Yong-Kweon Kim

Multifunctional Silver‐Embedded Magnetic Nanoparticles as SERS Nanoprobes and Their Applications

In this study, surface-enhanced Raman spectroscopy (SERS)-encoded magnetic nanoparticles (NPs) are prepared and utilized as a multifunctional tagging material for cancer-cell targeting and separation. First, silver-embedded magnetic NPs are prepared, composed of an 18-nm magnetic core and a 16-nm-thick silica shell with silver NPs formed on the surface. After simple aromatic compounds are adsorbed on the silver-embedded magnetic NPs, they are coated with silica to provide them with chemical and physical stability. The resulting silica-encapsulated magnetic NPs (M-SERS dots) produce strong SERS signals and have magnetic properties. In a model application as a tagging material, the M-SERS dots are successfully utilized for targeting breast-cancer cells (SKBR3) and floating leukemia cells (SP2/O). The targeted cancer cells can be easily separated from the untargeted cells using an external magnetic field. The separated targeted cancer cells exhibit a Raman signal originating from the M-SERS dots. This system proves to be an efficient tool for separating targeted cells. Additionally, the magnetic-field-induced hot spots, which can provide a 1000-times-stronger SERS intensity due to aggregation of the NPs, are studied.

Fabrication and experiment of a planar micro ion drag pump

A micro ion drag pump with planar electrodes on a glass substrate is fabricated and tested. The pump consists of a planar electrode pair array driven by DC voltage using unipolar conduction. Ethyl alcohol is pumped in both directions, and the flow rate and the pressure are measured in channels of depth 100 μm or 200 μm and width fixed at 3 mm. It is found that the pump can be fabricated easily and at a lower cost than the micro ion drag pumps previously investigated.

Protein patterning on silicon-based surface using background hydrophobic thin film

A new and convenient protein patterning method on silicon-based surface was developed for protein array by spin coating of hydrophobic thin film (CYTOP). Photolithographic lift-off process was used to display two-dimensional patterns of spatially hydrophilic region. The background hydrophobic thin film was used to suppress nonspecific protein binding, and the hydrophilic target protein binding region was chemically modified to introduce aldehyde group after removal of the photoresist layer. The difference in surface energy between the hydrophilic pattern and background hydrophobic film would induce easier covalent binding of proteins onto defined hydrophilic areas having physical and chemical constraints. Below 1 microg/ml of total protein concentration, the CYTOP hydrophobic film effectively suppressed nonspecific binding of the protein. During the process of protein patterning, inherent property of the hydrophobic thin film was not changed judging from static and dynamic contact angle survey. Quantitative analysis of the protein binding was demonstrated by streptavidin-biotin system.

UV-LIGA process for high aspect ratio structure using stress barrier and C-shaped etch hole

Abstract SU-8 is a well-known thick photoresist used in fabrication of high aspect ratio Micro EectroMechanical System (MEMS) structure. However, it is hard to get fine patterns in the high aspect ratio structures because of high internal stress and difficulty of removing SU-8. The purpose of this paper is to set up the process condition for both low film stress and high aspect ratio and to find design rules that make the pattern be less dependent on stress problem. Firstly, the mold fabrication process is optimized by adjustment of exposure and heat treatment. These two conditions control the amount of cross-linkage in polymer structure, which is the most important parameter of both pattern generation and remaining stress. Heat treatment is dealt with soft bake and post-exposure bake (PEB). Temperature and time duration of each step are varied with heat treatment condition. Exposure time is varied with exposure condition. Secondly, stress barrier and C-shaped etch hole are proposed for layout design scheme. The stress barrier is introduced to minimize stress from the large area polymerized SU-8 film. The etch hole designed to be the shape of character “C” instead of conventional square or wall type etch hole. Some test patterns are fabricated to evaluate the proposed process. Ultra Violet (UV)-LIGA process was performed by nickel electroplating with the mold fabricated through the proposed process to confirm the SU-8 as a good electroplating mold.

Surface-enhanced Raman scattering-active nanostructures and strategies for bioassays

Surface-enhanced Raman scattering (SERS) techniques offer a number of advantages in molecular detection and analysis, particularly in terms of the multiplex detection of biomolecules. So far, many new SERS-based substrates and analytical techniques have been reported. For easy understanding, various SERS techniques are classified into the following four categories: adsorption-mediated direct detection; antibody- or ligand-mediated direct detection; binding catalyzed indirect detection; and tag-based indirect detection. Among these, recent successes of SERS tagging/encoding (nano/micro) materials and detection methods are highlighted, including our recent works. Some novel SERS-based strategies for the detection of several biological molecules are also introduced.

Silicon micro XY-stage with a large area shuttle and no-etching holes for SPM-based data storage

A micro XY-stage with a 5/spl times/5 mm/sup 2/-area shuttle is fabricated for application in a nanometer-scale data storage device. A central shuttle of the device is designed as a large square on which a high-density recording medium is deposited. Perpendicularly combined comb-drive actuators allow the large shuttle free access in the x-y plane. No etching holes on the central shuttle are preferred in order to maximize the effective recording area. Therefore, a novel release process, Micro-Channel Assisted Release Process (/spl mu/CARP) is proposed to release a large plate structure without any etching holes and to resist downward sticking. The static and dynamic strokes of the device were measured. Mechanical interferences between x-and y-directional drives were estimated by finite-element method (FEM) analysis and compared with the experimental results.

Low-loss and compact V-band MEMS-based analog tunable bandpass filters

This paper presents compact V-band MEMS-based analog tunable bandpass filters with improved tuning ranges and low losses. For compact size and wide tuning range, the two-pole filters are designed using the lumped-elements topology with metal-air-metal (MAM) bridge-type capacitors as tuning elements. Capacitive inter-resonator coupling has been employed to minimize the radiation loss, which is the main loss contributor at high frequencies. Two filters have been demonstrated at 50 and 65 GHz. The 65-GHz analog tunable filter showed a frequency tuning bandwidth of 10% (6.5 GHz) with low and flat insertion losses of 3.3 /spl plusmn/ 0.2 dB over the entire tuning range.

V-band 2-b and 4-b low-loss and low-voltage distributed MEMS digital phase shifter using metal-air-metal capacitors

Low-loss digital distributed phase shifters have been developed using micromachined capacitive shunt switches for V-band applications. Instead or conventional metal-insulator-metal capacitors, high-Q metal-air-metal capacitors were used in series with the microelectromechanical system (MEMS) shunt capacitive switches to minimize the dielectric loss. The operation voltage for the phase shifters was also reduced by applying the bias directly to the MEMS shunt switches through choke spiral inductors. Fabricated 2-b (270/spl deg/) and 4-b (337.5/spl deg/) distributed phase shifters showed low average insertion losses of 2.2 dB at 60 GHz and 2.8 dB at 65 GHz, respectively. The average phase errors for 2-b and 4-b phase shifters were 6.5% and 1.3%, respectively. The return losses are better than 10 dB over a wide frequency range from 40 to 70 GHz. Most of the circuits operated at 15-35-V bias voltages. These phase shifters present promising solution to low-loss integrated phase shifting devices at the V-band and above.

Low-loss analog and digital micromachined impedance tuners at the Ka-band

Presents new types of analog and digital micromachined impedance tuners. Analog impedance tuners using resonant unit cells realized by tunable micromachined capacitors showed a wide tuning range equivalent to almost two quadrants of the Smith chart with a maximum voltage standing-wave ratio (VSWR) of 21.2 at the Ka-band. Frequency variability is also provided through the use of J-inverters with tunable capacitors. Also presented is a digital micromachined tuner, where the short-circuited shunt stubs are loaded with microelectromechanical system (MEMS) capacitive switches. The electrical length of the stub and the overall impedance of the tuner are thus controlled according to the switching states of the MEMS capacitors. The digital tuner presented impedance ranges suitable for load impedances of the RF power transistors and showed a high maximum VSWR of 32.3. Compared with the state-of-the art tuners using field-effect transistors, micromachined tuners of this paper show superior VSWR ranges as well as wide impedance ranges. Micromachined tuners are very promising for low-loss tuning of the monolithic circuits as well as for accurate noise and power characterization.

Direct nanomechanical machining of gold nanowires using a nanoindenter and an atomic force microscope

Nanomechanical characterization of gold nanowires with a height of 160 nm, width of 350 nm and length of 5 µm has been carried out. Hardness and elastic modulus of the unreleased wires were measured by nanoindentation techniques using a nanoindenter. Post-fabrication mechanical machining of the gold nanowires is demonstrated. An array of nanoscale indents was successfully made on the gold nanowires. Nanochannels, nanoslots and complex nanopatterns were fabricated on a single gold nanowire by directly scratching/sliding the wire surface with the atomic force microscope (AFM) tip. Bending tests were performed to generate nanogaps on the wires using the nanoindenter. Direct machining techniques using a nanoindenter and an AFM should find more applications in the integration and manufacturing of micro/nanodevices.