Materials Science Forum Vols. 717-720

Abstract: The current gain degradation of 4H-SiC BJTs with no significant drift of the on-resistance is investigated. Electrical stress on devices with different emitter widths suggests that the device design can influence the degradation behavior. Analysis of the base current extrapolated from the Gummel plot indicates that the reduction of the carrier lifetime in the base region could be the cause for the degradation of the gain. However, analysis of the base current of the base-emitter diode shows that the degradation of the passivation layer could also influence the reduction of the current gain.

Abstract: We present our latest developments in ultra high voltage 4H-SiC IGBTs. A 6.7 mm x 6.7 mm 4H-SiC N-IGBT with an active area of 0.16 cm2 showed a blocking voltage of 12.5 kV, and demonstrated a room temperature differential specific on-resistance of 5.3 mΩ-cm2 with a gate bias of 20 V. A 4H-SiC P-IGBT exhibited a record high blocking voltage of 15 kV, while showing a differential specific on-resistance of 24 mΩ-cm2. A comparison between P- and N- IGBTs in 4H-SiC is provided in this paper.

Abstract: The performance of a 12kV planar Clustered Insulated Gate Bipolar Transistor (CIGBT) is compared to an equivalent IGBT in 4H-SiC through extensive 2D numerical simulations. The CIGBT shows 40% reduction in Eoff-Vce(sat) trade off losses with a short circuit endurance time of more than 10µs.

Abstract: The impact of device concepts of Si insulated gate bipolar transistors (IGBTs) such as injection-enhanced IGBT (IEGT), high-conductivity IGBT (HiGT), and Si-limit IGBT on the performance of SiC IGBTs is examined. We first show that the forward characteristics of the original type of planer SiC IGBTs are much worse than those of SiC PiN diodes, even if the carrier lifetime is improved. Next, we show that the forward characteristics of SiC IEGTs and SiC HiGTs are comparable to those of SiC PiN diodes. Thus, device concepts of Si IGBTs are effective in improving the device performance of SiC IGBTs. Finally, it is shown that a SiC-limit IGBT can be realized when the mesa width is less than 0.5 μm.

Abstract: This paper will demonstrate how the newer Silicon Carbide material semiconductor power devices can contribute to carbon emissions reduction and the speed of adoption of electric vehicles, including hybrids, by enabling significant increases in the driving range. Two IGBT inverter leg modules of identical power rating have been manufactured and tested. One module has silicon-carbide (SiC) Schottky diodes as anti-parallel diodes and the other silicon PiN diodes. The power modules have been tested and demonstrate the superior electrothermal performance of the SiC Schottky diode over the Si PiN diode leading to a reduction in the power module switching losses.

Abstract: In this paper, for the first time, we report 12 kV, 1 cm² SiC GTOs demonstrated with a novel negative bevel termination, which improves the breakdown voltage by >3.5 kV compared to the conventional multiple-zone Junction Termination Extension (JTE). The significant improvement in the blocking voltage was attributed to the elimination of the electrical field crowding in the periphery of the mesa with conventional JTE termination. This new termination has been used in both electrically and optically triggered SiC GTOs. An ultrafast turn-on speed of 70 ns has been measured on 12 kV, 1 cm² SiC light triggered GTOs.

Abstract: The Army Research Laboratory has collaborated with Cree, Inc. and Silicon Power Corp. to develop 9 kV-blocking, 1.0 cm² Super-GTOs. In this study, several 1.0 cm² GTOs were individually switched up to 6.0 kA in a low-inductance, high dI/dt (2.1 kA/µs) circuit to evaluate turn-on delay and optimize the gate control. Turn-on delay was evaluated relative to gate drive current, and the delay was reduced by 1.1 µs when gate amplitude was increased from 1 A to 8 A. Increasing gate current delivered to each GTO also successfully reduced variation in turn-on delay from device to device by at least 50%, and mitigated mismatch in turn-on between pairs of GTOs switched in parallel. As silicon carbide material processing and device development continue to evolve, the ultimate solution will be to reduce remaining material defects and to control minority carrier diffusion length through more uniform doping across the wafer. These steps will enable modules of parallel GTOs to perform at maximum capability.

Abstract: 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 > 100 A Cathode currents and fast turn-on and turn-off times of 500 ns while switching 1300 V and 20 A.

Abstract: In this paper, we report a 0.1cm² 4H-SiC gate-turn-off (GTO) thyristor with 6 kV blocking voltage fabricated on a structure with a 60µm blocking layer. A relatively large area, high voltage 4H-SiC GTO that exhibits encouraging characteristic at the on- and off-states, and a low leakage current with 63% devices blocking 3kV or higher. Initial pulse testing result shows that the fabricated GTOs are capable of both high current density and high turn-off speed.

Abstract: This paper presents results attained with SiC GTO thyristors terminated by a single step and a graded etched JTE. The comparison of both types of devices reveals no significant difference in the on-state and switching characteristics but a higher blocking capability of some thyristors with the latter kind of termination. The best devices showed a forward breakdown voltage of nearly 6 kV, which is a distinct progress as against previous results of thyristors with a graded etched JTE. Furthermore, such GTO thyristors have been characterized dynamically for the first time.