Editing Radiation hardening (section)

==Radiation effects on electronics==
 {{more citations needed section|date=December 2021}}
<!-- rephrased largely from
http://www.mse.vt.edu/faculty/hendricks/mse4206/projects97/group02/effects.htm
with additions from several other sources -->

===Fundamental mechanisms===
Two fundamental damage mechanisms take place:

====Lattice displacement====
Lattice displacement is caused by [[neutron]]s, protons, alpha particles, heavy ions, and very high energy [[gamma photon]]s. They change the arrangement of the atoms in the [[crystal lattice]], creating lasting damage, and increasing the number of [[Carrier generation and recombination|recombination center]]s, depleting the [[minority carrier]]s and worsening the analog properties of the affected semiconductor [[p-n junction|junctions]]. Counterintuitively, higher doses over a short time cause partial [[Annealing (metallurgy)|annealing]] ("healing") of the damaged lattice, leading to a lower degree of damage than with the same doses delivered in low intensity over a long time (LDR or Low Dose Rate). This type of problem is particularly significant in [[bipolar transistor]]s, which are dependent on minority carriers in their base regions; increased losses caused by [[recombination (physics)|recombination]] cause loss of the transistor [[gain (electronics)#Electronics|gain]] (see ''[[#Resultant effects|neutron effects]]''). Components certified as ELDRS (Enhanced Low Dose Rate Sensitive)-free do not show damage with fluxes below 0.01 rad(Si)/s = 36 rad(Si)/h.

====Ionization effects====
Ionization effects are caused by charged particles, including ones with energy too low to cause lattice effects. The ionization effects are usually transient, creating [[glitch]]es and soft errors, but can lead to destruction of the device if they trigger other damage mechanisms (e.g., a [[latchup]]). [[Photocurrent]] caused by [[ultraviolet]] and X-ray radiation may belong to this category as well. Gradual accumulation of [[electron hole|holes]] in the oxide layer in [[MOSFET]] transistors leads to worsening of their performance, up to device failure when the dose is high enough (see ''[[#Resultant effects|total ionizing dose effects]]'').

The effects can vary wildly depending on all the parameters – type of radiation, total dose and radiation flux, combination of types of radiation, and even the kind of device load (operating frequency, operating voltage, actual state of the transistor during the instant it is struck by the particle) – which makes thorough testing difficult, time-consuming, and requiring many test samples.

===Resultant effects===
The "end-user" effects can be characterized in several groups:

<!--Ionization effectsNeutron effectsIonization effects-->
A neutron interacting with a semiconductor lattice will displace the atoms in the lattice. This leads to an increase in the count of recombination centers and [[deep-level defect]]s, reducing the lifetime of minority carriers, thus affecting [[bipolar junction transistor|bipolar devices]] more than [[CMOS]] ones. Bipolar devices on [[silicon]] tend to show changes in electrical parameters at levels of 10<sup>10</sup> to 10<sup>11</sup> neutrons/cm<sup>2</sup>, while CMOS devices aren't affected until 10<sup>15</sup> neutrons/cm<sup>2</sup>. The sensitivity of devices may increase together with increasing level of integration and decreasing size of individual structures. There is also a risk of induced radioactivity caused by [[neutron activation]], which is a major source of noise in [[high-energy astronomy|high energy astrophysics]] instruments. Induced radiation, together with residual radiation from impurities in component materials, can cause all sorts of single-event problems during the device's lifetime. [[gallium arsenide|GaAs]] [[light-emitting diode|LEDs]], common in [[optocoupler]]s, are very sensitive to neutrons. The lattice damage influences the frequency of [[crystal oscillator]]s. Kinetic energy effects (namely lattice displacement) of charged particles belong here too.

====Total ionizing dose effects====
Total ionizing dose effects represent the cumulative damage of the semiconductor lattice (''lattice displacement'' damage) caused by exposure to ionizing radiation over time. It is measured in [[rad (unit)|rads]] and causes slow gradual degradation of the device's performance. A total dose greater than 5000 rads delivered to silicon-based devices in a timespan on the order of seconds to minutes will cause long-term degradation. In CMOS devices, the radiation creates [[electron–hole pair]]s in the gate insulation layers,<ref>{{Cite journal
| last1 = Khoshnoud
| first1 = A.
| last2 = Yavandhassani
| first2 = J.
| title = Modeling of total ionizing dose (TID) effects on the nonuniform distribution of Si/SiO<sub>2</sub> interface trap energy states in MOS devices
| journal = Scientific Reports
| volume = 15
| pages = 17082
| year = 2025
| doi = 10.1038/s41598-025-01325-3
| url = https://www.nature.com/articles/s41598-025-01325-3
}}</ref> which cause photocurrents during their recombination, and the holes trapped in the lattice defects in the insulator create a persistent gate [[biasing]] and influence the transistors' [[threshold voltage]], making the N-type MOSFET transistors easier and the P-type ones more difficult to switch on. The accumulated charge can be high enough to keep the transistors permanently open (or closed), leading to device failure. Some self-healing takes place over time, but this effect is not too significant. This effect is the same as [[hot carrier degradation]] in high-integration high-speed electronics. Crystal oscillators are somewhat sensitive to radiation doses, which alter their frequency. The sensitivity can be greatly reduced by using [[swept quartz]]. Natural [[quartz]] crystals are especially sensitive. Radiation performance curves for TID testing may be generated for all resultant effects testing procedures. These curves show performance trends throughout the TID test process and are included in the radiation test report.

====Transient dose effects====
Transient dose effects result from a brief high-intensity pulse of radiation, typically occurring during a nuclear explosion. The high radiation flux creates photocurrents in the entire body of the semiconductor, causing transistors to randomly open, changing logical states of [[Flip-flop (electronics)|flip-flops]] and [[Memory cell (computers)|memory cells]]. Permanent damage may occur if the duration of the pulse is too long, or if the pulse causes junction damage or a latchup. Latchups are commonly caused by the X-rays and gamma radiation flash of a nuclear explosion. Crystal oscillators may stop oscillating for the duration of the flash due to prompt [[photoconductivity]] induced in quartz.

====Systems-generated EMP effects====
SGEMP effects are caused by the radiation flash traveling through the equipment and causing local [[ionization]] and [[electric current]]s in the material of the chips, [[circuit board]]s, [[electrical cable]]s and cases.

===Digital damage: SEE===
Single-event effects (SEE) have been studied extensively since the 1970s.<ref>{{cite book | last1=Messenger | first1=G.C. | last2=Ash | first2=Milton | title=Single Event Phenomena | publisher=Springer Science & Business Media | date=2013-11-27 | isbn=978-1-4615-6043-2 | pages=xii-xiii}}</ref>  When a high-energy particle travels through a semiconductor, it leaves an [[ion]]ized track behind. This ionization may cause a highly localized effect similar to the transient dose one - a benign glitch in output, a less benign bit flip in memory or a [[hardware register|register]] or, especially in [[Power semiconductor device|high-power transistors]], a destructive latchup and burnout. Single event effects have importance for electronics in satellites, aircraft, and other civilian and military aerospace applications. Sometimes, in circuits not involving latches, it is helpful to introduce [[RC circuit|RC]] [[time constant]] circuits that slow down the circuit's reaction time beyond the duration of an SEE.

====Single-event transient====
An SET happens when the charge collected from an ionization event discharges in the form of a spurious signal traveling through the circuit. This is de facto the effect of an [[electrostatic discharge]]. it is considered a soft error, and is reversible.

====Single-event upset====
[[Single-event upset]]s (SEU) or '''transient radiation effects in electronics''' are state changes of memory or register bits caused by a single ion interacting with the chip. They do not cause lasting damage to the device, but may cause lasting problems to a system which cannot recover from such an error. It is otherwise a reversible soft error. In very sensitive devices, a single ion can cause a [[multiple-bit upset]] (MBU) in several adjacent memory cells. SEUs can become '''single-event functional interrupts''' ('''SEFI''') when they upset control circuits, such as [[state machine]]s, placing the device into an undefined state, a [[test mode]], or a halt, which would then need a [[Reset (computing)|reset]] or a [[Power cycling|power cycle]] to recover.

====Single-event latchup====
An SEL can occur in any chip with a [[thyristor|parasitic PNPN]] structure. A heavy ion or a high-energy proton passing through one of the two inner-transistor junctions can turn on the [[thyristor]]-like structure, which then stays "[[short circuit|short]]ed" (an effect known as [[latch-up]]) until the device is power-cycled. As the effect can happen between the power source and substrate, destructively high current can be involved and the part may fail. This is a hard error, and is irreversible. Bulk CMOS devices are most susceptible.

====Single-event snapback====
A single-event snapback is similar to an SEL but not requiring the PNPN structure, and can be induced in N-channel MOS transistors switching large currents, when an ion hits near the drain junction and causes [[avalanche breakdown|avalanche multiplication]] of the [[charge carrier]]s. The transistor then opens and stays opened, a hard error which is irreversible.

====Single-event induced burnout====
An SEB may occur in power MOSFETs when the substrate right under the source region gets forward-biased and the drain-source voltage is higher than the breakdown voltage of the parasitic structures. The resulting high current and local overheating then may destroy the device. This is a hard error, and is irreversible.

====Single-event gate rupture====
SEGR are observed in power MOSFETs when a heavy ion hits the gate region while a high voltage is applied to the gate. A local breakdown then happens in the insulating layer of [[silicon dioxide]], causing local overheating and destruction (looking like a microscopic [[explosion]]) of the gate region. It can occur even in [[EEPROM]] cells during write or erase, when the cells are subjected to a comparatively high voltage. This is a hard error, and is irreversible.

===SEE testing===
While proton beams are widely used for SEE testing due to availability, at lower energies proton irradiation can often underestimate SEE susceptibility. Furthermore, proton beams expose devices to risk of total ionizing dose (TID) failure which can cloud proton testing results or result in premature device failure. White neutron beams—ostensibly the most representative SEE test method—are usually derived from solid target-based sources, resulting in flux non-uniformity and small beam areas. White neutron beams also have some measure of uncertainty in their energy spectrum, often with high thermal neutron content.

The disadvantages of both proton and spallation neutron sources can be avoided by using mono-energetic 14 MeV neutrons for SEE testing. A potential concern is that mono-energetic neutron-induced single event effects will not accurately represent the real-world effects of broad-spectrum atmospheric neutrons. However, recent studies have indicated that, to the contrary, mono-energetic neutrons—particularly 14 MeV neutrons—can be used to quite accurately understand SEE cross-sections in modern microelectronics.<ref>{{Cite conference|last1=Normand|first1=Eugene|last2=Dominik|first2=Laura|title=2010 IEEE Radiation Effects Data Workshop |date=20–23 July 2010|chapter=Cross Comparison Guide for Results of Neutron SEE Testing of Microelectronics Applicable to Avionics|page=8 |conference=2010 IEEE Radiation Effects Data Workshop|doi=10.1109/REDW.2010.5619496|isbn=978-1-4244-8405-8 }}</ref>