Yan Gao

Comparison of Static and Switching Characteristics of 1200 V 4H-SiC BJT and 1200 V Si-IGBT

In this paper, static and switching characteristics of a 1200 V 4H-silicon carbide (SiC) bipolar junction transistor (BJT) at a bus voltage of 600 V are reported for the first time. Comparison was made between the SiC BJT and a 1200 V Si insulated gate bipolar transistor (IGBT). The experimental data show that the SiC BJT has much smaller conduction and switching losses than the Si IGBT. The SiC BJT also shows an extremely large reverse bias safe operation area, and no second breakdown was observed. This removes one of the most unattractive aspects of the BJT. The results prove that, unlike Si BJTs, BJTs in 4H-SiC are good competitors for Si IGBTs.

Theoretical and Experimental Analyses of Safe Operating Area (SOA) of 1200-V 4H-SiC BJT

The safe operating area (SOA) of 1200-V SiC bipolar junction transistor (BJT) is investigated by experiments and simulations. The SiC BJT is free of the second breakdown even under the turn-off power density of 3.7 MW/cm2. The theoretical boundary of reverse-biased SOA caused by the false turn-on is obtained by simulations. The short-circuit capability of the 1200-V SiC BJT is also investigated theoretically and experimentally. Self-heating is considered by the nonisothermal simulation, and 1800-K maximum local temperature is the simulated critical temperature of device failure. The surface condition is very critical for short-circuit capability. From simulations, when the interface trap density increases, the critical temperature decreases. This is believed to be the reason why the experimental results show much shorter short-circuit withstand time than the simulation showed.

Performance Evaluation of SiC MOSFET/BJT/Schottky Diode in A 1MHz Single Phase PFC

SiC power devices have very promising future because their ultra low conduction and switching losses and ability of working at high temperatures. SiC MOSFET not only has very low switching loss but also shows no degradation in Rdson at 150°C. In order to achieve ultra low switching loss for SiC BJT, a new drive method is proposed and implemented. These characteristics make SiC power MOSFET/BJT devices attractive for high frequency single phase PFC applications. In this paper, a 1MHz all SiC PFC is designed and evaluated. Experimental results are presented in this paper. These results are also compared with silicon CoolMOS.

400kHz, 300W SiC BJT Based High Power Density PFC Converter

The SiC BJT is a very promising switching power device because of its ability to operate at high temperature. This capability, coupled with ultra low conduction and switching loss, will facilitate very high frequency operation. This will have a significant impact on applications such as PFC where power density is of high interest. In this paper, an all SiC PFC is designed and implemented. In order to achieve ultra low loss, a new drive method is implemented that uses a conventional MOSFET driver to drive the SiC BJT. Based on this method, the turn on and turn off loss of the SiC device can be reduced significantly. Based on the measured loss, the maximum operating frequency of the PFC converter is predicted. Experimental demonstration at 400kHz and 300W is presented in this paper.

Analysis of Operational Degradation of SIC BJT Characteristics

Degradation in both current gain and specific on-resistance of fabricated 4H-SiC BJTs have been observed after a short period of operation. In this paper, 1200 V BJTs were stressed and factors that cause the degradation are proposed. The degradation may be attributed to the increase of the surface states density along the SiC/SiO2 interface, which results in an increased surface recombination current and hence the degradation of the SiC BJT.

Analysis of SiC BJT RBSOA

The reverse biased safe operating area (RBSOA) of 1200V SiC BJT has been systematically analyzed by numerical simulation and experiments for the first time and compared with those for Si BJT. A square RBSOA of SiC BJT is predicted and verified by experiments. Our experiment results show that the SiC BJT can safely turn off 1100V, 67A (2990A/cm2 ), corresponding to 3.7 MW/cm peak turn-off power density. This is an extremely high power density indicating that no early second breakdown occurs

4H-SiC BJT Characterization at High Current High Voltage

A model that can perfectly describe the experiment results was developed. Based on the model, detailed analysis showed that the defect at the Base-Emitter epi-interface is the key factor that limits todays SiC BJT gain. The effect of emitter size also can be studied for SiC BJT. 1200V SiC BJT under study can operate at bus voltage as high as 700V. Until now, no such characterization has been made. In this paper, static and switching characteristics of 1200V SiC BJT at high current and high voltage are reported for the first time. The common emitter output characteristics with current up to 28A (1244A/cm 2 ) and the dynamic characteristics at a bus voltage of 700V and high load current were obtained. Turn off loss and turn off time as the function of turn off current was recorded, which showed that the turn off loss of SiC BJT is much smaller than Si IGBT. Experiments showed an extremely large RBSOA of SiC BJT. With zero voltage base drive, the SiC BJT can successfully turn off 2.7 MW/cm 2 power density. No second breakdown was observed which is the most unattractive aspect of Si BJT. All these experiments prove that, unlike Si BJT, SiC BJT is a good competitor to Si IGBT.

Emitter Size Effect in 4H-SiC BJT

SiC BJT with varying emitter width were investigated by numerical simulations as well as experiments. Emitter size effects (ESEs) are demonstrated in todays SiC BJT by comparing the characterization of BJT with different emitter width. Surface recombination current is found to be comparable with published result for heterojunction bipolar transistors (HBTs). In SiC BJT design, this effect has to be considered. A good surface passivation is required to reduce the effect of surface recombination on the current gain

Trench Power JFET with Integrated Junction Barrier Schottky Diode

A novel trench power JFET with integrated junction barrier Schottky (JBS) diode is proposed. A unit JFET cell pitch of 1.1 mum can be obtained. The specific on-resistance of the device is reduced to 14.4 mOmegamiddotmm2 which is close to state-of-art of power MOSFET. The integrated JBS diode shows 35% and 30% reduction on forward voltage drop and reverse recovery charge respectively compared with its p-n counterpart from the same integration technology

Integration of 1200V SiC BJT With SiC Diode

For the first time, the integration of 1200V SiC BJT with two types of SiC diode, PiN and MPS diode is designed, fabricated and characterized. Compared with the discrete anti-parallel diode, the integration solution will reduce the cost, size and packaging parasitic. The static characteristics show competitive BJT and diode performance in the integrated device as compared to discrete devices. The switching characteristics demonstrate the integrated MPS diode exhibits a 36.4% reduction in terms of peak reverse recovery value, and a 30% reduction on the reverse recovery charge as compared to the integrated PiN diode.