• Journal of Satellite, Information and Communications
• /
• v.9 no.1
• /
• pp.33-37
• /
• 2014

This paper introduces homogeneous liquid crystal (LC) orientations on chemically modulated polystyrene (PS) surfaces using various ion beam (IB) exposure time. Transparent PS was replaced with conventional polyimide material. As a non-contact process, IB bombardment process induced LC orientation in the direction parallel to the IB process. Through x-ray photoelectron spectroscopy, it was shown that the chemical compositional changes of the IB-irradiated PS surfaces were determined as a function of IB exposure time.Using this analysis, the optimal IB bombardment condition was determined at IB exposure time of up to 15 s. Moreover, thermal stability on IB-irradiated PS surfaces were carried out which showed that a relatively high IB exposure time induced a thermally stable LC alignment property.

• Proceedings of the KIEE Conference
• /
• 2002.11a
• /
• pp.257-259
• /
• 2002

In investigating the characteristics of a neural network, the use of planar microelectrode array shows several advantages over normal intracellular recording[1]. A transparent indium tin oxide(ITO) multi-electrode array(MEA) was fabricated and its top surface was insulated with photodefinable polyimide(HD-8001) except the exposed area for interfacing between the ITO electrodes and the neuronal cells. The exposed ITO electrodes were platinized in order to reduce the impedance between the electrodes and electrolyte. The one-minute platinization with $0.99nA/{\mu}m^2$ current density reduced the average impedance of the electrodes from $2.5M\Omega\;to\;90k\Omega$ at 1kHz in normal ringer solution. Cardiac cells were cultured on this MEA as a pilot study before neuron culture. The signals detected by the platinized electrodes had larger amplitudes and improved signal to noise ratio(SNR) compared to non-platinized electrodes. It is clear that microelectrodes need to have lower impedance to make reliable extracellular recordings, and thus platinization is essential part of MEA fabrication. Burst spike of cultured olfactory bulb was also detected with the MEA having platinized electrodes.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2013.02a
• /
• pp.473-473
• /
• 2013

전자종이, 입을 수 있는 디스플레이, 플렉서블 터치 스크린, 투과성 면 등과 같은 차세대 플렉서블 투명 전자소자는 기계적으로 유연하고 광학적으로 투명하며 무게가 가벼운 특성을 지녀야 할 것으로 예상된다. 현재까지는Indium tin oxide (ITO), zinc tin oxide (ZTO), carbon nano tube (CNT)와 polyimide 계열의 물질들이flexible, wearable, and transparent electronics (FWTEs) 소자의 electrode, active channel, dielectric layers로 제안되어 활발히 연구되었다. 최근에는 높은 이동도(~200,000 cm2/Vs) 및 유연성(fracture strain of 30%), 투명도 (97.5% for monolayer)와 같은 특성을 갖는 그래핀에 대한 연구가 활발히 진행되고 있다. 그러나 그래핀을 차세대 플렉서블 투명 전자소자 구현에 적용하기 위해서는 플렉서블하고 투명한 절연체의 확보 및 그래핀의 진성(intrinsic) 특성 유지 등과 같은 문제점들을 해결해야 한다. 따라서, 본 연구팀에서는 그래핀 기반 플렉서블 투명 전자소자의 게이트 절연층으로 적합한 poly-4-vinylphenol/poly (melamineco-formaldehyde) (PVP/PMF) 물질을 제시하고 이에 대한 전기적 재료적 분석을 수행하였다. 특히 다양한 PVP와 PMF의 비율 및 가열(annealing 혹은 curing) 온도에서 형성된 PVP/PMF 층의 화학 및 전기적 특성을 FT-IR, I-V, 그리고 C-V 측정을 통해 확인하였다. PVP/PMF는 유기절연 물질의 하나로서 높은 유연성과 투명도를 갖고 있을 뿐만 아니라 그래핀에 적용 시 그래핀의 진성 특성을 확보할 수 있다. 이는 PVP/PMF에 존재하는 hydroxyl (-OH) 그룹과 그래핀 상에서 정공(hole)을 공급하는 것으로 알려져 있는 -OH 그룹들간의 cross-linking 메커니즘에 의한 것으로 예상된다. 마지막으로 최적화된 PVP/PMF (낮은 hysteresis 전압)를 게이트 절연층에 적용하여 polyethylene terephthalate (PET) 기판 및 연구원의 손가락 위에 95.8%의 투명도 및 0에 가까운 Dirac point를 갖는 그래핀 기반 플렉서블 투명 전자소자를 성공적으로 집적하였다.

• Korean Journal of Materials Research
• /
• v.9 no.4
• /
• pp.355-361
• /
• 1999

We have synthesized the soluble polymide based side chain system with covalently attached NLO chromophore Disperse Red 1. The developed polymer is optically transparent in the range of optical communication wave-lengths. Its glass transition temperature$(T_g)$ and thermal decomposition temperature$(T_d)$ are $225^{\circ}C, 310^{\circ}C$ respectively. The poled film with the poling field of $100 V/\mu\textrm{m}$ shows that the dielectric constant is 3.37 at the 10-kHz frequency, the refractive indices of TM and TE modes are both 1.631 at $\lambda = 1300 nm$, and the Electro-optic coefficients are 4.6~9.2 pm/V at $\lambda = 1300 nm$. There are no decays of the EO coefficient in the poled polymer at $180^{\circ}C$ in one hour, and $90^{\circ}C$ in 500 hours.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2012.02a
• /
• pp.341-341
• /
• 2012

Recently, oxide semi-conductor materials have been investigated as promising candidates replacing a-Si:H and poly-Si semiconductor because they have some advantages of a room-temperature process, low-cost, high performance and various applications in flexible and transparent electronics. Particularly, amorphous indium-gallium-zinc-oxide (a-IGZO) is an interesting semiconductor material for use in flexible thin film transistor (TFT) fabrication due to the high carrier mobility and low deposition temperatures. In this work, we demonstrated improvement of flexibility in IGZO TFTs, which were fabricated on polyimide (PI) substrate. At first, a thin poly-4vinyl phenol (PVP) layer was spin coated on PI substrate for making a smooth surface up to 0.3 nm, which was required to form high quality active layer. Then, Ni gate electrode of 100 nm was deposited on the bare PVP layer by e-beam evaporator using a shadow mask. The PVP and $Al_2O_3$ layers with different thicknesses were used for organic/inorganic multi gate dielectric, which were formed by spin coater and atomic layer deposition (ALD), respectively, at $200^{\circ}C$. 70 nm IGZO semiconductor layer and 70 nm Al source/drain electrodes were respectively deposited by RF magnetron sputter and thermal evaporator using shadow masks. Then, IGZO layer was annealed on a hotplate at $200^{\circ}C$ for 1 hour. Standard electrical characteristics of transistors were measured by a semiconductor parameter analyzer at room temperature in the dark and performance of devices then was also evaluated under static and dynamic mechanical deformation. The IGZO TFTs incorporating hybrid gate dielectrics showed a high flexibility compared to the device with single structural gate dielectrics. The effects of mechanical deformation on the TFT characteristics will be discussed in detail.