Electric lamp and discharge devices – With getter – Gas or vapor device type
Reexamination Certificate
1998-10-07
2002-10-29
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With getter
Gas or vapor device type
C313S553000, C313S582000
Reexamination Certificate
active
06472819
ABSTRACT:
CLAIM FOR PRIORITY
This patent application claims priority under 35 U.S.C. § 119 from Italian Patent Application No. M197 A 002362, filed Oct. 20, 1997, which is incorporated herein by reference for all purposes.
BACKGROUND OF THE INVENTION
The present invention relates generally to plasma flat panel displays and, more particularly, to a getter system for plasma flat panel displays.
Plasma flat panel displays, which are sometimes referred to as “plasma display panels” or “PDP,” have long been studied as potential replacements for the cathode ray tube (CRT) displays presently used in devices such as televisions and computer monitors. It is expected that commercial products incorporating plasma flat panel displays will be brought to market in the near future.
A plasma flat panel display includes front and rear glass panels that are sealingly joined together along their peripheral edges with a low-melting point glass paste. A number of functional components, e.g., electrodes and phosphors, are provided in the inner space between the front and rear glass panels, which is filled with a mixture of rare gases. The principle of operation of a plasma flat panel display is the conversion of ultraviolet radiation into visible light by phosphors. The ultraviolet radiation is generated in the rare gas mixture when an electrical discharge is produced therein. Thus, to use a plasma flat panel display as a screen for a television or a computer monitor, it is apparent that a plurality of extremely small light sources is needed to form a suitable image. To satisfy this requirement, a plurality of electrode pairs for generating localized electrical discharges is provided in the inner space between the front and rear glass panels. The electrical discharges generated by the electrode pairs are confined within a small area by not only applying a potential difference to a predetermined pair of single electrodes, but also dividing the inner space between the front and rear glass panels into a series of microspaces, e.g., parallel channels having a width of about 0.1-0.3 mm.
FIGS. 1 and 2
illustrate the configurations used to define microspaces in two known plasma flat panel displays. As shown in
FIG. 1
, plasma flat panel display
10
includes front glass panel
11
and rear glass panel
12
. Front glass panel
11
carries a first series of electrodes
13
(indicated by the dashed lines) and rear glass panel
12
carries a second series of electrodes
14
. Walls
15
define a plurality of parallel channels
16
, each of which has one of electrodes
14
located therein. The second series of electrodes
14
is orthogonal to the first series of electrodes
13
. Referring to
FIG. 2
, in plasma flat panel display
20
a plurality of cell structures
21
divide the space between front glass panel
11
and rear glass panel
12
into small cells having a side dimension of, e.g., 0.1-0.3 mm. The cell structures
21
also define a plurality of parallel channels
16
. As shown in
FIG. 2
, the second series of electrodes
14
is oriented so that the electrodes pass through channels
16
, i.e., the electrodes are perpendicular to the direction of channels
16
. In plasma flat panel display
20
the first series of electrodes
13
, which is not shown in
FIG. 2
, is orthogonal to the second series of electrodes
14
.
The structures that define the microspaces, e.g., simple walls as shown in
FIG. 1
or more complex cell structures as shown in
FIG. 2
, extend over the entire surface of the front and rear glass panels, except for an edge area at the perimeter of the panels. In operation an image is formed on the front glass panel in an image-forming area, which corresponds with the area over which the microspace-defining structures extend. The edge area, which is typically 2-15 mm wide depending on the dimensions of the plasma flat panel display, defines a channel that has a high gas conductance and therefore serves as the primary gas conductance within the inner space between the front and rear glass panels. The channels defined in the image-forming area have a much lower gas conductance than the channel in the edge area and therefore serve as secondary gas conductance sources.
The rare gas mixture used to fill the inner space between the front and rear gas panels generally consists of helium and neon with minor amounts of xenon or argon. To ensure proper operation of a plasma flat panel display, the chemical composition of the rare gas mixture in which the plasma is formed must remain constant. If traces of atmospheric gases such as nitrogen, oxygen, water, or carbon oxides enter the rare gas mixture, then changes in the electrical operating parameters of the plasma flat panel display occur, as disclosed in the publication by W. E. Ahearn and O. Sahni, “Effect of reactive gas dopants on the MgO surface in AC plasma display panels,” IBM J. Res. Dev., Vol. 22, No. 6, November 1978, pp. 622-625. In the manufacturing of plasma flat panel displays, after the front and rear glass panels have been joined together, atmospheric gases are evacuated from the inner space by means of a pump connected to the inner space by means of a tiny hole formed at a corner of one of the panels at a position corresponding to the edge area. The rate at which the atmospheric gases can be evacuated from the inner space is limited because all the gas in the channels defined in the image-forming area flows into the channel at the edge area, thus creating an accumulation of gas that cannot be quickly removed. The pressure variation in the various areas of the inner space has not been studied in depth and, consequently, plasma flat panel display manufacturers use empirically determined evacuation times of several hours as a compromise between the conflicting demands of minimizing production time (and costs) and obtaining low residual pressures of atmospheric gases required for proper operation of the display. Another source of impurities in the inner space is the degassing of the materials disposed therein, e.g., the phosphors, caused by the heating and electronic bombardment that occurs during operation of the display.
Japanese Patent Publication No. 5-342991 discloses method of removing impurities from the inner space during the manufacturing of a plasma flat panel display. In this method a deposit of porous magnesium oxide, MgO, is provided along an edge of the display, with the ends of the deposit being connected to a source of direct current. When a voltage is applied, the MgO deposit is capable of sorbing certain impurities, e.g., water and carbon dioxide, from the inner space. Once the manufacturing process is finished, however, the electrical contacts are removed and the MgO deposit loses its ability to sorb impurities. Consequently, the MgO deposit does not sorb the gaseous impurities generated by the degassing of the components disposed within the inner space. Thus, this method does not provide a solution to the degassing problem, which causes the gaseous impurity concentration within the inner space to increase over the course of the display's service life.
In view of the foregoing, there is a need for an improved process of evacuating the inner space of plasma flat panel displays during manufacturing that reduces evacuation time. There is also a need for a mechanism for sorbing gaseous impurities that are generated within the inner space during the display's service life.
SUMMARY OF THE INVENTION
Broadly speaking, the invention fills this need by providing a getter system for use in plasma flat panel displays. The getter system includes one or more nonevaporable getter devices that are configured so that they do not significantly reduce the gas conductance within the inner space defined by the front and rear panels of the display.
In one aspect of the invention, a getter system for use in a plasma flat panel display is provided. The plasma flat panel display preferably has front and rear panels sealingly joined together at peripheral edges thereof to define an inner space and a plurality of walls disposed within the in
Amiotti Marco
Caloi Roberto M.
Carretti Corrado
Dort David B.
Guharay Karabi
Hickman Paul
Patel Ashok
Perkins Coie LLP
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