Search

Experimental results are presented on proton induced single-event-upsets (SEU) on a 65 nm silicon-on-insulator (SOI) SRAM. The low energy proton SEU results are very different for the 65 nm SRAM as compared with SRAMs fabricated in previous technology generations. Specifically, no upset threshold is observed as the proton energy is decreased down to 1 MeV; and a sharp rise in the upset cross-section is observed below 1 MeV. The increase below 1 MeV is attributed to upsets caused by direct ionization from the low energy protons. The implications of the low energy proton upsets are discussed for space applications of 65 nm SRAMs; and the implications for radiation assurance testing are also discussed. Index Terms--Proton irradiation, silicon-on-insulator (SOI) technology, single event upset (SEU), SRAM.

It is shown that protons and neutrons can induce enhanced degradation in power MOSFETs, including both trench and planar geometry devices. Specifically, large shifts in current-voltage characteristics can be observed at extremely low proton total dose levels (as low as ~ 2 rad(Si[O.sub.2])). These shifts can induce significant increases in device 'off' state leakage current. Neutron irradiations show similar degradation at equivalent fluence levels, even though neutrons do not deposit dose due to direct ionization. These data suggest that the mechanism responsible for the enhanced degradation is a microdose effect associated with secondary particles produced through nuclear interactions between protons and neutrons and the materials in integrated circuits. The secondary particles deposit enough charge in the gate oxide to induce a parasitic drain to source leakage path in the transistor. Although the results are demonstrated here for only trench and planar geometry power MOSFETs, microdose effects can impact the radiation response of other integrated circuit types. Hardness assurances issues implications are discussed. Index Terms--Microdose effects, neutron effects, power MOSFETs, proton effects, radiation effects, radiation hardness assurance, radiation hardness assurance methodology, radiation hardness assurance testing, single event effects.

Bipolar test structures were irradiated and annealed with various combinations of molecular hydrogen gas ambients, bias, and thermal conditions. The results show that the buildup and annealing behavior of defects in bipolar base oxides depend strongly on hydrogen concentration. Differences observed in trapped oxide charge annealing rates suggest that the charged defects created in hydrogen-rich environments may be attributed to different types of positive charge in addition to trapped holes. Index Terms--Bipolar oxide, gated bipolar devices, interface traps, hydrogen, oxide trapped charge, radiation-induced.

The effect of high energy proton irradiation and angle of incidence on single-event latchup (SEL) hardness is investigated as a function of temperature and power supply voltage to determine worst-case hardness assurance test conditions for space environments. SRAMs from several vendors were characterized for single-event latchup SEL hardness at proton energies from 20 to 500 MeV at temperatures of 25 [degrees]C and 80 [degrees]C, and at both normal and grazing angles of incidence. For all SRAMs investigated, the largest SEL cross section is observed for irradiation with protons with energies larger than 200 MeV. In addition, it is shown that for proton with energies [greater than or equal to] 400 MeV, there is not a significant increase in SEL cross section for grazing angles of incidence compared to normal incidence irradiation. Based on the results of several years of research, in addition to these new results, we propose a hardness assurance test procedure for qualifying parts for use in proton-rich space environments. Index Terms--COTS, hardness assurance, proton, radiation effects, SEU, single event, single-event latchup (SEL), SRAM.

The radiation effects community has developed a number of hardness assurance test guidelines to assess and assure the radiation hardness of integrated circuits for use in space and/or high-energy particle accelerator applications. These include test guidelines for total dose hardness assurance qualification and single event effects (SEE) qualification. In this work, issues associated with these hardness assurance test guidelines are discussed. For total dose qualification, the main test methodologies used in the U.S. and Europe are reviewed and differences between the guidelines are discussed. In addition, some key issues that must be considered when performing total dose hardness assurance testing are addressed. Following these discussions we review some emerging issues relevant to SEE device qualification that are not covered in present SEE test guidelines. The hardness assurance implications of these issues are addressed. Index Terms--Integrated circuit radiation effects, integrated circuit reliability, proton-induced single-event latchup, radiation effects, radiation hardening (electronics), radiation hardness assurance, radiation hardness assurance methodology, radiation hardness assurance testing, single event effects, single-event upset.

Electronic devices in space environments can contain numerous types of oxides and insulators. Ionizing radiation can induce significant charge buildup in these oxides and insulators leading to device degradation and failure. Electrons and protons in space can lead to radiation-induced total-dose effects. The two primary types of radiation-induced charge are oxide-trapped charge and interface-trap charge. These charges can cause large radiation-induced threshold voltage shifts and increases in leakage currents. Two alternate dielectrics that have been investigated for replacing silicon dioxide are hafnium oxides and reoxidized nitrided oxides (RNO). For advanced technologies, which may employ alternate dielectrics, radiation-induced voltage shifts in these insulators may be negligible. Radiation-induced charge buildup in parasitic field oxides and in SOI buried oxides can also lead to device degradation and failure. Indeed, for advanced commercial technologies, the total-dose hardness of ICs is normally dominated by radiation-induced charge buildup in either parasitic field oxides and/or SOI buried oxides. Heavy ions in space can also degrade the oxides in electronic devices through several different mechanisms including single-event gate rupture, reduction in device lifetime, and large voltage shifts in power MOSFETs. Index Terms--Aging, MOS devices, oxide breakdown, power MOSFETs, radiation effects, silicon-on-insulator, total dose effects.

Large, unexpected shifts in the current-voltage (IV) characteristics of commercial power MOSFETs irradiated with heavy ions have been observed. The shifts can be more than sixty-five times larger than the shifts resulting from total dose irradiation with gamma rays or electrons, and are shown to strongly depend on both the irradiation bias and the ion linear energy transfer (LET). These large shifts are a significant concern for devices intended to operate in low power space applications because it is shown that they can lead to off-state leakage currents greater than 1 A. The data are consistent with the formation of parasitic transistors resulting from the microdose deposited in the gate oxides of these devices by the heavy ions. These results have significant implications for hardness assurance testing of MOS devices for use in space. Index Terms--COTS, gamma ray, heavy ion, microdose, power MOSFETS, proton, radiation, total dose.

We irradiated floating gate (FG) memories with NOR and NAND architecture by using different TID sources, including 2 MeV, 98 MeV, and 105 MeV protons, X-rays, and [gamma]-rays. Two classes of phenomena are responsible for charge loss from programmed FGs: the first is charge generation, recombination, and transport in the dielectrics, while the second is the emission of electrons above the oxide band. Charge loss from programmed FGs irradiated with protons of different energy closely tracks results from [gamma]-rays, whereas the use of X-rays results in dose enhancement effects. Index Terms--Floating gate memories, proton irradiation, total ionizing dose.

The radiation hardness of nominally identical SRAM test chips fabricated in five commercial foundries is examined. Large variations in single-event latchup and total dose response are observed. The softest SRAMs fail functionally at ~200 krad(Si[O.sub.2]) and have a fairly large single-event latchup cross section. This is in contrast to the hardest foundry split which is nearly immune to single-event latchup at room temperature, and remains functional to a total dose of 400 krad(Si[O.sub.2]). Three of the splits show a similar increase in radiation induced leakage current, which is dependent on both the characterization bias as well as the pattern written to the memory array. The other two splits show neither a pattern nor a bias dependence on the leakage current. Heavy-ion microbeam experiments confirm that the most latchup sensitive area of these SRAMs is the peripheral circuitry, not the memory array itself. Qualification and hardened-by-design integrated circuit implications are discussed. Index Terms--Commercial foundry, COTS, heavy-ion, leakage current, neutron, proton, radiation effects, radiation response, SEL, SEU, single event, SRAM, total-dose.

To explore the impact of temperature on the post-irradiation response of ICs, we characterized the temperature response of transistors, SRAMs, and a custom mixed-signal ASIC. Devices were irradiated at room temperature and electrically characterized post irradiation as a function of temperature. Devices exhibit significantly more parametric degradation when characterized at elevated temperatures. In addition to parametric degradation, it is demonstrated that post-irradiation elevated temperature characterization can also induce functional failures at significantly lower total dose levels than at room temperature. As a result, to ensure system functionality, it is essential that devices be characterized over the full system temperature range pre- and post-irradiation. Recommendations for incorporating temperature testing into a hardness assurance test method (i.e., Method 1019) are suggested. Methods for minimizing the detrimental effects of elevated temperature anneals on hardness assurance testing are also discussed. Index Terms--Hardness assurance testing, integrated circuit radiation effects, integrated circuit reliability, radiation effects, radiation hardening (electronics).

The type of final chip passivation layer used to fabricate linear bipolar circuits can have a major impact on the total dose hardness of some circuits. It is demonstrated that National Semiconductor Corporation linear bipolar devices fabricated with only an amorphous silicon carbide passivation layer do not exhibit enhanced low-dose-rate sensitivity (ELDRS), while devices from the same production lot fabricated with other types of passivation layers are ELDRS sensitive. SiC passivation possesses mechanical, electrical and chemical properties that make it compatible with linear device fabrication processes. These properties of SiC passivation layers, combined with the excellent radiation response of devices passivated with SiC, make SiC passivation layers a very attractive choice for devices packaged in either ceramic or plastic-encapsulated packages for use in space environments. Index Terms--Enhanced low-dose-rate sensitivity (ELDRS), hardness assurance testing, integrated circuit reliability, integrated circuit testing, linear bipolar integrated circuits, mechanical stress, passivation layers, pre-irradiation elevated temperature stress, radiation effects, radiation hardening (electronics), radiation response, reliability screens, silicon carbide, thermal cycling, thermal stress effects.

The total dose hardness of several commercial power MOSFET technologies is examined. After exposure to 20 krad(Si[O.sub.2]) most of the n- and p-channel devices examined in this work show substantial (2 to 6 orders of magnitude) increases in off-state leakage current. For the n-channel devices, the increase in radiation-induced leakage current follows standard behavior for moderately thick gate oxides, i.e., the increase in leakage current is dominated by large negative threshold voltage shifts, which cause the transistor to be partially on even when no bias is applied to the gate electrode. N-channel devices biased during irradiation show a significantly larger leakage current increase than grounded devices. The increase in leakage current for the p-channel devices, however, was unexpected. For the p-channel devices, it is shown using electrical characterization and simulation that the radiation-induced leakage current increase is related to an increase in the reverse bias leakage characteristics of the gated diode which is formed by the drain epitaxial layer and the body. This mechanism does not significantly contribute to radiation-induced leakage current in typical p-channel MOS transistors. The p-channel leakage current increase is nearly identical for both biased and grounded irradiations and therefore has serious implications for long duration missions since even devices which are usually powered off could show significant degradation and potentially fail. Index Terms--Commercial-off-the-shelf (COTS), interface trap, leakage current, oxide trapped charge, power MOSFET, radiation effects, radiation hardened, radiation response, simulation, vertical double diffused power MOSFET (VDMOSFET).

The high and low dose rate responses of bipolar transistors in a bipolar linear circuit process technology have been studied with specially designed gated lateral pnp test transistors that allow for the extraction of the oxide trapped charge ([N.sub.ot]) and interface trap ([N.sub.it]) densities. The buildup of Not and Nit with total dose is investigated as a function of the irradiation gate voltage at 39 rad/s and 20 mrad/s for three variations of the final passivation layer (all variations had the same oxide covering the active region of the devices). The three variations in final passivation were selected to exhibit minimal degradation at high and low dose rate (no passivation), significant degradation at high and low dose rate (p-glass/nitride) and enhanced low dose rate sensitivity (ELDRS) (p-glass only). It is shown that the increase in base current is dominated by increased Nit and the 'true' low dose rate enhancement in the ELDRS parts occurs for zero and negative gate voltage, but is eliminated for large positive gate voltage and elevated temperature irradiation. Implications for ELDRS models are discussed. Index Terms--enhanced low dose rate sensitivity (ELDRS), p-glass/nitride.

The production and propagation of single-event transients in scaled metal oxide semiconductor (CMOS) digital logic circuits are examined. Scaling trends to the 100-nm technology node are explored using three-dimensional mixed-level simulations, including both bulk CMOS and silicon-on-insulator (SOI) technologies. Significant transients in deep submicron circuits are predicted for particle strikes with linear energy transfer as low as 2 MeV-[cm.sup.2]/mg, and unattenuated propagation of such transients can occur in bulk CMOS circuits at the 100-nm technology node. Transients approaching 1 ns in duration are predicted in bulk CMOS circuits. Body-tied SOI circuits produce much shorter transients than their bulk counterparts, making them more amenable to transient filtering schemes based on temporal redundancy. Body-tied SOI circuits also maintain a significant advantage in single-event transient immunity with scaling. Index Terms--Integrated circuit reliability, integrated circuit scaling, integrated circuit testing, radiation effects, radiation hardening (electronics), radiation response, single event effects, single event transient, single event upset.

The post-irradiation annealing behavior of total dose degradation in LM139 comparators fabricated in National Semiconductor Corporation's (NSC) enhanced low-dose-rate sensitive (ELDRS) linear bipolar technology is examined. Data show that a large fraction of the radiation-induced increase in input bias current recovers after a 100[degrees]C anneal. The recovery in input bias current is linked to a significant amount of interface-trap annealing at 100[degrees]C. This is qualitatively consistent with previous data on interface-trap annealing and recent models for interface-trap annealing associated with hydrogen motion at the silicon/silcon dioxide interface. The annealing results have implications for hardness assurance testing. If the radiation induced charge that is responsible for ELDRS (whether it be interface or border traps) can anneal at 100[degrees]C, these data suggest that elevated temperature irradiations sometimes used to bound the ELDRS response of ICs may also cause some annealing of radiation-induced charge. These data help explain why high-dose-rate irradiations at elevated temperatures in some cases underestimate low-dose-rate degradation. In addition, these data confirm that high-dose-rate irradiations followed by elevated temperature anneals do not mimic the mechanisms that cause enhanced degradation at low dose rates in devices with ELDRS. Index Terms--Bipolar linear integrated circuits, defect annealing, enhanced low-dose-rate sensitivity, hardness assurance testing, integrated circuit reliability, integrated circuit testing, passivation layers, pre-irradiation elevated temperature stress, radiation effects, radiation hardening (electronics), radiation response, thermal cycling, thermal stress effects, thermal stresses.

We examine the radiation response, annealing characteristics, and long-term reliability of capacitors with Al gates and [Al.sub.2][O.sub.3]-Si[O.sub.x][N.sub.y] gate dielectrics stacks which received a forming gas anneal (FGA) or an [O.sub.2] and FG anneal after high-[kappa] deposition. By comparison to a theoretical capacitance-voltage (CV) curve, the FG annealed devices are found to have a large preirradiation interface trapped charge density of ~7 + [10.sup.11] [cm.sup.-2], whereas devices annealed in [O.sub.2] and FG show a large density (~9 x [10.sup.11] [cm.sup.-2]) of negative bulk charge. The midgap voltage shift ([DELTA] [V.sub.mg]) increases monotonically with dose for both sets of devices, but the [O.sub.2] annealed devices exhibit 50% less trapping at a total dose of 2 Mrad(Si[O.sub.2]). The radiation-induced voltage shifts are found to recover during long duration biased anneals as a result of tunneling and thermal annealing. For short times and large biases, the annealing response is found to be dominated by tunneling. After 1,000 s of annealing, there is a 50% reduction in [DELTA] [V.sub.mg] for devices annealed at 2.0 MV/cm and a 7.5 % recovery for devices annealed at 1.0 MV/cm. For longer times, the annealing response of these devices is dominated by thermal annealing. Accelerated life testing shows these devices have a broad failure distribution with a large population of extrinsic failures. Extrapolation of the reliability data suggests these particular devices would have to be operated at an electric field less than ~2.5 MV/cm to achieve a ten-year operational lifetime. Improved reliability is, therefore, required before insertion into a manufacturing environment. Index Terms--Alternative dielectric, annealing, bias dependence, high-[kappa], interface trap, MOS capacitor, oxide trapped charge, processing, radiation effects, radiation response, reliability.

Mechanisms for enhanced low-dose-rate sensitivity are described. In these mechanisms, bimolecular reactions dominate the kinetics at high dose rates thereby causing a sub-linear dependence on total dose, and this leads to a dose-rate dependence. These bimolecular mechanisms include electron-hole recombination, hydrogen recapture at hydrogen source sites, and hydrogen dimerization to form hydrogen molecules. The essence of each of these mechanisms is the dominance of the bimolecular reactions over the radiolysis reaction at high dose rates. However, at low dose rates, the radiolysis reaction dominates leading to a maximum effect of the radiation. Index Terms--Bimolecular reaction, bipolar junction transistor, cracking, dimerization, dose rate, ELDRS, excess base current, hole, hydrogen, interface trap, kinetics, proton, radiation, recombination, silicon dioxide.

It is shown that final chip passivation layers can have a significant impact on total dose hardness. A number of final chip passivation layers are evaluated to identify films that mitigate enhanced low-dose-rate sensitivity (ELDRS) in National Semiconductor Corporation's linear bipolar technologies. It is shown that devices fabricated with either a low temperature oxide or a tetraethyl ortho silicate passivation do not exhibit significant ELDRS effects up to 100 krad(Si[O.sub.2]). Passivation studies on CMOS SRAMs suggest that it is unlikely that the passivation layers (or processing tools) are acting as a new source of hydrogen, which could drift or diffuse into the oxide and increase ELDRS sensitivity. Instead, it is possible that the passivation layers affect the mechanical stress in the oxide, which may affect oxide trap properties and possibly the release and mobility of hydrogen. Correlations between mechanical stress induced by the passivation layers and radiation degradation are discussed. Index Terms--Bipolar linear integrated circuits, enhanced low-dose-rate sensitivity, hardness assurance testing, integrated circuit reliability, integrated circuit testing, mechanical stress, passivation layers, pre-irradiation elevated temperature stress, radiation effects, radiation hardening (electronics), radiation response, thermal cycling, thermal stress effects, thermal stresses.

Final chip passivation layers are shown to have a major impact on the total dose hardness of bipolar linear technologies. It is found that devices fabricated without passivation layers do not exhibit enhanced low-dose-rate sensitivity (ELDRS) or pre-irradiation elevated-temperature stress (PETS) sensitivity, whereas devices from the same production lot fabricated with either oxide/nitride or doped-glass passivation layers are ELDRS and PETS sensitive. In addition, removing the passivation layers after fabrication can mitigate ELDRS and PETS effects. ELDRS and PETS effects do not appear to be inherently related to circuit design or layout, but are related to mechanical stress effects, hydrogen in the device, or a combination of the two. These results suggest that proper engineering of the final chip passivation layer might eliminate ELDRS and PETS effects in bipolar integrated circuits. Index Terms--Bipolar linear-integrated circuits, enhanced low-dose-rate sensitivity, hardness-assurance testing, integrated-circuit reliability, integrated-circuit testing, mechanical stress, passivation layers, pre-irradiation elevated-temperature stress, radiation effects, radiation hardening (electronics), radiation response, reliability screens, thermal cycling, thermal-stress effects, thermal stresses.

The geometric component of charge pumping current was examined in n-channel metal-oxide-silicon field effect transistors (MOSFETs) following low-temperature irradiation. In addition to the usual dependencies on channel length and gate bias transition time, the geometric component was found to increase with radiation-induced oxide-trapped charge density and decreasing temperature. A postirradiation injection of electrons into the gate oxide reduces the geometric component along with the density of oxide-trapped charge, which clearly demonstrates that the two are correlated. A fit of the injection data to a first-order model for trapping kinetics indicates that the electron trapping occurs predominantly at a single type of Coulomb-attractive trap site. The geometric component results primarily from the bulk recombination of channel electrons that fail to transport to the source or drain during the transition from inversion to accumulation. The radiation response of these transistors suggests that Coulomb scattering by oxide-trapped charge increases the bulk recombination at low temperatures by impeding electron transport. These results imply that the geometric component must be properly accounted for when charge pumping irradiated n-channel MOSFETs at low temperatures. Index Terms--Bulk recombination, capture cross-section, charge pumping, Coulomb scattering, geometric component, hot electrons, interface trap density, irradiation, low-temperature, mobility degradation, MOSFET, oxide-trapped charge, trapping kinetics.

This paper presents a new physics-based model for understanding the basic mechanism of single-event gate rupture (SEGR) in analog devices. This model accounts for the different competing physics mechanisms, such as carrier drift, diffusion, recombination in the drift diffusion, and Poisson's equations, to explain the dependence of SEGR on biasing voltage, cross section, and critical electric field strength. Hence, the model provides a more accurate method of understanding and predicting the breakdown of oxides from heavy-ion strikes. Index Terms--Dielectric breakdown, heavy ion, linear devices, oxide breakdown, single-event gate rupture (SEGR).

The signal recognition particle (SRP) of eukaryotic cells is a cytoplasmic ribonucleoprotein machine that arrests the translational elongation of nascent secretory and membrane proteins and facilitates their transport into the endoplasmic reticulum. The spatial pathway of SRP RNA processing and ribonucleoprotein assembly in the cell is not known. In the present investigation, microinjection of fluorescently tagged SRP RNA into the nucleus of mammalian cells was used to examine its intranuclear sites of localization. Microinjection of SRP RNA into the nuclei of normal rat kidney (NRK) epithelial cells maintained at 37 [degrees] C on the microscope stage resulted in a very rapid initial localization in nucleoli, followed by a progressive decline of nucleolar signal and an increase of fluorescence at discrete sites in the cytoplasm. Nuclear microinjection of a molecule corresponding to a major portion of the Alu domain of SRP RNA revealed a pattern of rapid nucleolar localization followed by cytoplasmic appearance of signal that was similar to the results obtained with full-length SRP RNA. In contrast, a molecule corresponding to the S domain of SRP RNA did not display nucleolar localization to the extent observed with full-length SRP RNA. An SRP RNA molecule lacking helix 6 of the S domain displayed normal nucleolar localization, whereas one lacking helix 8 of the S domain did not. These results, obtained by direct, real-time observation of fluorescent RNA molecules inside the nucleus of living mammalian cells, suggest that the processing of SRP RNA or its ribonucleoprotein assembly into the SRP involves a nucleolar phase.

An analysis of the protein profiles of the red snapper and eleven other fish species prepared by electrophoretic methods shows that these profiles are characteristic of the species and can be used to identify red snapper meat from other fishes meats. The methods used are isoelectric focussing, sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two-dimensional gel electrophoresis. A comparison of the results obtained by these methods is given.

Thr formation of pseudouridine nucleotides on unaltered human U2 RNA in a HeLa cell extract system was examined. The RNase T1 oligonucleotide fragments of U2 RNA, believed to harbor pseudouridine in vivo, are the only ones with evidence of this formation. The formation was totally blocked by various FUrd-containing mutant U2 RNAs.

Although methods of phylogenetic estimation are used routinely in comparative biology, direct tests of these methods are hampered by the lack of known phylogenies. Here a system based on serial propagation of bacteriophage T7 in the presence of a mutagen was used to create the first completely known phylogeny. Restriction-site maps of the terminal lineages were used to infer the evolutionary history of the experimental lines for comparison to the known history and actual ancestors. The five methods used to reconstruct branching pattern all predicted the correct topology but varied in their predictions of branch lengths; one method also predicts ancestral restriction maps and was found to be greater than 98 percent accurate., THE DEVELOPMENT OVER THE PAST four decades of explicit methods for phylogenetic inference [1] has permitted biologists to reconstruct the broad outlines of evolutionary history and to interpret comparative biological [...]

The transport properties at zero temperature of the electron gas in AlAs are studied. Transport measurements are used for describing the microscopic parameters of disorder and many-body effects.

Metal-oxide-silicon capacitors fabricated in a bipolar process were examined for densities of oxide trapped charge, interface traps and deactivated substrate accepters following high-dose-rate irradiation at 100 [degrees] C. Accepter neutralization near the Si surface occurs most efficiently for small irradiation biases in depletion. The bias dependence is consistent with compensation and passivation mechanisms involving the drift of [H.sup.+] ions in the oxide and Si layers and the availability of holes in the Si depletion region. The capacitor data were used to simulate the impact of accepter neutralization on the current gain of an irradiated npn bipolar transistor. Neutralized accepters near the base surface enhance current gain degradation associated with radiation-induced oxide trapped charge and interface traps by increasing base recombination. The additional recombination results from the convergence of carrier concentrations in the base and increased sensitivity of the base to oxide trapped charge. The enhanced gain degradation is moderated by increased electron injection from the emitter. These results suggest that accepter neutralization may complicate hardness assurance test methods for linear circuits, which are based on elevated temperature irradiations.