Magnetoresistive Element With Fct Free Layer for Low Switching Current

Solution Overview

Problem

Conventional MRAMs face challenges in reducing the switching current density as the cell size decreases, leading to difficulties in maintaining magnetic anisotropy energy and thermal stability, which limits their capacity and efficiency in storing nonvolatile information.

Innovation Solution

The use of a magnetoresistive element with a free layer having a face-centered tetragonal crystal structure and perpendicular magnetization, sandwiched by nonmagnetic layers with different crystal structures, and a fixed layer with a perpendicular magnetization, along with a tunnel barrier layer and cap layer, to enhance magnetic anisotropy and thermal stability, allowing for efficient spin injection and reduced switching current.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the cell size is reduced to increase memory capacity, then the storage density is improved, but the switching current density increases making magnetization switching difficult

Engineering Contradiction:

Improvestorage densityVSAvoidswitching current density

Core Design Contradiction:

Quantity of substanceVSUse of energy by moving object

Solution Approach 1:

The patent changes the magnetic anisotropy parameter from in-plane to perpendicular magnetization by modifying the crystal structure to fct with (001) orientation. This fundamental parameter change enables magnetization switching to occur at much lower current densities even in miniaturized cells, resolving the contradiction between high storage density and manageable switching current requirements

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material structures including the fct magnetic layer combined with specific nonmagnetic layers (Ru, Rh, Ir, Cu, Ag, Au, Al) and tunnel barrier layers (MgO, Al2O3). These composite structures provide both the perpendicular magnetic anisotropy needed for low switching current and the thermal stability required for reliable data retention in high-density configurations

Inventive Principle:

Principle #40Composite materials

2Quantity of substance

If the cell size is reduced to increase memory capacity, then the storage density is improved, but the thermal stability of magnetization decreases

Engineering Contradiction:

Improvestorage densityVSAvoidthermal stability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent changes the magnetic anisotropy parameter from in-plane to perpendicular magnetization by modifying the crystal structure to fct with (001) orientation. This fundamental parameter change enables magnetization switching to occur at much lower current densities even in miniaturized cells, resolving the contradiction between high storage density and manageable switching current requirements

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material structures including the fct magnetic layer combined with specific nonmagnetic layers (Ru, Rh, Ir, Cu, Ag, Au, Al) and tunnel barrier layers (MgO, Al2O3). These composite structures provide both the perpendicular magnetic anisotropy needed for low switching current and the thermal stability required for reliable data retention in high-density configurations

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 high thermal stability and efficient magnetization switching with a reduced switching current, enabling the development of high-capacity MRAMs with improved reliability and power efficiency.

Implementation Method 1

a free layer which contains a magnetic material and has an fct (face-centered tetragonal) crystal structure with a (001) plane oriented, the free layer having a magnetization which is perpendicular to a film plane and has a direction to be changeable by spin-polarized electrons

Methodology Applied

Scientific EffectSpin transfer torque (SMT):

Implementation Method 2

MRAMs (Magnetic Random Access Memories; also referred to as magnetic memories hereinafter) using ferromagnetic materials are expected as nonvolatile memories ensuring nonvolatility, high-speed operation, large capacity, and low power consumption. An MRAM has, as a storage element, an MTJ (Magnetic Tunnel Junction) element using a TMR (Tunneling MagnetoResistive) effect

Methodology Applied

Scientific EffectTunneling magnetoresistive (TMR) effect: Magnetoresistance

Data Source

PatentUS7596015B2Magnetoresistive element and magnetic memory

Publication Date: 2009.09.29 KIOXIA CORP

AI summary

A magnetoresistive element includes a free layer which contains a magnetic material and has an fct crystal structure with a (001) plane oriented, the free layer having a magnetization which is perpendicular to a film plane and has a direction to be changeable by spin-polarized electrons, a first nonmagnetic layer and a second nonmagnetic layer which sandwich the free layer and have one of a tetragonal crystal structure and a cubic crystal structure, and a fixed layer which is provided on only one side of the free layer and on a surface of the first nonmagnetic layer opposite to a surface with the free layer and contains a magnetic material, the fixed layer having a magnetization which is perpendicular to a film plane and has a fixed direction.