High Efficiency and Wide Color Gamut Liquid Crystal Displays

Liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both the color gamut and the light efficiency of LCD. QD emits saturated color and grants LCD the capability to reproduce color vivid images. Moreover, the QD emission spectrum can be custom designed to match to transmission band of color filters. To fully take advantage of QD\u27s unique features, we propose a systematic modelling of the LCD backlight and optimize the QD spectrum to simultaneously maximize the color gamut and light efficiency. Moreover, QD enhanced LCD demonstrates several advantages: excellent ambient contrast, negligible color shift and controllable white point. Besides three primary LCD, We also present a spatiotemporal four-primary QD enhanced LCD. The LCD\u27s color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5× increment in spatial resolution, 2× brightness enhancement, slightly larger color gamut and mitigated LC response requirement (~4ms). It can be employed in the commercial TV to meet the challenging Energy star 6 regulation. Besides conventional LCD, we also extend the QD applications to liquid displays and smart lighting devices. The second part of this dissertation focuses on improving the LCD light efficiency. Conventional LCD system has fairly low light efficiency (4%~7%) since polarizers and color filters absorb 50% and 67% of the incoming light respectively. We propose two approaches to reduce the light loss within polarizers and color filters. The first method is a polarization preserving backlight system. It can be combined with linearly polarized light source to boost the LCD efficiency. Moreover, this polarization preserving backlight offers high polarization efficiency (~77.8%), 2.4× on-axis luminance enhancement, and no need for extra optics films. The second approach is a LCD backlight system with simultaneous color/polarization recycling. We design a novel polarizing color filter with high transmittance ( \u3e 90%), low absorption loss (~3.3%), high extinction ratio (\u3e10,000:1) and large angular tolerance (up to ±50˚). This polarizing color filter can be used in LCD system to introduce the color/polarization recycling and accordingly boost LCD efficiency by ~3 times. These two approaches open new gateway for ultra-low power LCDs. In the final session of this dissertation, we demonstrate a low power and color vivid reflective liquid crystal on silicon (LCOS) display with low viscosity liquid crystal mixture. Compared with commercial LC material, the new LC mixture offers ~4X faster response at 20oC and ~8X faster response at -20°C. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: submillisecond response time at room temperature, vivid color even at -20oC, high brightness, excellent ambient contrast ratio, and suppressed color breakup. With this material improvement, LCOS display can be promising for the emerging wearable display market

Vertical Field Switching Blue Phase Liquid Crystals For Field Sequential Color Displays

Low power consumption is a critical requirement for all liquid crystal display (LCD) devices. A field sequential color (FSC) LCD was proposed by using red (R), green (G) and blue (B) LEDs and removing the lossy component of color filters which only transmits ~30% of the incoming white light. Without color filters, FSC LCDs exhibit a ~3X higher optical efficiency and 3X higher resolution density as compared to the conventional color filters-based LCDs. However, color breakup (CBU) is a most disturbing defect that degrades the image quality in FSC displays. CBU can be observed in stationary or moving images. It manifests in FSC LCDs when there is a relative speed between the images and observers’ eyes, and the observer will see the color splitting patterns or rainbow effect at the boundary between two different colors. In Chapter 2, we introduce a five-primary display by adding additional yellow(Y) and cyan(C) colors. From the analysis and simulations, five primaries can provide wide color gamut and meanwhile the white brightness is increased, as compared to the three-primary. Based on the five-primary theorem, we propose a method to reduce CBU of FSC LCDs by using RGBYC LEDs instead of RGB LEDs in the second section. Without increasing the sub-frame rate as three-primary LCDs, we can reduce the CBU by utilizing proper color sequence and weighting ratios. In addition, the color gamut achieves 140% NTSC and the white brightness increases by more than 13%, as compared to the three-primary FSC LCDs. Another strategy to suppress CBU is using higher field frequency, such as 540 Hz or even up to 1000 Hz. However, this approach needs liquid crystals with a very fast response time

Perception of Color Break-Up

Hintergrund. Ein farbverfälschender Bildfehler namens Color Break-Up (CBU) wurde untersucht. Störende CBU-Effekte treten auf, wenn Augenbewegungen (z.B. Folgebewegungen oder Sakkaden) während der Content-Wiedergabe über sogenannte Field-Sequential Color (FSC) Displays oder Projektoren ausgeführt werden. Die Ursache für das Auftreten des CBU-Effektes ist die sequenzielle Anzeige der Primärfarben über das FSC-System. Methoden. Ein kombiniertes Design aus empirischer Forschung und theoretischer Modellierung wurde angewendet. Mittels empirischer Studien wurde der Einfluss von hardware-, content- und betrachterbasierten Faktoren auf die CBU-Wahrnehmung der Stichprobe untersucht. Hierzu wurden zunächst Sehleistung (u. a. Farbsehen), Kurzzeitzustand (u. a. Aufmerksamkeit) und Persönlichkeitsmerkmale (u. a. Technikaffinität) der Stichprobe erfasst. Anschließend wurden die Teilnehmenden gebeten, die wahrgenommene CBU-Intensität verschiedener Videosequenzen zu bewerten. Die Sequenzen wurden mit einem FSC-Projektor wiedergegeben. Das verwendete Setup ermöglichte die Untersuchung folgender Variablen: die Größe (1.0 bis 6.0°) und Leuchtdichte (10.0 bis 157.0 cd/m2) des CBU-provozierenden Contents, das Augenbewegungsmuster des Teilnehmenden (Geschwindigkeit der Folgebewegung: 18.0 bis 54.0 °/s; Amplitude der Sakkade: 3.6 bis 28.2°), die Position der Netzhautstimulation (0.0 bis 50.0°) und die Bildrate des Projektors (30.0 bis 420.0 Hz). Korrelationen zwischen den unabhängigen Variablen und der subjektiven CBU-Wahrnehmung wurden getestet. Das ergänzend entwickelte Modell prognostiziert die CBU-Wahrnehmung eines Betrachters auf theoretische Weise. Das Modell rekonstruiert die Intensitäts- und Farbeigenschaften von CBU-Effekten zunächst grafisch. Anschließend wird die visuelle CBU-Rekonstruktion zu repräsentativen Modellindizes komprimiert, um das modellierte Szenario mit einem handhabbaren Satz von Metriken zu quantifizieren. Die Modellergebnisse wurden abschließend mit den empirischen Daten verglichen. Ergebnisse. Die hohe interindividuelle CBU-Variabilität innerhalb der Stichprobe lässt sich nicht durch die Sehleistung, den Kurzzeitzustand oder die Persönlichkeitsmerkmale eines Teilnehmenden erklären. Eindeutig verstärkende Bedingungen der CBU-Wahrnehmung sind: (1) eine foveale Position des CBU-Stimulus, (2) eine reduzierte Stimulusgröße während Sakkaden, (3) eine hohe Bewegungsgeschwindigkeit des Auges und (4) eine niedrige Bildrate des Projektors (Korrelation durch Exponentialfunktion beschreibbar, r2 > .93). Die Leuchtdichte des Stimulus wirkt sich nur geringfügig auf die CBU-Wahrnehmung aus. Generell hilft das Modell, die grundlegenden Prozesse der CBU-Genese zu verstehen, den Einfluss von CBU-Determinanten zu untersuchen und ein Klassifizierungsschema für verschiedene CBU-Varianten zu erstellen. Das Modell prognostiziert die empirischen Daten innerhalb der angegebenen Toleranzbereiche. Schlussfolgerungen. Die Studienergebnisse ermöglichen die Festlegung von Bildraten und Eigenschaften des CBU-provozierenden Content (Größe und Position), die das Überschreiten vordefinierter, störender CBU-Grenzwerte vermeiden. Die abgeleiteten Hardwareanforderungen und Content-Empfehlungen ermöglichen ein praxisnahes und evidenzbasiertes CBU-Management. Für die Vorhersage von CBU kann die Modellgenauigkeit weiter verbessert werden, indem Merkmale der menschlichen Wahrnehmung berücksichtigt werden, z.B. die exzentrizitätsabhängige Netzhautempfindlichkeit oder Änderungen der visuellen Wahrnehmung bei unterschiedlichen Arten von Augenbewegungen. Zur Modellierung dieser Merkmale können teilnehmerbezogene Daten der empirischen Forschung herangezogen werden.Background. A color-distorting artifact called Color Break-Up (CBU) has been investigated. Disturbing CBU effects occur when eye movements (e.g., pursuits or saccades) are performed during the presentation of content on Field-Sequential Color (FSC) display or projection systems where the primary colors are displayed sequentially rather than simultaneously. Methods. A mixed design of empirical research and theoretical modeling was used to address the main research questions. Conducted studies evaluated the impact of hardware-based, content-based, and viewer-based factors on the sample’s CBU perception. In a first step, visual performance parameters (e.g., color vision), short-term state (e.g., attention level), and long-term personality traits (e.g., affinity to technology) of the sample were recorded. Participants were then asked to rate the perceived CBU intensity for different video sequences presented by a FSC-based projector. The applied setup allowed the size of the CBU-provoking content (1.0 to 6.0°), its luminance level (10.0 to 157.0 cd/m2), the participant’s eye movement pattern (pursuits: 18.0 to 54.0 deg/s; saccadic amplitudes: 3.6 to 28.2°), the position of retinal stimulation (0.0 to 50.0°), and the projector’s frame rate (30.0 to 420.0 Hz) to be varied. Correlations between independent variables and subjective CBU perception were tested. In contrast, the developed model predicts a viewer’s CBU perception on an objective basis. The model graphically reconstructs the intensity and color characteristics of CBU effects. The visual CBU reconstruction is then compressed into representative model indices to quantify the modeled scenario with a manageable set of metrics. Finally, the model output was compared to the empirical data. Results. High interindividual CBU variability within the sample cannot be explained by a participant’s visual performance, short-term state or long-term personality traits. Conditions that distinctly elevate the participant’s CBU perception are (1) a foveal stimulus position on the retina, (2) a small-sized stimulus during saccades, (3) a high eye movement velocity, and (4) a low frame rate of the projector (correlation expressed by exponential function, r2 > .93). The stimulus luminance, however, only slightly affects CBU perception. In general, the model helps to understand the fundamental processes of CBU genesis, to investigate the impact of CBU determinants, and to establish a classification scheme for different CBU variants. The model adequately predicts the empirical data within the specified tolerance ranges. Conclusions. The study results allow the determination of frame rates and content characteristics (size and position) that avoid exceeding predefined annoyance thresholds for CBU perception. The derived hardware requirements and content recommendations enable practical and evidence-based CBU management. For CBU prediction, model accuracy can be further improved by considering features of human perception, e.g., eccentricity-dependent retinal sensitivity or changes in visual perception with different types of eye movements. Participant-based data from the empirical research can be used to model these features

Advanced liquid crystal displays with supreme image qualities

Several metrics are commonly used to evaluate the performance of display devices. In this dissertation, we analyze three key parameters: fast response time, wide color gamut, and high contrast ratio, which affect the final perceived image quality. Firstly, we investigate how response time affects the motion blur, and then discover the 2-ms rule. With advanced low-viscosity materials, new operation modes, and backlight modulation technique, liquid crystal displays (LCDs) with an unnoticeable image blur can be realized. Its performance is comparable to an impulse-type display, like cathode ray tube (CRT). Next, we propose two novel backlight configurations to improve an LCD\u27s color gamut. One is to use a functional reflective polarizer (FRP), acting as a notch filter to block the unwanted light, and the other is to combine FRP with a patterned half-wave plate to suppress the crosstalk between blue and green/red lights. In experiment, we achieved 97.3% Rec. 2020 in CIE 1976 color space, which is approaching the color gamut of a laser projector. Finally, to enhance an LCD\u27s contrast ratio, we proposed a novel device configuration by adding an in-cell polarizer between LC layer and color filter array. The CR for a vertically-aligned LCD is improved from 5000:1 to 20,000:1, and the CR for a fringe field switching LCD is improved from 2000:1 to over 3000:1. To further enlarge CR to fulfill the high dynamic range requirement, a dual-panel LCD system is proposed and the measured contrast ratio exceeds 1,000,000:1. Overall speaking, such an innovated LCD exhibits supreme image qualities with motion picture response time comparable to CRT, vivid color to laser projector, and contrast ratio to OLED. Along with other outstanding features, like high peak brightness, high resolution density, long lifetime, and low cost, LCD would continue to maintain its dominance in consumer electronics in the foreseeable future

Advanced Blue Phase Liquid Crystal Displays

Thin-film transistor (TFT) liquid crystal displays (LCDs) have become indispensable in our daily lives. Their widespread applications range from smartphones, laptops, TVs to navigational devices, data projectors and wearable displays. Over past decades, massive efforts have been invested in device development, material characterization and manufacturing technology. As a result, the performance of LCDs, such as viewing angle, contrast ratio, color gamut and resolution, have been improved significantly. Nonetheless, there are still urgent needs for fast response time and low power consumption. Fast response time helps reduce motion image blurs and enable color sequential displays. The latter is particularly attractive since it eliminates spatial color filters, which in turn triples optical efficiency and resolution density. The power consumption can be reduced greatly by using color sequential displays, but liquid crystals with submillisecond response time are required to minimize color breakup. The state-of-the-art gray-to-gray response time of nematic LCDs is about 5ms, which is too slow to meet this requirement. With the urgent needs for submillisecond response time, polymer-stabilized blue phase liquid crystal is emerging as a strong candidate for achieving this goal. Compared to conventional nematic LCDs, blue phase LCDs exhibit several revolutionary features: submillisecond gray-to-gray response time, no need for alignment layer, optically isotropic voltage-off state, and large cell gap tolerance. However, some bottlenecks such as high operation voltage, low optical transmittance, noticeable hysteresis and slow TFT charging remain to be overcome before their widespread applications can be realized. This dissertation is dedicated to addressing these challenges from material development and device design viewpoints. First, we started to investigate the device physics of blue phase LCDs. We have built a numerical model based on the refraction effect for simulating the electro-optics of blue phase devices. The model well agrees with experimental data. Based on this model, we explored approaches from device and material viewpoints to achieve low operation voltage. On the device side, with protrusion and etched electrodes, we can reduce the operating voltage to below 10V and enhance the transmittance to over 80%. On the material side, high Kerr constant is indeed helpful for lowering the operation voltage, but we also need to pay attention to the individual ?n and ?? values of liquid crystal host according to the device structures employed. High-?? LC hosts help enhance Kerr constant, leading to a reduced operation voltage; but they may be subject to serious capacitance charging issues due to the huge dielectric anisotropy. Our model provides important guidelines for future device design and material development. To further enhance transmittance and reduce voltage, we have proposed a Z-shaped electrode structure. By optimizing the device structure, we have successfully reduced the operating voltage to ~8V and enhanced optical transmittance to \u3e 95% based on a lower-?? LC host not subjecting to charging issues, showing comparable or even better performance than the mainstream LCDs. This is the first approach to achieve such a high transmittance in blue phase devices without using a directional backlight. By using zigzag structure, the color shift and gray inversion are in unnoticeable range. In addition, hysteresis affects the accuracy of grayscale control and should be suppressed. We have proposed a double exponential model to analyze the electric field effects of blue phase, and found that electrostriction effect is the root cause for hysteresis under strong electric field. To suppress the electrostriction effect in blue phase, a method to stabilize the blue phase lattice via linear photo-polymerization is demonstrated for the first time. By illuminating the mono-functional and the di-functional monomers with a linearly polarized UV beam, we can form anisotropic polymer networks, which in turn lead to anisotropic electrostrictions. In experiments, we found that when the polarization of UV light is perpendicular to the stripe electrodes, the electrostriction effect can be strongly suppressed. The resulting hysteresis is reduced from 6.95% to 0.36% and response time is improved by a factor of two. We foresee this approach will guide future manufacturing process. The approaches and studies presented in this dissertation are expected to advance the blue phase LCDs to a new level and accelerate their emergence as next-generation display technology. It is foreseeable that the widespread application of blue phase LCDs is around the corner

Low Voltage Blue Phase Liquid Crystal Displays

From cell phones, laptops, desktops, TVs, to projectors, high reliability LCDs have become indispensable in our daily life. Tremendous progress in liquid crystal displays (LCDs) has been made after decades of extensive research and development in materials, device configurations and manufacturing technology. Nowadays, the most critical issue on viewing angle has been solved using multidomain structures and optical film compensation. Slow response time has been improved to 2-5 ms with low viscosity LC material, overdrive and undershoot voltage, and thin cell gap approach. Moving image blur has been significantly reduced by impulse driving and frame insertion. Contrast ratio in excess of one million-to-1 has been achieved through local dimming of the segmented LED backlight. The color gamut would exceed 100% of the NTSC (National Television System Committee), if RGB LEDs are used. Besides these technological advances, the cost has been reduced dramatically by investing in advanced manufacturing technologies. Polymer-stabilized blue phase liquid crystal displays (BPLCDs) based on Kerr effect is emerging as a potential next-generation display technology. In comparison to conventional nematic devices, the polymer-stabilized BPLCDs exhibit following attractive features: (1) submillisecond response time, (2) no need for molecular alignment layers, (3) optically isotropic dark state when sandwiched between crossed polarizers, and (4) transmittance is insensitive to cell gap when the in-plane electrodes are employed. However, aside from these great potentials, there are still some tough technical issues remain to be addressed. The major challenges are: 1) the operating voltage is still too high (~50 Volts vs. 5 Volts for conventional nematic LCDs), and the transmittance is relatively low (~65% iv vs. 85% for nematic LCDs), 2) the hysteresis effect and residual birefringence effect are still noticeable, 3) the mesogenic temperature range is still not wide enough for practical applications (40 oC to 80 oC), and 4) the ionic impurities in these polymer-stabilized nano-structured LC composites could degrade the voltage holding ratio, which causes image sticking. In this dissertation, the BPLC materials are studied and the new BPLC device structures are designed to optimize display performances. From material aspect, the electro-optical properties of blue phase liquid crystals are studied based on Kerr effect. Temperature effects on polymer-stabilized blue phase or optically isotropic liquid crystal displays are investigated through the measurement of voltage dependent transmittance under different temperatures. The physical models for the temperature dependency of Kerr constant, induced birefringence and response time in BPLCs are first proposed and experimentally validated. In addition, we have demonstrated a polymer-stabilized BPLC mixture with a large Kerr constant K~13.7 nm/V2 at 20 oC and =633 nm. These models would set useful guidelines for optimizing material performances. From devices side, the basic operation principle of blue phase LCD is introduced. A numerical model is developed to simulate the electro-optic properties of blue phase LCDs based on in-plane-switching (IPS) structure. Detailed electrode dimension effect, distribution of induced birefringence, cell gap effect, correlation between operation voltage and Kerr constant, and wavelength dispersion are investigated. Viewing angle is another important parameter. We have optimized the device configurations according to the device physics studied. With proper new device designs, the operating voltage is decreased dramatically from around 50 Volts to below 10 Volts with a reasonably high transmittance (~70%) which enables the BPLCDs to be addressed by amorphous silicon thin-film transistors (TFTs). Moreover, weak wavelength v dispersion, samll color shift, and low hysteresis BPLCDs are achieved after their root causes being unveiled. Optimization of device configurations plays a critical role to the widespread applications of BPLCDs. In addition to displays, blue phase liquid crystals can also be used for photonic applications, such as light modulator, phase grating, adaptive lens and photonic crystals. We will introduce the application of blue phase liquid crystal as a modulator to realize a viewing angle controllable display. The viewing angle can be tuned continuously and precisely with a fast response time. The detailed design and performance are also presented in this dissertation

Green Grain: waste-free made easy: a system designed to reduce food packaging waste

O objetivo desta tese é desenvolver um sistema de compra de alimentos com desperdício zero e projetar uma marca que fosse um espelho desse ADN verdadeiro. Em última instancia, esta tese espera encontrar uma solução inovadora para reduzir a quantidade de embalagens descartáveis de alimentos que se tornam resíduos ambientais prejudiciais. O Design Thinking e a investigação ativa foram as metodologias que orientaram o projeto. Entrevistas, observações de sites, e questionários foram alguns dos métodos utilizados nas fases de inovação, iteração e produção. O teste de validação utilizou uma apresentação com uma recolha de dados quantitativos e qualitativos. Os dados foram analisados e reforçaram o sucesso tanto da marca, como do sistema inovador, que oferecem uma real, e percebida, mais valia para o ambiente.The objective of this thesis study is to develop a zero-waste system of buying food and to design a brand that reflects that honest approach. Ultimately, this thesis hopes to find a new and innovative solution to reduce the amount of one-time-use food packaging that becomes harmful environmental waste. Design thinking and action research comprised the methodologies that guided the project. Interviews, site observations, and polls were also included in innovation, iteration, and production. Validation testing utilized a presentation and survey with both quantitative and qualitative results. The data collected reinforced the success of both the brand and the innovation in offering real and perceived environmental value

Spray deposition for plastic electronics

Spray deposition is a promising technique for the solution processing of plastic electronic devices due to its potential for high-speed, large-scale device fabrication using low capital cost equipment. Most recent reports of spray-deposited electronic devices have used ultrasonic systems for film deposition to minimise surface roughness, but such systems suffer from low materials throughput, and are consequently ill-suited to industrial manufacturing. Gas-driven spray-heads enable higher throughput materials delivery but can result in an unacceptably rough film due to the large, broadly distributed droplet sizes that are often generated and the hard-impact nature of the deposition process. This thesis describes a new automated gas-driven spray coater for the controlled deposition of a broad variety of solution processed electronic materials. It is specifically suited to the deposition of polymer films such as poly(3-hexylthiophene) (P3HT), overcoming many of the usual disadvantages of conventional gas-driven spray coaters. Key features of the system include: a novel, high performance 3D-printed spray-head for the generation of ultrafine sprays; full three-dimensional position and velocity control of the spray head; integrated temperature control; and independent control of solution and gas flow rates. To determine the optimum solution composition for spray-deposition of P3HT films, the aggregation and gelation dynamics of various P3HT/o-xylene solutions were first investigated by static light scattering. On the basis of these measurements, we conclude that dilute solutions (with polymer concentration <5 mg/ml) of low (<20 kg/mol ) molecular weight polymer containing a small amount of a secondary solvent. are optimal for avoiding gelation and clogging of the spay-head. For higher weight material, heating of the solution is necessary to avoid gelation. The thesis also describes the development of an optical profiling technique for the characterisation of polymer films, which provides a fast method for quantitatively characterising the uniformity of large-area, thin polymer films. Using this technique, we were able to confirm that the spray-deposition system yields high quality, thin semiconducting polymer films, allowing for the controlled fabrication of active layers in organic photovoltaic devices from non-chlorinated solvents. The influence of solution composition and deposition variables such as gas pressure, solvent composition and substrate temperature were investigated, and optimised conditions for the deposition of high quality (device-grade) thin P3HT films were thereby identified. A maximum device efficiency of 4.0 % was achieved for the spray-deposited bulk heterojunction P3HT:fullerene films processed from xylene. The results indicate that, providing the active layer is continuous, high device efficiency may be achieved even with relatively rough films, spray-coated from non-chlorinated processing solvents.Open Acces

Semantic discovery and reuse of business process patterns

Patterns currently play an important role in modern information systems (IS) development and their use has mainly been restricted to the design and implementation phases of the development lifecycle. Given the increasing significance of business modelling in IS development, patterns have the potential of providing a viable solution for promoting reusability of recurrent generalized models in the very early stages of development. As a statement of research-in-progress this paper focuses on business process patterns and proposes an initial methodological framework for the discovery and reuse of business process patterns within the IS development lifecycle. The framework borrows ideas from the domain engineering literature and proposes the use of semantics to drive both the discovery of patterns as well as their reuse