Improvement in U-Shaped Channel SOI Lateral IGBT for Wider Reverse Bias Safe Operating Area

Abstract

In this article, the inductive turn-off failure mechanism of U-shaped channel silicon-on-insulator lateral insulated-gate bipolar transistor (SOI-LIGBT) under high-voltage and high-current is investigated by experiments and numerical simulations. First, the measured turn-off waveforms before and after failure are compared to infer the cause of the failure. Then, the failure is reproduced by calibrated three-dimensional simulations using Sentaurus TCAD. According to the simulation and measured results, the turn-off failure is resulted from the high impact ionization in the bird’s beak region. To reveal the failure mechanism, the turn-off failure process is divided into two phases. In phase I, the electrons generated by drastic impact ionization in the bird’s beak region act as the base current to keep the operation of parasitic PNP transistor after channel pinching off. In phase II, the parasitic NPN transistor is activated due to the hole current amplified by PNP, and thus, turn-off failure occurs. Based on the revealed turn-off failure mechanism, an improved U-shaped channel SOI-LIGBT with a P-top is proposed. The P-top is arranged in the bird’s beak region to reduce the impact ionization rate. The measured results demonstrate that no failure occurs when the improved device turns off under high-voltage and high-current conditions. Compared with the conventional U-shaped channel SOI-LIGBT, the improved device obtains 275% and 23% improvements in turn-off current at a bus voltage of 450 V and reverse bias safe operation area, respectively.