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The NSEU Sensitivity of Static Latch Based FPGAs and Flash Storage CPLDs. Joseph Fabula Jason Moore Austin Lesea Saar Drimer. This work has benefited from the use of the Los Alamos Neutron Science Center at the Los Alamos National Laboratory. This facility is funded by the

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the nseu sensitivity of static latch based fpgas and flash storage cplds

The NSEU Sensitivity of Static Latch Based FPGAs and Flash Storage CPLDs

Joseph Fabula

Jason Moore

Austin Lesea

Saar Drimer

This work has benefited from the use of the Los Alamos Neutron Science Center

at the Los Alamos National Laboratory. This facility is funded by the

US Department of Energy under Contract W-7405-ENG-36.

MAPLD2004

objectives of this study
Objectives of this Study
  • Measure the neutron single event upset cross section of various current CMOS processes

- Utilizing accelerated neutron beams to:

      • Test the upset potential of the static latches in FPGAs and CPLDs
      • Test the upset potential of the flash storage cells in CPLDs

- Utilizing applications atmospheric based tests to

      • Test the upset potential of the static latches in FPGAs
      • Calibrate the results of accelerated beam testing
  • Compare findings with other independent researchers

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test facilities used
Test Facilities Used
  • Accelerated Testing
    • Los Alamos Neutron Science Center
    • Hess spectrum accelerated neutron beam
    • Energy levels 1.5 to 600 MeV
  • Applications Testing (natural flux)
    • Xilinx San Jose – sea level
    • Xilinx Albuquerque – 5,200 feet
    • White Mountain Research Center – 12,000 feet
    • Mauna Kea Observatory – 13,500 feet

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devices tested
Devices Tested
  • Virtex II FPGA
    • XC2V6000
    • 150 nM CMOS Static-Latch based technology
  • Virtex II-Pro FPGA
    • XC2VP4 and XC2VP7
    • 130 nM CMOS Static-Latch based technology
  • Spartan 3 FPGA
    • XC3S100
    • 90 nM CMOS Static-Latch based technology
  • XPLA3 (CoolRunner I) CPLD
    • XCR3256XL
    • 350 nM CMOS FLASH based technology
  • CoolRunner II CPLD
    • XC2C256
    • 150 nM CMOS FLASH based technology

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fpga test fixtures
FPGA Test Fixtures

Virtex II

Virtex II-Pro

Spartan 3

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nseu 101
NSEU 101
  • Neutron Single Event Upsets
  • Where do Neutrons come from?

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nseu 1018
NSEU 101
  • How does the Neutron density (flux) vary?
    • Major factors are altitude and latitude

A. Taber and E. Normand, “Single Event Upset in Avionics”, IEEE Trans. Nucl. Sci. NS-40, 120, 1993

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nseu 1019
NSEU 101
  • How do neutrons effect Integrated Circuits?
  • Alpha particles have a high range and a low Linear Energy Transfer (LET). However, they are generated in the silicon, and can be in the vicinity of the sensitive areas of the IC.

alpha+

VSS

VDD

0

1

V=IR

I

p+

p+

n+

n+

R

+

-

+

-

n-

+

-

+

-

Sensitive Area

V

p-

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nseu 10110

ON

OFF

NSEU 101
  • Neutron Effects – from an digital designer’s point of view

OFF

ON

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how we tested nseu sensitivity
How we tested NSEU Sensitivity
  • Accelerated Testing vs Atmospheric Testing
    • Accelerated
      • Testing with Spallation Neutron sources
        • LANSCE spallation spectrum matches atmospheric neutrons
        • LANSCE source gives ~ 105 to106 acceleration
    • Atmospheric
      • We can use the natural radiation environment around us
      • Due to low rates, a very large number of devices are required
      • Testing times can be very long (many month to years)
        • Acceleration (up to 10X) is achievable by testing at altitude(s)
      • However, this test is the ultimate correlation for all accelerated tests
    • references
      • JEDEC Standard (JESD89) “Measurement and Reporting of Alpha Particles and Terrestrial Cosmic Ray- Induced Soft Errors in Semiconductor Devices”
      • IEC TC107-AR-8 (draft currently) Avionics Processes

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lansce
LANSCE
  • Los Alamos Neutron Science Center

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cpld flash accelerated data
CPLD (Flash) Accelerated Data

XCR3256XL (350 nM)

XC2C256 (150 nM)

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summary accelerated test results
Summary Accelerated Test Results

Static Latch Upset Results

Flash Storage Upset Results

This work has benefited from the use of the Los Alamos Neutron Science Center at the Los Alamos National Laboratory. This facility is funded by the US Department of Energy under

Contract W-7405-ENG-36.

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nseu 101 again

Effects of Terrestrial Cosmic Rays, J.F. Zeigler,

United States Air Force Academy.

http://www.srim.org/SER/SERTrends.htm

NSEU 101 (again)
  • How does the Neutron density (flux) vary?
    • A. Taber and E. Normand, “Single Event Upset in Avionics”, IEEE Trans. Nucl. Sci. NS-40, 120, 1993
    • E. Normand and T.J. Baker “Altitude and Latitude Variations in Avionics SEU and Atmospheric Neutron Flux”, IEEE Trans. Nucl. Sci. 40, 1484, 1993
    • J. Olsen, et al., “Neutron-Induced Single Event Upsets in Static RAMs observed at 10Km Flight Altitude”, IEEE Trans. Nucl. Sci. 40, 74, 1993
    • J. Hewitt, et al., “Ames Collaborative Sutdy of Cosmic Ray Neutrons: Mid-Latitude Flights”, Health Physics, 34, 375, 1978
    • O.C. Allkofer and P.K. Grieder, Physics Data: Cosmic Rays on Earth, Fachinformationszentrum Energie, Physik, Mathematik GmbH, Karlsruhe, 1984
    • C.S. Dyer, et. al., “Measurements of the SEU Environment in the Upper Atmosphere”, IEEE Trans. Nucl. Sci. NS-36, 2275, 1989
    • C.S. Dyer, et. al., “Measurements of Solar Flare Enhancements to the Single Event Upset Environment in the Upper Atmosphere”, IEEE Trans. Nucl. Sci., NS-37, 1929, 1990

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rosetta nseu testing
Rosetta NSEU Testing
  • What is Rosetta?
    • Atmospheric Test started in 7/2002
    • Rosetta stone provided correlation between languages/scripts. Rosetta experiment provides correlation to LANSCE test results
    • System of 100 2V6000s
      • Runs 24/7/365 – Internet Monitored
      • Read back and error logging 12 times a day
      • Each test contains >1.9 Gbits of config latches
    • Test operating at 4 altitudes
      • Sea Level – San Jose
      • 5,200 feet – Albuquerque
      • 12,000 feet – White Mountain Research Center
      • 13,500 feet – Mauna Kea Observatory
    • Additional testing started for VII-Pro (130 nM) and for Spartan-III (90 nM)

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slide20

Rosetta Board

100 XC2V6000

1.9 Gbits

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rosetta test results
Rosetta Test Results
  • Data shown is accurate as of 5/6/04
    • 3.18e6 total device hours
    • Rosetta/LANSCE correlation factor is 1.51
      • LANSCE is predicting worse results by a factor of 1.51

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logic failures vs seus seupi
Logic Failures vs SEUs(SEUPI)
  • Is there a difference? YES
    • An SEU does not necessarily cause a functional failure
      • Many Configuration Bits are not used
        • 90% of the FPGA is routing!
    • Example
      • Proton test of a V300
      • Two methods to evaluate:
      • Method 1:
        • Total Upsets / # 1 bit failures
        • 437/8 = 54.6
      • Method 2:
        • Total Upsets / # failures
        • 437 / 69 = 6.3
    • Conservatively, we use a factor of 10 (SEUPI factor)

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logic failures vs seus seupi23
Logic Failures vs SEUs(SEUPI)
  • Independent Confirmation
    • Work by BYU and LANL indicated that the logic upset multiplier can be as high as 25 - 100 for specific designs in a V1000
    • By logical extension, the larger the FPGA the higher the multiplier for any given logic implementation
    • BYU and LANL have developed a bit flip logic impact simulator for the V1000 that has been verified in Proton testing
    • Xilinx has extensive data on PIP utilization from the many EasyPath applications that we are supporting
    • Xilinx laboratories are developing software algorithms (SEUPI) to identify “critical” bits which may affect user logic
    • SEUPI analysis of specific customer applications has shown SEUPI factors from 10 to 80 with an mean of 42

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comparison with independent data
Comparison with Independent Data
  • Actel commissioned IROC to independently test various FPGAs for NSEU Effects
  • IROC tested Xilinx, Altera and Actel products
    • Test design was “n” 16x16 bit multipliers whose values were muxed to a common output. Mux line was 7 bits -> up to 128 multipliers supported
    • Pure combinatorial logic – no FFs!
      • “Focus was on configuration memory only”

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iroc analysis
IROC Analysis
  • Results
    • IROC unquivocally stated that Xilinx FPGAs do not exhibit NSEL (Neutron Single Event Latch), a potentially destructive effect seen in some recent ASICs and RAMs
    • IROC confirmed the existence of the SEUPI factor in Xilinx FPGAs – even though it was only in one design:
        • VII (14MeV test) = 6.67
        • VII (LANSCE) = 10
        • S3 (LANSCE) = 4.54
    • Reverse engineering of the IROC data confirmed Xilinx contention that the per-bit cross-section was improved by Xilinx in their 90nm technology vs their 150nm technology (see next slide)

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iroc analysis26
IROC Analysis
  • 150nm (V-II) vs 90nm (S-3)
    • Using IROCs data for the Number of SEUs and the Fluence (n/cm2) we can calculate the per-bit cross-section difference between technologies
  • Conclusion: S-3 (90 nM) cross-section is smaller!

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conclusions
Conclusions
  • LANSCE data provides good correlation with atmospheric testing when the correct energy model(s) are used
  • ROSETTA data indicates clear support for using the >10.0 MeV model for current process technology
  • Independent IROC data confirmed three of Xilinx key assertions, namely:
    • The sky is not falling as technology continues to shrink below 220 nM (Moore’s law still lives and our designers are smart)
    • Xilinx logic upset rates are greatly improved due to the documented SEUPI factor
    • Xilinx FPGAs do not exhibit Neutron Single Event Latch-up
  • The neutron cross sections have been stabilized as technology shrinks (compensating a sensitivity increase by a probability decrease function)
  • Xilinx designers are increasing the robustness of our state of the art static latches to the effects of atmospheric neutron flux
  • Current generations of Flash storage cells continue to be immune to neutron upset

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virtex ii mtbf calculations
Virtex II MTBF Calculations
  • Failure defined as incorrect operation of the FPGA
    • Time to Configuration Upset (Config Upset) =

1 / (# bits * Neutron Cross-Section (LANSCE) * Neutron Flux)

    • Config Upset Rosetta = Rosetta factor applied
    • Logic Upset = SEUPI factor applied
      • Ignoring the SEUPI factor is inaccurate! – you don’t use every configuration memory cell in an FPGA.

Calculations are at sea level = 14.4n-cm2/hr flux; Rosetta Factor = 1.5, SEUPI Factor = 10

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effects of altitude
Effects of Altitude
  • Virtex-II MTBF Calculations at 40K feet
    • Assumptions:
      • Neutron Flux of 3060 n-cm2/hr@ 40,000 feet
      • Rosetta Factor of 1.5
      • SEUPI Factor of 10

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mtbf calculations
MTBF Calculations
  • Failure defined as incorrect operation of the FPGA
    • Time to Configuration Upset (Config Upset) =

1 / (# bits * Neutron Cross-Section (LANSCE) * Neutron Flux)

    • Config Upset Rosetta = Rosetta factor applied
    • Logic Upset = SEUPI factor applied
      • Ignoring the SEUPI factor is inaccurate! – you don’t use every configuration memory cell in an FPGA.

Calculations are at sea level = 14.4n-cm2/hr flux; Rosetta Factor = 1.5, SEUPI Factor = 10

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effects of altitude32
Effects of Altitude
  • Spartan 3 MTBF Calculations at altitude
    • Assumptions:
      • Neutron Flux of 3060 n-cm2/hr @ 40,000 feet
      • Rosetta Factor of 1.5
      • SEUPI Factor of 10

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