Umamaheswara Vemulapati

The radial layout design concept for the Bi-mode insulated gate transistor

In this paper we present a new radial design concept for an optimized layout of anode shorts in the Bi-mode Insulating Gate Transistor (BiGT). The study shows that the arrangement of the n+-stripes plays a key role for the on-state characteristics of the BiGT. With the aid of 3D device simulations the visualization of the plasma distribution during the on-state conduction was obtained in a 0.25 × 4 mm2 large BiGT model area. The influence of the dimensioning and layout of the anode shorts was simulated and compared with measured on-state curves. A clear improvement of plasma distribution in the device when the stripes are arranged orthogonally (radially) to the pilot-IGBT boundary is observed in 3D simulations. Measurements confirm lower on-state losses as a result of better utilization of the device area.

Characterization of a Silicon IGBT and Silicon Carbide MOSFET Cross-Switch Hybrid

A parallel arrangement of a silicon (Si) IGBT and a silicon carbide (SiC) MOSFET is experimentally demonstrated. The concept referred to as the cross-switch (XS) hybrid aims to reach optimum power device performance by providing low static and dynamic losses while improving the overall electrical and thermal properties due to the combination of both the bipolar Si IGBT and unipolar SiC MOSFET characteristics. For the purpose of demonstrating the XS hybrid, the parallel configuration is implemented experimentally in a single package for devices rated at 1200 V. Test results are obtained to validate this approach with respect to the static and dynamic performance when compared to a full Si IGBT and a full SiC MOSFET reference devices having the same power ratings as for the XS hybrid samples.

1MW bi-directional DC solid state circuit breaker based on air cooled reverse blocking-IGCT

In this paper, we present the development of an air-cooled 1MW bi-directional DC Solid State Circuit Breaker (SSCB) based on recently developed 91mm, 2.5kV Reverse Blocking-IGCT (RB-IGCT). The power electronic switch (RB-IGCT) has been designed and optimized to have very low conduction losses, less than 1kW at 1kA (on-state voltage drop <; 1V at 1kA, 400K) and high turn-off current capability (> 6.5kA at 1.6kV, 400K) which are the most important concerns of semiconductor based circuit breaker. We also present the simulation and experimental results at the system level i.e. analyzed the influence of the Surge Arrester (SA) on the over-voltage transients during current interruption. We also analyzed the thermal management for the newly developed SSCB using ANSYS Icepak and validated experimentally.

Reverse conducting–IGBTs initial snapback phenomenon and its analytical modelling

Analytical models have been proposed to describe the onset current density for the initial snapback in the transistor on-state mode and in the blocking state of reverse conducting-insulated gate bipolar transistors (RC-IGBT) for the stripe and cylindrical designs of the anode shorts. In cylindrical case, there are two possible ways in designing the anode shorts and the authors have proposed an analytical model for each of them. The considered RC-IGBTs are vertical with soft punch-through type buffer designs. The analytical model has been evaluated with the aid of 2-D device simulations and measurements. The authors have investigated the initial snapback phenomenon for different voltage class devices at a given technology (anode and buffer profiles) and found out that the snapback voltage increases with the blocking capability but not the snapback current density. The authors have also observed that the initial snapback phenomenon is more pronounced at lower temperatures. From the analytical model as well as simulation and measurement results, the authors have found that for a given voltage class and technology, the p + -anode width is the only remaining design degree of freedom which determines the initial snapback. The adjustment of the on-state losses can then be done with the proportion of the n + -short region.

An experimental demonstration of a 4.5 kV “Bi-mode Gate Commutated Thyristor” (BGCT)

In this work we present the first experimental results of a Bi-mode Gate Commutated Thyristor (BGCT). The BGCT is a new type of Reverse Conducting-Integrated Gate Commutated Thyristor (RC-IGCT). In a conventional RC-IGCT, the IGCT and diode are integrated into a single wafer but they are fully separated from each other. The novel BGCT on the other hand features an interdigitated integration of diode- and GCT-areas. This interdigitated integration results in an improved diode as well as GCT area, better thermal distribution, soft turn-off/reverse recovery and lower leakage current compared to conventional RC-IGCTs. We have discussed the advantages of a new diode anode design in BGCT, which is shallower than that of the conventional RC-IGCT. We have successfully demonstrated the BGCT concept with 38 mm, 4.5 kV prototypes and compared the on-state, turn-off and blocking characteristics with conventional RC-IGCTs both in GCT- and diode-modes of operation.

The concept of Bi-mode Gate Commutated Thyristor-A new type of reverse conducting IGCT

In this paper, a new type of reverse conducting IGCT referred to as Bi-mode Gate Commutated Thyristor (BGCT) is discussed. The concept of the BGCT follows an interdigitated integration approach of an IGCT and Diode into a single structure while utilizing the same silicon volume in both GCT and Diode modes. This results in improved thermal behavior and current capability. The BGCT design concept differs from that of the conventional Reverse Conducting IGCT (RC-IGCT) since in the BGCT, each individual segment is designed either as a GCT cathode or Diode anode. With the aid of 2-D Sentaurus TCAD device simulations, we have compared the static and dynamic characteristics of a 91 mm 4.5 kV BGCT model in both GCT and diode modes with that of the equivalent RC-IGCT and asymmetric IGCT. Furthermore, we have also investigated the BGCT performance by varying the GCT to Diode segments ratio.

Recent advancements in IGCT technologies for high power electronics applications

In this paper, we review the progress made recently for further developing the Integrated Gate Commutated Thyristor (IGCT) device concept for high power electronics applications. A wide range of newly introduced IGCT technologies are discussed and recent prototype experimental results as well as novel structures and future trends of the IGCT technology are presented. This will provide system designers with a comprehensive overview of the potentials possible with this device concept.

Improving Current Controllability in Bi-Mode Gate Commutated Thyristors

The Bi-mode gate commutated thyristor (BGCT) is a new type of reverse conducting Gate Commutated Thyristor (GCT). This paper focuses on the maximum controllable current capability of BGCTs and proposes new solutions which can increase it. The impact of proposed solutions in the turn-ON and turn-OFF is also assessed. For this analysis, a 2-D mixed mode model for full-wafer device simulations has been developed and utilized.

Robust 3.3kV silicon carbide MOSFETs with surge and short circuit capability

An approach to implement electrically robust MOSFETs in a functioning half-bridge will be investigated. For the first time, reverse conducting 3.3kV SiC MOSFETs have been fabricated with dilferent cell pitches from 14μm (p1.0) to 26μm (pl.8) that are able to withstand short circuit pulse of up to 10μs and a 9ms surge current event up to 15x the nominal current. LinPak half-bridge modules have been fabricated showing reduction of the switching loss by more than 90% compared to a silicon IGBT/diode half bridge.

Current Sharing Behavior in Si IGBT and SiC MOSFET Cross-Switch Hybrid

The cross hybrid (XS) concept has been demonstrated experimentally with 3.3-kV Si Insulated Gate Bipolar Transistor (IGBTs) and SiC MOSFETs in parallel, and used to calibrate 2D Technology Computer Aided Design simulations. The XS hybrid offers lower switching losses compared with full Si IGBTs and reduced oscillations compared with full SiC MOSFETs. The current sharing mechanism between the IGBT and the MOSFET in the XS hybrid has been elucidated, showing that under typical switching conditions, the IGBT dissipate 98% of the XS hybrid turn-OFF losses compared with the SiC MOSFET. Since the current density of the IGBT in the XS hybrid is twice of that of the full IGBT solution, it exhibits higher dynamic avalanche. These features results in stress at device and package level, thereby compromising robustness and reliability. In order to overcome such issues, we show that increasing the turn-OFF gate resistance improves current sharing in the XS hybrid by delaying the turn-OFF of the MOSFET, and thereby suppressing dynamic avalanche in the IGBT.