C. K. Chung

Simulation and fabrication of pyrex glass drilling using CO 2 laser

The traditional glass drilling using mechanical processing and laser processing in air would produce many kinds of defects such as bugle, debris, crack and scorch. In this paper, we have applied the method of liquid-assisted laser processing (LALP) to reduce the temperature gradient, heat-affect zone region for achieving crack-free glass drilling. At the parameters of laser power 6 W, scanning speed 11.4 mm/s and 5 scanning passes by LALP, the crack-free hole with reduced heat-affect zone can be achieved compared to the traditional laser drilling in air. The alpha-step measured profile showed less bugle around the rim of LALP microstructure whose height was about 0.5–1.5 μm in 0.5–1.0 mm water depth while that in air was 6.9–10.5 μm. The relationship between cutting depth, scanning passes and water depths was studied. The ANSYS software was also used to analyze the temperature distribution and thermal stress field in air and water ambient during glass drilling. The higher temperature gradient in air induced higher stress for crack formation while the smaller temperature gradient in water had the less heat-affect zone range and eliminated the crack during processing.

Design and fabrication of an advanced rhombic micromixer with branch channels

Fluid dynamics and mixing transport of an advanced rhombic micromixer with branch channels have been designed and investigated by 3D numerical simulations and experiments. The CFD-ACE+ software was used for simulation and PDMS molding process was used for chip fabrication and experiment. Simulation results showed the advanced rhombic micromixer with branch channels enhanced much high mixing efficiency compared to cross-shape microchannels at the same Re. Compared to the pure rhombic microchannel, the branch-channel rhombic micromixer promoted the mixing efficiency at lower pressure drop at the same Re. Over 90% mixing enhanced by vortices had been achieved at Re > 80. Experimental results show this advanced rhombic micromixer enhances much mixing at Re 60 and uniform mixing at Re 120, respectively. This device is suitable to the application of high-throughput chemical production.

Mixing process of an obstacles micromixer with low pressure drop

Micro mixing is very important in some micro fluid systems. Common design of micromixers is the multi-layer microchannel together with the complicated fabrication process. In this study, the planar design and simple mixing structure were adopted. This obstacle micromixer had been successfully demonstrated by the CFD-ACE simulations and mixing experiments. At low Reynolds number, high mixing efficiency and low pressure drop cab be obtained. 93% mixing enhanced by vortices had been achieved at Re = 20. Experimental results also show good mixing efficiency at Re = 20. Because of high mixing efficiency and low pressure drop, this planar micromixer is easier to integrate with other micro devices in micro-total- analysis-systems.

Numerical analysis and experiments of capillarity-driven microfluid chip

Pumping of fluid is an important issue in the microfluidic system. Surface-directed capillary pump merits no external power input and low pressure drop in the microchannel compared to external syringe pump and built-in powered pumps. In this article, the numerical analysis and experiments of the capillarity-driven fluidic flow in the microchannel have been investigated. Varied width-to-depth-ratio microchannels were designed for simulation and experiments. The surface hydrophilicity of PDMS and glass materials was examined for fluidic chip fabrication and flow test. Low-viscosity DI water and high-viscosity human blood were used for capillarity-driven flow measurement. PDMS surface was first performed by oxygen plasma treatment for hydrophilic surface to enhance capillary force. But the hydrophobic recovery of PDMS occurred several ten minutes after oxygen plasma treatment. So, the intrinsic hydrophilic glass chips were used for high-viscosity human blood test. The flow velocity of fluid was relevant to the channel geometry and fluidic viscosity. It increased with width-to-depth ratio at constant channel depth and decreased with viscosity. The experimental results had a good agreement with simulation. It offered a good reference for future capillarity-driven microfluidic device in biomedical or biochemical application.

Characteristics of truncate-angle rhombic micromixer and rapid mold fabrication using CO 2 laser micromachining

Fluid dynamics and mixing transport of the rhombic micromixer with truncate angles have been investigated by 3D numerical simulations and experiments. Simulation result shows this rhombic microchannel with truncate angles has high mixing efficiency, compared to cross-shape microchannel. Over 90% mixing enhanced by vortices had been achieved at Re ≫ 100. Different to photolithography process, CO2 laser machine is used to fabricate the master mold rapidly. Experimental results show this rhombic micromixer enhances much mixing at Re 18.6 and uniform mixing at Re 186, respectively. This device is suitable to the application of high-throughput chemical production.

Effects of SiO 2 film thickness and operating temperature on thermally-induced failures in through-silicon-via structures

Abstract In the present study, the experimental results of the thermally induced failure (fracture) time for the components of copper through‑silicon via (TSV) structures and the time for electrical current breakdown (TBD) are obtained to investigate the effects of the thickness of the SiO2 film and the operating temperature. The numerical scheme is also developed to solve the distributions of transient temperature and stress in the specimen and the equivalent stress/strain for the elements in the Ti, SiO2 and Si components of the TSV structure. The equivalent element stress solutions incorporating with the Johnson-Cook (J-C) fracture model are provided to identify the earliest failure element and time in each of these three components and the TBD of the structure via the definition for the D factor. The applied models and numerical scheme are confirmed to be trustworthy from the comparison of the numerically predicted and experimental results for these failure time parameters. The effects of the operating temperature of specimens bottom surface and the film thickness of SiO2 on these time parameters have been evaluated precisely. The TBD time is elongated by increasing the thickness of either SiO2 or Ti film if the bottom surface is operating at a fixed temperature. The earliest failure time (tfailure) for the components of Ti, SiO2 and Si wafer and the TBD are always reduced by the rise of operating temperature.

Fabrication of microfluidic chip using foil-assisted CO2 laser ablation for suspended particles separation

Lab on a chip was mainly used in the simplification of biomedical detection step and separation was one of the indispensable pretreatment during the detection process. In this study, a combination channel of spiral and backward facing step patterns were designed to optimize the separation function without any extra power like electric or magnetic field. The foil-assisted CO2 laser method was used to fabricate a spiral microfluidic chip with polymethylmethacrylate polymer for the master of suspended particles separation. The laser ablation generated poor surfaces quality with bulge and scorches can be diminished using foil-assisted laser micromachining technique. The low-cost and time-saving procedure, including microchip fabrication and surface modification, has been developed to apply positively in microfluidic separation chip based on the flow distribution design of spiral dean vortices and backward facing step, which can provide 99% separation efficiency within a certain flow range.

The effect of sol-gel composition ratio on phase transformation of titanium dioxide under CO 2 laser annealing

The sol-gel solution was mixed by tetraisopropyl orthotitanate (TTIP), acetonylacetone, distilled water and alcohol at various molar ratios and coated on p-type silicon substructure for titanium oxide formation. Then the CO2 laser annealing in air at powers of 0.5, 1.5 and 3.0 W in the defocus mode was performed on the coatings for studying crystallization of titanium oxide. The microstructure and phase transformation of titanium dioxide were examined by X-ray diffraction pattern. Increasing TTIP concentration and decreasing laser power were favorable for anatase phase formation. The grain size of titanium dioxide calculated using Scherrers formula was between 10 and 32 nm, which increased with increasing laser power. The ANSYS simulation was employed to calculate temperature distribution of films to correlate with phase transformation of titanium dioxide. This sol-gel processing combined with CO2 laser annealing had advantages of low cost, controllable titanium dioxide phase, selective area annealing, large area fabrication and easy operating at room temperature.

Experiment and simulation of resistance of nanoporous dentin biomaterial to CO 2 laser irradiation

The resistance of nanoporous dentin biomaterial to CO2 laser irradiation was investigated by experiment and simulation for potential tooth hypersensitivity treatment. The controlled parameters were laser power of 0.03–0.150 W, scanning speeds of 11.4–34.2 mm/s and focus/defocus modes for studying interaction between laser energy and dentin of human tooth. Most of dentin specimens were etched after CO2 laser irradiation at the power larger than 0.075 W and the scanning speed of 11.4 mm/s. Compared with simulation results of temperature distribution, maximum surface temperature of those etched specimens are between 1961 and 3127 °C which exceeded the melting point (1570 °C) of dentins main content of hydroxyapatite (HA). Increasing scanning speed can reduce the linear density of laser output energy for just locally melting porous microstructure of dentin surface without etching. Varying focus mode can also improve the damage of nanoporous dentin microstructure. At parameters of 0.150 W power and 34.2 mm/s scanning speed under defocus operation, laser treatment was successful performed on the nano-HA coated dentin with well-molten sealing on tubules of porous microstructure at a simulate surface temperature about 574 °C, which was potential for dentin hypersensitivity cure application.

Investigation of acoustic properties and Raman scattering of AlN films for biosensor application

In this study, two approach of the molecular-level detection technique, acoustic-based and Raman-scattering-based detection, are adopted. The acoustic resonant signals are sensitive to the loading mass, such as nano particles and bio-molecules, while Raman scattering signals are highly surface sensitive to a wide range of adsorbate molecules. Aluminum nitride (AlN) thin film dominars both of the techniques. In the acoustic device, AlN acts as a piezoelectric layer to excite acoustic wave. In the Raman scattering experiment, the surface morphology of AlN give rise to a surface enhanced Raman signal. Thus, thin film bulk acoustic wave (TFBAW) properties as well as the surface enhanced Raman spectroscopy (SERS) signals of AlN are investigated. To obtain good piezoelectricity, a highly c-axis orientated AlN thin film is prepared by a reactive RF magnetron sputtering system. The c-axis orientated AlN possesses a pebble-like morphology, which is suitable for the SERS. Solidly-mounted resonators (SMR) are adopted to excite high frequency resonant signal, and the 1.5 GHz shear resonance signal is obtained. In the SERS measurement, the aqueous solution of Rhodamine 6G with concentration of 10−6 M added with 10 mM of sodium chloride was utilized to calibrate the enhancement factors.