arrays
Solution Approach 1:
The conductive layer is patterned with separated first and second conductive portions that are positioned to contact specific ends of the heavy-metal layer, enabling localized and selective voltage application to specific MTJ cells in dense arrays, thereby achieving precise writing control
Solution Approach 2:
The conductive layer is segmented into distinct first and second conductive portions that are spatially separated and independently controllable, allowing for selective addressing of individual memory cells or groups in dense arrays while maintaining low power operation
3Speed
If spin-transfer torque is used to change magnetization by applying spin-polarized current through MTJ, then writing speed is improved, but reliability deteriorates due to read disturbance and oxide breakdown from identical read/write access paths
Solution Approach 1:
The conductive layer is divided into separate first and second conductive portions that enable independent control of write and read operations, physically separating the current paths for writing and reading, thereby preventing read disturbance and oxide breakdown while maintaining fast write speeds through spin-orbit torque
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 proposed structure enhances memory density and reduces power dissipation by decoupling read and write paths, alleviating reliability issues and improving write efficiency, while allowing for lower driving voltages and increased endurance of the tunneling barrier layer.
Implementation Method 1
an in-plane charge current is injected into the heavy-metal (HM) layer of the three-terminal MTJ-based memory cells, a transverse pure-spin current is generated due to the spin-Hall effect (SHE)
Implementation Method 2
a transverse pure-spin current is generated due to the spin-Hall effect (SHE) and/or interface Rashba effect
Implementation Method 3
The conductive layer has an electric conductivity higher than that of the heavy-metal layer
Implementation Method 4
the magnetization of the free-layer can be changed by applying spin-polarized current directly through the MTJ cell without applying an external magnetic field
Data Source
AI summary
A magnetic memory structure includes a heavy-metal layer, a plurality of magnetic tunneling junction (MTJ) layer, a conductive layer and an insulation layer. In an example, the pinned-layer of the MTJ layers are arranged in a string form and disposed over the barrier-layer. In an example also disclosed, the pinned-layer, the free-layer of the MTJ layers are arranged in a string form. Whereas the pinned-layers are disposed over the barrier-layer and the free-layers are disposed over the heavy-metal layer. The conductive layer is formed under the heavy-metal layer and includes a first conductive portion and a second conductive portion separated from each other and connected with two end of the heavy-metal layer respectively. The insulation layer fills up an interval between the first conductive portion and the second conductive portion. The conductive layer has an electric conductivity higher than that of the heavy-metal layer.