Taiju Takahashi

Preliminary Study of Field Sequential Fullcolor Liquid Crystal Display using Polymer Stabilized Ferroelectric Liquid Crystal Display

Using a side-chain mesogenic polymer stabilized ferroelectric liquid crystal display (PS-FLCD) cell together with a two-dimensional array of red, green and blue light-emitting diodes (LEDs) as a modulated back light unit, we constructed a field sequential fullcolor (FSC) LCD. The PS-FLCD used in this research exhibits a high contrast ratio (230:1) with thresholdless monostability, grayscale capability, and a fast response speed (τ=40 µs). In the present research it is taken the advantages of the favorable characteristics of the PS-FLCD for implementing a FSC-LCD that has an 8×8 matrix format. The fabricated FSC-LCD, which is operated at the frame rate of 330 Hz, is shown to exhibit an excellent color gamut, color grayscale, and smearless moving color bars.

Mesogenic polymer-stabilized FLCDs exhibiting asymmetric and symmetric (V-shape) electrooptic characteristics

Abstract We have succeeded in fabricating a novel FLCD, which exhibits symmetric electrooptic (EO) characteristic called V-shape EO performance, by choosing an appropriate photocuring condition such as applied voltage waveforms and the concentration of photocurable mesogenic monomers. Our mesogenic polymer stabilized (MPS)-V-FLCD shows high contrast ratio owing to zig-zag defect free, continuous grayscale without accompanying switching domains, and good switchability with TFTs due to free from the value of the spontaneous polarization.

Fabrication of Defect-Free Ferroelectric Liquid Crystal Displays Using Photoalignment and Their Electrooptic Performance

A photoalignment technique has been utilized for fabricating zigzag-defect-free ferroelectric liquid crystal displays (FLCDs) using polyimide RN-1199, -1286, -1266 (Nissan Chem. Ind.) and adopting oblique irradiation of unpolarized UV light. A rubbing technique was also utilized for comparison. It is shown that among these polyimide materials, RN-1199 is the best for fabricating defect-free cells with C-1 uniform states, but RN-1286 requires low energy to produce a photoaligned FLC phase. We have conducted an analytical investigation to clarify the conditions for obtaining zigzag-defect-free C-1 states, and it is theoretically shown that zigzag-defect-free C-1 state is obtained using a low azimuthal anchoring energy at a low pretilt angle, while a zigzag-defect-free C-2 state is obtained by increasing azimuthal anchoring energy above a critical value, also at a low pretilt angle. The estimated critical value of the azimuthal anchoring energy at which a transition from the C-1 state to the C-2 state occurs is 3×10-6 J/m2 for the FLC material FELIX M4654/100 (Clariant) used in this research; this value is shown to fall in a favorable range which is measured in an independent experiment.

Monostabilization of Surface-Stabilized Ferroelectric Liquid Crystal Using Polymer Stabilization

Surface-stabilized ferroelectric liquid crystals (SSFLCs) fabricated by adopting polymer stabilization in terms of the UV photocure of doped photocurable monoacrylates with mesogenic side chains at a temperature where the LC medium is in the SmC* phase under the simultaneous application of a monopolar electric field, exhibit monostable electrooptical characteristics with grayscale capability without threshold. We suggest a model for explaining the monostability of this polymer-stabilized SSFLC by investigating theoretically the free energy of the SSFLC before and after the photocure.

MODELING AND COMPUTER SIMULATION OF THE ELECTROOPTIC RESPONSE OF POLYMER-STABILIZED FERROELECTRIC LIQUID CRYSTAL CELLS

The dynamical electrooptic (EO) response of mesogenic side-chain polymer-stabilized ferroelectric liquid crystal cells has been investigated based on the continuum theory. From numerical calculations, the transition from the bistable EO response to the monostable EO response for pulse-applied voltages is clearly demonstrated with increasing degree of polymer stabilization, where free energy originating from the polymer stabilization is formulated and adopted. The reduction of the fall time constant is revealed in this transition. These behaviors are shown to be in qualitative agreement with the results of independent experimental measurements.

Transient Behavior of Voltage Holding Ratio in Nematic Liquid Crystal Cells

The transient variations of a voltage holding ratio (VHR) with the progression of frames have been measured for two typical nematic liquid crystals (LCs), ZLI-4792 containing few ionic impurities and 5CB containing many more residual ionic impurities. Characteristic transient variations of the VHR were observed for both liquid crystal materials. To clarify the mechanism of exhibition of these characteristic transient variations of the VHR, a computer simulation was carried out. Qualitative agreement between the experimental results and the theoretically simulated results was confirmed.

Field Sequential Fullcolor LCDs using FLC Technology

Abstract We constructed field sequential fullcolor (FS-FC) LCDs using two kinds of mesogenic polymer stabilized FLCs; the first one is the Half V type (HV-FLCD) that exhibits asymmetric EO performance and the other is the V type (V-FLCD) exhibiting symmetric EO performance. As back a light system, we used a 2D array of red, green, and blue LEDs. We compared the performance of these two types of FS-FC-LCDs using two different kinds of FLCDs. It is concluded that a FS-FC LCD using a HV response may yield higher luminance at the white (light) state than that uses a V-FLCD.

Electrooptical properties of vertically aligned twisted nematic cells with negative dielectric anisotropy

Two types of vertically aligned twisted nematic (VATN) liquid crystal (LC) cells in which a chiral nematic LC with negative dielectric anisotropy is used are proposed. In one type of the VATN cells, both substrate surfaces are treated by rubbing to obtain a slight tilt angle from the normal of each substrate, and in another one, only one substrate surface is treated by rubbing. In this study, some electrooptical properties are investigated experimentally and by simulations. Similar T–V characteristics were obtained for both types of cell in which d/P0≈0.5 (ratio of the cell thickness to the equilibrium value of the chiral pitch). It is shown that these cells exhibit a good colorless black–white display image. The threshold voltage of VATN cells is expressed by π√{1-4(K22/K33)2(d/P0)2}K33/(e0 Δe).

Models of Molecular Alignment Structure in Polymer-Stabilized Ferroelectric Liquid Crystals

The electrooptical (EO) characteristics of polymer-stabilized ferroelectric liquid crystals (PSFLCs), which are fabricated by UV photocure of doped monoacrylates with mesogenic side chains at a temperature where the LC medium is in the SmC* phase under the simultaneous application of a bipolar square-pulsed AC electric field, depend on the polymer density. The PSFLC with low concentration of polymer exhibits a bistable EO performance accompanied by microsized domain switching. On the other hand, the PSFLC with high concentration of polymer exhibits a monostable V-shaped EO performance without a threshold. We propose a model to explain the effect of polymer density on the molecular alignment structure of the PSFLC by investigating theoretically the free energy.

Stabilization of bend alignment using optical polymerization of UV curable liquid crystalline monomers

Director profiles and electrooptical properties in polymer-stabilized π cells used in optically compensated bend (OCB) liquid crystal displays (LCDs) are theoretically investigated by introducing an additional term which expresses the effect of polymer stabilization on the free energy density. The conditions required to stabilize the bend alignment definitively have been theoretically clarified and experimentally confirmed. As a result, the bend alignment is successfully stabilized even if the twist state is more stable than the bend state before the application of polymer-stabilization treatment.