MRAM Write Method Using Ferromagnetic Resonance

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Solution Overview

Problem

Conventional magnetic random access memory (MRAM) cell writing processes are slow due to the need for long direct current pulses to change magnetic orientation, which can be accelerated by using a high frequency alternating current signal to initiate ferromagnetic resonance, allowing for a lower voltage direct current pulse to flip the magnetic orientation.

Innovation Solution

Applying a high frequency alternating current signal near the ferromagnetic resonance frequency of the MRAM cell, combined with a direct current pulse, to speed up the precession step and reduce the time and voltage required to change the magnetic orientation of the free layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If a direct current pulse is used to change magnetic orientation, then the magnetic orientation can be changed, but the writing process is slow requiring long pulse durations

Engineering Contradiction:

Improvewriting speedVSAvoidpulse duration

Core Design Contradiction:

SpeedVSDuration of action of moving object

Solution Approach 1:

The patent applies a high frequency alternating current signal (e.g., microwave frequency) to excite ferromagnetic resonance in the free layer, causing rapid precession of the magnetization vector. This periodic action accelerates the magnetic switching process, reducing the required pulse duration from nanoseconds to picoseconds, thereby significantly improving writing speed.

Inventive Principle:

Principle #19Periodic action

2Use of energy by moving object

If a direct current pulse is used to change magnetic orientation, then the magnetic orientation can be changed, but high voltage is required which increases power consumption

Engineering Contradiction:

Improvepower consumptionVSAvoidvoltage requirement

Core Design Contradiction:

Use of energy by moving objectVSPower

Solution Approach 1:

The patent utilizes ferromagnetic resonance (a form of magnetic vibration) to reduce the energy barrier for magnetic switching. By applying a high frequency alternating current signal that matches the resonant frequency of the free layer, the system exploits the natural precession motion to assist the switching process, thereby reducing the voltage and current requirements of the direct current pulse needed for orientation change, which lowers power consumption.

Inventive Principle:

Principle #18Mechanical vibration

3Productivity

If a high frequency alternating current signal is applied to initiate ferromagnetic resonance, then the precession step is accelerated, but the device complexity increases

Engineering Contradiction:

Improvewriting efficiencyVSAvoidsignal generation complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent employs a single write line that serves dual functions: it carries both the high frequency alternating current signal for exciting ferromagnetic resonance and the direct current pulse for completing the magnetic switching. This multi-functionality eliminates the need for separate signal generation and control circuits, thereby improving writing efficiency while avoiding increased device 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 method significantly reduces the time and voltage needed to flip the magnetic orientation, potentially shortening the write pulse by 50% and lowering the current requirement, thereby reducing power consumption and improving writing efficiency in MRAM arrays.

Implementation Method 1

applying an alternating current signal to a magnetic random access memory cell having a first magnetic orientation... excites a spin of a free layer of the magnetic random access memory cell into ferromagnetic resonance

Methodology Applied

Scientific EffectFerromagnetic resonance: Resonance

Implementation Method 2

applying a direct current pulse to the magnetic random access memory cell to change a magnetic orientation of the free layer from the first magnetic orientation to a second magnetic orientation

Methodology Applied

Scientific EffectSpin transfer torque:

Data Source

PatentUS11244714B2Assisted write method for magnetic random access memory

Publication Date: 2022.02.08 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A method of writing to a magnetic random access memory cell includes applying an alternating current signal to the magnetic random access memory cell having a first magnetic orientation, and applying a direct current pulse to the magnetic random access memory cell to change the magnetic orientation of the magnetic random access memory cell from the first magnetic orientation to a second magnetic orientation. The first magnetic orientation and the second magnetic orientation are different.