Advancing Power Electronics by Multidimensional Devices 

Yuhao Zhang

Thursday March 9th, 2023 – 1:00-2:00 pm

Dreese Labs 260 and zoom

Abstract: Power electronics technologies provide electrical energy conversion using semiconductor devices and passive components. The global power device market reaches US$40 billion and is rapidly expanding, driven by applications like electric vehicles, data centers, consumer electronics, electric grids and renewable energy processing. 

Power device advances are driven by materials and device architectures. In addition to using wide- or ultrawide-bandgap materials, multidimensional architectures – such as superjunction, multi-channel and multi-gate – can also improve device performance, regardless of the underlying material technology. These structures enable electrostatics engineering in additional dimensions and bring the benefits of geometrical scaling into power devices.

This talk presents our efforts in developing multidimensional power devices in gallium nitride (GaN), which have set several new records in power device performance and thus expanded the GaN’s application space from 10 V to 10 kV. These devices hold great potential for advancing the speed, efficiency, and form factor of power electronics systems, and some of them are currently being commercialized. In addition, our work on packaging, thermal management and device reliability/robustness evaluation will be also introduced, all of which are essential to exploiting the breakthrough device performance in power electronics systems.  

Bio: Dr. Yuhao Zhang is an assistant professor at the Center for Power Electronics Systems (CPES), the Bradley Department of Electrical and Computer Engineering, Virginia Tech, and he is leading the power semiconductor research at CPES. CPES is one of the largest university-based power electronics research centers in the U.S. Before joining CPES in 2018, he worked as a postdoctoral associate at the Massachusetts Institute of Technology (MIT) from 2017 to 2018. He received his Ph. D. and S. M., both in electrical engineering from MIT in 2017 and 2013, respectively. Before joining MIT, he received his B. S. in physics from Peking University in 2011. His research interest is at the intersection of power electronics, microelectronic devices, and advanced materials. He has authored over 100 journal papers (EDL, T-ED, T-PEL, Nature, Nature Electronics, etc.) and conference proceedings (IEDM, ISPSD, IRPS, APEC, etc.) and holds 5 granted U. S. patents. He received the MIT Microsystems Technology Laboratories Doctoral Dissertation Award in 2017, the IEEE George Smith Award in 2019, the National Science Foundation CAREER Award in 2021, the Outstanding New Assistant Professor Award of Virginia Tech Engineering in 2021, and the Faculty Fellow Award of Virginia Tech Engineering in 2022. His students received the Ph.D. Thesis Talk Award of the IEEE Power Electronics Society, the Virginia Tech Graduate Student of the Year Award, and the APEC Best Presentation Award.

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From Al(Ga)N/GaN to Ga2Opower switching devices: Status, challenges and perspectives of WBG devices

10-11 am,  20th May, 2021

Joachim Würfl

Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Strasse 4, 12489 Berlin – Germany

Abstract: Wide bandgap devices are very promising for future electronic systems and energy efficient solutions. This presentation provides an overview on different technologies for power switching devices with a special focus on particular issues to be handled for assuring industrial exploitation.  It will mainly relate to work going on at FBH, Berlin, Germany. Technology and performance of lateral and vertical GaN and Ga2O3 power switching devices will be considered and critically commented.

Biography: Dr. Joachim Würfl received his PhD in Electrical Engineering at the Technical University of Darmstadt, Germany in 1989 where he worked on technology and design of high temperature and high power GaAs-based devices. As a post-doctoral he developed micro-mechanical sensors based on III/V compound semiconductors at the same university. Dr. Würfl joined Ferdinand-Braun-Institut (FBH) in 1992 where he has been responsible for clean room technology, process development and processing of III/V optoelectronic and microwave devices. Additionally he has been in charge of design and development of power HBTs and power GaN devices. In 2007 he has been appointed head of the newly implemented research area GaN electronics. In this function he is managing several projects on GaN-based discrete power devices, X- and Ka-band MMICs as well as high voltage power devices including Galliumoxide technology. He is responsible for design, technological implementation, characterization and reliability testing of these devices. Furthermore he is CEO of the FBH spin-off company Berlin Microwave Technologies AG (BeMiTec). In terms of academic education Dr. Würfl delivers lectures at Technical University Berlin (TUB) and National Yang Ming Chiao Tung University (NYCU), Hsinchu, Taiwan.

Bulk β-Ga2O3 single crystals – growth by the Czochralski method and physical properties

10-11 am, 3rd June, 2021

Zbigniew Galazka

Leibniz-Institut für Kristallzüchtung, Max-Born-Str. 2, 12489 Berlin


Abstract: The quest for wide bandgap materials continuously increases to meet the demands of the environment on energy saving. Successful development of wide bandgap SiC- and GaN-based power devices is nowadays followed by the research on ultra-wide bandgap oxide semiconductors to further increase the conversion efficiency and switching high voltages. One of such materials, attracting recently the most scientific and technological attention, is b-Ga2O3. It is an n-type semiconductor with a bandgap of 4.85 eV, large breakdown filed of 8 MV/cm, a wide doping range with free electrons (roughly between mid 1015 – mid 1019 cm-3), and a good carrier mobility (around 150 cm2V-1s-1). The availability of bulk single crystals grown from the melt by the Czochralski, EFG, and Bridgman methods enables wafer preparation for homoepitaxial growth of thin films, and device fabrication. In addition to power electronics, b-Ga2O3 is also suitable for UV optoelectronics, such as solar- and visible-blind photodetectors, and for detection of nuclear radiation.

b-Ga2O3 is, however, thermally unstable at high temperatures, that in a combination with high melting point of about 1800°C makes the growth of large single crystals of high structural quality challenging. In particular, a high decomposition rate of Ga2O3, that requires a high oxygen concentration in a growth atmosphere, combined with the use of iridium crucibles had to be addressed and resolved. Here, I will discuss particularities of the growth of bulk b-Ga2O3 single crystals by the Czochralski method and highlight critical issues associated with the growth. This includes thermodynamic aspects of the growth, and impact of doping and free carries on the growth stability. The crystals will be discussed in terms of basic structural quality and electrical / optical properties. The electrical properties will be correlated with growth conditions, doping, and annealing.

Biography: Dr. Zbigniew Galazka is a crystal growth specialist at Leibniz-Institut für Kristallzüchtung (IKZ) in Berlin, Germany. He is experienced in growing a diversity of oxide single crystals for a variety of applications in both academic research and industrial developments. His current research focuses on the fast-emerging field of transparent semiconducting oxides to bring this class of materials to a higher level in terms of availability of bulk single crystals of emerging compounds. He was educated in Poland in micro- and optoelectronics at Warsaw University of Technology and made his PhD thesis at Institute of Electronic Materials Technology in Warsaw, where he worked for a decade on the Czochralski method. Next, he joined the industry at Photonic Materials in the UK as a principal scientist, and later at Saint-Gobain Crystals and Detectors in France as a project lead. Since a decade he leads the research on the transparent semiconducting oxides at IKZ.

GaN 2.0: A Breakthrough Semiconductor for RF, Power and Space

2 pm, Thursday 15th April, 2021

Tomás Palacios

Massachusetts Institute of Technology, Cambridge, MA, USA



Although Gallium Nitride (GaN) electronics is quickly becoming ubiquitous in both RF and power electronics applications, we are only starting to scratch the surface of the full potential of this amazing semiconductor material. This Seminar will summarize recent progress at MIT to improve the linearity of GaN RF amplifiers to realize the full potential of 5G communications, develop GaN computers that could one day take a lander to Venus,  and reduce the cost of vertical GaN power electronics by 100x.


Tomás Palacios is a Professor in the Department of Electrical Engineering and Computer Science at MIT. He received his PhD from the University of California – Santa Barbara in 2006, and his undergraduate degree in Telecommunication Engineering from the Universidad Politécnica de Madrid (Spain). His current research focuses on demonstrating new electronic devices and applications for novel semiconductor materials such as graphene and gallium nitride. His work has been recognized with multiple awards including the Presidential Early Career Award for Scientists and Engineers, the 2012 and 2019 IEEE George Smith Award, and the NSF, ONR, and DARPA Young Faculty Awards, among many others. Prof. Palacios is the founder and director of the MIT MTL Center for Graphene Devices and 2D Systems, as well as the Chief Advisor and co-founder of Cambridge Electronics, Inc. He is a Fellow of IEEE.


Towards the limits of GaN electronics

New technologies for efficient power devices, effective thermal management and faster electronics

10 am Thursday, April 22

Elison Matioli

Professor of Electrical Engineering

Ecole Polytechnique Fédérale de Lausanne (EPFL)


Electricity is the fastest growing form of end-use energy, however a considerable portion of the electricity consumed worldwide is wasted in power conversion, especially in power semiconductor devices. The outstanding properties of Gallium Nitride semiconductors for power electronic devices can enable significantly more efficient and compact future power converters. Despite the exceptional recent progress, the performance of current GaN power devices is still far below the limits of this material. Further improvements require a reduction of the on-resistance, while maintaining large voltage-blocking capabilities, along with an improved thermal management, which will enable higher efficiency, larger power density and smaller devices.

To address these challenges, this talk will discuss new technologies to drastically reduce the sheet resistance in these semiconductors. Combined with a judicious design of the electric field distribution, based on nanostructures, this approach enables to concurrently reduce the on-resistance and increase the breakdown voltage of power devices, leading to figures of merit far beyond the state-of-the-art [1].

To manage the large heat fluxes in power devices, I will present new technologies based on integrated microfluidic cooling inside the device. By co-designing microfluidics and electronics within the same semiconductor substrate, a monolithically integrated manifold microchannel cooling structure was produced with efficiency beyond what is currently available. Our results show that heat fluxes exceeding 1.7 kW/cm2 could be extracted using only 0.57 W/cm2 of pumping power. An unprecedented coefficient of performance (exceeding 10,000) for single-phase water-cooling was achieved, corresponding to a 50-fold increase compared to straight microchannels [2]. The proposed cooling technology should enable further miniaturization of electronics, potentially extending Moore’s law and greatly reducing the energy consumption in cooling of electronics. Furthermore, by removing the need for large external heat sinks, this approach enables the realization of very compact power converters integrated on a single chip.

Finally, this talk will discuss novel approaches for ultra-fast electronics based on picosecond switches and future directions for novel electronic devices [3]. 

Biography: Elison Matioli is a professor in the institute of electrical engineering at Ecole Polytechnique Fédérale de Lausanne (EPFL) since 2015. He received a B.Sc. degree in applied physics and applied mathematics from Ecole Polytechnique (Palaiseau, France), followed by a Ph.D. degree from the Materials Department at the University of California, Santa Barbara (UCSB) in 2010. He was a post-doctoral fellow in the EECS department at the Massachusetts Institute of Technology (MIT) until 2014. He has received the UCSB Outstanding Graduate Student – Scientific Achievement Award, 2013 IEEE George Smith Award, 2015 ERC Starting Grant Award, 2016 SNSF Assistant Professor Energy Grant Award and 2020 University Latsis Prize.


  1. Nela, J. Ma, C. Erine, P. Xiang, T.-H. Shen, V. Tileli, T. Wang, K. Cheng and E. Matioli,Multi-channel nanowire devices for efficient power conversion” Nature Electronics (2021),
  2. Van Erp, R. Soleimanzadeh, L. Nela, G. Kampitsis and E. Matioli, “Co-designing electronics with microfluidics for more sustainable cooling”, Nature 585, 211–216 (2020)
  3. S. Nikoo, A. Jafari, N. Perera, G. Santoruvo, E. Matioli, “Nanoplasma-Enabled Picosecond Switches for Ultra-Fast Electronics”, Nature, 579 (7800), 534-539, (2020)


Advances in III-N Devices for 5G and Beyond

2 pm Thursday, March 25

Patrick Fay

Professor of Electrical Engineering

University of Notre Dame

Abstract: Achieving the vision and promise of 5G (and beyond) communication systems requires significant advancements in device technologies.  To obtain the low latency and high bandwidths required on a mobile platform, devices offering millimeter-wave performance with low power consumption while simultaneously delivering low noise figure, high linearity, and the ability to be integrated into complex systems in compact form factors are essential.  The unique properties of the III-N material system (e.g. polarization, LO phonon mediated electron transport) enables new approaches for designing millimeter-wave transistors for switching and low-noise amplifier applications, while novel fabrication processing techniques such as epitaxial lift-off and the use of ferroelectric gate stacks provide additional options for realizing highly-integrated heterogeneous systems with enhanced performance.  In this talk, recent advances in these areas that promise to provide significant improvements will be presented.

Biography: Patrick Fay is a Professor in the Dept. of Electrical Engineering at the University of Notre Dame; he received a Ph.D. in electrical engineering from the University of Illinois at Urbana-Champaign in 1996.  His research focuses on the design, fabrication, and characterization of microwave and millimeter-wave electronic devices and circuits, as well as the use of micromachining techniques for the fabrication of RF through sub-millimeter-wave packaging. He established the High Speed Circuits and Devices Laboratory at Notre Dame, which includes device and circuit characterization capabilities at frequencies up to 1 THz.  He also oversaw the design, construction, and commissioning of the 9000 sq. ft. class 100 cleanroom housed in Stinson-Remick Hall at Notre Dame, and has served as the director of this facility since 2003.  Prof. Fay is a fellow of the IEEE, is an IEEE Electron Devices Society Distinguished Lecturer, and has published 11 book chapters and more than 350 articles in scientific journals and conference proceedings.


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