Engineering topics
Publications and source records attributed to Ladbury, Ray.
Proton-induced fission of high-Z (Atomic Number) materials can produce high fluxes of high-LET (Linear Energy Transfer) ions in microelectronics. We develop methods to evaluate risks for a range of destructive and nondestructive SEE (Single-Event Effects) modes caused by this threat.
After four decades of single-event effects testing, radiation engineers face pressure to find alternatives to reduce or eliminate testing costs. Many of these alternatives focus on use of archival test data to bound SEE risk for similar parts. This presentation examines the challenges and limitations of such analyses and suggests analysis techniques and goals that are likely to be most appropriate for such efforts.
In the 47 years since single-event effects were first observed in spacecraft electronics, radiation experts have developed an effective methodology supported by a nationwide infrastructure. A highly skilled workforce of radiation engineers has developed test facilities and methods, modeling and simulation techniques, and mitigation and design strategies to ensure space missions meet their performance and reliability requirements even in the harsh radiation environments of space. Now, increasing performance demands of space missions, the continued disruptive evolution of microcircuit technologies and growth and changes of the space industry have combined with an aging infrastructure are placing increasing strain on the radiation effects community, and the community is responding.
Although career tracks in science and engineering are often depicted as straight and smooth, many contain detours, side journeys and interruptions. In the end, these detours not only influence who we are, they can make us better scientists and engineers. In this presentation, Dr. Ladbury tells the tale of how his detours took him to far-flung locations from the Himalayan mountains to the African Savannah and eventually back to a rewarding career in radiation physics.
In 1972, when engineers at Hughes Aircraft Corporation discovered that errors in their satellite avionics were being caused by cosmic rays (so-called single-event effects, or SEE), Moore's Law was only 7 years old. Now, more than 45 years on, the scaling that drove Moore's Law for its first 35 years has reached its limits. However, electronics technology continues to evolve exponentially and SEE remain a formidable issue for use of electronics in space. SEE occur when a single ionizing particle passes through a sensitive volume in an active semiconductor device and generates sufficient charge to cause anomalous behavior or failure in the device. Because SEE can occur at any time during the mission, the emphasis of SEE risk management methodologies is ensuring that all SEE modes in a device under test are detected by the test. Because a particle's probability of causing an SEE generally increases as the particle becomes more ionizing, heavy-ion beams have been and remain the preferred tools for elucidating SEE vulnerabilities. In this talk we briefly discuss space radiation environments and SEE mechanisms, describe SEE test methodologies and discuss current and future challenges for use of heavy-ion beams for SEE testing in an era when the continued validity of Moore's law depends on innovation rather than CMOS scaling.
This part of the course first outlines the conventional Single Event Effect (SEE), radiation hardness assurance (RHA) approach, which emphasizes mission success. Next, Dr. Ladbury will discuss the challenges posed by new satellite platforms (e.g., cubesats, nanosats, etc.), where cost and schedule receive emphasis equal to if not greater than mission success. These additional pressures, along with growing demands to reduce size, weight and power, coupled with increased performance, drive many projects toward expanding their use of commercial-off-the-shelf (COTS) technologies. While this may reduce direct parts cost and procurement lead times, it undermines many cost-reduction strategies used for conventional SEE RHA and can make radiation testing and analysis one of the most significant risks or worse, a risk neglected altogether. That section will end with some approaches for restoring balance in the troika of mission success, cost, and schedule. This is captured in SEE RHA as risk management: identify the threat, evaluate the threat, and mitigate the threat.
Radiation Hardness Assurance (RHA) methodologies need to evolve to capitalize on the increased flexibility introduced by new models of space radiation environments. This presentation examines the characteristics of various radiation threats, the sources of error that RHA methodologies seek to control and the contributions of environment models to those errors. The influence of trends in microelectronic device technology is also considered.
Large solar particle events (SPE) threaten many elements of critical infrastructure. A 2013 study by Lloyds of London and Atmospheric and Environmental Research recently found that if a worst-case solar event like the 1859 Carrington Event struck our planet now, it could result on $0.6-$2.36 trillion in damages to the economy. In March 2014, researchers Y. D. Liu et al. revealed that just such an event had narrowly missed Earth in July 2012. The event was observed by the STEREO A spacecraft. In this presentation, we examine how the sun can pack such a punch from 150 million km away, the threats such solar particle events pose, their mechanisms and the efforts NASA and other space agencies are carrying out to understand and mitigate such risks.
Although system-level radiation hardening can enable the use of high-performance components and enhance the capabilities of a spacecraft, hardening techniques can be costly and can compromise the very performance designers sought from the high-performance components. Moreover, such techniques often result in a complicated design, especially if several complex commercial microcircuits are used, each posing its own hardening challenges. The latter risk is particularly acute for Commercial-Off-The-Shelf components since high-performance parts (e.g. double-data-rate synchronous dynamic random access memories - DDR SDRAMs) may require other high-performance commercial parts (e.g. processors) to support their operation. For these reasons, it is essential that system-level radiation hardening be a coordinated effort, from setting requirements through testing up to and including validation.
Single-event gate rupture (SEGR) is a potentially catastrophic failure mechanism of power MOSFETs biased in the off-state. In part due to the severity of-SEGR consequences and in part due to the difficulty of accurated SEGR rate estimation, SEGR mitigation me1hodologies emphasize risk avoidance, using heavy-ion accelerator testing to define safe operating conditions for a surface-incident linear energy transfer {LET). This "safe-operating area" (SOA) within which the device may be biased without experiencing SEGR is then often derated by a prescribed factor to ensure low risk of SEGR. Although research in 1996 indicated that such LET-based SEGR hardness requiremen1s could provide false assurance of safe operation unless one also considered· ion energy], most mission SEGR requirements are still specified in terms of surface-incident LET. Moreover, terrestrial SEGR tests at a given surface-incident LET are limited by the small number of ion species and energies available at heavy-ion accelerators. In comparison, the on-orbit radiation environment is composed of all of the naturally-occurring elements with peak fluxes at nearly GeV/nucleon energies. The primary objective of this study is to examine whether typical derating of high-energy heavy-ion accelerator test data bounds the risk for SEGR from higher-energy on-orbit ions with the mission LET requirement.
As NASA has evolved it's usage of spaceflight computing, memory applications have followed as well. In this slide presentation, the history of NASA's memories from magnetic core and tape recorders to current semiconductor approaches is discussed. There is a brief description of current functional memory usage in NASA space systems followed by a description of potential radiation-induced failure modes along with considerations for reliable system design.
Radiation requirements and trends. TID: 1) >90% of NASA applications are < 100 krads-Si in piecepart requirements. a) Many commercial devices (NVM and SDRAMs) meet or come close to this. b) Charge pump TID tolerance has improved an order magnitude over the last 10 years. 2) There are always a few programs with higher level needs and, of course, defense needs SEL: 1) Prefer none or rates that are considered low risk. a) Latent damage is a bear to deal with. 2) As we re packing cells tighter and even with lower Vdd, we re seeing SEL on commercial devices regularly (<90nm). a) Often in power conversion, I/O, or control areas. SEU: 1) It s not the bit errors, it s the SEFIs errors that are the biggest issues. a) Scrubbing concerns for risk, power, speed.
Statistical Methods outlined in [Ladbury, TNS20071 can be generalized for Monte Carlo Rate Calculation Methods Two Monte Carlo Approaches: a) Rate based on vendor-supplied (or reverse-engineered) model SEE testing and statistical analysis performed to validate model; b) Rate calculated based on model fit to SEE data Statistical analysis very similar to case for CREME96. Information Theory allows simultaneous consideration of multiple models with different complexities: a) Model with lowest AIC usually has greatest predictive power; b) Model averaging using AIC weights may give better performance if several models have similar good performance; and c) Rates can be bounded for a given confidence level over multiple models, as well as over the parameter space of a model.
This viewgraph presentation reviews the Single Event Effects (SEE) testing of the Phillips SA8016BW 2.5 GHz Synthesizer that was chose by the GLAST Program for Frequency Generation. Included in this are diagrams of the phased-locked loop (PLL), the synthesizer, and heater.
Believe it or not, this has been a simplistic look at starting a checklist for SEE testing. Given a memory that has 68 operating modes, when a SEU occurs that changes the mode, just how do you determine what's going on? Laser and microbeam tests can help, but not easily for modern packaged devices. Expanding this approach to other more complex devices such as ADCs or processors as well as analog devices should be considered. The recommendation is to use the existing text standards as the starting point. Just make your own checklist for the device/technology/issues being considered. At HEART 2007, we presented some of the burgeoning challenges associated with single event effect(SEE) testing of modern commercial memories: a) Package, device complexity, test fixture, and data analysis issues were discussed; b) "Complete" SEE Characterization would take 15 years; c) Qualification test costs have a greater than 4 times increase over the last decade. In this talk, we continue to explore the roles of technology with an emphasis on the existing SEE Test Procedures and some of the concerns related to modern devices. The primary objective of the briefing is to provide some overarching guidance concerning the many considerations involved in the formulation of a SEE test plan provided in a " Checklist" format.we note that there is no such thing as a complete check list and that the best approach is to develop a flexible test plan that takes into account the device type and functions, the device technology, circuit and package design, and, of course, test facility and beam characteristics.
This viewgraph presentation reviews the Statistical properties of Single Event Effects (SEE) rate calculations. The goal of SEE rate calculation is to bound the SEE rate, though the question is by how much. The presentation covers: (1) Understanding errors on SEE cross sections, (2) Methodology: Maximum Likelihood and confidence Contours, (3) Tests with Simulated data and (4) Applications.
The performance of the Michigan State SEETF during its inaugural runs is evaluated. Beam profiles and other diagnostics are presented, and prospects for future development and testing are evaluated.
A viewgraph presentation on various new space radiation environment models for spacecraft design is described. The topics include: 1) The Space Radiatio Environment; 2) Effects of Space Environments on Systems; 3) Space Radiatio Environment Model Use During Space Mission Development and Operations; 4) Space Radiation Hazards for Humans; 5) "Standard" Space Radiation Environment Models; 6) Concerns about Standard Models; 7) Inadequacies of Current Models; 8) Development of New Models; 9) New Model Developments: Proton Belt Models; 10) Coverage of New Proton Models; 11) Comparison of TPM-1, PSB97, AP-8; 12) New Model Developments: Electron Belt Models; 13) Coverage of New Electron Models; 14) Comparison of "Worst Case" POLE, CRESELE, and FLUMIC Models with the AE-8 Model; 15) New Model Developments: Galactic Cosmic Ray Model; 16) Comparison of NASA, MSU, CIT Models with ACE Instrument Data; 17) New Model Developmemts: Solar Proton Model; 18) Comparison of ESP, JPL91, KIng/Stassinopoulos, and PSYCHIC Models; 19) New Model Developments: Solar Heavy Ion Model; 20) Comparison of CREME96 to CREDO Measurements During 2000 and 2002; 21) PSYCHIC Heavy ion Model; 22) Model Standardization; 23) Working Group Meeting on New Standard Radiation Belt and Space Plasma Models; and 24) Summary.