Byeong-Yun Oh

Compositional investigation of liquid crystal alignment on tantalum oxide via ion beam irradiation

The homogeneously aligned liquid crystal display on Ta2O5 via ion beam (IB) irradiation was first embodied with controllability of pretilt angle depending on incident angle of the IB. As a result of x-ray photoelectron spectroscopic analysis, the intensity of Ta–O and O–Ta bondings as a function of incident angle behaved reversely with the pretilt angle and the lowest amplitude was observed at 45°. It revealed that the creation of pretilt angle was attributed to the irradiation of the IB by breaking Ta–O and O–Ta bonding so orientational order was generated by directional IB. Comparable electro-optical characteristics to rubbed polyimide were also achieved.

Surface reformation and electro-optical characteristics of liquid crystal alignment layers using ion beam irradiation

The surface modification characteristics of liquid crystal (LC) alignment layers irradiated with various argon (Ar) ion beam (IB) energies were investigated as a substitute for rubbing technology. Various pretilt angles were created on the IB-irradiated polyimide (PI) surfaces after IB irradiation, but the Ar ions did not alter the morphology on the PI surface, indicating that the pretilt angle was not due to microgrooves. The chemical bonding states of the IB-irradiated PI surfaces were analyzed in detail by x-ray photoelectron spectroscopy to verify the compositional behavior for the LC alignment. Chemical structure analysis showed that the alignment ability of LCs was due to the preferential reorientation of the carbon network due to the breaking of C=O double bonds in the imide ring parallel to the incident IB direction. The potential of applying nonrubbing technology to display devices was further supported by the superior electro-optical characteristics compared to rubbed PI.

Vertical alignment of liquid crystals on a fully oxidized HfO2 surface by ion bombardment

High-performance liquid crystals (LCs) driven at a 0.9 V threshold were demonstrated on very thin HfO2 films with vertical (homeotropic) alignment by ion bombardment. Atomic layer deposition was used to obtain LC orientation on ultrathin high-quality films of double-layer HfO2/Al2O3. X-ray photoelectron spectroscopy indicated that full oxidization of HfO2 film surfaces was induced by ion bombardment, shifting the Hf 4f spectra to lower binding energies. The increased intensities of the Hf 4f peaks after ion bombardment confirmed that nonstoichiometric HfOx was converted to the fully oxidized HfO2 surfaces.

High-performance ZnO thin-film transistor fabricated by atomic layer deposition

We report the fabrication and characteristics of a ZnO thin-film transistor (TFT) using a 50 nm thick ZnO film as an active layer on an Al2O3 gate dielectric film deposited by atomic layer deposition. Lowering the deposition temperature allowed the control of the carrier concentration of the active channel layer (ZnO film) in the TFT device. The ZnO TFT fabricated at 110 °C exhibited high-performance TFT characteristics including a saturation field-effect mobility of 11.86 cm2 V−1 s−1, an on-to-off current ratio of 3.09 × 107 and a sub-threshold gate-voltage swing of 0.72 V decade−1.

No-Bias-Bend Liquid-Crystal Display with an Intermediate Angle on Blended Polyimide via Ion-Beam Irradiation

We created a no-bias-bend (NBB) pi cell on a blended polyimide (PI) layer with intermediate pretilt angles using the ion-beam method. Various pretilt angles were easily obtained depending on the concentration of homeotropic PI. The plot of surface tension corresponded to the variation of the pretilt angle. We also observed a uniform alignment of the liquid crystals on the blended PI layer. The NBB pi cell had a low threshold voltage of 0.9 V and a fast response time of 5.4 ms.

Zinc oxide nanolevel surface transformation for liquid crystal orientation by ion bombardment

This paper introduces the characteristics of the zinc oxide (ZnO) inorganic film deposited by radio-frequency magnetron sputtering as an alternative alignment layer for liquid crystal display (LCD) applications. The crystalline structure related to the texture formation of ZnO (101¯3) was observed with a tilt angle of approximately 28.1° to the ZnO (0001) plane, leading to a smooth surface and high-density structure. Ion beam (IB) bombardment at various incident angles was used to induce liquid crystal (LC) alignment and cause the measured pretilt angle on ZnO films to assume a triangular contour. The orientation order of liquid crystal molecules was due to the van der Waals force for the vertical alignment of LCs with selective breaking of O–Zn bonds by IB bombardment. The contact angle contour as a function of the IB incident angle resembled the behavior of the pretilt angle. The pretilt angle is controllable by adjusting the surface features on ZnO films with IB bombardment. The electro-optic character...

Selective liquid crystal molecule orientation on ion beam irradiated tantalum oxide ultrathin films

We recently achieved the homogeneous alignment of liquid crystal (LC) on amorphous Ta2O5 layers. This study demonstrates that LC layers could be aligned either homogeneously or vertically by increasing the growth temperature of rf magnetron sputtering device and the irradiation time of the DuoPIGatron type Ar ion beam device causing uniform and dense plasma. We attained two LC orientations by observing Ta 4f and O 1s peak shifts with x-ray photoelectron spectroscopy. Moreover, the decreased thickness of layers with high-k dielectric constants helped to decrease driving LC voltages and in turn to achieve low power consumption.

Enhanced electro-optical properties of Y2O3 (yttrium trioxide) nanoparticle-doped twisted nematic liquid crystal devices

We report the electro-optic (EO) characteristics of a Y2O3 nanoparticle-doped nematic liquid crystal (NLC) system. After doping with 2 wt.% Y2O3 nanoparticles, LC alignment shows a homogeneous orientation state without aggregation and crack. In particular, the pretilt angle was slightly increased in proportion to Y2O3 doping concentration. Response time was improved by nearly 53%, and the threshold voltage for display operation was reduced from 4.2 V to 2.6 V. We assumed that superior EO properties were achieved by the Y2O3 nanoparticle, which reduces the field-screening effect of impurity ions. We also confirmed that enhanced EO characteristics were achieved without loss of light transmittance.

Superior optical properties of homogeneous liquid crystal alignment on a tin (IV) oxide surface sequentially modulated via ion beam irradiation

We first investigated the alignment characteristics of tin (IV) oxide (SnO(2)) thin films deposited by radio-frequency (RF) magnetron sputtering. This study demonstrates that liquid crystal (LC) molecules could be aligned homogeneously by controlling the Ion Beam (IB) irradiation energy densities. We also show that the pretilt angle of the LC molecules has a close relation with the surface energy. X-ray photoelectron spectroscopy (XPS) indicates that a non-stoichiometric SnO(2-x) surface converted by ion beam irradiation can horizontally align the LC molecules. The measured electro-optical (EO) characteristics showed high performance, comparable with those of rubbed and ion-beam irradiated polyimide (PI) layers.

A No-Bias-Bend Nematic LCD with a Medium Pretilt Angle Controlled by Ion-Beam Bombardment

This paper describes a no-bias-bend (NBB) IT cell based on a homeotropic polyimide layer with a midrange pretilt angle produced using the nonrubbing ion-beam (IB) method. Various pretilt angles in the range 1-89° were easily achieved depending on the IB exposure time. A chemical structure analysis confirmed that preferential reorientation of the carbon network was created by selectively breaking the weakest IT bonds of the C=O double bonds. The threshold voltage and favorable response time of the NBB IT cell without an initial critical voltage were 0.7 V and 6.6 ms.