Ferroelectric Capacitor Stress Modulation for MRAM Data Retention

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Solution Overview

Problem

The integration of magnetoresistive random access memory (MRAM) is hindered by the difficulty in disposing wiring that generates a magnetic field near the Magnetic Tunnel Junction (MTJ) element, and the deterioration of data retention characteristics due to reduced magnetic anisotropy, which increases the risk of magnetization reversal by thermal agitation.

Innovation Solution

A magnetic memory design incorporating a ferroelectric capacitor that applies stress to the MTJ element, using a spin transfer torque writing method to control the magnetization configuration, and varying the stress to adjust the magnetic anisotropy, thereby reducing the write current and improving data retention.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high magnetic anisotropy is used to maintain data retention, then thermal stability is improved, but magnetization switching current increases

Engineering Contradiction:

Improvedata retentionVSAvoidmagnetization switching current

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

A ferroelectric capacitor is introduced as an intermediary component between the MTJ element and the control circuit. The capacitor applies mechanical stress to the MTJ element through its electrostrictive effect, thereby mediating the interaction between electrical control signals and magnetic properties. This intermediary mechanism enables indirect control of magnetization switching, reducing the direct current burden while maintaining data retention through stress-assisted magnetic anisotropy modulation.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If spin-polarized current method is used to change magnetization, then integration is improved, but magnetization switching reliability deteriorates due to thermal agitation

Engineering Contradiction:

ImproveintegrationVSAvoidmagnetization stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The ferroelectric capacitor applies preliminary mechanical stress to the MTJ element before the spin-polarized current is applied for magnetization switching. This preliminary action modifies the magnetic anisotropy energy landscape, creating a more favorable condition for magnetization switching while enhancing thermal stability. By preparing the magnetic state in advance through stress application, the system achieves reliable switching with lower current requirements and improved resistance to thermal agitation.

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

The solution reduces the write current while maintaining high data retention characteristics, enabling efficient integration and stable data storage in MRAM.

Implementation Method 1

A magnetic memory design incorporating a ferroelectric capacitor that applies stress to the MTJ element

Methodology Applied

Scientific EffectFerroelectric effect:

Implementation Method 2

using a spin transfer torque writing method to control magnetization configuration

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 3

a magnetoresistive random access memory (MRAM) which makes use of a tunneling magnetoresistive effect

Methodology Applied

Scientific EffectTunneling magnetoresistive effect: Magnetoresistance

Data Source

PatentUS9196335B2Magnetic memory

Publication Date: 2015.11.24 KIOXIA CORP

AI summary

According to one embodiment, a magnetic memory includes magnetoresistive effect elements each including a first magnetic layer, a tunnel barrier layer, and a second magnetic layer which are successively stacked, and a ferroelectric capacitor provided above the magnetoresistive effect elements via an insulating layer, and including a lower electrode, a ferroelectric film, and an upper electrode which are successively stacked.