Kyoung-Woo Jo

High-resolution inchworm linear motor based on electrostatic twisting microactuators

A new inchworm micromotor using new electrostatic in-plane twisting microactuators has been designed, fabricated and characterized for nano-resolution manipulators. The proposed twisting mechanism was implemented employing a pair of differential electrostatic actuators with a high stiffness in the driving direction for stable positioning. The electromechanically coupled motion of the voltage–displacement relation was analyzed using a finite element method (FEM), confirming that the twisting actuator makes a tiny step movement efficiently. The proposed actuator was fabricated on a silicon-on-insulator (SOI) wafer with the device footprint of 2.2 × 2.8 mm2, and its nano-stepping characteristics were measured by an optical interferometer consisting of an integrated micromirror and optical fiber. The fabricated inchworm motor showed a minimum step displacement of 5.2 ± 3.8 nm (2σ) and 4.1 ± 2.9 nm (2σ) for cyclic motion in the +y- and the −y-directions, respectively, with the gripping voltage of 15 V and differential voltage of 1 V. As a result, the proposed inchworm micromotor could operate with a stroke of 3 µm and a bi-directional step displacement of less than 10 nm. The step displacement is the smallest value of in-plane-type micromotors so far, and its magnitude was controllable up to 120 nm/cycle by changing the differential voltage.

A glass reflowed microlens array on a Si substrate with rectangular through-holes

A thermally reflowed glass microlens array was fabricated on a Si substrate. Glass lenses are more durable and scratch-resistant than plastic lenses made by the same, simple thermal reflow process. The microlens was designed using the ray tracing technique and optimized by controlling the nominal diameter and height of glass cylinders. The glass cylinders were formed by wet etching a glass plate in a HF (49%) solution and reflowed to form a semi-spherical lens shape at 850 °C (glass transition temperature Tg = 820 °C) for 20 min in a furnace. Then, the Si substrate was etched in a TMAH (5%) solution to make rectangular through-holes underneath the microlens array for high optical transmission. The profile of the fabricated microlens was measured with a confocal microscope, and its optical characteristics (lens size, beam radius and focal length) were evaluated with a 633 nm laser diode beam. The experimental beam waist (minimum beam radius) at the focal point of 1000 µm was 8 µm, which was in good agreement with a calculated value. The results show that the microlens array can be used in a broad wavelength range from UV to the IR region.

Microplasma generation in a sealed microfluidic glass chip using a water electrode

A microplasma was generated in a sealed microfluidic glass chip for the application of the miniaturized chemical detection system, especially for water contaminants. The behavior of a microbubble as well as a microplasma was observed using a 1% NaCl solution with no metal contact in a sealed glass microchannel. A microplasma formed by water contents excluding air or inert gas showed clear emission spectrum in UV, visible, and near IR range. The detection of lead was demonstrated by measuring the intensity of the Pb emission line (at 406nm) with respect to the concentration.

Optical characteristics of a self-aligned microlens fabricated on the sidewall of a 45/spl deg/-angled optical fiber

We propose a self-aligned microlens fabricated on the sidewall of an optical fiber for a compact and high-throughput scanning optical microscopy (SNOM) application. The end face of the optical fiber is polished to have 45/spl deg/ for total internal reflection, and the microlens is fabricated on the sidewall of the optical fiber by exposing photoresist with ultraviolet light guided along the optical fiber. This method requires no active alignment and is compatible with standard photolithography. The microlens effectively focuses the illumination light emanating from the 45/spl deg/-angled fiber, resulting in a beam radius of 1.1 /spl mu/m at the focal length of 22.5 /spl mu/m. When an SNOM probe has an aperture size of 143 nm and the input optical power to the SNOM probe is 400 /spl mu/W, the optical throughput (the ratio of output to input power) is as high as 2.5/spl times/10/sup -4/, which is five times higher than without a microlens.

Crystalline Si-based in-plane tunable Fabry-Perot filter with wide tunable range

This paper presents crystalline Si-based tunable Fabry-Perot filter, which enables its integration to align with other optical devices on an in-plane substrate. This device features wide tuning range over 80 nm and high tuning sensitivity of 11.7 nm/V.

Dynamic Characterization of Human Breast Cancer Cells Using a Piezoresistive Microcantilever

In this paper, frequency response (dynamic compression and recovery) is suggested as a new physical marker to differentiate between breast cancer cells (MCF7) and normal cells (MCF10A). A single cell is placed on the laminated piezoelectric actuator and a piezoresistive microcantilever is placed on the upper surface of the cell at a specified preload displacement (or an equivalent force). The piezoelectric actuator excites the single cell in a sinusoidal fashion and its dynamic deformation is then evaluated from the displacement converted by measuring the voltage output through a piezoresistor in the microcantilever. The microcantilever has a flat contact surface with no sharp tip, making it possible to measure the overall properties of the cell rather than the local properties. These results indicate that the MCF7 cells are more deformable in quasi-static conditions compared with MCF10A cells, consistent with known characteristics. Under conditions of high frequency of over 50 Hz at a 1 μm preload displacement, 1 Hz at a 2 μm preload displacement, and all frequency ranges tested at a 3 μm preload displacement, MCF7 cells showed smaller deformation than MCF10A cells. MCF7 cells have higher absorption than MCF10A cells such that MCF7 cells appear to have higher deformability according to increasing frequency. Moreover, larger preload and higher frequencies are shown to enhance the differences in cell deformability between the MCF7 cells and MCF10A cells, which can be used as a physical marker for differentiating between MCF10A cells and MCF7 cells, even for high-speed screening devices.

Fiber-Optic Laser Doppler Vibrometer to Dynamically Measure MEMS Actuator With In-Plane Motion

An on-axis laser Doppler vibrometer (LDV), where the direction of the incident beam is the same as the direction of the movement of the actuator, intrinsically offers an accurate dynamic measurement, although it cannot be currently applied to MEMS actuators with in-plane motion due to its limited access to the sidewall. The only currently available method is an off-axis LDV, which still shows serious measurement errors, depending on the target surface pattern of the device. In this paper, an on-axis fiber-optic LDV (FLDV) with a 45deg-angled optical fiber is proposed as a means of measuring the in-plane motion of a MEMS actuator. The device demonstrated displacements in the range between 6.5 mum at 2 Hz and 11.0 mum at 280 Hz, corresponding to the minimum and maximum velocities of 81.6 mum/s and 19.3 mm/s, respectively. The measurement capability of the proposed FLDV is then confirmed to cover the movement of most MEMS actuators such that it can greatly enhance the flexibility of dynamic measurements in MEMS actuators.

Optical characteristics of a refractive optical attenuator with respect to the wedge angles of a silicon optical leaker

We design, fabricate, and characterize the micromachined refractive variable optical attenuator (VOA) with a wedge-shaped silicon optical leaker (SOL). The vertical structures of the VOA device can be simply fabricated by deep reactive ion etching with no sidewall metallization, and the 8 degrees angled fibers are employed for a high return loss even in air-ambient conditions. The SOL successively transmits and refracts part of the incident light far outside the acceptance angle of the output fiber, showing an effective optical attenuation. The fabricated VOA gives high optical performances, such as a response time of 6 ms, a return loss of 39 dB, an insertion loss of 0.6 dB, an attenuation range of 43 dB, and a polarization-dependent loss (PDL) of a 10% attenuation level, including a wavelength-dependent loss. The optical characteristics of the VOA are also theoretically investigated with respect to the wedge angles of the SOL. The experimental characteristics are in good agreement with the theoretical values calculated, considering light scattered from the endface of an optical fiber and sidewall of the SOL. The PDL estimation was confirmed especially to sufficiently explain the fundamental characteristic of the PDL for the refractive VOA.

Inline Fiber Optic Chemical Sensor Using a Self-Aligned Epoxy Microbridge With a Metal Layer

We propose the use of a self-aligned epoxy microbridge with a metal layer for a low-cost, easy-to-make inline fiber optic chemical sensor that can sense the concentration of chemical solutions. The key component of the sensor is a cylindrical epoxy microbridge that can be assembled between input and output optical fibers by self-aligned UV curing. The microbridge is made from an epoxy that can rapidly diffuse liquid. The top of the microbridge was coated with Au/Ti to block diffusion of the surrounding solution and to induce optical dissipation that depends on the concentration of the chemical solution. We tested our fiber optic chemical sensor for deionized (DI) water and NaCl solution. The medium surrounding the microbridge asymmetrically diffuses into the epoxy microbridge due to the metal layer. The asymmetrical diffusion, consequently, makes a major change to the refractive index on the bottom of the microbridge, thereby altering the propagation mode of light. As a result, depending on the concentration of the NaCl solution, a fraction of the propagated light is absorbed into the metal layer. The sensitivity, which refers to the ratio of the concentration change and optical power, was experimentally confirmed to be 0.103 (wt%/photon count)

Conformability and optical reflectance of Ti∕Au film sputtered on the Si vertical sidewalls

A high quality reflective vertical surface is required for various optical micro electro mechanical system (MEMS) devices. In this paper, we discuss an extensive investigation of Ti∕Au sputtering, with respect to temperature, pressure, and electric power input, followed by rapid thermal annealing (RTA) to improve the adhesion and reflection characteristics of a vertical micromirror. The vertical surface was fabricated by means of the deep reactive ion etching (DRIE) process of a silicon-on-insulator (SOI) wafer, with an 80-μm-thick layer of Si. Then, 20-nm-thick Ti and 200-nm-thick Au films were deposited on the vertical surface as adhesion and reflective layers, respectively, using rf/dc magnetron sputtering. The Au films were deposited at room temperature (20°C) and annealed at 380°C for 30s in a RTA chamber. While taking into consideration the conformability and the reflectance of the Au vertical mirror, the process conditions were optimized at an argon pressure of 10mTorr and an electric power input o...