SiC Transistor Cell Clamp Structure for ESD Overvoltage Protection

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Solution Overview

Problem

There is a need to increase the reliability of silicon carbide power semiconductor devices with minimal additional process complexity, as they are susceptible to overvoltage events and have high intrinsic breakdown voltage, making them prone to damage from electrostatic discharge.

Innovation Solution

A silicon carbide device with a transistor cell featuring a bidirectional clamp structure, comprising a floating well and doped regions of opposing conductivity types, which forms a pn junction and provides a low-resistive ohmic path between the gate electrode and clamp regions, effectively protecting against overvoltage events by short-circuiting and dissipating excess voltage without damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If integrated protection elements are added to silicon carbide devices, then device reliability increases, but process complexity increases

Engineering Contradiction:

Improvedevice reliabilityVSAvoidprocess complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The clamp structure is integrated directly into the silicon carbide device body, merging the protection function with the main device structure. The first and second clamp regions are formed as part of the device fabrication process, eliminating the need for separate protection elements and reducing process complexity while maintaining reliability enhancement

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The clamp regions serve multiple functions: they provide overvoltage protection, define breakdown characteristics, and protect the gate dielectric. This multi-functionality allows a single structural feature to address multiple reliability concerns without requiring additional separate protection circuits

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Power

If silicon carbide devices operate at high breakdown voltages, then power handling capability increases, but susceptibility to electrostatic discharge damage increases

Engineering Contradiction:

Improvepower handling capabilityVSAvoidelectrostatic discharge susceptibility

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The clamp regions are pre-formed during device fabrication to establish controlled breakdown characteristics before the device is put into service. These regions act as predetermined weak points that will break down first during electrostatic discharge events, protecting the main device structure from damage

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The high breakdown voltage characteristic that makes silicon carbide devices susceptible to electrostatic discharge is converted into a benefit by creating controlled breakdown paths through the clamp regions. These regions intentionally break down at lower voltages to dissipate energy safely, transforming the vulnerability into a protection mechanism

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 bidirectional clamp structure enhances the reliability of silicon carbide devices by efficiently decoupling breakdown characteristics from blocking voltage, reducing leakage, and protecting the gate dielectric from overvoltage events like electrostatic discharge, while maintaining low resistance and high breakdown current handling capabilities.

Implementation Method 1

A floating well and the doped region form a pn junction. A first clamp region having the second conductivity type extends into the floating well... effectively protecting against overvoltage events by short-circuiting and dissipating excess voltage without damage

Methodology Applied

Scientific EffectAvalanche breakdown: Avalanche Breakdown

Data Source

PatentUS11876133B2Silicon carbide device with transistor cell and clamp region

Publication Date: 2024.01.16 INFINEON TECHNOLOGIES AG

AI summary

A silicon carbide device includes a transistor cell with a source region and a gate electrode. The source region is formed in a silicon carbide body and has a first conductivity type. A first low-resistive ohmic path electrically connects the source region and a doped region of a second conductivity type. The doped region and a floating well of the first conductivity type form a pn junction. A first clamp region having the second conductivity type extends into the floating well. A second low-resistive ohmic path electrically connects the first clamp region and the gate electrode.