SiC IGBT Research Articles

Impact of Cell Layout and Device Structure on On-Voltage Reduction of 6.5-kV n-Channel SiC IGBTs

A box cell layout and a hole-barrier structure were used to realize low-on-voltage n-channel 4H-SiC IGBTs with 6.5-kV blocking capability. Box cell layout can increase the channel width, leading to reduction of the channel resistance and an enhancement of electron injection from an emitter. Hole-barrier structure, which is a potential barrier for holes to prevent them from flowing out of the emitter, can enhance conductivity modulation. An on-voltage of 3.98 V at a collector current of 100 A/cm2 was achieved from a fabricated SiC IGBTin this study. Since the on-voltage of a SiC IGBT with a conventional structure was 4.81 V at the same collector current, the effect of our new structure was successfully shown to reduce the on-voltage of SiC IGBTs. An estimation of each voltage component involved in the on-voltage was also carried out by utilizing a device simulation, and the estimation shows that a SiC IGBT incorporating a box layout and hole-barrier structure will thus have quite a low drift-layer voltage and an on-voltage close to the limit determined by the bipolar built-in voltage.

(Invited) Practical Considerations of Si Vs SiC Technology in High POWER, High Frequency Inverters for Industrial Induction Heating Applications

Introduction The paper aims to give practical technical considerations for choosing Si vs SiC technology in practical high frequency, high power inverters for industrial induction heating applications. Actual inverters, for this application, are resonant inverters, in a current of in a voltage–fed configuration. For current–fed inverters, the basic switch is a turn-on or turn-off controlled device (IGBT of MOS) in series with a diode, while in voltage–fed inverters the basic switch is a turn-on or turn-off controlled device with a diode in antiparallel. Si vs SiC diodes in high power inverters High power converters, both current-fed or voltage fed, require paralleling high frequency diodes. With Si technology, diodes have to be matched due to their negative thermal coefficient, making in this case, the use of SiC diodes a much more robust solution due to its positive thermal coefficient. Manufacturing as well as maintenance costs compensate the over cost of SiC technology. But on the other hand, many of the hardening application require a large number of power cycles and considering power cycling (PC) capabilities, the use of SiC diodes offers worst PC capabilities as the higher increase of the junction Temperature ΔTj due to higher body resistance of the SiC diode in comparison with the Si counterpart. For that reason, long term reliability has to be when using SiC diodes instead Si ones. The following figure shows the increase of the die temperature of SiC and Si diodes under the same conditions (1). Figure 1 Another aspect influencing the PC capacity is related the different material properties of both materials. Figure 2 shows that under the same junction temperature increase ΔTj, the power cycling capacity of SiC diodes is about one third of the equivalent Si Diodes (2). Figure 2 As a conclusion the use of Si or SiC diodes is a trade-off between paralleling and power cycling capabilities and the decision on the optimal diode technology is dependent on the application. Si IGBT vs SiC MOSFET in high power inverters SiC MOSFETs are specially adapted to high frequency applications as per their lower switching losses. The following figure shows the required number of semiconductor devices of a 240 kW/400 kHz induction welder as well as the better overall efficiency of the inverter (3). Figure 3 Figure 4 shows the 200 kW/ 400 kHz the developed all SiC inverter prototype for testing SiC technology capacity vs IGBT technology. Figure 4 Based on the experimental results from the above prototype, the curves for the optimal technology, depending the frequency in voltage-fed inverters for induction heating are shown in the next figure. Figure 5 Consequently, the above experimental results show that up to 100 kHz, IGBT is the optimal technology for induction heating inverters, while from 150 kHz until 500 kHz SiC technology offers better power capability. The range from 100 to 150 kHz can be optimal covered with IGBT technology and advanced control techniques (interleaved Pulse Density Modulation-PDM ) or with SiC technology with actual PDM controllers. Conclusions The replacement of Si diodes by SiC diodes improves robustness of high power inverters for industrial induction heating applications due to their ability to be paralleled, but in applications, as hardening, with a large number of Power Cycles, the direct replacement is questionable due to the lower Power Cycling capacity of SiC diodes vs Si ones. The use of SiC MOSFETs is specially encouraged in very high frequency induction, high power induction heating inverters, as in the case of welders operating at frequencies above 150 kHz. On the opposite, SiC technology does not give an optimal solution at lower frequencies than 100 kHz, being in that case SI-IGBT technology the optimal one. In the final paper a much more deeper view on the above considerations, based on our experimental results, will be described for the optimal use of Si vs SiC technology in high frequency, high power resonant inverters for industrial induction heating applications. Bibliography 1.- Ortiz González, J., Alatise O., Nobee N., Hu J., Mawby P., “ Electrothermal Considerations for Power Cycling in SiC Technologies” CIPS 2016 Proc.- Nürnberg. 2.- Herold Ch, Schaeffer M., Sauerland F.,Poller T., Lutz J., Schilling O., “ Power Cycling Capability of Modules with SiC Diodes” Proc. CIPS 2014 Conference. Nürnberg 3.- Dede, E. “A 100kW Full SiC Inverter for Induction Heating Applications”, Proc. ISiCPEAW 2015 Workshop. Stockholm 2015. Figure 1

Power Amplifiers Based on SiC Technology for MHD Mode Control in Fusion Experiments

The effective control of magnetohydrodynamic instabilities in fusion experiments by means of actively controlled coils calls for challenging dynamic requirements to the relevant power supply (PS) systems. The first part of this paper gives an overview on typical requirements and technological solutions adopted in some present fusion experiments. Then, the advantages of SiC devices with respect to the Si ones are described in this paper, including lower switching losses, higher switching speed, higher operating junction temperature, and higher voltage capability. As an application example, this paper reports on the case of the PS system for resistive wall mode control in the JT-60SA satellite tokamak, where analyses showed the difficulty of satisfying the demanding requirements in terms of high current bandwidth (3 kHz) and short latency ( $ ) with a simple H-bridge topology adopting standard IGBT. On the contrary, the use of Si–SiC IGBT with the same topology can allow meeting the specifications, as demonstrated by the development and test of such a power amplifier, rated for $300~A_{{\mathrm{pk}}}$ and 240 V.

Electro-Thermal TCAD Model for 22 kV Silicon Carbide IGBTs

This paper presents the current progress in the development of an electro-thermal numerical model for 22 kV 4H-silicon carbide IGBTs. This effort involved the creation of a TCAD model based on doping profiles and structural layers to simulate the steady-state and switching characteristics of recently-fabricated experimental devices. The technical challenge of creating this high voltage SiC IGBT model was incorporating semiconductor equations with sub-models representing carrier mobility, generation, recombination, and lattice heat flow effects with parameters conditioned for 4H-silicon carbide material. Simulations of the steady-state and switching characteristics were performed and later verified with laboratory measurements for an N-type SiC IGBT rated for 22 kV with an active area of 0.37 cm2 and a drift region of 180 μm.

6.5 kV n-Channel 4H-SiC IGBT with Low Switching Loss Achieved by Extremely Thin Drift Layer

Thin drift layers were used to realize n-channel 4H-SiC IGBTs with an extremely low switching loss. The thickness of a drift layer was 60 μm, which was designed for a blocking voltage of 6.5 kV. An on-voltage of 5.4 V was obtained at a collector current of 100 A/cm2 and the specific differential on-resistance at 100 A/cm2 was 20 mΩcm2 at room temperature, indicating proper bipolar operation. A switching evaluation of the SiC IGBTs was performed with a bus voltage of 3.6 kV and a load current of 10 A, and a turn-off loss of 1.2 mJ was obtained. This turn-off loss is very small compared to the values in the current literatures, and was estimated to be an over 80% reduction. The series operation of thin-drift-layer 6.5 kV SiC IGBTs can ensure a lower switching loss than the single operation of higher blocking voltage devices in power conversion systems.

Device design assessment of 4H–SiC n-IGBT – A simulation study

A theoretical design assessment is presented using two dimensional numerical computer aided design (TCAD) tool for 15–20kV 4H–SiC IGBTs. Physical parameters of the layer structures such as drift layer thickness, doping in the drift layer, JFET region width and interface charges underneath the gate region are varied to predict the device performance. Performance is further assessed at different temperatures and with different carrier lifetime in the drift layer. Using identical set of physical device parameters (doping, thicknesses), simulated structure was first calibrated with the experimental data. Simulations show that a minority carrier lifetime in the drift layer of 1.0–1.6μs produces a close match with the experimental device. An on-resistance first decays with temperature (i.e., increased in ionization level, and increase in minority carrier lifetime), stays nearly constant with further increase in the temperature (may be all carriers are now fully ionized and increase in carrier lifetime is compensated with decrease in the carrier mobility) and finally increases linearly with temperature (>450K) due to decrease in the carrier mobility. A significant increase in the forward voltage drop is observed with the presence of interface trap charges. Increasing JFET region width slightly decreases the forward on-state voltage. A drift layer of at least 175μm thick with a doping concentration of <2.0×1014cm−3 is required to get a blocking voltage of 20kV for 4H–SiC IGBTs assuming a minority carrier lifetime of 1μs in the drift layer.

Integrated SiC Anode Switched Thyristor Modules for Smart-Grid Applications

Silicon Carbide Anode Switched Thyristors (ASTs) overcome major limitations of conventional Si and SiC IGBT and GTO Thyristor solutions by providing robust, latch-up free turn-off at high currents, current saturation in the output characteristics, and a wide safe operating area (SOA) through series current controlled device turn-off. In this work, detailed static and switching characteristics of 6.5 kV-class SiC ASTs are reported, which include a low on-state voltage drop of 4 V at 100 A/cm2, slight positive temperature co-efficient of Von, current saturation at &gt; 100 A Cathode currents and fast turn-on and turn-off times of 500 ns while switching 1300 V and 20 A.

Smart grid technologies

The need for power semiconductor devices with high-voltage, high- frequency, and high-temperature operation capability is growing, especially for advanced power conversion and military applications, and hence the size and weight of the power electronic system are reduced. Development of 15-kV SiC IGBTs and their impact on utility applications is discussed.

9 kV 4H-SiC IGBTs with 88 mΩ·cm&lt;sup&gt;2&lt;/sup&gt; of R &lt;sub&gt;diff, on&lt;/sub&gt;

SiC IGBTs are suitable for high power, high temperature applications. For the first time, the design and fabrication of 9 kV planar p-IGBTs on 4H-SiC are reported in this paper. A differential on-resistance of ~ 88 m(cm2 at a gate bias of –20 V is achieved at 25°C, and decreases to ~24.8 m(cm2 at 200°C. The device exhibits a blocking voltage of 9 kV with a leakage current density of 0.1 mA/cm2. The hole channel mobility is 6.5 cm2/V-s at room temperature with a threshold voltage of –6.5 V resulting in enhanced conduction capability. Inductive switching tests have shown that IGBTs feature fast switching capability at both room and elevated temperatures.

High temperature SiC trench gate p-IGBTs

Various design issues pertaining to SiC-based IGBTs are described. A trench gate, p-channel IGBT was considered the most appropriate structure for fabrication in SiC. The fabrication and characterization of high temperature SiC IGBTs with high current levels are presented. Using optimized emitter processing, 6H-SiC p-IGBTs show a higher current capability than 4H-SiC p-IGBTs because of their lower emitter contact resistance and higher MOS channel mobility. Since IGBTs rely on minority carrier injection, the low bulk mobility parallel to the c-axis in 6H-SiC was not found to severely affect the current carrying capability as compared with 4H-SiC IGBTs in the present design. Measured results of these devices are described from room temperature to the 350-400/spl deg/C temperature range. For both polytypes, the current capability was found to be much larger when their MOS gates were fabricated in the 112~0 crystal direction compared with the 1100 crystal direction. The emitter (p-type) contact anneal was also found to significantly affect the performance of SiC IGBTs. 4H-SiC IGBTs showed a -85 V blocking capability (room temperature) and on-current of 100 mA at 350/spl deg/C. 6H-SiC IGBTs were demonstrated with -400 V blocking capability (at 25/spl deg/C) and 2 A at 400/spl deg/C.

Evaluation of high-voltage 4H-SiC switching devices

In this paper, the on-state and switching performance of 4H-SiC UMOSFETs, TIGBTs, BJTs, SIThs, and GTOs with voltage ratings from 1 to 10 kV are simulated at different temperatures. Comparison with silicon devices highlights the advantages of SiC technology. SiC BJTs suffer the same problem as Si BJTs, namely the degradation of current gain with increased voltage rating which makes them unsuitable for applications above 4 kV. SiC MOSFETs dominate applications below 4 kV for their attractive conduction performance and advantages such as ease of use. Above 3 kV, SiC MOSFETs are not as attractive as SiC bipolar devices because of their high on-state voltages. In the voltage range simulated, SiC IGBTs, SIThs, and GTOs have comparable current handling ability. Considering the GTOs slow switching speed and drive complexities, IGBTs and SIThs are a better choice in the voltage range 4-10 kV. Calculations based on conduction loss and switching loss indicate that SiC SIThs are superior to IGBTs except in high-temperature and high-frequency applications where IGBTs are better. The need to provide a large gate current during turnoff and turn-off failure caused by gate debiasing, decreases the attractiveness of the SITh.

A simulation study of high voltage 4H-SiC IGBTs

This paper evaluates the performance of high voltage 4H-SiC IGBTs. The static and dynamic characteristics of SiC IGBTs with various high voltage ratings and structures at different temperatures are obtained by 2D numerical and analytical simulations. Discrepancies in the device performance are investigated. Comparison with silicon IGBTs is also included.