US3670201A - Gas discharge display device with perimetrical cathode - Google Patents

Abstract

A display device employing a planar array of elements disposed on a dielectric substrate. The dielectric substrate is affixed to a metallic plate which functions as an anode element in an electrical discharge while a perimetrical metallic strip serves as a cathode element. These components are disposed between two non-conductive plates in which a partial vacuum is created and backfilled with an inert gas. The non-conductive plate proximate the display surface of the array of elements is transparent enabling an undistorted view of the segments. A relatively large potential applied between the anode and the cathode elements sustains the electrical discharge thereby providing a source of free electrons in the area between the elements and the transparent plate. The application of a small bias voltage between selected segments of the array of elements and the anode element produces a thin luminous sheath over the energized segments which provides a sharply defined display.

Description

United States Patent Veron GAS DISCHARGE DISPLAY DEVICE WITH PERIMETRICAL CATI'IODE Inventor: Harry Veron, Framingham, Mass.

Assignee: Sperry Rand Corporation Filed: July l0,- 1970 Appl. No.: 52,761

U.S.Cl. ..3l5/l69 TV,3l3/l09.5,313/2l0, 313/217, 313/220 Int. Cl. ..H05b 37/00 Field of Search ..313/109.5, 210, 209, 217, 220; 315/169 R, 169 TV References Cited UNITED STATES PATENTS Kayatt Primary Erandner-Roy Lake Assistant Examiner-Palmer C. Demeo Attorney-S. C. Yeaton ABSTRACT A display device employing a planar array of elements disposed on a dielectric substrate. The dielectric substrate is affixed to a metallic plate which functions as an anode element in an electrical discharge while a perimetrical metallic strip serves as a cathode element. These components are disposed between two non-conductive plates in which a partial vacuum is created and backfilled with an inert gas. The nonconductive plate proximate the display surface of the array of elements is transparent enabling an undistorted view of the segments. A relatively large potential applied between the anode and the cathode elements sustains the electrical discharge thereby providing a source of free electrons in the area between the elements and the transparent plate. The application of a small bias voltage between selected segments of the array of elements and the anode element produces a thin luminous sheath over the energized segments which provides a sharply defined display.

6 Claims, 1 Drawing Figure PATENTEBJum 1972 3.670.201

V IN new we HA RR) VERON ATTORNEY:

1 GAS DISCHARGE DISPLAY DEVICE WITH PERIME'I'RICAL CATI-IODE BACKGROUND OF THE INVENTION 1. Field of the Invention The disclosed invention pertains to the field of displays and .more specifically to displays utilizing an electrical dischargein a gas.

2. Description of the Prior Art Gas discharge display devices usually employ a luminous portion of an electrical discharge through a gas as part of the illumination for the display elements. This discharge is referred to as a glow discharge and is produced between an anode element and a cathode element by inelastic collisions of electrons and atoms of the gas. These collisions'cause electrons in high energy levels of the atoms to rise to higher levels, then eventually fall back and release photons. To provide a sustained glow discharge, a relatively large electric field is applied between the anode and cathode to impart high acceleration to the free electrons initially present between the elements. The highly accelerated electrons collide with atoms of the gas freeing electrons in the higher energy levels of the atoms. The remaining gas atoms are then ionized and accelerated toward the cathode element. When the ionized atoms impinge on the surface of the cathode they produce more free electrons which are then accelerated toward the anode resulting in a sufficient number of collisions with atoms of the gas to maintain the glow discharge.

The most frequently employed portion of a cold-cathode discharge is the negative glow which occurs near the cathode. This negative glow usually emits diffuse illumination and therefore requires some external filtering or other means to sharpen the resulting image of the cathode display elements. The dimming capability of such a display is limited in that there is a relatively high minimum voltage below which the discharge will not be maintained, that is, the device isnot continuously dimmable to zero light output.

Moreover, the lifetime of a gas discharge display device is limited by sputtering which is the rate that material is emitted or eroded from the cathode. Material is removed from the cathode element as a result of the ionized gas atoms impinging on the surface of the cathode. The rate at which material is removed from the cathode is related to the number of ions and the energy of the ions impinging on the cathode. Removal of an appreciable amount of material from the cathode element causes changes in the electrical characteristics of the display and increases the probability of short-circuiting the display elements. In the prior art devices the large voltage drops in the cathode region imparted large energy levels to the ions thereby increasing the rate at which material was removed from the cathode and decreased the life of the display.

SUMMARY OF THE INVENTION The present invention provides a display including a plurality of thin film metallic elements disposed on a dielectric substrate which is epoxied to a metallic plate. The metallic plate is and centrally disposed with respect to a perimetrical metallic strip. These components are afiixed to a portion of a dielectric material which is used as a backing surface. Energized segments of the thin film metallic elements are viewed through a second transparent portion of dielectric material which is mounted over the components.

Initially a vacuum is created in the space bounded by the two dielectric plates and the perimetrical metal strip. Subsequently, an inert gas such as neon is then partially backfilled into the vacuum. A relatively large potential is applied between the metallic plate which functions as an anode and the perimetrical metallic strip which serves as a cathode thereby maintaining an electrical discharge. The electrical discharge provides a source of free electrons over the area of the anode. Low level bias voltages are applied between the anode and selected segments of the thin film metallic elements which accelerate the electrons in the area immediately in front of the energized segments. A thin luminous sheath is produced in front of each energized segment that is essentially a type of anodeglow from which a sharply defined image is obtained. The thin luminous sheath over the energized segments is a spatial charge region due mainly to electrons.

The number of electrons and the associated energy of these electrons are relatively small because the bias voltage levels are low. Consequently, the rate at which material is removed from the energized elements is low and the life of the display is increased.

Since the bias voltage levels which are used to energize selected segments of the display elements are low, the device can be readily adapted for use with digital logic circuitry with a minimum of interfacing electronics. Further, the luminosity of the display can be varied without changing the voltage level between the anode and cathode that sustains the electrical discharge, thereby enabling the luminosity to be continuously dimmed to zero light output.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE is an isometric view including a partial schematic diagram of an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT I form the inverse brush cathode 11. A metallic anode plate 13 is centrally disposed within the ring .11 and also may be fabricated from aluminum. Affixed to the plate 13 is a piece of dielectric material 14 that may be comprised of a glass substrate. A plurality of display elements 15 are disposed on the dielectric material 14 and are coplanar with the anode plate 13. Y

The plurality of display elements 15 can be thin metallic films including, for example, stainless steel. These components are interposed between two circular plates 16 and 17 to form an integral tube unit. The circular plate 16, which covers the front of the displaydevice 10, is transparent to allow. direct viewing of the display elements 15. The back plate 17 has a centrally located opening 23 in which the anode plate 13 is secured with an adhesive sealant. vA vacuum is created within the tube unit by attaching a vacuum pump to access port 18 and reducing the pressure. The .unit is then partially backfilled through the access port 18 with a typical inert gas such as neon. The inverse brush cathode 11 is connected to the negative terminal of a d.c. voltage source 19. The anode plate 13, the positive terminal of the d.c. voltagev source 19 and the negative terminal of the d.c. bias voltage source 20 are maintained at ground potential. The positive terminal of the d.c. bias source 20 is coupled to the plurality of display elements 15 through variable resistance 21 and a plurality of switches 22. DC voltage source 19 applies a relatively large potential between the anode plate 13 and the inverse brush cathode 11 to provide a source of free electrons in an inverse brush electrical discharge.

It is known that the grazing incidence of ions on a metallic surface greatly increases the secondary electron yield per ion over direct incidence of ions on a metal surface. In the inverse brush cathode, the surface areas of the holes 12 are nearly parallel to the incoming ions. Therefore, a larger number of ions will graze the surface areas in the inverse brush cathode than in a flat cathode. As a result, the inverse brush cathode produces a larger number of electrons per unit area than a flat cathode operating under the same conditions. The resulting inverse brush electrical discharge produces a dim glow over the area enclosed by the inverse brush cathode. Activating specific switches of the plurality of switches 22 applies a relatively low level bias potential from the d.c. bias source 20 to selected segments of the plurality of display elements 15. This potential energizes the selected segments and accelerates the electrons immediately in front of the energized segments thereby causing an increase in collisions between these electrons and atoms of the gas. As a result, a luminosity is observed above each energized segment which is essentially a type of anode glow. This type of glow is very sharply defined and covers a small region just forward of each energized segment. The intensity of the glow produced is much greater than the dim glow due to the inverse brush electrical discharge and sufficient contrast is provided to be visible in room light. In one embodiment of the invention, the contrast was increased by masking of? the area around the anode plate 13.

In a specific embodiment of the present invention the inverse brush cathode I1 and the anode plate 13 were fabricated from aluminum. The display elements 15 were deposits of stainless steel films approximately 1,500 Angstroms thick on a glass substrate which measured 1.0 by 0.6 inches. A fixed format numeric display was used with each number 8 element measuring typically %-inch high by rii-inch wide. The inverse brush cathode 11 was secured to a back plate 17 which comprised a circular piece of Pyrex having an opening 23, centrally positioned with respect to the inverse brush cathode 11. The anode plate 13 was affixed within the opening 23 with an adhesive. A second circular piece of Pyrex was attached to the front of the inverse brush cathode l1 and permitted direct viewing of the display elements 15. The assembled unit was placed on a vacuum station and pumped down to a pressure of approximately 10' torr and then backfilled with neon to a pressure of about 0.3 torr. An inverse brush electrical discharge was maintained by applying a potential of 500 volts d.c. between the cathode 11 and the anode 13. The current through the discharge was maintained at 2.5 milliamps using a 40K ohm ballast resistor in series with the dc. voltage source 19 and the cathode 11. Typical bias voltages between the display elements 15 and ground ranged from 3 to +10 volts do. and the corresponding currents ranged from 0.25 to 1.7 milliamps. The biasing voltage range to go from zero to visible light output in room light was a function of the number of segments energized, the gas pressure in the tube and the voltage between the cathode l1 and the anode 13.

Because the power consumption for this type display is in the milliwatt range and the voltage levels are low, the display is extremely attractive in that the entire display can be energized directly from digital logic circuitry with minimal interfacing electronics. Further, the bias voltage with respect to the anode is low and electrons accelerated through small voltage drops are not likely sputtering agents; therefore, the life of the display is extended.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made within the purview of the appended claims without departing from the true scope and spirit of the invention in its broader aspects.

lclaim:

1. A display device comprising,

vacuum tube means having a transparent viewing surface and partially filled with an inert gas,

perimetrical cathode means disposed behind said viewing surface,

anode plate means centrally disposed with respect to said perimetrical cathode means,

a source of voltage coupled between said cathode means and said anode means for providing a source of free electrons in an electrical discharge within the space bounded by said perimetrical cathode means,

dielectric means disposed within said anode plate means,

display element means having a plurality of segments affixed to said dielectric means and substantially co-planar with said anode means,

bias voltage means, and

switching means connected between said bias voltage means and said display element means for energizing selected segments of said plurality of segments which accelerates free electrons in said electrical discharge which are proximate said energized selected segments thereby producing a sharply defined luminous image over said selected segments.

2. A display device as described in claim 1 in which said display element means include thin metallic strips in a fixed format numeric display.

3. A display device as described in claim 1 in which said perimetrical cathode means includes means for providing an inverse brush discharge.

4. A display device as described in claim 1 in which said bias voltage means is a low level voltage including a variable voltage means for providing continuous dimming to zero light output of said sharply defined luminous image.

5. A display device as described in claim I in which said switching means includes integrated switching circuits.

6. A display device comprising a backing plate, a transparent cover plate and an aluminum perimetrical strip disposed between said backing plate and said cover plate enclosing a vacuum that is partially backfilled with an inert gas such as neon, said aluminum strip having holes drilled into its interior surface to enable said strip to function as an inverse brush cathode, an aluminum plate affixed to said backing plate and centrally disposed with respect to said aluminum strip, a glass substrate mounted within said aluminum plate, display elements disposed on said glass substrate, supply voltage means connected between said aluminum strip, functioning as an inverse brush cathode, and said aluminum plate, serving as an anode connected to ground, said supply voltage means producing a source of free electrons in an inverse brush electrical discharge, variable low level bias voltage means applied between said display elements and said anode, and integrated circuit switching means for connecting said variable bias voltage means to selected segments of said display elements producing a sharply defined luminous image of said selected segments.

Claims (6)

1. A display device comprising, vacuum tube means having a transparent viewing surface and partially filled with an inert gas, perimetrical cathode means disposed behind said viewing surface, anode plate means centrally disposed with respect to said perimetrical cathode means, a source of voltage coupled between said cathode means and said anode means for providing a source of free electrons in an electrical discharge within the space bounded by said perimetrical cathode means, dielectric means disposed within said anode plate means, display element means having a plurality of segments affixed to said dielectric means and substantially co-planar with said anode means, bias voltage means, and switching means connected between said bias voltage means and said display element means for energizing selected segments of said plurality of segments which accelerates free electrons in said electrical discharge which are proximate said energized selected segments thereby producing a sharply defined luminous image over said selected segments.

2. A display device as described in claim 1 in which said display element means include thin metallic strips in a fixed format numeric display.

3. A display device as described in claim 1 in which said perimetrical cathode means includes means for providing an inverse brush discharge.

4. A display device as described in claim 1 in which said bias voltage means is a low level voltage including a variable voltage means for providing continuous dimming to zero light output of said sharply defined luminous image.

5. A display device as described in claim 1 in which said switching means includes integrated switching circuits.

6. A display device comprising a backing plate, a transparent cover plate and an aluminum perimetrical strip disposed between said backing plate and said cover plate enclosing a vacuum that is partially backfilled with an inert gas such as neon, said aluminum strip having holes drilled into its interior surface to enable said strip to function as an inverse brush cathode, an aluminum plate affixed to said backing plate and centrally disposed with respect to said aluminum strip, a glass substrate mounted within said aluminum plate, display elements disposed on said glass substrate, supply voltage means connected between said aluminum strip, functioning as an inverse brush cathode, and said aluminum plate, serving as an anode connected to ground, said supply voltage means producing a source of free electrons in an inverse brush electrical discharge, variable low level bias voltage means applied between said display elements and said anode, and integrated circuit switching means for connecting said variable bias voltage means to selected segments of said display elements producing a sharply defined luminous image of said selected segments.

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