MRAM PSC Structure With Nonmagnetic Insertion for Low-Current Switching

Solution Overview

Problem

Existing MRAM devices require large spin currents for switching due to high magnetization of the free layer, which limits their commercial applicability and stability, and the precessional mode of the free-layer magnetization becomes un-deterministic when the magnetization is lowered, affecting the orthogonal spin transfer effect.

Innovation Solution

A precessional spin current structure with a nonmagnetic insertion layer is introduced, where the precessional spin current magnetic layer has a magnetization direction that freely rotates, allowing spin transfer torque to assist switching throughout the entire precession cycle, reducing the switching current requirement and enhancing thermal stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the magnetization of the free layer is increased to improve thermal stability, then the switching current requirement increases, but the device becomes less commercially applicable and the precessional mode becomes un-deterministic

Engineering Contradiction:

Improvethermal stabilityVSAvoidswitching current requirement

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The free layer is segmented into two distinct layers: a first free layer with high magnetization for thermal stability and a second free layer with low magnetization for easy switching. These layers are coupled through an exchange coupling layer, allowing each layer to perform its specialized function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs a composite magnetic structure combining two different ferromagnetic layers with contrasting magnetization properties. The first free layer (e.g., CoFeB) provides high magnetization for stability, while the second free layer (e.g., CoFe) provides low magnetization for low switching current, creating a composite system that achieves both thermal stability and energy efficiency.

Inventive Principle:

Principle #40Composite materials

2Use of energy by moving object

If the magnetization of the free layer is decreased to reduce switching current, then the device becomes more commercially applicable, but the precessional mode of magnetization becomes un-deterministic

Engineering Contradiction:

Improveswitching current requirementVSAvoidprecessional mode determinism

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The free layer is segmented into two distinct layers: a first free layer with high magnetization for thermal stability and a second free layer with low magnetization for easy switching. These layers are coupled through an exchange coupling layer, allowing each layer to perform its specialized function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

An exchange coupling layer (e.g., Ru or Ir) acts as an intermediary between the first and second free layers, transmitting spin angular momentum from the high-magnetization layer to the low-magnetization layer. This intermediary ensures deterministic precessional mode while enabling low switching current operation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If a single free layer is used, then the device structure is simpler, but it cannot simultaneously achieve both high thermal stability and low switching current

Engineering Contradiction:

Improvefree layer structureVSAvoidperformance stability

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The free layer is segmented into two distinct layers: a first free layer with high magnetization for thermal stability and a second free layer with low magnetization for easy switching. These layers are coupled through an exchange coupling layer, allowing each layer to perform its specialized function without compromising the other.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The dual-layer free layer structure performs multiple functions simultaneously: the first layer provides thermal stability through high magnetization, while the second layer enables low switching current through low magnetization. The exchange coupling layer facilitates spin transfer between layers, making the overall structure multi-functional.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 significantly reduces the switching current needed for MRAM devices, improves the stability of the free layer, and ensures deterministic magnetization switching by maintaining spin torque effectiveness throughout the entire precession cycle.

Implementation Method 1

Spin transfer torque or spin transfer switching, uses spin-aligned (polarized) electrons to change the magnetization orientation of the free layer in the magnetic tunnel junction

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

the nonmagnetic precessional spin current insertion layer is constructed of a material having a spin diffusion length exceeding two (2) nanometers

Methodology Applied

Scientific EffectSpin diffusion:

Implementation Method 3

The insulator between the reference layer and the free layer enables tunneling of electrons from the free layer to the reference layer

Methodology Applied

Scientific EffectTunneling:

Implementation Method 4

Due to the spin-polarized electron tunneling effect, the electrical resistance of the cell change due to the orientation of the magnetization of the two layers

Methodology Applied

Scientific EffectMagnetoresistance:

Data Source

PatentUS12075706B2Precessional spin current structure with non-magnetic insertion layer for MRAM

Publication Date: 2024.08.27 INTEGRATED SILICON SOLUTION CAYMAN INC

AI summary

A magnetoresistive random-access memory (MRAM) is disclosed. MRAM device has a magnetic tunnel junction stack having a significantly improved performance of the free layer in the magnetic tunnel junction structure. The MRAM device utilizes a precessional spin current (PSC) magnetic structure in conjunction with a perpendicular MTJ where the in-plane magnetization direction of the PSC magnetic layer is free to rotate. The precessional spin current magnetic layer a first and second precessional spin current ferromagnetic layer separated by a nonmagnetic precessional spin current insertion layer.