Joon Shik Park

Determination of trace metals by anodic stripping voltammetry using a bismuth-modified carbon nanotube electrode.

A bismuth-modified carbon nanotube electrode (Bi-CNT electrode) was employed for the determination of trace lead, cadmium and zinc. Bismuth film was prepared by in situ plating of bismuth onto the screen-printed CNT electrode. Operational parameters such as preconcentration potential, bismuth concentration, preconcentration time and rotation speed during preconcentration were optimized for the purpose of determining trace metals in 0.1M acetate buffer solution (pH 4.5). The simultaneous determination of lead, cadmium and zinc was performed by square wave anodic stripping voltammetry. The Bi-CNT electrode presented well-defined, reproducible and sharp stripping signals. The peak current response increased linearly with the metal concentration in a range of 2-100 microg/L. The limit of detection was 1.3 microg/L for lead, 0.7 microg/L for cadmium and 12 microg/L for zinc (S/N=3). The Bi-CNT electrode was successfully applicable to analysis of trace metals in real environments.

Simulation and Fabrication of Silicon Micro-Grippers Actuated by Piezoelectric Actuator

The eight types of micro-grippers with silicon were simulated by ANSYS and fabricated by MEMS(Micro Electro Mechanical System) process. Each type of micro-grippers had a small difference in design shape such as beam width, gap between beams. In order to modify design shape, these micro-grippers were estimated and simulated in point of structure, actuation characteristics by changing design factors. Micro-grippers were composed of five parts which were piezoelectric actuation part, fixing part, rotation arms, the block and gripping jaws. The shape of gripping jaws was designed as the teeth of a saw to reduce adhesion force by decreasing the contact area. The 10.2 µm movement by piezoelectric actuator at 120 V generated the 142.8 µm gripping range of a micro-gripper in real measurement. In the case of simulation result, the gripping range of 162 µm was generated at the same condition. This gripping range was enough to handle small objects like micro-parts

Effect of the Palladium Mid-Layer on the Cyclic Oxidation of Platinum Aluminide Bond Coating

Platinum/Palladium modified aluminide coatings prepared by aluminide pack cementation on the nickel base superalloy Inconnel 738. The platinum/palladium modified aluminide coating of cyclic oxidation behavior at 1200°C was investigated by TGA, XRD and SEM/EDS. Platinum/Palladium modified aluminide coatings showed better cyclic oxidation resistance than Platinum modified aluminide coating and palladium modified aluminide coating compared. Pt and Pd alloy played an enough role in alumina stabilization and in delaying the degradation of β-phase.

Fabrication and wafer-level packaging of Si electrostatic microgripper for micro assembly

The wafer-level packaging of an electrostatic Si microgripper was investigated. It is important to ensure safe handling and freedom from damage during fabrication and assembly of micro devices. Some reliability problems have occurred during packaging or handling of the microgripper, regardless of actuation principles. After pre-release of the sacrificial layer, a new wafer-level packaging was processed by anodic bonding between a glass wafer with through-holes and a Si wafer device. A laser dicing has been performed before wire bonding for freedom from damage during both dicing and packaging processes. After the laser dicing, post-releasing has been done. The diced chips were actuated by applied voltage from 0 V/sub dc/ to 15 V/sub dc/. The jaws of the fabricated microgripper have been actuated from 0 /spl mu/m to 25 /spl mu/m.

Silicon to Silicon Wafer Bonding at Low Temperature Using Residual Stress Controlled Evaporated Glass Thin Film

Silicon to silicon wafer bonding at low temperature of 300 °C using residual stress controlled evaporated 2 ㎛ thick Pyrex glass thin film (briefly, glass thin film) on silicon wafer was investigated. It was found that residual stresses of 2 ㎛ thick glass films on silicon wafers were strongly dependent upon moisture contents and annealing processes. Residual stresses of asdeposited glass films with compressive stress of -150 MPa could be changed to more compressive stress of -230 MPa by moisture absorption. However, after annealing process at 200 °C to 400 °C for 30 min, residual stresses were remarkably changed to tensile stresses of about 75 MPa to 130 MPa, respectively. For the reliable wafer bonding process, the evaporated glass thin films should be annealed in the range of 200 °C to 500 °C for 30 min. So, bare silicon to bare silicon and bare silicon to patterned silicon were bonded at 300 °C and 30 V ~ 60 V for 15 min using 2 ㎛ thick glass film with residual stress of 130 MPa which were generated after the annealing process of 400 °C for 30 min. These results could be used for low temperature silicon to silicon wafer bondings for applications of micro sensors, micro actuators and micro fluidics devices.

Fabrication of Glass Mixing Channels and Silicon Detection Cell with 45˚ Mirror Surfaces for the Indophenol Sensing Device

Design and fabrication of micro mixing cells and detection cells were investigated. Glass micro mixing cells with island structures among channels were fabricated using sand blaster methods. Depth and width of mixing channel were 200 ㎛ and 180 ㎛ and island size was 90 ㎛ by 90 ㎛. Two 45° mirrors surfaces faced on each other in one detection cell which were fabricated by silicon anisotropic etching using 20% TMAH (Tetramethylammonium hydroxide) solution with 20% or 30% IPA (iso propyl alcohol) at 80°C, respectively. Up side glass wafer for mixing cell and down side silicon wafer for detection cell were bonded using anodic bonding method at 350ı, -600 V and 300 N. Synthetic indophenol was injected at inlet and moved to the detection cell through the mixing channel. HeNe laser of 632.8 nm was focused on one side of a 45° mirror, and passed through indophenol solution until the other side of a 45° mirror. The light of 632.8 nm was absorbed in indophenol solution between two 45° mirrors at detection cell. By the Beer-Lambert’s law, indophenol concentration could be calculated from the measured result of the absorbance.