US 3875442 A
A display panel has a gas-tight envelope, two planar main electrodes which are arranged in the envelope parallel with each other, one of which is a cold cathode in the form of a metal plate and the other is an anode in the form of a metal screen, and a cathodeluminescent panel consisting of a transparent electrode coated with a phosphor layer, which is positioned behind the anode.
Description (OCR text may contain errors)
United States Patent 1191 Wasa et a]. Apr. 1, 1975 DISPLAY PANEL  Inventors: Kiyotaka Wasa, Mara; Fumio References Cited Hosomi; Shigeru Hayakawa, both of UNITED STATES PATENTS Osaka Japan 3,622,828 11 /1971 2111" 3I3/l08 B x Agsignee; Matsushita Electric Indusrial Co. 3,77l.008 ll/l973 Chen et al. 3l3/2l7 X Ltd., Kadoma, Osaka, Japan Primary E.\'aminerRudolph V. Rolinec  Filed May 1973 Assistant Emminer-Lawrence J. Dahl I2 I] Appl. No.: 363,870 Attorney, Agent, or Firm-Wenderoth, Lind & Ponack I 30] Foreign Application Priority Data  ABSTRACT June 2. 1972 Japan 47-55275 A di l nel has a gas-tight envelope, two planar Junc I973 Japan 47-6-3400 main electrodes which are arranged in the envelope June I973 Japan a 47-63401 parallel with each other. one of which is a cold cath- Dcc. 20. 1972 Japan 47-l2870l de i the form of a metal plate and the other is an anode in the form of a metal screen, and a cathodelul l Cl 3l3/l93, 313/188. 3| minescent panel consisting of a transparent electrode 315/169 TV, 340/3 coated with a phosphor layer, which is positioned be- [51 Int. Cl H0lj [7/00, H05b 37/00 hi d h d (58] Field of Search 3|5/l69 R, I69 TV;
3l3/l88. 217, I93; 340/336 i t i 5 Claims, 11 Drawing Figures PATMEDAFR r s-*5 3, 875.442
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DISPLAY PANEL BACKGROUND OF THE INVENTION This invention relates to a display panel. and more particularly to a large flat TV panel which is a lowvoltage cathode-luminescent matrix display system in a gas plasma.
Nowadays. for a display system. it is desired to have a large size flat panel television display having a high resolving capability. Although some small size flat panel display devices have been developed using a LED (light emitting diode) matrix or an EL (electroluminescent) matrix. it is very difficult to provide a large size flat panel display device with these conventional display devices. One of the reasons is the large power dissipation at the matrix panel thereof.
SUMMARY OF THE INVENTION Therefore. an object of the present invention is to provide a novel cathodeluminescent flat display panel which has a small power dissipation.
Another object of the present invention is to provide a novel cathodelumincscent flat panel for numerical display which has a small power dissipation.
A further object ol'the invention is to provide a novel cathodeluminescent matrix system for a large size flat TY panel which has a small power dissipation.
The objects are achie\ ed by providing a display panel comprising a gastight envelope. two flat planar main electrodes arranged within said gas-tight envelope parallel with each other. one of said two planar electrodes being a cold cathode and the other of said two planar electrodes being an anode.
BRIEF DESCRIPTION OF THE DRAWINGS These and other objects. features and advantages of the invention will become more apparent upon a reading of the following detailed description and drawings. in which:
FIG. I is a cross-sectional view. with the parts somewhat enlarged for clarity of a flat display panel in accordance with the present invention:
FIG. 2 is a diagrammatic view for showing a modified display panel for numerical display in accordance with the present invention:
FIG. 3 is a cross-sectional view ofa flat display panel. for one picture element. in accordance with the present invention.
FIG. 4 is a graph illustrating operating characteristics of a tlat display panel in accordance with the present invention:
FIG. 5 is a diagrammatic view for showing a flat display panel in accordance with the present invention; and
FIGS. 6 to II are diagrammatic views for showing various types ol'elcctrodes for a Ilat display panel in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I. a display panel according to the present invention comprises a transparent gas-tight envelopc designated by a reference numeral 1, two planar main electrodes 2 and 3 which are arranged within said gas-tight en velopc 1 parallel with each other and a cathodeluminescent panel 4. One ofthe two main electrodes. the electrode 2. is a cold cathode in the form of a metal plate. and the other electrode 3 is an anode in the form of a metal screen. The cathodeluminescent panel 4 consists of a transparent glass plate 7. a transparent electrode 5 formed on said transparent glass plate 7, and a phosphor layer 6 coated on said transparent electrode 5. The phosphor layer 6 is positioned be hind the anode 3. as shown in FIG. 1.
The phosphor layer 6 is made of. for example. zinc oxide which can be excited with low-energy electrons. Operable materials for the main electrodes 2 and 3 include nickel. molybdenum. tungsten. titanium. aluminum. etc. Operable materials for the transparent electrode 5 includes tin oxide. titanium oxide. indium oxide. etc. The gas-tight envelope 1 contains ionizable medium. such as hydrogen. helium. krypton. neon. argon. nitrogen or mixture thereof. at a pressure ranging from l0 to II) torrs.
In operation, a cold-cathode glow discharge is maintained between the main electrodes 2 and 3 by a voltage Vd provided from a source 8. Typical values of the voltage Vd range from 200 to 300 volts. The phosphor layer 6 is immersed in a gas plasma which comes through the openings in the anode screen 3. When no bias circuit 9 is provided between the anode 3 and the transparent electrode 5, the phosphor layer 6 is surrounded by an ionic sheath and it is negatively biased below the potential of surrounding plasma. Because of this negative bias. it repels the electrons in the gas plasma and prevents them from reaching the surface of the phosphor layer 6. Therefore. the phosphor layer 6 is only slightly excited.
The inventors have found that by providing a bias circuit 9. comprising an external battery having a voltage E., of It) to 20 volts. which is connected between the anode 3 and the transparent electrode 5, as shown in FIG. I. so as to bias the transparent electrode 5 positively with respect to the surrounding plasma. an electron current Id of about ImA/cm which is 50 to 70 percent of the discharge current between the main electrodes 2 and 3. flows into the transparent electrode 5 through the phosphor layer 6. and accordingly the phosphor layer 6 is excited and luminous light is emitted. When the phosphor layer 6 is thin enough to pass the luminescent light. green cathode luminescent light is observed with a brightness of about 50 IL from the direction 11 at the back of the phosphor layer 6. The brightness can be easily controlled by controlling the electron current by making the voltage Ed of the bias circuit 9 adjustable. Since the electrons in the gas plasma diffuse uniformly from the discharge region. the electron current density at the surface of the phosphor layer 6 is essentially uniform over the whole layer. This makes it possible to provide a large cathodeluminescent flat panel or flat panel light of a uniform brightness.
The display panel of the present invention can be made to be a numerical display panel by modifying the transparent electrode 5. Referring to FIG. 2, a numerical display panel of the invention comprises a modified transparent electrode 12 of the luminescent panel 4. The transparent electrode 12 consists of seven segments insulated from each other for each numeral. In operation. a cold-cathode glow discharge is maintained between the main electrodes. similarly to FIG. 1, and a positive bias of ID to 20 volts is supplied to appropriate segments of the transparent electrode so as to display a pattern representing a number. Further. an al- 3 phabetical display panel or a graphic display panel can also be easily made by modifying the pattern of the segments of the transparent electrode.
Moreover. a flat TV panel for a cathodeluminescent x-y matrix display system can be made by modifying the anode 3 and the transparent electrode 5 of HG. l. Referring to FIG. 3. one picture element of the .r-y matrix display system according to the invention com prises a plane cold cathode 2, three parallel anode wires 13 insulated from each other. and a transparent strip-electrode 14x. The anode wires 13 consist of a central wire 13y and two end wires. The strip-electrode l4.\' and the anode wires 13 are perpendicular to each other. The diameter of the anode wires 13 is. for example. 0.3mm. The anode wires 13 are spaced. for exampie. from the cathode 2 aat a distance of ltlmm and from the strip-electrode 141 at a distance of lmm. In operation, a cold-cathode glow discharge is maintained between the cathode 2 and the central wire 13y. When the strip-electrode 141' is positively biased by the external bias circuit 9. the phosphor layer 6 is excited and so green light is observed from the direction 1] at the back of the glass plate along the strip-electrode.
it has been found by the inventors that when the two end wires ofthe three parallel anode wires 13 are negatively biased relative to the central anode wire l3 by a voltage Vp from an external battery 15, as shown in FIG. 3. the spread of the electrons away from the control anode 13y is suppressed and they are limited to a discharge region near the central anode 13y. and a bright green color spot is formed at the crossing point 16 between the central anode 13v and the stripelectrode NA. This color spot can be used as a picture element. and its diameter is. for example. 0.5mm. The size of the color spot decreases with the increase of the negative bias voltage Vp. as indicated by the curve 17 in FIG. 4. it is pret'erable that the negative bias voltage Vp he kept in a range of to 5[) volts. When a pulse of voltage is applied between the central anode wire 13y and the strip-electrode 1-'l.\'. the brightness of the color spot (picture element) is proportional to the pulse amplitude within a certain voltage limit and pro portional to the pulse width. During the pulse. the time response for the luminescence is less than 5p. sec.
Such a picture element can be usefully employed as a flat TV panel ol'a cathodeluminescent matrix display system. FlG. 5 shows a flat TV panel system according to the invention comprising a plurality of stripelectrodes 14 which are insulated with each other and a plurality of parallel metal anode wires 13 which are fixed to an insulating frame 18 and which are insulated from each other. The strip-electrodes l4 and the anode wires 13 cross each other so as to form a cathodeluminescent .r-y matrix system having picture elements at a crosspoints between the strip-electrodes l4.\ and the anode wires 13. In operation. the anode wires and the strip-electrodes correspond to the vertical scanning electrode v-direction) and the horizontal scanning electrode (.r-direction). respectively. All of the anode wires are biased positively with respect to the cathode plate 2. which is slightly below the sparking voltage between the anode wires and the cathode plate 2. For example. for a sparking voltage ol 240 volts between the anode wires and the cathode plate. the anode wires are biased at 220 volts relative to the cathode plate. below the sparking voltage by 20 volts.
in order to scan the .r-y matrix system by using the so-called one line at a time method. a positive vertical scanning pulse is superposed by turns on the anode wires 13 and the anode wires are scanned during the horizontal scanning period. The amplitude of the vertical scanning pulse is. for example. 40 volts. Then. a glow discharge is generated near the anodes 13. When a horizontal scanning pulse of a positive voltage. for example lO to 20 volts. the amplitude or the pulse width of which is modulated by a video signal, is applied by turns to the strip-electrodes l4 synchronously with the vertical scanning pulse signal. numerous green light spots corresponding to the video signal appear on the cathodeluminescent panel. It will be understood that a flat mono-color TV panel can be easily made by using the flat panel described above.
in the flat panel according to the invention. because the scanning pulse voltage is very low. 10 to 40 volts as described hereinbefore. there is an advantage that solid-state circuits can be used for the scanning circuits. Moreover. because the anodes not being vertically scanned are biased negatively with respect to the anode being vertically scanned. interaction between the vertical lines can be reduced. Also, because the strip electrodes which are not being horizontally scanned are biased negatively with respect to the strip-electrode being horizontally scanned due to the presence of the ionic sheath as described hereinbefore. interaction between the horizontal lines can be reduced. Since the power conversion efficiency of low-voltage excited 2110 is l percent or more. the flat TV panel of the invention can be made in almost any size and yet will have a small power dissipation. The following table shows the power dissipation for various sizes of the tint panel according to the invention.
Power dissipation of cathodeliminescent flat potter conscrsion elliclcnc l' From the Table, it will be understood that the power dissipation of the flat panel of the invention is less than 200W even for a inch TV. Such a low voltage operation and small power dissipation are very advantageous for consumer electronics.
it is apparent that various modifications can be made in the construction ofthe anode electrode. the cathode electrode and the cathodeluminescent panel without departing from the spirit and scope of the invention.
FIG. 6 shows examples of various forms of the anode screen 3 shown in FIG. 1. i.e. an anode screen having a strip-like structure 19. a holed structure 2], and net structure 220.
FIGS. 7 to It) show various examples of modified form of the main electrodes shown in H6. 1. In FIG. 7, a hollow cathode is used instead of the planar cathode 2 in FIG. I so as to increase the ionization efficiency between the main electrodes and also to prevent scattering and loss of the electrons in the gas discharge across the interspace between the main electrodes. FIG. 8 shows another construction of the main electrodes in which the anode and the cathode consist of a plurality of parallel metal wires positioned in the same plane so as to reduce the thickness of the display panel. FIGS. 9 and 10 show modified constructions of the main electrodes shown in FIG. 8, which are modified so as to increase the ionization efficiency between the main electrodes and also to prevent scattering and loss of the electrons in the gas discharge across the interspace between the main electrodes. In FIG. 9, the modified main electrodes comprises cathode plate 2 having a plurality of parallel grooves. and a plurality of anode wires. the anode wires being embedded in the grooves. ln FIG. Ill. additional grid electrode 23 is positioned at the back of the modified main electrodes shown in FIG. 8. Said additional grid electrode is negatively biased by an external battery Vg so as to prevent scattering and loss of the electrons behind the main electrodes.
Referring to FIG. II. there is illustrated a modified cathodeluminescent panel 24 for a color flat TV panel. comprising transparent strip-electrodes 25, 26 and 27 coated with three kinds of phosphor layers. respectively and black color layer 28 having insulating properties between these strip-electrodes. These phosphor layers can emit light ofthe three primary colors. for instance. red. blue and green light. In operation. the modified cathodeluminescent panel 24 is used instead of the cathodeluminescent panel shown in FIG. 5. The black color layer 28 can block the most of the light from the discharge between the main electrodes. One of the anode wires and the three strip-electrodes 25., 16 and 27 an form a color picture element when the current density of the three strip-electrodes is modulated individually by color video signals. This makes it possible to provide a color flat panel display.
It is thought that the invention will be understood from the above description. It is believed that the novel display panel. according to the present invention. can provide not only a numerical or graphic display but also a large size flat panel having high resolving power with low-operating voltage and small power dissipations.
What is claimed is:
l. A display panel comprising a transparent gas-tight envelope. an ionizable medium in said envelope. two planar main electrodes within said gas-tight envelope lying in different planes and parallel with each other and substantially coextensive with each other. one of said two planar electrodes being a cold cathode and the other ot'said two planar electrodes being an anode. said anode consisting of a metal screen. said electrodes being for maintaining a cold cathode glow discharge therebetween when a voltage is applied thereacross.
and a cathodeluminescent panel positioned on the other side of said anode from said cathode, said cathode-luminescent panel consisting of a transparent glass plate. a transparent electrode means on said transparent glass plate. and a phosphor layer coated on said transparent electrode means. said phosphor layer being on the side of said panel toward said anode.
2. A display panel as claimed in claim 1, in which said transparent electrode means comprises at least one set consisting of seven segments insulated from each other and arranged in a pattern so as to display a numeral when certain segments are luminescent.
3. A display panel as claimed in claim I, in which said transparent electrode means consists of a plurality of parallel strip-electrodes insulated from each other and said metal screen consists of a plurality of parallel anode wires insulated from each other. said stripelectrodes and said anode wires crossing with each other so as to form a cathodeluminescent .v-y matrix display system having a plurality of picture elements. each picture element of said cathodeluminescent .r-y matrix system consisting of one of said plurality of strip-electrodes and three of said plurality of anode wires. one central anode wire and two end anode wires. and bias means coupled to said anode wires biasing said two end anode wires negatively relative to said central anode wire.
4. A display panel as claimed in claim I. in which said transparent electrode means consists of a plurality of parallel strip-electrodes insulated from each other and said metal screen consists of a plurality of parallel metal wires insulated from each other. said stripelectrodes and said anode wires crossing each other so as to form a cathodeluminescent .r-y matrix display system. said anode wires and said strip-electrodes constituting the vertical scanning electrodes and the horizontal scanning electrodes of said cathodeluminescent .r-y matrix display system. respectively. bias means coupled to said anode wires for biasing said anode wires positively relative to said cathode with a voltage slightly below the sparking voltage between said anode wires and said cathode. whereby a positive vertical scanning pulse can be superposed by turns on said anode wires. and a positive horizontal scanning pulse which is modulated according to the amplitude or pulse width of a video signal can be applied by turns to said stripelectrodes synchronously to the vertical scanning pulse signal for causing said panel to display an image corresponding to said video signal.
5. A display panel as claimed in claim 4, in which said plurality of strip-electrodes are in groups of three. and the respective strip-electrodes in each group are coated with three kinds of phosphor layers which emit light of the three primary colors. respectively. so as to display a color video image.
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