SiC MOSFET Built-In Diode Layout for Surge and Stacking Fault Control
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Solution Overview
Problem
Silicon carbide-based MOSFETs face increased on-resistance due to stacking faults caused by reflux currents through bipolar-operating pn junction diodes, leading to reduced reliability, and have limited surge current withstand capacity, which can result in device destruction from high surge voltages.
Innovation Solution
Incorporating a Schottky barrier diode (SBD) as a built-in diode and strategically placing pillar regions in the silicon carbide layer to operate the pn junction diode at a lower voltage during surge currents, thereby suppressing stacking fault growth and enhancing surge current withstand capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a pn junction diode is used as a built-in diode in silicon carbide MOSFET, then the device can handle reflux currents, but stacking faults grow due to carrier recombination energy, increasing on-resistance and reducing reliability
Solution Approach 1:
The patent extracts the harmful bipolar operation mode from the diode function by introducing a unipolar Schottky barrier diode configuration. This separates the reflux current handling capability from the harmful carrier recombination effects, allowing the device to maintain adaptability while improving reliability.
Solution Approach 2:
The patent changes the operational parameters of the diode by transitioning from bipolar pn junction operation to unipolar Schottky barrier operation. This parameter change eliminates the stacking fault growth mechanism while preserving the essential diode function for reflux current handling.
2Reliability
If a Schottky barrier diode is provided to suppress stacking fault growth, then reliability improves, but surge current withstand capacity remains limited and device destruction can occur from high surge voltages
Solution Approach 1:
The patent introduces an intermediary pn junction diode structure that activates during surge conditions. This intermediary element provides an additional current path that supplements the Schottky barrier diode, enabling the device to withstand high surge currents while maintaining the reliability benefits of unipolar operation during normal conditions.
Solution Approach 2:
The patent creates a dynamic system where the diode structure adapts its behavior based on operating conditions. During normal operation, the Schottky barrier provides unipolar conduction for reliability, while during surge events, the pn junction component activates to provide additional surge current handling capability.
3Adaptability or versatility
If high surge voltage is applied to MOSFET beyond steady state, then surge current flows to meet demand, but heat generation destroys the MOSFET
Solution Approach 1:
The patent implements preliminary protective action by designing a diode structure with inherent low forward voltage characteristics. This preliminary design feature ensures that during surge events, the diode conducts current with minimal voltage drop before excessive heat can generate, preemptively protecting the MOSFET from thermal destruction.
Solution Approach 2:
The patent converts the potentially harmful high surge voltage into a beneficial effect by utilizing the diode's forward conduction特性. The surge voltage that would normally cause destructive heating is instead channeled through the diode's low-resistance path, where it is dissipated safely, transforming a harmful condition into a protective mechanism.
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 solution effectively suppresses the growth of stacking faults, improving the reliability and surge current withstand capacity of silicon carbide-based MOSFETs by ensuring the pn junction diode operates at a lower voltage during surge events, thus preventing device destruction.
Implementation Method 1
By providing a Schottky barrier diode (SBD) operating in a unipolar manner in the MOSFET as a built-in diode, it is possible to suppress the growth of a stacking fault in the silicon carbide layer
Implementation Method 2
when a reflux current is made to flow by using a pn junction diode that operates in a bipolar manner, a stacking fault grows in a silicon carbide layer due to the recombination energy of the carriers
Implementation Method 3
a gate insulating layer provided between the gate electrode and the second silicon carbide region, the gate insulating layer provided between the gate electrode and the third silicon carbide region, and the gate insulating layer provided between the gate electrode and the second region
Data Source
AI summary
A semiconductor device of embodiments includes: a first electrode; a second electrode; a gate electrode extending in a first direction; and a SiC layer. The SiC layer includes: a first conductive type first SiC region having a first region, a second region facing the gate electrode, and a third region in contact with the first electrode; a second conductive type second SiC region between the second region and the third region; a second conductive type third SiC region, the second region interposed between the second SiC region and the third SiC region; a second conductive type fourth SiC region, the third region interposed between the second SiC region and the fourth SiC region; a first conductive type fifth SiC region; a second conductive type sixth SiC region between the first region and the second SiC region; and a second conductive type seventh SiC region between the first region and the second SiC region and distant from the sixth SiC region in the first direction.