SBIR-STTR Award

The Office of Naval Research (ONR) has issued this SBIR topic to fund the development of a solid-state closing switch capable of producing high power UWB electrical pulses with dV/dt of up to 200 V/ps, 10-90% risetime 200 ps or faster, and 300 ps durations. Achieving switching speeds this fast at medium-to-high voltage levels (240 V and above) is not possible with nanosecond switching technologies that rely on carrier motion through a structure because carriers traveling at their saturated velocity will travel approximately only 1/5th the distance of the depletion region of a Si device with an electrostatic breakdown rating of 1 kV. To achieve these specifications, Transient Plasma Systems, Inc. (TPS), in collaboration with General Electric Global Research (GE), proposes to develop a two-terminal device that is switched via an avalanche process, in which switching times are governed not by time of flight of saturated velocity carriers, but instead by the ionization rate in the high-field region of the device that exists when electric fields up to and in excess of twice the static breakdown voltage are applied. This proposed effort will investigate Silicon Avalanche Shaping/Sharpening (SAS) device structures for both Si and SiC, with Si being viewed as the conservative approach for achieving the threshold specifications of this topic. Less work has been done to investigate the capabilities of SiC for SAS devices, but its superior material properties suggest it is likely well suited for impact-ionization avalanche switching, which does not rely on long minority carrier lifetime for practical implementation. TPS and GE have a demonstrated track record collaborating on SiC devices for pulsed power applications, having collaborated on an ARMY SBIR on high voltage, high dI/dt SiC thyristor for munition fuzing applications. More recently, TPS and GE have collaborated in the development of SiC DSRDs, and GE recently reported modeling work on a SiC DSRD as a >10 kV pulsed power opening switch using MIXED-MODE simulation. For this effort, TPS and GE propose to conduct MIXED-MODE TCAD simulations for Si and SiC avalanche diodes. The simulation results will be bench marked against measured data taken from existing devices that are not optimized for avalanche pulse shaping, but have a reasonably close structure. Dynamic material properties required for accurate TCAD simulation will be extracted from bench top measured data for both Si and SiC candidate devices. TPS and GE will position themselves to fabricate optimized Si and SiC SAS devices during Phase II to achieve the specifications outlined in the topic, in particular the goal dV/dt of 200 V/ps and dynamic breakdown rating that is 3x higher than static. TPS is not aware of a compact solid-state switching technology that has demonstrated that level of performance.

Benefit:
The research and development that will be conducted during Phase I and II of this SBIR will result in the development of a compact solid-state switch that is capable of switching high voltage, high power impulses on timescales that are faster than any solid-state switch that has been developed in the United States. This type of switch is enabling technology for the development of compact, broadband impulse generators that would lead to a significant jump in capability for lightweight, fieldable directed energy sources. In the short term, this jump in switching capability would unlock new applications expected to drive follow-on R&D. 6.1 basic research programs enabled by nanoseconds pulsed power systems are critical to building an understanding that is needed to design deployable systems with the technology. There are at least 50 universities and research labs with programs investigating applications using pulsed electric fields and plasmas driven by fast high-voltage pulses, and the TPS team has relationships with many of them. The addressable market for pulse generators for research is estimated to be greater than $10M/year. Longer term applications enabled by this technology include a means to achieve high-speed, global strike and reconnaissance capability, longer-range with lower thermal signature, as well as EM armor, EM guns and HPM generators and portable directed energy weapons. In addition to DoD applications, the devices developed with this SBIR are expected to increase efficacy for several commercial pulsed power applications for which TPS is working to develop commercial solutions. Peer reviewed publications and internal R&D conducted at TPS has shown that fast pulse risetime made possible by the proposed switches can have a major impact for plasma and pulsed electric field applications that are large and growing market segments in auto, heavy transport, energy, medical, and agriculture. TPS technology has demonstrated improvements in fuel efficiency in engines by over 20% and improved ignition of a broader range of fuels (e.g. gasoline, natural gas, jet fuel) compared to traditional ignition methods, exhaust remediation, drag reduction in airfoils by more than 30%, improved wine quality and quantity and reduced maturation time after its application to wine grapes, microbial disinfection, and a noninvasive cancer treatment that leaves no scars. Despite all the opportunities, it is critical for an emerging company to remain focused in order to effectively leverage its core capabilities. Therefore, TPS is focused on platform technology and is establishing strategic relationships with well-positioned firms to leverage those capabilities in market segments of interest. TPS plans to utilize existing relationships with high-technology system integrators in conjunction with consultation with our government partners, to push TPS technology from research and development to deployment as part of a system approach.

Keywords:
directed energy, directed energy, high power microwave, Impact Ionization, Picosecond High Voltage Pulse, Solid state pulse generator, Broadband Pulse, Silicon Avalanche Shaper, Sub-nanosecond Pulse Generator

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.