Patent Publication Number: US-2007120459-A1

Title: Field emission display device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to flat panel displays and, more particularly, to a field emission display device (FED) capable of protecting electron emitters from damage.  
      2. Description of Related Art  
      In recent years, display devices have become increasingly important in life. For example, computers, the Internet, televisions, cellphones, personal digital assistants (PDAs), and digital cameras, all have to exchange messages under the control of a display. As compared to conventional cathode ray tube (CRT) displays, new-generation flat panel displays have the light, small and ergonomic features, but they also have the disadvantages of poor viewing angle, low brightness and high power consumption.  
      In the developing flat panel display technologies, FEDs have the feature of good images quality the same as the CRT displays and are unlike liquid crystal displays (LCDs) that have the disadvantages of poor viewing angle, small range of operating temperature, and long response time. Generally, an FED can provide the features of high yield, short response time, good communication for display, high brightness over 100 ftL, thinner and lighter structure, wide angle of view, large range of operating temperature, high performance efficiency, and good recognition of slanting direction.  
      In addition, an FED can be used without a backlight module, and even under the outdoor sunshine, it can provide a satisfactorily high brightness. The developing nanotechnologies have provided novel electron emission materials to FEDs. One of the materials is the carbon nanotube (CNT), which forms a CNT-type FED to replace an electron-tip emission device that has the disadvantages of short lifetime and difficult manufacture. The CNT-type FED is operated upon the principle of CNT-tip discharge. Accordingly, the FEDs compete strongly with the LCDs to the extent of replacing them.  
      The FEDs have the similar operating principle to the typical CRTs. Namely, at a vacuum environment below 10 −6  torr, an electric field is applied to draw electrons out of the cathode microtips, and the electrons are accelerated by a positive voltage at the anode plate to bombard the phosphor layer on the anode plate so as to generate luminescence. Typically, an FED controls a voltage difference between a cathode and a gate electrode such that each electron emitter emits electrons at the assigned time.  
      An FED typically includes cathodes, spacers, electron emitters and gate electrodes prepared on a bottom substrate, wherein the electron emitters easily suffer the reduced quality after undergoing a series of processes. Accordingly, in order to comply with the requirement of a high precision FED, it is important to protect the electron emitters from damage.  
      Therefore, it is desirable to provide an improved FED to mitigate and/or obviate the aforementioned problems.  
     SUMMARY OF THE INVENTION  
      The object of the invention is to provide a field emission display (FED) device, which is prepared by reducing or even eliminating the gate structure to thereby protect an electron emitter from damage and further obtain a better production yield.  
      According to a feature of the invention, a field emission display (FED) device is provided. The FED device includes a top substrate, a bottom substrate and an intermediate plate set located between the top substrate and the bottom substrate. The top substrate has a phosphor layer and an anode. The bottom substrate has a bottom plate, one or more cathodes, and one or more electron emitters. The intermediate plate set has one or more metal plates with multiple holes, one or more insulating layers with multiple holes, and a gate layer.  
      In the FED device, the cathodes are located on the bottom plate, and the electron emitters are located on the cathodes. Each insulating layer is located between the gate layer and a metal plate for electrical insulation. The gate layer has a gap from the bottom substrate. Thus, the processing steps prepared for the bottom substrate can be reduced to prevent the electron emitters from damage and to further increase the production yield.  
      For isolating the influence of a high electric field applied to the electrodes at the top substrate on the electrodes at the bottom substrate, the intermediate plate set preferably includes multiple metal plates, and an insulating layer is located between the metal plates for electrical insulation and easy control in operation.  
      In the FED device, the holes of the metal plates can be arranged in any pattern. Preferably, a pattern of M×N matrix is arranged, for M, N are an integer greater than zero. The holes of the metal plates can be in any shape, but a tetragon, round, polygon, irregular shape, or a combination thereof is preferred. Besides, the holes of the metal plates can be patterned into trenches in parallel to one another, i.e., the metal plates can be discontinuous metal plates.  
      In the FED device, the holes of the insulating layers can be arranged in any pattern. Preferably, a pattern of M×N matrix is arranged, for M, N are an integer greater than zero. The holes of the insulating layers can be in any shape, but a tetragon, round, polygon, oval, irregular shape, or a combination thereof is preferred. Besides, the holes of the insulating layers can be patterned into trenches in parallel to one another, i.e., the insulating layers can consist of discontinuous insulator.  
      The gate electrodes can be any gate electrodes suitable for a typical planar FED, but a plurality of ring-shaped gate electrodes with holes, a gate plate with multiple holes, or a plurality of stripe-shaped gate electrodes are preferred. The ring-shaped gate electrodes can be arranged in any form and have a one-to-one relation with respect to the electron emitters, such that each electron emitter can accurately emit electrons at an assigned time.  
      In a preferred manner of the invention, the metal plates, the insulating layers and the gate layer of the intermediate plate set are formed in a stack, wherein the gate layer is arranged the closest to the bottom substrate and has a gap from the bottom substrate, and an insulating layer is sandwiched in between the gate layer and a metal plate. Besides, an insulating layer is preferably sandwiched in between the metal plates, and the heights of the insulating layers are adjusted with the interlayer distance between the metal plates. The location and number of metal plates are not limited but depend on the process needs.  
      In another preferred manner of the invention, the holes of the insulating layers and the metal plates can be matched to thus have the same arrangement and pattern. Similarly, the gate layer can be matched with the pattern of the holes of the metal plates according to the process needs. As the gate layer consists of the ring-shaped gate electrodes with holes, the holes preferably have a shape as same as that of the metal plates. As the gate layer is the gate plate with the holes, the holes preferably have a shape the same as that of the metal plates.  
      The holes of the metal plates can be in any arrangement with respect to the top and bottom substrates. In a preferred embodiment of the invention, when the electron emitters of the bottom substrate are formed in a dot shape, the holes of the metal plates and the electron emitters have a one-to-one arrangement, but are not limited to it. For example, the holes of the metal plates and the electron emitters can be in a one-to-multiple or multiple-to-one arrangement, depending on the shapes of the electron emitters and the metal plates, or the manufacturing cost.  
      Besides, the cathodes can be in any shape, but preferably are in a dot shape, a continuous or a discontinuous stripe shapes. The cathodes can be formed of any material suitable for the cathode of a typical FED.  
      Since each pixel of the FED has a respective field emission array, and the electron emitters emit electrons by applying an external bias voltage between the cathodes and the gate electrodes, the structures of the gate electrodes, the cathodes and the electron emitters can be correspondingly matched in shape to thereby control the accurate time of emitting electrons by each electron emitter and further the display time for each pixel.  
      For the holes of the metal plates, the aperture diameter can be equal or not equal to the inner diameter. The inner surfaces (wall surfaces) of the holes can be in any pattern, but preferably are of a pattern selected from the group of vertical, slanting, concave-slanting, convex-slanting surface, and combinations thereof, and more preferably are a combination of upward and downward concave-slanting surfaces.  
      The metal plates can be any kind of metal plate, but preferably they are formed of a sheet metal coated on a surface with an electron amplification material. The electron amplification material can be a metal alloy such as silver-magnesium alloy, copper-beryllium alloy, copper-barium alloy, gold-barium alloy, gold-calcium alloy, tungsten-barium-gold alloy, ferro-nickel alloy or the combination thereof; or a metal oxide such as oxides of beryllium, oxides of magnesium, oxides of calcium, oxides of strontium, oxides of barium or the combination thereof.  
      Electrons emitted by the electron emitters are accelerated, due to a voltage difference between the top substrate and the bottom substrate, to move from the bottom substrate to the top substrate and bombard on the phosphor layer particles of the phosphor to accordingly generate a light visible to human eye.  
      Since the number and distribution uniformity of electrons are a key of lighting brightness and illumination uniformity, the invention applies an on-demand voltage, other than the voltages of the anode and the cathode, to effectively increase the number of electrons to generate the secondary electrons through the metal plates, or effectively focus the electrons emitted on targets. Accordingly, the number of electrons bombarding into the phosphor layer is increased, and the entire brightness and color contrast of pixels are increased.  
      In the invention, for enhancing the stability and solid support capability of the entire FED structure, the FED device can further include one or more spacers located on two sides between the top substrate and the bottom substrate to accordingly support the gap distance between the intermediate plate set and the top and bottom substrates. Alternatively, the side of the gate layer facing the bottom substrate can selectively include an insulating spacer to maintain a gap and provide the solid support effect. In addition, the side of the metal plate the closest to the top substrate can further include an insulating spacer to provide the solid support effect.  
      The insulating spacers can be formed of any typical insulating material.  
      The electron emitters can be applied to any typical FED, but preferably are of a carbon nanotube (CNT)-type FED. The electron emitters can be formed of any typical material capable of emitting electrons, but preferably are of a carbon-based material selected from the group of black lead, diamond, diamond-like carbon, carbon nanotube (CNT), carbon  60  and the combination thereof. In a preferred embodiment of the invention, the FED device uses a CNT as an electron emitter.  
      The FED device further includes a shield layer on the top substrate to tightly surround the phosphor layer for preventing the light leakage or increasing the color contrast. The bottom substrate further includes one or more switches, which are connected to the cathodes for driving the electron emitters on the cathodes. The switches can be any typical passive or active driving switch, but preferably are of a thin film transistor (TFT), thin film diode, or a matrix scanning drive circuit.  
      In the invention, the structure of the FED device is improved to prevent the electron emitters from damage, effectively focus or increase the electrons bombarding the phosphor layer. Accordingly, the entire brightness and color contrast of pixels are enhanced.  
      Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a schematic cross-section view of a field emission display (FED) device according to a preferred embodiment of the invention;  
       FIG. 2  is a schematic cross-section view of a field emission display (FED) device according to a preferred embodiment of the invention;  
       FIG. 3  is a schematic cross-section view of an intermediate plate set according to a preferred embodiment of the invention;  
       FIG. 4  is a schematic cross-section view of an intermediate plate set according to a preferred embodiment of the invention;  
       FIG. 5  is a schematic cross-section view of an intermediate plate set according to a preferred embodiment of the invention; and  
       FIG. 6  is a schematic cross-section view of an intermediate plate set according to a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     First Embodiment  
       FIG. 1  is a schematic cross-section view of a field emission display (FED) device  100  according to a preferred embodiment of the invention. In  FIG. 1 , the FED device  100  includes a top substrate  10  having a transparent plate  11 , an anode  12 , a phosphor layer  13  and a shield layer  14 ; a bottom substrate  20  having a bottom plate  21 , multiple stripe-shaped cathodes  22  and multiple dot-distributed electron emitters  23 ; and an intermediate plate set  30  located between the top substrate  10  and the bottom substrate  20 . The intermediate plate set  30  has one or more metal plates  31  with multiple round matrix holes, an insulating layer  32  with multiple round matrix holes, and a gate layer  33  with round holes. The gate electrodes  33  are separated from the bottom substrate  20  by a gap.  
      The phosphor layer  13  is formed of a phosphor or light-emitting material. The transparent plate  11  is of a glass or other transparent material. The anode  12  is formed of a transparent and electrically conductive material such as an indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). The electron emitters  23  are formed of a carbon nanotube (CNT) material. The insulating layer  32  is formed of an insulating material such as the aluminum oxide or the magnesium oxide.  
      The stripe-shaped cathodes  22  are arranged in parallel on the bottom plate  21 . The electron emitters  23  are formed on the cathodes  22  in a form of dot distribution.  
      It is to be noted that the structures of the cathodes  22  and the gate electrodes  33  can be in an alternative form, not limited to the aforementioned. For example, if the gate layer consists of the ring-shaped gate electrodes  33  with round holes, the cathodes  22  can be formed or distributed in a pattern of dots, discontinuous stripes or other typical cathode forms. If the gate layer is a gate plate with holes, the cathodes  22  are matched in a discontinuous shape such as a dot or stripe form to separately control each electron emitter on the cathodes to emit electrons at the assigned time.  
      The metal plates  31 , the insulating layer  32  and the ring-shaped gate electrodes  33  are formed into a stack, and the insulating layer  32  is sandwiched in between the metal plates  31  and the ring-shaped gate electrodes  33  for electrical insulation. The holes of the insulating layer  32  and the ring-shaped gate electrodes  33  are patterned to match with the metal plates  31  on the shape and the arrangement, and correspond to the electron emitters  23  in a one-to-one manner. Such an arrangement is only an example, and the alternatives can be given by those skilled in the prior art.  
      A voltage difference between the cathodes  22  and the gate electrodes  33  is controlled to separately control each electron emitter  23  to emit electrons at an assigned time, so as to further control the time of a color light generation by the phosphor layer  13  corresponding to the electron emitter  23 . In addition, the electrons emitted by the electron emitter  23  and influenced by the voltage difference are accelerated toward the top substrate  10  and bombard on the phosphor layer  13  to react with the phosphor material and generate a visible light. The visible light is viewable by human eye when the light travels through the transparent plate  11  to the outside.  
      The surfaces of the metal plates  31  are coated with a ferro-nickel or silver-magnesium alloy for electron amplification, and the round matrix holes thereof correspond to the electron emitters  23  in a one-to-one manner. In this case, electrons pass through the intermediate plate set  30  and bombard on the electron amplification material coated on the surfaces of the metal plates  31  when moving from the bottom substrate  20  to the top substrate  10  due to an external bias voltage, so as to obtain the doubled number of electrons (secondary electrons). In addition, the metal plates  31  can isolate the influence of the high electric field from the anode  12  of the top substrate  10  on the cathodes  22  of the bottom substrate  20 . Further, an additional potential can be applied to the metal plates  31  to focus the electrons for more effective bombarding.  
      As shown in  FIG. 1 , the holes of the metal plates have different inner diameters and different aperture diameters. In addition, the inner surfaces  311  (wall shapes) of the holes consist of a concave-slanting surface and a convex-slanting surface in order to increase the bombarding areas when the electrons pass through the metal plates  31 .  
      In this embodiment, the process for the top substrate  10  and the bottom substrate  20  can be any process for preparing typical FED top and bottom substrates. For example, a screen printing, sputtering, coating, lithography or etching technique can be used to form the FED device. In addition, in such a structure, the processing steps for the invention can be reduced to thus reduce the electron emitter from damage and obtain a better production yield.  
     Second Embodiment  
       FIG. 2  is a schematic cross-section view of a field emission display (FED) device  200  according to a preferred embodiment of the invention. In  FIG. 2 , the FED device  200  includes a top substrate  40 , a bottom substrate  50  and an intermediate plate set  60 . In this embodiment, the top and bottom substrates  40  and  50  have structures identical to the respective substrates  10  and  20 , and the intermediate plate set  60  also includes the metal plates  61 , the insulating layer  62  and the ring-shaped gate electrodes  63 , but the elements of the set  60  have a different arrangement than those of the first embodiment.  
      As shown in  FIG. 2 , the structure of the intermediate plate set  60  is extended from the intermediate plate set  30  of the first embodiment in which only a layer of metal plates is shown. In this embodiment, two layers of metal plates are added above the layer of metal plates shown in the intermediate plate set  30 , and an insulating spacer  62  is disposed between the metal plates for electrical insulation. In addition, an insulating spacer  62  is disposed respectively on the top and the bottom of the intermediate plate set  60  for supporting the entire space configuration and maintaining the gaps between the intermediate plate set  60  and the top and bottom substrates to thereby provide a stable solid support.  
      The multi-layer structure of the set  60  can increase the bombarding frequency of electrons to further generate more secondary electrons for bombarding the phosphor layer. Accordingly, the FED device can have the feature of high brightness, even with a low driving voltage.  
     Third Embodiment  
      This embodiment is identical to the first embodiment except the intermediate plate set  30 . The intermediate plate set  30  includes a gate plate with multiple holes, as shown in  FIG. 3 . The holes of the gate plate have a round pattern the as same as the holes of the metal plates. In addition, in order to separately control each electron emitter to emit electrons at the assigned time, the cathodes are arranged or distributed in a pattern of dots or discontinuous stripe.  
     Fourth to Sixth Embodiments  
      As cited, the metal plates of the FED device can have the holes with same or different inner diameters and aperture diameters. The inner surfaces (wall surfaces) of the holes can be in any pattern, but preferably are in a pattern selected from the group of vertical, slanting, concave-slanting, convex-slanting surface, and combinations thereof. Accordingly, the structures of the intermediate plate sets are selectively formed of vertical, slanting, concave-slanting, convex-slanting surface and the combinations, as shown in FIGS.  4  to  6 . In addition, the inner diameter and the aperture diameter are the same in  FIG. 4  and not the same as in  FIGS. 5 and 6 . Accordingly, the intermediate plate set can be arranged adaptively upon the requirements of low driving voltage, high electron amplification effect and low manufacturing cost.  
      As cited, upon the structure of the FED device, the process for the bottom substrate can be simplified to thereby prevent the electron emitters from damage and obtain a better production yield to benefit the market competition.  
      Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the spirit and scope of the invention as hereinafter claimed.