Breaking through permeability–selectivity trade-off of thin-film composite membranes assisted with crown ethers

In this study, we deployed a modified interfacial polymerization process to incorporate multifunctional crown ethers (CEs) into thin-film composite (TFC) polyamide membranes. CE additives acted as both the phase-transfer catalyst and co-solvent to facilitate the diffusion of amine monomers into the organic phase via interacting with amine monomers (form the host-guest inclusion complex), and enhanced the free volume content of the selective layer, therefore facilitating water transport and inhibiting the diffusion of salt ions. Various characterization techniques were employed to elucidate the modification mechanism as a function of CE chemical and physical properties on the microstructure of resultant TFC membranes and consequently separation performances. Compared to TFC membranes produced from traditional interfacial polymerization method, CE-modified membranes exhibited a 146% water flux enhancement and 59% lower reverse salt fluxes with a suitable draw solution. CE-modified membranes also showed the improved antifouling behavior and chemical stability in various harsh conditions.     

Automated assessment of thigh composition using machine learning for Dixon magnetic resonance images

Objectives

To develop and validate a machine learning based automated segmentation method that jointly analyzes the four contrasts provided by Dixon MRI technique for improved thigh composition segmentation accuracy.

Materials and methods

The automatic detection of body composition is formulized as a three-class classification issue. Each image voxel in the training dataset is assigned with a correct label. A voxel classifier is trained and subsequently used to predict unseen data. Morphological operations are finally applied to generate volumetric segmented images for different structures. We applied this algorithm on datasets of (1) four contrast images, (2) water and fat images, and (3) unsuppressed images acquired from 190 subjects.

Results

The proposed method using four contrasts achieved most accurate and robust segmentation compared to the use of combined fat and water images and the use of unsuppressed image, average Dice coefficients of 0.94 ± 0.03, 0.96 ± 0.03, 0.80 ± 0.03, and 0.97 ± 0.01 has been achieved to bone region, subcutaneous adipose tissue (SAT), inter-muscular adipose tissue (IMAT), and muscle respectively.

Conclusion

Our proposed method based on machine learning produces accurate tissue quantification and showed an effective use of large information provided by the four contrast images from Dixon MRI.

     

Modeling the effect of barrier thickness and low-k dielectric on circuit reliability using 3D model

The continuous scaling down of the device size and escalating circuit speed drives the requirement for EM-resistant Cu interconnect with diffusion barrier and the low-k dielectric. The study of barrier layer thickness and low-k dielectric effect in a complete 3D circuit is necessary as the actual physical implementation of an integrated circuit in a wafer is indeed 3D in nature. This paper investigates the effect of barrier layer thickness and low-k dielectric on the circuit reliability of a complete 3D circuit model. It was found that the maximum atomic flux divergence (AFD) value increases with decreasing barrier layer thickness, which implied a shorter EM lifetime with thinner barrier. Low-k dielectric will give a higher maximum AFD due to higher stress gradient, and thus a shorter EM lifetime.     

Mathematical model of low-temperature wafer bonding under medium vacuum and its application

Low-temperature direct wafer bonding was successfully performed under medium vacuum level. A mathematical model was developed based on the qualitative understanding of the bonding mechanisms. The model combined the diffusion-reaction model of water in SiO/sub 2/ and the diffusion theory in porous media. It is found that the model agrees well with the experimental data. This model can be applied to predict the effects of annealing time, annealing temperature, ambient vacuum, wafer orientation, and wafer dimension on the bond strength.     

Nondestructive void size determination in copper metallization under passivation

A novel nondestructive failure analysis technique to rapidly locate tiny voids in narrow metallization line covered with passivation is proposed, based on the simulation results. In this technique, the current alteration in a metal line under study is recorded continuously when it is subjected to electron beam scanning and biased by a small external voltage. Finite-element analysis is performed to simulate the temperature distribution and current alteration in the metal line. The electron-beam heating is demonstrated as the most important factor contributing to the current alteration. Reconstruction of voids with any shape (such as wedge or slit) is possible on the basis of the gradient of the current alteration. It is found that the minimum detectable void size can be as low as 50 nm. Experimental verification of the technique is underway.     

Enhanced finite element modelling of Cu electromigration using ANSYS and matlab

An enhanced finite element modeling methodology based on commercial software ANSYS Multi-physics and Matlab is developed for the study of electromigration. Various driving forces, namely electron wind force migration (EWM), thermomechanical stress gradient induced migration (SM) and temperature gradient induced migration (TM) are simulated and the resulting atomic flux of metal atoms is calculated based on a non-standard use of ANSYS static thermal analysis routine. An automatic link between ANSYS and Matlab is developed to enhance the capability of ANSYS data postprocessing module in the calculation of atomic flux divergence (AFD). The simulation of a polycrystalline Cu thin film identifies a new potential EM reliability hazard in Cu interconnects which agrees well with experimental observations.     

Applications of multi-walled carbon nanotube in electronic packaging

Thermal management of integrated circuit chip is an increasing important challenge faced today. Heat dissipation of the chip is generally achieved through the die attach material and solders. With the temperature gradients in these materials, high thermo-mechanical stress will be developed in them, and thus they must also be mechanically strong so as to provide a good mechanical support to the chip. The use of multi-walled carbon nanotube to enhance the thermal conductivity, and the mechanical strength of die attach epoxy and Pb-free solder is demonstrated in this work.     

Room temperature observation of point defect on gold surface using thermovoltage mapping

In this work, we apply thermovoltage imaging using scanning tunneling microscope to observe atomic scale surface imperfections at room temperature. Thermovoltage mapping can provide high resolution (down to 1 nm) images of standing waves in metal at room temperature, thus avoiding the need for low temperature scanning tunneling microscopy for the investigation of the standing waves. In order to generate a thermovoltage between the sample and tip, the sample (Au(1 1 1)) is heated to about 40 °C above the room temperature and surface scanning is performed. Heating the sample is simpler than heating the tip by laser irradiation. The thermovoltage technique can be applied to estimate surface defect density and the severity of the surface defects in materials, which can be a useful tool for the reliability study of nano-scale materials and devices.     

Effect of stressed-skin action on optimal design of cold-formed steel square and rectangular-shaped portal frame buildings

Cold-formed steel (CFS) portal frames can be a viable alternative to conventional hot-rolled steel portal frames. They are commonly used for low-rise commercial, light industrial and agricultural buildings. In this paper, the effect of stressed-skin action on the optimum design of CFS portal frames is investigated by conducting a minimum cost design optimisation on a building of span of 6 m, height-to-eaves of 3 m and frame spacing of 3 m; the effect of different number of bays are considered. For the purpose of this study, it is assumed that gables are rigid.The effect of stressed-skin action is larger for“square-shaped” buildings (i.e. when the span and length are the same on plan) and decreases as more bays are added(i.e. as the building becomes more “rectangular-shaped” on plan). The results of the minimum cost optimisation indicate that if stressed-skin action is taken into account, the cost of the internal frame can be reduced by around half for “square-shaped” buildings. It should be noted that this is a minimum cost optimisation, which is not the same as a minimum weight optimisation. It is also shown that a safe design of internal frames could be obtained by ignoring wind loads (i.e. designing the frame only for gravity loads),but this is limited to buildings having a “square-shape”.     

RTS系列耐温耐盐聚合物的合成与性能

在实验室研制成功三种水溶性耐温耐盐聚合物（ＲＴＳ系列），简介了合成方法，评定了水溶液流变性、粘温性、盐敏性、抗剪切性及在高温高盐介质中的老化性。ＲＴＳ系列聚合物的耐温耐盐性明显优于两种部分水解聚丙烯酰胺对照样品，与美国菲利浦公司的耐温耐盐聚合物ＨＥ－１００相当甚至更好。