Large-area, high-voltage thyristors for HVDC converter

Large-area, high-voltage thyristors with the ratings of 1500A, 4000V for converters of high-voltage direct current transmission systems have been developed. By improvement in the aluminum diffusion technique, high accuracy of diffusion and long carrier lifetime were attained. To increase the effective conducting area up to eighty percent of the wafer area, the sigma shaped edge contouring technique has been used. A gamma-ray irradiation was used for precise control of the reverse recovery charge. By using a computer aided design which considered the impurity profile, the dynamic characteristics of the device were calculated and the structure was designed.