HEMT Multi-Layer Passivation for Reduced Drain Current Drift

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Solution Overview

Problem

Conventional high electron mobility transistors (HEMTs) suffer from drain current drift and gate/drain leakage due to charge build-up in electron traps at the semiconductor layer surface, leading to non-linearities and passive intermodulation distortion, particularly in high power and high frequency applications.

Innovation Solution

The HEMTs incorporate a multi-layer passivation structure with silicon-rich silicon nitride layers and spacer passivation layers to modulate electron traps, reducing charge accumulation and improving drain current stability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional passivation structures are used in HEMTs, then device simplicity is maintained, but drain current drift and gate/drain leakage occur due to charge build-up in electron traps

Engineering Contradiction:

Improvedrain current stabilityVSAvoidpassivation structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The passivation structure is divided into multiple discrete layers including a first silicon nitride layer, a second silicon nitride layer with different material composition, and a spacer passivation layer. Each layer serves specific functions in modulating electron traps and preventing charge build-up, thereby resolving the drain current drift issue while maintaining manageable structural complexity through functional segmentation.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent employs composite passivation structures combining different silicon nitride layers with varying material compositions and a spacer passivation layer. This composite approach creates a multi-functional passivation system that effectively modulates electron traps and prevents charge accumulation, improving drain current stability without excessive complexity increase.

Inventive Principle:

Principle #40Composite materials

2Reliability

If multi-layer passivation structures with different material compositions are implemented, then charge accumulation is reduced and drain current stability improves, but device fabrication complexity increases

Engineering Contradiction:

Improvedrain current stabilityVSAvoidfabrication complexity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

Different regions of the passivation structure utilize silicon nitride layers with locally optimized material compositions. The first and second silicon nitride layers have different compositions tailored to specific functional requirements, allowing effective electron trap modulation and charge build-up prevention while maintaining a systematic fabrication approach that manages manufacturing complexity.

Inventive Principle:

Principle #3Local quality

3Object-generated harmful factors

If spacer passivation layers are added to modulate electron traps, then passive intermodulation distortion is reduced, but manufacturing steps increase

Engineering Contradiction:

Improvepassive intermodulation distortionVSAvoidnumber of manufacturing steps

Core Design Contradiction:

Object-generated harmful factorsVSDevice complexity

Solution Approach 1:

The spacer passivation layer acts as an intermediary element between the silicon nitride layers and the underlying semiconductor structures. This intermediary layer effectively modulates electron traps and reduces passive intermodulation distortion while integrating into the existing fabrication process flow, adding manageable complexity through a single functional component.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 improved passivation structure significantly reduces drain current drift, maintaining quiescent drain current within 10% of peak current, enhancing performance in high power and high frequency applications by minimizing non-linearities and passive intermodulation distortion.

Implementation Method 1

Methodology Applied

Scientific EffectElectron trap modulation:

Implementation Method 2

When a HEMT is in its 'on' or conducting state, a two-dimensional electron gas (2DEG) is formed at the heterojunction of the channel layer and the barrier layer.

Methodology Applied

Scientific EffectTwo-dimensional electron gas formation:

Implementation Method 3

The 2DEG is an accumulation layer in the smaller bandgap material and can contain a very high sheet electron concentration. Additionally, electrons that originate in the wider-bandgap barrier layer transfer to the 2DEG layer, allowing a high electron mobility due to reduced ionized impurity scattering.

Methodology Applied

Scientific EffectIonized impurity scattering reduction:

Data Source

PatentUS12464759B2High electron mobility transistors having reduced drain current drift and methods of fabricating such devices

Publication Date: 2025.11.04 MACOM TECH SOLUTIONS HLDG INC

AI summary

A high electron mobility transistor comprises a semiconductor layer structure that includes a channel layer and a barrier layer and source and drain contacts on the semiconductor layer structure. A gate contact and a multi-layer passivation structure are provided on the semiconductor layer structure between the source contact and the drain contact. The multi-layer passivation structure comprises at least first and second silicon nitride layers that have different material compositions. A spacer passivation layer is provided on sidewalls of the first and second silicon nitride layers. A material composition of the spacer passivation layer is different than a material composition of at least one of the layers of the multi-layer passivation structure.