EP0741402B1 - Electric discharge tubes or discharge lamps, flat panel display, low-temperature cathode and method for their fabrication - Google Patents

Description

The invention relates to an electric discharge tube or discharge lamp one or more low temperature cathodes, a flat screen with one or more low temperature cathodes, one low temperature cathode and one Process for the production of the low temperature cathode.

Conventional screens contain an electric discharge tube, which after the Principle of the Braun tube works. This involves electrons from a cathode accelerated, distracted and finally hit a curved fluorescent screen. This design requires a large depth or a strong curvature of the Screen, because otherwise due to the different distances from the electron source to the front of the screen only the representation of the characters in the Center would appear sharp, but distorted at the edge.

Flat screens have been on the market for a number of years. In the Flat panel display design competing several principles. The present The invention relates, inter alia, to flat screens with active systems where the screen does not work with the light of the surroundings like the liquid crystal screens, but shines itself. This includes the plasma screen and the flat tube.

Flat screens were developed for the three market segments of office automation, audio / video technology as well as navigation and entertainment.
In the office area, the mobile applications are particularly noteworthy, starting with notebook computers, personal digital assistants, fax machines and mobile phones. In the audio and video area, the flat screens should not only be used in camcorders, but also in television sets and monitors.
The third area includes flat screens as monitors for navigation systems in cars and airplanes, but also the displays of game consoles.

The large space requirement of the Braun tube is a disadvantage. He will causes all electrons to be provided from a single cathode and can be brought to the desired position of the fluorescent screen via deflection units and are responsible for all pixels. The cathodes of this conventional one Cathode ray tubes are hot cathodes ("thermionic cathodes"). Electron beam generation is based on the glow emission. The conventional heatable Cathode is e.g. from a nickel tube, on the front of which a special one easily electron-emitting oxide layer, e.g. made of barium oxide. The heating wire embedded in the nickel tube insulates the cathode about 1200 Kelvin (900 ° C) so that electrons from the oxide layer into the vacuum be "steamed" out of the tube.

The flat screens, on the other hand, have the electrons in several wire cathodes, Ribbon cathodes or generated in flat field emitters. Every cathode is therefore only responsible for a few pixels.

The production of appropriate cathodes is for all types of flat screens a key technology. Considerable efforts have already been made to cathodes adapted to the flat screen technology and new cathode materials to develop. The extended wire cathodes, flat ribbon cathodes or Flat cathodes, which are used in flat screens, can clearly lower emission than the conventional point cathode. After this It is a disadvantage of the conventional hot cathode that the high cathode temperature must be kept constant and the heating additional energy consumed, one of these developments concerns the production of cold cathodes.

Previous developments in the field of cold cathodes are e.g. Tips field emitter (Microtip emitter) or semiconductor emitter (AC cathodes = avalanche Cold Cathodes). see e.g. WO-A-9 423 571 which is a microcrystalline Describes amorphous diamond emission material. A disadvantage of the tip field emitter cathodes is burnout individual peaks and the high current noise of the individual peaks. AC cathode have the disadvantage that their emission is extremely localized and high Adjustment accuracy in cathode positioning required.

It is therefore the object of the present invention to provide an electrical discharge tube or discharge lamp with an improved cathode put. Another aspect of the invention relates to a flat screen with a improved cathode and an improved cathode.

According to the invention, the object is achieved by an electrical discharge tube or discharge lamp with one or more low-temperature cathodes, the one Bracket, possibly with heating or cooling, one on the bracket applied conductive sub-layer, possibly a substrate with dispensing material, and a top layer with a nanostructure made of ultrafine particles, the top layer having a surface layer made of an emission material has several components formed emitter complex.

Such discharge tubes or discharge lamps are characterized by high Reliability and a long service life under normal loads. The emission is stable, this favors a constant image quality throughout Lifetime of the discharge lamp or discharge tube. The invention Discharge tubes or discharge lamps have short switching times and offer that Advantage that their construction is simplified and their energy consumption is low.

A preferred embodiment of the discharge tubes or Discharge lamps are characterized in that they have a grid control electrode includes.

With such a grid control electrode, it is possible to emit one of several low-temperature cathodes according to the invention or individual surface segments a low-temperature cathode by changing the field strength Taxes.

A flat screen according to the invention contains one or more low temperature cathodes, a bracket, possibly with heating or cooling, a conductive sub-layer applied to the holder, optionally a Substrate with dispensing material, and a top layer with a nanostructure ultrafine particles, the top layer being a surface layer made of a Has emitter complex formed with multiple components, include.

A flat screen according to the invention is easy to manufacture because of the manufacturing no submicron lithography is required. It has low energy consumption, it is brighter and can operate within wide temperature ranges of the ambient temperature operated from -30 ° C to 100 ° C. It has a very good resolution and is suitable for black and white screens and color screens.

A low-temperature cathode according to the invention is composed of one Bracket, possibly with heating or cooling, one on the bracket applied conductive sub-layer, possibly a substrate with dispensing material, and a top layer with a nanostructure made of ultrafine particles, wherein the cover layer is a surface layer made of an emission material with multiple components formed emitter complex.

• niedrige Austrittsarbeit auf der makroskopischen Oberfläche
• hohe Dichte an "Kristallitspitzen" aus ultrafeinen Partikeln
• niedriger Krümmungsradius der emittierenden Kristallitspitzen, dies unterbindet ein Ausbrennen der Spitzen
• hohe elektrische Leitfähigkeit und gute Strombelastbarkeit.
• unempfindlich gegen Kontamination
• große Uniformität
• hohe Emissionsreserve bei Ionenbombardement.

Such low-temperature cathodes offer the following advantages:

• low work function on the macroscopic surface
• high density of "crystallite tips" made of ultrafine particles
• low radius of curvature of the emitting crystallite tips, this prevents the tips from burning out
• high electrical conductivity and good current carrying capacity.
• insensitive to contamination
• great uniformity
• high emission reserve during ion bombardment.

According to a preferred embodiment of the low-temperature cathode after the Invention, it is characterized in that it is for an operating temperature is prepared between 20 ° C and 500 ° C.

The low-temperature cathode according to the invention can be used on the one hand as a real cold cathode and is particularly well suited as a cold controllable electron emitter for flat displays. On the other hand, with a moderate heating to an operating temperature of 200 ° C to 300 ° C, the threshold field strength can be reduced to almost zero. At 500 ° C, that is 250 ° C below the operating temperature of oxide wire cathodes, the current density of 0.1 A / cm ² required for line cathodes is already achieved.

It is preferred that the emission material comprises a first component, the metals, especially refractory metals, and their alloys, contains a second component, the scandium, yttrium, lathan, the lanthanides, or actinides, and / or their compounds, in particular their oxides, contains and / or a third Component that contains alkaline earths and / or their compounds.

An emitter complex is formed from these components during the formation a particularly low work function.

According to a particularly preferred embodiment, the emission material comprises as the first component tungsten, as the second component oxidic compounds of the Scandiums and as third components oxidic compounds of barium.

With this composition of the emission material were the lowest values for work done.

It is preferred that the components of the emission material individually or together in the lower layer and / or the substrate and / or the cover layer are included. In this way, a reservoir of emission material be provided to form the emitter complex.

It is preferred that the emitter complex formed has a work function <2.8 eV Has.

A low-temperature cathode, which is characterized by this, has particular advantages is that the ultrafine particles have a grain size of 1 to 100 nm. They are particularly well suited as field emitters because they have surface structures and Surface modulations from particles in the diameter range from 1 to 100 nm have, i.e. relatively small radii of curvature in dense particle and tip distribution have on the macroscopic surface.

It is preferred that the nanostructure of the cover layer is nanocrystalline or nanoamorphic and is optionally nanoporous and the structure size 1 to 1000 nm is.

The invention also has the task of a manufacturing method for the invention To provide low-temperature cathodes.

According to the invention, this object is achieved by a method in which first step a pre-body with a holder, with one on the holder applied conductive sub-layer, optionally with a substrate Dispensing material and with a top layer with a nanostructure made of ultra-fine Particles, and the components of the emission material individually or together in the lower layer and / or the substrate and / or the cover layer contains, is produced and in a second step the emitter complex as Surface layer is formed on the top layer.

This method creates very uniformly emitting low-temperature cathodes get their emission properties, especially the cold emission scatters little.

It is preferred that the formation at a temperature ≥ 800 ° C in an ultra-high vacuum or high vacuum with a residual gas pressure and applying one electrical field.

It is particularly preferred that the residual gas pressure is 10 10 ^-4 mbar and the residual gas contains noble gases, nitrogen, hydrogen and / or oxygen, each with a partial pressure of 10 10 ^-5 mbar.

A method is further preferred in which the formation by a Sintering treatment at a temperature> 500 ° C and under vacuum or Gas atmosphere containing noble gases, nitrogen, hydrogen and / or oxygen, he follows.

It is preferred that the top layer be made with an ultrafine nanostructure Particles is produced by laser ablation.

It is particularly preferred that laser ablation deposition be performed under vacuum he follows. This results in a particularly thin and even top layer.

In the following the invention is further explained with reference to a figure and there will be Examples given.

Fig. 1 shows the current-voltage characteristics of a low-temperature cathode according to the invention at 300 ° C, 200 ° C and room temperature.

An electric discharge tube or discharge lamp consists of four functional groups, electron beam generation, beam focusing, beam deflection and the fluorescent screen.

The electron gun of the discharge tubes according to the invention or discharge lamps contains an arrangement of one or more low-temperature cathodes. For example, the electron gun system a point cathode or a system of one or more wire cathodes, flat ribbon cathodes or be flat cathodes. Wire cathodes, ribbon cathodes and Area cathodes do not have to be activated over their entire area, they can the active top layer is only contained in individual surface segments.

The electron gun can also be a grid control electrode included, each of one of several of the low-temperature cathodes of the invention or one or more surface segments of a low-temperature cathode can be controlled. About this grid control electrode an electric field strength E with values of 5 V / µ ≤ E ≤ 15 V / µm is applied and the Emission of these segments or single cathodes by changing the field strength controlled.

A flat panel display according to the invention can be a modified cathode ray tube, a flat tube, or its variation, the field emitter display. In particular, the invention relates to a field emitter display. Field emitter displays are a modification of the cathode ray tubes. Both use one high energy electron beam to activate light emitting phosphors and to create an image. With the conventional cathode ray tube, a single one touches Electron beam from each of the three fairly large electron guns - one each for each color - one after the other from the many picture elements (pixels). On the other hand provides the electron generation system of a field emitter display with countless small ones Electron sources are available, one for each pixel.

The field emitter display according to the invention can thus have the following structure to have: Two glass plates, an anode plate and a cathode plate are by spacers Cut. The cathode plate has metallic conductive strips with a thin layer of cold cathode material according to the invention are covered. The Anode plate has similar stripes that have a transparent conductor, e.g. out doped tin oxide, as a base layer and as a top layer with a layer a phosphor. Anode plate and cathode plate are with spacers interconnected, with the cathode and anode strips at 90 ° to each other turned and facing each other. The two plates become vacuum tight connected. On the outside an electronic circuit is attached, which allows that each strip can be controlled independently. The principle of this embodiment is that of a matrix controlled diode.

According to another embodiment, the flat screen according to the invention can a flat tube containing a series of linear wire cathodes which a beam of rays is generated, each individual beam a small rectangular area of the screen is assigned.

The low temperature cathodes according to the invention can be of their type Be point cathodes or wire cathodes. Particularly advantageous properties is achieved, however, if the cathodes according to the invention are used as surface cathodes are trained. To do this, they can be applied to a flat ribbon substrate, or on a plate through which emitting cathode strips or segments insulating strips are separated. Also a type with a large "emitter lawn" is possible.

The holder can be a silicon wafer or a glass plate, e.g. for a Field emitter display. The holder can also be a wire, e.g. for flat Screen tubes with multiple cathode wires. For punctiform cathodes the holder also from the well-known metal tubes made of nickel, molybdenum or similar. exist, which is equipped with a heating coil that allows the cathode Operating temperatures up to 500 ° C, especially at 200 ° C to 300 ° C.

The conductive underlayer is usually made of a metal, e.g. Tungsten. It can also consist of several layers of metal, e.g. from a layer of tungsten and a tungsten / rhenium layer.

The substrate in the sense of the invention can be a porous tungsten layer, as is known from conventional I-cathodes. Such porous tungsten layers can contain rhenium, iridium, osmium, ruthenium, tantalum, molybdenum or scandium oxide in the laminate. These porous layers with a percolation structure are produced by powder metallurgy. They contain a barium compound in the pores of the layer as a source of barium. Such barium compounds are, for example, oxidic barium-calcium-aluminum compounds, of the general composition xBaO ₂ yCaO zAl ₂ O ₃ with x = 4, y = 1, z = 1 or x = 5, y = 3, z = 2 or x = 5, y = 3, z = 0. After formation, the top layer is covered with an active surface layer that has a very low work function. This layer is very thin, on the order of a monolayer, and contains an emitter complex that contains barium, scandium and oxygen.

According to another embodiment of the invention, there is the compact, flat Lower layer of tungsten, the rhenium, iridium, osmium, ruthenium, tantalum, Contains molybdenum or scandium oxide.

In this embodiment, the substrate layer is omitted. The cover layer contains tungsten, which is alloyed with rhenium, osmium, optionally also with iridium, ruthenium, tantalum, and / or molybdenum. It also contains scandium oxide or scandium oxide mixed with the oxides of other rare earth metals such as europium, samarium and cerium. It is also possible that it consists of scandium tungstates such as Sc ₆ WO ₁₂ or Sc ₂ W ₃ O ₁₂ .

However, the cover layer can also be built up in multiple layers, in particular as a double layer, from the above-mentioned layer compositions, the best results being achieved if a layer containing scandium is the outer layer. This top layer also contains a barium source, which contains a barium-containing oxidic compound such as BaO or xBaO ₂ yCaO zAl ₂ O ₃ with x = 4, y = 1, z = 1 or x = 5, y = 3, z = 2 or x = 5 , y = 3, z = 0. These barium-containing compounds can be mixed with calcium or strontium oxide.

This cover layer is preferably 100 to 500 nm thick. The tungsten portion of the Top layer consists of ultrafine particles with a diameter of 1 to 50 nm deposited in a nanostructured layer. The others both components are also deposited as ultra-fine particles and partly between, partly on the tungsten particles. From the three components is formed upon activation of the emitting surface complex, which as Surface layer lies on the top layer.

The low-temperature cathodes according to the invention are in a two-stage Process manufactured.

It is possible to start from known types of cathodes, such as L-cathodes, I-cathodes, B-cathodes or M-cathodes, and to produce a hybrid from these documents with the new cover layer. On the other hand, it is also possible to use gas or silicon disks which are coated with an underlayer made of conductive material according to the invention. These documents are brought into the deposition chamber of a laser ablation deposition system. It is favorable to use an excimer laser as the laser, which, in contrast to CO ₂ lasers, can also ablate tungsten without any problems. The tungsten-containing component is deposited first, the scandium-containing component second, and the barium-containing component third. It is favorable to use multitargets that contain all three components on a target arrangement. The emission properties of the finished low-temperature cathode are influenced favorably if the gas atmosphere in the ablation deposition process consists of high-purity argon or argon / hydrogen. Furthermore, it is advantageous if the underlays for the cover layer are heated in the process.

In the second process step, the emitter complex is in the surface layer educated. This activation step can be a thermal, voltage based Activation, a simple sintering or a superficial sintering in one Be a laser beam.

The thermal, voltage-based activation should take place under vacuum. On The simple option is to place the low-temperature cathode in the finished discharge tube to activate. For this purpose, the cathode is heated to approx. 800 ° C and voltage created. The associated current-voltage diagram also sets one Quality control.

If the top layer consists of very fine particles with an average grain size> 10 nm, the activation can also be carried out in a simple sintering at 800 ° C consist. In the case of cover layers with larger particles, the activation step in pulsed laser treatment at 1000 ° C to 1100 ° C.

The low-temperature cathodes according to the invention are distinguished by excellent Emission at low temperatures because it has a very low work function to have.

1 shows the current-voltage characteristic of low-temperature cathodes according to the invention in double logarithmic plots at 300 ° C, 200 ° C and shown at room temperature. The temperatures were considered as radiation temperatures specified. They were determined pyrometrically.

The total emission consists of glow emission and field emission. The contribution of the glow emission according to the Richardson equation i 0 = A R T 2 exp (- / kT) falls below 1nA at 200 ° C. However, field emission starts at a threshold of 1.2 kV, which very quickly delivers emission currents> 3µA when the field is increased further. With a diode spacing d = 160 µm, as can be determined from the Child-Langmuir equation, there follows a field emission threshold field strength of 7.5 V / µm, which represents a very good value for cold emission and is only reached as a peak value by a few other cathodes ,

With an ALT test, a lifespan of 1000 hours was reached.

Claims (17)

1. A low-temperature cathode comprising a holder, which, if necessary, includes:

   a heating or cooling element;

   a conductive bottom layer which is applied to said holder;

   if necessary a substrate with a dispenser material; and

   a top coating of ultrafine particles having a nanostructure, said top coating having a surface layer consisting of an emitter complex formed from an emission material comprising several components.
2. An electric discharge tube or discharge lamp including one or more low-temperature cathodes as claimed in claim 1.
3. An electric discharge tube or discharge lamp as claimed in claim 2, characterized in that it comprises a grid-control electrode.
4. A flat-panel display screen having one or more low-temperature cathodes as claimed in claim 1.
5. A low-temperature cathode as claimed in claim 1, characterized in that it can suitably be used at an operating temperature in the range between 20°C and 500°C.
6. A low-temperature cathode as claimed in claims 1 and 5, characterized in that the emission material comprises a first component, which contains metals, in particular refractory metals and the alloys thereof, a second component, which contains scandium, yttrium, lanthanum, the lanthanides or actinides and/or their compounds, in particular their oxides, and/or a third component which contains alkaline earths and/or their compounds.
7. A low-temperature cathode as claimed in claims 1, 5 and 6, characterized in that the first component of the emission material is tungsten, the second component consists of oxidic compounds of scandium and the third component consists of oxidic compounds of barium.
8. A low-temperature cathode as claimed in claims 1 and 5, characterized in that the components of the emission material are individually or jointly included in the bottom layer and/or substrate and/or top coating.
9. A low-temperature cathode as claimed in claim 1 and 5, characterized in that the emitter complex formed has a work function < 2.8 eV.
10. A low-temperature cathode as claimed in claims 1 and 5, characterized in that the ultrafine particles have a grain size in the range from 1 to 100 nm.
11. A low-temperature cathode as claimed in claims 1 and 5 to 10, characterized in that the nanostructure of the top coating is nanocrystalline or nano-amorphous and, if necessary, nanoporous, and the size of the structure ranges from 1 to 1,000 nm.
12. A method of manufacturing a low-temperature cathode as claimed in claim 1, in which, in a first step, a semi-finished product is manufactured which comprises a holder on which a conductive bottom layer is provided, if necessary a substrate with a dispenser material, and a top coating of ultrafine particles having a nanostructure, said semi-finished product containing the components of the emission material either separately or jointly in the bottom layer and/or the substrate and/or the top coating, and, in a second step, the emitter complex is formed as a surface layer on the top coating.
13. A method as claimed in claim 12, characterized in that the formation takes place at a temperature ≥ 800°C in an ultra-high vacuum or high vacuum at a residual gas pressure, while applying an electric field.
14. A method as claimed in claim 13, characterized in that the residual gas pressure is ≤ 10^-4 mbar and the residual gas contains noble gases, nitrogen, hydrogen and/or oxygen, which each have a partial pressure ≤ 10^-5 mbar.
15. A method as claimed in any one of claims 12 to 14, characterized in that the formation process consists in sintering at a temperature > 500°C in a vacuum or in a gas atmosphere containing noble gases, nitrogen, hydrogen and/or oxygen.
16. A method as claimed in any one of claims 12 to 15, characterized in that the top coating of ultrafine particles having a nanostructure is manufactured by means of laser-ablation deposition.
17. A method as claimed in claim 16, characterized in that said laser-ablation deposition takes place at a pressure below atmospheric.

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