SiC Trench-Gate Device Depletion Layer Control

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Solution Overview

Problem

Trench-gate silicon carbide semiconductor devices experience increased on resistance due to the lateral extension of the depletion layer from a protective layer in the on state, which narrows the current path and concentrates electric fields, potentially leading to gate insulating film breakdown.

Innovation Solution

A silicon carbide semiconductor device with a depletion suppressing layer of higher first-conductivity-type impurity concentration than the drift layer, formed on the side surface of the protective layer, to suppress the extension of the depletion layer and maintain a wider current path in the on state.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a protective layer is provided in the drift layer below the trench, then electric field concentration in the trench bottom is reduced, but the depletion layer laterally extends in the drift layer from the protective layer in the on state, narrowing the current path and increasing on resistance

Engineering Contradiction:

Improveelectric field concentration in trench bottomVSAvoidon resistance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The protective layer is divided into multiple segments: a first protective layer extending from the trench bottom to a first depth, and a second protective layer extending from the first depth to a second depth greater than the first depth. This segmentation allows each layer to independently manage electric field distribution at different depths, reducing lateral depletion layer extension while maintaining vertical field control.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first protective layer and second protective layer are assigned different local qualities through their distinct depth positions and conductivity characteristics. The first protective layer (closer to trench bottom) and second protective layer (deeper in drift layer) create localized electric field management zones, enabling precise control of field distribution without excessive lateral depletion.

Inventive Principle:

Principle #3Local quality

2Object-affected harmful factors

If the protective layer extends deeply into the drift layer, then electric field control is improved, but the depletion layer extension narrows current path more significantly, increasing on resistance

Engineering Contradiction:

Improveelectric field distributionVSAvoidcurrent path width

Core Design Contradiction:

Object-affected harmful factorsVSLength of moving object

Solution Approach 1:

By segmenting the protective layer into two distinct depth zones (first protective layer at shallower depth, second protective layer at greater depth), the invention controls electric field distribution vertically without causing excessive lateral depletion. Each segment manages field control in its specific depth range, preserving current path width in the on state.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The invention transitions from a single-layer protective structure to a multi-layer vertical structure, managing electric field control in the vertical dimension (depth) rather than relying on lateral extension. This dimensional approach allows deep field control while maintaining horizontal current path integrity.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

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 configuration effectively reduces the on resistance of the silicon carbide semiconductor device while maintaining the integrity of the gate insulating film by minimizing electric field concentration and preventing breakdown.

Implementation Method 1

a depletion suppressing layer of the first conductivity type formed in the drift layer so as to be in contact with a side surface of the protective layer, the depletion suppressing layer having a first-conductivity-type impurity concentration higher than that of the drift layer

Methodology Applied

Scientific EffectDepletion layer extension suppression:

Implementation Method 2

a protective layer of the second conductivity type formed in the drift layer... a depletion layer extends from the protective layer in the off state, and the electric field in the trench bottom can be reduced accordingly

Methodology Applied

Scientific EffectElectric field reduction through depletion layer:

Data Source

PatentUS9972676B2Silicon carbide semiconductor device

Publication Date: 2018.05.15 MITSUBISHI ELECTRIC CORP

AI summary

A silicon carbide semiconductor device includes: a drift layer of a first conductivity type made of silicon carbide; a well region of a second conductivity type formed on the drift layer; a source region of a first conductivity type formed on the well region; a gate insulating film formed on an inner wall of a trench extending from a front surface of the source region through the well region, at least a part of a side surface of the gate insulating film being in contact with the drift layer; a gate electrode formed in the trench with the gate insulating film therebetween; a protective layer of the second conductivity type formed in the drift layer; and a depletion suppressing layer of the first conductivity type formed in the drift layer so as to be in contact with a side surface of the protective layer.