Magnetic Memory Using SOT and STT for Writing Efficiency
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Solution Overview
Problem
Magnetic memory technologies face challenges with high leakage current and limited writing efficiency due to high inversion current density and time delays in magnetization reversal, particularly in spin transfer torque (STT) based systems, which affect the longevity and speed of magnetic random access memory (MRAM) devices.
Innovation Solution
A magnetic memory configuration that incorporates a series circuit of magnetoresistance effect elements and transistors, utilizing both spin-orbit torque (SOT) and STT effects, where SOT current is applied first to induce magnetization reversal, followed by STT current to enhance writing efficiency and reduce leakage current, with specific connections and voltage control to optimize data writing and reading operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spin transfer torque (STT) is used for magnetization reversal, then writing efficiency improves and current required decreases with element size, but inversion current density becomes high reducing element life
Solution Approach 1:
The patent applies spin-orbit torque (SOT) before spin transfer torque (STT) to preliminarily align magnetization in the free layer along the easy axis. This preliminary action reduces the subsequent STT current density required for magnetization reversal, thereby improving element life while maintaining writing efficiency. The SOT current flows through a separate heavy metal layer, preparing the magnetic state before the writing current is applied.
2Productivity
If spin transfer torque (STT) is used for magnetization reversal, then writing efficiency improves, but time difference until magnetization reversal occurs increases
Solution Approach 1:
The patent uses SOT as a preliminary action to rapidly align magnetization along the easy axis before applying STT. This two-stage approach reduces the total time for magnetization reversal by preparing the magnetic state in advance, thereby reducing the time difference until magnetization reversal occurs while maintaining the writing efficiency benefits of STT.
Solution Approach 2:
The patent employs a two-stage periodic action sequence: first applying SOT current to induce magnetization alignment, then applying STT current for magnetization reversal. This periodic application of different torque mechanisms optimizes both speed and efficiency, reducing the overall writing time compared to using STT alone.
3Productivity
If current flows through magnetoresistance effect element for SOT effect, then magnetization reversal is achieved, but leakage current increases
Solution Approach 1:
The patent segments the current path by introducing a separate heavy metal layer for SOT current flow, distinct from the magnetoresistance effect element. The SOT current flows laterally through the heavy metal layer to generate spin-orbit torque, while the STT current flows vertically through the magnetoresistance effect element for magnetization reversal. This segmentation eliminates the leakage current issue by preventing high-density SOT current from passing through the delicate magnetoresistance effect element.
Solution Approach 2:
The heavy metal layer acts as an intermediary that converts charge current into pure spin current via the spin Hall effect. This intermediary mechanism allows magnetization reversal to be achieved without requiring high current density to flow directly through the magnetoresistance effect element, thereby reducing leakage current and improving element 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
The proposed configuration increases the margin for data writing and reading while reducing leakage current, thereby improving the speed and longevity of magnetic memory devices by leveraging the distinct mechanisms of SOT and STT effects.
Implementation Method 1
it has been proposed that magnetization reversal using a pure spin current generated in accordance with a spin-orbit interaction could be applied
Implementation Method 2
A pure spin current that has undergone spin-orbit-interaction induces a spin-orbit torque (SOT) and induces magnetization reversal in accordance with the SOT
Implementation Method 3
a system performing writing (magnetization reversal) using a spin transfer torque (STT) generated by flow a current in a stacking direction of a magnetoresistance effect element
Implementation Method 4
a giant magnetoresistance (GMR) element formed by a multi-layered film with a ferromagnetic layer and a nonmagnetic layer
Implementation Method 5
a tunnel magnetoresistance (TMR) element using an insulating layer (a tunnel barrier layer or a barrier layer) as a nonmagnetic layer
Data Source
AI summary
Provided is a magnetic memory including: a first bit line, a second bit line, and a third bit line; a word line; a first magnetoresistance effect element; a first transistor; a second magnetoresistance effect element; and a second transistor, wherein free layers of the first and second magnetoresistance effect elements and the second bit line are connected, a fixed layer of the first magnetoresistance effect element and a source terminal of the first transistor are connected, a drain terminal of the first transistor and the first bit line are connected, a fixed layer of the second magnetoresistance effect element and a drain terminal of the second transistor are connected, a source terminal of the second transistor and the third bit line are connected, and the word line is connected to each of a gate terminal of the first transistor and a gate terminal of the second transistor.