• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2010.06a
• /
• pp.26-26
• /
• 2010

Cadmium sulfide (CdS) thin film for flexible optical device applications were prepared at $H_2(Ar+H_2)$ flow ratios on polyethersulfon(PES) flexible polymer substrates at room temperature by radio frequency magnetron sputtering technique. The CdS thin films deposited at room temperature showed a (002) preferred orientation and the smooth surface morphologies. Films deposited at a hydrogen flow ratio of 25% exhibited a photo- and dark-sheet resistance of about 50 and $2.7{\times}10^5{\Omega}$/square, respectively. From the result of the bending test, CdS films exhibit a strong adhesion with the PES polymer substrates and the $Al_2O_3$ passivation layer deposited on the CdS films only shows an increase of the resistance of 8.4% after exposure for 120 h in air atmosphere.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2012.05a
• /
• pp.59.1-59.1
• /
• 2012

Organic thin-film transistors (OTFTs) with printable semiconductors are promising candidate devices for flexible active-matrix (AM) display applications. Yet, stable operation of actual display panels driven by OTFTs has seldom been reported up to date. Here, we demonstrate a flexible reflective type polymer dispersed liquid crystal (PDLC) display, in which inkjet-printed OTFT arrays are used as driving elements with excellent areal uniformity in terms of device performance. As the active semiconductor, a novel, ambient processable conjugated copolymer was synthesized. The stability of the devices with respect to electrical bias stress was improved by applying a channel-passivation layer, which suppresses the environmental effects and hence reduces the density of trap states at the channel/dielectric interface. The combination of high performance and high stability OTFT devices enabled the successful realization of stable operating flexible color-displays by inkjet-printing.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2004.08a
• /
• pp.623-624
• /
• 2004

The coating and estimation of gas and moisture barriers on polymer and glass substrates are receiving very much attention in passivation of organic light emitting devices (OLEDs). In this study, the encapsulation and lifetime measurement techniques of OLEDs were presented. The degradation mechanisms of bare and encapsulated OLEDs were investigated by the visual lifetime measurement (VLM) system with the parameters such as a pixel luminance(L), a luminance rms roughness(dL), a brightness area ratio(R), an edge degradation depth(D), etc.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2006.08a
• /
• pp.1170-1173
• /
• 2006

Active layer patterned OTFT was obtained on a plastic substrate using the optimal growth condition of pentancene thin films as active layer and parylene thin films as passivation layer. Tranditional photolithography was performed to use a dry etch to pattern the material stack. The pentacene thin film and parylene thin film were deposited onto a plastic substrate using PC-OVD and CVD, respectively.

• Journal of Korean Vacuum Science & Technology
• /
• v.3 no.1
• /
• pp.24-29
• /
• 1999

The characteristic behaviors of CH3Br were examined first for the dry etching of polysilicon in a Cl2/CH3Br/O2 plasma. CH3Br is revealed one of the excellent additive gases to control anisotropy of etching profile and to give no undercutting for various typed of polysilicons. CH3Br acts as a passivation precursor on the side wall in etch cavity by forming polymer-like films such as CHxBry(x+y=1,2). The decrease of etch selectivity due to the reaction if the C-containing species from CH3Br with the surface O atoms of SiO2 was overcome by the addition of O2 into plasma, resulting that the selectivity increased by 2~3 times. According to the results of optical emission signals, CH3Br should be dissociated into several fragments to give more hydrogen atoms than bromine atoms in our helical resonator system.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.162-162
• /
• 2014

최근 들어 wearable computing에 대한 수요가 증가하면서 flexible device에 대한 연구가 활발히 진행되고 있다. 하지만, flexible device를 구현하기 위해서는 기판의 damage를 줄이기 위한 저온공정, device life-time 향상을 위한 passivation, 와이어 본딩 등 다양한 문제들이 해결 되어야 한다. 이러한 문제들 중, polymer 기판과 금속간의 접착력을 향상시키기 위해서 많은 연구자들은 기판의 표면에 adhesive layer를 도포하거나 금속잉크의 solvent를 변화시키는 등의 연구를 진행해왔다. 종래의 연구는 기존 device를 대체 할 수 있을 정도의 생산성과 polymer 기판에 대한 열 적인 손상 이 문제가 되었다. 종래의 문제를 해결하기 위하여 저온공정, in-line system이 가능한 준 준 대기압 플라즈마를 사용하였다. 본 연구에서는 금속잉크를 Ink-jet으로 jetting하여 와이어 본딩 하는 과정에서 전도성 ink의 선폭을 유지시키고 접착력을 향상하기 위하여 준 대기압 플라즈마 공정을 이용하여 이러한 문제점을 해결하고자 하였다. Polymer 기판 표면에 roughness를 만들기 위해 대략 수백 nm 크기를 갖는 graphene flake를 spray coating하여 마스크로 사용하고 준 대기압 플라즈마를 이용하여 표면을 식각 함으로써 roughness를 형성시켰다. 준 대기압 플라즈마를 발생시키기 위해 double discharge system에서 6 slm/1.5 slm (He/O2) gas composition을 하부 전극에 흘려보내고 60 kHz, 5 kV 파워를 인가하였다. 동시에 상부 전극에는 30 kHz, 5 kV 파워를 인가하여 110초 동안 표면 식각 공정을 진행하였다. Graphene flake mask가 coating되어 있는 유연기판을 산소 플라즈마 처리 한 후 물에 3초 동안 세척하여 표면에 남아있는 graphene flake를 제거하고 6 slm/0.3 slm (He/SF6)의 유량으로 주파수와 파워 모두 동일 조건으로 110초 동안 표면 처리를 하였다. Figure 1은 표면 개질 과정과 graphene flake를 mask로 사용하여 얻은 roughness 결과를 SEM을 이용하여 관찰한 결과이다. 이와 같이 실험한 결과 ink와 기판간의 접촉면적을 늘려주고 접촉 각을 조절하여 Wenzel model 을 형성 할 수 있는 표면 roughness를 생성하였고 표면의 화학적 결합을 C-F group으로 치환하여 표면의 물과 접촉각 이 $47^{\circ}$에서 $130^{\circ}$로 증가하는 것을 확인하였다.

• Journal of the Optical Society of Korea
• /
• v.9 no.1
• /
• pp.16-21
• /
• 2005

Using a cantilever type nanoprobe having a 100㎚m aperture at the apex of the pyramidal tip of a near-field scanning optical microscope (NSOM), nanopatterning of polymer films are conducted. Two different types of polymer, namely a positive photoresist (DPR-i5500) and an azopolymer (Poly disperse orange-3), spincoated on a silicon wafer are used as the substrate. A He-Cd laser with a wavelength of 442㎚ is employed as the illumination source. The optical near-field produced at the tip of the nanoprobe induces a photochemical reaction on the irradiated region, leading to the fabrication of nanostructures below the diffraction limit of the laser light. By controlling the process parameters properly, nanopatterns as small as 100㎚ are produced on both the photoresist and azopolymer samples. The shape and size variations of the nanopatterns are examined with respect to the key process parameters such as laser beam power, irradiation time or scanning speed of the probe, operation modes of the NSOM (DC and AC modes), etc. The characteristic features during the fabrication of ordered structures such as dot or line arrays using NSOM lithography are investigated. Not only the direct writing of nano array structures on the polymer films but also the fabrication of NSOM-written patterns on the silicon substrate were investigated by introducing a passivation layer over the silicon surface. Possible application of thereby developed NSOM lithography technology to the fabrication of data storage is discussed.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.08a
• /
• pp.80-81
• /
• 2012

Recently, one of the critical issues in the etching processes of the nanoscale devices is to achieve ultra-high aspect ratio contact (UHARC) profile without anomalous behaviors such as sidewall bowing, and twisting profile. To achieve this goal, the fluorocarbon plasmas with major advantage of the sidewall passivation have been used commonly with numerous additives to obtain the ideal etch profiles. However, they still suffer from formidable challenges such as tight limits of sidewall bowing and controlling the randomly distorted features in nanoscale etching profile. Furthermore, the absence of the available plasma simulation tools has made it difficult to develop revolutionary technologies to overcome these process limitations, including novel plasma chemistries, and plasma sources. As an effort to address these issues, we performed a fluorocarbon surface kinetic modeling based on the experimental plasma diagnostic data for silicon dioxide etching process under inductively coupled C4F6/Ar/O2 plasmas. For this work, the SiO2 etch rates were investigated with bulk plasma diagnostics tools such as Langmuir probe, cutoff probe and Quadruple Mass Spectrometer (QMS). The surface chemistries of the etched samples were measured by X-ray Photoelectron Spectrometer. To measure plasma parameters, the self-cleaned RF Langmuir probe was used for polymer deposition environment on the probe tip and double-checked by the cutoff probe which was known to be a precise plasma diagnostic tool for the electron density measurement. In addition, neutral and ion fluxes from bulk plasma were monitored with appearance methods using QMS signal. Based on these experimental data, we proposed a phenomenological, and realistic two-layer surface reaction model of SiO2 etch process under the overlying polymer passivation layer, considering material balance of deposition and etching through steady-state fluorocarbon layer. The predicted surface reaction modeling results showed good agreement with the experimental data. With the above studies of plasma surface reaction, we have developed a 3D topography simulator using the multi-layer level set algorithm and new memory saving technique, which is suitable in 3D UHARC etch simulation. Ballistic transports of neutral and ion species inside feature profile was considered by deterministic and Monte Carlo methods, respectively. In case of ultra-high aspect ratio contact hole etching, it is already well-known that the huge computational burden is required for realistic consideration of these ballistic transports. To address this issue, the related computational codes were efficiently parallelized for GPU (Graphic Processing Unit) computing, so that the total computation time could be improved more than few hundred times compared to the serial version. Finally, the 3D topography simulator was integrated with ballistic transport module and etch reaction model. Realistic etch-profile simulations with consideration of the sidewall polymer passivation layer were demonstrated.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2010.02a
• /
• pp.457-457
• /
• 2010

Flexible organic light emitting diodes (F-OLEDs) requires excellent moisture permeation barriers to minimize the degradation of the F-OLEDs device. Specifically, F-OLEDs device need a barrier layer that transmits less than $10^{-6}g/m^2/day$ of water and $10^{-5}g/m^2/day$ of oxygen. To increase the life time of F-OLEDs, therefore, it is indispensable to protect the organic materials from water and oxygen. Severe groups have reported on multi-layerd barriers consisting inorganic thin films deposited by plasma enhenced chemical deposition (PECVD) or sputtering. However, it is difficult to control the formation of granular-type morphology and microscopic pinholes in PECVD and sputtering. On the contrary, atomic layer deoposition (ALD) is free of pinhole, highly uniform, conformal films and show good step coverage. Thus, $Al_2O_3/TiO_2$ multi-layer was deposited onto the polyethersulfon (PES) substrate by electron cyclotron resonance atomic layer deposition (ECR-ALD), and the water vapor transmission rates (WVTR) were measured. WVTR of moisture permeation barriers is dependent upon density of films and initial state of polymer surface. A significant reduction of WVTR was achieved by increasing density of films and by applying low plasma induced interlayer on the PES substrate. In order to minimize damage of polymer surface, a 10 nm thick $TiO_2$ was deposited on PES prior to a $Al_2O_3$ ECR-ALD process. High quality barriers were developed from $Al_2O_3$ barriers on the $TiO_2$ interlayer. WVTR of $Al_2O_3$ by introducing $TiO_2$ interlayer was recorded in the range of $10^{-3}g/m^2.day$ at $38^{\circ}C$ and 100% relative humidity using a MOCON instrument. The WVTR was two orders of magnitude smaller than $Al_2O_3$ barriers directly grown on PES substrate without the $TiO_2$ interlayer. Thus, we can consider that the $Al_2O_3/TiO_2$ multi-layer passivation can be one of the most suitable F-OLEDs passivation films.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.04a
• /
• pp.39-40
• /
• 2008

We have examined post-annealing and passivation for the transparent bottom gate IGZO TFT having an inverse co-planar structure. The oxygen-vacuum two step annealing enhanced the field effect mobility up to 18 $cm^2$/Vsandthesub-threshold swing down to 0.2V/dec. However, the hysterysis and the bias stability problems could not be solved just by post-annealing. Thus, we have passivated the bottom gate IGZO TFTs with organic and inorganic materials. $Ga_2O_3$, $Al_2O_3$, $SiO_2$ and some polymer materials were effective materials for passivations. The hysterysis and the stability of the TFTs were remarkably improved by the passivations. We have manufactured the AMOLED panel with the transparent bottom gate IGZO TFT array successfully.