This progress may be crucial for future space probes, jet engines, pharmaceutical processes, and many other applications that require circuits under extreme conditions. Alan Mantoth, a professor of electrical engineering and computer science at the University of Arkansas, said that silicon carbide high-temperature chips enable scientists to place sensors in locations that were previously impossible to place. Mantus was not involved in this new research on gallium nitride. He explained that gallium nitride chips can play the same role in monitoring energy intensive manufacturing processes in natural gas turbines, chemical plants, and refineries, as well as systems that have not yet been thought of.
He said, "We can place this electronic device in places that silicon simply cannot imagine
The performance potential of silicon carbide and gallium nitride under such extreme conditions comes from their wide bandgap. The wide bandgap is the energy gap between the valence band (where electrons bind to molecules) and the conduction band (where electrons can freely participate in current flow) of a material. At high temperatures, electrons in materials with narrow band gaps are always excited enough to reach the conduction band. This poses a problem for the transistors as they will not be able to turn off. The wide bandgap of silicon carbide and gallium nitride requires more energy to excite electrons to the conduction band, so that the transistor will not accidentally remain in the on state at high temperatures.
Compared with silicon carbide, gallium nitride also has some unique characteristics that make its chips perform better under high temperature conditions. The Chu team described their integrated circuit in IEEE Electronic Device Letters this month, which is composed of gallium nitride high electron mobility transistors (HEMTs). The structure of GaN HEMT includes a layer of aluminum gallium nitride film and a layer of gallium nitride. This structure attracts electrons to the interface between two materials.
This layer of electrons is called a two-dimensional electron gas (2DEG), with extremely high concentration and minimal movement resistance. This means that the charge moves faster in 2DEG, allowing the transistor to respond to voltage changes and switch between on and off states faster. The faster movement speed of electrons also enables transistors to carry larger currents at a given voltage. It is more difficult to manufacture 2DEG using silicon carbide, which makes it more challenging for its chips to achieve the performance of gallium nitride devices.
Professor Chu's graduate student Yixin Xiong explained that in order for GaN HEMTs to operate at 800 ° C, some structural adjustments are needed. Some of these measures include minimizing leakage current to the maximum extent possible, that is, the charge that will infiltrate even when the transistor should be turned off. They use tantalum silicide barrier layers to protect device components from environmental influences and prevent the metal outer layer on the side of the device from contacting two-dimensional electron gas (2DEG), as contact with 2DEG further increases leakage current and transistor instability.
Chu said that the development and manufacturing process of chips is much faster than he expected. The team was originally confident in the success of the experiment, he said. But the result was "faster than my best guess," he said.
Despite the significant advantages of gallium nitride, Mantus still has doubts about its long-term reliability compared to silicon carbide. He explained, "People have always been concerned that gallium nitride may develop microcracks at extreme temperatures of 500 ℃ and above, and this phenomenon may not necessarily occur in silicon carbide, so gallium nitride may have reliability issues
Professor Chu also believes that long-term reliability is an area that needs improvement. He said, "We can make some technological improvements: one is to improve its reliability at high temperatures. Currently, I think we can maintain it at a temperature of 800 ℃ for about 1 hour
Gallium Nitride and Silicon Carbide
Mr. Xiong stated that there is still a lot of work to be done to improve the device. He explained that in addition to minimizing leakage current, another function of the tantalum silicide barrier layer is to prevent potential reactions between titanium and AlGaN thin films in the device, thereby damaging the two-dimensional electron gas (2DEG). Mr. Xiong ultimately hopes to completely remove titanium from the device. I want to say that the ultimate goal is to no longer rely on titanium, "he concluded.
Despite potential lifespan challenges, the team's chips are still pushing the limits of electronic device operation, such as on the surface of Venus. If you can maintain it at 800 ℃ for 1 hour, it means you can maintain it for a longer time at 600 ℃ or 700 ℃, "explained Zhu Diwen. The ambient temperature of Venus is 470 ℃, so the new temperature record of GaN may be useful for electronic devices in Venus probes.
Mantus explained that the number 800 ℃ is also important for hypersonic aircraft and weapons. The friction generated by their extremely high speed can raise the surface temperature to 1500 ℃ or higher. What many people don't realize is that when you fly at speeds of 2 or 3 Mach, air friction creates an extreme environment at the leading edge of the wing... guess what? Your radar is located there. Other processing equipment is also located there. These applications are exactly why the US Department of Defense is interested in extreme temperature resistant electronic products, "Mantus said.

When it comes to future plans, Chu stated that the next step is to "expand the scale of the equipment to make it run faster". He also believes that due to the scarcity of chip suppliers capable of operating at such extreme temperatures, the chip may soon be commercialized. I think it's quite mature. Although it still needs some improvements, the advantage of high-temperature electronic products is that it currently has no other options, "he said.
However, the victory of gallium nitride circuits over silicon carbide may not last long. Mantus' laboratory also manufactures high-temperature chips and is working hard to make silicon carbide reach the high temperature level required for Chu to create chips. We will manufacture circuits and attempt to achieve the same temperature using silicon carbide, "Mantus said. Although it is currently unclear who will ultimately win, at least one thing is certain: competition is still heating up.