GeneSiC Semiconductor (United States)

ABSTRACT Despite having an npn epitaxial structure resembling a Si BJT, the switching performance of the SiC Junction Transistor or SJT is purely controlled by its terminal capacitances, similar to a SiC MOSFET or JFET. Further, the absence of a “high-resistance” SiC MOS channel in the SJT means that the SJT’s RON,sp is solely limited by the resistance of the n- drift region. Recently released SJTs feature RON,sp as low as 2 mΩ-cm2 for a breakdown voltage (BV) of 1600 V, and a RON,sp of 2.4 mΩ-cm2, for a breakdown voltage of 2000 V. Current gains > 100 are achieved, even on the highest current SJTs. Unlike Si BJTs, SJTs do not suffer from second breakdown, and can perform under unclamped inductive switching (UIS) conditions, even at full rated collector currents. Near-∞ Early voltage and a negative temperature co-efficient of current gain in a SJT ensure low collector currents under short-circuited load conditions, resulting in short-circuit withstand time as high as 14 µs, even at > 80% of the maximum rated BV. Recent technological developments have significantly improved the stability of the SJT current gain (β) under high-current stress conditions. A 1000-hour long, 200 A/cm2 DC current stress results in only 10% reduction of the current gain (β) during the early stages of the stress test, while the β is perfectly stable for the remainder (>90%) of the stress duration. Similar β compression is observed, whether the collector current stress is applied at DC, or at a high switching frequency ≥ 200 kHz.

ABSTRACTElectrical performance and reliability of SiC Junction Transistors (SJTs) and Schottky rectifiers are presented. The 650 V/50 A-rated SiC SJTs feature current gains (β) up to 110 at room-temperature, 70 at 250°C, and stable breakdown characteristics. Single current pulse measurements indicate an almost invariant β up to 800 A/cm2 at 175°C – a measure of the SOA boundary for pulsed current SJT operation. Lower than 5 mA/cm2 leakage currents are measured on the SJTs at the rated blocking voltage and at 250°C. 1200 V Schottky rectifiers designed for high-temperature operation display < 3 mA/cm2 leakage currents up to 250°C. A 10x reduction in leakage current and 23% reduction in junction capacitance are observed when compared to the nearest competitor. The high-temperature Schottky rectifiers and SJTs display stable breakdown voltages and on-state characteristics after long-term HTRB stressing. A significant improvement in current gain stability is achieved by fine-tuning the fabrication process.

A physics based compact model for SiC Junction Barrier Schottky (JBS) diodes is presented which features a comprehensive physical description of the DC and CV behavior of SiC JBS diodes. For the first time, modeling of leakage current for JBS diode in circuit simulation is done. The model includes temperature scaling of its parameters to enable modeling of the diodes over a wide range of temperature (25 °C to 175 °C). The model has been validated using characterization data from a 1200 V, 3 A SiC JBS diode from GeneSiC. Excellent agreement is shown between device measurements and simulation for all regimes of operation of the diode.

The stability of the electrical characteristics of SiC n-p-n bipolar junction transistors (BJTs) is investigated under long-term avalanche-mode, dc, and pulsed-current operation. There is absolutely no change in the blocking I-V characteristics after a 934-h repetitive avalanche stress test. Long-term operation of the base-emitter diode (open-collector mode) alone does not result in any degradation of the ON-state voltage drop V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> or current gain β. Long-term operation in common-emitter mode results in negligible V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> or β degradation, if the base plate is maintained at 25°C. A greater degradation of β results upon increasing the base-plate temperature. The same total electrical charge, if passed through the BJT as a pulsed current, instead of a dc current, results in smaller β reduction. It is also shown that the β degradation can be reversed by annealing at ≥200°C, suggesting the possibility of degradation-free operation of SiC BJTs, when operating in pulsed current mode at ≥200°C temperatures.