Center for Power Electronics Systems

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1 kV GaN-on-Si Quasi-Vertical Schottky Rectifier
Qin, Yuan; Xiao, Ming; Zhang, Ruizhe; Xie, Qingyun; Palacios, Tomás; Wang, Boyan; Ma, Yunwei; Kravchenko, Ivan; Briggs, Dayrl P.; Hensley, Dale K.; Srijanto, Bernadeta R.; Zhang, Yuhao (IEEE, 2023-07)
This work demonstrates quasi-vertical GaN Schottky barrier diodes (SBDs) on 6-inch Si substrate with a breakdown voltage (BV) over 1 kV, the highest BV reported in vertical GaN-on-Si SBDs to date. The deep mesa inherently in quasi-vertical devices is leveraged to form a self-aligned edge termination, and the mesa sidewall is covered by the p-type nickel oxide (NiO) as a reduced surface field (RESURF) structure. This novel termination enables a parallel-plane junction electric field of 2.8 MV/cm. The device also shows low turn-on voltage of 0.5 V, and low specific on-resistance of 1.1 m ·cm2. Moreover, the device exhibits excellent overvoltage robustness under the continuous 800 V stress in the unclamped inductive switching test. These results show the good promise of the low-cost vertical GaN-on-Si power diodes.
1 kV Self-Aligned Vertical GaN Superjunction Diode
Ma, Yunwei; Porter, Matthew; Qin, Yuan; Spencer, Joseph; Du, Zhonghao; Xiao, Ming; Wang, Yifan; Kravchenko, Ivan; Briggs, Dayrl P.; Hensley, Dale K.; Udrea, Florin; Tadjer, Marko; Wang, Han; Zhang, Yuhao (IEEE, 2024-01)
This work demonstrates vertical GaN superjunction (SJ) diodes fabricated via a novel self-aligned process. The SJ comprises n-GaN pillars wrapped by the charge-balanced p-type nickel oxide (NiO). After the NiO sputtering around GaN pillars, the self-aligned process exposes the top pillar surfaces without the need for additional lithography or a patterned NiO etching which is usually difficult. The GaN SJ diode shows a breakdown voltage (B V) of 1100 V, a specific on-resistance ( RON) of 0.4 mΩ⋅ cm2, and a SJ drift-region resistance ( Rdr) of 0.13 mΩ⋅ cm2. The device also exhibits good thermal stability with B V retained over 1 kV and RON dropped to 0.3 mΩ⋅ cm2 at 125oC . The trade-off between B V and Rdr is superior to the 1D GaN limit. These results show the promise of vertical GaN SJ power devices. The self-aligned process is applicable for fabricating the heterogeneous SJ based on various wide- and ultra-wide bandgap semiconductors.
10-kV Ga₂O₃ Charge-Balance Schottky Rectifier Operational at 200 ^◦C
Qin, Yuan; Xiao, Ming; Porter, Matthew; Ma, Yunwei; Spencer, Joseph; Du, Zhonghao; Jacobs, Alan G.; Sasaki, Kohei; Wang, Han; Tadjer, Marko; Zhang, Yuhao (IEEE, 2023-08)
This work demonstrates a lateral Ga2O3 Schottky barrier diode (SBD) with a breakdown voltage (BV) over 10 kV, the highest BV reported in Ga2O3 devices to date. The 10 kV SBD shows good thermal stability up to 200◦C, which is among the highest operational temperatures reported in multi-kilovolt Ga2O3 devices. The key device design for achieving such high BV is a reduced surface field (RESURF) structure based on the p-type nickel oxide (NiO), which balances the depletion charges in the n-Ga2O3 channel at high voltage. At BV, the chargebalanced Ga2O3 SBD shows an average lateral electric field (E-field) over 4.7 MV/cm at 25 ◦C and over 3.5 MV/cm at 200◦C, both of which exceed the critical E-field of GaN and SiC. The 10 kV SBD shows a specific on-resistance of 0.27 ·cm2 and a turn-on voltage of 1 V; at 200◦C, the former doubles and the latter reduces to 0.7 V. These results suggest the good potential of Ga2O3 devices for mediumand high-voltage, high-temperature power applications.
2 kV, 0.7 mΩ·cm² Vertical Ga₂O₃ Superjunction Schottky Rectifier with Dynamic Robustness
Qin, Yuan; Porter, Matthew; Xiao, Ming; Du, Zhonghao; Zhang, Hongming; Ma, Yunwei; Spencer, Joseph; Wang, Boyan; Song, Qihao; Sasaki, Kohei; Lin, Chia-Hung; Kravchenko, Ivan; Briggs, Dayrl P.; Hensley, Dale K.; Tadjer, Marko; Wang, Han; Zhang, Yuhao (IEEE, 2023)
We report the first experimental demonstration of a vertical superjunction device in ultra-wide bandgap (UWBG) Ga2O3. The device features 1.8 μm wide, 2×1017 cm-3 doped n-Ga2O3 pillars wrapped by the charge-balanced p-type nickel oxide (NiO). The sidewall NiO is sputtered through a novel self-align process. Benefitted from the high doping in Ga2O3, the superjunction Schottky barrier diode (SJ-SBD) achieves a ultra-low specific on-resistance (RON,SP) of 0.7 mΩ·cm2 with a low turn-on voltage of 1 V and high breakdown voltage (BV) of 2000 V. The RON,SP~BV trade-off is among the best in all WBG and UWBG power SBDs. The device also shows good thermal stability with BV > 1.8 kV at 175 oC. In the unclamped inductive switching tests, the device shows a dynamic BV of 2.2 kV and no degradation under 1.7 kV repetitive switching, verifying the fast acceptor depletion in NiO under dynamic switching. Such high-temperature and switching robustness are reported for the first time in a heterogeneous superjunction. These results show the great potential of UWBG superjunction power devices.
2012 CPES Annual Report
Center for Power Electronics Systems (Virginia Tech. Center for Power Electronics Systems, 2012)
The Center for Power Electronics Systems at Virginia Tech is a research center dedicated to improving electrical power processing and distribution that impact systems of all sizes – from battery – operated electronics to vehicles to regional and national electrical distribution systems. Our mission is to provide leadership through global collaborative research and education for creating advanced electric power processing systems of the highest value to society. CPES, with annual research expenditures about $4-5 million US dollars, has a worldwide reputation for its research advances, its work with industry, and its many talented graduates. From its background as an Engineering Research Center for the National Science Foundation during 1998 - 2008, CPES has continued to work towards making electric power processing more efficient and more exact in order to reduce energy consumption. Power electronics is the “enabling infrastructure technology” that promotes the conversion of electrical power from its raw form to the form needed by machines, motors and electronic equipment. Advances in power electronics can reduce power conversion loss and in turn increase energy efficiency of equipment and processes using electrical power. This results in increased industrial productivity and product quality. With widespread use of power electronics technology, the United States would be able to cut electrical energy consumption by 33 percent. This energy savings in the United States alone is estimated to be the equivalent of output from 840 fossil fuel based generating plants. This savings would result in enormous economic, environmental and social benefits.
2013 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2013)
The CPES industrial consortium is designed to cultivate connectivity among researchers in academia and industry, as well as create synergy within the network of industry members. The CPES industrial consortium offers: The best mechanism to stay abreast of technological developments in power electronics; The ideal forum for networking with leadingedge companies and top-notch researchers; The CPES connection provides the competitive edge to industry members via: Access to state-of-the-art facilities, faculty expertise, top-notch students; Leveraged research funding of over $4-10 million per year; Industry influence via Industry Advisory Board and research champions; Intellectual properties with early access for Principal Plus and Principal members via CPES IPPF (Intellectual Property Protection Fund); Technology transfer made possible via special access to the Center’s multi-disciplinary team of researchers, and resulting publications, presentations and intellectual properties; Continuing education opportunities via professional short courses offered at a significant discount. The CPES industrial consortium offers the ideal forum for networking with leading-edge companies and top-notch researchers and provides the best mechanism to stay abreast of technological developments in power electronics.
2014 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2014)
Over the past two decades, CPES has secured research funding from major industries, such as GE, Rolls-Royce, Boeing, Alstom, ABB, Toyota, Nissan, Raytheon, and MKS, as well as from government agencies including the NSF, DOE, DARPA, ONR, U.S. Army, and the U.S. Air Force, in research pursuing high-density system design. CPES has developed unique high-temperature packaging technology critical to the future powerelectronic industry. In the HDI mini-consortium, the goal of high power density will be pursued following two coupled paths, both leveraging the availability of wide-bandgap power semiconductor, as well as high-temperature passive components and ancillary functions. The switching frequency will be pushed as high as component technologies, thermal management, and reliability permit. At the same time, the maximum component temperatures will be pushed as high as component technologies, thermal management, and reliability permit. The emergence of wide‐bandgap semiconductors such as Silicon Carbide (SiC) and Gallium Nitride (GaN) makes it possible to realize power switches that operate at frequency beyond 5 MHz and temperature beyond 200° C. As the switching frequency increases, switching noise is shifted to higher frequency and can be filtered with small passive components, leading to improved power density. Higher operating temperatures enable increased power density and applications under harsh environments, such as military systems, transportation systems, and outdoor industrial and utility systems.
2015 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2015)
In its efforts to develop power processing systems to take electricity to the next step, CPES has developed research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; (5) high density integration. These technology areas target applications that include: (1) Power management for information and communications technology; (2) Point-of-load conversion for power supplies; (3) Vehicular power conversion systems; (4) Renewable energy systems. In 2015, CPES sponsored research totaled approximately $2.2 million. The following abstracts provide a quick insight to the current research efforts.
2016 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2016)
In its effort to develop power processing systems to take electricity to the next step, CPES has cultivated research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; and (5) high density integration. These technology areas target applications that include: (1) Power management for information and communications technology; (2) Point-of-load conversion for power supplies; (3) Vehicular power converter systems; and (4) High-power conversion systems. In 2016, CPES sponsored research totaled approximately $2.1 million. The following abstracts provide a quick insight to the current research efforts.
2017 CPES Annual Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2017)
In its effort to develop power processing systems to take electricity to the next step, CPES has cultivated research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; and (5) high density integration. These technology areas target applications that include: (1) power management for information and communications technology; (2) point-of-load conversion for power supplies; (3) vehicular power converter systems; and (4) high-power conversion systems. In 2016, CPES sponsored research totaled approximately $2.4 million. The following abstracts provide a quick insight to the current research efforts.
2018 CPES Annual Report
(Virginia Tech, 2018)
In its effort to develop power processing systems to take electricity to the next step, CPES has cultivated research expertise encompassing five technology areas: (1) power conversion technologies and architectures; (2) power electronics components; (3) modeling and control; (4) EMI and power quality; and (5) high density integration. These technology areas target applications that include: (1) power management for information and communications technology; (2) point-of-load conversion for power supplies; (3) vehicular power converter systems; and (4) high-power conversion systems. In 2018, CPES sponsored research totaled approximately $2.9 million. The following abstracts provide a quick insight to the current research efforts.
Anti-islanding detection for three-phase distributed generation
(United States Patent and Trademark Office, 2017-04-25)
Wobbling the operating frequency of a phase-locked loop (PLL), preferably by adding a periodic variation is feedback gain or delay in reference signal phase allows the avoidance of any non-detection zone that might occur due to exact synchronization of the phase locked loop operating frequency with a reference signal. If the change in PLL operating frequency is periodic, it can be made of adequate speed variation to accommodate and time requirement for islanding detection or the like when a reference signal being tracked by the PLL is lost. Such wobbling of the PLL operating frequency is preferably achieved by addition a periodic variable gain in a feedback loop and/or adding a periodically varying phase delay in a reference signal and/or PLL output.
Artificial Neuronal Devices Based on Emerging Materials: Neuronal Dynamics and Applications
Liu, Hefei; Qin, Yuan; Chen, Hung-Yu; Wu, Jiangbin; Ma, Jiahui; Du, Zhonghao; Wang, Nan; Zou, Jingyi; Lin, Sen; Zhang, Xu; Zhang, Yuhao; Wang, Han (Wiley-V C H Verlag, 2023-03)
Artificial neuronal devices are critical building blocks of neuromorphic computing systems and currently the subject of intense research motivated by application needs from new computing technology and more realistic brain emulation. Researchers have proposed a range of device concepts that can mimic neuronal dynamics and functions. Although the switching physics and device structures of these artificial neurons are largely different, their behaviors can be described by several neuron models in a more unified manner. In this paper, the reports of artificial neuronal devices based on emerging volatile switching materials are reviewed from the perspective of the demonstrated neuron models, with a focus on the neuronal functions implemented in these devices and the exploitation of these functions for computational and sensing applications. Furthermore, the neuroscience inspirations and engineering methods to enrich the neuronal dynamics that remain to be implemented in artificial neuronal devices and networks toward realizing the full functionalities of biological neurons are discussed.
Avoiding internal switching loss in soft switching cascode structure device
(United States Patent and Trademark Office, 2017-08-15)
In a cascode switching device, avalanche breakdown of a control transistor and loss of soft switching or zero voltage switching in a high voltage normally-on depletion mode transistor having a negative switching threshold voltage and the corresponding losses are avoided by providing additional capacitance in parallel with a parallel connection of drain-source parasitic capacitance of the control transistor and gate-source parasitic capacitance of the high voltage, normally-on transistor to form a capacitive voltage divider with the drain-source parasitic capacitance of the high voltage, normally-on transistor such that the avalanche breakdown voltage of the control transistor cannot be reached. The increased capacitance also assures that the drain source parasitic capacitance of the high voltage, normally-on transistor is fully discharged before internal turn-on can occur.
Center Program Snapshot
Lee, Fred C.; Boroyevich, Dushan (Virginia Tech, 2009-04)
This book provides a comprehensive introduction to CPES research, education,and outreach.
Center Program Snapshot (April 2009)
Center for Power Electronics Systems (Virginia Tech. Center for Power Electronics Systems, 2009-04)
With the widespread use of power electronics technology, the United States would be able to cut electrical energy consumption by 33 percent. The energy savings, by today’s measure, is equivalent to the total output of 840 fossil fuel-based generating plants. This would result in enormous economic, environmental and social benefits. The engineers of the Center for Power Electronics Systems (CPES) are working to make electric power processing more efficient and more exact in order to achieve these benefits. The effort requires close collaboration with industry and with researchers across universities and fields of endeavor. Electrification is considered the greatest engineering feat of the 20th century by the National Academy of Engineering. The dream of CPES engineers is to take electricity to the next step and develop power processing systems of the highest value to society.
Colossal tunability in high frequency magnetoelectric voltage tunable inductors
Yan, Yongke; Geng, Liwei D.; Tan, Yaohua; Ma, Jianhua; Zhang, Lujie; Sanghadasa, Mohan; Ngo, Khai D. T.; Ghosh, Avik W.; Wang, Yu U.; Priya, Shashank (2018-11-27)
The electrical modulation of magnetization through the magnetoelectric effect provides a great opportunity for developing a new generation of tunable electrical components. Magnetoelectric voltage tunable inductors (VTIs) are designed to maximize the electric field control of permeability. In order to meet the need for power electronics, VTIs operating at high frequency with large tunability and low loss are required. Here we demonstrate magnetoelectric VTIs that exhibit remarkable high inductance tunability of over 750% up to 10 MHz, completely covering the frequency range of state-of-the-art power electronics. This breakthrough is achieved based on a concept of magnetocrystalline anisotropy (MCA) cancellation, predicted in a solid solution of nickel ferrite and cobalt ferrite through first-principles calculations. Phase field model simulations are employed to observe the domain-level strain-mediated coupling between magnetization and polarization. The model reveals small MCA facilitates the magnetic domain rotation, resulting in larger permeability sensitivity and inductance tunability.
Correlation between tunability and anisotropy in magnetoelectric voltage tunable inductor (VTI)
Yan, Yongke; Geng, Liwei D.; Zhang, Lujie; Gao, Xiangyu; Gollapudi, Sreenivasulu; Song, Hyun-Cheol; Dong, Shuxiang; Sanghadasa, Mohan; Ngo, Khai D. T.; Wang, Yu U.; Priya, Shashank (Springer Nature, 2017-11-22)
Electric field modulation of magnetic properties via magnetoelectric coupling in composite materials is of fundamental and technological importance for realizing tunable energy efficient electronics. Here we provide foundational analysis on magnetoelectric voltage tunable inductor (VTI) that exhibits extremely large inductance tunability of up to 1150% under moderate electric fields. This field dependence of inductance arises from the change of permeability, which correlates with the stress dependence of magnetic anisotropy. Through combination of analytical models that were validated by experimental results, comprehensive understanding of various anisotropies on the tunability of VTI is provided. Results indicate that inclusion of magnetic materials with low magnetocrystalline anisotropy is one of the most effective ways to achieve high VTI tunability. This study opens pathway towards design of tunable circuit components that exhibit field-dependent electronic behavior.
CPES : 10-Year Progress Report
Center for Power Electronics Systems; Uncork-it, Inc. (Virginia Tech. Center for Power Electronics Systems, 2010-04)
A major strength of CPES is its ability to use a wealth of existing resources and industrial collaboration. Virginia Tech, the University of Wisconsin-Madison (UW), and Rensselaer Polytechnic Institute (RPI) are the nation’s leaders in power electronics and advanced power semiconductor materials and devices. These three universities have combined forces with North Carolina A&T State University (NCA&T) and the University of Puerto Rico-Mayagüez (UPRM), which are institutions with solid reputations in the quality of their undergraduate engineering programs as well as their power electronics and related research. Virginia Tech brings expertise in high-frequency power conversion devices and circuit technologies, power electronics packaging, and systems integration. The University of Wisconsin has expertise in industrial and utility-grade power conversion, electric machines and motor drives, and industrial controls. RPI’s expertise involves novel discrete power semiconductor materials, process techniques, power devices, and smart power ICs. North Carolina A&T contributes knowledge of nonlinear control, neural networks, and fuzzy logic-based intelligent control, and the University of Puerto Rico-Mayagüez has expertise in controls and electric machines. The resources and expertise of researchers from each of these institutions have contributed to the success of the Center. CPES industry members have been the critical key in our success. From the beginning, industry members have been enthusiastic and involved, helping shape goals and contributing to the management of the ERC. Since 1998, CPES research goals have evolved and the collaborations with industry and university researchers have strengthened. CPES succeeded in changing the technology of power electronics, while increasing knowledge and participation in the field. As we graduate from the NSF ERC program, we look forward to building on our global collaboration and changing the way electricity is used.
CPES : Mini-Consortium Brochure
Center for Power Electronics Systems (Virginia Tech. Center for Power Electronics Systems, 2011-04)
The CPES mini-consortium model provides a unique mechanism for all participants in power electronics – including industry competitors – to pool efforts to address their common challenges and develop pre-competitive Advances. Companies and organizations join CPES as a Principal Plus Member and choose the mini-consortium option. Annual membership fees are $50,000. Research results generated within a miniconsortium are shared among its members, and intellectual properties developed under the CPES industry consortium are shared among all Principal-level members as described on the next page. The research and IP benefits are only part of what makes the mini-consortium effective. The distinctive feature of the model is discussion among all participants, which then shapes and guides research toward overcoming the major barriers in the field. Competitive plans and technologies are protected, yet participants can discuss their mutual technical problems. Miniconsortium interactions take place in the quarterly review meetings.

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