One of the benefits of the interest in nanomaterials and graphene in particular is that the tools for investigating the material properties and the means for producing the materials continue to evolve. Electronics and more specifically semiconductors have been challenged to operate at “high” temperatures. 125oC is the “normal” maximum operating temperature for widely distributed electronics. This limit is the typical specified upper value for both military and automotive electronics. [Note: the temperature of a vehicle can reach these extremes in the engine compartment.] This temperature limit was developed based on the stresses created in a device due to expansion/contraction, changes in the mobility of electronics at higher temperatures, possible unwanted chemical reactions (e.g., dendrite growth), and having minor lattice faults propagate. There are a number of other concerns, but these provide examples of issues with higher temperatures.
There has been s quantity of research in finding 2 dimensional materials that can be fabricated and exist in the presence of possible external factors. (For readers who are unfamiliar with 2 dimension materials, the term refers to crystalline materials that are one atom thick. Although, there are some unusual properties in materials that are a few atoms think and these may be included in the overall category.) Some of the early research investigated Boron Nitride (BN) and Molybdenum Disulfide (MoS2). (A listing of some recent materials is available on Wikipedia [Ref. 1]. The potential applications have not matured. Research continues to look for materials that can provide reliable performance in extreme conditions.
Recent development [Ref. 2] have provided a hope for very high temperature electronics. MoS2 has been shown to have the potential for transistors working above 220oC. The explanation for MoS2 being superior to Silicon is that the MoS2 bandgap is 1.9 eV versus Silicon 1.2 eV. (Note: the actual material survives about the working temperature, but the entire circuitry has to be able to function.) When a semiconductor device is operated, there are portions of the device that are operating well above the measured temperature. A significant portion of the power into the device is converted into heat.
This brings us to the question: “So What?” The reason for the interest in higher temperature electronics is there are many applications where having better understanding of the actual events that are occurring would be very valuable. Applications where this would provide information includes jet engines and deep wells that include both oil & gas and geothermal. If you want to learn about higher temperature transistors, please check the work from the University of Utah on plasma transistors [Ref. 3] for potential applications in nuclear reactors at temperatures of up to 790oC.
As pointed out in the last blog, the main issue will remain the ability to mass produce these novel devices in sufficient quantities. To compete against traditional transistors in most applications, the quantity produced must be very large. Current semiconductor manufacturing techniques produce billions of transistor per second with very high yield. We are not close to that with anything under development. It will be a while before that happens, but not an extremely long time.
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