Spiral junction termination

A new junction termination structure composed of a decreasing width spiral diffused resistor connecting anode and cathode region is presented. Leakage current through the spiral resistor results in optimized voltage distribution between the spiral turns which effectively reduces high electric field at the anode junction curvature. By circuit mode device modeling approach, the influence of several design parameters of importance on the breakdown properties were investigated. A major concern was shown to be the possibility of a premature reach-through between the spiral turns, resulting in increased leakage current and soft breakdown characteristics. A design with nonuniform spiral width and optimized spacing between the spiral turns is proposed, enabling almost ideal breakdown voltages with reduced spiral leakage current and eliminated reach-through between the spiral turns. Low susceptibility to oxide charges is confirmed by irradiation test, showing improvement of breakdown properties after irradiation. Further improvement in operation is obtained by a floating spiral structure due to spiral resistance limiting the increase of the multiplication induced current through the spiral. In comparison with common termination structures the spiral junction termination offers simple design and processing, close to ideal breakdown voltages and high reliability of operation.