Dual Magnetic Tunnel Junction Stack With Shoulder Electrode Layout

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Solution Overview

Problem

Current non-volatile magnetic memory devices face challenges in forming a spin-orbit torque material as a top electrode for the upper magnetic tunnel junction, which damages the magnetic free layer and is difficult to achieve with existing technology.

Innovation Solution

A material layer stack design for non-volatile magnetic memory that eliminates the need for a spin-orbit torque material as a top electrode, featuring a shoulder structure and a single layer magnetic electrode common to both tunnel junctions, allowing independent writing and reading of two data bits with decoupled read and write paths.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a spin-orbit torque material is formed as a top electrode for the upper magnetic tunnel junction, then magnetization switching can be achieved, but the magnetic free layer is damaged or destroyed and the formation is difficult with existing technology

Engineering Contradiction:

Improvemagnetic free layer integrityVSAvoidformation of spin-orbit torque material as top electrode

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent extracts the spin-orbit torque material from the top electrode position and places it at the bottom of the stack instead. This allows the top electrode to be a simple conductive material that does not damage the magnetic free layer, while the spin-orbit torque material remains in contact with the magnetic layer to enable magnetization switching through spin transfer torque.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent inverts the conventional structure by placing the spin-orbit torque material at the bottom rather than the top of the magnetic tunnel junction stack. This inversion resolves the manufacturing difficulty and damage issue while preserving the essential spin-orbit torque functionality for magnetization switching.

Inventive Principle:

Principle #13The other way round (Inversion)

2Device complexity

If two magnetic tunnel junctions share a common pinned layer, then device complexity is reduced, but independent writing and reading of two bits becomes difficult

Engineering Contradiction:

Improvecommon pinned layer structureVSAvoidindependent writing and reading of two bits

Core Design Contradiction:

Device complexityVSEase of operation

Solution Approach 1:

The patent segments the magnetic tunnel junction into two independent stacks, each with its own pinned layer and free layer. The first stack has a first pinned layer and first free layer, while the second stack has a second pinned layer and second free layer. This segmentation allows independent control and operation of each bit storage location while maintaining a relatively compact structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces a non-magnetic spacer layer as an intermediary between the two magnetic tunnel junction stacks. This spacer layer physically separates the two structures, enabling independent electrical contact and control pathways for each bit, while still allowing the overall device to function as an integrated memory cell.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

Enables efficient and independent writing and reading of two data bits in parallel or sequence, reducing power dissipation and contact resistance, and supports Boolean logic operations, suitable for machine learning applications with improved latency and energy efficiency.

Implementation Method 1

A first magnetic tunnel junction and a second magnetic tunnel junction are provided between a first end face of the stack, e.g., the bottom face, and a second end face of the stack, e.g., the top face

Methodology Applied

Scientific EffectSpin-orbit torque:

Implementation Method 2

The first magnetic tunnel junction and the second magnetic tunnel junction are adapted for magnetic polarization switching assisted by spin-orbit torque and spin-torque transfer respectively

Methodology Applied

Scientific EffectSpin-transfer torque:

Implementation Method 3

each magnetic tunnel junction has an associated reconfigurable magnetoresistance which is adapted for storing a bit

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS11832525B2Dual magnetic tunnel junction stack

Publication Date: 2023.11.28 INTERUNIVERSITAIR MICRO ELECTRONICS CENT (IMEC VZW)

AI summary

The material layer stack includes first and second magnetic tunnel junctions and a first top electrode formed on a top face of the stack. A shoulder is formed on a lateral face of the stack and divides the stack into a lower portion and an upper portion. A tunnel barrier of the first magnetic tunnel junction is comprised by the lower stack portion and a tunnel barrier of the second magnetic tunnel junction by the upper stack portion. A second top electrode is formed on the shoulder. Each magnetic tunnel junction is adapted to store a bit as a reconfigurable magnetoresistance of its magnetic electrodes. Preferably, a bottom face of the stack is connected to a conductor supporting current induced magnetic polarization switching for the first magnetic tunnel junction by spin-orbit torque. Magnetic polarization switching for the second magnetic tunnel junction is preferably achieved by spin-transfer torque.