Discharge diagnosis of high Xe concentration and high‐γ protective layer in PDPs

Abstract— The high‐Xe‐concentration and high‐γ (ion‐induced secondary‐electron emission coefficient) protective layer have been diagnosed from both experimentation and simulation. The experimental results show that there is a great increase in luminance and luminous efficacy, while the breakdown voltage decreases in the high‐Xe and high‐γ discharge. In the high‐Xe discharge, the great increase in VUV radiation mainly results from an increase in excimer VUV emission. The application of high‐Xe concentration can greatly increase the luminous efficacy, while the high‐γ protective layer can promote it further. Considering that the total discharge efficiency can be divided into the electron heating efficiency, the Xe excitation efficiency, and the VUV radiation efficiency, both the electron heating efficiency and Xe excitation efficiency increased for a high‐Xe discharge; while for a high‐γ discharge, the increase in electron heating efficiency contributes to the improvement in discharge efficiency.     

Protective layer for high‐efficiency PDPs driven at low voltage

Abstract— The sustain pulse voltage of a panel for 66‐kPa Ne + Xe (5–30%) with an (SrCa)O protective layer is 20–40% lower than that with an MgO protective layer. The luminous efficiency of the panel with a Ne + Xe (30%) (SrCa)O protective layer is 1.5 times that of the conventional panel with a Ne + Xe (10%) MgO protective layer; the sustain pulse voltages of these panels are almost the same. The power loss caused by panel capacitance is proportional to the second power of the sustain pulse voltage. Using the (SrCa)O protective layer for Xe (5–30%), the power loss is reduced by 35–60% compared with the MgO protective layer. It follows that, using the (SrCa)O protective layer, we can increase the Xe content with little power loss and thus achieve high‐efficiency PDPs. As for MgO and CaO with Xe ions, electrons are probably ejected from only the defect states. On the other hand, as for the SrO with Xe ions, it is likely that electrons can be ejected from not only defect states but also the valance band. This seems to be the reason why the driving voltage is lower with the (SrCa)O protective layer than with the MgO protective layer.     

Characterization of micro‐cell discharge in AC‐PDPs by spatio‐temporal optical emission spectroscopy

Abstract— We have developed highly resolved spatio‐temporal optical emission spectroscopy to investigate the discharge characteristics of coplanar type ac plasma‐display panels (AC‐PDPs). Spatio‐temporal emission profiles were measured for relevant lines of atomic He, Ne, Xe, and ionic Xe in He‐Xe and Ne‐Xe systems with various Xe concentrations and total gas pressures. The surface‐discharge behavior in coplanar PDPs has been clarified.     

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.     

Discharge characteristics and low‐voltage driving of high‐Xe‐content PDPs

Abstract— High‐Xe‐content PDPs attain improved luminous efficiency, but with sacrifices of higher sustain and address voltages and slower discharge build‐up. By examining PDPs with 3.5–100% Xe contents, it was revealed that space‐charge priming as well as wall‐charge accumulation are effective in obtaining low‐voltage and high‐speed operation. In addition, it was found that the effectiveness is emphasized for higher‐Xe‐pressure PDPs. In this respect, erase addressing is more favorable than write addressing, especially for high‐Xe‐pressure PDPs. The formative time lag of the discharge and diffusion/drift of the space charges are shorter for high Xe contents. In this respect, high‐Xe‐content PDPs have a potential for high‐speed addressing, if driven adequately. The use of space‐charge priming, however, is limited by the duration between the priming and scan pulses. Accumulation of wall charges is limited by ignition of a self‐erase discharge with which all the wall charges are dissipated. Although the highest efficiency and luminance are attained with a 100%‐Xe panel, the optimum Xe gas content, considering the sustain pulse voltage and drive voltage margin, would be 70% Xe + Ne.     

Discharge analysis of high‐efficacy PDP with a luminous efficacy of 5 lm/W

Abstract— The discharge mechanism concerning the width of the display electrodes in high‐Xe‐content gas mixtures to improve the luminous efficacy of PDPs has been researched. It was found that a luminous efficacy of 5 lm/W was realized for a high‐Xe‐content gas mixture and narrower display electrodes. For a high‐Xe‐content gas mixture, the luminous efficacy increases as the display electrode becomes narrower. This phenomenon was analyzed by observing the emission from a discharge cell. The observation data indicate that a high electron heating efficiency contributes to increased luminous efficacy along with narrow electrodes for a high‐Xe‐content gas mixture as well as high excitation efficiency.     

Influence of He‐Ne‐Xe gas composition on vacuum ultraviolet ray spectra in plasma‐display panels

The vacuum ultraviolet (VUV) ray emission characteristics for plasma‐display panels (PDPs) were studied with respect to various three‐component (He‐Ne‐Xe) and two‐component (He‐Xe and Ne‐Xe) gas systems. In the 4% Xe‐25% Ne‐He balance and 4% Xe‐He balance, an increase in the pressure contributed to an increase in the 147‐nm atomic emission, and above a certain point this decreased, while in the 4% Xe‐Ne balance it was saturated. The 172‐nm dimer emission showed a nearly linear increasing behavior with pressure and Xe content irrespective of its composition. In the various Xe with 25% Ne‐He balance gases, it was shown that total integrated VUV intensity can directly represent the luminance of real panels with the same gas compositions. Xe‐content variation showed similar characteristics of VUV emission as pressure variation both in two‐component (various Xe‐Ne balance) and three‐component (various Xe‐25% Ne‐He balance) systems. Therefore, different compositions with the same Xe partial pressure showed nearly the same optical properties. For the case of Ne content variation with 4% Xe, the 147‐nm peak increased and the 172‐nm peak decreased to 85% Ne, but above this point both intensities decreased.     

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.     

Dependency of PDP efficacy on gas pressure

The dependency of the efficacy of an alternating‐current surface‐discharge plasma‐display panel (PDP) on the gas pressure was investigated for several Xe‐Ne gas mixtures. Also, the sustain voltage was varied. Monochrome 4‐in. test panels, with a design which resembles the one used in mainstream commercial products, were used. The experimental panel efficacy and emission characteristics were compared to the results of a numerical discharge model. A strong increase in the efficacy for increasing voltage was found in high‐gas‐pressure mixtures with a high Xe concentration. An increase in the electron‐heating efficiency and of the Xe‐excitation efficiency contribute, about equally, to the increase in efficacy. The increase in the Xe‐excitation efficiency is due to an increase in the excitation in the lower Xe levels induced by a lowering of the electron temperature. The contribution of the increasing Xe‐dimer radiation fraction to the efficacy improvement is relatively small. These results imply an efficient panel design comprised of the combination of a high Xe concentration, a high gas pressure, and a high sustain voltage. A high luminance and a high efficacy are concurrent for such a design. A 4‐in. test panel containing a mixture of 13.5% Xe in Ne at 800 hPa has been realized, demonstrating a white luminance of 2600 cd/m² and an efficacy of 3.1 lm/Wfor continuous operation at 50 kHz and 230 V.     

Cathode‐luminescence diagnostics of MgO,MgO:Si,MgO:Sc,and MgCaO

Abstract— The cathode‐luminescence (CL) emission of crystalline MgO, MgO:Si, MgO:Sc, and MgCaO, often used as a protective‐layer material in PDPs, were measured. In some of these materials, it was found that the UV emission band is located at a shorter wavelength than published in the literature and depends upon the type of impurities or doping. MgCaO‐pellet material is found to contain a separate CaO phase. It is concluded that the recombination mechanism is thermally assisted in most of these materials, while only in the case of MgO:Sc tunneling recombination was found.     

Surface characterization of MgO:Al,N films with meta‐stable de‐excitation spectroscopy and x‐ray photoelectron spectroscopy

Abstract— It is shown that meta‐stable de‐excitation spectroscopy (MDS) is one of the most useful characterization methods to analyze the interaction between the discharge gas and the surface of the material and is applied to MgO:Al,N films. From the results of the measurement and analysis of helium MDS and the in‐situ discharge experiment, it is confirmed that the limited composition films of MgO:Al,N have potentially a larger secondary‐electron‐emission coefficient (γ) compared with that of MgO. The improvement in γ is caused by the electron‐occupied tailing state at around the top of the valence band which is generated by the introduction of Al,N to MgO films. Also, the O1s spectra measured by x‐ray photoelectron spectroscopy (XPS) shows that the stable surfaces are formed with the introduction of Al,N to MgO films.     

Radio‐frequency plasma‐display cell

Abstract— This paper demonstrates that it is possible to improve the basic parameters of plasma displays (efficiency, primarily) using AC voltages with frequencies so high that the amplitude of the electron‐drift oscillations is smaller than the inter‐electrode gap. In this case, the voltage drop on sheaths is much smaller than that in the low frequency or DC discharge and, correspondingly, the energy losses in ion heating are also small. Electron losses in the RF discharge are of the diffusion character and sufficiently lower than the losses in a typical AC plasma‐display panel (AC PDP), in which the electron drift to the electrodes is predominant. Hence, the energy cost of gas ionization in the cells of radio‐frequency PDPs (RF PDPs) is also rather low. In the long run, about 80% of the energy absorbed in the RF discharge goes into excitation of the energy level of a Xe atom, yielding UV radiation. The experiments performed show that efficiency of a RF PDP is five times higher than the efficiency of existing AC PDPs and DC PDPs and can exceed 5 lm/W.     

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.     

Application of AC plasma display panels to radiation detectors

Radiation detector proposals that use plasma display panels are rare. In this work, we confirmed a radiation detector that uses plasma display panels that are focused on the breakdown voltage shift in the ramp waveform. We adapted the cell structures, gas contents, and waveforms of plasma display panels (AC‐PDPs) for radiation detectors. Hard X‐rays and gamma rays induce electron emission into the discharge gas, resulting in generating electrons, electron multiplication, and charge accumulation on dielectrics. The radiation dose rate of hard X‐rays and gamma rays (Cs137) is measured as a breakdown voltage shift between anodes and cathodes. For gamma rays, the detection sensitivity in this experiment is not as high as in the case of hard X‐rays, but the detector can locate gamma rays. These results suggest that adapted AC‐PDPs can detect both hard X‐rays and gamma rays and can be used in a large two‐dimensional radiation detector.     

Front address structure for high luminous efficacy and low address voltage in ACPDPs

Abstract— 8‐in. AC plasma display panels with front address (FA) structures were developed. Deep barrier ribs, high‐Xe‐content gas, and long sustain gaps were applied to FA structures to achieve high luminous efficacy. The FA structures have several advantages over conventional structures. Because address electrodes are closer to sustain electrodes, FA PDPs can be driven at lower address voltages, under the condition of deep barrier ribs or high‐Xe‐content gas, than conventional PDPs. A disadvantage of FA PDPs is relatively high capacitance between the sustain electrodes and address electrodes compared to that of conventional PDPs.     

Studies on a LaF3‐coated MgO protecting layer in AC‐plasma‐display panels

A new protecting layer, a LaF₃‐coated MgO layer, in color AC‐plasma‐display panels (PDPs) was studied in order to overcome the weakness of the conventional single MgO protecting layer. The material characteristics of the new layer were examined by using variations in the deposition process. The display characteristics were also examined by implementing their processes to actual PDPs. It was demonstrated that this method is effective in lowering the firing and sustaining voltages of PDPs and enhancing the brightness of the panel as well.     

High‐speed low‐voltage driving of high‐Xe‐content PDPs with priming particles

Abstract— Power savings, image‐quality improvement, and cost reduction are the major issues facing PDP development. High‐Xe‐content PDPs have attained improved luminous efficiency, but with sacrifices in higher switching and sustain voltages and slower discharge build‐up. By examining PDPs having 3.5%–30% Xe content, it was found that utilization of the space‐charge priming effect as well as wall‐charge accumulation are effective in obtaining a low operating voltage and a high switching speed. The improvements are enhanced for higher Xe pressures. By using space‐charge priming, the statistical time lag of the discharge triggering for the 30% Xe content is reduced significantly and becomes approximately equal to that of 3.5% Xe content. Once triggered, the formative time lag of the discharge becomes shorter and the space charge experiences diffusion/drift; hence, accumulation of the wall charge is faster for discharges with higher Xe contents. These indicate that the use of an erase addressing scheme, rather than a write addressing scheme, is preferable when driving high Xe‐content PDPs, because the erase addressing scheme provides the addressing operation with an abundant amount of priming particles. Also, the drive voltages are lower for the erase addressing scheme. In order to reduce the address voltage, it is effective to accumulate wall charges prior to addressing. It was found that there are limiting values for the charge accumulation, above which self‐erase discharges ignite and the wall charge is dissipated. The self‐erase discharge occurs at relatively low wall voltages when the Xe percentages becomes higher. The sustain pulse voltage can be reduced while keeping the luminous efficiency high by increasing the sustain pulse frequency. As the frequency is increased, a residual amount of space charge created by the preceding sustain pulse increases. Due to the priming effect of these space charge, the build‐up of the discharge current becomes faster, resulting in a lower voltage.     

High‐efficacy plasma‐display designs achieving 5 lm/W

Abstract— Under high‐Xe‐content conditions, the luminous characteristics were evaluated for the sustaining electrode width and the sustaining pulse cycle. It was recognized that the proper designs for them in a high‐Xe‐content gas mixture make it possible to obtain high luminous efficacy. In this research, it was found that narrower electrodes can gain higher luminous efficacy in high‐Xe‐content conditions. The dependency of the luminous characteristics on the electrode width was analyzed and the differences of discharge phenomena from low‐Xe‐content conditions, which explain the dependency on the electrode width, were recognized. In an 8‐in. test panel, 5.2 lm/W of the maximum white efficacy was obtained. The found phenomenon that narrower electrodes are more advantageous for the luminous efficacy is favorable in high‐definition PDPs.     

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.     

Time‐averaged spatial profile of Xe excitation efficiency in PDPs

Abstract— The Xe excitation efficiency for various Xe content was analyzed by monitoring the panel luminance and IR emission intensity. It was found that dependences of the Xe excitation efficiency and luminous efficacy on the sustain voltage show almost the same tendency. A decrease for increasing sustaining voltage was found in a low‐Xe‐content panel and an increase was found in a high‐Xe‐content panel. A reduction in the effective electron temperature and a reduction in plasma saturation contribute to the efficacy improvement. The time‐averaged spatial profile of the Xe excitation efficiency in PDPs was investigated by measuring the distribution of IR and blue‐phosphor emissions. The results show that the Xe excitation efficiency is similar in the cathode and anode regions even though the spatial and time development of the discharge in these regions is very different. An extended theory that takes into account not only the radiative transition process but also the collisional de‐excitation process from Xe** to Xe* is proposed for investigating the pressure dependence of the Xe excitation efficiency. By using the proposed theory, it was found that Xe excitation efficiency increases, attains a maximum value at 30% Xe, then decreases as the Xe content is increased, when the rate coefficient of the collisional de‐excitation process is less than 1.0 × 10^?10 cm³/sec.