Circuits and sensors can substitute for human observers and controllers in nuclear reactors, satellites, space probes, and other places where people can’t go or can’t stay long because of radiation. But that same radiation can affect circuits and sensors, too.
The problem was apparent as early as 1964, when the IEEE Nuclear and Plasma Sciences Society held its first Nuclear and Space Radiation Effects Conference to cover radiation’s impact on electronic parts and systems. Now in its 45th year, NSREC is still the only U.S. conference that covers space radiation effects in detail, says Paul Dodd, the general conference chair of this year’s session, to be held from 14 to 18 July in Tucson, Ariz.
The nuclear industry and nuclear weapons programs were the first to encounter these problems, Dodd says, but with the advent of the space program and the launch of Earth-orbiting satellites, the effects of natural space radiation also became important.
SINGLE-EVENT EFFECTS “Radiation can result in cumulative damage through ionization or displacement damage,” Dodd says. “Single particles can also cause temporary malfunctions or even permanent damage. Radiation-induced soft temporary errors can be the largest source of failures in commercial electronics.”
There are ways to harden circuits and components against radiation, but the means available today come at the cost of decreased speed, increased chip area, or higher power consumption. Circuits can be made self-healing, at the expense of building in redundant elements. The most brute-force approach is triple modular redundancy, whereby three circuits or components process the same data or signals, and a dissenting output is rejected, outvoted by the other two.
“Single-event effects (SEEs) can range from simple data corruption in memories, to voltage or current transients in analog circuits, to destructive burnout or rupture of dielectrics in power devices,” Dodd says. “As you can imagine, detecting them depends on what the effect is. Large, modern terrestrial computer memories often use error detection and correction coding to detect and prevent soft errors. Detecting and diagnosing upsets in complex microprocessors and the like is much more difficult.”
And SEEs have been growing in importance as the transistors and other elements on ICs shrink.
“Today’s devices are so small that it takes a very small amount of charge to upset a memory state,” Dodd says. Or, as IEEE Fellow Timothy Oldham, who chairs the society’s Radiation Effects Steering Group, puts it, “The difference between a ‘1’ and a ‘0’ is now many fewer electrons than it used to be.” Therefore, Dodd says, “Just about all makers of ICs for earthbound applications now test for single-event susceptibility.
LEADOFF TUTORIAL Because of that, this year’s NSREC’s traditional, opening-day tutorial short course is devoted to single-event soft errors. Although many conferences aim such tutorials at students and newcomers, NSREC is more inclusive. “We try to make sure that speakers cover not only basic information that people new to the field may not yet know, but also new research,” Dodd says, “and about 75 percent of those who attend the conference come to the short course.”
Many of the technical sessions held after the tutorials are expected to address single-event effects, as well as total-ionizing dose and displacement damage effects, which are also important in many areas.
The technical program will include about 50 oral presentations and 60 poster presentations, plus a workshop devoted to recent findings that are more data intensive than analytical, organizers say. Most NSREC papers are candidates for the IEEE Transactions on Nuclear Science, but the data workshop papers are to be published separately. NSREC maintains a liaison with its European equivalent, the Radiation and Its Effects on Components and Systems Conference, and some papers from that conference also are published in IEEE journals.