Electric lamp and discharge devices – With gas or vapor – Three or more electrode discharge device
Utility Patent
1998-06-11
2001-01-02
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Three or more electrode discharge device
C313S584000, C313S643000
Utility Patent
active
06169364
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a display device comprising at least one compartment containing an ionizable gas, walls of the compartment being provided with electrodes for selectively ionizing the ionizable gas, during operation, and comprising an electro-optical layer of an electro-optical material, and means for activating the electro-optical layer.
Display devices for displaying monochromatic or color images include plasma-addressed liquid-crystal display devices, the so-called PALC-displays, which are preferably thin-type displays. PALC-displays are used as television and computer displays.
A display device of the type mentioned in the opening paragraph is disclosed in U.S. Pat. No. 5,596,431 (PHA 60 092). The thin-type display device described in said document comprises a display screen having a pattern of (identical) so-called data storage or display elements and a plurality of compartments. Said compartments are filled with an ionizable gas and provided with electrodes for (selectively) ionizing the ionizable gas during operation. In the known display device, the compartments are mutually parallel, elongated channels (formed in a so-called channel plate), which serve as selection means for the display device (the so-called plasma-addressed row electrodes). The application of a voltage difference across the electrodes in one of the channels of the channel plate, causes electrons to be emitted (from the cathode), which electrons ionize the ionizable gas, thereby forming a plasma (plasma discharge). If the voltage across the electrodes in one channel is switched off and the gas de-ionized, a subsequent channel is energized. At the display-screen side of the display device, the compartments are sealed by a (thin) dielectric layer (“microsheet”) provided with a layer of an electro-optical material and further electrodes serving as the so-called data electrodes are column electrodes of the display device. Said further electrodes are provided on a substrate. The display device is formed 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
A disadvantage of the known display device resides in that such display devices have a limited service life.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to provide, inter alia, a display device having a longer service life.
To achieve this, the display device in accordance with the invention is characterized in that the ionizable gas comprises a gas of the group formed by hydrogen, deuterium and deuterium hydrogen, and in that the display device is provided with means for supplying hydrogen, deuterium or deuterium hydrogen to the ionizable gas.
At the beginning of a plasma-discharge cycle in the display device, a plasma discharge is created in the compartment or in one of the compartments (for example the channels of a PALC-display) by applying a (relatively high) voltage pulse (the so-called “strobe” pulse) across the electrodes in the compartment. Charged particles are created in such a plasma discharge The voltage across and the current through the discharge reach a stationary state (the so-called “steady state”) within a few &mgr;s. After switching off the plasma discharge, the grey level of each display element is checked by applying a (relatively low) voltage across the corresponding further electrode (the data electrode or the column electrode). As a result, a part of the charged particles is drawn towards the (thin) dielectric layer (“microsheet”), which causes an electric field to be formed across the electro-optical layer. As a result, the electro-optical layer is charged like a capacitor until the complete data voltage is present across the layer, causing the transparency of the electro-optical layer to change (for example, it becomes more or less transparent). The degree of transparency is determined by the value of the data voltage. After the discharge has disappeared in the so-called “afterglow”, the compartment forms an insulator and the electro-optical layer remains charged. A new plasma discharge in the compartment acts as a reset of the display element.
In general, the display device comprises a number of compartments, each compartment including at least two electrodes for ionizing the gas.
Important parameters of the plasma-discharge cycle of the display device are the electric conductivity of the plasma discharge and the decay of the conductivity in the afterglow period. If the decay in conductivity of the plasma discharge takes place too slowly, the discharge may continue while a next data line is already being written, which is undesirable. Too rapid a decay of the conductivity also has adverse effects.
The (carrier) gas which is most commonly used in display devices of the type mentioned in the opening paragraph is helium (He). The ignition voltage of the plasma discharge can be reduced by adding small quantities of a gas (of the order of a few percent) to the helium. In general, the ionization potential of such gases is lower than that of helium. The resultant mixtures are referred to as Penning mixtures. A well-known additional gas is hydrogen (H
2
). The use of such gas mixtures does not only influence the ignition characteristic of the plasma discharge but also, for example, the current necessary to maintain the discharge (the so-called sustain current) and the afterglow characteristic of the discharge.
The inventors have recognized that, as regards the service life of the display device, it is important that the composition of the ionizable gas or mixture of gases remains constant during said service life. As the concentrations of the additional gas(es) (added to the helium) are relatively low, it is desirable to take measures to ensure that the (partial) pressure of the additional gas(es) remains as constant as possible. A loss of additional gas(es) can be attributed to diffusion of such gases from the compartment of the display device, or to implantation of such gases, for example, in the electrodes, or to compounding of such gases, as a result of which they no longer contribute to the characteristic of the ionizable gas (plasma discharge, sustain voltage, afterglow characteristic). This results, in the case of hydrogen, in the formation of hydrides.
Checking the pressure of the additional gas(es) is made possible by providing the display device with means for regulating the pressure of the additional gas(es). This is preferably achieved by incorporating materials in the display device which supply hydrogen, deuterium or deuterium hydrogen.
Materials which are suitable for the purpose of the invention ensure a constant partial pressure of the additional gas, said pressure having the desired level for the ionizable gas and being at least substantially independent of the concentration of the gas in the material of the means. Examples of such suitable materials include VZ
2
, LZ
3
, PdZ
0.6
, LaNi
5
Z
6
, LaNi
2
Z
x
, LaCo
5
Z
x
, Zr—Mn—Z
x
or Pd—Ag—Z
x
, wherein L is a lanthanide and Z is hydrogen and/or deuterium. Examples of suitable lanthanum hydrides are LaH
3
and CeH
3
. Other suitable hydride-forming or deuteride-forming materials are Y, Sc and Ti. Further suitable materials comprise compounds of the L&xgr;
2
Z
x
and L&xgr;
5
Z
x
types, wherein L is a lanthanide and &xgr; is, for example, Ni or Co, which compounds may be stoichiometric or non-stoichiometric.
The means are preferably provided in a kind of “reservoir”, for example a chamber of the display device which comprises the pump connection of the display device. The means are situated in this chamber, which is also referred to as “exhaust box”, for example in the form of a layer applied to (one of) the walls of the chamber, or in the form of a pellet of the material, which regulates the partial pressure of the additional gas. As this chamber is in communication with the compartment or compartments of the display device, the partial pressure of the additional gas in each of the compart
Notten Petrus H. L.
Van Maaren Martinus H.
Van Slooten Udo
Day Michael H.
Fox John C.
Gerike Matthew T.
U.S. Philips Corporation
LandOfFree
Electro-optical display device with ionizable gas does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electro-optical display device with ionizable gas, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electro-optical display device with ionizable gas will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2455863