Abstract:
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.

Description:
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 DRAWINGS 
     FIG. 1 is a perspective exploded view of type of display panel which uses the invention; and 
     FIG. 2 is a sectional view through the tubulation attached to the panel of FIG. 1. 
    
    
     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 &#34;ink&#34; 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° C. to about 460° 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: 
     
         ______________________________________Constituent        Weight %______________________________________Silver Flake       20-30Silver Powder      15-25Spherical Nickel Powder              10-30Glass Frit         20-25Vehicle            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&#34; long, 25 microns thick and 20 mils wide: 
     
         ______________________________________                   about      aboutabout 10 ohms      about 20 ohms                   30 ohms    40 ohms______________________________________15% nickel cermet      20% nickel cermet                   25% nickel 30% nickel85% 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.