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Single event upset

Single event upset

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A single event upset is a change of state caused by ions or electro-magnetic radiation striking a sensitive node in a micro-electronic device, such as in a microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

, semiconductor memory
Semiconductor memory
Semiconductor memory is an electronic data storage device, often used as computer memory, implemented on a semiconductor-based integrated circuit. Examples of semiconductor memory include non-volatile memory such as Read-only memory , magnetoresistive random access memory , and flash memory...

, or power transistors. The state change is a result of the free charge created by ionization
Ionization
Ionization is the process of converting an atom or molecule into an ion by adding or removing charged particles such as electrons or other ions. This is often confused with dissociation. A substance may dissociate without necessarily producing ions. As an example, the molecules of table sugar...

 in or close to an important node of a logic element (e.g. memory "bit"). The error in device output or operation caused as a result of the strike is called an SEU or a soft error
Soft error
In electronics and computing, a soft error is an error in a signal or datum which is wrong. Errors may be caused by a defect, usually understood either to be a mistake in design or construction, or a broken component. A soft error is also a signal or datum which is wrong, but is not assumed to...

. The SEU itself is not considered permanently damaging to the transistor's or circuits' functionality unlike the case of single event latchup
Latchup
Latchup is a term used in the realm of integrated circuits to describe a particular type of short circuit which can occur in an improperly designed circuit...

 (SEL), single event gate rupture (SEGR), or single event burnout
Burnout
Burnout or burn-out may refer to:*Burnout , a psychological term for a syndrome characterized by long-term exhaustion and diminished interest, especially in one's career*Burnout , when a vehicle's tires are spun so they smoke...

 (SEB). These are all examples of a general class of radiation effects in electronic devices called single event effects.

History


Single event upsets were first described during above ground nuclear testing
Nuclear testing
Nuclear weapons tests are experiments carried out to determine the effectiveness, yield and explosive capability of nuclear weapons. Throughout the twentieth century, most nations that have developed nuclear weapons have tested them...

, from 1954 to 1957, when many anomalies were observed in electronic monitoring equipment. Further problems were observed in space electronics during the 1960s, although it was difficult to separate soft-fails from other forms of interference. In 1978, the first evidence of soft error
Soft error
In electronics and computing, a soft error is an error in a signal or datum which is wrong. Errors may be caused by a defect, usually understood either to be a mistake in design or construction, or a broken component. A soft error is also a signal or datum which is wrong, but is not assumed to...

s from alpha particle
Alpha particle
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is classically produced in the process of alpha decay, but may be produced also in other ways and given the same name...

s in packaging materials was described by Timothy C. May
Timothy C. May
Timothy C. May, better known as Tim May, is a technical and political writer, and was an electronic engineer and senior scientist at Intel in the company's early history...

 and M.H. Woods. In 1979, James Ziegler of IBM, joined with W. Lanford of Yale
Yale University
Yale University is a private, Ivy League university located in New Haven, Connecticut, United States. Founded in 1701 in the Colony of Connecticut, the university is the third-oldest institution of higher education in the United States...

, first described the mechanism whereby a sea level cosmic ray
Cosmic ray
Cosmic rays are energetic charged subatomic particles, originating from outer space. They may produce secondary particles that penetrate the Earth's atmosphere and surface. The term ray is historical as cosmic rays were thought to be electromagnetic radiation...

 could cause a single event upset in electronics.

Cause


Terrestrial SEU arise due to cosmic particles colliding with atoms in the atmosphere, creating cascades or showers of neutrons and protons, which in turn may interact with electronics. At deep sub-micrometre geometries, this affects semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 devices in the atmosphere.

In space, high energy ionizing particles exist as part of the natural background, referred to as galactic cosmic rays (GCR). Solar particle events and high energy protons trapped in the Earth's magnetosphere (Van Allen radiation belts) exacerbate the problem. The high energies associated with the phenomenon in the space particle environment generally render increased spacecraft shielding useless in terms of eliminating SEU and catastrophic single event phenomena (e.g. destructive latch-up). Secondary atmospheric neutrons generated by cosmic rays can also be of energies capable of producing SEUs in electronics on aircraft flights over the poles or at high altitude. Trace amounts of radioactive elements in chip packages
Integrated circuit packaging
Integrated circuit packaging is the final stage of semiconductor device fabrication per se, followed by IC testing.Packaging in ceramic or plastic prevents physical damage and corrosion and supports the electrical contacts required to assemble the integrated circuit into a system.In the integrated...

 also lead to SEUs.

Testing for SEU sensitivity


The sensitivity of a device to SEU can be empirically estimated by placing a test device in a particle
Elementary particle
In particle physics, an elementary particle or fundamental particle is a particle not known to have substructure; that is, it is not known to be made up of smaller particles. If an elementary particle truly has no substructure, then it is one of the basic building blocks of the universe from which...

 stream at a cyclotron
Cyclotron
In technology, a cyclotron is a type of particle accelerator. In physics, the cyclotron frequency or gyrofrequency is the frequency of a charged particle moving perpendicularly to the direction of a uniform magnetic field, i.e. a magnetic field of constant magnitude and direction...

 or other particle accelerator
Particle accelerator
A particle accelerator is a device that uses electromagnetic fields to propel charged particles to high speeds and to contain them in well-defined beams. An ordinary CRT television set is a simple form of accelerator. There are two basic types: electrostatic and oscillating field accelerators.In...

 facility. This particular test methodology is especially useful for predicting the SER (soft error rate) in known space environments, but can be problematic for estimating terrestrial SER from neutrons. In this case, a large number of parts must be evaluated, possibly at different altitudes, to find the actual rate of upset. When testing microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

s for SEU, the software used to exercise the device must also be evaluated to determine which sections of the device were activated when SEUs occurred.

SEUs and circuit design


By definition, SEUs are non-destructive events. Howevever, under the proper circumstances (of both circuit design, process design, and particle properties) a "parasitic
Parasitic structure
In a semiconductor device, a parasitic structure is a portion of the device that resembles in structure some other, simpler semiconductor device, and causes the device to enter an unintended mode of operation when subjected to conditions outside of its normal range...

" thyristor
Thyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...

 inherent to CMOS designs can be activated, effectively causing an apparent short-circuit from power to ground. This condition is referred to as latchup
Latchup
Latchup is a term used in the realm of integrated circuits to describe a particular type of short circuit which can occur in an improperly designed circuit...

, and in absence of constructional countermeasures often destroys the device from thermal runaway
Thermal runaway
Thermal runaway refers to a situation where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result...

. Most manufacturers design to prevent latch-up, and test their products to ensure that latch-up does not occur from atmospheric particle strikes. In order to prevent latch-up in space, epitaxial
Epitaxy
Epitaxy refers to the deposition of a crystalline overlayer on a crystalline substrate, where the overlayer is in registry with the substrate. In other words, there must be one or more preferred orientations of the overlayer with respect to the substrate for this to be termed epitaxial growth. The...

 substrates, silicon on insulator
Silicon on insulator
Silicon on insulator technology refers to the use of a layered silicon-insulator-silicon substrate in place of conventional silicon substrates in semiconductor manufacturing, especially microelectronics, to reduce parasitic device capacitance and thereby improving performance...

 (SOI) or silicon on sapphire
Silicon on sapphire
Silicon on sapphire is a hetero-epitaxial process for integrated circuit manufacturing that consists of a thin layer of silicon grown on a sapphire wafer. SOS is part of the Silicon on Insulator family of CMOS technologies...

 (SOS) are often used to further reduce or eliminate the susceptibility.

In digital and analog circuits, a single event may cause one or more voltages pulses (i.e. glitches) to propagate through the circuit, in which case it is referred to as a single-event transients. Since the propagating pulse is not technically a change of "state" as in a memory SEU, one should differentiate between SET and SEU. If a SET propagates through digital circuitry and results in an incorrect value being latched in a sequential logic unit, it is then considered an SEU.

Further reading


General SEU

SEU in programmable logic devices

SEU in microprocessors

SEU related masters theses and doctoral dissertations