Papers by Author: Yong Jun Ko

Abstract: 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.

Abstract: 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.

Abstract: This paper reports a low-cost microthermostat that is able to maintain a constant temperature necessary for restriction enzyme digestion. Polydimethylsiloxane (PDMS) and Pyrex glass were used to make the microthermostat, because PDMS is a cheap and mass-producible material and both PDMS and glass have very good biocompatibility compared to the more commonly used silicon. A heater made of Au wiring patterned on Pyrex glass was used to control the temperature. A PDMS replica molding technique was used to fabricate a reaction chamber with 3.6 μl capacity. Restriction enzyme digestion was performed by using the fabricated microthermostat and by a conventional method. Then, using gel electrophoresis, we compared results between the microthermostat and conventional methods. It was found that restriction enzyme digestion using the microthermostat required 5 min of heating.

Abstract: 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.

Abstract: 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.