US3735183A

US3735183A - Gaseous discharge display device with a layer of electrically resistive material

Info

Publication number: US3735183A
Application number: US00144872A
Authority: US
Inventors: F Walters
Original assignee: Ferranti PLC
Current assignee: Ferranti International PLC
Priority date: 1971-05-19
Filing date: 1971-05-19
Publication date: 1973-05-22
Anticipated expiration: 1990-05-22

Abstract

A visual display device incorporates an array of direct-current discharge devices. A block of electrically insulating material has a plurality of gas-filled cavities, each forming a discharge space for one discharge device, or a single gas-filled cavity common to all discharge devices. A plurality of transparent anode conductors on a face of a second block of electrically insulating material, sealed to the first block, and in registration with the cavities, form anode electrodes for one co-ordinate of the array. Cathode electrodes are carried by a face of a third block of electrically insulating material, also sealed to the first block, and those cathode electrodes of the other co-ordinate of the array are connected by way of electrically resistive material to one of a plurality of cathode conductors. The cathode conductors, which are isolated from the discharge space or spaces, cathode electrodes and electrically resistive material are all carried on said face of the third block.

Description

United States Patent [191 Walters GASEOUS DISCHARGE DISPLAY DEVICE WITH A LAYER OF ELECTRICALLY RESISTIVE MATERIAL [75] Inventor:

I Frank Walters, Bury, England [73] Assignee: Ferranti Limited, Hollinwood, En-

gland [22] Filed: May 19, 1971 [21] Appl. No.: 144,872

[56] References Cited UNITED STATES PATENTS 3,603,837 9/1971 Turner ..3l3/220 3,553,458 1/1971 Schagen... ..3l5/l69 R X 3,206,638 9/1965 Moore ....3l5/l69 TV X 3,334,269 8/1967 L'Heureux ..315/l69 TV X [451 May 22,1973

Primary Examiner-Palmer C. Demeo Attorney-Cameron, Kerkam & Sutton [5 7] ABSTRACT A visual display device incorporates an array of directcurrent discharge devices. A block of electrically insulating material has a plurality of gas-filled cavities, each forming a discharge space for one discharge device, or a single gas-filled cavity common to all discharge devices. A plurality of transparent anode conductors on a face of a second block of electrically insulating material, sealed to the first block, and in registration with the cavities, form anode electrodes for one co-ordinate of the array. Cathode electrodes are carried by a face of a third block of electrically insulating material, also sealed to the first block, and those cathode electrodes of the other co-ordinate of the array are connected by way of electrically resistive material to one of a plurality of cathode conductors. The cathode conductors, which are isolated from the discharge space or spaces, cathode electrodes and electrically resistive material are all carried on said face of the third block.

28 Claims, 7 Drawing Figures Patented May 22, 1973 3,735,183

2 Sheets-Sheet 1 5 19 F164. 75 vi? GASEOUS DISCHARGE DISPLAY DEVICE WITH A LAYER OF ELECTRICALLY RESISTIVE MATERIAL THIS INVENTION relates to visual display devices, and in particular to such devices comprising an array of gas-filled direct-current cold-cathode dischai' ge devices each of which may be struck or extinguished to produce a display of the required form.

Visual display devices are known which incorporate an array of direct-current discharge devices formed by one or more gas-filled cavities in a block of an electrically insulating material such as glass or ceramic. A set of conductors is formed on a furtherblock which is then sealed to the first block so that the conductors form one electrode of each discharge device. Each discharge device is also provided with a second electrode carried by a face of a third block, also sealed to the first block, and a series impedance connected between that second electrode and one of a second set of conductors.

It has usually been necessary to arrange the series impedances and the second set of conductors outside the display device, though copending application Ser. No. 869,799 now issued as US. Pat. No. 3,603,837 assigned to the assignee of the present invention describes and claims a display device with integral load resistors in which the two sets of conductors may be produced in the same manner.

It is an object of the invention to provide a visual display device of the type described in which the load impedances are formed in a simple manner within the display device.

According to present inventions a visual display device incorporating an array of direct current discharge devices comprises a first block of electrically insulating material having one or more gas filled discharge spaces, a second block of electrically insulating material sealed to the first block, a set of electrical conductors on the second block, each conductor forming a first electrode of at least one of said discharge devices a third block of electrically insulating material sealed to the first block and a plurality of second electrodes, one for each of said discharge devices, carried by a face of the third block adjacent to the discharge space or spaces, at least one set of further electrical conductors formed on said face of the third block and electrically isolated from each discharge space, and a layer of electrically resistive material carried by said face of the third block and connecting each second electrode to a selected one of the, or each, set of further conductors.

The second electrodes, further conductors and electrically resistive material may all be formed on the surface of the third block. V

The discharge spaces in the first block may comprise a plurality of cavities arranged in a two co -ordinate array and each conductor on the second block may form an electrode for each cavity associated with one co-ordinate of the array, each one of the, or each, set of further conductors being connected to the second electrodes associated with the cavities of the other coordinates of the array.

The invention will now be described with reference to the accompanying drawings, in which:

FIG. I is a sectional side view of a display device according to a first embodiment of the invention;

FIG. 2 is an enlarged 'view of part of FIG. I;

FIG. 3 is a sectional side view of a display device according to a second embodiment;

FIGS. 4, 5 and 6 are enlarged views of parts of three further embodiments; and

FIG. 7 is an enlarged sectionalview of a further embodiment.

The display device shown in FIGS. 1 and 2 is made in three parts. The center spacer 10 is a block of glass or similar material having formed in it a matrix of small cavities 11. These cavities may, for example, be of circular or square cross-section, and are preferably arranged in the rows and columns of a rectangular matrix. The upper block 12, of a similar material to spacer 10, carries on its underside a number of parallel transparent evaporated anode conductors 13, say of stannic oxide, only one of which is shown in FIG. 1. Each anode conductor 13 passes across the top of all the cavities 11 in one row of'the array, which is intended to be viewed from the top as shown in the FIG. 1.

The lower block 14, also of a similar material to spacer l0, carries'the cathode electrodes 15, load resistors l6 and cathode conductors 17 for the entire matrix of discharge tubes. Each discharge tube has an individual cathode electrode 15 and individual load resistor 16. The cathode conductors 17 comprise a number of parallel strips similar to anode conductors 13, each strip interconnecting the load resistors 16 associated with a particular column of the matrix. The cathode conductors are spaced from the electrodes of adjacent columns by an air gap or by an insulating material. The complete display device therefore comprises a plurality of discharge cells defined by the cavities 11 in the block 10, the cavities being filled with a suitable gas and closed by the

covers

12 and 14. The joints between the various blocks are sealed with a suitable material and provide a gas seal for the device.

The formation of the cathode electrodes 15, load resistors l6 and cathode conductors 17 on the lower cover plate 14 requires a number of operations, and the various components may be made from a number of alternative materials. The load resistors 16 are formed first, by a screen printing process, and are arranged in the appropriate positions on the lower cover plate 14. The resistive material may, for example, be ruthenium dioxide or thallium oxide. The ruthenium oxide requires to be fired at about 650 C, whilst the thallium oxide may be fired at about 500 C. Either the cathode conductors or the electrodes may be formed next. The cathode conductors 17 need not be transparent, and may be formed by evaporating through a mask a layer of chromium with a covering of gold. Finally, the cathode electrodes are formed by a similar process, and may be formed at the same time as the conductors if the same materials are used. 7

Each cell of the display device may be caused to conduct by applying a dc. potential between the anode conductor 13 and cathode conductor 17 which together uniquely define the desired cell. A display may be built up by causing a number of cells to conduct simultaneously.

The resulting display device has the form shown in FIG. 1. However, it is not essential to use a spacer block 10 as shown, and this may be replaced by a builtup layer 18 of glass formed by screen printing. The latter arrangement results in a device as shown in FIG. 3, in which the walls 18 defining each individual cell are formed by one or more screen printing operations 3 using a suitable glass. This is used in paste form and subsequently fired. The glass walls 18 cover the load resistors 16 and the cathode conductors 17, leaving exposed only the cathode electrodes 15. The cavities produced have inclined walls due to the build-up of successive layers of the walls 18.

Alternatively, the spacer formation defining individual cells may be omitted altogether, though a spacer is necessary around the edge of the display device. However, if this is done the cathode conductors must be covered with an insulating material to prevent discharges taking place other than in the required positions.

FIG. 4 illustrates such an arrangement, where each individual load resistor 16 and all the cathode conductors 17 on the block 14 are covered by an insulating layer of glass 19 formed by screen printing and firing a suitable paste. The anode conductors are formed as described previously on the block 13. Only the cathode electrode 15 of each cell on the block 14 is exposed, and thus the discharges will take place between these electrode and the appropriate row or anode conductors 13.

As before there is a choice of materials for the conductors, electrodes and resistors, though the materials referred to above are particularly suitable.

Using the constructions referred to above it is possible to provide a matrix of discharge tubes with the individual cells spaced about 0.03 inches apart. This spacing is determined to a certain extent by the resistance of the material used to form the load resistors. If a closer spacing of individual cells is required then a construction such as that shown in FIG. may be used. In this arrangement the cathode electrode and possibly part of the load resistor of one cell overlaps the resistor and cathode conductor of another, being insulated from it by a layer of glass.

As will be seen from FIG. 5 only the cathode conductors 17 are actually formed on the surface of the block 14. The cathode electrodes are formed on top of a layer 19 of insulating glass which covers each cathode conductor and its associated load resistors. It will be seen from a comparison of FIGS. 4 and 5 that the cathode electrodes may be arranged much closer together using the arrangement of FIG. 5 than was possible with the earlier arrangements.

Although in the embodiments described above the resistive material is insulated from the discharge space, this is in fact not essential, owing to the high resistivity of the material. However, it is essential that the cathode conductors be separated from the discharge space. Hence the simple arrangement of FIG. 6 may be used. In this arrangement, the cathode conductors 17 are formed on the surface of the block 14 and then a complete layer 16 of resistive material is formed. The cathode electrodes 15 are then formed on the surface of the resistive layer. Due to the high resistivity of the material forming the layer 16, only the required cell will conduct owing to the greater distances between a selected cathode conductor and the cathode electrodes associated with another cathode conductor. Hence there will be no risk of the wrong cells conducting.

In a further embodiment, shown in FIG. 7, the lower block 14 carries the cathode electrodes, and a plurality of load resistors and cathode conductors for each discharge cell of the matrix. The resistors are built up in a stack, with insulating material supporting and isolating the various layers. As shown in FIG. 7, three sets of cathode conductors are formed, the three conductors shown being denoted by the

references

17a, 17b and 17c respectively. A first layer 16a of resistive material is formed on the surface of the block 14 with one end of the layer in electrical contact with one of the cathode conductors 17a. Alongside the resistive layer is formed an insulating layer 1911. This insulating layer supports a second layer 16b of resistive material which is connected to a second conductor 17b at one end and which overlaps the first resistive layer 16a at the other end. The remainder of the resistive layer 16a and the conductor 17a are covered by a second layer of insulating material. A third layer of resistive material 16c is formed over the insulating layer 19b, overlapping layer 16b at one endand making contact with conductor 170 at the other end. The remainder of resistive layer 16b is covered with an insulating layer 20.

Each cell of the display device thus has one anode connection and three possible cathode connections, any one cell being caused to conduct by applying a suitable d.c potential between the anode conductor 13 and a selected one of the cathode conductors 17 which together uniquely define the desired cell.

The intensity of the discharge within the cell depends upon the cathode conductor which is selected. If conductor 170 is used, this is connected through a single resistive layer to the cathode electrode 15, giving a discharge of the maximum intensity. Cathode conductor 17b, however, is connected to the cathode electrode through resistive layer 16b in series with part of layer 16c. Hence the total resistance is greater and the discharge current will be lower, giving a discharge of lower intensity. Similarly, the use of cathode conductor 17a causes the total series resistance to be that of layer 160 plus part of each of

layers

16b and 16c. This gives the maximum series resistance and hence the lowest intensity discharge. This arrangement may be used with only two, or with more than three, resistive layers and sets of cathode conductors.

Other forms of construction are also possible, so long as they satisfy the requirement that the load resistors are supported by the surface which carries the associated cathode conductors. For example, a spacer as shown at 10 on FIG. 1 may be used with constructions of FIGS. 4, 5 and 6, with the spacer separated from the lower cover plate 14' with its resistors and electrodes. The spacer 10 then serves to locate the discharge of each cell in a precise position.

The anode conductors 13 need not be transparent, so long as they are thin enough to avoid seriously obscuring the discharge.

Although in the above embodiments the series resistors have been connected to the cathode electrode of each cell, the resistors may alternatively be connected on the anode side of the circuit.

What we claim is:

1. A visual display device incorporating an array of direct-current discharge devices comprising a first block of electrically insulating material having one or more gas filled discharge spaces, a second block of electrically insulating material sealed to the first block, a set of electrical conductors on the face of the second block adjacent the space or spaces, each conductor forming a first electrode of at least one of said discharge devices, a third block of electrically insulating material sealed to the first block and a plurality of second electrodes, one for each of said discharge devices, carried by a face of the third block adjacent the discharge space or spaces, at least one set of further electrical conductors on said face of the third block and electrically isolated from each discharge space, a layer of electrically resistive material, carried by said face of the third block and connecting each second electrode to a selected one of the, or each, set of further conductors and a layer of insulating material covering the face of the third block, except in the vicinity of the second electrodes, and the resistive material and each further conductor on the surface of the third block.

2. A visual display device as claimed in claim 1 in which each second electrode is stacked over a further conductor associated with an adjacent second electrode.

3. A visual display device as claimed in claim 1 in which the layers of electrically resistive material connecting each second electrode to one further conductor of each of a plurality of sets are stacked one above the other and are separated by electrically insulating material.

4. A visual display device as claimed in claim 1 in which the discharge spaces in the first block comprise a plurality of cavities arranged in a two co-ordinate array.

5. A visual display device as claimed in claim 4 in which each conductor on the second block forms an electrode for each cavity associated with one coordinate of the array and each one of the, or each set of, further conductors is connected to the second electrodes associated with the cavities of the other coordinate of the array.

6. A visual display device as claimed in claim 1 in which the first, second and third blocks are of the same electrically insulating material.

7. A visual display device as claimed in claim 6 in which the electrically insulating material is glass.

8. A visual display device as claimed in claim 1 in which the electrically resistive material is thallium oxide.

9. A visual display device as claimed in claim 1 in which the electrically resistive material is ruthenium dioxide.

10. A visual display device as claimed in claim 1 in which the conductors on the second block are transparent.

11. A visual display device as claimed in claim 10 in which the transparent conductors are of stannic oxide.

12. A visual display device as claimed in claim 1 in which the further conductors are of chromium plated with gold.

13. A visual display device incorporating an array of direct-current discharge devices comprising one or more gas filled discharge spaces formed between a first and a second block of electrically insulating material, a set of electrical conductors on the face of the first block adjacent the discharge space or spaces, each conductor forming a first electrode of at least one of said discharge devices, means for sealing said second block of electrically insulating material to the first block, a plurality of second electrodes, one for each of said discharge devices, carried by a face of the second block adjacent the discharge space or spaces, at least one set of further electrical conductors on said face of the second block, said further electrical conductors being electrically isolated from each discharge space, a layer of electrically resistive material, carried by said face of the second block and connecting each second electrode to a selected one of the, or each, set of further conductors and a layer of insulating material covering the resistive material and each further conductor on the surface of the second block.

14. A visual display device as claimed in claim 13 in which the second electrodes, further conductors and electrically resistive material are all formed on the surface of the second block, said layer of insulating material extending to said face of said second block between each said second electrodes and the adjacent one of the, or each, set of further conductors.

15. A visual display device as claimed in claim 13 including spacer means between said first and said second block defining said discharge spaces.

16. A visual display device as set forth in claim 15 wherein said spacer means comprise built up insulative wall sections covering the electrically resistive material and each further section.

17. A visual display device as set forth in claim 15 wherein said discharge spaces have inclined walls forming spaces of increasing cross-section extending from the second block to the first block.

18. A visual display device as claimed in claim 13 in which each second electrode is stacked over a further conductor associated with an adjacent second electrode.

19. A visual display device as claimed in claim 13 in which the layers of electrically resistive material connecting each second electrode to one further conductor of each of a plurality of sets are stacked one above the other and are separated by electrically insulating material.

20. A visual display device as claimed in claim 13 in which the discharge comprising a plurality of cavities arranged in a two co-ordinate array.

21. A visual display device as claimed in claim 19 in which each conductor on the first block forms an electrode for each cavity associated with one co-ordinate of the array and each one of the, or each set of, further conductors is connected to the second electrodes associated with the cavities of the other co-ordinate of the array.

22. A visual display device as claimed in claim 13 in which the first and second blocks are of the same electrically insulating material and in which the second electrodes, further conductors and electrically resistive material are all formed on the surface of the second block, said layer of insulating material extending to said face of said second block between each said second electrodes and the adjacent one of the, or each, set of further conductors.

23. A visual display device as claimed in claim 22 in which the electrically insulating material is glass.

24. A visual display device as claimed in claim 13 in which the electrically resistive material is thallium oxide.

25. A visual display device as claimed in claim 13 in which the electrically resistive material is ruthenium dioxide.

26. A visual display device as claimed in claim 13 in which the conductors on the second block are transparent.

27. A visual display device as claimed in claim 26 in which the transparent conductors are of stannic oxide.

28. A visual display device as claimed in claim 13 in which the further conductors are of chromium plated with gold.

Claims

2. A visual display device as claimed in claim 1 in which each second electrode is stacked over a further conductor associated with an adjacent second electrode.
3. A visual display device as claimed in claim 1 in which the layers of electrically resistive material connecting each second electrode to one further conductor of each of a plurality of sets are stacked one above the other and are separated by electrically insulating material.
4. A visual display device as claimed in claim 1 in which the discharge spaces in the first block comprise a plurality of cavities arranged in a two co-ordinate array.
5. A visual display device as claimed in claim 4 in which each conductor on the second block forms an electrode for each cavity associated with one co-ordinate of the array and each one of the, or each set of, further conductors is connected to the second electrodes associated with the cavities of the other co-ordinate of the array.
6. A visual display device as claimed in claim 1 in which the first, second and third blocks are of the same electrically insulating material.
7. A visual display device as claimed in claim 6 in which the electrically insulating material is glass.
8. A visual display device as claimed in claim 1 in which the electrically resistive material is thallium oxide.
9. A visual display device as claimed in claim 1 in which the electrically resistive material is ruthenium dioxide.
10. A visual display device as claimed in claim 1 in which the conductors on the second block are transparent.
11. A visual display device as claimed in claim 10 in which the transparent conductors are of stannic oxide.
12. A visual display device as claimed in claim 1 in which the further conductors are of chromium plated with gold.
13. A visual display device incorporating an array of direct-current discharge devices comprising one or more gas filled discharge spaces formed between a first and a second block of electrically insulating material, a set of electrical conductors on the face of the first block adjacent the discharge space or spaces, each conductor forming a first electrode of at least one of said discharge devices, means for sealing said second block of electrically insulating material to the first block, a plurality of second electrodes, one for each of said discharge devices, carried by a face of the second block adjacent the discharge space or spaces, at least one set of further electrical conductors on said face of the second block, said further electrical conductors being electrically isolated from each discharge space, a layer of electrically resistive material, carried by said face of the second block and connecting each second electrode to a selected one of the, or each, set of further conductors and a layer of insulating material covering the resistive material and each further conductor on the surface of the second block.
14. A visual display device as claimed in claim 13 in which the second electrodes, further conductors and electrically resistive material are all formed on the surface of the second block, said layer of insulating material extending to said face of said second block between each said second electrodes and the adjacent one of the, or each, set of further conductors.
15. A visual display device as claimed in claim 13 including spacer means between said first and said second block defining said discharge spaces.
16. A visual display device as set forth in claim 15 wherein said spacer means comprise built up insulative wall sections covering the electrically resistive material and each further section.
17. A visual display device as set forth in claim 15 wherein said discharge spaces have inclined walls forming spaces of increasing cross-section extending from the second block to the first block.
18. A visual display device as claimed in claim 13 in which each second electrode is stacked over a further conductor associated with an adjacent second electrode.
19. A visual display device as claimed in claim 13 in which the layers of electrically resistive material connecting each second electrode to one further conductor of each of a plurality of sets are stacked one above the other and are separated by electrically insulating material.
20. A visual display device as claimed in claim 13 in which the discharge comprising a plurality of cavities arranged in a two co-ordinate array.
21. A visual display device as claimed in claim 19 in which each conductor on the first block forms an electrode for each cavity associated with one co-ordinate of the array and each one of the, or each set of, further conductors is connected to the second electrodes associated with the cavities of the other co-ordinate of the array.
22. A visual display device as claimed in claim 13 in which the first and second blocks are of the same electrically insulating material and in which the second electrodes, further conductors and electrically resistive material are all formed on the surface of the second block, said layer of insulating material extending to said face of said second block between each said second electrodes and the adjacent one of the, or each, set of further conductors.
23. A visual display device as claimed in claim 22 in which the electrically insulating material is glass.
24. A visual display device as claimed in claim 13 in which the electrically resistive material is thallium oxide.
25. A visual display device as claimed in claim 13 in which the electrically resistive material is ruthenium dioxide.
26. A visual display device as claimed in claim 13 in which the conductors on the second block are transparent.
27. A visual display device as claimed in claim 26 in which the transparent conductors are of stannic oxide.
28. A visual display device as claimed in claim 13 in which the further conductors are of chromium plated with gold.