Tianqi Liu

Monte Carlo predictions of proton SEE cross-sections from heavy ion test data *

The limits of previous methods prompt us to design a new approach(named PRESTAGE) to predict proton single event effect(SEE) cross-sections using heavy-ion test data.To more realistically simulate the SEE mechanisms,we adopt Geant4 and a location-dependent strategy to describe the physics processes and the sensitivity of the device.Cross-sections predicted by PRESTAGE for over twenty devices are compared with the measured data.Evidence shows that PRESTAGE can calculate not only single event upsets induced by indirect proton ionization,but also direct ionization effects and single event latch-ups.Most of the PRESTAGE calculated results agree with the experimental data within a factor of 2-3.The limits of previous methods prompt us to design a new approach(named PRESTAGE) to predict proton single event effect(SEE) cross-sections using heavy-ion test data.To more realistically simulate the SEE mechanisms,we adopt Geant4 and a location-dependent strategy to describe the physics processes and the sensitivity of the device.Cross-sections predicted by PRESTAGE for over twenty devices are compared with the measured data.Evidence shows that PRESTAGE can calculate not only single event upsets induced by indirect proton ionization,but also direct ionization effects and single event latch-ups.Most of the PRESTAGE calculated results agree with the experimental data within a factor of 2-3.

Investigation of Threshold Ion Range for Accurate Single Event Upset Measurements in Both SOI and Bulk Technologies

Experimental evidences are presented showing obvious differences in threshold ion range for silicon-on-insulator (SOI) and bulk static random access memories (SRAMs). Single event upset (SEU) cross sections of SOI SRAMs start to decline off the Weibull curve at ion ranges of 20.7 μm to 40.6 μm, depending on the ion species and also the thickness of metallization layers. Whereas for the bulk SRAMs, threshold range of Bismuth beam is unexpectedly larger than 60.4 μm. Underlying mechanisms are further revealed by Monte Carlo simulations and in-depth analysis. The relative location of ions Bragg peak to the sensitive region and also the position of ion LET in the σ-LET curve of test device turn out to be two key parameters in determining the threshold ion range which can explain the experimental results. Significant discrepancies are observed in the deposited energy spectrums in sensitive regions of bulk SRAM by ions at different sides of the Bragg peak, but with almost the same LET at die surface (all with ion range larger than 30 μm). Energy straggling of incident ions at the die surface is considered by Monte Carlo calculations. Implications for hardness assurance testing are also discussed. A formula is proposed for calculating the “worst case” threshold ion range.

Large energy-loss straggling of swift heavy ions in ultra-thin active silicon layers

Monte Carlo simulations reveal considerable straggling of energy loss by the same ions with the same energy in fully-depleted silicon-on-insulator (FDSOI) devices with ultra-thin sensitive silicon layers down to 2.5 nm. The absolute straggling of deposited energy decreases with decreasing thickness of the active silicon layer. While the relative straggling increases gradually with decreasing thickness of silicon films and exhibits a sharp rise as the thickness of the silicon film descends below a threshold value of 50 nm, with the dispersion of deposited energy ascending above ±10%. Ion species and energy dependence of the energy-loss straggling are also investigated. For a given beam, the dispersion of deposited energy results in large uncertainty on the actual linear energy transfer (LET) of incident ions, and thus single event effect (SEE) responses, which pose great challenges for traditional error rate prediction methods.

Supply voltage dependence of single event upset sensitivity in diverse SRAM devices

Experimental evidences are presented showing the variety of supply voltage dependence of single event upset (SEU) sensitivity in diverse SRAM devices. Devices under test (DUTs) from Alliance Memory, ISSI and IDT companies with different technologies were irradiated by several kinds of heavy ions at Heavy ion Research Facility in Lanzhou (HIRFL) cyclotrons. For the Alliance 256 kb SRAM device, SEU cross section increases by more than one order of magnitude as supply voltage decreases from 5.0 V to 3.0 V. SEU data of Alliance 64 kb SRAM also exhibits significant supply voltage dependence. The reduction of critical charge is the predominant factor worsening the device performance. While for the Alliance 8 Mb, ISSI 2 Mb and IDT 256 kb SRAM devices, no obvious trend was observed, which is attributed to the negligible net contribution of competing mechanisms. Those results suggest that the worst-case supply voltage for evaluation of SEU sensitivity depends on the test devices.

Influence of deposited energy in sensitive volume on temperature dependence of SEU sensitivity in SRAM devices

The effects of temperature on the single-event upset (SEU) response of commercial and radiation-hardened SRAMs are investigated by experiment. The results showed that the SEU sensitivity relied on the temperature during the testing. However, it was also observed the amplitude of energy deposition of ions in sensitive volume of SRAM devices is able to affect the SEU sensitivity. When the deposited energy in sensitive volume is far larger than the critical value of inducing a SEU occurrence, the SEU sensitivity both in Bulk and SOI technologies displays a less temperature dependency. This result is attributed to the impact of energy deposition on the ion-induced transient pulse shape. The deposited energy in sensitive volume by different ions was estimated by Monte Carlo simulation and the role of energy deposition in transient pulse shape was discussed. The conclusion of detailed analysis is agreement with the results obtained in experiments.