HIGH-POWER PICOSECOND CURRENT SWITCHING BY SILICON DIODE USING TUNNELING-ASSISTED IMPACT IONIZATION FRONT

New principle of high-power ultrafast current switching based on tunneling-assisted impact ionization front in silicon diode structures has been experimentally implemented and theoretically studied. A voltage pulse with amplitude of 180 kV and a front duration of 400 ps was applied to a semiconductor device containing 44 series connected silicon diode structures located in a 50-Omega transmission line. Due to sharp nonuniformity of the applied voltage distribution across the length of the device the switching process presents a successive breakdown of the series connected structures. Each successive structure breaks down with a shorter time interval as the electromagnetic shockwave builds. The current switching by the individual structure takes around 30 to 50 ps, and is initiated at electric field of about 1 MV/cm in the vicinity of the p-n junction, where tunneling ionization of the silicon begins. At such conditions the rise time of the output voltage wave is determined by the switching time and inductance of a few last structures and can be less than 100 Ps to a peak voltage over 100 kV. In experiments in 50-Omega transmission line we have obtained 150-kV output pulses having 80 to 100 ps rise time. The maximum current and voltage rise rates are record for semiconductor switches and amount to 30 kA/ns and 1.5 MV/ns, respectively.