Radiation hardening
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2008-07-11T08:40:53Z
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{{Expert-subject|Electronics}}
'''Radiation hardening''' is a method of designing and testing electronic components and systems to make them resistant to damage or malfunctions caused by high-energy subatomic particles and electromagnetic radiation, such as would be encountered in outer space, high-altitude flight, around nuclear reactors, or during warfare.
Most radiation-hardened chips are based on their commercial equivalents, with some manufacturing and design variations that reduce the susceptibility to interference from Electromagnetic radiation. Due to the extensive development and testing required to produce a radiation-tolerant design of a [[microelectronics|microelectronic]] chip, radiation-hardened chips tend to lag behind the cutting-edge of developments.
== Problems caused by radiation ==
Environments with high levels of [[ionizing radiation]] create special design challenges. A single [[charged particle]] can knock thousands of [[electron]]s loose, causing electronic [[noise]] and signal [[spike]]s. In the case of [[digital circuit]]s, this can cause results which are inaccurate or unintelligible. This is a particularly serious problem in the design of [[satellite|artificial satellites]], [[spacecraft]], [[military aircraft]], [[nuclear reactor|nuclear power stations]], and [[nuclear weapon]]s.
In order to ensure the proper operation of such systems, manufacturers of [[integrated circuit]]s and [[sensor]]s intended for the ([[military]]) [[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 [[solar wind]] and the [[Van Allen radiation belt]]s for satellites, [[nuclear reactor]]s in power plants for sensors and control circuits, residual radiation from [[isotope]]s in [[Soft error#Package decay|chip packaging materials]], [[cosmic radiation]] for both high-altitude airplanes and satellites, and [[nuclear explosion]]s for potentially all military and civilian electronics.
* [[Cosmic ray]]s come from all directions and consist of approx. 85% [[proton]]s, 14% [[alpha particle]]s, and 1% [[heavy ion]]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> [[electronvolt|eV]], though there are even particles with energies up to [[Oh my god particle|10<sup>20</sup> eV]]. The atmosphere filters most of these, so they are primarily a concern for high-altitude applications like stratospheric jets and satellites.
* [[Coronal mass ejection|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 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 the atmosphere, causing them to raise up, and decelerating the low-orbit satellites.
* [[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.
* [[Secondary particle]]s result from interaction of other kinds of radiation with structures around the electronic devices.
* [[Nuclear reactor]]s produce [[gamma radiation]] and [[neutron radiation]] which can affect sensor and control circuits in [[nuclear power plant]]s.
* [[Nuclear explosion]]s produce a short, extremely intense surge of the entire spectrum of electromagnetic radiation, [[electromagnetic pulse]] (EMP), [[neutron radiation]], and flux of both primary and secondary charged particles. In case of a [[nuclear warfare|nuclear war]] they pose a potential concern for all civilian and military electronics.
* [[Soft error#Package decay|Chip packaging materials]] were an insidious source of radiation that was found to be causing [[soft error]]s 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 code|ECC]] codes to detect and often correct DRAM errors.
== Radiation effects on electronics ==
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===Fundamental mechanisms===
Two fundamental damage mechanisms take place:
* ''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 [[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 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. This type of damage is especially important for [[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|gain]]. See ''[[#resultant effects|neutron effects]]''.
* ''Ionization effects'' are 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]]. [[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 - 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.
===Resultant effects===
The "end-user" effects can be characterized in several groups:
* ''Neutron effects'' : A neutron interacting with the semiconductor [[lattice]] will displace its atoms. This leads to increase of the count of [[recombination center]]s and [[deep-level defect]]s, reducing the lifetime of [[minority carrier]]s, 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/cm², CMOS devices aren't affected until 10<sup>15</sup> neutrons/cm². 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 [[neutron activation]], 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 [[light-emitting diode|LEDs]], common in [[optocoupler]]s, are very sensitive to neutrons. Kinetic energy effects (namely lattice displacement) of charged particles belong here too.
* ''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 [[rad (unit)|rads]] 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 [[CMOS]] devices, the radiation creates [[electron–hole pair]]s in the gate insulation layers, which cause [[photocurrent]]s during their [[recombination (physics)|recombination]], and the holes trapped in the lattice defects in the insulator create a persistent gate bias 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.
* ''Transient dose effects'' : The short-time high-intensity pulse of radiation, typically occurring during a [[nuclear explosion]]. The high radiation flux creates [[photocurrent]]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 [[p-n junction|junction]] damage or causes a [[latchup]]. Latchups are commonly caused by the [[x-ray]]s and [[gamma radiation]] flash of a nuclear explosion.
* ''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.
* ''Single-event effects (SEE)'' are phenomena affecting mostly digital devices; see the following section for an overview of the various types of SEE.
===Digital damage: SEE===
Single-event effects (SEE), mostly affecting only [[digital]] devices, were not studied extensively until relatively recently. 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 register, or, especially in high-power transistors, a destructive [[latchup]] and [[burnout]]. Single event effects have importance for electronics in [[satellite]]s, [[aircraft]], and other both [[civilian]] and [[military]] [[aerospace]] 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 an SEE.
* ''[[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. 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]] (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 [[latchup]]) 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.
* ''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 [[electrostatic discharge]].
* ''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 [[open circuit|open]]s and stays opened.
* ''Single-event induced burnout (SEB)'' may occur in power [[MOSFET]]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.
* ''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 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.
== Radiation-hardening techniques ==
*Physical:
** Hardened chips are often manufactured on [[Electrical insulation|insulating]] [[wafer (electronics)|substrate]]s instead of the usual [[semiconductor]] wafers. [[Silicon oxide]] ([[silicon on insulator|SOI]]) and [[sapphire]] ([[silicon on sapphire|SOS]]) are commonly used. While normal commercial-grade chips can withstand between 5 and 10 k[[Rad (unit)|rad]], space-grade SOI and SOS chips can survive doses many orders of magnitude greater.
** [[radiation shield|Shield]]ing the package against [[radioactivity]], to reduce exposure of the bare device.
** [[Capacitor]]-based [[Dynamic random access memory|DRAM]] is often replaced by more rugged (but larger, and more expensive) [[Static Random Access Memory|SRAM]].
** Choice of substrate with wide [[band gap]], which gives it higher tolerance to [[deep-level defect]]s; eg. [[silicon carbide]] or [[gallium nitride]].
** Shielding the chips themselves by use of depleted [[boron]] (consisting only of [[isotope]] Boron-11) in the [[borophosphosilicate glass]] layer protecting the chips, as boron-10 readily captures neutrons and undergoes alpha decay (see [[soft error#Cosmic rays|soft error]]).
*Logical:
** [[Error-correcting code|Error correcting memory]] uses additional [[parity]] bits to check for and possibly correct corrupted data. Since radiation 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 parity for data errors, then writing back any corrections to the RAM.
** [[Redundancy (engineering)|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. 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.
** [[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.
==Nuclear hardness for telecommunication==
In [[telecommunication]], the term '''nuclear hardness''' has the following meanings:
# An expression of the extent to which the performance of a [[system]], [[facility]], or device is expected to degrade in a given nuclear environment.
# The physical attributes of a system or [[electronic component]] that will allow survival in an environment that includes [[nuclear radiation]] and [[electromagnetic pulse]]s (EMP).
===Notes===
# Nuclear hardness may be expressed in terms of either [[susceptibility]] or vulnerability.
# The extent of expected performance [[Degradation (telecommunications)|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.
# 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]].
# 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 is verified by test and analysis techniques.
===References===
==Books and Reports==
* Holmes-Siedle, A. G. and Adams, L (2002). Handbook of Radiation Effects (Oxford University Press, England 2002). ISBN 0-19-850733-X
* E.Leon Florian, H.Schonbacher and M.Tavlet (1993). Data compilation of dosimetry methods and radiation sources for material testing.Report No.CERN/TIS-CFM/IR/93-03. (CERN, Geneva, CH 1993).
* T-P. Ma. and P.V. Dressendorfer (eds) (1989). Ionizing Radiation Effects in MOS Devices and Circuits. (John Wiley and Sons, New York 1989)
* G. C. Messenger and M. S. Ash (1992).The effects of radiation on electronic systems” (Van Nostrand Reinhold, New York, 1992).
* T.R.Oldham (Ed.) (2000). Ionizing radiation effects in MOS oxides.(World Scientific Publishing Co., USA, 2000). ISBN 9810233264.
* R.D. Schrimpf and D.M. Fleetwood (eds) (2004) Radiation Effects and Soft Errors in Integrated Circuits and Electronic Devices (World Scientific 2004) ISBN 981-238-940-7.
* D.K. Schroder, ' Semiconductor Material and Device Characterization' John Wiley & Sons, Inc., 1990.
* J.H. Schulman and W.D. Compton (1963).Color Centers in Solids. (Pergamon, 1963).
* V.A.J. van Lint and A.G. Holmes-Siedle (2000). Radiation effects in electronics in R.A. Meyers (ed), Encyclopedia of Physical Science and Technology, 3rd Edition.(Academic Press, New York. 2000)
* V.A.J. Van Lint, T.M. Flanagan, R.E. Leadon, J.A. Naber and V.C. Rogers (1980). Mechanisms of Radiation Effects in Electronic Materials (Wiley, New York 1980).
* G. D. Watkins (1986). In: “Deep Centers in Semiconductors”. Ed. S.T. Pantelides. (Gordon and Breach: New York, 1986) Chapter 3.
* S.J.Watts, “ Overview of radiation damage in silicon detector- models and defect engineering, Nucl. Instr. and Meth. in Phys. Res. A, 386, 149-155,(1997).
* J.F. Ziegler, J.P. Biersack, and U. Littmark (1985), The Stopping and Range of Ions in Solids, Volume 1, Pergamon Press, 1985.
==Standards==
* [[Federal Standard 1037C]] ([http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm link])
== Examples of rad-hard computers==
* The [[Proton 200k]] SBC by [[Space Micro Inc.]], introduced in 2004, is the successor to the Space Micro [[Proton 100k]]. The Proton 200k mitigated SEU with its proprietary [[TTMR Technology]], and, SEFI with [[H-Core Technology]]. The processor is the high speed [[Texas Instrument DSP]].
* The [[Proton 100k]] SBC by [[Space Micro Inc.]], introduced in 2003, uses an updated voting scheme called Time-Triple Modular Redundancy (TTMR) which mitigates SEU without using the three processors in the older Triple Modular Redundancy(TMR)technology. The [[TTMR Technology]] uses voting within the same commercially available processor.
* The [[RCA 1802|RCA1802]] [[8-bit]] [[central processing unit|CPU]], introduced in 1976, was the first serially-produced radiation-hardened [[microprocessor]].
* The [[System/4 Pi]], made by [[IBM]] and used onboard the [[Space Shuttle program|Space Shuttle]] ([[AP-101]] variant), is based on the [[System/360]] architecture.
* The [[RAD6000]] [[single board computer]] (SBC), produced by [[BAE Systems]], includes a rad-hard [[IBM POWER]]-architecture CPU.
* The [[RAD750]] SBC, also produced by BAE Systems, and based on the [[PowerPC G3|PowerPC 750]] processor, is the successor to the RAD6000.
* The [[United States Department of Energy|U.S. DOE]] [[Sandia National Laboratories]] manufactures a rad-hard variant of the [[Intel]] [[Pentium]].
* The [[RH32]] is produced by [[Honeywell]] Aerospace.
* The [[RHPPC]] is produced by Honeywell Aerospace. Based on hardened [[PowerPC 600#PowerPC_603e_.2F_603ev|PowerPC 603e]].
* The [[SCS750]] built by [[Maxwell Technologies]], which votes three [[PowerPC 750]] cores against each other to mitigate radiation effects.
* The [[Boeing Company]], through its Satellite Development Center, produces a very powerful radiation hardened space computer variant based on the PowerPC 750.
* The [[ERC32]] and [[LEON]] are radiation hardened processors designed by Gaisler Research and the [[European Space Agency]]. They are described in synthesizable VHDL available under the [[GNU Lesser General Public License]] and [[GNU General Public License]] respectively.
* The [[RH1750]] processor is manufactured by [[GEC-Plessey]].
* The [[Coldfire]] M5208 used by General Dynamics is a low power (1.5 Watt) radiation hardened alternative.
* The [[Mongoose-V]] used by NASA is a 32-bit microprocessor for spacecraft on-board computer applications (i. e. [[New Horizons]]).
==See also==
{{portalpar|Electronics|Nuvola_apps_ksim.png}}
* [[Soft error]]
* [[Communications survivability]]
* [[Mars Reconnaissance Orbiter#Electronic systems|Mars Reconnaissance Orbiter]]
* [[MESSENGER#Spacecraft and subsystems|MESSENGER Mercury probe]]
* [[Mars Exploration Rover#Power and electronic systems|Mars rovers]]
* [[Electromagnetic pulse hardening]] (see [[TEMPEST]] and [[Faraday cage]])
==External links==
* [http://www.zerosoft.net/ Links to Internet resources and on-line tool to estimate the soft error sensitivity of circuits]
*[http://www.cotsjournalonline.com/home/article.php?id=100088 (I)ntegrated Approach with COTS Creates Rad-Tolerant (SBC) for Space] – By Chad Thibodeau, Maxwell Technologies; ''COTS Journal'', Dec 2003
*[http://www.sandia.gov/media/rhp.htm Sandia Labs to develop (...) radiation-hardened Pentium (...) for space and defense needs] – Sandia press release, 8 Dec 1998<br>(also includes a general "backgrounder" section on Sandia's manufacturing processes for radiation-hardening of microelectronics)
*[http://www.reed-electronics.com/electronicnews/article/CA526020.html?industryid=22121 Honeywell Takes Rad-Hard to 0.15-Micron] – By Jessica Davis, ''Electronic News'', 19 Apr 2005
*[http://www.ieee-uffc.org/freqcontrol/quartz/vig/vigrad.htm Radiation effects on quartz crystals]
*[http://rd49.web.cern.ch/RD49 CERN-LHCC RD49 Project]
[[Category:Military communications]]
[[Category:Integrated circuits]]
[[Category:Avionics computers|*Radiation hardening]]
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[[Category:Radiation effects]]