JP4760505B2 - Plasma display panel - Google Patents

Description

  The present invention relates to a plasma display panel that can realize stable discharge in a plasma display panel used for a display device or the like.

  As a display device for displaying a high-definition television image on a large screen, there is an increasing expectation for a display device using a plasma display panel (hereinafter referred to as PDP). A PDP basically includes a front panel and a back panel.

  The front panel includes a glass substrate, a display electrode including a striped transparent electrode and a bus electrode formed on one main surface thereof, a dielectric layer that covers the display electrode and functions as a capacitor, and a dielectric And a protective layer formed on the layer. On the other hand, the back panel includes a glass substrate, striped address electrodes formed on one main surface thereof, a base dielectric layer covering the address electrodes, a partition formed on the base dielectric layer, It is comprised with the fluorescent substance layer each light-emitted in red, green, and blue formed between the partition walls.

  The front panel and the rear panel are hermetically sealed with the electrode forming surfaces facing each other, and a discharge gas (discharge cell) formed by the barrier ribs is filled with a discharge gas such as Ne-Xe at a pressure of 400 Torr to 600 Torr. Has been. By selectively applying a video signal voltage to the display electrodes, the discharge gas is discharged, and the ultraviolet rays generated thereby excite the phosphor layers of each color to emit red, green, and blue light, thereby realizing color image display. ing.

  The protective layer is required to have a protective performance that protects the dielectric layer from ion bombardment caused by gas discharge, and a high electron emission performance to realize a highly responsive discharge by lowering the discharge voltage. Magnesium (MgO) thin films are used.

In order to realize highly responsive discharge according to the pulse of the video signal voltage, an example is disclosed in which the MgO thin film contains aluminum, silicon, and boron (see, for example, Patent Documents 1 and 2).
JP 2003-132801 A JP 2004-103273 A

  2. Description of the Related Art In recent years, there has been a demand for higher definition of PDP discharge cells with higher definition of images. When a television image is displayed with an increase in the number of scanning lines as the resolution becomes higher, in order to complete all sequences within 1 field = 1/60 [s], high-speed driving for applying a signal voltage is required. Become. In addition, with a reduction in cost by a simple drive method such as a single scan method, high-speed discharge responsiveness has been required.

  In response to these requirements, the conventional protective layer made of MgO thin film has a problem in that a discharge delay is likely to occur and a lighting failure occurs. In order to solve these discharge delays, the above example is disclosed in which aluminum or other elements are doped into the MgO thin film to increase the electron emission performance from the surface of the MgO thin film, thereby reducing the discharge delay time. It is thought that when aluminum is mixed in the material of the MgO thin film and heated and oxidized, a band structure having a wide energy width is formed in a relatively shallow energy band of the MgO band structure, and as a result, the electron emission performance is improved. Yes.

  The discharge delay time is determined depending on three factors: temperature, standby time, and space charge. It is known that the conventional method of adding aluminum improves the dependency of temperature and space charge, and the method of adding silicon improves the dependency of standby time. However, it is impossible to satisfy all of the three dependencies by balancing these, and there arises a problem that the discharge delay for high-speed driving such as further high definition cannot be solved.

  The present invention has been made in view of the above problems, and an object thereof is to eliminate a discharge delay and realize a PDP excellent in image quality.

In order to solve the above problems, the PDP of the present invention is a PDP in which an electrode formed on a substrate is covered with an insulating layer and the insulating layer is covered with a protective layer , and the protective layer is mainly composed of magnesium oxide, and has a weight ratio. (Hereinafter, all concentration indications are weight ratios), including aluminum: 900 ppm to 2400 ppm, silicon: 0.1 ppm to 25 ppm, and zinc: 15 ppm to 100 ppm.

  With such a configuration, it is possible to realize a protective layer with a small total variation against discharge delay, and to realize a PDP that can be single-scanned in a high-resolution model without degrading image quality.

Furthermore, when the concentration of aluminum contained in magnesium oxide is 900 ppm to 1600 ppm and the concentration of silicon is 0.1 ppm to 25 ppm, it is possible to realize a PDP with no reduction in luminance without reducing productivity. .

Furthermore, when the concentration of zinc contained in the protective layer is 15 ppm to 100 ppm, it is possible to realize a protective layer that reduces the discharge voltage while maintaining a performance with a small total variation, thereby realizing a PDP without a discharge delay. it can.

  As described above, according to the PDP of the present invention, the standby time dependency is improved, and a protective layer having a small overall variation including temperature dependency, space charge dependency, etc. is realized, and a PDP without discharge delay is realized. can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment)
FIG. 1 is a cross-sectional perspective view showing a configuration of a PDP manufactured by a method for manufacturing a PDP using a magnesium oxide raw material in an embodiment of the present invention. As shown in FIG. 1, the PDP 1 is composed of a front panel 2 and a back panel 3. The front panel 2 has scan electrodes 12a and sustain electrodes 12b alternately formed in stripes on the front glass substrate 11, and further, the dielectric glass layer 13 and the magnesium oxide as the insulating layers. It is formed by covering with a protective layer 14 made of (MgO).

On the other hand, the back panel 3 has an address electrode 22 formed in a stripe shape on a back glass substrate 21 and a base dielectric layer 23 formed so as to cover the address electrode 22. Further, the barrier ribs 24 are formed in stripes on the base dielectric layer 23 so as to sandwich the address electrodes 22, and the phosphor layer 25 is provided between the barrier ribs 24. The front panel 2 and the rear panel 3 are arranged to face each other, the peripheral portion is sealed, and a discharge gas 4 is enclosed in a space partitioned by the partition wall 24 to form a discharge space 4 having discharge cells. The phosphor layers are usually arranged in order of phosphor layers 25 of three colors of red, green, and blue for color display. Further, in the discharge space 4, for example, a discharge gas formed by mixing neon (Ne) and xenon (Xe), for example, is usually sealed at a pressure of about 0.67 × 10 ⁵ Pa.

  Next, a driving method of the PDP will be described. FIG. 2 is a block diagram showing the configuration of the driving circuit of the PDP. The drive circuit includes an address electrode drive unit 31, a scan electrode drive unit 32, and a sustain electrode drive unit 33. The address electrode driver 31 is connected to the address electrode 22 of the PDP, the scan electrode driver 32 is connected to the scan electrode 12a, and the sustain electrode driver 33 is connected to the sustain electrode 12b.

  In general, in an AC type PDP, a method of expressing gradation by dividing one frame of video into a plurality of subfields (SF) is used. In this method, one SF is further divided into four periods in order to control the gas discharge in the discharge cells. FIG. 3 is a time chart showing drive waveforms in one SF, and these four periods will be described with reference to FIG. In FIG. 3, wall charges are uniformly accumulated in all discharge cells in the PDP in order to facilitate discharge during the setup period. In the address period, the write discharge of the discharge cells to be lit is performed. In the sustain period, the discharge cells written in the address period are turned on and kept on. During the erase period, the discharge of the discharge cells is stopped by erasing the wall charges.

  In the setup period, a voltage higher than that of the address electrode 22 and the sustain electrode 12b is applied to the scan electrode 12a to discharge the gas in the discharge cell. The charges generated thereby are accumulated on the wall surface of the discharge cell so as to cancel the potential difference among the address electrode 22, the scan electrode 12a, and the sustain electrode 12b. Negative charges are accumulated as wall charges on the surface of the protective layer 14 near the scan electrodes 12a, and positive charges are wall charges on the surface of the phosphor layer 25 near the address electrodes 22 and the surface of the protective layer 14 near the sustain electrodes 12b. Accumulated as. Due to the wall charges, a predetermined wall potential is generated between the scan electrode 12a and the address electrode 22 and between the scan electrode 12a and the sustain electrode 12b.

  In the address period, when the discharge cell is lit, a voltage is applied between the scan electrode 12a and the address electrode 22 in the same direction as the above-described wall potential, and a voltage is applied between the scan electrode 12a and the sustain electrode 12b in the same direction as the wall potential. Is applied to cause a write discharge. As a result, negative charges are accumulated on the phosphor layer 25 surface and the protective layer 14 surface, and positive charges are accumulated as wall charges on the protective layer 14 surface in the vicinity of the scanning electrode 12a. As a result, a predetermined wall potential is generated between sustain electrode 12b and scan electrode 12a.

  In the sustain period, a higher voltage is applied to the scan electrode 12a than the sustain electrode 12b. That is, a sustain discharge is generated by applying a voltage in the same direction as the above-described wall potential between the sustain electrode 12b and the scan electrode 12a. Thereby, cell lighting can be started. Then, pulses can be emitted intermittently by applying a pulse so that the polarity is alternately switched between the sustain electrode 12b and the scan electrode 12a. In the erase period, since an incomplete discharge is generated by applying a narrow erase pulse to the sustain electrode 12b and the wall charges disappear, erase is performed.

  Although the number of scanning lines increases as the discharge cell structure becomes higher in definition, it is necessary to end all sequences within 1 field = 1/60 [s] when displaying a television image. In order to respond to this, it is necessary to perform high-speed driving by narrowing the pulse width of the address pulse applied in the address period. However, since there is a “discharge delay” in which the discharge is performed with a considerable delay from the rise of the pulse, the probability of the end of the discharge within the applied pulse width is low, and writing to a cell that should be originally lit can be performed. This causes a phenomenon that a lighting failure occurs. It is considered that the discharge delay is caused mainly by the fact that initial electrons that become a trigger when discharge is started are not easily released from the surface of the protective layer 14 into the discharge space.

  Therefore, if it is possible to create a situation in which initial electrons are easily emitted, it is considered that discharge delay can be effectively prevented. As a method for this, a method of increasing the drive pulse voltage in the address period and the sustain period or shortening the distance between the electrodes can be considered. However, the increase in the pulse voltage has a limit in suppressing the discharge delay time in relation to the breakdown voltage of the switching element of the drive circuit. Moreover, shortening the distance between the electrodes simultaneously reduces the height of the partition wall 24. When the height of the barrier ribs 24 is lowered, the discharge space itself is reduced, and the wall area per unit volume surrounding the plasma is increased. Therefore, the efficiency is reduced due to so-called wall loss that the plasma disappears when it collides with the wall surface. Will be.

  The discharge delay time is affected by the configuration, material, and driving method of the PDP, but is particularly affected by the protective layer 14 and further depends on temperature, standby time, space charge, and the like. 4 and 5 are diagrams showing an example of the standby time dependency of the discharge delay time. 4 and 5, the horizontal axis represents the time from the initializing discharge to the actual application of the address pulse as the standby time, and the vertical axis represents the discharge delay time measured by applying the actual address pulse. A numerical value, which is called a statistical delay time, is used as a measure of the likelihood of occurrence of discharge.

  Since the smaller the value on the vertical axis is, the easier the discharge is to occur, the discharge error, that is, the write error is reduced.On the other hand, if the value is too small, the wall charge generated by initialization is reduced in time. A discharge error is caused when an address discharge is actually attempted. On the other hand, if this value is too large, a discharge error occurs because no discharge occurs within a predetermined time. Therefore, it is desirable that this value falls within a certain range. This range varies depending on the PDP discharge cell size, the number of pixels, the subfield configuration of the screen, and the like, but cannot be determined unconditionally. However, it is important to reduce variations so as to reproduce various lighting states.

  That is, the waiting time on the horizontal axis is determined while expressing various images. Considering the case where various subfield configurations are used and the initialization pulse is performed only once in one screen (field) to improve dark place contrast, the time from the initial stage to the address pulse is 10 μsec. There is a possibility of having a width of about 5 msec. Therefore, the standby time dependency can be expressed by the ratio of the maximum value and the minimum value of the discharge delay time in this range of standby time, and the ratio is preferably as small as possible.

  FIG. 4 similarly shows the temperature dependence of the discharge delay. That is, the surface temperature of the PDP was changed in the range of −20 ° C. to 90 ° C., and the discharge delay time with respect to the standby time was measured. As shown in FIG. 4, it can be seen that the discharge delay has temperature dependence. Therefore, it is desirable that the maximum value and the minimum value of the discharge delay time due to temperature dependency in the same standby time be small.

  On the other hand, FIG. 5 shows the space charge dependence of the discharge delay. Before applying the initialization pulse, a strong discharge is generated in the discharge cell space, and the number of pulses of the strong discharge is increased until there is almost no change in the discharge delay time. In addition, as a standard of the number of pulses in which the change in the discharge delay time with the increase in the number of pulses is almost eliminated, the number of pulses is 200 to 300. In the embodiment of the present invention, the discharge delay time when the number of pulses is minimum and the maximum is measured and plotted at each standby time, and the discharge delay time at the maximum pulse number and the discharge delay at the minimum pulse number are plotted. The ratio that maximizes the ratio to time is defined as a multiple. Therefore, in FIG. 5, the ratio of the discharge delay time of 100 nsec with the minimum number of pulses when the standby time is 100 μsec and the discharge delay time of 40 nsec with the maximum number of pulses is the largest ratio with respect to the standby time. 5 is shown.

  Based on these standby time dependency, temperature dependency, and space charge dependency, the overall variation with respect to the discharge delay time was obtained by the following procedure and used as an evaluation scale. First, the logarithm (common logarithm: base is 10) of the ratio of the maximum value and the minimum value of all values in the figure is obtained using FIG. 4 showing the standby time dependency and the temperature dependency. Next, regarding the space charge dependency of FIG. 5, the maximum value of the ratio of the discharge delay time in the same standby time is obtained in the range from the maximum to the minimum number of sustain pulses given in the discharge delay time measurement. Is a multiple. These were obtained as products as in the following equation, and the total variation was obtained.

  Although the overall variation is obtained as a magnification, it can be said that if the magnification is small, the discharge delay time is small, and the protective layer 14 is of good quality with small temperature dependency, standby time dependency, and space charge dependency.

  If the MgO thin film is doped with aluminum (Al) or other elements to increase the electron emission performance from the surface of the MgO thin film in order to solve the discharge delay, the MgO band structure has a relatively shallow energy band. It is considered that a wide band structure is formed and the electron emission characteristics are improved. However, such a method of adding Al improves temperature dependency and space charge dependency, but does not improve standby time dependency. On the other hand, the method of adding silicon (Si) improves the standby time dependency, but does not improve the temperature dependency and space charge dependency.

  In the present invention, the concentration of aluminum and silicon contained in the magnesium oxide is controlled, the main component is magnesium oxide containing silicon and aluminum, the aluminum concentration is 900 ppm to 2400 ppm, and the silicon concentration is The protective layer 14 with a small total variation is realized by setting it to 0.1 ppm to 30 ppm.

  That is, an impurity having a band structure having a sharp distribution with respect to time dependency can be provided in a portion relatively close to the energy of the Al band band. As a result, even if the standby time becomes long and electrons are sequentially taken away, it is considered that an electron source capable of supplying electrons is provided, and the standby time dependency can be reduced. Si can be considered as an impurity having such characteristics. It has been found that the temperature dependence becomes very large when a large amount of Si is introduced. This is because electrons supplied from a band structure having a sharp distribution are abundant in the amount supplied, but there is a great difference in the probability of electron emission. For this reason, it is considered that a difference in the amount of electrons emitted occurs due to an energy difference due to a temperature change, and as a result, the temperature dependence becomes strong.

  That is, when Si is mixed as the second impurity, the dependence on the standby time can be made very small, but a sharp level becomes larger in a shallower level than the broad band structure of the original Al. On the contrary, the temperature dependency becomes strong. Therefore, by finding the optimum Si concentration, it is possible to realize an MgO protective layer that satisfies all three characteristics of temperature dependence, standby time dependence, and space electrification dependence and has a small discharge delay time. Further, by mixing a certain amount of Zn, the discharge voltage can be reduced without impairing these characteristics. More preferably, the metal elements such as iron (Fe), calcium (Ca), and chromium (Cr), which are impurities that form a band structure near these levels, should be limited to a certain amount or less. Further desirable results are obtained.

  In the embodiment of the present invention, a vacuum deposition method is used as a method for forming the protective layer 14. That is, a protective layer 14 containing aluminum and silicon is formed on the dielectric glass layer 13 of the front panel 2 by electron beam vacuum deposition. The following deposition conditions are used as the deposition conditions of the vacuum deposition method, and a magnesium oxide sintered body containing 1000 ppm to 8000 ppm of aluminum and 0.1 ppm to 25 ppm of silicon is used as a deposition raw material. Further, the deposition conditions at this time are as follows.

Deposition conditions deposition ^{pressure: 0.2 × 10 -2 Pa~6 × 10} -2 Pa
Substrate (front glass substrate) temperature: 150 ° C to 400 ° C
O ₂ (oxygen) flow rate: 0 ccm to 200 ccm
Electron beam power: 5kw ~ 15kw
Film-forming rate (dynamic rate): 120 nm · m / min to 1200 nm · m / min
Instead of the vacuum deposition method, the protective layer 14 may be formed by a sputtering method using the target of the above components.

  Using the above-described vapor deposition method, a PDP having a protective layer 14 in which the Al concentration and the Si concentration were changed was created, and the overall variation with respect to the discharge delay was evaluated. FIG. 6 is a diagram showing the total variation with respect to the discharge delay, with the horizontal axis representing the Al concentration in the protective layer 14 and the vertical axis representing the Si concentration in the protective layer 14. As described above, the smaller the overall variation is, the better the drive characteristics are. However, the desired range for the drive characteristics is that if the overall variation is 4 times or less, the single scan in the high resolution model can be made without reducing the image quality. It becomes possible to do.

  Therefore, if the total variation in FIG. 6 is within the density range of the region B, which is 4 times or less, it is possible to perform single scanning in the high resolution model without degrading the image quality. That is, the concentration of Al is 900 ppm to 2400 ppm, and the concentration of silicon is 0.1 ppm to 30 ppm.

  Furthermore, within the density range of the region A where the total variation is within 3 times, it is possible to further improve image quality such as brightness and contrast, and a more desirable density range. That is, the concentration of aluminum is 900 ppm to 1600 ppm, and the concentration of silicon is 0.1 ppm to 25 ppm.

  FIG. 7 is a diagram showing an X-ray diffraction result of the MgO protective layer, and RINT-2200HL manufactured by Rigaku is used as an apparatus used. FIG. 7 (a) shows the case where the film formation rate when forming the MgO protective layer is standard, and FIG. 7 (b) shows the result when the film formation rate is increased to about 800 nm · m / min or more. It is. As shown in FIG. 7, the protective layer 14 in the embodiment of the present invention is oriented in the (111) plane where 2θ has a peak intensity in the vicinity of 36.9 deg. As shown in FIG. 7A, the peak intensity is 850 cps to 1200 cps or more at the standard film formation rate, and the protective layer 14 having relatively high crystallinity is obtained. In this case, since the electron emission performance of MgO itself is high, it is possible to improve the discharge delay time without increasing the ratio of electron emission from the impurity level produced by Al. However, when the film forming rate is increased and the dynamic rate exceeds 800 nm · m / min, the crystallinity of (111) orientation deteriorates as shown in FIG. 7B, and 2θ is around 36.9 deg. The peak intensity decreases to about 550 cps to 750 cps. This is because the electron emission performance deteriorates from MgO itself. In that case, the discharge delay time can be improved by increasing the electron emission from the impurity level produced by Al.

  Therefore, in the PDP according to the embodiment of the present invention, when the MgO protective layer is formed under a condition where the film forming rate is high, the film is formed so as to increase the impurity concentration of Al.

  Further, as described above, by mixing a certain amount of Zn, it is possible to expect an effect of reducing the discharge voltage while improving the driving characteristics due to the discharge delay. FIG. 8 is a diagram showing the overall variation when the Zn concentration contained in the protective layer 14 is increased. Specifically, the Zn concentration is increased from 100 ppm to 120 ppm. As shown in FIG. 8, when the Zn concentration is increased, the range region of the optimum magnification of the overall variation characteristic shown in FIG. 6 is narrowed, and the region where the overall variation is within 3 times disappears. FIG. 9 shows a change in the discharge voltage due to a change in the Zn concentration, and shows how much the discharge voltage is reduced or increased compared to the protective layer 14 having a Zn concentration of 10 ppm in the protective layer 14. From the results of FIG. 9, it can be seen that if the Zn concentration is 15 ppm or more, the discharge voltage is reduced, and it is desirable that the Zn concentration in the protective layer 14 is 15 ppm to 100 ppm.

  Furthermore, it is preferable to limit metal elements such as Fe, Ca, and Cr, which are impurities that form bands, to a certain amount or less. In this embodiment, Fe, Cr, and Ca are all set to 30 ppm or less. FIG. 10 is a diagram showing the total variation when the concentration of these impurities contained in the protective layer 14 is increased. Specifically, the concentration of these impurities is increased from 30 ppm to 200 ppm. As shown in FIG. 10, it can be seen that when the concentration of these impurities is increased, the region that satisfies the optimum overall variation characteristic becomes narrower. Therefore, it is desirable that Fe, Cr, and Ca are all 30 ppm or less.

  As described above, according to the PDP of the present invention, it is possible to realize a PDP that does not have a discharge delay and that can be single-scanned in a high-resolution model with high image quality.

  According to the present invention, a high-definition and high-resolution PDP that can be single-scanned is realized, which is useful for a high-definition, large-screen display device.

Sectional perspective view which shows the structure of PDP in embodiment of this invention The block diagram which shows the structure of the drive circuit of the PDP Time chart showing the drive waveform of the PDP The figure which shows the temperature dependence and standby time dependence of the discharge delay of the PDP The figure which shows the space charge dependence and waiting time dependence of the discharge delay of the PDP The figure which shows the total variation with respect to the discharge delay of the PDP The figure which shows the X-ray-diffraction result of the protective layer of the PDP The figure which shows the total variation at the time of increasing Zn density | concentration contained in the protective layer of the PDP The figure which shows the change of the discharge voltage by the change of Zn density | concentration of the protective layer of the PDP The figure which shows the total variation at the time of increasing impurity concentration, such as Fe, Ca, Cr contained in the protective layer of the PDP

Explanation of symbols

1 PDP
DESCRIPTION OF SYMBOLS 2 Front panel 3 Back panel 4 Discharge space 11 Front glass substrate 12a Scan electrode 12b Sustain electrode 13 Dielectric glass layer 14 Protective layer 21 Back glass substrate 22 Address electrode 23 Base dielectric layer 24 Partition 25 Phosphor layer 31 Address electrode drive part 32 Scan electrode driver 33 Sustain electrode driver

Claims (1)

A plasma display panel in which an electrode formed on a substrate is covered with an insulating layer and the insulating layer is covered with a protective layer, wherein the protective layer contains magnesium oxide as a main component and includes the following components by weight ratio: Plasma display panel.
Aluminum: 900 ppm to 2400 ppm
Silicon: 0.1 ppm to 25 ppm
Zinc: 15 ppm to 100 ppm

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