Electric lamp and discharge devices – With luminescent solid or liquid material – Vacuum-type tube
Reexamination Certificate
1998-08-06
2001-05-22
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Vacuum-type tube
C313S309000, C313S558000, C315S169300
Reexamination Certificate
active
06236156
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a micro vacuum pump for maintaining vacuum in a chamber and an apparatus including the same. And, more particularly, the present invention relates to a micro vacuum pump that is capable of maintaining a high degree of vacuum, enhancing exhaust performance, and securing quality over an extended period of time.
2. Description of Related Art
Most apparatuses requiring a vacuum environment employ diverse exhausting methods to enhance the degree of internal vacuum. For example, there are semiconductor manufacturing apparatuses incorporating deposition treatment units, dry etching units, etc., or surface observing apparatuses incorporating electron microscopes, etc. These apparatuses employ ion pumps or turbo-molecular pumps or other types of vacuum pumps that are large and provide high exhausting speed to exhaust the interior of the vacuum chambers of the apparatuses at all times thereby to maintain a high degree of vacuum.
Vacuum airtight apparatuses such as cathode ray tubes (CRTs) or flat panel displays do not carry out regular exhaust by large, expensive vacuum pumps because they are required to achieve reduced size and weight and lower cost. In the vacuum airtight apparatuses, getters composed of metal materials such as barium are activated in the vacuum chambers in the vacuum airtight apparatuses to adsorb residual gases so as to maintain substantially the vacuum.
In a CRT, which is one of those vacuum airtight apparatuses, a getter material placed in the tube is evaporated by external high-frequency induction heating or the like so that it adheres to the inner wall of the tube thereby to exhaust any gas in the tube. In this case, the getter material adhering to the inner wall of the tube is chemically active and adsorbs a residual gas, thus enhancing the vacuum in the tube. In a flat panel display also, the vacuum in the display is retained by the adsorption of a residual gas by a getter material as in the case of the CRT.
Hitherto, a micro vacuum pump adapted to secure vacuum in a vacuum chamber by such an exhausting method has been employing a getter device that has been disclosed under a title “GETTER DEVICE AND FLUORESCENT DISPLAY TUBE HAVING THE GETTER DEVICE” in Japanese Unexamined Patent Publication No. Hei 7-29520 (1995).
In the getter device proposed in the publication, protrusions or emitter cones
103
are disposed on a surface of a cathode electrode
102
opposed to a getter
101
so that they face against the getter
101
as shown in FIG.
1
. The getter
101
is made of barium or other metal material. The emitter cones
103
are conical. A gate electrode
105
is mounted on a cathode electrode
102
via an insulator layer
104
and provides the surfaces opposed to the getter
101
. The gate electrode
105
is provided with holes to be formed around the respective emitter cones
103
. The insulator layer
104
also has holes. The gate electrode
105
provides driving forces for the emitter cones
103
to emit electrons.
In this constitution, relative to the cathode electrode
102
, a positive potential differences Vp is supplied to the getter
101
serving as the anode and a positive potential differences Vg is supplied to the gate electrode
105
. And an electric field is supplied to the emitter cones
103
on the cathode electrode
102
. The emitter cone
103
to which the electric field has been supplied emits electrons passing through the hole of the gate electrode
105
. The electrons collide against the getter
101
to activate the getter
101
. The activated getter
101
develops enhanced reactivity to other atoms and adsorbs gaseous molecules that form the ambient residual gas. This enables the vacuum in the vacuum chamber to be maintained.
Another example that employs a micro vacuum pump is a vacuum airtight apparatus that has been disclosed under a title “VACUUM AIRTIGHT APPARATUS AND DISPLAY DEVICE” in Japanese Unexamined Utility Model Publication No. Hei 7-18341 (1995).
The vacuum airtight apparatus described in the publication is used for a display device that employs a field emission cathode. In this type of display device, an anode electrode
111
that provides a screen has a fluorescent surface
110
on the surface opposed to a cathode electrode
112
as shown in FIG.
2
. Relative to the cathode electrode
112
, a high potential difference Vp is supplied to the anode electrode
111
. For this reason, electrons are emitted from a plurality of protrusions or emitter cones
113
provided to match the pixels on the cathode electrode
112
. The emitted electrons pass holes of a gate electrode
115
and a focusing electrode
116
disposed via two insulator layers
114
and the focusing electrode
116
disposed near the anode electrode
111
before they reach the surface of the anode electrode
111
. The focusing electrode
116
positioned in the vicinity of the anode electrode
111
is constituted by getter materials. The gate electrode
115
and the focusing electrode
116
are set at potential differences Vg
1
and Vg
2
respectively and have the almost same potential to that of the cathode electrode
112
.
In this configuration, the electrons emitted from the emitter cones
113
collide against the surface of the anode electrode
111
and a gas is sputtered from the surface of the anode electrode
111
. The sputtered and released gas has positive ionic molecules, so that it is effectively caught and collected by the focusing electrode
116
composed of the getter materials that have substantially the same potential as that of the cathode electrode
112
. As a result, the residual gas present in the vacuum chamber can be efficiently captured as not to affect the electron emitting capability of the emitter cones
113
.
In the conventional micro vacuum pumps described above, the getters are activated and the activated getters adsorb the gaseous molecules in the vacuum chamber. Hence, active gases including oxygen- and carbon-based gases can be adsorbed, however, inert gases including argon cannot be adsorbed.
Thus, there has been a problem in that the capability of exhausting rare gases, i.e. inert gases, is deteriorated and the quality and performance required of the vacuum pumps cannot be ensured. This means that unstable images, deteriorated luminance, or shorter service life has been observed when driving a CRT, flat panel display, or the like in such a vacuum environment.
Further, in the vicinity of the emitter cones or the protrusions, ionized residual gases such as argon having a high sputtering yield pour down on the negative-electrode protrusions and inevitably damage the protrusions that emit electrons in the getter device. This leads to marked deterioration in the electron emitting property and makes it difficult to retain stable gettering performance with good repeatability over a long period of time.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been made with a view toward solving the problems described above. And it is an object thereof to provide a micro vacuum pump that ensures quality and good repeatability and maintains stable getter action over a prolonged period of time, and an apparatus assembling the same.
To this end, according to one aspect of the invention, there is provided a micro vacuum pump including a first conductive substrate that has many protrusions each of which has the identical form with the above emitter cone and a second conductive substrate disposed with a predetermined interval from the first conductive substrate so that it is opposed to the protrusions. A gate electrode is mounted via an insulator layer on the first conductive substrate and near the protrusions so that it is opposed to the second conductive substrate. A negative potential is supplied to the second conductive substrate, and a negative potential is supplied to the gate electrode, relatively to the protrusions or the first conductive substrate.
With this arrangement, an active gas and a rare gas are ionized in the vicinity of the protrusions
NEC Corporation
Patel Vip
Williams Joseph
Young & Thompson
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