A comparison of electronic-reliability prediction models

One of the most controversial procedures in reliability is the use of reliability prediction techniques based on component failure data to estimate system failure rates. The International Electronics Reliability Institute (IERI) at Loughborough University is in a unique position. Over many years, much reliability information has been collected from leading British and Danish electronic manufacturing companies. These data are of such high quality that IERI can perform the comparison exercise with many circuit boards (CB) of different types. Several CB were selected from the IERI field-failure database and their reliability was predicted and compared with the observed field-performance. The prediction techniques were based on the: M217E [US Mil-Hdbk-217E]; HRD4; Siemens (SN29500); CNET; and Bellcore (TR-TSY-000332) models. For each model, the associated published failure rates were used. Hence, parts count analyses were performed on several CB from the database; these analyses were compared with the field failure rate. The prediction values differ greatly from the observed field behavior and from each other. Further analysis showed that each prediction model was sensitive to widely different physical parameters. The results are summarized. Some of the models are more sensitive to a factor that varies according to an Arrhenius model, such as temperature and electrical stress, while others are more sensitive to the discrete π factors used to model environment and quality     

2DEG base hot electron transistors fabricated using MBE and in situion beam lithography

A vertical hot electron transistor incorporating a two-dimensional electron gas (2DEG) base has been fabricated in the GaAs-AlGaAs materials system. The difficulties caused by the need to form selective ohmic contacts to the different conducting layers have been overcome using a combination of in situ focused ion beam (FIB) isolation and molecular beam epitaxial (MBE) regrowth. This has allowed a high yield of working devices to be achieved with a typical common emitter current gain of h_FE=6 at low temperatures     

Fabrication of Sub‐10 nm Metallic Lines of Low Line‐Width Roughness by Hydrogen Reduction of Patterned Metal–Organic Materials

The fabrication of very narrow metal lines by the lift‐off technique, especially below sub‐10 nm, is challenging due to thinner resist requirements in order to achieve the lithographic resolution. At such small length scales, when the grain size becomes comparable with the line‐width, the built‐in stress in the metal film can cause a break to occur at a grain boundary. Moreover, the line‐width roughness (LWR) from the patterned resist can result in deposited metal lines with a very high LWR, leading to an adverse change in device characteristics. Here a new approach that is not based on the lift‐off technique but rather on low temperature hydrogen reduction of electron‐beam patterned metal naphthenates is demonstrated. This not only enables the fabrication of sub‐10 nm metal lines of good integrity, but also of low LWR, below the limit of 3.2 nm discussed in the International Technology Roadmap for Semiconductors. Using this method, sub‐10 nm nickel wires are obtained by reducing patterned nickel naphthenate lines in a hydrogen‐rich atmosphere at 500 °C for 1 h. The LWR (i.e., 3 σ_LWR) of these nickel nanolines was found to be 2.9 nm. The technique is general and is likely to be suitable for fabrication of nanostructures of most commonly used metals (and their alloys), such as iron, cobalt, nickel, copper, tungsten, molybdenum, and so on, from their respective metal–organic compounds.     

Dynamic interactions between accommodation and convergence

Frequency-domain equations were derived for the current dual-interaction model of accommodation and convergence control, and its adaptive behavior was related to the system's parameters. Contrary to predictions based on the steady-state performance of the model [18], dynamic analysis showed that the AC/A is sensitive to the method of measurement and a procedure is established for its reliable determination. Additionally, the results provided theoretical support for the empirical finding that low AC/A and CA/C ratios are associated with high accommodative and convergence adaptation, respectively [15]. The derived equations should help future studies relate the physiological behavior of accommodative and convergence to specific model parameters.     

CSRS-MAC: Cluster Based Synchronous Radio Scheduling MAC Protocol Using Carrier Sense Multiple Access for Wireless Sensor Network

Wireless Personal Communications - Wireless sensor network is gaining popularity due to its large-scale deployment in Internet of Things. The constraints of resources influence the protocol design...     

Analysis of dynamic magnetic resonance images

Dynamic magnetic resonance (MR) imaging with contrast agents is a very promising technique for studying tissue perfusion in vivo. A temporal series of magnetic resonance images of the same slice are acquired following the injection of a contrast agent into the blood stream. The image intensity depends on the local concentration of the contrast agent, so that tissue perfusion can be studied by the image series. A new method of analyzing such series is described here. Nonparametric linear regression is used for modeling the image intensity along the series on a pixel by pixel basis. After modeling, some relevant quantities describing the time series are obtained and displayed as images. Due to its flexibility, this approach is preferred to parametric modeling when pathology is present since this can induce a wide spread of patterns for the pixel image intensity along time. Results of the application of the method to series of dynamic magnetic resonance images from ischaemic rat brains after the injection of the susceptibility agent Sprodiamide Inj. (Dy-DTPA-BMA) are shown and compared to results from a related known method.     

A monolithic DC temperature compensation bias scheme for multistageHEMT integrated circuits

This work benchmarks the first demonstration of a multistage monolithic HEMT IC design which incorporates a DC temperature compensated current-mirror bias scheme. This is believed to be the first demonstrated monolithic HEMT bias scheme of its kind. The active bias approach has been applied to a 2-18 GHz five-section low noise HEMT distributed amplifier which achieves a nominal gain of 12.5 dB and a noise figure <2.5 dB across a 2-18 GHz band, The regulated current-mirror scheme achieves better than 0.2% current regulation over a 0-125°C temperature range, The RF gain response was also measured over the same temperature range and showed less than 0.75 dB gain degradation. This results in a -0.006 dB/°C temperature coefficient which is strictly due to HEMT device G_m variation with temperature. The regulated current-mirror circuit can be employed as a stand-alone V_gs-voltage reference circuit which fan be monolithically applied to the gate bias terminal of existing HEMT ICs for providing temperature compensated performance, This monolithic bias approach provides a practical solution to DC bias regulation and temperature compensation for HEMT MMICs which can improve the performance, reliability, and cost of integrated microwave assemblies (IMAs) used in space-flight military applications     

Advanced Call Scheduling for Testing a Telecommunications Network

This paper describes an advanced scheduling system and method for generating large volumes of calls to be used for testing a telecommunications network. The system is capable of preparing large-scale and complex network tests by viewing the task as a scheduling problem. The various requirements of the scheduling problem are analysed and represented as constraints or optimisation criteria. A fast heuristic method is proposed for solving the problem. The approach is based on a greedy algorithm for constructing solutions and it incorporates limited backtracking and dynamic value-ordering heuristics. The algorithm and system are currently being used for call charge verification in BT's PSTN and CSP networks.     

116-fs soliton source based on an Er-Yb codoped waveguide amplifier

A passively mode-locked soliton ring fiber laser is investigated that utilizes a 4.5-cm erbium-ytterbium (Er-Yb) codoped waveguide amplifier as the gain element. The resulting short cavity (1.3 m of fiber) eliminates multipulsing behaviour and reduces the effects of resonant sidebands, enabling generation of 116-fs solitons with a pulse energy of 160 pJ at a fundamental repetition rate of 130 MHz