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Introduction
In today’s increasingly interconnected world, electronic devices and systems are becoming integral to our daily lives, from smartphones and laptops to critical infrastructure and aerospace technologies. However, these electronic systems are vulnerable to a variety of external factors, including radiation from sources such as cosmic rays, solar flares, and even man-made events like nuclear detonations.
Single-event effects (SEEs) are a critical concern, where a single radiation particle strike can disrupt electronic components, potentially leading to malfunctions or failures. To tackle this challenge head-on, DARPA, the Defense Advanced Research Projects Agency, has initiated the Advanced Sources for Single-event Effects Radiation Testing (ASSERT) program. In this article, we will explore the ASSERT program, its objectives, and the impact it may have on the reliability of electronic systems.
Understanding Single-Event Effects
Radiation threatens electronic systems from three main natural sources – galactic cosmic rays,
charged particles trapped by planetary magnetic fields, and solar particle events – and from manmade sources such as particle accelerators, reactors, and nuclear weapons. Electronics are
susceptible to upset, degradation, and failure resulting from total ionizing dose (TID),
displacement damage dose (DDD), and the instantaneous response to single ionizing particles,
i.e., “single-event effects” (SEE).
Total Ionizing Dose (TID) is a measure of the cumulative energy deposited by ionizing radiation in electronic components over time. This can occur due to sources like cosmic rays and gamma rays. TID gradually leads to the accumulation of charge and other electrical effects within semiconductor materials, which can ultimately cause changes in electronic characteristics and performance degradation.
Displacement Damage Dose (DDD), on the other hand, results from the displacement of atoms within materials due to energetic particle impacts, typically from sources like neutrons. This displacement creates lattice defects and structural damage within semiconductor materials, affecting their electrical properties. DDD is particularly relevant in environments where neutron radiation is prevalent, such as nuclear reactors and space missions.
Single-Event Effects (SEEs) are sudden and instantaneous disruptions or malfunctions caused by a single ionizing particle strike on a critical point within an electronic device. These effects can be caused by various forms of ionizing radiation, including heavy ions, neutrons, and protons. Unlike TID and DDD, SEEs are isolated events, but they can have severe consequences. SEEs can manifest as Single-Event Upsets (SEUs), flipping the state of memory cells; Single-Event Latch-ups (SELs), causing overcurrent conditions; or Single-Event Transients (SETs), leading to temporary signal disturbances.
The significance of these radiation-induced effects is particularly pronounced in critical systems, such as the U.S. nuclear arsenal, spacecraft, avionics, server farms, and autonomous vehicles. In these applications, the failure or malfunction of electronic components due to TID, DDD, or SEEs can have far-reaching consequences, including data corruption, system failure, or, in some cases, catastrophic outcomes.
To mitigate these effects, extensive radiation testing and hardening measures are employed. These measures aim to ensure that electronic systems remain reliable and functional even in the presence of ionizing radiation.
Limitations of Current SEE Testing
Currently, the primary approach for Single-Event Effects (SEE) testing in the United States relies on heavy-ion sources. These sources generate large-diameter beams used to qualify the radiation resistance of electronic components at both the part and board levels. These beams can have substantial spot areas, ranging from a few square centimeters to as large as 60 cm × 60 cm, and can penetrate materials to depths of hundreds of microns. However, the landscape of advanced electronics is evolving rapidly.
Emerging advanced electronic systems are becoming increasingly intricate and integrated. They can encompass digital, analog, and optical functionalities, utilizing three-dimensional (3D) architectures and diverse material types. These 3D components are expected to extend over multiple millimeters vertically and exhibit a complexity that makes it challenging, if not impossible, to disassemble them into their constituent parts for radiation testing using traditional heavy-ion sources.
To meet the demands of SEE testing for fully-integrated electronic components, a new type of irradiation source is necessary. This source must offer a unique combination of characteristics, including multi-millimeter penetration depths, linear energy transfers (LETs) representative of space radiation, and precise spatial resolution and control. These attributes are crucial for achieving the precision needed to investigate sensitive areas of electronic systems and identify potential faults. Unfortunately, current SEE testing methods are incapable of fulfilling all these requirements simultaneously. Therefore, the development of innovative radiation sources and techniques has become imperative to evaluate and qualify next-generation microelectronics.
In addition to providing new capabilities for 3DHI radiation qualification, ASSERT sources must be compact and cost-effective to enable implementation in laboratory and industrial settings where they can become incorporated into the development process. In this way, radiation qualification will be integrated throughout the design and fabrication flow, with ASSERT sources providing the means to rapidly identify radiation design flaws and to facilitate swift correction and design optimizations. A key program goal is to reduce the time from design to radiation-qualified component by a factor of ten.
The ASSERT Program: Objectives and Funding Opportunity Description
The Microsystems Technology Office (MTO) at DARPA is leading the ASSERT program, seeking innovative proposals for the research and development of experimental radiation sources and techniques for SEE testing of advanced node and 3D heterogeneously integrated (3DHI) electronics.
Current SEE testing methods rely on heavy-ion sources that produce large-diameter beams for part- and board-level radiation qualification of electronics. However, emerging advanced electronics are more complex and integrated than previous generations, making traditional testing methods inadequate. SEE testing of fully-integrated components requires an irradiation source that provides multi-millimeter penetration depths, space-radiation-relevant LETs, and fine spatial resolution. Existing methods cannot simultaneously fulfill all these requirements, necessitating the development of new sources and techniques.
The ASSERT program is structured around two primary Technical Challenges (TCs):
- TC1: Achieving deep penetration depths with space-radiation-relevant linear energy transfers (LETs).
- TC2: Creating charge tracks with fine spatial resolution.
Technical Challenge #1: Achieving deep penetration depths in SEE testing is crucial for assessing the resilience of complex 3D electronic devices and stacked packaging. To meet this challenge, radiation sources must generate charge tracks with Linear Energy Transfers (LETs) representative of space radiation, ranging from 0.1 to 100 MeV-cm²/mg, while penetrating silicon to depths of up to 5 mm. Importantly, these sources should penetrate through relevant packaging materials, oxides, overlayers, metallization, and more without requiring time-consuming and potentially destructive procedures like delidding or substrate thinning. Current alternatives, such as ion microbeam approaches, offer fine spatial resolution but lack the necessary penetration depth, whereas pulsed laser methods, although providing precise spatial resolution, face limitations related to optical access and metallization penetration.
Technical Challenge #2: Achieving fine spatial resolution is essential for addressing the complexity of emerging 3D electronic devices. These highly integrated systems require sub-micron beams with the precision to selectively investigate sensitive areas and isolate faults resulting from charge tracks. The shape and lateral extent of the deposited charge profile are critical for accurately replicating device responses triggered by heavy-ion strikes. Additionally, precise knowledge of the charge profile’s position is essential for targeted probing of the Device Under Test (DUT). Existing ion-based approaches, including heavy-ion and ion microbeams, fall short of meeting these requirements due to limitations related to mass, energy, and beam space charge. In contrast, pulsed laser alternatives can achieve the necessary spatial resolution and positioning accuracy, but their reliance on clear, unmetallized surfaces restricts their applicability in various advanced electronic topologies.
Both of these challenges are interconnected, and proposals must address both aspects. The ultimate goal of the program is to enhance the reliability of electronic systems, particularly in critical applications such as the U.S. nuclear arsenal, spacecraft, avionics, and terrestrial systems like server farms and autonomous vehicles.
The ASSERT program also aims to significantly reduce testing time, aiming for a tenfold reduction in the time it takes to qualify radiation-hardened components. Achieving this goal requires the development of innovative sources that enable rapid identification of radiation design flaws and facilitate swift corrections and design optimizations.
“Today it takes on the order of five to 10 years to design, fully qualify, and deploy a rad-hard part. If you think about processors from 10 years ago, they are at least four orders of magnitude behind modern computing performance,” stated Dr. David Abe, ASSERT programme manager.
Moreover, it’s essential to emphasize that data obtained from the new radiation sources developed under the ASSERT (Advanced Sources for Single-event Effects Radiation Testing) program must be rigorously validated by comparing it to relevant heavy-ion data. This validation process ensures that the novel SEE sources can accurately replicate the responses of electronic devices when subjected to the radiation encountered in strategic Department of Defense (DoD) programs, space missions, airborne systems, and terrestrial applications that demand high reliability in radiation-rich environments.
Program Structure and Objectives
The ASSERT program seeks to develop novel, compact SEE test sources and techniques to
enable the radiation-hardness characterization of advanced 3D components, inform the new device designs and selection, update radiation-hardening-by-design (RHBD) rules, and validate new computational models and simulation tools. ASSERT sources will be used to characterize mixed-signal devices containing a multiplicity of materials including but not limited to silicon, GaAs, wide bandgap materials such as SiC and GaN, and emerging ultrawide bandgap materials such as cubic boron nitride, gallium oxide, and silicon nitride.
The ASSERT program spans 54 months, divided into three phases: Phase 1 (18 months), Phase 2 (24 months), and Phase 3 (12 months). Phase 1 focuses on designing high-energy particle sources for SEE testing and demonstrating their feasibility through proof-of-concept demonstrations. Computational simulations and experiments are used to support the viability of the proposed sources in meeting program objectives.
The program’s key objectives include:
- Generating linear energy transfers (LETs) ranging from 0.1 to 100 MeV-cm²/mg at the sensitive regions of the devices.
- Achieving independently variable penetration depths up to 5 mm in silicon.
- Achieving spot diameters of less than 1 µm at the surface of the devices in Phases 1 and 2, and less than 0.2 µm at 5 mm penetration depth in Phase 3.
- Developing and validating a predictive SEE testing approach using ASSERT sources.
AWARDS
The DARPA ASSERT program is a collaborative effort involving researchers from academia, industry, and government.
University of California, Berkeley was awarded $10 million to develop a new source of protons for SEE testing. The source will be based on a technology called laser-driven ion acceleration, which is a promising new method for producing high-energy particles.
Massachusetts Institute of Technology was awarded $8 million to develop a new method for SEE testing that uses a combination of protons and neutrons. The method is designed to be more efficient and cost-effective than existing methods.
Stanford University was awarded $6 million to develop new software tools for analyzing the results of SEE testing. The tools will be used to improve the understanding of SEE mechanisms and the development of new mitigation techniques.
Here are some of the other organizations that have been awarded grants in the DARPA ASSERT program:
- Colorado State University
- Los Alamos National Laboratory
- Oak Ridge National Laboratory
- Sandia National Laboratories
- University of Maryland, College Park
- University of New Mexico
- University of Washington
The program is expected to make significant progress in developing new and improved sources and methods for SEE testing, which will help to improve the reliability and robustness of electronic systems in harsh radiation environments.
Conclusion
The DARPA ASSERT program represents a pivotal effort in advancing radiation testing and mitigating Single-Event Effects (SEEs) in electronic systems. By developing innovative radiation sources and testing techniques, DARPA aims to bolster the resilience and reliability of electronic systems across various industries, including aerospace, defense, healthcare, and consumer electronics. The program’s ultimate success will not only enhance national security but also ensure that our electronic devices continue to operate reliably in the face of radiation challenges, ushering in a future of increased safety and dependability.
