Performance and reliability enhancement for CVD tungsten polycidedCMOS transistors due to fluorine incorporation in the gate oxide

The impacts of CVD tungsten polycide (WSi_x) on MOSFET performance and reliability are studied in this letter. The WSi_x process is shown to enhance the S/D lateral extent for both N- and P-channel devices via C_GD and L_eff measurements, confirming previous suspicion. This enhanced S/D extent is found to be easily modulated by drain-to-gate bias, which is favorable for achieving both higher drive currents and higher S/D punch-through voltages than those of non-WSi_x devices. Both electron and hole mobility for the WSi_x device are also slightly higher and closer to the published data compared to the non-WSi_x case. These effects together yield about >5% improvement for nMOSFET and >10% improvement for pMOSFET in drive current at a given punch-through voltage. The channel hot-electron lifetime for the n-channel WSi_x device is about 10 times higher than that of the non-WSi_x one. These enhancements in both performance and reliability make the WSi_x device very attractive fog VLSI CMOS technologies     

Delay spread measurements for the digital cellular channel inToronto

The paper describes a set of measurements performed in the Toronto area, in order to assess the impact of multipath propagation on the performance of the TIA IS-54 digital standard. Five existing cells were systematically surveyed: two in downtown Toronto, two in the suburbs, and one in a suburban/rural area. A sweeping correlator apparatus with a 0.1 μs resolution and 910 MHz carrier frequency, and an omnidirectional antenna was used. In one of the cells, the measurements were repeated with a 60 degree beamwidth directional antenna. A fairly sophisticated thresholding technique was applied in order to reduce the impact of noise. Generally, the measurements with the omnidirectional antenna exhibit multipath propagation with considerably smaller excess delays than some reported, but are consistent with earlier results obtained in the U.S. and Europe. Sectorization was found to considerably reduce the multipath effects. Very large delay components appear to be due mostly to the combination of large transmitter-receiver distances and a large degree of shadowing, and could probably be avoided to a large extent by standard cellular engineering techniques. In view of these results, it seems that the long delay (high selectivity) problem has been somewhat overemphasized in the past, at least for areas like Toronto. Problems associated with short delays (flat fading), on the contrary, appear to have been underestimated in the case of dense urban environments     

The effect of adjacent channel interference on the capacity of FDMAcellular systems

In FDMA cellular radio systems, the adjacent channel interference (ACI) is suppressed by the IF filter and also by a distance factor. Channels immediately adjacent to each other in frequency are assigned to different cells and, as such, the distance plays a role in reducing their mutual interference. The authors study the feasibility of optimizing the frequency spacing between carriers such that the combined effect of distance and IF filter will be enough to control the interference while allowing the maximum number of channels in a given bandwidth. They also study the decision feedback equalizer (DFE) as a means to reduce any excess ACI that results from reducing the channel spacing. The paper starts with a model that estimates the cumulative probability density of the signal to adjacent channel interference ratio (SIR) as a function of the channel spacing. They then present the results of a computer simulation study to estimate the performance of DFE in mitigating the effect of ACI. The results indicate that, under the conditions of slow flat fading and selection diversity, the DFE is very effective in reducing the effect of excess ACI interference which allows for a considerable reduction in the frequency spacing     

Development of statistical theory in reliability engineering: A survey

Statistical theory and its applications have played a significant role in the advancement of methodology and techniques for solving various problems in reliability engineering. Different criteria of aging have been introduced for modelling and characterizations of wear properties. Some real life engineering reliability operations arising in maintenance and replacement policies formulations are investigated as convolution, mixture and formation of coherent systems. Shock models are studied for shocks arriving according to Poisson process and causing damages with specific form of aging. Cumulative damage models have been also studied by many researchers. Statistical hypotheses testing are used to test whether a certain, censored or uncensored data has exponential or a specific aging propety.In this paper we present a unified state of the art type of survey for the research and developments in these problems. In particular we expose the main recent contributions, trace the trend of research and highlight the possible direction of further research.     

Generalized formulation of yield, variability, minimax and Taguchi circuit optimization problems

A generalized formulation of several circuit design problems, such as manufacturing yield optimization, circuit performance variability minimization, deterministic and statistical minimax design, Income Index maximization, Taguchi approach, etc., is developed. Several other “intermediate” problems can be defined in a sense similar to the one used in Zadeh's fuzzy set theory. A specific problem is identified by the selection of a generalized membership function ω(·) of the acceptability region, and a sequence of the values of the “smoothing” parameter β. Generalized gradient formulas are developed, and various possible algorithmic implementations discussed. As a result, trade-offs between different design strategies can be investigated by circuit designers, within one coherent methodology.     

Probabilistic approach to some problems of system safety

Measures of direct importance of unrepairable system components, based on the multilinear expansions, are introduced. Various characteristics of system quality of performance are discussed. Cases of binar and multistate components are studied. The measure of specific importance, considering the cost of reliability component's improvement, is defined. The multilinear expansion for a system of multistate components, giving the possibility to estimate measures of the direct importance of components and levels of components performance as well, is discussed. The limit transition to continuum structures is performed. Some measures of importance for repairable systems are introduced.     

Aspects of the transpiration model for aerofoil design

Transpiration is a technique in which extra non-physical normal flows are created on an aerofoil surface in order to form a new streamline pattern such that the surface streamlines no longer follow the aerofoil surface under inviscid flow. The transpiration model is an important technique adopted in aerofoil design either to avoid mesh regeneration when aerofoil profile co-ordinates are adjusted or to find shape corrections in inverse design methods. A first-order approximation (with respect to the normal streamline displacement) to the transpiration model is commonly adopted; it is shown that this can be a poor approximation especially in regions of high curvature. In this paper more accurate approximations are developed to address this problem and improve the accuracy.     

The effects of flow split ratio and flow rate in manifolds

This paper reports a combined experimental and numerical investigation of three-dimensional steady turbulent flows in inlet manifolds of square cross-section. Predictions and measurements of the flows were carried out using computational fluid dynamics and laser Doppler anemometry techniques respectively. The flow structure was characterized in detail and the effects of flow split ratio and inlet flow rate were studied. These were found to cause significant variations in the size and shape of recirculation regions in the branches, and in the turbulence levels. It was then found that there is a significant difference between the flow rates through different branches. The performance of the code was assessed through a comparison between predictions and measurements. The comparison demonstrates that all important features of the flow are well represented by the predictions.     

Analysis of a soliton-based logic module for a ring network

We analyze and numerically study the code-matching logic module that is the central element in a proposed soliton-based ring network system running at peak rates of 100 Gb/s. The proposed network is packet-switched, and fast logic is required to route each packet. That is the function of the code-matching logic module, and four soliton logic gates that can perform fast logic are the key devices in its design. The behavior of the code-matching logic module is governed by a large set of parameters, and we simulate it by varying many of these parameters. The physical effects that occur in these devices and their significance are analyzed. The results indicate that the logic module will work but within a restricted parameter range