SiC MISFET Integrated Freewheeling Diode
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Solution Overview
Problem
Silicon carbide (SiC) semiconductor devices face challenges with high turn-on voltage and reverse recovery current due to the use of body diodes as freewheeling diodes, leading to increased loss and reduced switching rates, and the high cost of SiC Schottky barrier diodes (SBDs) increases circuit costs.
Innovation Solution
A semiconductor device with a metal-insulator-semiconductor field effect transistor (MISFET) structure that operates as either a transistor or a diode based on gate voltage, using a channel region to reduce turn-on voltage and eliminate the need for a separate freewheeling diode, by setting the gate potential to control current flow through the channel rather than the body diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a body diode is used as a freewheeling diode in SiC-FET, then the device can provide freewheeling current path, but the turn-on voltage increases and reverse recovery current occurs leading to increased loss
Solution Approach 1:
The patent combines the freewheeling diode function with the SiC-FET by forming a pn junction within the FET structure itself. The p-type body region and n-type drift layer create an integrated body diode that provides freewheeling current path while reducing turn-on voltage compared to separate external diodes, thereby lowering conduction loss during freewheeling operation.
Solution Approach 2:
The patent optimizes the doping concentrations of the p-type body region and n-type drift layer to achieve lower turn-on voltage for the body diode. By carefully controlling the doping parameters, the body diode exhibits reduced forward voltage drop compared to conventional SiC-FET body diodes, thereby reducing conduction loss while maintaining adequate reverse blocking capability.
2Ease of operation
If a body diode is used as a freewheeling diode in SiC-FET, then the device can provide freewheeling current path, but the switching rate decreases due to reverse recovery current
Solution Approach 1:
The integrated body diode structure allows for coordinated optimization of the FET and diode characteristics. The pn junction is formed within the same semiconductor substrate as the FET channel, enabling the diode to turn off more quickly by utilizing the same depletion region dynamics as the FET, thereby reducing reverse recovery current and improving switching rate.
3Loss of energy
If SiC Schottky barrier diodes are used to replace body diode, then reverse recovery current is eliminated, but the circuit cost increases significantly
Solution Approach 1:
The SiC-FET structure provides its own freewheeling diode function through the integrated pn junction, eliminating the need for separate external freewheeling diodes. This self-service approach reduces component count and circuit cost while maintaining adequate switching performance through the optimized body diode characteristics.
4Device complexity
If the number of components is reduced by using integrated body diode, then circuit cost and size decrease, but conduction loss increases due to high turn-on voltage
Solution Approach 1:
The patent optimizes the doping concentrations and junction depth of the pn junction to achieve lower turn-on voltage. By adjusting the p-type body region doping and n-type drift layer doping parameters, the body diode exhibits reduced forward voltage drop, thereby reducing conduction loss while maintaining the component reduction benefit of integration.
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 approach reduces conduction and switching losses, allows for higher switching rates, and decreases the number of components needed, thereby lowering circuit costs and size while maintaining high reliability.
Implementation Method 1
a gate electrode, which is arranged on the gate insulating film... making the drain electrode and the source electrode electrically conductive with each other through the second silicon carbide semiconductor layer
Data Source
AI summary
A semiconductor element including an MISFET exhibits diode characteristics in a reverse direction through an epitaxial channel layer. The semiconductor element includes: a silicon carbide semiconductor substrate of a first conductivity type, semiconductor layer of the first conductivity type, body region of a second conductivity type, source region of the first conductivity type, epitaxial channel layer in contact with the body region, source electrode, gate insulating film, gate electrode and drain electrode. If the voltage applied to the gate electrode is smaller than a threshold voltage, the semiconductor element functions as a diode wherein current flows from the source electrode to the drain electrode through the epitaxial channel layer. The absolute value of the turn-on voltage of this diode is smaller than the turn-on voltage of a body diode that is formed of the body region and the first silicon carbide semiconductor layer.