Neutrons for radiation Neutrons for radiation hardness studies: hardness studies: Neutron induced Neutron induced

Single Event EffectsSingle Event Effects

Jeffery Wyss (wyss@unicas.it)INFN Padova &

University of Cassino

Jeffery Wyss (Jeffery Wyss (wyss@unicas.itwyss@unicas.it))INFN INFN PadovaPadova &&

University of Cassino

17 November 200917 November 2009

Edited and corrected10 December 2009

Edited and corrected10 December 2009

Prof. Jeffery Wyss of the University of Cassino is associated with the INFN of Padova. Email: wyss@unicas.it, wyss@pd.infn.it. Cell phone 345-3163072

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• atmospheric neutrons • neutron induced Single Event Effects (SEE) in electronics• concerns for SEE• why SEE tests• “accelerated” SEE testing at neutron facilities• ISIS & ANITA• fast neutron source at LNL? considerations

What is this short talk about?

This short talk will focus on neutrons produced by energetic cosmic rays in the earth’s atmosphere and the effects they induce in electronics at sea level. A short over-view is given of neutron induced single event effects (SEE), of why these effects are of growing concern for electronics applications, andof why and how tests are performed at accelerator facilities such as ISIS at the Rutherford Appleton Labs and at ANITA at the Svedberg labs. In closing we discuss what could be done at the 70 MeV high current cyclotron of Legnaro.

extensiveair shower

Under 20 km altitude neutrons dominate as cause of SEE in avionic systems!

In mountains and even at sea level there are enough neutrons to be a concern for

electronics that play vital roles (e.g. power devices for locomotives,

pace-makers in CMOS electronics, …)

NOTE: neutron flux at sea level is~ 18 neutrons/cm2-hour

with E>2 MeVwhich may cause SEE in electronics

NOTE: neutron flux at sea level is~ 18 neutrons/cm2-hour

with E>2 MeVwhich may cause SEE in electronics

Shower maximum at ~18 km

The interaction of high energy cosmic rays with the earth’s atmosphere generates cascading showers of electromagnetic and secondary particles including energetic neutrons. The shower maximum is at an altitude of around 60,000 feet. At normal aircraft altitudes of 30,000 to 35,000 feet the secondary particles are mostly neutrons that may cause Single Event Effects (SEE) in microelectronic devices and avionic electronic systems onboard commercial jets. Since the 1990s SEE generated by atmospheric neutrons are the dominant threat to the strict high-reliability requirements of aircraft electronics and indeed the aircraft electronics industry has always been at the forefront of mitigating against neutron induced SEE and has been demanding the use of intense accelerator based neutron beams for ‘accelerated’ reliability testing of electronic components and systems; a few hours in the neutron beam mimics many thousands of hours in the real environment. Avionic and space industry have a long standing tradition of SEE testing.

In recent years the continuous drive for miniaturization of electronic devices and complexity of systems has meant that the SEE problems known to occur at high flight altitudes and even in mountains have inevitably started to emerge in terrestrial based electronics. At sea level there are more than enough neutrons to cause great concern for the fast growing spectrum of electronic applications, from the large power electronics in train locomotives to very small feature size electronics embedded in sophisticated systems that play vital roles such as automotive electronics, high-end computing, communications, and medical equipment such as pace-makers. At sea level the flux of neutrons with energy above 2 MeVwhich may cause SEE in modern electronics is n(E > 2 MeV) 18 neutrons/cm2-hour.

Electronic systems are finding new markets and neutron SEE testing is becoming of critical importance in the terrestrial electronics industry well outside the traditional aerospace and defense industries.

Note: 3540 % of neutrons are in 110 MeV rangeNote: 3540 % of neutrons are in 110 MeV range

• sea level, • New York city, • mid-level Solar activity, • outdoors

This figure shows the differential flux of neutrons at sea level over the energy range of interest to SEE.

The flux of neutrons with energy greater than 1 MeV is n(E > 1 MeV) = 21 n cm-2 h-1. For neutron energies greater than 10 MeV the flux decreases to n(E > 10 MeV) = 13 n cm-2 h-1. In other words ~40% of the terrestrial neutrons are in the 1–10 MeV energy range [1].

[1] M. S. Gordon, P. Goldhagen, K. P. Rodbell, T. H. Zabel, H. H. K. Tang, J. M. Clem, and P. Bailey, “Measurement of the flux and energy spectrum of cosmic-ray induced neutrons on the ground”, IEEE Trans. Nucl. Sci., vol. 51, no. 6, pp. 3427–3434, Dec. 2004.

Sea level 32000 ft(~10 km) at flight altitudes

the total flux is ~300 times Sea

Level

Neutron intensity with altitude, latitudeNeutron intensity with altitude, latitudeand percentageand percentage

NOTE: these effects are induced by SINGLE neutrons (not total dose effects)

NOTE: these effects are induced by SINGLE neutronsSINGLE neutrons (not total dose effects)

Data corruption Noisy Images System shutdowns Circuit damage

Neutron induced effectsNeutron induced effectsin electronics near sea levelin electronics near sea level

1. they depend on energy of neutron2. in particular they are threshold effects3. the rate of effects scales with flux

1. they depend on energy of neutron2. in particular they are threshold effects3. the rate of effects scales with flux

Radiation effects in a semiconductor device occurs when there is a deposition of energy in the form of atomic displacement and or ionization. In both cases the effects can be cumulative (bulk damage and total dose effects) or instantaneous (Single Event Effects).

When a particle strikes a device it can transfer energy to the medium both by atomic displacement and/or ionization:

1. the particle transfers kinetic energy to the atoms and damages the structure of the medium (Non-Ionizing Energy Loss, NIEL). Noticeable effects after many particles;

2. the particle ionizes the medium (Total Ionizing Dose, TID). Noticeable effects in non-conductors after many particles;

3. the particle creates a dense localizes plasma that may perturb the device (single event effect).

At sea level total dose effects are completely negligible while single event effects are a great concern.

Single Event Effects (SEE) represent any measurable effect induced by the passage of a single highly ionizing particle: the dense localized plasma created by a single highly ionizing particle within semiconductor devices may result in many different classes of perturbations such as data corruption, transient disturbance or high-current conditions. A SEE occurs from charge deposition and collection at a sensitive node. The sensitive node is a reverse-biased junction where built in electric fields allows charge collection from a sensitive volume. The SEE occurs when the charge Q deposited in the sensitive volume by the ionizing particle is higher than some critical threshold value QC. The rate of SEE depends on the flux of particles through the sensitive volume that deposit a charge Q > QC. Neutron induced Single Event Effects (SEE) in electronics near sea level are induced by single neutrons. The rate of SEE depends on the flux of neutrons with sufficient energy to induce the effect.

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neutron induced Single Event Effectsneutron induced Single Event Effects (SEE)(SEE)A neutron interacts with a nucleus to produce a heavily ionizing secondarythat then causes an anomalous macroscopic effect in an electronic device

A single fast neutron that interacts with a nucleus may produce a variety of secondary particles – protons, neutrons, alpha particles and even heavy recoil nuclear fragments. The strongly ionizing secondaries may deposit bursts of free electron-hole pairs in the silicon that may be collected at pn junctions and produce a current spike (noise pulse) that can alter data or be interpreted as a valid signal by the circuit and lead to an error depending on the amplitude and duration of the perturbation.

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fast neutronfast neutron--induced reactions on induced reactions on 2828SiSi

Elastic scatteringElastic scattering

Inelastic scatteringInelastic scattering

CaptureCapture

TransmutationTransmutation

FragmentationFragmentation

(n, (n, ))

(n, p)(n, p)

28Si

--rayray

The neutron may interact with a silicon nucleus (see figure), but also with any other elements present in the device (packaging, metallizations, dopants,…)

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Ionization by recoils and fragmentsIonization by recoils and fragments

dQ/d

x(fC/

m)

dQ/d

x(fC/

m)

The linear energy transfer (ionization stopping power) and rangeas a function of energy. The top figure refers to a recoiling silicon nucleus. The bottom figure refers to an alpha particle.

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SEE may occur for Eneutron > 10 MeVbut even at lower energies ~24 MeV as active volumes

of newest devices become smaller!

SEE may occur for Eneutron > 10 MeVbut even at lower energies ~24 MeV as active volumes

of newest devices become smaller!

thresholdsthresholds

The table reports neutron threshold energies for some processes of interest.

Technological developments bring smaller and faster devices that operate at reduced bias voltages, but they then present an increased susceptibility to neutrons of in the 110 MeV range (and below).

SEE problem with thermal neutrons was due to use of Boron-10 in the cover glass layer of some microchips (Borophosphosilicateglass - BPSG). BPSG was used as for a polishing technique. It has been replaced with a Chemical Mechanical Polishing (CMP) technique. LESSON LEARNED

NOT only fast neutrons!NOT only fast neutrons!thermal neutrons too (lesson learned!)thermal neutrons too (lesson learned!)

Thermal neutron may induce SEE when Boron concentration becomes extremely high (e.g. P-MOSFETS)

Boron-10 has a high cross-section for emission of an ionizing alpha particle (dQ/dx = 12 fC/m)when struck by a thermal neutron

Single Event Effects by Boron neutron capture.

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SEESEE--OLOGYOLOGY

Single Event Upset (SEU)Single Event Drain Current Collapse (SEDC2)Single Event Disturb (SED)Single Event Transient (SET)Single Event Functional Interrupt (SEFI)

Single Event Burnout (SEB) in power DMOS transistorSingle Event Snapback (SES) in MOSFETSingle Event Gate Rupture (SEGR) in DMOS transistorSingle Event Latch-up (SEL) in CMOS technologies

destructive Events

(hard errors)

NON-destructive Events

(SOFT ERRORS)

For a given radiation field the mechanisms of an SEE and thePROBABILITY of occurrence

are strongly device and technology dependent.

For a given radiation field the mechanisms of an SEE and thePROBABILITY of occurrence

are strongly device and technology dependent.

The nature of the device determines the active volumes that may collect charge and how a single event effect becomes manifest; i.e. SEE sensitivity depends on device type and technology. Indeed as the complexity of devices and systems grow, their responses to radiation appear to diversify and new failure modes are routinely observed.

Non-destructive functional errors (soft errors) are induced by ionizing particle strikes. They include single-event upsets (SEU), multiple-bit upsets (MBU), single event functional interrupts (SEFI), single-event transients (SET) that, if latched, become SEU, and single event latchup (SEL) where the formation of parasitic bipolar action in CMOS wells induce a low impedance path between power and ground, producing a high current condition (Note that SEL can also cause latent and hard errors).

In general, soft errors may be induced by alpha particles emitted from radioactive impurities in materials nearby the sensitive volume, such as packaging, solder bumps, etc., and by highly ionizing secondary particles produced from the reaction of both thermal and high-energy neutrons with component materials.

Upset (SEU): change in logic state, e.g. SRAM memory

Latch Up (SEL): creation of low-impedance short circuit that triggers a parasitic PNPN structure that stops proper functioning

Single Event Burnout (SEB): an ion induced current flow turns on the parasitic npn transistor below the source that leading to device destruction if sufficient short-circuit energy is available.

Single Event Gate Destruction/Rupture (SEGD/R): an ion through the gate (but avoiding the p-regions), generates a plasma filament through the n-epilayer that applies the drain potential to the gate oxide, damaging (increased gate leakage) or rupturing the gate oxide insulation (device destruction).

permanent damage to power transistors or other high voltage devices

Requires power cycle to correct; may be destructive

temporary loss in equipment functionality temporary modification to system behaviour functionality returns without power cycle

Single Event Effects (SEE)

electronic systems are more and more complex as feature sizes decrease increasing likelihood of neutron indcued SEE causing a system failure and increases the probability of a neutron defeating error correction mechanisms (multiple bit upsets)

Developments towards smaller faster devices at lower bias voltages have increased SEE susceptibility in the 110 MeV range (and below) making soft errors more likely as they are then sensitive to the greater proportion (~40%) of atmospheric neutron flux.

SEE threat also from low energy “thermal” neutrons through a reaction of boron present as dopant in semiconductors. Thermal neutrons are generated within moderating materials (concrete in buildings; fuel in aircraft;…)

Complex and error prone electronics

Commercial off-the-shelf state-of-the-art electronics used at sea level electronics are more likely to suffer from neutron induced SEE as they are more susceptible to a greater proportion of the atmospheric neutron flux (3540%) [1].

[1] J. Baggio, D. Lambert, V. Ferlet-Cavrois, P. Paillet, C. Marcandella, and O. Duhamel, “Single Event Upsets Induced by 1–10 MeV Neutronsin Static-RAMs Using Mono-Energetic Neutron Sources”, IEEE Trans. Nucl. Sci., vol. 54, no. 6, pp. 2149-2155, Dec. 2007

The SEE issue: general need of SOCIETY for more The SEE issue: general need of SOCIETY for more reliable electronics:reliable electronics:

Avionic and space industry has a long standing tradition of radiation testing, especially SEE

Electronics extensively used in ACTIVE SECURITY & HIGH RELIABILITY APPLICATIONS with widespread everyday use: vehicles (not only airplanes, but trains, automotives,…) and in high-end computing, medical equipment, nuclear industry

the SEE issue for industry has been seriously investigated for its reliability implications even at sea level in everyday life: Semiconductor companies: IBM (since’80s), Intel, STMicroelectronics, TI, Infineon, Cypress, Xilinx,…, but few SEE comprehensive data from companies are available in open literature Semiconductor IC customers: even less prone to show their interest, basically no data available

at sea level SEE is dominated by Soft Errors. If not properly mitigated, the Soft Error Rate may reach 105 FIT = 1 error/104 hrs ~ 1 yr(Failure-In-Time: 1 FIT = 1 error/109 hrs of operation) Note: reliability in advanced ICs is improving down to some 10-100 FIT

Industrial News reports

• “Timely testing avoids cosmic ray damage to critical auto electronics”,John Wood and Earl Caustin, MOSAID Systems, 15/6/2006

• “Cosmic rays damage automotive electronics”, Martin Mason, Actel Corporation, 31/5/2006

• “Alpine lab enters rarified air of soft-error test”, Junko Yoshida, 25/9/2006

• “SEU mitigation in Stratix III Devices”, May 2007

Industry is showing great concern.

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“… semiconductor memory failures induced by cosmic radiation are

no longer [only] an aerospace problem. Such failure mechanisms must be accounted for

in automotive electronics systems design.”www.automotivedesignline.com, June 2006

“… semiconductor memory failures induced by cosmic radiation are

no longer [only] an aerospace problem. Such failure mechanisms must be accounted for

in automotive electronics systems design.”www.automotivedesignline.com, June 2006

R. Baumann, IEEE-TDMR, 2005

“Soft errors have become a huge concern in advanced computer chipsbecause,

uncorrected, they produce a failure ratethat is higher than all the other reliability mechanisms combined!”

“Since chip SER [Soft Error Rate] is viewed by many as a LEGAL LIABILITYLEGAL LIABILITY

(selling something that you know may fail), the public literature in this field is sparse

and always makes management nervous.”J. Ziegler and H. Puchner, “SER-History, Trends

and Challenges”, Cypress Semiconductors, 2004

Increasingly important to have neutron sources for SEE tests.

Need to evaluate the expected error/failure rate of components and whole systems, including large ones like whole computers (e.g. servers).

Neutron induced SEE is:

a real and increasing problem do to use of complex microchip technologies in wider commercial and economic activity; no single technological solution in near future.

SEE tests and numerical simulation techniques are indispensible for clarifying mechanisms and for the quantification of current and future trends in SEE.

Neutron SEE testingSEE tests use: Neutron beams (accelerated – faster than

natural rate) Field tests: a large number of devices can be

operated under low intensity radiation at diverse atmospheric locations (sea level, then mountains at various altitudes), and much PATIENCE

High Altitude Research StationJungfraujoch, CH, 3580m (46.50 N, 80 E)

There are basically two ways to determine the SEE rate:

1. real-time testing (field tests): test a large number of actual devices for a long enough period of time (weeks or months) until enough SEE have been accumulated to give a confident estimate of the error rate. If the test is performed in a location that is similar to the actual use environment, this method gives a direct measurement of the actual error rate. It requires no intense radiation sources, and no extrapolations to final conditions of use, etc., but it does require a system capable of monitoring hundreds or thousands of devices in parallel, for long periods of time (a lot of patience). Some field tests are performed on top of high mountains.

2. ‘accelerated’ tests: In accelerated testing, devices are exposed to a radiation source whose intensity is much higher than the ambient levels of radiation the device would normally encounter. Useful data is obtained in a fraction of the time required by real-time testing and complete evaluations can be done in a few hours or days instead of weeks or months. The disadvantage of accelerated testing is that the results must be extrapolated to natural conditions.

Why SEE testingInternational STANDARDIZATION of testing methods is one of the most important issues in the silicon industry

because reliable products and systems cannot be designed without SEE tolerance data of devices using

globally common gauges.

atmospheric like-spectraJEDEQ standards forworldwide semiconductor industryhttp://www.jedeq.org

JESD89A (Oct. 2006)REFERENCE differential neutron flux(sea level, New York city, mid-level Solar activity, outdoors)

JEDEC SOLID STATE TECHNOLOGY ASSOCIATIONJEDEC STANDARD“Measurement and Reporting of Alpha Particle and Terrestrial Cosmic Ray Induced Soft Errors in Semiconductor Devices” JESD89A(Revision of JESD89, August 2001)OCTOBER 2006

Neutron-induced SEE testing

• Neutron testing requirements include:– Atmospheric spectrum (for ground-like and

avionic-like testing)– High neutron flux for accelerated testing (107109

times faster than natural)– Mono-energetic neutrons USEFUL to resolve

energy dependence• Tests not only of individual devices but also of whole

electronic systems or component testing of representative equipment in order to establish the risks and the reliability level of complex systems.

High energy particle beams may be used to simulate how the atmospheric neutrons induce single event upsets in microelectronic components at a highly accelerated rate; a few hours of irradiation mimics many thousands of hours in the real environment. Three different types of ‘accelerated’facilities are used:

1) spallation neutron source;2) quasi-monoenergetic neutron source;3) monoenergetic proton source.

Spallation neutron sources provide neutrons over a wide range of energies, with the shape of the spectrum that should be as similar as possible to that of the terrestrial neutron environment. Mono-energetic neutron and proton sources have been shown to be effective for measuring the SEE response of products and circuits at several energies, which can be used to obtain the SEE rate from the full spectrum of the terrestrial neutron flux.

SEE event effects are energy dependent and mono-energetic neutrons and protons allow one to resolve features such as the threshold energy for SEE to occur.

Standardized “accelerated” neutron induced SEE Testing Facilities

• Los Alamos National Laboratory, New Mexico, USA (de facto STANDARD)• Tri-University Meson Facility, Vancouver, Canada• Zvedberg laboratories, Uppsala University, Sweden • ISIS (Rutherford Appleton, UK)• Japan (Takasaki; Osaka)

• Legnaro??

ICE House at LANSCE (LOS ALAMOS NEUTRON SCIENCE CENTER). Best

white source! E up to 800 MeV, close to natural atmospheric spectrum, but limited

thermal neutron flux

Tri-University Meson Facility (TRIUMF), Canada. High flux atmospheric-like

spectrum up to 450 MeV. But limited accessibility for electronic component

testing. Available a lower flux large area source for large device and system

testing.

Japan: two high intensity quasi-monoenergetic sources, one up to 90 MeV

(Tohoku University & TIARA, Takasaki), the other upto 400 MeV (Osaka Research

Center for Nuclear Physics)

Svedberg Laboratory (TSL), Sweden. Has quasi-monoenergetic

source between 20180 MeV. The white spectrum does not extend to

high energy where important effects are seen E>200 MeV.

ISIS (Rutherford Appleton Labs): Vesuvio, and soon ChipIR

EUROPEEUROPE

Production of spallation neutrons at ISIS:

Protons 800 MeV, pulsed 50 HzI ≈ 200 µAP = 160 kW power into W targetf~2×1016 neutrons/s (average)

≈52 m

The ISIS-Vesuvio test facility

Rutherford Appleton Laboratory, UK

In 2005-2006 the first SEE measurements in Europe of electronic components (FPGA, SRAM, Flash memories) under a continuous neutron energy spectrum have been performed at the ISIS-RAL labs, Didcot,UK, by British (SPAESRANE) and Italian research groups

The ISIS-Vesuvio test facility(designed and built within an italian british project)

Università di Milano-Bicocca: G. GoriniUniversità di Padova: M. Bagatin, A. Manuzzato, S. Gerardin, P. Rech, A. PaccagnellaUniversità di Roma2, Tor-Vergata: C. Andreani, A. Pietropaolo, G. Cardarilli, S. Pontarelli, A. SalsanoISIS: C. Frost

ISIS 2nd

target station

MUCH BETTER

Svedberg Laboratory, Uppsala SwedenSvedberg Laboratory, Uppsala SwedenTwo ways of producing neutrons for testing electronic

components and systems for neutron-induced SEE

1. Atmospheric-like Neutrons from Thick TArget, [ANITA] facility:bare 24mm thick tungsten (99.8% pure) to stop 180 MeV protons from cyclotron; i.e. a spallation neutron source with a white neutron spectrum that resembles atmospheric spectrum. For standard Iprot = 200 nA, neutron flux n(E>10 MeV) 106 cm-2 s-1

1. Quasi Mono-energetic Neutron [QMN] facility:thin (224mm) lithium targets enriched (99.99%) with variable proton energy (max ~180 MeV) quasi-monoenergetic neutron source with controllable peak Eneutron in range 11175 MeV . For typical current 5A, typical neutron flux 5105 n cm-2s-1

Svedberg ANITA and QMN facilities Svedberg ANITA and QMN facilities

2.5 m

~ 3.5 m

This is a schematic layout of the ANITA and QMN facilities at the Svedberg Laboratory. Downstream of the 180 MeVcyclotron, the proton beam is guided either to a thick tungsten target or a thin 7Li target, the ANITA or QMN modes of operation, respectively.

In the QMN mode a bending magnet sends the spent proton beam to a beam dump. In the ANITA mode the target is situated inside the massive bending magnet in a concrete cave for shielding the surrounding areas against neutrons and gammas produced in the target.

The neutrons beam is formed geometrically by a collimator aperture in a 1-m thick iron frontal wall which separates the neutron produce cave from the user area. This distance of the standard test station from the ANITA tungsten target is 2.5 m while the distance from the lithium QMN target is 3.5 m (the thin target is before the dipole magnet). The user area is described in some detail in extra slide 1.

Back of the envelope estimates of neutron spectra and fluxes at Legnaro cyclotron: • protons 70 MeV (continuous)• I = 200 nA I=5500 A• distance from thick target 2.5 m 3.5 m

Based on toy GEANT4

ConsiderationsConsiderations LegnaroLegnaro ((ANITAANITA--likelike))

The new 70 MeV proton cyclotron could be used to produce a “white” atmospheric-like spectrum of fast neutrons.

A toy-montecarlo (GEANT4) was used to compare the neutron differential spectra and neutron fluxes from 70 MeV protons with those from 180 MeV (like ANITA) on simple bare thick tungsten targets.

5107 protonsbeam = 2mm

2107 protonsbeam = 2mm

180 MeV protonson 24 mm W

70 MeV protonson 5 mm W

at 2.5 m distance

at 2.5 m distance

Differential spectra of neutrons through

30cm-by-30cm area (test board) at 0o and

at a distance of 2.5 m from target

n(E>10 MeV) = 3.2 105 cm-2 s-1

n(1<E<10 MeV) = 1.1 106 cm-2 s-1

Iprotons = 1.5 A

n(10<E<50 MeV) = 2.8 105 cm-2 s-1

n(E>10 MeV) = 5.8 105 cm-2 s-1

n(1<E<10 MeV) = 1.1 106 cm-2 s-1Iprotons = 200 nA

n(10<E<50 MeV) = 2.4 105 cm-2 s-1

Straight-forward toy simulations were performed to compare the neutron spectrum and fluxes obtained from 180 MeV protons on a 24 mm thick tungsten target (ANITA-like) with the neutron spectrum and fluxes obtained from 70 MeVprotons on a 5 mm thick target, thick enough to stop the protons. The figures shows the energy spectra of neutrons incident on a test-board area of 30cm-by-30 cm placed at 0o at a distance of 2.5 m from the thick targets.

The energy of the spallation neutrons extends out to the beam energy but otherwise the shape of neutron energy spectrum for 70 MeV protons is similar to that for 180 MeV protons. In the bottom figure the 70 MeV spectrum can be directly compared with the ANITA-like 180 MeV spectrum (blue dashed curve) by taking I70 = 500 nA and I180 = 200 nA respectively. For I70 = 1.5 A and I180 = 200 nA the yields of neutrons in the range 1 < En <50 MeV are equivalent (see the fluxes reported in the figure).

The toy-GEANT4 simulator, intended to evaluate relative yields, was compared with data in literature and was found to underestimate the values reported in literature by 3040%:

1. extra slide 3 shows a fit to the real standard ANITA spectrum; 2. extra slide 4 shows published energy-angle distribution of neutron yields of 68

MeV protons on a thick copper target that allows a rough back-of-the-envelope estimate of neutrons fluxes. Extra slide 5 shows the simulated energy spectrum of neutrons through an area 30cm-by-30cm placed at 0o at a distance of 1.5 m from the target.

The LNL shield wall between the thick W target and the user area will be 3 m thick. We conclude that at a working distance of 3.5 m, a fast neutron thick target facility at the Legnaro 70 MeV cyclotron with just I70 ~ 3 A would be equivalent, in the 150 MeV energy range, to the existing ANITA facility.

LegnaroLegnaro –– white white spectrumspectrum

neutron spectrum reaches out to lower energies

However: not as wasteful as biggest machines to study low energy SEE (1<E<10 MeV) spectrum shape in energy range 1<E<50 MeV is COMPARABLE to standard ANITA

LegnaroFigure adapted from Alexander V. Prokofiev

None of the commonly used fast-neutron facilities for ‘accelerated’SEE testing produce neutrons with an energy spectrum that is perfectly similar to the atmospheric one at the surface of the earth, in particular because the GeV energy region is not reachable.

The figure shows the white spectra of existing facilities: the atmospheric spectra (terrestrial, thick back line) is multiplied by an acceleration factor of 3108; the blue curve is that of ANITA. The LNL spectrum (sketched in red) could be achieved with a beam current of ~3 A and would be comparable to the spectrum at ANITA for neutrons in the 150 MeV energy range (see previous slide). The acceleration factor of the LNL facility could be higher still by using higher beam currents.

The proposed ChipIR facility at ISIS will be working soon and the spectral shape -not shown on this plot but in extra slide 2 - will be greatly improved respect to the spectrum at the ISIS-VESUVIO facility. It is expected to compare very well with the atmospheric one.

Technological developments bring smaller and faster devices thatoperate at reduced bias voltages, but the individual electronic devices present an increased SEE susceptibility of in the 110 MeV range. In this respect it is worth pointing out the waste it would be to investigate the SEE sensitivity of electronics to low energy neutrons at the higher energy spallation machines.

To scale data taken at Legnaro to other facilities need to obtain a correlation coefficient between Legnaro and LANSCE;

e.g. obtain the LANSCE-equivalent flux [Platt08-09]

This is done by measuring well known representative devices belonging to several different technologies at LNL and then at one of the “known” facilities (LANSCE/ANITA/ISIS).

LNL vs Rest of the world?Will need to correlate results measurements at Legnaro with

data obtained at other facilties with spectra more closely matching the atmospheric one.

- This approach works reasonably well for SEU (demonstrated by ISIS-VESUVIO),but may have limitations for SEL and MBU (multiple bit upsets). [see extra slide 5]

Note a similar method is used for heavy-ion facilities across Europe by ESA that differ with respect to ion energies, LETs and ranges.

To effectively compare the LNL facility with a standard facility, despite different neutron energy spectra, one must compare the SEE behavior of well known devices at LNL with the behavior at the standard facility, obtain a correlation coefficient and thereby express the neutron flux in “standard equivalent units”. This technique has been shown to work reasonably well for SEU by experimenters at the ISIS-VESUVIO facility. For this purpose they used a charge-coupled device to image and monitor SEE (see extra slide 5).

The correlation coefficient of all working facilities respect toLANSCE (the de facto standard) have been obtained, and hence the correlation coefficient of the LNL facility could be obtained by comparing with any one of the working facilities.

LegnaroLegnaro fast monofast mono--energetic neutronsenergetic neutrons

~ 31057 max

also at 3.5 m~ 3105 (typical)

for 25<Ep<90 MeVat 3.5m

Max fluxn(E~Epeak) cm-2 s-1

5500 A5 A(typical)

current (nA)

For instance 25,35,45,55,70

25,50,70,80,90,100,110,150,180

Energy beam Ep (MeV)LegnaroQMN

Svedberg typical

quasi-monoenergeticneutron energy spectrum

(QMN mode)

The high currents available at the Legnaro cyclotron would allow the copious production of quasi-monoenergetic neutrons, a very useful tool to resolve the energy dependence of SEE.

34

SEE topics that may be studied (1<En<50 MeV)

SOFT ERROR studies SEE in POWER DEVICES testing of WHOLE ELECTRONIC SYSTEMS

N.B. Power devices do not follow down-scaling dimensions and voltages: they exhibit larger sensitivity to neutron-induced effects, even at sea level Destructive event in a COTS

120V DC-DC ConverterDestructive event in a COTS

120V DC-DC Converter

K. LaBel, EWRHE 2004

The SEE topics that could be studied would be vast, ranging fromSOFT errors in digital electronics to HARD errors and failures in power devices. In addition one could perform the testing of whole electronic systems or of components and representative equipment in order to establish the risks and reliability levels of complex systems.

Devices that may suffer from neutron induced SEE include: •memory devices; •processors; •Field Programmable Gate Arrays (FPGAs); •Electro-optical devices; •Solid State Switching.

Then there are power devices. MOSFETs and other devices are known (2005) to be susceptible down to seal level, including: •bipolar junction transistors (BJT); •insulated gate bipolar transistors (IGBT); •thyristors; •high voltage diodes; •small signal epitaxial npn BJT; •CMOS PWM controllers and drivers.

35

very useful intense white spectrum facility wide range of fluxes

copious mono-energetic neutrons of significant interest

would be the only fast neutron source in Italy

need to plan test station carefully

targets

SEE test facility at the LNL 70 MeV cyclotron

• ensure good uniformity over largest area• for quasi-monoenergetic mode need to plan for dipole magnet

A SEE fast neutron test facility at the 70 MeV cyclotron would be a very useful facility. High currents would require elaborate targets, but with startup proton currents of a fewA and simple targets the facility would be already be equivalent to the Svedberg ANITA and QMN facilities in the 150 MeV energy range.

The design of the building hosting the cyclotron must include from the beginning an irradiation area able to compromise experimental needs and safety costs. Downstream of the thick target the shielding wall and the test user area need to be planned carefully:

a) a long test area would allow multiple users to simultaneously irradiate devices over a wide range of fluxes;

b) an adjustable collimator in the shielding wall downstream of the thick target to allow, when wide-open, irradiating large complex systems (e.g. a whole computer).

In addition the production of quasi-monoenergetic neutrons from thin lithium targets needs a dipole to dump the spent proton beam (see SLIDE 28 – Svedberg ANITA and QMN facilities).

36

would almost complete irradiation facilities for radiation damage studies at Legnaro

SIRAD (30MeV protons and heavy ions) X-ray machine gamma source

fast neutron source protons up to 70 MeV (useful for SEE too!)

test station at SPES accelerator to study SEE due to capture ofthermal neutrons by boron.

electronics testing at LNL

A fast neutron test station at the 70 MeV cyclotron would be a very important facility for the radiation damage community in Italy.

Of course the direct mono-energetic proton beam could be used to perform energy resolved SEE studies and the test station should be designed to allow for this.

37

ENDEND

Extra slides belowExtra slides below

Acknowledgments:For the precious discussions and suggestions, I thank Dario Bisello, Alessandro Paccagnella and Simone Gerardin. For the patience and hard work, I gratefully thank Nicola Pozzobon.

Svedberg user areaSvedberg user area• Neutrons enter user area through a variable collimator

(aperture size, shape). Aperture size ranges 030 cm (time to change collimator aperture need ~ 30’)

• User area extends from 2.5m to ~15 m downstream of tungsten production target

• Beam axis 1.5 m above floor• Area for user equipment not less than 50m2, height 2.5 m• At standard ANITA user position (SUP) 2.5 m

downstream:

• Minimum ANITA neutron field at user position at end of beam line 5 n (E > 10MeV) cm-2s-1

1. standard ANITA neutron flux: 106 n (E>10MeV) cm-2s-1

for standard Iproton = 200 nA. Acceleration factor ~ 3108

2. minimum ANITA field: 200 n (E>10MeV) cm-2s-1

Extra slide 1

Extra slide 1

ISIS ChipIR – 06/12/2007 proposal for discussion

W target,Beryllium reflector and special composite moderator

times 4107

times 3105

Extra slide 2

DASHED atmospheric spectraat 10 km

Extra slide 2

The much improved expected neutron spectra for the two beam modes – pencil and flood - at ChipIR, the proposed 2nd test station for electronics testing at ISIS. The atmospheric neutron spectrum at 10 km of altitude is also shown multiplied by the corresponding acceleration factors.

[1]

Extra slide 3

Extra slide 3

The fluxes reported in this figure are the integrals of the fit function over the energy intervals.

[1] A.V. Prokofiev, J. Blomgren, S.P. Platt, R. Nolte, S. Röttger, A.N. Smirnov, “ANITA – a New Neutron Facility for Accelerated SEE Testing at the Svedberg Laboratory”, 47° Annual InternationReliability Physics Symposium, Montreal, 2009

At = 0o

in range 10<E<30 MeVdouble differential yield ~ 10-4 n MeV-1 Sr-1 proton-1

910-5 n MeV-1 Sr-1 proton-1

Iprotons = 5 A == 3.12 1013 protons/s

in range 1030 MeVdifferential flux is

~1.25 105 n MeV-1 cm-2 s-1

n(10<E<30 MeV) ~ 2.5106 n cm-2 s-1

n(E>10 MeV) ~ 4106 n cm-2 s-1

1cm2 at =0o and at 150 cmfrom production target

~ 1/(150)2= 4.4 10-5 Sr

white spectrum white spectrum (thick Cu target) at (thick Cu target) at LegnaroLegnaro

Extra slide 4

Extra slide 4

The energy-angle distributions of neutron yields from a 68 MeVprotons on a thick Cu target. In this plot [1] it is important to note that the data at various angles are multiplied by a scale factor so as to separate the data points and aid reading. The factor for the data at 0o is 106. In the 10<E<30 MeV energy range the double differential neutron yield is n(10<E<30 MeV) ~ 10-4 n MeV-1 Sr-1 per proton.

This data can be used to perform an estimate of the neutron yield. For Iproton = 5 A, a rough back-of-the-envelope estimate of the flux of neutrons at 0o at a distance of 1.5 m from the target gives: •n(10<E<30 MeV) 2.5 106 n cm-2 s-1, •n(E>10 MeV) 4 106 n cm-2 s-1.

[1] M. Maiti, M. Nandy, S.N. Roy, P.K. Sarkar, Nuclear Instruments and Methods in Physics Research B 215 (2004) 317-325

GEANT4 GEANT4 ““checkcheck””

68 MeV protonson 7.1 mm Cu

Simulation30107 protonsbeam = 2mm

n(E>10 MeV) = 2.8 106 n cm-2 s-1

For Iprotons = 5 A

Differential spectra of neutrons through30cm-by-30cm area (test board)

at 0o and at a distance of 1.5 m from target

Extra slide 5

n(10<E<30 MeV) = 1.6 106 n cm-2 s-1

Extra slide 5

A GEANT4 simulation of 68 MeV protons on Copper target 7.1 mm thick. The figure shows the energy spectra of neutrons incident on a test-board area of 30cm-by-30 cm placed at 0o at a distance of 1.5 m from the target.

The GEANT4 flux estimates shown above for Iproton = 5 A are 30% and 40% low respect to the rough back-of-the-envelope estimates reported on the previous slide.

CCD Imaging SEE monitor (ISEEM) used to characterize the neutron field at the

VESUVIO Single Event Effects test facility at ISIS

Images transient charge packets generated by ionizing particles produced in neutron interactions [1]

Extra slide 6

Extra slide 6

The Imaging SEE monitor (ISEEM) was developed to compare the ISIS-VESUVIO neutron spectrum with the one at LANCSE.

[1] Simon Platt, Zoltán Török, Chris D. Frost, Stuart Ansell, “Charge collection and Single-Event Upset Measurements at the ISIS Neutron Source”, IEEE Trans. Nucl. Sci., vol. 55, no. 4, pp. 2126–2132, Aug. 2008.