SiC Rectifier Layer Structure for Thermal Stability

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Solution Overview

Problem

In semiconductor rectifier devices using SiC, current concentration and thermal breakdown occur due to reduced resistance as temperature increases, leading to increased on-voltage and potential device failure.

Innovation Solution

The semiconductor rectifier device is designed with a specific layer structure including a drift layer, minority carrier absorption layer, high-resistance semiconductor layer, and cathode contact layer, where impurity concentrations and thicknesses are carefully controlled to maintain a positive temperature coefficient of resistance, preventing breakdown and ensuring stable operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the thickness of the drift layer is reduced to lower resistance and electrical loss, then the on-voltage decreases, but the resistance increases as temperature increases leading to current concentration and thermal breakdown

Engineering Contradiction:

Improveelectrical lossVSAvoidthermal breakdown resistance

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The drift layer is segmented into multiple regions with different impurity concentrations (first drift layer with lower concentration, second drift layer with higher concentration). This segmentation allows the first region to maintain low resistance for reduced electrical loss while the second region provides positive temperature coefficient to prevent thermal breakdown.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the drift layer are assigned different impurity concentrations tailored to their specific functions. The first drift layer has lower impurity concentration optimized for low resistance, while the second drift layer has higher impurity concentration optimized for positive temperature coefficient and thermal stability.

Inventive Principle:

Principle #3Local quality

2Reliability

If the thickness of the drift layer is reduced using SiC physical properties, then the resistance can be suppressed to low level, but the resistance increases with temperature causing current concentration

Engineering Contradiction:

Improvedevice stabilityVSAvoidtemperature-induced resistance increase

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The impurity concentration parameter is changed across different regions of the drift layer. By creating a gradient from lower to higher impurity concentration, the device achieves both low resistance operation and positive temperature coefficient to counteract temperature-induced resistance increase.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The drift layer is constructed as a composite structure with two distinct semiconductor regions having different impurity concentrations. This composite approach combines the benefits of low resistance (from the lower concentration region) with thermal stability (from the higher concentration region).

Inventive Principle:

Principle #40Composite materials

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 controlled layer structure and impurity concentrations effectively increase resistance with temperature, preventing current concentration and thermal breakdown, thus maintaining device stability and performance.

Implementation Method 1

a minority carrier absorption layer that adjoins the drift layer and is made of a first conductivity type semiconductor having a higher concentration than that of the drift layer

Methodology Applied

Scientific EffectMinority carrier recombination:

Implementation Method 2

a high-resistance semiconductor layer that adjoins the minority carrier absorption layer, has less thickness than the drift layer and is made of a first conductivity type semiconductor having a concentration lower than that of the minority carrier absorption layer

Methodology Applied

Scientific EffectPhonon scattering:

Data Source

PatentUS8648447B2Semiconductor rectifier device

Publication Date: 2014.02.11 KK TOSHIBA

AI summary

A semiconductor rectifier device using an SiC semiconductor at least includes: an anode electrode; an anode area that adjoins the anode electrode and is made of a second conductivity type semiconductor; a drift layer that adjoins the anode area and is made of a first conductivity type semiconductor having a low concentration; a minority carrier absorption layer that adjoins the drift layer and is made of a first conductivity type semiconductor having a higher concentration than that of the drift layer; a high-resistance semiconductor area that adjoins the minority carrier absorption layer, has less thickness than the drift layer and is made of a first conductivity type semiconductor having a concentration lower than that of the minority carrier absorption layer; a cathode contact layer that adjoins the semiconductor area; and a cathode electrode.