1. Radiation Environment and Their Effects on Electronics

Mission success in the near-Earth space environment hinges on a thorough understanding of the prevalent radiation sources (as illustrated in Fig. 1.1). These sources can be broadly categorized into three primary types:

Solar activity plays a crucial role in shaping the near-Earth space radiation environment. Solar flares and CMEs can significantly enhance the flux of SEPs, potentially creating intense radiation bursts that can overwhelm spacecraft shielding. Furthermore, solar activity can also indirectly influence the intensity of GCRs and trapped radiation. During periods of high solar activity, the Earth’s magnetosphere becomes more compressed, allowing a higher flux of GCRs to penetrate into the inner regions near-Earth space. Additionally, energetic solar wind particles can interact with the magnetosphere, leading to enhanced particle populations within the Van Allen belts.

Therefore, understanding and monitoring solar activity through observations of sunspots and other solar phenomena is critical for predicting the radiation environment that spacecraft and sensitive electronics may encounter in near-Earth space.

Numerous space missions have been specifically designed to measure and comprehend solar activity, recognizing its significance for life on Earth and its influence on mission planning and design. A notable example is the Solar and Heliospheric Observatory (SOHO), a joint mission between the European Space Agency (ESA) and NASA, which was launched in 1995 and continues to operate successfully.

The Sun’s activity follows an approximate 11-year cycle, characterized by periods of high (solar maximum, about 7 years) and low (solar minimum, about 4 years) activity. Figure 1.2 presents solar activity measurements and predictions for the upcoming cycles based on the sunspot number, also known as the Wolf number. Sunspots are cooler, darker regions on the Sun’s surface associated with intense magnetic activity.

While the Sun continuously emits a low-energy stream of particles known as the solar wind, primarily consisting of protons and electrons with some heavier ions, significant radiation events are associated with solar flares and coronal mass ejections (CMEs). These infrequent but powerful events release a substantial number of highly energetic particles into space. Solar wind particles typically have energies ranging from kiloelectronvolts (keV) to gigaelectronvolts (GeV) and can reach speeds up to 80% of the speed of light.

Highly energetic particles originating from intense solar activities are particularly concerning due to their ability to rapidly reach Earth’s atmosphere within hours or days. These energetic particles pose a dual threat: endangering astronauts and disrupting electronic systems in space [2]. The intensity of the solar wind and the frequency of solar particle events are directly influenced by solar activity, specifically the number of sunspots. During the solar maximum, particularly the declining phase, CMEs and solar flares occur more frequently [3].

Interestingly, solar activity has an inverse correlation with the flux of galactic cosmic rays (GCRs). GCRs are high-energy particles originating from outside the solar system and have the lowest particle flux among the radiation sources in near-Earth space. However, due to their high energy, they are highly penetrating and pose a significant threat to space-borne electronics and human health. Shielding technology offers limited protection against GCR radiation exposure.

During periods of high solar activity, the Sun’s magnetic field strengthens, acting as a more effective shield against incoming particles from beyond the solar system. This leads to a decrease in the flux of GCRs reaching Earth’s vicinity [5‐7]. Conversely, during solar minimum periods, the weakened solar magnetic field allows a higher GCR flux to penetrate into near-Earth space. Understanding and monitoring solar activity and its associated radiation environment is crucial for several reasons:

Solar events, such as solar storms and CMEs, have been documented for centuries. The Carrington event of 1859 serves as a powerful historical example. This massive solar storm caused significant disruptions to early telegraph systems and produced auroras visible across the globe [8, 9]. It was one of the first instances where the consequences of a solar event affecting Earth were recognized. One event in this level could be very catastrophic nowadays as modern technology is completely dependent on electricity. A more recent example occurred in January 2022, where a significant solar storm originating from a CME caused unexpected impacts on orbiting satellites [10, 11]. The solar energy from the CME increased atmospheric drag, pulling several satellites out of their intended orbits. This incident, unfortunately resulting in the loss of multiple satellites, underscores the importance of considering solar activity’s potential effects when designing space missions.

The third radiation component in the near-Earth environment is the trapped particle radiation in the Van Allen radiation belts, illustrated in Fig. 1.3. As can be seen in Fig. 1.3, the outer belt is wider than the inner belt, and it is also the most unstable due to the weaker influence of the Earth’s magnetosphere. Similar to the GCRs, the trapped radiation suffers influence from the solar activity, and it is modulated such that the higher the activity, the higher is the electron flux and the lower the proton flux and vice versa [12]. Van Allen radiation belts have been always a concern for space mission designs due to their impact on electronic reliability. Protons are able to induce a variety of effects ranging from parametric degradation due to absorbed dose to even singular effects.

These radiation effects are further detailed in the next section. The analysis of the proton flux in the inner belt is highly important for any space mission targeting low-Earth orbit (LEO) as, for example, several Earth observation instruments and the International Space Station (ISS) shown in Fig. 1.3. Overall, a comprehensive understanding of the dynamics and composition of the trapped radiation belts plays a crucial role in developing effective measures to safeguard satellites against the adverse impacts of space weather.

Another crucial consideration in the design of spaceborne components is the anomaly within the Earth’s magnetosphere, known as the South Atlantic Anomaly (SAA). This anomaly arises from a slight tilt and offset between the Earth’s geomagnetic and rotational axes, causing a significant weakening of the Earth’s magnetic field over the South Atlantic region. This weakened field allows energetic particles from the Van Allen belts and galactic cosmic rays (GCRs) to penetrate lower altitudes than they typically would elsewhere, resulting in a zone of increased radiation exposure. Figure 1.4 illustrates this phenomenon, showing the AP8 MIN model’s depiction of high-flux protons reaching altitudes as low as 500 km and below in the SAA region.

The presence of the SAA poses a significant challenge for spacecraft operating in LEO. The intense radiation environment within the SAA can potentially damage sensitive electronics onboard satellites. As a result, many satellites employ a precautionary measure of switching off sensitive electronic components when traversing the SAA to avoid potential damage, particularly from stochastic events (discussed in the next chapter).

When cosmic rays enter the Earth’s atmosphere, they interact with atmospheric atoms, primarily nitrogen and oxygen molecules, leading to the production of secondary radiation. Similarly, these secondary particles can also interact with atmospheric atoms, creating a cascade effect and generating additional secondary particles. This phenomenon is known as a cosmic ray air shower, and it is illustrated in Fig. 1.5. In this example, the primary cosmic particle is a highly energetic proton that collides with the nuclei of a nitrogen atom in the air. These collisions lead to the production of secondary particles, including protons, neutrons, pions \(\pi \), kaons K, and muons \(\mu \). This process continues until the secondary particles have insufficient energy to sustain further interactions. Pions and kaons are unstable particles with short lifespans. They rapidly decay into various particles, including muons, electrons \(e^{-}\), positron \(e^{+}\) (antiparticle of electrons), neutrinos \(\nu \), and photons \(\gamma \).

Cosmic ray air showers are comprised of various secondary particles, each with unique properties. Muons are particularly noteworthy due to their relatively long lifespan compared to pions and kaons, despite still being short-lived compared to stable particles like protons and electrons. Although their average lifetime is just 2.2 microseconds; this allows them to travel several kilometers through the atmosphere before decaying. Similar to electrons, muons are fundamental particles. However, their much greater mass grants them significantly higher penetration power. Muons can traverse several centimeters of materials like silicon, potentially reaching sensitive electronic components within spacecraft or even electronics on the ground. Historically, secondary neutrons were considered the primary contributors of radiation damage in electronic devices exposed to the atmospheric environment. However, with advancements in miniaturization and increased device sensitivity, muons pose a growing threat to system reliability by inducing radiation damage in microelectronics [14‐17].

It is important to note that the cascade of secondary interactions triggered by a high-energy cosmic ray is a complex process with numerous possible reaction pathways. These pathways depend heavily on the specific energy, angle of incidence, and characteristics of the primary particle, along with the properties of the target atoms it interacts with. While Fig. 1.5 provides a simplified illustration, the true nature of these interactions involves a vast array of potential reactions. The flux and composition of atmospheric radiation are subject to fluctuation, influenced by various factors. Solar activity notably impacts the influx of particles bombarding the upper atmosphere, while the Earth’s nonuniform magnetic field results in spatial variations in radiation intensity and composition. Regions with weaker magnetic fields, such as the South Atlantic Anomaly discussed earlier, experience heightened fluxes of energetic particles.

Altitude also plays a pivotal role. As we descend through the atmosphere, particle flux initially rises due to collisions with atmospheric nuclei, generating secondary particles. This increase peaks at the Pfotzer maximum, after which flux diminishes due to energy loss through interactions, absorption by atmospheric molecules, and decay of unstable particles [18]. For instance, neutron flux increases with decreasing altitude, reaching its peak density of approximately \(10^4\) neutrons per square centimeter per hour (\(\mbox{n/cm}^2/\mbox{h}\)) at around 20 km [19, 20]. However, this density drastically declines to about 20 \(\mbox{n/cm}^2/\mbox{h}\) at ground level, a mere fraction of its peak value, approximately 0.2%. Apart from neutrons and muons, protons are also a concern for ground-level atmospheric applications, although typically exhibiting lower fluxes when compared to energies up to 400 MeV [21].

While the probability of failure induced by secondary cosmic ray particles is relatively low at ground level, it can still be a concern for safety-critical systems that rely heavily on electronics. These systems require extremely high reliability, and even a small chance of failure can have significant consequences. Therefore, understanding the particle flux and composition at different altitudes and locations is crucial for assessing the radiation threat and designing reliable systems for atmospheric applications.

Another hostile environment with a very particular radiation field is encountered in particle accelerators used in high-energy physics research laboratories. A very good example is the world’s largest collider, the large hadron collider (LHC) in the European Organization for Nuclear Research (CERN) in which, in its current design, protons can be accelerated up to 7 TeV. The LHC is a circular collider as shown in the layout in Fig. 1.6 where the eight octants, the interaction points (IP), and the direction of the beams are illustrated. There are four main interaction points where the physics experiments are hosted: interaction point 1 (IP1) hosts the ATLAS experiment, the general-purpose LHC experiment where the world’s largest particle detector is installed; interaction point 2 (IP2) hosts the ALICE experiment, a large ion collider detector dedicated to heavy-ion physics; interaction point 5 (IP5) hosts the compact muon solenoid (CMS) experiment, which is another general-purpose detector similar to ATLAS with a broad physics program and a different magnet system; and, lastly, the interaction point 8 (IP8) hosts the LHCb experiment, in which, different from the previous experiments, the large hadron collider beauty is a collection of subdetectors used to detect the forward particles from the collisions and to investigate the beauty quark (b quark).

The performance of particle colliders such as the LHC is mostly associated with its physics production, i.e., the number of particle collisions and the production of new physics. Generally, it is measured by the energy that the injected particles can be accelerated to and by the integrated luminosity (number of observed inelastic collisions) measured by their detectors. During the LHC physics run 2 (2015–2018), an average integrated luminosity of 50 \(\mbox{fb}^{-1}\) (femtobarns) per year was achieved. This high luminosity allowed for a significant number of collision events to be recorded and analyzed. However, with the high luminosity (HL) LHC upgrade project, the nominal annual integrated luminosity is expected to reach over 250 \(\mbox{fb}^{-1}\). The increase in integrated luminosity and the corresponding increase in the number of collisions also lead to higher radiation levels in different areas of the accelerator. These elevated radiation levels can pose operational challenges, such as reduced beam availability caused by beam dumps resulting from magnet quenching (loss of superconductivity) or system failures due to radiation effects on electronics.

The LHC radiation environment consists of a mixed field with a variety of particles and energies which vary along the different locations in the accelerator complex. It depends not only on the different beam loss mechanisms at play but also on the accelerator settings such as the beam intensity and collimator settings [23, 24]. In this context, there are three main sources of radiation generally related to beam losses:

The monitoring of radiation levels in particle accelerators serves multiple crucial purposes. It not only safeguards the integrity and performance of the accelerator itself but also ensures the safety of personnel working in the underground beam lines. While delving into the intricacies of radiation protection measures falls beyond the scope of this book, it is essential to acknowledge their significance in such radioactive environments. Additionally, radiation hardness assurance (RHA) methodologies play a pivotal role in qualifying components and systems to withstand the harsh radiation environment, mitigating the risk of system failures induced by high radiation levels [23, 26‐28]. When examining the impact of radiation on electronics, particular attention is given to high-energy hadrons (HEH) and neutrons, as they dominate the particle spectrum within the LHC environment. Figure 1.7 presents a representative lethargy spectrum encountered at the LHC, considering the relevant hadrons such as protons, charged pions, and kaons, as well as neutrons. This spectrum was simulated using FLUKA, a widely validated Monte Carlo transport code extensively utilized in accelerator research and beyond [29‐31]. As depicted in Fig. 1.7, three distinct energy ranges stand out, with varying abundances and effects on electronic reliability. High-energy hadrons exhibit a prominent flux peak in the several hundred MeV range, while neutrons span a range from thermal energies up to 20 MeV [32]. These energy ranges are of significant relevance when assessing the potential impact of radiation on electronic systems. By comprehending the characteristics and intensities of these particles, strategies can be devised to harden electronics against radiation-induced challenges and ensure their reliable operation in the demanding environment of particle accelerators [27].

In Table 1.1, the approximate HEH annual fluxes are presented for the different radiation environments, from space, i.e., the International Space Station (ISS) and low-Earth orbits, to ground and accelerator environments. For instance, the HEH fluxes at CERN’s accelerator complex, from the injector chain to the LHC ring, can be comparable to the fluxes observed in commercial flights (around \(10^{7}/\mbox{cm}^{2}/\mbox{yr}\)) and in space (\(10^{8}-10^{9}/\mbox{cm}^{2}/\mbox{yr}\)); however, depending on the location in machine, it can reach levels way beyond (up to \(10^{12}/\mbox{cm}^{2}/\mbox{yr}\)).

As technology advances and transistors are placed in closer proximity to each other, the critical charge required to trigger an SEE is reduced. Consequently, a single incident particle is able to induce sufficient charge collection from multiple neighboring electrodes. This phenomenon is known as charge sharing effect. The work developed by Amusan et al. [45] provides an analysis of the charge sharing effect in adjacent N-channel metal-oxide semiconductor (NMOS) and P-channel metal-oxide semiconductor (PMOS) transistors based on TCAD simulations. The 130 nm CMOS devices, based on the International Business Machines corporation (IBM) twin well technology, were characterized using advanced simulation tools such as Synopsis DEVISE and DESSIS. In the simulation setup, a particle hit was precisely targeted at the center of the drain region, perpendicular to the surface of the device structure. It is worth noting that for the purpose of these simulations, the influence of angular effects was omitted in the analysis. The authors used two particular notations: active device, which refers to the device directly struck by the particle and actively collecting the carriers, and the passive device, which represents the device not directly impacted by the particle but passively collecting the diffused carriers. In Fig. 1.14, the collected charge is shown for the active and passive devices when PMOS and NMOS transistors are used.

The results of this study clearly demonstrate that passive PMOS devices are capable of collecting a greater amount of charge compared to passive NMOS devices. Specifically, the passive PMOS device collected approximately 40% of the charge collected by the active PMOS device, while the passive NMOS transistor collected less than 25% of the charge. The authors attribute this discrepancy to the disparity in carrier diffusion coefficients between electrons and holes, as well as the bipolar amplification effect that enhances charge collection in PMOS devices [45, 46].

While the charge sharing mechanism is responsible for the increased SEE sensitivity in deeply scaled technologies, it has also been shown to reduce the pulse width of SETs in combinational cells [47, 48]. Due to the similar time constant for the circuit delay and the diffusion process, the radiation-induced transient is able to activate the charge collection in electrodes from following stage of circuits in such a way that the resultant transient is shortened (i.e., quenched). This phenomenon is referred to as the pulse quenching effect (PQE). To observe the PQE in a circuit, an inverting relationship between logic stages is required. Both charge sharing and the pulse quenching effect are intricate and critical mechanisms that heavily depend on the specific device technology and design strategies employed. Therefore, acquiring a comprehensive understanding of their impact is of utmost importance for accurately assessing the sensitivity of modern electronic components to single-event effects.