Silicon Carbide-based Power Electronics for Small Fission Reactors

Fission power systems (FPS) are a candidate power source for long duration NASA surface missions to the Moon and Mars, and offer significant advantages over competing options, including longer life, operational robustness, and mission flexibility. Electronics associated with the power conversion and power management and distribution (PMAD) systems in FPS have to operate reliably under high temperature (100s of deg C), high power (1-10 kWe), and severe radiation. Silicon carbide (SiC) is a promising solution with superior electronic properties for power applications. SiC devices offer higher temperature operation, higher breakdown voltages, and higher power conversion efficiency than silicon devices. However, vulnerability to heavy-ion induced failure and uncertainty in response to nuclear radiation are challenges facing FPS applications of SiC technology. CFDRC, Vanderbilt University, and Wolfspeed propose a modeling and experiment-based approach using commercial SiC technology to address this challenge. In Phase I, we applied the MRED radiation transport code to determine neutron-induced secondary ion spectra, developed a physics-based model of the selected SiC MOSFET using CFDRCs NanoTCAD software, and performed simulations to investigate sensitivity to design parameters, ion characteristics, and applied bias. In Phase II, we will transition to a higher-voltage SiC MOSFET technology for greater relevance to FPS applications, and characterize electrical and radiation performance via experiments. We will use the MRED toolkit for higher fidelity calculations of secondary particles and compare the impact of heavy ions (background environment) and fission neutrons. We will adapt the existing TCAD model, perform detailed simulations to understand key underlying mechanisms, and parametrically analyze design features to identify guidelines for higher radiation tolerance. Promising solutions will be prototyped, tested, and delivered to NASA. Fission power systems (FPS) are a candidate power source for long duration NASA surface missions to the Moon and Mars. Electronics associated with the power conversion and power management and distribution systems in FPS have to operate under high temperature, high power, and severe radiation. Silicon carbide (SiC) is a robust technology with superior electronic properties for power applications. However, vulnerability to heavy-ion induced failure and uncertainty in response to nuclear radiation are challenges. INNOVATIONS: (1) Characterization results for radiation effects (due to fission neutrons and background space radiation) in commercial high-voltage SiC devices; (2) Verified physics-based models for analysis of electrical and radiation response of SiC MOSFETs as a function of operating conditions; (3) Insight into physical mechanisms behind coupled electric field, radiation and temperature effects in SiC MOSFETs; and (4) Radiation-tolerant SiC MOSFET designs based on Wolfspeed’s commercial process to meet NASA requirements for FPS applications. TECHNICAL OBJECTIVES: (1) Characterize commercial high-voltage SiC MOSFET technology for FPS applications via modeling and experiments, obtain insight into mechanisms; (2) Develop design guidelines for radiation-tolerant MOSFETs; (3) Develop physics-based (TCAD) modeling capability for analyses and design of SiC devices. WORK PLAN: PHASE I RESULTS: (1) Calculated neutron-generated secondary ions based on interaction with SiC integrated circuit; (2) Developed TCAD model of 1200 V SiC MOSFET and verified against published data; (3) Performed TCAD modeling of neutron-induced ion strikes in SiC MOSFETs, identified response mechanisms as function of ion location/range, LET, and bias. PHASE II TASKS: (1) Transition to 1700 V SiC MOSFETs for higher relevance to Kilopower FPS applications, and characterize electrical and radiation performance via experiments; (2) Develop TCAD model of baseline 1700 V device, calibrate for electrical behavior, perform detailed ion-strike simulations to understand/verify underlying mechanisms; (3) Perform radiation transport simulations and compare fission neutron vs. background radiation effects; (4) Perform extensive parametric simulations for design features, identify hardening guidelines; (5) Fabricate radiation tolerant variants of MOSFETs, verify performance via electrical and heavy-ion tests; (6) Deliver models, test data, prototypes to NASA

Radiation tolerant, high voltage/high temperature SiC power electronics can lead to lower PMAD system weight, and is an enabling technology for Kilowatt-class fission power systems. It supports NASA science and exploration missions such as: Moon and Mars missions for in-situ resource utilization experiments, pre-crew surface stations, etc. The developed modeling and analysis tools will be a Cross-Cutting Technology that provides capability to all NASA missions that require power electronics. Radiation tolerant SiC power electronics are applicable in DoD space systems (communication, surveillance, missile defense), commercial satellites, and nuclear power systems. High-voltage/high-temperature SiC power devices, through applications in high-voltage converters, motor drives, etc., are promising for all-electric and hybrid cars, grid-scale energy storage systems, engine sensors, etc.

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