SiC MOSFET Built-In SBD Structure for Surge Current Reliability
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Solution Overview
Problem
Silicon carbide-based MOSFETs face reliability issues due to stacking fault growth and increased on-resistance, and have limited surge current tolerance, which can lead to device breakdown under high surge currents.
Innovation Solution
Incorporating a Schottky Barrier Diode (SBD) as a built-in diode in the MOSFET and optimizing the silicon carbide layer structure with specific impurity concentrations and electrode configurations to enhance surge current tolerance and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pn junction diode is used as a built-in diode in the MOSFET, then it allows reflux current to flow, but stacking fault grows in the silicon carbide layer due to carrier recombination energy, increasing on-resistance and reducing reliability
Solution Approach 1:
The patent changes the operating mode of the built-in diode from bipolar operation (pn junction) to unipolar operation (Schottky barrier diode). This parameter change in the diode's conduction mechanism eliminates carrier recombination in the drift region, thereby preventing stacking fault growth while maintaining reflux current capability.
Solution Approach 2:
The patent converts the harmful effect of carrier recombination (which causes stacking faults) into a beneficial outcome by using a Schottky barrier diode that allows reflux current without carrier recombination in the drift region. The harm of bipolar conduction is transformed into the benefit of unipolar conduction that protects the silicon carbide crystal structure.
2Reliability
If a Schottky Barrier Diode 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 diode structure into multiple regions with different doping concentrations (first doped region with higher concentration, second doped region with lower concentration). This segmentation allows the diode to handle surge currents effectively while maintaining unipolar operation to prevent stacking faults, thus resolving the contradiction between reliability and surge current tolerance.
Solution Approach 2:
The patent applies local quality by creating regions with different doping concentrations within the diode structure. The higher doped region near the Schottky contact provides low resistance for surge current handling, while the lower doped region maintains the unipolar operation characteristics to prevent stacking fault growth, thereby achieving both high reliability and high surge current tolerance.
3Power
If the MOSFET operates at high breakdown voltage, then it enables high power applications, but on-resistance increases when stacking faults occur
Solution Approach 1:
The patent changes the conduction parameter of the built-in diode from bipolar to unipolar operation. This parameter change prevents carrier recombination in the high-voltage drift region, eliminating stacking fault growth that would otherwise increase on-resistance and compromise reliability in high-power applications.
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 surge current tolerance and reliability of silicon carbide-based MOSFETs by suppressing stacking fault growth and increasing the maximum allowable peak current, thereby reducing the risk of device breakdown.
Implementation Method 1
By providing a Schottky Barrier Diode (SBD) that performs unipolar operation as a built-in diode in the MOSFET, it is possible to suppress growth of the stacking fault in the silicon carbide layer
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, and a thermal conductivity of about three times
Implementation Method 3
the MOSFET is used as a switching element connected to an inductive load. In this case, even when the MOSFET is turned off, it is possible to allow a reflux current to flow using the built-in diode
Data Source
AI summary
A semiconductor device according to an embodiment includes a semiconductor chip having a transistor region and a diode region, a first conductor, and a second conductor. The semiconductor chip includes a first electrode, a second electrode, a silicon carbide layer between the first electrode and the second electrode, and a gate electrode. The transistor region is provided with a third electrode spaced apart from the first electrode and close to the diode region. One end of the first conductor is in contact with the first electrode, and one end of the second conductor is in contact with the third electrode.