Yasuo Toko

Amorphous twisted nematic–liquid‐crystal displays fabricated by nonrubbing showing wide and uniform viewing‐angle characteristics accompanying excellent voltage holding ratios

A new twisted‐nematic (TN)–liquid‐crystal display (LCD) device has been prepared without rubbing, which is called the no‐rubbing (NR) technique. The device is shown to exhibit wide and uniform viewing‐angle characteristics without showing a contrast inversion in the vertical direction of the cell. This characteristic is achieved in particular by filling chiral‐molecular‐doped nematic LCs (NLCs) in the isotropic phase into a cell. The substrate surfaces of the cells are either bare indium‐tin‐oxide films or those coated with polymer materials such as polyimide. These films are optically and structurally isotropic in a quasi‐macroscopic scale (say, 100×100 μm2). In particular, the polymer films are capable of stabilizing and homogenizing the distribution of the NLC directors at the surfaces. The TN‐LCDs fabricated by the NR technique, called amorphous TN‐LCDs, are also featured by the excellent voltage holding ratio which is necessary to achieve good active matrix driving, and, furthermore, the device exhib...

Analytical Simulation of Electrooptical Performance of Multidomain Twisted Nematic Liquid Crystal Displays

A simulation of the electrooptical (EO) performance of an amorphous twisted nematic liquid crystal display (a-TN-LCD) has been performed. The a-TN-LCDs are prepared by filling chiral-molecule-doped NLCs into empty cells in the isotropic phase and cooling them to room temperature; the inner surfaces of the cells are topographically and optically homogeneous and no rubbing is performed. The a-TN-LCDs exhibit wide and uniform viewing angle characteristics and suitable EO performance for gray-scale operation, in comparison with those of conventional TN-LCDs. These characteristics of the a-TN-LCD are successfully reproduced and explained by computer simulation.

35.3: Improvement of Transmitted Light Efficiency in SH-LCDs Using Quarter-Wave Retardation Films

For improving the transmitted light efficiency we have theoretically and experimentally studied mulit-domain Super-Homeotropic (SH) LCDs combined with two •/4 retardation films. As a result, the transmitted light efficiency of the LCD panel is improved up to 1.6 times that of a conventional SH panel, so that the steepness of the electro-optical characteristics is also improved. We then show that the further improvement of the efficiency can be achieved by using a cholesteric film and the obtaioned final improvement in the transmitted light efficiency is about 2 times that of conventional SH panel.

Characteristics of Nanoparticle Doped Nematic Liquid Crystals in Low Temperature

The LC material showing fast response characteristics at a low temperature is needed in the current LCDs. LCDs embedded with metal nanoparticles of Ag/Pd show a short response time by 3 to 5 times compared to those without nanoparticles. This phenomenon is shown to be attributed to the reduction of rotational viscosity be 70% at room temperature and be 30% at a low temperature (−20°C) and also to the alteration of elastic constants by doping nanoparticles.

Evaluation of Pretilt Angle and Polar Anchoring Strength of Amorphous Alignment Liquid Crystal Display from Capacitance Versus Applied Voltage Measurement

Abstract The pretilt angle and the anchoring strength are important parameters in liquid crystal displays (LCDs). However, in the case of amorphous LCDs (a-LCDs), it is difficult to evaluate these parameters by means of conventional measurement method due to non-uniformity of the LC directors. In this paper, we report the simultaneous evaluation method of the pretilt angle and the polar angle anchoring strength of a-LCDs by fitting the theoretical values based on the elastic continuum theory to the data obtained by the measurement of capacitance versus applied voltage (C-V) characteristics. We evaluate the pretilt angle and the polar anchoring strength of a-LCD using the polyimide alignment films. We confirm the pretilt angle and the polar anchoring strength of a-LCD are strongly dependent on surface energy of the polyimide alignment film.

Characteristics of Liquid Crystal Display Fabricated by Alignment Transcription Method

Abstract We have developed a novel fabrication method of an LCD without rubbing treatment on the substrate surfaces of the cell. In this method, LC alignment is transcribed from an original rubbed substrate to a counter substrate that is coated with non-rubbed polymer, and is fixed on the surface by memory effect of the interface between LC molecules and the polymer surface. This transcribed and memorized alignment on the non-rubbed polymer is rather stable. Therefore, it is possible to fabricate the LCD by putting the transcribed polymer substrate separated from the original substrate upon another substrate. It is found that the LCDs having various alignment such as multi-domain structure can be made easily without generating dust and static electricity caused by the rubbing.

Optical Compensation Method for In-plane Switching Twisted Nematic Mode

We have proposed an in-plane switching twisted nematic (IT) mode. The characteristics of the IT mode are the wide viewing angle, the narrow cell gap error tolerance, and the relative fast response time. However, an IT mode needs a high electric field to obtain a high contrast ratio. To improve this situation, we propose a compensation method using a twisted nematic liquid crystal (LC) film or a twisted discotic LC film. Specifically, the latter can achieve the wide viewing angle, the high contrast ratio and the decrease in the driving voltage. In this paper, a compensation method using a film is suggested and evaluated by numerical calculation.

Fast electro‐optical response at low temperature for metal nanoparticle embedded STN‐LCDs (Invited Paper)

— STN-LCDs embedded with special metal nanoparticles of Ag/Pd are shown to be useful for a direct-multiplexed dot-matrix STN-LCD with 320 × 240 pixels and show a fast response time by 3–5 times compared to those without nanoparticles. This phenomenon is shown to be attributed to the reduction of rotational viscosity by 70% at room temperature and by 30% at a low temperature (−20°C). The alteration of elastic constants by doping nanoparticles could be also essential.

Characterization of Bistable Hybrid-Twisted Nematic Liquid Crystal Mode by Means of Renormalized Transmission Spectroscopic Ellipsometry

We report on how to determine asymmetrical director distribution throughout a liquid crystal layer such as a bistable hybrid-twisted nematic (BHTN) liquid crystal device by means of renormalized transmission spectroscopic ellipsometry. The advantage of the plural oblique incidence spectroscopic ellipsometry (POISE) is that the azimuthal angle as well as the tilt angle with a relatively high zenithal angle can be determined simultaneously without using a special cell with a coupling prizm. It was demonstrated that five device parameters, namely, cell gap, pretilt angles of upper and lower surfaces, twist angle of the director alignment, and azimuthal angle of the entrance liquid crystal director, can be determined uniquely. It is experimentally confirmed that each bistable state has an opposite twist sense and the twist angle difference between two stable states is approximately 180°.

12.5L: Late-News Paper: Fast Switching Super Twisted Nematic Liquid Crystal Displays Doped with Silver and Palladium Nanoparticles

This paper reports for the first time that the metal nanoparticle doping technology in STN-LCDs is effective for realizing their fast response speed particularly at low temperature. The ratio of Ag and Pd of the metal nanoparticle doped in the liquid crystal is changed, and the condition suitable for the direct multiplexed dot matrix driving is found. It is demonstrated that the switching speed of STN-LCD is improved particularly at the low temperature, say, −30°C over three times.