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Current filaments are inherently three-dimensional phenomena regardless of the chip topography, which can be stripe-or checkerboard-shaped. Therefore, we consider an alter-native mapping of the real-chip IGBT cell topography to a quasi-3D simulation geometry in order to attain a computationally affordable approximation of 3D-filamentation effects that limit the SOA. The new approach extends that of...
A failure mechanism in the edge termination of a 1200V IGBT during overcurrent turn-off is studied with simulations and verified by experiments. The position of the destruction in the experiment can be correlated to the formation of a critical filament in the simulation. The destruction mechanism is investigated in detail. It is only observed if the IGBT enters its current saturation regime. I.e.,...
TCAD simulations of power devices are an important tool to investigate destruction mechanisms of power diodes and IGBTs. It is found that the dynamics of filamentation is the key for understanding the limits of the safe operation area. For both diodes and IGBTs, destructive and non-destructive filamentation mechanisms are identified and the resulting destruction mechanisms are discussed.
An improved understanding of the physical processes leading to the formation of current filaments and latch-up in large arrays of monolithically integrated high voltage (3.3kV) trench-IGBT cells during the turn-off process of the device is the prerequisite for enhancing the robustness of the device. To this end, numerical simulations have been performed revealing the rim of the safe-operating area...
We present a theoretical analysis of the formation of current filaments leading to the latch-up state that can occur during the turn-off process in a cell array of high-voltage (3.3 kV) trench insulated-gate bipolar transistors (trench IGBTs). Our investigations, based on self-consistent physical device simulations, aim at understanding the behavior of multiple cells, i.e. parallel cells as well as...
In the last ten years, the hardening of silicon high power devices against cosmic-radiation-induced failure gained decisive importance. A systematic improvement of the robustness against cosmic radiation requires a fundamental physical understanding of the microscopic mechanisms which lead to the failure or even destruction of power devices. We performed detailed 3D thermo-electrical device simulations...
A method for the calculation of failure rates due to cosmic rays is presented. The method is based on the output of standard device simulation tools and is applied to IGBTs and free-wheeling diodes. Different models for the failure rate density are compared with respect to their consistency with experimental data. The method is applied both to the active area and to the edge termination of IGBTs....
During Short-Circuit (SC) operations, strong current oscillations of IGBTs can appear. Simulation studies also confirm this. No parasitic inductances are required for such oscillations. A simplified equivalent circuit of the device, which is basically an RC oscillator, is able to reproduce the oscillations. The occurrence of oscillations depends on the model parameters, which can be related to the...
In IGBTs avalanche breakdown usually sets on in the edge termination structure. In consequence of electrical crosstalk, the destruction mechanism in very thin devices is confined to the neighboring cells in the active part of the chip. Thus, in order to achieve the largest possible safe-operating area, design optimization has to focus on the edge termination structure and the neighboring active cells...
Simulations and measurements on IGBT chips with a VLD edge termination structure reveal a periodic sequence of sharp current peaks in the avalanche breakdown regime. These current peaks are caused by a current filamentation process initiated and sustained by the interplay between a dynamically modulated electric field and localized self-heating. This mechanism makes it possible that the IGBT chip...
We show that the "variation of lateral doping" (VLD) edge termination technique (Fig. 1) exhibits a surprisingly high robustness in the avalanche regime. This is the consequence of a self-limiting time-periodic current filamentation mechanism, which prevents the VLD structure from being destroyed, in contrast to stable stationary current filaments staying permanently at the same location...
The long term stability and special drift phenomena of different trench IGBT structures under multiple switching tests are experimentally evaluated. It can be confirmed that a state of the art trench IGBT structure shows a very stable dynamic performance, but another device structure with so called "unprotected" trenches undergoes a significant change in the switching behaviour within millions...
We studied different destruction modes of planar cell 1200V "non-punch-through" and "fieldstop" insulated gate bipolar transistors in forward blocking mode using simulation tools. Branches of negative differential resistance are explained with certain device properties and a dynamic distortion of the electric field. Careful design of the device avoid these regions which may lead...
The high-current turn-off behaviour of trench IGBTs with dense shunting of the parasitic npn and with shallow p emitters was investigated both by simulation and experiment. In spite of current localization mechanisms (dynamic avalanche, npn transistor injection) there is no indication for a regenerative on-state under isothermal conditions, even at high temperatures up to 750K. Stable current filamentation...
Trench IGBTs show very high stability against latching with appropriate layout of the p-body/trench distance. This is in accordance with the simulation results. Simulation of parallel devices resulted in unexpected alternating high current states indicating the possibility of moving filaments as has been reported from dynamic avalanche investigations
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