The present invention relates to a plasma display panel for use in a display device or the like, and a manufacturing method for the same.
Recently, calls for higher performances such as high-definition (high-vision) displays and flat panel displays have grown in the field of displays. In response to these calls, various research and development are being made.
Typical flat panel displays are liquid crystal displays (LCDs) and plasma display panels (PDPs). Particularly, PDPs are thin and suitable for large-scale screens, with products using 50-inch class PDPs having already been developed.
PDPs can roughly be divided into two types: direct current (DC) type; and alternating current (AC) type. The present mainstream is AC-type PDPs that are suitable for being made larger in size.
In general, PDPs are constructed of phosphor cells of respective colors arranged in matrix. As one example, Japanese Laid-Open Patent Application No. 9-35628 discloses an AC surface-discharge type PDP. This PDP has the following panel construction. A front glass substrate and a back glass substrate are arranged in parallel with barrier ribs interposed between them. On the front glass substrate, pairs of display electrodes (scanning electrodes and sustaining electrodes) are formed in parallel. These electrodes are covered with a dielectric layer. On the back glass substrate, address electrodes are formed so as to face the scanning electrodes at right angles. Phosphor layers of respective colors (red, green, and blue) are formed in spaces divided by the barrier ribs between the front and back substrates. A discharge gas is enclosed in the spaces to form cells that emit red, green and blue light. By a driving circuit applying voltage to each electrode, discharge occurs and ultraviolet rays are emitted. Phosphor particles (red, green, and blue) in the phosphor layers are excited with these ultraviolet rays to emit light, resulting in a luminescent display.
In the PDP described above, glass plates manufactured from a sodium borosilicate glass material using a float method are typically used for the front glass substrate and the back glass substrate. For the display electrodes and the address electrodes, Crxe2x80x94Cuxe2x80x94Cr (chromium-copper-chromium) electrodes are sometimes used, and silver electrodes that are relatively cheap are often used.
In general, the silver electrodes are formed using a thick-film forming method. To be more specific, a silver paste made of Ag particles, a glass frit, resin, solvent, and the like is applied as a pattern using a screen-printing method. Alternatively, a film made of Ag particles, a glass frit, resin, and the like is applied using a lamination method and is patterned. In either case, the applied paste or the applied film is baked at the temperature of 500xc2x0 C. or higher to fuse Ag particles together for improving conductivity as well as to remove resin.
The dielectric layer is usually formed by applying a paste made of powdered lead glass with a low melting point or the like and resin, using the screen-printing method, a die coat method, the lamination method, or the like, and baking the applied paste at the temperature of 500xc2x0 C. or higher.
The PDP using such silver electrodes as described above is known to have the following problem. From the silver electrodes, Ag diffuses as ions into the glass substrate and the dielectric layer. The diffused Ag ions are reduced to generate Ag colloids. Due to this, the glass substrate and the dielectric layer yellow easily. This yellowing causes a decrease in the color temperature of full-white images when the PDP is driven, deteriorating image quality of the PDP.
This yellowing of the glass substrate and the dielectric layer causes deterioration in the luminance of blue cells and a decrease in the color temperature of full-white images.
To solve this yellowing problem in the PDP, as one example, Japanese Laid-Open Patent Application No. 10-255669 discloses a technique for abrading a surface layer with a thickness of 1 xcexcm to 1000 xcexcm of a glass substrate, by mechanically polishing the surface of the glass substrate.
This technique is considered effective in preventing the yellowing of the glass substrate. However, it is extremely difficult to uniformly abrade 1 xcexcm or thicker surface part of such a large glass substrate that is used in the PDP in a short period of time. For example, it takes at least several tens minutes to abrade the 1 xcexcm-thick surface part of the glass substrate with an Oskar-type polishing device. Furthermore, by abrading 1 xcexcm or thicker surface part of the glass substrate, the thickness of the glass substrate as a whole may become uneven.
Accordingly, new solutions to the yellowing in the PDP that use the silver electrodes are being sought.
The present invention aims to provide a technique for relatively easily preventing a PDP that use the sliver electrodes from yellowing, and also, to provide a PDP that is capable of displaying images with high luminance and high quality utilizing this technique. Note that the term xe2x80x9csilver electrodexe2x80x9d as used herein is intended to include an electrode substantially made of silver such as a silver alloy electrode.
The present invention proposes the following four techniques with which the above aim can be fulfilled.
A first technique is to form the silver electrodes from an alloy which is mainly composed of Ag and contains a transition metal (at least one selected from the group consisting of Cu, Cr, Co, Ni, Mn, and Fe), or to form the silver electrodes from Ag and glass that contains a transition metal oxide (at least one selected from the group consisting of CuO, CoO, NiO, Cr2O3, MnO, and Fe2O3).
A second technique is to form the sliver electrodes from an alloy which is mainly composed of Ag and contains a metal (at least one selected from the group consisting of Ru, Rh, Ir, Os, and Re), or to form the silver electrodes from Ag and glass that contains a metal oxide (at least one selected from the group consisting of RuO2, RhO, IrO2, OsO2, ReO2, and PdO).
A third technique is to form the silver electrodes from Ag particles each coated with a metal (such as Pd, Cu, Cr, Ni, Ir, or Ru) or with a metal oxide (such as SiO2, Al2O3, NiO, ZrO2, Fe2O3, ZnO, In2O3, CuO, TiO2, or Pr6O11).
Here, the following ways (1) to (3) can be employed for coating a surface of each Ag particle with a metal or a metal oxide:
(1) A surface of an Ag particle is coated with a metal using an electroless plating method.
(2) A surface of an Ag particle is coated with a metal oxide or a metal using a mechanofusion method.
(3) A surface of an Ag particle is coated with a metal oxide using a sol-gel method.
A fourth technique is to provide the following setting in a glass substrate for use in the PDP. In the glass substrate for use in the PDP, the concentration of metal ions to be contained in a part of the substrate from its surface to 5 xcexcm in depth is set at 1000 ppm or less, the metal ions possessing reducing action on Ag ions.
Such a glass substrate for use in the PDP can be manufactured as follows. A normal glass substrate is made to go through a step in which metal ions that possess reducing action on Ag ions are removed by etching the substrate, or a step in which the reducing action of the metal ions on Ag ions is deactivated by heating the substrate.
The yellowing of the glass substrate and the dielectric layer can be prevented with any of the above four techniques, thereby improving the luminance of blue cells of the PDP and the color temperature of full-white images. Also, when any of the above four techniques is employed, the conductivity of the sliver electrodes can be ensured.
The following describes the reasons why the above four techniques of the present invention can prevent such yellowing.
FIG. 3 is for explaining a mechanism that causes yellowing of a glass substrate and a dielectric layer in a conventional PDP.
As shown in the figure, yellowing of the glass substrate occurs through the following steps I to IV:
I. During a baking process for forming silver electrodes or during a baking process for forming a dielectric glass layer, Ag in the electrodes is ionized.
II. The Ag ions diffuse into the glass substrate surface and the dielectric layer.
III. The diffused Ag ions are reduced by metal ions that exist in the vicinity of the glass substrate surface and in the dielectric layer (the metal ions possess reducing action on Ag ions, and include Sn ions that exist mainly around the glass substrate surface, and Na ions and Pb ions that exist in the dielectric glass).
IV. The reduced Ag is then precipitated as Ag colloidal particles, and the Ag colloidal particles grow.
The Ag colloidal particles have the absorption region at the wavelength of 400 nm, and so cause the yellowing of the substrate and the dielectric layer.
With regard to the mechanism for silver to cause yellowing of glass, xe2x80x9cGlass Handbookxe2x80x9d (ASAKURA SHOTEN: Jul. 15, 1977, P.166) describes the following phenomena. When Ag+and Sn2+coexist in the glass, the thermal reduction reaction proceeds as 2Ag++Sn2+xe2x86x922Ag+Sn4+. The book also describes that Ag colloids cause coloring of the glass. Another relevant book is xe2x80x9cJournal of Non Crystalline Solids Vol50, (1982), P107-117xe2x80x9d written by J. E. SHELBY and J. VITKO. Jr.
In view of these books"" teachings, the first technique of the present invention enables the transition metal or the transition metal oxide included in the silver electrodes to prevent Ag ions from diffusing, thereby preventing Ag colloidal particles from growing. Moreover, the transition metal or the transition metal oxide is colored with a red to blue color that is complementary to a yellow color. This also helps prevent the yellowing.
Also, with the second technique, platinum group metals (or Re) or their oxides included in the silver electrodes have the pinning effect which suppresses Ag ions to diffuse into the glass substrate and in the dielectric glass, and at the same time suppresses Ag ions to be reduced. Accordingly, a smaller number of Ag colloidal particles end up growing, thereby preventing the yellowing.
Also, with the third technique, metal oxides or metals coating the surfaces of the Ag particles prevent Ag ions from diffusing during baking. This reduces a number of Ag collide particles that end up growing.
Also, with the fourth technique, the concentration of metal ions that possess reducing action on Ag ions in the vicinity of the surface of the substrate in the PDP is set at 1000 ppm or less. Therefore, even if Ag ions diffuse from the silver electrodes onto the surface of the substrate, a chance of the Ag ions being reduced is low. Accordingly, a smaller number of Ag colloidal particles end up growing.