The scientific paper by members of the Brazilian community on Materials research featured this month is: GeO2/Ge structure submitted to annealing in deuterium: Incorporation pathways and associated oxide modifications.Bom, N.M.; Soares, G.V.; Hartmann, S.; Bordin, A.; Radtke, C. Applied Physics Letters 105, 141605 (2014); DOI: 10.1063/1.4898062.
Clarifying the processing of germanium for applications in micro and nanoelectronics
Germanium (Ge) is one of the semiconductor materials listed as possible alternatives to silicon for applications in the micro and nanoelectronics industry. However, the processing of materials based in germanium, aiming to optimize its electric properties for these applications is still presented as a challenge to the science.
In this context, a research team from the Federal University of Rio Grande do Sul (UFRGS) investigated the heat treatment (annealing) of germanium structures in deuterium atmosphere (hydrogen isotope which allows the use of analytical techniques specified for its quantification). The results of the study were recently published in the renowned periodical Applied Physics Letters (APL).
The study which the cited article derived from is part of the PhD research, in progress, by Nicolau Molina Bom, supervised by Professor Claudio Radtke in the framework of the postgraduate program in Microelectronics from UFRGS. “This work came up as a sequency of studies developed during my Masters, involving systems of aluminium oxide on germanium (Al2O3/Ge)”, Nicolau reports.
In the Masters’ research, also supervised by Radtke, Bom observed that the deposition of dielectric materials on germanium substrates, as well as its processing by means of heat treatment, induces the semiconductor oxidation and the formation of zirconium dioxide (GeO2). Due to reactions that occur between the oxide that is formed and the germanium substrate, the structure causes physical and chemical changes which bring about the degradation of its electric properties. “Thus, it became clear that the understanding of these mechanisms was fundamental to the use of germanium in industrial applications”, says Bom.
Incorporation of hydrogen
In the article published in APL, the authors report that the heat treatment was carried out in samples of germanium oxide on germanium (GeO2/Ge), of germanium oxide on silicon (GeO2/Si) and of silicon dioxide on silicon (SiO2/Si). One of the effects of the treatment evinced by means of analysis was the hydrogen incorporation, to greater proportions in GeO2/Ge than in SiO2/Si.
Authors assigned this effect to the occupation by hydrogen atoms of oxygen vacancies (points of crystalline network in which there are “vacancies” in the place of atoms that would be expected to be there), brought about during the heat treatment, in the interior of the germanium dioxide and in the GeO2/Ge interface.
Another effect observed by scientists was the oxide layer volatilization, mainly at temperatures superior to 450 oC, leading to changes in the chemical structure of the remaining oxide layer.
Schematic representation of the main results of the article, sent by Nicolau Bom.
Contribution and work applications
“The greatest merit of our study consists in clarifying the physical and chemical process involved in the incorporation of hydrogen in GeO2/Ge structures”, evaluates Nicolau Bom, who is the corresponding author of the article. “Besides, the understanding of these interactions will have a key role in the choice of the appropriate processing parameters in industrial applications involving germanium”, adds him.
In fact, results of this study can be applied, for example, in the development of metal oxide semiconductor field-effect transistors (MOSFET) based in germanium structures. “The MOSFET is the “flagship” of the micro/nanoelectronics industry and is a reference for the Moore’s law”remarks Bom. However, according to the PhD Candidate, the results presented in the cited article can also be useful in manufacturing devices with innovative architectures, such as the quantum well field-effect transistor (QWFET). “The high performance presented by QWFETs – due to the high mobilities obtained by the quantum confinement – set this device as a promising alternative to overcome the physical limitations of the conventional MOSFETs”, states Bom.
The study that the APL article derived from was funded by the INCT Namitec, INCT of Surface Engineering, CNPq, CAPES and FAPERGS.
Physics, Chemistry, Surface Science and Micro/nanoelectronics
The APL article inserts itself in a greater context of research, in the group of “Physical-chemistry of solid surfaces and interfaces” (FQSSI) at UFRGS. The central idea that guides this work is to understand the physical-chemical mechanisms involved in alternative materials to the classic structure SiO2/Si, in such a way to overcome the limitations of the silicon-based nanoelectronics . “In this context, the interdisciplinarity between physics, chemistry and engineering is a natural consequence of this work, where the knowledge derived from the different fields of study complement each other in the investigation of these systems”, remarks him.
Besides the studies about germanium, the group counts on works developed around dielectrics which door has high dielectric constant (the so-called high-k), SiC (material oriented to applications in extreme conditions of temperature, voltage and frequency) and graphene.
Four of the five authors. From left to right, Samuel Hartmann, Nicolau Molina Bom, Cláudio Radtke e Anderson Bordin.
Com bolsa PNPD/CNPq, por 6 meses. Já disponível; renovável por mais 1 ano.
Local: Instituto de Física, UFRGS – Porto Alegre, RS (Programa de Pós-Graduação nível 7, o máximo, por avaliação da CAPES).
Perfil do candidato: Doutorado em Física, Química, Engenharia ou Ciência dos Materiais. Conhecimentos anteriores relacionados ao projeto serão apreciados.
Informações e candidatura: Enviar link para CV-Lattes ou CV completo, indicação de dois professores-pesquisadores de referência para contato (telefone, e-mail, carta de recomendação) e um parágrafo sobre motivações/expectativas para flavio.horowitz@ufrgs.br, até 31/05/2014 (ou, em 2ª chamada, 10/06/2014).
Fernando Claudio Zawislak was born in 1935, in the city of Santa Rosa, state of Rio Grande do Sul (RS), in a family with Polish origins, which lived in the rural area. In decade of 1940, his parents sent him to Porto Alegre, the capital of Rio Grande do Sul, with one of his siblings, so they could study in a boarding school. In 1952, the whole family moved to the city, proceeding with the decision to prioritize the education of the children.
In 1958, Fernando Zawislak graduated in Physics in the Federal University of Rio Grande do Sul (UFRGS). From 1960 to 1961, he took a research internship in the Van de Graff Laboratory of the University of São Paulo (USP) with Professors Oscar Sala and Ernst Hamburguer. There, he had the first contacts with research. Then, he returned to the Physics Institute of UFRGS, started and coordinated an experimental research group in the field of Nuclear Physics. In said field, advised by Professor John D. Rogers, he was granted the PhD degree, for which he was approved “with honors” in 1967, becoming the first PhD in Physics graduated by UFRGS. From 1968 to 1970, he attended his postdoctoral studies in the California Institute of Technology (Caltech), in the United States.
In 1979, he started working in the field of ion implantation and use of ion beam techniques to modify and analyze materials. With this goal, he worked as a visiting researcher for a year in the Ion Implantation Laboratory of Orsay, in the University of Paris (France). In 1981, he founded the UFRGS’ Ion Implantation Laboratory, upon acquiring a 400 kV accelerator. In 1996, he managed to buy a 3 MV accelerator, which allowed to expand the activities of the laboratory to new fields, as semiconductors, polymers, metals and alloys, to name a few. He coordinated the Ion Implantation Laboratory since its foundation up to 2009. Today, the Laboratory is the largest of its kind in Latin America, counting, among its results, with more than 60 graduated doctors, approximately 1,000 papers, and studies developed jointly with groups from Argentina, Australia, Brazil, Denmark, France, Germany, New Zealand, South Korea, Spain and United States. During the decade of 1990, Zawislak took part in the planning and raising of funds of UFRGS’ Electron Microscopy Center and the creation of the UFRGS’ Graduate Studies Program in Materials Science (PGCIMAT).
Professor Zawislak retired from UFRGS in 2005. He is an Emeritus Professor of the institution, a level 1A (the highest one) researcher of the BrazilianCouncil for Scientific and Technological Development (CNPq), sitting member of the Brazilian Academy of Sciences, as well as Commander with the Grand Cross of the Brazilian National Order of Scientific Merit. During his career, he graduated 14 doctors and 16 masters, authored or co-authored more than 160 scientific articles in indexed international journals, and was the chairman of, among others, two of the most important international conferences in the field of ion implantation, the Ion Beam Modification of Materials (in the city of Canela, RS, 2000) and the Radiation Effects in Insulators (in the city of Gramado, RS, 2003), both held for the first time in a Latin American country.
Following there is a brief interview with the researcher.
SBPMat Newsletter: – In your own point of view, what are your main contributions to Materials Science and Engineering? Tell us what led you to achieve them, as well.
Fernando Zawislak: – I started my scientific career working in the field of Experimental Nuclear Physics. I even completed my Doctorate in this field. In 1968, I went to California to attend my postdoctoral studies in the California Institute of Technology. There, in this institute, the field of Materials Science was getting started, and, more specifically, the field of ion implantation and analysis of ion beams. The United States had decided to invest heavily in the field of interdisciplinarity, mainly in Materials Sciences. There, in Caltech, I didn’t work with Materials, but followed the studies. Then I thought, “If I have the opportunity, I am going to start this field of ion implantation and materials studies with ion beams in Brazil.”
California was one of the three or four places in the world where the field of ion implantation and materials analysis was being established. And I used to attend the seminars, despite working in other field. Then, I returned to Brazil in 1970, but only in 1982 I managed to install the Ion Implantation Laboratory. It was a radical change in my life, but I think this is important: all researchers should, if possible, change their fields once or twice along their careers, in order to always move to a more modern one. I was working in an old field, in which it was hard to publish, while ion implantation was just beginning, and until now is very important.
In this field of Materials Science, which I started in 1982, when I changed mine, I acquired the first implanter, and graduated, in this twenty-something years, up to my retirement, many doctors and masters, authored more than one hundred published papers and developed studies, basically, in the field of materials nanostructures and modification of materials with ion beams.
Actually, I was interested in interdisciplinarity, and the field of Materials Science is clearly interdisciplinary. Such interdisciplinarity is absolutely necessary, as the United States discovered, founding, around that time, twenty interdisciplinary centers. So, in Brazil, once I returned, I started to struggle for this interdisciplinarity. Everyone was in favor, really, but neither the university, nor the funding agencies supported the interdisciplinary fields. There was domination of the classic subjects. Each department focused its own field, and, when new ones were on the rise, people didn’t want to share, didn’t want lose students, scholarships… Well, but we struggled quite a lot, and I was one of those who fought for the creation of the Graduate Program in Materials Sciences in UFRGS, jointly with colleagues from Physics, Chemistry, Engineering. And we managed to do it.
Then, the results of my activity with Materials were, on one hand, the Laboratory of Ion Implantation, and, on the other, the creation of the Graduate Studies in Materials Science. I also acted very intensely, trying to convince people, during scientific meetings, that it was absolutely crucial to enter in the interdisciplinary field, because all great advancements in research and innovation are interdisciplinary.
Up to this day, the Ion Implantation Laboratory is the largest in Latin America, and is similar in efficiency and equipment to many good labs around the world. Our laboratory has 25 doctors, considering that there are always 21 or 22 permanent ones, and 3 or 4 postdoctoral fellows. It counts with 30 graduate students, half a dozen of technicians, plus the undergratuate students… We have a total of more than 50 people in the lab. I headed it until 2010, when I was replaced by my colleague, a young man, Pedro Grande.
The Graduate Studies course in Materials Science, I think, is also doing very well, but there are hardships yet. I supervised students of the course, but now I am retired.
SBPMat Newsletter: – In your opinions, what are the main current challenges in the field of ion implantation, regarding Materials Science and Engineering?
Fernando Zawislak: – I think the key point about ion implantation is that it comprises several fields of research, starting with Physics, Chemistry, many types of Engineering, Biology, Genetics, Geology, which are all fields where the ion implantation and, mainly, the analysis of materials in the accelerator, are important. We managed to measure very small amounts of impurities, for example. For the last five years, we introduced microbeams, beams focused to the size of a micron. Such beams have conditions to analyze microstructures from Geology or Microelectronics. Now, we have two accelerators in the lab, a smaller one, which was the first, and another, with 3 MV, acquired in the end of the decade of 1990. The techniques, such as RBS, MEIS etc, even measure the shapes and sizes of the nanoparticles. We implant a impurity in a matrix, and, depending on the energy of the implantation, and the temperature, we can produce nanoparticles from 2 or 3 nm to 100 nm. So, I think that the future and the challenges are both great, and the technique has a lot of potential in many fields. For example, we are analyzing the wine made in Rio Grande do Sul. I think that the lab is doing very well. I retired but, thank God, I was well replaced. Now, it is doing even better than when I was the coordinator.
SBPMat Newsletter: – Tell us which are your main current occupations, and your projects for the future.
Fernando Zawislak: – Well, I am not really thinking that much about the future. I have been retired for ten years, I’m an Emeritus Professor. I still receive CNPq’s sponsorship, as I continue to produce papers, but now my productivity, strictly in research, is decreasing. I’m using my time to help younger colleagues, attending some societies, some councils… In short, activities for someone who is already retired. My last student, a doctor, graduated last year, and I’m not accepting students anymore, but I still help, if they ask me for something.
SBPMat Newsletter: – Would you like to leave a message to our readers who are starting their careers as scientists?
I think that what is important for researchers is choosing a career in a field that they like. As a Professor, many students asked me “Which career my children should follow”? , and I used to answer “Any one, as long as they like it. All are good”.
I also think that young people, now, shouldn’t narrow their undergraduate studies in just one field, that much. I think they should be open-minded to interdisciplinarity, collaborate with other colleagues, and eventually attend subjects in other fields. To me, it is very important, because focusing too much in one field has a very restricted specter: they may end up teaching at a university. And I think that the expectation in Brazil is for young people to move on from college and create industries, innovation, etc.
Penultimate advice: choose an advisor that works in a modern field of work.
And the last one is: you must have an entrepreneurial spirit. That is lacking. In Brazil, this issue of the interaction between the industry and university is frequently discussed, but there is no way, it is not possible to transform an “old” industrial that became rich making screws, and convince him that he must hire doctors and build a research lab. The young people are the ones who must initiate this. In the results of our universities, some successes in technological innovation were achieved by students that complete their doctorate and even their undergraduate studies. So, how do we produce young entrepreneurs? They must look for internships, in the industry, if possible, and go to a country where there is such entrepreneurial culture, as, for example, the United States, Germany, Korea or Japan, Here in Brazil, chemists generally display more of an entrepreneurial spirit than physicists, some fields of engineering too, but it is still lacking, and it is extremely important. It would be important to make youth aware that they can leave college and go to a new field, to make technonogical innovation happens.
