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{{short description|Processes and techniques used for making electronic devices resistant to ionizing radiation}}
] designed for environments with high levels of ] have special design challenges. A single ] of radiation can knock thousands of ]s loose, causing electronic ], signal ]s, and in the case of ]s, plainly incorrect results. This is a particularly serious problem in the design of ]s, ], ], ]s, and ]s. In order to ensure the proper operation of such systems, manufacturers of ]s and ]s intended for the (]) ] markets employ various methods of '''radiation hardening'''. The resulting systems are said to be '''rad(iation)-hardened''', '''rad-hard''', or (within context) '''hardened'''.
{{distinguish|hard radiation|radiation embrittlement}}
{{for|hardening of materials caused by radiation|radiation damage}}
'''Radiation hardening''' is the process of making ] and circuits resistant to damage or malfunction caused by high levels of ] (] and high-energy ]),<ref>{{Cite encyclopedia |title=Radiation hardening |last=Messenger |first=George C. |encyclopedia=AccessScience |doi=10.1036/1097-8542.566850}}</ref> especially for environments in ] (especially beyond ]), around ]s and ], or during ]s or ].


Most ] are susceptible to radiation damage, and '''radiation-hardened''' ('''rad-hard''') components are based on their non-hardened equivalents, with some design and manufacturing variations that reduce the susceptibility to radiation damage. Due to the low demand and the extensive development and testing required to produce a radiation-tolerant design of a ] chip, the technology of radiation-hardened chips tends to lag behind the most recent developments.<ref name=":0">{{Cite web |last=Heyman |first=Karen |date=2024-02-15 |title=SRAM Scaling Issues, And What Comes Next |url=https://semiengineering.com/sram-scaling-issues-and-what-comes-next/ |access-date=2024-10-24 |website=Semiconductor Engineering |language=en-US}}</ref> They also typically cost more than their commercial counterparts.<ref name=":0" />
Most radiation-hardened chips are based on their more mundane commercial equivalents, with some manufacturing and design variations that reduce the susceptibility to radiation and electrical and magnetic interference. Typically, the hardened variants lag behind the cutting-edge commercial products by several technology generations due to the extensive development and testing required to produce a radiation-tolerant design.


Radiation-hardened products are typically tested to one or more resultant-effects tests, including total ionizing dose (TID), enhanced low dose rate effects (ELDRS), neutron and proton displacement damage, and single event effects (SEEs).
== Major radiation damage sources==


==Problems caused by radiation==
Typical sources of exposition of electronics to ionizing radiation are ] and the ]s for satellites, ]s in power plants for sensors and control circuits, residual radiation from ]s in ], ] for both high-altitude airplanes and satellites, and ]s for potentially all military and civilian electronics.
{{See also|Radiation damage}}


Environments with high levels of ionizing radiation create special design challenges. A single ] can knock thousands of ]s loose, causing ] and ]s. In the case of ]s, this can cause results which are inaccurate or unintelligible. This is a particularly serious problem in the design of ]s, ], future ]s,<ref>{{cite news |title=Quantum computers may be destroyed by high-energy particles from space |url=https://www.newscientist.com/article/2252933-quantum-computers-may-be-destroyed-by-high-energy-particles-from-space/ |access-date=7 September 2020 |work=New Scientist}}</ref><ref>{{cite news |title=Cosmic rays may soon stymie quantum computing |url=https://phys.org/news/2020-08-cosmic-rays-stymie-quantum.html |access-date=7 September 2020 |work=phys.org |language=en}}</ref><ref>{{cite journal |last1=Vepsäläinen |first1=Antti P. |last2=Karamlou |first2=Amir H. |last3=Orrell |first3=John L. |last4=Dogra |first4=Akshunna S. |last5=Loer |first5=Ben |last6=Vasconcelos |first6=Francisca |last7=Kim |first7=David K. |last8=Melville |first8=Alexander J. |last9=Niedzielski |first9=Bethany M. |last10=Yoder |first10=Jonilyn L. |last11=Gustavsson |first11=Simon |last12=Formaggio |first12=Joseph A. |last13=VanDevender |first13=Brent A. |last14=Oliver |first14=William D. |title=Impact of ionizing radiation on superconducting qubit coherence |journal=Nature |date=August 2020 |volume=584 |issue=7822 |pages=551–556 |doi=10.1038/s41586-020-2619-8 |pmid=32848227 |arxiv=2001.09190 |bibcode=2020Natur.584..551V |s2cid=210920566 |url=https://www.nature.com/articles/s41586-020-2619-8 |access-date=7 September 2020 |language=en |issn=1476-4687}}</ref> ], nuclear power stations, and ]s. In order to ensure the proper operation of such systems, manufacturers of ]s and ]s intended for the ] or ] markets employ various methods of radiation hardening. The resulting systems are said to be '''rad(iation)-hardened''', '''rad-hard''', or (within context) '''hardened'''.
* ]s come from all directions and consist from approx. 85% ]s, 14% of ]s, and 1% of ]s, together with ultraviolet radiation and x-rays. Most effects are caused by particles with energies between 10<sup>8</sup> and 2*10<sup>10</sup> ], though there are even particles with energies up to 10<sup>20</sup> eV. They are mostly filtered by the atmosphere, so are concern just for high-altitude applications like stratospheric jets and satellites.


==Major radiation damage sources==
* ] come from the direction of the ] and consist of large flux of high-energy (several GeV) protons and heavy ions, again accompanied with UV and x-ray radiation. They cause a scale of problems for satellites, ranging from radiation damage to loss of altitude by heating up the upper regions of atmosphere, causing them to raise up, and decelerating the low-orbit satellites.
Typical sources of exposure of electronics to ionizing radiation are the ]s for satellites, nuclear reactors in power plants for sensors and control circuits, particle accelerators for control electronics (particularly ] devices), residual radiation from ]s in ], ] for spacecraft and high-altitude aircraft, and ]s for potentially all military and civilian electronics.


Secondary particles result from interaction of other kinds of radiation with structures around the electronic devices.
* ] contain electrons (up to about 10 MeV) and protons (up to 100s MeV) trapped in the ]. The particle flux in the regions farther from the Earth can vary wildly depending on the actual conditions of the sun and the ]. Due to their position they pose a concern for satellites.


* ] contain electrons (up to about 10 MeV) and protons (up to 100s MeV) trapped in the ]. The particle flux in the regions farther from the Earth can vary wildly depending on the actual conditions of the Sun and the ]. Due to their position they pose a concern for satellites.
* ]s result from interaction of other kinds of radiation with structures around the electronic devices.
* Nuclear reactors produce ] and ] which can affect sensor and control circuits in ]s.
* ]s produce high energy protons and electrons, and the secondary particles produced by their interactions produce significant radiation damage on sensitive control and particle detector components, of the order of magnitude of 10 MRad/year for systems such as the ].<ref>{{cite conference|url=https://cds.cern.ch/record/1481526/|title=Radiation Damage to Electronics at the LHC|last1=Brugger|first1=M.|date=May 2012|publisher= |book-title= |pages=THPPP006|location=], ]|conference=3rd International Particle Accelerator Conference|id=}}</ref>
* ] were an insidious source of radiation that was found to be causing ]s in new ] chips in the 1970s. Traces of ] in the packaging of the chips were producing alpha particles, which were then occasionally discharging some of the capacitors used to store the DRAM data bits. These effects have been reduced today by using purer packaging materials, and employing ]s to detect and often correct DRAM errors.
* ]s come from all directions and consist of approximately 85% ]s, 14% ]s, and 1% ], together with ] and gamma-ray radiation. Most effects are caused by particles with energies between 0.1 and 20 ]. The atmosphere filters most of these, so they are primarily a concern for spacecraft and high-altitude aircraft, but can also affect ordinary computers on the surface.<ref>{{cite journal |last1=Ziegler |first1=J. F. |last2=Lanford |first2=W. A. |title=Effect of Cosmic Rays on Computer Memories |journal=Science |date=16 November 1979 |volume=206 |issue=4420 |pages=776–788 |doi=10.1126/science.206.4420.776|pmid=17820742 |bibcode=1979Sci...206..776Z |s2cid=2000982 }}</ref><ref>{{cite journal |last1=Ziegler |first1=J. F. |last2=Lanford |first2=W. A. |title=The effect of sea level cosmic rays on electronic devices |journal=Journal of Applied Physics |date=June 1981 |volume=52 |issue=6 |pages=4305–4312 |doi=10.1063/1.329243|bibcode=1981JAP....52.4305Z }}</ref>
* ] come from the direction of the ] and consist of a large flux of high-energy (several GeV) protons and heavy ions, again accompanied by X-ray radiation.
* Nuclear explosions produce a short and extremely intense surge through a wide spectrum of electromagnetic radiation, an ] (EMP), neutron radiation, and a flux of both primary and secondary charged particles. In case of a nuclear war they pose a potential concern for all civilian and military electronics.


==Radiation effects on electronics==
* ]s produce ] and ]. They are important for sensor and control circuits in ]s.
{{more citations needed section|date=December 2021}}

* ]s produce a short, extremely intense surge of the entire spectrum of electromagnetic radiation, ] (EMP), ], and flux of both primary and secondary charged particles. In case of a ] they pose a potential concern for all civilian and military electronics.

* ] are an insidious source of radiation found to be causing ]s of new DRAM chips in 1970s. Traces of radioactive elements in the packaging of the chips were producing alpha particles, which then caused havoc on the matrix of capacitors. These effects are today reduced by using non-contaminated packaging materials, and employing ] DRAM modules, which make it possible to detect DRAM changes and, unlike the older ] detection, even correct the single-bit ones.

== Radiation effects on electronics ==
<!-- rephrased largely from <!-- rephrased largely from
http://www.mse.vt.edu/faculty/hendricks/mse4206/projects97/group02/effects.htm http://www.mse.vt.edu/faculty/hendricks/mse4206/projects97/group02/effects.htm
with additions from several other sources --> with additions from several other sources -->


===Fundamental mechanisms=== ===Fundamental mechanisms===

Two fundamental damage mechanisms take place: Two fundamental damage mechanisms take place:


====Lattice displacement====
* ''Lattice displacement'', caused by neutrons, protons, alpha particles, heavy ions, and very high energy gamma photons. They change the arrangement of the atoms in the lattice, creating lasting damage, and increasing the number of ]s, depleting the ]s and worsening the analog properties of the affected semiconductor ]. Counterintuitively, higher doses over short time cause partial ] ("healing") of the damaged lattice, leading to lower degree of damage than with the same doses delivered in low intensity over a long time. This type of damage is especially important for ]s, which are dependent on minority carriers in their base regions; increased losses caused by ] cause loss of the transistor ]. See '']''.
Lattice displacement is caused by ]s, protons, alpha particles, heavy ions, and very high energy ]s. They change the arrangement of the atoms in the ], creating lasting damage, and increasing the number of ]s, depleting the ]s and worsening the analog properties of the affected semiconductor ]. Counterintuitively, higher doses over a short time cause partial ] ("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 ]s, which are dependent on minority carriers in their base regions; increased losses caused by ] cause loss of the transistor ] (see '']''). 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'', caused by charged particles, including the ones with energy too low to cause lattice effects. The ionization effects are usually transient, creating glitches and soft errors, but can lead to destruction of the device if they trigger other damage mechanisms, eg. a latchup. ] caused by ultraviolet and x-ray radiation may belong to this category as well. Gradual accumulation of ] in the oxide layer in ] transistors leads to worsening of their performance, up to device failure when the dose is high enough; see '']''.
Ionization effects are caused by charged particles, including ones with energy too low to cause lattice effects. The ionization effects are usually transient, creating ]es and soft errors, but can lead to destruction of the device if they trigger other damage mechanisms (e.g., a ]). ] caused by ] and X-ray radiation may belong to this category as well. Gradual accumulation of ] in the oxide layer in ] transistors leads to worsening of their performance, up to device failure when the dose is high enough (see '']'').


The effects can vary wildly depending on all the parameters - the type of radiation, total dose and the radiation flux, combination of types of radiation, and even the kind of the 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 a lot of test samples. 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=== ===Resultant effects===

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


<!--Ionization effectsNeutron effectsIonization effects-->
* ''Neutron effects'' : A neutron interacting with the semiconductor ] will displace its atoms. This leads to increase of the count of ]s and ]s, reducing the lifetime of ]s, thus affecting ] more than ] 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>, CMOS devices aren't affected until 10<sup>15</sup> neutrons/cm<sup>2</sup>. The sensitivity of the devices may increase together with increasing level of integration and decreasing size of individual structures. There is also the risk of induced radioactivity caused by ], which is a major source of noise in high energy astrophysics instruments. Induced radiation, together with residual radiation from impurities in used materials, can cause all sorts of single-event problems during the device's lifetime. GaAs ], common in ]s, are very sensitive to neutrons. Kinetic energy effects (namely lattice displacement) of charged particles belong here too.
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 ]s, reducing the lifetime of minority carriers, thus affecting ] more than ] ones. Bipolar devices on ] 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 ], which is a major source of noise in ] 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. ] ], common in ]s, are very sensitive to neutrons. The lattice damage influences the frequency of ]s. Kinetic energy effects (namely lattice displacement) of charged particles belong here too.


====Total ionizing dose effects====
* ''Total ionizing dose effects'' : The cumulative damage of the semiconductor lattice (''lattice displacement'' damage) caused by ionizing radiation over the exposition time. It is measured in ] and causes slow gradual degradation of the device's performance; total dose greater than 5000 rads delivered to silicon-based devices in seconds to minutes will cause long-term degradation. In ] devices, the radiation creates ]s in the gate insulation layers, which cause ]s during their ], and the holes trapped in the lattice defects in the insulator create a persistent gate bias and influence the transistors' ], making the N-type ] 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.
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 ] 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 ]s in the gate insulation layers, which cause photocurrents during their recombination, and the holes trapped in the lattice defects in the insulator create a persistent gate ] and influence the transistors' ], 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 ] 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 ]. Natural ] 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'' : The short-time high-intensity pulse of radiation, typically occurring during a ]. The high radiation flux creates ]s in the entire body of the semiconductor, causing transistors to randomly open, changing logical states of flip-flops and memory cells. Permanent damage may occur if the duration of the pulse is too long, or if the pulse causes ] damage or causes a ]. Latchups are commonly caused by the ]s and ] flash of a nuclear explosion.
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 ] and ]. 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 ] induced in quartz.


* ''Systems-generated EMP effects (SGEMP)'' are caused by the radiation flash traveling through the equipment and causing local ionization and electric currents in the material of the chips, circuitboards, cables and cases. ====Systems-generated EMP effects====
SGEMP effects are caused by the radiation flash traveling through the equipment and causing local ] and ]s in the material of the chips, ]s, ]s and cases.

* ''Single-event effects (SEE)'' are phenomenons affecting mostly only digital devices; see the following section for an overview of the various types of SEE.


===Digital damage: SEE=== ===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 ]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 ] or, especially in ], 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 ] ] circuits that slow down the circuit's reaction time beyond the duration of an SEE.


====Single-event transient====
Single-event effects (SEE), mostly affecting only ] devices, were not studied extensively until relatively recently. When a high-energy particle travels through a semiconductor, it leaves an ]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 register, or, especially in high-power transistors, a destructive ] and ]. Single event effects have importance for electronics in ]s, ]s, and other both ] and ] ] applications. Sometimes in circuits not involving latches it is helpful to introduce RC time constant circuits, slowing down the circuit's reaction time beyond the duration of a SEE.
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 ]. it is considered a soft error, and is reversible.


====Single-event upset====
* '']s (SEU)'', also called "]s" 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. In very sensitive devices, a single ion can cause a ] (MBU) in several adjanced memory cells. SEUs can become ''Single-event Functional Interrupts'' (''SEFI'') when they cause placing the device into an undefined state, a test mode, or a halt, which needs a reset or a power cycle for a recovery.
]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 ] (MBU) in several adjacent memory cells. SEUs can become '''single-event functional interrupts''' ('''SEFI''') when they upset control circuits, such as ]s, placing the device into an undefined state, a ], or a halt, which would then need a ] or a ] to recover.


====Single-event latchup====
* ''Single-event ] (SEL)'' can occur in any chip with a ] structure. A heavy ion or a high-energy proton passing through one of the two inner-transistor junctions can open the thyristor-like structure, which then stays opened (an effect known as ]) 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. Bulk CMOS devices are most susceptible.
An SEL can occur in any chip with a ] structure. A heavy ion or a high-energy proton passing through one of the two inner-transistor junctions can turn on the ]-like structure, which then stays "]ed" (an effect known as ]) 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====
* ''Single-event transient (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 ].
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 ] of the ]s. The transistor then opens and stays opened, a hard error which is irreversible.


====Single-event induced burnout====
* ''Single-event snapback'', similar to SEL but not requiring the PNPN structure, can be induced in N-channel MOS transistors switching large currents, when an ion hits near the drain junction and causes avalanche multiplication of the charge carriers. The transistor then opens and stays opened.
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====
* ''Single-event induced burnout (SEB)'' may occur in power ]s 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.
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 ], causing local overheating and destruction (looking like a microscopic ]) of the gate region. It can occur even in ] 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===
* ''Single-event gate rupture (SEGR)'' was 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 overheat and destruction (looking like to a microscopic explosion) of the gate region. It can occur even in ] cells during write or erase, when the cells are subjected to a comparatively high voltage.
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>
== Radiation-hardening techniques ==


==Radiation-hardening techniques==
*Physical:
] of the 1886VE10 ] prior to ] ]]]
** Hardened chips are often manufactured on ] ]s instead of the usual ] wafers. ] (]) and ] (]) are commonly used. While normal commercial-grade chips can withstand between 5 and 10 k], space-grade SOI and SOS chips can survive doses many orders of magnitude greater.
] of the 1886VE10 ] after a ] ] process has been used]]
** ]ing the package against ], to reduce exposure of the bare device.
** ]-based ] is often replaced by more rugged (but larger, and more expensive) ].
** Choice of substrate with wide ], which gives it higher tolerance to ]s; eg. ] or ].
** Use of depleted ] (consisting only of ] Boron-11) in the ] layer protecting the chips, as boron-10 readily captures neutrons and undergoes alpha decay (see ]).
*Logical:
** ] uses additional ] bits to check for and possibly correct corrupted data.
** ] elements can be used at the system level. Three separate microprocessor boards may independently compute an answer to a calculation and compare their answers. Any system that produces a minority result will recalculate. Logic may be added such that if repeated errors occur from the same system, that board is shut down.
** Redundant elements may be used at the circuit level. A single bit may be replaced with three bits and separate "voting logic" for each bit to continuously determine its result. This increases area of a chip design by a factor of 5, so must be reserved for smaller designs. But it has the secondary advantage of also being "fail-safe" in real time. In the event of a single-bit failure (which may be unrelated to radiation), the voting logic will continue to produce the correct result without resorting to a watchdog timer. System level voting between three separate processor systems will generally need to use some circuit-level voting logic to perform the votes between the three processor systems.
** ] will perform a hard reset of a system unless some sequence is performed that generally indicates the system is alive, such a write operation from an onboard processor. During normal operation, software schedules a write to the watchdog timer at regular intervals to prevent the timer from running out. If radiation causes the processor to operate incorrectly, it is unlikely the software will work correctly enough to clear the watchdog timer. The watchdog eventually times out and forces a hard reset to the system. This is considered a last resort to other methods of radiation hardening.


===Physical===
== Examples of rad-hard computers==
Hardened chips are often manufactured on ] ]s instead of the usual ] wafers. Silicon on insulator (]) and silicon on ] (]) are commonly used. While normal commercial-grade chips can withstand between 50 and 100 ] (5 and 10 k]), space-grade SOI and SOS chips can survive doses between 1000 and 3000 ] (100 and 300 k]).<ref>
* The ] ] ], introduced in 1976, was the first serially-produced radiation-hardened ].
{{Citation
* The ], made by ] and used onboard the ] (] variant), is based on the ] architecture.
| author = Microsemi Corporation
* The ] ] (SBC), produced by ], includes a rad-hard ]-architecture CPU.
| publication-date = March 2012
* The ] SBC, also produced by BAE Systems, and based on the ] processor, is the successor to the RAD6000.
| title = RTSX-SU Radiation-Tolerant FPGAs (UMC)
* The ] ] manufactures a rad-hard variant of the ] ].
| type = Datasheet
* The ] is produced by ] Aerospace.
| url = http://www.actel.com/documents/RTSXSU_DS.pdf
* The ] is produced by Honeywell Aerospace.
| access-date = May 30, 2021}}
* The ] built by ], which votes three ] cores against each other to mitigate radiation effects.
</ref><ref>
* The ], through its Satellite Development Center, produces a very powerful radiation hardened space computer variant based on the PowerPC 750.
{{Citation
* The ] ] is a radiation hardened variant developed in conjunction with the ].
| author = Atmel Corporation
* The ] processor is manufactured by ].
| publication-date = 2008
| title = Rad Hard 16 MegaBit 3.3V SRAM MultiChip Module AT68166H
| type = Datasheet
| url = https://ww1.microchip.com/downloads/en/DeviceDoc/at68166h_ds.pdf
| access-date = May 30, 2021
}}</ref> At one time many ] chips were available in radiation-hardened versions (RadHard).<ref name="verkasalo" /> While SOI eliminates latchup events, TID and SEE hardness are not guaranteed to be improved.<ref name=amartology/>

Choosing a substrate with wide ] gives it higher tolerance to deep-level defects; e.g. ] or ].{{citation needed|date=March 2022}}

Use of a special ] provides increased radiation resistance.<ref>{{Cite web|url=http://www.cpushack.com/2009/07/27/the-other-atmel-radiation-hardened-sparc-cpus/|title=The other Atmel: Radiation Hardened Sparc CPU's &#124; the CPU Shack Museum|date=27 July 2009}}</ref> Due to the high development costs of new radiation hardened processes, the smallest "true" rad-hard (RHBP, Rad-Hard By Process) process is 150&nbsp;nm as of 2016, however, rad-hard 65&nbsp;nm FPGAs were available that used some of the techniques used in "true" rad-hard processes (RHBD, Rad-Hard By Design).<ref name="avnet">{{Cite web|url=https://www.avnet.com/wps/wcm/connect/onesite/de21c984-9388-47b0-85cb-d1b02310a936/def-aero-satellite-wp.pdf?MOD=AJPERES&CVID=mXtnMby&CVID=mXtnMby&attachment=true&id=1575672031818|title = Avnet: Quality Electronic Components & Services}}</ref> As of 2019 110&nbsp;nm rad-hard processes are available.<ref>{{cite web |url=https://www.onsemi.com/pub/Collateral/BRD8079-D.PDF |title=Aerospace & Defense Solutions |website=Onsemi}}</ref>

Bipolar integrated circuits generally have higher radiation tolerance than CMOS circuits. The low-power Schottky (LS) ] can withstand 1000&nbsp;krad, and many ] can withstand 10,000&nbsp;krad.<ref name="verkasalo">{{Cite conference|last1=Leppälä|first1=Kari|last2=Verkasalo|first2=Raimo|date=17–23 September 1989|title=Protection of Instrument Control Computers against Soft and Hard Errors and Cosmic Ray Effects|conference=International Seminar on Space Scientific Engineering|citeseerx=10.1.1.48.1291}}</ref> Using ] transistors, which have an unconventional physical construction, together with an unconventional physical layout, can also be effective.<ref>{{cite conference | last1=Benigni | first1=Marcello | last2=Liberali | first2=Valentino | last3=Stabile | first3=Alberto | last4=Calligaro | first4=Cristiano | title=Design of rad-hard SRAM cells: A comparative study | conference=27th International Conference on Microelectronics Proceedings | year=2010 | doi=10.1109/miel.2010.5490481}}</ref>

Magnetoresistive ], or ], is considered a likely candidate to provide radiation hardened, rewritable, non-volatile conductor memory. Physical principles and early tests suggest that MRAM is not susceptible to ionization-induced data loss.<ref>
{{cite conference | first1 = B. | last1 = Wang | first2 = Z. | last2 = Wang | first3 = C. | last3 = Hu | first4 = Y. | last4 = Zhao
| first5 = Y. | last5 = Zhang | first6 = W. | last6 = Zhao
| title = 2018 IEEE International Magnetics Conference (INTERMAG) | chapter = Radiation Hardening Techniques for SOT-MRAM Peripheral Circuitry | pages = 1–2
| publisher = 2018 IEEE International Magnetics Conference (INTERMAG) | date = 2018
| doi = 10.1109/INTMAG.2018.8508368| isbn = 978-1-5386-6425-4 }}</ref>

]-based ] is often replaced by more rugged (but larger, and more expensive) ]. SRAM cells have more transistors per cell than usual (which is 4T or 6T), which makes the cells more tolerant to SEUs at the cost of higher power consumption and size.<ref>{{cite journal |url=https://www.jstage.jst.go.jp/article/elex/14/12/14_14.20170413/_pdf |title=A novel SEU hardened SRAM bit-cell design |author1=Tiehu Li |author2=Yintang Yang |author3=Junan Zhang |author4=Jia Liu |journal=IEICE Electronics Express |volume=14 |issue=12 |pages=1–8}}</ref><ref name="avnet"/>

====Shielding====
]ing the package against ] is straightforward to reduce exposure of the bare device.<ref>{{Cite web|url=https://www.militaryaerospace.com/computers/article/16707204/the-evolving-world-of-radiationhardened-electronics|title = StackPath| date=2 June 2018 }}</ref>

To protect against neutron radiation and the ] of materials, it is possible to shield the chips themselves by use of ] (consisting only of isotope boron-11) in the ] ] protecting the chips, as naturally prevalent boron-10 readily ] and undergoes ] (see ]).

===Logical===
] (ECC memory) uses redundant bits to check for and possibly correct corrupted data. Since radiation's effects damage the memory content even when the system is not accessing the RAM, a "]" circuit must continuously sweep the RAM; reading out the data, checking the redundant bits for data errors, then writing back any corrections to the RAM.

] elements can be used at the system level. Three separate ] boards may independently compute an answer to a calculation and compare their answers. Any system that produces a minority result will recalculate. Logic may be added such that if repeated errors occur from the same system, that board is shut down.

Redundant elements may be used at the circuit level.<ref>{{cite conference|last=Platteter|first=Dale G.|date=October 1980|title=Protection of LSI Microprocessors using Triple Modular Redundancy|conference=International IEEE Symposium on Fault Tolerant Computing}}</ref> A single bit may be replaced with three bits and separate "]" for each bit to continuously determine its result (]). This increases area of a chip design by a factor of 5, so must be reserved for smaller designs. But it has the secondary advantage of also being "fail-safe" in real time. In the event of a single-bit failure (which may be unrelated to radiation), the voting logic will continue to produce the correct result without resorting to a ]. System level voting between three separate processor systems will generally need to use some circuit-level voting logic to perform the votes between the three processor systems.

Hardened latches may be used.<ref>{{cite conference|last1=Krishnamohan|first1=Srivathsan|last2=Mahapatra|first2=Nihar R.|title=Proceedings of the 15th ACM Great Lakes symposium on VLSI - GLSVSLI '05 |date=2005|chapter=Analysis and design of soft-error hardened latches|page=328 |conference=Proceedings of the 15th ACM Great Lakes symposium on VLSI|doi=10.1145/1057661.1057740|isbn=1595930574 }}</ref>

A watchdog timer will perform a hard reset of a system unless some sequence is performed that generally indicates the system is alive, such as a write operation from an onboard processor. During normal operation, software schedules a write to the watchdog timer at regular intervals to prevent the timer from running out. If radiation causes the processor to operate incorrectly, it is unlikely the software will work correctly enough to clear the watchdog timer. The watchdog eventually times out and forces a hard reset to the system. This is considered a last resort to other methods of radiation hardening.

==Military and space industry applications==
Radiation-hardened and radiation tolerant components are often used in military and aerospace applications, including point-of-load (POL) applications, satellite system power supplies, step down ]s, ]s, ]s,<ref>{{Cite web|url=https://www.militaryaerospace.com/articles/2016/06/radiation-hardened-space-fpga.html|title=FPGA development devices for radiation-hardened space applications introduced by Microsemi|last=Mil & Aero Staff|date=2016-06-03|website=Military & Aerospace Electronics|access-date=2018-11-02}}</ref> FPGA power sources, and high efficiency, low voltage subsystem power supplies.

However, not all military-grade components are radiation hardened. For example, the US ] features many radiation-related tests, but has no specification for single event latchup frequency. The ] space probe may have failed due to a similar assumption.<ref name=amartology>{{cite web |last=Shunkov |first= >V. |title=Common misconceptions about space-grade integrated circuits |url=https://habr.com/en/post/518366/ |website=habr.com |date= 9 September 2020 |language=en}}</ref>

The market size for radiation hardened electronics used in space applications was estimated to be $2.35 billion in 2021. A new study has estimated that this will reach approximately $4.76 billion by the year 2032.<ref>{{cite news |last=Diagle |first=Lisa |url=https://militaryembedded.com/comms/communications/rad-hard-electronics-for-space-to-reach-476-billion-by-2032-study-says |title=Rad-hard electronics for space to reach $4.76 billion by 2032, study says |work=Military Embedded Systems |date=2022-06-17 |accessdate=2022-06-18 }}</ref><ref>{{cite web | url=https://www.researchandmarkets.com/reports/5589889/radiation-hardened-electronics-for-space | title=Radiation-Hardened Electronics for Space Application Market - A Global and Regional Analysis: Focus on Platform, Manufacturing Technique, Material Type, Component, and Country - Analysis and Forecast, 2022-2032 }}</ref>

==Nuclear hardness for telecommunication==
In ], the term ''nuclear hardness'' has the following meanings:
1) an expression of the extent to which the performance of a ], facility, or device is expected to degrade in a given nuclear environment, 2) the physical attributes of a system or ] that will allow survival in an environment that includes ] and electromagnetic pulses (EMP).

===Notes===
# Nuclear hardness may be expressed in terms of either ] or ].
# The extent of expected performance ] (''e.g.,'' outage time, ] lost, and equipment damage) must be defined or specified. The environment (''e.g.,'' radiation levels, overpressure, peak velocities, energy absorbed, and electrical stress) must be defined or specified.
# The physical attributes of a system or component that will allow a defined degree of ] in a given environment created by a nuclear weapon.
# Nuclear hardness is determined for specified or actual quantified environmental conditions and physical parameters, such as peak radiation levels, overpressure, velocities, energy absorbed, and electrical stress. It is achieved through ]s and it is verified by test and analysis techniques.

==Examples of rad-hard computers==
* The ], made by ] and used on board the ] (] variant), is based on the ] architecture.
* The ] ] ], introduced in 1976, was the first serially-produced radiation-hardened microprocessor.
* ], Russian 50&nbsp;MHz microcontroller designed by Milandr and manufactured by Sitronics-Mikron on 180&nbsp;nm bulk-silicon technology.
* ] based:
** The ] M5208 used by General Dynamics is a low power (1.5&nbsp;W) radiation hardened alternative.
* ] based:
** The ] manufactured by ].
* The Proton 100k SBC by Space Micro Inc., introduced in 2003, uses an updated voting scheme called TTMR which mitigates ] (SEU) in a single processor. The processor is Equator BSP-15.{{Citation needed |date=May 2024}}
* The ] SBC by Space Micro Inc, introduced in 2004, mitigates SEU with its patented ] (TTMR) technology, and single event function interrupts (SEFI) with H-Core technology. The processor is the high speed ] ] ]. The Proton200k operates at 4000 MIPS while mitigating SEU.{{Citation needed |date=May 2024}}
* ] based:
** The ] is produced by ] Aerospace.
** The ] used by NASA is a 32-bit microprocessor for spacecraft onboard computer applications (i. e. ]).
** The ] is a 32-bit microprocessor, compatible with ], developed by ], manufactured by ], Russia.
* ] / ] based:
** The ] ] (SBC), produced by ], includes a rad-hard ] CPU.
** The ] is produced by Honeywell Aerospace. Based on hardened ].
** The SP0 and SP0-S are produced by Aitech Defense Systems is a 3U cPCI SBC which utilizes the SOI ], ] based, capable of processing speeds ranging from 833&nbsp;MHz to 1.18&nbsp;GHz.<ref>{{cite web | title=SP0 3U CompactPCI Radiation Tolerant PowerPC® SBC | website=Aitech Rugged COTS Solutions | date=2013-12-15 | url=http://www.rugged.com/sp0-3u-compactpci-radiation-tolerant-powerpc%C2%AE-sbc | archive-url=https://web.archive.org/web/20140623055258/http://www.rugged.com/sp0-3u-compactpci-radiation-tolerant-powerpc%C2%AE-sbc | archive-date=2014-06-23 | url-status=dead}}</ref>
** The ] SBC, also produced by BAE Systems, and based on the ] processor, is the successor to the RAD6000.
** The SCS750 built by ], which votes three ] cores against each other to mitigate radiation effects. Seven of those are used by the ].
** The ], through its Satellite Development Center, produces a radiation hardened space computer variant based on the PowerPC 750.
** The BRE440 by ]. IBM ] core based ], 266 ], PCI, 2x Ethernet, 2x UARTS, DMA controller, L1/L2 cache <ref></ref>
** The ] processor, is the successor to the RAD750 based on the ].
* ] based:
** The ] and ] 2, 3, 4 and 5 are radiation hardened processors designed by Gaisler Research and the ]. They are described in synthesizable VHDL available under the ] and ] respectively.
** The Gen 6 ] (SBC), produced by Cobham Semiconductor Solutions (formerly ] Microelectronics Solutions), enabled for the ] microprocessor.<ref>{{Cite web|url=https://ams.aeroflex.com/pagesproduct/prods-hirel-sbc.cfm|title=Single Board Computer (SBC) Family|publisher=]|archive-url=https://web.archive.org/web/20190408051900/https://www.cobhamaes.com/pagesproduct/prods-hirel-sbc.cfm|archive-date=2019-04-08|url-status=live|access-date=2018-11-02}}</ref>
* ] based:
** The Vorago VA10820, a 32-bit ARMv6-M ].<ref>{{Cite web|url=https://www.voragotech.com/products/va10820-radiation-hardened-arm%C2%AE-cortex%C2%AE-m0-mcu|title=VA10820 - Radiation Hardened ARM Cortex-M0 MCU|publisher=Vorago Technologies|archive-url=https://web.archive.org/web/20190214100930/https://www.voragotech.com/products/va10820-radiation-hardened-arm%C2%AE-cortex%C2%AE-m0-mcu|archive-date=2019-02-14|url-status=live|access-date=2018-11-02}}</ref><!-- <ref>{{Cite web|url=https://www.militaryaerospace.com/articles/2016/06/radiation-hardened-space-processor.html|title=Air Force, NASA to develop radiation-hardened ARM processor for next-generation space computing|website=www.militaryaerospace.com|access-date=2018-11-02}}</ref> -->
** ] and the ] are developing HPSC, a Cortex-A53 based processor for future spacecraft use <ref>{{cite report| last=Powell | first=Wesley A. | title=High-Performance Spaceflight Computing (HPSC) Project Overview | website=NASA Technical Reports Server (NTRS) | date=2018-11-13 | url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20180007636.pdf}}</ref>
** ] DAHLIA, a Cortex-R52 based processor<ref></ref>
* ] based:
** ] NOEL-V 64-bit.<ref>{{cite web |url=https://www.gaisler.com/index.php/products/processors/noel-v |title=NOEL-V Processor |website=Cobham Gaisler |access-date=14 January 2020}}</ref>
** ] ] has selected ] to develop a new HPSC processor, based on ] Intelligence X280<ref>{{cite web| title=NASA Makes RISC-V the Go-to Ecosystem for Future Space Missions | website=sifive | date=2022-09-22 | url=https://www.sifive.com/press/nasa-selects-sifive-and-makes-risc-v-the-go-to-ecosystem}}</ref><ref>{{cite web| title=NASA JPL Selects Microchip for Game-Changing Spaceflight Computing Processor | website=microchip | date=2022-09-27 | url=https://www.microchip.com/en-us/about/media-center/blog/2022/spaceflight-computing-processor}}</ref><ref>{{cite web| title=NASA Awards Next-Generation Spaceflight Computing Processor Contract | website=nasa | date=2022-08-15 | url=https://www.nasa.gov/news-release/nasa-awards-next-generation-spaceflight-computing-processor-contract/}}</ref>

{{See also|Comparison of embedded computer systems on board the Mars rovers}}


==See also== ==See also==
{{Portal|Electronics}}
* ]
* ] * ]
* EMC-aware programming
* ], ]
* ] * ]
* ] * ]
* ] * ]
* ]
* ]
* ]

==References==
{{Reflist|30em}}

==Books and Reports==
* {{Cite book|title=Rad-hard Semiconductor Memories|last1=Calligaro|first1=Christiano|last2=Gatti|first2=Umberto|publisher=River Publishers|year=2018|isbn=978-8770220200|series=River Publishers Series in Electronic Materials and Devices}}
* {{Cite book|title=Handbook of Radiation Effects|last1=Holmes-Siedle|first1=Andrew|last2=Adams|first2=Len|publisher=Oxford University Press|year=2002|isbn=0-19-850733-X|edition=Second}}
* {{Cite report|title=Data compilation of dosimetry methods and radiation sources for material testing|last1=León-Florian|first1=E.|last2=Schönbacher|first2=H.|date=1993|publisher=]|id=CERN-TIS-CFM-IR-93-03|last3=Tavlet|first3=M.}}
* {{Cite book|title=Ionizing Radiation Effects in MOS Devices and Circuits|last1=Ma|first1=Tso-Ping|author1-link=Tso-Ping Ma|author2-link=Paul Dressendorfer|last2=Dressendorfer|first2=Paul V.|publisher=John Wiley & Sons|year=1989|isbn=0-471-84893-X|location=New York}}
* {{Cite book|title=The Effects of Radiation on Electronic Systems|last1=Messenger|first1=George C.|last2=Ash|first2=Milton S.|publisher=Van Nostrand Reinhold|year=1992|isbn=0-442-23952-1|edition=Second|location=New York}}
* {{Cite book|title=Ionizing Radiation Effects in MOS Oxides|last=Oldham|first=Timothy R.|publisher=World Scientific|year=2000|isbn=978-981-02-3326-6|series=International Series on Advances in Solid State Electronics and Technology|doi=10.1142/3655}}
* {{Cite book|title=Archive of Radiation Effects Short Course Notebooks (1980–2006)|last=Platteter|first=Dale G.|publisher=]|year=2006|isbn=1-4244-0304-9}}
* {{Cite book|title=Radiation Effects and Soft Errors in Integrated Circuits and Electronic Devices|last1=Schrimpf|first1=Ronald D.|last2=Fleetwood|first2=Daniel M.|publisher=World Scientific|isbn=978-981-238-940-4|series=Selected Topics in Electronics and Systems|volume=34|date=July 2004|doi=10.1142/5607}}
* {{Cite book|title=Semiconductor Material and Device Characterization|last=Schroder|first=Dieter K.|publisher=John Wiley & Sons|year=1990|isbn=0-471-51104-8|location=New York}}
* {{Cite book|title=Color Centers in Solids|last1=Schulman|first1=James Herbert|last2=Compton|first2=Walter Dale|publisher=Pergamon Press|year=1962|series=International Series of Monographs on Solid State Physics|volume=2}}
* {{Cite book|title=Encyclopedia of Physical Science and Technology|last1=Holmes-Siedle|first1=Andrew|last2=van Lint|first2=Victor A. J.|publisher=Academic Press|year=2000|isbn=0-12-227423-7|editor-last=Meyers|editor-first=Robert A.|edition=Third|volume=13|location=New York|chapter=Radiation Effects in Electronic Materials and Devices}}
* {{Cite book|title=Mechanisms of Radiation Effects in Electronic Materials|last1=van Lint|first1=Victor A. J.|last2=Flanagan|first2=Terry M.|last3=Leadon|first3=Roland Eugene|last4=Naber|first4=James Allen|last5=Rogers|first5=Vern C.|journal=NASA Sti/Recon Technical Report A |publisher=John Wiley & Sons|year=1980|isbn=0-471-04106-8|volume=1|page=13073 |location=New York|bibcode=1980STIA...8113073V}}
* {{Cite book|title=Deep Centers in Semiconductors: A State-of-the-Art Approach|last=Watkins|first=George D.|publisher=Gordon and Breach|year=1986|isbn=2-88124-109-3|editor-last=Pantelides|editor-first=Sokrates T.|edition=Second|location=New York|chapter=The Lattice Vacancy in Silicon|author-link=George D. Watkins}}
* {{Cite journal|last=Watts|first=Stephen J.|date=1997|title=Overview of radiation damage in silicon detectors — Models and defect engineering|journal=]|volume=386|issue=1|pages=149–155|doi=10.1016/S0168-9002(96)01110-2|bibcode=1997NIMPA.386..149W}}
* {{Cite book|title=The Stopping and Range of Ions in Solids|last1=Ziegler|first1=James F.|last2=Biersack|first2=Jochen P.|last3=Littmark|first3=Uffe|publisher=Pergamon Press|year=1985|isbn=0-08-021603-X|volume=1|location=New York}}


==External links== ==External links==
* ] ( {{Webarchive|url=https://web.archive.org/web/20110301100455/http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |date=2011-03-01 }})
* &ndash; By Chad Thibodeau, Maxwell Technologies; ''COTS Journal'', Dec 2003
* – By Chad Thibodeau, Maxwell Technologies; ''COTS Journal'', Dec 2003
* &ndash; Sandia press release, 8 Dec 1998<br>(also includes a general "backgrounder" section on Sandia's manufacturing processes for radiation-hardening of microelectronics)
* – Sandia press release, 8 Dec 1998<br />(also includes a general "backgrounder" section on Sandia's manufacturing processes for radiation-hardening of microelectronics)
* &ndash; By Jessica Davis, ''Electronic News'', 19 Apr 2005
*
*

{{Radiation}}


{{DEFAULTSORT:Radiation Hardening}}
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] ]
] ]
]
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Latest revision as of 20:03, 30 December 2024

Processes and techniques used for making electronic devices resistant to ionizing radiation Not to be confused with hard radiation or radiation embrittlement. For hardening of materials caused by radiation, see radiation damage.

Radiation hardening is the process of making electronic components and circuits resistant to damage or malfunction caused by high levels of ionizing radiation (particle radiation and high-energy electromagnetic radiation), especially for environments in outer space (especially beyond low Earth orbit), around nuclear reactors and particle accelerators, or during nuclear accidents or nuclear warfare.

Most semiconductor electronic components are susceptible to radiation damage, and radiation-hardened (rad-hard) components are based on their non-hardened equivalents, with some design and manufacturing variations that reduce the susceptibility to radiation damage. Due to the low demand and the extensive development and testing required to produce a radiation-tolerant design of a microelectronic chip, the technology of radiation-hardened chips tends to lag behind the most recent developments. They also typically cost more than their commercial counterparts.

Radiation-hardened products are typically tested to one or more resultant-effects tests, including total ionizing dose (TID), enhanced low dose rate effects (ELDRS), neutron and proton displacement damage, and single event effects (SEEs).

Problems caused by radiation

See also: Radiation damage

Environments with high levels of ionizing radiation create special design challenges. A single charged particle can knock thousands of electrons loose, causing electronic noise and signal spikes. In the case of digital circuits, this can cause results which are inaccurate or unintelligible. This is a particularly serious problem in the design of satellites, spacecraft, future quantum computers, military aircraft, nuclear power stations, and nuclear weapons. In order to ensure the proper operation of such systems, manufacturers of integrated circuits and sensors intended for the military or aerospace markets employ various methods of radiation hardening. The resulting systems are said to be rad(iation)-hardened, rad-hard, or (within context) hardened.

Major radiation damage sources

Typical sources of exposure of electronics to ionizing radiation are the Van Allen radiation belts for satellites, nuclear reactors in power plants for sensors and control circuits, particle accelerators for control electronics (particularly particle detector devices), residual radiation from isotopes in chip packaging materials, cosmic radiation for spacecraft and high-altitude aircraft, and nuclear explosions for potentially all military and civilian electronics.

Secondary particles result from interaction of other kinds of radiation with structures around the electronic devices.

  • Van Allen radiation belts contain electrons (up to about 10 MeV) and protons (up to 100s MeV) trapped in the geomagnetic field. The particle flux in the regions farther from the Earth can vary wildly depending on the actual conditions of the Sun and the magnetosphere. Due to their position they pose a concern for satellites.
  • Nuclear reactors produce gamma radiation and neutron radiation which can affect sensor and control circuits in nuclear power plants.
  • Particle accelerators produce high energy protons and electrons, and the secondary particles produced by their interactions produce significant radiation damage on sensitive control and particle detector components, of the order of magnitude of 10 MRad/year for systems such as the Large Hadron Collider.
  • Chip packaging materials were an insidious source of radiation that was found to be causing soft errors in new DRAM chips in the 1970s. Traces of radioactive elements in the packaging of the chips were producing alpha particles, which were then occasionally discharging some of the capacitors used to store the DRAM data bits. These effects have been reduced today by using purer packaging materials, and employing error-correcting codes to detect and often correct DRAM errors.
  • Cosmic rays come from all directions and consist of approximately 85% protons, 14% alpha particles, and 1% heavy ions, together with X-ray and gamma-ray radiation. Most effects are caused by particles with energies between 0.1 and 20 GeV. The atmosphere filters most of these, so they are primarily a concern for spacecraft and high-altitude aircraft, but can also affect ordinary computers on the surface.
  • Solar particle events come from the direction of the sun and consist of a large flux of high-energy (several GeV) protons and heavy ions, again accompanied by X-ray radiation.
  • Nuclear explosions produce a short and extremely intense surge through a wide spectrum of electromagnetic radiation, an electromagnetic pulse (EMP), neutron radiation, and a flux of both primary and secondary charged particles. In case of a nuclear war they pose a potential concern for all civilian and military electronics.

Radiation effects on electronics

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Fundamental mechanisms

Two fundamental damage mechanisms take place:

Lattice displacement

Lattice displacement is caused by neutrons, protons, alpha particles, heavy ions, and very high energy gamma photons. They change the arrangement of the atoms in the crystal lattice, creating lasting damage, and increasing the number of recombination centers, depleting the minority carriers and worsening the analog properties of the affected semiconductor junctions. Counterintuitively, higher doses over a short time cause partial 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 transistors, which are dependent on minority carriers in their base regions; increased losses caused by recombination cause loss of the transistor gain (see 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 glitches 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 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 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:

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 defects, reducing the lifetime of minority carriers, thus affecting bipolar devices more than CMOS ones. Bipolar devices on silicon tend to show changes in electrical parameters at levels of 10 to 10 neutrons/cm, while CMOS devices aren't affected until 10 neutrons/cm. 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 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. GaAs LEDs, common in optocouplers, are very sensitive to neutrons. The lattice damage influences the frequency of crystal oscillators. 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 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 pairs in the gate insulation layers, 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-flops and 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 currents in the material of the chips, circuit boards, electrical cables and cases.

Digital damage: SEE

Single-event effects (SEE) have been studied extensively since the 1970s. When a high-energy particle travels through a semiconductor, it leaves an ionized 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 register or, especially in 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 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 upsets (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 machines, placing the device into an undefined state, a test mode, or a halt, which would then need a reset or a power cycle to recover.

Single-event latchup

An SEL can occur in any chip with a 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 "shorted" (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 multiplication of the charge carriers. 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.

Radiation-hardening techniques

Radiation hardened die of the 1886VE10 microcontroller prior to metalization etching
Radiation hardened die of the 1886VE10 microcontroller after a metalization etching process has been used

Physical

Hardened chips are often manufactured on insulating substrates instead of the usual semiconductor wafers. Silicon on insulator (SOI) and silicon on sapphire (SOS) are commonly used. While normal commercial-grade chips can withstand between 50 and 100 gray (5 and 10 krad), space-grade SOI and SOS chips can survive doses between 1000 and 3000 gray (100 and 300 krad). At one time many 4000 series chips were available in radiation-hardened versions (RadHard). While SOI eliminates latchup events, TID and SEE hardness are not guaranteed to be improved.

Choosing a substrate with wide band gap gives it higher tolerance to deep-level defects; e.g. silicon carbide or gallium nitride.

Use of a special process node provides increased radiation resistance. Due to the high development costs of new radiation hardened processes, the smallest "true" rad-hard (RHBP, Rad-Hard By Process) process is 150 nm as of 2016, however, rad-hard 65 nm FPGAs were available that used some of the techniques used in "true" rad-hard processes (RHBD, Rad-Hard By Design). As of 2019 110 nm rad-hard processes are available.

Bipolar integrated circuits generally have higher radiation tolerance than CMOS circuits. The low-power Schottky (LS) 5400 series can withstand 1000 krad, and many ECL devices can withstand 10,000 krad. Using edgeless CMOS transistors, which have an unconventional physical construction, together with an unconventional physical layout, can also be effective.

Magnetoresistive RAM, or MRAM, is considered a likely candidate to provide radiation hardened, rewritable, non-volatile conductor memory. Physical principles and early tests suggest that MRAM is not susceptible to ionization-induced data loss.

Capacitor-based DRAM is often replaced by more rugged (but larger, and more expensive) SRAM. SRAM cells have more transistors per cell than usual (which is 4T or 6T), which makes the cells more tolerant to SEUs at the cost of higher power consumption and size.

Shielding

Shielding the package against radioactivity is straightforward to reduce exposure of the bare device.

To protect against neutron radiation and the neutron activation of materials, it is possible to shield the chips themselves by use of depleted boron (consisting only of isotope boron-11) in the borophosphosilicate glass passivation layer protecting the chips, as naturally prevalent boron-10 readily captures neutrons and undergoes alpha decay (see soft error).

Logical

Error correcting code memory (ECC memory) uses redundant bits to check for and possibly correct corrupted data. Since radiation's effects damage the memory content even when the system is not accessing the RAM, a "scrubber" circuit must continuously sweep the RAM; reading out the data, checking the redundant bits for data errors, then writing back any corrections to the RAM.

Redundant elements can be used at the system level. Three separate microprocessor boards may independently compute an answer to a calculation and compare their answers. Any system that produces a minority result will recalculate. Logic may be added such that if repeated errors occur from the same system, that board is shut down.

Redundant elements may be used at the circuit level. A single bit may be replaced with three bits and separate "voting logic" for each bit to continuously determine its result (triple modular redundancy). This increases area of a chip design by a factor of 5, so must be reserved for smaller designs. But it has the secondary advantage of also being "fail-safe" in real time. In the event of a single-bit failure (which may be unrelated to radiation), the voting logic will continue to produce the correct result without resorting to a watchdog timer. System level voting between three separate processor systems will generally need to use some circuit-level voting logic to perform the votes between the three processor systems.

Hardened latches may be used.

A watchdog timer will perform a hard reset of a system unless some sequence is performed that generally indicates the system is alive, such as a write operation from an onboard processor. During normal operation, software schedules a write to the watchdog timer at regular intervals to prevent the timer from running out. If radiation causes the processor to operate incorrectly, it is unlikely the software will work correctly enough to clear the watchdog timer. The watchdog eventually times out and forces a hard reset to the system. This is considered a last resort to other methods of radiation hardening.

Military and space industry applications

Radiation-hardened and radiation tolerant components are often used in military and aerospace applications, including point-of-load (POL) applications, satellite system power supplies, step down switching regulators, microprocessors, FPGAs, FPGA power sources, and high efficiency, low voltage subsystem power supplies.

However, not all military-grade components are radiation hardened. For example, the US MIL-STD-883 features many radiation-related tests, but has no specification for single event latchup frequency. The Fobos-Grunt space probe may have failed due to a similar assumption.

The market size for radiation hardened electronics used in space applications was estimated to be $2.35 billion in 2021. A new study has estimated that this will reach approximately $4.76 billion by the year 2032.

Nuclear hardness for telecommunication

In telecommunication, the term nuclear hardness has the following meanings: 1) an expression of the extent to which the performance of a system, facility, or device is expected to degrade in a given nuclear environment, 2) the physical attributes of a system or electronic component that will allow survival in an environment that includes nuclear radiation and electromagnetic pulses (EMP).

Notes

  1. Nuclear hardness may be expressed in terms of either susceptibility or vulnerability.
  2. The extent of expected performance degradation (e.g., outage time, data lost, and equipment damage) must be defined or specified. The environment (e.g., radiation levels, overpressure, peak velocities, energy absorbed, and electrical stress) must be defined or specified.
  3. The physical attributes of a system or component that will allow a defined degree of survivability in a given environment created by a nuclear weapon.
  4. Nuclear hardness is determined for specified or actual quantified environmental conditions and physical parameters, such as peak radiation levels, overpressure, velocities, energy absorbed, and electrical stress. It is achieved through design specifications and it is verified by test and analysis techniques.

Examples of rad-hard computers

See also: Comparison of embedded computer systems on board the Mars rovers

See also

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