Floated Guard Rings on 4H-Silicon Carbide Power Diodes: Electrical and Thermal Improvements

This study verified the concept of the electrically floated guard ring formation on 4H-silicon carbide (4H-SiC) power diodes. On power diodes, the electrical breakdown voltages (V br s), reverse recovery currents (and times), and the internal device temperatures are three major interests to ensure the reliable operations of the devices. In my previous works, the V br s may be expanded when the carrier recombination volumes are large by eliminating carriers before they cause another impact ionization, then this recombination will also eliminate excessive carriers relevant to the reverse recoveries, and the internal device temperature can be cooled by the floated metal formations on the semiconductors by securing thermal flux routes. Therefore, the floated and non-electrically passivated metals with very fast surface recombination velocities (SRVs) have the potentials to expand V br s, suppress reverse recoveries, and the effective device coolings. This study simulated both the PiN diodes and the Schottky barrier diode (SBD) when the metal guard rings are formed or not formed. The results revealed that the guard rings are effective exclusively on PiNDs, and on the SBD the improvements have not been observed. Although V br s are NOT expanded, the thermal flux routes surely secured and the guard rings are useful to allow larger current densities in terms of internal device temperatures. On the dynamic characteristics, the guard rings work to suppress reverse recovery currents (RRCs) by recombining excessive carriers. and also contributed to shorten reverse recovery time (τRR) on n +-substrate PiN diode. No harmful effects on the forward characteristics observed. This guard ring technique can be implemented on the side-regions on the mesa-structure power diodes.