COTS for the LHC radiation environment: the rules of the game Federico Faccio CERN Federico Faccio - CERN

Outline Introduction Summary of radiation effects Risk management Dealing with the radiation hazard: fundamental steps Conclusion Federico Faccio - CERN

Why talking about COTS? COTS = Commercial Off The Shelf No effort made to improve, assure or even test the radiation tolerance Poor or no traceability of origin (what REALLY is inside the package??) Cheaper and better performance, sometimes there is no alternative to their use The cost of using COTS is higher than the bare part cost: testing and logistic are expensive! Federico Faccio - CERN

Summary of radiation effects Permanent SEEs Total Ionizing Dose (TID) Potentially all components SEL CMOS technologies SEB Power MOSFETs, BJT and diodes SEGR Cumulative effects Power MOSFETs Displacement damage Bipolar technologies Optocouplers Optical sources Optical detectors (photodiodes) Single Event Effects (SEE) Transient SEEs Combinational logic Operational amplifiers Static SEEs SEU, SEFI Digital ICs Federico Faccio - CERN

Risk management at system level (top-down) Use of COTS => risk avoidance Mission: LHC and experiments running Which failure tolerable? How often? = Where? f (system) Risk management at system level (top-down) Do we have enough experience and competence in the same organizational unit? (learning process is time and resources consuming!) Federico Faccio - CERN

Dealing with the radiation hazard Get a good knowledge of the environment Define the requirements for the components Understand the effects Identify the candidate components Test the candidate components Engineer the system Federico Faccio - CERN

The radiation environment Knowledge in “meaningful” terms: TID Displacement damage SEEs Total Dose [krad, Gy] 1 MeV equivalent neutron fluence (n/cm2) Fluence and energy distribution of main particles (p/cm2)  20MeV  (E,all hadrons)dE or at least Get the most precise estimate of the environment Taylor the safety factor Safety factor = cost Federico Faccio - CERN

Effects of the environment CMOS technologies Memories (SRAM, DRAM, Flash, EEPROM) FPGAs Microprocessors and DSPs Bipolar technologies Power devices Optocouplers Federico Faccio - CERN

CMOS technologies (1) Displacement damage TID Sensitive with dose rate effects Variable failure levels SEL Not very likely in LHC A few known sensitive components: K5 mp from AMD, SRAMs, ADCs, DSPs, FPGAs SEGR, SB Very unlikely Federico Faccio - CERN

CMOS technologies (2) SEU: memories SRAMs Sensitive with low threshold Sometimes MBU Stuck bits only with high LET DRAMs Sensitive with low threshold Situation improved with decreased cell area and better signal over noise sp comparable to SRAMs SEFI possible (low s) Flash Memories Errors in the complex control circuitry with different consequences Higher threshold than SRAMs-DRAMs Much lower sp (100-1000 times) EEPROMs Write mode more sensitive than read Higher threshold than SRAMs-DRAMs SEFI possible Federico Faccio - CERN

CMOS technologies (3) SEU: FPGAs SRAM-based Loss of configuration: consequences? Low threshold: likely in LHC Requires reprogramming Antifuse-based ONO antifuses sensitive to destructive event with high threshold A-Si antifuses more robust FF and combinatorial logic gates: Sensitive in both technologies (FF implementation with  sensitivity) TMR can be integrated in antifuse-based In new Virtex series, TMR can be safely integrated SEFI: Can happen in both technologies (SEU in JTAG circuitry) with low s Solutions proposed by both Actel and Xilinx Radiation tolerant products available (on epi substrate) Variability in radiation performance (esp. TID and SEL) Documented mitigation techniques exist for both Actel and Xilinx Federico Faccio - CERN

CMOS technologies (4) SEU effects strongly application-dependent SEU: microprocessors and DSPs SEU effects strongly application-dependent Testing has to be performed running a representative program SEU consequences: very variable (no effect, calculation error, code stopped, …) Most devices are sensitive in a proton environment, hence in LHC Federico Faccio - CERN

Simultaneous effects: Bipolar technologies Simultaneous effects: they add up TID Leakage paths and b degradation Sensitive with dose rate effects (ELDR) Variable failure levels Displacement damage b degradation PNP are affected from 3•1011 p/cm2 (50MeV) NPN are affected from 3•1012 p/cm2 (50MeV) Voltage regulators, comparators, op amps SEL SET At the output of comparators Rail-to-rail signal Federico Faccio - CERN

Power devices Sensitive to TID and displacement damage Power MOSFETs, bipolar and diodes SEB Sensitive in hadron environment (also 14MeV n) De-rating often required (of variable %) P-channel MOSFETs are much less sensitive Power MOSFETs and IGBTs SEGR Very rare in an hadron environment Dependent on Vgs (sensitive for Vgs < -20V) Dependent on gate oxide thickness Most data refer to HI: de-rate as indicated for experiments run with LET of 26 MeVcm2mg-1 Federico Faccio - CERN

Optocouplers Sensitive to TID and displacement damage Sensitive to SET CTR decreases after 1-5•1010 p/cm2 (4N49 Micropac and Optek, P2824 Hamamatsu) Degradation of LED and ptotodetector Other devices, with different LED and coupling LED/phototransistor, have good resistance (6N140, 6N134, 6N139 from HP) Sensitive to SET Sensitivity increases with speed Sensitive to direct ionization from p+ (angular effect) Might induce transient out dropout in DC-DC conv. Federico Faccio - CERN

The radiation requirements (theory) Know the system where the component operates (top-down) Cumulative effects: Simulation Test procedures COTS variability Estimated level • SF Destructive SEEs: No destructive SEE Transients and SEU Acceptable rate for the system Federico Faccio - CERN

The radiation requirements (headaches) Cumulative effects: Which SF???? Simulation accurate Test procedures correct COTS variability systematic Taylor the SF Destructive SEEs: Example Envir. = 1011 h/cm2 1000 components s = 10-11 cm2? Which limit on cross-section? Which limit on HI LETth? Transients and SEU Estimate the error rate in the real environment Evaluate the system-level impact of each error Federico Faccio - CERN

The candidate components Search for radiation data Databases on web (often obsolete): JPL compendia, GSFC, DTRA, SPUR, …. NSREC “Workshop records” December issue of Trans. Nucl. Science ESA/ESTEC final presentation day (soon database?) For FPGA, look in the manufacturer’s home page for fresh data How to interpret SEE data? Rough guidelines based on “Computational method to estimate SEU rates in an accelerator environment” (NIM, August 00) Federico Faccio - CERN

How to interpret SEE data (1) You have data for mono-energetic p or n beams (60-200MeV)! SEErate = sp/n • flux (all hadrons above 20MeV) Example Xilinx XC4010XL: s100MeV n = 4.4•10-15 cm2/bit Estimated flux = 2•103 cm-2s-1 (=1011 cm-2) => SEErate = 8.8•10-12 errors/(bit s) Each chip contains about 283k configuration bits => SEErate chip = 2.5•10-6 s-1 For each 110 FPGA, one looses its configuration each hour! Federico Faccio - CERN

How to interpret SEE data (2) You only have Heavy Ion data... … but you have the Weibull fit parameters! 20 40 60 80 100 120 Deposited energy cross section (cm 2 ) Weibull curve Probability curves from the simulation of the environment 1 3 Federico Faccio - CERN

How to interpret SEE data (3) You only have Heavy Ion data... … and you do not have the Weibull fit parameters... You can just have a feeling: LETth < 5 MeVcm2mg-1 => quite sensitive LETth > 15 MeVcm2mg-1 => not sensitive Federico Faccio - CERN

Testing the candidate parts Never use data from a database as a source for qualification, only to identify candidate parts! Radiation source Irradiation procedure Board-level testing and hybrid devices Federico Faccio - CERN

- rare SEU under-estimate (CMS: HCAL, Muons, Cavern) Radiation source 60Co TID Low energy neutrons (nuclear reactor) Displacement damage SEEs Mono-energetic hadron beams (60-200 MeV p) With 60 MeV: - rare SEU under-estimate - Is the energy enough for SEB/SEGR? Global test plan (CMS: HCAL, Muons, Cavern) What about thermal neutrons? (they have not been taken into account for the experiments) Federico Faccio - CERN

Preferential access conditions for high-E proton beams Preferential agreement with 2 facilities established since several years through the RD49/COTS project : CRC (Cyclotron Research Centre) in UCL, Louvain-la-Neuve (Be) > protons (60MeV), Heavy Ions, neutrons (low intensity) - PSI (Paul Scherrer Institute) in Villigen (Ch) > protons (250MeV) Federico Faccio - CERN

Irradiation procedure (1) Prompt + Latent charge buildup Irradiation + Annealing Test methods give worst case picture CMOS TID ELDR effect JPL advice: Bipolar TIDspec < 30krad 50 & 0.005 rad/s test at room T compare if failure in any condition (@TID<1.5TIDspec) => do not use! TIDspec > 30krad test up to 30krad in 3 conditions: 50 & 0.005 rad/s at room T, 1rad/s at 90oC compare if comparable => use 90oC test BUT take an additional SF = 2 on TIDspec Federico Faccio - CERN

Irradiation procedure (2) Displacement damage - room T, all grounded - measurement of s - representative conditions - needs a dedicated setup - careful to SEFI - with h-beams => in air and packaged E (MeV) s SEU, SET Vds sSEB rated Vds - measurement of s - protect the component! - needs a dedicated setup - for SEB & SEGR look for derating conditions SEL, SEB, SEGR Federico Faccio - CERN

Board-level testing & hybrids Less infos on actual safety margins It can be difficult to trace back the origin of problems Use for go/no go tests only! Can give useful infos on system response (esp. SEU) Hybrid devices Difficult to know what is in the hybrid (proprietary designs, no infos from the manufacturer) Examples on DC-DC power converters (JPL, NASA) Federico Faccio - CERN

Qualify the components Engineer the system Is the tolerance sufficient? Qualify the components to be used Test the candidate components Yes Qualification OK? No Is there an alternative component? No Yes Yes Use the components No Reduce requirements: - refine the environment knowledge - use mitigation techniques (for SEU) - foresee replacement if possible - modify the system Federico Faccio - CERN

Summary Radiation effects Risk management risk avoidance impossible with COTS! more efficiently applied at system level! Steps to deal with the radiation hazard know the environment understand the effects define the requirements identify the candidate components test engineer the system Federico Faccio - CERN

Big challenge for all LHC teams! Conclusion Main rule of the game: System Environment Radiation hazard To merge knowledge on Big challenge for all LHC teams! Federico Faccio - CERN

Reference material This presentation, made at the 6th Workshop on Electronics for the LHC Experiments (Cracow, September 2000), has been followed by a full paper with an extensive set of references (79 papers). The paper can be found as: - F.Faccio, “COTS for the LHC radiation environment: the rules of the game”, proceedings of the 6th Workshop on Electronics for the LHC Experiments, CERN 2000-010, CERN/LHCC/2000-041, 25 October 2000, page 50 Federico Faccio - CERN