Papers by Umamaheswara Reddy Vemulapati
In this paper a comprehensive review on SiC power module challenges and technology approaches is ... more In this paper a comprehensive review on SiC power module challenges and technology approaches is given. These challenges originate from SiC-specific reduced chip area, from high power and high loss density operation, from high temperature capability, from fast switching transients and from high electric field operation. New approaches based on advanced integrated cooling, low-profile integrated topside bonding and low-inductance architectures are outlined and discussed.
2014 IEEE Workshop on Wide Bandgap Power Devices and Applications, 2014
In this paper a comprehensive review on SiC power module challenges and technology approaches is ... more In this paper a comprehensive review on SiC power module challenges and technology approaches is given. These challenges originate from SiC-specific reduced chip area, from high power and high loss density operation, from high temperature capability, from fast switching transients and from high electric field operation. New approaches based on advanced integrated cooling, low-profile integrated topside bonding and low-inductance architectures are outlined and discussed.
This paper presents an experimental investigation of the dynamic performance of SiC 6.5kV JBS dio... more This paper presents an experimental investigation of the dynamic performance of SiC 6.5kV JBS diodes. Using a hybrid Si SPT IGBT/SiC JBS diodes combination, we have analyzed the turn-off behavior limits of SiC JBS diodes and compared the result against a state-of-the-art Si PiN diode. The experimental results show that the JBS diodes can handle about 40A/chip at 125°C before going into thermal runaway. This maximum turn-off current value increases by about 50% when the diodes are operated at room temperature. The diodes dI/dt behaviour appear to be virtually independent of the DC-link voltage (at RG=18Ω). The comparison between turn-off curves for 6.5kV SiC and Si diodes shows that the use of SiC JBS diodes reduces the reverse recovery losses by more than 98%.
An approach to implement electrically robust MOSFETs in a functioning half-bridge will be investi... more An approach to implement electrically robust MOSFETs in a functioning half-bridge will be investigated. For the first time, reverse conducting 3.3kV SiC MOSFETs have been fabricated with dilferent cell pitches from 14μm (p1.0) to 26μm (pl.8) that are able to withstand short circuit pulse of up to 10μs and a 9ms surge current event up to 15x the nominal current. LinPak half-bridge modules have been fabricated showing reduction of the switching loss by more than 90% compared to a silicon IGBT/diode half bridge.
In this paper, the use of 3.3 kV SiC MOSFETs, Fast Si IGBTs and the mix of both in the so called ... more In this paper, the use of 3.3 kV SiC MOSFETs, Fast Si IGBTs and the mix of both in the so called Cross-Hybrid Switch (XS) and Bimode Cross-Hybrid Switch (BXS) are considered for their application on Galvanically Insulated Modular Converters (GIMC) cells. The semiconductors typically operate under Soft Switching conditions to allow high frequency operation resulting in size and weight minimization while keeping a high efficiency. The high frequency (10 kHz) and Soft Switching operation in the selected semiconductors have been first evaluated by applying 2D semiconductor device simulations. The simulation results allow to identify the impact of device parameters such as the Si IGBTs Lifetime adjustment and the Si IGBT – SiC MOSFET chip surface ratio on the BXS devices, over the on-state and switching losses. Accordingly, different 3.3kV dual HiPak testing samples have been implemented and experimentally evaluated on a 200 kW DC/DC GIMC cell test bench. The comparison between the 3.3 kV Fast Si IGBTs, SiC MOSFETs and BXS shows clear functional benefits of using MV SiC MOSFETs in resonant mode operation, allowing an increase of the GIMC cell power capability by 30 - 35 % for the same module current rating compared to the use of Fast IGBTs. In a similar way, the BXS devices can provide and intermediate power capability increase of around 20-25%, minimizing the installed Si and SiC chip area that can be used as an enabler for improvement of the GIMC technology impacting the cost and performance of the semiconductor devices applied on the GIMC cells
This paper gives an overview of the recent progress of high voltage silicon based power devices f... more This paper gives an overview of the recent progress of high voltage silicon based power devices for high power grid applications, traction- and industrial drives. The first part of the paper covers the latest developments of thyristor based technologies whereas the second and third part focuses on IGBT-type devices and the corresponding packaging technologies.
IEEE Electron Device Letters, Sep 1, 2016
The cross hybrid (XS) concept has been demonstrated experimentally with 3.3-kV Si Insulated Gate ... more The cross hybrid (XS) concept has been demonstrated experimentally with 3.3-kV Si Insulated Gate Bipolar Transistor (IGBTs) and SiC MOSFETs in parallel, and used to calibrate 2D Technology Computer Aided Design simulations. The XS hybrid offers lower switching losses compared with full Si IGBTs and reduced oscillations compared with full SiC MOSFETs. The current sharing mechanism between the IGBT and the MOSFET in the XS hybrid has been elucidated, showing that under typical switching conditions, the IGBT dissipate 98% of the XS hybrid turn-OFF losses compared with the SiC MOSFET. Since the current density of the IGBT in the XS hybrid is twice of that of the full IGBT solution, it exhibits higher dynamic avalanche. These features results in stress at device and package level, thereby compromising robustness and reliability. In order to overcome such issues, we show that increasing the turn-OFF gate resistance improves current sharing in the XS hybrid by delaying the turn-OFF of the MOSFET, and thereby suppressing dynamic avalanche in the IGBT.
IEEE Electron Device Letters, 2016
2019 IEEE Applied Power Electronics Conference and Exposition (APEC)
Application of the Integrated Gate Commutated Thyristor as a switching element in the medium volt... more Application of the Integrated Gate Commutated Thyristor as a switching element in the medium voltage series resonant converter for DC-DC conversion offers the opportunity for increased conversion efficiency and higher switching frequency of the converter. Low current turn-off, already discussed in the previous works, shows promising results for increasing operating frequency of the converter, thus enabling the use of physically smaller components in the design, decreasing the total volume and weight of the solution. This paper presents the results of the switch characterization under single resonant current pulse operation, providing further insight into the turn-off process, relevant timing intervals and resulting losses, supported by TCAD simulations and experimental results.
PCIM Europe 2018; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, Jun 5, 2018
PCIM Europe 2019; International Exhibition and Conference for Power Electronics, Intelligent Motion, Renewable Energy and Energy Management, May 7, 2019
2017 19th European Conference on Power Electronics and Applications (EPE'17 ECCE Europe), 2017
A large area (150mm) high voltage (6.5kV) Reverse Conducting-Integrated Gate Commutated Thyristor... more A large area (150mm) high voltage (6.5kV) Reverse Conducting-Integrated Gate Commutated Thyristor (RC-IGCT) has been developed for low frequency high power electronics applications. The devices were fabricated with GCT to diode active area ratio of 1.4. The RC-IGCT wafers were designed with an outer ring gate structure to minimize the stray impedance for the gate signal and also to improve the thermal behavior of the device. In addition, the HPT+ (High Power Technology) platform has been employed in the GCT part to increase the safe operation area of the device (to achieve high controllable turn-off current capability). In this paper we present the measurement results of the 150mm, 6.5kV RC-IGCT during conduction and turn-off in both GCT (switch)- and diode-modes of operation. In addition, we have compared the technology trade-off curve of the 150mm, 6.5kV RC-IGCT with the state-of-the-art 6.5kV HiPak IGBT modules in switch-mode.
A parallel arrangement of a Silicon (Si) IGBT and a Silicon Carbide (SiC) MOSFET is experimentall... more A parallel arrangement of a Silicon (Si) IGBT and a Silicon Carbide (SiC) MOSFET is experimentally demonstrated. The concept referred to as the Cross Switch “XS” hybrid aims to reach optimum power device performance by providing low static and dynamic losses while improving the overall electrical and thermal properties due to the combination of both the bipolar Si IGBT and unipolar SiC MOSFET characteristics. For the purpose of demonstrating the XS hybrid, the parallel configuration was implemented experimentally in a single package for devices rated at 1200V. Test results were obtained to validate this approach with respect to the static and dynamic performance when compared to a full Si IGBT and a full SiC MOSFET reference devices having the same power ratings as for the XS hybrid samples. Furthermore, an advanced Bimode Cross Switch Hybrid (BXS) is also demonstrated for 3300V devices by combining a Si RC-IGBT or BIGT with SiC MOSFETs. The BXS provides both Switch and diode mode o...
As MVDC technology is slowly finding its way into the area of energy distribution, there is a nee... more As MVDC technology is slowly finding its way into the area of energy distribution, there is a need for reliable, efficient, compact and low maintenance medium voltage DC-DC converters, as a counterpart to AC transformers. Given the typical operating conditions and the design practices, IGCT manufacturers have paid, so far, little attention to the switch's behaviour under low loads (below 10% of the device rated current) and this information is mostly unavailable in the datasheets. Low current turn-off performance of the IGCT, typical to some resonant converters, is explored throughout this paper, supported by TCAD simulations and test results obtained from a dedicated test setup. These tests show the prolonged duration of the turn-off process as the turn-off current decreases, which must be correctly taken into account during converter design.
IEEE Transactions on Industrial Electronics, 2019
IEEE Electron Device Letters, 2018
This document is the author's post-print version, incorporating any revisions agreed during the p... more This document is the author's post-print version, incorporating any revisions agreed during the peer-review process. Some differences between the published version and this version may remain and you are advised to consult the published version if you wish to cite from it.
IEEE Electron Device Letters, 2019
A new type of high voltage termination, namely the "deep p-ring trench" termination design for hi... more A new type of high voltage termination, namely the "deep p-ring trench" termination design for high voltage, high power devices is presented and extensively simulated. Termination of such devices consumes a large proportion of the chip size; the proposed design concept not only reduces the termination silicon area required, it also removes the need for an additional mask as is the case of the traditional p+ ring type termination. Furthermore, the presence of the pring under and around the bottom of the trench structure reduces the electric field peaks at the corners of the oxide which results in reduced hot carrier injection and improved device reliability.
2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe), 2016
In this paper, we present for the first time, the experimental results of a “Bimode Cross Switch ... more In this paper, we present for the first time, the experimental results of a “Bimode Cross Switch (BXS)-Hybrid” built with 3.3kV Silicon Enhanced Trench Bi-mode IGBTs (Si-ET-BIGT) and Silicon Carbide MOSFETs (SiC-MOSFET). Also, we have compared the static (on-state) and dynamic (switching) characteristics of the 3.3kV BXS-Hybrid (1 × Si-ET-BIGT + 2 × SiC-MOSFET) with the full SiC-MOSFET (4 × SiC-MOSFET) and full Si-ET-BIGT (2 × Si-ET-BIGT) reference samples. In addition, we have investigated the MOS gate control (blanking time tbl) influence in diode-mode during reverse recovery of the BXS-Hybrid and compared the results to those of the full Si-ET-BIGT. The experimental results show that BXS-Hybrid offers 45% and 75% reduction in the turn-off losses (in switch-mode) compared to full Si-ET-BIGT at nominal current (125A) and half-nominal current, respectively for nearly the same on-state voltage drop (at nominal current) or even much lower (at half nominal current). Also, the results show that the BXS-Hybrid offers 46% and 49% reduction in the reverse recovery losses (in diode-mode) compared to full Si-ET-BIGT at nominal current and half-nominal current, respectively. Furthermore, the results show that the reverse recovery losses can be reduced as much as 55% with the BXS-Hybrid compared to that of the full Si-ET-BIGT if the MOS gate control technique is used (for the tbl of 2μs). In addition, the BXS-Hybrid eliminates or reduces the oscillations compared to full SiC-MOSFET solution. In this study, the MOS gates of the devices in the BXS-Hybrid were connected together and controlled by the same single gate unit (with one common gate resistor).
2016 28th International Symposium on Power Semiconductor Devices and ICs (ISPSD), 2016
In this work we present the simulation and experimental results of the “Cross Switch (XS)-Hybrid”... more In this work we present the simulation and experimental results of the “Cross Switch (XS)-Hybrid” built with 3.3kV Si-IGBTs and SiC-MOSFETs. We have analyzed the switching performance, mainly the turn-off behavior of the XS-Hybrid (a parallel arrangement of a Si-IGBT and a SiC-MOSFET) with the aid of Sentaurus TCAD device simulations. We discuss in detail the current sharing mechanism between these two devices and hence the distribution of the turn-off losses and the stress (peak power density, dynamic avalanche) on the devices during switching. In addition, we have investigated the turn-off behavior of the XS-Hybrid by variation of the area ratio between the Si-IGBT and SiC-MOSFET, variation of the gate resistance, and variation of the gate resistance ratio. To investigate the switching behavior of the XS-Hybrid, first the simulation models have been adjusted to match the experimental results of the 3.3kV Si-IGBT and SiC-MOSFET. Furthermore, the simulation and experimental results of the 3.3kV XS-Hybrid are compared with the full 3.3kV Si-IGBT and full 3.3kV SiC-MOSFET reference devices.
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Papers by Umamaheswara Reddy Vemulapati