Multilayered MTJ Pillar with Metallic Spacer for Pressure Sensors

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Solution Overview

Problem

Current pressure sensors, particularly those using multilayered magnetic tunnel junction (MTJ) pillars, face challenges in accurately sensing pressure magnitude and location with high sensitivity and low failure rates, often experiencing drifting and imprecision.

Innovation Solution

A sub-micrometer pressure sensor design featuring a multilayered MTJ pillar with non-magnetic metallic spacers between magnetic free layers, enhancing sensitivity and switching to a binary 'on' or 'off' state with minimal drift and low error rates.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a multilayered MTJ pillar with two ferromagnetic plates separated by a thin dielectric layer is used, then pressure sensing capability is achieved, but the sensor exhibits drifting and high failure rate

Engineering Contradiction:

Improvefailure rateVSAvoidpressure sensing accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The magnetic free layer is divided into two separate ferromagnetic plates (first and second magnetic free layers) separated by a non-magnetic metallic spacer. This segmentation allows independent magnetization control of each plate, enabling more stable and reliable pressure sensing by preventing the drifting issues observed in single-layer configurations.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

A non-magnetic metallic spacer is introduced as an intermediary layer between the two magnetic free layers. This spacer mediates the interaction between the magnetic plates, allowing for controlled magnetic coupling while preventing direct contact that would cause instability and failure. The spacer enables reliable pressure sensing by maintaining consistent spacing and magnetic properties.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If large arrays of piezoelectric or magnetostrictive materials are used, then measurable electric response is achieved, but sensitivity to pressure magnitude and location is reduced

Engineering Contradiction:

Improvepressure location precisionVSAvoidsensor area

Core Design Contradiction:

Measurement precisionVSQuantity of substance

Solution Approach 1:

The patent changes the fundamental operating parameters by using a multilayered MTJ structure with specific magnetic layer configurations and thicknesses. This allows achieving high precision in pressure location sensing (sub-micrometer level) while maintaining a compact form factor, eliminating the need for large arrays of piezoelectric or magnetostrictive materials.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The sensor employs a composite structure combining multiple ferromagnetic layers, a non-magnetic metallic spacer, and a tunnel barrier layer. This composite material architecture enables both high sensitivity to pressure magnitude and precise location detection within a small area, overcoming the limitations of single-material piezoelectric or magnetostrictive approaches.

Inventive Principle:

Principle #40Composite materials

3Measurement precision

If the MTJ pillar structure is simplified, then manufacturing is easier, but sensitivity and pressure sensing accuracy deteriorate

Engineering Contradiction:

Improvepressure sensing sensitivityVSAvoidMTJ pillar structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies local quality by giving different functional properties to different layers within the MTJ pillar. The first and second magnetic free layers have specific magnetization characteristics, the non-magnetic metallic spacer has controlled thickness and material properties, and the tunnel barrier layer has specific resistance characteristics. This localized optimization of each layer's properties achieves high sensitivity while maintaining manufacturability through standardized fabrication processes.

Inventive Principle:

Principle #3Local quality

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 sub-micrometer pressure sensor achieves precise pressure sensing with improved sensitivity and reliability, reducing failure rates and maintaining performance over time.

Implementation Method 1

a non-magnetic metallic spacer separating a first magnetic free layer from a second magnetic free layer

Methodology Applied

Scientific EffectMagnetic separation:

Implementation Method 2

Pressure sensors containing a multilayered magnetic tunnel junction (MTJ) pillar that includes two ferromagnetic plates, each of which can hold a magnetization

Methodology Applied

Scientific EffectMagnetostriction: Magnetostriction

Data Source

PatentUS11226252B2Multilayered magnetic free layer structure in magnetic tunnel junction arrays for sub-micrometer resolution pressure sensors

Publication Date: 2022.01.18 INTERNATIONAL BUSINESS MACHINE CORPORATION

AI summary

A sub-micrometer pressure sensor is provided that includes a multilayered magnetic tunnel junction (MTJ) pillar that contains a non-magnetic metallic spacer separating a first magnetic free layer from a second magnetic free layer. The presence of the non-magnetic metallic spacer in the multilayered MTJ pillar improves the sensitivity without compromising area, and makes the pressure sensor binary (either “on” or “off”) with little or no drift, and sensitivity change over time. Moreover, the resistivity switch in such a pressure sensor is instantly and a low error rate is observed.