Magnetoresistive Memory Cell Switching via Ferroelectric Exchange Coupling

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Solution Overview

Problem

Current magnetoresistive memory devices face challenges in efficiently controlling the magnetization direction of free layers using spin-transfer torque, as they rely on unpolarized electrical currents, which limits data storage capabilities.

Innovation Solution

Incorporating a ferroelectric material layer between the middle electrode and the second terminal electrode, which induces strain in a perpendicular magnetic anisotropy layer, modulating the interlayer exchange coupling between the free layer and the reference layer, allowing for reversible magnetization direction changes through ferroelectric-controlled exchange coupling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If spin-transfer torque is used to control magnetization direction in magnetoresistive memory devices, then data storage capability is improved, but control efficiency is limited due to reliance on unpolarized electrical currents

Engineering Contradiction:

Improvemagnetization control reliabilityVSAvoidswitching efficiency

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent changes the physical state of the system by introducing a ferroelectric layer that can be switched between different polarization states. This parameter change (ferroelectric polarization) directly controls the magnetization direction in the free layer, enabling efficient and reliable magnetization control without relying on unpolarized electrical currents.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The ferroelectric layer acts as an intermediary between the electrical control signal and the magnetic storage layer. By applying voltage to the ferroelectric layer, its polarization state changes, which in turn controls the magnetization direction of the free layer through exchange coupling, providing a more efficient control mechanism than direct spin-transfer torque.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If conventional magnetoresistive memory structures are used, then device simplicity is maintained, but data storage capability and operational efficiency are limited

Engineering Contradiction:

Improvedata storage capabilityVSAvoidmemory cell structure

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent employs a composite structure combining ferromagnetic layers (reference layer, free layer), nonmagnetic spacer layer, and ferroelectric material layer. This composite structure enables the memory device to leverage both magnetic and ferroelectric properties, significantly enhancing data storage capability and operational efficiency compared to conventional structures.

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The magnetoresistive memory cell structure is designed to perform multiple functions: the reference layer provides a stable magnetic reference, the free layer stores data through variable magnetization, the nonmagnetic spacer layer enables exchange coupling, and the ferroelectric layer provides efficient write control. This multi-functional design enhances overall device performance without excessive complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 reliable and efficient switching of magnetization states in magnetoresistive memory cells, enhancing data storage capabilities by leveraging ferroelectric-controlled strain to alter the interlayer exchange coupling, thus improving the resistance states and operational efficiency.

Implementation Method 1

Incorporating a ferroelectric material layer between the middle electrode and the second terminal electrode, which induces strain in a perpendicular magnetic anisotropy layer

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

Spin-transfer torque (STT) refers to an effect in which the orientation of a magnetic layer in a magnetic junction structure or spin valve is modified by a spin-polarized current

Methodology Applied

Scientific EffectSpin-transfer torque:

Data Source

PatentUS12106790B2Magnetoresistive memory device and method of operating same using ferroelectric-controlled exchange coupling

Publication Date: 2024.10.01 SANDISK TECHNOLOGIES LLC

AI summary

A magnetoresistive memory cell includes a magnetoresistive layer stack containing a reference layer, a nonmagnetic spacer layer, and a free layer. A ferroelectric material layer having two stable ferroelectric states is coupled to a strain-modulated ferromagnetic layer to alter a sign of magnetic exchange coupling between the strain-modulated ferromagnetic layer and the free layer. The strain-modulated ferromagnetic layer may be the reference layer or a perpendicular magnetic anisotropy layer that is located proximate to the ferroelectric material layer. The magnetoresistive memory cell may be configured as a three-terminal device or as a two-terminal device, and may be configured as a tunneling magnetoresistance (TMR) device or as a giant magnetoresistance (GMR) device.