What Is a SiC Diode?
SiC diodes are semiconductor devices made from a compound of silicon (Si) and carbon (C).
SiC has about 10 times the dielectric breakdown strength and 3 times the band gap of silicon (Si), enabling the creation of smaller yet higher breakdown voltage circuit elements. SiC diodes, a prominent type of SiC power semiconductors, are used in discrete products or integrated into modules for applications in inverters, converters, IGBTs, and other devices.
The Schottky barrier diode, a type of SiC diode, is notable for its compact design and high-efficiency switching capabilities with low forward voltage. However, growing SiC wafers is more challenging than Si wafers, and processing SiC for semiconductor devices is also more complex. Thus, SiC diodes are not expected to entirely replace Si diodes but rather to coexist and be used for specific applications.
Uses of SiC Diodes
SiC diodes are extensively used in electric vehicle inverters, contributing to increased vehicle range and reduced power consumption.
They are also employed in trains, leading to electricity cost savings due to reduced power consumption. Despite higher initial costs, using SiC diodes can lower operational expenses. For example, the latest Tokaido Shinkansen trains use inverters equipped with SiC diodes.
SiC diodes are compact, lightweight, and capable of handling high voltages and currents with minimal efficiency loss at high frequencies. As their cost decreases, they are expected to be increasingly adopted in high-power consumption devices.
Like SiC, gallium nitride (GaN) semiconductors are also gaining attention. SiC is generally used in higher voltage and power devices, whereas GaN is preferred for higher frequency operations.
Principle of SiC Diodes
SiC diodes can handle higher voltages and currents and operate at higher temperatures than traditional Si diodes, thanks to the superior physical properties of SiC wafers.
SiC has a larger band gap, dielectric breakdown field strength, and thermal conductivity compared to Si. For instance, the band gap of SiC is 3.26 eV compared to Si’s 1.12 eV, the breakdown field strength of SiC is 2.5 MV/cm compared to Si’s 0.3 MV/cm, and SiC’s thermal conductivity is 4.9 W/(cm・K) compared to Si’s 1.5 W/(cm・K).
Among various SiC wafer crystal structures, 4H-SiC has particularly advantageous characteristics for power devices.
Types of SiC Diodes
There are mainly two types of SiC diodes: SiC Schottky barrier diodes and SiC pn-junction diodes.
1. SiC Schottky Barrier Diode
This diode type features a metal Schottky connection to SiC, where electron movement generates current. It is known for high-speed operation and high breakdown voltage, significantly outperforming conventional Si diodes in terms of breakdown voltage.
2. SiC pn-Junction Diode
The SiC pn-junction diode uses a pn junction structure and is characterized by higher breakdown voltage and lower resistance compared to SiC Schottky barrier diodes. This efficiency is due to the accumulation of holes as minority carriers in the n-type layer.