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

Impact of Carriers Injection Level on Transients of Discrete and Paralleled Silicon and 4H-SiC NPN BJTs

The 4H-SiC vertical NPN BJTs are attractive power devices with potentials to be used as high power switching devices with high voltage ratings in range of 1.7 kV and high operating temperatures. In this paper, the advantages of the 4H-SiC NPN BJTs in terms of switching transients and current gain over their silicon counterparts is illustrated by means of extensive experimental measurements and modelling, including investigation of high level injection, as a common phenomenon in bipolar devices that influences the switching rates and DC current gain. The two device types have been tested at 800 V with maximum temperature of 175 °C and maximum collector current of 8 A. The turn-ON and turn-OFF transition in Silicon BJT is seen to be much slower than that of the SiC BJT while the transient duration will increase with increasing temperature and decreases with larger collector currents. The common-emitter current gain of SiC BJT is also found to be much higher than silicon counterparts, increasing with temperature in low injection levels but decreasing in higher injection levels in both devices. The rate of increase of current gain slows down toward stability as the collector current increases, known as the high-level injection. Current sharing imbalance among parallel connected devices is also investigated, which are shown to be evidently dependant on temperature and base resistance in Silicon BJT, while the current collapse in also seen in SiC BJT at high injection levels with high base resistance. The turn-OFF delay is seen to be temperature dependant in single and paralleled Silicon BJTs while almost non-existent in SiC device

Effects of Pressure and Doping on Ruddlesden-Popper phases Lan+1NinO3n+1

Recently the discovery of superconductivity with a critical temperature Tc up to 80 K in Ruddlesden-Popper phases Lan+1NinO3n+1 (n = 2) under pressure has garnered considerable attention. Up to now, the superconductivity was only observed in La3Ni2O7 single crystal grown with the optical-image floating zone furnace under oxygen pressure. It remains to be understood the effect of chemical doping on superconducting La3Ni2O7 as well as other Ruddlesden-Popper phases. Here, we systematically investigate the effect of external pressure and chemical doping on polycrystalline Ruddlesden-Popper phases. Our results demonstrate the application of pressure and doping effectively tunes the transport properties of Ruddlesden-Popper phases. We find pressure-induced superconductivity up to 86 K in La3Ni2O7 polycrystalline sample, while no signatures of superconductivity are observed in La2NiO4 and La4Ni3O10 systems under high pressure up to 50 GPa. Our study sheds light on the exploration of high-Tc superconductivity in nickelates.Comment: 21 papes, 8 figures and 1 tabl