Some technological revolutions are flashy, and some are almost invisible. We’re quite familiar with the flashy ones; they’ve given us powerful computers we can hold in the palms of our hands, devices that can pinpoint our locations by way of orbiting satellites, and the ability to bank and shop without leaving our homes.
But none of these innovations would have occurred without the technology that delivers power to them. Over the last half century, a more subtle revolution in power electronics has provided us with compact and efficient semiconductor devices that can manipulate, regulate, and convert electricity from one form to another.
Silicon has long been the semiconductor of choice for such power electronics. But soon this ubiquitous substance will have to share the spotlight. Devices made from silicon carbide (SiC)—a faster, tougher, and more efficient alternative to straight silicon—are beginning to take off. Simple SiC diodes have already started to supplant silicon devices in some applications. And over the last few years, they’ve been joined by the first commercially available SiC transistors, enabling a new range of SiC-based power electronics. What’s more, SiC wafer manufacturers have steadily reduced the defects in the material while increasing the wafer size, thus driving down the prices of SiC devices. Last year, according to estimates made by wafer maker Cree, the global market for silicon carbide devices topped US $100 million for the first time.
Within five years, we should see this market balloon as SiC devices find their way into power electronics for hybrid and all-electric vehicles, creating simpler and more efficient power systems. SiC power devices will also become vital in solar and wind energy creation, by reducing the energy lost as electricity is converted to a form that can be used on the power grid. Eventually, silicon carbide could remake the grid itself by eliminating the need for bulky substation transformers, thereby saving an enormous amount of energy that is now wasted as electricity makes its way from power plants and other sources to its final destination. Although the field of SiC power electronics is still relatively immature, we expect it’s in for a big growth spurt.
Silicon-based devices are so mature and inexpensive to manufacture, it might be hard to believe that any material could shake silicon from its perch. But silicon carbide is quite special. Many of the material’s most attractive properties stem from a single physical feature: SiC’s bandgap, the energy needed to excite electrons from the material’s valence band into the conduction band. Silicon carbide electrons need about three times as much energy to reach the conduction band, a property that lets SiC-based devices withstand far higher voltages and temperatures than their silicon counterparts.
One of the biggest advantages this wide bandgap confers is in averting electrical breakdown. Silicon devices, for example, can’t withstand electric fields in excess of about 300 kilovolts per centimeter. Anything stronger will tug on flowing electrons with enough force to knock other electrons out of the valence band. These liberated electrons will in turn accelerate and collide with other electrons, creating an avalanche that can cause the current to swell and eventually destroy the material.
Because electrons in SiC require more energy to be pushed into the conduction band, the material can withstand much stronger electric fields, up to about 10 times the maximum for silicon. As a result, a SiC-based device can have the same dimensions as a silicon device but withstand 10 times the voltage. What’s more, a SiC device can be less than a tenth the thickness of a silicon device but carry the same voltage rating, because the voltage difference does not have to be spread across as much material. These thinner devices are faster and boast less resistance, which means less energy is lost to heat when a silicon carbide diode or transistor is conducting electricity.