Papers by Author: Mats Reimark

Abstract: Vertical epitaxial NPN SiC BJTs for 1200 V rating were fabricated. Very low collector-emitter saturation voltages VCESAT=0.5 V at IC=6 A (JC=140 A/cm2) and T=25 °C and VCESAT=1.0 V at IC=6 A and T=250 °C were measured. The common emitter current gain at IC=6 A is 71 at T=25 °C and 32 at T=250 °C, respectively. A SPICE model was developed for the BJT including the parasitic capacitances of the internal pn junctions, as well as temperature dependence of the current gain and the collector series resistance. The IC-VCE characteristics of the BJT are in good agreement with the SPICE model between 25 °C and 250 °C. Fast switching measurements were performed showing a VCE voltage fall-time of 22 ns and a VCE voltage rise-time of 11 ns.

Abstract: The mechanisms of bipolar degradation in silicon carbide BJTs are investigated and identified. Bipolar degradation occurs as result of stacking fault (SF) growth within the low-doped collector region. A stacking fault blocks vertical current transport through the collector, driving the defective region into saturation. This results in considerable drop of emitter current gain if the BJT is run at a reasonably low collector-emitter bias. The base region does not play any significant role in bipolar degradation. Long-term stress tests have shown full stability of large-area high-power BJTs under minority carrier injection conditions provided the devices are fabricated using low Basal Plane Dislocation (BPD) material. However, an approximately 20% current gain compression is observed for the first 30-60 hours of burn-in under common emitter operation, which is related to instability of surface recombination in the passive base region.

Abstract: This paper reports large active area (15 mm2) 4H-SiC BJTs with a low VCESAT=0.6 V at IC=20 A (JC=133 A/cm2) and an open-base breakdown voltage BVCEO=2.3 kV at T=25 °C. The corresponding room temperature specific on-resistance RSP-ON=4.5 mΩcm2 is to the authors knowledge the lowest reported value for a large area SiC BJT blocking more than 2 kV. The on-state and blocking characteristics were analyzed by device simulation and found to be in good agreement with measurements. Fast switching with VCE rise- and fall-times in the range of 20-30 ns was demonstrated for a 6 A 1200 V rated SiC BJT. It was concluded that high dynamic base currents are essential for fast switching to charge the BJT parasitic base-collector capacitance. In addition, 10 μs short-circuit capability with VCE=800 V was shown for the 1200 V BJT.