Spin Torque Oscillator MRAM Cell for Low Current Switching

Solution Overview

Problem

Current spin-transfer torque (STT) magnetoresistive random access memory (MRAM) cells face challenges in efficiently flipping the magnetization of the free layer between parallel and antiparallel states due to high current densities required for switching, which can lead to increased power consumption and heat generation.

Innovation Solution

The MRAM cell design incorporates a spin torque layer and a spin polarization layer with conical magnetizations, coupled through antiferromagnetic modes, to provide an initial non-vertical torque to the free layer's magnetization, reducing the current density needed for switching by allowing precession around a vertical axis parallel to the reference layer's magnetization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high current density is applied to flip the magnetization of the free layer, then the switching between parallel and antiparallel states is achieved, but power consumption and heat generation increase

Engineering Contradiction:

Improvemagnetization switchingVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The magnetic structure is segmented into multiple functional layers including a reference layer with fixed magnetization, a free layer with switchable magnetization, and a spin torque oscillator stack with spin torque layer and spin polarization layer. This segmentation allows the switching function to be distributed across multiple specialized components, reducing the current burden on any single layer and enabling more efficient magnetization flipping with lower power consumption.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The spin torque oscillator stack acts as an intermediary between the current source and the free layer. The spin torque layer generates spin-polarized current that mediates the magnetization switching of the free layer, while the spin polarization layer provides the necessary spin polarization. This intermediary mechanism enables more efficient angular momentum transfer and reduces the overall current density required for switching, thereby reducing power consumption and heat generation.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If high current density is applied to flip the magnetization of the free layer, then the switching between parallel and antiparallel states is achieved, but heat generation increases

Engineering Contradiction:

Improvemagnetization switchingVSAvoidheat generation

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The magnetic structure is segmented into multiple functional layers including a reference layer with fixed magnetization, a free layer with switchable magnetization, and a spin torque oscillator stack with spin torque layer and spin polarization layer. This segmentation allows the switching function to be distributed across multiple specialized components, reducing the current burden on any single layer and enabling more efficient magnetization flipping with lower power consumption.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The spin torque oscillator stack acts as an intermediary between the current source and the free layer. The spin torque layer generates spin-polarized current that mediates the magnetization switching of the free layer, while the spin polarization layer provides the necessary spin polarization. This intermediary mechanism enables more efficient angular momentum transfer and reduces the overall current density required for switching, thereby reducing power consumption and heat generation.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If conventional spin valve structure is used, then the device complexity is low, but the switching efficiency is insufficient

Engineering Contradiction:

Improvestructure complexityVSAvoidswitching efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The magnetic structure is segmented into multiple functional layers including a reference layer with fixed magnetization, a free layer with switchable magnetization, and a spin torque oscillator stack with spin torque layer and spin polarization layer. This segmentation allows the switching function to be distributed across multiple specialized components, reducing the current burden on any single layer and enabling more efficient magnetization flipping with lower power consumption.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The spin torque oscillator stack employs a composite structure combining spin torque layer and spin polarization layer with conical magnetizations coupled through antiferromagnetic modes. This composite material approach enables the generation of initial non-vertical torque on the free layer's magnetization, facilitating more efficient switching. The composite structure leverages the complementary properties of different magnetic layers to achieve superior switching efficiency compared to conventional single-layer spin valve structures.

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 lowers the switching current for both parallel to antiparallel and antiparallel to parallel transitions, reducing power consumption and heat generation while maintaining efficient data storage through magnetization flipping.

Implementation Method 1

Spin-transfer torque (STT) refers to an effect in which the orientation of a magnetic layer in a magnetic tunnel junction or spin valve is modified by a spin-polarized current. When the spin-polarized current flows through a free layer of a magnetic tunnel junction or a spin valve, the electrons in the spin-polarized current can transfer at least some of their angular momentum to the free layer, thereby producing torque to magnetize the free layer.

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 2

The MRAM cell design incorporates a spin torque layer and a spin polarization layer with conical magnetizations, coupled through antiferromagnetic modes, to provide an initial non-vertical torque to the free layer's magnetization, reducing the current density needed for switching by allowing precession around a vertical axis parallel to the reference layer's magnetization.

Methodology Applied

Scientific EffectConical magnetization precession: Precession

Data Source

PatentUS11309487B2Spin transfer torque MRAM with a spin torque oscillator stack and methods of making the same

Publication Date: 2022.04.19 SANDISK TECHNOLOGIES LLC

AI summary

A MRAM cell includes a magnetic tunnel junction containing a reference layer having a fixed magnetization direction, a free layer, and a nonmagnetic tunnel barrier layer located between the reference layer and the free layer, a spin torque oscillator stack, and a first nonmagnetic spacer layer located between the free layer and the spin torque oscillator stack.