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Junghoon Choi

Bio: Junghoon Choi is an academic researcher from LG Electronics. The author has contributed to research in topics: Crystalline silicon & Solar cell. The author has an hindex of 13, co-authored 26 publications receiving 453 citations.

Papers
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Patent
04 Feb 2010
TL;DR: In this paper, a solar cell and a method for manufacturing the same is described, which includes a substrate of a first conductive type, an anti-reflection layer that is positioned on the substrate and is formed of a transparent conductive oxide material.
Abstract: A solar cell and a method for manufacturing the same are disclosed. The solar cell includes a substrate of a first conductive type, an anti-reflection layer that is positioned on the substrate and is formed of a transparent conductive oxide material, a plurality of emitter layers on the substrate, the plurality of emitter layers being of a second conductive type opposite the first conductive type, a plurality of first electrodes on the plurality of emitter layers, and a plurality of second electrodes that are electrically connected to the substrate and are positioned to be spaced apart from the plurality of first electrodes. The first electrodes and the second electrodes are positioned on the same surface of the substrate.

112 citations

Journal ArticleDOI
TL;DR: In this article, the authors evaluated the contact resistance of amorphous Si ( a- Si:H)/transparent conducting oxide (TCO) in terms of the contribution to the series resistance ( R s ) and fill factor ( FF ) in the Si heterojunction back-contact (HBC) solar cell.

64 citations

Proceedings ArticleDOI
08 Jun 2003
TL;DR: In this article, an integrated MEMS optical flying head (OFH) is presented for a small form factor with high-density portable data storage, which 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.
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.

33 citations

Journal ArticleDOI
TL;DR: In this paper, a large-stroke, piezoelectrically actuated linear motor with zero-power latching for portable electronics is presented, where the rotor is tethered to the metal guide by magnetostatic attraction due to its permanent magnets.
Abstract: This paper reports the design, fabrication and characterization of a large-stroke, piezoelectrically actuated linear motor with zero-power latching for portable electronics. The motor consists of a stator having a micromachined piezoelectric actuator and a high-permeability metal guide, a permanent magnet rotor, and an integrated position sensor. The rotor is tethered to the metal guide by magnetostatic attraction due to its permanent magnets. The resulting frictional forces are sufficient to immobilize the rotor to the stator. This does not require any power, and the combined bearing-braking feature is thus termed zero-power latching. The integrated position sensor demonstrates the feasibility of precisely monitoring the rotor position. The completed actuator has a volume of 1 mm(w) × 3 mm(t) × 5 mm(l). With a 50 kHz driving frequency, precision of 5 μm at a scalable full-stroke of 5 mm and a speed of 10 mm/s at 50 kHz was achieved. A capacitive position sensor was also designed into the motor, and was able to determine the rotor position with a sensitivity of 1 fF/μm.

33 citations

Journal ArticleDOI
TL;DR: In this paper, a 2/spl times/2 microelectromechanical system optical switch is presented, which 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.
Abstract: This paper presents the design, fabrication, and measurement results of a 2/spl times/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.

29 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a silicon heterojunction with interdigitated back contacts was presented, achieving an efficiency of 26.3% and a detailed loss analysis to guide further developments.
Abstract: The efficiency of silicon solar cells has a large influence on the cost of most photovoltaics panels. Here, researchers from Kaneka present a silicon heterojunction with interdigitated back contacts reaching an efficiency of 26.3% and provide a detailed loss analysis to guide further developments.

2,052 citations

Journal ArticleDOI
TL;DR: In this article, the structure of an interdigitated back contact was adopted with crystalline silicon heterojunction solar cells to reduce optical loss from a front grid electrode, a transparent conducting oxide (TCO) layer, and a-Si:H layers as an approach for exceeding the conversion efficiency of 25%.
Abstract: The crystalline silicon heterojunction structure adopted in photovoltaic modules commercialized as Panasonic's HIT has significantly reduced recombination loss, resulting in greater conversion efficiency. The structure of an interdigitated back contact was adopted with our crystalline silicon heterojunction solar cells to reduce optical loss from a front grid electrode, a transparent conducting oxide (TCO) layer, and a-Si:H layers as an approach for exceeding the conversion efficiency of 25%. As a result of the improved short-circuit current (J sc ), we achieved the world's highest efficiency of 25.6% for crystalline silicon-based solar cells under 1-sun illumination (designated area: 143.7 cm 2 ).

1,061 citations

Journal ArticleDOI
TL;DR: In this paper, a heterojunction interdigitated back contact solar cell with conversion efficiency of 26.6% was developed, which was independently confirmed by Fraunhofer Institute for Solar Energysystem Callab.

394 citations

Patent
01 Aug 2014
TL;DR: In this article, a method and an apparatus for transmitting broadcast signals thereof are disclosed, which includes encoding DP data according to a code rate, bit interleaving the LDPC encoded DP data, mapping the bit-interleaved DP data onto constellations, MIMO (Multi Input Multi Output) encoding the mapped DP data.
Abstract: A method and an apparatus for transmitting broadcast signals thereof are disclosed. The method for transmitting broadcast signals includes encoding DP data according to a code rate, wherein the encoding further includes LDPC encoding the DP data according to the code rate, bit interleaving the LDPC encoded DP data, mapping the bit interleaved DP data onto constellations, MIMO (Multi Input Multi Output) encoding the mapped DP data, and time interleaving the MIMO encoded DP data; building at least one signal frame by arranging the encoded DP data; and modulating data in the built signal frame by OFDM method and transmitting the broadcast signals having the modulated data, wherein the step of modulating includes inserting CPs in the built signal frame based on a CP set which includes information about locations of CPs, wherein the CP set is defined based on FFT size.

225 citations

Patent
21 Oct 2011
TL;DR: In this article, a nanowire array is described, which consists of a substrate and a plurality of nanowires extending essentially vertically from the substrate, each of which has uniform chemical along its entire length.
Abstract: A nanowire array is described herein. The nanowire array comprises a substrate and a plurality of nanowires extending essentially vertically from the substrate; wherein: each of the nanowires has uniform chemical along its entire length; a refractive index of the nanowires is at least two times of a refractive index of a cladding of the nanowires. This nanowire array is useful as a photodetector, a submicron color filter, a static color display or a dynamic color display.

195 citations