Hou Mingdong

Monte Carlo evaluation of spatial multiple-bit upset sensitivity to oblique incidence

We investigate the impact of heavy ion irradiation on a hypothetical static random access memory (SRAM) device. Influences of the irradiation angle, critical charge, drain-drain spacing, and dimension of device structure on the device sensitivity have been studied. These prediction and simulated results are interpreted with MUFPSA, a Monte Carlo code based on Geant4. The results show that the orientation of ion beams and device with different critical charge exert indispensable effects on multiple-bit upsets (MBUs), and that with the decrease in spacing distance between adjacent cells or the dimension of the cells, the device is more susceptible to single event effect, especially to MBUs at oblique incidence.

Raman spectrum study of graphite irradiated by swift heavy ions

Highly oriented pyrolytic graphites are irradiated with 40.5-MeV and 67.7-MeV 112Sn-ions in a wide range of fluences: 1 × 1011 ions/cm2−1 × 1014 ions/cm2. Raman spectra in the region between 1200 cm−1 and 3500 cm−1 show that the disorder induced by Sn-ions increases with ion fluence increasing. However, for the same fluence, the amount of disorder is greater for 40.5-MeV Sn-ions than that observed for 67.7-MeV Sn-ions, even though the latter has a slightly higher value for electronic energy loss. This is explained by the ion velocity effect. Importantly, ~ 3-cm−1 frequency shift toward lower wavenumber for the D band and ~ 6-cm−1 shift toward lower wavenumber for the 2D band are observed at a fluence of 1 × 1014 ions/cm2, which is consistent with the scenario of radiation-induced strain. The strain formation is interpreted in the context of inelastic thermal spike model, and the change of the 2D band shape at high ion fluence is explained by the accumulation of stacking faults of the graphene layers activated by radiation-induced strain around ion tracks. Moreover, the hexagonal structure around the ion tracks is observed by scanning tunneling microscopy, which confirms that the strains near the ion tracks locally cause electronic decoupling of neighboring graphene layers.

Impact of temperature on single event upset measurement by heavy ions in SRAM devices

The temperature dependence of single event upset (SEU) measurement both in commercial bulk and silicon on insulator (SOI) static random access memories (SRAMs) has been investigated by experiment in the Heavy Ion Research Facility in Lanzhou (HIRFL). For commercial bulk SRAM, the SEU cross section measured by 12C ions is very sensitive to the temperature. The temperature test of SEU in SOI SRAM was conducted by 209Bi and 12C ions, respectively, and the SEU cross sections display a remarkable growth with the elevated temperature for 12C ions but keep constant for 209Bi ions. The impact of temperature on SEU measurement was analyzed by Monte Carlo simulation. It is revealed that the SEU cross section is significantly affected by the temperature around the threshold linear energy transfer of SEU occurrence. As the SEU occurrence approaches saturation, the SEU cross section gradually exhibits less temperature dependency. Based on this result, the experimental data measured in HIRFL was analyzed, and then a reasonable method of predicting the on-orbit SEU rate was proposed.

Investigation of the dependence of fraction of damage phase in garnet irradiated by 1 GeV Ar ions on electronic energy loss and irradiation dose

Abstract The dependence of fraction of damage phase on electronic energy loss (Se) and irradiation dose (φt) in 1 GeV Ar ion irradiated garnet was investigated by means of sample-tilting X-ray diffraction (STD), Mossbauer spectroscopy and saturation magnetization measurement. It is found that the fraction of damage phase Fd is a linear function of the product of Se and ln(φt) under a certain irradiation dose. The slopes of the lines are decreasing with the increase of irradiation dose. This regular phenomenon suggests that the influence of irradiation dose on the creation of damage phase is increasing with the increase of irradiation dose in the electronic stopping power regime.

Modeling the applicability of linear energy transfer on single event upset occurrence

Geant4 tools were used to model the single event upset (SEU) of static random access memory cells induced by heavy ion irradiation. Simulated results obtained in two different regions of incident ion energies have been compared in order to observe the SEU occurrence by energetic ions and their effects on the radial ionization profile of deposited energy density. The disagreement of SEU cross sections of device response and radial distribution of deposited energy density have been observed in both low energy and high energy regions with equal linear energy transfer (LET) which correspond to the both sides of the Bragg peak. In the low energy region, SEUs induced by heavy ions are more dependent upon the incident ion species and radial distribution of deposited energy density, as compared with the high energy region. In addition, the velocity effect of the incident ion in silicon in the high energy region provides valuable feedback for gaining insight into the occurrence of SEU.

Double Ionization of Helium by Partially Stripped Oxygen Ions

New measurement of the ratio of the double ionization cross section to that of the single ionization of helium induced by 2.0-7.5 MeV partially stripped Oq+ ion (q = 1,2,3,4) is presented. Combining the measured data with the Olson-Schlachter scaling, the double ionization cross section of helium by partially stripped oxygen ion is obtained. It is found that the v/qeff dependence of the obtained double ionization cross section agrees well with the (v/qeff)-4 law.