Liutauras Storasta

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 6.5 kV IGBTs for High-Power Medium-Frequency Soft-Switched Applications

Medium voltage high-power applications are usually realized using high voltage semiconductors (3.3 kV and above) operated in the hard switching mode with low switching frequencies (several hundreds of hertz). However, for high-power dc-dc converters employing a transformer for galvanic isolation, it is attractive to increase the switching frequency so that the transformer size can be reduced. An increase of the switching frequency implies an increase of the switching losses, and this has to be mitigated somehow, usually by choice of resonant topologies or soft switching techniques. Main focus of the paper is on the operation of the insulated gate bipolar transistor (IGBT) within a high-power dc-dc LLC resonant converter, in order to explore interactions between semiconductor and circuit properties, which both must be simultaneously considered in order to achieve the best utilization of a high voltage power semiconductor operating at higher switching frequencies. For these purposes, switching properties of a standard 6.5 kV IGBT are compared with switching properties of two different optimized versions of a 6.5 kV IGBT. Experimental results are included to support theoretical considerations and findings.

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.

Bipolar transistor gain influence on the high temperature thermal stability of HV-BiGTs

In this paper we present the detailed investigation of the influence of the internal bipolar PNP transistor gain on the thermal stability of high voltage IGBTs and BiGTs. The bipolar gain is controlled by means of anode and buffer design and by the introduction of anode shorts. The influence of the different buffer and anode doping profiles and the different layouts in the case of anode-shorted designs are analyzed. Temperature dependent leakage current measurements confirm that the lowering of the leakage current and its subsequent weak temperature dependency can be achieved by buffer and anode engineering albeit with certain design trade-off restrictions. Nevertheless, another effective approach for suppressing the leakage current and its dependency on temperature is achieved by the introduction of anode shorts as demonstrated in reverse conducting IGBT or BiGT structures. Such designs eliminate to a large extent the internal bipolar transistor action in the BiGT anode shorted designs while allowing different anode and buffer doping profiles for the design trade-offs. Despite the fact that the lifetime control in the BiGT drift region causes the leakage current to increase, the temperature coefficient remains unchanged, hence, making the hard switched BiGT suitable for high temperature operation.

BIGT control optimisation for overall loss reduction

In this paper we present the latest results of utilizing MOS-control (MOSctrl) to optimize the performance of the Bi-mode Insulated Gate Transistor (BIGT) chip. The adaption of the BIGT technology enables higher output power per footprint. However, to enable the full performance benefit of the BIGT, the optimisation of the known standard MOS gate control is necessary. This optimisation is being demonstrated over the whole current and temperature range for the BIGT diode turn-off and BIGT turn-on operation. It is shown that the optimum control can offer a performance increase up to 20% for high voltage devices.

Demonstration of an enhanced trench Bimode Insulated Gate Transistor ET-BIGT

In this paper, a 3300V Bimode Insulated Gate Transistor BIGT chip utilizing an Enhanced Trench MOS cell is demonstrated. The paper provides an insight into the ET-BIGT device design along with the static and dynamic electrical results obtained from the first manufactured prototypes. The combined advantages of a low loss Enhanced Trench cell concept and BIGT chip integration sets a new milestone for delivering higher output power for the next generation BIGT power modules.

Short circuit behavior of the Bi-mode Insulated Gate Transistor (BIGT)

The BIGT is a Reverse Conducting IGBT device which combines functionality of a high power IGBT and fast diode on a single chip. In this paper, an investigation of the IGBT mode short circuit performance of the BIGT is carried out. The behavior of the BIGT under IGBT mode short circuit conditions is illustrated by measurements on a 3.3kV 1500A HiPak1 module and then supported by circuit and detailed device physics simulations. The short circuit conditions of type II and type III are discussed, with the variations introduced due to the gate control of the BIGT when operated in reverse conducting mode. Comparison to standard IGBTs with Soft-Punch-Through (SPT) technology in a HiPak2 module is also provided.