Analysis of performance of SiC bipolar semiconductor devices for grid-level converters

Recent commercialization of SiC bipolar devices, including SiC BJT, SiC MPS diode and SiC PiN diodes have enabled potential candidates to replace their SiC unipolar counterparts. However, the prospects of 4H-SiC power bipolar devices still need further investigation. This thesis compares the static and dynamic performance and reliability for the commercial SiC bipolar devices including SiC BJT, SiC MPS diode and SiC PiN diode and their similarly rated Silicon counterparts mainly by means of experimental measurements.Through comprehensive double-pulse measurements, 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 time will increase with temperature and decreases with collector currents. The common-emitter current gain (β) of SiC BJT is also found to be much higher than its Silicon counterpart. Significant turn-off delay is observed in single Si BJT which becomes worse when in parallel connection as it aggravates the current mismatch across the two devices, while this delay is almost non-existent in SiC devices. The current collapse seen in single SiC BJT is mitigated by parallel connection. These are dependant on temperature and base resistance, especially in the case of Silicon BJT. The static performance of power Silicon and SiC BJT has also been evaluated. It has been found that the higher base-emitter junction voltage of SiC BJTs enables quasi-saturation mode of operation with low on-resistance, which is also the case for Silicon BJTs only at high base currents. In terms of DC gain measured under steady state operation, the observed negative temperature coefficient (NTC) of β in SiC BJTs and the positive coefficient (PTC) in Silicon BJTs can make the β of SiC BJT lower than that in Silicon at high temperatures. It has been found that parallel connection promotes both the on-state conductivity and current gain in Silicon BJTs and conductivity in SiC BJTs.The characterization of power diodes reveals that the superior switching performance of the SiC MPS & JBS diode when compared with the Si PiN diode is due to the absence of the stored charge. This also leads to the larger on-state voltage in both SiC diodes and becomes worse at high currents under high temperatures. Through comprehensive Unclamped Inductive Switching (UIS) measurements, it is seen that the avalanche ruggedness of SiC MPS & JBS diodes outperform that of the closely rated Silicon PiN diode taking advantage of the wide-bandgap properties of SiC. Higher critical avalanche energy and thus better avalanche ruggedness can also be observed in SiC JBS diode compared with the SiC MPS diode. SiC MPS diodes can compete with Si PiN diodes in terms of the surge current limits, while the SiC JBS diode failed under a lower electrothermal stress. This is observed by the dramatic increase in its reverse leakage current at lower voltages.The 15 kV SiC PiN diodes feature smaller device dimensions, less reverse recovery charge and less on-resistance when compared to the 15 kV Silicon PiN diodes. Nevertheless, when evaluating its long-term reliability by using the aggravated power cycling configuration, the high junction temperature together with the dislocation defects in the SiC PiN diode accelerate its degradation. Such degradations are not observed in Silicon PiN diodes for the same junction temperature and high-temperature stress periods

Study of Novel Power Semiconductor Devices for Performance and Reliability.

Power Semiconductor Devices are crucial components in present day power electronic systems. The performance and efficiency of the devices have a direct correlation with the power system efficiency. This dissertation will examine some of the components that are commonly used in a power system, with emphasis on their performance characteristics and reliability. In recent times, there has a proliferation of charge balance devices in high voltage discrete power devices. We examine the same charge balance concept in a fast recovery diode and a MOSFET. This is crucial in the extending system performance at compact dimensions. At smaller device and system sizes, the performance trade-off between the ON and OFF states becomes all the more critical. The focus on reducing the switching losses while maintaining system reliability increases. In a conventional planar technology, the technology places a limit on the switching performance owing to the larger die sizes. Using a charge balance structure helps achieve the improved trade-off, while working towards ultimately improving system reliability, size and cost. Chapter 1 introduces the basic power system based on an inductive switching circuit, and the various components that determine its efficiency. Chapter 2 presents a novel Trench Fast Recovery Diode (FRD) structure with injection control is proposed in this dissertation. The proposed structure achieves improved carrier profile without the need for excess lifetime control. This substantially improves the device performance, especially at extreme temperatures (-40oC to 175oC). The device maintains low leakage at high temperatures, and it\u27s Qrr and Irm do not degrade as is the usual case in heavily electron radiated devices. A 1600 diode using this structure has been developed, with a low forward turn-on voltage and good reverse recovery properties. The experimental results show that the structure maintains its performance at high temperatures. In chapter 3, we develop a termination scheme for the previously mentioned diode. A major limitation on the performance of high voltage power semiconductor is the edge termination of the device. It is critical to maintain the breakdown voltage of the device without compromising the reliability of the device by controlling the surface electric field. A good termination structure is critical to the reliability of the power semiconductor device. The proposed termination uses a novel trench MOS with buried guard ring structure to completely eliminate high surface electric field in the silicon region of the termination. The termination scheme was applied towards a 1350 V fast recovery diode, and showed excellent results. It achieved 98% of parallel plane breakdown voltage, with low leakage and no shifts after High Temperature Reverse Bias testing due to mobile ion contamination from packaging mold compound. In chapter 4, we also investigate the device physics behind a superjunction MOSFET structure for improved robustness. The biggest issue with a completely charge balanced MOSFET is decreased robustness in an Unclamped Inductive Switching (UIS) Circuit. The equally charged P and N pillars result in a flat electric field profile, with the peak carrier density closer to the P-N junction at the surface. This results in an almost negligible positive dynamic Rds-on effect in the MOSFET. By changing the charge profile of the P-column, either by increasing it completely or by implementing a graded profile with the heavier P on top, we can change the field profile and shift the carrier density deeper into silicon, increasing the positive dynamic Rds-on effect. Simulation and experimental results are presented to support the theory and understanding. Chapter 5 summarizes all the theories presented and the contributions made by them in the field. It also seeks to highlight future work to be done in these areas

FEM-based analysis of avalanche ruggedness of high voltage SiC Merged-PiN-Schottky and Junction-Barrier-Schottky diodes

Through comprehensive experimental measurements and TCAD simulation, it is shown that the avalanche ruggedness of SiC MPS & JBS diodes outperforms that of closely rated Silicon PiN diodes taking advantage of the wide-bandgap properties of SiC which leads to a high ionization and activation energy given the strong covalent bonds. Although the MPS diode structure favours a high reverse blocking voltage with small leakage current and a high current conduction, the localise current crowding caused by the multiple P+ implanted region leads to the avalanche breakdown at lower load currents than the SiC JBS diode. The results of Silvaco TCAD Finite Element modellings have a good agreement with the experimental measurements, indicating that SiC JBS diode can withstand the high junction temperature induced by avalanche in line with the calculated avalanche energy

SiC power MOSFETs performance, robustness and technology maturity

Relatively recently, SiC power MOSFETs have transitioned from being a research exercise to becoming an industrial reality. The potential benefits that can be drawn from this technology in the electrical energy conversion domain have been amply discussed and partly demonstrated. Before their widespread use in the field, the transistors need to be thoroughly investigated and later validated for robustness and longer term stability and reliability. This paper proposes a review of commercial SiC power MOSFETs state-of-the-art characteristics and discusses trends and needs for further technology improvements, as well as device design and engineering advancements to meet the increasing demands of power electronics

Robustness and reliability review of Si and SiC FET devices for more-electric-aircraft applications

Increased electrification of traditionally hydraulic and pneumatic functions on aircrafts has put power electronics at the heart of modern aviation. Aircraft electrical power systems have traditionally operated at 115 V AC and 28 V DC with a constant speed generator and transformer rectifier units converting jet engine power into electrical power. However, due to the increasing trend towards the More Electric Aircraft (MEA), 270 V DC systems are likely in the future. This calls into question, the power semiconductor device technology that enables the on-board power converters needed for electro-mechanical actuation as well as solid-state circuit breakers for system protection. Silicon IGBTs have been the work-horse of power electronics, but as switching speeds increase due to the need for high frequency operation, the bipolar nature of IGBT tail currents become a limiting factor for improved energy conversion efficiency. A number of unipolar FET technologies, including SiC trench MOSFETs, SiC planar MOSFETs, silicon super-junction MOSFETs and SiC JFETs in cascode with a low voltage Si MOSFET, have become commercialized at around 650 V. However, reliability and robustness, especially against single event burn-out and/or single event gate rupture is critical. This paper experimentally investigates the performance of the listed FET devices under Unclamped Inductive Switching and Bias Temperature Instability/gate oxide stress tests

シリコンカーバイドパワーMOSFETsの破壊耐量ならびにそのメカニズムに関する研究

筑波大学 (University of Tsukuba)201

Gate stability of GaN-Based HEMTs with P-Type Gate

status: publishe