What makes gallium oxide power electronics so successful over competitors has to do with the material being composed of a 5–electron-volt bandgap, which is approximately 3.4 eV higher than gallium nitride and 3.3 eV higher than silicon carbide. Bandgap measures the energy required to boost an electron into a conducting state. A larger bandgap allows material to withstand a stronger electric field, which makes it possible to use a thinner device for a given voltage. This is so important because the thinner the device, the lower its resistance is, thus making it much more efficient.
Flosfia’s engineers have found a way to improve the device’s architecture and make the diode chip thinner. The method involves growing the gallium oxide crystal on a sapphire substrate. Flosfia chief technology officer Masaya Oda found that “the gallium oxide epilayer can easily lift off the sapphire substrate.” Separating the device from the foundation allows the chip to be bonded to a highly conductive, heat-sucking material, which lets it operate at a lower temperature.
Since sapphire is notably cheaper and already marketed due to its use in light-emitting-diode manufacturing, it makes the most sense to use. To make gallium oxide devices, the process involves heating sapphire substrate, where a mist of particles is then swept into the chamber of nonreactive “carrier gas.” The mist contains metal compounds and decomposes when it hits the hot substrate, thus forming a film of gallium oxide. Because the chamber never has to be completely evacuated, the entire process can be cycled through quickly, which also cuts down on the cost.
During the testing process, the engineers at Flosfia noted the results: one device combined a breakdown voltage of 531-V (the potential needed to reverse the flow of current) with an on-resistance of 0.1 mΩ/cm2, which significantly exceeds the limits with silicon carbide.
The highest breakdown voltage reported was 855 V. This may sound like a modest number, but because the diodes are bare chips, this is perfectly normal. By introducing insulating layers into the simple device, significant improvement will be made.
These findings indicate that gallium oxide semiconductors have the potential to become industry leaders once they are commercialized and their benefits are broadcasted.