The secret of SiC's sudden success

Silicon carbide has been touted as a wonder material for power semiconductors, but it has only recently become a commercial success. What was the impetus for SiC's success, and what are the future prospects?

Silicon carbide (SiC) has existed since recorded history (it occurs naturally as a product of cosmic phenomena such as supernovae), but it was first synthesized in 1891. After discovering that the lustrous hexagonal crystals were nearly as hard as diamond and could be produced industrially in large quantities as chips and powders, Aschen found SiC as an incredibly effective abrasive and had his first career. It gave me an opportunity to build.

Of course, for today's electronics engineers, SiC serves a completely different role. SiC power semiconductors can increase energy conversion efficiency, withstand higher voltages and currents, and withstand higher operating temperatures than traditional silicon-based devices, making them ideal for power supplies in data centers, wind and solar power generation. It provides important benefits for equipment such as power conditioning modules, traction inverters in electric vehicles.

But why now? Since the early 20th century, there have been researchers who have studied the electrical properties of SiC. However, these properties were marginal and SiC was quickly replaced by compounds such as gallium arsenide and gallium nitride. With a 10- to 100-fold increase in output, these compounds became the first LEDs, and SiC remained in the lab as a synthetic semiconductor material still looking for applications.

All of this was 40 years before the transistor was discovered, but SiC's properties offer compelling theoretical advantages as semiconductor technology advances. The thermal conductivity of SiC is 3.5 times that of silicon. It can be heavily doped to achieve high conductivity, while maintaining high electric field strengths without failure. Not only does it operate to high temperatures, it is mechanically very stable and has a low coefficient of thermal expansion. So how did silicon emerge at the dawn of the transistor revolution?

The simple answer to this question is economics. Historically, SiC's Achilles heel has been relatively poor in mass productivity, making it difficult to produce high-quality SiC crystals. A wide variety of defects such as edge dislocations, various screw dislocations, triangular defects, and basal plane dislocations occurred in large numbers even on small-sized wafers. In addition, the reverse blocking performance of transistors and diodes is degraded, and the devices do not work effectively. There was also a problem with the interface between SiC and silicon dioxide (SiO2), which is necessary for manufacturing MOSFETs and IGBTs.

Silicon paved the way

While these challenges have prevented chip makers from realizing the full performance, power density and reliability improvements possible with SiC, silicon semiconductors have proven easy to manufacture at commercial yield levels. and has taken the world of power electronics by storm. However, silicon technology is currently unable to deliver the continuous improvements required in areas such as data center power, automotive and renewable energy.

Fortunately, researchers' efforts to overcome traditional barriers to commercialization of SiC are bearing fruit. The increased purity of SiC wafers has improved yields and enabled manufacturers to transition from 4-inch wafers to 6-inch wafers. This is believed to reduce device costs by 20-50%. Production of 6-inch wafers started around 2012. In addition, the development of processes such as nitridation (annealing with nitrogen dioxide or nitrogen oxide) has made it possible to grow silicon dioxide films on SiC substrates, which is required for the production of high-performance power MOSFETs and IGBTs. Masu.

While silicon-based devices have more or less reached their performance limits, ingenious designers continue to squeeze every last drop of performance, but the latest SiC technology is advancing even faster. Optimized device architecture and dimensions, improved parasitic diode behavior, and new package construction enable SiC native performance to outperform silicon as a high-performance, high-efficiency, ultra-rugged successor in today's most demanding applications Big gains are realized that extend the top advantage. Also, higher voltage devices such as UnitedSiC's 1200V SiC JFET are emerging.

Many projects cannot afford to start with a clean circuit design, and some SiC MOSFETs are not an easy drop-in upgrade of existing silicon devices, requiring circuit re-optimization, It is necessary to review the gate drive voltage and improve the switching frequency.

Qorvo's cascode can provide the bridge from the silicon of the past to the future of SiC that some system vendors need. Co-packaging low-voltage silicon MOSFETs and SiC JFETs to drive high power makes possible drop-in upgrades necessary to take advantage of SiC efficiency, robustness, and power density commitments can be minimized. Companies like Sweden's Micropower Group, a manufacturer of industrial battery backup systems, have successfully replaced obsolete silicon MOSFETs with Qorvo's SiC cascodes, resulting in a 10% efficiency improvement at light loads and a immediately succeeded in increasing the efficiency of the 1%.

After more than 100 years and career changes, the time has come for SiC to play an active role as a valuable power semiconductor technology.

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