Pascale M. Gouker

Single Event Transients in Digital CMOS—A Review

The creation of soft errors due to the propagation of single event transients (SETs) is a significant reliability challenge in modern CMOS logic. SET concerns continue to be exacerbated by Moores Law technology scaling. This paper presents a review of digital single event transient research, including: a brief historical overview of the emergence of SET phenomena, a review of the present understanding of SET mechanisms, a review of the state-of-the-art in SET testing and modelling, a discussion of mitigation techniques, and a discussion of the impact of technology scaling trends on future SET significance.

Generation and Propagation of Single Event Transients in 0.18-

Single event transients were characterized experimentally in fast logic circuits fabricated in 0.18-mum FDSOI CMOS process using laser-probing techniques. We show that the transient pulse widens as it propagates; the widening is largely eliminated by the body contact. Good agreement is observed between pulsed-laser and heavy ion testing.

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At the 2000 IEEE Nuclear and Space Radiation Effects Conference, it was shown that the negative shift in flatband voltage that results from hole injection is reduced in oxides that have been implanted with large doses of Al, Si, or P ions. In the present paper, we study the basic mechanism responsible for this reduced shift in the flatband voltage in more detail by comparing electron and hole trapping in Si and Ar implanted oxides. We find that in Si implanted oxides, the reduction in the shift of the flatband voltage is accompanied by the formation of entities in the oxide that have a large electron capture cross section, and that can become positively charged by photoemitting electrons. Photoluminescence studies indicate that these entities are Si nanoclusters. Oxides implanted with large doses of Ar do not form clusters, and these oxides show neither a reduction in the shift of the flatband voltage nor the formation of large capture cross-section electron traps. We show evidence that the nanoclusters reduce the shift of the flatband voltage by trapping protons formed during hole injection.

Fully Depleted SOI

Factors that affect single-event transient pulse widths, such as drift, diffusion, and parasitic bipolar transistor parameters, are also strong functions of operating temperature. In this paper, SET pulse-width measurements are performed over a wide temperature range in both bulk and fully-depleted SOI (silicon on insulator) technologies. The average pulse-width increases with temperature for the bulk process, but not for the FDSOI process.

The role of nanoclusters in reducing hole trapping in ion implanted oxides

We studied the total dose radiation effects from an X-ray source in submicron fully depleted n-channel field effect transistors on conventional SOI wafers, after substrate removal, and after buried oxide thinning. A significant enhancement in radiation tolerance is observed both after substrate removal and after subsequent buried oxide thinning.

Temperature Dependence of Digital Single-Event Transients in Bulk and Fully-Depleted SOI Technologies

Heavy- ion-induced single events transients (SETs) in advanced digital circuits are a significant reliability issue for space-based systems. SET pulse widths in silicon-on-insulator (SOI) technologies are often significantly shorter than those in comparable bulk technologies. In this paper, heavy-ion-induced digital single-event transient measurements are presented for a 180-nm fully depleted SOI technology. Upset cross-sections for this technology with and without body-ties are analyzed using 3-D TCAD simulations. Pulse broadening is shown to lengthen the measured SET pulse widths significantly for the circuit without body contacts.

Substrate removal and BOX thinning effects on total dose response of FDSOI NMOSFET

The amounts of charge collection by single-photon absorption (SPA) and by two-photon absorption (TPA) laser testing techniques have been directly compared using specially made SOI diodes. For SPA measurements and some TPA measurements, the back substrates of the diodes were removed by etching with XeF2. With the back substrates removed, the amount of TPA induced charge collection can be correlated to the amount of SPA induced charge collection. There are significant differences, however, in the amount of TPA induced charge collection for diodes with and without substrates. For the SOI diodes of this study, this difference appears to arise from several contributions, including nonlinear-optical losses and distortions that occur as the pulse propagates through the substrate, as well as displacement currents that occur only when the back substrate is present. These results illustrate the complexity of interpreting TPA and SPA single-event upset measurements.

Heavy-Ion-Induced Digital Single Event Transients in a 180 nm Fully Depleted SOI Process

The metal-filled vias through the buried oxide are integrated with silicon-on-insulator (SOI) MOSFETs. The FET temperature, measured directly using integrated junction diodes, can be lowered by as much as 25degC with these vias. In addition to enhanced DC characteristics, lowered gate resistance and output conductance further improve the RF performance and the extent of improvement is dependent on the FET design.

Direct Comparison of Charge Collection in SOI Devices From Single-Photon and Two-Photon Laser Testing Techniques

United States. Defense Advanced Research Projects Agency (Air Force Contract FA8721-05-C-0002)

Effects of Through-BOX Vias on SOI MOSFETs

Abstract Photo-assisted charge injection techniques in conjunction with capacitance–voltage measurements have been used to study electron and hole trapping in thermal oxides implanted with up to 1×1016 cm−2 Si or Ar. Defects having large cross sections for electron trapping and photoionization are found in oxides implanted with large doses of Si, but not of Ar, suggesting the formation of Si clusters. It is also found that the magnitude of the shift in the flatband voltage, ΔVfb, resulting from hole trapping is increased in oxides implanted with up to 1×1015 cm−2 Si or Ar. In oxides implanted with higher doses of Si, however, ΔVfb is decreased. An explanation is proposed involving trapping of radiolytic hydrogen at Si clusters.