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Seungjun Chung,Jongsu Jang,Jinwoo Kim,Yongtaek Hong 대한전자공학회 2009 ITC-CSCC :International Technical Conference on Ci Vol.2009 No.7
We used inkjet-printed silver electrodes for gate and source/drain electrodes and organic dielectric layer to fabricate a thermally evaporated pentacene-based organic thin-film transistor (OTFT). Inkjet-printing process conditions for silver electrodes and gate dielectric layer were carefully optimized to produce a good surface roughness of 2.38 and 3.8㎚ in RMS value respectively. Especially, inkjet-printed cross-linked poly (4-vinylphenol) (PVP) has good performance for gate insulation layer comparing spin coated PVP layer. Our device showed a good mobility of 0.097㎠/Vs, a threshold voltage of -9V, and an on/off ratio of about 10?.
All-Inkjet-Printed Organic Thin-Film Transistor Inverter on Flexible Plastic Substrate
Seungjun Chung,Seul Ong Kim,Soon-Ki Kwon,Changhee Lee,Yongtaek Hong IEEE 2011 IEEE electron device letters Vol.32 No.8
<P>We report an all-inkjet-printed inverter using two p-type organic thin-film transistors (OTFTs) on a flexible plastic substrate. Metal-organic precursor-type silver ink, poly-4-vinylphenol solution, and 6,13-bis (triisopropylsilylethynyl)-pentacene solution were used to print gate and source/drain electrodes, gate-dielectric layer, and active semiconductor layer, respectively. By optimizing fabrication conditions, we obtained OTFTs with a mobility of 0.02 cm<SUP>2</SUP>/V·s, an on/off ratio of 10<SUP>4</SUP>, and a threshold voltage of -1.2 V, and inverters with good switching performance showing a gain of 7.8 at a supply voltage of <I>V</I><SUB>DD</SUB> = -40 V .</P>
Surface planarization issues of metal foil substrates for flexible electronics applications
Seungjun Chung,Jaewook Chung,Yongtaek Hong 대한전자공학회 2007 ITC-CSCC :International Technical Conference on Ci Vol.2007 No.7
Surface planarization capability and electrical and thermal stability of several low-k materials have been tested for different metal foil substrates including kovar, invar, and stainless steel foil substrates. Atomic force microscope measurement showed a significant reduction of the surface roughness after applying an organic planarization layer on the metal foil substrates. Capacitance-voltage and current-voltage behavior under different thermal and electrical stress conditions for flexible electronics applications showed good thermal and electrical stabilities of the organic planarization layers.
Contact Resistance of Inkjet-Printed Silver Source–Drain Electrodes in Bottom-Contact OTFTs
Seungjun Chung,Jaewook Jeong,Donghyun Kim,Yunhwan Park,Changhee Lee,Yongtaek Hong IEEE 2012 Journal of display technology Vol.8 No.1
<P>In this paper, we report contact resistance analysis between inkjet-printed silver source-drain (S/D) electrodes and organic semiconductor layer in bottom-contact organic thin-film transistors (OTFTs) using transmission line method (TLM). Inkjet-printed silver electrodes, spin-coated PVP and evaporated pentacene were used as gate and S/D electrodes, gate dielectric layer and semiconductor layer, respectively. On a common gate electrode, S/D electrodes with various channel length from 15 to 111 m were printed for TLM analysis. The same bottom-contact OTFT with evaporated silver S/D electrodes was also fabricated for reference. We extracted contact resistances of 1.79 M cm and 0.55 M cm for inkjet-printed and evaporated silver electrodes, respectively. Higher contact resistance for inkjet-printed silver electrodes can be explained in terms of their relatively poor surface properties at electrode edge that can cause small pentacene molecule grain or slight oxidation of surface during the printed silver sintering process.</P>
Chung, Seungjun,Jang, Mi,Ji, Seon‐,Beom,Im, Hwarim,Seong, Narkhyeon,Ha, Jewook,Kwon, Soon‐,Ki,Kim, Yun‐,Hi,Yang, Hoichang,Hong, Yongtaek WILEY‐VCH Verlag 2013 ADVANCED MATERIALS Vol.25 No.34
<P><B>High‐performance all‐inkjet‐printed organic inverters</B> are fabricated on flexible substrates. By introducing end‐functionalized polystyrene on both surfaces of inkjet‐printed source/drain Ag electrodes and poly(4‐vinylphenol) dielectrics, organic‐compatible and hydroxyl‐free interfaces between those layers and 6,13‐bis(triisopropylsilylethynyl)pentacene drastically reduce the interfacial trap and contact resistance. The resulting organic inverters show a full up‐down switching performance and a high voltage gain of 19.8.</P>
Chung, Seungjun,Karim, Muhammed Ahosan Ul,Kwon, Hyuk-Jun,Scheideler, William,Subramanian, Vivek Institute of Electrical and Electronics Engineers 2017 Journal of microelectromechanical systems Vol. No.
<P>We report a high-speed inkjet-printed three-terminal microelectromechanical(MEM) relay with a doubleclamped beam that exploits the enhanced stiffness of the double-clamped structure to improve electrical performance. To minimize mechanical delay and pull-in voltage, the contact gap between the channel-beam and drain, and the stiffness of the beam and shape of the drain was carefully designed and optimized through a 3-D finite element simulation. The double-clamped beam prevents stiction-related failure between the channel-beam and drain despite the contact gap being only 370 nm for a > 500 mu m long beam. The resulting printed relay delivers a turn-ON delay of 8 mu s at a gate voltage of 10 V, a pull-in voltage of only 7.2 V, immeasurable off-leakage, excellent subthreshold swing, and a small hysteresis window of 2 V without any bending or collapsing of the beam. The device also shows reliable operation over 105 cycles while maintaining a high ON/OFF ratio of 108, and extremely low ON-state resistance</P>
Compliant Thermoelectric Generators Toward Self-Powered Flexible Electronics
Seungjun Chung(정승준) 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.2
Softening of thermoelectric generators (TEGs) allows conformal contact with arbitrary-shaped heat sources, which offers an opportunity to realize self-powered flexible applications. However, existing flexible thermoelectric devices inevitably exhibit reduced thermoelectric conversion efficiency due to the parasitic heat loss in high-thermal-impedance polymer substrates and poor thermal contact arising from rigid interconnects. In this talk, I would like to introduce various state of the art flexible thermoelectrics for self-powered applications. In particular, our recent efforts to improve the thermoelectric performance of compliant organic/inorganic TEGs will be highlighted which facilitate to achieve high energy conversion efficiency in TEGs capable of conforming to 3D surfaces of heat sources simultaneously.
정승준(Seungjun Chung),이재현(Jae-Hyun Lee),김장주(Jang-Joo Kim),홍용택(Yongtaek Hong) 대한전자공학회 2007 대한전자공학회 학술대회 Vol.2007 No.11
We report properties and bias-temperature-stress (BTS) stability of the planarized stainless steel (SS) foil substrates and their application to top-emission organic light-emitting diodes (TEOLEDs). We used benzocyclobutene (BCB) for planarization material. After applying BCB layer on the SS foil substrate, we successfully reduced the surface roughness from 60±20(RMS)㎚ to 1.2±0.4(RMS)㎚, which was measured by an atomic force microscope (AFM) method. The BCB layer showed a good BTS stability when we performed the BTS test by applying 80V across the BCB layer at 80℃. Capacitance and leakage current for the BCB layer was changed to 1.11㎋/㎠ and 207.2㎩/㎠ from its original values of 1.03㎋/㎠ and 64.5㎩/㎠, respectively, after 3hours BTS test We fabricated TEOLED on the BCB-planarized SS foil substrate am compared its performance with the TEOLED fabricated on a silicon substrate. Although the surface roughness of the planarized BCB SS foil substrate was higher than that of the silicon substrate (0.145±0.324㎚, RMS), we obtained similar performance of 2000㏅/㎡ luminance at 0.3㎃/㎠ (6.5V) and operation stability of 130 hours of half-luminance lifetime, from both devices