A Novel Fast-Switching SOI LIGBT with Anode Junction Paralleled by a Diode

Abstract

The silicon-on-insulator lateral insulated gate bipolar transistor (LIGBT) exhibits an enormous turn-off time because of a long current tail and a degraded breakdown voltage owing to the gain of the parasitic open-base p-n-p transistor. A novel LIGBT is proposed in this paper, where the anode junction (P-collector/N-buffer) is paralleled by a polysilicon P+/N+ diode. In the blocking state, all electrons generated by the voltage-sustaining layer can entirely flow to the anode through the diode without the hole injection into the drift region, which completely eliminates the function of the open-base transistor and makes the breakdown voltage equal to that of a PN junction. In the on state, since the built-in potential of the P-collector/N-buffer junction $(V_{\text{bi}})$ is smaller than that of the P+/N+ junction, the voltage drop of the P-collector/N-buffer junction can rapidly boost to the $V_{\text{bi}}$ at low anode current, so snapback-free can be realized. In the turn-off transient, the electron in the N-drift region can be extracted by the diode without the hole injection, contributing to the fast-switching characteristic. The results from TCAD simulation indicate that the current turn-off time and the turn-off loss of the proposed device are decreased by 65.9% and 77.3%, respectively, and the breakdown voltage is increased by 7.3%, compared with the conventional one. Furthermore, an excellent tradeoff between the turn-off energy loss and on-state voltage is accomplished, i.e., with the identical on-state voltage of 1.63 V, the proposed device demonstrates a huge improvement of 27.9% in turn-off energy loss.