Solid-state, Sub-nanosecond Pulse Sharpener for Generating High Power Impulses

In the Phase I Base effort of this program Transient Plasma Systems, Inc. (TPS) investigated the development of a solid-state electrical closing switch that is capable of producing high power electrical impulses with rising edges that are faster than 200 ps.  TPS subcontracted with GE Research to perform MIXED-MODE technology computer-aided design (TCAD) simulations to investigate the capability of both Si and SiC for a device that meets the performance specifications outlined by the solicitation – primarily that the device can switch voltages up to and beyond 3 kV in less than 300 ps.  The work performed during the Phase I Base effort showed that up to 3kV pulse with risetime below 300ps can be generated using a single p/n junction in Silicon SAS diodes when triggers with an 1ns input pulse. It was also found that a SiC device is capable of up to 9kV pulse with rise time below 100ps. In these devices, larger area chips can provide higher amplitude pulses but with larger capacitive feed-through prior to the closing of the SAS diode. Also, increasing input pulse dV/dt can significantly improve the performance of SAS diode. Additionally, an investigation into the effect of intrinsic region thickness in Si SAS diodes showed that punch-through diodes are superior SAS devices compare to non-punch-through diodes. Based on these results, TPS and GE have submitted a Phase II SBIR proposal intended to fund the design, fabrication and testing of both Si and SiC devices that can achieve the requested specifications.  The modeling conducted so far indicates that Si should be capable of achieving the threshold specifications and that SiC can exceed the specifications, with a single junction rating of up to 9 kV and sub-100 ps switching capability.  TPS and GE recommend that Si still be considered as part of follow-on work because the material cost of a Si device is significantly less than SiC and requires less advanced capital equipment to manufacture the parts.  Additionally, a process for assembling stacked Si junctions to achieve higher voltage has already been developed.  TPS believes Si has potential as a very near-term solution (within the scope of a Phase II effort) to achieve these specifications for assemblies made of multiple bonded junctions for voltages up to 10 kV and beyond.  The superior material properties of SiC should result in a more power dense and faster switch; however less work has been conducted up to this point on designing and packaging multiple junctions for the high voltages ultimately required for the end application.  These design challenges will be investigated during the Phase II effort.