SOS Diodes: New Powerful Devices for Nanosecond Interruption of Current

The SOS effect was revealed in ordinary high-voltage semiconductor diodes intended to rectify alternating current by a certain combination of the current density and the pumping time. Subsequently a special semiconductor structure for operation under conditions of the SOS effect was developed. It had an extra hard recovery regime and served as the basis for creation of high-voltage semiconductor devices of a new class, namely, SOS diodes representing solid-state nanosecond opening switches with high-density currents having the following parameters: working voltage of hundreds of kV, cutoff currents of units and tens of kA, current interruption time of units of nanoseconds, and the pulse repetition rate of the kilohertz level [9, 13, 16, 20, 21, 22, 28].

Fic. 1

A typical construction of the SOS-diode is shown in Fig. 1. The opening switch represents a series assembly of elementary diodes braced by dielectric pins between two output electrode plates. Every elementary diode consists of a heatsink with several soldered-on series semiconductor structures.

Fig. 2

Figure 2 illustrates a typical oscillogram of a reverse current passing through a SOS-diode with the structure having the surface area of 1 cm2. The cutoff current is 5.5 kA and the current interruption time with respect to 0.1-0.9 of the amplitude equals 4.5 ns. The switching rate is 1200 kA/чs, a figure which is nearly 3 orders of magnitude higher than the current rise rate in ordinary fast thyristors.

Fig. 3

Figure 3 shows the external appearance and Table 1 gives technical characteristics of SOS-diodes. The most powerful device (item 1 in Fig. 3) having the structure with the surface area of 4 cm2 operates at 200 kV and cuts off current of 32 kA, which corresponds to the interruption power of 6 GW. The device (item 3) has been designed to operate at a high pulse repetition rate continuously. This device has a more developed system of heatsinks and operates at the pulse repetition rate of 2 kHz, the cutoff current of 1-2 kA and the voltage of 100-120 kV. The device under item 5 is intended to generate pulses having the length of a few nanoseconds. It interrupts current of 1 kA in 500 ps with a short pumping time [17, 19, 23, 31, and 32].

Table I. Specifications of the SOS-diodes