4.5.3.2 On-State Characteristics

The on-state performance of the proposed SA-LIGBT has been simulated and compared with the conventional device. Figure 4.47 shows the comparison of the on-state characteristics of a conventional SOI LIGBT, a conventional SOI SA-LIGBT, and the proposed SOI SA-LIGBT which has a trench oxide at the drain/anode region. As can be seen in the figure, SA-LIGBTs have a NDR region which cannot be found in conventional LIGBTs. This is due to the two different conduction mechanisms responsible for the current flow.

The NDR corresponds to the snap-back regions in the I-V curves in Figure 4.47. With the proposed structure the snap-back voltage is reduced effectively compared to the conventional SA-LIGBT which has a same $p^+$-anode length. The snap-back voltage of the proposed SOI SA-LIGBT is 1.95V which is reduced by about 20% compared to the conventional SA-LIGBT (about 2.45V) which has the same device parameters. It shows that the trench oxide at the drain/anode can suppress the NDR effectively without increasing the $p^+$-anode length.

Figure 4.48 shows the I-V characteristics of the proposed SOI SA-LIGBT. Because of the weak injection of the $pnp$-bipolar structure compared to the conventional LIGBT, the current density of the proposed SA-LIGBT is lower than that of the conventional LIGBT.

Figure 4.47: I-V comparison of the conventional SOI-LIGBT and the conventional and proposed SOI SA-LIGBTs. A reduced snap-back voltage of the proposed device can be seen.

Figure 4.48: On-state characteristics of the proposed SOI SA-LIGBT and a conventional SOI-LIGBT. The considerable improvement of the latch-up can be seen.

However, the forward bias safe operating area (FBSOA) limited by the latch-up parasitic thyristor inherent in its structure is increased compared to the conventional SOI-LIGBT.

I-V curves in the figure show that the SA-LIGBT has good saturation currents up to $V_\mathrm{G}$ $=$ 30V and $V_\mathrm{A}$ $=$ 80V without latch-up behavior.