IGBT Current Suppressing Layer for Voltage Stability

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Solution Overview

Problem

Silicon carbide (SiC) bipolar devices face challenges with forward voltage degradation over time due to Basal Plane Dislocations, leading to increased on-resistance and power dissipation at high temperatures, especially for high voltage applications above 10 kV.

Innovation Solution

The development of an insulated gate bipolar transistor (IGBT) with a current suppressing layer having a higher doping concentration than the drift layer, combined with an epitaxial structure, to reduce forward voltage drop and maintain high blocking capability, achieved through specific doping concentrations and layer thicknesses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If bipolar operation is used to reduce drift layer resistance via conductivity modulation, then forward voltage drop is reduced, but forward voltage degradation over time occurs due to Basal Plane Dislocations

Engineering Contradiction:

Improveforward voltage dropVSAvoidforward voltage stability over time

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

A current suppressing layer is introduced as an intermediary component between the drift layer and the emitter. This layer has higher doping concentration than the drift layer, which allows it to suppress the harmful effects of Basal Plane Dislocations while maintaining the beneficial conductivity modulation effect for reducing forward voltage drop.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The current suppressing layer is positioned locally in the device structure where it can specifically address the dislocation issues without affecting the overall bipolar operation. The layer has distinct local properties (higher doping concentration) that differ from the drift layer, allowing targeted suppression of current conduction paths affected by BPDs.

Inventive Principle:

Principle #3Local quality

2Strength

If drift layer thickness is increased to achieve higher blocking voltage capability, then blocking voltage is improved, but on-resistance increases substantially

Engineering Contradiction:

Improveblocking voltage capabilityVSAvoidon-resistance

Core Design Contradiction:

StrengthVSLoss of energy

Solution Approach 1:

The doping concentration parameter of the current suppressing layer is changed to be higher than that of the drift layer. This parameter change allows the device to maintain low on-resistance even with thick drift layers required for high blocking voltage, by compensating for the resistance increase through the highly doped suppressing layer.

Inventive Principle:

Principle #35Parameter changes

3Strength

If drift layer thickness is increased for higher blocking voltage, then blocking voltage is improved, but power dissipation increases at high temperatures due to bulk mobility reduction

Engineering Contradiction:

Improveblocking voltage capabilityVSAvoidpower dissipation

Core Design Contradiction:

StrengthVSLoss of energy

Solution Approach 1:

The current suppressing layer acts as an intermediary that mitigates the temperature-dependent mobility reduction effects. By having higher doping concentration, this layer provides a more stable conduction path that is less sensitive to temperature-induced bulk mobility changes, thereby reducing power dissipation at high temperatures.

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 IGBT design achieves a significant reduction in forward voltage drop and on-resistance, enhancing power switching applications by suppressing current conduction and maintaining high blocking voltage, even at elevated temperatures.

Implementation Method 1

bipolar operation to reduce the drift layer resistance via conductivity modulation resulting from injected minority carriers

Methodology Applied

Scientific EffectConductivity modulation: Conduction (electrical)

Implementation Method 2

maintaining high blocking capability, achieved through specific doping concentrations and layer thicknesses

Methodology Applied

Scientific EffectElectric field blocking: Electric Field

Data Source

PatentUS9064840B2Insulated gate bipolar transistors including current suppressing layers

Publication Date: 2015.06.23 WOLFSPEED INC

AI summary

An insulated gate bipolar transistor (IGBT) includes a first conductivity type substrate and a second conductivity type drift layer on the substrate. The second conductivity type is opposite the first conductivity type. The IGBT further includes a current suppressing layer on the drift layer. The current suppressing layer has the second conductivity type and has a doping concentration that is larger than a doping concentration of the drift layer. A first conductivity type well region is in the current suppressing layer. The well region has a junction depth that is less than a thickness of the current suppressing layer, and the current suppressing layer extends laterally beneath the well region. A second conductivity type emitter region is in the well region.