AlGaN Hetero-junction Layer Segmentation for Normally-off GaN Devices

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Solution Overview

Problem

Existing semiconductor devices with hetero-junction structures of GaN and AlGaN face challenges in controlling the 2-dimensional electron gas concentration and breakdown voltage due to the criticality of AlGaN electron donor layer thickness, leading to difficulties in maintaining a stable breakdown voltage and on-resistance.

Innovation Solution

A semiconductor device with a horizontal switching configuration featuring a hetero-junction structure of GaN and AlGaN layers, where the AlGaN layer is divided into two parts with different Al mixed crystal ratios, the first AlGaN layer with a higher ratio and the second AlGaN layer with a lower ratio, inducing a minus fixed charge to control the 2-dimensional electron gas concentration and reduce on-resistance while maintaining a high breakdown voltage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the AlGaN electron donor layer thickness is thinned by etching to reduce piezoelectric polarization and control 2DEG concentration, then the breakdown voltage decrease is restricted, but the thickness control becomes difficult leading to unstable 2DEG concentration

Engineering Contradiction:

Improvebreakdown voltage stabilityVSAvoidAlGaN layer thickness control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The invention changes the Al mixed crystal ratio parameter in the AlGaN layer to control piezoelectric polarization and 2DEG concentration. By adjusting the Al composition ratio rather than relying solely on thickness control, the patent achieves stable breakdown voltage and controlled electron gas concentration without the manufacturing precision issues of etching-based thickness reduction.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses a composite structure with multiple AlGaN layers having different Al mixed crystal ratios. This composite approach allows different regions to have different polarization characteristics, enabling independent control of breakdown voltage and 2DEG concentration while maintaining manufacturing stability.

Inventive Principle:

Principle #40Composite materials

2Reliability

If the AlGaN electron donor layer thickness is significantly reduced to control 2DEG concentration, then the piezoelectric polarization is restricted, but the on-resistance increases and breakdown voltage becomes unstable

Engineering Contradiction:

Improvebreakdown voltage controlVSAvoidon-resistance control

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies local quality by creating regions with different Al mixed crystal ratios within the AlGaN layer. The first AlGaN layer has a higher Al ratio for strong polarization and high 2DEG concentration, while the second AlGaN layer has a lower Al ratio for reduced polarization and controlled electron gas. This spatial variation in material composition allows independent optimization of breakdown voltage and on-resistance.

Inventive Principle:

Principle #3Local quality

3Device complexity

If a single AlGaN layer with uniform thickness is used, then the structure is simple, but the 2DEG concentration and breakdown voltage cannot be independently controlled

Engineering Contradiction:

ImproveAlGaN layer structureVSAvoidelectrical characteristic control

Core Design Contradiction:

Device complexityVSAdaptability or versatility

Solution Approach 1:

The patent segments the AlGaN electron donor layer into multiple layers with different Al mixed crystal ratios. This segmentation allows independent control of electrical characteristics in different regions, enabling separate optimization of 2DEG concentration and breakdown voltage while maintaining a relatively simple overall device structure.

Inventive Principle:

Principle #1Segmentation

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 allows for precise control of the 2-dimensional electron gas concentration and breakdown voltage, ensuring a stable and well-controlled increase in on-resistance and breakdown voltage, making the device a normally-off type with improved electrical performance.

Implementation Method 1

carriers of 2-dimensional electron gas (hereinafter, referred to as 2DEG) are induced by piezoelectric effect and intrinsic polarization effect

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

carriers of 2-dimensional electron gas (hereinafter, referred to as 2DEG) are induced by piezoelectric effect and intrinsic polarization effect

Methodology Applied

Scientific EffectPolarization effect: Polarisation

Data Source

PatentUS10062747B2Semiconductor device

Publication Date: 2018.08.28 DENSO CORP

AI summary

In a semiconductor device, an AlGaN layer includes a first AlGaN layer and a second AlGaN layer. The second AlGaN layer is positioned between a gate structure portion and a drain electrode and is divided into multiple parts in an arrangement direction in which the gate structure portion and the drain electrode are arranged. A second Al mixed crystal ratio of the second AlGaN layer is less than a first Al mixed crystal ratio of the first AlGaN layer. Accordingly, the semiconductor device is a normally-off-type device and is capable of restricting a decrease of a breakdown voltage and an increase of an on-resistance.