A high-linearity 100-element diode grid mixer

Grid-mixer arrays can achieve high linearity and dynamic range through quasi-optical power combining. We present a 100-element single-ended diode grid mixer operating at 2.45 GHz. Each element incorporates two diodes in series. We measure an input third-order intercept of 11 W (40.5 dBm), and output third-order intercept of 3.4 W (35.4 dBm), and an associated conversion loss of 5.1 dB. The power-handling capability of the array is 100 times larger than that of a microstrip mixer using a single element. The local oscillator (LO) drive requirement for the entire array is 1.4 W (31.6 dBm). The angular dependence of the array's IF power is also presented and is in agreement with theory     

A new methodology for the identification of ball bond degradation during high-temperature aging tests on devices in standard plastic packages

We describe a new methodology for the “in situ” identification of wire-bond degradation at early stages during high-temperature aging tests on devices with standard plastic packages. This methodology is based on the measurement of the changes in wire bond resistance, which is deduced from the I(V) characteristics of the ESD protection diodes on each contact pad of the circuit. In a first stage, the measurement procedure is described, with emphasis on the initial temperature calibration. This procedure allows for an “in situ” measurement sequence, where the packages stay in the aging chamber, at elevated temperature, during the electrical tests on the pad connections performed at different aging durations. By following accurately the package temperature, using a thermocouple, it is possible to correct for slight changes and thus get a reliable I–V measurement for each interconnection. In the second stage, the aging test results are described, showing the evolution of each individual interconnection. We were able to identify the onset of wire-bond degradation through the progressive increase of their resistance. To allow for better determination of the degradation process, once an increase in wire bond resistance was detected, complete I(V) curves were recorded at the pin(s) of interest. For each pin of a TQFP64 package, the tests were performed at least twice a day, with increased density when initial failure is detected (one complete measurement every 3 h). This strategy allowed for the detection of different behaviors on the wire bonds: good ball bonds (i.e. ball bonds with no change in their resistance), ball bond with intermittent opens (these ball bonds are in the process of degradation, and thermo-mechanical stresses induced in the resin by very small temperature changes are sufficient to open or close the circuits) and completely destroyed ball bonds, for which the resistance stays in an “high” level. This approach to wire-bond degradation in plastic packages is very powerful in terms of the number of interconnections which can be followed “in real time” and especially has the advantage, over other classical approaches, that the devices under test stay operational, contrary to what occurs with other types of destructive testing. These electrical test results are compared with metallographic investigations performed after a series of mechanical tests on the ball bonds (wire pull/ball shear tests) on a set of identical devices which undergone exactly the same High Temperature Storage (HTS) aging for 2000 h at 165 °C.     

Sequential environmental stresses tests qualification for automotive components

The purpose is to create a new qualification methodology for plastic encapsulated electronic components used in an automotive environment at high temperature. It is based on the acceleration of failure mechanisms like ball bond lift (due to intermetallic Au–Al thickness growth), by combination of environmental stresses. The delamination measurement was used as an indicator of potential assembly weaknesses. An optimized package sequential qualification test flow is proposed.     

Simultaneous Determination of Volatile Metal (Pb, Hg, Sn, In, Ga) and Nonmetal Species (Se, P, As) in Different Atmospheres by Cryofocusing and Detection by ICPMS

A sensitive method for multielemental speciation analysis of volatile metal and metalloid compounds in air has been developed. The analytes are sampled simultaneously in the field by cryofocusing on a small glass wool-packed column at -175 °C. Detection is performed in the laboratory by low-temperature GC hyphenated with ICPMS. Oxygen addition in the carrier gas was used to reduce interferences originating from the presence of volatile carbon-containing species in the samples. Plasma stability during analysis was monitored continuously by internal standardization (Xe). This system provides routine absolute detection limits of 0.06-0.07 pg (as Pb) for tetraalkyllead species (Me(4)Pb, Et(4)Pb), 0.2 pg (as Sn) for tetraalkyltin species (Me(4)Sn, Et(4)Sn), 0.8 pg (as Hg) for mercury species (Hg(0), Me(2)Hg, Et(2)Hg), and 2.5 pg (as Se) for selenium species (Me(2)Se). This instrumentation makes it possible to collect small air sample volumes and has been successfully applied to the determination of volatile metal and metalloid species in the atmosphere in urban and rural locations. Qualitative application in the semiconductor industry is also reported with regard to the detection of arsenic (ASH(3), tert-butylarsine), phosphorus (PH(3), tert-butylphosphine), alkylindium, and gallium species.     

Experimental evidence of damaged zones in thin Ta2O5 anodic layers on polycrystalline tantalum foils

The challenge recently demanded of electrolytic tantalum capacitors is to be able to operate above the frequency of 1 MHz which can be carried out insofar as their equivalent series resistance (ESR) is sufficiently small. Now, the mechanical quality of the oxide layers plays a determining part in the value of the ESR and the purpose of the present work is to detect in the oxide layer the areas most likely to be damaged but not yet cracked. It is shown that weaker zones exist in the oxide layer. These zones are revealed by chemical etching. The relative damaged area of one sample relative to another is correlated with the grain size ratio, by means of XPS, SEM and liquid capacitance measurements. It is established that the amorphous oxide is preferentially etched just above the grain boundaries of the tantalum substrate. These results lead to the conclusion that annealing at the greatest possible temperature has the best effect on the mechanical quality of the oxide layer.     

DC-sputtered Bi(Pb)SrCaCuO films on single (MgO) and polycrystalline (MgO,CuO) substrates

Bi(Pb)SrCaCuO films have been deposited on single (MgO) and polycrystalline (poly MgO, CuO) substrates by DC sputtering. All the films became superconducting after post-annealing them in air. The films on single crystal MgO showedT _c onset at 120 K andT _c at 92 K. However, the extrapolated zero resistivity is obtained at 106 K. The ac susceptibility showed an onset at 106 K and a sharp transition at 85 K. The films on poly MgO and poly CuO had aT _c=72 K. The preparation, X-ray diffraction and morphology of these samples are presented.     

Laminar flow around corners triggers the formation of biofilm streamers

Bacterial biofilms have an enormous impact on medicine, industry and ecology. These microbial communities are generally considered to adhere to surfaces or interfaces. Nevertheless, suspended filamentous biofilms, or streamers, are frequently observed in natural ecosystems where they play crucial roles by enhancing transport of nutrients and retention of suspended particles. Recent studies in streamside flumes and laboratory flow cells have hypothesized a link with a turbulent flow environment. However, the coupling between the hydrodynamics and complex biofilm structures remains poorly understood. Here, we report the formation of biofilm streamers suspended in the middle plane of curved microchannels under conditions of laminar flow. Experiments with different mutant strains allow us to identify a link between the accumulation of extracellular matrix and the development of these structures. Numerical simulations of the flow in curved channels highlight the presence of a secondary vortical motion in the proximity of the corners, which suggests an underlying hydrodynamic mechanism responsible for the formation of the streamers. Our findings should be relevant to the design of all liquid-carrying systems where biofilms are potentially present and provide new insights on the origins of microbial streamers in natural and industrial environments.     

Brain-Computer Interfaces, Virtual Reality, and Videogames

Major challenges must be tackled for brain-computer interfaces to mature into an established communications medium for VR applications, which will range from basic neuroscience studies to developing optimal peripherals and mental gamepads and more efficient brain-signal processing techniques.     

Experimental design methodology applied to adsorption of metallic ions onto fly ash

The objective of this study was to define operating conditions which would conciliate a high removal of the five metallic cations (Cu2+, Ni2+, Zn2+, Cd2+, Pb2+) and a low desorption of these metal ions from the contaminated sorbents. To achieve this goal the strategy relied on the use of experimental design methodology. The influence of four parameters (fly ash/lime mass ratio, type of fly ash/lime sorbent, solution temperature, and sorbent concentration) on the removal at pH = 5 and the stabilization of the five metallic ions was studied. In the first step, the influence of three parameters on the removal of Cu2+ ions was studied (R2 = fly ash/lime mass ratio, type of sorbent, temperature). It was found that the same set of parameter values would produce both the highest removal and the lowest desorption for this cation: R2 = 9 g g(-1), sorbent B (made by mixing fly ash and lime in water, then drying this paste at 105 degrees C for 24 h), temperature of suspension equal to 60 degrees C. The formation of calcium silicate hydrate (CSH), resulting from the pozzolanic activity of fly ash, is assumed to be partially responsible for these mechanisms. In the second step, simplex methodology and Doehlert matrix were used to find the conditions in a 2D space (sorbent concentration, temperature of solution) that would give the highest removal from a solution containing five metallic cations and the lowest desorption of these five cations adsorbed on the contaminated sorbents. Then, the system response that had to be optimized was the total metallic ions concentration (TMIC, mol L(-1)). A TMIC was measured both for adsorption and leaching experiments. These responses were modelized using a second-order polynomial and the surface responses were plotted for adsorption and desorption results. A difference was observed between operating conditions reaching the highest adsorption from those that gave the lowest desorption. However, an adsorbent concentration around 122 g L(-1) and a solution temperature of 66 degrees C would lead simultaneously to a high adsorption and a low desorption.