STT Device Oxide Seed Layer Spin Pumping

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Solution Overview

Problem

In spin transfer torque (STT) devices, the damping effect caused by spin pumping from the free layer to the adjacent seed layer increases the DC critical current required to initiate oscillation, which is undesirable when a seed layer is necessary for proper crystalline growth, and existing solutions like oxide layers cannot be used due to direct contact requirements.

Innovation Solution

Incorporating an intermediate oxide layer between the write pole and the free layer, along with a nonmagnetic electrically conducting buffer layer to remove spin polarization from the write pole, and using a multilayer structure with a metal or metal alloy seed layer and oxide layer to reduce damping effects.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a metal or metal alloy seed layer is placed in direct contact with the free layer to promote proper crystalline growth, then the crystalline structure of the free layer is improved, but the damping effect increases due to spin pumping from the free layer to the seed layer

Engineering Contradiction:

Improvecrystalline growthVSAvoiddamping effect

Core Design Contradiction:

Manufacturing precisionVSLoss of energy

Solution Approach 1:

An intermediate oxide layer is introduced between the metal seed layer and the free layer. This oxide layer acts as a mediator that blocks the spin current flow from the free layer to the seed layer, thereby reducing the damping effect while still allowing the seed layer to provide proper crystalline growth template for the free layer.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Use of energy by moving object

If the DC critical current density is reduced to lower power consumption, then the energy efficiency is improved, but the ability to overcome damping and initiate oscillation is worsened

Engineering Contradiction:

Improvepower consumptionVSAvoidoscillation initiation

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The oxide layer, which initially might seem to add resistance and hinder current flow, actually converts the harmful spin pumping effect into a beneficial reduction of damping. By blocking the spin current leakage to the seed layer, the oxide layer allows the spin torque to more effectively drive the free layer oscillation, thereby reducing the critical current density needed to initiate and sustain oscillation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 intermediate oxide layer reflects spin current and reduces damping, allowing for lower DC critical currents and improved oscillation stability of the free layer's magnetization, while maintaining proper crystalline growth and performance.

Implementation Method 1

the free layer generates spin current into the adjacent metal or metal alloy seed layer. This well-known effect, referred to as 'spin pumping'

Methodology Applied

Scientific EffectSpin pumping:

Implementation Method 2

Spin transfer torque (STT) is an effect in which the orientation of the magnetization of a magnetic layer in a magnetic tunnel junction (MTJ) or giant magnetoresistance (GMR) spin valve can be modified using a spin-polarized current

Methodology Applied

Scientific EffectSpin transfer torque:

Implementation Method 3

The intermediate oxide layer reflects spin current from spin pumping by the free layer

Methodology Applied

Scientific EffectSpin current reflection:

Data Source

PatentUS10839833B1Spin transfer torque device with oxide layer beneath the seed layer

Publication Date: 2020.11.17 WESTERN DIGITAL TECHNOLOGIES INC

AI summary

A spin transfer torque (STT) device is formed on an electrically conductive substrate and includes a ferromagnetic polarizer layer near the substrate, a ferromagnetic free layer, and a nonmagnetic spacer layer between the ferromagnetic polarizer layer and the ferromagnetic free layer. A multilayer structure is located between the substrate and the ferromagnetic polarizer layer. The multilayer structure includes a metal or metal alloy seed layer for the ferromagnetic polarizer layer and an intermediate oxide layer below and in contact with the seed layer. The intermediate oxide layer reflects spin current from the write pole and thus reduces undesirable spin pumping of the ferromagnetic polarizer layer.