IGBT FWD Region Asymmetric Cathode Width Design

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Solution Overview

Problem

Conventional reverse conducting IGBTs (RC-IGBTs) experience increased forward voltage drop and electrical loss due to the high carrier density in the n-type inversion layer, leading to snapping in the voltage-current curve, which affects the efficiency of power converting equipment like inverters.

Innovation Solution

The semiconductor device design features a narrower n+ cathode region width compared to the FWD anode region width, with a trench gate structure in the FWD region, facilitating electron flow through a high-resistance n− drift layer and suppressing adverse effects on forward voltage drop, while maintaining IGBT performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a conventional RC-IGBT structure with uniform anode and cathode regions is used, then the device can be manufactured with standard processes, but the forward voltage drop increases and electrical loss increases due to high carrier density in the n-type inversion layer

Engineering Contradiction:

Improvestandard manufacturing processVSAvoidelectrical loss

Core Design Contradiction:

Ease of manufactureVSLoss of energy

Solution Approach 1:

The patent applies asymmetry by making the cathode region width narrower than the anode region width in the FWD region. This asymmetric design creates a specific carrier distribution that reduces the forward voltage drop and electrical loss while maintaining manufacturability with standard semiconductor processing techniques.

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent implements local quality by creating different region widths at different locations: the cathode region has a narrower width compared to the anode region width in the FWD area. This localized structural variation optimizes the electrical characteristics specifically in the FWD region without affecting other parts of the device.

Inventive Principle:

Principle #3Local quality

2Loss of energy

If the n+ cathode region width is made narrower to reduce forward voltage drop, then the FWD performance improves, but the device complexity increases due to asymmetric structure requirements

Engineering Contradiction:

Improveforward voltage dropVSAvoidasymmetric structure

Core Design Contradiction:

Loss of energyVSDevice complexity

Solution Approach 1:

The patent deliberately introduces asymmetry between the cathode and anode region widths to reduce forward voltage drop. The narrower cathode region width compared to the anode region width creates favorable carrier distribution that lowers electrical loss, accepting the trade-off of increased structural complexity.

Inventive Principle:

Principle #4Asymmetry

3Reliability

If a trench gate structure is added to the FWD region, then reverse recovery characteristics improve with reduced peak current and voltage oscillations, but the device complexity and manufacturing difficulty increase

Engineering Contradiction:

Improvereverse recovery characteristicsVSAvoidtrench gate structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies segmentation by dividing the gate structure into two distinct types: a planar gate structure in the IGBT region and a trench gate structure in the FWD region. This segmentation allows each region to have optimized gate characteristics, with the trench gate improving reverse recovery behavior while the planar gate maintaining IGBT performance.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements local quality by providing different gate structures in different regions: the FWD region receives a trench gate structure to improve reverse recovery characteristics, while the IGBT region maintains a planar gate structure. This localized optimization enhances overall device performance without uniformly increasing complexity throughout the entire device.

Inventive Principle:

Principle #3Local quality

4Loss of energy

If the cathode region width is reduced to suppress carrier flow, then forward voltage drop decreases, but the manufacturing precision requirements increase

Engineering Contradiction:

Improveforward voltage dropVSAvoidcathode region width control

Core Design Contradiction:

Loss of energyVSManufacturing precision

Solution Approach 1:

The patent establishes an asymmetric width relationship where the cathode region width is intentionally made narrower than the anode region width. This asymmetric design achieves forward voltage drop reduction while the width difference provides manufacturing tolerance, making the precision requirement manageable through standard fabrication processes.

Inventive Principle:

Principle #4Asymmetry

Data Source

PatentUS10658360B2Semiconductor device with an insulated-gate bipolar transistor region and a diode region

Publication Date: 2020.05.19 FUJI ELECTRIC CO LTD

AI summary

On a front surface side of an n− semiconductor substrate, an emitter electrode and trench gates each including a p base layer, a trench, a gate oxide film and a gate electrode are provided in an IGBT region and a FWD region. Among p base layers each between adjacent trenches, p base layers having an n+ emitter region are the IGBT emitter region and the p base layers not having the n+ emitter region are the FWD anode region. A lateral width of an n+ cathode region is narrower than a lateral width of the FWD anode region. A difference of a lateral width of the FWD anode region and a lateral width of the n+ cathode region is 50 μm or more. Thus, a semiconductor device may be provided that reduces the forward voltage drop while suppressing waveform oscillation during reverse recovery and having soft recover characteristics.