Patent Abstract:
A field emission display (FED) having a grid plate with spacer structure and fabrication method thereof. A first wplate having first electrodes and electron emitters on a first surface is provided. A second plate having second electrodes and phosphor regions on a second surface is also provided, wherein the second surface is opposite the first surface. A grid plate with spacer structure and passages having grid electrodes is positioned between the two plates to maintain a predetermined interval. When a specific voltage is applied between the first electrode and the second electrode, electrons extracted from the electron emitters are accelerated by the grid electrodes through the passages to impact the phosphor regions.

Full Description:
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 092112272 filed in TAIWAN on May 6, 2003, which is herein incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a field emission display (FED) and fabrication method thereof, and more specifically to a triode-type field emission display (FED) having a grid plate with spacer structure and fabrication method thereof. 
   2. Description of the Related Art 
   Field emission display (FED) is a kind of flat panel display attracting intense notice in recent years. The main reason is that it not only has the thin and light characteristics of a liquid crystal display (LCD), but also the high brightness and self emission advantages of cathode ray tube (CRT) displays. 
     FIG. 1   a  is a schematic diagram showing the structure of a conventional diode-type (cathode and anode) field emission display. According to the conventional diode-type field emission display  10 , the anode electrode  18  provides a high voltage environment to attract electrons emitted from the emission source  12  formed on the cathode electrode  16  of a cathode plate  14 , and the electrons impact the phosphor layer  23  on the anode plate  18  resulting in light emission. Since the maximum voltage difference between the cathode electrode  16  and the anode electrode  18  is only 600V, the conventional field emission display has disadvantages of short life span and low brightness. 
   To overcome the above drawbacks of the diode-type field emission display, a triode type (cathode, anode, and gate electrode) field emission display having high voltage difference has been disclosed.  FIG. 1   b  is a schematic diagram showing the structure of a typical triode-type field emission display. 
   The main difference from the diode-type field emission display is an additional gate electrode  34 . The gate electrode  34  is formed on an insulating layer  36  between the anode electrode  48  and the cathode electrode  40  to control the voltage, resulting in low voltage requirement of electrons emitted from the field emission source  38  of cathode plate  41 . The voltage difference  47  between the anode electrode  48  and the cathode electrode  40  is then boosted to 4 KV, and the speed of electrons hitting the phosphor layer  49  formed on the anode plate  46  is increased. 
   However, in the manufacturing process of conventional gate-controlled triode field emission display  30 , complicated and multiple photolithographic and etching steps have to be employed to precisely form the cathode electrode  40  and the gate electrode  34  on predetermined locations of the cathode plate  41  at the same time, and it is extremely difficult to prevent misregistration between the cathode electrode  40  and the gate electrode  34 . As a result, the complicated manufacturing process of field emission display reduces throughput and yield. 
   U.S. Pat. No. 6,380,671 discloses a triode-type field emission display  50 . As shown in  FIG. 2 , a grid plate  53  with a plurality of grid electrodes  55  and through-holes  60  is positioned between the anode plate  52  and the cathode plate  51 , and spacers are erected between the grid plate  53  and each of the plates  52  and  54  to maintain a predetermined interval against the atmospheric pressure. 
   The grid electrodes  55  onto the grid plate  53  enhance the emission of electrons from the emission source  57  and accelerate the electrons passing through-holes  60  in the grid plate  53  to impact the phosphor layers formed on the anode plate  52 . Compared with the conventional triode-type field emission display, the grid electrodes  55  are formed on the grid plate rather than on the same plate with cathodes, resulting in simplification of the manufacturing process of the field emission display. 
   However, since an additional grid plate  53  is positioned between the cathode plate  51  and anode plate  52 , different lengths of spacers  62  and  64  have to be erected between the anode plate  52  and the grid plate  53 , and between the cathode plate  51  and the grid plate  53  respectively. Due to the essential double spacer attachment processes in the manufacturing process of the field emission display, the number of spacers erected between each two plates is doubled, and the probability of misregistration is increased substantially. Processing time is increased and production is slowed resulting from the additional alignment and attachment processes for increased spacers, particularly in manufacturing process for large display. 
   While spacers are pre-positioned in desired positions on the grid plate used in another conventional manufacturing process, the additional alignment and attachment processes are performed while spacers are pre-positioned in desired positions on the grid plate. As a result, the manufacturing process still cannot reduce the processing time of spacer positioning and the probability of misregistration. 
   SUMMARY OF THE INVENTION 
   Accordingly, an object of the present invention is to provide a triode-type field emission display for which the manufacturing process is simplified and the throughput and yield are increased by use of a grid plate with spacer structure formed integrally therewith to separate the anode plate from the cathode plate, rather than conventional spacers. 
   Another object of the present invention is to provide a fabrication method of a field emission display to obtain a field emission display having a grid plate with spacer structure according to the present invention. 
   To achieve the first object, according to the present invention, a field emission display comprises a first plate having a first surface, and first electrodes and electron emitters formed on the first surface of the first plate. A second plate having a second surface opposite the first surface is provided, and second electrodes and phosphor regions are formed on the second surface of the second plate. 
   A grid plate with spacer structure has grid electrodes thereon and passages therethrough, being positioned between the first plate and the second plate to maintain a predetermined interval using overhangs of the spacer structure formed integrally with the grid plate. When a specific voltage is applied between the first electrode and the second electrode, electrons extracted from the electron emitters are accelerated by the grid electrodes through the passages to impact the phosphor regions. 
   The present invention also provides a fabrication method of a field emission display having a grid plate with spacer structure, including the following steps. 
   First, a first plate having a first surface is provided, with first electrodes and a plurality of electron emitters formed thereon. 
   Next, a second plate with a second surface opposite the first surface is provided, with second electrodes and a plurality of phosphor regions formed thereon. 
   Next, a grid plate having a plurality of first spacer overhangs, second spacer overhangs, grid electrodes, and passages is provided. The grid plate is positioned between the first plate and second plate to maintain a predetermined interval, wherein the grid plate is combined with the first plate through the first spacer overhangs acting as spacers and combined with the second plate through the second spacer overhangs acting as spacers. 
   When a specific voltage is applied between the first electrode and the second electrode, electrons extracted from the electron emitters are accelerated by the grid electrodes through the passages to impact the phosphor regions. 
   Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
   Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the present invention, and wherein: 
       FIG. 1   a  is a cross-section illustrating a conventional diode-type field emission display. 
       FIG. 1   b  is a cross-section illustrating a conventional triode-type field emission display. 
       FIG. 2  is an exploded view of a conventional triode-type field emission display showing the attachment thereof. 
       FIG. 3  is an exploded view of the field emission display in accordance with the present invention, showing the attachment thereof. 
       FIGS. 4   a  and  4   b  are schematic bottom views of the grid plate in accordance with the present invention. 
       FIGS. 5   a  and  5   b  are schematic top views of the grid plate in accordance with the present invention. 
       FIGS. 6   a  and  6   b  are cross-sections illustrating the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following embodiments are intended to illustrate the invention more fully without limiting the scope of the claims, since numerous modifications and variations will be apparent to those skilled in this art. 
     FIG. 3  is an exploded view of the field emission display having a grid plate with spacer structure in accordance with the present invention showing the attachment thereof. 
   The field emission display  100  includes a cathode plate  110 , an anode plate  130 , and a grid plate  120  having spacer structure. Herein, the term “grid plate having spacer structure” describes a grid plate having a plurality of overhangs on both upper and lower surfaces, wherein the overhangs are formed integrally with the grid plate and act as spacers in the attachment of field emission display. 
   Herein, the above cathode plate  110  includes cathode electrodes  114  and a plurality of electron emitters  116  formed thereon. The manufacturing process of the cathode plate  110  comprises forming the cathode electrodes  114  on an insulating substrate  112 . Sequentially, electron emitters  116  are formed on the cathode electrodes  114 , wherein the cathode electrodes  114  can be metal electrodes and formed optionally in any pattern. The electron emitters  116  are preferably nanotube emitter arrays, and more preferably carbon nanotube arrays. In addition, the electron emitters  116  are separated by first predetermined regions  118  to allow subsequent combination of the grid plate  120 . 
   The above anode plate  130  includes a plurality of anode electrodes  134  formed thereon, and a plurality of phosphor regions  136  formed on the anode electrodes  134 . The manufacturing process of the anode plate  130  comprises forming the anode electrodes  134  on a transparent substrate  132 . The phosphor regions  136  are formed on the anode electrodes  134 , wherein the transparent substrate  132  may be a glass substrate and a suitable material for anode electrode  134  may be indium tin oxide (ITO). In addition, the phosphor regions  136  are separate by a second predetermined region  138  to allow subsequent combination of the grid plate  120 . 
   Referring to  FIG. 3 , the grid plate  120  according to the present invention is a substrate  122  having a plurality of first spacer overhangs  124 , second spacer overhangs  126 , and passages  125  therethrough, with a plurality of grid electrodes  123  formed on the same side as the first spacer overhangs  124  of the substrate  122 . In the present invention, the first spacer overhangs  124  are positioned subsequently on the first predetermined regions  118 , serving as spacers to combine the grid plate  120  with the cathode plate  110 . The second spacer overhangs  126  are positioned subsequently on the second predetermined regions  138 , serving as spacers to combine the grid plate  120  with the anode plate  130 . 
   The substrate  122  serving as the grid plate  120  has a plurality of overhangs which maintain a predetermined interval between the cathode plate  110  and the anode plate  130  in the field emission display. As a main feature and a key aspect of the present invention, the substrate  122  having a plurality of overhangs and passages is integrally formed. Namely, the spacer overhangs  124  and  126  and passages  125  of the substrate  122  are formed simultaneously in the manufacturing process of the substrate  122 . 
   Photosensitive glass or ceramic can be molded into the substrate  122  by photolithographic and etching processes. In a preferred embodiment, pre-designed patterned mask layers are formed on a commercially available photosensitive glass, FOTURAN (available from mikroglas technik AG). 
   Subsequently, the photosensitive glass is exposed to ultraviolet light with a wavelength of 290–330 nm. With the UV exposure step, silver atoms of the photosensitive glass are released from the illuminated areas. 
   After exposure, the photosensitive glass is baked at 400˜500° C. During the heat treatment, the illuminated areas of the photosensitive glass crystallize around the silver atoms. The crystalline regions, when etched with an acid at room temperature, such as 10% solution of hydrofluoric acid, have an etching rate higher than that of the vitreous regions. If wet chemical etching is supported by ultrasonic or spray etching, the resulting structures display a large aspect ratio. 
   Optional repeat of the above steps completes the fabrication of the substrate  122  having a plurality of spacer overhangs  124  and  126  and passages  125  according to the present invention. 
   As well, another fabrication method comprises the substrate  122  having a plurality of spacer overhangs and passages being molded from photostructurable glass or ceramic by 3D laser exposure. 
   In another preferred embodiment, multiple laser lights volumetrically pattern a photostructurable material, such as a photoceram, via direct-write processing. The multiple laser lights, with wavelength from 248 to 355 nm, permit varied penetration depth of the ultraviolet light and determine the effective height of the microstructure being patterned. 
   Through an exposure, the laser light remains stationary and the photoceram is moved partially to produce the desired pattern. To implement the 3D Laser exposure process, a computer program, such as a CAD-CAM soft, is used to control the path and pattern of the incident laser lights. 
   Furthermore, plastic materials, such as dielectric, plastic, glass, or ceramic, can be used to form the integrally formed substrate  122  having spacer overhangs through molding techniques in other podssible embodiments of the present invention. 
   After fabrication of the substrate  122 , a plurality of grid electrodes  123  are formed thereon to obtain the grid plate  120  according to the present invention, the grid electrodes  123  located on either side of the first spacer overhangs  124  adjacent to the passages  125 . Preferably, the grid electrodes  123  are formed by sputtering, electron beam evaporation, thermal evaporation, or chemical vapor deposition, and patterned by photolithography. 
     FIG. 4   a  is a schematic bottom view of the grid plate  120 , viewed from the side of the first spacer overhangs  124 , showing the relationship between the grid electrodes  123 , the first spacer overhangs  124 , and the passages  125 .  FIG. 4   b  is a schematic bottom view in accordance with another embodiment of the present invention. 
     FIG. 5   a  is a schematic top view of the grid plate  120  in accordance with another preferred embodiment of the present invention, viewed from the side of the second spacer overhangs  126 , showing the relationship between the second spacer overhangs  126  and the passages  125 . 
   In another preferred embodiment as shown in  FIG. 5   b , the substrate  122  has a plurality of trenches, separating the second spacer overhangs, serving as exhaust channels  128 , facilitating the vacuum exhaust in the sealing process of the field emission display to avoid the field emission electrons being affected by residual gas. The exhaust channels  128  can be formed simultaneously in the manufacturing process of the substrate  122 . 
   After the fabrications of the cathode plate  110  according to the present invention, the grid plate  120 , and the anode plate  130  according to the methods mentioned above, the above three plates are aligned and attached. As shown in  FIG. 3 , the grid plate  120  is positioned between the cathode plate  110  and anode plate  130  to maintain a predetermined interval, wherein the grid plate  120  is combined with the cathode plate  110  by attaching the first spacer overhangs  124  to the first determined region  118 , and with the anode plate by attaching the second spacer overhangs  126  to the second determined region  118 . 
   After alignment and attachment, a sealing process, such as tubeless vacuum packing, is used to package the structure to obtain the field emission display  100  according to the present invention.  FIG. 6   a  is a cross-section of the field emission display according to a preferred embodiment. 
   In the present invention, the interval of the anode plate  130  between two second spacer overhangs  126  positioned thereon is defined as an anode contact window  129 , and the interval of the passage between the locations of the grid electrodes on either side of the electron emitter  116  is defined as an electron emitting window  127 . One aspect of the invention, the anode contact window  129  can be designed larger than the phosphor region  136  to facilitate vacuum exhaust in the sealing process. 
   Another aspect of the invention, the electron emitting window  127 , can be designed larger than the anode contact window  129  to lower the operational voltage of the grid electrodes  123 , as shown in  FIG. 6   b.    
   In the present invention, the fabrication method of field emission display allows a large screen field emission display without the conventional complicated process by separately providing a cathode layer and a grid layer. The grid and cathode electrodes are fabricated separately, forming the grid electrodes on the grid plate, allowing the complicated multiple photolithographic and etching formation of the cathode electrodes and the grid electrodes on one side of the cathode plate to be avoided. 
   Moreover, the fabrication method of the field emission display according to the present invention allows formation of electron emitters onto the cathode electrodes directly, and, as a result, is suitable for fabricating a field emission display having carbon nanotube films as electron emitters. 
   Furthermore, the grid plate having a plurality of overhangs serving as spacers of field emission display is formed integrally. Compared with the conventional triode-type field emission display, alignment and attachment used in fabricating the field emission display according to the present invention are simplified substantially resultingly. Accordingly, throughput and yield for the field emission display according to the present invention are improved. 
   While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Technology Classification (CPC): 7