US 3769543 A
A low voltage gas discharge display device, the individual cells of which are addressable by half-select pulses applied to selected control and collector electrodes. In the "off" or standby state, low glow discharge occurs between an anode and a cathode which are electrically common to all of the cells. Control electrode lines, associated with rows of cells, are biased to create a current impeding ion sheath across the respective cell holes therethrough to the positively biased collector electrode lines associated with columns of cells. Half-select pulses applied to a control and collector electrode line act to reduce the ion sheath across the hole at the interselection thereof and initiate positive column glow discharge therethrough.
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Description (OCR text may contain errors)
United States Patent Pennebaker Oct. 30, 1973 LOW VOLTAGE GAS DISCHARGE DISPLAY Primary ExaminerRoy Lake  Inventor: William B. Peunebaker, Camel, Assistant Examiner-Lawrence Dahl Attorney-John A. Jordan et al. NY.
 Assignee: International Business Machines  ABSTRACT 'l Armonkv A low voltage gas discharge display device, the indi-  Filed; Dec. 30, 71 vidual cells of which are addressable by half-select 'pulses applied to selected control and collector elec- [211 P N 213,946 trodes. In the off" or standby state, low glow discharge occurs between an anode and a cathode which  C] 5 9 TV 313/1095, 315/169 R are'electrically common to all of the cells. Control 51 Int. Cl. uosb 37/00 electrode lines associated with rows of cells,  Field of Search sis/109.5; ased 10 Create a current impeding ion Sheath across 315/169 R 169 TV the respective cell holes therethrough to the positively biased collector electrode lines associated with col- 5 References Cited umns of cells. Half-select pulses applied to a control UNITED STATES PATENTS and collector electrode line act to reduce the ion 3 336 99 8/1967 O M 315/169 R sheath across the hole at the interselection thereof and eara 3,626,245 12/1971 Rosenberg at all 315/169 R inmate positive column glow discharge therethrough. 3,042,823 7/1962 Willard 315/169 R 14 Claims, 2 Drawing Figures 3 GAS l lie v L 19 --17 f W li CONTROL PATENTEDHCTBO I973 3. 769,543
CONTROL F| 2 I INVENTOYR WILLIAM B. PENNEBAKER ATTO R NEY LOW VOLTAGE GAS DISCHARGE DISPLAY BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to low voltage gas discharge display devices, and more particularly to low voltage DC gas discharge display devices.
2. Description of the Prior Art There exists in the prior art somewhat of a variety of gas discharge display devices. One common type of gas discharge display device known in the art is the AC gas discharge display device, i.e. AC gas panel display. One of the difficulties of the AC gas panel display resides in the fact that control of the panel requires relatively large magnitudes of voltage. Typically, 80 volt (or more) pulses may be required to drive the panel to selectively control display thereon. Accordingly, the pulsing circuitry required to selectively drive and control the AC gas panel is necessarily complex and costly. In addition, the power supply circuitry required for AC gas panels is, likewise, complex and costly.
One of the reasons for the large magnitude of switching voltage required for AC panels, and the complexity involved therewith, resides in the fact that the AC panel uses light from the negative glow of the gas discharge and, accordingly, the selective firing and extinguishing of this type of glow discharge requires pulses that operate to completely turn on and off the discharge.
In accordance with the principles of the present invention, a low voltage DC gas discharge display device is provided whereby light from positive column glow discharge is employed for purposes of addressable display. More particularly, the gas discharge display device of the present invention comprises an array of gas cells, with the individual cells of the array having at one end thereof, a first layer of conductive material which acts as a cathode, electrically common to all of the cells. A second layer of conductive material, insulatably removed from the first layer of conductive material and having a plurality of cylindrical holes therein which communicate with said first layer of conductive material, acts as an anode electrically common to all of the cells of the array, in a conventional manner. In addition, a third layer of material acts to insulate the anode layer from a plurality of opaque control electrode lines, each control line being common to a particular row of cells in the array, and having holes therein of a smaller dimension than, and at locations corresponding to, the holes in the layer of conductive anode material. A further layer of insulating material then acts to space the various control lines from a plurality of transparent conductive collector electrode lines with individual ones of said plurality of collector lines being common to the cells in the respective columns of said array of cells.
In accordance with such an arrangement, low glow gas discharge may be maintained in all of the cells, between the common anode and cathode thereof. During such discharge, an ion sheath is formed surrounding the control lines, thereby blocking gas discharge through the respective holes therein. Thus, little light is visible from the cells at the display surface thereof. However, by pulsing selected ones of said control and collector lines, intense positive column glow discharge may be initiated in the hole of the selected control line, adjacent the selected collector line, whereby the intense glow is visible through the transparent collector line at the surface of the display device. Since in such an arrangement, the switching on" and off of the positive column glow discharge is achieved in the presence of the low glow sustaining discharge between anode and cathode, low switching voltages may operatively be employed for the switching thereof. In addition to low switching voltages, the arrangement in accordance with the present invention allows half-select switching, whereby positive column glow discharge may be latched into a selected hole by application of pulses to the appropriate ones of both a control and collector line.
The use of a control electrode to provide a controllable glow discharge is generally known in the prior art. Typical of such arrangements is that described in an article entitled Glow Thyratrons" in CONTROL, pg. 124, Vol. 5, September 1962, and those described by Hagen in U.S. Pat. No. 2,612,617 and Van Daelen in U.S. Pat. No. 3,479,547. However, the prior art fails to provide a simple, bright and economic display device, whereby low voltage half-select pulses may be employed to selectively address and switch the individual cells of an array of gas cells to a stable high glow state, for purposes of display.
SUMMARY OF THE INVENTION It is therefor an object of the present invention to provide an improved gas discharge display device.
It is a further object of the present invention to provide a DC gas discharge display device, having bistable switching characteristics.
It is yet a further object of the present invention to provide a gas discharge device employing low voltage switching.
It is yet still a further object of the present invention to provide a gas discharge display device, the individual cells of which are addressable by half-select switching.
It is another object of the present invention to provide a low voltage DC gas discharge display device which operates in a manner so as to allow simple and low cost switching circuitry to be employed for the control thereof.
It is yet another object of the present invention to provide a gas discharge display device fabricated in the form of an array of individual discharge cells, each cell of which may be quiescently biased into a low glow state by low voltage DC, and which is selectively addressable to be driven into a stable positive columnhigh glow discharge state by low voltage half-select control pulses.
In accordance with the principles of the present invention, a display device is formed from an array of discharge cells, with the anode and cathode of each cell electrically common with one another, and with opaque control electrodes therefor common to the cells in rows of the array and with the transparent collector electrodes therefor common to the cells in columns of the array. Small holes have been placed in the control electrode lines, at locations corresponding to the intersection of the columns and rows of the array.
The cathode as described is quiescently biased sufficiently negative to strike and maintain a low glow DC discharge between the anode and cathode sections in each of the cells. A positive potential somewhat greater than the ionization potential of the gas employed is applied to each of the collector electrode lines and, a negative potential is applied to each of the control electrode lines. Although the collector electrode lines are biased positively, no current flows to them so long as the control electrode lines are biased sufficiently negative such that the space charge limited ion sheath surrounding them blocks the small holes therethrough, to the collector electrode lines. However, if the bias on a selected control electrode line is made sufficiently less negative, the ion sheath thereof may contract to a point where it no longer can block the control hole thereof, whereby electrons may penetrate the hole. By biasing a selected one of the collector electrode lines more positively, a sufficient number of electrons may be induced to penetrate the hole adjacent thereto, whereby the gas discharge in the cell thereof bistably switches from the low glow discharge between anode and cathode to a high intensity positive column discharge between cathode and selected collector electrode line.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiment of the invention as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a cross-sectional view of the display device, in accordance with the present invention, taken along section lines 1-1, of the top view shown in FIG. 2.
FIG. 2 shows a top view of the arrays of cells, of the gas discharge device of the present invention.
DETAILED DESCRIPTION OF THE DRAWING In the cross-sectional view of the display device, shown in FIG. 1, view plate 1, forming the display surface, is shown at the bottom. View plate 1 may comprise any of a variety of transparent materials. Typically, the view plate may be made of glass. Likewise, the remainder of the outer shell or envelope 3 that contains the plasma of the display device may be fabricated from glass. Sealed within the envelope of the display device is a plasma 5. Typically, the plasma may comprise a gas such as helium, or helium with small traces of argon. In this regard, it is clear that any inert gas may be employed, such as, for example, neon with a dopant of approximately 1% argon or nitrogen. The gas is introduced to the desired pressure, in accordance with cell dimensions applied potentials, and the like. Typically, the cells are operated somewhat above the minimum on the Paschen curve.
As shown in the cross-sectional view of FIG. 1, cathode 7 is arranged to be common to the row of chambers 9, 11, 13, and 17, fabricated in the insulating spacer 19 and anode 21. Typically, cathode 7 may comprise a plate or sheet of metal, such as molybdenum. It is clear, in this regard, that the cathode may be in the form of a thin film sheet of molybdenum, or altematively in the form of a stack of thin film sheets of molybdenum, to form a laminate, for example. Insulating spacer 19 may be fabricated from glass, for example. Anode 21, like cathode 7, may be fabricated from molybdenum. It can be seen that the main chambers of cells 9, ll, 13, 15 and 17 (the larger cylinders located in anode 21) communicate with cathode 7 via the smaller chambers or holes 9a, 11a, 13a, 15a and 17a in spacer 19. As is clear from the drawing, terminals 23 and 25 act to allow a biasing potential to be applied to the cathode and anode, respectively. Typically, the anode 21 is grounded while the cathode 7 is maintained at approximately l volts. However, it is clear that other voltage levels may be employed, and that voltage levels may vary in accordance with the particular arrangement embodied.
As shown in the cross-sectional view of FIG. 1, control line 27 is spaced from anode 21 by insulating spacers 29, 31, 33, 35 and 37. Rather than employ insulating spacers, however, metallic spacers such as gold stand-offs may be employed where they are arranged to be mounted on insulating spacer 38, without making contact with control line 27. As shown, holes 39, 41, 43, 45 and 47, in control line 27 are arranged to allow plasma to communicate from the respective cell chambers in the anode to the respective collector lines 49, 51, 53, and 57. As can be seen, the collector electrode lines are positioned in slots in spacer 38. These control lines, it should be appreciated, are fabricated from a transparent conductive material, such as a thin metal oxide layer like lnO or SnO. Spacer 38 may be fabricated from any of a variety of insulating materials, such as glass. Control line 27 may be fabricated from any conductive material. Typically, the control lines may be fabricated from molybdenum or tungsten.
As shown in FIG. 1, a bias potential may be applied to control line 27 via terminal 48. Typically, the bias potential applied to the control lines may range from a 5 volts to a l5 volts. As can be seen, the array of holes 39, 41, 43, 45 and 47 in control line 27 are slightly to the right of center of the respective main chambers located in anode 21. On the other hand, chamber holes 9a, 11a, 13a, 15a and 17a in spacer 19 are somewhat to the left of center of the respective main chambers, located in anode 21. As will be more clear, hereinafter, this offset between the holes in spacer 19 and opaque control line 27 acts to partially obscure, as seen from view plate 1, the low glow discharge between cathode 7 and anode 21. Thus, it is clear that while the respective collector lines in the array are fabricated to be transparent so as to allow the high intensity positive column glow discharge through holes 3947 to be seen, the respective control lines (as shown in FIG. 2) of the array are fabricated to be opaque so as to obscure the low glow background discharge between the cathode and anode. It should be recognized, that the transparent collector lines may be directly deposited upon the inner face of view plate 1. Any of a variety of techniques, such as vapor deposition or sputtering techniques, may be employed to deposit the transparent collector lines.
In FIG. 2, there is shown a top view of the display device, in accordance with the present invention. As can be seen, 25 cells have been shown in a 5 X 5 cell array. However, as suggested by the broken lines, a larger or smaller array may likewise be implemented. The respective rows of the array are addressed by application of switching pulses to the respective control electrode lines at terminals 48, 58, 68 and 78. The respective columns of the array are addressed by application of switching pulses to the respective collector electrode lines at electrodes 39a, 41a, 43a, 45a and 47a.
Before describing the operation of the display device in accordance with the present invention, it should be recognized that the array of discharge cells have been arranged in a manner so that the various cells operate independently from one another. This independence can be achieved to a large extent by placing the anode relatively close to the cathode. A typical 5 X 5 array may, for example, comprise a center-to-center spacing for the cells of the array of 0.25 cm. The dimensions of the individual cells may comprise an anode diameter and thickness of 0.150 cm and a control electrode hole or opening of 0.035 cm. It should be recognized that the diameter of the holes in insulating spacer 19 may be smaller than the anode diameter, as shown in FIG. 1, or of the same size. In addition, the control lines may be deposited to a thickness of 0.012 cm on a glass spacer of 0.025 cm. Finally, the spacing between the anode and cathode may be of the order of 0.015 cm. It should be recognized that these values are typical and in no way critical or limiting, and that any of a variety of dimensions and arrangements may likewise readily be employed, in accordance with the principles of the present invention.
Although any of a variety of gasses may be employed, helium or helium with argon have been found to be particularly effective. With the anode grounded, DC cathode voltages (on terminal 23) ranging from l 50 volts to 200 volts have been found effective to bias the cathode so that the discharge between anode and cathode runs slightly in the abnormal glow region. wheretantalum might, for example, be employed as the cathode material, the high end of the voltage range would be employed Pure helium may be introduced into envelope 3 of the display device to a typical pressure of approximately 90 Torr. on the other hand, helium with 0.2 percent argon, for example, may be introduced to a lower pressure of approximately 70 Torr.
The various control electrode lines may be biased slightly negative, while the various collector electrode lines may be biased to a positive level somewhat in excess of the ionization potential. For example, the respective collector electrode lines may be biased, as hereinabove indicated with respect to FIG. 1 (via terminals 48, 58, 68 and 78) to a potential in the range from 5 volts to l5 volts. Typically, the collector electrode lines would be biased to 50 volts and the control electrode lines would be biased to volts.
Accordingly, with reference to FIG. 1, even though the collector electrode lines 49, 51, 53, 55 and 57 are biased positively, no current flows to these lines so long as the control electrode line 27 shown here is biased sufficiently negative so that the space charge limited ion sheath surrounding this control line blocks the holes 39, 41, 43, 45 and 47 therein. Under these conditions, only a small amount of the light generated by the cells 9-17 is visible at view plate 1, i.e. that portion of the sustaining glow between anode and cathode which is visible through the control holes 39-47. If new the control bias is made less negative, the ion sheath contracts. If the ion sheath contracts sufficiently so that it no longer effectively blocks the control holes, electrons will penetrate the hole and, if enough are allowed to penetrate the hole, the cell switches to a different stable state. The current flow to the collector causes additional ionization which lowers the impedance between the collector electrode lines and negative glow, and more current then flows. When the entire discharge current flows to the collector electrode lines, a second stable state has been reached.
In this second stable state, an intense glow forms where the current passes through the small control holes (39-47) to form positive column glow discharge.
Since the collector electrode lines are transparent, the intense glow is readily visible at the viewing surface of the display device. The stability of the second stable state is considered to be due to the high plasma density, in the vicinity of the control holes. When the control electrode line potential returns to its initial negative DC bias, the ion sheath can no longer block the opening, but rather can only constrict the opening thereby further enhancing the current density through the opening, and thus the brightness of the glow. Thus, it can be seen that when the control electrode potential is made less negative for a sufficient period of time, positive column glow discharge can be achieved in the control holes thereof. The control electrode potential, as is evident in this regard, may readily be made less negative by applying a positive control pulse of appropriate magnitude and duration to the control terminal therefor.
Since the duration of the control pulse required for switching cells to positive column glow discharge is dependent upon collector potential, half-select pulse writing and erasing may be employed. Accordingly, control pulses, of a duration insufficient in themselves to cause switching, may be employed with the simultaneous application of positive collector electrode pulses which raise the collector potential to the point where the applied control pulse is sufficient to cause switching. Accordingly, with reference to FIG. 2 in the embodiment thus far described, application to respective terminals 41a and 48 of coincident positive pulses of, for example, a magnitude of 10 volts and a duration of approximately 1.5 ,us, would act to initiate positive column glow discharge in cell 11. With reference to FIG. 1, pulses of such magnitude and duration would be effective to reduce the ion sheath over hole 41 and increase the potential on collector line 51 such that sufficient current would flow to latter to initiate positive column glow discharge.
With reference to FIG. 2 then, it can be seen that the cell at the intersection of the selected control and collector lines is switched from a stable low glow background discharge state between anode and cathode to a stable high glow foreground positive column discharge state by the respective application of concurrent positive half-select pulses thereto. Likewise, pointby-point erasure of selected cells may be achieved by applying negative half-select pulses to the appropriate collector and control electrode lines. It should be recognized that the magnitude and duration of read and write pulses will vary in accordance with the particular arrangement implemented. For example, the type of electrode material employed, the type of plasma employed, the relative dimensions of the cells and openings thereof, the amount of impurities within the plasma, and the like, act to affect the magnitude and duration of the half-select pulses required for cell switching. It need only be recognized by those skilled in the art that increase in the collector potential acts to increase the cell switching speed and, that for halfselect switching control pulses of insufficient duration to cause switching may be made effective to switch by such increase in collector potential.
Although operation has thus far been described with the cathode biased by a fixed DC voltage, it should be understood that operation of the DC gas discharge display device, in accordance with the present invention, may be effected in a pulsed mode. One particular way of operating in a pulsed mode is to bias the cells of the display device with a voltage insufficient to sustain discharge in the cells in the 37 off" or standby state (low glow discharge), but sufficient to maintain positive column glow discharge in the cells in the on state, and to periodically pulse the cathode to a more negative potential for purposes of writing. The manner by which this may be accomplished can be seen when it is recognized that when cells are pulsed into the positive column glow discharge or on state, a positive shift in the plasma potential is effected, whereby the sustaining voltage level of the on cell is shifted in the positive direction. Accordingly, the cathode may be pulsed with pulses of a magnitude sufficient to sustain positive column glow discharge in the on cells, but insufficient to sustain low glow discharge in the off cells in the standby state.
it should be noted that when operating in the pulsed mode, the half-select pulses to the control and collector electrode lines may be synchronized with the pulses to the cathode. It should also be noted that other methods are likewise readily evident and available for operating the display device, in accordance with the present invention. For example, the pulsing of the cathode may be employed for turning on selected cells. In this latter regard, the cathode may be arranged in lines, in the manner of the control or collector lines.
Likewise, the cell design may readily be modified for a color and/or gray scale arrangement. For example, multiple collector-control pairs may be incorporated into a single cell. For example, three multiple collectorcontrol pairs may be employed in a single cell. Positive column glow discharge, then, may readily be sustained in only one of the three control holes of a single cell. Where positive column glow discharge is present in one control hole and another is triggered in the same cell, the first glow may be extinguished. By appropriate bias on the various multiple collector-control pairs in a cell or, alternatively, by the use of filters in association therewith, color and/or gray scale may readily be achieved.
It can be seen that in accordance with the display device of the present invention, half-select pulse addressing is readily achievable. In addition, operation of the display device does not depend on constant secondary electron emission from the cathode and thus, operation is less sensitive to cathode sputtering. In addition, by the present invention ahighly bright read-write display device which retains its write state by DC voltages without the need for refresh signals, is provided.
While the invention has been particularly shown and described with reference to the preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and deto delineate each of the cathodes of the respective cells of said array of cells;
second conductive plate member means separated from said first conductive plate member means by said layer of insulation means and having an array of holes therethrough corresponding to said array of cells with the walls of the respective holes of said array of holes forming respective anode surfaces for said array of cells and with respective ones of said holes forming said anode surfaces arranged to communicate through said holes in said layer of insulation to the respective cathodes of said first conductive plate member means;
conductive control electrode strips separate from one another and insulatably mounted over each of the respective rows of holes in said array of holes of said second conductive plate member means with each of said conductive control electrode strips having apertures therethrough at positions corresponding to each of said holes of said array of holes so as to form a row of apertures along the length of each said strips and columns of apertures across said strips;
transparent conductive collector electrode strips separate from one another and insulatably mounted adjacent said display surface over each of said respective columns of apertures across said conductive control electrode strips;
means to apply a potential to bias said first conductive plate member means negatively with respect to said second conductive plate member means so as to maintain a stable low glow DC discharge state in each cell;
means to apply a potential to bias each of said collector electrode strips positively; means to apply a potential to bias each of said control electrode strips negatively so as to create an ion sheath across each of said apertures sufficient to prevent electrons from passing there through to said positively biased collector electrode strips; and
means to apply pulses to selected ones of respective control and collector electrode strips so that the cell at the interseciton of the selected one of said control and collector electrode strips has both the ion sheath across the aperture thereof reduced and the potential at the collector electrode adjacent thereto increased so as to thereby allow electrons to penetrate through the said aperture thereof to said collector electrode and establish a stable high intensity positive column glow discharge therein visible through said transparent collector electrode.
2. The device as set forth in claim 1 wherein the area of the aperture openings is small compared to the area of the hole openings in said second conductive plate member means.
3. The device as set forth in claim 2 wherein said second conductive plate member means is substantially at ground potential and said collector electrode strips are biased at approximately 50 volts.
4. The device as set forth in claim 3 wherein the respective apertures in said control electrode strips for each of the respective cells are off-set from the corresponding holes in said layer of insulation means for each of the respective cells and said control electrode strips are opaque.
5. The device as set forth in claim 4 wherein said transparent collector electrode strips are made of an oxide of metal.
6. The device as set forth in claim 5 wherein said metal is taken from the group consisting of Sn and In.
7. The device as set forth in claim 5 wherein the gas in said envelope includes helium, said first and said second conductive members are made of molybdenum and said opaque control electrode strips are made of tungsten.
8. The device as set forth in claim 7 wherein halfselect pulses of approximately l0 volts each applied to respective ones of said control and collector electrode strips act to switch discharge in the cell at the intersection thereof from the stable low glow DC discharge state between the anode and cathode thereof to said stable high intensity positive column gow discharge state through the aperature thereof between said cathode and the pulsed collector electrode strip.
9. A gas discharge display device comprising an envelope filled with gas capable of supporting glow discharge and having at least one surface thereof which is transparent so as to provide a display surface whereby selected ones of local regions of a plurality of regions within said envelope made to glow may be displayed therethrough, the improvement comprising:
first electrode means mounted within said envelope,
said first electrode means including a first plurality of electrode areas electrically coupled to one another;
second electrode means mounted within said envelope adjacent said first electrode means, said 'second electrode means including a second plurality of electrode areas respective ones of which are adjacent to and separate from respective ones of said first plurality of electrode areas such that upon application of a potential thereacross gas present between respective ones of said first and second electrode areas may be caused to undergo a first stable low glow discharge condition;
collector electrode means interposing said second electrode means and said display surface within said envelope and mounted adjacent to and separate from each of the respective ones of said second plurality of electrode areas such that upon application of a potential of sufficient magnitude thereto gas present therebetween may be caused to undergo a second stable high glow discharge condition;
control electrode means interposing each of the respective ones of said second plurality of electrode areas and said collector electrode means and arranged so that a sufficient potential applied thereto causes a current impeding ion sheath to be formed thereat to thereby control said second stable high glow discharge condition;
means to apply a potential between said first and second electrode means so as to cause said first stable low glow discharge condition between each of respective ones of said first and second plurality of electrode areas;
means to apply a first control potential to said control electrode means so as to cause a current impeding ion sheath to be formed thereat sufficient when said first stable discharge condition exists to prevent charge flow to said collector electrode means and bring about said second stable discharge condition; and
means to apply a collector potential to said collector electrode means which potential is insufficient to cause said second stable discharge condition when said first control potential is applied to said control electrode means but which is sufficient to cause said second stable discharge condition when said first control potential is reduced to provide a second control potential smaller than said first control potential.
10. The display device as set forth in claim 9 wherein said first and second plurality of electrode areas comprise a two dimentional array of rows and columns of said first and second electrode areas.
11. The display device as set forth in claim 10 wherein said collector electrode means mounted adjacent to and separate from each of the respective ones of said second plurality of electrode areas comprises a separate collector electrode for each column of said second electrode areas and wherein said control electrode means interposing each of the respective ones of said second plurality of electrode areas and said collector electrode means comprises a separate control electrode for each row of said second electrode areas.
12. The display device as set forth in claim 11 wherein each of the separate collector electrodes for each column comprises a transparent conductive line and wherein each of the separate control electrodes for each row comprises an opaque conductive line.
13. The display device as set forth in claim 12 wherein said opaque conductive lines each have a row of apertures therethrough along the length of said lines at locations corresponding to the locations of each electrode area in the said rows of said second electrode areas.
14. The display device as set forth in claim 13 wherein said first electrode means comprises a conductive plate with each area of said plurality of electrode areas thereof being delineated by respective ones of a plurality of holes in a layer of insulator in contact therewith and wherein each respective electrode area of said second plurality of electrode areas comprises the inner surface area of a hole in a conductive plate with each hole thereof respectively communicating with corresponding respective ones of said plurality of holes in said layer of insulator and with said conductive plate being held in spaced-apart relationship from said first electrode means by said layer of insulator.