An analytic model for turn off in the silicon-on-insulator LIGBT

Lateral insulated gate bipolar transistors (LIGBTs) in silicon-on-insulator (SOI) show a unique turn off characteristic when compared to junction-isol ated RESURF LIGBTs or vertical IGBTs. The turn off characteristic shows an extended 'terrace' where, after the initial fast transient characteristic o f IGBTs due to the loss of the electron current, the current stays almost a t the same value for an extended period of time, before suddenly dropping t o zero. In this paper, we show that this terrace arises because there is a value of LIGBT current during switch off where the rate of expansion of the depletion region with respect to the anode current is infinite. Once this level of anode current is approached, the depletion region starts to expand very rapidly, and is only slopped when it reaches the n-type buffer layer surrounding the anode. Once this happens. the current rapidly drops to zero . A quasi-static analytic model is derived to explain this behaviour. The a nalytically modelled turn off characteristic agrees well with that found by numerical simulation. (C) 1999 Elsevier Science Ltd. All rights reserved.