Effect of gas pressure on permanent dark image sticking on a bright screen in AC plasma‐display panels

Abstract— The permanent dark‐image‐sticking phenomenon on a bright screen was examined under various gas pressures in a 42‐in. ACPDP with an He(35%)‐Xe(11%)‐Ne gas composition. Infrared‐emission observations reveal that the discharge characteristics related to the MgO surface are almost the same in both the discharge and non‐discharge cells, whereas luminance observations show a deterioration in the visible‐conversion characteristics related to the phosphor layer in both the discharge and non‐discharge cells. Consequently, the permanent dark‐image‐sticking phenomenon on a bright screen is found to be strongly related to the deposition on the phosphor layer to the Mg species sputtered from the MgO surface due to a repetitive strong sustain discharge. For a decrease in gas pressure, the permanent dark image sticking on a bright screen became worse due to a severe degradation of the visible‐conversion characteristics of the phosphor layer caused by the deposition of higher amounts of sputtered Mg species on the phosphor layer, as confirmed by various measurements, such as V_t closed curves, time‐of‐flight secondary‐ion mass spectrometry, photoluminescence, and atomic‐force‐microscope analyses.     

How to reduce light leakage and clipping in local‐dimming liquid‐crystal displays

Abstract— In conventional LCDs, the backlight is set to maximum luminance regardless of the image. For dark scenes, this approach causes light leakage and power waste. Especially, light leakage in dark scenes degrades the contrast ratio of LCDs; to circumvent this problem, local‐dimming systems have been proposed. In these systems, the LED backlight is divided into several local blocks and the backlight luminance of each local block is controlled individually, and pixel values are adjusted simultaneously according to the luminance profile of the dimmed backlight. In this paper, a method of determining the LED backlight luminance of each local block depending on the image is proposed; this method significantly improves the image quality of LCDs. First, we introduce methods of quantifying light‐leakage at dark gray levels and clipping at bright gray levels. Then, the proposed method to determine the dimming duty, which controls the LED backlight luminance by compromising between these two measures, was derived. The proposed algorithm preserves the original image with little clipping distortion and effectively reduces light leakage.     

Influence of sustaining frequency on the production efficiency of excited Xe atoms studied in unit cell microplasma for ACPDPs using spectroscopic diagnostics

Abstract— The effects of the driving frequency of the sustaining‐voltage pulses on microplasmas in a cell of an ac plasma‐display panel (ACPDP) were investigated using spectroscopic diagnostics [optical emission spectroscopy (OES) and laser‐absorption spectroscopy (LAS)]. The unit discharge cell has a structure similar to that of a general commercial ACPDP, but it is prepared for three‐dimensional (3‐D) observation using a pair of micro‐prisms. When the near‐IR emission by OES and the absorption signal by LAS were observed in the front and side views simultaneously, it was determined that the discharge was concentrated at the center of the discharge space and quickly responded to an applied electrical potential as the sustaining frequency increases. The production efficiency of excited Xe**(2p) atoms and vacuum‐ultraviolet (VUV) photons, which was estimated from the spectroscopy results with the measured power dissipated in the discharges, increased as the frequency of the sustain pulses increases to 100 kHz. At 250 kHz, however, the efficiency remarkably decreased because of an inefficient time for excimer formation and, possibly, for wall‐charge formation. From the quantitative analysis of the efficiency, the most‐efficient frequency for the sustain voltage was around 100 kHz in the case of Xe(5%)‐Ne at 500 Torr, i.e., the efficiency depended on both the priming particles [excited Xe*(1s⁵) atoms] in space and the charged particles on the dielectrics.     

Recent research and development on 71‐in.‐diagonal color PDPs

Abstract— The World's first 71‐ and 76‐in.‐diagonal ACPDPs with full high‐definition resolution (1920 × 1080), a high luminance of 800 cd/m², and a dark‐room contrast ratio of 1200:1 have been developed using a highly efficient barrier‐rib structure. Also a new MgO protective layer and a film‐type optical filter were developed to improve picture quality. To fabricate large‐sized panels over 70 in. on the diagonal, an improved uniform exposing technology for the patterning of electrodes, a green sheet method for the transparent dielectric layer, and a co‐processed bus and black‐matrix (CPBB) method were used.     

Inorganic EL devices with high‐performance blue phosphor and application to 34‐in. flat‐panel televisions

Abstract— A high‐performance inorganic electroluminescence (EL) device has been successfully developed by using an EL structure with a thick dielectric layer (TDEL) and sputtered BaAl₂S₄:Eu blue phosphor. The luminance and efficacy were higher than 2300 cd/m² and 2.5 lm/W at L⁶⁰, 120 Hz, respectively. Furthermore, the luminance at L⁶⁰, 1.2 kHz was more than 23,000 cd/m². The phosphor layer has a single‐phase and a highly oriented crystalline structure. The phosphor also shows high stability in air. A 34‐in. high‐definition television (HDTV) has been developed by combining a TDEL structure and color‐conversion materials. The panels with an optimized color filter demonstrated a peak luminance of 350 cd/m², a color gamut of more than 100% NTSC, and a wide viewing angle similar to that of plasma‐display panels. The high reproducibility of the 34‐in. panels using our pilot line has been confirmed.     

Improvement in image quality of a 5.8‐in. OTFT‐driven flexible AMOLED display

Abstract— The image quality of an OTFT‐driven flexible AMOLED display has been improved by enhancing the performance of OTFTs and OLEDs. To reduce the operating voltage of OTFTs on a plastic film, Ta²O⁵ with a high dielectric constant was used as a gate insulator. The organic semiconductor layer of the OTFT was successfully patterned by a polymer separator, which is an isolating wall structure using an organic material. The OTFT performance, such as its current on/off ratio, carrier mobility, and spatial uniformity on the backplane, was enhanced. A highly efficient phosphorescent OLED was used as a light‐emission device. A very thin molybdenum oxide film was introduced as a carrier‐injection layer on a pixel electrode to reduce the operating voltage of the OLED. After an OTFT‐driven flexible AMOLED display was fabricated, the luminance and uniformity on the display was improved. The fabricated display also showed clear moving images, even when it was bent at a low operating voltage.     

Development of a new blue CaMgSi2O6:Eu2+ phosphor for PDPs

Abstract— A blue‐light‐emitting Eu²⁺‐doped CaMgSi₂O₆ phosphor having a long lifetime for a plasma‐display panel (PDP) was developed. The CaMgSi₂O₆:Eu²⁺(CMS:Eu) phosphors show no luminance degradation during the baking process, and an equivalent photoluminescence peak intensity compared to that of the conventional blue‐phosphor BaMgAl₁₀O₁₇:Eu²⁺ (BAM) after baking. CMS: Eu shows a poor luminescent characteristic for the Xe excimer band excitation due to the lack of absorption. To introduce the absorption center for the Xe excimer band, we performed Gd‐codoping of CMS: Eu as a sensitizer and found a new excitation band around 172 nm, which originated from Gd³⁺. The test PDPs panels using synthesized CMS: Eu phosphor and CMS: Eu, Gd phosphor were examined to investigate the luminescent and aging characteristics of a Xe‐discharge excitation source. The CMS: Eu panel shows an emission peak intensity comparable to that of the BAM panel (i.e., a comparable stimuli L/CIEy, 93% of BAM), while the CMS: Eu, Gd panel shows poorer blue emission intensity compared to the BAM panel (up to 53% of total stimuli of BAM). The CMS: Eu panel and the CMS: Eu, Gd panel show less luminance degradation than the BAM panel under the aging test, and the panel retains 90% of its luminance after 300 hours of driving. It was found that CMS: Eu appears to be a candidate for a new blue PDP phosphor because of its longevity in a Xe‐discharge plasma environment.     

高动态范围图像梯度压缩算法

高动态范围（HDR）图像是一种可以表示实际场景中亮度大范围变化的图像类型,图像中的像素值正比于场景中对应点的实际亮度值,因此,可以更好地表示场景中亮区和暗区的光学特性。为了在常规显示硬件上显示HDR图像,采用梯度压缩算法,在亮度图像梯度域上对大梯度进行衰减,压缩图像亮度的动态范围。实验结果表明,该算法能对HDR图像进行较高视觉质量的显示。     

Implications of microcavity plasma devices for new plasma‐display‐panel cell structures with improved luminosity

Abstract— The unique properties of microcavity plasma devices, and their potential to provide the basis for alternative PDP cell structures of improved luminosity, are described. Arrays as large as 500 × 500 (250,000) inverted pyramid microcavity devices, each with an emitting aperture of 50 × 50 μm² and designed for AC or bipolar excitation, have been fabricated in Si and operated in the rare gases and Ar/N₂ mixtures at pressures up to and beyond 1 atm. For a device pitch of 100 μm, the array filling factor is 25% and the device packing density is 10⁴ cm^?2. Measurements of the unoptimized radiant output of 500 × 500 arrays of Si microplasma devices, operating in Ne/(5–50)% Xe mixtures and photoexciting (in transmission mode) a 20‐μm‐thick film of green phosphor, yield values of the luminous efficacy up to 7.2 ± 0.6 lm/W for a Ne/50% Xe mixture (total pressure of 800 Torr) excited by a 20‐kHz sinusoidal voltage waveform. Sustaining voltages ranging from ～250 to 340 V (RMS) yield luminance values up to ～2000 cd/m² for Ne/50% Xe mixtures but the incorporation of field emitters or MgO into the microcavity is expected to significantly reduce the required operating voltage. Also, the fabrication of microplasma devices in ceramic multilayer structures or glass for scaling the display area is discussed briefly. Recent laser spectroscopic measurements of Xe(a ³Σ_u⁺) absorption in the visible and near‐infrared suggest steps to be taken in PDP cell design, particularly as the Xe content in Ne/Xe mixtures is increased.     

Electron‐beam deposition of MgO on plastic substrate and manufacturing flexible flat fluorescent lamp

Abstract— A flexible fluorescent lamp that utilizes the same plasma discharge mode as in PDPs has been manufactured. The structure of the flexible lamp is simple and easy to manufacture. All‐plastic materials including plastic substrates, barrier ribs (spacers), and sealants for low‐temperature manufacturing processing have been adopted except for the phosphor and MgO thin film. The MgO thin films were coated on the plastic substrates as a protection layer against the plasma discharge. The adhesion and biaxial texture of MgO thin film deposited on the plastic substrates, poly‐ethyle‐nenaphthalate (PEN) and polycarbonate (PC), at low temperature (100–180°C) has been characterized. The MgO film on PEN shows good adhesion under a repeated bending test. The manufactured flexible lamp consists of two plastic substrates of about 3 in. on the diagonal, barrier rib (spacer), and external ITO electrodes. The Ne‐Xe (5%) gas mixture at 100–200 Torr was used for the discharge gas. A maximum surface luminance of about 100 cd/m² was achieved for a 1 ‐kHz AC pulse.     

Performance of the efficacy enhancement layer using nano‐particles in PDPs

Abstract— A nano‐particle dielectric layer was experimentally placed between a conventional dielectric layer and a MgO thin film. This greatly reduces the discharge current and enhances high luminous efficacy. The current reduction might reflect a capacitance reduction in the entire dielectric layer due to the extremely low permittivity of the nano‐particle layer which includes a large amount of space. The luminous efficacy is improved more than what is expected because of the reduction in capacitance. The layer affects the MgO film properties such as crystal growth size, orientation, cathode luminescence, and exo‐electron emission. As a result, it improves the statistical delay in addressing. This might be caused by the large crystal growth of MgO due to the surface roughness of the nano‐particle layer underneath. The particle size required to optimize the roughness of the large growth is about 10–50 nm. The rise in the discharge voltage accompanied by the nano‐particle layer insertion is improved when the layer is properly patterned. A reduction in luminance is prevented when it is patterned in narrow lines along the X—Y gaps while the improvement in address delay strongly depends on the areal ratio of the nano‐particle layer.     

Relationship between exo‐electron currents from MgO thin film and statistical delay time in ACPDPs

Abstract— The exo‐electron currents from a ACPDP test panel with or without MgO crystals sprayed on MgO film were measured directly after eliminating of the wall‐voltage effect. An inverse relationship was established between the statistical delay time and exo‐electron currentfrom the MgO cathode film. The spraying of MgO crystals on MgO thin film was observed to reduce the statistical delay time dramatically even for the same exo‐electron currents measured. The shift of the inverse curve may be attributed to an increased discharge success probability by the MgO crystals sprayed.     

Quantitative evaluation of image sticking on displays with different gradual luminous variation

Abstract— To comparatively evaluate various driving methods of an electronic display in respect to image sticking, a consistent and reliable quantification method is required. For proper evaluation, the entire area of a display is often monitored by using a chessboard pattern, and long‐range gradual luminous variation in the background is eliminated. Estimation in terms of a single number is also preferred for simple comparison of image sticking. However, the prior method that uses the initial luminance for normalization and estimates the range‐to‐maximum ratio is not well‐suited for the driving methods that relieve image sticking by restoring luminance uniformity. We have developed a method of extracting reference values for normalization and introduced the relative standard deviation (RSD) into our estimation. The resulting method is insensitive to the temporal change in the long‐range gradual luminous variation and sufficiently indicative to allow driving methods to be compared effectively. The reference extraction method and the indicative capability of the RSD have been assessed by experiments using a real active‐matrix organic light‐emitting‐diode (AMOLED) display cell.     

Moving‐image‐sticking phenomenon induced by an outside force in liquid‐crystal displays

Abstract— Image deformation caused by an outside force is observed to remain for hours at high gray levels for liquid‐crystal displays (LCDs) in the multi‐domain (MD) vertical‐alignment (VA) mode. This so‐called moving‐image‐sticking phenomenon demonstrated a non‐symmetric luminance profile for the left and right viewing direction for MDVA‐mode LCDs which have original symmetric viewing‐angle characteristics. The generation of a stable reverse‐tilt domain by an outside force was assumed to be the cause of this phenomenon, and the stability of a reverse‐tilt domain under an electric fringe field was calculated by changing the electric‐fringe‐field distribution which determines the LC tilt direction. The domain of a given tilt direction is calculated to change to other tilt direction induced by a fringe field at a low gray condition, but to remain unchanged at a high gray condition. This agrees with the observed trends of duration time of the moving‐image‐sticking phenomenon.     

A MgF2/MgO multiple protecting layer in ac plasma‐display panels

Abstract— A MgF²/MgO multiple protecting layer coated on a MgO layer in ac plasma‐display panels (AC‐PDPs) was developed to obtain high brightness and low driving voltages. The material characteristics of this layer were examined by carefully changing the deposition conditions, and the display characteristics of AC‐PDPs using this protecting layer were studied. It was demonstrated that this new method is effective in lowering the firing and sustaining voltages of PDPs and enhancing the brightness of the panel as well.     

Improved discharge characteristics using MgO single‐crystal particles and advanced CEL structure

Abstract— Pioneer Corporation introduced plasma‐display‐panel (PDP) TVs in 2005, which achieved the highest dark‐room contrast ratio of 4000:1 at the time. These PDPs had a novel discharge cell structure consisting of a crystal emissive layer (CEL) on a MgO protective thin film. This cell structure is refered to as a CEL structure. Magnesium‐oxide single‐crystal particles, which have a unique luminance peak around 230–250 nm and a good exo‐electron‐emission property, were found to be an excellent material for CEL and were utilized in CEL panels. In 2007, newly developed PDP TVs in which CEL was formed on a phosphor layer, in addition to the previous CEL structure, were introduced, and this discharge cell structure is refered to as advanced CEL structure. By using the new cell structure, the opposed discharge characteristics have been drastically improved, and a stable reset discharge has been realized with only a weak opposed discharge. As a result, black luminance has been drastically reduced, and a dark‐room contrast ratio of over 20,000:1, the highest ever reported, has been achieved.     

Properties and cathodoluminescence of Y2O2S:Eu thin films

Abstract— Europium‐activated yttrium oxysulfide thin films were fabricated by electron‐beam deposition of Y₂O₂S:Eu with consequent annealing in an H₂S/Ar gas mixture. Transformations in film composition and surface morphology as well as corresponding changes in the optical, photoluminescent, and cathodoluminescent properties were studied and will be discussed. It is shown that 248‐nm laser irradiation of heat‐treated films improves cathodoluminescence by as much as 30%, supposedly due to annealing. The developed phosphor films have a luminance comparable to that of annealed europium‐activated yttrium oxide films and improved color properties (CIE color coordinates: x = 0.624, y = 0.329), and are suitable for display and optoelectronics applications.     

OLED‐based pico‐projection system

Abstract— Two pico‐projection systems, a monochrome green and a full‐color system, based on high‐efficiency OLED microdisplays (VGA; pixel size, 12 μm) are presented. Both optical systems are described by a numerical aperture of about 0.3, a magnification of 15x, and a working distance of 300–360 mm. The frequency limit of both systems is 42 cycles/mm at an image contrast of about 60%. The monochrome projection system with a volume smaller than 10 cm³ consists of one green OLED and a projection lens with five elements. The measured luminance in the image plane is about 0.061 lm. The image has a diagonal of 150 mm with a working distance of about 300 mm and has a considerable image contrast of 396:1. The second system combines three high‐brightness OLEDs, red, green, and blue colored, together with a projection lens and an image‐combining element, and an X‐Cube to achieve full‐color projection. The estimated luminance value for the three‐panel projection unit with an OLED luminance of 10,000 cd/m² for each display will be about Φcalculated = 0.147 lm. In this paper, the system concepts, the optical designs, and the realized prototypes of the monochrome and full‐color projection system are presented.     

Towards a generic OLED lifetime model

Abstract— The limitations of t^1/2 lifetime testing for OLED displays are discussed in the context of permanent and recoverable luminance decay. Different pixel drive schemes, operating temperature, and schemes of gray‐level generation are all found to be important in determining the operational lifetime where both permanent and recoverable contributions to the luminance decay exist. In addition, the importance of assessing lifetime with respect to a particular usage model is introduced and a method of lifetime characterization is devised to account for all of the factors discussed. The method measures luminance degradation over a series of operating cycles where the stress factors on the display are randomly generated for each cycle. The luminance degradation is then analyzed with linear regression, and the regression fit coefficients give an understanding of the degradation in different usage models so that an assessment of the display's suitability for a particular application can be made.     

High‐contrast driving method for advanced CEL structure with magnesium oxide single‐crystal powder in ACPDP

Abstract— A new driving method for an advanced‐CEL‐structure panel has been developed. Picture qualities have been upgraded. Discharge time lags are drastically shortened by priming electron emission from magnesium oxide (MgO) single‐crystal powder, refered to as a crystal emissive layer (CEL). The advanced‐CEL‐structure panel has CEL material on the surface of not only the surface‐discharge‐electrode side but also on the address‐electrode side. This panel structure enables a stable opposed discharge when the address electrode functions as a cathode. By utilizing the opposed discharges in the reset and LSB‐SF sustain periods, the dark‐room contrast ratio has been drastically increased to over 20,000:1, which is higher than five times that of the conventional method, and the luminance of the least‐significant‐bit sub‐field (LSB‐SF) is as low as 0.1 cd/m², which is one‐fourth that of the conventional method. The high‐picture‐quality PDP TVs refered to as “KURO” that employs these technologies have been introduced into the marketplace.