Kyoung-Sun Seo

A continuous cell separation chip using hydrodynamic dielectrophoresis process

This paper presents a high-throughput continuous cell separation chip using hydrodynamic dielectrophoresis (DEP) process. We design the continuous cell separation chip with three electrodes, where the cells in positive DEP affinity are separated from the central streamline. In the experimental study, we use the mixture of viable (live) and nonviable (dead) yeast cells as sample cells to be separated. We obtain the continuous cell separation conditions in the DEP affinity test: the sinusoidal electric fields of 5 MHz, 8V/sub p-p/ have been applied across the electrode array of 20 /spl mu/m gaps immersed in the medium conductivity of 5 /spl mu/S/cm. Using switched AC signal under these conditions, we continuously separate the yeast cells at the mixture flow rates of 0.1/spl sim/1 /spl mu/l/min. The purity of the separated viable and nonviable yeast cells has been measured in the range of 95.9/spl sim/97.3% and 64.5/spl sim/74.3%, respectively.

An SOI optical microswitch integrated with silicon waveguides and touch-down micromirror actuators

We present an SOI optical microswitch for applications to an integrated optical transceiver module, connected with optical I/O ports, source (LD) and receiver (PD). The optical microswitch consists of the waveguides and the micromirror actuators, all fabricated by the silicon layer on an SOI wafer. In the normally off-state, the micromirrors bypass the input signal to the output port. In the on-state, however, the actuated micromirrors provide optical interconnections between I/O ports and PD/LD, respectively. The present waveguide switch uses actuated micromirrors, thus providing more reliable optical path change than the conventional electro-optic or thermo-optic waveguide switches. In addition, we simplify the structure and the process of the microswitch by using the silicon waveguides and the silicon mirror-actuators, all fabricated by the ICP etching of an identical SOI wafer.

Trapping and extraction of target DNA molecules using periodically crossed electrophoresis in the micropillar array

This paper presents a DNA (Deoxyribose Nucleic Acid) extractor based on an electrophoresis using periodically crossed electric fields in a micropillar array. The DNA extractor, having nanometer entropic barriers and micropillar array, was fabricated by micromachining processes. Under the crossed electric field, the DNA molecules, whose reorientation time is longer than the period of the crossed field, are trapped in the micropillar array. We applied the electric fields, crossed at 120/spl deg/, to the DNA molecules in the micropillar array distributed in 120/spl deg/ direction. Three different DNA, including /spl lambda/, micrococcus and T4 show reorientation times of 4.80 /spl plusmn/ 0.44sec, 7.12 /spl plusmn/ 0.75sec, and 9.71 /spl plusmn/ 0.30sec for /spl lambda/ DNA(48.5 kbp), micrococcus DNA (115 kbp), and T4 DNA (169.8 kbp), respectively at E=5V/0.8cm. In the fabricated DNA extractor, T4 DNA cannot come out of the micropillar array for the crossed electric field of 5V/0.8cm at a 10 second interval. We have demonstrated that the present DNA extractor separates DNA molecules longer than a critical value, which can be adjusted by the magnitude and the period of the electric field across the micropillar array.

Self-focusing chips for size-dependent DNA separation in nonuniformly distributed asymmetric electric fields

This paper presents the first experimental study to realize a DNA separation chip based on the self-focusing effect in a micropillar array. The present self-focusing chip redistributes DNA molecules within a specific area of micropillar arrays based on the size- and field-dependent nonlinearity of DNA drift velocity. Compared to conventional electrophoresis chips, the present self-focusing chip reduces a substantial amount of the separation channel length, the influence of sample starting location, and the necessity of time-consuming continuous monitoring process. We focus on the design of DNA self-focusing chips, with identifying the nonlinearity of DNA drift velocity using three different DNA molecules including /spl lambda/ DNA (48.5 kbp), micrococcus DNA (115 kbp), and T4 DNA (169.8 kbp) in microfabricated test chips. It is demonstrated that the present DNA self-focusing chips have potentials not only for the miniaturization of DNA analysis systems, but also for the tunable capability of the target DNA size to be separated, trapped and extracted.

A bulk-micromachined silicon micromirror for tunable optical switch applications

A bulk-micromachined electrostatic micromirror has been presented for tunable optical switching devices. A silicon micromirror with (111) crystalline planes has been fabricated. It measures 1000 /spl mu/m/spl times/400 /spl mu/m/spl times/90 /spl mu/m. The optical switching function has been obtained by an electrostatic drive of the micromirror in the direction parallel to the substrate. In a static performance test, stable deflection of the micromirror has been observed up to the threshold deflection of 26.5 /spl mu/m with the threshold voltage of 330 V. In a dynamic test, the resonant switching frequency has been measured as 590 kHz. For the DC bias voltage range of 50-300 V with an AC drive voltage of 10 V, a continuous reduction of the resonant switching frequency has been demonstrated with the maximum frequency reduction of 23.7%.

Tunable Micromirror Switches Using (110) Silicon Wafer

A frequency-tunable silicon micromirror has been fabricated and tested for applications to optomechanical switching devices. A high-aspect-ratio single crystal silicon micromirror has been fabricated by an anisotropic etching of (110) silicon wafers. The micromirror, vertical to the substrates, is suspended by two pairs of boron-diffused microflexures. Static and dynamic optical switching functions have been obtained by an electrostatic drive of the micromirror in the direction parallel to the substrate. In the static mirror operation, a threshold deflection of 2 6 . 5 ~ has been obtained at the DC drive voltage of 330V. In the dynamic test, the resonant frequency of the suspended micromirror has been measured as 590Hz. The resonant switching frequency of the micromirror has been tuned in the range of 585-450Hz by varying the DC bias voltage in the range of 50-3OOV.

An optical microswitch chip integrated with silicon waveguides and touch-down electrostatic micromirrors

We present an silicon-on-insulator (SOI) optical microswitch, composed of silicon waveguides and electrostatically actuated gold-coated silicon micromirrors integrated with laser diode (LD) receivers and photo diode (PD) transmitters. For a low switching voltage, we modify the conventional curved electrode microactuator into a new microactuator with touch-down beams. We fabricate the waveguides and the actuated micromirror using the inductively coupled plasma (ICP) etching process of SOI wafers. The fabricated microswitch operates at the switching voltage of 31.7 ± 4 V with the resonant frequency of 6.89 kHz. Compared to the conventional microactuator, the touch-down beam microactuator achieves 77.4% reduction of the switching voltage. We observe the single mode wave propagation through the silicon waveguide with the measured micromirror loss of 4.18 ± 0.25 dB. We discuss a feasible method to achieve the switching voltage lower than 10 V by reducing the residual stress in the insulation layers of touch-down beams to the level of 30 MPa. We also analyze the major source of micromirror loss, thereby presenting design guidelines for low-loss micromirror switches.

An electrostatically-tunable switching micromirror using [110] silicon wafers

A bulk-micromachined electrostatic micromirror has been designed, fabricated and tested for applications to tunable optomechanical switching microdevices. Static deflections of the micromirror have been measured up to 26.5 /spl mu/m with a DC threshold voltage of 330 V. Resonant switching frequencies have been tuned in the ranges of 580-450 Hz by varying the DC bias voltage within 50-300 V for an AC drive voltage of 10 V.

MicroOptoMechanical characterization of a mechanically deflected free-standing polymer waveguides

MEMS-based micro-optical devices have received increasing attention in the areas of information and optical communication. Among them, monolithically integrated optical devices show strong potential for small-size, high-density applications. The integrated optical devices require optical interconnections between movable (e.g. pickup) and stationary optical components (e.g. light source and detector). Conventional optical interconnection has been made by fiber-optic cables or waveguide channels on a flexible ribbon. In this paper, we propose a free-standing (or suspended) waveguide as a new optomechanical interconnection, that can act not only as an optical path but also as a mechanical suspension for an integrated optical device. This has motivated the study on the mechanical behavior and the optical characteristics of the free-standing waveguide. We experimentally characterize the micromechanical behavior and the optical loss of a mechanically deflected free-standing polymer waveguide. We especially focus on the evaluation of the waveguide bending loss, generated by mechanical deflection.