The Platform for Advanced Characterisation - Grenoble (PAC-G) supports Industrial companies such as Airbus in the qualification of electronic components. For instance, PAC-G helps investigate the threat of the thermal neutrons induced SEU rate at ground level and at aircraft altitudes. The PAC-G offer an easy access to two high quality neutron facilities dedicated to neutron-induced Single Event Effects (SEE) tests. Fast and Thermal neutron tests are required to assess the reliability of highly integrated devices for critical applications; high energy neutrons can in addition help to prepare proton and heavy ion tests. The PAC-G allows you to have access, on the same site, to a broad spectrum of neutron energies from fast to thermal neutrons (14 MeV, 2.5 MeV and 25 meV).

1. I N S T I T U T D E R E C H E R C H E T E C H N O L O G I Q U E
Platform for Advanced Characterisation – Grenoble (PAC-G)
Cécile Weulersse (Airbus)
Sabrine Houssany, Nicolas Guibbaud, Jaime Segura-Ruiz, Jérôme Beaucour, Florent Miller and Maria-Magdalena Mazurek
Contribution of Thermal Neutrons to Soft Error Rate
Technique: Neutron radiation
hardness testing
Industrial case study

2. Page 2
1. Context
2. Environments
3. Radiation testing
4. Soft error rates & contributions
5. Conclusion
 At ground
 Aircraft
 Devices
 Facilities
 Cross-sections
What we offer
Why Neutron Radiation hardness Testing?
Neutron-induced single event effects (SEE) and
radiation hardness testing facilities of the PAC-G
offer you a homogeneous and adjustable neutron
flux, with a precise dosimetry and radioprotection to
ensure your safety during the tests.
Industrial Case Study
Complementary service:
2D & 3D imaging available to complement
your device characterisation. Imaging with neutrons
or synchrotron X-rays offer non-destructive
measurements of packaged devices.
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3. 1. Context
Page 3
S.-J. Wen et al, “B10 finding and correlation to thermal neutron soft error rate sensitivity for SRAMs in the sub-mciron technology”, IEEE 2010.
Y.-P. Fang and A. S. Oates, “Thermal neutron-induced soft errors in advanced memory and logic devices, IEE T-DMR 2014.
 Reintroduction of 10B in sub-65nm devices, due to the use of
B2H6 or BCl3 carrier gas in processing tungsten plug
 Recent increase in thermal neutron SER
 Thermal neutron energies <0.4 eV (peak at ~25meV)
 During 1990s, thermal neutrons were a significant source of soft errors (8X)
 IC manufacturers removed BPSG (or 10B in BPSG)
 Isotope Boron-10 has the largest cross-section
(> several order than others) and can fission into highly
ionizing secondaries (7Li recoil nucleus and alpha)

4. FinFET
TSMC**
*N. Seifert et al, “Soft Error Rate improvements in 14nm technology featuring 2nd generation 3D tri-gate transistors,” IEEE TNS, 2015.
**Y.-P. Fang and A. S. Oates, “Characterization of single bit and multiple cell soft error events in planar and FinFET SRAMs,” 2016.
***H. Zhang, Thermal neutron-induced soft-error rates for flip-flop designs in 16-nm bulk FinFET technology, IRPS 2017.
14nm FinFET SER , Intel* FF designs in 16nm FinFET***
Page 4
 Based on published data, from 10 to 30% contribution of thermal-neutron-induced SER
for FinFET devices at sea level (depending on 10B containment, critical charge values,
FF design…)
 Objectives: to investigate the threat of the thermal neutrons induced SEU rate
at ground level and at aircraft altitudes
10%
2-3%
8-20% 30%
1. Context

5.  Thermal neutron (nther) flux scales with latitude and
longitude in a manner similar to the high energy
neutron (nHEN) flux
 Dependent on surrounding environment  2X
variation outdoors
Page 5
*M. S. Gordon et al, “Measurement of the flux and energy spectrum of cosmic-ray induced neutrons on the ground,” IEEE TNS, 2004.
Measured neutron spectra*
Range of
thermal
neutrons
 Average flux at sea level: 6.5 nther/cm2/h (JESD89A)
 Moreover, the thermal flux is more quickly attenuated by building materials than is for the
high energy neutron flux, except in the case of a small amount of material.
2. Environment - At ground
 ratio nther / nHEN = 0.5

6. Neutron fluxes at various locations
in a Boeing-747 ( Dyer’s simulations)**
Page 6
*IEC 62396-5, “Process management for avionics – Atmospheric radiation effects – Part 5: Assessment of thermal neutron fluxes and single event effects in avionics systems”.
**Dyer et al, “Monte Carlo calculations of the influence on aircraft radiation environments of structures and Solar Particle Events,” IEEE TNS, 2001.
2. Environment - Aircraft
 IEC* proposes an average value between simulations and measurements:
 Conservative approach recommended by IEC* (in case of devices which may contain 10B
and have not been tested under nther):
 ratio nther / nHEN = 1.1 (inside aircraft)
 SER (nther+nHEN) = 7.6 x SER nHEN
 At aircraft altitude (12 km)
 But, high flux variations inside an aircraft due to the
presence of hydrogenous materials that thermalize the
nHEN flux. The thermal fraction may increase by 12X
(based on simulations).
 ratio nther / nHEN = 0.1 – 0. 25 (outside)

7. Page 7
 Confirm the drastic increase of thermal neutron flux
 Worst case ratio nther / nHEN = 2.8 (similar to Dyer’s simulations)
 Bounding of the thermal neutron enhancement
Ratio
Dyer (2001) MULASSIS
Cockpit
Worst case
Composite layers
Worst case
Middle of a 40cm
kerosene layer
< 𝟏𝒆𝑽
> 𝟏𝟎𝑴𝒆𝑽 𝒆𝒙𝒕𝒆𝒓𝒏𝒂𝒍
2.5 3.1 0.4
𝑬𝒒𝒖𝒊𝒗. 𝟐𝟓𝒎𝒆𝑽
> 𝟏𝟎𝑴𝒆𝑽 𝒆𝒙𝒕𝒆𝒓𝒏𝒂𝒍
/ 2.8 0.4
𝑬𝒒𝒖𝒊𝒗. 𝟐𝟓𝒎𝒆𝑽
> 𝟏𝟎𝑴𝒆𝑽 𝒊𝒏𝒕𝒆𝒓𝒏𝒂𝒍
1.75
(< 1 eV)
2.8 0.6
 Simple 1D simulations using MULASSIS (based on Geant4)
2. Environment - Aircraft

8. Page 8
 90 nm bulk CMOS - 4 Mbit SRAM – Cypress
 45 nm bulk CMOS - SRAM-based FPGA (CLB & BRAM) – Xilinx
 28 nm bulk CMOS - 4 core-µprocessor
 L1 data & instruction cache, L2 cache
 Stand-by configuration
 Protection mechanisms deactivated
3. Radiation testing - Devices

9.  63 MeV protons – UCL - Belgium
 Spallation neutron source – ANITA - TSL - Sweden
 Thermal neutrons – ILL-D50 - Grenoble - France
 Platform for Advanced Characterisation (PAC-G) instrument D50
 In our experiments
- Flux 1-3x107 neutrons/cm2/s
- Fluence up to 1x1011 neutrons/cm2
- Spot size of 100 mm2
Page 9
Maximum flux
around 13 meV
3. Radiation testing - Facilities

10.  The thermal sensitivity is high on the most advanced device.
SEU cross section
(cm2/bit)
Thermal neutrons
25.8 meV
(ILL-D50)
60 MeV protons
(UCL)
Atmospheric
neutrons
(TSL*)
Ratio
𝑻𝒉𝒆𝒓𝒎𝒂𝒍 𝒏𝒆𝒖𝒕𝒓𝒐𝒏𝒔
𝑯𝒊𝒈𝒉−𝒆𝒏𝒆𝒓𝒈𝒚 𝒏𝒆𝒖𝒕𝒓𝒐𝒏𝒔
90 nm SRAM 3.9x10-16 1.5 x10-14 / 0.03
45 nm CLB 2.7 x10-15 9.6 x10-15 9.8 x10-15** 0.3
45 nm BRAM 1.2 x10-14 2.2 x10-14 2.4 x10-14** 0.5
28nm µprocessor
(cache cells)
9.4 x10-15 6.8 x10-15 / 1.4
*Specified to be a low thermal neutron flux (<1% of the integrated flux)
**Based on neutrons > 10 MeV
Page 10
3. Radiation testing - Cross-sections

11. SER (FIT/Mbit)
at sea level
Thermal neutron contribution to neutron SER
Thermal
neutrons
High-energy
neutrons
At sea level
At 40,000 feet (12 km) inside
aircraft
90 nm SRAM 3 195* 1% 3%*
45 nm CLB 17 125 12% 24%
45 nm BRAM 75 290 21% 37%
28 nm µprocessor
(cache cells)
61
88*
136**
41%*
31%**
60%*
50%**
*Based on high-energy neutron flux >10 MeV for * and >1 MeV for **
Page 11
ratio of 1.1ratio of 0.5
 For 28 nm µprocessor, thermal neutron SER contributes to
 30-40% at sea level,
 50-60% in aircraft.
4. Soft error rates & contributions

12. • We verify the significant thermalisation of the neutron flux inside of airliners
• We confirm the sub-65nm thermal neutron sensitivity that should not be neglect.
• Based on 1.1 ratio, 50-60% contribution from thermal neutrons, could be higher if used
the ratio of 2,8 obtained in simulations
• IEC is still very conservative due to 2 sources of uncertainty regarding thermal neutron SER:
• Different sensitivity among devices,
• Very distinct radiation environments inside aircrafts:
 requires measurements at specific locations.
Page 12
5. Conclusion

13.  Kalvin Buckley and Jaime Segura of ILL - Institut Laue–Langevin
 Part of this study was funded by the DEMETER project (ENIAC/ECSEL JU
funding).
 Part of the beamtime on D50 was allocated by the IRT Nanoelec, supported by the
French State in the frame of the program “Investissements d’Avenir”, under the
reference ANR-10-AIRT-05.
 The industrial company
Link to the article: Weulersse C., Houssany S., Guibbaud N., Segura-Ruiz J., Beaucour J., Miller F., Mazurek M. - Contribution of thermal neutrons to soft error rate -
IEEE Transactions on Nuclear Science (2018). https://ieeexplore.ieee.org/abstract/document/8309271/
Page 13
Many thanks to:

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15. Platform for Advanced Characterisation-Grenoble (PAC-G)
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support@pac-grenoble.eu
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