Development of a Semiconductor Opening Switch at Soreq NRC

The semiconductor opening switch (SOS) diode, invented in Russia around three decades ago, is attractive for a variety of pulsed power applications due to its ability to interrupt currents of thousands of amperes in several nanoseconds in inductive storage generators. This allows delivering hundreds of megawatts into the load. The SOS has a p+-p-n-n+ structure, where the p-n junction depth could be $\sim 200~\mu $ m. Thus, the fabrication process of such structure requires a long diffusion time at a very high temperature, and was not suited for mass production in regular fabs. We present the design, simulation, fabrication, and testing of a Si SOS diode developed at Soreq NRC. It consists of a $180~\mu $ m epitaxial structure with a p-n junction depth of $\sim 110~\mu $ m. In a single die testing, we used a fast driving circuit. A peak negative voltage of 1515 V with a rise time of 1.56 ns was obtained on a matched $50~\Omega $ load. The voltage rise rate, of 0.97 kV/ns, is the highest record obtained for a single Si current interruption die. In order to test the diode at high voltages (HVs), we used two setups of SOS-based generators based on magnetic compression. We compared its original SOS diode developed in Russia with a stack of epi-SOS diodes. In the first setup, an epi-SOS made of 65 dies in series with a cross section of 25 mm2 was used. The reverse current was 927 A. The peak load voltage on a $46~\Omega $ load was 37.4 kV with a rise time of 25 ns. In the second setup, an epi-SOS made of 130 dies in series with various cross sections of 1, 2, and 3 cm2 was used. For the 3 cm2 stack, a 173-kV, 7.5-ns rise time pulse was obtained on a $\sim 224~\Omega $ low-inductance resistive load.

I. Introduction

High-voltage (HV) current interruption diodes include mainly the drift-step-recovery diode (DSRD) and the semiconductor opening switch (SOS) [1], [2], [3], [4]. These diodes operate at typical reverse current densities of hundreds and thousands of A/cm², respectively, and their opening times are of the order of ~1 and ~3 ns, respectively. When used with an energy stored inductor, due to the fast current interruption time by these diodes, up to several hundreds of kV induced voltage pulse is generated and can be delivered to a load. Thus, these diodes are key elements in all solid-state HV pulse generators operating with high repetition (up to MHz) frequencies and with almost unlimited life time.