Yoo Min Ahn

Surface Roughness and Material Removal Rate of Lapping Process on Ceramics

Lapping is a widely used surface finishing process for ceramics. An experimental investigation is conducted into the lapping of alumina, Ni−Zn ferrite and sodium silicate glass using SiC abrasive to study the effect of process parameters, such as abrasive particle size, lapping pressure, and abrasive concentration, on the surface roughness and material removal rate during lapping. A simple model is developed based on the indentation fracture and abrasive particle distribution in the slurry to explain various aspects of the lapping process. The model provides predictions for the surface roughness,Ra andRt, on the machined surface and rough estimation for the material removal rate during lapping. Comparison of the predictions with the experimental measurements reveals same order of magnitude accuracy.

Feasibility of on-chip detection of endotoxin by LAL test

The LAL (Limulus amebocyte lysate) test for the detection and quantification of endotoxin is based on the gelation reaction between endotoxin and LAL from a blood extract ofLimulus polyphemus. The test is labor intensive, requiring dedicated personnel, a relatively long reaction time (approximately 1 h), relatively large volumes of samples and reagents and the detection of the end-point is rather subjective. To solve these problems, a miniaturized LOC (labon-a-chip) prototype, 62 mm (L)×18 mm (W), was fabricated using PDMS (polydimethylsiloxane) bonded to glass. Using this prototype, in which 2 mm (W)×44.3 mm (L)×100 μm(D) microfluidic channel was constructed, turbidometric and chromogenic assay detection methods were compared, and the chromogenic method was found the most suitable for a small volume assay. In this assay, the kinetic-point method was more accurate than the end-point method. The PDMS chip chickness was found to be minimized to around 2 mm to allow sufficient light transmittance, which necessitated the use of a glass slide bonding for chip rigidity. Due to this miniaturization, the test time was reduced from 1 h to less than 10 min, and the sample volume could be reduced from 100 toca. 4.4 μL. In summation, this study suggested that the LOC using the LAL test principle could be an alternative as a semi-automated and reliable method for the detection of endotoxin.

Effect of Plating Condition on the Mechanical Properties and Residual Stress of Electroplated Copper Film

This paper discusses the effect of plating condition on the mechanical properties and residual stress of electroplated Cu film. The inlaid copper structure was fabricated on silicon wafer where silicon oxide was thermally grown. Seed layer was deposited by sputtering method followed by copper electro-deposition. Copper was electrodeposited with IBM paddle type electroplating machine Residual stress, hardness, elastic modulus, and surface roughness of electroplated copper film were investigated at various organic additives in plating solution and current types with a nanoindenter and a surface profilometer. The dishing amounts in chemical mechanical polishing (CMP) was also investigated at various additives. The results show that, in the case of residual stress, the copper film deposited at higher additive or PC current result in lower residual stress. The additives do not significantly affect the mechanical properties of Cu deposit.

Surface Modification Effect of Wettability on the Performance of PDMS-Based Valveless Micropump

Experimental investigation and numerical simulation on the effect of surface wettability on the performance of a polydimethylsiloxane (PDMS) based diffuser micropump are presented. A valveless micro membrane pump with piezoelectric actuation has been examined. Using a replica molding technique, the valveless micropump was made of PDMS on a Pyrex glass substrate. A thin piezoelectric (PZT) disc was used as an actuator. Poly vinyl alcohol (PVA) and octadecyltrichlorosilane (OTS) coatings, which make the coated surface hydrophilic and hydrophobic, respectively, were used to modify the surface wettability inside the pump. In our experiments, the contact angle of the PDMS surface changed from 96.6 o to 29.1 o and 99.6 o by PVA and OTS coatings, respectively, and the contact angle of glass changed from 33.2 o to 17.5 o and 141.8 o. A self-priming process was numerically simulated in a diffuser element using a computational fluid dynamics program (CFD-ACE+). The results show that fewer gas bubbles were created in the hydrophilic coated pump than in the hydrophobic coated one as time progressed. This agrees well with experimental observations. Steady-state flow rates of the micropump were measured. Compared to the non-coated pump, the flow rate increased slightly with the hydrophobic coating but decreased with the hydrophilic coating. We determine that surface wettability significantly affects the performance of a PDMS-based micropump.

The basic study about the effect of single point grinding on the bending strength of brittle material

Single point grinding was investigated by using a sliding indentation apparatus. Sharp indenter sliding against brittle solid produces a scratch with a median crack. The size of the crack depends on the applied indenter load and the sliding speed. The effect of the crack size and its orientation on bending strength of glass is investigated experimentally. It is shown that the tested glass has high bending strength when the indenter load is low, bending direction is parallel to the scratch, and sliding speed is low. The results of bending test are predictable by fracture mechanics analysis including residual stress effect. This study makes it possible to understand the influence of grinding conditions on the bending strength of ground ceramics.

The Effects of Current Type and Density on Dishing Phenomena in CMP Process

The dishing phenomena of soft materials in chemical mechanical polishing (CMP) process were problematic in delineating inlaid metal patterns. The inlaid copper structures were fabricated on Si wafer where SiO2 was thermally grown. Seed layer was deposited by thermal evaporate method followed by copper electrodeposition. Copper was electrodeposited with IBM paddle type electroplating machine to obtain uniform thickness of coating. The dishing amounts were measured at various current density and current type. The dishing amounts with pattern density and line width were also measured. The losses of copper were not sensitively dependent on current density however those were dependent on current type. The dishing amount of copper was decreased at high pattern density especially over 50% and increased with line width. Surface topology and grain size of coating were investigated with surface profilometer and FESEM.

Electrochemical Kinetics Study of Electroless Copper Plating for Electronics Application

Electroless copper plating was investigated for the electronics applications, such as a metallization for ULSI and MEMS etc. The role of electrolyte composition on the kinetics and mechanism of the electroless copper deposition process was described. Electrochemical techniques were employed for the investigations. The mixed potential and current were determined and then those were compared with experimental deposition rate. The kinetics is strongly influenced by the pretreatment and additive concentrations.

Electric Signal Detection of a Microfilter-Based Biochip for Immunoassay Using Microbead, Nanogold Particle, and Silver Enhancement

This paper presents a microbiochip which can detect an antigen-antibody reaction through an electrical signal in real time with high sensitivity and low sample volume by using nanogold particle and silver enhancement. A filtration method using the microbead is adopted for sample immobilization. The chip is composed of an inexpensive and biocompatible Polydimethylsiloxane (PDMS) layer and Pyrex glass substrate. Platinum microelectrodes for electric signal detection were fabricated on the substrate and microchannel and pillar-type microfilters were formed in the PDMS layer. Successively introducing polystyrene microbeads precoated with protein A, anti-protein A (which was the first antibody) and the second antibody conjugated with nanogold particles into the microchannel, the resulting antigen-antibody complex was fixed on the bead surface. The injection of silver enhancer increased the size of nanogold particles tagged with the second antibody. As a result, microbeads were connected to each other and formed an electrical bridge between microelectrodes. Resistance measured through the electrodes showed a difference of two orders of magnitude between specific and nonspecific immunoreactions. The developed immunoassay chip reduced the time necessary for an antigen-antibody reaction to 10 min, thus shortening the overall analysis time from 3 hours to 50 min. The immunoassay chip reduces analysis time for clinical diagnoses, is simple, and has high sensitivity.

An Electrical Signal Detection System for a Microbiochip with Gold Nanoparticles

In this paper, an electrical signal detection system for microbiochips is proposed to overcome the limitations of conventional optical systems such as bulky system size and high manufacturing cost. An electrical detection system with interdigitated microelectrodes is fabricated using MEMS technology. High conductive nano size gold particles were selected for the system to detect biological reactions between bio materials in the microbiochip. Experiments were performed with variations of particle densities and electrode gaps. In addition, a simulation to predict the electrical resistance of the microbiochip was developed. Both the simulation and experimental data show that the conductivity increases as the gap becomes narrower and the particle density higher.