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Posted: May 12, 2014
The end of silicon as material of reference for power electronics devices
(Nanowerk Spotlight) In the long history of semiconductor devices fabrication, the word “semiconductor” has almost always stood for “silicon”.
Basically, all the history of microelectronics, from the invention of the transistor made by William Shockley in 1956 until now, has been based on silicon as the material of reference.
While it is true that other materials such as gallium arsenide have been used for specific applications such as infra-red light emitting diodes and solar cells and that some particular applications in photonics have not adopted silicon due to some inherent limitations of this material, this has almost never been the case with conventional, mainstream microelectronics.
The recent rise of the new market of power electronics creates new challenges for engineers and material specialists as this new market requires a totally new set of material properties that do not exactly match those of silicon. The biggest point of attention for power electronics is breakdown voltage, that is, the highest voltage applicable to the device before it breaks down and starts to become non-functional.
Traditional silicon MOSFET devices have a breakdown voltage that is relatively low and not enough for many applications so much research has been done in the past on devices capable of withstanding higher voltages
Probably the currently most viable solution to the problem has been found by General Electric engineer and scientist Dr. Jayant Baliga who introduced the insulated-gate bipolar transistor (IGBT) in the early 80s.
The introduction of the IGBTs has been proven extremely successful for the power electronics industry as IGBT devices have a higher breakdown voltage than MOSFETs, even if there are some drawbacks such as the switching speed, which is usually higher in MOSFETs than IGBTs. Therefore IGBTs have been used in a wide range of applications such as electric vehicles, high-speed trains among others.
However, with the always more demanding power electronics industry looking for devices capable of sustaining higher voltages, the adoption of new, more capable materials has been studied.
As Herve Branquart, director of automotive solutions at ON Semiconductor, stated recently “there are limits about the use of silicon [in the power electronics market] and adoption of new materials has to be investigated”.
Two materials have emerged as the most prominent candidates for the replacement of silicon for power electronics devices: silicon carbide (SiC) and gallium nitride (GaN).
Even if silicon carbide and gallium nitride are without doubt the main two candidates for replacing in part or totally silicon in power electronics, as Drew Nelson, president and CEO wafer manufacturer IQE, stated: "alternatives [for power electronics] are not limited [to GaN and SiC] but you can work with virtually all the materials in the periodical table to find the best compound that fit your customer needs”
The main reason behind the adoption of silicon carbide and gallium nitride is without doubt the higher breakdown voltage due to their much wider band gap that allows devices built with such materials to be more compact and smaller per given voltage requirement when compared to their silicon-built counterparts.
It remains to be seen which of the two will become the heir of silicon as material of reference for the power electronics industry.
By Matteo Martini, a nanotechnology expert based in Tokyo Japan, CEO of Martini Tech and specialized in nanoimprinting, PSS patterning, GaN MOCVD deposition, sputtering, MEMS foundry and other microfabrication-related services.