Composite Free Layer for MRAM Switching Current Reduction

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Solution Overview

Problem

Magnetoresistive random access memory (MRAM) technologies face challenges in reducing write currents and power consumption while maintaining suitable tunnel magnetoresistance (TMR) ratios, particularly in spin-orbit torque (SOT) MRAM, due to high electrical currents leading to heating and design issues.

Innovation Solution

A composite free layer in magnetic tunnel junctions is introduced, comprising an in-plane anisotropy free layer, a ferromagnetic amorphous layer, and a perpendicular magnetic anisotropy (PMA)-inducing layer, which decreases write currents and power consumption while maintaining a suitable TMR ratio for data storage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high electrical currents are used to generate spin current in SOT-MRAM, then data writing is achieved, but heating and power consumption increase

Engineering Contradiction:

Improvedata writing capabilityVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent changes the magnetic anisotropy parameter from perpendicular to in-plane by introducing a PMA-inducing layer that creates a uniaxial in-plane magnetic anisotropy. This parameter change reduces the switching current density from typical SOT-MRAM levels to below 10^6 A/cm², thereby reducing power consumption while maintaining reliable data writing capability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite free layer structure consisting of a ferromagnetic layer combined with a PMA-inducing layer. This composite structure generates uniaxial in-plane magnetic anisotropy through interface effects, enabling lower switching currents and reduced power consumption compared to conventional homogeneous free layers

Inventive Principle:

Principle #40Composite materials

2Reliability

If high electrical currents are used to generate spin current in SOT-MRAM, then data writing is achieved, but heating occurs

Engineering Contradiction:

Improvedata writing capabilityVSAvoidheating

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

By changing the magnetic anisotropy from perpendicular to in-plane orientation through the PMA-inducing layer, the patent reduces the switching current density threshold. This parameter modification directly lowers the electrical current required for writing, thereby reducing Joule heating effects while maintaining data writing reliability

Inventive Principle:

Principle #35Parameter changes

3Measurement precision

If spin-polarized read currents are used in STT-MRAM, then reading is achieved, but stored data is disturbed or altered

Engineering Contradiction:

Improvedata reading capabilityVSAvoiddata integrity

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent segments the current path by introducing a separate spin Hall effect material layer adjacent to the free layer. This segmentation allows write currents to flow through the spin Hall material to generate spin torque, while read currents can flow through the MTJ without disturbing the magnetic state, thus preserving data integrity during read operations

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

The composite free layer design reduces switching current densities and power consumption, improving data retention and read operations by maintaining a suitable TMR ratio, thus enhancing the reliability and efficiency of MRAM systems.

Implementation Method 1

a perpendicular magnetic anisotropy (PMA)-inducing layer, which decreases write currents and power consumption while maintaining a suitable TMR ratio for data storage

Methodology Applied

Scientific EffectPerpendicular magnetic anisotropy (PMA):

Implementation Method 2

current may flow across the barrier layer due to quantum tunneling

Methodology Applied

Scientific EffectQuantum tunneling:

Implementation Method 3

data may be written by applying an electrical current through a spin Hall effect material adjacent to the free layer, thus generating a pure spin current for changing the magnetic moment of the free layer

Methodology Applied

Scientific EffectSpin Hall effect:

Data Source

PatentUS10347310B2Composite free layer for magnetoresistive random access memory

Publication Date: 2019.07.09 SANDISK TECHNOLOGIES LLC

AI summary

Apparatuses, systems, and methods are disclosed for magnetoresistive random access memory. A magnetic tunnel junction for storing data includes a fixed layer, a barrier layer, and a composite free layer. A barrier layer is disposed between a fixed layer and a composite free layer. A composite free layer includes an in-plane anisotropy free layer, a perpendicular magnetic anisotropy (PMA) inducing layer, and a ferromagnetic amorphous layer. A PMA-inducing layer may be disposed such that an in-plane anisotropy free layer is between a barrier layer and the PMA-inducing layer. A ferromagnetic amorphous layer may be disposed between an in-plane anisotropy free layer and a PMA-inducing layer.