Kwang Seok Yun

A surface-tension driven micropump for low-voltage and low-power operations

In this paper, we first report a micropump actuated by surface tension based on continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in a microchannel filled with an electrolyte as actuation energy for the micropump. This allows low voltage operation as well as low-power consumption. The micropump is composed of a stack of three wafers bonded together. The microchannel is formed on a glass wafer using SU-8 and is filled with electrolyte where the mercury drop is inserted. The movement of the mercury pushes or drags the electrolyte, resulting in the deflection of a membrane that is formed on the second silicon wafer. Another silicon wafer, which has passive check valves and holes, is stacked on the membrane wafer, forming inlet and outlet chambers. Finally, these two chambers are connected through a silicone tube forming the complete micropump. The performance of the fabricated micropump has been tested for various operation voltages and frequencies. We have demonstrated actual liquid pumping up to 70 /spl mu/l/min with a driving voltage of 2.3 V and a power consumption of 170 /spl mu/W. The maximum pump pressure is about 800 Pa at the applied voltage of 2.3 V with an operation frequency of 25 Hz.

A micropump driven by continuous electrowetting actuation for low voltage and low power operations

In this paper we first report a micropump actuated by continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in the microchannel filled with an electrolyte as actuation energy. We have fabricated the CEW actuator, silicone rubber pumping membranes and copper flap check valves, and have demonstrated actual liquid pumping up to 63 /spl mu/l/min at the applied voltage of 2.3 Vpp. The maximum pump pressure is about 600 Pa at the applied voltage of 2.3 Vpp with operation frequency of 10 Hz.

A low-voltage two-axis electromagnetically actuated micromirror with bulk silicon mirror plates and torsion bars

In this paper, a new micromirror structure has been proposed and fabricated. The proposed micromirror is electromagnetically actuated along two-axis at low voltage using an external magnetic field. The mirror plates and torsion bars are made of bulk silicon and the actuation coils are made of electroplated copper. The maximum deflection angles have been measured as /spl plusmn/4.35/spl deg/ for x-axis actuation and /spl plusmn/15.7/spl deg/ for y-axis actuation. The actuation voltages are below 4.2 V for x-axis actuation and 1.76 V for y-axis actuation, respectively.

A disposable DNA sample preparation microfluidic chip for nucleic acid probe assay

A new DNA sample preparation microfluidic chip for Nucleic Acid (NA) probe assay has been proposed. The proposed microfluidic chip is composed of three parts: microfilter, micromixer and DNA purification chip. We have fabricated a microsieve type filter with an array of 2.2 /spl mu/m diameter holes. We have also demonstrated the mixing can be successfully achieved for low Reynolds number below 50 by using the fabricated micromixer. The fabricated DNA purification chip has shown a binding capacity of 15 ng/cm/sup 2/ and a minimum extractable input concentration of 100 copies/200 /spl mu/L. The proposed microfluidic chip can be applied for low-cost, disposable sample preparation of NA probe assays.

A High-Speed Single Crystal Silicon AFM Probe Integrated with PZT Actuator for High-Speed Imaging Applications

A new high speed AFM probe has been proposed and fabricated. The probe is integrated with PZT actuated cantilever realized in bulk silicon wafer using heavily boron doped silicon as an etch stop layer. The cantilever thickness can be accurately controlled by the boron diffusion process. Thick SCS cantilever and integrated PZT actuator make it possible to be operated at high speed for fast imaging. The resonant frequency of the fabricated probe is 92.9 ㎑ and the maximum deflection is 5.3 ㎛ at 3 V. The fabricated probe successfully measured the surface of standard sample in an AFM system at the scan speed of 600㎛/sec

Microfluidic components and bio-reactors for miniaturized bio-chip applications

In this paper miniaturized disposable micro/nanofluidic components applicable to bio chip, chemical analyzer and biomedical monitoring system, such as blood analysis, micro dosing system and cell experiment, etc are reported. This system includes various microfluidic components including a micropump, micromixer, DNA purification chip and single-cell assay chip. For low voltage and low power operation, a surface tension-driven micropump is presented, as well as a micromixer, which was implemented using MEMS technology, for efficient liquid mixing is also introduced. As bio-reactors, DNA purification and single-cell assay devices, for the extraction of pure DNA from liquid mixture or blood and for cellular engineering or high-throughput screening, respectively, are presented.

Electromagnetic actuation and microchannel engineering of a polymer micropen array integrated with microchannels and sample reservoirs for biological assay patterning

A polymer (SU-8) micropen array was fabricated for application to biological assay patterning. The micropen, which is integrated with a microchannel and a sample reservoir, can be actuated by Lorentz force induced on an integrated metal actuator. Current to a metal line deflects the micropen up to 1.8μm by electromagnetic force induced from external permanent magnets. Red ink is loaded in the reservoir and is automatically drawn to the end point of the microchannel by capillary force. A red-ink dot with a diameter of 11μm was successfully placed onto paper by the fabricated micropen.

Development of a wireless environmental sensor system and MEMS-based RF circuit components

This paper reports a miniaturized environmental sensor system integrated with RF communication module. This system has been developed for on-site monitoring of water pollution by heavy metal ions. The system is composed of an electrochemical sensor, a custom potentiostat module, and an RF module for wireless communication. Also, the authors presented monolithic MEMS VCOs integrated with high-Q MEMS inductors and MEMS transmission lines for low-power wireless transceiver applications. Phase noise of the proposed MEMS VCOs has been improved by more than 7 dBc/Hz compared with their CMOS counterparts at 1MHz offset from center frequencies of 5GHz and 13 GHz, respectively.

Three Dimensional Electrode Structure Controlled by Dielectrophoresis for Flow-Through Micro Electroporation System

A three dimensional electrode structure for flow-through micro electroporation is proposed to achieve well-controlled cell positioning in a confined region. In this structure, cell position is actively performed by using dielectrophoresis in a three dimensional electrode structure. Compared with conventional planar electrode structures, the proposed electrode structure can achieve excellent aligning of cells not only in horizontal dimension but also in vertical dimension for receiving uniform electrical field during electroporation. The effectiveness of the proposed structure is validated by both numerical simulation using a commercial tool, CFD-ACE+, and experiments using the fabricated microfluidic chip. The results are compared with conventional parallel finger electrode structures under the same conditions.

Micromachined ultrasound transducer array for cell stimulation with high spatial resolution

In this work, we present a piezoelectric micromachined ultrasonic transducer (pMUT) array for local stimulation on cultured cells with a high spatial resolution for the first time. We used a bulk piezoelectric film that has a higher piezoelectric coefficient (d31) than that of the thin film materials to achieve high acoustic power within a small membrane. The 500-μm-wide and 55-μm-thick transducer membrane exhibits a resonant frequency of 780 kHz, which is within the effective frequency range for stimulating cells. We also demonstrate successful in vitro experiments by stimulating cells using the fabricated pMUT array and verifying the stimulation using fluorescence calcium imaging. Using fluorescence imaging, we observed an increase in Ca2+ level of TRPA1 expressing HEK293T cells under ultrasound sonication, which confirms that TRPA1 channel in HEK293T cells was activated by ultrasound.