High-Temperature Transistors Hit New Record

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Two semiconductors – silicon carbide and gallium nitride – are the rivals in a heated competition (literally) to make circuits capable of operating at the highest temperatures. The silicon carbide chips had taken the lead, operating at 600 ° C but the gallium nitride, which has unique characteristics that make it more functional at high temperatures, has now exceeded the SIC. Researchers from the Pennsylvania State University led by Rongming CHU, professor of electrical engineering, have designed a gallium nitride chip capable of operating at 800 ° C – enough to melt the table salt.

Development could be essential to future space probes, jet engines, pharmaceutical processes and a multitude of other applications that need circuits for extreme conditions. High temperature fleas in silicon carbide have allowed scientists to put sensors in places they were not able before, explains Alan Mantooth, an eminent professor of electrical and computer engineering at the University of Arkansas, which was not involved in the new result of Gallium nitride. He explains that the Gallium nitride chip could do the same to monitor the health of natural gas turbines, manufacturing processes with high energy intensity in chemical factories and refineries, and the systems of which no one has thought yet.

“We can put this kind of electronics in places that silicon cannot even imagine going,” he says.

The silicon carbide potential and gallium nitride to occur in such extreme conditions comes from their large prohibitions. These are the energy differences between the valence bands of materials, where the electrons are linked to the molecule and the conduction strip, where they are free to contribute to the flow of electricity. At high temperatures, electrons in materials with a narrower prohibited strip are still sufficiently excited to reach the conduction strip. This presents a problem for transistors because they will not be able to go out. Large prohibitions of silicon carbide and gallium nitride require more energy to excite electrons to the conduction strip, so that transistors are not always involuntarily lit in high temperature environments.

Gallium nitride also has unique characteristics compared to silicon carbide which allow its chips to work better in high heat conditions. IC of the CHU group, which they described this month IEEE electronic device lettersis made up of what are called transistors with reduced mobility of gallium nitride (HEMT). The structure of Gan Hemts implies a film of aluminum gallium nitride on a layer of gallium nitride. The structure attracts electrons to the interface between the two materials.

This layer of electrons – called a two -dimensional electronic gas (2deg) – is very concentrated and moves with little resistance. This means that the load moves much faster in the 2deg, which led the transistor to be able to respond to tension changes and to switch more quickly between its states and outside the states. The faster electron movement also allows the transistor to transport more current in response to a given tension. The 2deg is more difficult to produce using silicon carbide, which makes it more difficult for its chips to correspond to the performance of gallium nitride devices.

To coax a HEMT GAN in the operation at 800 ° C, made some modifications to its structure, explains Yixin Xiong, a student graduated from CHU. Some of these measures involved minimizing the leakage current, the load that sneaks even when the transistor is supposed to be extinguished. They did it using a tantalum sicide barrier to protect the components of the environment from the environment and preventing the outer layer from the metal on the sides of the device to touch the 2deg, which would have further increased the leakage and instability in the transistor.

Penn State engineers have tested 800 ° C -raised electronic mobility transistors.Rongming CHU / Pennsylvania State University

CHU says that the chip research and manufacturing process has become much faster than it had planned. The team had been convinced that the experience would work, he said. But it was “faster than my best supposition,” he says.

Despite the notable advantages it presents, Mantooth is concerned with the long -term reliability of Gallium nitride compared to silicon carbide. “One of the things that people have been concerned about GAN at these extreme temperatures, 500 ℃ and more, is microfractures or microfissuries [which is] Not something we necessarily see in silicon carbide, so there can be reliability problems ”with Gan, he explains.

CHU is suitable that long -term reliability is an area of improvement, saying: “There are some technical improvements that we can make: it is more reliable to a high temperature. Right now, I think we can keep 800 ℃ for probably an hour. ”

Gallium nitride vs silicon carbide

There is still a lot of work to do to improve the device, explains Xiong. He explains that apart from the minimization of the leakage current, a function of the Sicide Tantale barrier is to prevent the titanium from the device from reacting potentially with the film Algan, which could destroy the 2deg. Finally, Xiong wants to completely remove the titanium from the device. “The ultimate goal, I would say, is not to count on titanium,” he concludes.

Despite its potential challenges of longevity, the group’s chip pushes the limits of the place where electronics can work, as on the surface of Venus. “If you can maintain it for an hour at 800 ℃, this means that at 600 or 700 ℃, you can keep it longer,” said CHU. The ambient temperature of Venus is 470 ℃, so the new Gan temperature record could be useful for electronics in a Venus probe.

The figure of 800 ℃ is also important for planes and hypersonic weapons, explains Mantooth. Their extreme speeds generate a friction which can heat the surface to 1500 ℃ or more. “One of the things that many people do not do is that when you fly to Mach 2 or Mach 3, the friction of the air creates an extreme environment on the wing attack edge … and guess what? This is where your radar is. This is where there are other treatment equipment.

Regarding plans for the future, CHU says that the next steps are to “develop the device to make it work more quickly”. He also thinks that the chip can be ready for marketing not too far, because there are so few flea suppliers capable of operating at such extreme temperatures. “I think it’s quite ready. This requires some improvements, but the right thing about high temperature electronics is that there is nothing else there, “he said.

The victory of the gallium nitride circuit against his companions in silicon carbide may not last long. The Mantooth laboratory also manufactures high temperature fleas and works to obtain silicon carbide to reach the heat levels that CHU has. “We will make circuits to try to attack the same temperatures with silicon carbide,” explains Mantooth. Although it is not clear that will eventually end up over, at least one thing is certain: the competition is still heating up.