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Focused, pulsed X-rays are used to generate single-event transients (SETs) in metal–insulator–semiconductor (MIS)-gate AlGaN/GaN high-electron-mobility transistors (HEMTs) in order to investigate the mechanisms responsible for SETs. Unlike Schottky-gate GaN HEMTs, where current flows between gate and drain when the device is biased “OFF,” for the MIS-gate HEMTs, current flows between the source and drain. The presence of the SiNx insulating layer under the gate effectively blocks electrons on the gate from moving into the semiconductor. Short-duration SETs at the gate are caused by the collection of holes injected by the X-rays. SETs collected at the source and drain have an initial short-duration component, followed by a long-duration tail that can last for hundreds of nanoseconds. The long tails are due to positive charges (holes) that are less mobile than the electrons and so take longer to exit the HEMT, and to holes that become trapped at defects in the material. The holes lower the potential barrier between the source and the region under the gate, allowing for the injection of electrons that flow from the source to the drain. The durations of the SET tails are determined by the lifetimes of the trapped holes that are found to vary with X-ray photon energy and electrical bias. [ABSTRACT FROM AUTHOR]

A focused, pulsed x-ray beam was used to compare SET characteristics in pristine and proton-irradiated Al0.3Ga0.7N/GaN HEMTs. Measured SET amplitudes and trailing-edge decay times were analyzed as was the collected charge, obtained by integrating the SET pulses over time. SETs generated in proton-irradiated HEMTs differed significantly from those in pristine HEMTs with regard to the decay times and collected charge. The decay times have previously been shown to be attributed to charge trapping by defect states that are caused either by imperfect material growth conditions or by proton-induced displacement damage. The longer decay times observed for proton-irradiated HEMTs are attributed to the presence of additional deep traps created when protons lose energy as they collide with the nuclei of constituent atoms. Comparison of electrical parameters measured before and immediately following exposure to the focused x-ray beam showed little change, confirming the absence of significant charge buildup in passivation layers by the x-rays themselves. A major advantage of the pulsed x-ray technique is that the region under the metal gate can be probed for single-event transients from the top side, an approach incompatible with pulsed-laser SEE testing that involves the use of visible light. [ABSTRACT FROM PUBLISHER]

The propagation of Analog Single Event Transients (ASETs) to multiple outputs of Bipolar Junction Transistor (BJTs) Integrated Circuits (ICs) is reported for the first time. The results demonstrate that ASETs can appear at several outputs of a BJT amplifier or comparator as a result of a single ion or single laser pulse strike at a single physical location on the chip of a large-scale integrated BJT analog circuit. This is independent of interconnect cross-talk or charge-sharing effects. Laser experiments, together with SPICE simulations and analysis of the ASET’s propagation in the s-domain are used to explain how multiple-output transients (MOTs) are generated and propagate in the device. This study demonstrates that both the charge collection associated with an ASET and the ASET’s shape, commonly used to characterize the propagation of SETs in devices and systems, are unable to explain quantitatively how MOTs propagate through an integrated analog circuit. The analysis methodology adopted here involves combining the Fourier transform of the propagating signal and the current-source transfer function in the s-domain. This approach reveals the mechanisms involved in the transient signal propagation from its point of generation to one or more outputs without the signal following a continuous interconnect path. [ABSTRACT FROM PUBLISHER]

The Variable Depth Bragg Peak method has been investigated for single event latchup testing by comparing latchup cross sections for heavy ions at low and high energies and by pulse height analysis. Results show that, unlike for an SOI device previously tested, where the charge collection depth is very small (70 nm), the comparison is not straightforward for latchup because of the large charge collection volumes involved. The variation in LET with depth for lower-energy ions greatly affects the comparison, but, if a charge collection depth of 50~\mu\m is assumed and the LET is averaged over that distance, the comparison improves significantly. [ABSTRACT FROM PUBLISHER]

The synergistic effect between Total Ionizing Dose (TID) and Analog Single Event Transient (ASET) in LM124 operational amplifiers (opamps) from three different manufacturers is investigated. This effect is clearly identified on only two manufacturers by three, highlighting manufacturer dependent. In fact, significant variations were observed on both the TID sensitivity and the ASET response of LM124 devices from different manufacturers. Hypotheses are made on the cause of the differences observed. A previously developed ASET simulation tool is used to model the transient response. The effects of TID on devices are taken into account in the model by injecting the variations of key electrical parameters obtained during Co^60 irradiation. An excellent agreement is observed between the experimental responses and the model outputs, independently of the TID level, the bias configuration and the manufacturer of the device. [ABSTRACT FROM PUBLISHER]

The impact of the positive feedback loop on analog single event transient (ASET) shapes was investigated for a comparator-with-hysteresis circuit. Simulation based on previous developed ASET simulation tool is used to model the impact of the power supply voltage, the input voltage level and the injected energy. Simulation results show that these kinds of circuits are sensitive to flip-flop effects. This phenomenon occurs if the input voltage is in the hysteresis band range. In this case, simulations show that the ASET can latch the output into a non-desired state by changing the state of the circuit on his transfer characteristic curves. Laser experiments were conducted and show that the simulation outputs are in agreement with the experimental collected data. [ABSTRACT FROM AUTHOR]

Pulsed laser test results for NAND flash memories are compared with broad beam heavy ion results and also with heavy ion results obtained with the collimated Milli-Beam™ source. The pulsed laser measurements reported here, with smaller focused spot sizes and as a function of the incident pulse energy, serve to reconcile the previously reported inconsistencies. The Milli-Beam™ and pulsed laser results appear to be consistent, and differences from the broad beam heavy ion results can be explained. The results suggest that the high current SEFIs reported by us and others arise from multiple ion (or multiple photon) interactions, and are not associated with single ion strikes. [ABSTRACT FROM AUTHOR]

A high level model is developed using circuit analysis to predict the synergy effect observed on a three stages operational amplifier. This model makes possible to explain and to predict the analog single event transients propagation in circuitry. The effect of total ionizing dose is taken into account by varying the model parameters using the monitoring of the usual supply current induced degradation of the operational amplifier. [ABSTRACT FROM AUTHOR]

The concept of charge efficacy is introduced as a measure of the effectiveness of incident charge for producing single-event upsets. Efficacy is a measure of the single-event upset (SEU) sensitivity within a cell. It is illustrated how the efficacy curve can be determined from standard heavy-ion or pulsed laser SEU crosssection data, and discussed how it can be calculated from combined charge collection and circuit analysis. Upset rates can be determined using the figure of merit approach, and values determined from the laser cross-sections or from the mixed-mode simulations. The standard integral rectangular parallel-piped (IRPP) method for upset rate calculation is re-examined assuming that the probability of upset depends on the location of the hit on the surface. It is concluded that it is unnecessary to reformulate the IRPP approach. [ABSTRACT FROM AUTHOR]

Abstract: Background: N-terminal pro-brain natriuretic peptide (NT-proBNP) allows us to rule out left ventricular dysfunction (LVD) in the general population at a recommended cut-off concentration of 125 pg/mL. It was our objective to reassess this cut-point in outpatients after myocardial infarction. Methods and Results: NT-proBNP was assessed in 418 randomly selected outpatients who had experienced myocardial infarction and 352 siblings who had not experienced myocardial infarction (control). Left ventricular ejection fraction (LVEF) and mass-index (LVMI) were assessed by echocardiography. NT-proBNP was elevated in outpatients after myocardial infarction (mean [±SEM], 305 ± 25 pg/mL vs control, 84 ± 8 pg/mL; P < .01) and was correlated inversely with LVEF (P < .001). When patients were stratified according to the presence or absence of heart failure, NT-proBNP was elevated significantly throughout all LVEF strata (each P < .05). On regression analysis, NT-proBNP was correlated independently with LVEF, LVMI, heart failure, and glomerular filtration rate (all P < .01). In patients with heart failure, the optimal cut-point for the detection of an LVEF <35% was 348 pg/mL (sensitivity 80%; specificity 69%) and for the detection of an LVEF <45% was 260 pg/mL (sensitivity 60%; specificity 60%). The relative risk for LVD in the presence of elevated NT-proBNP increased from 2.7 to 7.7 (EF < 35%) and from 1.4 to 2.4 (EF < 45%) when these cut-points were applied instead of the 125 pg/mL cut-point. An LVEF of <35% could be ruled out in symptomatic outpatients after myocardial infarction with a negative predictive value of 97% (cut-point 348 pg/mL) and in asymptomatic outpatients after myocardial infarction with a negative predictive value of 98% (cut-point 157 pg/mL). Conclusion: NT-proBNP is higher in outpatients after myocardial infarction than in the general population. In symptomatic patients, a cut-point of 348 pg/mL yields satisfactory sensitivity and specificity for the detection of significant LVD (EF < 35%). Furthermore, significant LVD can be virtually ruled out in symptomatic and asymptomatic outpatients after myocardial infarction at below-threshold concentrations. [Copyright &y& Elsevier]

Interface positive charge induced in thin oxides (582 Å thick) of metal-oxide-silicon devices by Fowler–Nordheim injection and x-ray irradiation was evaluated based on measurements of room-temperature annealing characteristics. Results showed that in the low-dose regime, the dose dependence of the density and distribution of the positive charge was different for the two forms of stress. However, at higher doses, the positive charge density produced by both methods increased monotonically while its spatial extent decreased and became more localized at the interface. These latter results are attributed to a buildup of negative charge in the oxide that neutralizes the positive charge furthest from the interface, whereas the differences at low dose are due either to the different character of the positive charge generated by the two techniques or to the much smaller electron density present during irradiation than injection. [ABSTRACT FROM AUTHOR]