Investigation of effects of lateral boundary conditions on current filament movements in Trench-Gate IGBTs

When designing the reliability of high voltage power devices, it is very useful to confirm the behavior of current filaments in various structures and situations by Technology CAD simulation. Current filaments are caused by the electrical instability inherent in the device when a large voltage is applied to the device or a large current flows through the device, which is the current concentration phenomenon into only a few cells and moves around mainly in the plane of the cell region of the device. The ease of movement of the current filament is determined by the design of the device structure and has a great impact on device reliability. This design is difficult to examine by actual measurement, so simulations are often used. Since device simulations with a large three-dimensional (3D) structure take a huge amount of calculation time, it is common to cut out a part of the chip as small as possible and set boundary conditions on each cut surface to build a simulation setup that fits the purpose of the simulation. In 2D current filament simulations, it is known that when the reflective boundary condition (ideal Neumann) are imposed on the sidewalls, the boundary condition can significantly affect the results. In this work, to the best of my knowledge, I clearly show for the first time the relationship between the current filament movements and lateral boundary conditions in a large-scale three-dimensional trench-gate IGBT structure under conditions especially in which the current filament is highly mobile. In this case, the convergence is very poor and the calculation is difficult, so I also describe how to calculate it well by mathematical settings.