What is SiC and why is SiC for power devices?

2021-09-28 即思创意
SiC MOSFET,SiC Schottky rectifier

Rugged and High Efficiency:Silicon carbide (SiC) is a compound semiconductor material with the energy bandgap of 3.2eV. The wide bandgap of SiC enables it to withstand roughly 10 times of electric field compared to conventional Silicon semiconductors (bandgap = 1.1eV).

The power devices are used to regulate the electric power (current and voltage). Ideally, power devices should have zero electric resistance (therefore no conduction loss), instant switching (no switching loss), and infinite voltage blocking capability (zero leakage current). However, in reality, engineers are facing trade-offs among characteristics of different kinds of power devices.

Power devices use an epitaxial layer to withstand the voltage. In order to withstand a higher voltage, the doping concentration of the epitaxial layer has to be lower and the thickness of the epitaxial layer has to be thicker. A lightly-doped, thick epitaxial layer increases the resistance of power devices per unit area, which increases the cost and reduces the performance. Therefore, in Si power devices, simple unipolar devices are used only for rated voltage smaller than 400V, and for rated voltage larger than 600V, the majority of commercial devices use super junction structures or bipolar devices such as IGBT to reduce the electric resistance by means of charge balance and conductivity modulation. Although these sophisticated structures improve the specific on resistance, they also come with some side effects such as more severe EMI, higher switching loss (tailing current).

In SiC, because of its 10 times strength to withstand electric field, its theoretical specific on-resistance can be 200 times smaller than Si counterpart, which enables people to use SiC to manufacture high voltage devices with simple structures. Today, unipolar SiC power devices, including SiC MOSFETs and SiC Schottky rectifiers, have been commercialized for voltage rating up to 3300V, which is unreachable by any other semiconductor materials.

  • 10X higher dielectric strength than Si 

  • 200X lower specific on-resistance than Si 

  • High temperature operation 

  • 5X higher avalanche energy density


This Trend is Set to Continue

SiC power devices have been increasingly adopted by applications whenever the cost/performance is justified. The trend of replacing Si with SiC is set to continue and will accelerate.


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