Pumps – Electrical or getter type
Reexamination Certificate
1999-09-15
2002-07-23
Patel, Ashok (Department: 2879)
Pumps
Electrical or getter type
C313S553000, C313S554000, C313S556000, C313S558000, C313S559000, C313S562000, C417S048000, C417S051000
Reexamination Certificate
active
06422824
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a getter assembly for use in a vacuum display panel and more particularly, relates to a getter assembly for use in a vacuum display panel that consists of a non-evaporative getter and an evaporative getter positioned juxtaposed to each other such that ions emitted by the evaporative getter upon activation substantially shields the non-evaporative getter so that gases emitted by the non-evaporative getter upon activation does not affect a state of vacuum in the display panel.
BACKGROUND OF THE INVENTION
In the fabrication of vacuum display devices such as FED (field emission device), PDD (plasma display device) and VFD (vacuum fluorescence display) etc., the degree of high vacuum achieved in a cavity of the device directly affects the quality and the lifetime of the device. Achieving a high vacuum in such devices is therefore an utmost important condition in fabricating devices of high quality and reliability. An effective means for reducing or eliminating residual gases in the cavity of the device, in turn, determines the degree of high vacuum that can be achieved. These gases may include H
2
, CO
2
, CO, H
2
or any other gases emitted during the tip-off process from the molten glass and any other gases that tend to chemically absorb to the surfaces of the components in the device.
In most vacuum display devices, electrons are emitted from electron emitters such as microtips in a FED device for generating the display. When residual gases exist in the cavity of the device, the emitted electrons cause ionization of the residual gases which not only reduces the efficiency of the device, but also causes arcing problem resulting in serious damage to the device.
In the fabrication of vacuum display devices, a vacuum between about 10
−6
and 10
−7
Torr is normally required in order for the device to function properly. For instance, when a FED device is fabricated between two glass plates in which an upper glass plate is coated with a fluorescent coating on an inside surface and the lower glass plate is formed with a multiplicity of microtips on an inside surface, and after the upper and the lower glass plates are fused together by side panels of glass (by a fusing agent such as glass frit), at least one vent tube is left open for the lip final withdrawal of air and gases from the cavity by a vacuum pump. During the vacuum withdrawal process, the cavity is pumped by a high vacuum pump while the device baked at a temperature between 300~400° C. for several hours. The pumping and the baking process normally get rid of most gases in the cavity, however, some gases which have strong absorption characteristics are attached to the device walls (especially at the bake temperature) and cannot be eliminated. Thus, after the vent tubes are sealed, the minute amount of residual gases cause a drop in the vacuum and furthermore, may cause ionization when bombarded by the electrons leading to severe damages to the device.
The residual gases in the cavity of a vacuum display device have been investigated to determine their sources or origin. One of the main sources of the residual gases is the molten glass material during the sealing or the tip-off of the vent tubes. Another major source of the residual gases is the material that is used to form the microtips, in the case of a field emission display device. It has been found that the microtip material tends to absorb gases that cannot be released at the normal bake temperature of 300~400° C. Since it is impossible to completely eliminate the residual gases in a vacuum display device cavity after the device is sealed from the atmosphere, methods and devices for eliminating such residual gases after tip-off have been developed to resolve the outgassing problem occurred in the fabrication of such devices.
Getter materials are first developed to meet the needs of high vacuum during the process and the life of electron tubes many years ago. Pure barium encapsulated in iron or nickel tubes of small diameters was first utilized for such purpose. A compound of barium-thorium was also used for getters in the early development stage of the material. More recently developed getter materials can be classified into the categories of the evaporative getters (EG) and the non-evaporative getters (NEG). The most popular materials used as evaporative getters are Ba and Ti. For instance, Ba has been widely used in electronic applications such as CRT tubes. Ba is frequently used in the form of a compound of Ba/Al, such as BaAl
4
, an intermetallic compound. A typical Ba/Al compound is supplied commercially by the SAES Company of Milan, Italy.
In more recently developed electronic devices which utilize higher power, the high operating temperature and the high voltage make the use of evaporative type getter materials such as barium impossible. The non-evaporative getter materials become necessary and are developed for such use. A typical non-evaporative getter can be a thin layer of zirconium or titanium powder deposited on an anode strip. Metal alloys that contain zirconium or titanium such as a zirconium-aluminum alloy have also been developed for use as non-evaporative getters.
The getter materials normally require activation by an electrical current in order to function as a gas absorber. An activated and unsaturated getter surface readily reacts with residual gases that normally present in vacuum display devices which includes H
2
, H
2
O, CO, CO
2
, N
2
and O
2
. When evaporative getters are utilized, activation is achieved by evaporating the getter material and thus creating a fresh unsaturated metallic film that readily absorbs gases by a chemical reaction. The function of the non-evaporative getters is more complex which normally involves an activation process carried out by properly heating the getter material and promoting a bulk diffusion of oxygen of a passivating surface layer until the surface is sufficiently clean to start absorbing the impinging gases.
The evaporative getter materials, i.e., frequently barium-containing materials, operate in a temperature range of 800° C.~1200° C. from an alloy that releases vapor of the metal getter material. The non-evaporative getter materials normally operate at different temperature ranges which consist of alloys based on titanium and/or zirconium. The evaporative and non-evaporative getter materials each having its own characteristics and benefits that are not achievable by the other. The combined use of EG and NEG therefore presents unique advantages that combines both that offered by the EG and the NEG. Even though the combination use of EG and NEG has been attempted by others, no effort has ever been made in the positioning of the two different types of getter materials in order to achieve an optimum result in absorbing residual gases in a vacuum device.
It is therefore an object of the present invention to provide a getter assembly for use in a vacuum display panel that does not have the drawbacks or shortcomings of the conventional getter assemblies.
It is another object of the present invention to provide a getter assembly for use in a vacuum display panel wherein the EG and NEG are uniquely positioned to compliment the function of each getter and to achieve an optimum result.
It is a further object of the present invention to provide a getter assembly for use in a vacuum display panel wherein an evaporative getter is positioned juxtaposed to a non-evaporative getter in a cavity of the device.
It is still another object of the present invention to provide a getter assembly for use in a vacuum display device wherein an evaporative getter and a non-evaporative getter are positioned juxtaposed to each other while each is connected to an electrode for activating by an electrical current.
It is still another object of the present invention to provide a getter assembly for use in a vacuum display device wherein an evaporative getter and a non-evaporative getter are both mounted inside a cavity of the device juxtaposed to each other.
I
Jean Ruey-Feng
Lee Cheng-Chung
Industrial Technology Research Institute
Patel Ashok
Tung Randy W.
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