Jing-Tang Wu

Fabrication of a nano/micro hybrid lens using gas-assisted hot embossing with an anodic aluminum oxide (AAO) template

This paper reports a novel and effective method for the fabrication of a polymeric nano/micro hybrid lens array. The nanostructure and microlens arrays are fabricated on the same polycarbonate (PC) substrate by hot embossing in sequence. First, an anti-reflection PC film with sub-wavelength nanostructures is fabricated using an anodic aluminum oxide (AAO) template. The anti-reflection characteristic of nanostructures on the PC film is evaluated. Then an array of convex microlenses is formed from the nanostructured PC film using a stainless steel mold with a microhole array. Both processes employ gas-assisted hot embossing to perform the partial protrusion of the film into nano-sized or micro-sized holes in the AAO template and steel mold. The optical property of the microlens has been verified. This proposed technique has proven its potential for effectively fabricating a nano/micro hybrid lens array on a polymeric substrate.

A gasbag-roller-assisted UV imprinting technique for fabrication of a microlens array on a PMMA substrate

Roller imprinting has been one of the most effective replication techniques due to its continuous nature and mass productivity. To improve the pressure uniformity and enhance the replication precision, a novel gasbag-roller-assisted UV imprinting process is designed and developed in this study. A belt-type polydimethylsiloxane (PDMS) mold with cavities for forming a microlens array is prepared. A gasbag roller is employed to exert pressure on the contact area between the PDMS mold and a PMMA substrate. Due to the isotropic pressure provided by the gasbag roller, the contact area between the mold and the substrate is increased and the uniformity of the imprinting pressure is enhanced. Precise replication and complete UV curing are thus achieved. A gasbag-roller-assisted UV-based imprinting facility is constructed, and the experiments are conducted. The results prove that a microlens array can be successfully fabricated on a 2 mm thick PMMA substrate. The shape profile and optical property of the microlens are also evaluated.

Novel fabrication of an Au nanocone array on polycarbonate for high performance surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) with enormous enhancements has been applied for ultra-sensitive detection in various fields, but the fabrication of large-scale, controllable and cost-effective substrates is a major challenge. We propose a novel fabrication process with a gas-assisted hot embossing process and an anodic aluminum oxide template to obtain the SERS substrate on a 1 × 1 cm polycarbonate film. The SERS spectra of 4-mercaptobenzoic acid (PMBA) on the gold substrate have been measured. The enhancement factors are between 3.99 × 107 and 4.92 × 107, depending on the heights of nanocones, which can be controlled by the embossing temperature and pressure. The simple and inexpensive SERS substrate has potential for wide application in SERS-based sensors.

Micromechanical behavior of single-crystalline Cu6Sn5 by picoindentation

The micromechanical behavior of single-crystalline Cu6Sn5 is studied by micropillar compression in a picoindenter. The compound Cu6Sn5 is important because it is used as a structural material in microbumps of advanced electronic packages. Micropillars of Cu6Sn5 with known crystallographic orientations were fabricated by focused ion beam machining. Pillars with the c-axis perpendicular to the load direction tended to possess higher strain to failure and lower Young’s modulus. Measured Young’s modulus from micropillar compression was compared with results from nanoindentation measurements. The modulus values from micropillar compression were consistently smaller than those from nanoindentation measurements.

Effect of Ag concentration on Ni/Sn-xAg/Ni micro joints under space confinement

Previous studies have shown that voids were observed in 3D IC-scaled micro joints of Ni/Sn/Ni solid state reaction under severe space confinement and Ag addition can effectively eliminate the void formation. Therefore, the present study is aimed at investigation of the lower limit of Ag concentration which prevents void formation and also the effect of Ag concentration when primary Ag3Sn appears. The solid state diffusion couple, Ni/Sn-xAg/Ni, was prepared by thermal compression with six different Ag concentrations from 0 to 8.0 wt.%. After thermal compression bonding, samples were placed at 200°C for isothermal aging process. Subsequent observation of cross-section showed that as-bonded Ag3Sn initially formed as fine particles dispersed in Sn matrix. Then, Ag3Sn particles coarsened during aging and were likely heterogeneously located at the Ni3Sn4 layer. After Sn was completely consumed, Ag3Sn particles were located at the middle of sandwich structure and microstructure of various Ag concentrations were distinct. A nearly void-free sandwich structure could be established by adding more than 3.5 wt. % Ag in solder when Sn was fully consumed. In addition, the relation between the area fraction of continuous Ag3Sn layer and Ag concentration was found linear.