Publications

Rohr, Garth R.; Miller, William K.; Davis, Ryan A.; Calkins, David C.; Roach, R.A.; Walsh, David S.; McElhanon, James R.; rasberry, Roger D.

Abstract not provided.

Proceedings of SPIE - The International Society for Optical Engineering

Rasberry, Roger D.; Rohr, Garth R.; Miller, William K.; Udd, Eric; Blach, Noah T.; Davis, Ryan A.; Olson, Walter R.; Calkins, David C.; Roach, R.A.; Walsh, David S.; McElhanon, James R.

The assurance of the integrity of adhesive bonding at substrate interfaces is paramount to the longevity and sustainability of encapsulated components. Unfortunately, it is often difficult to non-destructively evaluate these materials to determine the adequacy of bonding after manufacturing and then later in service. A particularly difficult problem in this regard is the reliable detection/monitoring of regions of weak bonding that may result from poor adhesion or poor cohesive strength, or degradation in service. One promising and perhaps less explored avenue we have recently begun to investigate for this purpose centers on the use of (chirped) fiber Bragg grating sensing technology. In this scenario, a grating is patterned into a fiber optic such that a (broadband) spectral reflectance is observed. The sensor is highly sensitive to local and uniform changes across the length of the grating. Initial efforts to evaluate this approach for measuring adhesive bonding defects at substrate interfaces are discussed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

AIP Conference Proceedings

Banks, James C.; Walla, Lisa A.; Walsh, David S.; Doyle, Barney L.

Controlatron neutron generators are used for testing neutron detection systems at Sandia National Laboratories. To provide for increased tube lifetimes for the moderate neutron flux output of these generators, metal hydride (ZrT 2) target fabrication processes have been developed. To provide for manufacturing quality control of these targets, ion beam analysis techniques are used to determine film composition. The load ratios (i.e. T/Zr concentration ratios) of ZrT 2 Controlatron neutron generator targets have been successfully measured by simultaneously acquiring RBS and ERD data using a He ++ beam energy of 10 MeV. Several targets were measured and the film thicknesses obtained from RBS measurements agreed within ±2% with Dektak profilometer measurements. The target fabrication process and ion beam analysis techniques will be presented. © 2009 American Institute of Physics.

Proposed for publication in X-Ray Spectrometry.

Doyle, Barney L.; Walsh, David S.; Rossi, Paolo R.; Kotula, Paul G.

Sandia and Rontec have developed an annular, 12-element, 60 mm{sup 2}, Peltier-cooled, translatable, silicon drift detector called the SDD-12. The body of the SDD-12 is only 22.8 mm in total thickness and easily fits between the sample and the upstream wall of the Sandia microbeam chamber. At a working distance of 1 mm, the solid angle is 1.09 sr. The energy resolution is 170 eV at count rates <40 kcps and 200 eV for rates of 1 Mcps. X-ray count rates must be maintained below 50 kcps when protons are allowed to strike the full area of the SDD. Another innovation with this new {mu}PIXE system is that the data are analyzed using Sandia's Automated eXpert Spectral Image Analysis (AXSIA).

Doyle, Barney L.; Walsh, David S.; Kotula, Paul G.; Rossi, Paolo R.

Abstract not provided.

Dodd, Paul E.; Walsh, David S.; Buller, Daniel L.; Doyle, Barney L.

The effects of photocurrents in nuclear weapons induced by proximal nuclear detonations are well known and remain a serious hostile environment threat for the US stockpile. This report describes the final results of an LDRD study of the physical phenomena underlying prompt photocurrents in microelectronic devices and circuits. The goals of this project were to obtain an improved understanding of these phenomena, and to incorporate improved models of photocurrent effects into simulation codes to assist designers in meeting hostile radiation requirements with minimum build and test cycles. We have also developed a new capability on the ion microbeam accelerator in Sandia's Ion Beam Materials Research Laboratory (the Transient Radiation Microscope, or TRM) to supply ionizing radiation in selected micro-regions of a device. The dose rates achieved in this new facility approach those possible with conventional large-scale dose-rate sources at Sandia such as HERMES III and Saturn. It is now possible to test the physics and models in device physics simulators such as Davinci in ways not previously possible. We found that the physical models in Davinci are well suited to calculating prompt photocurrents in microelectronic devices, and that the TRM can reproduce results from conventional large-scale dose-rate sources in devices where the charge-collection depth is less than the range of the ions used in the TRM.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Guo, B.N.; El Bouanani, M.; Renfrow, S.N.; Nigam, M.; Walsh, David S.; Doyle, Barney L.; Duggan, J.L.; McDaniel, F.D.

To design more radiation-tolerant integrated circuits (ICs), it is necessary to design and test accurate models of ionizing-radiation-induced charge collection dynamics. A new technique, diffusion-time-resolved ion-beam-induced charge collection (DTRIBICC), is used to measure the average arrival time of the diffused charge, which is related to the average time of the arrival carrier density at the junction. Specially designed stripe-like test junctions are studied using a 12 MeV carbon microbeam with a spot size of ∼1 μm. The relative arrival time of ion-generated charge and the collected charge are measured using a multiple parameter data acquisition system. A 2-D device simulation code, MEDICI, is used to calculate the charge collection dynamics on the stripe-like test junctions. The simulations compare well with experimental microbeam measurements. The results show the importance of the diffused charge collection by junctions, which is especially significant for single-event upsets (SEUs) and m ultiple-event upsets (MEUs) in electronic devices. The charge sharing results also indicate that stripe-like junctions may be used as position-sensitive detectors with a resolution of ∼0.1 μm. © 2001 Elsevier Science B.V. All rights reserved.

Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms

Walsh, David S.; Dodd, Paul E.; Shaneyfelt, Marty R.; Schwank, James R.

Silicon-on-insulator (SOI) technology exhibits three main advantages over bulk silicon technology for use in radiation environments. (1) SOI devices are immune to latchup, (2) the volume of the sensitive region (body) and hence total charge collection per transient irradiation is much reduced in SOI devices and (3) the insulating layer blocks charge collection from the substrate (i.e., no funneling effect). This effectively raises the single event upset (SEU) threshold for the SOI device. However, despite their small active volume SOI devices are still vulnerable to single event effects (SEE). Inherent in the SOI transistor design is a parasitic npn bipolar junction transistor (BJT), where the source-body-drain acts as an emitter-base-collector BJT. An ion strike to a floating (not referenced to a specific potential) body creates a condition where the excess minority carriers in the drain-body cause the parasitic BJT to turn on and inject more charge into the drain than was deposited in the device by the ion. In extreme cases the floating body effect (FBE) can trigger a high-current state called single-event snapback (SES) where channel conduction is sustained indefinitely through regenerative electron-impact ionization near the drain junction. Tying the body to the source limits the emitter-base current and reduces the sensitivity of the device to single ion strikes. Unfortunately, the body-tie loses effectiveness with distance due to resistivity, and in regions far enough from the tie the BJT is still in effect. Using the Sandia nuclear microprobe we have created charge collection maps on Sandia CMOS6rs SOI FETs of varying channel widths. These devices have body ties at both ends of the channel region. Results clearly demonstrate that distance of the ion strike from the body tie has an inverse effect upon charge collection and SES sensitivity due to the resistivity of the channel. Experimental results compare well with DAVINCI simulations and electrically induced snapback thresholds. In addition, an intere sting saturation effect of SES versus the amount of injected charge is observed. © 2001 Elsevier Science B.V. All rights reserved.

Proceedings of SPIE - The International Society for Optical Engineering

Vizkelethy, G.; Doyle, Barney L.; Walsh, David S.; James, R.B.

Ion Beam Induced Charge Collection (IBICC) is a proven albeit relatively new method to measure the electronic transport properties of room temperature radiation detectors. Using an ion microbeam, the charge collection efficiency of CZT detectors can be mapped with submicron resolution and maps of the electron mobility and lifetime can be calculated. The nuclear microprobe can be used not only for characterizing detectors but also with the use of Time Resolved IBICC (TRIBICC) and lateral IBICC/TRIBICC we can deduce information about the electron and hole mobility and lifetime profiles, and about the variation of electric field along the detectors' axes. The Sandia Nuclear Microprobe has been and is being used routinely to characterize CZT detectors and measure their electronic transport properties. In this paper we will present the results of these measurements for different detectors. Furthermore the damage effects caused by the probing beam will be discussed and a simple model will be presented to explain the characteristic charge collection efficiency pattern observed after high dose irradiation. © 2000 SPIE.

Horn, Kevin M.; Doyle, Barney L.; Walsh, David S.; Dodd, Paul E.

Abstract not provided.

Doyle, Barney L.; Walsh, David S.; Renfrow, S.N.

Abstract not provided.

IEEE Transactions on Nuclear Science

Dodd, Paul E.; Shaneyfelt, Marty R.; Walsh, David S.; Schwank, James R.; Hash, Gerald L.; Jones, Rhonda L.; Draper, Bruce L.; Winokur, Peter S.

The characteristics Of ion-induced charge collection and single-event upset are studied in SOI transistors and circuits with various body tie structures. Impact ionization effects including single-event snapback are shown to be very important. Focused ion microbeam experiments are used to find single-event snapback drain voltage thresholds in n-channel SOI transistors as a function of device width. Three-Dimensional device simulations are used to determine single-event upset and snapback thresholds in SOI SRAMS, and to study design tradeoffs for various body-tie structures. A window of vulnerability to single-event snapback is shown to exist below the single-event upset threshold. The presence of single-event snapback in commercial SOI SRAMS is confirmed through broadbeam ion testing, and implications for hardness assurance testing of SOI integrated circuits are discussed.

Applied Physics Letters

Walsh, David S.; Walsh, David S.; Doyle, Barney L.

To design more radiation tolerant Integrated Circuits (ICs), it is essential to create and test accurate models of ionizing radiation induced charge collection dynamics within microcircuits. A new technique, Diffusion Time Resolved Ion Beam Induced Charge Collection (DTRIBICC), is proposed to measure the average arrival time of the diffused charge at the junction. Specially designed stripe-like junctions were experimentally studied using a 12 MeV carbon microbeam with a spot size of 1 {micro}m. The relative arrival time of ion-generated charge is measured along with the charge collection using a multiple parameter data acquisition system. The results show the importance of the diffused charge collection by junctions, which is especially significant in accounting for Multiple Bit Upset (MBUs) in digital devices.

Sexton, Frederick W.; Walsh, David S.; Doyle, Barney L.; Dodd, Paul E.

Under this effort, a new method for studying the single event upset (SEU) in microelectronics has been developed and demonstrated. Called TRIBICC, for Time Resolved Ion Beam Induced Charge Collection, this technique measures the transient charge-collection waveform from a single heavy-ion strike with a {minus}.03db bandwidth of 5 GHz. Bandwidth can be expanded up to 15 GHz (with 5 ps sampling windows) by using an FFT-based off-line waveform renormalization technique developed at Sandia. The theoretical time resolution of the digitized waveform is 24 ps with data re-normalization and 70 ps without re-normalization. To preserve the high bandwidth from IC to the digitizing oscilloscope, individual test structures are assembled in custom high-frequency fixtures. A leading-edge digitized waveform is stored with the corresponding ion beam position at each point in a two-dimensional raster scan. The resulting data cube contains a spatial charge distribution map of up to 4,096 traces of charge (Q) collected as a function of time. These two dimensional traces of Q(t) can cover a period as short as 5 ns with up to 1,024 points per trace. This tool overcomes limitations observed in previous multi-shot techniques due to the displacement damage effects of multiple ion strikes that changed the signal of interest during its measurement. This system is the first demonstration of a single-ion transient measurement capability coupled with spatial mapping of fast transients.