Reliability Implications Research Articles

Organizational meta‐scripts as a source of high reliability: the case of an army armored brigade

AbstractMany high‐reliability organizations must deal with the problem of requisite cognitive variety in operators of interactively complex technological systems. The present study describes an organizational script strategy dealing with this problem, based on development of shared meta‐scripts sustained by continuous learning. Analysis of mission briefing and debriefing protocols in an armored brigade indicated that most task‐related interactions were based on script language (i.e., verbs and action phrases signifying particular meta‐scripts and relevant contingencies). These protocols suggest that script‐trained operators construe complex missions as interchangeable combinations of 15 meta‐scripts, reducing cognitive demands or requisite variety to manageable proportions. An ongoing learning process, maintained via repeated script‐based feedback during debriefings, further reduces cognitive demands by increasing available variety in operators. Implications for performance reliability in ordinary organizations are discussed. Copyright © 2003 John Wiley & Sons, Ltd.

Asynchronous periodic contact modes for rotor vibration within an annular clearance

The dynamics of a multimode rotor-bearing system are analysed when the rotor contacts with a stator having annular clearance. By transforming to a rotating frame, all possible steady state rotor vibration modes that involve periodic contact with the surround may be predicted. Using a harmonic decomposition with generalized fundamental frequency, periodic solutions are obtained for rotor motions that involve asynchronous periodic contact. The analytical solutions are compared with previously published experimental results, which are predicted with considerable accuracy thus confirming the efficacy of the approach. Solutions are obtained for different test cases, which show how the amplitude and stability of the periodic contact modes are dependent on system parameters and operating conditions. In particular, for increased unbalance levels, the amplitude of the contact mode vibration is increased and the response of the rotor progresses from a bouncing forward whirl to a backward whirl-type motion. The nature of the identified rotor responses and implications for machine operation and reliability are discussed.

A Breakdown of Reliability Coefficients by Test Type and Reliability Method, and the Clinical Implications of Low Reliability

The author presented descriptive statistics for 937 reliability coefficients for various reliability methods (e.g., alpha) and test types (e.g., intelligence). He compared the average reliability coefficients with the reliability standards that are suggested by experts and found that most average reliabilities were less than ideal. Correlations showed that over the past several decades there has been neither a rise nor a decline in the value of internal consistency, retest, or interjudge reliability coefficients. Of the internal consistency approaches, there has been an increase in the use of coefficient alpha, whereas use of the split-half method has decreased over time. Decision analysis and true-score confidence intervals showed how low reliability can result in clinical decision errors.

Practical Implications of Reliability and Performance-Based Assessments

Practical Implications of Reliability and Performance-Based Assessments

Influence of electroless nickel plating on I– V characteristics and its implications for reliability in ZnO-based ceramic varistors

A comparison experiment was designed and carried out to study the influence of electroless nickel plating on ZnO-based ceramic varistors. It was found that the influence was not caused by permeation of the plating solution; the influence was directly related to nickel deposition. It is proposed that adsorbed hydrogen atoms generated in electroless plating can diffuse into ZnO ceramic varistors and undergo a reduction reaction with them, which result in a substantial increase in the leakage current of the varistors. Some implications for the influence of electroplating on I– V characteristics and for the long-term degradation of ZnO varistors are also discussed, in which much attention is paid to the reduction reaction of atomic hydrogen generated by electrolysis of water.

Pharmacogenetics of codeine metabolism in an urban population of children and its implications for analgesic reliability

Codeine analgesia is wholly or mostly due to its metabolism to morphine by the cytochrome P450 enzyme CYP2D6, which shows significant genetic variation in activity. The aims of this study were to investigate genotype, phenotype and morphine production from codeine in children undergoing adenotonsillectomy, and to compare analgesia from codeine or morphine combined with diclofenac. Ninety-six children received either codeine 1.5 mg kg(-1) or morphine 0.15 mg kg(-1) in a randomized, double-blind design. Genetic analysis was performed and plasma morphine concentrations at 1 h were determined. Postoperative analgesia and side-effects were recorded. Forty-seven per cent of children had genotypes associated with reduced enzyme activity. Mean (SD) morphine concentrations were significantly lower (P<0.001) after codeine [4.5 (0.3) ng ml(-1)] than after morphine [24.7 (1.5) ng ml(-1)], and morphine and its metabolites were not detected in 36% of children given codeine. There was a significant relationship between phenotype and plasma morphine (P=0.02). More children required rescue analgesia after codeine at both 2 (P<0.05) and 4 h after administration (P<0.01). Fifty-six per cent of children vomited after morphine and 29% after codeine (P<0.01). Neither phenotype nor morphine concentration was correlated with either pain score or the need for rescue analgesia (r=-0.21, 95% confidence interval -0.4, -0.01). Reduced ability for codeine metabolism may be more common than previously reported. Plasma morphine concentration 1 h after codeine is very low, and related to phenotype. Codeine analgesia is less reliable than morphine, but was not well correlated with either phenotype or plasma morphine in this study.

Voltage dependence of hard breakdown growth and the reliability implication in thin dielectrics

Hard breakdown (HBD) is shown to be a gradual process with the gate current increasing at a predictable rate exponentially dependent on the instantaneous stress voltage and oxide thickness. This is contrary to conventional wisdom that maintains that HBD is a fast thermally driven process. The HBD degradation rate (DR) for a 15 /spl Aring/ oxide scales from >1 mA/s at 4 V to <1 nA/s at 2 V, extrapolating to <10 fA/s at use voltage. Adding the HBD evolution time to the standard time-to-breakdown potentially reduces the projected fail rate of gate dielectrics by orders of magnitude.

Physical investigation of trap-related effects in power HFETs and their reliability implications

This paper presents a detailed physical investigation of trapping effects in GaAs power HFETs. Two-dimensional numerical simulations, performed using a hydrodynamic model that includes impact ionization, are compared with experimental results of fresh as well as hot-carrier-stressed HFETs in order to gain insight of intertwined phenomena such as the kink in the dc output curves, the hot-carrier degradation of the drain current, and the impact-ionization-dominated reverse gate current. Thoroughly consistent results show that: 1) the kink effect is dominated by the traps at the source-gate recess surface; and 2) as far as the hot-carrier degradation is concerned, only a simultaneous increase of the trap density at the drain-gate recess surface and at the channel-buffer interface (again at the drain side of the channel) is able to account for the simultaneous decrease of the drain current and the increase of the impact-ionization-dominated reverse gate current.

Reliability implications in advanced embedded two-transistor-Fowler–Nordheim-NOR flash memory devices

Tail bits appearing during program/erase operation or after retention stresses are major threats to the floating-gate non-volatile memory reliability. Two-transistor (2T)-Fowler–Nordheim (FN)-NOR memories circumvent part of the tail bit induced problems of single transistor NOR and NAND configurations. However, the tail bits still represent a point of concern in the 2T-FN-NOR memory reliability, because of disturbs and stresses induced by application of the inhibition voltage and because of charge retention. In this paper the impact of tail bits in 2T-flash memory is investigated and it is suggested how to tackle this problem from design and process point of view.

Numerical simulations of stress induced void evolution and growth in interconnects

We model stress driven void growth and evolution in representative interconnect microstructures. Our computations account for several kinetic processes involved in interconnect failures, including surface diffusion, interface and grain boundary diffusion, as well as sliding on grain boundaries or the interconnect/passivation interface. Depending on the relative rates of these processes, we predict several different regimes of behavior for the void. In some cases the void remains rounded, leading to a long interconnect life. For critical combinations of material properties, however, the void propagates across the line as a narrow slit, causing rapid failure. Our analysis suggests that the extent of inelastic slip between the interconnect and the surrounding passivation plays a central role in this transition. Implications for interconnect reliability are discussed.

Critical issues of growth optimization for Ga0.5In0.5P/GaAs heterojunction bipolar transistors

This work reports on optimization of MOVPE growth procedures for high-quality, highly uniform (4 inch) and highly reliable Ga0.5In0.5P/GaAs-HBTs in a commercial multiwafer reactor. Appropriately to this application the main focus of research have been improvements in base-layer transport properties and their implications for HBT device characteristics and reliability. Different carbon-doping techniques are compared with regard to GaAs:C material quality and GaInP/GaAs-HBT device performance. Base-doping homogeneity and hydrogen incorporation were further aspects of optimization. The obtained differences in HBT device performance and reliability depending on base-growth conditions confirm the importance of optimization of this particular step in the growth process.

Analysis of thermal stresses in metal interconnects with multilevel structures

The evolution of thermal stresses in aluminum interconnects was analyzed numerically. Particular attention was devoted to the effects of multilevel arrangement, which have been largely ignored in past studies. Two-dimensional models based on long metal lines with different aspect ratios and cross-sectional arrangements were employed. The metallization, taken to include thin refractory layers sandwiching the aluminum conductor, was embedded within silicon oxide dielectric on top of the silicon substrate. A thermal cooling process was simulated by recourse to the finite element method. It was found that the incorporation of refractory layers increases the stress in aluminum lines. The line aspect ratio, rather than the multilevel nature, plays the most important role in affecting the thermal stress. Issues related to interconnect stress modeling and reliability implications are discussed.

Breakdown Modes and Breakdown Statistics of Ultrathin SiO2 Gate Oxides

The dielectric breakdown of ultra-thin silicon dioxide films used as gate insulator in MOSFETs is one of the most important reliability issues in CMOS technology. In this paper, two main aspects of oxide breakdown are considered: the modeling of the breakdown statistics and the properties of the two main breakdown modes, namely Soft Breakdown and Hard Breakdown. The most invoked models for the breakdown statistics that relate defect generation and breakdown are reviewed. Particular attention is paid to the percolation models and to a recent cell-based analytic picture. The scaling of the breakdown distribution with oxide thickness is considered and it is shown that both pictures are equivalent for ultra-thin oxides. It is shown that soft and hard breakdown show coincident statistics and this is used to conclude that both breakdown models are triggered by the formation of the same kind of defect-related conduction paths. The big differences in the post-breakdown conduction properties are attributed to phenomena occurring during the very fast breakdown current runaway that determine the area of the final breakdown spot. The properties of soft and hard breakdown are explained within the common framework of a model based on quantum-point-contact conduction. This mesoscopic approach to the post-breakdown conduction is shown to explain the main experimental results including conductance quantization after hard breakdown, the area and thickness independence of the soft-breakdown I(V) characteristics and the statistical correlation between current level and normalized conductance. Finally, we deal with some open questions and relevant issues that are now subject of intensive investigations. The fact that some breakdown events can be tolerated for some digital applications is considered. In this regard, the distinction between breakdown and device failure distributions is made and some implications for device reliability are discussed. It is argued that energy dissipation during the breakdown runaway can determine the breakdown efficiency, the prevalence ratio of soft to hard breakdown, and their variations with stress conditions, experimental setup (series impedance) and sample characteristics.

BREAKDOWN MODES AND BREAKDOWN STATISTICS OF ULTRATHIN SiO2 GATE OXIDES

The dielectric breakdown of ultra-thin silicon dioxide films used as gate insulator in MOSFETs is one of the most important reliability issues in CMOS technology. In this paper, two main aspects of oxide breakdown are considered: the modeling of the breakdown statistics and the properties of the two main breakdown modes, namely Soft Breakdown and Hard Breakdown. The most invoked models for the breakdown statistics that relate defect generation and breakdown are reviewed. Particular attention is paid to the percolation models and to a recent cell-based analytic picture. The scaling of the breakdown distribution with oxide thickness is considered and it is shown that both pictures are equivalent for ultra-thin oxides. It is shown that soft and hard breakdown show coincident statistics and this is used to conclude that both breakdown models are triggered by the formation of the same kind of defect-related conduction paths. The big differences in the post-breakdown conduction properties are attributed to phenomena occurring during the very fast breakdown current runaway that determine the area of the final breakdown spot. The properties of soft and hard breakdown are explained within the common framework of a model based on quantum-point-contact conduction. This mesoscopic approach to the post-breakdown conduction is shown to explain the main experimental results including conductance quantization after hard breakdown, the area and thickness independence of the soft-breakdown I(V) characteristics and the statistical correlation between current level and normalized conductance. Finally, we deal with some open questions and relevant issues that are now subject of intensive investigations. The fact that some breakdown events can be tolerated for some digital applications is considered. In this regard, the distinction between breakdown and device failure distributions is made and some implications for device reliability are discussed. It is argued that energy dissipation during the breakdown runaway can determine the breakdown efficiency, the prevalence ratio of soft to hard breakdown, and their variations with stress conditions, experimental setup (series impedance) and sample characteristics.

MOSFET Gate Oxide Reliability Anode Hole Injection Model and its Applications

We review the development of the anode hole injection (AHI) model for reliability projection of the silicon dioxide gate dielectric. The experimental and theoretical foundation of the AHI model is presented. Recent development and implications for the reliability of ultra-thin oxides are discussed. AHI is used to illuminate the questions of E versus 1/E models and field-driven versus voltage-driven models. Building on the concept of effective thinning, the AHI model is applied for the interpretation of defect-induced breakdown data and for optimizing oxide screening conditions. Circuit level reliability projection as a function of operating time, temperature, and power supply voltage is also illustrated.

Effect of humidity and temperature on the tensile strength of polyimide/silicon nitride interface and its implications for electronic device reliability

A new strategy for improving, predicting, and optimizing the mechanical reliability of interfaces appearing in electronic devices, substrates, and their packages, is introduced. An essential feature of this strategy is to measure the fundamental tensile strength of interfaces devoid of any material plasticity and geometry effects and quantify changes in the measured strengths by exposing interfaces to varying levels and duration of in-situ temperature rise and relative humidity. These fundamental strength charts can now to be used in conjunction with simulations capable of predicting time-dependent stress concentrations, moisture accumulation, and temperature rise at critical interfaces during processing and service, and thus, predict device reliability from a fundamental standpoint. Since these latter simulations are already well developed and largely available, implementation of the proposed strategy requires development of largely unavailable database on the degradation of the interfaces’ intrinsic tensile strengths. As a start, this paper presents such a data for the polyimide/Si 3N/Si interface system, which besides serving as an exemplar, has importance in device fabrication. The strength data is gathered using the laser spallation technique, in which a laser-generated stress wave on the backside of the substrate pries off the coating deposited on its front surface. This work extends this technique for multilayer testing. Interestingly, the degrading effect of each variable was found to fall in two separate regimes of moderate and strong effect. Uncovering of such transition zones is of obvious importance in reliability studies.

Exploration strategies, performance, and error consequences when learning a complex computer task

When trying to learn a complex task, people can use different strategies. They can use systematic exploration in which they take on an active approach to discover the computer functions and make use of problem solving steps such as planning, evaluation of feedback, and control of emotion and motivation. Alternatively, they can use non-systematic strategies like trial-and-error, rigid exploration, and encapsulation in information seeking. This study examined whether the exploration strategies were related to error consequences and performance when people learned a new computer program. Strategies were assessed by means of coding. Analysis showed strong correlations between strategies, error consequences, and task performance. These results can have implications for training design and human reliability in dealing with complex devices.

Exploration strategies, performance, and error consequences when learning a complex computer task

When trying to learn a complex task, people can use different strategies. They can use systematic exploration in which they take on an active approach to discover the computer functions and make use of problem solving steps such as planning, evaluation of feedback, and control of emotion and motivation. Alternatively, they can use non-systematic strategies like trial-and-error, rigid exploration, and encapsulation in information seeking. This study examined whether the exploration strategies were related to error consequences and performance when people learned a new computer program. Strategies were assessed by means of coding. Analysis showed strong correlations between strategies, error consequences, and task performance. These results can have implications for training design and human reliability in dealing with complex devices.

Global (interconnect) warming

This article presents a comprehensive analysis of the thermal effects in advanced high-performance VLSI interconnect systems arising due to self-heating under various circuit conditions, including electrostatic discharge (ESD). Technology (Cu, low-k, etc.) and scaling effects on the thermal characteristics of the interconnects, and on their electromigration (EM) reliability, have been analyzed simultaneously, which have important implications for providing robust and aggressive deep sub-micron (DSM) interconnect design guidelines. The analysis takes into account the effects of increasing interconnect (Cu) resistivity with decreasing line dimensions and the effect of a finite barrier metal thickness. Furthermore, the impact of these thermal effects on the design (driver sizing) and optimization of the interconnect length between repeaters at the global-tier signal lines are investigated. Finally, the reliability implications for minimum-sized vias in optimally buffered signal nets will also be quantified.

Molecular model for intrinsic time-dependent dielectric breakdown inSiO2 dielectrics and the reliability implications for hyper-thin gateoxide

SiO2 films, at constant electric field, show a significantreduction in time-dependent dielectric breakdown (TDDB) performance when thethickness tox is scaled below 4.0 nm. This reduction in TDDB performance iscoincident with and scales with the increase in direct tunnelling (DT) leakagethrough these hyper-thin oxide films. Assuming that the increase in DT leakageleads to more hole injection and trapping in the SiO2, the enhanceddielectric degradation rate with tox reduction can be explained on the basisof an intrinsic molecular model where hole capture serves to catalyze Si-Obond breakage.