Temperature and switching rate dependence of crosstalk in Si-IGBT and SiC power modules

The temperature and dV/dt dependence of crosstalk has been analyzed for Si-IGBT and SiC-MOSFET power modules. Due to a smaller Miller capacitance resulting from a smaller die area, the SiC module exhibits smaller shoot-through currents compared with similarly rated Si-IGBT modules in spite of switching with a higher dV/dt and with a lower threshold voltage. However, due to high voltage overshoots and ringing from the SiC Schottky diode, SiC modules exhibit higher shoot-through energy density and induce voltage oscillations in the dc link. Measurements show that the shoot-through current exhibits a positive temperature coefficient for both technologies, the magnitude of which is higher for the Si-IGBT, i.e., the shoot-through current and energy show better temperature stability in the SiC power module. The effectiveness of common techniques of mitigating shoot-through, including bipolar gate drives, multiple gate resistance switching paths, and external gate-source and snubber capacitors, has been evaluated for both technologies at different temperatures and switching rates. The results show that solutions are less effective for SiC-MOSFETs because of lower threshold voltages and smaller margins for negative gate bias on the SiC-MOSFET gate. Models for evaluating the parasitic voltage have also been developed for diagnostic and predictive purposes. These results are important for converter designers seeking to use SiC technology

Impact of Temperature and Switching Rate on Properties of Crosstalk on Symmetrical & Asymmetrical Double-trench SiC Power MOSFET

In this paper, the properties of crosstalk on SiC planar MOSFET, SiC symmetrical double-trench MOSFET and SiC asymmetrical double-trench MOSFET is investigated on a half-bridge topology, to enable analysis of the impact of temperature, drain-source transition speed and gate resistance on the severity of the shoot-through current and induced gate voltage. The experimental measurements, performed on a wide range of temperatures and switching rates, show that the two selected symmetrical and asymmetrical double-trench MOSFETs exhibit higher induced gate voltage during crosstalk with the same external gate resistance compared with the planar SiC MOSFET, yielding a higher shoot-through current. Therefore, in continuous initiation of intentional crosstalk, the two double-trench MOSFETs experience more temperature rise, especially for symmetrical one which leads the device to verge of failure within minutes while the temperature rise in other two devices is significantly lower. The different trends of shoot-through current with temperature on DUTs reveals that they are dominated by different mechanisms, i.e., influenced by threshold voltage and inversion layer carriers’ mobility. A model is developed for prediction of shoot-through current during crosstalk which is validated for the 3 device structures. The comparison of the modelled results with the measurement proves its capability to predict the crosstalk behaviour

An investigation of temperature sensitive electrical parameters for SiC power MOSFETs

This paper examines dynamic Temperature Sensitive Electrical Parameters (TSEPs) for SiC MOSFETs. It is shown that the output current switching rate (dIDS/dt) coupled with the gate current plateau (IGP) during turn-ON would be the most effective under specific operating conditions. Both parameters increase with the junction temperature of the device as a result of the negative temperature coefficient of the threshold voltage. The temperature dependency of dIDS/dt has been shown to increase with the device current rating (due to larger input capacitance) and external gate resistance (RGEXT). However, as dIDS/dt is increased by using a small RGEXT, parasitic inductance suppresses the temperature sensitivity of the drain and gate current transients by reducing the “effective gate voltage” on the device. Since the temperature sensitivity of dIDS/dt is at the highest with maximum RGEXT, there is a penalty from higher switching losses when this method is used in real time for junction temperature sensing. This paper investigates and models the temperature dependency of the gate and drain current transients as well as the compromise between the increased switching loss and the potential to implement effective condition monitoring using the evaluated TSEPs

Analysis of dynamic performance and robustness of silicon and SiC power electronics devices

The emergence of SiC power devices requires evaluation of benefits and issues of the technology in applications. This is important since SiC power devices are still not as mature as their silicon counterparts. This research, in its own capacity, highlights some of the major challenges and analyzes them through extensive experimental measurements which are performed in many different conditions seeking to emulate various applications scenarios. It is shown that fast SiC unipolar devices, inherently reduce the switching losses while maintain low conduction losses comparable with contemporary bipolar technologies. This translates into lower temperature excursions and an enhanced conversion efficiency. However, such high switching rates may trigger problems in the device utilizations. The switching rates influenced by the device input capacitance can cause significant ringing in the output, especially in SiC SBDs. Measurements show that switching rate of MOSFETs increases with increasing temperature in turn on and reduces in turn off. Hence, the peak voltage overshoot and oscillation severity of the SiC SBD increases with temperature during diode turn off. This temperature dependence reduces at the higher switching rates. So accurate analytical models are developed for predicting the switching energy in unipolar SiC SBDs and MOSFET pairs and bipolar silicon PiN and IGBT pairs. A key parameter for power devices is electrothermal robustness. SiC MOSFETs have already demonstrated such merits compared to silicon IGBTs, however not for MOSFET body diodes. This research has quantified this in comparison with the similarly rated contemporary device technologies like CoolMOS. In a power MOSFET, high switching rates coupled with the capacitance of drain and body causes a displacement current in the resistive path of P body, inducing a voltage on base of the parasitic NPN BJT which might forward bias it. This may lead to latch up and destruction if the thermal limits are surpassed. Hence, trade offs between switching energy and electrothermal robustness are explored for the silicon, SiC and superjunction power MOSFETs. Measurements show that performance of body diodes of SiC MOSFETs is the most efficient due to least reverse recovery. The minimum forward current for inducing dynamic latch up decreases with increasing voltage, switching rate and temperature for all technologies. The CoolMOS exhibited the largest latch up current followed by the SiC and silicon power MOSFETs. Another problem induced by high switching rates is the electrical coupling between complementing devices in the same phase leg which manifests as short circuits across the DC link voltage. This has been understood for silicon IGBTs with known corrective techniques, however it is seen that due to smaller Miller capacitance resulting from a smaller die area, the SiC module exhibits smaller shoot through currents in spite of higher switching rates and a lower threshold voltage. Measurements show that the shoot through current exhibits a positive temperature coefficient for both technologies the magnitude of which is higher for the silicon IGBT. The effectiveness of common techniques of mitigating shoot through is also evaluated, showing that solutions are less effective for SiC MOSFET because of the lower threshold voltages and smaller margins for a negative gate bias

Reliability analysis of planar and symmetrical & asymmetrical trench discrete SiC Power MOSFETs

Silicon Carbide MOSFETs are shown in research to outperform Silicon counterparts on many performance metrics, including switching rates and power losses. To further improve their performance, trench and double-trench structures have recently been developed. To replace conventional planar SiC MOSFETs, besides the performance parameters which are mostly stated in datasheets, reliability studies under stress are also needed. This thesis presents a comprehensive comparison between 3rd generation trench SiC power MOSFETs, namely symmetrical double-trench and asymmetrical trench with planar SiC power MOSFETs on four aspects of: switching slew rates (dI/dt & dV/dt), crosstalk characteristics, bias temperature instability and power cycling stability.First, the dynamic performance in both 1st quadrant and 3rd quadrant has been eval- uated on the differences in stress by dI/dt & dV/dt and resultant losses. This is key in understanding many other reliability criterions, i.e. severity of crosstalk induced switchings. In the 1st quadrant, the source current and drain-source voltage switching rates at both turn-ON and turn-OFF are measured under a range of test conditions. Both the symmetrical and asymmetrical trench MOSFETs have up to 2 times faster voltage and current slew rates compared with the planar one. They also indicate only slight changes in switching rate with junction temperature. In the 3rd quadrant, the reverse recovery peak current and total reverse recovery charge are measured with respect to junction temper- ature and load current level. Both the symmetrical and asymmetrical trench MOSFETs have less than half of the reverse recovery charge of that of the planar SiC MOSFET.In the evaluation of crosstalk characteristics, peak shoot-through current and induced gate voltage at crosstalk are measured with respect to junction temperature and external gate resistance. With particularly large external gate resistances connected to intentionally induce parasitic turn-ON, the symmetrical double-trench MOSFET is shown to be more prone to crosstalk with 23 A peak shoot-through current measured while it is only 10 A for asymmetrical trench and 4 A for planar MOSFET under similar test conditions. As the temperature increase, the peak shoot-through current drops for the symmetrical double-trench, while constant for the asymmetrical trench and rising for the planar device.Threshold voltage drift is also measured to reflect the degradation happened with bias temperature instability at various junction temperatures, stressing voltages and time periods. Under low-magnitude gate stress (within the range of datasheets) in both positive and negative bias cases, there is more threshold drift observed on the two trench MOSFETs at all junction temperatures than the planar MOSFET. When the stress magnitude is raised, there is less threshold drift observed on the two trench MOSFETs.To evaluate the ruggedness in continuous switchings, the devices are placed under repetitive turn-ON events. The thermal performance under such operation are compared. The asymmetrical trench MOSFET experiences the highest case temperature rise while the least is observed for the planar MOSFET. With an external heatsink equipped to achieve more efficient cooling, the repetitive turn-ON test transforms into the conventional power cycling. In this condition, both the symmetrical and asymmetrical trench MOSFETs fail earlier than the degraded (but not failed) planar MOSFET

β\beta-Ga₂O₃ in Power Electronics Converters: Opportunities & Challenges

In this work, the possibility of using different generations of $\beta$-Ga2O3 as an ultra-wide-bandgap power semiconductor device for high power converter applications is explored. The competitiveness of $\beta$-Ga2O3 for power converters in still not well quantified, for which the major determining factors are the on-state resistance, $R_{{\rm ON}}$, reverse blocking voltage, $V_{{\rm BR}}$, and the thermal resistance, $R_{{\rm th}}$. We have used the best reported device specifications from literature, both in terms of reports of experimental measurements and potential demonstrated by computer-aided designs, to study power converter performance for different device generations. Modular multilevel converter-based voltage source converters are identified as a topology with significant potential to exploit these device characteristics. The performance of MVDC & HVDC converters based on this topology have been analysed, focusing on system level power losses and case temperature rise at the device level. Comparisons of these $\beta$-Ga2O3 devices are made against contemporary SiC-FET and Si-IGBTs. The results have indicated that although the early $\beta$-Ga2O3 devices are not competitive to incumbent Si-IGBT and SiC-FET modules, the latest experimental measurements on NiOX/$\beta$-Ga2O3 and $\beta$-Ga2O3/diamond significantly surpass the performance of incumbent modules. Furthermore, parameters derived from semiconductor-level simulations indicate that the $\beta$-Ga2O3/diamond in superjunction structures delivers even superior performance in these power converters

β-Ga₂O₃ in Power Electronics Converters:Opportunities & Challenges

In this work, the possibility of using different generations of β-Ga2O3 as an ultra-wide-bandgap power semiconductor device for high power converter applications is explored. The competitiveness of β-Ga2O3 for power converters in still not well quantified, for which the major determining factors are the on-state resistance, RON, reverse blocking voltage, VBR, and the thermal resistance, Rth. We have used the best reported device specifications from literature, both in terms of reports of experimental measurements and potential demonstrated by computer-aided designs, to study power converter performance for different device generations. Modular multilevel converter-based voltage source converters are identified as a topology with significant potential to exploit these device characteristics. The performance of MVDC & HVDC converters based on this topology have been analysed, focusing on system level power losses and case temperature rise at the device level. Comparisons of these β-Ga2O3 devices are made against contemporary SiC-FET and Si-IGBTs. The results have indicated that although the early β-Ga2O3 devices are not competitive to incumbent Si-IGBT and SiC-FET modules, the latest experimental measurements on NiOX / β-Ga2O3 and β-Ga2O3 /diamond significantly surpass the performance of incumbent modules. Furthermore, parameters derived from semiconductor-level simulations indicate that the β-Ga2O3 /diamond in superjunction structures delivers even superior performance in these power converters

Modeling, Measurement and Mitigation of Fast Switching Issues in Voltage Source Inverters

Wide-bandgap devices are enjoying wider adoption across the power electronics industry for their superior properties and the resulting opportunities for higher efficiency and power density. However, various issues arise due to the faster switching speed, including switching transient voltage overshoot, unstable oscillation, gate driving and evaluation difficulty, measurement and monitoring challenge, and potential load insulation degradation. This dissertation first sets out to model and understand the switching transient voltage overshoots. Unique oscillation patterns and features of the turn-on and turn-off overvoltage are discovered and analyzed, which provides new insights into the switching transient. During the experimental characterization, a new unstable oscillation pattern is found during the trench MOSFET\u27s turn-off transient. The MOSFET channel may be falsely turned back on, resulting in severe oscillation and possible loss of control. Time-domain and large-signal analytical models are established, which reveals the negative impact of common-source inductances and unconventional capacitance curve of trench MOSFET. Besides the devices themselves, another determining part in their switching transient behavior is the gate driver. A programmable gate driver platform is proposed to readily adapt to different power semiconductors and driving schemes, which can greatly facilitate the evaluation and comparison of different devices and driving schemes. The faster switching speed of wide-bandgap devices also requires more demanding measurement and monitoring solutions. A novel combinational Rogowski coil concept is proposed, which leverages the self-integrating feature to further increase the bandwidth. Prototypes achieved more than 300 MHz bandwidth, while keeping the cross-sectional area less than 2.5 mm$^2$. Finally, the very high voltage slew rate of wide-bandgap devices may negatively impact the motor load insulation. Attempting to fully utilize the higher switching frequency capability, sinewave and $dv/dt$ filters are compared. It is shown that sinewave filters can achieve higher efficiency and power density than $dv/dt$ filters, especially for high frequency applications