Flat-panel display and method of manufacture

A flat-panel display is constructed by sealing a metal flange to a frame on a glass pane, then mounting an electrode structure against the pane within the frame, then placing an impervious malleable sheet over the electrode structure, then sealing the sheet to the flange, and then pumping air from the space between the sheet and the glass pane, and backfilling as required.

The present invention relates in general to luminescent flat-panel displays 
and to methods of manufacturing such panels, and it relates in particular 
to an improvement of the invention disclosed in U.S. Pat. No. 4,303,847 
and assigned to the same assignee as is the present invention. 
BACKGROUND OF THE INVENTION 
The above-identified copending application discloses a flat-panel display 
in which a compliant display-producing electrode structure is held against 
the rear face of a glass panel by a thin, impervious, malleable sheet 
which overlies the electrode structure and is hermetically sealed to the 
panel through a continuous area surrounding the viewing area of the glass 
panel. The hermetic seal described in the said application is formed by a 
conventional glass-to-metal sealing process which is carried out at high 
temperatures of the order of 400.degree. C. to 800.degree. C. after the 
electrode structure has been mounted in the panel. Consequently, the 
electrode structure must withstand the high temperatures required to 
effect the necessary glass-to-metal seal. This requisite has severely 
restricted the choice of materials available for use in the electrode 
structure, and has also limited the types of electrode structures which 
may be used. For example, because of the expansion and subsequent 
contraction of the components of the panel, thermal matching of the 
components is desirable. 
SUMMARY OF THE INVENTION 
Briefly, there is provided in accordance with the present invention an 
improved modification of the panel and method of fabrication thereof which 
enables the use of electrode structures, components and materials which 
are unable to withstand high temperatures such as those required to effect 
glass-to-metal seals, which temperatures are ordinarily in the range of 
400.degree. C. to 600.degree. C. but are higher where borosilicate glass 
is used. In keeping with one aspect of the invention, a thin metal flange 
is initially sealed to a continuous area of the glass panel surrounding 
the window or viewing area by any suitable glass-to-metal sealing method. 
Thereafter, the electrode structure is positioned over the viewing area of 
the glass panel, a compressible insulating blanket and a metal foil rear 
sheet are placed over the electrode structure, and the rear metal sheet is 
hermetically sealed to the flange in a welding or other suitable 
low-temperature or localized heating operation wherein the temperatures of 
the electrode structures need not be appreciably raised above ambient. The 
pressure in the cavity which is located between the rear sheet and the 
glass panel and which contains the electrode structure is then reduced to 
below ambient pressure whereby the electrode structure is compressed 
against the glass panel by the rear sheet. 
It may thus be seen that the electrode structure need not be subjected to 
temperatures exceeding the normal operating temperatures of the panel, 
thereby facilitating the design and manufacture of the electrode structure 
and of the panel.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention constitutes an improvement of the flat-panel displays 
and methods of manufacture disclosed in U.S. Pat. No. 4,303,847 and the 
specification and drawings of that patent are incorporated herein by 
reference. This invention may be used with many different types of 
displays including, inter alia, plasma-discharge panels, 
cathodoluminescent panels, electroluminescent panels, liquid-crystal 
panels, electrophoretic panels and electrochromic panels. 
Irrespective of the type of panel, however, a flat-panel display embodying 
the present invention utilizes a front glass sheet or pane, a 
substantially compliant or comformable electrode structure positioned 
against the rear face of the glass pane over the window or viewing area 
thereof, and a thin, substantially gas-impervious, malleable rear sheet 
which covers the rear side of the blanket. Although not necessary, a 
compressible pad or blanket covering the rear of the electrode structure 
and located directly beneath the rear sheet is preferred. If the internal 
structure is such that substantial gaps or voids exist into which the rear 
foil or blanket may be drawn, a screen or pliable perforated metal support 
may be interposed between the blanket and foil and the internal structure 
so as to provide a bridge or brace over the void. This brace supports the 
blanket and foil against being pushed into the void by the external 
pressure. The rear sheet is then sealed to a metal flange, which flange 
was hermetically sealed to the glass pane in a previous sealing operation 
prior to mounting of the electrode structure to the glass pane. The space 
between the glass pane and the rear sheet is then evacuated and may be 
back-filled with a suitable gas if the particular type of display system 
used requires back-filling. The pressure in the cavity is normally 
maintained below ambient wherefor the rear sheet is drawn toward the glass 
pane and holds the electrode structure in a fixed position against the 
glass pane. The cavity in which the electrode structure is located is thus 
sealed from the ambient without the exertion of any substantial tensile, 
sheer or compressive forces on the glass pane. Moreover, the glass pane 
thus provides the primary support member in the panel, and the seals 
between the glass pane and the metal flange and between the rear sheet and 
the metal flange are not support members nor are any substantial stresses 
exerted on these seals during either the manufacture or use of the panel. 
The manner in which the panel is evacuated and back-filled does not 
constitute a part of this invention but may be carried out in any suitable 
manner including those disclosed in the said copending application. 
Referring particularly to FIG. 1, a flat-panel display is generally 
identified by the reference character 10 and comprises a glass pane 12 at 
the front (bottom as viewed in FIG. 1) and a gas-impervious, malleable 
rear sheet 14. The central portion of the sheet 14 overlies the 
display-producing electrode structure 17 which is disposed against the 
rear face of the glass pane 12. The peripheral area of the sheet 14 is 
hermetically sealed to a metal flange 16 which is hermetically sealed to 
the glass pane throughout a continuous area surrounding the electrode 
structure 17. A plurality of electric conductor elements or leads 18 which 
may be screened onto the pane 12 sealably extend into the cavity within 
the panel and are electrically connected to the appropriate elements in 
the electrode structure. These leads extend from the panel and may be 
connected to the control circuits for the panel. 
As best shown in FIG. 2, the flange 16 is hermetically sealed to the glass 
pane 12 by a frit-type seal 20. Considered in greater detail, four glass 
strip members 22 are laid over the glass pane along the four side edges 
thereof. The leads 18 extend between one or more of these strips and the 
underlying surface of the glass pane 12. For convenience of assembly the 
leads may be tack-glued to the pane with a suitable cement. The flange 16 
is a continuous flat member formed of a gas-impervious material such as 
aluminum or copper foil, and it is placed on the strips 22 with its inner 
edge 16a spaced outwardly from the inner edges 22a of the frame strips 22 
and with its outer edges 16b positioned a substantial distance outwardly 
of the outer edges 22b of the strips 22. For convenience, the flange 16 
may be tack-glued to the frame strips. A moat, not shown, is then used to 
hold the frit in place while the frit seal bead 20 is effected. The 
sealing bead hermetically seals the frame pieces 22 to the pane 12 and to 
the flange member 16. If the leads 18 are separate wires they may be 
provided with an intermediate loop portion 18a to permit the molten frit 
to flow thereunder during the sealing operation so as to effect a hermetic 
seal to the leads 18. Inasmuch as the sealing process requires the melting 
of the frit, it is usually carried out at a high temperature exceeding 
400.degree. C. 
After the glass pane 12 has cooled to substantially ambient temperature the 
electrode structure 17 is positioned on the rear face of the glass pane 12 
over the display area or window of the panel, and the leads 18 are 
suitably connected thereto. As is explained in the said application, it is 
desirable that the electrode structure 17 be compliant so that it will 
readily conform to the rear face of the pane 12 when subsequently pressed 
against it. With the electrode structure thus positioned on the pane 12, a 
thin insulating sheet 26 is placed over the display-producing structure 17 
and a stress-distributing and bridging member such as wire-mesh screen 25 
is placed over the insulating sheet. The sheet 26 may be a sheet of 
aluminium oxide paper having a thickness of twenty mils. Then a 
compressible insulating sheet 24, hereinafter called a blanket, is placed 
over the wire-mesh or perforated-metal screen 25. The blanket 24 extends 
outwardly beyond the outer sides of the frame strips 20 but with the outer 
edges of the blanket spaced inwardly from the outer edge of the flange 16. 
If desired, the blanket 24, the screen 25 and/or the insulator 26 may be 
omitted. The gas-impervious, malleable, thin sheet 14, which is preferably 
soft metal foil such as aluminum or copper foil, is placed over the rear 
side of the blanket 24, if used, otherwise it is placed over the rear side 
of the internal structure 17. The peripheral portion of the sheet 14 is 
then hermetically sealed to the peripheral portion of the flange 16 to 
provide a continuous seal. In FIG. 2 this seal is shown to be effected by 
a sealing bead 27 bonded to the adjacent surfaces of the sheet 14 and to 
the flange 16. However, other types of seals, such as butt seals, may be 
used. Where both the sheet 14 and the flange 16 are metal, they may be 
hermetically sealed together by welding. However, irrespective of the 
sealing method which is used, it is desirable that the temperature of the 
glass pane 12 and the electrode structure 17 not be changed appreciably 
during the sealing operation. 
Upon subsequent evacuation of gasses from the space in which the electrode 
structure 17 is enclosed, the pressure differential across the rear sheet 
will cause it to be drawn downwardly over the electrode structure 17 and 
the overlying blanket 24 thereby to hold the electrode structure in the 
predetermined desired position against the glass pane 12. 
As may be seen from an inspection of FIG. 3, the frit sealing bead 20 
extends inwardly from the inner corners formed by the frame pieces 22 
thereby to seal over the spaces at the corners between the frame members 
22. 
In FIG. 2 the rear surface of the electrode structure 17 is illustrated as 
being flat. However, it may have any configuration which, for example may 
be undulating or irregular. 
Referring now to FIGS. 4A and 4B, there is shown one edge of a novel 
flat-panel display in two successive stages of manufacture. As shown in 
FIG. 4A, one of several metal leads 30 lies against the rear face of a 
glass pane 32 constituting the face and principal support member of the 
panel. A glass frame strip or member 34 rests on the leads 18 and on the 
pane 32 near the edge thereof. It will be understood that four such strips 
are provided and surround the viewing area of the pane 32 in the same 
manner in which the frame members 22 surround the viewing area of the pane 
12 in FIGS. 1-3. A unitary, rectangular annular metal flange 35 is placed 
on the frame pieces 34, and if desired, the flange 35 is tack-glued to the 
frame pieces with a suitable cement. Pieces of metal foil or the like 36 
and 38 are then used to form a moat into which powdered or slurried frit 
or other suitable sealant is placed. The inner metal foil piece 36 is 
located interiorly of the inner edges of the frame pieces, and the outer 
metal foil piece 38 is located outwardly of the inner edge 35a of the 
flange member 35. It may thus be seen that the moat completely surrounds 
the central viewing area of the glass pane 32. 
With the moat filled with a suitable sealant such as frit, the entire 
assembly is placed in an oven and heated to the sealing temperature of the 
sealant for the necessary time to insure a hermetic seal to the pane 32, 
the leads 30, the frame pieces 34 and the flange member 35. After the 
panel has been cooled to about ambient temperature the foil pieces 36 and 
38 are removed as by peeling them away without damaging the integrity of 
the seal. It should be noted that frit contracts a substantial amount when 
melted, wherefor the moat must be substantially deeper than the height of 
the final sealing bead 42 where frit is used as the sealant. The electrode 
structure 17 is then positioned over the viewing area of the glass pane 32 
and a compressible pad or blanket 44 of insulating material may be placed 
thereover. A thin, malleable metal foil sheet 46 is then placed over the 
blanket 44 and the edge portions of the sheet 46 are hermetically sealed 
to the flange member 35 in any suitable sealing process, such, for 
example, as welding. 
As shown, a tubulation 48 is preassembled to the central area of the foil 
sheet 46 for use in evacuating and backfilling the cavity within the 
panel. The tubulation includes a glass or metal tube 50 having an external 
annular flange sealed to the inner surface of the sheet 46. A screen 54 
extends across the inner side of the flange 52 to prevent the blanket or 
parts thereof from being sucked into the tubulation during the evacuation 
process. After completion of the evacuation and backfilling process the 
tube 50 may be sealed in any well known manner such, for example, as by 
melting or crimping. 
In FIG. 5 there is shown another panel construction wherein the edge flange 
member is used to form the moat for frit. In this embodiment of the 
invention the edge pieces 60 are placed on a glass pane 62 over the leads 
64 as in the other embodiments of this invention described hereinabove. A 
metal foil member 66 is then mounted to the pane over the leads, as shown, 
and a continuous annular metal flange member 68 is mounted to the frame 
pieces 60. The flange member 68 has an intermediate reverse bend therein 
to provide an upstanding section 70 which functions as the outer wall of 
the moat in which the frit is placed. The panel assembly as thus partially 
fabricated is placed in an oven wherein the frit melts. After cooling, a 
sealing bead 72 provides a hermetic seal between the glass pane 62, the 
frame pieces 60, the leads 64 and the flange member 68. The inner moat 
member 66 is then removed as by peeling it off, and the panel is completed 
in the manner described in connection with the embodiment of the invention 
shown in FIGS. 4A and 4B. 
Each metal flange member used in the several disclosed embodiments of the 
present invention is preferably a thin metal foil which does not exert any 
appreciable forces on the glass pane and frame pieces during and after the 
cooling process. However, somewhat thicker material can be used for the 
flange members, but in that case care must be taken to provide a good 
thermal match between the flange member and the frame pieces. Of course, 
the frame pieces and the glass pane should be thermally matched and are 
preferably adjacent pieces cut from the same sheet of glass. 
Referring to FIGS. 6 and 7 there is shown another embodiment of the 
invention wherein the frame extends above the electrode structure and the 
central portion of the rear sheet is depressed inwardly toward the 
electrode structure. This depression may be formed by the evacuation 
process or the rear sheet may be preformed before assembly thereof to the 
panel. 
Considered in greater detail, a plurality of frame pieces 76 are initially 
sealed together at their adjoining edges to form a rectangular frame, and 
the frame is then placed on a glass pane 78 around the central viewing 
area in the manner shown in FIG. 6 and sealed to the pane 78 by frit or 
other suitable sealant. At this same time a continuous metal foil flange 
80 may be sealed to the top edge of the frame. It will be understood that 
a plurality of conductors 82 may extend through the seal beneath the frame 
or through the frame. The conductors 82 may be pieces of wire or flat 
metal strips or they may be thick or thin films screened onto the pane or 
onto the frame pieces. Inasmuch as the internal operating structure of the 
panel is not yet in place, these sealing operations can be carried out at 
high temperatures. If desired, the frame may be a different insulating 
material, and it may be molded directly onto the pane 78. 
After the frame has been sealed in place the electrode structure 83 may be 
placed against the pane 78 over the viewing area thereof. If the panel is 
to be operated at about atmospheric pressure, some means may be used to 
fixedly position the electrode structure 83 within the frame. A thin 
insulating sheet or blanket 87 may then be placed over the internal 
structure, a stress-distributing member of wire mesh of perforated metal 
86 placed over this insulator, and a blanket 85 placed over the 
stress-distributing member. An impervious malleable sheet 89 is then 
placed over the blanket 85. If desired, insulator 87, metal member 86, or 
blanket 85 may be omitted. It may be seen that the flange 80 and the rear 
sheet 89 extend a substantial distance outwardly of the blanket and they 
are sealed together in any suitable manner such, for example, as by 
welding or by means of a sealant material which sets up at lower 
temperatures. Both the flange 80 and the sheet 89 may be thin metal foil 
so that they can be folded back over the panel. 
Where the operating pressure in the panel is below atmospheric, the cavity 
therein is evacuated and backfilled where necessary through a suitable 
tubulation which may, for example, extend through the rear sheet. 
There is thus provided in accordance with the present invention an improved 
flat-panel display and method of manufacturing same. The front panel 
constitutes the principal support member with the remaining structure 
being compliant so as not to establish undue stresses in the front panel. 
The rear, impervious sheet is sealed to a continuous flange which itself 
is sealed to the panel through a continuous area surrounding the viewing 
area of the panel. While it is preferable to use a malleable rear sheet, 
either the rear sheet or the flange can be formed of a relatively stiff 
material. However, it is important that at least one of them be flexible 
or malleable to permit the rear sheet to be pressed toward the front panel 
against the operating display structure. 
In the preferred embodiments of the invention described hereinabove, the 
flexible rear sheets are sealed to the flanges and then the cavity within 
the panel is exhausted and backfilled where necessary. However, for some 
applications of the invention it may be desirable to complete the seal 
between the rear sheet and the panel after the panel has been exhausted 
and backfilled. 
In accordance with this aspect of the invention the panel is assembled and 
the rear sheet is not completely sealed to the flange, i.e., one or more 
gaps may be provided between the flange and the seal or the rear sheet and 
flange may not be sealed together at all. The panel is then placed in a 
vacuum oven and exhausted at an elevated temperature. The panel is then 
backfilled and the sheet and flange completely sealed together while the 
panel is still in the oven. 
While the present invention has been described in connection with 
particular embodiments thereof, it will be understood by those skilled in 
the art that many changes and modifications may be made without departing 
from the true spirit and scope of the present invention. Therefore, it is 
intended by the appended claims to cover all such changes and 
modifications which come within the true spirit and scope of this 
invention.