Low Power MTJ Analog Memory via Voltage-Controlled Magnetic Anisotropy

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Solution Overview

Problem

Current analog memory technologies face challenges in efficiently varying resistance levels for multi-state storage, particularly in magnetic tunnel junction devices, where domain wall movement and voltage-controlled magnetic anisotropy are not fully utilized to achieve reliable and power-efficient resistance changes.

Innovation Solution

A magnetic tunnel junction stack with a high resistance tunnel barrier and a voltage-controlled magnetic anisotropy write layer, where the write layer is adjacent to the tunnel barrier and includes a magnetic material in direct contact, allowing for voltage-induced changes in spin orientation and resistance levels by altering the magnetic domain configuration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If domain wall movement is used to induce resistance change in magnetic tunnel junction devices, then analog memory can be realized, but power consumption increases and reliability decreases

Engineering Contradiction:

Improveresistance change reliabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent replaces the mechanical domain wall movement mechanism with a voltage-controlled magnetic anisotropy mechanism. Instead of moving domain walls physically through the magnetic layer (which consumes high current and generates heat), the invention uses voltage applied to the tunnel barrier to control the magnetic anisotropy energy landscape, thereby controlling magnetization switching without mechanical movement. This substitution of the underlying physical mechanism resolves the contradiction by eliminating the need for high-current domain wall propulsion.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent changes the control parameter from current-driven domain wall motion to voltage-controlled magnetic anisotropy. By applying voltage to the tunnel barrier, the magnetic anisotropy energy barrier is modulated, enabling magnetization switching at much lower power levels. This parameter change from current to voltage control, and from mechanical movement to energy landscape modulation, directly addresses the power consumption and reliability issues associated with domain wall movement.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If voltage-controlled magnetic anisotropy is implemented in conventional MTJ structures, then resistance levels can be varied, but multi-state storage reliability is insufficient

Engineering Contradiction:

Improvemulti-state storage reliabilityVSAvoidresistance level variation capability

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent applies local quality by creating distinct magnetic regions with different anisotropy characteristics within the magnetic tunnel junction. By engineering specific layers (such as the CoFeB free layer and CoFe pinned layer) with controlled thicknesses and compositions, and by applying voltage locally to the tunnel barrier, the invention creates localized magnetic states that can be independently controlled. This local differentiation enables reliable multi-state storage while maintaining the ability to vary resistance levels through voltage control.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs composite material structures combining multiple ferromagnetic layers (CoFeB, CoFe, CoFeNi) with specific magnetic properties. The free layer uses CoFeB with perpendicular magnetic anisotropy, while the pinned layer uses CoFe with in-plane anisotropy. This composite structure enables independent control of write and read operations through voltage-controlled magnetic anisotropy, achieving both reliable multi-state storage and versatile resistance variation capability without contradiction.

Inventive Principle:

Principle #40Composite materials

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 configuration enables reliable and efficient resistance variation, allowing for multiple resistance states with low power consumption, enabling effective multi-state data storage without relying on spin transfer torque or domain wall propagation.

Implementation Method 1

a first voltage controlled magnetic anisotropy write layer. The first voltage controlled magnetic anisotropy write layer may be adjacent the high resistance tunnel barrier, and the voltage controlled magnetic anisotropy write line may include a magnetic material in direct contact with a high resistance tunnel barrier

Methodology Applied

Scientific EffectVoltage-controlled magnetic anisotropy:

Implementation Method 2

The domain wall movement inside magnetic medium can induce resistance change. By using the resistance change, analog memory can be realized.

Methodology Applied

Scientific EffectDomain wall movement:

Implementation Method 3

magnetic tunnel junction stack, a first high resistance tunnel barrier

Methodology Applied

Scientific EffectTunneling magnetoresistance: Magnetoresistance

Data Source

PatentUS11664059B2Low power MTJ-based analog memory device

Publication Date: 2023.05.30 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A memory system may include a magnetic tunnel junction stack, a first high resistance tunnel barrier, and a first voltage controlled magnetic anisotropy write layer. The first voltage controlled magnetic anisotropy write layer may be adjacent the high resistance tunnel barrier, and the voltage controlled magnetic anisotropy write line may include a magnetic material in direct contact with a high resistance tunnel barrier.