Spin-Orbit Torque MRAM Current Density Reduction
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Solution Overview
Problem
Conventional magnetic random access memory technologies face scalability issues and Joule heating problems due to high electric current densities required for magnetization reversal, which hinder their use in nanoscale devices and impact durability and reliability.
Innovation Solution
Applying two alternating electric currents non-collinearly in the heavy-metal layer of a ferromagnetic/heavy-metal bilayer, with correlated phases to maintain constant total current density magnitude and rotate direction, reducing the minimal reversal current density to as low as 10^8 A/m^2, allowing for faster magnetization reversal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional magnetic field induced magnetization reversal is used, then device durability is improved, but scalability and field localization are worsened for nanoscale devices
Solution Approach 1:
The patent replaces conventional magnetic field induced magnetization reversal with spin-orbit torque (SOT) mechanism. Instead of using external magnetic fields to reverse magnetization, the invention utilizes spin current generated by heavy metal layers through spin-Hall effect or Rashba effect to exert torque on the magnetic layer, achieving magnetization reversal without magnetic fields. This substitution enables better scalability and localization for nanoscale devices while maintaining durability.
2Adaptability or versatility
If spin-transfer-torque magnetic random-access memory is used, then alternative technology in nano-spintronics is achieved, but Joule heating, device durability, and reliability are worsened
Solution Approach 1:
The patent segments the current path from the memory cell by introducing a separate heavy metal layer adjacent to the magnetic layer. The write current flows through the heavy metal layer to generate spin current, while the read current flows through the magnetic tunnel junction. This segmentation prevents write current from passing through the memory cell, eliminating Joule heating and improving reliability.
Solution Approach 2:
The heavy metal layer acts as an intermediary that converts charge current into spin current through spin-Hall effect or Rashba effect. This intermediary mechanism allows magnetization reversal without direct current flow through the magnetic tunnel junction, avoiding Joule heating while maintaining nano-spintronics functionality.
3Object-generated harmful factors
If SOT-MRAM is used, then Joule heating is avoided, but electric current density required for magnetization reversal is worsened to 10^11-10^12 A/m^2
Solution Approach 1:
The patent optimizes material parameters including selecting heavy metal layers with high spin-Hall angle (such as Pt, Pd, Ir, Rh) and tuning the thickness of the heavy metal layer to enhance spin current generation efficiency. By changing these material parameters, the required current density is reduced from 10^11-10^12 A/m^2 to more practical levels while maintaining the advantage of avoiding Joule heating.
4Speed
If current density is increased to 10^12 A/m^2 for reasonable switching speed, then switching speed is improved to GHz range, but device durability and reliability are worsened
Solution Approach 1:
The patent employs dynamic control of spin current parameters including pulse width, amplitude, and timing to achieve efficient magnetization reversal. By optimizing the temporal characteristics of the write current pulse and utilizing precessional dynamics of magnetization, the invention achieves GHz switching speeds with lower current densities, improving both speed and reliability.
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 approach significantly lowers the current density required for magnetization reversal to 10^9 A/m^2, improving switching speed and device durability while avoiding Joule heating, enabling efficient and reliable operation of spin-orbit torque magnetic random access memory devices.
Implementation Method 1
an electric current in the heavy metal layer generates a pure spin current through the spin-Hall effect that flows perpendicularly into a magnetic layer
Implementation Method 2
The spin current produces spin-orbit torques (SOT) through spin angular momentum transfer and/or the Rashba effect
Implementation Method 3
The spin current produces spin-orbit torques (SOT) through spin angular momentum transfer and/or the Rashba effect
Data Source
AI summary
Methods and devices for a spintronic device of spin-orbit torque magnetic random access memory (SOT-MRAM) are provided. A unit cell of a device can comprise a ferromagnetic (or ferrimagnetic or antiferromagnetic) layer on the heavy metal layer, and a current source configured to transmit either non-collinear current pulses in the heavy-metal layer or two perpendicular currents in the heavy metal layer. The current pulses exhibit a phase difference, and the magnitude of a sum of the respective current pulses is constant (in its simplest form) and the flow direction of the pulses is time-dependent.