JP4967457B2 - Plasma display panel - Google Patents

Description

  The present invention relates to a plasma display panel (PDP) used for an image display device or the like.

  An AC surface discharge type PDP has a front substrate on which a plurality of display electrodes composed of scan electrodes and sustain electrodes are formed, and a rear substrate on which a plurality of address electrodes are formed so as to be orthogonal to the display electrodes. They are arranged so as to face each other, and the periphery is sealed, and a discharge gas such as neon and xenon is sealed in the discharge space. The display electrode is covered with a dielectric layer, and a protective film is formed on the dielectric layer. Then, a predetermined voltage is applied to each electrode to generate a discharge in the discharge space, and the phosphor layer provided on the back substrate is caused to emit light, thereby displaying an image.

The role of the protective film includes protecting the dielectric layer from ion bombardment caused by discharge, and emitting exoelectrons for generating address discharge. Protecting the dielectric layer from ion bombardment plays an important role in preventing an increase in discharge voltage, and emitting exoelectrons to generate address discharge is an address discharge error that causes image flickering. It is an important role to prevent. For example, Patent Document 1 discloses a PDP having a protective film having high electron emission performance and excellent sputter resistance.
JP 2003-317631 A

  In general, the protective film is formed by a vacuum deposition method, a sputtering method, or an ion plating method. In any case, the surface side of the protective film, which is the side exposed to the discharge gas, has a low density. Film. The surface side of such a protective film is gradually sputtered while the PDP is lit, and the discharge characteristics change as the PDP continues to be used over a long period of time, making it difficult to drive the PDP. was there.

  The present invention has been made to solve such problems, and provides a PDP capable of suppressing a change over time in the discharge characteristics of the PDP after the aging process and performing stable display over a long period of time. With the goal.

  In order to achieve the above object, a PDP according to the present invention includes a first substrate and a second substrate which are disposed to face each other so as to form a discharge space therebetween, and a scan electrode provided on the first substrate. And a sustain electrode, a dielectric layer formed on the first substrate so as to cover the scan electrode and the sustain electrode, and a protective film formed on the dielectric layer, the protective film A region having a refractive index of 1.5 or less with respect to light having a wavelength of 600 nm is formed from the surface to the thickness direction of the protective film, and the thickness of the region is 150 nm or less.

  According to the present invention, stable display can be performed even when the PDP is lit for a long period of time.

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

  FIG. 1 is a perspective view in which a part of an AC surface discharge type PDP is cut away. In this PDP, the front panel 1 and the rear panel 2 are arranged to face each other and the periphery is sealed to form a discharge space 3 therebetween, and a discharge gas composed of neon, xenon, or the like is enclosed in the discharge space 3. Configured.

  The front panel 1 has the following configuration. That is, on the front substrate (first substrate) 4, which is a glass substrate, a plurality of display electrodes 7 composed of stripe-shaped scanning electrodes 5 and stripe-shaped sustain electrodes 6 are formed, and between adjacent display electrodes 7. A light shielding layer 8 is formed. A dielectric layer 9 is formed so as to cover the display electrodes 7 and the light shielding layer 8, and a protective film 10 is formed on the dielectric layer 9.

  The rear panel 2 has the following configuration. That is, a plurality of stripe-shaped address electrodes 12 are formed on a rear substrate (second substrate) 11 that is a glass substrate so as to be orthogonal to the scan electrodes 5 and the sustain electrodes 6, and the dielectric is formed so as to cover the address electrodes 12. Layer 13 is formed. A partition 14 parallel to the address electrode 12 is provided on the dielectric layer 13 and between the address electrodes 12, and a phosphor layer 15 is formed between the partitions 14. The dielectric layer 13 functions to control the discharge current and reflect visible light generated by the phosphor layer 15 to the front panel 1 side.

  A discharge cell, which is a minimum unit of display, is formed at a portion where the scan electrode 5 and the sustain electrode 6 and the address electrode 12 intersect three-dimensionally, and a PDP display area (area for image display) is formed by all the discharge cells. The Then, the scan pulse is applied to the scan electrode 5 and the address pulse is applied to the address electrode 12 to generate the address discharge, thereby sequentially selecting the discharge cells to be lit for each scan electrode 5 and then scanning. A sustain discharge is generated by alternately applying a sustain pulse to the electrode 5 and the sustain electrode 6, and light transmitted through the front panel 1 by exciting and emitting the phosphor of the phosphor layer 15 by vacuum ultraviolet rays generated by the sustain discharge. To display a color image.

  FIG. 2 shows a configuration diagram of an example of a vacuum evaporation apparatus used when forming the protective film 10 of the PDP. The vacuum deposition apparatus includes five chambers: a substrate carry-in chamber 21, a substrate heating chamber 22, a film forming chamber 23, a cooling chamber 24, and a substrate carry-out chamber 25, and the substrate 31 is transferred from the substrate carry-in chamber 21 to the substrate carry-out chamber. It is conveyed toward 25. As an example, two electron beam guns 32 are installed on the lower wall surface of the film forming chamber 23, and the electron beams 35 are condensed from the respective electron beam guns 32 toward the thin film raw material 34 accommodated in the concave portion of the ring hearth 33. And irradiated. As a result, the thin film raw material 34 is locally heated and heated to evaporate, and a protective film is formed on the substrate 31 moving above the ring hearth 33. The substrate 31 is obtained by forming the scanning electrode 5, the sustaining electrode 6, the light shielding layer 8, and the dielectric layer 9 on the front substrate 4, and is protected on the dielectric layer 9 using the vacuum evaporation apparatus of FIG. The front panel 1 is produced by forming the film 10.

  When the front panel 1 and the separately manufactured back panel 2 are opposed to each other and the periphery is sealed with frit glass, and a discharge gas is sealed in the discharge space 3, a PDP is obtained. The PDP manufactured in this way cannot change its discharge characteristics with time and realize stable performance. Therefore, generally, after the PDP is manufactured, an aging process is performed in which a predetermined voltage is applied and discharged in all the discharge cells to stabilize the discharge characteristics.

  FIG. 3 shows an example of a result when the protective film 10 of the PDP that has been subjected to the aging process is analyzed using a spectroscopic ellipsometer (UVISEL manufactured by Joban Yvon). The spectroscopic ellipsometer analyzes the film thickness and the refractive index using data obtained by making light incident on the film and measuring the interference light of the reflected light. By analyzing the protective film 10 on the assumption that it is a multilayer film, The film thickness and refractive index of each layer can be determined. That is, when light is incident on the multilayer film, the light is reflected according to the difference in refractive index at the boundary between the layers, so that the sum of the reflected light at the boundary between the layers is measured as interference light. By analyzing the data of the measured interference light, the assumed film thickness and refractive index of each layer of the multilayer film can be obtained. The horizontal axis of FIG. 3 is the distance from the surface of the protective film 10 (distance in the thickness direction of the protective film 10), and the refractive index is high on the dielectric layer 9 side as shown in FIG. The refractive index is lowered on the surface, and the refractive index changes more rapidly than the inner portion of the protective film 10 particularly on the surface side of the protective film 10 (the side exposed to the discharge space 3). The refractive index on the vertical axis is a value for light having a wavelength of 600 nm.

  Here, when the protective film 10 is formed while continuously transporting the substrate 31 as shown in FIG. 2, the surface side portion of the protective film 10 is not in the normal direction of the substrate 31 but with respect to the substrate 31. Thus, the thin film raw material 34 is incident from an oblique direction, and low energy particles are likely to adhere, resulting in a sparse film with low density. On the other hand, the portion of the sparse film on the inner side (side closer to the dielectric layer 9) formed by the incidence of the thin film raw material 34 from the normal direction of the substrate 31 or the direction close thereto is It becomes a dense film with high density.

  A sparse film with low density is weaker to ion sputtering than a dense film with high density, so most of it is not sputtered in the aging process, but part will remain until after the aging process, In a normally used lighting state of the PDP, it is gradually sputtered with time. Since the surface state of the protective film 10 greatly affects the electron emission characteristics, the protective film 10 is sputtered over time and the surface state changes, that is, the discharge state changes over time. As the PDP continues to be used for a long period of time, it is possible that appropriate discharge control and driving cannot be performed with the initial setting voltage set after the aging process.

From the above, the portion having a small refractive index on the surface side of the protective film 10 is a sparse film having a low density, and the portion having a large refractive index inside the protective film 10 is a dense film having a high density. Yes. When the refractive index portion is smaller than the refractive index portion, the portion where the refractive index is smaller is more susceptible to ion sputtering, so that it is more likely to be sputtered during normal use of the PDP. The change in the characteristics of the PDP with time increases.

  FIG. 4 shows changes over time in the complete lighting voltage of the PDP in the life test for two PDPs having protective films having different film thicknesses on the low refractive index portion on the surface side. (A) is a case of PDP in which the film thickness of the low refractive index portion on the surface side of the protective film 10 is smaller than that in (b). In this life test, the display area of the PDP is divided into a lighting area (area that is lit in the life test) and a non-lighting area (area that is not lit in the life test), and the life test is performed by lighting only in the lighting area. After the life test, the refractive index distribution of the protective film 10 is obtained by a spectroscopic ellipsometer (UVISEL manufactured by Joban Yvon) using the non-lighting region. The complete lighting voltage is a sustain pulse voltage (suspension pulse peak value) necessary for lighting all the discharge cells in the lighting region of the PDP.

  FIG. 4 shows that (a) shows a small change over time in the complete lighting voltage, but (b) shows a large change over time as compared with (a). When the change over time is large as shown in (b), it is considered that the complete lighting voltage exceeds the initial setting voltage including the voltage margin, which may lead to a lighting failure of the PDP.

  Therefore, in order to suppress the change in characteristics of the PDP over time, the film thickness of the low refractive index portion on the surface of the protective film, which greatly affects the change in characteristics, is thin and is almost sputtered in the aging process or remains after the aging process. In addition, it is necessary that the film thickness of the low refractive index portion does not greatly affect the change in characteristics of the PDP over time.

  From FIG. 3, it can be seen that the refractive index of the surface of the general protective film prepared by the continuous transport film forming method rapidly decreases from about 1.5. This indicates that the refractive index of the film formed by the low energy particles adhering to the outermost surface is 1.5 or less, and by setting the thickness of the portion where the refractive index is 1.5 or less to a predetermined value or less. It is considered that the change in characteristics of the PDP over time can be suppressed.

  Therefore, the relationship between the thickness of the region having a refractive index of 1.5 or less (this region is defined as the surface layer) in the surface portion of the protective film 10 and the increase in the complete lighting voltage in the PDP life test was examined. Here, five types of PDPs for performing the life test were prepared. For these PDPs, the protective film 10 was formed using the vacuum deposition apparatus shown in FIG. 5, the same components as those in FIG. 2 are denoted by the same reference numerals, and the vacuum deposition apparatus illustrated in FIG. 5 includes a substrate carry-in chamber 21, a substrate heating chamber 22, a film formation chamber 23, a cooling chamber 24, The substrate carry-out chamber 25 is composed of five chambers. A difference from the vacuum vapor deposition apparatus of FIG. 2 is that a shutter 26 is provided in the film forming chamber 23, and a part of the thin film raw material 34 evaporated by the shutter 26 is blocked. As shown in FIG. 5, when the film is formed with the length L of the shielding part (the part shielding the thin film raw material 34) of the shutter 26 set appropriately, the film is incident on the film surface from an oblique direction at the end of the film formation of the protective film 10. The low-energy particles are blocked, and the protective film 10 having a thin surface layer is formed. Then, by forming the protective film 10 with different lengths L, PDPs (5 types of PDPs) having different surface layer thicknesses were produced.

  In this life test, similarly to the description related to FIG. 4 described above, the display area of the PDP is divided into a lighting area and a non-lighting area, and the life test is performed by lighting only in the lighting area. The refractive index distribution of the protective film 10 was obtained by a spectroscopic ellipsometer using the portion of the lighting region, and the thickness of the portion having a refractive index of 1.5 or less was obtained. Further, the complete lighting voltage is a sustain pulse voltage necessary for lighting all the discharge cells in the lighting region of the PDP. In the life test, the change over time is measured until the complete lighting voltage rises and becomes saturated, The difference between the full lighting voltage at the time of saturation and the full lighting voltage at the start of the life test was determined, and this was taken as the increase in the complete lighting voltage.

  FIG. 6 shows the relationship between the thickness of the surface layer of the protective film 10 obtained as described above and the increase in the complete lighting voltage (voltage increase). From FIG. 6, when the thickness of the surface layer of the protective film 10 is 20 nm, 50 nm, and 100 nm, that is, when the thickness of the surface layer is 100 nm or less, the rising voltage in the life test is almost constant at 3 to 4V. I understand that. This indicates that the voltage rise is caused by other factors, not depending on the surface state of the protective film 10. When the thickness of the surface layer exceeds 100 nm, the voltage increase increases with the increase in the thickness of the surface layer, and the voltage increase when the thickness of the surface layer is 150 nm is about 9 V. Is within a range where it can be lit normally. Moreover, when the thickness of the surface layer exceeded 150 nm, the complete lighting voltage was not saturated within a realistic lighting time, and continued to rise. In this case, when the lighting of the PDP is continued for a long time, it is considered that the set voltage in the initial state is exceeded, and there is a possibility that a lighting failure such as a non-lighting may occur. That is, it is difficult to initially set a voltage including a margin for the voltage increase.

  From the above results, by setting the thickness of the surface layer of the protective film 10 to 150 nm or less, it is possible to prevent a lighting failure from occurring even if the PDP is continuously turned on for a long time. Furthermore, by setting the thickness of the surface layer of the protective film 10 to 100 nm or less, the voltage increase with time can be minimized, and the change in the lighting state with time can be suppressed.

  That is, scan electrode 5 and sustain electrode 6 provided on front substrate 4, dielectric layer 9 formed on front substrate 4 so as to cover scan electrode 5 and sustain electrode 6, and on dielectric layer 9 A region having a refractive index of 1.5 or less with respect to light having a wavelength of 600 nm is formed in the thickness direction of the protective film 10 from the surface of the protective film 10, and the thickness of the region is By setting the thickness to 150 nm or less, it is possible to obtain a PDP in which the occurrence of lighting failure is suppressed over a long period of time. Furthermore, by setting the thickness of the region to 100 nm or less, a PDP having more excellent characteristics can be obtained.

  Note that the method for forming the protective film 10 is not limited to the above-described vacuum deposition method, and a sputtering method, an ion plating method, or the like can also be used. In this case, the protective film can be adjusted by adjusting the film formation conditions. The thickness of the ten surface layers can be controlled.

  As described above, according to the present invention, it is possible to provide a stable PDP in which the occurrence of lighting failure is suppressed even when the PDP is lit for a long period of time.

The perspective view which shows a part of plasma display panel by one embodiment of this invention Configuration diagram showing an example of a vacuum evaporation system The figure which shows the refractive index change of the film thickness direction of the protective film The figure which shows the time-dependent change of the complete lighting voltage of the plasma display panel in the life test The block diagram which shows an example of the vacuum evaporation system for manufacturing the plasma display panel by one embodiment of this invention The figure which shows the relationship between the thickness of the surface layer of a protective film, and the amount of voltage rise

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front panel 2 Back panel 3 Discharge space 4 Front board (1st board)
5 Scan Electrode 6 Sustain Electrode 7 Display Electrode 9 Dielectric Layer 10 Protective Film 11 Back Substrate (Second Substrate)
12 Address electrode 21 Substrate loading chamber 22 Substrate heating chamber 23 Deposition chamber 24 Cooling chamber 25 Substrate unloading chamber 26 Shutter 31 Substrate

Claims (3)

A first substrate and a second substrate disposed opposite to each other so as to form a discharge space therebetween, a scan electrode and a sustain electrode provided on the first substrate, and so as to cover the scan electrode and the sustain electrode A dielectric layer formed on the first substrate and a protective film formed on the dielectric layer, and light having a wavelength of 600 nm from the surface of the protective film in the thickness direction of the protective film. An area having a refractive index of 1.5 or less is formed, and the thickness of the area is 150 nm or less. The plasma display panel according to claim 1, wherein the thickness of the region is 100 nm or less. The plasma display panel according to claim 1, wherein the protective film is made of magnesium oxide.

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