Radiation-hardened Electronics Research Articles

A 100-Mrad (Si) JFET-Based Sensing and Communications System for Extreme Nuclear Instrumentation Environments

Dry cask storage is one of two storage methods approved by the U.S. Nuclear Regulatory Commission for spent fuel after removal from reactor cores. Dry casks consist of a stainless steel canister enclosed in a concrete overpack to contain the hazardous radioactive spent fuel rods and provide radiation shielding. Monitoring spent fuel storage casks is desired to ensure the safe containment of the enclosed spent fuel, but is very difficult due to the related harsh temperature and radiation environment. The sensors and associated electronics to monitor temperature, pressure, and/or radiation need to survive high temperatures and radiation doses for extended time periods. For this reason, there is a severe need for radiation-hardened electrical systems that survive well beyond the existing capabilities of commercially available radiation-rated electronic components, which have primarily been developed for space applications. Junction-gate field-effect transistor (JFET) devices are inherently radiation hardened [exceeding 100 Mrad (Si)]. When JFETs are used as building blocks for sensing and communication electronics (i.e., oscillators, amplifiers, filters, and mixers), inherently radiation-hardened circuits can be achieved. To this end, JFET-based radiation-hardened electronics interfacing with cask-embedded sensors capable of driving modulated sensor signals through a stainless steel barrier were designed and tested at a dose rate of approximately 500 krad/h (Si) to beyond a 200-Mrad (Si) total ionizing dose. After 200 Mrad (Si), the sensor and communication circuit signals were correctly decoded at the receiver despite oscillator drift. The results from this experiment demonstrate the potential for creating more complex radiation-hardened JFET-based electrical systems for nuclear environments.

Hydrogen etching of 4H–SiC(0001) facet and step formation

SiC has attracted much interest due to its vast applications in high power, high frequency and radiation-hardened electronics at high temperatures. Although the growth and processing technology for SiC wafers has matured, scratches created during surface preparation will unavoidably deteriorate both device performances and the quality of materials which are fabricated on it. Hydrogen etching has been proposed as an effective approach to obtain ideal SiC surfaces with large atomically flat steps. Here, we reported a systematical investigation on the effects of processing parameters to the hydrogen etching of 4H–SiC (0001). Accordingly, a new two-step etching method was developed with a specifically designed crucible to take advantage of the found correlation between those parameters and the terrace features. The method demonstrates high efficiency to realize atomically uniform SiC surface morphology with more than 70% coverage of the sample surface. It offers a possible route for large scale industrial SiC wafer planarization.

Neutron irradiation effects on gallium nitride-based blue LEDs

Gallium nitride (GaN) is a promising material for radiation-hardened electronics in outer space environment. This work focuses on radiation hardness evaluation of GaN device using commercial GaN quantum-well light-emitting diodes (LEDs). Both the electrical and optical properties of GaN LEDs were characterized before and after neutron irradiation. The light emission intensity was found to increase significantly after 1014n/cm2 of neutron irradiation in the Ohio State University Research Reactor (OSURR) at room temperature. The extracted values from the I-V curve after irradiation also demonstrate such optical improvements of the GaN LED after 1014n/cm2 of neutron irradiation.

Analyzing Gamma-Ray Irradiation Effects on Carbon Nanotube Top-Gated Field-Effect Transistors.

Carbon nanotube (CNT) field-effect transistors (FETs) and integrated circuits (ICs) have been predicted and demonstrated to be some of the most promising candidates for radiation-hardened electronics. The studies mainly focused on the radiation response of the whole transistors, and experiments or analyses to reveal the detailed radiation responses of different components of the FET were absent. Here, we use a controllable experimental method to decouple the total ionizing dose (TID) radiation effects on different individual components of top-gate CNT FETs, including the CNT channel, gate dielectric, and substrate. The substrate is found to be more vulnerable to radiation damage than the gate dielectric and CNT film in FETs. Furthermore, the CNT film not only acts as a radiation-hardened semiconducting channel but also protects the channel/substrate interface by partially shielding the substrate from radiation damage. On the basis of the experimental data, a model is built to predict the irradiation resistance limit of CNT top-gated FETs, which can withstand at least 155 kGy irradiation.

Radiation-Induced DC Parametric Degradation of Enhancement Mode GaN-on-(111)Silicon High-Electron-Mobility Transistors

AlGaN/GaN high-electron-mobility transistors (HEMTs) for applications in radiation environments has required the exact determination of their radiation hardness. Although bulk GaN is the preferred substrate for the epitaxial growth of GaN and AlGaN, (111) silicon is a possible substrate for HEMT devices. The stability of electrical parameters of enhancement-mode (E-mode) GaN HEMTs under gamma irradiation is an essential characterization for reliability. The present work reports the transfer characteristics degradation of E-mode GaN HEMTs under various total dose irradiation from 5krad up to 60Mrads. This represents the first comprehensive total dose study ranging from a few krads up the tens of Mrads. The measured device-to-device variations within groups of devices are presented. The evolutions of critical DC parameters with accumulated total dose is found to be significant at low doses and saturates at high dose levels. The degradation mechanism is very similar to the reported radiation-induced shallow electron traps that trap and release electrons in the near surface GaN and AlGaN layers. Due to the unique properties including high breakdown voltage, high electron mobility and high thermal stability, wide-bandgap semiconductor power electronic devices, especially Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs), have shown great promise in space, defense and nuclear applications, which often involve radiation-hardened electronics that require high radiation tolerance to fluxes of neutrons or gamma ray of devices. To turn the promising potential of GaN HEMTs into reality, investigations on the influence of irradiation on the device performance and reliability are essential. Many studies have investigated the radiation hardness of group III–nitride compound semiconductor devices under various irradiation types, such as electrons, protons, neutrons, and X-rays and at various total irradiation doses. They generally showed higher radiation tolerance compared with Si because of high displacement energy of GaN, demonstrating the favorability of GaN devices in hard radiation environments. Many studies have investigated the influence of 60Co gamma radiation on the device electrical characteristics. However, they were all focusing on depletion mode (D-mode) devices. Enhancement mode (E-mode) GaN-on-Si transistors have been commercially available for years. Their major advantages over D-mode devices are elimination of negative voltage supply and the enabling of direct-coupled FET logic (DCFL) for digital circuits. They also improve the efficiency of commercial DC-DC converters in various power levels and topologies. A previous work on gamma radiation of E-mode GaN-on-Si HEMTs only reported cumulative total doses of up to 1 Mrads (Si). The present work provides a complete coverage of low-to-high irradiation doses from 5krads up to 60Mrads (Si), for commercially available E-mode GaN HEMTs and the devices are characterized to gauge variations in the critical DC parameters. To the best of the author’s knowledge, the present work is the first to investigate the gamma radiation tolerance of E-mode GaN HEMTs covering such a wide range of total doses. This facilitates the observation of the complete degradation behavior of DC parameters in hard radiation applications of the E-mode GaN HEMTs. The devices were supplied in the form of 0.9mm square passivated die with round solder bumps for contacts. They have a rated continuous drain-to-source voltage VDS of 60V, and a rated continuous drain current ID of 1A. These GaN-on-Si devices were fabricated on Si wafers considering process compatibility and cost. An aluminum nitride (AlN) thin layer was grown on the Si wafer to be a seed layer for the AlGaN/GaN heterostructure. Subsequently, the AlGaN/GaN heterostructure was grown on the AlN layer, with a thin AlGaN layer grown above the highly resistive GaN serving as a strained interface between the GaN and AlGaN crystal layers, allowing the creation of a two-dimensional electron gas (2DEG) filled with abundant free electrons with ultra-high mobility. The gate electrode was processed subsequently forming a depletion region under the gate. As an E-mode transistor, the device is turned on by applying a positive bias to the gate. All the irradiations were conducted at room temperature by 60Co gamma-rays with a flux of 318.5Rads (Si)/s, at the dry-cell panoramic gamma irradiator in the University of Maryland Radiation Facilities. The entire irradiation procedure consists of two parts. The first part is higher-dose irradiation with total doses of up to 60Mrads based on two stages. At the first stage, the devices were irradiated at 10Mrads, while at the second stage, the devices were irradiated for another 50Mrads, with three of them taken out after 25Mrads during the second stage. The second part is lower-dose irradiations with total doses of up to 2Mrads. The temperature throughout the irradiation process was monitored to be below 30°C.

CSP Hybrid Space Computing

Space is a hazardous environment for electronic systems; therefore, the traditional approach to space computing relies upon radiation-hardened electronics, which are characteristically more expensive, larger, less energy-efficient, and generations behind in performance and functionality of modern commercial processors. Conversely, modern commercial processors, while providing the utmost in performance and energy efficiency, are susceptible to space radiation. The desire for more autonomous missions combined with growing demands for more detailed products from advanced sensors have challenged organizations to stay relevant by “doing more with less” to meet future requirements. To meet this need, researchers at the National Science Foundation Center for High-Performance Reconfigurable Computing have developed a new design concept in hybrid space computing that features fixed and reconfigurable processor architectures merged with an innovative system design that is a combination of three technologies: commercial devices, radiation-hardened components, and fault-tolerant computing. This concept has culminated in the development of several novel research platforms, most significantly the CSPv1 flight computer, which was successfully deployed on the International Space Station. Before flight, this CSPv1 design was analyzed and tested on the ground with reliability models and radiation tests. Recent in-flight data have validated the design and shown that CSPv1 exceeds reliability expectations predicted by models.

Multi-gigabit low-power radiation-tolerant data links and improved data motion in trackers

We present a set of links based on data-transmission IP in 130nmdesigned for rapid integration into ASIC designs. These links aredesigned for use in very high radiation environments as occur in highenergy physics experiments. The designs are additionally low power andsmall area, easing integration with other electronic systems. Theselinks are well suited to use in tracking detectors. Trackers, due totheir close proximity to the collision, are subject to very highlevels of radiation, and hence require such radiation hardenedelectronics. The portfolio of radiation hardened data transmissionblocks consists of a 1Gbps serializer/deserializer with a very lowpower consumption ~1mW for each. A differentialtransmitter and differential receiver rated at 3GHz, both designed tobe much faster than needed, as insurance against radiationdamage. Finally, the impact of a prototype low-latency, low-power( < 60mW total link power) 5Gbps link is considered. Case analysis ofthe impacts of using lower powered, higher speed blocks inhypothetical trackers is studied, showing power improvements relativeto alternative technologies.

Radiation-Hardened Electronics and Ferroelectric Memory for Space Flight Systems

The National Aeronautics and Space Administration (NASA) is developing high-tolerance, radiation-hardened electronics for missions in and beyond Low Earth orbit. Ferroelectric-based electronics are highly viable candidates for these electronics because of their inherent radiation-hardened property. Since standard memory devices are prone to damage caused by radiation, ferroelectric memory may provide the needed radiation-tolerance. To test the effectiveness of ferroelectric random access memory (FRAM) in Low Earth orbit, a 512 K Ramtron FRAM will be flown on a Low Earth orbit satellite that will be launched by NASA. This paper discusses the advantages of ferroelectric electronics and outlines the Low Earth orbit ferroelectric memory test experiment.