Developing radiation-hardened (rad-hard) electronics that can operate reliably within a near- or in-core environment can improve nuclear reactor safety and operational efficiency through early pre-amplification, analog and digital signal processing, and analog-to-digital conversion. Wide bandgap (WBG) semiconductors offer a potential solution to rad- hard by offering increased temperature and radiation resistance, higher voltage and current limits, and faster switching. Two WBG semiconductor of interest are gallium nitride (GaN) and silicon carbide (SiC), both of which have shown high temperature and ionizing radiation tolerance. This project focuses on testing samples of WBG transistors under reactor operation at the Ohio State University (OSU)-Nuclear Reactor Laboratory (NRL) to better understand the mixed gamma/neutron effects and limitations for rad-hard circuit design. Irradiation experiments with in situ measurements are needed to confirm and map device performance with high radiation (>1 MGy; 10^16 n/cm^2) of existing commercial GaN high electron mobility transistor (HEMT) and SiC junction-gate field-effect transistor (JFET) technology. Furthermore, irradiation experiments with in situ measurements are needed to discover the neutron limits and behavior of OSU research-grade GaN HEMTs to 10^18 n/cm^2 or failure. If successful the OSU research grade devices will be the first transistors (to the authors’ knowledge) that have remained operational beyond 10^17 n/cm^2. The OSU-NRL offers unique capability for easy in situ measurement and monitoring of electrical devices both using their in-core accelerated irradiation facility (AIF) and near-core 9.5” dry well facility (DWF). The in situ measurement capability of the OSU-NRL offers the opportunity to monitor the device performance over increasing doses as opposed to the traditional “cook-and-look” approach typically performed with only post-irradiation characteristics. For the two concurrent irradiations, the team will characterize transistor performance using current-voltage (I-V) measurements of more than 16 selected devices. The measurements will be performed using an existing Oak Ridge National Laboratory (ORNL) designed data acquisition system composed of source measure units (SMUs) and programmable reed relays. After irradiation, post-irradiation examination will be performed using SMU or a semiconductor parameter analyzer. The electrical characterizations of the transistors will be used to develop compact circuit models (Verilog-A or SPICE) which will include the effects of radiation degradation, valuable data for DOE NE programs.

Due to the neutron limitations of modern commercial-off-the-shelf (COTS) electronics, present day in- or near-core sensors and instrumentation of nuclear reactors require lengthy cabling and containment penetrations to interface with their supporting electronics and control systems. Lengthy cabling results in electronically noisy signals complicating the already difficult task of reactor instrumentation and control (I&C), and as each sensor is passive, it may require its own individual cable requiring larger or more containment penetrations. Wireless sensor communication links provide a potential solution to minimize cabling and penetration requirements for sensors, thereby increasing safety and signal fidelity. State-of-the-art radiation-hardened (rad-hard) electronics are a critical limitation for nuclear I&C. Research and development in rad-hard electronics and electronics material technology is essential to enable safer operation with improved monitoring and control of the existing nuclear reactor fleet and next generation reactors. While silicon (Si) based electronics have been irradiated to beyond 1 MGy total ionizing dose (TID), the neutron limitations of Si-based electronics are on the order of 10^14 n/cm^2. Electronic circuits based on wide bandgap (WBG) materials are becoming more prominent in power and radio frequency (RF) electronics applications due to higher temperature, current, and voltage limitations and, in the case of gallium nitride (GaN), faster switching speeds. Silicon carbide (SiC) devices have shown radiation tolerance (>1 MGy; 10^16 n/cm^2). However, modern SiC devices show an increased susceptibility to neutron induced single-event burnouts (SEBs). While GaN devices have shown similar TIDs to Si- and SiC-based devices, little data is available on their neutron limitations. This team has successfully irradiated research-grade GaN high electron mobility transistors (HEMTs) to 10^16 n/cm^2 with minimal effects shown. This proposal seeks to irradiate single transistor elements and rudimentary circuits of commercially available GaN HEMTs and SiC junction-gate field-effect transistors (JFETs) to understand their limitations and effects. Furthermore, we propose to irradiate the research-grade GaN HEMTs to 10^18 n/cm^2 or device failure. Understanding the limitations and the mixed gamma/neutron effects of the commercial and research-grade devices will guide the commercial market into developing rad-hard GaN-based electronics to support reactor I&C.