A snapback-free RC-IGBT with Alternating N/P buffers

A 1200V-class Reverse Conducting IGBT with Alternating N+/P Buffers (AB) is proposed and its mechanism is investigated for the first time. The AB RC-IGBT features a buffer layer with alternately doped N+ and P regions. The AB is separated from the collector by a part of N-drift region. The P buffer serves as the electron barrier during the unipolar mode and forces the electrons to flow through the high-resistance N-drift region between the buffer and the collector. Consequently, the snapback is suppressed with a fairly small cell pitch of 30μm. In the blocking state, the P buffer is fully depleted while the N+ buffer is not fully depleted yet. Therefore, the electric field terminates in the buffer layer and a high BV is ensured. The turn-off loss of the proposed AB RC-IGBT is reduced by 20% compared with that of the conventional RC-IGBT for the same forward on-state voltage drop.