Magnetic Memory Storage Layer Segmentation for Low Write Current

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Solution Overview

Problem

Spin transfer torque MRAMs face challenges in reducing write current while maintaining thermal stability and minimizing error rates due to the probabilistic nature of magnetization reversal, which affects memory holding time and error occurrence.

Innovation Solution

A magnetic memory design with a multilayered storage structure, including a high Ku layer and a low Ku layer, where the exchange coupling constant between these layers is reduced to 5 erg/cm2 or less, allowing for a shorter write current and improved thermal stability, thereby reducing write and read errors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of moving object

If the write current value is decreased, then the area of one memory cell can be reduced, but the memory holding time shortens

Engineering Contradiction:

Improvearea of memory cellVSAvoidmemory holding time

Core Design Contradiction:

Area of moving objectVSDuration of action of stationary object

Solution Approach 1:

The storage layer is divided into multiple magnetic layers with different anisotropy energies (high Ku layer and low Ku layer). This segmentation allows the system to achieve both low write current and long memory holding time by distributing the functional requirements across different layers - the low Ku layer facilitates easy magnetization reversal for writing, while the high Ku layer provides thermal stability for data retention.

Inventive Principle:

Principle #1Segmentation

2Area of moving object

If the write current value is decreased, then the chip area can be reduced, but thermal stability of the storage layer deteriorates

Engineering Contradiction:

Improvechip areaVSAvoidthermal stability of storage layer

Core Design Contradiction:

Area of moving objectVSStability of the object's composition

Solution Approach 1:

The storage layer is segmented into multiple magnetic layers with different anisotropy energies. The low Ku layer enables low write current operation, while the high Ku layer maintains thermal stability, resolving the contradiction between reducing chip area and maintaining thermal stability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The storage layer uses a composite magnetic structure combining materials or configurations with different anisotropy properties. This composite approach allows simultaneous achievement of low write current (through the low Ku layer) and high thermal stability (through the high Ku layer), enabling compact chip design without sacrificing data retention.

Inventive Principle:

Principle #40Composite materials

3Area of moving object

If the write current is reduced, then the memory cell area decreases, but error rates increase

Engineering Contradiction:

Improvememory cell areaVSAvoiderror rate

Core Design Contradiction:

Area of moving objectVSReliability

Solution Approach 1:

Dividing the storage layer into multiple magnetic layers with different anisotropy energies reduces the write current requirement while maintaining reliable magnetization reversal. The segmented structure ensures that each layer can be reliably switched at lower current densities, thereby reducing error rates even as cell area decreases.

Inventive Principle:

Principle #1Segmentation

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 effectively reduces the write current while maintaining thermal stability, leading to longer memory holding times and lower error rates by controlling the magnetization reversal process through a multilayered structure with optimized exchange coupling.

Implementation Method 1

The tunnel resistance between the reference layer and the storage layer takes a high resistance state or a low resistance state depending on the relative magnetization arrangement of the two ferromagnetic layers.

Methodology Applied

Scientific EffectMagnetoresistance: Magnetoresistance

Implementation Method 2

there exists a spin transfer torque method which changes the magnetization direction of the storage layer by a spin transfer torque. Magnetization reversal is caused by supplying a current with a predetermined value or more to the MTJ element.

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 3

Magnetization reversal caused by a spin transfer torque is a Poisson process that occurs with the aid of thermal energy of room temperature, that is, phonons.

Methodology Applied

Scientific EffectThermal activation:

Data Source

PatentUS8530987B2Magnetic memory including a magnetoresistive element

Publication Date: 2013.09.10 KIOXIA CORP

AI summary

A magnetic memory includes a magnetoresistive element. The magnetoresistive element includes a reference layer having an invariable magnetization direction, a storage layer having a variable magnetization direction, and a spacer layer provided between the reference layer and the storage layer. The storage layer has a multilayered structure including first and second magnetic layers, the second magnetic layer is provided between the first magnetic layer and the spacer layer and has a magnetic anisotropy energy lower than that of the first magnetic layer, and an exchange coupling constant Jex between the first magnetic layer and the second magnetic layer is not more than 5 erg/cm2.