Researchers from the University at Buffalo recently announced a working microscopic transistor made from up-and-coming semiconductor, gallium oxide.
Needle probes on the terminals of the gallium oxide transistor. Image used courtesy of Ke Zeng via the University at Buffalo
What Is Gallium Oxide?
Gallium oxide (Ga2O3) looms prominently as a new semiconductor material. The primary reason is its high bandgap. A bandgap is a measure of how much energy an orbiting electron must absorb in order to “escape” its atom and move from the constricted valence band to the conduction band, analogous to a space vehicle escaping earth’s orbit. In the conduction band, the “liberated” electrons are free to conduct electricity. That bandgap is 4.8 electron volts for gallium oxide, while silicon’s bandgap is 1.1 electron volts. Other competing semiconductors such as gallium nitride and silicon carbide also have slightly lower bandgaps at 3.3 and 3.4 electrons respectively.
Semiconductors devised of gallium oxide, with its higher bandgap, can handle more power and take up less space than devices fabricated with semiconductors with lower bandgaps.
Gallium oxide's crystalline structure. Image courtesy of Orci [CC BY-SA 3.0]
They can also tolerate higher temperatures, which is a major advantage for the rough and tumble world of automotive engineering. This could help solve what Gregg Jessen, principal electronics engineer at the Air Force Research Laboratory, described in an article published in the American Institute of Physics as one of the greatest problems involved in controlling power with semiconductors: the waste of power within a device and the troublesome heat thereby generated.
Another real issue with silicon-based devices is that practical limits in “scaling up” such devices are quickly reaching the possible limits. Not so with gallium oxide, because of its exceptional electrical field strength. As reported in an article published Applied Physics Letters, Jensen and Masataka Higashiwaki make the case that gallium oxide could allow for FETs “with smaller geometries and aggressive doping profiles that would destroy any other FET material.”
A Gallium Oxide MOSFET
Uttam Singisetti, associate professor Department of Electrical Engineering at the University of Buffalo, along with fellow researchers, have taken advantage of gallium oxide’s properties to develop a MOSFET with a breakdown voltage 1,850 volts, more than doubling the previous best for this technology.
This is significant because the higher bandgap means that such a device can handle more power at the same size and weight than previous devices could.
Screenshot from the University at Buffalo
The device they built is 5 micrometers wide and, according to Singisetti, this relatively large size makes it unsuitable for mobile devices. Rather, it is more suited for higher-power applications such power plants and motorized vehicles of all sorts.
As Singisetti states, “We’ve been boosting the power-handling capabilities of transistors by adding more silicon. Unfortunately, that adds more weight, which decreases the efficiency of these devices.” Further, “Gallium oxide may allow us to reach, and eventually exceed, silicon-based devices while using fewer materials. That could lead to lighter and more fuel-efficient electric vehicles.”
Applications for Gallium Oxide Semiconductors
It’s no secret that silicon is the go-to material today for semiconductor devices. But semiconductors are increasingly being called on to fill new roles and certainly one of the greatest challenges facing engineers today is building components that can handle ever more power—without making bandgap demands of space and weight. This is especially true in the automotive field because, while electrically powered vehicles are still thin on the ground, modern cars and trucks are increasingly being controlled electronically.
Semiconductors, electrical cables, and motors are replacing pumps, fan belts, and hydraulics. Yet, these clean, efficient electrical systems, while not requiring as much power as the troublesome, polluting mechanical systems they replace, will nonetheless require controlled power. The promise of gallium oxide devices is more power, less space, and less weight. Keep an eye on research in this space for more semiconductor advancements.
You can see the breakdown of a gallium oxide device at its 1,850-volt threshold in the video below: