Turn-off failure in multi-finger SOI-LIGBT used for single chip inverter ICs

In this paper, the clamped inductive turn-off failure of the Silicon-on-Insulator Lateral Insulated Gate Bipolar Transistor (SOI-LIGBT) with multiple fingers under high-voltage and high-current conditions is investigated. First, the measured turn-off waveforms combining with the on-state I-V characteristics of the failed device are discussed to distinguish the probable cause of the failure. Then, two-dimensional (2-D) electrothermal simulations are performed to reproduce the failure by using Sentaurus TCAD. The failure is originated from an inhomogeneous depletion behavior among the paralleled fingers during the turn-off, which gives rise to the non-uniform current-sharing and the subsequent current crowding in single finger. As a result, the latch-up of the device takes place. The simulation indicates that the current crowding is formed mainly through an internal path in the silicon. In order to verify the failure mechanism, an improved device with deep-oxide trenches arranged between the adjacent fingers is fabricated. The measured results demonstrate that no failure occurs when the improved device turns off under high-voltage and high-current conditions.