Multi-compartment getter-containing flat-panel device

Details Multi-compartment getter-containing flat-panel device Multi-compartment getter-containing flat-panel device

1999-02-25

2001-02-27

Patel, Nimeshkumar D. (Department: 2879)

Electric lamp and discharge devices

With getter

C313S561000, C313S563000, C313S495000

Reexamination Certificate

active

06194830

ABSTRACT:

FIELD OF USE
This invention relates to gettering—i.e., the collection and removal, or effective removal, of small amounts of gases from an environment typically at a pressure below room pressure. In particular, this invention relates to techniques for activating getters used in structures such as flat-panel devices, and to structures designed to house the getters.
BACKGROUND
A flat-panel device contains a pair of generally flat plates connected together through an intermediate mechanism. The two plates are typically rectangular in shape. The thickness of the relatively flat structure formed by the two plates and the intermediate connecting mechanism is small compared to the diagonal length of either plate.
When used for displaying information, a flat-panel device is typically referred to as a flat-panel display. The two plates in a flat-panel display are commonly termed the faceplate (or frontplate) and the baseplate (or backplate). The faceplate, which provides the viewing surface, is part of a faceplate structure containing one or more layers formed over the faceplate. The baseplate is similarly part of a baseplate structure containing one or more layers formed over the baseplate. The faceplate structure and the baseplate structure are sealed together, typically through an outer wall.
A flat-panel display utilizes various mechanisms such as cathode rays (electrons), plasmas, and liquid crystals to display information on the faceplate. In a flat-panel cathode-ray tube (“CRT”) display, electron-emissive elements are typically provided over the interior surface of the baseplate. When the electron-emissive elements are appropriately excited, they emit electrons that strike phosphors situated over the interior surface of the faceplate which consists of transparent material such as glass. The phosphors then emit light visible on the exterior surface of the faceplate. By appropriately controlling the electron flow, a suitable image is displayed on the faceplate.
Electron emission in a flat-panel CRT display needs to occur in a highly evacuated environment for the display to operate properly and to avoid rapid degradation in performance. The enclosure formed by the faceplate structure, the baseplate structure, and the outer wall is thus fabricated in such a manner as to be at a high vacuum, typically a pressure of 10
−7
torr or less for a flat-panel CRT display of the field-emission type. Any degradation of the vacuum can lead to various problems such as non-uniform brightness of the display caused by contaminant gases that degrade the electron-emissive elements. The contaminant gases can, for example, come from the phosphors. Degradation of the electron-emissive elements also reduces the working life of the display. It is thus imperative that a flat-panel CRT display be hermetically sealed, that a high vacuum be provided in the hermetically sealed (airtight) enclosure, and that the high vacuum be maintained thereafter.
A field-emission flat-panel CRT display, commonly referred to as a field-emission display (“FED”), is conventionally sealed in air and then evacuated through tubulation provided on the display.
FIG. 1
illustrates how one such conventional FED appears after the sealing and evacuation steps are completed. The FED in
FIG. 1
is formed with baseplate structure
10
, faceplate structure
11
, outer wall
12
, and multiple spacer walls
13
. The FED is evacuated through pump-out tube
14
, now closed, provided at opening
15
in baseplate structure
10
.
Getter
16
, typically consisting of barium, is commonly provided along the inside of tube
14
for collecting contaminant gases present in the sealed enclosure. This enables a high vacuum to be maintained in the FED during its lifetime. Getter
16
is of the evaporable (or flashable) type in that the barium is evaporatively deposited on the inside of tube
14
.
Getter
16
typically performs in a satisfactory manner. However, tube
14
protrudes far out of the FED. Accordingly, the FED must be handled very carefully to avoid breaking getter-containing tube
14
and destroying the FED. It is thus desirable to eliminate tube
14
. In so doing, the location for getter
16
along the inside of tube
14
is also eliminated.
Simply forming an evaporable barium getter at a location along the interior surface of baseplate structure
10
or/and faceplate structure
11
is unattractive. Specifically, a getter typically needs a substantial amount of surface area to perform the gas collection function. However, it is normally important that the active-to-overall area ratio—i.e., the ratio of active display area to the overall interior surface area of the baseplate (or faceplate) structure—be quite high in an FED. Because an evaporable barium getter is formed by evaporative deposition, a substantial amount of inactive area along the interior surface of the baseplate structure or/and the faceplate structure would normally have to be allocated for a barium getter, thereby significantly reducing the active-to-overall area ratio. In addition, the active components of the FED could easily become contaminated during the getter deposition process. Some of the active FED components could become short circuited.
A non-evaporable getter is an alternative to an evaporable getter. A non-evaporable getter typically consists of a pre-fabricated unit. As a result, the likelihood of damaging the components of an FED during the installation of a non-evaporable getter into the FED is considerably lower than with an evaporable getter. While a non-evaporable getter does require substantial surface area, the pre-fabricated nature of a non-evaporable getter generally allows it to be placed closer to the actual display elements than an evaporable getter.
Non-evaporable getters are manufactured in various geometries.
FIGS. 2
a
and
2
b
(collectively “FIG.
2
”) illustrate the basic geometries for two conventional non-evaporable getters manufactured by SAES Getters. See Borghi, “St121 and St122 Porous Coating Getters,” SAES Getters, Jul. 27, 1994, pages 1-13. The getter in
FIG. 2
a
consists of metal wire
18
A covered by coating
19
A of gettering material. The getter in
FIG. 2
b
consists of metal strip
18
B covered by coating
19
B of gettering material. A porous mixture of titanium and a zirconium-containing alloy typically forms the gettering material in these two non-evaporable getters.
Upon being placed in a highly evacuated environment, each of the getters in
FIG. 2
is activated by raising the temperature of getter coating
19
A or
19
B to a suitably high value, typically 500° C., for a suitably long activation time, typically 10 min. At constant activation time, the getter performance can be increased by raising the activation temperature. For the getters of
FIG. 2
, the activation temperature can be as high as 900-950° C. above which the getters may be permanently damaged. Alternatively, as the activation temperature is increased, equivalent performance can be achieved at reduced activation time. The opposite occurs as the activation temperature is lowered to as little as 350° C. below which the gettering performance of the getters in
FIG. 2
is significantly curtailed.
A getter typically consists of a porous mixture of particles that sorb gases which contact the outer surfaces of the particles. When the non-evaporable getters of
FIG. 2
are activated in a high vacuum environment, sorbed gases present on the outer surfaces of the getter particles diffuse into the bulk of the getter particles, leaving their outer surfaces free to sorb more gases. The amount of gas which can be accumulated in the bulk of getter particles that are accessible to the gases is typically much more than the maximum amount of gas that the getter can sorb on the outer surfaces of the accessible particles. When the accessible outer getter surface is filled or partially filled with sorbed gases, the getter can be re-activated in a high vacuum environment to transfer the gases on the accessible outer surface to the bulk of the getter particles and again le

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