Papers by Author: Ranbir Singh

Abstract: Bipolar silicon carbide devices are attractive for high power applications offering high voltage devices with low on-state voltages due to plasma flooding. Unfortunately, these devices suffer from bipolar degradation, which causes a significant degradation of the on-state voltage. To explore the generation of stacking faults, which cause the degradation, the impact of the current density and temperature on bipolar degradation is investigated in this work. The analysis is done by stressing the base-collector diode of 1.2 kV bipolar junction transistors (BJTs) as well as the BJTs in common-emitter mode operation with different current densities at different temperatures.

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: This paper reports the progress of the thick epitaxy development at Dow Corning. Epiwafers with thickness of 50 – 100 m have been grown on 4° off-axis 76mm 4H SiC substrates. Smooth surface with RMS roughness below 1nm and defect density down to 2 cm-2 are achieved for 80 - 100 m thick epiwafers. Long carrier lifetime of 2 – 4 s are routinely obtained, and low BPD density in the range of 50 down to below 10 cm-2 is confirmed. High voltage JBS diodes have been successfully fabricated on these wafers with thick epitaxial layers.

Abstract: 1200 V-Class Super-High Current Gain Transistors or SJTs developed by GeneSiC are distinguished by low leakage currents of 2. Two-stage cascaded SJTs display a record high current gain of 3475. Results from detailed on-state, blocking, switching and reliability characterization of 1200 V-class 4 mm² and 16 mm² SiC SJTs are presented in this paper.

Abstract: Sharp avalanche breakdown voltages of 12.9 kV are measured on PiN rectifiers fabricated on 100 µm thick, 3 x 10¹⁴ cm-3 doped n- epilayers grown on n+ 4H-SiC substrates. This equates to a record high 129 V/µm for a > 10 kV device. Optimized epilayer, device design and processing of the SiC PiN rectifiers result in a > 60% blocking yield at 10 kV, ultra-low on-state voltage drop and differential on-resistance of 3.75 V and 3.3 mΩ-cm² at 100 A/cm² respectively. Open circuit voltage decay (OCVD) measured carrier lifetimes in the range of 2-4 µs are obtained at room temperature, which increase to a record high 14 µs at 225 °C. Excellent stability of the forward bias characteristics within 10 mV is observed for a long-term forward biasing of the PiN rectifiers at 100 A/cm2. A PiN rectifier module consisting of five parallel large area 6.4 mm x 6.4 mm 10 kV PiN rectifiers is connected as a free-wheeling diode with a Si IGBT and 1100 V/100 A switching transients are recorded. Data on the current sharing capability of the PiN rectifiers is also presented.

Abstract: Improvements in the quality and consistency of 4H-SiC epitaxy wafers are now starting to enable growth of commercial SiC power device applications in areas such as inverters for photo-voltaic systems and power supplies. Recent work has achieved very low epitaxy surface roughness and very low BPD (Basal plane dislocation) in the on 4 degree off-axis substrates. In this paper, we report characterization of the very low BPD epitaxy wafers and a newly observed triangular defect.

Abstract: This study is focused on the design and fabrication of large-area (4.1x4.1 mm2 and 8.2x8.2 mm2), 8.1 kV 4H-SiC GTO Thyristors. The anode and gate fingers of Thyristors were designed with involute, cellular or hexagonal patterns. Forward blocking voltages as high as 8106 V and On-state voltage drop (Von) and differential specific on-resistance (Ron,sp) as low as 3.8 V and 6 mΩ-cm2 at 100 A/cm2 were measured on these devices. About 59% of 4.1 x4.1 mm2 and 29% of 8.2x8.2 mm2 Thyristors blocked voltages in excess of 6 kV. Detailed investigations revealed the impact of different anode/gate finger geometries on the device characteristics. Preliminary pulsed power characterization of the GTO Thyristors was also performed.

Abstract: Correlation between carrier lifetime and forward voltage drop in 4H-SiC PiN diodes has been investigated. PiN diodes from the drift layer of 20 m shows breakdown voltage of 3.3 kV and forward voltage drop as low as 3.13 V at 100A/cm2. Variation of calculated forward voltage drop ( ) from measured carrier lifetimes is very comparable to measured of fully processed PiN diodes. Measured carrier lifetime and of PiN diodes also show good spatial correlation. Wafer level lifetime mapping can be employed to assess and predict of PiN diodes.

Abstract: For the first time, large area 10 kV SiC power devices are being produced capable of yielding power modules for high-frequency megawatt power conversion. To this end, the switching performance and power dissipation of silicon carbide (SiC) n-channel IGBTs and MOSFETs are evaluated using numerical simulations software over an extended current range to determine the best device suitable for 10 kV applications. Each device is also optimized for minimal forward voltage drop in the on-state.

Abstract: The development of 10 kV silicon carbide (SiC) MOSFETs and Junction Barrier Schottky (JBS) diodes for application to a 13.8kV 2.7 MVA Solid State Power Substation (SSPS) is shown. The design of half-bridge power modules has extensively used simulation, from electron level device simulations to the system level trade studies, to develop the most efficient module for use in the SSPS. In the work presented within, numerical simulations and experimental results are shown to demonstrate the design and operation of 10 kV JBS diodes. It is shown that JBS diodes at 10 kV can reduce 31% of the switching losses at 20 kHz than the fastest SiC PiN diodes.