Electric lamp and discharge devices – With getter
Reexamination Certificate
1999-06-04
2001-01-09
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With getter
C313S560000, C313S561000, C313S481000, C445S055000, C445S041000, C445S042000
Reexamination Certificate
active
06172460
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a display device comprising at least one compartment which contains an ionizable gas mixture, at least one composite gas of which is a gas of the group constituted by at least hydrogen, said compartment being provided with electrodes for selectively ionizing the ionizable gas during operation, and a getter material in connection with the ionizable gas.
The invention also relates to a method of manufacturing such a display device.
Display devices for displaying monochromatic or color images are, inter alia, plasma-addressed liquid crystal display devices, referred to as PALC displays, preferably of the flat-panel type. PALC displays are used as television and computer displays.
A display device of the type described in the opening paragraph is known from EP-A 0 833 363. The display device of the flat-panel type described in this patent application has a display screen with a pattern of (identical) data storage or display elements and a multitude of compartments. The compartments are filled with an ionizable gas and are provided with electrodes for (selectively) ionizing the ionizable gas during operation. In the known display device, the compartments have the shape of parallel, elongated channels (shaped as a channel plate) which function as selection means for the display device (the plasma-addressed row electrodes). By applying a voltage difference across the electrodes in one of the channels of the channel plate, electrons are emitted (from the cathode), which electrons ionize the ionizable gas while forming a plasma (plasma discharge). When the voltage across the electrodes in one channel is switched off and the gas is deionized, a subsequent channel is switched on. At the display screen side of the display device, the compartments are closed by a (thin) dielectric layer (“microsheet”) provided with a layer of an electro-optical material, and further electrodes which function as data electrodes or column electrodes of the display device. The further electrodes are provided on a substrate. The display device is constituted by the assembly of the channel plate with the electrodes and the ionizable gas, the dielectric layer, the layer of the electro-optical material and the further electrodes.
To increase the lifetime of such display devices, decrease the ignition voltage of the plasma and obtain a more rapid extinction of the plasma, several percents of hydrogen are added to an ionizable (basic) gas such as helium in the known display device. The hydrogen gas is supplied in a getter which consists of a ZrVFe alloy in the known display device and is secured by means of a resilient construction in an exhaust box of the compartment.
In practice, the getter is first secured in the exhaust box, whereafter the exhaust box is fritted to the channel plate at approximately 450° C. The frit comprises an organic binder. The getter material is then contaminated with vapor of this binder so that the necessary exhaust time will be longer. To prevent hydrogen from escaping due to excessive temperatures in subsequent thermal treatments and to prevent such a high pressure build-up in the channel plate that the microsheet breaks, the exhaust box is placed in a water-cooled metal capsule during this thermal treatment. Besides the above-mentioned contamination of the getter material, this method has the drawback that the orientation material is not cured or insufficiently cured at the area of the cooled part when using liquid crystal material as an electro-optical material.
More generally, this manufacturing method has the drawback that heating and supplying the getter material with hydrogen results in an unwanted delay in the manufacture of the display device.
OBJECTS AND SUMMARY OF THE INVENTION
It is, inter alia, an object of the present invention to obviate one or more of said drawbacks.
To this end, a display device according to the invention is characterized in that the getter material is accommodated in a capsule of radiation-absorbing material.
The invention is based on the recognition that, due to the use of a capsule to be introduced into the exhaust box at a later stage, the getter material therein can be supplied in advance, whereafter the capsule can be introduced into the vacuum space at a later point of time and opened after completion of the panel. Since the getter material is now not supplied in advance in a holder in the exhaust box, which is subsequently fritted to the channel plate at approximately 450° C. with an organic binder, the contamination mentioned above will be prevented. To be able to open the getter material-filled capsule at a later stage, for example, by means of a laser, this capsule is made of a radiation-absorbing material.
Since the hydrogen gas (or another suitable gas comprising a gas of the group constituted by at least hydrogen, deuterium and hydrogen deuterium) is accommodated in advance in the getter material in a separate capsule which is not subjected to high temperature treatments, the risk of explosion of the capsule is negligible, even with very thin walls of the capsule (2 mm). Breakage of the microsheet is thereby prevented. The getter material is preferably completely enclosed by the wall of the (preferably tubular) capsule. The material used for the capsule may be, for example steel or blue glass which satisfactorily absorbs energy of a laser so that the capsule can be easily opened afterwards. Another suitable material is an alloy with a shape memory. The capsule used should have such a wall thickness that it can withstand the pressure of the hydrogen which is being released during a possible thermal treatment. To this end, the ratio between wall thickness and internal diameter is preferably between 0.3 and 3.
Since the getter material is not contaminated and the capsules can be filled (charged) parallel to the filling of the channel plate, the manufacturing step for filling the display panel with ionizable gas is considerably shorter. Moreover, the cooling treatment may be dispensed with so that the orientation layer of the LC material is cured throughout its surface.
The capsule is preferably arranged in a kind of “reservoir” for example in a chamber of the display device comprising the exhaust connection of the display device, also referred to as “exhaust box”
Instead of making use of the exhaust box for accommodation of the means, the means may be alternatively arranged in one or more compartments.
According to the invention, a method of manufacturing such a display device is characterized in that the method comprises at least the steps of:
i) filling the compartment with an ionizable gas, at least one composite gas of which comprises a gas of the group constituted by hydrogen, deuterium and hydrogen deuterium,
ii) supplying a capsule of radiation-transmissive material with a getter material, comprising the gas of the group constituted by hydrogen, deuterium and hydrogen deuterium,
iii) introducing the capsule into the compartment and subsequently sealing the compartment,
iv) opening the capsule.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.
REFERENCES:
patent: 5525861 (1996-06-01), Banno et al.
patent: 5525862 (1996-06-01), Miyazaki et al.
patent: 5917283 (1999-06-01), Roberson et al.
patent: 6057643 (2000-05-01), Kurai
patent: 0833363A2 (1998-04-01), None
Damen Johannes P. M.
Van Bommel Cornelus H. M.
Van Rijswijk Ronald
Patel Ashok
U.S. Philips Corporation
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