Seedless Cu Electroplating on Ru-W Thin Films for Metallisation of Advanced Interconnects

For decades, Ta/TaN has been the industry standard for a diffusion barrier against Cu in interconnect metallisation. The continuous miniaturisation of transistors and interconnects into the nanoscale are pushing conventional materials to their physical limits and creating the need to replace them. Binary metallic systems, such as Ru-W, have attracted considerable attention as possible replacements due to a combination of electrical and diffusion barrier properties and the capability of direct Cu electroplating. The process of Cu electrodeposition on Ru-W is of fundamental importance in order to create thin, continuous, and adherent films for advanced interconnect metallisation. This work investigates the effects of the current density and application method on the electro-crystallisation behaviour of Cu. The film structure, morphology, and chemical composition were assessed by digital microscopy, atomic force microscopy, scanning and transmission electron microscopies, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The results show that it was possible to form a thin Cu film on Ru-W with interfacial continuity for current densities higher than 5 mA·cm⁻²; however, the substrate regions around large Cu particles remained uncovered. Pulse-reverse current application appears to be more beneficial than direct current as it decreased the average Cu particle size.     

George G. Thompson (1914–2008).

Presents an obituary for George G. Thompson (1914–2008). George G. Thompson died peacefully on July 12, 2008, in Worthington, Ohio, after a brief illness. He was 94 years old. Although he had retired almost 30 years before his death, he had a remarkable memory and keen analytical skills to the very end of his life. He was best known for his research and writing on developmental and educational psychology. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

“Seedless” electrochemical deposition of copper on physical vapor deposition-W2N liner materials for ultra large scale integration (ULSI) devices

Electrochemical studies are designed to identify processes that provide adequate nucleation and thin film growth directly on ultrathin, air-exposed physical vapor deposition (PVD)-tungsten nitride diffusion barriers. In this study, it is shown that very thin copper films can be nucleated directly on a conducting PVD-W₂N liner surface. A complex chemistry model based on mass balance and thermodynamic equilibrium has been applied to numerous ammoniacal platting bath compositions and the resulting concentration profiles inserted into the Nernst equation. Comparing the experimental results with the predicted model indicates that a strong adhesion is associated with the reduction of several copper-ammonia complexes at the metal nitride surface. Nucleation, growth mechanisms, and film resistivity are found to be dependent on the reduction potential, electrolyte velocity, and platting bath chemistry.     

HPLC-DAD-ESI-MS analysis of flavonoid compounds in 5 seedless table grapes grown in Apulian Region

Flavonoids present in skin extracts of red seedless table grape varieties Summer Royal, Autumn Royal, and Crimson, and white seedless varieties Carati and Thompson were analyzed by HPLC-DAD-MS, in 3 y of study (2006 to 2008). The anthocyanins, delphinidin-3-O-glucoside, cyanidin-3-O-glucoside, petunidin-3-O-glucoside (with their corresponding p-coumaroyl derivatives), peonidin-3-O-glucoside, and malvidin-3-O-glucoside (with their corresponding acetyl, caffeoyl, and p-coumaroyl derivatives) were found. In addition the flavonols quercetin-3-O-glucuronide, quercetin-3-O-rutinoside, quercetin-3-O-glucoside, kaempferol-3-O-glucoside, kaempferol-3-O-galactoside, and the flavan-3-ols procyanidin B1, procyanidin B2, and catechin were also detected. Anthocyanins were the main flavonoids in red grapes ranging from 24 (Crimson) to 500 (Summer Royal) mg/kg fresh weight of grapes; consistent levels of flavonols and flavan-3-ols were also quantified in all varieties. To determine the effective climatic influence on flavonoids content in field conditions, viticultural practices have been developed, that could exclude the effects of direct solar radiation from confounding the assessment of those related to thermal conditions alone. A strong positive correlation was determined between flavonoids and temperature data that seem to be responsible for the difference of these metabolites along the years; furthermore, it has been possible to define a linear relationship (R(2) = 0.6871, P = 0.0057) between thermal amplitude and total flavonoids values in the red grapes. PRACTICAL APPLICATION: Grapes are economically the most important fruit species in the world and approximately 30% of its production is used as fresh fruit. Because of the very important role of flavonoids in food quality as well as their health-promoting properties, and considering that our experiments were performed along 3 consecutive years, gathered results in this research are quite promising to give a useful information on the flavonoid contents and their evolution in 5 seedless table grapes that are widespread in Mediterranean regions but also in California and South America, and are grown in a viticultural climate (Apulia, South Italy) very close to some regions of Spain, Turkey, Tunisia, and Israel.     

Optical method using rotating Glan–Thompson polarizers to independently vary the power of the excitation and repumping lasers in laser cooling experiments

A simple optical technique consisting in the rotation of Glan–Thompson polarizers is applied to independently vary and control the power of the cooling laser and the repumping laser in laser cooling experiments of ⁸⁷Rb. For our experimental conditions, which include initial laser powers of approximately 48 mW (for each laser), it was observed that the atom cloud was still visible after reducing the power of the cooling laser to ～10 mW while keeping the power of the repumping laser at its initial level. On the other hand, the atom cloud maintained visibility after reducing the power of the repumping laser to ～103 µW while keeping the power of the excitation laser at its initial level. In both cases the power variation of the lasers is achieved without altering the frequency or tuning characteristics of the lasers.     

原子力显微镜在马氏体相变切变角测定中的应用

由于原子力显微镜具有很高的横向分辨率和纵向分辨率，可以精确测定马氏体相变浮凸角，为马氏体相变切变角的精确测定奠定了基础。以Fe-30Mn-6Si形状记忆合金的应力诱发巴氏体相变切变角为例，利用原子力显微镜测出表现浮凸角，再经理论修正获得切变角。结果表明，原子力显微镜测定具有很高的精度和方法简便的特点。     

Finite Element Analysis of Nonlinear Fully Coupled Thermoelectric Materials

A complete nonlinear coupled finite element algorithm for thermoelectric materials is developed and implemented within a two-dimensional finite element code. Starting from a suitable formulation of the constitutive (including Seebeck, Joule, Peltier and Thompson effects) and equilibrium equations, residual vectors and consistent tangent matrices are formulated and implemented in a standard four-node isoparametric element with two degrees of freedom per node (voltage and temperature). The nonlinearities arise due to the coupling between the electric and thermal fluxes, to the dependence of the discretized material parameters with the independent variable temperature and to a convective-type term, representing the thermal energy that electrons carry. Three examples for Bi₂Te₃ thermoelements are presented. The first two compare the numerical results with simplified, one-dimensional analytical solutions. The first example is related to a linear uncoupled evaluation, the second to a nonlinear coupled Seebeck effect. Perfect agreement is obtained between the analytical (obtained by considering the material properties constant in the second case) and numerical solutions. The first two examples show that the dependency of the material coefficents is not important for one-dimensional cases. The third example, without direct analytical solution due to the complete coupling and material nonlinearity, studies the two-dimensional Peltier effect of a thermopair.     

Decision making policy for RF energy harvesting enabled cognitive radios in decentralized wireless networks

Cognitive radio (CR) paradigm with radio frequency energy harvesting (RFEH) have significant potential to improve the network throughput by utilizing vacant spectrum using battery-operated self-sustainable radio terminals. Research efforts relevant to these paradigms are focused on the mode selection policies which decide when to switch from CR mode (i.e., opportunistic vacant spectrum access mode) to the RFEH mode (i.e., battery charging using ambient RF energy) and vice-versa. So far, very little attention has been paid to the dual but competing task of frequency band selection in CR and RFEH modes under partially observable environment in the decentralized wireless networks. Furthermore, the need of tunable bandwidth frequency band access for CRs and lower subband switching cost (SSC) for energy efficient implementation have made the design of the decision making policy (DMP) more challenging. In this paper, a new CR-RFEH DMP has been proposed for RFEH enabled CR terminals in the decentralized wireless networks. The proposed DMP consists of three sub-units: 1) Bayesian approach based tunable Thompson sampling algorithm for subband statistics estimation, 2) Thompson sampling algorithm based subband access scheme exploiting the past collision events to minimize collisions among CRs, and 3) Mode selection scheme. Simulation results show that the proposed DMP offers 10–35% improvement in the throughput of the decentralized network and 40–90% reduction in the number of subband switchings compared to existing DMPs. The simulation results are then validated using real radio signals on the proposed USRP testbed.     

The saucor, a new stereological tool for analysing the spatial distributions of cells, exemplified by human neocortical neurons and glial cells

The 3D spatial arrangement of particles or cells, for example glial cells, with respect to other particles or cells, for example neurons, can be characterized by the radial number density function, which expresses the number density of so-called 'secondary' particles as a function of their distance to a 'primary' particle. The present paper introduces a new stereological method, the saucor, for estimating the radial number density using thick isotropic uniform random or vertical uniform random sections. In the first estimation step, primary particles are registered in a disector. Subsequently, smaller counting windows are drawn with random orientation around every primary particle, and the positions of all secondary particles within the windows are recorded. The shape of the counting windows is designed such that a large portion of the volume close to the primary particle is examined and a smaller portion of the volume as the distance to the primary object increases. The experimenter can determine the relation between these volumina as a function of the distance by adjusting the parameters of the window graph, and thus reach a good balance between workload and obtained information. Estimation formulae based on the Horvitz-Thompson theorem are derived for both isotropic uniform random and vertical uniform random designs. The method is illustrated with an example where the radial number density of neurons and glial cells around neurons in the human neocortex is estimated using thick vertical sections for light microscopy. The results indicate that the glial cells are clustered around the neurons and the neurons have a tendency towards repulsion from each other.