Materials Science Forum Vols. 778-780

Abstract: SiC, a wide band gap semiconductor, is capable of robust operation at temperatures well above 600°C. SiC bipolar transistors are well suited for applications at high temperatures as, unlike MOSFET, it does not have a critical gate oxide, and hence oxide reliability at high temperatures is not an issue. In this paper, the design of optimized emitter coupled logic technology circuits using 4H-SiC bipolar transistors is presented. The circuits work over a wide range of temperatures and power supply voltages at high speeds, demonstrating the potential of robust high speed ECL integrated circuits in SiC for small-scale logic applications.

Abstract: In this work, a 4H-Silicon Carbide (SiC) Bipolar Junction Transistor (BJT) capable of operating at high temperatures up to 673 K is demonstrated. Comprehensive characterization including current gain, early voltage, and intrinsic voltage gain was performed. At elevated temperatures, although the current gain of the device is reduced, the intrinsic voltage gain increases to 5900 at 673 K, suggesting 4H-SiC BJT has the potential to be used as a voltage amplifier at extremely high temperatures.

Abstract: In this work, large area SiC BJTs with good long-term stability in 1000 hrs DC stress tests are demonstrated. It is also illustrated how wafer scanning techniques can be used to reject BJT dies with basal plane dislocations, thereby eliminating the risk for bipolar degradation.

Abstract: A 12 kV class 4H-SiC thyristor with a pilot thyristor (an amplification step) has been triggered to a current I_max = 1310 A in a mixed resistive-inductive load circuit. In order to further increase the I_max, the homogeneity of the initially turned-on region should be improved and/or additional amplification steps introduced

Abstract: This study addresses the transient and steady-state performance of a >13 kV SiC ETO as a Solid-State Circuit Breaker (SSCB). The developed SiC-ETO is based on a 1 cm², 15 kV SiC p-GTO with an extremely low differential resistance. Static performance of the device, including the on-state voltage drop at different temperatures and different currents has been carried out in this paper. Furthermore, transient performance of the device, including the turn off energy of the device has been studied. Also, the superior performance of the p-type SiC-ETO has been exploited to design and implement a solid-state circuit breaker. The studies verify the superiority of the SiC p-ETO compared to other solid state devices for this application.

Abstract: A 1 cm x 1 cm 4H-SiC N-IGBT exhibited a blocking voltage of 20.7 kV with a leakage current of 140 μA, which represents the highest blocking voltage reported from a semiconductor power switching device to this date. The device used a 160 μm thick drift layer and a 1 μm thick Field-Stop buffer layer, and showed a V_F of 6.4 V at an I_C of 20 A, and a differential R_on,sp of 28 mΩ-cm². Switching measurements with a supply voltage of 8 kV were performed, and a turn-off time of 1.1 μs and turn-off losses of 10.9 mJ were measured at 25°C, for a 8.4 mm x 8.4 mm device with 140 μm drift layer and 2 μm F-S buffer layer. The turn-off losses were reduced by approximately 50% by using a 5 μm F-S buffer layer. A 55 kW, 1.7 kV to 7 kV boost converter operating at 5 kHz was demonstrated using the 4H-SiC N-IGBT, and an efficiency value of 97.8% was reported.

Abstract: This paper addresses the design diagnostic study of 4H-SiC based IGBTs using two dimensional numerical computer simulations. Using identical set of physical device parameters (doping, thicknesses), simulated structure was first calibrated with the experimental data. A minority carrier life time in the drift layer of 1.0 1.6 μs and contact resistivity of 0.5 - 1.0 x 10^-4 Ω-cm² produces a close match with the experimental device. A decay in the device transconductance and threshold voltage is observed with increasing temperature. The on-resistance first decays with temperature (i.e., increased in ionization level, and increase in minority carrier life time), stays nearly constant with further increase in the temperature (may be all carriers are now fully ionized and increase in carrier life time is compensated with decrease in the carrier mobility) and finally increases linearly with temperature (> 450 K) due to decrease in the carrier mobility. The design of buffer layer is investigated that shows lower on-state losses with thin high doped buffers. For the design of devices over 15 20 kV, the design of drift layer demands a doping of < 2.0 x 10¹⁴ cm^-3 with epitaxial layer quality giving a carrier life time over 2.0 μs.

Abstract: High-voltage SiC p-channel insulated-gate bipolar transistors (p-IGBT) utilizing current-spreading layer (CSL) formed by ion implantation are fabricated and their properties characterized. A high blocking voltage of 15 kV is achieved at room temperature by optimizing the JFET length. An ampere-class p-IGBT exhibited a low forward voltage drop of 8.5 V at 100 A/cm² and a low differential specific on-resistance of 33 mΩ cm² at 250 °C, while these values were high at room temperature. For further reduction of the forward voltage drop in the on-state and temperature stability, the temperature dependence of the JFET effect and carrier lifetime in p-IGBTs are investigated. Optimization of the JFET length using an epitaxial CSL, instead of applying ion implantation and lifetime enhancement, could lead to a further reduction of the forward voltage drop.

Abstract: In order to test the response of radiation-induced current with wide range of dose rate, a Silicon Carbide (SiC) dosimeter is exposed to gamma-rays emitted from a ⁶⁰Co source. The SiC dosimeter in this study is made of a high purity semi-insulating 4H-SiC with nickel and aluminum electrodes. We have successfully demonstrated that the radiation-induced currents in the dosimeter show a linear relationship with the dose rate, and are repeatable and stable.

Abstract: Silicon carbide (SiC) radiation detectors were realized by ¹⁰B implantation into the metal contact in order to avoid implantation-related defects within the sensitive area of the 4H-SiC pn junction. No post implantation annealing was performed. Such detectors respond to thermal neutrons showing consistent counting rates as function of external reverse bias voltages and radiation intensity.