Neutron irradiation tests of the currently available electronics for the CMS barrel muon detector were performed using Thermal and fast neutrons at E&lt; 11MeV. The Single Event Upset rate on the Static RAM was measured, while upper limits are derived for events having experienced no failure. The results are used to guess the upper limits on the mean time between failures in the whole barrel muon detector

Agosteo, S

Castellani, L

D'Angelo, G

Favalli, A

Lippi, I

Martinelli, R

Zotto, P L

GIULINI CASTIGLIONI AGOSTEO, STEFANO LUIGI MARIA

D'ANGELO, GIOVANNI

FAVALLI, ANDREA

ZOTTO, PIERLUIGI

L. Castellani

A. Lippi

R. Martinelli

Archivio istituzionale della ricerca - Politecnico di Milano

First Evaluation of Neutron Induced Single Event Effects on the CMS Barrel Muon Electronics

S. Agosteo

l. Castellani

G. D'angelo

A. Favalli

I. Lippi

Archivio istituzionale della ricerca - Università di Padova

First Evaluation of neutron induced Single Event Effects on the CMS barrel muon electronics

S. AGOSTEO

L. CASTELLANI

G. D'ANGELO

A. FAVALLI

I. LIPPI

R. MARTINELLI

First evaluation of neutron induced Single Event Effects on the CMS barrel muon electronics

Castellani, Lorenzo

Lippi, Ivano

Martinelli, Roberto

Zotto, Pierluigi

CERN Document Server

First evaluation of neutron induced Single Events Effect on the CMS barrel muon electronics

First Evaluation of Neutron Induced Single Event Effectson the CMS Barrel Muon ElectronicsS. Agosteo1, L. Castellani2, G. D’Angelo1, A. Favalli1, I. Lippi2, R. Martinelli2 and P. Zotto31) Dip. di Ingegneria Nucleare (CESNEF) del Politecnico di Milano, Italy2) Dip. di Fisica dell’Università and sez. INFN di Padova, Italy3) Dip. di Fisica del Politecnico di Milano and sez. INFN di Padova, ItalyPierluigi.Zotto@pd.infn.itAbstractNeutron irradiation tests of the available electronicsfor the CMS barrel muon detector were performed usingthermal and fast neutrons. The Single Event Upset rateson static RAMs were measured, while upper limits arederived for devices having experienced no failure. Theresults are used to guess the mean time between failuresin the whole barrel muon detector.I. INTRODUCTIONThe LHC detectors will be working inside the highestradiation field ever experienced in high energy physics.Several studies were done in order to check the radiationtolerance of the detector itself and investigations weredone in order to assess the tolerance of electronics.The barrel muon chambers are a particular case withinthe general scenario. The radiation dose absorbed afterten years of operation at LHC is negligible (less than0.2Gy). The expected neutron fluence is not high enoughto generate a relevant bulk damage (less than2.5 x 1010 n/cm2), nevertheless detector electronics couldstill be disturbed or even damaged because of SingleEvent Effects (SEE). Besides it will not be accessible,since most of it is located within the cavern, lodged on thechambers.We expect therefore that most of the reliability ofthese electronics will be associated to the probability ofoccurrence of these rare Single Event Effects induced bythe interaction of the ionizing particles with the silicon.II. NEUTRON BACKGROUND EXPECTATIONSMuon chambers are shielded by the iron yoke againstthe effects of charged low energy particles, and thebackground particle flux will be dominated by neutronsthermalizing within the cavern. Neutrons are produced allaround inside the cavern by beam halo interactions withmagnets on the LHC beam line and the detector itself.Extensive simulation studies [1] were done to estimatethe rate of background particles at all positions insideCMS. Some results of the simulation are shown inFigure 1, where the energy spectra of neutrons at differentpositions in the detector are reported. Although theMontecarlo calculations for low energy neutrons areusually affected by large errors, we have an indication ofthe expected neutron rate. We see that the neutronbackground is linearly decreasing with energy and isnaturally ending around 100 MeV in the outermost stationand at few hundred MeV in the innermost one, that issuffering from high energy neutrons flooding through theCMS calorimeters and coil. The fast and thermal neutronfluence are expected to be each one around 500 n cm-2s-1.Figure 1: Expected  neutron fluence through the innermost(MB1) and the outermost (MB4) muon barrel stations.III. SINGLE EVENT EFFECTSPHENOMENOLOGYThe Single Event Effects are associated to individualionizing particles and their occurrence is given as a crosssection that provides the probability that a particle hittinga squared centimetre of a silicon device produces a SEE.The most likely effect is called Single Event Upset(SEU) and affects all kinds of memory devices (SRAM,DRAM and FLASH memories, microprocessors andDSPs, FPGAs and logic programmable state machines,etc.). It is detected as a modification of the memory stateand is usually recoverable by data rewriting. Memoryupset is caused by the deposition, inside a device sensitivenode, of a charge higher than a given threshold. Thischarge value is dependent on both technology and devicelayout [2]. Even system architecture plays a relevant rolein SEU sensitivity: critical data can be protected eitherusing less sensitive technologies or implementingredundant logic. Occasionally the energy depositionassociated to the interacting particle can be the cause of alatch-up (SEL) or a gate rupture (SEGR) or even a deviceburnout (SEBO) [3]: these effects could be destructiveand generally cannot be recovered. Both SEL and SEBOeffects can be reduced by system architecture design. As amatter of fact, while the permanent damage associated toSEL can be eliminated using power supply and input-output overcurrent protection circuitry, the power deviceburnout probability can be reduced to a safety levellimiting the operating voltage to a fraction of thebreakdown value.All the measurements done until now confirm that theSEU cross section is depending both on the technologyused for integrated circuits production and on theprocessing chain actually used in the factory. Theassociated technological parameters are usually not wellcontrolled since two orders of magnitude in the quotedresults are a typical variation.Very recent tests [4] proved that thermal neutrons arecausing SEU. The responsible mechanism could beneutron capture from the 10B isotope (19.9% of naturalboron), normally present in semiconductor technologiesas a dopant and in the glass passivation layer, followed bynucleus de-excitation with a-particle emission throughthe reaction 10B(n,a)7Li. Both the lithium nucleus and thea-particle release locally enough energy to cause thememory cell change of state [4,5].Fast neutrons interact with 28Si atoms producingrelevant recoil energy already at neutron energy around0.1 MeV, but only neutrons with an incident energyhigher than 3 MeV should contribute to the SEU crosssection: the relevant reactions are in fact 28Si(n,p)28Alwith a 4 MeV threshold and 28Si(n,a)25Mg with a2.7 MeV threshold [5]. Published results claim that SEUcross section has an energy threshold and is slowlyincreasing with energy up to a saturation value at100 MeV neutrons energy [6].In this scenario, the whole existing literature agreesthat, if the neutron background is going to be a problem,the existing data cannot be used directly to estimate SEUprobability of a device, unless you can tolerate largesafety margins. It is therefore recommended to get oneselfown measurements done .IV. MEASUREMENTS SETUPCMS barrel muon detector electronics will deal with awide spectrum of neutron energies. Our irradiation testsaim to evaluate effects due to the fast neutrons below100 MeV or the thermal portion of the neutron spectrum.Low energy neutrons are copiously produced in thenuclear laboratories by scattering of proton or deuteronnuclei accelerators on low atomic mass nuclei targets.The Van de Graaff accelerator at INFN laboratory ofLegnaro (LNL) produces neutrons through the reaction9Be(d,n)10B, with a maximum deuteron energy of 7 MeV.The neutron rate is high enough to allow an easyintegration of ten LHC years in a short time. The emittedneutron spectrum [7] is shown in Figure 2a for severalincident deuteron energies. The emitted neutron spectrahigh-end is limited to about En = 11MeV.Figure 2: Neutron energy spectra (a) at LNL and (b) at UCLThe UCL laboratory provides a facility for a wideneutron spectrum using the reaction 9Be(p, )9B, with amaximum incident proton energy of 65 MeV optionallycleaning the neutrons with a polyethylene/iron filter. Thespectrum in our test setup is shown in Figure 2b: theneutron energy is roughly flat in the range 20-60 MeV. Thermal neutrons were generated at LNL using thedeuteron beam. The moderator [8] is sketched in Figure 3.The Beryllium target is enclosed in an heavy water tanksurrounded by very thick graphite walls. The fastneutro s produced in the d-Be scattering are thereforemoderated by the heavy water and reflected from thegraphite, thermalizing and remaining inside the graphite.The irradiation cavity is situated on top of the heavywater tank in backward position with respect to theberyllium target in order to minimize the residual fastneutron content.Figure 3: Sketch of the neutron moderator.The devices ready to be tested were the first prototypeof the slow control board, the readout front-end board anda prototype trigger board. The list of relevant integratedcircuits is shown in Table 1: in particular three controlboards were tested.Device registers were initialized to a standard pattern,verified by the readout system with a two seconds cycle.Every time an alteration of the memory state wasdetected, the time, the integrated current on the target, theaddress and the datum were stored for data analysis.Table 1:  List of tested components with relevantcharacteristics of each device.Device Productor/Type/YearLow Drop RegulatorMICREL/29501-3.3BU/1997µP MOTOROLA/MC68HC16/1994FLASH ATMEL/AT29C101A-12PC/1996SRAM SONY/CXK581000AM-70LL/1993EPROM ATMEL/AT27C512R-15JC/1995OpticaltransceiverHONEYWELL/HFM2600-1 /1998ASIC TSS ES2 0.7 µm / TOP5 ceramic package/1997ASIC BTI ATMEL 0.5 µm/LTCC substrate & in dies /1997ASIC MAD AMS 0.8 µm/BiCMOS/1997V. SEU CROSS SECTION EVALUATIONThe tests aimed to the observation of Single EventUpsets due to thermal or fast neutrons and to thedetermination of the SEU cross section for every device.The existence of thresholds and its dependence onneutron energy was investigated as well as the uniformityof behaviour among different pieces of the same device.A. Thermal neutronsThe boards were irradiated with thermal neutrons onfour data taking periods. Since the neutron flux inside thegraphite is modified by the inserted boards, we had to getthe actual neutron flux measuring the activation of Indiumand Cadmium-Indium (to get non thermal contribution)targets placed just in front of the integrated circuits.After a total rate of ~7x1010 n/cm2 the only deviceexperiencing SEU was one of the SRAMs. Figure 4shows the plot of the SEU numbers versus the integratedneutron flux for all the test periods. The fact that theresults are sitting on a line is an indication that there areno total dose effects, i.e. no saturation due to devicedegradation. The slope of the average line fitted in thisplot is a measurement of the SEU cross section of thedevice. Results are collected and summarized in Table 3.Figure 4: SEU progressive number versus integrated neutronflux in the thermal neutron run.B. Threshold  searchAs we already stressed there is some evidence that anenergy  threshold on fast neutrons induced SEU crosssection is existing. The known physics processes indicatethat this threshold should be in the few MeV region. Asevidenced by the energy spectra of Figure 2a, theneutrons produced in the 9Be(d,n)10B reaction were notmonochromatic. Measurements with the thick Berylliumtargets using different incident deuteron energy arenonetheless useful to give an indication of the existenceof a threshold, since the fraction of neutrons withEn > 1MeV in the production spectra is largely modifiedas a function of the beam energy.Figure 5: Uncorrected SEU cross section evaluation onSRAM # 1 as a function of the incident deuteron energy.The SEU cross section as a function of the incidentdeuteron energy evaluated considering an equalcontribution from all neutrons produced is shown inFigure 5. Its behaviour is consistent with the existence ofa threshold around 3 MeV, as loosely determined foldingthis distribution with the spectra of Figure 2a. This resultagrees with the opening thresholds of the 28Si(n,p)28Aland 28Si(n,a )25Mg reactions in addition to the neutronelastic scattering on silicon.C. Fast neutrons at En  < 11 MeVA complete test was done only at Ed = 6.5 Mevintegrating a total rate of ~1012 n/cm2 .We used the MCNP Montecarlo code to determine theneutrons flux expected through our devices with a carefuldescription of the test area in order to account forneutrons scattering on the walls, the floor and on therelevant devices inside the measurement area.As expected after the thermal neutron test, we had alarge number of SEU from SRAM#1. The SEU number atEd = 6.5MeV is shown as a function of time in Figure 6.With fast neutrons we could observe also SEU onSRAM#2. Although this RAM is of the same type andproduction lot, we obtained a SEU cross section twoorders of magnitude lower than SRAM#1 (4 SEU after1.52x1012 n/cm2 against 135 SEU after 0.75x1012 n/cm2).Figure 6: SEU progressive number on SRAM # 1 versusintegrated neutron flux at Ed = 6.5 MeVThus we experienced the effect reported in theexisting literature of big variations for the same device.Results are collected in Table 3 assuming that onlyneutrons with En > 3 MeV contribute to the cross section.D. Fast neutrons at 10 < E n < 70 MeVAnother effect reported in literature is the dependenceof SEU cross section on neutron energy. The data takenduring the LNL test were limited to energies barelyexceeding the threshold and more than one order ofmagnitude lower than the expected maximum neutronenergy at LHC. We completed this preliminaryinvestigation testing the devices at UCL using a 65 MeVproton beam incident on a beryllium target. Theintegrated neutron flux was again ~1012 /cm2. Globallywe tested 6 SRAM of the same type and lot: results arecompared in Table 2.Looking at the table we see that we have variation upto two orders of magnitude for the SEU cross section ofthe SEU cross section depending on the piece weirradiated. Instead considering the same piece we foundan increase of the cross section of a factor ~20 withdeuteron energy and therefore a clear importantdependence on neutron energy.While none of the other devices underwent SEU onthe lowest energy run, at UCL we registered few of themon the 1 kbyte microprocessor internal RAM. The crosssections were 3.85x1011 cm2 and 1.25x1011 cm2  for thetwo tested pieces. Comparing the fault probability per bitof the SRAM and the microprocessor (128 kbytes versus1 kbyte) we find that the latter is of the same order of theworst RAM ( ~10-15 cm2/bit).E. SEU uniformity verificationIt is interesting to check if there are more sensitivepositions inside the SRAM, or if the probability of a SEUhappening inside the chip is equally distributed: weverified that the addresses were different and we found nopreferred bit flipping within the statistics precision.Another interesting check is the verification if the bitchange from High Õ  Low was more probable than theone from Low Õ  High. Figure 7, taken from a thermalneutron run, supports the understanding of anhomogeneity of the SEU cross section.Figure 7: SEU on SRAM # 1 divided by type of bitmodificationVI. SEE ON MUON FRONT-ENDThe readout front-end electronics is composed by acharge integrator and a variable threshold discriminator.Since the front-end circuit is a charge sensitive device, theassociated SEE is the detection of energy depositioninside the circuit simulating a pulse over threshold.Two prototypes were tested both on thermal and fastneutrons. Since access to the boards was easy wemodified the threshold settings in order to verify that SEEcross section was depending on the actual threshold.Figure 8 reports the SEE cross section in the thresholdscan run for fast neutrons. In this case the quoted SEEcross section assumes that all neutrons in the spectrumhave the same probability to induce a SEE. Thesystematic errors cannot be estimated, but the result iswell below the input noise expected from interactionsinside the gas volume. Hence we can state that we don’tTable 2: Comparison of SEU cross sections for SRAMs of same type and lot in different testconditions explained in the text. Errors (about 50%) are not included for sake of clarity.SEU cross section (cm2) on SRAM#1 #2 #3 #4 #5 #6Thermal 1.13x10-09 <1.38x10-10 - - - -LNL 7.03x10-10 4.28x10-12 6.28x10-11 4.41x10-12 - -UCL 1.03x10-08 8.99x10-11 - - 1.50x10-10 1.70x10-10expect problems with noise induced from SEE on thefront end readout electronics.Figure 8: SEE on front end device as a function of discriminatorthreshold at Ed = 6.5 MeV.VII. RESULTS SUMMARYResults of the various tests are collected in Table 3considering only the worst result for each device. Wequote a 90% confidence level upper limit of the SEUcross section for all the devices which experienced nofailure. The error in the SRAM SEU cross section is thesquared sum of statistical and systematical error. Thelatter one is due to the uncertainty of the total neutronflux and is dominating our calculation.The Mean Time Between Failures is computed for thewhole barrel muon detector, considering the number ofpieces of each chip used in the electronics layout. Weconsidered 50000 BTI chips and few hundred pieces ofthe other devices. using the neutron flux expected fromMontecarlo  for each of the energy ranges we used. Thepoor result for the BTI in the thermal run is due to thelarge number of pieces, but the quite comfortable result ofthe other tests suggests that no problem should arise.VIII. RADIATION DAMAGE VERIFICATIONAfter the whole bunch of tests, each device wasirradiated with more than 2x1012 n/cm2, equivalent to theexpected flux after much more than ten years of operationat LHC. We therefore verified the status of each deviceafter irradiation to see if the neutrons had produced anypermanent damage. The only device showing adeterioration was the Trigger Server ASIC (TSS), whichafter ~1012 n/cm2 was drawing a standby current increasedby 10% with respect to the same current before the tests.The technology used for this device is old and it will beredone in the same 0.5 µm technology of the BTI chip.Besides none of the devices underwent a destructive SEE.IX. CONCLUSIONSWe measured neutron induced SEE both in the fastenergy region below 70 MeV and in the thermal energyregion and gave a first measurement of SEU cross sectionor derived upper limits for some devices to be used in themuon barrel electronics. Some evidence of a thresholdand energy dependence of the cross section was found.X. REFERENCES[1] CMS Muon Technical Proposal, CERN/LHCC 97-32,1997.[2] P.E. Dodd et al., IEEE Trans. On Nucl. Science, vol.43,No.6, Dec 1996.[3] D.L. Oberg et al., IEEE Trans. On Nucl. Science, vol.43,No.6, Dec 1996[4] P.J. Griffin et al., IEEE Trans. On Nucl. Science, vol.44,No.6, Dec 1997[5] E. Normand, IEEE Trans. on Nucl. Science, vol.45,No.6, Dec 1998[6] K. Johansson et al., IEEE Trans. On Nucl. Science,vol.45, No.6, Dec 1998[7] J. W. Meadows, NIM. A324(1993)239.     D.L. Smith et al.,NIM A241(1985)507.[8] S. Agosteo et al., Advances in Neutron Capture Therapy,Vol 1, 1997            S. Agosteo et al, Rad. Prot. Dos., Vol. 70, p. 559 (1997)Table 3: SEU cross section and expected mean time between failures in the whole CMS muon barrel detector due to neutrons ofdifferent energy. We considered 500 n/cm2 of thermal neutrons, 20 n/cm2 with 3<En<10 MeV and 30 n/cm2 with En>10 MeV .SEU cross section (cm2) Mean Time Between Failures (hours)Device Thermal LNL UCL Thermal LNL UCLLD reg < 1.38x10-10 < 1.40x10-11 < 1.00x10-12 < 64 < 15587 < 147892µP < 1.38x10-10 < 1.40x10-11 (3.85±2.3)x10-11 < 385 < 95340 23088FLASH < 1.38x10-10 < 1.46x10-12 < 1.00x10-12 < 385 < 91101 < 474734SRAM (1.13±0.2)x10-9 (7.03±3.7)x10-10 (1.03±0.6)x10-8 23.5 1263 23EPROM < 1.38x10-10 < 1.61x10-11 < 1.00x10-12 < 385 < 83043 < 474734Optolink < 1.38x10-10 < 1.43x10-11 < 1.00x10-12 < 385 < 93231 < 474734ASIC TSS < 2.68x10-10 < 9.46x10-12 < 33 < 32225ASIC BTI < 1.75x10-10 < 1.31x10-11 < 1.00x10-12 < 1.5 < 507 < 4436

First evaluation of neutron induced single event effects on the CMS barrel muon electronics

First evaluation of neutron induced single event effects on the CMS barrel muon electronics

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