Three-Terminal MRAM AC Write-Assist for Low Read Disturb

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Solution Overview

Problem

Existing MRAM devices require high switching currents and are prone to precessional modes that make switching deterministic only for one direction, limiting their commercial applicability and efficiency.

Innovation Solution

A magnetic tunnel junction stack with a free layer that uses a programming current pulse comprising an alternating perturbation current synchronized with the precession frequency of the free magnetic layer, reducing switching currents and enhancing switching efficiency for both magnetization directions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional spin transfer torque is used to switch magnetization direction, then switching can be achieved, but high switching currents are required and switching is deterministic only for one direction

Engineering Contradiction:

Improveswitching determinismVSAvoidswitching current

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent applies periodic AC current pulses at the precession frequency of the free layer to assist magnetization switching. The AC current creates time-varying spin transfer torque that resonates with the natural precession of the magnetization vector, enabling deterministic switching in both directions with reduced current magnitude compared to conventional DC spin transfer torque methods

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent exploits the mechanical vibration analogy by driving the magnetization precession at its resonant frequency using AC current. This resonant excitation amplifies the switching effect and enables controlled, deterministic magnetization reversal in both directions while reducing the required current magnitude

Inventive Principle:

Principle #18Mechanical vibration

2Reliability

If high switching currents are used to ensure deterministic switching, then switching reliability improves, but read disturb increases due to precessional modes

Engineering Contradiction:

Improveswitching determinismVSAvoidread disturb

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

By using periodic AC current at the precession frequency, the patent achieves deterministic switching without requiring excessively high current magnitudes. The resonant assistance from AC current reduces the need for high DC current components that would otherwise be required to overcome damping and ensure deterministic switching, thereby reducing read disturb

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent utilizes the natural precession frequency of the free layer as a feedback mechanism. By synchronizing the AC current frequency with the precession frequency, the system creates constructive interference that enhances switching efficiency and determinism while operating at lower current levels, thus minimizing read disturb effects

Inventive Principle:

Principle #23Feedback

3Speed

If conventional DC programming current is used, then switching can be achieved, but switching times are long and high-speed switching is not achieved

Engineering Contradiction:

Improveswitching speedVSAvoidswitching time

Core Design Contradiction:

SpeedVSDuration of action of moving object

Solution Approach 1:

The patent employs AC current pulses at the precession frequency to drive rapid magnetization switching. The resonant excitation causes the magnetization vector to precess coherently and switch directions much faster than conventional DC methods, achieving sub-nanosecond switching times while maintaining determinism in both switching directions

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent changes the temporal parameters of the programming current from static DC to dynamic AC at resonant frequency. This parameter change exploits the resonant response of the magnetization system to achieve ultrafast switching speeds, reducing switching time from conventional nanosecond or microsecond scales to sub-nanosecond regimes

Inventive Principle:

Principle #35Parameter changes

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 significantly reduces switching currents and times while maintaining high-speed switching for both switching directions, improving the overall performance and efficiency of MRAM devices.

Implementation Method 1

The spin-polarized electrons exert a spin transfer torque on the magnetization vector of the free magnetic layer, thereby causing switching of the magnetization direction of the free magnetic layer

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

The first frequency is synchronized with the predetermined precession frequency of the free magnetic layer, such that the in-plane spin torque component provides a net benefit of assisting in the precessional motion of the magnetization vector

Methodology Applied

Scientific EffectPrecession: Precession

Data Source

PatentUS10199083B1Three-terminal MRAM with ac write-assist for low read disturb

Publication Date: 2019.02.05 INTEGRATED SILICON SOLUTION CAYMAN INC

AI summary

Methods and structures useful for magnetoresistive random-access memory (MRAM) are disclosed. The MRAM device has a magnetic tunnel junction stack having a significantly improved performance of the free layer in the magnetic tunnel junction structure. The MRAM device also utilizes a three-terminal structure, thereby allowing efficient writing of the bit without a concomitant increase in read disturb.