SiC MOSFET Built-In SBD Structure for Surge Current Reliability
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Solution Overview
Problem
Silicon carbide (SiC) MOSFETs face reliability issues due to increased on-resistance and stacking fault growth caused by reflux currents, and have limited surge current tolerance, which can lead to device failure under high surge voltages.
Innovation Solution
Incorporating a Schottky Barrier Diode (SBD) as a built-in diode in the MOSFET, with specific impurity concentration and structural arrangements to reduce stacking fault growth and enhance surge current tolerance, including a diode region between transistor regions to manage current flow and heat distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a pn junction diode is used as a built-in diode in the MOSFET, then it is possible to allow a reflux current to flow, but a stacking fault grows in the silicon carbide layer due to recombination energy of carriers, causing on-resistance to increase
Solution Approach 1:
The patent changes the fundamental parameter of the built-in diode from a pn junction diode to a Schottky barrier diode. This parameter change alters the conduction mechanism from bipolar (with carrier recombination) to unipolar (without significant recombination), thereby eliminating stacking fault growth while maintaining reflux current capability
Solution Approach 2:
The patent converts the harmful recombination effect in pn junction diodes into a beneficial feature by using a Schottky barrier diode whose unipolar operation inherently prevents carrier recombination. The Schottky diode's metal-semiconductor junction provides a different physical mechanism that achieves reflux current flow without the harmful side effects
2Reliability
If a Schottky Barrier Diode (SBD) is provided as a built-in diode to suppress stacking fault growth, then reliability is improved, but surge current tolerance is limited
Solution Approach 1:
The patent segments the built-in diode structure into multiple Schottky barrier diodes arranged in parallel within the MOSFET. This segmentation allows the surge current to be distributed across multiple diode junctions, preventing any single junction from being overwhelmed while maintaining the overall reliability benefits of Schottky barrier technology
Solution Approach 2:
The patent designs the Schottky barrier diode structure to perform multiple functions simultaneously: it provides unipolar operation to suppress stacking faults, enables reflux current flow, and through proper configuration, achieves enhanced surge current tolerance. The multi-functional design resolves the contradiction by making the same structure serve both reliability and surge current requirements
3Power
If a large surge current flows into the MOSFET, then the MOSFET can handle high current demands, but a large surge voltage is applied generating heat and breaking the MOSFET
Solution Approach 1:
The patent incorporates Schottky barrier diodes with optimized contact areas and configurations before surge events occur. These pre-configured diodes act as protective elements that clamp surge voltages and provide low-impedance current paths, cushioning the MOSFET against thermal damage before the surge can cause breaking
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 improves the reliability and surge current tolerance of SiC MOSFETs by suppressing stacking fault growth and managing high surge currents, thereby enhancing the overall performance and longevity of the devices.
Implementation Method 1
providing a Schottky Barrier Diode (SBD) that performs unipolar operation as a built-in diode in the MOSFET
Implementation Method 2
silicon carbide has excellent physical properties such as a band gap of three times, a breakdown field strength of about ten times
Implementation Method 3
metal oxide semiconductor field effect transistor (MOSFET) capable of operating at a high breakdown voltage, a low loss
Data Source
AI summary
A semiconductor device according to an embodiment includes a transistor region and a diode region. The transistor region includes a first silicon carbide region of n-type having a first portion in contact with a first plane, a second silicon carbide region of p-type, a third silicon carbide region of n-type, and a gate electrode. The diode region includes the first silicon carbide region of n-type having a second portion in contact with the first plane and a fourth silicon carbide region of p-type. The semiconductor device includes a gate wiring electrically connected to the gate electrode. A distance between a high-concentration portion included in the fourth silicon carbide region and the gate wiring is larger than a distance between a high-concentration portion included in the second silicon carbide region and the gate wiring.