RFC diode with high avalanche stability and UIS capability

In this paper, we propose a novel backside design for Relaxed Field of Cathode (RFC) diode which realizes high avalanche stability and Undamped Inductive Switching (UIS) capability. In the case of the conventional RFC diode, wide recovery SOA is realized by forming p-layer on the backside of the edge termination area which reduces the carrier concentration at on-state and suppresses the carrier concentration on the boundary region during recovery. On the other hand, the avalanche stability at off-state of the conventional RFC diode is degraded comparing to pin diode. The failure analysis and numerical simulation taught that the avalanche stability degradation is caused by the secondary breakdown of the vertical parasitic pnp-transistor structure at the anode end. To suppress the effect of the parasitic pnp-transistor, an layer with well-adjusted width (W _n ) is placed precisely under the edge of the anode area on the cathode side as the carrier sink for the electron. As a result, the new RFC diode with novel backside design obtains high avalanche stability and UIS capability without negative impact on total losses, snap-off capability and recovery SOA.