• Fibers and Polymers
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• v.2 no.1
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• pp.123-130
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• 2001

Photoresponsive side chain copolymer and homopolymer containing an aminonitroazobenzene were synthesized for studying photoisomerization behavior and photo-induced anisotropy. Trans-to-cis photoisomerization was observed under the exposure of a circularly polarized visible light with UV-Vis absorption spectroscopy. Reorientation of polar azobenzene molecules induced optical anisotropy under a linearly polarized light at 532nm. Polarized absorption spectroscopy was employed to investigate the anisotropy of the polymer film during irradiationg of the excitation light. Layers of two photosensitive polymers were used for aligning liquid crystal(LC) molecules instead of one of the rubbed polyimide layers in the conventional twisted nematic cell. For producing homogeneous alignment of a nematic LC molecule, a linearly polarized light was exposed to the films of two polymers. The stability of the LC alignment upon the linearly polarized light exposure was also studied.

• Journal of the Microelectronics and Packaging Society
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• v.11 no.4 s.33
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• pp.1-5
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• 2004

A multi-layer flexible substrate is composed of copper(Cu)/polyimide that are known as good electrical conductivity, and low dielectric constant, respectively. In this study. conductor line of $5{\mu}m$-pitch was successfully fabricated without non-uniform pattern shape by electroplating copper and coating polyimide on patterned stainless steel. For multi-layer flexible substrate, via holes were drilled by UV laser and filled with electroplating copper and tin. And then, the PI layer with vias and conductor lines was stripped from stainless steel substrate. The PI layers were laminated at once with careful alignment between layers. Solid state reaction between tin and copper during lamination formed the intermetallic compounds of $Cu_6Sn_5$($\eta$-phase) and $Cu_3Sn$($\epsilon$-Phase) and achieved a complete inter-connection by vertically positioning the plugged via holes on via pad. The via formation process has several advantages; such as better electrical property and lower cost than V type via and paste via.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.776-779
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• 2006

The alignment of liquid crystal (LC) is one of the key issues of liquid crystal display (LCD) technologies. In this study, we aligned polyimide (as the LC alignment layer) by ALT plasma beam and to realize the stability and characteristics of this technology. The characteristics such as anchoring energy, pre-tilt angle, voltage holding ratio(VHR) and residual direct current(Rdc) were discussed. Besides, we applied it to the in plane switch (IPS) mode 23" WXGA real panel, the performance parameters and electrical properties were measured and compared with those of rubbing alignment. From the result, we demonstrated a successful LC alignment treatment process in real panel by ALT plasma beam.

• Polymer(Korea)
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• v.30 no.2
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• pp.97-107
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• 2006

In spite of excellent thermomechanical performance the majority of aromatic polyimides are so poor in processability due to their high backbone rigidity that their applications are greatly limited. The introduction of long side chains not only enhances their processiblity but also makes useful contribution to discovering new application fields. In this article, a variety of novel aromatic polyimides with flexible side chains were prepared either from new dimines or new dianhydrides to measure the influence of the side chains on structure and properties of the polymers and their new applications as liquid crystal alignment layers, photosensitive polymers, alternating multilayer nano-films and photoluminescent materials are discussed.

• Macromolecular Research
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• v.15 no.2
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• pp.114-128
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• 2007

Polyimides are one of the most important classes of polymers used in the microelectronics and photoelectronics industries. Because of their high thermal stability, chemical resistance, and good mechanical and electric properties, polyimides are often applied in photoresists, passivation and dielectric films, soft print circuit boards, and alignment films within displays. Recently, fully aliphatic and alicyclic polyimides have found applications as optoelectronics and inter layer dielectric materials, due to their good transparencies and low dielectric constants $(\varepsilon)$. The low molecular density, polarity and rare probability of forming inter- or intra-molecular charge transfers, resulting in lowering of the dielectric constant and high transparency, are the most striking characteristics of aliphatic polyimide. However, the ultimate end use of polyimides derived from aliphatic monomers is in their targeted applications that need less stringent thermal requirements. Much research effort has been exerted in the development of aliphatic polyimide with increased thermal and mechanical stabilities, while maintaining their transparencies and low dielectric constants, by the incorporation of rigid moieties. In this article, the recent research process in synthesizing fully aliphatic polyimides, with improved dimensional stability, high transparency and low $\delta$values, as well as the characterizations and future scope for their application in micro electric and photo-electronic industries, is reviewed.

• Journal of Satellite, Information and Communications
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• v.10 no.2
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• pp.75-79
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• 2015

In this study, we investigated the electro-optical (EO) characteristic of fringe-field switching (FFS) mode cell by the ion beam alignment method on the a-C:H thin film. The suitable inorganic thin films for FFS cell and the aligning capabilities of nematic liquid crystal (NLC) using the new alignment material of a-C:H thin film were studied. An excellent voltage-transmittance (V-T) and response time curve of the ion beam aligned FFS-LCD was observed with oblique ion beam exposure on the a-C:H thin films. Also, the V-T hysteresis characteristics of the ion beam-aligned FFS-LCD with IB exposure on the a-C:H thin films is almost the same as that of the rubbing-aligned FFS cell on a polyimide surface.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.430-430
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• 2007

In general, polyimides (PIs) are used in liquid crystal displays (LCDs) as alignment layer of liquid crystals (LCs). Up to date, the rubbing alignment technique has been widely used to align liquid crystals on the PI surface, which is suitable for mass-production of LCDs because of its simple process and high productivity. However, this method has some disadvantages. Rubbed PI surfaces include the debris left by the cloth and the generation of electrostatic charges during rubbing process. Therefore, rubbing-free techniques for LC alignment are strongly required in LCD technology. In this experiment, PI was uniformly coated on indium-tin-oxide electrode substrates to form LC alignment layers using a spin-coating method and the PI layers were subsequently imidized at 433 K for 1 h. The thickness of the PI layer was set at 50 nm. The LC alignment layer surfaces were exposed to an $Ar^+$ ion-beam under various ion-beam energies. The antiparallel cells and twisted-nematic (TN) cells for the measurement of pretile angle and electro-optical characteristics were fabricated with the cell gap of 60 and $5\;{\mu}m$, respectively. The LC cells were filled with nematic LC (NLC, MJ001929, Merck) and were assembled. The NLC alignment capability on ion-beam-treated PI was observed using photomicroscope and the pretilt angle of the NLC was measured by the crystal-rotation method at room temperature. Voltage-transmittance (V-T) and response time characteristics of the ion-beam irradiated TN cell were measured by a LCD evaluation system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.159-159
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• 2009

We characterize a flexible self-assembled liquid crystal display (LCD) fabricated from a polyimide (PI) alignment layer with polydimethylsiloxane pixel walls. Ion beam (IB) irradiation aligned LC molecules in the PI layer and bonded two flexible plastic substrates in a one-step assembly of the pixel walls. X-ray photoelectron spectroscopic analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy provided chemical and physical evidence for the formation of stable chemical bonds between the PI layer and the PDMS pixel walls in addition to the important maintenance of a uniform 6 um gap between the two substrates without the use of any epoxy resins or other polymers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.04a
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• pp.41-41
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• 2008

In general, polyimides (PIs) are used in alignment layers in liquid crystal displays (LCDs). The rubbing alignment technique has been widely used to align the LC molecules on the PI layer. Although this method is suitable for mass production of LCDs because of its simple process and high productivity, it has certain limitations. A rubbed PI surface includes debris left by the cloth, and the generation of electrostatic charges during the rubbing induces local defects, streaks, and a grating-like wavy surface due to nonuniform microgrooves that degrade the display resolution of computer displays and digital television. Additional washing and drying to remove the debris, and overwriting for multi-domain formation to improve the electro-optical characteristics such as the wide viewing angle, reduce the cost-effectiveness of the process. Therefore, an alternative to non-rubbing techniques without changing the LC alignment layer (i.e, PI) is proposed. The surface of LC alignment layers as a function of the ion beam (IE) energy was modified. Various pretilt angles were created on the IB-irradiated PI surfaces. After IB irradiation, the Ar ions did not change the morphology of the PI surface, indicating that the pretilt angle was not due to microgrooves. To verify the compositional behavior for the LC alignment, the chemical bonding states of the ill-irradiated PI surfaces were analyzed in detail by XPS. The chemical structure analysis showed that ability of LCs to align was due to the preferential orientation of the carbon network, which was caused by the breaking of C=O double bonds in the imide ring, parallel to the incident 18 direction. The potential of non-rubbing technology for fabricating display devices was further conformed by achieving the superior electro-optical characteristics, compared to rubbed PI.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.5
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• pp.362-368
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• 2021

A homeotropic liquid crystal (LC) alignment state on rubbed fluorinated self-assembled monolayers (FSAMs) is described according to alkyl chain length. A simple procedure, gas-phase method, for the preparation of FSAM was used. The average optical transmittance in the visible light range of FSAMs were 76.63% to 78.21%, which were superior to the conventional polyimide layer having a transmittance of 75.89%. In addition, the excellent homeotropic LC alignment characteristics of FSAMs were observed through pretilt angle measurement and polarized optical microscope images. By measuring the contact angles and the surface energies of FSAMs, it was confirmed that pretilt angles of LC molecules increased according to the alkyl chain length. High optical transparency and uniform homeotropic LC alignment characteristics of FSAMs showed the possibility of FSAMs as an LC alignment layers.