**Acknowledgements**

**Figure 20.** Comparison of the SER component values obtained by TIARA-G4 NVM simulation and from exposition to

Another interesting point of comparison comes from the ratio of the numbers of upset cells to the numbers of cells for which VT have shifted but not enough to cross the limit of 5.7 V delimiting the two logical states. Although statistics are low for data of Fig. 18, the ratio (number of cells B/number of cells A) can be roughly evaluated to 50%. From simulation results with a much larger statistics, this ratio is 40.7%, which is clearly in the same order of magnitude. Beyond the fact that this point consolidates the comparison between experiment and simula‐ tion, this result shows that the number of impacted cells with a final VT ranging between the sense voltage value and the edge of the initial Gaussian distribution is approximately two times

In conclusion, we developed in this work a numerical simulation code (TIARA-G4 NVM) capable of computing the soft-error rate of floating-gate flash memories induced by the two main natural radiation components at ground-level: the atmospheric high-energy neutrons and the alpha-particles emitted from ultra-traces of radioactive contaminants in circuit materials. Based on Geant4 geometry classes, elements and materials, the code is able to reproduce the circuit geometry from silicon substrate to back-end-of-line levels with fidelity. In complement to geometrical aspects, TIARA-G4 NVM also integrates a new module describing the charge loss from floating gates as a function of the properties (LET) of the incident ionizing particles. Using this code, we performed extensive Monte Carlo simulations

memory architecture designed by STMicroelectronics. Values of the SER for atmospheric neutrons and alpha-particle emitters have been computed and expressed, respectively, at sealevel (New-York City) and for a concentration of 238U in the circuit materials separately

cells) related to a 90 nm NOR floating-gate flash

natural radiation in Rousset and on ASTEP.

388 Computational and Numerical Simulations

**6. Conclusion**

larger than the number of cells verifying the upset criterion.

on large arrays of memory cells (up to 105

The authors would like to acknowledge G. Just, A. Regnier and J.L. Ogier from STMicroelec‐ tronics (Reliability and Electrical Characterization Laboratory, Rousset Plant, France) for their contribution to the electrical characterization of the flash memory wafers and Sébastien Sauze (ASTEP platform) for his technical and support. They also sincerely acknowledge their past post-doc students Sébastien Martinie (now at CEA-LETI, Grenoble) and Sébastien Serre (now at TRAD, Toulouse) for their different contributions to this work. The logistical support of the Institute for Radio astronomy at Millimeter Wavelengths (IRAM) is finally gratefully acknowl‐ edged.
