R.A. Weller

Broadcom Corporation, Irvine, California, United States

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Publications (186)213.87 Total impact

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    ABSTRACT: Recently (IEEE Trans. Nucl. Sci., Vol. 60, No. 3, pp. 1876-1911, 2013), Reed published an anthology of contributions from different research groups, each developing and/or applying Monte Carlo-based radiation transport tools to simulate a variety of effects that result from energy transferred to a semiconductor material by a single particle event. The Tool suIte for rAdiation Reliability Assessment (TIARA) simulation platform and its development by STMicroelectronics and Aix-Marseille University is described in this paper as a complement to this anthology.
    IEEE Transactions on Nuclear Science 01/2014; 61(3):1498-1500. · 1.22 Impact Factor
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    ABSTRACT: This paper investigates total-ionizing dose effects on the electrical characteristics of HfO2/Hf-based bipolar resistive-random-access-memory (RRAM) devices. 10-keV x-ray irradiation does not cause significant changes in resistance at levels up to 7 Mrad( SiO2). Excess carriers generated by x-ray irradiation in the HfO2 layer recombine or are trapped at defect sites in the HfO2 layer or at interfaces between layers. They have no effect, however, on the conductive path of the RRAM devices. 1.8 MeV proton irradiation causes resistance degradation through simultaneous introduction of oxygen vacancies and displacement damage. TRIM simulations are used to explain the physical mechanisms of the radiation-induced damage. The devices are promising for radiation-hardened memory applications.
    IEEE Transactions on Nuclear Science 12/2013; 60(6):4540 - 4546. · 1.22 Impact Factor
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    ABSTRACT: This anthology contains contributions from eleven different groups, each developing and/or applying Monte Carlo-based radiation transport tools to simulate a variety of effects that result from energy transferred to a semiconductor material by a single particle event. The topics span from basic mechanisms for single-particle induced failures to applied tasks like developing websites to predict on-orbit single event failure rates using Monte Carlo radiation transport tools.
    IEEE Transactions on Nuclear Science 06/2013; 60(3):1876-1911. · 1.22 Impact Factor
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    ABSTRACT: Charge collection mechanisms in AlGaN/GaN MOS-HEMTs are investigated. Device types include those with no gate oxide, and those with ${rm HfO}_2$ and ${rm Al}_2{rm O}_3$ gate oxides. Simultaneous charge collection is observed at the gate and the drain or the source, depending on strike location. Heavy ion data coupled with device simulations show that the introduction of a thin ${rm HfO}_2$ layer in the gate stack introduces only a small valence band barrier, reducing but not preventing collection of holes at the gate in ${rm HfO}_2$-gate devices. Furthermore, using ${rm Al}_2{rm O}_3$ gate oxide increases the valence band barrier over that of the ${rm HfO}_2$, to the point where the radiation-induced transient is not detectable.
    IEEE Transactions on Nuclear Science 01/2013; 60(6):4439-4445. · 1.22 Impact Factor
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    ABSTRACT: Transient capture measurements on an irradiated diode show the effect of increasing ion LET and varying strike location on transient current response. Significant modulation of the electrostatic potential in the device depletion region during and after the strike profoundly affects transient characteristics. The peak transient current tends to saturate with increasing ionization intensity. The saturation depends on device parameters and the applied bias. A previously developed analytical model is used to describe the mechanisms responsible for this trend. Ion strikes near the device contacts produce transients that are significantly different than strikes away from the contacts, but still in the active region of the device. This is attributed to well potential modulation effects. Device-level simulations, broadbeam heavy-ion measurements, and two-photon absorption single-event effects testing are used to investigate these phenomena. The implications of these results for highly-scaled technologies are also discussed.
    IEEE Transactions on Nuclear Science 01/2013; 60(6):4150-4158. · 1.22 Impact Factor
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    ABSTRACT: We present experimental evidence of single-event upsets in 28 and 45 nm CMOS SRAMs produced by single energetic electrons. Upsets are observed within 10% of nominal supply voltage for devices built in the 28 nm technology node. Simulation results provide supporting evidence that upsets are produced by energetic electrons generated by incident X-rays. The observed errors are shown not to be the result of “weak bits” or photocurrents resulting from the collective energy deposition from X-rays. Experimental results are consistent with the bias sensitivity of critical charge for direct ionization effects caused by low-energy protons and muons in these technologies. Monte Carlo simulations show that the contributions of electron-induced SEU to error rates in the GEO environment depend exponentially on critical charge.
    IEEE Transactions on Nuclear Science 01/2013; 60(6):4122-4129. · 1.22 Impact Factor
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    ABSTRACT: Charge collection by multiple junctions is investigated using broadbeam heavy-ion and backside laser current transient measurements. The probability that significant charge is collected by more than one junction is greater for laser-generated events compared to heavy-ion measurements, which is attributed to the larger carrier generation track radius for the laser. With both sources, the probability of collecting charge on multiple junctions saturates at high charge generation levels. Effects caused by the interaction between junctions on the transient current waveforms is determined using position-correlated two-photon absorption laser analysis. The total charge collected for ion strikes between four adjacent junctions is shown to be approximately the same as for a direct strikes on a single junction, even though the incident ion does not pass through the depletion region of a biased junction.
    IEEE Transactions on Nuclear Science 01/2013; 60(6):4159-4165. · 1.22 Impact Factor
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    ABSTRACT: Measurements of single particle displacement damage are presented as discrete increases in reverse-biased diode leakage current, or current steps, caused by individual heavy ions in $^{252}{rm Cf}$-irradiated JFET diodes. The maximum size of measured current steps agrees with calculations obtained from the expression for Shockley-Read-Hall generation when the radiation-induced defect density is derived from Monte Carlo simulations of atomic displacements and the electric field enhancement of defect emission is taken into account. The distribution of the current steps shows good agreement with experimental data.
    IEEE Transactions on Nuclear Science 01/2013; 60(6):4094-4102. · 1.22 Impact Factor
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    ABSTRACT: Pulsed-laser induced charge-collection measurements in a bulk silicon diode are used to investigate charge collection mechanisms during high-level carrier generation conditions. The recently developed Ambipolar Diffusion with a Cutoff (ADC) model for charge collection is used to emphasize the significance of the carrier densities, electric fields, and potential throughout the entire device in response to high-level carrier generation events. Device-level simulations are used to show that for high carrier density, short-track events, carriers are confined close to the junction by a strong electric field that forms underneath the region of high carrier density. These simulations are used to explain why, for some of the experimental data shown here, almost all of the generated charge can be collected, even if the peak carrier generation is located several micrometers away from the depletion region boundary. The physical framework for charge collection provided by the ADC model is compared to other analytical charge collection models, such as the funnel model, to emphasize that the more general approach it provides makes it well suited to situations where other analytical charge-collection models cannot be directly applied.
    IEEE Transactions on Nuclear Science 12/2012; 59(6):2710-2721. · 1.22 Impact Factor
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    ABSTRACT: An efficient method for estimating the characteristics of ion-induced current pulse transients is presented and related to the corresponding mechanisms of single-event charge collection. The method is focused on characterizing the prompt response of a reverse biased p-n junction under relatively low level conditions (LET <; 10 MeV-cm2/mg). This method is shown to be accurate when compared to 3D finite element simulations, while reducing solution time such that current pulse calculations can be run in series with both energy deposition and circuit simulations.
    IEEE Transactions on Nuclear Science 12/2012; 59(6):2704-2709. · 1.22 Impact Factor
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    ABSTRACT: Monte-Carlo radiation transport simulations are used to evaluate the implications of track structure on the response of microelectronics to energy deposition from ionizing radiation events. Results show that average track structure models cannot fully account for effects on microelectronics devices from energy deposition by δ-rays. Additionally, results indicate that δ-ray energy deposition events are capable of depositing up to 10 keV of energy within a 50 nm cube at radial distances greater than 10 μm from an ionizing particle event.
    Applied Physics Letters 08/2012; 101(5). · 3.79 Impact Factor
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    ABSTRACT: Enhanced rates of oxide growth have been observed on silicon upon exposure to 10-keV X-ray irradiation. Oxide thicknesses were determined using spectroscopic ellipsometry on irradiated and control samples, and confirmed via X-ray photoelectron spectroscopy. The oxidation rate varied with the radiation total dose and dose rate. The increased oxidation rate is attributed to the generation of ozone, which decomposes into molecular oxygen and highly reactive atomic oxygen at the surface of the Si wafer. The generation of ozone by 10-keV X-rays was found to increase linearly with increasing dose rate. UV irradiation led to similarly enhanced oxidation rates. The potential application of this phenomenon to dosimetry is explored.
    IEEE Transactions on Nuclear Science 01/2012; 59(4):781-785. · 1.22 Impact Factor
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    ABSTRACT: Single particle displacement damage events are reported in silicon diodes irradiated with 252Cf and 241Am. In situ measurements of reverse current show the result of displacement damage incurred from individual fission fragments in 252Cf irradiated diodes. Discrete increases in reverse current exceeding 20 fA are measured. The increases are temporally correlated with fission fragment-induced ionization events. The ratio of the damage factor associated with fission fragments to the damage factor associated with alpha particles is in good agreement with the ratio of non-ionizing energy loss calculated for fission fragments to NIEL calculated for alpha particles.
    IEEE Transactions on Nuclear Science 01/2012; 59(6):3054-3061. · 1.22 Impact Factor
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    ABSTRACT: Soft errors produced by ionizing radiation pose significant challenges for integrated circuits and electronic devices. The challenges and solutions change significantly as feature sizes become smaller and device topologies change. This paper reviews soft errors in advanced electronics, with emphasis on highly scaled CMOS technologies.
    Solid-State and Integrated Circuit Technology (ICSICT), 2012 IEEE 11th International Conference on; 01/2012
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    ABSTRACT: The effects of radiation on modern electronics are not well understood; devices with length scales below 60 nm are sensitive across a wider range of input energies and respond differently to different species than larger devices. This is not a trivial issue: existing predictive failure models are off by as much as three orders of magnitude. Complicating the problem is that modern devices have dozens of operating modes, requiring orders of magnitude more testing time. This increase in the required time (and cost) for ground testing, coupled with the greatly reduced cost (and development time) for space experimentation via CubeSats, has made spaceflight a sensible complement to ground testing. The Institute for Space and Defense Electronics (ISDE) at Vanderbilt University has partnered with the Space Systems Research Laboratory at Saint Louis University to develop Argus, a proposed flight campaign of perhaps a dozen CubeSat-class spacecraft spanning years. Argus will fly an array of radiation-effects modeling experiments; on-orbit event rates will be compared against ground predictions to help calibrate new predictive models developed at ISDE. Argus leverages COTS CubeSat systems and the extremely simple payload requirements to field a set of very low-cost, very automated passive platforms developed by students at both institutions. This paper will describe the challenges in modeling radiation effects on modern electronics as well as the new models developed at ISDE. The Argus campaign concept and drivers will be discussed, and the first two missions will be presented: COPPER, which flies in late 2012, and Argus-High, proposed for a 2013 launch.
    IEEE Aerospace Conference Proceedings 01/2012;
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    ABSTRACT: Scaling of complementary metal oxide semiconductor (CMOS) technologies to the sub-100 nm dimension regime increase the sensitivity to pervasive terrestrial radiation. Diminishing levels of charge associated with information in electronic circuits, interactions of multiple transistors due to tight packing densities, and high circuit clock speeds make single event effects (SEE) a reliability consideration for advanced electronics. The trend to adapt and apply commercial IC processes for space and defense applications has provided a catalyst to the development of infrastructure for analysis and mitigation that can be leveraged for advanced commercial electronic devices. In particular, modeling and simulation, leveraging the dramatic reduction in computing cost and increase in computing power, can be used to analyze the response of electronics to radiation, to develop and evaluate mitigation approaches, and to calculate the frequency of problematic events for target applications and environments.
    International Journal of High Speed Electronics and Systems 11/2011; 18(04).
  • Source
    Marcus H. Mendenhall, Robert A. Weller
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    ABSTRACT: In Monte Carlo particle transport codes, it is often important to adjust reaction cross sections to reduce the variance of calculations of relatively rare events, in a technique known as non-analogous Monte Carlo. We present the theory and sample code for a Geant4 process which allows the cross section of a G4VDiscreteProcess to be scaled, while adjusting track weights so as to mitigate the effects of altered primary beam depletion induced by the cross section change. This makes it possible to increase the cross section of nuclear reactions by factors exceeding 10^4 (in appropriate cases), without distorting the results of energy deposition calculations or coincidence rates. The procedure is also valid for bias factors less than unity, which is useful, for example, in problems that involve computation of particle penetration deep into a target, such as occurs in atmospheric showers or in shielding.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 09/2011; 667. · 1.14 Impact Factor
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    ABSTRACT: Monte Carlo simulations demonstrate that electrons in a Europa-like radiation environment produce single events capable of depositing more than 100 keV in a shielded focal plane array (FPA). Aluminum shielding slows down high energy free space electrons through collisions. Incident electrons can also generate secondary particles within shielding through electromagnetic cascades, nuclear interactions, and other mechanisms. When incident electrons and secondary particles deposit energy in FPA pixels, the result is transient increases in background noise. We compare the energy deposition integral cross sections and estimate the single event effect rate for a range of electron energies incident upon an FPA shielded with 1, 5, and 10 cm of aluminum.
    IEEE Transactions on Nuclear Science 07/2011; · 1.22 Impact Factor
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    ABSTRACT: A new methodology of prediction for SEU is proposed based on SET modeling. The modeling of multi-node charge collection is performed using the ADDICT model for predicting single event transients and upsets in bulk transistors and SRAMs down to 65 nm. The predicted single event upset cross sections agree well with experimental data for SRAMs.
    IEEE Transactions on Nuclear Science 07/2011; · 1.22 Impact Factor
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    ABSTRACT: MRED (Monte Carlo Radiative Energy Deposition) is Vanderbilt University's Geant4 application for simulating radiation events in semiconductors. Geant4 is comprised of the best available computational physics models for the transport of radiation through matter. In addition to basic radiation transport physics contained in the Geant4 core, MRED has the capability to track energy loss in tetrahedral geometric objects, includes a cross section biasing and track weighting technique for variance reduction, and additional features relevant to semiconductor device applications. The crucial element of predicting Single Event Upset (SEU) parameters using radiation transport software is the creation of a dosimetry model that accurately approximates the net collected charge at transistor contacts as a function of deposited energy. The dosimetry technique described here is the multiple sensitive volume (MSV) model. It is shown to be a reasonable approximation of the charge collection process and its parameters can be calibrated to experimental measurements of SEU cross sections. The MSV model, within the framework of MRED, is examined for heavy ion and high-energy proton SEU measurements of a static random access memory.
    AIP Conference Proceedings. 06/2011; 1336(1).

Publication Stats

2k Citations
213.87 Total Impact Points


  • 2011
    • Broadcom Corporation
      Irvine, California, United States
  • 1988–2011
    • Vanderbilt University
      • • Department of Electrical Engineering and Computer Science
      • • Department of Physics and Astronomy
      • • Department of Mechanical Engineering
      Nashville, Michigan, United States
  • 2000
    • Auburn University
      • Department of Physics
      Auburn, AL, United States
  • 1989
    • California Institute of Technology
      • Division of Physics, Mathematics, and Astronomy
      Pasadena, CA, United States
  • 1983–1989
    • Yale University
      New Haven, Connecticut, United States
  • 1985
    • University of New Haven
      New Haven, Connecticut, United States