Trench Gate MISFET Avalanche Breakdown Control
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Solution Overview
Problem
The p channel trench gate type power MISFET with an overheat cutoff circuit experiences reduced avalanche capability, as the electrons generated during avalanche breakdown are injected into the gate electrode, causing a voltage drop and leading to thermal runaway and breakdown due to the gate cutoff resistor.
Innovation Solution
A semiconductor device with a trench gate type MISFET having a p-type channel and a resistive element between the gate pad and gate electrode, featuring a high-concentration n-type semiconductor region formed directly below the body contact region, which shifts the avalanche breakdown point away from the trench sidewall, reducing electron injection into the gate electrode and preventing voltage drops across the gate cutoff resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gate cutoff resistor is provided between the gate electrode and gate terminal to enable overheat cutoff function, then the device can prevent thermal breakdown through overheat protection, but the avalanche capability is reduced due to electron injection into the gate electrode causing voltage drop
Solution Approach 1:
The patent introduces a high-concentration n-type semiconductor region specifically at the bottom of the contact trench, creating a localized region with different electrical properties. This local modification changes the electric field distribution and avalanche breakdown characteristics in the critical area near the gate electrode, preventing electron injection while maintaining the overheat cutoff function through the gate resistor.
Solution Approach 2:
The high-concentration n-type semiconductor region acts as an intermediary structure between the contact trench and the gate electrode. It modifies the electric field distribution and serves as a barrier that prevents direct electron injection into the gate electrode during avalanche events, thereby protecting the gate cutoff resistor from voltage drops while maintaining overheat protection capability.
2Ease of manufacture
If the avalanche breakdown point is located near the trench sidewall, then the device structure is simpler, but electrons are injected into the gate electrode causing voltage drop and thermal runaway
Solution Approach 1:
The patent modifies the local electrical properties at the bottom of the contact trench by introducing a high-concentration n-type semiconductor region. This creates a localized area with enhanced electron concentration that alters the electric field distribution, shifting the avalanche breakdown point away from the trench sidewall and preventing electron injection into the gate electrode, thereby improving reliability without complicating the overall trench gate structure.
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 enhances the reliability of the p channel trench gate type power MISFET by preventing thermal breakdown and maintaining safe operation, while maintaining adequate avalanche capability and breakdown voltage.
Implementation Method 1
shifts the avalanche breakdown point away from the trench sidewall, reducing electron injection into the gate electrode
Data Source
AI summary
A trench is formed so as to reach a p−-type epitaxial layer from an upper surface of a source region. A gate electrode is formed so as to bury the trench. Each of body contact trenches is formed away from the gate electrode. A body contact region is formed at the bottom of the body contact trench. An n-type semiconductor region that is a feature of the present invention is formed in a layer below each body contact region. The impurity concentration of the n-type semiconductor region is higher than a channel forming area and lower than the body contact region.