Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2002-01-03
2003-10-21
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C345S074100
Reexamination Certificate
active
06636002
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a field emission display, and in particular to a field emission display (FED), a method for measuring a vacuum degree thereof, and a method for automatically activating a getter thereof which can constantly maintain the vacuum degree of an FED panel during an operation period, by monitoring variations of the vacuum degree in the panel, and feeding back variations of an anode current to a getter heating device to automatically reactivate the getter when a current value of the anode is reduced over a predetermined value.
2. Description of the Related Art
Generally, the FED requires an internal vacuum degree of a panel below 10
−7
Torr during the operation in the same way as CRT.
However, gases such as O
2
, H
2
O, CO
2
, CO, H
2
and CH
4
are generated from a fluorescent material, metal, insulating material and glass substrate during the operation of the FED. Since the oxidative gases such as O
2
, H
2
O, CO
2
and CO oxidize a metal tip particularly, a work function of the metal tip is changed so as to deteriorate an electron emission property.
In addition, the emitted gas molecules collide with electrons emitted from the metal tip, and thus are ionized to generate metal positive ions. The metal positive ions are accelerated toward the cathode due to a high electric field between the panels, and sputters the metal tip, thereby damaging the metal tip.
As publicly known, when the FED has been used for a long time (over about 10,000 hours), the vacuum degree of the panel is increased by 10
−3
Torr. Here, discharge between the anode and the cathode may seriously damage the panel.
In order to solve the foregoing problems, there has been suggested a method for increasing a vacuum degree of a panel through the adsorption of internal gases by using a getter. That is, the getter removes reactive gases such as O
2
, H
2
O, CO
2
, CO, H
2
and CH
4
according to chemical reaction with the gases on the activated surface. The getter is divided into an evaporation type getter and a non-evaporation type getter. The evaporation type getter is a mixture of BaAl
4
alloy and Ni powder which is put in a special vessel. In addition, the evaporation type getter requires a high temperature heating activation process at a temperature of 850° C.
Currently, the evaporation type getter has been applied to the CRT having a large exhaust space. However, when the evaporation type getter is applied to the FED, it is difficult for the evaporation type getter to be applied because the substrate glass cannot endure such a high activation temperature.
The non-evaporation type getter contains a metal alloy of Zr and Ti and a slight amount of Al, V and Fe. Since an activation temperature of the non-evaporation type getter is about 400° C., the non-evaporation type getter is applied to the FED. However, the getter applied to the FED is activated once in an initial sealing process, and the surface of the getter is gradually saturated by gas particles outgassed from the panel. When the surface of the getter is completely covered by the surface adsorption of the gas molecules, the getter cannot normally play a part in a pump.
Accordingly, when the FED is used, the surface of the getter should be cleaned by periodically reactivating the getter. However, the getter applied to the conventional FED cannot be reactivated during use of the FED. It is also difficult to precisely measure a reactivation point of the getter.
SUMMARY OF THE INVENTION
In accordance with the present invention, a field emission display (FED) includes: a monitoring emitter being installed at an outer portion of an active area of a cathode plate, and receiving a constant voltage; and a current measuring electrode being disposed at an outer portion of an active area of an anode plate, and receiving a constant voltage to measure the current flowing to the monitoring emitter.
Here, the current measuring electrode is positioned to face the monitoring emitter, and the constant voltage is applied thereto, individually from a display voltage of the cathode plate and the anode plate.
In addition, a method for measuring a vacuum degree of an FED includes the steps of: measuring current variations of a monitoring emitter in electron emission of a display emitter, when the vacuum degree is changed by gas molecules outgassed from a panel of the FED; and monitoring variations of the vacuum degree in the panel of the FED according to the measured current variations of the anode.
A method for automatically activating a getter of an FED includes the steps of: setting up an aimed vacuum degree according to an optimal operation state of the FED; measuring an anode current in the aimed vacuum degree by a voltage applied to a monitoring emitter and a voltage applied to a current measuring electrode, and feeding back the anode current to a heating device of the getter; and automatically operating the heating device to automatically reactivate the getter, when the current of the anode is reduced from a current value for the aimed vacuum degree below a predetermined range.
The aimed vacuum degree ranges from 10
−8
Torr to 10
−6
Torr.
REFERENCES:
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patent: 5847495 (1998-12-01), Yamanobe et al.
patent: 6059627 (2000-05-01), Dean et al.
patent: 6144350 (2000-11-01), Fujii et al.
patent: 6169356 (2001-01-01), Ohnishi et al.
patent: 6231412 (2001-05-01), Kawade et al.
patent: 6246178 (2001-06-01), Isono
patent: 6344711 (2002-02-01), Ohnishi et al.
patent: 6384541 (2002-05-01), Ohnishi et al.
A Ming D
Lee & Hong
LG Electronics Inc.
Wong Don
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