Chiral SOT Bottom Electrode for Axial Spin-Polarized MRAM Switching

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Solution Overview

Problem

Conventional MRAMs using spin-transfer torque (STT) face inefficiencies due to spin-current polarization being perpendicular to its transmission direction, limiting the effectiveness of SOT assistance for switching perpendicularly magnetized magnetic free layers.

Innovation Solution

A chiral SOT via structure is introduced as a bottom electrode, featuring a bi- or multi-layered composition with materials like β-Ta, β-W, and Cu, which facilitates charge-to-spin current conversion with axial spin-polarization, enhancing SOT efficiency by forming a spiral-pattern for both charge and spin-current conduction.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional SOT metal structure is used, then the structure is simple, but the spin-current polarization is perpendicular to transmission direction which limits SOT assistance efficiency

Engineering Contradiction:

ImproveSOT assistance efficiencyVSAvoidelectrode structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent employs a composite chiral SOT metal electrode structure combining multiple materials (e.g., CoFeB, MgO, Pt) with specific magnetic and electrical properties. This composite structure enables simultaneous achievement of perpendicular spin polarization and efficient charge-to-spin current conversion, resolving the contradiction between SOT assistance efficiency and structural simplicity.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The patent introduces a chiral (spiral/curved) geometric structure to the SOT metal electrode, where the spiral growth pattern creates tilted interfaces that generate perpendicular spin polarization. This curvature-based design transforms the conventional flat interface into a three-dimensional chiral structure, enabling efficient spin-current generation with axial polarization without excessive complexity.

Inventive Principle:

Principle #14Spheroidality (Curvature)

2Productivity

If spin-current is polarized perpendicular to transmission direction, then the structure is conventional, but the switching efficiency of magnetic free layer is limited

Engineering Contradiction:

Improveswitching speedVSAvoidcharge current consumption

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent changes the fundamental parameter of spin polarization direction from perpendicular-to-transmission (conventional) to axial/perpendicular-to-surface (chiral). This parameter change in spin polarization orientation enables more efficient spin transfer to the magnetic free layer, improving switching speed and reducing the charge current required for magnetization switching.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the conventional spin transfer mechanism with a chiral spin-orbit torque mechanism. By utilizing the spin Hall effect in a chiral structure, the system generates spin currents with axial polarization that more effectively couple to the perpendicularly magnetized free layer, substituting the traditional switching mechanism with a more efficient one.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 chiral SOT via structure achieves high-efficiency conversion of charge current to axially polarized spin-current, improving the switching of perpendicularly magnetized nanomagnets, thus overcoming the inefficiencies of prior art by aligning spin-polarization with current propagation.

Implementation Method 1

chiral spin-orbit-torque (SOT) metal bottom electrode

Methodology Applied

Scientific EffectSpin-orbit torque:

Implementation Method 2

The chiral SOT metal bottom electrode enables the charge current, spin current and spin polarization directions to be in the same direction

Methodology Applied

Scientific EffectSpin Hall Effect:

Data Source

PatentUS20240107896A1MRAM structure with chiral spin-orbit-torque metal electrode

Publication Date: 2024.03.28 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A magnetoresistive random access memory (MRAM) structure is provided that includes a chiral spin-orbit-torque (SOT) metal bottom electrode under the bottom magnetic free layer where the chiral SOT metal bottom electrode is surrounded by a via dielectric. The chiral SOT metal bottom electrode enables the charge current, spin current and spin polarization directions to be in the same direction which is perpendicular to the surface of the chiral SOT via structure.