SiC-MOSFET Bypass Diode for Solid State Relay Reliability
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Solution Overview
Problem
SiC-MOSFETs in solid state relays experience increased on-resistance due to crystal defects caused by current flowing through pn junction diodes, leading to high power consumption and reliability issues, especially with repetitive switching.
Innovation Solution
External bypass semiconductor elements, such as silicon diodes or Si-MOSFETs, are connected in parallel to compound semiconductor elements with a lower turn-on voltage, preventing current flow through the pn junction diodes and reducing crystal defects, thereby suppressing on-resistance increases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current flows through pn junction diodes in SiC-MOSFETs, then the device can operate with high withstand voltage and small on-resistance, but crystal defects increase causing on-resistance to increase over time
Solution Approach 1:
The patent segments the current path by introducing a separate bypass current path that is distinct from the main current path through the pn junction diode. This allows the main current to flow through the MOSFET channel while reverse recovery current flows through the bypass path, preventing crystal defect accumulation in the epitaxial layer
Solution Approach 2:
The patent introduces an external bypass element (such as a Schottky diode or another MOSFET) as an intermediary component that provides an alternative current path. This bypass element mediates the reverse recovery current flow, preventing it from passing through the pn junction diode and causing crystal defects in the SiC epitaxial layer
2Productivity
If SiC-MOSFETs are used for high repetition switching operations, then power conversion efficiency is improved, but crystal defects accumulate causing on-resistance to increase
Solution Approach 1:
The patent implements preliminary protection by providing the bypass current path before crystal defects can accumulate. The bypass element is pre-configured to handle reverse recovery current, preventing the harmful effects from occurring during high-repetition switching operations
Solution Approach 2:
The bypass element acts as a cushioning mechanism that absorbs the harmful reverse recovery current before it can damage the epitaxial layer. This protective measure is in place beforehand to handle the stress of repeated switching operations
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 reduces on-resistance and enhances the reliability of SiC-MOSFETs by preventing crystal defect growth, maintaining output contact reliability even with high repetition of switching operations.
Implementation Method 1
External bypass semiconductor elements, such as silicon diodes or Si-MOSFETs, are connected in parallel to compound semiconductor elements with a lower turn-on voltage, preventing current flow through the pn junction diodes
Implementation Method 2
a light emitting element 110, such as an LED, which generates an optical signal in response to an input signal
Implementation Method 3
a photoelectric conversion unit 120 including a photodiode array 121 which receives the optical signal and produces an electromotive force
Data Source
AI summary
A semiconductor device includes one or more unipolar compound semiconductor element; and bypass semiconductor elements externally connected to the respective compound semiconductor elements in parallel. A turn-on voltage of the bypass semiconductor elements is smaller than a turn-on voltage of the compound semiconductor elements in the direction from the source to the drain.