Dong Cheul Han

Surface Properties of Poly(ethylene terephthalate) Films Modified by Inductively Coupled Plasma with Ar/N2 Mixture Gases

We have investigated the effects of an inductively coupled plasma (ICP) treatment using Ar and N2 gas mixtures on the surfaces properties of poly(ethylene terephthalate) (PET) films. The Ar/N2 ICP-modified PET surfaces have been characterized by X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle measurements. The experimental results reveal that ICP treatment with Ar/N2 mixture gas induces physical and chemical changes of PET surface, showing the increases of surface roughness and hydrophilic functional groups in the surface Also, the contact angle of distilled water on the surface becomes smaller with increasing RF power applied to ICP antenna, resulting in higher adhesion energy.

Fabrication of Transparent Semiconducting Indium Zinc Tin Oxide Thin Films and Its Wet Chemical Etching Characteristics in Hydrochloric Acid

We have fabricated the transparent semiconducting indium zinc tin oxide (IZTO) thin films on polymeric substrates at room temperature by RF-magnetron sputtering method, and investigated their wet chemical etching behavior in HCl solution. The study has revealed that the control of O2 flow rate during deposition attribute to the variation of resistivity for IZTO films, resulting in the conductor–semiconductor conductivity transition. The increasing etchant molarity and temperature of etching solution lead to the increase in etching rate of IZTO films according to the chemical dissolution reaction. As a result, the IZTO active channel is defined successfully, suggesting sufficient possibility for the application to flexible transparent thin film transistors.

Surface Modification of Poly(ethylene terephthalate) Polymeric Films by Inductively Coupled Oxygen Plasma

In this study, the surfaces of poly(ethylene terephthalate) (PET) films have been modified by high density inductively coupled plasma (ICP) using the oxygen gas. The ICP-modified PET surfaces have been characterized by atomic force microscopy, X-ray photoelectron spectroscopy, and contact angle measurement as a function of RF power applied to ICP antenna. The experimental results reveal that the exposure of PET films to ICP leads to the roughening surface and the increase of oxygen containing-functional groups such as O–C=O and C–O at the surface. Also, the contact angle of distilled water on the surface decreases with increasing RF power, resulting in the increase in the adhesion energy.

Remarkable Improvement of Organic Solar Cells Lifetime with Zn-doped In2O3 Electrode as UV-blocking TCO

We have studied the lifetime improvement of organic solar cells (OSCs) based on the conjugated polymer:fullerene blends using an ultra-violet (UV) blocking transparent conducting oxide (TCO). Without additional passivation films/layers or changing of structure, the performance of the OSC using UV blocking TCO was comparatively stable under the strong UV exposure. When 30 mW/cm2 of UV was irradiated for 300 seconds, the VOC and FF of the OSC without UV blocking TCO decreased to 87% and 64%, respectively. As a result, power conversion efficiency (PCE) decreased to 54%. However, the VOC and FF of OSC with UV blocking TCO slightly decreased to 96% and 87%, respectively.

Transparent Zn-Doped In2O3 Electrode Prepared by Radio Frequency Facing Target Sputtering for Flexible Dye-Sensitized Solar Cells

For the application to transparent electrode in flexible dye-sensitized solar cells (DSSCs), Zn-doped In2O3 (In2O3:Zn) thin films have been fabricated on polyethylene naphthalate (PEN) substrate by the radio frequency facing target sputtering method, and their characteristics have been investigated as a function of deposition pressure. X-ray diffraction study reveal that the structure of In2O3:Zn thin films is amorphous nature. The film morphology is slightly sensitive to the deposition pressure. At the sputtering pressure of 0.40 Pa, In2O3:Zn thin film on PEN exhibits a sheet resistance of about 12.4 Ω/□ and average transmittance of about 85% at 550 nm wavelength, resulting in the highest value for figure of merit. The flexible DSSC device with the In2O3:Zn electrode shows the efficient solar-to-electrical power conversion efficiency (η), which is the maximum η value of 4.6% under simulated air mass 1.5 irradiation (100 mW/cm2).

Chemical Surface Pre-treatment of Carbon Nanotube for Improving the Thermal Conductivity of Carbon Nanotube-Epoxy Composite

For improving the thermal conductivity of carbon nanotube-epoxy composite, we have performed the chemical surface pre-treatment of multi-walled carbon nanotube (MWCNT) and investigated its effects. In the experiments, the mixtures of nitric and sulfuric acid have been used as the surface modifier for MWCNT. The chemical surface pre-treatments by acid mixtures lead to the production of oxygen-containing functional groups on the surfaces of MWCNT. Also, the surface area and pore volume of acid-treated MWCNT (AT-MWCNT) become larger than those of pristine MWCNT. By actions of the chemical pre-treatment, AT-MWCNT is well dispersed and forms the heat flow network in epoxy matrix, resulting in higher thermal conductivity of carbon nanotube-epoxy composite.

Characteristics of Facing Target-Sputtered Amorphous InGaZnO Thin Films as the Active Channel Layer in Transparent Thin Film Transistor on Polymeric Substrate

For an application to the channel layer in flexible transparent thin-film transistor (TFT), we have prepared the amorphous indium gallium zinc oxide (a-InGaZnO) thin films on unheated polyethylene naphthalate (PEN) substrate by facing target sputtering. Two types of a-InGaZnO TFT design, one top gate configuration and the other bottom gate, have been fabricated for comparison with each other. The experimental results reveal that the top gate a-InGaZnO TFT is shown to be superior TFT performances, compared with bottom-gate structure. As a result, the top gate a-InGaZnO TFTs operate in depletion mode with a threshold voltage of −0.5 V, a mobility of 6.0 cm2/Vs, an on-off ratio of >106, and a sub-threshold slope of 0.95 V/decade. In addition, the optical transmittance of about 74% at 550nm wavelength is represented for the top gate a-InGaZnO TFT on PEN.

Fabrication of Flexible Temperature & Humidity Sensor Using Inkjet-printing Technology

Abstract This paper presents the inkjet-printed flexible temperature and humidity sensor(F-TH sensor) using PEDOT:PSS. The series, meshand parallel type sensing element using PEDOT:PSS ink was printed on the overhead projector(OHP) film. The fabricated sensor ofeach structure has the temperature sensitivity of 140 Ω/ o C, 29 Ω/ o C and 1.4 Ω/ o C with linearity, respectively. Also the fabricated sensorwas not only possible to measure a temperature, but also to detect humidity. The humidity sensitivity of 400 Ω/%RH, 3.4 Ω/%RH and3 Ω/%RH with linearity, respectively. The fabricated F-TH sensor is expected for the various applications such as electronic devices,bio-healthcare, industrial field.Keywords: Inkjet print, Flexible sensor, Temperature sensing, Humidity sensing 1. 서론 최근 유연한 전자기기에 대한 관심이 높아지고 있으며, 이애 따라 유연성 기판의 사용이 용이한 인쇄 전자 산업 및 인쇄 전자 기술에 대한 관심도 함께 높아지고 있다[1-6]. 잉크젯 프린팅은 비접촉식 프린팅 기술로써 노즐로부터 액적(drop)을 분사하여 기판위에 패턴을 직접 인쇄하는 기술이다. 기존의 포토리소그래피 기술과 비교하였을 때 빠른 패턴 제작이 가능하고, 공정과정이 줄어시간과 공정비용을 절감할 수 있으며, 재료의 낭비가 적어 전자기기, 의료·바이오, 산업 분야 등에서 유용한 기술이다. 현재 잉크젯 프린팅 공정을 이용하여 인쇄 전자 소자 제작 및 유연성 회로,디스플레이, 센서, 배터리 등의 인쇄 전자 기기에 적용하기 위한연구가 많이 진행되고 있다[7,8]. 잉크젯 프린팅 기술은 대부분 전도성 잉크를 이용하여 프린트회로기판(PCB), RFID, 전극 및 배선등의 소자분야에 적용[9-12]뿐만 아니라, LCD 칼라필터 공정 등에 적용되고 있다[13]. 이러한 잉크젯 프린팅 기술로 제작하는 센서의 경우 가볍고, 공정이 간단하며, 저렴한 공정비용, 유연성 기판 적용이 가능하고, 상온 공정 등의 장점이 있어 유연성 전자기기의 구동 소자로서 각광받고 있다. 잉크젯 프린팅 기술을 이용한유연성 센서의 개발은 경량화, 간편화, 휴대성 등의 강점을 가지고 있어서 유비쿼터스 시대에 활용하기 위한 유용한 소자이다. 본 연구에서는 유연한 기판 위에 유기태양전지에 주로 사용되는 P형 전도성 고분자 물질인 PEDOT:PSS 잉크를 이용하여,잉크젯 프린팅 기법으로 유연성 온·습도 감지 소자를 개발하고, 구조 별 소자의 특성을 비교했다.