The High Temperature Problem
Electronics are being deployed in all kinds of applications ranging from the kitchen counter to outer space. The ability to integrate complex capabilities into a tiny space has made electronics the most powerful technology on the planet, and this power allows for any application to be transformed.
But for all the benefits that electronics provides, there are some applications that are very difficult (if not impossible) to deploy them. One such application is extreme heat environments, and this is due to the fact that modern electronics are based on semiconductors such as silicon, solder made from tin and silver, and polymers such as PLA and ABS.
None of these materials are well suited to extended operation above roughly 100˚C, and prolonged exposure often causes failure. However, there are some environments on earth that can reach well over 200˚C, so how do you deploy electronic components in such places?
One option is to install a cooling system that cools down the surrounding air, and then uses this air to cool the electronic components. This is exactly what the Soviets did in the 70s when deploying the Venera lander to Venus. As the temperature on the surface of Venus is around 460˚C, the lander needed to keep itself cool, and the only way to do this was to use refrigeration.
Another option is to switch out electronic components with those designed to work at higher temperatures. While this can be done with ease with resistors and capacitors, doing so with semiconductors is another story. Components that can withstand high temperatures often suffer from increased size, higher cost, and worse performance, thus limiting the degree to which they can be integrated.
Overall, the inability to operate naively in high temperature environments currently limits what engineers can do. If electronics can be easily integrated into high temperature environments, then it would allow for all kinds of applications including deep earth drilling, space exploration, and even nuclear reactor monitoring.
Researchers Create High Temperature Memory Device
Recently, researchers from the University of Southern California have created a high temperature memory device using graphene which is able to function at 700 degrees Celsius, which is hotter than the melting point of some common metals, and is comparable to the lower range of molten lava temperatures. The device, called a memristor, can store information, perform computing operations, and withstand extreme temperatures which makes it ideal for extreme environments.
The new device utilises a tungsten layer as the top electrode, hafnium oxide ceramic as the middle layer, and graphene as the base electrode. The choice for using tungsten as the top layer came down to tungsten having one of the highest melting points among metals (about 3422˚C), while the use of graphene prevents tungsten atoms from diffusing into the hafnium oxide layer, which would otherwise cause short circuits and damage.
According to the researchers, their device is able to store data for more than 50 hours at 700˚C without the need for refreshing, and can survive more than one billion switching cycles. Furthermore, the device is able to operate on just 1.5V with operation speeds in the tens of nanoseconds.
The potential applications for such a device extend far beyond the realm of everyday life. For example, it could be useful for missions where electronics must withstand temperatures around or above 500˚C (for example, reentry from space), and a device that can survive these temperatures would not only reduce mission risk, but also allow for more advanced electronics to be deployed.
Such a device could also be critical in deep-earth drilling for geothermal energy, where equipment faces very high temperatures in hot rock and fluids. These systems would also benefit from the use of high-temperature electronics because harsh downhole conditions make communication and instrumentation challenging.
High-temperature electronics could also find themselves beneficial in nuclear reactors and fusion experiments which both see extremely high levels of radiation and temperatures. The use of high-temperature electronics in such environments would benefit closer observation and maintenance, something which fusion reactors would benefit from.
While the memristor developed by the team is a major step towards high-temperature electronics, the researchers still believe that logic circuits also need to be developed before such devices can be deployed. Furthermore, the current devices were hand-built at sub-microscale in a lab, indicating that scaling up will take time.
Could this be the key to future high-temperature electronics?
It is no secret that many in the industry believe that graphene will play a critical role in future electronics, and there are several reasons for this belief.
The first reason for this belief comes down to its ability to conduct electricity extremely well, which would allow for very fast devices. Graphene-based devices have shown potential for very high-frequency operation (GHz–THz ranges) in research settings.
Graphene is a semimetal with zero bandgap, which complicates making conventional transistors that switch off cleanly. Its high temperature tolerance and mechanical strength also make it attractive for electronics in harsh applications.
But while it is a fantastic material, it has one major drawback that continues to hold it back: it has not been used at scale in commercial electronics. Individual graphene transistors and small circuits have been demonstrated in labs, but large-scale integration has not been achieved. This means that graphene is still more of a long-term promise than a current reality.
Unless researchers can figure out how to reliably integrate graphene into advanced CMOS fabrication processes at scale, it will be difficult for graphene to become a mainstream commercial material. But if researchers can achieve this, then there is no doubt that graphene will become a major material in future electronics.
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