Improvement of luminance and luminous efficacy in PDPs

Abstract— The dependence of PDP luminance and efficacy on the input power was investigated for several Xe‐Ne gas mixtures. The input power was varied in two ways: namely, by changing the dielectric‐layer capacitance (thickness) and by changing the sustain voltage. A distinctly different behavior was found; for increasing capacitance the efficacy decreases markedly, whereas for increasing sustain voltage the efficacy increases. A design window comprising the combination of a high Xe concentration and a high sustain voltage was suggested. In this window, a high luminance and a high efficacy are concurrent. A 4‐in. test panel with 10% Xe in Ne has been realized showing a white luminance of 2040 cd/m² and an efficacy of 2.3 lm/W for continuous sustaining at 50 kHz with a sustain voltage of 225 V.     

High‐efficiency PDP micro‐discharges

Abstract— High‐efficiency plasma‐display‐panel micro‐discharge characteristics will be discussed. An increase in the discharge efficiency for a higher‐Xe‐content gas mixture is well known. In this article, the interdependency of the capacitive design, the sustain voltage, and the Xe content will be discussed. A high panel efficacy was obtained, especially for the design and driving conditions that govern the development of a fast discharge. A fast discharge was observed for a higher discharge field at sustain voltages higher than 200 V. A +C‐buffer design, where the extra capacitance acts as a local on the panel power source that lowers the voltage decrease inherent to the discharge of the discharge capacitance upon firing, and efficient priming of the discharge at higher sustain frequency, also stimulates a fast‐discharge development. Apparently, a “high‐efficiency fast‐discharge mode” exists. It is proposed that in this mode the cathode sheath is not, or incompletely, formed during the increase in the discharge current, and the electric field in the discharge cell is dominated not by the space charges but by the externally applied voltage. The effective discharge field is lowered, resulting in a lower effective electron temperature and more efficient Xe excitation. Also, under a fast discharge build‐up condition, the electron‐heating efficiency increases, due to a decrease in the ion heating losses in the cathode sheath. In a 4‐in. color plasma‐display test panel, operating in a high‐efficiency discharge mode and containing a 50%Xe in Ne gas mixture, a panel efficacy of 5 lm/W concurrent with a luminance of 5000 cd/m² was realized. This result was obtained at a sustain voltage of 260 V. These data compare favorably with alternative high‐efficacy panel design approaches.     

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.     

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.     

Characteristics of a high‐Xe‐concentration 4‐in. PDP

The performance of two 4‐in. color PDP test panels with a default and a high‐Xe‐concentration gas mixture will be discussed. The default panel with a gas mixture of 3.5% Xe in Ne and a filling pressure of 665 hPa was compared with a panel containing a gas mixture of 13.5% Xe in Ne and a filling pressure of 800 hPa. The panels contain a green phosphor, YBO₃:Tb, which showed less saturation at high UV load compared with a Willemite phosphor. The panel performance was compared in addressed conditions. For the default panel, a white luminance of 710 cd/m² and an efficacy of 1.6 lm/W was found, while for the high‐Xe‐partial‐pressure panel, a white luminance of 2010 cd/m² and an efficacy of 3.8 lm/W was realized. The increase of the driving voltages, about 20–30 V, is moderate. Finally, color saturation is improved at high Xe partial pressure.     

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.     

High‐efficacy drive of spatial positive‐column‐discharge PDP with delayed D pulses

Abstract— A thick‐film ceramic‐sheet PDP provides a long sustain discharge gap of 0.45 mm, enabling the use of positive column discharges. The discharges are established in the middle of the discharge space and are completely free from touching the surface of substrates. This allows for the reduction in diffusion losses of the charged particles. To further improve the efficacy, delayed D pulses are applied to the address electrodes during the sustain period. Although the pulses only draw a little current, they perturb the electric field, reducing the peak discharge current and hence resulting in higher efficacy and luminance. The efficacy and luminance increase by 35% and 38%, respectively, with the delayed D pulses. These pulses are incorporated into the contiguous‐subfield erase‐addressing drive scheme for TV application. A short gap of 70 μm between the sustain and data electrodes generates a fast‐rising discharge and allows a high‐speed addressing of 0.25 μsec. This provides 18 contiguous subfields for the full‐HD single‐scan mode, with 70% light emission duty. A luminous efficacy of 6.0 lm/W can been attained using Ne + 30% Xe 47 kPa, a sustain voltage of 320 V, and a sustain frequency of 3.3 kHz, when the luminance is 157 cd/m². Alternatively, the panel can achieve 4.2 lm/W and 1260 cd/m² by increasing the sustain frequency to 33 kHz.     

High‐frequency drive of high‐Xe‐content PDPs for high efficiency and low‐voltage performance

Abstract— It has been well known that the luminous efficiency of PDPs can be improved by increasing the Xe content in the panel. For instance, the efficiency is improved by a factor 1.7 when the Xe content is increased from 3.5% to 30%. The sustain pulse voltage, however, increases from 180 to 230 V by a factor 1.3. It was found that the increase in the sustain pulse voltage can be suppressed by increasing the sustain pulse frequency. The high‐frequency operation further increases the luminous efficiency. If the Xe content is increased from 3.5% to 30% and the drive pulse frequency is increased from 147 to 313 kHz, the luminous efficiency becomes 2.7 times higher and the luminance 4.5 times higher. Furthermore, the increase in the sustain pulse voltage is suppressed 1.1 times, from 180 to 200 V. A mechanism of attaining high efficiency and low‐voltage performance can be considered as follows. A train of pulses is applied during a sustain period. As the sustain pulse frequency is increased, the pulse repetition rate becomes faster and a percentage of the space charge created by the previous pulse remains until the following pulse is applied. Due to the priming effect of these space charge, the discharge current build‐up becomes faster, the width of the discharge current becomes narrower, ion‐heating loss is reduced, and the effective electron temperature is optimized so that Xe atoms are excited more efficiently. The intensity of Xe 147‐nm radiation, dominant in low‐pressure Xe dis‐charges, saturates with respect to electron density due to plasma saturation. This determines the high end of the sustain pulse frequency.     

High‐luminance and highly luminous‐efficient AC‐PDP with DelTA cell structure

To improve PDP performance, we developed an AC‐PDP with the Delta Tri‐Color Arrangement (DelTA) cell structure and arc‐shaped electrodes. The experimental panel has a pixel pitch of 1.08 mm and luminous efficacy of 3 lm/W at a luminance of 200 cd/m² despite its conventional gas mixture of Ne and Xe (4%) and conventional phosphor set. Moreover, its peak luminance can be greater than 1000 cd/m². The strong dependence of luminous efficacy on the sustain voltage is also discussed in this paper.     

High luminance and luminance efficiency in PDPs driven by radio‐frequency pulses

Abstract— Conventional AC‐PDPs has a relatively low efficiency which is close to 1.5 lm/W. Only 15–20% of the supplied energy is consumed by the Xe excitation, and 60% of energy is consumed by ion heating. If the ac sustain period is replaced by a rf sustain period, due to the oscillating and low electric field, almost 60% of the supplied energy is spent in Xe excitation while only 20% is used up in ion heating. In this paper, we show a new hybrid‐type PDP; the plasma is formed by ac writing pulses, and then it can be sustained due to rf sustaining pulses. When 40‐MHz frequency pulses were applied to the panel during the rf sustain period, the luminance was 1500–2000 cd/m² in a Ne‐Xe composition at 200–400 Torr. The luminance efficiency was around 4 lm/W.     

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.     

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.     

Luminous efficacy evaluation of XeI excimer for ACPDP

We demonstrate for the first time a luminous efficacy of a XeI excimer PDP comparable to that of a conventional Xe/Ne‐mixture PDP using 6‐in. ACPDPs. For the conventional PDP as a reference, a mixture of Xe: Ne = 4:96(%) with a total gas pressure of 60.0 kPa (450 torr) was used. For the XeI PDP, Ne‐buffered mixtures with the same total gas pressure were tried, and a mixture of I₂:Xe: Ne = 0.02:7.1:92.88 (%) showed an efficacy as high as that of the conventional Xe PDP.     

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.     

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.     

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.     

Discharge properties and chemical stability of SrZrO films

Abstract— MgO thin film is currently used as a surface protective layer for dielectric materials because MgO has a high resistance during ion sputtering and exhibits effective secondary electron emission. The secondary‐electron‐emission coefficient γ of MgO is high for Ne ions; however, it is low for Xe ions. The Xe content of the discharge gas of PDPs needs to be raised in order to increase the luminous efficiency. Thus, the development of high‐γ materials replacing MgO is required. The discharge properties and chemical surface stability of SrO containing Zr (SrZrO) as the candidate high‐γ protective layer for noble PDPs have been characterized. SrZrO films have superior chemical stability, especially the resistance to carbonation because of the existence of a few adsorption sites due to their amorphous structure. The firing voltage is 60 V lower than that of MgO films for a discharge gas of Ne/Xe = 85/15 at 60 kPa.     

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.     

Improvement of luminous efficiency using high helium content in full‐HD plasma‐display panels

Abstract— The influence of the Xe (15%) and He (70%) fractions on the discharge and driving characteristics was compared in 50‐in. full‐HD plasma‐display panels. The same improvement in the luminous efficacy was obtained when increasing either the Xe or He fraction. However, the discharge current with a high He fraction was smaller than that with a high Xe fraction. While the breakdown voltage was hardly influenced by an increase in the He fraction, it was significantly changed when increasing the Xe fraction. The formative and statistical time lags were only slightly changed with a high He fraction, yet significantly increased with a high Xe fraction. In addition, the relatively low luminance and driving‐margin characteristics with a high He fraction were compensated for by controlling the capacitance of the upper dielectric layer.     

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.