• Journal of the Microelectronics and Packaging Society
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• v.14 no.1
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• pp.27-31
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• 2007

The cpapcitors with MIM(metal-insulator-metal) structures using PVP gate insulation films were prepared for the application of flexible organic thin film transistors (OTFT). The co-polymer organic insulation films were synthesized by using PVP(poly-4-vinylphenol) as a solute and PGMEA(propylene glycol monomethyl ether acetate) as a solvent. The cross-linked PVP insulation films were also prepared by addition of poly(melamine-co-formaldehyde) as thermal hardener. The leakage current of the cross- linked PVP films was found to be about 1.3 nA on Al/PES(polyethersulfone) substrate, whereas, on ITO/ glass substrate was about 27.5 nA indicating improvement of the leakage current at Al/PES substrates. Also, the capacitances of all prepared samples on ITO/glass and Al/PES substrates w ere ranged from 1.0 to $1.2nF/cm^2$, showing very similar result with the calculated capacitance values.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.885-888
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• 2004

We have prepared and investigated the properties of photoinitiator-free photosensitive polyimide gate insulatos for organic thin-film transistors (OTFTs). The precursor was prepared from a dianhydride, 3,3',4,4'-Benzophenone tetracarboxylic dianhydride (BTDA) and novel aromatic diamine, 7-(3,5-diaminobenzoyloxy) coumarine (DA-CM). Photo-patternability of the polyimide precursor film and surface morphology of the films before and after photo-patterning process were investigated and negative pattern with a resolution of 50 ${\mu}m$ was obtained nicely. In addition, we have fabricated OTFTs with pentacene and photosensitive polyimide as a semiconductor and a gate insulator; respectively. According to the device geometry, the ${\mu}$, current modulation ratio and subthreshold swing of the devices were around 0.2${\sim}$0.4 $cm^2$/Vs, more than $10^5$ and around 3${\sim}$5 V/dec, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1046-1048
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• 2004

Performances of organic thin film transistors (OTFTs) can be detrimentally affected by the state of the gate dielectric. Because of the bad stability of polymers, OTFTs with polymer gate dielectrics often provide abnormal characteristics. In this study, we report the condensation effect of the polymer gate dielectric layer. For the observations of the effect of the condensation, the spin-coated polymer layers with various deposition conditions were fabricated and left under low vacuum condition for several days. It is observed that the thickness of polymer layer and the electrical characteristic of OTFTs vary with the condensation time.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.31-32
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• 2010

In our previous reports [1-3], electron transport for the switching and memory devices using alkyl thiol-tethered Ru-terpyridine complex compounds with metal-insulator-metal crossbar structure has been presented. On the other hand, among organic memory devices, a memory based on the OFET is attractive because of its nondestructive readout and single transistor applications. Several attempts at nonvolatile organic memories involve electrets, which are chargeable dielectrics. However, these devices still do not sufficiently satisfy the criteria demanded in order to compete with other types of memory devices, and the electrets are generally limited to polymer materials. Until now, there is no report on nonvolatile organic electrets using nano-interfaced organic monomer layer as a dielectric material even though the use of organic monomer materials become important for the development of molecularly interfaced memory and logic elements. Furthermore, to increase a retention time for the nonvolatile organic memory device as well as to understand an intrinsic memory property, a molecular design of the organic materials is also getting important issue. In this presentation, we report on the OFET memory device built on a silicon wafer and based on films of pentacene and a SiO2 gate insulator that are separated by organic molecules which act as a gate dielectric. We proposed push-pull organic molecules (PPOM) containing triarylamine asan electron donating group (EDG), thiophene as a spacer, and malononitrile as an electron withdrawing group (EWG). The PPOM were designed to control charge transport by differences of the dihedral angles induced by a steric hindrance effect of side chainswithin the molecules. Therefore, we expect that these PPOM with potential energy barrier can save the charges which are transported to the nano-interface between the semiconductor and organic molecules used as the dielectrics. Finally, we also expect that the charges can be contributed to the memory capacity of the memory OFET device.[4]

• 한국정보디스플레이학회:학술대회논문집
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• 2000.01a
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• pp.215-216
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• 2000

We fabricated the thin-film transistors using organic semiconductor, pentacene, on $SiN_x$, gate insulator. X-ray diffraction experiments were performed for the sample after heat-treatments at higher temperatures. We confirmed that we obtained "thin-film phase" from the condition used here. From the electrical measurements, we also confirmed that no charges are accumulated at the interface between organic and insulating layer, and FET characteristics of the organic FET using pentacene was discussed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.190-193
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• 2002

The processing technology of organic thin-film transistors (Ons) performances have improved fur the last decade. Gate insulator layer has generally used inorganic layer, such as silicon oxide which has properties of a low electrical conductivity and a high breakdown field. However, inorganic insulating layers, which are formed at high temperature, may affect other layers termed on a substrate through preceding processes. On the other hand, organic insulating layers, which are formed at low temperature, dose not affect pre-process. Known wet-processing methods for fabricating organic insulating layers include a spin coating, dipping and Langmuir-Blodgett film processes. In this paper, we propose the new dry-processing method of organic gate dielectric film in field-effect transistors. Vapor deposition polymerization (VDP) that is mainly used to the conducting polymers is introduced to form the gate dielectric. This method is appropriate to mass production in various end-user applications, for example, flat panel displays, because it has the advantages of shadow mask patterning and in-situ dry process with flexible low-cost large area displays. Also we fabricated four by four active pixels with all-organic thin-film transistors and phosphorescent organic light emitting devices.

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1301-1305
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• 2005

The performance of OTFT with $PVP-TiO_2$ composite, as a gate insulator, is reported, including the effect of surfactant for synthesizing the composite material. According to our investigation results, it was one of critical issues to prevent the aggregation of $PVP-TiO_2$ particles during the synthesis process. From this point of view, $PVP-TiO_2$ particles were treated using Tween80, as a surfactant, and we could reduce the aggregated $PVP-TiO_2$ clusters. As a result, the OTFT with the composite insulator showed the threshold voltage of about -8.3 V and the subthreshold slope of about 1.5 V/decade, which are the optimized properties compared to those of OTFTs with bare PVP, in this study. It is thought that these characteristic improvements are originated from the increase in the dielectric constant of the PVP-based insulator by compositing with high-k particles.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.344-344
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• 2014

Transparent amorphous oxide semiconductors such as a In-Ga-Zn-O (a-IGZO) have advantages for large area electronic devices; e.g., uniform deposition at a large area, optical transparency, a smooth surface, and large electron mobility >10 cm2/Vs, which is more than an order of magnitude larger than that of hydrogen amorphous silicon (a-Si;H).1) Thin film transistors (TFTs) that employ amorphous oxide semiconductors such as ZnO, In-Ga-Zn-O, or Hf-In-Zn-O (HIZO) are currently subject of intensive study owing to their high potential for application in flat panel displays. The device fabrication process involves a series of thin film deposition and photolithographic patterning steps. In order to minimize contamination, the substrates usually undergo a cleaning procedure using deionized water, before and after the growth of thin films by sputtering methods. The devices structure were fabricated top-contact gate TFTs using the a-IGZO films on the plastic substrates. The channel width and length were 80 and 20 um, respectively. The source and drain electrode regions were defined by photolithography and wet etching process. The electrodes consisting of Ti(15 nm)/Al(120 nm)/Ti(15nm) trilayers were deposited by direct current sputtering. The 30 nm thickness active IGZO layer deposited by rf magnetron sputtering at room temperature. The deposition condition is as follows: a rf power 200 W, a pressure of 5 mtorr, 10% of oxygen [O2/(O2+Ar)=0.1], and room temperature. A 9-nm-thick Al2O3 layer was formed as a first, third gate insulator by ALD deposition. A 290-nm-thick SS6908 organic dielectrics formed as second gate insulator by spin-coating. The schematic structure of the IGZO TFT is top gate contact geometry device structure for typical TFTs fabricated in this study. Drain current (IDS) versus drain-source voltage (VDS) output characteristics curve of a IGZO TFTs fabricated using the 3-layer gate insulator on a plastic substrate and log(IDS)-gate voltage (VG) characteristics for typical IGZO TFTs. The TFTs device has a channel width (W) of $80{\mu}m$ and a channel length (L) of $20{\mu}m$. The IDS-VDS curves showed well-defined transistor characteristics with saturation effects at VG>-10 V and VDS>-20 V for the inkjet printing IGZO device. The carrier charge mobility was determined to be 15.18 cm^2 V-1s-1 with FET threshold voltage of -3 V and on/off current ratio 10^9.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2007.04a
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• pp.3-4
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• 2007

고분자 반도체를 이용한 유기 박막트랜지스터(OTFT) 소자 제작시 특성 향상을 위해 Self-Assemble Monolayer (SAM)을 이용한 유기 Gate 절연막과 source/drain 전극의 표면처리에 대해 설명하였다. Gate insulator의 경우 소수성 SAM이 고분자 반도체와의 상호작용으로 배열도를 향상시켜 이동도를 증가시켰으며, 전극처리의 경우 접촉저항을 낮추어 injection을 증대시키는 효과를 나타내었다. 각각의 경우 적용되는 SAM 재료와 효과를 극대화시키기 위한 처리공정 전반에 대해 설명하였다.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.487-490
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• 2006

We propose a new method to achieve well-defined surface properties of the polymeric gate dielectrics without using SAM technique and inserting another organic/inorganic buffer layer. Pentacene thin film transistors(OTFTs) fabricated with the polyimide gate insulators with different side chain structures were demonstrated. Further, a relationship between the surface properties (surface morphology, surface energy, etc) of the films and the performance of OTFTs have investigated, which will be given in more detail in presentation.