Novel Backside Structure for Reverse Conducting Insulated-Gate Bipolar Transistor With Two Different Collector Trench

A novel reverse-conducting insulated gate bipolar transistor (RC-IGBT) with two different collector trench (DCT) is proposed. One of the collector trenches is filled with heavily doped N-type polysilicon (N-poly) and the other is filled with heavily doped N- and P-poly. An electron accumulation layer is formed along the sidewall of trench owing to built-in potential difference between the N-poly and the N-drift region. The electron accumulation layer and collector trenches block the electric field, which behaves just like the N-buffer layer of the conventional RC-IGBT (Con. RC-IGBT). Similarly, due to potential difference between the P-poly and N-drift region, a high-density hole inversion layer is formed to narrow the electron current path as a high resistance. The DCT RC-IGBT achieves snapback-free in a small cell pitch without additional control. Moreover, the DCT RC-IGBT shows better tradeoff between turn-off loss and ON-state voltage drop than that of con. RC-IGBT. For the same forward voltage drop, the turn-off loss is reduced by 26%.