Jong Bok Kim

Variable liquid crystal pretilt angles on various compositions of alignment layers

The authors introduce variable liquid crystal (LC) pretilt angles via ion beam (IB) irradiation of silicon carbide (SiC) layers of various compositions. To control the composition of the SiC layer, the authors altered the rf power ratio between the graphite target and silicon target. The pretilt angle of the silicon-rich SiC layer was constant regardless of IB irradiation angle; however, the carbon-rich SiC layer showed variable pretilt angles, depending on IB irradiation angle. The authors attribute variable pretilt angle to the competition between van der Waals interactions, favoring the vertical alignment, and pi-pi interactions, favoring the LC alignment parallel to IB direction.

Ion-beam induced liquid crystal alignment on diamond-like carbon and fluorinated diamond-like carbon thin films

Homogeneous and homeotropic orientations of nematic liquid crystal (NLC) are investigated on various inorganic thin films which are exposed to Ar ion-beam. It is the novel investigations which results in a completely dry processing technique for both the thin film deposition and alignment steps. In the case of homogenous alignment on diamond-like carbon (DLC) layer, optical band gap and the polar surface energy are investigated in order to elucidate the alignment mechanism by ion beam (IB) irradiation. We elucidate the role of surface polarity in DLC films with respect to the LC orientation. On the other hand, FDLC thin films are selected by homeotropic alignment layer with regard to the relationship between surface tension and LC orientation. Selected pretilt angles in the range of 71.1–89.8° can be easily obtained with ion beam irradiation. It is sensitively changed by thin films composition and the angle of ion beam irradiation.

No bias pi cell using a dual alignment layer with an intermediate pretilt angle

The authors fabricated a no-bias pi cell using a dual alignment layer with an intermediate pretilt angle via a rubbing. In the dual alignment layer system, the competition between crest region favoring the vertical alignment and trough region favoring planar alignment made it possible to achieve various pretilt angles, and adjusted pretilt angle from 90° to 20° with rubbing. In addition, as the intermediate pretilt angle plays a role in eliminating the activation energy and thus allowing formation of the initial bend state in pi cell fabrication, this approach achieved a no-bias pi cell for a liquid crystal display with both low power consumption and fast response.

Liquid crystal pretilt angle control using adjustable wetting properties of alignment layers

The authors demonstrate the production of amorphous fluorinated carbon (a-C:F) thin film with adjustable wetting properties, inducing variable liquid crystal (LC) pretilt angles. To control the surface wetting properties, they apply a dual radio frequency magnetron system with a controlled power ratio of targets. In this manner we obtain various compositional surfaces with fluorine and carbon components and adjust the surface energy with regard to the various compositions. Whereas the fluorine-rich a-C:F layer shows a preference for homeotropic (vertical) LC alignment, the carbon-rich a-C:F layer shows a planar LC alignment. To achieve uniform LC alignment with a proper pretilt angle, an accelerated Ar+ ion beam irradiates the films after the deposition process. The ion beam selectively destroys the surface bonding of the a-C:F films, yielding an intermediate pretilt angle.

Superhydrophobic modification of gate dielectrics for densely packed pentacene thin film transistors

Pentacene organic thin film transistors (OTFTs) with low-k and high-k hybrid gate dielectrics by CF4 plasma treatment exhibited excellent device performance with field effect mobilities (maximum 1.41cm2∕Vs), a low threshold voltage of +1V, and on/off current ratios of 105 at −5V gate bias. After CF4 plasma treatment, fluorine atoms diffuse into the interior low-k polymer and eliminate ionic impurities which reduce the leakage current density and overall pentacene initial growth on the superhydrophobic surface is significantly improved. It seems apparent that proper surface treatment is desirable for higher quality pentacene film and improving the performance of OTFTs.

Liquid Crystal Alignment Effects and Electro Optical Performances of Twisted Nematic-Liquid Crystal Display Using Ion-Beam Alignment Method on Nitrogen-doped Diamond Like Carbon Thin Film Layer

Nitrogen-doped diamond-like carbon (NDLC) thin films exhibit a high electrical resistivity that is similar to the properties shown by diamond-like carbon (DLC) thin films. The diamond-like transport property in NDLC thin films comes from a material consisting of sp2-bonded carbon versus the sp3-bonded carbon of DLC. In addition, NDLC thin films have a better thermal stability than the DLC thin films, because C:N bonding in the NDLC thin films is stronger against thermal stress than C:H bonding in the DLC thin films. The liquid crystal (LC) alignment effects of ion beam irradiation on the NDLC thin films and the electro optical (EO) performances of the ion-beam-aligned twisted nematic (TN)-liquid crystal display (LCD) with oblique ion beam exposure on an NDLC thin film surface were studied. A good uniform nematic liquid crystal (NLC) alignment with ion beam exposure on the NDLC thin films was observed. In addition, good EO properties, a residual DC property and particularly the good thermal stability of the ion-beam-aligned TN-LCD on NDLC thin films was achieved.

Liquid Crystal Alignment Effects using a Sio Thin Film

ABSTRACT We studied the nematic liquid crystal (NLC) aligning capabilities using the new alignment material of a SiO thin film. The homogenous alignment was obtained by using ion beam (IB) exposure on the SiO thin film, when positive type NLC (Δϵ > 0) was injected into the LC cell. However, the homeotropic alignment was obtained using ion beam exposure on the SiO thin film, when negative type NLC (Δϵ > 0) was injected into the LC cell. The LC aligning capability on the SiO thin film depends on the dielectric anisotropy type of LC.

High-performance and low-voltage pentacene thin film transistors fabricated on the flexible substrate

We report on the fabrication of low operating voltage pentacene thin film transistors with PVP (poly-4-vinylphenol)/CeO2–SiO2/PVP triple dielectric layers on a flexible substrate. Our triple dielectric layers exhibited a markedly reduced leakage current characteristic and a relatively high capacitance. The field effect mobility, on/off current ratio and subthreshold slope obtained from pentacene thin film transistors were 0.67 cm2 V s−1, 105 and 0.36 V dec−1, respectively. It was demonstrated that the spin-coating polymer layer can be used to planarize the surface irregularities and to improve the dielectric and device properties.

The Alignment Effect of Nematic Liquid Crystal on NDLC Thin Films Surface

ABSTRACT We studied the nematic liquid crystal (NLC) aligning capabilities using the new alignment material of Nitrogen doped diamond-like carbon (NDLC) thin film. The NDLC thin film exhibits high electrical resistivity and thermal conductivity that are similar to the properties shown by diamond-like carbon (DLC) thin films. The diamond-like properties and nondiamond-like bonding make NDLC an attractive candidate for applications. A high pretilt angle of about 9.9° by ion beam (IB) exposure on the NDLC thin film surface was measured. A good LC alignment is achieved by the IB alignment method on the NDLC thin film surface at annealing temperature of 200°C. The alignment defect of the NLC was observed above annealing temperature of 250°C. Consequently, the high pretilt angle and the good LC alignment by the IB alignment method on the NDLC thin film surface can be achieved.

Inorganic Alignment Layers Using Noncontact Method for Liquid Crystal Displays

Inorganic alignment materials were deposited on indium–tin-oxide (ITO) glass by reactive sputtering deposition. After deposition, inorganic alignment materials such as a-SiOx and a-SiOx:H were irradiated using an Ar+ ion beam (IB) for liquid crystal (LC) alignment. On the basis of the experimental results, an a-SiOx film deposited by sputtering does not align LCs regardless of IB treatment, but an a-SiOx:H film treated with varying IB energies, IB incident angles, IB doses, and IB irradiation times has excellent alignment properties and electro optical properties, the same as polyimide (PI). We investigated period of the stability of an inorganic alignment layer treated with IB after a long time. From the experimental results, the inorganic alignment layer irradiated with an IB does not experience degradation of its electro optical properties. These results imply that an inorganic alignment layer irradiated with IB can be adopted as an LC alignment layer instead of rubbed PI and that hydrogen plays an important role in LC alignment due to the difference in alignment properties between a-SiOx films and a-SiOx:H films.