Study of failure mechanism in the modern IGBT with a highly doped N-buffer layer

Modern IGBT structure with a highly doped buffer layer showed a MOSFET-like behavior at low collector-emitter voltage when the gate was fully turned-on. This significantly increased the conduction loss and resulted in scrap chips. Its failure mechanism has been systematically studied in this paper to reveal the underlying device physics inside the IGBT microstructure using energy-band theory, numerical simulation and equivalent circuit methods. It is reported that both tunneling current and low injection efficiency of highly doped p-emitter/n-buffer junction are root causes, and the latter deactivates the bipolar function, so that the device is dominated by MOSFET action only under low collector-emitter voltage condition. The paper will be concluded by presenting excellent measured performances of IGBTs using optimized p-emitter/n-buffer junction.