Youngjoo Yee

LG Electronics, Sŏul, Seoul, South Korea

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Publications (34)26.02 Total impact

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    ABSTRACT: This paper reports a novel high-sag microlens array (MLA) film with a full fill factor and presents its application to organic light emitting diodes (OLEDs) for the purpose of improving their outcoupling efficiency. A gapless hexagonal MLA film having a high sag ratio is proposed and fabricated by a simple micromachining process including trench formation and the conformal vapor phase deposition of a polymer. By applying the MLA films to OLED panels, the outcoupling efficiency was increased by a maximum of 48% without any apparent color shift. A high-sag MLA film with a full fill factor is expected to impart remarkable optical efficiency to various display or lighting applications with flat panel light sources including OLEDs.
    Journal of Micromechanics and Microengineering 04/2008; 18(6):065003. · 1.79 Impact Factor
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    ABSTRACT: A microelectromechanical systems (MEMS)-based, micro-optical fiber coupler to obtain a high power laser diode beam is integrated with a fiber rod lens and an array of SU-8 lenses, through each of which the laser beams emitted from the laser diodes are collimated vertically and horizontally, respectively, thus increasing the coupling efficiency. The fibers bundle and the laser diodes are assembled in one package on a silicon optical bench. The optical properties of the SU-8 lenses are suitable for high power laser diode application. The collimation of the beams passing the rod lens and the SU-8 lenses was confirmed. According to the simulation and experimental results, the coupling efficiency of the fiber coupler was increased by the insertion of the SU-8 lenses when the emitter width of the laser diode was wide.
    Japanese Journal of Applied Physics 01/2007; 46:5473-5477. · 1.07 Impact Factor
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    ABSTRACT: This paper reports a microlens array (MLA) film with full fill factor and presents its application to organic light emitting diode (OLED) for improving outcoupling efficiency. Gapless MLA film having high sag ratio is proposed and fabricated by simple micromachining process including trench formation and conformal vapor phase deposition of polymer. As applying MLA film to OLED panel, the outcoupling efficiency increased by maximum 48%. High-sag MLA optical film with full fill factor is expected to give remarkable optical efficiency to various display or lighting applications of the flat panel light sources including OLED.
    01/2007;
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    ABSTRACT: We present the design, fabrication and measurement results of a comb-driven electrostatic scanning micromirror. Instead of a conventional micromirror having uniform thickness across the entire reflective surface, a diaphragm mirror plate supported by an array of diamond-shaped frame structures is fabricated monolithically. The fabrication process is a simple sequence of silicon deep etch processes on both sides of the silicon-on-insulator (SOI) substrate without the substrate bonding process. The micromirror is fabricated on the device layer of the substrate. The mirror plate undergoes a rotational motion by an electrostatic force between the movable comb electrodes connected to the micromirror and stationary comb electrode formed on the handle wafer. A scanning micromirror with a 10 µm thick diaphragm mirror plate, having a planar dimension of 1.5 × 1.5 mm2, supported by an array of 110 µm thick rhombic support frames, was fabricated and tested. A mechanical deflection angle of 8.5° at a resonance frequency of 19.55 kHz and a pressure of 7 mTorr was obtained. A prototype of the raster scanning laser projection display system was developed using the fabricated micromirror as the horizontal scanner and a galvanomirror as the vertical scanner, respectively.
    Journal of Micromechanics and Microengineering 04/2006; 16(5):1033. · 1.79 Impact Factor
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    ABSTRACT: The paper presents the design, fabrication and measurement of an electrostatic scanning micromirror having a diaphragm mirror plate supported by an array of diamond shaped frame structures. Instead of supporting the diaphragm mirror of a different material with a stiff rim structure at the circumference, the diaphragm mirror plate and the frame structure are fabricated monolithically in the same layer of single-crystal-silicon (Nee, J.T. et al., Proc. IEEE Int. Conf. MEMS, p.704-9, 2000). The scanning micromirror with a 10 μm-thick diaphragm mirror plate, having a planar dimension of 1.5×1.5 mm<sup>2</sup>, supported by an array of 110 μm-thick rhombic stiffening frames, was fabricated and tested. A mechanical deflection angle of 8.5° at the resonance frequency of 19.55 kHz and 44% reduction of dynamic deformation (Conant, R.A. et al., Proc. IEEE/LEOS Int. Conf. Optical MEMS, p.49-50, 2000), in comparison to the conventional rectangular parallelepiped micromirror, were obtained.
    Solid-State Sensors, Actuators and Microsystems, 2005. Digest of Technical Papers. TRANSDUCERS '05. The 13th International Conference on; 07/2005
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    ABSTRACT: An integrated and miniaturized optical flying head (OFH) is presented for a small form factor with high-density portable optical data storage. It is composed of a high numerical aperture (NA) objective lens, a microlens actuator for adjusting the position of the objective lens, an integrated air-bearing-slider (ABS), and an embedded magnetic-field-modulation (MFM) coil for magneto-optical recording. To adjust the optimal focal length of the lens, a parallel-plate vertical actuator is adopted. In addition, the area-optimized torsion type H-shape spring is used for vertical actuation. The glass ABS structure and the double metal layer MFM coil are fabricated on a transparent substrate, bonded to the silicon actuator. The overall size of the integrated OFH, assembled with the high numerical aperture (NA=0.85) objective lens, is mm (length×width×thickness), which makes it small enough to be furnished in a portable optical data storage device. A prototype of small optical drive is also developed to satisfy the form factor of PCMCIA type II. The prototype includes the integrated and miniaturized OFH and the basic operation of the drive is tested.
    Sensors and Actuators A: Physical. 09/2004;
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    ABSTRACT: The design and fabrication of an electrostatic MEMS variable optical attenuator (VOA) is described. The VOA is a reflection type with a folded micromirror actuated by a comb-drive actuator. The VOA is fabricated by a simple single-mask process. One photolithography and subsequent deep silicon reactive ion etching define all the microstructures of the VOA. The folded micromirror structure can reduce the overall size of the device by enabling the parallel alignment of an input fiber and an output fiber. Lensed fibers are used to maximize the coupling efficiency and the ease of assembly. The electrooptic characteristics and dynamic characteristics of fabricated VOA are measured. The initial insertion loss is 0.5 dB at 1550 nm and the maximum attenuation is 45 dB, respectively. The polarization dependent loss is measured to be 0.2 dB at 20-dB attenuation. The response time for maximum attenuation is less than 5 ms.
    IEEE Journal of Selected Topics in Quantum Electronics 06/2004; · 4.08 Impact Factor
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    ABSTRACT: This paper presents the design, fabrication, and measurement results of a 2×2 microelectromechanical systems optical switch. The switch comprises an electromagnet and lensed fibers assembled with a micromachined movable vertical micromirror. The optical switch utilizes the out-of-plane motion of the vertical micromirror actuated by electromagnetic force compared to the comb-driven linear actuation achieved by the electrostatic force. At a wavelength of 1550 nm, the insertion loss of 0.2-0.8 dB and the polarization-dependent loss of 0.02-0.2 dB are measured. The switching time is 1 ms. A novel method of realizing a latchable optical switch using an electromagnetic actuator is also provided and verified. The latch mechanism is based on the latchability of the electropermanent magnet instead of the mechanical one using conventional arch-shaped leaf springs.
    IEEE Journal of Selected Topics in Quantum Electronics 06/2004; · 4.08 Impact Factor
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    ABSTRACT: A micro optical flying head is presented for high-density PCMCIA-sized small form factor(SFF) optical data storage. It is composed of a high numerical-aperture(NA) objective lens, a micro lens actuator for adjusting the position of the lens to optimize the focal point to the recording layer of an optical disk, and an integrated air-bearing surface for flying over the spinning disk. The overall size of the fabricated micro optical flying head, assembled with high NA(0.85) objective lens, is as small as 3 mm×1.6 mm×0.5 mm(in length×width×thickness), which makes it suitable for the optical data storage device of mobile applications. Also, a basic operation of a PCMCIA type II optical drive prototype including the micro optical flying head is tested and presented.
    Micro Electro Mechanical Systems, 2004. 17th IEEE International Conference on. (MEMS); 02/2004
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    ABSTRACT: In a small-form-factor (SFF) optical disk drive (ODD), the optical flying head (OFH) on a thin-cover-layered plastic disk requires not only uniformity of the cover layer thickness of the disk media, but also the flying stability of OFH on the plastic disk surface with low flying height variation, as well as precise tolerance management in the OFH assembly. Therefore, in order to develop a practical optical pickup head interfaced to the plastic disk, we designed the OFH with a parallel-plate electrostatic actuator for the vertical positioning of the objective lens for better flying characteristics. The flying height of the OFH is designed to be 200 nm to increase air-bearing stiffness. On the other hand, a UV resin cover layer is adopted as a protective layer and a hard and stiff plastic substrate is also adopted to increase the durability of the disk. In the evaluation of the stability of the OFH and the durability of the disk, we introduce computational and experimental results on the flying height variation of the OFH, additionally we investigated the characteristics of the durability of various plastic disks.
    Japanese Journal of Applied Physics 01/2004; 43:4752-4758. · 1.07 Impact Factor
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    ABSTRACT: A reflection type VOA with folded micromirror was designed and fabricated. The proposed mirror structure can reduce the size of device by parallel alignment of the two fibers. Lensed fibers are used for high coupling efficiency and ease of assembly. The initial insertion loss is about 0.6 dB and the maximum attenuation is about 30 dB. The switching time of the fabricated VOA is about 1 ms.
    Optical MEMS, 2003 IEEE/LEOS International Conference on; 09/2003
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    ABSTRACT: An electromagnetic 2×2 MEMS optical switch having non-mechanical latch mechanism is presented. In this research, the latch characteristics of the electro-permanent magnet are verified with a simple driving circuit. In addition, the iron cover on the micromirror chip is shown to further reduce the power consumption. Through the latch functionality and the optimization of the electromagnetic circuit, power consumption of the switch can be reduced down to a quarter level.
    Optical MEMS, 2003 IEEE/LEOS International Conference on; 09/2003
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    ABSTRACT: A prototype of ultra small optical drive was studied and developed in order to see the feasibility of mobile application, which is targeted to be attachable into the PCMCIA II slot in small mobile devices. A new design and fabrication technology of optical flying head (OFH) for first surface MO recording was studied, and an effective OFH precisely equipped with high NA lens and MO coil was developed based on miniaturization technology. Design consideration of small form factor optical drive is discussed. Some technical issues and barriers in designing and manufacturing the OFH are introduced. Head-disk interface for reliability and flying stability on plastic disk media was tested and evaluated. Basic tracking and read-write performances in a test bed system were tested.
    Proc SPIE 09/2003;
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    ABSTRACT: An integrated MEMS optical flying head(OFH) is presented for a small form factor with high-density portable data storage. It is composed of a high numerical-aperture(NA) objective lens, a micro lens actuator for adjusting the position of the lens, an integrated air-bearing-slider(ABS), and an embedded magnetic-field-modulation(MFM) coil for magneto-optical recording. For adjusting the optimal focal length of the lens, a vertical comb-driven actuator and a parallel plate actuator are adopted. In addition, the area-optimized torsion spring is used for vertical actuation. The ABS structure and the double layer MFM coil are fabricated on a transparent substrate bonded to the silicon actuator. The overall size of the integrated MEMS OFH assembled with the high NA(0.85) objective lens is 3 mm? 1.6 mm? 0.5 mm(in length? width? thickness), which makes it suitable for a portable optical storage device.
    TRANSDUCERS, Solid-State Sensors, Actuators and Microsystems, 12th International Conference on, 2003; 07/2003
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    ABSTRACT: MEMS technology is fast becoming the new enabling technology for areas that require the performance and cost advantages it brings. In this paper, as one of its promising application areas, MEMS technology for a ultra small optical pickup module is presented. The optical flying head is constructed by integration of micromachined devices such as micro slider, micro coil, microactuator, and micro lens within 0.5 mm in height. The basic optical unit comprised of refractive and diffractive optical elements including LD, PD, polarizers, and collimating lens is built by wafer level stacking within its dimension of 3.0×3.0×5.5 mm<sup>3</sup>. By assembling of the optical flying head and the basic optical unit onto a swing arm, it is possible to obtain an ultra small pickup system which can be applied in mobile environment.
    TRANSDUCERS, Solid-State Sensors, Actuators and Microsystems, 12th International Conference on, 2003; 07/2003
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    ABSTRACT: This paper presents the design, fabrication process and measurement results of a 2×2 MEMS optical switch. The switch comprises of an electromagnet and lensed fibers assembled with a micromachined movable vertical micromirror. At a wavelength of 1550 nm, the insertion loss of 0.2-0.8 dB and the polarization dependent loss (PDL) of 0.02-0.2 dB are measured. The switching time is 1 ms. Novel method of realizing latchable optical switch using electromagnetic actuator is also provided and verified. The optical switch utilizes straw-cutter-like rotational motion of the shutter mirror compared to the comb-driven linear actuation achieved by the electrostatic force. The latching mechanism is based on the latchability of the electro-permanent magnet instead of the conventional arch-shaped mechanical leaf springs.
    Micro Electro Mechanical Systems, 2003. MEMS-03 Kyoto. IEEE The Sixteenth Annual International Conference on; 02/2003
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    ABSTRACT: A large-angle electrostatic force actuated two-axis rotational micro-mirror has been proposed and demonstrated. A built-in air gap has been introduced in between the mirror and the bottom electrode to provide sufficient space for the rotation of the mirror. As a result, a large tilt angle has been achieved without using additional actuators. The gap was produced in such a way that the grounded mirror plate and the bottom electrode were made separately in different substrates and then combined. The measured tilt angles were as large as /spl plusmn/7.5/spl deg/ and /spl plusmn/6.4/spl deg/ in the x and y direction, and the pull-in voltages for the two axes were approximately 100 V. The micro-mirror was successfully used to steer an optical beam.
    IEEE Photonics Technology Letters 12/2002; · 2.04 Impact Factor
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    ABSTRACT: An actuated micromirror having two-degree of freedom in rotational motion around the orthogonal axes is designed and fabricated. Suspended unimorph PZT actuators independently control the rotation of the micromirror along the two perpendicular axes. The PZT actuators located symmetrically around the axes of the actuation are mechanically isolated with each other during their operation by a gimbaled structure. The mechanical cross talk between each axis of actuation is well suppressed less than 7% due to the gimbals. The rotation angle θ of the micromirror reaches 0.75° under the applied bias of 15 V while maintaining the profile of the reflected laser beam without significant degradation
    Micro Electro Mechanical Systems, 2001. MEMS 2001. The 14th IEEE International Conference on; 02/2001
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    ABSTRACT: A PZT actuator integrated onto cantilever structure was fabricated for high speed atomic force microscopy (AFM). Five different electrodes were used to investigate the effect of top electrodes on the adhesion and the electrical properties in the PZT capacitors. The PZT capacitors with RuO2 top electrodes exhibited the best characteristics of five electrodes. The tip deflection and the resonant frequency of the PZT actuator were 11 μim at 10 V and 79 kHz, respectively. The PZT actuator provided much better AFM image quality and imaging speed than those done by using the conventional bulk PZT tube scanner. The creep distortion in the AFM image was greatly improved by using the high speed PZT film actuator.
    Integrated Ferroelectrics 02/2001; 35(1-4):185-197. · 0.38 Impact Factor
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    ABSTRACT: A micromirror actuated by piezoelectric cantilevered unimorphs is proposed as a fine-tracking device for high-density optical data storage. Bending motions of the metal/PZT/metal unimorphs translate an integrated micromirror along the out-of-plane vertical direction. The micromirror alters the optical path of the incident laser beam and linearly steers the reflected laser beam by its out-of-plane parallel actuation. Numerical analysis shows that the actuated micromirror can satisfy the tracking speed imposed by the requirement on the access time for the high-density optical data storage up to few tens Gbit/in.2 owing to the light mass of the micromirror. In this paper, preliminary characteristics of the micromachined PZT actuated micromirror (PAM) are reported. Only a 3600Å-thick PZT film deposited by sol–gel process shows both good electrical and mechanical characteristics for the fine-tracking actuator. The micromirror can be easily actuated up to several micrometers under low voltage operation condition well below 10V.
    Sensors and Actuators A-physical - SENSOR ACTUATOR A-PHYS. 01/2001; 89(1):166-173.

Publication Stats

229 Citations
26.02 Total Impact Points

Institutions

  • 2000–2006
    • LG Electronics
      Sŏul, Seoul, South Korea
  • 2000–2001
    • The Seoul Institute
      Sŏul, Seoul, South Korea
  • 1995–2000
    • Seoul National University
      • Department of Electrical and Computer Engineering
      Sŏul, Seoul, South Korea
  • 1996
    • University of California, Berkeley
      Berkeley, California, United States