Thermal Spin Torque Transfer MRAM Free Layer Segmentation

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Solution Overview

Problem

Conventional MRAM devices require a large amount of current to write to a free layer of a tunnel junction, leading to potential electromigration problems and transistor size issues at advanced nodes.

Innovation Solution

A thermal spin torque transfer MRAM device with a magnetic tunnel junction featuring a reference layer, a tunnel barrier layer, and a free layer with multiple layers of varying Curie temperatures, where at least one layer is non-magnetic at a write temperature, reducing the current needed to write to the free layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If heat is applied to the tunnel junction to write to the free magnet, then the magnetic polarity of the free magnet can be changed, but a large amount of current is required which may make transistors too large and cause electromigration problems

Engineering Contradiction:

Improvewriting capabilityVSAvoidcurrent requirement

Core Design Contradiction:

Ease of operationVSUse of energy by moving object

Solution Approach 1:

The free layer is segmented into multiple sub-layers with different Curie temperatures. During writing, only the sub-layers with lower Curie temperatures are heated above their transition point, while sub-layers with higher Curie temperatures remain magnetic. This segmentation allows selective thermal activation of only the necessary portion of the free layer, significantly reducing the total current required for writing while maintaining the ability to change the overall magnetic polarity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention changes the thermal parameter distribution by introducing multiple Curie temperature values within the free layer. By controlling the write temperature to be between the lowest and highest Curie temperatures of the sub-layers, the patent achieves selective magnetization switching. This parameter change approach allows the system to write with lower current than would be required if the entire free layer had to be heated above a single high Curie temperature.

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If a single-layer free magnet is used, then the structure is simple, but a large current is required to change magnetic polarity

Engineering Contradiction:

Improvefree layer structureVSAvoidwriting current

Core Design Contradiction:

Device complexityVSUse of energy by moving object

Solution Approach 1:

The free layer is divided into multiple sub-layers with different Curie temperatures. This segmentation allows the system to target specific sub-layers for thermal activation during writing operations, reducing the total energy required compared to heating an entire single-layer free magnet above a high Curie temperature.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The free layer is constructed as a composite structure combining multiple ferromagnetic materials with different Curie temperatures. This composite approach leverages the lower Curie temperature materials to enable writing at reduced current levels, while the higher Curie temperature materials provide thermal stability during normal operation. The composite structure achieves both low writing current and high thermal stability simultaneously.

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 approach allows for efficient writing to the free layer with significantly less energy, reducing the current required by a quarter and enhancing thermal stability, thus addressing the challenges of conventional MRAM devices.

Implementation Method 1

the tunnel junction programming circuit is configured to apply a current through the magnetic tunnel junction to generate a write temperature in the magnetic tunnel junction

Methodology Applied

Scientific EffectJoule heating: Joule Heating

Implementation Method 2

The free layer includes a first layer having a first Curie temperature and a second layer having a second Curie temperature different from the first Curie temperature

Methodology Applied

Scientific EffectCurie point transition: Curie Point (ferromagnetic)

Implementation Method 3

thermal spin torque transfer magnetoresistive random access memory

Methodology Applied

Scientific EffectSpin torque transfer:

Data Source

PatentUS8947915B2Thermal spin torqure transfer magnetoresistive random access memory

Publication Date: 2015.02.03 GLOBALFOUNDRIES US INC

AI summary

A thermal spin torque transfer magnetoresistive random access memory (MRAM) apparatus includes a magnetic tunnel junction and a tunnel junction programming circuit. The magnetic tunnel junction includes a reference layer having a fixed magnetic polarity, a tunnel barrier layer, and a free layer on an opposite side of the tunnel barrier layer from the reference layer. The free layer includes a first layer having a first Curie temperature and a second layer having a second Curie temperature different from the first Curie temperature. The tunnel junction programming circuit is configured to apply a current through the magnetic tunnel junction to generate a write temperature in the magnetic tunnel junction and to write to the free layer of the magnetic tunnel junction.