Page 12 - NEW Armstrong Book - 2

Victor Veliadis,
IEEE Fellow; Executive Director
and CTO at PowerAmerica; and Professor of Electrical and Computer Engineering at North Carolina State University
In an increasingly electrified, technology-driven world, power electronics are central to the entire clean-energy– manufacturing economy. Silicon power devices have domi- nated power electronics because of their low-cost volume production, excellent starting material quality, ease of pro- cessing, and proven reliability and ruggedness. Although Si power devices continue to make significant progress, they are approaching their operational limits, primarily because of their poor high-temperature performance and their rela- tively low bandgap and critical electric field, which result in high conduction and switching losses.
Wide-bandgap silicon carbide power semiconductor devices have emerged as highly efficient alternatives to their vener- able MOSFET and IGBT Si counterparts. With smaller form factors, reduced cooling requirements, and established reli- ability, SiC devices are cost-effective silicon replacements at the system level while allowing for novel circuit archi- tectures and simplification. In particular, as environmen- tal awareness and a worldwide push for a zero-emissions economy gain prominence, the energy efficiency offered by SiC solutions is a strong driver in their wide market accep- tance and mass commercialization.
SiC devices are fabricated on high-quality epitaxial lay- ers deposited on native substrates. Homoepitaxial growth allows for better control of defect incorporation, significantly improves thermal performance, accommodates the growth of thick layers that facilitate very high-voltage operation, simplifies overall device design, and enables cost reductions. It should be noted, however, that conventional SiC sub- strate growth is more complex and time-consuming than that of Si, requiring the use of large seeds and high process temperatures — all of which have high cost implications. Commercial SiC epitaxial wafers are of excellent quality and available from multiple vendors. “Killer” defects limit- ing SiC device yields have practically been eliminated. Basal- plane dislocations, which can degrade device performance, are the major remaining defect and are being aggressively addressed.
High-yield manufacturing at volume fabs is a prerequi- site for mass SiC commercialization. Numerous well- established processes from silicon technology have been successfully transferred to SiC. In addition, several fabrica- tion processes specific to SiC have been developed and are at a stage of maturity. Today, SiC is produced in dedicated fabs as well as alongside silicon fabrication. The latter prom- ises SiC manufacturing at the economy scale of silicon and is a particularly attractive model. Overall, a vibrant world- wide fab infrastructure produces cost-effective 650-V to 1.7-kV SiC devices, having successfully duplicated the inte- grated device manufacturer, foundry, fabless, and design- house models used for silicon fabrication.
Commercially available SiC devices have a vertical struc- ture for conducting current and are thus dominant in 900-V applications. This is because higher-voltage capability in vertical power devices is engineered by optimizing the dop- ing and increasing the thickness of their drift layers, while the device’s lateral extent on the wafer surface remains unchanged. Below 900 V, and for the lucrative 650-V market in particular, lateral GaN, vertical SiC, and Si devices are all highly competitive. Device selection is application-specific in this voltage range and is driven by current, frequency, effi- ciency, and cost considerations.
The energy efficiency offered by SiC solutions is a strong driver in their wide market acceptance and mass commercialization.
SiC devices are steadily displacing their incumbent Si coun- terparts in vehicle electrification applications such as trac- tion motor drives, DC/DC converters, on-board chargers, and fast-charging architectures. They are enabling efficient data center power architectures that simplify waste heat management. SiC devices have been inserted in photovoltaic inverters and energy storage interfaces, while 6.5-V to 10-kV engineering samples have demonstrated compelling sys- tem advantages in DC microgrids, industrial variable-speed motor drives, and voltage-transmission applications. The power MOSFET has emerged as the SiC device of choice and is commercially available in planar and trench configurations from several vendors.
Barriers to SiC mass commercialization persist. The pri- mary hurdles are the cost premium over silicon devices, lin-
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