MRAM MTJ Stack Dual-Layer Passivation for Oxygen and Moisture Protection

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Solution Overview

Problem

Magnetic random access memory (MRAM) devices face poor thermal stability due to damage from oxygen and moisture affecting the ferromagnetic free layer and tunneling barrier layer in magnetic tunnel junction (MTJ) cells, leading to reliability issues.

Innovation Solution

A dual-layer passivation layer is implemented around the MTJ stack, comprising an oxygen-free dielectric film adjacent to the sidewalls and a moisture-blocking metal oxide layer, deposited using plasma-free techniques to prevent oxidation and moisture damage, enhancing protection for the MTJ stack.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional single-layer passivation is used, then manufacturing is simpler, but thermal stability and reliability are poor due to oxygen and moisture damage

Engineering Contradiction:

Improvethermal stabilityVSAvoidpassivation structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The passivation layer is segmented into two distinct functional layers: an oxygen-free dielectric film (first passivation layer) and a moisture-blocking metal oxide layer (second passivation layer). Each layer targets a specific harmful factor, with the oxygen-free layer preventing oxidation of the ferromagnetic free layer and tunneling barrier, and the metal oxide layer providing moisture barrier protection. This segmentation resolves the contradiction by achieving superior reliability through specialized protection while maintaining reasonable structural complexity.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs a composite passivation structure combining two different material systems: an oxygen-free dielectric material (such as silicon nitride or silicon carbide) and a metal oxide material (such as aluminum oxide or tantalum oxide). This composite approach leverages the complementary properties of each material—the oxygen-free dielectric's oxidation resistance and the metal oxide's moisture barrier capability—to achieve enhanced thermal stability and reliability that neither material could provide alone.

Inventive Principle:

Principle #40Composite materials

2Productivity

If plasma deposition techniques are used, then deposition efficiency is higher, but plasma damage occurs to the MTJ stack

Engineering Contradiction:

Improvedeposition efficiencyVSAvoidplasma damage

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediary approach by specifying deposition methods that avoid direct plasma exposure of the MTJ stack. Instead of using conventional plasma-enhanced chemical vapor deposition (PECVD) or sputtering that cause plasma damage, the invention employs plasma-free alternatives such as atomic layer deposition (ALD) or chemical vapor deposition (CVD). These intermediary methods achieve adequate deposition efficiency without the harmful plasma effects, resolving the contradiction between productivity and damage prevention.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If thicker passivation layers are used, then protection is better, but manufacturing precision and device dimensions are affected

Engineering Contradiction:

Improveprotection effectivenessVSAvoiddimensional control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies local quality by providing different passivation layers with optimized thicknesses tailored to their specific protective functions. The oxygen-free dielectric film has a thickness sufficient to prevent oxygen diffusion to the MTJ stack, while the metal oxide layer has a thickness optimized for moisture barrier performance. This localized optimization of each layer's thickness ensures adequate protection effectiveness while maintaining precise dimensional control and avoiding excessive overall thickness that would compromise manufacturing precision.

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 dual-layer passivation layer effectively shields the MTJ stack from environmental moisture and oxygen, improving thermal stability and reliability of the MRAM device by preventing plasma damage and oxidation, thereby enhancing the durability of the ferromagnetic free layer and tunneling barrier layer.

Implementation Method 1

an oxygen-free film formed around the MTJ stack... effectively shields the MTJ stack from environmental moisture and oxygen, improving thermal stability and reliability of the MRAM device by preventing plasma damage and oxidation

Methodology Applied

Scientific EffectOxidation prevention: Oxidation

Implementation Method 2

a moisture-blocking film formed around the oxygen-free film... effectively shields the MTJ stack from environmental moisture

Methodology Applied

Scientific EffectMoisture blocking: Absorption (physical)

Implementation Method 3

deposited using plasma-free techniques to prevent oxidation and moisture damage

Methodology Applied

Scientific EffectPlasma-free deposition: Chemical Vapour Deposition

Data Source

PatentUS8809976B2Method and structure for a MRAM device with a bilayer passivation

Publication Date: 2014.08.19 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

The present disclosure provides a magnetoresistive random access memory (MRAM) device. The MRAM device includes a magnetic tunnel junction (MTJ) stack on a substrate; and a dual-layer passivation layer disposed around the MTJ stack. The dual-layer passivation layer includes an oxygen-free film formed adjacent sidewalls of the MTJ stack; and a moisture-blocking film formed around the oxygen-free film.