Experimental Mechanics in Nano and Biotechnology

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Authors: Da Feng Chen, He Jun Du, Wei Hua Li, Hai Qing Gong
Abstract: A dielectrophoretic barrier is generated with two layers of microelectrode structures so called paired electrode array (PEA) constructing face to face on the top and bottom sides of a microchannel. The barrier is designed to control the movement of particles in combination with a fluid flow. Depending on the relative strength of the DEP force and hydrodynamic force, microparticles or cells carrying by a laminar flow can either penetrate the barrier or be deflected from there. The threshold velocity at which the barrier firstly fails to hold back the particles is a significant parameter to validate the performance of the device. This paper presents an experimental study on the performance of the microfabricated paired electrode array. The electrodes were fabricated with conventional microfabrication techniques. Micron-sized latex beads were used in the investigation. The holding capacity was defined by measuring the threshold velocity of the system. The results provide crucial information for the design of the dielectrophoretic barrier for microparticle manipulation and separation.
Authors: Heung Shik Lee, Chong Du Cho, Usik Lee
Abstract: Silicon based magnetostrictive structures were fabricated for micro-wireless actuators, and finite element models were developed to predict mechanical characteristics of the actuated structures. These structures can be used to design wireless micro-vehicles and multi-function packaged micro-devices. In the fabrication process, amorphous magnetostrictive films of the optimized binary compound Tb0.4Fe0.6 and Sm0.47Fe0.53 were deposited with various thicknesses on the silicon membrane by DC magnetron sputtering using cast composite targets. Magnetic fields lower than 2KOe were applied for micro-system applications. These films have been tested in a simple cantilever arrangement and the predicted magnetostrictions of the actuated membranes through the developed FE models have been calculated.
Authors: Taik Min Lee, Young Ho Seo, Kyung Hyun Whang, Doo Sun Choi
Abstract: A novel piezoelectric micro-actuator with actuating range amplification structure has been proposed. This actuator is unique in that the leverage type amplification structure enables large actuating movement with low voltage. In case of general piezoelectric thin film actuator, applied voltage is low and almost zero power is consumed. Its switching time is very fast in comparison with electrostatic actuators and thermal actuators. However, the most drawback of piezoelectric actuator is short actuating range. A 100μm length PZT actuator can only make movement of 100. In this research, we suggest an actuator which can provide geometric amplification of the PZT strain displacement in lateral direction. The lateral piezoelectric MEMS actuator was fabricated and its actuating range was measured. The actuator shows maximum lateral displacement of 1.1μm, and break-down-voltage of the thin film PZT actuator is above 16V.
Authors: Sun Rock Choi, Dong Sik Kim, Sung Hoon Choa
Abstract: The thermal properties of thin films, such as thermal conductivity and diffusivity, are important in design and analysis of MEMS (micro electro mechanical systems), particularly in microscale thermal systems and high-power electronic/optoelectronic devices. In the present study, the thermal conductivity and diffusivity of a variety of thin film materials, which are commonly used in MEMS applications, are measured. The samples include Au, Sn, Mo, Al/Ti alloy, AlN, and SiC. The Au sample is deposited by the e-beam evaporation technique while the rest of the metallic samples are deposited by sputtering processes. The AlN and SiC films are also prepared by sputtering processes. In the experiment, the thermal diffusivities of metallic thin films are measured by two independent methods — the AC calorimetric method and photothermal mirage technique. The thermal conductivities of dielectric thin films are measured by the 3 omega technique. The results show that the thermal transport properties of some of the films are significantly smaller than those of the same material in bulk form. Especially, the AlN and SiC thin films exhibit pronounced thermal conductivity reduction because of the size effect. The electrical conductivities of the metallic thin films are measured as well. The results for Au and Sn are consistent with the thermal conductivity, confirming the Wiedmann-Franz law. However, Al/Ti and Mo thin films show considerable deviation from the law. The results are analyzed based on the XRD (X-Ray diffraction) and AFM (Atomic Force Microscope) measurement.
Authors: Woong Cho, Yong Jun Ko, Yoo Min Ahn, Joon Yong Yoon, Nahm Gyoo Cho
Abstract: Experimental investigation and numerical simulation on the effect of surface wettability on the performance of a polydimethylsiloxane (PDMS) based diffuser micropump are presented. A valveless micro membrane pump with piezoelectric actuation has been examined. Using a replica molding technique, the valveless micropump was made of PDMS on a Pyrex glass substrate. A thin piezoelectric (PZT) disc was used as an actuator. Poly vinyl alcohol (PVA) and octadecyltrichlorosilane (OTS) coatings, which make the coated surface hydrophilic and hydrophobic, respectively, were used to modify the surface wettability inside the pump. In our experiments, the contact angle of the PDMS surface changed from 96.6 o to 29.1 o and 99.6 o by PVA and OTS coatings, respectively, and the contact angle of glass changed from 33.2 o to 17.5 o and 141.8 o. A self-priming process was numerically simulated in a diffuser element using a computational fluid dynamics program (CFD-ACE+). The results show that fewer gas bubbles were created in the hydrophilic coated pump than in the hydrophobic coated one as time progressed. This agrees well with experimental observations. Steady-state flow rates of the micropump were measured. Compared to the non-coated pump, the flow rate increased slightly with the hydrophobic coating but decreased with the hydrophilic coating. We determine that surface wettability significantly affects the performance of a PDMS-based micropump.
Authors: Yong Kyung Cho, Hong Gyu Jeon, Dae Hyun Cho, Young Ze Lee
Abstract: DLC (Diamond Like Carbon) films show very desirable surface interactions with high hardness, low friction coefficient, and good wear-resistance properties. The friction behavior of hydrogenated DLC film is dependent on tribological environment, especially surrounding temperature. In this work, the tribological behaviors of DLC (Diamond-like carbon) films, prepared by the radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method, were studied in elevated temperatures. The ball-on-disk tests with DLC films on steel specimens were conducted at a sliding speed of 60 rpm, a load of 10 N, and surrounding various temperatures of 25, 40, 55 and 75. The results show considerable dependency of DLC tribological parameters on temperature. The friction coefficient decreased as the surrounding temperature increased. After tests the wear tracks of hydrogenated DLC film were analyzed by optical microscope, scanning electron spectroscopy (SEM) and Raman spectroscopy. The surface roughness and 3-D images of wear track were also obtained by an atomic force microscope (AFM).
Authors: Sang Hwa Jeong, Gwang Ho Kim, Kyoung Rae Cha
Abstract: With the increasing demand for VBNS and VDSL, the development of the kernel parts of optical communication such as PLC(Planar Light Circuit), Coupler, and WDM elements has increased. The optical transmitter and the receiver module need precise and mechanical alignment within a few micrometers to couple the semiconductor device, optical fiber and waveguide. The alignment and the attachment technology are very important in the fabrication of an optical element. Presently, the alignment of the optical element is time consuming, and an effective alignment algorithm has not yet to be developed. In this paper, the optical element alignment of the multi-axis ultra precision stage is studied. Two alignment algorithms applied to the ultra precision multi-axis stage are used, the field search algorithm and the peak search algorithm. The automation program to improve the characteristics of the optical element alignment system is developed by Labview programming and is composed of three tabs, the field search tab, plotting tab and peak search tab. The developed program is applied to an actual system to determine the improvement in alignment performance.
Authors: Sung Jun Lee, Ji Hyun Park, Chang Hyun Lim, Won Kyu Jeong, Seog Moon Choi, Yong Soo Oh
Abstract: By the development of high power LED for solid states lighting, the requirement for driving current has increased critically, thereby increasing power dissipation. Heat flux corresponds to power dissipation is mainly generated in p-n junction of LED, so the effective removal of heat is the key factor for long lifetime of LED chip. In this study, we newly proposed the silicon package for high power LED using MEMS technology and estimated its heat dissipation characteristic. Our silicon package structure is composed of base and reflector cup. The role of base is that settle LED chip at desired position and supply electrical interconnection for LED operation, and finally transfer the heat from junction region to outside. For improved heat transfer, we introduced the heat conductive metal plated trench structure at the opposite side of LED attached side. The depth and the diameter of trench were 150 and 100um, respectively. Copper with high thermal conductivity than silicon was filled in trench by electroplating and the thickness of copper was about 100um. Reflector cup was formed by anisotropic wet etching and then, silicon package platform could be fabricated by eutectic bonding between base and reflector cup. The thermal resistance of silicon package was about 6 to 7K/W from junction to case, and also, thermal resistance reduction of 0.64K/W was done by metal plated trench. This result could be comparable to that of other high power LED package. Our silicon package platform is easy to be expanded into array and wafer level package. So, it is suitable for future high efficiency and low cost package.
Authors: Jun Hyub Park, Man Sik Myung, Yun Jae Kim, Chang Seung Lee, Sung Hoon Choa, Woo Seong Che
Abstract: A new tensile tester using an electromagnetic-force actuator (voice coil) was developed to measure the mechanical characteristics of surface-micromachined thin film materials. The tester has a load cell with maximum capacity of 0.5N and a non-contact position measuring system based on the principle of capacitance micrometry with 0.1nm resolution for displacement measurement. The tester was applied for tensile testing of Al-3%Ti thin films with dimensions of 1000μm long, 50-480μm wide and 1.0 and 1.1 μm thick. The Al-3%Ti is commonly used in RF(radio frequency) microelectromechanical systems(MEMS) switch. The specimen with holes and bridges was designed for easy tensile test. The holes at center of grip end are able to make alignment and gripping easy. The bridges are to remove the side supports easily and extract specimen from wafer without sawing. It was found that the mean tensile strengths of Al-3%Ti are 140-380MPa, depending on the width of specimens and converging to a certain tensile strength as the width decreases.
Authors: Dong Weon Lee, Young Soo Choi, Il Kweon Oh
Abstract: This paper describes an integrated tunneling sensor for applications of an electronic nose and a scanning probe microscope. Ultra-thin silicon dioxide having a thickness of ~2 nm is used as a material of the tunneling sensor. It provides much higher sensitivity in comparison with others sensing methods. The tunneling sensor is placed on a fixed edge where the maximum strain arises. As additional masses or forces are added to the surface of the cantilever, the thickness of the thin silicon dioxide layer is slightly decreased. By using exponential nature of electron tunneling dominated by the thickness of the silicon dioxide it can be used as an ultra-high sensitive sensor. The thin dioxide is fabricated by dry oxidation using a vertical furnace. The cantilever structures are defined by conventional MEMS technologies. Current density of the tunneling sensor is evaluated as a function of voltage and is compared with numerical analysis based on direct tunneling phenomena.

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