Short circuit robustness of 1200 V SiC switches

Abstract

Short-circuit (SC) robustness of 1200 V-rated SiC npn Junction Transistors (SJTs) and commercial power DMOSFETs is investigated. Due to low overdrive base currents and low short-circuit currents the absence of short-channel effects, SJTs demonstrate superior SC capability including: (a) minimum short-circuit withstand time (tSc) of 14 μs, even at Vds=1000 V (b) Perfectly stable output and blocking characteristics after the application of 10,000, 10 μs long SC pulses at 800 V, and (c) tSC ≥ 18 μs at 800 V up to (at-least) 175°C base-plate temperatures. In contrast, commercial (Gen-II) 1200 V/80 mΩ SiC MOSFETs exhibit catastrophic failure beyond tSC = 7 μs at 500 V, and tSC = 3 μs at 800 V, due to excessive SC currents of > 200 A resulting in junction temperatures in excess of 650°C. Also, the MOSFET's drain leakage currents increase by a factor of 120, and the Vth reduces by 20%, after the application of 7 μs-long SC pulses at 500 V. Electro-thermal simulations indicate a significantly lower junction temperature for SJTs during short circuit pulses as compared to SiC MOSFETs.