There are still obstacles to bridge before nanoelectronics can be integrated in our everyday electronics, and thereby bring better performance and reduced energy needs. One of the challenges is about the production of the transistors, MOSFETs, that need be of a good and consequent quality. In order to make it possible to address that problem in a systematic way Markus Hellenbrand has focused his thesis work on measuring and analysing the defects, or ‘traps’ in the electrically active material in the vertical MOSFET stacks. The thesis is titled ‘Electrical Characterisation of III-V Nanowire MOSFETs’ and will be defended 12 June at 9:15. We have spoken to the author.
Markus Hellenbrand’s research has covered a range of topics around metal-oxide-semiconductor field-effect transistors. This term describes one of the most important components of all our electrical applications like computers, smartphones, servers to host information on the internet and so on.
“The common goal of all my investigations was to find out how transistors can be improved for lower power consumption and for higher operation frequencies”, Markus comments.
“In the Nanoelectronics group, where I did my research, we use so-called III-V materials to build transistors. These materials have very good current transport properties, which allow lower supply voltages than in the current industry standard silicon. Like with many things, unfortunately, it is difficult to fabricate perfect materials, so that real manufactured transistors suffer from material defects. I measured the effects of such defects on the transistor performance, for example electrical noise or drift during operation, so that we know what will have to be improved. I also measured the high frequency performance to find out what limits the operation frequency of these transistors, and I looked into so-called Tunnel Transistors, which use quantum mechanical tunnelling to control the device current”, he continues.
Left: Measurement (circles with error bars) of low-frequency noise in a III-V nanowire MOSFET with a fitted model (lines). Right: From such measurements, the number of material defects Nbt in the gate oxide can be calculated. The different lines represent different types of transistors; curved lines and straight lines in boxes represent different models.
What made you want to pursue a PhD?
“I always wanted to know more about everything and always wanted to understand how things work. According to my parents already as a small child. The idea of doing research, of finding out really new things myself, and of really immersing myself in a subject of my choice sounded just so fascinating. So I wanted to pursue PhD studies already since high school. And indeed, it has been rewarding, I am not disappointed”, Markus says.
“Physics is the most interesting subject for me since it is concerned with the most fundamental things in the world – about what is keeping everything together, and about how everything works. At the same time, I want to do something that can benefit society. In nanoelectronics, my PhD subject, I believe that these two come together perfectly. Nanoelectronics combines quite fundamental physics with the aim to create devices that can improve life for everyone."
Will your results come to use?
“In nanoelectronics, as in many other engineering subjects, we have to be aware that our research has to be many years ahead of industry applications. It takes a long time to come all the way from basic science to consumer applications and nowadays, most research is a ‘contribution to the bigger picture’ rather than the one revolutionary finding, which changes the world. So it is unlikely that my research this far will lead to specific applications on a store shelf where I can say ‘Hey look, this is from my research!’. However, it is quite certain that the principles which I worked on will be applied in future transistor technologies. Some of my findings, as for instance my model for high frequency transistor operation, are certainly relevant immediately. Other results will be useful for ongoing research that will continue for several years”, Markus says.
What are your plans?
“I want to stay in academia and continue to find out new things! Besides doing a PhD, it has been a dream of mine to work at the University of Cambridge in the UK and indeed, I was offered a position as a research associate there beginning in September. I will be working on more fundamental material physics again, which I am very excited about. I will have to see, how the ongoing pandemic will complicate moving to the UK, but I am hopeful that it will work out one way or the other."