Criterion for the Stability Against Thermal Runaway During Blocking Operation and Its Application to SiC Diodes

Silicon-Schottky diodes are well known for their poor blocking behavior at high temperatures and high blocking voltages. This behavior is particularly problematic, because the high leakage currents [1] lead to self-heating, which increases the leakage further. Due to this fatal feedback loop, a thermal runaway [2] may occur. Silicon carbide (SiC) devices are supposed to show much lower leakage current levels and a better thermal stability. However, early SiC-Schottky diodes were affected by nonideal leakage current densities [3]-[5] and, therefore, seriously threatened by thermal runaway as well. In this paper, the blocking stability of commercial SiC-Schottky and SiC-p-i-n diodes is investigated. Due to different leakage mechanisms in SiC-Schottky and SiC-p-i-n diodes, both the device types show different voltage and temperature dependences of the leakage current. Nevertheless, the derived stability criterion (SC) is a reasonable approximation for both the diode types. In agreement with the SC, experimental results prove that thermal stability is reached during high-temperature operation and even under worst cooling conditions. Within the specified operating range, thermal runaway is, thus, no longer a limiting factor. However, the risk of a thermal runaway has to be reassessed when going to higher voltage, higher operating temperatures, and less cooling as promised by the SiC devices.