High-voltage silicon carbide junction rectifiers and GTO thyristors.

摘要

This work implements high-voltage, vertical, bipolar power devices made from 4H-SiC and evaluates their electrical performance. 4H-SiC PiN junction rectifiers and gate turn-off (GTO) thyristors have been designed and fabricated in sizes from 300 to 2400 μm in diameter and are investigated theoretically and experimentally. On-wafer measurements of fabricated devices are used to characterize their electrical performance up to 300°C.; The 4H-SiC PiN junction rectifiers are made by ion-implantation of the p+ anode and achieve blocking voltages of up to 4.5 kV with leakage currents of less than 10−5 A/cm2 at room temperature. A three-zone implanted junction termination extension is used for high-voltage edge termination and allows a planar device structure unlike epitaxially grown junctions where mesa etching is required. A differential on-resistance of 2.8 mΩ·cm2 and on-state voltage of 3.7 V at 100 A/cm2 have been measured at room temperature while reverse recovery measurements of 0.6 A rated devices show very fast switching (t_rr 100 ns) compared to commercial silicon PiN rectifiers (t_rr ∼ 1 μs) with 1 kV, 1 A rating.; 4H-SiC asymmetrical GTO thyristors with n+ substrates are investigated with two different fabrication approaches. Fabrication and operation of the first reported SiC thyristor with an implanted layer, namely an n-base, has been demonstrated. These GTOs show on-state voltages of 6–10∼V at room temperature and blocking voltages from 30 to 90∼V, lower than expected due to n-base punchthrough. Further optimization of the n-base implant is needed to improve implant activation and reduce implant damage. GTOs fabricated from an all-epitaxially grown structure exhibit on-state voltages of 6.0 V at room temperature and 4.4 V at 300°C. Blocking voltages of up to 1100 V and leakage currents of less than 10−5 A/cm 2 are measured up to 250°C. Switching measurements indicate fast turn-on (0.9 μs) and fast turnoff (0.3 μs) at 150°C. Turn-off times increase with temperature as in silicon, while turn-on times decrease with temperature, opposite that in silicon. The effect of anode geometry on SiC GTO switching behavior has been demonstrated for the first time where faster turn-on is achieved with involute anodes while fastest turn-off is achieved with concentric interdigitated anodes. Comparison of implanted versus epitaxially grown GTOs indicate that while implanted GTOs are a potentially attractive alternative for future implementation, the epitaxially grown GTO is at present the preferred approach for 4H-SiC.