1. Field of the Invention
The present invention relates to a field emission display. Specifically, the present invention relates to a field emission display having an improved barrier array.
2. Description of Prior Art
Field emission displays are well known in the art and are widely used since they have a small volume, low power consumption, high contrast ratio, large viewing angle and are suitable for mass production. In an FED device, electrons are emitted from tips formed on cathode electrodes by applying a voltage to the tips. The electrons impinge on a phosphor screen formed on a back of a transparent plate and thereby produce an image.
A conventional field emission display employs metal microtips as emitters. However, it is difficult to precisely fabricate extremely small metal microtips for the field emission source. This difficulty greatly limits miniaturization of a conventional field emission display. In addition, metal microtips themselves are prone to wear out after a long period of use.
Carbon nanotubes produced by arc discharge between graphite rods were first discovered and reported in an article by Sumio lijima entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). Carbon nanotubes have excellent mechanical properties, high electrical conductivity, nano-size tips, and other advantages. Due to these properties, it has been suggested that carbon nanotubes could be an ideal material for field emission applications.
In both convention field emission displays that use metal microtips as emitters and in field emission displays that use carbon nanotubes as emitters, a barrier array is used to separate and insulate the cathode and the gate electrodes. To achieve superior display quality, the barrier array should be made with high accuracy and uniformity throughout the entire barrier array, and the material of which the barrier array is made should not be porous, since otherwise air may become trapped in the pores. Furthermore, such applications as field emission displays demand that the barrier have a flat upper surface and highly accurate height. Thus the barrier array is a critical element in a field emission display.
The two main methods for making barrier arrays in the art are the screen printing method and the sandblasting method. In the screen printing method, a barrier array is formed by repeatedly screen printing and drying paste material on a substrate, and then baking the assembly. However, during the repeated printing and drying procedure, it is difficult to ensure that the barrier array has a flat upper surface and uniform height, and this leads to increases in production costs. In addition, it is also difficult to fabricate the barrier array to a high precision when using the screen printing method. Thus, screen printing is not suitable for mass production of high quality barrier arrays used in field emission displays.
In the sandblasting method, which is widely used, material for the barrier array is applied to a substrate at a predetermined thickness, and then dried. Then a protective film having the shape of the desired barrier array is formed on the assembly, or a sand blasting mask is attached to the assembly. Sand is injected at high pressure so that unwanted portions of the material are removed, thus forming the barrier array. Finally, the barrier array is baked. However, the whole manufacturing process takes a considerable time, and control of the sand injection must be highly accurate. The sandblasting method is not very reliable, and is also prone to contaminate the manufacturing environment with sand.
Other methods for making barrier arrays for flat panel displays comprise photolithography, molding, and casting. However, all these methods require mating of a substrate with suitable pastes, as well as drying and baking processes. This makes these methods unduly time-consuming. Furthermore, it is difficult to fabricate barrier arrays using these methods to a high precision.
As described above, these difficulties of barrier array manufacturing greatly limit mass production of field emission displays having high precision. Thus a field emission display with an improved barrier array which overcomes the above-mentioned problems is desired
In view of the above-described drawbacks, an object of the present invention is to provide a field emission display which has a high precision barrier array.
Another object of the present invention is to provide a field emission display having a barrier array which is suitable for mass production at low cost.
A further object of the present invention is to provide a field emission display having a barrier array which is made in an environmentally friendly manner.
In order to achieve the objects set out above, a field emission display having a barrier array in accordance with the present invention comprises a substrate; cathode electrodes formed on the substrate, the cathode electrodes together with the substrate defining a pixel pattern; a plurality of emitters formed on the cathode electrodes; a barrier array defining a plurality of openings therethrough according to the pixel pattern, the barrier array comprising a shadow mask with an insulative layer formed thereon; gate electrodes formed on the barrier array; and a phosphor screen spaced from the substrate. This field emission display employs the known technology for making a shadow mask in the field of CRTs. In addition, a thickness and a material of the shadow mask can be selected according to the particular requirements of the field emission display required. Furthermore, the thickness and the material of the insulative layer can be determined by the insulative performance required for the field emission display. Moreover, the barrier array may be formed in sufficient size that it can be subdivided for use in one or more field emission displays. In summary, the present invention provides a field emission display having a barrier array made to a high degree of precision which is low in production cost. The barrier arrays are also suitable for mass production in an environmentally friendly manner.
Other objects, advantages and novel features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:
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A preferred method for growing the carbon nanotubes 31 directly on the cathode electrodes 21 comprises the following steps: depositing a silicon layer (not shown) on the cathode electrodes 21 to a thickness of several tens of nanometers; depositing a catalyst layer (not shown) on the silicon layer to a thickness in the range from 1 nanometer to several tens of nanometers, the catalyst layer being iron, cobalt, nickel or any suitable combination alloy thereof; annealing the catalyst layer at 300˜400° C. for almost 10 hours; heating the cathode electrodes 21 with the catalyst layer up to 650˜700° C. in flowing protective gas; introducing a carbon source gas, such as acetylene; and thus forming carbon nanotubes 31 extending from the cathode electrodes 21.
A mask is provided prior to forming the shadow mask 44. The mask has a predetermined pattern corresponding to the pixel pattern of the field emission display. The shadow mask 44 is then formed by photolithographic etching using the mask. Thus, the shadow mask 44 also has the predetermined pattern. The pattern comprises a plurality of openings 42 evenly arranged in an array according to the pixel pattern of the field emission display (see
In the preferred method of making the barrier array 41, alumina is used as the insulative material, and electrophoretic deposition is used to form the insulative layer 43. In the electrophoretic deposition, the shadow mask 44 is used as an anode, and aluminum metal is used as a cathode. An electrolyte comprises aluminum ions. In the preferred method, the electrolyte comprises methyl alcohol (600 ml), magnesium sulfate (6 g), aluminum nitrate (30 ml), alumina (900 g), and deionized water (600 ml). The time needed for the electrophoretic deposition is determined by a required thickness of the insulative layer 43 of the field emission display, which in turn is determined according to a required insulative performance of the field emission display. In the preferred embodiment, the thickness of the alumina is 80 micrometers, and the time for electrophoretic deposition is 3 minutes.
The barrier array 41 is formed once an insulative layer 43 of alumina material has been deposited on the shadow mask 44 to a predetermined thickness. After insulative layer 43 has been deposited on the shadow mask 44, the barrier array 41 is preferably soaked in a solution for a predetermined time to clean surfaces of the barrier array 41. In the preferred method, the solution comprises ethyl cellulose (85 g), butyl alcohol (60 ml) and xylene (3400 ml, 3°), and the predetermined time is 1˜5 minutes. Then, the barrier array 41 is cured.
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It will be apparent to those having skill in the field of the present invention that the field emission display of the present invention is not only suitable employment with carbon nanotubes as emitters, but is also suitable employment with metal microtips as emitters.
Because making a shadow mask is a known technology in the field of CRTs, the above-described preferred embodiment according to the present invention is convenient to make. In addition, a thickness and a material of the shadow mask can be selected according to the particular requirements of the field emission display desired. Furthermore, the thickness and the material of the insulative layer 43 can be determined according to the insulative performance required for the field emission display. Moreover, the barrier array may be formed in sufficient size that it can be subdivided for use in one or more field emission displays. In summary, the present invention provides a field emission display having a barrier array made to a high degree of precision which is low in production cost. The barrier array is also suitable for mass production in an environmentally friendly manner.
It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.
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