Showing papers by "Hoi Sing Kwok published in 2000"

Characterization of the MIC/MILC interface and its effects on the performance of MILC thin-film transistors

Abstract: Process and material characterization of the crystallization of amorphous silicon by metal-induced crystallization (MIC) and metal-induced lateral crystallization (MILC) using evaporated Ni has been performed. An activation energy of about 2 eV has been obtained for the MILC rate. The Ni content in the MILC area is about 0.02 atomic %, significantly higher than the solid solubility limit of Ni in crystalline Si at the crystallization temperature of 500/spl deg/C. A prominent Ni peak has been detected at the MILC front using scanning secondary ion mass spectrometry. The MIC/MILC interface has been determined to be highly defective, comprising a continuous grain boundary with high Ni concentration. The effects of the relative locations of this interface and the metallurgical junctions on TFT performance have been studied.

Three-terminal bistable twisted nematic liquid crystal displays

Abstract: A three-terminal bistable twisted nematic liquid crystal display has been demonstrated. This display makes use of a combination of strong in-plane electric fields and vertical electric field for switching between the φ and the φ+π twist states. The lifetimes of the two bistable twist states are infinite, which is a significant improvement over conventional bistable twisted nematic displays.

Behavior of the drain leakage current in metal-induced laterally crystallized thin film transistors

Abstract: Although conventional metal-induced laterally crystallized (MILC) thin film transistors (TFTs) are better than solid phase crystallized (SPC) TFTs in many device performance measures, they are less ideal in others, owing to the higher leakage current and early drain breakdown. It has been found that degradation can be reduced by eliminating the overlap of the metallurgical junctions of the source/drain regions, formed by metal-induced crystallization (MIC), and the grain boundaries at the MIC/MILC interface. Here, the drain leakage current (Ilk) behavior of MILC TFTs with and without overlap has been studied. It is observed that under certain gate bias conditions, the relative magnitude of Ilk for the two kinds of devices exhibits an interesting reversal as the drain bias is varied. ” 2000 Elsevier Science Ltd. All rights reserved.

Optically optimized transmittive and reflective bistable twisted nematic liquid crystal displays

Abstract: A new Mueller matrix approach is developed for the design of optical modes for all nematic liquid crystal displays (LCD). In particular, for linearly polarized light going into the LC cell, conditions for linear polarization and circular polarization outputs are obtained. By considering the switching between different polarization modes, new transmittive and reflective bistable twisted nematic (BTN) LCD operating conditions with optimized contrast and brightness are discovered. A passive matrix driven single polarizer reflective BTN display was fabricated with reasonably good measured optical performance and fast selection time.

Trichroic prism assembly for separating and recombining colors in a compact projection display

Abstract: A trichroic prism assembly design, believed to be new, is proposed and demonstrated. This new design has the advantages of low s- and p-polarization dependence in the reflectance spectra of the optical coatings. Hence it can be used for both color separation and color recombination with polarization change. This new trichroic prism assembly is especially useful in a compact color projector employing reflective liquid-crystal light valves.

P-55: Contrast and Brightness Enhancement of RTN-LCDs Using Antireflective Layers

Abstract: New constructions of RTN-LCDs with antireflective (AR) coatings were proposed. Both one polarizer and Polarizer Beam Splitter (PBS) variants were considered. The AR coatings can be made both in the outer surface of the one-polarizer RTN-LCD and on the upper substrate between the glass plate and aligning layer. The damping of the LCD reflection in the “dark” state of one-polarizer RLCD by introducing AR layers considerably improves the contrast ratio and only slightly affects the brightness of RLCD. The application of AR-layers in PBS-RLCD results in an improved brightness.

Application of metal-induced unilaterally crystallized polycrystalline silicon thin-film transistor technology to active-matrix organic light-emitting diode displays

Abstract: Active matrix (AM) flat-panel displays (FPDs) based on organic light-emitting diodes (OLEDs) are being hotly pursued as alternatives to liquid crystal displays (LCDs). Unlike LC pixels, which are voltage-driven, OLED pixels are current-driven, Since the amorphous silicon (a-Si) thin-film transistors (TFTs) typically used in LCDs suffer from limited current-driving capability and high photosensitivity, polycrystalline silicon (poly-Si) TFTs based on metal-induced unilateral crystallization (MIUC) of a-Si are investigated for AMOLED displays. Particular attention is paid to (1) optimizing TFT structural design and (2) resolving issues related to the integration of MIUC TFT and OLED.

0°–360° bistable nematic liquid crystal display with large dΔn and high contrast

Abstract: A new mode of 0°–360° bistable twisted nematic (BTN) liquid crystal display is developed by using a parameter space method. This new mode possesses a large dΔn value that provides a possibility of using a 4.8–7 μm cell gap and a 6.5 V operating voltage for the new 0°–360° BTN cells. The high-contrast ratios above 80 within −80°–80° viewing-angle ranges are obtained experimentally in a horizontal direction, and the highest contrast ratio achieved is up to 250. In the contrast ratio, the experiment’s results concur with the simulation results.

Polarizing beam splitter

Abstract: A polarizing beam splitter is described that is optimised not for the maximum possible extinction ratio, but to provide a wide acceptance angle over substantially the whole visible range while still providing an adequate extinction ratio for use in specific applications such as a LCD projector display.

π/2 and 5π/2 twisted bistable nematic liquid crystal display

Abstract: A π/2 and 5π/2 twist bistable nematic liquid crystal cell is optimized in optics by a parameter space approach. The cell possesses good contrast ratio, a preferable dΔn value, a wide viewing angle, and black–white display. Three switching wave forms can be used to switch the cell between π/2 and 5π/2 twist states. Controlling the selection voltage amplitude can provide gray scales for the cell.

Optimization of reflective bistable twisted nematic displays with retardation compensation

Abstract: The contrast ratios of reflective bistable twisted nematic liquid crystal displays with a rear quarter-wave film are optimized by means of a parameter space approach. By plotting the contrast ratio as a function of the twist angle and thickness-birefringence product (dΔn) of the display, the regions where the displays show the best contrast ratio are clearly shown. Both the absolute reflectance and the wavelength dispersion of two bistable twisted states are investigated. It is confirmed that superhigh contrast ratio (infinite in principle), reflectance about 95% with polarized-light input, a large dΔn value (0.63 μm), and low dispersion are possible for such reflective bistable liquid crystal display.

High Performance Transmittive Bistable Twisted Nematic Liquid Displays

Abstract: Several new transmittive bistable twisted nematic liquid display (BTN-LCD) modes are developed. Unlike previous versions, these BTN modes do not require cross polarizers. Experiments confirmed that these modes have high contrast ratio and reasonably high transmittance. The dispersion characteristics of some of these modes are comparable to ordinary waveguiding TN modes. That is, they afford true black/white operations without any need for further color compensation.

Comb-on-plane switching electrodes for liquid-crystal displays

Abstract: — Although the common twisted-nematic liquid-crystal displays (TN-LCD) has excellent contrast and low color dispersion, it suffers from small viewing angle when driven into the homeotropic state. Among the many techniques proposed, in-plane switching (IPS) has been quite effective in improving viewing angle. However, there may be difficulty in adopting conventional IPS to higher-definition displays because it suffers from limited storage capacitance and reduced transmittance. A new comb-on-plane switching (COPS) electrode design is proposed. Compared to conventional IPS, COPS allows for lower switching voltage and offers advantages including naturally scalable storage capacitance, wide viewing angle with TN-like high transmittance, and low color dispersion.

47.3: Thin Photo‐Patterned Internal Polarizers for LCDs

Abstract: the novel technology of thin photo-patterned polarizers for LCDs. The polarizer consists of small regions with different orientations of the absorption axis and/or colors. It can be placed on the interior of the LCD cell substrate. The polarizer material consists of thin (about 0.3-0.7 micrometers) lyotropic dye layers, transferred to the substrates by UV-curing glue or by the "photo-alignment" method. We use photo-chemically stable dyes as the photo-alignment layers for the lyotropic LC and as the thin photo-patterned polarizers.

18.1: On the Minimization of Flicker and Image Retention in Silicon Light Valves

Abstract: The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong We have performed a systematic characterization of flicker and image retention in silicon light valves. It was found that there were four mechanisms accounting for the flicker and image retention. These four mechanisms were residual DC charge on silicon surface, voltage holding ratio of the LC cell, voltage holding ratio of the silicon panel, and parasitic capacitor coupling. Causes of these mechanisms were identified and solutions for the minimization of flicker were found for each mechanism. Among these solutions, the frame rate multiplication was the most useful for all these four flicker mechanisms.

Cost-effective Driving Scheme for Bistable Cholesteric Displays

Abstract: For VLSI implementation, low operation voltage and switching current are the major concerns. Yet, none of the driving schemes published so far has addressed this combined issue. We studied the electro-optic characteristics of bistable cholesteric displays at the low transition voltage in this paper, and the effect of slew-rate on the maximum output current and average output power in a forthcoming paper. The dynamic responses were measured and an efficient scheme was devised accordingly. The most cost-effective addressing time was 4 ms/line using the low-end twist nematic (TN) or super twist nematic (STN) mixtures.

Effect of Waveform Slew-rate on Bistable Cholesteric Displays

Abstract: Since the typical peak-to-peak voltage needed to drive the bistable cholesteric display is two to three times higher than that for super twist nematic (STN) displays, the transient current can be excessively large and detrimental to most semiconductor drivers. To reduce the maximum switching current, the voltage transition time should be restricted in addition to reducing the peak voltage. In this paper, we studied the effect of slew-rate on the maximum output current, average output power and the dynamic optical responses. Based on circuit theory, we obtained a good agreement between experimental and calculated results. The optimal settings can be incorporated into our driving scheme so that low voltage and current requirements can be met for very large-scale integration (VLSI) implementation.

Liquid crystalline polyacetylenes with tunable luminescent properties

Abstract: Development of advanced polymeric materials with both liquid crystallinity and light emissivity is of scientific interest and technological importance. In this study, we studied light emission from tetrahydrofuran solutions of a liquid crystalline polyacetylene, poly(11-{[(4'-heptoxy-4- biphenylyl)carbonyl]oxy}-1-undecyne), in the electrical field. The field exerts little effect on the photoluminescence of the polymer solution with a low concentration (0.10 mM). The photoluminescence of a concentrated solution (11.3 mM) is, however, noticeably quenched under an electrical field with a field strength of > 300 kV/m. When the field strength is increased to >= 367 kV/m, the bimodal emission spectrum of the solution changes to a monomodal one. Thus, both the emission intensity and spectral profile of the luminescence of the concentrated solution can be tuned by the electrical field, which is probably caused by the aggregate dissociation and mesogen realignment induced by the external stimulus.

Broadband large-acceptance-angle polarizing beam splitters for reflective LCD projectors

Abstract: In projectors employing reflective liquid crystal light valves, polarizing beam splitters (PBS) have to be used. However, ordinary wide bandwidth PBSs have relatively small acceptance angles. This reduces the optical efficiency of the projectors. In this paper we present new designs for the PBS which has the advantage of large acceptance angles without compromising the operating bandwidth.

High-contrast SXGA silicon light valves for high-definition video projectors

Abstract: We have developed a highly integrated liquid-crystal-on-silicon light valve for three-panel color projector. The silicon panel was designed and fabricated by a 0.35μm, 3-metal and dual-voltage CMOS process with a spatial resolution of 1280 x 1024 pixels. The pixel pitch was 12μm, the fill factor was 90% and the display area was 0.77 in diagonal. Eight-bit digital data drivers and gamma-correction circuitry were integrated into the silicon panel for true gray scale and full color representation. The display panel was assembled with a mixed twisted nematic and birefringence liquid crystal cell for high contract at CMOS compatible voltage. Contrast ratio was typically 200:1 at 5.5Vrms. In addition, silicon surface layers, liquid crystal materials, pixel structures and driving schemes were carefully optimized for the minimization of visual flicker. Flicker ratio of less than 3% was achieved at 60Hz frame rate. The optical sub-system utilized a trichroic prism assembly for both color separation and recombination. With this trichroic prism assembly incorporating three silicon light valves, a compact and high-contrast SXGA video projector was demonstrated.

Bistable twisted nematic liquid crystal displays with twist angle of ±11 degrees

Abstract: The present invention provides the conditions for new bistable twisted nematic liquid crystal displays, in particular the necessary twist angles, liquid crystal retardation values, input and output polarizer angles, for both transmissive and reflective liquid crystal displays.

Liquid crystal display with nonspecular reflectors

Abstract: The present invention deals with liquid crystal displays where the incident light and reflected light going through the display are not specularly related. The incident light can be at a range of angles to the display while the reflected light, i.e. the viewing direction is at or nearly normal to the display. For such nonspecular liquid crystal displays, the polarizer angles, the input/output directors of the liquid crystal cell, and the liquid crystal cell retardation have to be specially optimized to obtain the best viewing effects. Conventional liquid crystal display modes do not work optimally in this nonspecular situation. We also disclose the new image-mode and shadow-mode nonspecular liquid crystal displays. Such displays have very bright background and are free from viewing glare common in most liquid crystal displays. The present invention applies to all twist angles, e.g. the 90° TN, the 120° and 150° HTN, the 180°, 240° and 270° STN displays.

P-2: Re-Crystallized Metal-Induced Laterally Crystallized Polycrystalline Silicon for System-on-Panel Applications

Abstract: Metal-induced lateral crystallization (MILC) has been promoted as an enabling polycrystalline silicon (poly-Si) technology for system-on-panel (SOP) applications. It is reported presently that the recrystallization of MILC poly-Si leads to significant improvement in material characteristics and device performance. Re-crystallized metal-induced unilaterally crystallized (RC-MIUC) poly-Si thin film transistors exhibit high mobility, low threshold voltage, steep sub-threshold slope and low gate-induced drain-leakage, thus making them applicable to realizing high performance 3-dimensional integrated circuits and SOPs.