RE:AXE SiC Development Another take on it, the SiC advantages are making alot of technological advances in different industries, AXE is the earliest inventor for the oilfield purpose, I'm happy to be part of the evolution:
SiC Power Technology Status and Barriers to Mass Commercialization
Victor Veliadis
February 4, 2022
SiC operates at high currents and frequencies and is fabricated in silicon fabs with only a modest capital investment.
Silicon (Si) power devices have dominated power electronics due to their low-cost volume production, excellent starting material quality, ease of fabrication, and proven reliability. Although Si power devices continue to improve, they are approaching their operational limits primarily due to their relatively low bandgap, critical electric field, and thermal conductivity that result in high conduction and switching losses, as well as poor high-temperature performance. Silicon carbide’s (SiC’s) large bandgap and critical electric field allow for high-voltage devices with thinner layers, which lowers resistance and associated conduction and switching losses. Combined with SiC’s large thermal conductivity, high-temperature operation at high power levels is possible with simplified thermal management. Furthermore, thinner device layers and low specific on-resistance allow for a smaller form factor that reduces capacitance. This enables efficient operation at frequencies well above those of silicon, which minimizes the size of passive system components. Thus, the SiC-based system is more efficient, lighter, has smaller volume, and is cost-competitive (despite the higher-than-Si device cost), as bulky magnetics and heatsinks are minimized.
These compelling efficiency and system benefits have led to significant development efforts over the last two decades and SiC planar and trench MOSFETs, and JFETs are commercially available from several vendors as discrete components and high-power modules in the 650- to 1,700-V voltage range. Presently, power-electronic engineers can select Si, SiC, and gallium nitride (GaN) components for use in their systems. There are, of course, numerous tradeoffs when selecting the right material device for an application and voltage: Current, frequency, efficiency, temperature, and cost are important considerations.
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Figure 1: Voltage ranges in which Si, SiC, and GaN are competitive
Voltage ranges in which Si, SiC, and GaN are particularly competitive are shown in Figure 1. Si is reliable, rugged, cheap, and capable of high-current efficient operation at “lower” frequencies. It is particularly competitive in the 15- to 650-V range. GaN offers efficient high-frequency operation at a reasonable cost, as it is fabricated in CMOS-compatible fabs and foundries exploiting the silicon manufacturing economies of scale. GaN devices are lateral — unlike SiC power devices, which have a vertical configuration — and this simplifies packaging and IC fabrication. However, the lateral configuration practically limits operation to ~650 V (with one GaN vendor offering a 900-V device), and SiC is the best solution above that voltage rating. SiC is efficient and operates at high currents and frequencies. Although not fully CMOS-compatible, it is fabricated in silicon fabs with only a modest capital investment in additional SiC-specific equipment. Multiple established Si processes have been successfully transferred to SiC, and specific SiC processes are at a stage of maturity in numerous fabs worldwide. Overall, SiC is cost-competitive, as it is processed in mature-node fully depreciated large-volume Si fabs, providing the surplus wafer capacity that maximizes fab utilization and profits.
High-impact application opportunities, in which SiC devices are displacing their incumbent Si counterparts, have emerged and include xEV and rail power electronics with reduced losses and reduced cooling requirements; novel data center topologies with reduced cooling loads and higher efficiencies; variable-frequency drives for efficient high-power electric motors at a reduced overall system cost; more efficient, flexible, and reliable grid applications with reduced system footprint; and “more electric aerospace,” with weight, volume, and cooling system reductions contributing to energy savings. With respect to EVs, the majority currently utilize a 400-V bus architecture, so 650-V SiC devices compete with the mature and rugged silicon IGBTs, while GaN competes in the lucrative traction inverter, DC/DC converter, and on-board charger markets. Thus, the 650-V range is a “battleground” in which each material device brings distinct and compelling competitive advantages. It should be noted that for higher efficiency — longer range for the same battery or the same range for a smaller battery — and fast charging, EVs are rapidly transitioning to an 800-V bus architecture. At this voltage, 1,200-V SiC MOSFETs have an overall advantage, as they were commercialized in 2011 and have gone through several generations of optimization. SiC insertion in EVs, happening now, is a volume application opportunity that can spur further SiC manufacturing economies of scale and lower system costs.
As SiC continues to grow, the industry is lifting the last barriers to mass commercialization that include higher-than-Si device cost, the presence of basal plane dislocations (BPDs), reliability and ruggedness concerns, and the need for a workforce skilled in SiC power technology to keep up with the rising demand. Currently, the SiC wafer represents 55% to 70% of the overall SiC device cost, a consequence of its unique complex fabrication specifics. Conventional SiC substrates are primarily grown by the seeded sublimation technique at temperatures of ~2,500C, which creates process control challenges. Crystal expansion is limited, requiring the use of large high-material–quality seeds, and the sublimation growth rates can be relatively low, in the order of 0.5 to 2 mm/h. Dislocations propagate through the boule and are present in the device wafers. Furthermore, SiC material hardness, which is comparable to that of diamond, makes sawing and polishing SiC substrates slow and costly relative to Si. In many applications, however, insertion of SiC reduces overall system cost compared with Si, even though SiC devices can cost 2× to 3× more than their Si counterparts. This is due to passive component miniaturization and cooling system simplification enabled by efficient high-frequency SiC operation.
The majority of “killer” defects have been virtually eliminated in modern SiC wafers. BPDs are the major remaining defect degrading device performance and compromising yields. BPDs can propagate from the wafer substrate through the thickness of the epitaxial layers where devices are fabricated. BPDs can also be generated during the high-temperature ion-implantation fabrication process. In commercial wafers, more than 95% of substrate BPDs propagate as relatively “benign” threading edge dislocations in epitaxial layers grown off-axis by CVD. Threshold-voltage instability is the main remaining reliability concern in SiC MOSFETs, which dominate SiC-based power-electronic applications. It is primarily due to the oxide traps at the SiC/gate-oxide interface. A positive shift in the SiC MOSFET’s threshold voltage has the deleterious effect of increasing conduction losses, while a negative shift is undesirable, as it can spontaneously turn the transistor on. SiC devices can be made more rugged by leveraging design tradeoffs. This, combined with intelligent gate drives, can provide adequate short-circuit protection.
To train the wide-bandgap (WBG) workforce and accelerate clean-energy manufacturing, job creation, and energy savings, the U.S. Department of Energy created the PowerAmerica consortium (Figure 2). Today, PowerAmerica is member-supported/-driven and addresses gaps in WBG power semiconductor technology to catalyze its growth.
Figure 2: PowerAmerica is a member-supported/-driven consortium addressing gaps in WBG semiconductor power technology to accelerate clean energy manufacturing, job creation, and energy savings.
In the past six years, PowerAmerica invested $147 million in over 200 power SiC/GaN university-/industry-collaborative projects addressing all major applications, including automotive and rail traction, on-board chargers, aerospace, photovoltaic, flexible alternative-current transmission systems, high-voltage DC systems, microgrids, energy storage, motor drives, UPS, and data centers. Its educational activities have trained 410 university students in applied WBG projects and engaged over 3,700 attendees in tutorials, short courses, and webinars. This contributes to an experienced workforce skilled in fully realizing the WBG system insertion potential.
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Victor Veliadis is the Chief Executive and CTO of PowerAmerica. Prior to entering academia and taking an executive position at Power America in 2016, he spent 21 years in the semiconductor industry where his work included design, fabrication, and testing of 1-12 kV SiC SITs, JFETs, MOSFETs, Thyristors, JBS and PiN diodes, and GaN devices for military radar amplifiers, as well as financial and operations management of a commercial semiconductor fab.