Method Of Manufacture Of Display Device Utilizing Gas Discharge

Abstract

Each of a pair of spaced glass insulating substrate components has a plurality of mutually isolated conductive electrode layers on a surface thereof. Each surface faces the other and each plurality of electrode layers face the other. A layer of insulating material is applied to cover the electrode layers on each surface. A plurality of spaces are etched in a second layer of insulating material. The second layer is positioned between and joins the first layers of insulating material with the spaces between such layers sealed air tight, so that ionizable gas fills the spaces.

Parent Case Text

This application is a Continuation-in-Part of application Ser. No. 832,062, filed June 11, 1969 for "Display Device Utilizing Gas Discharge", now abandoned.

Description

DESCRIPTION OF THE INVENTION

The present invention relates to a display device. More particularly, the invention relates to a method of manufacture of a display device utilizing gas discharge.

A neon tube type display device is well known as a display device utilizing gas discharge. The neon tube type display device comprises a plurality of coplanarly disposed gas discharge tubes. Each gas discharge tube of the display device comprises a pair of electrodes in a hermetically sealed space, hereinafter referred to as a cell, filled with an ionizable gas such as, for example, neon, under pressure. When a signal having a magnitude greater than a discharge initiating voltage is applied between the electrodes of a cell, a glow discharge is initiated.

Since the glow discharge continues during the entire period of application of the signal, even if the applied signal is AC rather than DC, it is very convenient that each discharge be facilely operated for display purposes. When a number of cells are joined in a single sheet or panel, however, in a panel type arrangement, it becomes necessary to separate the cells not only electrically, but also physically, in order to eliminate uncertainity of discharge caused by non-uniformity of the discharge characteristics of the cells. The cells are considered to be independent of each other although they are not separated by walls.

It has been suggested that, in order to overcome the aforedescribed disadvantage, th electrodes of each cell be provided outside the cell in order to provide a capacitive reactance between each of the electrodes and the envelope of the cell interposed between the electrodes. The capacitive reactance separates the cells in a panel from each other electrically. In such a device, a voltage having a high frequency of several tens of megahertz is applied between the electrodes of a cell, so that an electric field varying at high speed is produced within the cell and ionizes the gas filling the cell to produce a continuous discharge. The disadvantage of such a device is that it requires signals of very high frequency and high voltage in order to operate as desired, so that its components are complex and of large size.

It has also been suggested that a physical structure similar to that of the foregoing device be utilized, which has a wall charge due to the discharge of the cell. The wall charge is an electrical charge deposited on the inner surfaces of an envelope on the sides of the electrodes. The advantage of this device is that the pulse discharge may be produced by AC signals having a relatively low frequency and a relatively low voltage.

An object of the invention is to provide a method of manufacture of a display device utilizing gas discharge which has great mechanical strength and low firing potential.

An object of the present invention is to provide a method of manufacture of a display device utilizing gas discharge which is discharged by a voltage of relatively low magnitude and frequency.

An object of the present invention is to provide a method of manufacture of a display device utilizing gas discharge which comprises cell walls of smaller thickness than glass.

An object of the present invention is to provide a method of manufacture of a display device utilizing gas discharge which comprises cell walls of greater dielectric constant than glass.

Another object of the invention is to provide a single method of manufacture of a display device utilizing gas discharge which has uniform electrical characteristics.

Another object of the invention is to provide a method of manufacture of a display device utilizing gas discharge which is free from secular deterioration.

Another object of the present invention is to provide a method of manufacture of a display device utilizing gas discharge which is of simple structure, but operates with efficiency, effectiveness and reliability.

In accordance with the invention, a method of manufacture of a display device utilizing gas discharge and having a pair of basic plates of insulating material at least one of which is transparent, each having a primary surface and a plurality of conductive electrode layers formed on each primary surface, and covered by an insulating layer, a portion of insulating material being provided between the insulating layers to form a plurality of spaces therebetween, comprises forming a first layer of metal compound insulating material covering the conductive layer on the primary surface of each of the basic plates. A second layer of metal compound insulating material is formed on the first insulating layer of at least one of the basic plates. The metal compound insulating material of the second layer is susceptible to a higher etching speed than the metal compound insulating material of the first layers in the same etchant condition. The second insulating layer is etched throughout its thickness in a predetermined pattern to provide a plurality of spaces therethrough. Both insulating plates are sealed in a condition that the conductive layers on the primary of each of the basic plates face each other so as to enclose ionizable gas in the spaces formed through the second insulating layer.

In order that the present invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is an exploded perspective view of an embodiment of a display device of known type;

FIG. 2 is a sectional view, taken along the lines II -- II, of FIG. 1;

FIG. 3 is a circuit diagram illustrating the electrical equivalent of the embodiment of FIG. 1;

FIG. 4 is a sectional view of an embodiment of the display device manufactured by the method of the invention and corresponds to FIG. 2;

FIG. 5 is a part perspective, part sectional view, of part of another embodiment of the display device manufactured by the method of the invention; and

FIG. 6 is a sectional view of the embodiment of FIG. 5.

In the FIGS., the same components are identified by the same reference numerals.

The known device of FIG. 1 has a wall charge due to the discharge of the cell. In FIG. 1, a thin glass plate 1 has a plurality of small holes 101, 102, 103, 104, and so on, formed therethrough in a regular matrix-like pattern. Each of the holes 101, 102, and the like, functions as the principal portion or envelope of a cell.

A thin glass plate 2 has a plurality of parallel, equidistantly spaced, electrodes of equal widths 201, 202, 203 and 204 formed thereon. The electrodes 201, 202, 203 and 204 are called X electrodes and comprise thin strips of electrically conductive material on the surface of the plate 2 opposite that which faces the plate 1. The X electrodes are positioned in correspondence with the correspondingly aligned ones of the holes through the plate 1.

A thin glass plate 3 has a plurality of parallel, equidistantly spaced, electrodes of equal widths 301, 302, 303 and 304 formed thereon. The electrodes 301, 302, 303 and 304 are called Y electrodes and comprise thin strips of electrically conductive material on the surface of the plate 3 opposite that which faces the plate 1. The Y electrodes are perpendicular to the X electrodes and are positioned in correspondence with the correspondingly aligned ones of the holes through the plate 1.

The X and Y electrodes may comprise transparent conductive films such as, for example, thin gold films or Nesa films. The three thin glass plates 1, 2 and 3 of the display device of FIG. 1 are positioned in the order shown and are in abutment with each other in the manner shown in FIG. 2. Each of the holes 101, 102, and so on, is evacuated and an ionizable gas such as, for example, helium, neon, or a mixture of either with a small amount o nitrogen, is sealed therein after the plates 1, 2 and 3 are hermetically sealed together.

FIG. 2 illustrates the cells formed by the holes 101, 102, 103 and 104. Each of the holes is surrounded by glass of the plates 1, 2 and 3. A voltage is applied to each of the cells formed by the holes 101, 102, 103 and 104 via each of the X electrodes 201, 202, 203 and 204 and the Y electrode 301.

Each of the cells, between its X and Y electrodes, functions as three series-connected capacitors. The capacitors C1 are formed of the capacitances between the glass plates 2 and 3 and the capacitor C2 is formed of the capacitance of the cell.

If a specific AC voltage, divided in accordance with the capacitive reactances of the capacitors shown in FIG. 3, is applied to the cell 101, for example, and said voltage attains a specific magnitude, the gas filling said cell breaks down, is ionized, and produces a discharge and light emission. If the dimensions of the cell are relatively small and the frequency of the applied voltage is relatively low, charged particles produced by the discharge move toward the cell walls of the side of either electrode of opposite polarity and are deposited on the wall surfaces. The charges adhering to the wall surfaces are known as wall charges. The wall charges produce between the walls a voltage having a polarity opposite that of the applied voltage, so that the discharge disappears.

During the next half cycle of the applied AC voltage, the voltage resulting from the wall charge produced by the previous discharge is present in the cell. The voltage resulting from the wall charge is known as the wall voltage. Therefore, when the sum of the wall voltage and a distributed voltage due to the applied voltage reaches a discharge magnitude, the cell discharges again. Such discharge produces between the two wall surfaces a wall voltage opposite in polarity to that previously produced. The later discharge causes the earlier discharge to disappear in a short time. The process of discharge, production of wall charge and wall voltage and disappearance of discharge is thus repeated for each half cycle of the applied voltage.

More particularly, the cell discharges when a voltage having a magnitude equal to the discharge initiation magnitude is applied to said cell from the outside. Thereafter, however, due to the existence of the wall voltage, the cell maintains an intermittent discharge due to the application of a voltage having a magnitude which is less than the discharge initiation magnitude. The lower magnitude voltage may be called a sustaining voltage. If the continuing condition of intermittent discharge is called the ON condition, and the inoperative condition is called the OFF condition, a display device having a plurality of cells may be made by the sustaining voltage to store the ON condition previously written-in by the application of the discharge initiating voltage from outside the cells.

In order to terminate the discharge, however, and to change condition to the OFF condition, the applied voltage must be of sufficiently high frequency, compared to the speed of movement of the charge particles within the cell, to halt the production of the wall voltage by the discharge. With the aforementioned property, the device of FIG. 1 may be sufficiently utilized as a display device having a memory function.

In the aforedescribed device of FIG. 1, it is desirable that the discharge voltage of the cell be as low as possible. When the plates 1, 2 and 3 are glass, however, it is difficult to make the thickness of said plates equal to or less than about 0.15 mm. due to manufacturing limits. It is therefore impossible to decrease the magnitude of the applied voltage required for discharge to less than 200 to 500 volts. The discharge voltage is not only related to the thickness of the glass plates 1, 2 and 3, however, but also to the type of gas filling the holes or spaces and the pressure of said gas. Even when the gas and its pressure are considered, it is difficult to provide a voltage having a magnitude less than that mentioned. If the plates 2 and 3 are made of a material having a large dielectric constant, the voltage of the cell may be increased, although the applied voltage remains the same. As long as the plates are glass, however, there is very little prospect for improvement.

In accordance with the invention, and as shown in FIG. 4, the first insulating layers 6 and 11 and the second insulating layer 7 are formed of different metal compounds. The metal compound insulating material of the second insulating layer 7 is susceptible to a higher etching speed than the metal compound insulating material of the first insulating layers 6 and 11.

FIG. 4 illustrates the display device manufactured by the method of the invention. In FIG. 4, a transparent glass plate 4 has a thickness which is sufficient to withstand normal handling in manufacture and the difference in pressures within the cell and without. A plurality of X electrodes are formed on a surface of the plate 4. The X electrodes comprise thin gold films on Nesa films. A layer 6 of silicon nitride covers the X electrodes. The layer 6 may be formed by sputtering to a thickness of about 10 microns. The layer 6 may be formed by any suitable process such as, for example, evaporation or screen printing, well known in the thin film and thick film arts, when a process other than sputtering is required.

A plurality of spaced portions or layer segments 7 of silicon oxide are formed on the layer 6 of silicon nitride. The spaces 8 between adjacent spaced portions 7 of silicon oxide function as the cells. The portions or layer segments 7 have a thickness of approximately several microns. From a practical point of view, it is difficult to form the silicon oxide layer segments 7 with the cells 8 formed therebetween, from the beginning. The layer segments 7 are formed by a photo-etching process known in the semiconductor art, as shown in FIGS. 4 and 5.

In a known photo-etching process, silicon oxide is sputtered over the surface of the layer 6 and forms a layer 7. A photoresistive material is coated on the layer 7. The photo-resistive material is irradiated by light after a mask is placed on said material in the configuration and arrangement of the cells. The portion of the photoresistive material corresponding to the cells is protected from the light by the mask and is dissolved by an applied organic solvent. The portions of the photoresistive material uncovered by the mask are hardened by exposure to the light and remain as the layer or portion 7.

The layer is then immersed in an etchant of hydrofluric acid and ammonium fluoride, so that the parts of the silicon oxide which correspond to the cells 8 are etched out. The silicon nitride layer 6 stops the progress of the etchant. When the etchant reaches the silicon nitride layer 6, said layer is removed from said etchant and said layer is washed with water. Since the etchant reacts much more rapidly with the silicon oxide than with the silicon nitride, the depth of cells 8 is generally uniform, even if there is a difference in the speed of etchant reaction in the areas corresponding to the different ones of said cells. The layer is then immersed in hot sulfuric acid at 180.degree.C to remove the exposed photoresistive film remaining on the silicon oxide layer 7. The layer is then washed with water and dried. The cells are then completely formed.

When the first insulating layers 6 and 11 are of aluminum oxide and the second insulating layer 7 is of silicon oxide, the attainable ratio of etching speeds is 1:10. This enables uniform spaces or cells 8 to be easily formed through the silicon oxide layer 7.

The silicon oxide layer or portion 7 is covered by a glass plate 9, similar to the glass plate 4, having Y electrodes 10 formed thereon. The Y electrodes are transparent conductive parallel strips of film equidistantly spaced from each other and of equal widths. The Y electrodes 10 extend perpendicularly to the X electrodes 5. The Y electrodes 10 are covered by a layer 11 of silicon oxide which abuts the layer 7. The Y electrodes 10 are formed on a surface of the glass plate 9 which faces the surface of the glass plate 4 on which the X electrodes 5 are formed.

After the complete device is assembled, with its next-adjacent parts in abutment with each other, and then sealed airtight from the atmosphere or hermetically sealed, thereby sealing the cells 8, the cells 8 are evacuated and filled with ionizable gas. Said sealing process may be performed by any suitable means such as, for example, the application of glass having a low melting point or another suitable bonding agent to the peripheral areas of said device.

The display device of the present invention is very strong in structure and has great mechanical strength. The mechanical strength of the device may be increased by utilizing glass plates 4 and 9 of relatively great thickness. Due to the utilization of insulation comprising silicon compounds in the display device of the invention, the first insulating layers may be very thin and very narrow wall spaces may be provided for the cells, due to their formation by sputtering. This permits the considerable decrease of the discharge voltage and is unattainable with known types of display device utilizing glass insulation.

Although silicon compounds are illustrated as the insulating materials in the described embodiment of the invention, said insulating materials may comprise aluminum oxide, titanium oxide, tantalum oxide and barium titanate having large dielectric constants. The insulating material may thus generally comprise metal compounds. When compounds of titanium and tantalum having large dielectric constants are utilized as the insulating material, the voltage distributed and applied to the cells from the applied voltage may be increased.

The insulating layers may be formed by the evaporating process as well as by sputtering, and, if necessary, may be formed by a process involving pyrolysis of metal compounds, as hereinbefore described, or a screen printing process. The screen printing process may be utilized to facilely form layers of greater thickness relative to those formed by other processes, and may therefore be utilized to advantage in forming cells having relatively large spaces between their walls, relative to the pressure of the gas sealed therein.

As is known in the art, the relationship between the sealed-in gas in the cells and the discharge gap may be expressed as

Vf = f(p,d)

or Vf is a function of p and d, or Paschen's Law, wherein Vf is the discharge voltage, p is the pressure of the gas in the cell and d is the length of the discharge gap.

As stated herein, it is difficult to decrease the discharge voltage in the known method by means other than a thin glass plate comprising three thin sheets of glass. Since a thicker glass basic plate may be utilized in the method of the invention, breakage may be eliminated.

The discharge voltage of the display device produced by the method of the invention depends upon the length d of the discharge gap, as indicated in the aforedescribed relation. Accordingly, the depth of the cell or space 8 is uniform throughout the display device. A difference in the depth of the cells or spaces 8 results in an erroneous address, so that the quality of the display device is inadequate if there are differences in such depths. Cells or spaces having uniform depth may be produced, however, by the method of the invention, due to the differences in the speed of etching in the different materials of the first and second layers. The resultant display device thus has uniform electrical characteristics.

Insulating material utilized for the first insulating layers covering the electrodes may comprise solder glass. However, ion bombardment produces sputtering in discharge, since a large quantity of lead oxide is present in the solder glass. This results in the disadvantage of lead being deposited as a black coating on the inside surfaces of the device. This effect worsens as the discharge voltage increases with operating time, thereby shortening the life of the display device. In accordance with our invention, the method of manufacture produces a display device utilizing aluminum oxide or silicon nitrate, in which there is little likelihood of sputtering phenomena, as the first insulating layers on the inside surfaces of the device.

The desired layers of insulation may be formed by the screen printing process by first forming electrodes comprising transparent conductive films on a glass substrate. A silk screen or stainless screen having a formed pattern therein in accordance with the dimensions, shape and arrangement of the cells is placed on the electrodes. A roller coated with insulating paste is utilized to print said paste in the form of the pattern. The paste pattern is then fired and hardened. The insulating paste may comprise an organic binder and a solvent added to the insulating metal compounds of the aforedescribed types, and has a muddy consistency. Chemicals, such as etchants and photoresistive materials, may be arbitrarily selected and utilized.

FIGS. 5 and 6 illustrate another embodiment of the display device of the invention. In the embodiment of FIGS. 5 and 6, the cells are joined to each other and communicate with each other. This embodiment may thus be manufactured with greater facility than the embodiment of FIG. 4, in which the cells or spaces 8 are isolated from each other.

In forming the embodiment of FIGS. 5 and 6, transparent conductive film strips 5 are formed on a glass plate 4 and a silicon nitride layer 6 is formed on the conductive strips 5. Silicon oxide layers 12, in the shape of strips, are formed on the layer 6 of silicon nitride. The strips 12 are spaced from each other and thus form gaps or spaces 13 between adjacent ones of said strips.

Transparent conductive film strips 5' are formed on a glass plate 4' and a silicon nitride layer 6 is formed on the conductive strips 5'. Silicon oxide layers 12', similar to the strips 12, are formed on the layer 6' of silicon nitride perpendicularly to the strips 12. The component elements are so tightly joined that the strips 12 and 12' are mutually perpendicular (FIG. 6). Although the cells 13 are in mutual or common communication, only the parts of wide gap, across which the X and Y electrodes mutually extend, function as the cells. The part of narrow gap is a mere gap portion which serves to make the pressure of the gas in the cells uniform.

In some cases, it is advantageous to utilize a thin glass plate having holes formed therethrough, as shown in the embodiment of FIG. 1, instead of an insulating metal compound layer, for defining the length of the cells in the display device shown in FIGS. 4 and 6. This is due to the fact that the sputtering process, the evaporating process and the pyrolysis of compounds process are much too time-consuming when they are utilized to form the insulating layer to more than a specific thickness. The screen printing method is less time-consuming than the aforementioned three processes, but is more time-consuming than the process which utilizes a thin glass plate.

Although in the foregoing examples, the X and Y electrodes and the plates supporting said electrodes are transparent, only one of these groups of electrodes and the corresponding supporting plate need be transparent, if it is unnecessary to observe the discharge light of the cells from both sides of the display device. One of the substrates or support plates may then comprise a ceramic material and the corresponding electrodes may be formed on the ceramic plate as metal foil.

The X and Y electrodes need not necessarily be linearly disposed and at right angles to each other. Any suitable arrangement of electrodes may be utilized, depending upon the purposes of the display. The electrodes may thus extend radially, or in concentric circles, or in other configurations.

Although in the aforedescribed embodiments of the invention the partitions of insulating material are provided between each adjacent pair of cells to isolate the cells or to narrow the interconnecting path therebetween, it is possible to eliminate such partitions in another embodiment, because the gas discharge within the cells is not principally affected by such partitions.

While the invention has been described by means of specific examples and in specific embodiments, we do not wish to be limited thereto, for obvious modifications will occur to those skilled in the art without departing from the spirit and scope of the invention.

Claims

We claim:

1. A method of manufacture of a display device utilizing gas discharge and having a pair of basic plates of insulating material at least one of which is transparent, each having a primary surface and a plurality of conductive electrode layers formed on each primary surface and covered by an insulating layer, a portion of insulating material being provided between the insulating layers to form a plurality of spaces therebetween, said method comprising the steps of forming a first layer of metal compound insulating material covering the conductive layer on the primary surface of each of the basic plates; forming a second layer of metal compound insulating material on the first insulating layer of at least one of the basic plates, the metal compound insulating material of the second layer being susceptible to a higher etching speed than the metal compound insulating material of the first layers in the same etchant condition; etching the second insulating layer throughout its thickness in a predetermined pattern to provide a plurality of spaces therethrough; and sealing both basic plates in a condition that the conductive layers on the primary of each of the basic plates face each other so as to enclose ionizable gas in the spaces formed through the second insulating layer.