Heung-Shik Lee
Inha University
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Publication
Featured researches published by Heung-Shik Lee.
Sensors | 2007
Heung-Shik Lee; Chongdu Cho; Myeong-Woo Cho
We have developed a wireless-controlled compact optical switch by silicon micromachining techniques with DC magnetron sputtering. For the optical switching operation, micro mirror is designed as cantilever shape size of 5mm×800μm×50μm. TbDyFe film is sputter-deposited on the upper side of the mirror with the condition as: Ar gas pressure below 1.2×10-9 torr, DC input power of 180W and heating temperature of up to 250°C for the wireless control of each component. Mirrors are actuated by externally applied magnetic fields for the micro application. Applied beam path can be changed according to the direction and the magnitude of applied magnetic field. Reflectivity changes, M-H curves and X-ray diffractions of sputtered mirrors are measured to determine magneto-optical, magneto-elastic properties with variation in sputtered film thickness. The deflected angle-magnetic field characteristics of the fabricated mirror are measured.
ieee sensors | 2009
Heung-Shik Lee; Chongdu Cho; Sung Pil Chang
In this study, a gas pressure sensing device based on stainless steel diaphragm and titanium substrate for use at harsh environment is presented. To illustrate these principles, array type capacitive gas pressure sensors based on a stainless steel and titanium have been designed and fabricated. For the fabrication of the sensor, both of bulk and surface micromachined techniques are used with conventional machining fabrication. As results, characteristics of the fabricated gas pressure sensor are estimated in terms of diaphragm deflection and capacitance change by external pressure. as illustrated by the portions given in this document.
IEEE Transactions on Magnetics | 2008
Heung-Shik Lee; Chongdu Cho
In this paper, we have developed the flexible polyimide based magnetostrictive multibody actuators and investigated the magneto-mechanical characteristics of TbFe/Ni/TbFe layered thin film sputtered on the polyimide substrate with different thickness ratios for micro devices. The developed actuator is operated by magnetic field applied along with the length direction of each cantilever of the multibody design. In the fabrication process, micromachining techniques are adopted for the design of multicantilever shape of flexible polyimide substrate, thicknesses of 127 mu m. And TbFe/Ni/TbFe multilayer films with thicknesses of 0.2/0.1/0.2, 0.1/0.1/0 mum are sputter-deposited on the cantilever part of the actuator using designed mask (500 mum thick) for selective dc magnetron sputtering. After the sputter process, X-ray diffraction studies are also carried out to determine the film structure and thickness of the sputtered film. As results, magnetization and magnetostriction of each actuator are measured, and discussed the results of external magnetic field lower than 0.5 T for micro-systems applications.
ieee sensors | 2006
Heung-Shik Lee; Chongdu Cho; Sung Pil Chang
In this paper, electro-mechanical characteristics of stainless steel diaphragm have been studied as a potential robust substrate and a diaphragm material for micromachined devices. Lamination process techniques combined with traditional micromachining processes have been investigated as suitable fabrication technologies. To illustrate these principles, capacitive pressure sensors based on a stainless steel diaphragm have been designed, fabricated and characterized. Each sensor uses a stainless steel substrate, a laminated stainless steel film as a suspended movable plate and a fixed, surface micromachined back electrode of electroplated nickel. The finite element method is adopted to investigate residual stresses formed in the process. The sensitivity of the device fabricated using these technologies is 9.03 ppm kPa-1 with a net capacitance change of 0.14 pF over a range 0~178 kPa.
Journal of Rare Earths | 2008
Heung-Shik Lee; Chongdu Cho
Abstract In this article, it was suggested a TbFe/Co/Dy trilayered GM (Giant Magnetostrictive) film type actuator and investigated the magnetomechanical characteristics of the actuator for micro application. The trilayered films were fabricated at different thickness ratios to get an optimized structure. TbFe had positive GM properties, and cobalt, dysprosium layers made the magnetostriction property of composite film increase in low magnetic field. To fabricate the Si based microactuator with trilayered film, micromachining processes including RIE (Reactive Ion Etching) and selective DC magnetron sputtering techniques were combined. The deposited film thicknesses were measured by X-ray diffraction (XRD). As a result, the magnetization of the film on the fabricated actuator was observed to characterize the magnetic properties of the TbFe/Co/Dy film using VSM (Vibrating Sample Magnetometer). The magnetostriction of the actuator was determined by measuring the differences of curvature of the film coated silicon substrates using the optical cantilever method, and the deflections were also estimated under the external magnetic field lower than 0.5T for micro-system applications.
IEEE Sensors Journal | 2008
Heung-Shik Lee; Sung Pil Chang; Chongdu Cho
This paper investigates multiarrayed (6 times 6) sensors based on laminated stainless steel membrane on the stainless steel substrate. For the fabrication of those sensors, micromachining techniques are combined with lamination process techniques. For the lamination between diaphragm and substrate, hot pressing technique is used with epoxy resin. The finite-element method is adopted to investigate the mechanical characteristics of membrane formed in the process and the electromechanical characteristics of sensors are measured. As results, the sensitivity of the device fabricated using these technologies is 9.03 ppm kPa-1 with a net capacitance change of 0.14 pF over a range 0-178 kPa.
Journal of Applied Physics | 2011
Heung-Shik Lee; Chongdu Cho; Alan T. Zehnder; Kyuwon Choi
This paper reports the design, fabrication, and performance characterization of a magnetostrictive microworm actuator. The suggested worm actuator is partially coated with NiFe film of 10 μm thickness. This actuator consists of a body plate of 50 μm thickness and four legs fabricated using SU-8 spin coating together with development and bonding process. Three square sections of NiFe film of 10 μm thickness are in turn electroplated on the top and bottom sides of the SU-8 body. The external magnetic fields are controlled for sinusoidal form of 3 Hz frequency. For the magnetomechanical characterization of the film, the magnetic moment is examined using a vibrating sample magnetometer. For assaying the movement of the actuator, the curvatures of each section under the applied external magnetic field are measured using a microscope measurement system with electromagnet set. The results show wave shape movement and maximum contractile distance between the end tips of legs is 0.777 mm.
Journal of Micro-nanolithography Mems and Moems | 2009
Heung-Shik Lee; Chongdu Cho; Dae-Seok Shin; Sung Pil Chang
We present the control of magnetostriction and magnetization of the magnetostrictive thin film via additional electric field with original low magnetic field for microelectromechanical systems (MEMS) application. To examine the electric field effect on the magnetostrictive thin film deposited on each substrate, Si and polyimide (Kapton, Dupont Corp.) substrates are used. During the measurement of magnetization and magnetostriction, 0-to 50-V electric fields are applied under 0.5-T magnetic fields. As a result, 3% of magnetostriction is enhanced compare with no electric field.
Proceedings of SPIE | 2010
Heung-Shik Lee; Bongjun Kim; Chongdu Cho
In this paper, wireless optical system was developed by using array type TbDyFeNi thin film actuator. The effect of Ni content on the magneto-mechanical properties of the Tb0.24Dy0.76Fe2 system, for wireless micro actuator with the effect of deposited film thickness of TbDyFeNi on silicon substrate, was also investigated. To create the device, array shape silicon substrates were bulk micromachined, and Tb0.24Dy0.76Fe2-xNix, (x=0, 0.5, 1.2, 2.0) films were sputter-deposited on the back side of substrate by selective DC magnetron sputtering techniques. After the sputter process, magnetization and effective mgnetoelastic coupling coefficient and magnetostriction of the sample were measured for the magnetomechanical characterizaztion. For the operation, each branch of the array type actuator has different length and out-ofplane motion. Each branch was actuated by externally applied magnetic fields up to 0.5T and motion of the branches made inclined movement. As a result, deflected angle of the actuator due to the movement of array type actuator to external magnetic fields were observed.
international conference on mems, nano, and smart systems | 2009
Heung-Shik Lee; Chongdu Cho
In this study, four kinds of substrates (Si, glass, Fe, polyimide) with the magnetostrictive thin film layers were prepared and investigated to characterize the magnetic and mechanical behaviors due to the different substrates. The substrates were fabricated to have cantilever shapes of 50, 150, and 500um thickness, on which 1 ~ 10 μm thick TbDyFe films are deposited by DC magnetron sputtering . The magnetization of each sample was examined using VSM (Vibrating Sample Magnetometer) and magnetostriction was measured using capacitance method to characterize magneto-mechanical behaviors. The magnetostriction induced deflections were compared and discussed with possibility of micro actuator applications.