Ink for forming resistive structures and display panel containing the same

An ink for use in forming resistive structures for use in a gas discharge display panel containing mercury vapor to inhibit cathode sputtering, the ink comprising a mixture of silver and nickel with the nickel being controllably oxidized to impart the desired resistivity to the mixture and the final resistive body in the display panel.

BACKGROUND OF THE INVENTION 
There are many types of electronic devices which use resistive structures 
for various reasons. One type of device is a gas discharge display panel 
described herein and in copending application Ser. No. 890,471 of Edgar L. 
Harvey filed concurrently herewith. Various methods are known for making 
conductive or resistive structures or runs and materials are known for 
making them. However, these known methods using known materials, are 
relatively inexact, and time-consuming trimming operations are required to 
achieve the desired resistivity or conductivity. The present invention 
provides a resistive structure whose resistivity or conductivity can be 
well controlled so that complex and time consuming procedures are not 
required to achieve a desired resistivity in the final product.

DESCRIPTION OF THE INVENTION 
The ink of the invention is particularly suited for forming resistive 
bodies in a display panel of the type described and claimed in patent 
application Ser. No. 890,471, filed concurrently herewith by Edgar L. 
Harvey. Briefly referring to FIGS. 1 and 2, this panel 10 includes a 
substrate or base plate 20 having a top surface 22 on which conductive 
runs 24 (only some of which are shown) for making connection to the 
cathodes are formed and on which the desired resistive body 30 is formed. 
The runs 24 and resistive body 30 can be formed on the top surface and 
suitably interleaved or the resistive body can be formed first, then 
coated with an insulating layer and then the cathode runs formed. The 
aforementioned Harvey application describes one suitable arrangment of 
these portions of the panel. 
The resistive body 30, in one form, is a continuous line-like resistor made 
up of a plurality of segments which run back and forth across the base 
plate so that portions thereof are close to the seal area of the panel and 
other portions curve around and are close to the tubulation hole 40 
through which mercury vapor enters the interior of the panel from a 
mercury supply 42 in a tubulation 44 secured to the base plate in 
alignment with the hole 40. 
The cathode runs 24 are formed by a screening and firing operation and the 
resistor run 30 is also formed by a screening and firing operation as 
described in detail below. 
An insulating layer 50 covers the resistive run 30 and the cathode 
connector runs 24 if they are on the top surface of the base plate and 
this layer 50 is formed by screening and then firing. 
Groups of cathode segments 60 are screened on the insulating layer 50 and 
make connection to their runs 24 through vias (not shown) in the 
insulating layer. The cathodes 60 are also processed by a baking operation 
and another insulating layer is usually provided on the groups of cathodes 
to outline them. This too involves a firing operation. This layer and 
other features are not shown to simplify the drawings since they are well 
known in the art. 
The panel 10 includes a glass face plate 70 which carries transparent 
conductive anodes 80 on its inner surface with each anode overlying a 
group of cathode segments 60. 
After the face plate 70 and base plate 20 are sealed together hermetically, 
the panel is processed to completion and this processing includes filling 
the panel envelope with an ionizable gas, such as neon or argon or the 
like, through the tubulation 44 and providing a source of mercury 42 in 
the tubulation from which mercury vapor is introduced into the envelope to 
minimize cathode sputtering when the cathodes glow during panel operation. 
Briefly, the material or "ink" of the invention which is used to make the 
resistor run 30 includes a plurality of metal elements in such form that 
when the material is placed on a substrate and the substrate is 
incorporated in a display panel by a process which includes several 
heating operations, the final body of resistance material has the desired 
resistance or very close to the desired resistance. The processing steps 
used in making the panel include several heating operations and the 
resistive body is formed early in the assembly process and it is able to 
accept all of the subsequent heating operations without having its 
resistance seriously affected. 
In brief, the material or ink of the invention comprises a combination of 
(1) a conductive component containing silver which is normally fired in 
air to maintain its conductivity and (2) a conductive component containing 
nickel which is normally fired in nitrogen to retain its conductivity but 
which oxidizes when fired in air. The mixture of the two components is 
first fired in air in a controlled manner so that the nickel is 
controllably oxidized and then any additional heating is carried out in a 
nitrogen atmosphere. The resultant resistive body has a closely 
predetermined resistance. 
In the foregoing material, the nickel is in the form of a powder having a 
particle size in the range of about two to about ten microns. This 
particles size provides the optimum nickel surface for oxidation during 
the processing operation to achieve the desired resistance. 
The silver component is made up of a combination of silver flakes and 
silver powder. This use of flakes and powder also combines with the nickel 
powder to provide optimum packing of the silver and the nickel and optimum 
control of the overall conductivity of the final resistive body as it 
undergoes multiple firings during the manufacture of the panel. In the 
silver component, the silver powder has a particle size in the range of 
about 0.8 microns to about 1.2 microns. The silver flakes are less than 
about ten microns in length. 
The glass frit used in the ink of the invention is a low temperature binder 
glass which serves to insure proper wetting of the nickel and silver in 
the firing process used in forming the resistive body. The glass frit 
preferably has a melting point in the range of about 440.degree. C. to 
about 460.degree. C. 
The ink also includes a vehicle which is not a critical constituent and is 
provided to impart proper screening characteristics to the ink. 
Typical ink compositions embodying the invention include: 
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Constituent Weight % 
______________________________________ 
Silver Flake 20-30 
Silver Powder 15-25 
Spherical Nickel Powder 
10-30 
Glass Frit 20-25 
Vehicle 13-20 
______________________________________ 
Another ink composition according to the invention includes a silver cermet 
(silver and a glass frit) and a nickel cermet (nickel and a glass frit). 
The silver cermet includes 70% silver (35% flakes and 35% powder) and 30% 
glass frit. The nickel cermet includes 85% spherical nickel powder and 15% 
glass and the following are some mixes of these two cermets for obtaining 
the indicated resistances in a resistor run which is 48" long, 25 microns 
thick and 20 mils wide: 
______________________________________ 
about about 
about 10 ohms 
about 20 ohms 
30 ohms 40 ohms 
______________________________________ 
15% nickel cermet 
20% nickel cermet 
25% nickel 30% nickel 
85% silver cermet 
80% silver cermet 
75% silver 70% silver 
______________________________________ 
The vehicle used in the ink of the invention is typically an ethyl 
cellulose/ester alcohol vehicle. 
The ink is made in a generally conventional manner including suitable 
mixing and blending operations and, to form the desired resistive body, 
the ink is screened on a substrate. After screening, the substrate is 
fired in air to remove binders and primarily to oxidize the nickel. The 
firing time and temperature are selected to achieve the desired oxidation 
of the nickel and the resistance caused by the oxidation can be measured 
as the firing operation proceeds. After the desired resistance is 
achieved, the air firing is discontinued.