Multiferroic MRAM with Defect-Engineered Regions for Multi-State Storage

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Solution Overview

Problem

Current spintronic devices, such as magnetoresistive random access memory (MRAM) cells, face limitations in achieving multiple stable magnetoresistive states due to the binary nature of their magnetic switching, which restricts their data storage capabilities to only two states, limiting their programmability and storage capacity.

Innovation Solution

Incorporating magnetoelectric multiferroic regions with varying structural defect densities between electrodes in magnetic tunnel junctions, allowing for deterministic switching of magnetization and ferroelectric polarization through applied electrical fields without external magnetic fields, enabling multiple stable resistance states.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If binary magnetic switching is used in magnetoresistive random access memory (MRAM) cells, then the device structure is simple and easy to manufacture, but the data storage capability is limited to only two states

Engineering Contradiction:

Improvedata storage capabilityVSAvoiddevice structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent segments the magnetoelectric multiferroic layer into multiple distinct regions, each with different structural defect densities. This segmentation creates multiple stable magnetization states (three or more) within the device, enabling enhanced data storage capability beyond the traditional binary two-state limitation while maintaining a relatively simple overall device structure.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by creating regions with different structural defect densities within the magnetoelectric multiferroic layer. Each region has tailored local properties (different defect densities) that result in different magnetization switching characteristics, allowing the device to achieve multiple stable states and improved data storage capability.

Inventive Principle:

Principle #3Local quality

2Adaptability or versatility

If multiple magnetoelectric multiferroic portions with different structural defect densities are incorporated, then multiple stable magnetoresistive states are achieved, but the manufacturing process becomes more complex

Engineering Contradiction:

ImproveprogrammabilityVSAvoidmanufacturing process

Core Design Contradiction:

Adaptability or versatilityVSEase of manufacture

Solution Approach 1:

The patent applies preliminary action by creating the magnetoelectric multiferroic layer first as a continuous structure, and then subsequently introducing structural defects into specific regions. This sequential approach allows for controlled creation of multiple stable states through defect engineering while maintaining ease of manufacture, as the defect introduction can be done through targeted ion bombardment or other localized processing techniques after the base layer is formed.

Inventive Principle:

Principle #10Preliminary action

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 enables the creation of devices with three or more magnetoresistive states, enhancing data storage capabilities by allowing ternary, quaternary, or higher bit values, and facilitating efficient programming and switching without the need for external magnetic fields.

Implementation Method 1

Each of the plurality of magnetoelectric multiferroic portions is magnetically coupled to the ferromagnetic free layer of a respective one of the plurality of magnetic junctions

Methodology Applied

Scientific EffectMagnetoelectric coupling: Magnetoelastic Effects

Implementation Method 2

Spin-transfer torque (STT) refers to an effect in which the orientation of a magnetic layer in a magnetic tunnel junction or spin valve is modified by a spin-polarized current. When the spin-polarized current flows through a free layer of a magnetic tunnel junction or a spin valve, the electrons in the spin-polarized current can transfer at least some of their angular momentum to the free layer, thereby producing a torque on the magnetization of the free layer.

Methodology Applied

Scientific EffectSpin-transfer torque: Angular Momentum

Implementation Method 3

A resistance differential of a magnetic tunnel junction between different magnetization states of the free layer can be employed to store data within the magnetoresistive random access memory (MRAM) cell depending if the magnetization of the free layer is parallel or antiparallel to the magnetization of the polarizer layer

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Data Source

PatentUS11222920B2Magnetic device including multiferroic regions and methods of forming the same

Publication Date: 2022.01.11 SANDISK TECHNOLOGIES LLC

AI summary

A magnetic device includes a first electrode, a second electrode, a plurality of magnetic junctions each containing a ferromagnetic reference layer and a ferromagnetic free layer located between the first electrode and the second electrode, and a plurality of magnetoelectric multiferroic portions having different structural defect densities located between the first electrode and the second electrode. Each of the plurality of magnetoelectric multiferroic portions is magnetically coupled to the ferromagnetic free layer of a respective one of the plurality of magnetic junctions.