Segmented Gate Electrode for IGBT Latch-Up Prevention
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Solution Overview
Problem
Power semiconductor devices, such as IGBTs, face the challenge of latch-up during unexpected events like load shorts, where large currents and high voltages can cause carriers in the drift layer to flow through parasitic npn transistors, leading to device malfunction.
Innovation Solution
The design incorporates a gate electrode with two portions of different depths embedded in trenches, where the deeper portion reduces current flow near the second layer, preventing latch-up by controlling the flow of positive hole currents and minimizing base currents in parasitic npn transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional IGBT structure is used to control large current, then the device can function as a switching element, but latch-up occurs during unexpected events like load shorts due to carrier flow through parasitic npn transistors
Solution Approach 1:
The gate electrode is segmented into two distinct portions: a first portion extending into the first layer (n- drift layer) and a second portion extending into the second layer (p base layer) deeper than the first portion. This segmentation allows different regions of the gate electrode to control current flow in different layers, preventing latch-up by blocking carrier flow through the parasitic npn transistor while maintaining normal switching operation.
Solution Approach 2:
The gate electrode structure implements local quality by having different depths at different locations. The second portion extends deeper into the p base layer compared to the first portion, creating a localized region that specifically addresses the latch-up problem in the base layer without affecting the overall device characteristics or threshold voltage.
2Reliability
If carrier density in the n- drift layer is increased to reduce on voltage, then the resistance of the drift layer decreases, but switching loss increases due to more carriers remaining upon turning-off
Solution Approach 1:
The segmented gate electrode structure allows independent control of carrier injection into different layers. The first portion controls carrier injection into the n- drift layer for conductivity modulation, while the second portion controls carrier flow in the p base layer. This segmentation enables optimization of on voltage without proportionally increasing switching loss.
Solution Approach 2:
The gate electrode structure changes the electrical parameters of different layers differently. By extending the second portion deeper into the p base layer, it modifies the base region characteristics to reduce switching loss while the first portion maintains adequate carrier density in the drift layer for low on voltage.
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
This configuration effectively prevents latch-up occurrences without altering the basic characteristics of the device, such as threshold voltage and on voltage, by utilizing the micro-loading effect in trench etching to manage electric field strengths and current paths.
Implementation Method 1
the gate electrode includes a first portion projecting into the first layer through the first region and the second layer, and a second portion projecting into the first layer through the second region and the second layer. The second portion projects into the first layer deeper than a depth in which the first portion projects into the first layer
Data Source
AI summary
A semiconductor layer has a first layer of first conductive type, a second layer of second conductive type, and a third layer. The third layer has a first region of first conductive type, and a second region of second conductive type. A second electrode is in contact with each of the first and second regions. A trench is formed on the semiconductor layer at a surface opposite to its surface facing a first electrode. A gate electrode is embedded in the trench with a gate insulating film interposed therebetween. The gate electrode includes a first portion projecting into the first layer through the first region and the second layer, a second portion projecting into the first layer through the second region and the second layer. The second portion projects into the first layer deeper than a depth in which the first portion projects into the first layer.