A preview of some of the most interesting papers appearing in the March 2008 issue of the Journal of the SID. To obtain access to these articles on-line, please go to www.sid.org
Edited by Aris Silzars
Sang Soo Kim
Bong Hyun You
Nam Deog Kim
Brian H. Berkeley
Samsung Electronics Co.
Abstract — Samsung has developed a high-resolution full-HD (1920 x 1080) 120-Hz LCD-TV panel using a novel pixel structure and a motion-compensated frame-interpolation (McFi) single-chip solution. Our latest work includes launch of a 70-in. full-HD panel, the world's largest LCD TV in mass production, with a 120-Hz frame rate. A serious problem involving the charging time margin has been completely overcome through the use of a new alternative 1G-2D pixel structure and a new driving scheme. Compared with conventional dot-inversion driving, our new dot-inversion method, which is a spatial averaging technique, can save power because the column drivers are operated using vertical inversion driving. In addition, McFi, which merges individual ME/MC and timing-controller (TCON) ICs and memories, has been developed and applied in a mass-production product for the first time ever. The McFi solution provides 120-Hz driving with the lowest possible system cost. Motion-picture response time (MPRT) has been reduced from 15 to 8 msec. Moreover, for the case of 24-Hz film source mode, motion judder has been completely eliminated. As a result, a lineup consisting of 40-, 46-, 52-, 70-, and 82-in. LCD-TV panels with high quality and manufacturability has been made possible.
The new advanced 1G-2D pixel structure and driving method have enabled the module composition shown in Fig. 16. In large-sized or high-speed-driven LCD TVs, source drivers are typically located at both the top and bottom of the panel. However, our 70-in. panel only requires a single bank of column drivers, resulting in lower cost and a simplified module assembly process.
FIGURE 16 — Module structure with single-bank source drivers.
Se Hwan Kim
Eung Bum Kim
Jae Hwan Oh
Ji Ho Hur
Kyung Hee University
Abstract — A 2.0-in. a-Si:H TFT-LCD with embedded TFT sensors for the control of the backlight intensity according to the ambient light intensity has been developed. Two types of a-Si:H TFT sensors with various channel widths were embedded into a TFT backplane with bottom- and top-gate structures for measuring the ambient light and backlight illumination, respectively. The output signal, measured by a readout IC, increased with backlight intensity until 20,000 lux.
TFT-LCDs with LED backlight units have the advantages of wide color gamut, tunable white point, high dimming ratio, long lifetime, and environmental compatibility. But the light intensity of an LED is temperature dependent. Color and white luminance levels are not stable over a wide range of temperature due to inherent long-term aging characteristics. In order to minimize color-point variation and brightness variation over time, optical feedback is a key technology for LED backlighting systems.
FIGURE 2 — The design of a TFT backplane with TFT photosensors for controlling backlight brightness.
Brian H. Berkeley
Sang Soo Kim
Abstract — This paper presents thermally adaptive driving (TAD) technology for response-time compensation (RTC) of an LCD with an integrated sensor. The TAD system is comprised of an analog sensor, an analog sensor signal conditioning, and a digital feedback algorithm. The integrated thermal sensor provides accurate temperature measurement of the liquid-crystal layer. The TAD controller has an eight-step look-up-table (LUT) and compensates response time based on the panel temperature. The TAD system reduces response time by nearly 34% over the temperature range 0–60°C. This paper also presents a thermal sensor which has been integrated onto an LCD. The sensor uses metal (Mo/Al) film as a temperature detection layer, and its fabrication requires no manufacturing process changes. The sensor shows very good linearity, sensitivity, and reliability.
Considering backlight and ambient heat-source dependencies, the best place to measure the panel temperature is on the LCD panel itself. Furthermore, the best internal placement point is at the same layer as the actual liquid crystal. It is impractical to make a thermal sensor that is sufficiently thin and small to be installed within the liquid-crystal layer. It is also difficult to attach an external sensor and its circuitry to the LCD glass along the narrow black border around the edge of the panel. Moreover, doing so would increase production cost and process time. We have developed a new technology for measuring LCD temperature accurately. Our approach uses a gate metal resistor sensor integrated onto the LCD panel, as depicted in Fig. 1.
FIGURE 1 — Metal-film-type thermal sensor integrated onto an LCD panel.
Y. W. Li
H. S. Kwok
Hong Kong University of Science Technology
Abstract — Passive-matrix-driven field-sequential-color (FSC) displays were successfully fabricated. It makes use of a new multiplex driving scheme that does not depend on voltage averaging. Instead, a transient response of the liquid crystal is employed. An addressing and response time of less than 70 μsec and 2.0 msec, respectively, are used. Scanning time compensation is also introduced to improve the brightness uniformity of the display.
The response time for 0 V ® 12 V switching is only 150 μsec. Furthermore, the no-bias free relaxing time τD is found to be less than 2 msec for any driving voltage. In other words, if the data voltage VD and scanning voltage VS can be selected according to this criteria, the LC cell can be addressed and totally relaxed within about 2 msec. A modified driving method is therefore proposed and is depicted in Fig. 2. The total pixel response time, τTOTAL, contains three time individuals: τ1, τ2 + τ3, and τ4. τ1 is the LC addressing time with the selection pulse VSEL = VS + VD.
FIGURE 2 — Waveform across a pixel and corresponding optical response of this pixel.
Abstract — Here, an electrophoretic liquid-crystal (EPLC) display, which employs a suspension of pigments with liquid crystals and exhibits switching with threshold and fast response, is presented, enabling video rate. The dielectric anisotropy of the LC medium, allowed by applying voltage switching between states with high and low dielectric permittivity, is responsible for this unusual electrophoretic switching.
FIGURE 1 — A schematic representation of an EPLC display with dyed liquid crystal and white pigments.
FIGURE 10 — Plastic version of 85-dpi 100 x 100 passive-matrix-addressed EPLC display with black dyed LC and white pigments, controlled by a 40-V electrical driver.
Industrial Technology Research Institute
Abstract — Based on the drop-on-demand characteristics of ink-jet printing, the multi-domain alignment liquid-crystal display (LCD) could be achieved by using patterned polyimide materials. These polyimide ink locations with different alignment procedures could be defined in a single pixel, depending on the designer's setting. In this paper, the electro-optical design, polyimide ink formulation, and ink-jetting technology was combined to demonstrate the application of multi-domain alignment liquid-crystal-display manufacturing. The first one was a multi-domain vertical-alignment LCD. After choosing the horizontal alignment material pattern on the vertical alignment film, the viewing angle reached 150° without compensation film. The second one was a single-cell-gap transflective LCD by integrating the horizontal alignment in the transmissive region and hybrid alignment in the reflective region in the same pixel. In addition, this transflective LCD was also demonstrated in the form of a 2.4-in. 170-ppi prototype.
The schematic cross section of the test cell is shown in Fig. 2. The LC molecules aligned vertically in the vertical alignment nematic (VAN) region. In the hybrid alignment nematic (HAN) region, the LC molecules oriented vertically on one side of the glass and horizontally on the other. While both the VAN and HAN liquid crystal exist in the same pixel, the LC molecules away from the alignment layers turn into random orientation.
FIGURE 2 —The schematic cross section of the test cell. The HAN mode is adapted by ink-jet technology.
Micro Analysis Lab
Abstract — Image-sticking phenomenon is one of the most important issues affecting LCDs, especially LCD TV. It is known that image sticking is caused by residual DC voltage. An analysis of the cause that induces image sticking on a real LCD cell is very difficult to perform and is rarely reported. In this paper, the impurities that cause boundary image sticking on a real MVA cell were analyzed by examining a cross section of a cell, the bulk LC layer, the vicinity of the LC layer, the LC layer/PI alignment film interface using microanalysis methods such as infrared micro-spectroscopy (μ-IR) and micro-sampling mass spectrometry (μ-MS). It is clarified that there is quite a bit of aromatic acid at the boundary of the image-sticking area than in the normal area at the LC/PI alignment film interface on the color-filter side, not the TFT side, and it is assumed that aromatic carboxylic acid, a negatively charged material, is condensed at the LC/PI alignment film interface on the color filter side by an electrically driven DC component inducing an electric-condenser residual DC voltage.
A sample normally black, MVA-mode active-matrix LCD, combined with a TFT array and color filter (CF), was tested. The cell was electrically driven with a 1-cm-wide stripe pattern for several hours under the usual electrical conditions, and it was observed to appear on an ~0.5-mm-wide gray line at the boundary area between the driven stripe and the non-driven area of a halftone mode, inducing boundary image sticking. After marking the gray-line area on glass, electrically driven shut down and quenching, the cell was cut off to analyze the gray-line area (boundary image-sticking area, abnormal) and undriven area (normal) for comparison.
FIGURE 20 — Schematic diagram of boundary image sticking (the residual DC voltage). Upper: model diagram. Lower: concentration diagram of impurities.
Changhun Chriss Hwang
OLEDON Co., Ltd.
Abstract — Whether or not the manufacturing of the large-sized OLED devices in display and lighting industry succeeds will strongly depend on the concept of a thermal evaporation source and the manufacturing tool. The most important factors in OLED-device manufacturing are the organic material utilization and the TACT time. An in-line tool for OLED manufacturing using a novel belt-source evaporation technique is proposed. The belt source maintains the organic film uniformity at 3% and provides high material utilization of over 80%, and the in-line system can achieve this in 1-min TACT time.
The belt-source evaporation technique has been developed as a new vacuum thermal evaporation as shown in Fig. 17. The organic molecules evaporating from the LPS sources are deposited on the lower area of the belt plate during motion. Once the deposition area of the belt arrives at the substrate position, the shutter closes the LPS sources so that organic gas is no longer emitted on metal plate. Then, the sheet heater provides radiation heating to the metal plate and the organic film preliminary deposited on the metal plate sublimates all the way down in a way of flashing evaporation, through a shadow mask to the substrate.
FIGURE 17 — Belt-source evaporation.
Ezekiel S. Bhasker
University of California
Abstract — Tiled displays provide high resolution and large scale simultaneously. Projectors can project on any available surface. Thus, it is possible to create a large high-resolution display by simply tiling multiple projectors on any available regular surface. The tremendous advancement in projection technology has made projectors portable and affordable. One can envision displays made of multiple such projectors that can be packed in one's car trunk, carried from one location to another, deployed at each location easily to create a seamless high-resolution display, and, finally, dismantled in minutes to be taken to the next location – essentially a pack-and-go display. Several challenges must be overcome in order to realize such pack-and-go displays. These include allowing for imperfect uncalibrated devices, uneven non-diffused display surfaces, and a layman user via complete automation in deployment that requires no user invention. The advances made in addressing these challenges for the most common case of planar display surfaces is described. First, a technique to allow imperfect projectors is presented. Next, a technique to allow a photometrically uncalibrated camera is presented. Finally, a novel distributed architecture that renders critical display capabilities such as self-calibration, scalability, and reconfigurability without any user intervention is discussed. These advances are important milestones towards the development of easy-to-use multi-projector displays that can be deployed anywhere and by anyone.
FIGURE 10 — Left: Initially, every display unit thinks that it is the only display unit present and is therefore solely responsible for displaying the whole image. Middle: After configuration identification, each display unit knows the display configuration – total number of projectors, and total display dimensions – and their own coordinates in the array. Thus, they know which parts of the display they are responsible for but still do not know the relative orientations of their neighbors. Thus, the image is not seamless. Right: after alignment, each display unit matches geometrically and photometrically with its neighbors to create a seamless display.
Abstract — An ink-jet-printing method applied to the microdeposition of high-viscosity resin, including optimization of phosphor dispersion for light-emitting-diode (LED) packaging was examined for the first time. An ultrasonic ink-jet-printing method was used, in which ink droplets are ejected by a focused ultrasonic beam from a nozzle-less printhead. To fabricate white LEDs, high-viscosity phosphor-dispersed resin was deposited to form an encapsulant dome. Two types of methods to control phosphor sedimentation for color uniformity were examined; one is heating the lead frame during the resin deposition, and the other is hydrophobic surface treatment of the lead frame base enabling the fabrication of a small encapsulant dome. For light direction control, a silicone microlens was deposited on an encapsulant dome using the ink-jet method. The results show that ultrasonic ink-jet printing is an applicable technique to optimize and modify on-demand optical characteristics of LED devices.
Figure 1 shows the fundamental principle of the ultrasonic ink-jet printhead where an ultrasonic beam generated by transducers is focused on the free liquid surface by an acoustic lens and a droplet is ejected. Ultrasonic ink-jet printing has the following advantages: (1) nozzle-less structure, which leads to less clogging and uniform droplet size with no tails; (2) a small restriction of ink properties, such as high viscosity and large-particle inclusion; (3) droplet size depends on an ultrasonic wavelength (the droplet diameter is approximately equal to the wavelength), that is, the size is controllable by transducer frequency; and (4) simple head structure, i.e., no need for a narrow ink path and chamber.
FIGURE 1 — Schematic of ultrasonic ink-jet printhead.
Abstract — As the panel size and the frame frequency of TFT-LCDs increases, driving issues become much more important for larger-sized and higher-resolution TFT-LCDs. In our previous paper, the pre-emphasis driving method was proposed to shorten the driving time of the data line with heavy loads of the large-sized TFT-LCDs. This paper proposes a simulation model based on the evaluation results of the developed pre-emphasis source driver, and the issues of driving the data line with heavy loads are reviewed. The single-, pre-emphasis, and dual-driving methods are compared in terms of their driving time and power consumption for large-sized TFT-LCDs with various resistances and capacitances of the data lines. At a panel load of 250-pF capacitance and 15-kΩ resistance in full-HD resolution, the pre-emphasis driving can reduce the pixel driving time to 66% with a 54% increase in the analog power consumption.
Figure 7 shows the optimized simulated waveform of pre-emphasis driving at the load condition of 350-pF capacitance and 20-kΩ resistance. There are six voltage waveforms that are the three points of data-line potential, and there are another three points of the pixel electrode potential of the near, central, and far-end nodes of the data line. The potentials of all the points of the data line are within the range of VNEAR and VFAR, and the pixel electrode potentials of all the pixels are within the range of VNEAR_PIXEL andVFAR_PIXEL.
FIGURE 7 — The simulated voltage waveforms of the pre-emphasis driving method at the data line resistance of 20 kΩ and the data line capacitance of 350 pF.
Richard I. McCartney
Abstract — As thin-film-transistor liquid-crystal-display (TFT-LCD) panels become larger and provide higher resolution, the propagation delay of the row and column lines, the voltage modulation of Vcom, and the response time of the liquid crystal affect the display images now more than in the past. It is more important to understand the electrical characteristics of TFT-LCD panels these days. There are several commercial products that simulate the electrical and optical performance of TFT-LCDs. Most of the simulators are made for panel designers. However, this research is for circuit, system, and panel designers. It is made in a SPICE and Cadence environment as a commercial circuit-design tool. For circuit and system designers, it will help to design the circuit around a new driving method. Also, it can be easily modified for every situation. It also gives panel designers design concepts. This paper describes the electrical model of a 15-in. XGA (1024 x 768) TFT-LCD panel. The parasitic resistance and capacitance of the panel are obtained by 3-D simulation of a subpixel. The accuracy of these data is verified by the measured values of an actual panel. The developed panel simulation platform, the equivalent circuit of a 15-in. XGA panel, is simulated by HSPICE. The results of simulation are compared with those of experiment, according to changing the width of theOE signal. The proposed simulation platform for modeling TFT-LCD panels can be especially applied to large-sized LCD TVs. It can help panel and circuit designers to verify their ideas without making actual panels and circuits.
LCD panels can be modeled by resistors and capacitors as shown in Fig.1.When row (gate) and column (data) line signals propagate through each line to the other side of panel, they are delayed by the resistance and capacitance in each line. Each row and column line should be together with the Vcom, common electrode. The Vcom is made of indium tin oxide (ITO). It is not a perfect conductor and has resistance. Therefore, the Vcom model should be made to consider voltage changes of neighboring pixels.
FIGURE 1 — The simplified TFT-LCD panel.