Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J11/00—Gas-filled discharge tubes with alternating current induction of the discharge, e.g. alternating current plasma display panels [AC-PDP]; Gas-filled discharge tubes without any main electrode inside the vessel; Gas-filled discharge tubes with at least one main electrode outside the vessel
  • H01J11/10—AC-PDPs with at least one main electrode being out of contact with the plasma
  • H01J11/12—AC-PDPs with at least one main electrode being out of contact with the plasma with main electrodes provided on both sides of the discharge space
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2211/00—Plasma display panels with alternate current induction of the discharge, e.g. AC-PDPs
  • H01J2211/20—Constructional details
  • H01J2211/22—Electrodes
  • H01J2211/225—Material of electrodes

Definitions

• Gaseous discharge devices of the kind specified are known from U.S. Patents No. 3,775,764; 3,781,600; and 4,027,197. These known gaseous discharge devices utilize the transfer of trapped charges resulting from the discharge.
• an ionizable gas is contained within an enclosure which has a plurality of dielectric-coated transfer electrodes arranged parallel but offset from one another on opposite side walls thereof.
• the transfer electrodes are ⁇ apacitively coupled to the ionizable gas by their dielectric coating.
• a suitable thickness of this dielectric coating includes the range 13-25 microns.
• information is entered into the device via an input electrode which does not have the capacitive-coupling dielectric coating and is, thus, direct-coupled to the ionizable gas. That is, the device is serially addressed by applying a voltage of predetermined magnitude between the direct-coupled input electrode and the first or nearest opposite dielectric-covered transfer electrodes. These two electrodes form the first cell within the device. By the proper application of a potential on the electrodes, the gas in the cells, formed by successive pairs of nearest adjacent, opposite electrodes, is discharged and electric charge trapped on the coated walls of the electrode is used to transfer this gaseous discharge throughout the length of the device.
• information is erased via an erase electrode, which, like the input electrode, does not have the capacitive dielectric coating previously mentioned, and is, thus, directly-coupled to the ionizable gas.
• the interior walls of the tube adjacent the gas may be coated with a layer of magnesium oxide in order to improve the performance of the tube.
• All the electrodes including dielectric-coated transfer electrodes and the direct-coupled input and erase electrodes may be coated with the magnesium oxide layer for obtaining the characteristics of low operating voltage and stable life of the device, as shown in Fig. 5.
• the magnesium oxide layer is made sufficiently thin in comparison with the dielectric coating of the transfer electrodes to preserve the direct coupled characteristics of the input and erase electrodes.
• the magnesium oxide layer achieves a low operating voltage since magnesium oxide is an excellent secondary electron emitter.
• the magnesium oxide layer provides stable life since magnesium oxide is a refractory material which is immune to damage by ion bombardment and has a high melting point.
• an electrode for a gaseous discharge device of the kind including an envelope defining a channel containing an ionizable gas, characterized by a conductive base, a metal oxide layer formed on said base, and a dielectric layer formed on said metal oxide layer.
• the metal oxide layer has a sheet resistivity of less than 5.5 x 10 10 ohms per square.
• Fig. 1 is a schematic cross-sectional view of a conventional direct-coupled input electrode in a plasma charge transfer display device
• Fig. 2 is a schematic cross-sectional view of a conventional direct-coupled erase electrode in a plasma charge transfer display device
• Fig. 3 is a schematic cross-sectional view of an input electrode incorporating the principles of the present invention.
• Terminals 1, 2, 3, 4 can be connected through a suitable switch (not shown) to a suitable voltage source (not shown) for sequentially applying voltage pulses to each of the transfer electrodes.
• the input electrode is made of the same conductive material as the transfer electrodes and is directly coupled to the encapsulated ionizable gas.
• metal or carbon may be used for forming the conductive base of the input and transfer electrodes
• one conventional material that has been found to work very well is a paste consisting of 50-95% by weight silver and 50-5% by weight glass frit. This material, when fired, provides a conductive metallic electrode due to the silver particles dispersed in the glass matrix with the glass serving to adhere the silver to the substrate.
• the input and erase electrodes shown respectively in Figs. 1 and 2 were bare except for the thin magnesium oxide coating 12 applied over them. In a preferred embodiment of the present invention, shown in Figs.
• a coating 14 is applied between the conductive base 13 of the input electrode I and the magnesium oxide dielectric layer 12 and coating 17 is applied between the conductive base 16 of the erase electrode E and magnesium oxide layer 12.
• This coating 14 (and 17) is a slightly conductive metal oxide having a high electrical resistivity.
• a preferred example of a suitable material for coatings 14 and 17 is a ruthenium oxide-based resistor paste.
• Formula No. 600-105 sold by Thick Film Systems Inc., Santa Barbara, California. This paste, having an unfired viscosity at 25°C of 750 ⁇ 150 poise, when fired at a temperature of about 600°C is believed to become essentially glass but nevertheless has a finite small conductivity due to the ruthenium oxide material dispersed within the glass.
• the ruthenium oxide conductive coating eliminates contamination of the magnesium oxide by the input electrode.
• a suitable pre-fired thickness of the ruthenium oxide-based material 14, 17 is in the range of 10-30 microns. While the preferred thickness of the coating is believed not limited to the above mentioned range, D.C. operation was preserved and the stability and other operational characteristics of the display d-evice were found to be the same when ruthenium oxide coating of the above thickness range was used.
• the above-described ruthenium oxide coating is rated as having a sheet resistivity of approximately 1 megohm per square when fired at a temperature of 600°C. Although no precise values of resistivity are available, it is estimated that the ruthenium oxide coating resistivity resulting from the exemplary 575°C firing temperature is about 10 megohms per square. Both values are well below the established upper limit of about 5.5 x 10 10 ohms per square.
• resistor pastes made from oxides of thallium, palladium, iridium, indium, tungsten, tan tallum, rhodium, copper, bismuth, and lead.
• the erase electrode E (Fig. 4) at the other end of the display panel is used to clear the display.
• the erase electrode in the present embodiment is directly coupled to the encapsulated gas by means of the metallic oxide coating 17 applied between the bare erase electrode conductive base 16 and the magnesium oxide film 12.
• the above discussion of the metallic oxide coating for the input electrode applies to the erase electrode as well and the preferred metal oxide is also the ruthenium oxide-based material.
• all of the electrodes 1 1 , 2 1 , 3 1 , 4 1 , etc. including the input electrode I (conductive base 13 thereof) and the erase electrode E (conductive base 16 thereof) can be formed on the substrate walls 10-10, by using a silk screening technique to pattern the electrodes and then firing the "green" electrode material.
• Another conventional method of forming the electrodes is by a photoresist technique in which the conductive pattern is achieved by etching away a conductive coating applied on the inner surface of each of the substrate walls 10-10.
• all of the electrodes except the input and erase electrodes are covered with the dielectric layer 11.
• the input and erase electrodes are then separately covered with the metallic oxide layer which is fired preferably at 575°C to form layers 14, 17 for the input and erase electrodes.
• the dielectric layer 12 is formed to ultimately form an enclosure to contain the ionizable medium.
• the two substrates 10-10 are then aligned and joined to the substrate 7 by heat treatment.
• An exhaust port in one of the substrates is utilized to evacuate the cavities, i.e., channels 8, and thereafter an ionizable gas is introduced therein, and the device sealed.
• a keep-alive cell is formed by the pair of keep-alive electrodes 6-6 which are capa citively coupled to the gas.
• the electrodes 6-6 are connected to a source 18 of alternating pulse voltage of suitable magnitude to ionize the gas within the keep alive cell for facilitating "firing" or discharge of the first cell formed by the input electrode I and the first electrode 1 1 .
• the device is serially addressed by applying suitable voltage pulses to the input electrode and/or the electrode 1 1 .
• a voltage V s is applied between the first and second transfer electrodes, 1 1 and 2 1 respectively.
• Vwc When V s of suitable polarity is applied to the first and second transfer electrodes, Vwc adds algebraically such that the total voltage between the two is greater than the firing voltage V f and a gaseous plasma discharge occurs. It should be noted that if no discharge had occurred in the first cell I-1 1 , no trapped charge would be present on the electrode 1 1 . Then, when Vs is applied between the first and second electrodes, no gaseous plasma discharge would occur in the cell 1 1 -2 1 . By sequentially applying V s to successive cells and. thus utilizing the trapped charge on the electrode wall of the previously-discharged cell, this charge and the trapped charge initiated by the input pulse can be transferred to any cell along the length of the plasma charge transfer device.
• the slightly conductive metal oxide coating 14 on the input electrode enables direct electrical connection .of the input electrode I to the encapsulated gas without the previous contamination problems.
• the metal oxide coating functions both as a highly resistive protective cover, and also. in a limited sense, as a conductor. That is, when a potential suitable for inputting charge is applied to the input electrode such that V i > V f and therefore a plasma discharge is initiated in cell I-1 1 , the high resistivity coating 14 dissipates any undesirable charge buildup on the input electrode in time for the next voltage pulse to be. applied to the input.
• the coating 14 has sufficient conductivity to give rise to only a slight current through the coating and thereby reduce the possibility of breakdown of the overlying protective magnesium oxide coating on the input electrode.
• the conductive coating 17 on the erase electrode enables direct electrical connection of the erase electrode E to the encapsulated gas, like the input electrode I, without the previous contamination problems.
• wall charge is formed on the wall of the electrode 4 .
• the wall charge is transferred to the erase electrode which, being maintained at the relatively low or ground voltage, extinguishes the discharge.
• the high resistivity coating 17 dissipates undesirable charge build up on the erase electrode and protects the overlying magnesium oxide coating in the same manner as explained in connection with the input electrode coating 14.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Gas-Filled Discharge Tubes (AREA)
• Liquid Crystal (AREA)

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• 1981
  • 1981-06-29 EP EP19810901995 patent/EP0056040A4/en not_active Ceased
  • 1981-06-29 JP JP56502522A patent/JPS57501005A/ja active Pending
  • 1981-06-29 WO PCT/US1981/000894 patent/WO1982000220A1/en not_active Application Discontinuation

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