Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 4) Energy shocks. <s> IGBTs are available with short-circuit withstand times approaching those of bipolar transistors. These IGBTs can therefore be protected by the same relatively slow-acting circuitry. The more efficient IGBTs, however, have lower short-circuit withstand times. While protection of these types of IGBTs is not difficult, it does require a reassessment of the traditional protection methods used for bipolar transistors. An in-depth discussion on the behavior of IGBTs under different short-circuit conditions is carried out and the effects of various parameters on permissible short-circuit time are analyzed. The paper also rethinks the problem of providing short-circuit protection in relation to the special characteristics of the most efficient IGBTs. The pros and cons of some of the existing protection circuits are discussed and, based on the recommendations, a protection scheme is implemented to demonstrate that reliable short-circuit protection of these types of IGBTs can be achieved without difficulty in a PWM power convertor motor drive application. > <s> BIB001 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 4) Energy shocks. <s> In this paper, reverse-recovery failure modes in modern fast power diodes are investigated. By the aid of semiconductor device simulation tools, a better view is obtained for the physical process, and operating conditions at which both diode snappy recovery and dynamic avalanching occur during the recovery period in modern high-frequency power electronic applications. The work presented here confirms that the reverse-recovery process can by expressed by means of diode capacitance effects which influence the reverse-recovery characteristics. The paper also shows that the control of the carrier gradient and the remaining stored charge in the drift region during the recovery phase influence both failure modes and determine if the diode exhibits soft, snappy, or dynamic avalanche recovery characteristics. <s> BIB002 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 4) Energy shocks. <s> This paper will discuss the different principal short circuit failure modes of IGBTs focusing on the new Trench-/Field-Stop-IGBT device concept. Beside the short circuit robustness limitation regarding an over temperature destruction, a new failure mode, the so called short circuit current destruction mode, is described. Necessary design aspects for Trench-/Field-Stop devices resulting in a superior short circuit robustness at least as good as the well established Non Punch Through IGBTs - are derived and proved experimentally by extreme single (e.g. Tj=200/spl deg/C!) and repetitive short circuit pulse tests (e.g. 50.000 times). <s> BIB003 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 4) Energy shocks. <s> This work presents the behavior of single-chip insulated gate bipolar transistors (IGBT) devices under repetitive short-circuit operations. The 600 and 1200 V nonpunch through IGBTs as well as 600 V COOLMOS (trademark of Infineon Technologies) have been tested. The repetition of these severe working conditions is responsible for devices ageing, and results unavoidably in the components failure. A series of experimental tests were made in order to determine the number of short-circuit operations the devices can support before failure for different dissipated energies. The temperature influence has been also investigated. Results show two distinct failure modes depending on the dissipated energy during the tests. A critical value of short-circuit energy has been pointed out which separates these failure modes. Experimental and numerical investigations have been carried out in order to analyze these failure modes. A detailed analysis of the physical mechanisms occurring during the short-circuit failures for dissipated energies equal or lightly higher than the critical value is presented. <s> BIB004 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 4) Energy shocks. <s> Four short circuit electrical configurations leading to the Trench IGBT failures are studied in detail by the help a two dimensional physically-based device simulator. By analyzing different internal physical parameters, it was highlighted that the failure occurring during the turn-on is due to a high impact ionization generation rate, whereas the failures occurring during on- state, at the turn-off and the one occurring some microseconds after turn-off are due to a thermal runaway phenomenon. <s> BIB005 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 4) Energy shocks. <s> Abstract This paper presents experimental and numerical investigations on the delayed failure mode of IGBT devices observed under short-circuit operations. For short-circuit energies lightly higher than a critical value, the default current may be successfully turned-off but a leakage current takes place leading to a thermal runaway and finally to a delayed failure. Numerical investigations have been carried out and a detailed analysis of the physical mechanisms occurring during the delayed failure mode is presented. We show that the classical short-circuit failure mode (energy limited) is a limit case of the delayed failure mode with zero delay time to failure. So, the analysis is extended to the energy limited case and give better understanding of the failure process of this last failure mode. An electro-thermal model including the device and the solder layer is presented as well as all leakage current components models like saturation, thermal and avalanche generation currents. A detailed description of the thermal runaway is given and main parameters influence on critical energy value are presented, especially, case temperature and solder layer thickness. Finally, numerical results allow to show that the critical energy which separates two failure modes corresponds to a threshold temperature of about 650 °C in the vicinity of the junction location which seems to be independent of test conditions. <s> BIB006 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 4) Energy shocks. <s> In this work we will focus on the short circuit destruction of IGBTs after turn-off. Electro-thermal device simulations and experimental verifications have been carried out to study the failure mechanism and identify the improvement potential. Heat diffusion to the front and back side chip surfaces after the short circuit pulse causes temperature rises at the pn-junctions which in turn inject thermally induced leakage currents into the drift region. They can lead to self-heating up to device destruction if the heat transport out of the chip is limited by a poor thermal setup. The combination of a significant heat capacity at the chip front side with a significant reduction of the thermal resistance of the solder layer has been found to be most efficient for increasing the short circuit capability. 1200V trench field-stop IGBTs with a thick front side metallization – made of copper instead of aluminum – have been fabricated and have been attached to the DBC by a newly developed diffusion soldering process. This way the critical short circuit energy before destruction has been increased by 80% which has also been predicted by simulation. In contrast, attaching a separate heat capacity by soldering a molybdenum cube to the chip front side did not yield the expected improvement. Active IGBT cells which could be not covered by the heat sink failed at the original energy level. <s> BIB007 </s> Catastrophic failure and fault-tolerant design of IGBT power electronic converters - an overview <s> 4) Energy shocks. <s> Emerging applications (e.g. electric vehicles, renewable energy systems, more electric aircrafts, etc.) have brought more stringent reliability constrains into power electronic products because of safety requirements and maintenance cost issues. To improve the reliability of power electronics, better understanding of failure modes and failure mechanisms of reliability–critical components in power electronic circuits are needed. Many efforts have been devoted to the reduction of IGBT failures, while the study on the failures of freewheeling diodes is less impressive. It is of importance to investigate the catastrophic failures of freewheeling diodes as they could induce the malfunction of other components and eventually the whole power electronic circuits. This paper presents an overview of those catastrophic failures and gives examples of the corresponding consequences to the circuits. <s> BIB008
During short circuit at the on-state, failure may happen due to high power dissipation. The high power dissipation within a short time is defined as energy shock. The high short-circuit current will result in energy shock and high temperature BIB005 BIB001 . However, IGBT will not immediately fail even the junction temperature exceed the rated temperature. Until reaching the intrinsic temperature (about 250°C for the doped silicon), further rise in junction temperature would lead to exponential increase in the carrier concentration and thermal runaway. With further increase of temperature, the silicon die may become fatally damaged and the contact metal may also migrate into the junctions. Even the short-circuit current is successfully turned-off, short-circuit failure could still happen after several microseconds, which is called delayed failure in BIB003 . It is verified by experiments and numerical simulation that large leakage current leads to the thermal runaway  . A "critical energy (E C )" is proposed to explain the mechanisms of catastrophic failure and wear out failure under repetitive shortcircuit operations BIB004 . When short-circuit energy is below E C , IGBT may survive for more than 10 4 times repetitive shortcircuit operations before failed. However, when short-circuit energy is far beyond E C , IGBT may fail after first short-circuit due to thermal runaway. A further experimental investigation show that IGBT can turn-off successfully after short-circuit but fails after several microseconds when the short-circuit energy is lightly higher than E C . It is still challenging to determine the exact value of E C , even though many experiments and numerical simulations have been done in the prior-art research BIB004 BIB006 . A recent research also demonstrates this failure mechanism in trench gate field-stop structure IGBT by comprehensive experiments  . Since trench-gate field-stop IGBT has a smaller heat capacity BIB003  , a state-of-the-art process has been proposed which can increase E C by 80% according to simulations BIB007 . The basic principle is to use a thicker front side metallization, made of copper instead of aluminum, and a newly developed diffusion soldering process to attach the direct bonded copper (DBC) substrates. Furthermore, it is worth mentioning that IGBTs can fall into short-circuits due to external causes, like the dynamic avalanche of freewheeling diodes; therefore it is also crucial to design high performance freewheeling diodes BIB002 BIB008  . A summary of IGBT short-circuit failure mechanisms is presented in Table I . As discussed before, short-circuit currents inevitably introduce high energy and temperature to IGBT chips, therefore it is important to design an efficient thermal management to improve the ability of withstanding shortcircuits in order to have time to detect failure and protect IGBTs.