Sung-Sik Yun

A micromachined in-plane tunable optical filter using the thermo-optic effect of crystalline silicon

This paper presents a micromachined in-plane tunable optical filter using the thermo-optic effect of crystalline silicon. The device was fabricated by a silicon deep reactive ion etching process with a silicon-on-insulator wafer and thermal oxide removal to improve the sidewall smoothness. Optical fibers could be horizontally aligned on the fabricated TOF device by exploiting in-plane device structures, which enable TOFs to easily connect with other optical components. Tunability of the TOFs was experimentally achieved through thermal modulation of optical path length by heating the silicon etalon. As the input voltage increases, a notch in the reflectance spectrum shifts to a longer wavelength with an average tuning sensitivity of 0.9 nm K−1 and a best bandwidth of 1.1 nm. The proposed device can be utilized for spectroscopy or optical communication.

Handheld mechanical cell lysis chip with ultra-sharp silicon nano-blade arrays for rapid intracellular protein extraction

This paper presents a handheld mechanical cell lysis chip with ultra-sharp nano-blade arrays fabricated by simple and cost effective crystalline wet etching of (110) silicon. The ultra-sharp nano-blade array is simply formed by the undercutting of (110) silicon during the crystalline wet etching process. Cells can be easily disrupted by the silicon nano-blade array without the help of additional reagents or electrical sources. Based on the bench-top test of the proposed device, a handheld mechanical cell lysis chip with the nano-blade arrays is designed and fabricated for direct connection to a commercial syringe. The direct connection to a syringe provides rapid cell lysis, easy handling, and minimization of the lysate dead volume. The protein concentration in the cell lysate obtained by the proposed lysis chip is quantitatively comparable to the one prepared by a conventional chemical lysis method.

Fabrication of morphological defect-free vertical electrodes using a (1 1 0) silicon-on-patterned-insulator process for micromachined capacitive inclinometers

This paper presents a novel fabrication method of scalloping-free and footing-free vertical electrodes for micromachined capacitive inclinometers with a high sensing resolution. The proposed fabrication method is based on additional crystalline wet etching of a (1 1 0) silicon that is bonded to a silicon substrate with a patterned insulator layer. The sensing electrodes, which are aligned to the (1 1 1) plane, have very smooth sidewalls because the morphological defects formed by the silicon deep reactive ion etching (DRIE) process are drastically reduced in the crystalline wet etching. The fabricated capacitive inclinometer with smooth sensing electrodes was evaluated in terms of capacitance change and resolution. The capacitance of the fabricated inclinometer is changed from −0.246 to 0.258 pF for the inclination angle (−90° to 90°). The temporal deviation of the capacitance is as small as 0.2 fF, which leads to a high resolution of 0.1° or less for ±45°.

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.

Volume-producible fabrication of a silicon nanowire via crystalline wet etching of (1 1 0) silicon

This study presents a fabrication method of a mass-producible silicon nanowire (SiNW) using a (1 1 0) silicon wafer. Microscale silicon lines, patterned in standard photolithography, are reduced to 300 nm in width in a two-step wet-etching process. The silicon lines are transformed into the SiNW by a thermal oxidation process. The formation of SiNW after thermal oxidation was verified using a numerical oxidation simulation considering the two-dimensional growth of the oxide. After thermal wet oxidation at 970 °C for 50 min, silicon lines of 300 nm in width were transformed into the SiNWs of an inverse triangular cross-section with an effective width of approximately 70 nm. At the same time, the fabricated SiNWs were electrically isolated from the substrate without using an expensive silicon-on-insulator wafer. The pH sensing test, which is usually performed as a preliminary experiment for the biosensor applications, was conducted with respect to various pH solutions. The experimental sensitivity to the pH level was 0.55 nS pH−1, when the voltage applied to the SiNW was 1 V. The SiNW has been completely fabricated by using only a conventional semiconductor process instead of a costly and time-consuming e-beam lithography process for the nanoscale patterning. The proposed fabrication method was successfully confirmed to have the potential of mass-producible and cost-effective SiNW devices for nano-biosensor applications.

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.

Novel Micro Capacitive Inclinometer with Oblique Comb Electrode and Suspension Spring Aligned Parallel to {111} Vertical Planes of (110) Silicon

A novel high resolution micro capacitive inclinometer has been developed using (110) silicon. KOH crystalline wet etching was employed after silicon deep reactive ion etching (DRIE) to reduce morphologic defects on the sidewalls of oblique comb electrodes aligned parallel to vertical {111} plane. Suspension springs are also parallel to other vertical {111} plane to secure the width during KOH wet etching. The sensitivity (pF/°) was increased because the oblique comb electrodes change both the overlapped area and gap during operation. The capacitance changed from -0.8 to 0.8 pF for -90° -90° and resolution was estimated at 0.18° or less for ±80°.

A micromirror scanner with vertical combs tilted by assembly process

We have developed a simple assembly technology to realize the tilted vertical combs for electrostatic micromirror scanners. The in-plane vertical comb electrodes are easily transformed into out-of-plane tilted comb by asymmetrical pushing down the levers of the spring that is attached to the micro mirror. The fabricated mirror scanner showed the optical scan angle of up to 1.3deg at 60 V and the resonant frequency of 3.15 kHz.

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...