The reliability of three kinds of high heat-resistant resins has been evaluated under high temperatures. These resins were applied to insulation substrates and a high temperature storage test has been carried out. The insulation performance of the resins was evaluated by applying 20 kV between a pair of electrodes on the substrate covered with resin. The insulation performance at 20 kV was maintained in samples with two of the three kinds of resins for 1,000 hours at 225oC. In a higher temperature storage test at 250oC, samples with one of the kinds of resin were not able to maintain insulation of 20 kV for 200 hours, while the two remaining resins were not able to maintain the insulation for 1,000 hours. In most samples that were not able to maintain the insulation, cracks or detachments were seen. Hardening caused by oxidation of the resin and differences in the coefficient of linear thermal expansion (CTE) are considered as causes of the cracks or detachments. It is thought to be necessary to lower the CTE of the resin and inhibit its oxidation in order to use it at more than 250oC for long periods of time.
We successfully fabricated 13-kV, 20-A, 8 mm × 8 mm, drift-free 4H-SiC PiN diodes. The fabricated diodes exhibited breakdown voltages that exceeded 13 kV, a forward voltage drop of 4.9–5.3 V, and an on-resistance (RonAactive) of 12 mW·cm2. The blocking yield at 10 kV on a 3-in wafer exceeded 90%. We investigated failed devices using Candela defect maps and light-emission images and found that a few devices failed because of large defects on the chip. We also demonstrated that the fabricated diodes can be used in conducting high-voltage and high-current switching tests.
Insulating properties of package for ultrahigh-voltage, high-temperature devices have been investigated. While all the packages have enough insulating strength at room temperature, deterioration of the insulating property at high temperature has been found with some packages. The authors have found that this deterioration is attributed to degrade the insulation property of AlN ceramics for DBC substrate at high temperature and that there is a various degree in the deterioration.
Temperature dependence simulations of forward characteristics for 4H-SiC pin diodes with Shockley-type stacking faults are performed in order to investigate the mechanism of the TEDREC phenomena. The forward voltage drops of both n-type and p-type drift layers at room temperature increase as the length of the Shockley-type stacking fault increases. When the diodes are compared to each other at the same temperature, the differences between the forward voltage drops do not change significantly up to 150 oC, but the differences suddenly narrow in the range from 150 °C to 200 °C. The Shockley-type stacking fault prevents current from flowing at room temperature. The current, however, flows throughout the drifted diode when the temperature is raised.
In 4H-SiC PiN diodes, Shockley-type stacking faults expand from basal plane dislocations under conducting forward current. We report for the rst time overlapped single Shockley-type stacking faults in a 4H-SiC PiN diode after forward conduction. In photoluminescence measurements, we observed not only an emission peak at 425 nm, which corresponds to the single Shockley-type stacking fault, but also one at 432 nm. In cross-sectional cathode luminescence images, emission lines at 425 nm and 432 nm merge and become straight. Transmission electron microscope images showed that the structure at the position with the 432 nm emission overlapped the single Shockley-type stacking faults.
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