Twisted Nematic Liquid Crystal Display Research Articles

P‐12.4: Low Voltage Switchable Bistable Twist Nematic Display

The most common electronic paper technology is E‐ink, which enables many novel applications such as e‐readers, watches and electronic shelf labels. However, due to the TFT backplane driving and complex production processes, the cost of this technology is high, which limits its popularity. Recently, a low‐cost π‐bistable twist nematic (π‐BTN) liquid crystal display with a high pretilt angle is proposed. It has the same structure and production method as an ordinary liquid crystal display. Passive driving enables the manufacture of high‐resolution bistable displays without the use of thin‐film transistors. Compared with the current bistable twist nematic display technology, the high pretilt angles structure helps to achieve a lowvoltage and fast‐respond bistable display. This wide viewing angle, high contrast and TFT‐free display is a promising candidate for flexible displays.

The Effect of Chemically Modified Multi-Walled Carbon Nanotubes on the Electro-Optical Properties of a Twisted Nematic Liquid Crystal Display Mode

In this study, we have chemically modified multi-walled carbon nanotubes (MWNTs) with different side chains for better dispersion in liquid crystal solutions, and fabricated twisted nematic liquid crystal cells doped with such MWNT derivatives. The introduction of MWNT derivatives affects the alignment of LC molecules with or without external electric fields. Electro-optical property tests showed that the contrast ratio changed slightly with the sharp decrease in drive voltage, improving the drive ability of the twisted nematic liquid crystal display (TN-LCD) mode.

A Resolution-Enhanced Digital Micromirror Device (DMD) Projection System

In this paper we present a resolution-enhanced system for digital micromirror device (DMD) projected images by utilizing time multiplexing and birefringence in order to achieve this with static components only. This provides a less expensive solution than reducing the size of the hardware pixels and can also be applied to higher resolution displays, as and when, these become available. Birefringent materials have different refractive indices for linearly polarized light with orthogonal polarization directions. A high-resolution projected image can be observed by overlapping two or three native resolution images at shifts of one half or one third of a DMD pixel diagonal respectively on successive frames. The optical components comprise a custom-made quartz plate as the birefringent component and an off-the-shelf twisted nematic liquid crystal display (TN-LCD) screen as a polarization rotator that is synchronized with the DMD frame rate. This paper covers the principle of operation and the system design. The functioning of the display is verified using enlarged images of the letter `R' and a checkerboard pattern that are formed from a small number of DMD pixels.

P‐136: A Low Voltage, Switchable, Bistable‐Twist‐Nematic Display

The most common electronic paper technology is E‐ink, which enables many novel applications such as e‐readers, watches and electronic shelf labels. However, due to the TFT backplane driving and complex production processes, the cost of this technology is high, which limits its popularity. Recently, a low‐cost π‐bistable twist nematic (π‐BTN) liquid crystal display with a high pretilt angle is proposed. It has the same structure and production method as an ordinary liquid crystal display. Passive driving enables the manufacture of high‐resolution bistable displays without the use of thin‐film transistors. Compared with the current bistable twist nematic display technology, the high pretilt angles structure helps to achieve a low‐voltage and fast‐respond bistable display. This wide viewing angle, high contrast and TFT‐free display is a promising candidate for flexible displays.

Study on polyvinylidene fluoride as alignment layer in twist-nematic liquid crystal display

ABSTRACTThe material with high dielectric constant can significantly affect the distribution of the electric field, so this kind of material has great potential in liquid crystal display. In this paper, polyvinylidene fluoride (PVDF) as alignment layer in liquid crystal display was analysed. The optical property, mechanical property, thermal stability and electrical property of PVDF were measured. Experiments show that the absorbance of PVDF material is 0.2 (or less) in visible light, which is better than the conventional alignment material polyimide (PI). The alignment effect can be generated by mechanical friction and the liquid crystal molecules are ordered or aligned, and PVDF can maintain good thermal stability as temperature is lower than 400°C. Since the dielectric constant of PVDF is usually between 6.0 and 8.0, it has significant effect on the distribution of the electric field in the liquid crystal display, and its dielectric loss is also less than PI. The lower operating voltage and the faster response time are obtained from the experiment. It can be confirmed by the experiments that PVDF could be used in liquid crystal display (LCD) as the alignment layer to improve LCD’s characteristics.

Liquid crystal displays, LC-materials and LPP photo-alignment

ABSTRACTThe invention of the twisted nematic liquid crystal display (TN-LCD) by Schadt and Helfrich in 1970 started the development of field-effect LCDs.Today, LCDs are the dominant flat panel display technology. Milestones in the ongoing research and development are sub-millisecond responding nematic liquid crystal (LC) materials, integration of silicon-driving electronics into display substrates, complex optical thin-films enabling excellent image quality and, last but not least, high resolution, contact-free photo-alignment/pattering of monomeric liquid crystals in displays and surface-aligned liquid crystal polymer (LCP) optical films. Photo-alignment of liquid crystal molecules by the linear photo-polymerization (LPP) technology enables high resolution, fast responding multi-domain LCDs with broad fields of view and complex, ultra-thin liquid crystal polymer retarder films. LCD-applications range from reflective displays for digital watches with virtually zero power consumption to large-area flat television screens with photographic resolution as well as to optical security elements and integrated optics devices. The commercial impact of the global LCD technology is illustrated by its annual turnover above $140billion.The seminar gives a personal overview of the multidisciplinary efforts between applied physics, material sciences and engineering which have enabled nematic liquid crystals of becoming the dominant flat panel display technology since 1970.

Solution-Derived Hafnium Lanthanum Oxide Films Prepared Using Ion-Beam Irradiation and Their Applications as Alignment Layers for Twisted-Nematic Liquid Crystal Displays

Solution-Derived Hafnium Lanthanum Oxide Films Prepared Using Ion-Beam Irradiation and Their Applications as Alignment Layers for Twisted-Nematic Liquid Crystal Displays

Vortex beam generation and other advanced optics experiments reproduced with a twisted-nematic liquid-crystal display with limited phase modulation

In this work we propose the use of twisted-nematic liquid-crystal spatial light modulators (TN-LC-SLM) as a useful tool for training students in the manipulation of light beams with phase-only masks. In particular, we focus the work on the realization of phase-only gratings and phase-only spiral phases for the generation of vortex beams, beams carrying orbital angular momentum (OAM). Despite the extensive activity in this field, its experimental implementation for educational purposes is limited because it requires the use of very expensive high-resolution liquid-crystal on silicon (LCOS) SLMs. Here, we show that a low-cost experimental implementation can be done with older TNLC technology. However, these devices, intended for display applications, exhibit rather limited optical phase modulation properties in comparison with modern LCOS devices, such as a very low range of phase modulation and a general coupled intensity modulation. However, we show that a precise characterization of their retardance parameters permits their operation in useful modulation configurations. As examples, we include one continuous phase-only configuration useful for reproducing the optimal triplicator phase grating, and a binary π-phase modulation. We include experiments with the realization of different phase diffraction gratings, and their combination with spiral phase patterns and lens functions to generate a variety of vortex beams.

Temperature-Dependent Behavioral Model of Active-Matrix Liquid Crystal Displays for All Types of Liquid Crystals

This paper proposes a temperature-dependent behavioral circuit model to predict optical characteristics of an active-matrix liquid crystal display with twisted-nematic (TN), patterned vertical alignment (PVA), and fringe-field switching (FFS) modes. The optical responses of liquid crystal displays (LCDs) are strongly affected by ambient temperature. We optimized time-constant parameters that describe the movement of liquid crystal molecules so that simulated optical responses of TN, PVA, and FFS LCDs best fit to the measured ones depending over the temperature range from 0 to 50 °C. We found that the time-constant parameters have a linear relationship with the ambient temperature, which enables us to anticipate the optical responses at any given temperature. The simulation results of the transient responses show excellent matches with the measurement ones regardless of ambient temperature.

Liquid Crystal Alignment on Solution Derived Zinc Oxide Films via Ion Beam Irradiation.

A 75-nm-thick ZnO film was deposited by a sol-gel method on indium-tin oxide (ITO)-coated glass. This film served as a liquid crystal (LC) alignment layer. We report the fabrication and characteristics of this film after ion-beam (IB) irradiation. Uniform LC alignment was achieved at an IB incident energy above 2400 eV. The IB-treated ZnO surface was analyzed by X-ray photoelectron spectroscopy (XPS), monitoring the intensity of the Zn 2p and O 1s peaks as a function of IB-irradiation energy density. The electro-optical (EO) characteristics of a twisted nematic-liquid crystal display (TN-LCD) were comparable to rubbed polyimide.

Solution-Derived Zn-Doped GaO Films as Alignment Layers for Twisted-Nematic Liquid Crystal Displays Using Ion-Beam Bombardment

This letter demonstrates liquid crystal (LC) alignment on solution-derived Zn-doped GaO (ZnGaO) films using an ion beam (IB) method. Homogeneous and uniform LC alignment was achieved on IB-irradiated ZnGaO films. X-ray photoelectron spectroscopy was used to analyze the chemical bonding states of the IB-irradiated ZnGaO surfaces to verify the compositional behavior for LC alignment. In addition, ZnGaO films with twisted nematic cells exhibited electro-optical characteristics comparable with those of a conventional polyimide layer for potential LC display applications.

Nematic liquid crystals and twisted-nematic LCDs

Since 1970, scientific and technological progress of the twisted-nematic liquid crystal display (TN-LCD) technology and subsequent polarisation-controlled field-effect LCDs strongly depended on the discovery, development and manufacturing of novel nematic liquid crystals. New experimental techniques had to be developed for determining all display-relevant LC-material parameters and correlating them with molecular structural elements and display performance. TN-LCDs with low operating voltage and power consumption, faster response, broader operating temperature range, multiplexability and, last but not least, long lifetime were some of the goals. Progress in LC-material R&D, device physics and display manufacturing broadened the range of TN-LCD applications from seven-segment, directly addressed displays in the early 1970s to increasingly more complex LCDs with higher information content. Examples include super-twisted nematic-LCDs in the 1980s and thin-film transistor-addressed TN-LCD monitors in the 1990s and beyond.

Predicting wavelength dependency of optical modulation of twisted nematic liquid crystal display in the visible range

One of the main problems in liquid crystal spatial light modulators (LC-SLM) is the prediction of their optical modulation behavior for different wavelengths; this coupled phase/amplitude modulation can be hard to measure for specific wavelengths and setups, yet it is required to be included in the study of a number of SLM's applications. This work proposes a simulation model to predict the phase/amplitude modulation for different twisted nematic liquid crystal displays (TN-LCD) optical setups, this model incorporates the effects of wavelength in addition to other parameters which already have been studied before like twist angle as internal parameter and polarizers angles, we verified the accuracy of our model compared to results of previously published work.

Super-fast switching of twisted nematic liquid crystals with a single-wall-carbon-nanotube-doped alignment layer

The application of a single-wall carbon-nanotube (SWCNT) and polyimide (PI) composite thin film on an indium tin-oxide (ITO) glass substrate, working as the command surface in a twisted nematic liquid crystal display (LCD), is described. SWCNTs were chopped and oxidized in a strong acid medium to make them more miscible in a polyimide solution. A film of this newly-developed PISWCNT composite was rubbed to determine the director direction for the LC molecules. The newlyfabricated command surface was examined using a laser beam profiler and atomic force microscopy. Sizes of shortened SWCNTs were characterized by using field-emission scanning electron microscopy (FE-SEM). Finally, small-sized test panels were fabricated from this composite-coated ITO glass, and their electro-optic performances were measured. Although the operating voltage to switch a cell was increased by around 41%, the switching speed was improved remarkably. The rise time of the test cells was found to be improved by around 10.12% and the decay time by around 29.77%. Thus, an overall improvement of around 16.12% in the total switching time was achieved. The change in the surface morphology of the newly-developed composite materials was found to be one of the factors responsible for the faster switching of the device. Detailed discussions are given in this report to explain the faster switching of the newly-developed twisted nematic liquid crystal display (TN-LCD). The device can be useful for practical applications.

P‐120: Nucleation‐control Bistable Twist Nematic Display

AbstractA fast π bistable twist nematic (π‐BTN) liquid crystal display controlled by nucleation process is developed. The nucleation induced by the patterned spacer inside the cell. The response time is fast and it depends on the density of patterned spacer.

Polarization modulation polarimeter for measuring two-dimensional distribution of five cell parameters of a twisted nematic liquid crystal display

In this study, an intensity-sensitive polarization modulation polarimeter (IPMP) was proposed and set up in order to measure the cell parameters of a twisted-nematic liquid crystal display (TNLCD). Both Yeh and Gu's transfer matrix and Lien's transfer matrix of a TNLCD are used and they are able to characterize all five cell parameters of a TNLCD including the cell gap, pretilt angle, rubbing angle, twist angle and untwisted phase retardation simultaneously. The optical setup is based on a single CCD camera and the ratio of p- and s-linear polarization intensity signals whereas we rotate a calibrated quarter wave plate to produce the polarization modulation during measurement. Thus, all five cell parameters are determined numerically by use of the least square curve fitting algorithm between the measured data and theoretical prediction following Yeh & Gu's and Lien's models of a TNLCD at same time. Finally, the advantages of this proposed IPMP are discussed.

High-transmittance liquid-crystal displays using graphene conducting layers

We report the use of graphene as a highly transparent conductive film in liquid-crystal displays (LCDs). Graphene films were synthesised via chemical vapour deposition, transferred onto glass substrates, and then used to fabricate typical twisted nematic LCD cells. LCD cells using graphene as transparent electrodes exhibited optical transmittances 7.7% higher than LCD cells fabricated using conventional conducting layers based on indium tin oxide (ITO) films. The device characteristics of LCD cells based on graphene electrodes, such as threshold voltage and voltage holding ratio, were comparable to those of conventional LCD cells based on ITO electrodes. These results indicate that graphene is a promising transparent conductive film compared to ITO, yielding LCDs with significantly improved optical transmittance.

Electro-optical Properties of Twisted Nematic Liquid Crystal Displays Fabricated with TIPS-pentacene Doping

This paper introduces 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) doped liquid crystal (LC) alignment properties on a rubbed polyimide (PI) layer as a function of the doping concentration of TIPS pentacene. Pretilt angles, photomicrographs, and electro-optical properties of TIPS pentacene doped LCs were comparable to those of pure LCs. However, TIPS pentacene in a LC medium supported twisted nematic-liquid crystal displays (TN-LCDs) to improve electro-optical properties. The threshold voltages observed in the TN cells decreased as the TIPS pentacene concentration increased. In addition, suitable response times were observed in TN cells.

Edge linking and image segmentation by combining optical and digital methods

We present a hybrid method for segmentation of intensity images, which combines an optical contouring technique and digital algorithms for linking edge points or image segmentation. In a first stage, the digital image to be processed is displayed in a twisted-nematic liquid-crystal display (LCD), which is placed between a polarizer⿿analyzer pair at 45 deg (instead of 90 deg as occurs in standard LCDs). It is not difficult to demonstrate that the proposed setup produces a resultant image with very pronounced dark contours at middle intensity. After the optical preprocessing, two different digital algorithms are applied: an edge linking algorithm (modified chain code) and a simple thresholding technique for image segmentation. The proposed procedure works well with monochromatic and color images. The method could be useful as a robust technique for segmentation of large images in real-time, which presents potential applications in medical and biological imaging.

Programmable color tuning of a multiline laser by means of a twisted nematic liquid crystal display

An optical system useful to tune in a controlled way the color of a triline argon krypton (Ar-Kr) laser by means of a twisted nematic liquid crystal display (TNLCD) is presented. The optical setup employs a 4f system and two blazed gratings to first separate and then recombine the spectrum of the light beam. The TNLCD is included in the intermediate focal plane operating in the amplitude modulation mode to control the relative transmission of each spectral line. The resulting color is accurately predicted by using a previously developed physical model of the spectral and voltage dependence of the TNLCD birefringence. By simply changing the gray level image addressed to the display, the Ar-Kr laser is color modulated at a video rate, thus becoming an interesting, reconfigurable, coherent light source for applications such as multicolor holography or color inspection.