Yun-Ho Jang

Bead affinity chromatography in a temperature-controllable microsystem for biomarker detection

This paper describes a temperature-controllable bead affinity chromatography (BAC) in a microsystem for biomarker detection, and preparing samples for matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS) analysis. Cancer marker proteins were captured in the microsystem by BAC with RNA aptamer-immobilized microbeads. The captured proteins were then denatured and released from the microbeads by controlling temperature. The microsystem consists of a microreactor for trapping microbeads and a temperature control unit for thermal treatment of the trapped beads. We used polymethylsilxoane or single crystalline silicon in fabricating two different types of reaction chamber to compare the differences in performance originated from the materials. Carcinoembryonic antigen was concentrated and purified from human serum using the microsystem and detected by MALDI-TOF MS to demonstrate the usefulness of the microsystem. The microsystem simplifies a sample preparation process required for protein analysis and cancer biomarker detection, which will accelerate the process of cancer research.

Improvement of Maskless Photolithography of Bio Pattern with Single Crystalline Silicon Micromirror Array

This study focuses on the enhancement of maskless photolithography as well as the peptide synthesis application with single crystalline silicon micromirrors. A single crystalline silicon micromirror array has been designed and fabricated in order to improve its application to the peptide synthesis. A micromirror rotates about ± 9° at the pull-in voltage, which can range from 90.7 V to 115.1 V. A 210㎛-by-210 ㎛ micromirror device with 270 ㎛ mirror pitch meets the requirements of an adequately precise separation for peptide synthesis. Synthetic 16 by 16 peptide array corresponds to the same number of micromirrors. The large size of peptide pattern and the separation facilitate biochip experiments using fluorescence assay. The peptide pattern has been synthesized on the GPTS-PEG200 surface with BSA-blocking and thereupon the background was acetylated to reject non-specific bindings. Hence, an averaged slope at the pattern edge has been distinguishably improved in comparison to patterning results from an aluminum micromirror.

Production of a hepatoprotective cerebroside from suspension cultures of Lycium chinense

Abstract Suspension cultures derived from Lycium chinense Miller seedlings produced significant amounts of a hepatoprotective cerebroside. Callus was induced from the stem of aseptic seedlings of L. chinense and maintained on MS solid media supplemented with 1.0 ppm 2,4-D and 0.1 ppm kinetin. Suspension cultures were established, and the cells were grown in the same liquid media in the dark. Lyophilized cells were extracted with a combined reagent of chloroform and methanol (2:1, v/v). An aqueous suspension of the evaporated cell extract was partitioned with chloroform, and the chloroform layer was subjected to silicic acid column chromatography followed by semi-preparative reverse phase C8 high pressure liquid chromatography. The purified compound showed hepatoprotective activity comparable to that shown by silymarin, and the structure was identified as 1-O-(β-d-glucopyranosyl)-(2S,3R,4E,8Z)-2-N-2′-hydroxy-(palmitoyl)-4,8-sphingadiene on the basis of spectral data. The content of the compound in cultured cell was tenfold higher than that of the fruit of L. chinense. The biosynthesis of the compound in cultured cell systems appears to parallel cell growth.

Design, fabrication and characterization of an electromagnetically actuated addressable out-of-plane micromirror array for vertical optical source applications

In this paper we present the design, fabrication and characterization of a micromirror array for an out-of-plane right angle reflection in applications of hologram memory devices. The operation involves rotation of micromirrors supported by torsional springs by an external magnetic field, and the use of electrostatic actuation to address each micromirror. The mechanical properties, such as elasticity, of the torsional springs were verified by the Tresca and the von Mises stress criteria. The springs were designed for a 45° angular out-of-plane rotation. Surface micromachined aluminum is used as the micromirror, and torsional springs and electroplated nickel bars as magnetic materials. A 4.9 µm thick photoresist was used as a sacrificial layer to release the micromirror from the bottom substrate. The relationships between the applied magnetic field and angular deflections have been investigated, and clamping experiments have been performed within the magnetic field. The measured micromirror characteristics include a lapsed time of less than 0.5 ms, and a settling time of 5 ms. The repetitive operation test was performed to see how long the device could operate with an upper plate. The average value of angular rotation angle of 30 micromirrors is about 44.530 ± 0.250° showing good uniformity.

Thermal de-isolation of silicon microstructures in a plasma etching environment

This paper presents a theoretical and experimental strategy for thermal de-isolation of silicon microstructures during a plasma etching process. Heat sinking blocks and thin metal layers are implemented around a thermally isolated mass to avoid severe spring width losses by a steep temperature rise. Thermal de-isolation significantly reduces the fabrication errors from −51.0% to −9.0% and from −39.5% to −6.7% for spring widths and resonant frequencies, respectively. Thermal de-isolation also reduces the standard deviation of resonant frequencies from 8.7% to 1.5% across a wafer, which clearly demonstrates the proposed method.

Numerical analysis and demonstration of a 2-DOF large-size micromirror with sloped electrodes

We report on the numerical analysis and demonstration of a two-degree-of-freedom (2-DOF) micromirror with a large mirror plate and a reduced actuation voltage. The micromirror consists of two layers, namely, a top layer and a bottom layer. In the top layer, the flat reflection surface is comprised of single crystalline silicon, while the bottom layer has sloped electrodes allowing for a decrease in the actuation voltage. The sloped electrodes are fabricated by time-delayed electroplating using nickel. Two different types of electrodes, a cone-type electrode and a wedge-type electrode, are designed for the mirror plate actuation and for the frame actuation, respectively. The mirror size is 1.5 mm × 1.5 mm, and the distance between the top and bottom layers is 65 µm. The slope angle of the bottom electrode is 10.3° for the cone-type electrode and 11.3° for the wedge-type electrode. The mechanical maximum tilt angles are measured at 2.7° with 127 V and 3.1° with 120 V for the cone-type electrode and wedge-type electrode, respectively. The cone-type electrode and the wedge-type electrode provide decreased actuation voltages of 49.3% and 62.1%, respectively, compared to a parallel-type electrode. This design is useful for building large-size mirrors actuated by electrostatic forces.

A 50-110 GHz ohmic contact RF MEMS silicon switch with high isolation

This paper presents the new concept of RF MEMS silicon contact switch and its verification for high isolation at 50–110 GHz. A high isolation is achieved by locating the floating top contact electrode 30 µm apart from the bottom coplanar waveguide (CPW) signal line in lateral direction at initial off-state. The switch contact is realized by the dual axis movement, namely a lateral movement by comb electrodes and a following vertical movement by a bottom electrode. The actuation voltages are measured for dual axis movement. The isolation of the switch was measured at 50–110 GHz to prove the concept of isolation improvement using dual axis movement.

Monolithic fabrication of optical benches and scanning mirror using silicon bulk micromachining

This paper details an optical scanning mirror with a 54.74? inclined reflective plane and optical benches to align the optical components simply in a monolithic silicon substrate so as to implement a miniaturized laser scanner. The scanning mirror was designed and fabricated to achieve laser scanning on a miniaturized scale so that fluorescence detection of arrays of patterns on biochips can be performed by a handheld system. The inclined (1?1?1) reflective plane of the scanning mirror was formed by the KOH wet etching process, and proved to be a very appropriate structure for the assembly of optical scanning systems composed of a laser input and a scanning mirror in a silicon substrate. The optical benches, torsion spring and comb electrodes were fabricated using the DRIE process. The scanning mirror is actuated by its moment of inertia, the electrostatic torque of the comb electrodes and the restoring torque of the torsion spring. As designed, the scanning mirror is 2165 ? 778 ?m2 in an upper part of the rotor of the mirror, and the chip size including optical bench guides is 9 ? 10 ? 1 mm3. The deflection angle of the scanning mirror was measured by a laser displacement meter (LC2420, Keyence, Japan), and the optical components were assembled and aligned in optical bench guides to observe the laser scanning. The deflection angle of the scanning mirror depends on matching the frequency of the driving signal and the mechanical oscillation of the scanning mirror, and a maximum deflection angle of ?7? was obtained when a 16 V peak?peak square wave was applied to the comb electrodes. The scanning mirror with an inclined reflective plane and optical benches fabricated in a monolithic silicon substrate was proved to be a smart structure to implement a handheld-type scanning system for biochip application.

Engineering design guide for etch holes to compensate spring width loss for reliable resonant frequencies

This paper describes design guidance for a compensation method of spring width loss during silicon deep RIE (reactive ion etch) process. We found that a compensation factor (CF), defined by circumference (C) of unit etch hole divided by its area (A), is directly related to the variation of resonant frequencies of silicon MEMS resonators. We proposed 5 models with different etch hole shapes and investigated the effect of etch holes on resonant frequencies. The model with proposed etch holes showed three fold smaller variation of resonant frequencies than other models with conventional etch holes.

RF MEMS suspended band-stop resonator and filter for frequency and bandwidth continuous fine tuning

We firstly propose the concept of a frequency and bandwidth fine-tuning method using an RF MEMS-based suspended tunable band-stop resonator. We experimentally show the feasibility of the continuously tuned resonator, including a second-order filter, which consists of cascaded resonators to achieve center frequency and bandwidth fine tuning. The structure consists of a freestanding half-wavelength (λ/2) resonator connected to a large displacement comb actuator. The lateral movement of the λ/2 resonator over the main transmission line produces different electromagnetic decoupling values from the main transmission line. The decoupled energy leads to continuous center frequency and bandwidth tuning using the band-stop resonator circuit for fine-tuning applications. The freestanding λ/2 resonator plays the role of a variable capacitor as well as a decoupling resonator in the proposed structure. The fabricated tunable filter shows suitability for Ku-band wireless communication system applications with continuous reconfiguration.