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Monte-Carlo radiation transport code is coupled with SPICE circuit level simulation to identify regions of single event upset vulnerability in an SEU hardened flip-flop, as well as predict single event upset cross sections and on-orbit soft error rates under static and dynamic operating conditions. Index Terms--Geant4, MRED, rate prediction, SEU, SPICE.

As integrated circuits become smaller and more complex, it has become increasingly difficult to simulate their responses to radiation. The distance and time scales of relevance extend over orders of magnitude, requiring a multi-scale, hierarchical simulation approach. This paper demonstrates the use of multi-scale simulations to examine two radiation-related problems: enhanced low-dose-rate sensitivity (ELDRS) in bipolar transistors and single-event effects (SEE) in CMOS integrated circuits. Examples are included that demonstrate how information can be passed from simulation tools operating at one level of abstraction to those operating at higher levels, while maintaining accuracy and gaining insight. Index Terms--Integrated circuits, multi-scale simulation, radiation, single-event effects, total ionizing dose.

Heavy ion cross section data taken from a hardened-by-design circuit are presented which deviate from the traditional single sensitive volume or classical rectangular parallelepiped model of single event upset. TCAD and SPICE analysis demonstrate a SEU mechanism dominated by multiple node charge collection. Monte Carlo simulation is used to model the response and predict an on-orbit error rate. Index Terms--Geant4, MRED, rate prediction, SEU.

This work draws on experimental and simulation results to derive a generalized SEU response model for bulk SiGe HBTs. The model was validated using published heavy ion and new proton data gathered from high-speed HBT digital logic integrated circuits fabricated in the IBM 5AM SiGe BiCMOS process. Calibrating to heavy ion data was sufficient to reproduce the proton data without further adjustment. The validated model is used to calculate upset event rates for low-earth and geosynchronous orbits under typical conditions. Index Terms--Deep trench isolation, Geant4, geosynchronous orbit, low-earth orbit, rate prediction, silicon-germanium HBT, single-event upset.

The RADSAFE simulation framework is described and applied to model SEU in a 0.25 [micro]m CMOS 4 Mbit SRAM. For this circuit, the RADSAFE approach produces trends similar to those expected from classical rectangular parallelepiped models, but more closely represents the physical mechanisms responsible for SEU in the SRAM circuit. Index Terms--GEANT4, heavy-ion, RADSAFE, SEU, TCAD.

Three-dimensional TCAD models are used in mixed-mode simulations to analyze the effectiveness of well contacts at mitigating parasitic PNP bipolar conduction due to a direct hit ion strike. 130 nm and 90 nm technology are simulated. Results show careful well contact design can improve mitigation. However, well contact effectiveness is seen to decrease from the 130 nm to the 90 nm simulations. Index Terms--Guard contacts, singe-event effects, technology computer-aided design (TCAD) modeling, parasitic bipolar conduction.

Simulation results for the full galactic cosmic ray environment demonstrate that current accelerator-based test methods using linear energy transfer as the engineering metric to characterize single event effects are not sufficient to capture the nuclear reaction portion of the response. Nuclear reactions contribute significantly to on-orbit single-event rates as compared to those from direct ionization induced by the primary ions. Based on these results, the applicability of current single-event test methods to predicting on-orbit event rates is examined and improved procedures are identified. For devices with critical charge values that are in the range where nuclear reactions may play a role in determining the event rate, ground-based tests should include irradiation with several types of ions of different energies to identify the contribution of these reactions to the measured SEE cross section. Index Terms--Nuclear reactions, single event effect rate, single event effects.

A novel mechanism for upset is seen in a commercially available 0.25 [micro]m 10-T SEE hardened SRAM cell. Unlike traditional multiple node charge collection in which diffusions near a single event strike collect the deposited carriers, this new mechanism involves direct drift-diffusion collection at an NFET transistor in conjunction with parasitic bipolar conduction in nearby PFET transistors. The charge collection with the parasitic bipolar conduction compromise the SEE hardened design, thus causing upsets. The mechanism was identified using laser testing and three-dimensional TCAD simulations. Index Terms--Charge sharing, parasitic bipolar, single event upset.

Simulations show that neglecting ion-ion interaction processes (both particles having Z > 1) results in an underestimation of the total on-orbit single event upset error rate by more than two orders of magnitude for certain technologies. The inclusion of ion-ion nuclear reactions leads to dramatically different SEU error rates for CMOS devices containing high Z materials compared with direct ionization by the primary ion alone. Device geometry and material composition have a dramatic effect on charge deposition in small sensitive volumes for the spectrum of ion energies found in space, compared with the limited range of energies typical of ground tests. Index Terms--Charge deposition, Geant4, heavy ion, MRED, single-event upset (SEU), SEU error rate.

Heavy ion irradiation was simulated using a Geant4 based Monte-Carlo transport code. Electronic and nuclear physics were used to generate statistical profiles of charge deposition in the sensitive volume of an SEU hardened SRAM. Simulation results show that materials external to the sensitive volume can affect the experimentally measured cross-section curve. Index Terms--Cross section, Geant4, MRED, single event upset.