A.M. Chugg

Single particle dark current spikes induced in CCDs by high energy neutrons

This paper presents an analysis of dark signal nonuniformity induced in a charge coupled device (CCD) by 90 MeV neutrons. Random telegraph signal switching between multiple levels was seen for some dark current spikes. The probability distribution of the dark current spikes is shown to be pseudo-exponential and the distribution remains exponential during annealing, but with an increasing decay constant. Similar dark current spikes were also observed to be generated in an APS device exposed to high energy neutrons at the WNR facility.

Comparison between SRAM SEE cross-sections from ion beam testing with those obtained using a new picosecond pulsed laser facility

A new pulsed laser facility has been developed to extend laser testing techniques to generate upset cross-section curves. The objective has been to establish an economical laser-based bulk screening capability for SEE susceptibility.

Broadening of the variance of the number of upsets in a read-cycle by MBUs

This work presents A technique for establishing the proportion of multiple bit upsets (MBUs) in single event effects (SEE) test results based on a more sophisticated analysis of existing trial data and not requiring a memory map. The technique is demonstrated and verified with reference to recent neutron SEE results in charge coupled devices, since multi-pixel events are plentiful in these data and the mean number of pixels per event can be independently established through image analysis. This technique is most easily applied when the fraction of MBUs is relatively large, so it is predicted to become increasingly important in the future, as feature size reduction is expected to increase the proportion of MBUs.

The Random Telegraph Signal Behavior of Intermittently Stuck Bits in SDRAMs

This paper reports behavior analogous to the Random Telegraph Signal (RTS) seen in the leakage currents from radiation induced hot pixels in Charge Coupled Devices (CCDs), but in the context of stuck bits in Synchronous Dynamic Random Access Memories (SDRAMs). Our analysis suggests that pseudo-random sticking and unsticking of the SDRAM bits is due to thermally induced fluctuations in leakage current through displacement damage complexes in depletion regions that were created by high-energy neutron and proton interactions. It is shown that the number of observed stuck bits increases exponentially with temperature, due to the general increase in the leakage currents through the damage centers with temperature. Nevertheless, some stuck bits are seen to pseudo-randomly stick and unstick in the context of a continuously rising trend of temperature, thus demonstrating that their damage centers can exist in multiple widely spaced, discrete levels of leakage current, which is highly consistent with RTS. This implies that these intermittently stuck bits (ISBs) are a displacement damage phenomenon and are unrelated to microdose issues, which is confirmed by the observation that they also occur in unbiased irradiation. Finally, we note that observed variations in the periodicity of the sticking and unsticking behavior on several timescales is most readily explained by multiple leakage current pathways through displacement damage complexes spontaneously and independently opening and closing under the influence of thermal vibrations.

Analyses of CCD images of nucleon-silicon interaction events

Sets of image frames were captured from a CCD device exposed to continuous beams of high energy neutrons. The tracks of short-range fragments from nuclear spallation interactions in the silicon of the devices pixels have been analyzed in respect of their frequency, intensity, directionality and other pertinent parameters. A comparison between these results and the predictions of computer code models of nucleon interactions in silicon is presented. Comparisons are also made with equivalent images of neutron events in an APS camera.

Assessment of neutron- and proton-induced nuclear interaction and ionization models in Geant4 for Simulating single event effects

This paper examines the performance of the Geant4 radiation transport toolkit for the simulation of energy deposition from proton- and neutron-nuclear interactions in silicon microelectronics. The results show that for large (/spl sim/300 /spl mu/m) to small (/spl sim/0.5 /spl mu/m) feature-size devices, the nucleon-nuclear and electromagnetic interaction models within the toolkit provide energy deposition spectra and single event upset rate predictions that are in good agreement with experimental data. The new Binary Cascade and Classical Cascade models, together with the nuclear pre-equilibrium model in Geant4, do not significantly differ in the results they produce. For small feature-size devices, it is shown that it is necessary to consider the effects of ionization by particles produced by nuclear interactions several micrometers above the sensitive volume.

Analyses of images of neutron interactions and single particle displacement damage in CCD arrays

The purpose of this work is to understand the interaction of high energy neutrons with CCDs with the aim of deploying them in flight experiments to gather a database of atmospheric neutron interaction events in silicon cells. The new results in this paper include: 1) early-time multilevel RTS signals from dark current spikes, which have never been resolved before and 2) improved resolution of the frequency distributions of event intensity and comparison with results from a radiation transport code. This work adds to the state of the art by providing a novel perspective on the formation and evolution (annealing) of displacement damage complexes in silicon and by demonstrating that CCDs can provide an attractive combination of spatial and intensity resolution for the interaction events of neutrons and other particles within silicon cells.

Probing the charge-collection sensitivity profile using a picosecond pulsed laser at a range of wavelengths

A new empirical methodology is defined and demonstrated in which the charge collection sensitivity profile of single-event effect (SEE)-susceptible nodes in microcircuits is calculated on the basis of laser pulse measurements of the upset threshold at a range of wavelengths.

A CCD miniature radiation monitor

A miniature radiation monitor (MRM) device has been developed, which utilizes a charge-coupled device (CCD) as its sensitive element. Its shielding configuration has been designed to mitigate the displacement damage threat in space environments, while also introducing a good degree of directional sensitivity.

A Statistical Technique to Measure the Proportion of MBU's in SEE Testing

Neutron SEE data for memories shows that the distribution of MBUs is a geometrical progression. We demonstrate that this permits the proportion of MBUs to be calculated from the mean and variance of the errors per read-cycle