SOT MRAM Array Layout With Shared Bit Lines for Low-Energy Writes
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Solution Overview
Problem
Existing spin-transfer torque (STT) magnetoresistive random access memory (MRAM) devices face challenges with high write error rates, high write energy consumption, and slower writing speeds due to the direct flow of electrical current through the magnetic tunnel junction during programming.
Innovation Solution
A spin-orbit torque (SOT) magnetoresistive memory device with shared bit line connections and a specific array configuration, utilizing a nonmagnetic heavy metal SOT layer to generate a spin current perpendicular to the electrical current, reducing current flow through the magnetic tunnel junction and enhancing endurance, write speed, and lowering energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If write current flows directly through the magnetic tunnel junction in STT-MRAM, then programming operation can be performed, but write error rate increases and write energy consumption increases
Solution Approach 1:
The patent introduces a spin-orbit torque layer as an intermediary between the write current source and the magnetic tunnel junction. This mediator layer generates spin current through spin-orbit coupling, which then acts on the magnetization of the free layer without requiring direct current flow through the MTJ, thus reducing write error rates while maintaining programming functionality
Solution Approach 2:
The patent replaces the direct electrical current flow mechanism with a spin current mechanism generated through spin-orbit torque effects. Instead of using conventional STT where current flows directly through the MTJ, the system uses spin current generated in an adjacent conductive layer to exert torque on the magnetization, achieving more reliable writing with lower error rates
2Ease of operation
If write current flows directly through the magnetic tunnel junction in STT-MRAM, then programming operation can be performed, but write energy consumption increases
Solution Approach 1:
The spin-orbit torque layer serves as a mediator that converts electrical current into spin current more efficiently. This intermediary layer enables the write operation to be performed with lower energy consumption by avoiding direct current flow through the high-resistance MTJ tunnel barrier, instead using spin current generated in the adjacent conductive layer to switch magnetization
Solution Approach 2:
The patent changes the fundamental parameter of how current interacts with the magnetic layer - from direct charge current flow through the MTJ to spin current generation via spin-orbit coupling in an adjacent layer. This parameter change enables more energy-efficient writing by utilizing the spin Hall effect or Rashba effect to generate the necessary torque without requiring high current densities through the tunnel junction
3Ease of operation
If write current flows directly through the magnetic tunnel junction in STT-MRAM, then programming operation can be performed, but writing speed decreases
Solution Approach 1:
The patent substitutes the direct current flow mechanism with spin-orbit torque-based magnetization switching. This replacement enables faster writing speeds because the spin current generated in the adjacent conductive layer can more rapidly exert torque on the magnetization, achieving nanosecond-scale switching without the limitations of direct MTJ current flow
Solution Approach 2:
The spin-orbit torque mechanism enables rapid, periodic switching of magnetization states through controlled injection of spin current. The periodic action of spin current generation and magnetization switching allows for high-speed writing operations by repeatedly flipping the magnetization state at nanosecond intervals without the delays associated with direct current flow through the MTJ
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 SOT memory cells exhibit lower write error rates, require less write energy, and achieve nanosecond-scale writing speeds, offering improved performance over STT memory cells.
Implementation Method 1
use switching of magnetization direction of a free magnetic layer by injection of an in-plane current in an adjacent conductive layer, which is referred to as a spin-orbit torque (SOT) layer
Data Source
AI summary
A spin-orbit-torque (SOT) magnetoresistive memory device includes an array of repetition units. Each of the repetition units contains a first magnetic tunnel junction (MTJ) located over and electrically contacting a first lower electrode, a second MTJ located over and electrically contacting a second lower electrode, a spin current metal line located over a top surface of the first MTJ and a top surface of the second MTJ, a first selector element electrically connected to a first end of the spin current metal line, and a second selector element electrically connected to a second end of the spin current metal line.