What are SiC power devices?
SiC SBD Features
1. Device structure and features
Incorporating SiC high-speed device construction into Schottky barrier diodes (SBDs) makes it possible to achieve withstand voltages greater than 600V (in contrast to ~200V with silicon SBDs).
As a result, replacing existing mainstream PN junction diodes (fast recovery types) significantly reduce recovery loss, contributing to lower noise and greater compactness in passive components such as coils due to increased power supply efficiency and higher frequency operation.
This ensures support for power factor correction circuits (PFCs) and rectifier bridges, making them suitable for a wider range of applications, including AC, power supplies, solar power conditioners, EV rapid chargers.
2. SiC SBD forward characteristics
The rise voltage of SiC SBDs is less than 1V - equivalent to that of FRDs.
Rise voltage is determined by the height of the Schottky barrier. However, although designing a lower normal barrier height makes it possible to reduce the rise voltage, this comes at the expense of leakage current, which increases during reverse bias. In response, ROHM has successfully devised a process for its 2nd generation SBDs that reduces rise voltage by approx.
0.15V while maintaining leakage current and recovery characteristics equivalent with conventional products.
In addition, temperature dependence differs significantly from Si FRDs, with Vf increasing along with operating resistance at high temperatures.
This helps to prevent thermal runaway, ensuring worry-free operation even when connected in parallel.
3. SiC SBD reverse recovery characteristics
In silicon high-speed PN diodes (FRDs) large transient current flows the moment the direction switches from forward to reverse, which can lead to large losses when shifting to a reverse bias condition during this time.
When forward current is applied, minority carriers accumulated in the drift layer contribute to electrical conduction until they disappear (storage time). This increases both recovery time and recovery current as the forward current rises and temperature grows, causing significant loss.
In contrast, SiC SBDs are majority carrier devices (unipolar) that do not use minority carriers for electrical conduction, so in principle minority carrier accumulation does not occur. As a result, only a small amount of current flows for discharging the junction capacitance, achieving considerably less loss than silicon FRDs.
This transient current is largely independent of temperature and forward current, making stable high-speed recovery possible under virtually any environment. Reduction of noise that occurs due to reverse recovery current can also be expected.