IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 59, NO. 6, DECEMBER 2012 3235 Analysis of Commercial Punch-Through IGBTs Behavior Under Co Irradiation: Turn-Off Switching Performances Evolution Boubekeur Tala-Ighil, Amrane Oukaour, Hamid Gualous, Bertrand Boudart, Bertrand Pouderoux, Jean-Lionel Trolet, and Marc Piccione Abstract—This paper deals with the effects of Co gamma irradiation on punch-through commercial insulated gate bipolar transistors turn-off switching behavior. The response of the threshold voltage, the gate-emitter leakage current, the collector leakage current, the collector-emitter breakdown voltage and the turn-off switching parameters under three different in situ gate biases are described. Charge trapping in the gate oxide causes the decrease of the threshold voltage. It is shown that the decrease of this parameter and the modifications in the Miller plateau level and width result in an increase of the turn-off delay time, the collector current fall-time, the collector-emitter voltage rise-time, and consequently an increase of the turn-off switching losses and a decrease of the turn-off overshoot collector-emitter voltage. Index Terms—Insulated gate bipolar transistor, total ionizing dose, turn-off switching parameters. I. INTRODUCTION B ECAUSE of their low cost, ready availability, high perfor- mances, the use of COTS (Commercial-Off-The-Shelf) devices wherever and whenever possible has evolved to become the main method of procurement in powering systems in nearly all military, aerospace and nuclear power applications. The de- vices that make up the power bus such as distribution units, cir- cuit breakers, and power converters are COTS devices. However, the use of COTS devices raises a series of questions concerning their reliability in a radiation environment. Unfor- tunately, most often there is no alternative to the use of these commercial devices, and system designers have to manage the risk associated to their use. The most successful and higher per- forming systems will be those that manage this risk the most successfully. The management of this risk requires a thorough understanding of the reliability and the failure mechanisms as- sociated with the selected device. In the field of power electronics, the Insulated Gate Bipolar Transistor (IGBT) is one of the most serious candidates for Manuscript received January 03, 2012; revised April 12, 2012; accepted May 24, 2012. Date of publication October 19, 2012; date of current version De- cember 11, 2012. The authors are with the Université de Caen Basse-Normandie, EA 4253, F-50130 Cherbourg-Octeville, France (e-mail:boubekeur.tala-ighil@uni- caen.fr; amrane.oukaour@unicaen.fr; hamid.gualous@unicaen.fr; bertrand. boudart@unicaen.fr; bertrand.pouderoux@unicaen.fr). J. L. Trolet and M. Piccione are with the Ecole des Applications Militaires de l’Energie Atomique, F-50115 Cherbourg-Octeville, France (e-mail:jean-li- onel@eamea.fr; marc.piccione@marine.defense.gouv.fr). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TNS.2012.2216289 an evaluation with the aim of a use in radiation environments. There has been an increasing interest in evaluating this device in such environments. Most studies have focused only upon the devices’ SEE (Single Event Effects) performances, threshold voltage shifts and for some of them, some static parameters such as the gate leakage current and the collector leakage current [1]–[15]. Nevertheless, all these studies have failed to examine how the various parameters linked to the switching mode op- eration are affected by ionizing radiation under different bias conditions. These parameters are of a great importance for de- vices intended to be used in static power converters. This paper deals with the effects of total ionizing dose of gamma radiation on punch-through IGBTs under different in situ gate biases. A particular interest is taken in the switching parameters and, in the context of this paper, we have chosen to focus specifically on the turn-off switching parameters. II. DESCRIPTION OF THE IGBT An n-channel IGBT is fundamentally a double diffused ver- tical n-channel power MOSFET built on a p-substrate. The IGBT combines, in a single device, the simple gate-drive characteristics of the MOSFETs with the high current and low saturation voltage capability of bipolar transistors. The IGBT is used in medium to high power applications such as switched-mode power supply, traction motor control and induction heating. Two technologies of IGBTs, NPT (Non-Punch-Through) structure (the most basic one) and PT (Punch-Through) struc- ture, are currently competing to provide the best compromise between switching and conduction losses. The PT structure incorporates an additional and highly doped buffer layer between the basis (drift region) and the substrate. Fig. 1 shows the vertical cross section through one of the fun- damental cells of the PT IGBT structure. An IGBT chip consists of many such elements connected in parallel. The polysilicon layer, the gate, is arranged such that it over- laps the , and regions. On the top, the emitter contact is made by aluminium which overlaps the and regions. On the other side of the wafer, the collector contact is made by aluminium contact on the region. In the normal mode of operation, the collector is made posi- tive. When gate is at zero potential, no main current flows from collector to the emitter. When gate potential is made positive, electrons are attracted in the p region below the gate oxide and 0018-9499/$31.00 © 2012 IEEE