Lifetime considerations of high voltage semiconductor diodes for pulsed power applications

A novel pulse generator scheme using a fast recovery pseudospark switch and a stack of high-power semiconductor diodes was tested. The prototype pulse generator is able to drive capacitive loads of over 150 nF, at peak voltages of up to 40 kV, pulse duration of 6 to 15 μs (FWHM, full width at half maximum), and repetition rates of up to 80 pps. Nominal pulse current is between one and 1.5 kA peak. The main limitation in lifetime is caused by the high peak current load in the semiconductor diodes during flashover in the ESP. Diode current can reach up to 8 kA in some cases. A variety of different types of diodes has been investigated, with different physical constructions, i.e. fast high-power press-pack types as well as smaller type, fast, stud-mount diodes. Although the larger press-pack diodes experienced a considerably longer absolute lifetime in these experiments as expected, the comparison of lifetime versus current/charge density on the chip reveals advantages of the stud-mount design (with the diode chip soldered to the substrate) over the press-pack design. The experimental results are discussed in terms of an optimization strategy to achieve the highest power density at minimum cost and volume.