Neutron-Induced Multiple-Bit Upset

1. Neutron-Induced Multiple-Bit Upset Alan D. Tipton1, Jonathan A. Pellish1, Patrick R. Fleming1, Ronald D. Schrimpf1,2, Robert A. Reed2, Robert A. Weller1,2, Marcus H. Mendenhall3 • Vanderbilt University, Department of Electrical Engineering and Computer Science, Nashville,TN • Vanderbilt University, Institute for Space and Defense Electronics, Nashville, TN • Vanderbilt University, W. M. Keck Free Electron Laser Center, Nashville, TN alan.tipton@vanderbilt.edu

2. Objective Model multiple-bit upset for 90 nm CMOS technology Calibrate to experimental neutron data Status Device description created Simulation is good agreement with experimental data Results overview MBU for neutron irradiation exhibits an angle dependence MBU for neutron irradiation exhibits frontside/backside dependence Future work Begin modeling of 65 nm technology Characterize impact of angular dependence on error rate Update alan.tipton@vanderbilt.edu

3. Outline • Background • Multiple-bit upset (MBU) • Neutron-induced MBU • Modeling • Monte-Carlo Radiative Energy Deposition (MRED) • Results • Single-bit • Multiple-bit • Conclusion • Future work alan.tipton@vanderbilt.edu

4. Outline • Background • Multiple-bit upset (MBU) • Neutron-induced MBU • Modeling • Monte-Carlo Radiative Energy Deposition (MRED) • Results • Single-bit • Multiple-bit • Conclusion • Future work alan.tipton@vanderbilt.edu

5. Multiple-bit upset increases with scaling • Reliability • Memory design • Testing • Multiple-bit upset (MBU) has been shown to increase for smaller technologies • Feature size small relative to radiation events Nucleon-Induced MBU Maiz et al. Tosaka et al. Kawakami et al. Hubert et al. from Seifert, et al., Intel.IRPS, 2006. alan.tipton@vanderbilt.edu

6. Neutrons induce nuclear reactions Incident Neutron • Neutron-induced nuclear reactions • Secondary products are ionizing particles that induce soft errors Nuclear Reaction Heavy-Ion Sensitive Nodes alan.tipton@vanderbilt.edu

7. Outline • Background • Multiple-bit upset (MBU) • Neutron-induced MBU • Modeling • Monte-Carlo Radiative Energy Deposition (MRED) • Results • Single-bit • Multiple-bit • Conclusion • Future work alan.tipton@vanderbilt.edu

8. Modeling methodology • 90 nm SRAM model • Sensitive node • Charge collection volume • Technology Computer Aided Design (TCAD) Model • Simulation - MRED (Monte-Carlo Radiative Energy Deposition) Code • Energy deposition cross section - ED(E) • Multiple node cross section - M(E) Sensitive Node Metallization Neutron Spectrum TCAD MRED ED(E) M(E) alan.tipton@vanderbilt.edu

9. MRED irradiated the TCAD device • TCAD structure created from layout and process information for a 90 nm SRAM • Device imported into MRED and simulated using Los Alamos Neutron Lab (LANL) WNR beam line neutron spectrum Copper lines Tungsten vias Single Cell Silicon bulk alan.tipton@vanderbilt.edu

10. LANL neutron beam • WNR beam spectrum imported into MRED • Fluence comparable to cosmic-ray neutron fluence B. E. Takala, “The ICE House: Neutron Testing Leads to More Reliable Electronics,” Los Alamos Science, 30 November 2006. alan.tipton@vanderbilt.edu

11. MRED simulates ionization and nuclear processes • MRED tracks energy deposition through all layers • Energy deposition at each sensitive node is calculated Sensitive Nodes Cell Array n+Si C+3n+2p++3  alan.tipton@vanderbilt.edu

12. Outline • Background • Multiple-bit upset (MBU) • Neutron-induced MBU • Modeling • Monte-Carlo Radiative Energy Deposition (MRED) • Results • Single-bit • Multiple-bit • Conclusion • Future work alan.tipton@vanderbilt.edu

13. Energy deposition cross section • ED(E)Cross section to deposit at least E in the sensitive volume • Relationship to SEU cross section SEU = ED (Qcrit) Charge Generated (fC) Energy Deposited (MeV) alan.tipton@vanderbilt.edu

14. 45° 0° 90° Single volume energy deposition • ED(E) is the corresponding cross section to deposit energy E or greater in a single sensitive volume • Exhibits a slight angle dependence • Shape of sensitive volume Charge Generated (fC) Energy Deposited (MeV) alan.tipton@vanderbilt.edu

15. Frontside vs backside • Backside shows increased cross section alan.tipton@vanderbilt.edu

16. 45° 0° 90° Multiple volume energy deposition • MBU  2 or more physically adjacent bits • M(E) is the corresponding cross section to deposit energy E or greater in multiple volumes • Exhibits a slight angle dependence • Cell spacing • Kinematics of reaction products Charge Generated (fC) Energy Deposited (MeV) alan.tipton@vanderbilt.edu

17. Multiple bit multiplicity • MBU characterized for bit multiplicity • Probability of an event decreases with increasing multiplicity #Events(multiplicity) fluence alan.tipton@vanderbilt.edu

18. The fraction of MBU exhibits an angle dependence • Fraction of MBU  (# of MBU events) (# of upset bits) • Fraction of MBU increases for neutrons at grazing angles • Testing and error calculations must account for angular dependencies alan.tipton@vanderbilt.edu

19. Conclusion • Multiple-bit upset is increasing for highly-scaled devices • Neutron irradiation has been modeled using MRED for a 90 nm CMOS technology • Cross section differs between frontside and backside irradiation • Fraction of MBU exhibits an angle dependence for neutron irradiation • Fraction increases at grazing angles • Neutron testing must account for these dependencies alan.tipton@vanderbilt.edu

20. Future work • Finish 90 nm work and publish findings • Model 90 nm experimental neutron data • Begin work on 65 nm technology • Create process and design based model • Proton and heavy-ion testing Fall/Winter 2007 • Examine impact of angular dependence on error rate alan.tipton@vanderbilt.edu