Abstract:
A field emission display with reflection layer has an improved insulating supporting device. The major feature is to place a reflection layer on the insulating supporting device. From the special structure, the insulating supporting device can enhance the emission efficiency of the phosphors powder rather than the primary function of the insulating support. The field emission display with reflection layer has an anode structure, a cathode structure and the supporting device.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the structure of a field emission display. The feature is related to the reflection layer settled on the insulating supporting device between the cathode and the anode with a special effect of raising the brightness of the field emission display. 
   BACKGROUND OF THE INVENTION 
   There are various kinds of flat panel display (FPD) including, for example, field emission display (FED), liquid crystal display (LCD), plasma display panel (PDP), organic light emitter device (OLED), and liquid crystal projection display. The common features of such displays are that they are thin and light weight. According to the property of every flat panel display, some of them can be applied on the small scale panel for devices such as cellular phones; only a few are suitable for application in medium or large scale devices such as computer monitors or TV displays. Yet another application for flat panel displays further comprises super large scale display device such as an outdoor digital exhibition board. But the technologies of every kind of flat panel display are all progressing toward the object of high display quality together with large scale display and extended service life for application. 
   One of the rising new technologies for display is the field emission display developed in the recent years. The major feature is its self-emitting ability, which makes it superior to the LCD (lacking a self-emitting ability). Further the other benefits of large watching angle, low power consumption, high response efficient and the wide operation temperature can achieve the display quality like a traditional cathode ray tube (CRT). But the FED is lighter and thinner than the CRT. In addition, the recently developed new technology of nano-carbon-tube to be used on the FED area can promote the development of the FED. 
   A traditional three-electrodes FED  1   a  is shown in  FIG. 1 . The structure comprises at least an anode structure  10  and a cathode structure  20  in a structure unit. The insulation supporting device  15  (or spacer) is settled between the anode structure  10  and the cathode structure  20  as the boundary device in the vacuum environment and the support between the anode structure  10  and the cathode structure  20 . Reference is made to  FIG. 1 , in which an anode structure  10  comprises at least an anode glass-plate  11 , an anode conductive layer  12 , and a phosphors layer  13 . A cathode comprises at least a cathode glass-plate  21 , a cathode conductive layer  22 , an electron emitting layer  23 , a dielectric layer  24 , and a gate electrode layer  25 . The insulating supporting device  15  acting as boundary device can arrange the location of the anode structure  10  and the cathode structure  20  to maintain the vacuum area between the anode structure  10  and the cathode structure  20 . The anode conductive layer  12  can provide high voltage to induce the electron emitting layer  23  to generate electrons for emission to the phosphors layer  13  of the anode to excite the phosphors layer  13  to generate light. Thus, for the electrons moving in the FED, a vacuum pumping device induces a vacuum level of 10 −7  torr in a FED to provide a good moving path for the electrons. Also, pollution of and chemical reaction on the electron emitting layer  23  or the phosphors layer  13  should be avoided. In order to push the electrons with enough power to strike to the phosphors layer  13  to produce sufficient light radiation, a suitable gap between the cathode structure and the anode structure should be maintained to let the electrons to generate sufficient acceleration. 
   The above-described FED, however, excites the phosphors layer  13  to radiate light at a low voltage. The anode voltage is generally applied below 5 KV and this is very little compared to the anode voltage (at least higher than 20 KV) of the anode of CRT. So the emitting energy of the electrons of the cathode is still limited and the lighting brightness is limited, as well. For the brightness issue is also being presented, such as high density of nano-carbon-tube for raising the electrical current density, high efficiency low voltage phosphors layer, and the improvement of driving electrical circuit. One of the useful method is to set a reflection layer  14  to raise the radiating efficiency of the phosphors layer. 
   The above-mentioned method of reflection layer can be illustrated by a certain CRT application. The electron emitter has a certain distance to the anode screen. For example, from referring to the conventional 17-inch CRT, the certain distance is at least 200 millimeters. The certain distance allows speed of the electrons from the cathode to be enhanced and to strike to phosphors layer with 20 KV. Regarding the raised emission efficiency and the uniformity of the phosphors layer  82 , reference is made to  FIG. 7  to illustrate the metal reflection layer  84  being coated on the phosphors layer  82  on the glass plate  80 . The coated metal reflection layer  84  can reflect light deflected or reverse-emitted by the phosphors layer  82 . The structure of the anode has the black block array  81  and the metal mask  83  controls emission of the electron beam  85 . But from observing the structure of FED, the voltage applied on the anode is usually beyond 5 KV and the distance between the anode and the cathode is usually a few millimeters or less. Thus the electron emitting layer  23  can only emit low energy (lower than the CRT electron emitting energy) electrons. If the same method of coating the metal reflection layer  84  on the anode structure (with the phosphors layer) of the FED, as in the conventional CRT, is used, the electrons cannot fully penetrate the metal reflection layer  84  to emit light. In addition, the electron power in the FED is reduced by the metal reflection layer to cause the low radiating efficiency (of light) of the phosphors layer. 
   For the above reason, another conventional technique from the Taiwan Patent in Pub. No. 289126 discloses a special structure in  FIG. 2 . The said special structure includes the anode glass plate  91  to carry the phosphors powder layer  93 , anode conductive layer  95  and the black block array  94 . The supporting device  96  (having the supporting function between the anode and cathode) has the reflection layer  92  attached on the surface facing the phosphors powder layer  93 . The reflection layer  92  can reflect the deflected light or reverse-emitted light generated from the phosphors powder layer  93 . In particular, the reflection layer  92  is not directly attached to the phosphors powder layer  93 . The said reflection layer  92  structure arrangement can raise the brightness by not absorbing the electrons. But the whole process of the technique in  FIG. 2  is by the method of exposure with developing-out and the complex thin film process is applied by high equipment cost. In addition, the 20 inches display panel is difficult to manufacture by the special structure of the thickness in 500 μm. So the application area of display panel is in need of a simple and easy application method. 
   In recent years, a new style of support device in the display panel is frequently applied in the LCD display panel as a layer separating device.  FIG. 5  shows the structure of the supporting device provided by the thermal expansion modulus similar to that of glass. The thickness of the whole display panel is from about 500 μm to 1500 μm. A plurality of holes  42  can be also etched in the supporting device. The holes have the diameter size to match the array cell requirement on the anode or cathode. The supporting device also can act as the device to support the whole structure between the anode and the cathode. Since the FED contains a vacuum area inside, the two panels of the anode and the cathode prevent collapse thereof. The conventional supporting device of the FED usually employs glass balls, cross-shaped glass or glass strips. The supporting devices bind the anode and the cathode to the supporting device with a fixing chemical in a binding process. The fixing chemical is applied in the binding process by sintering. For an FED image display, the scale of the supporting device is usually maintained of 50 μm to 200 μm. The outline dimension of the supporting device is very small and causes complications described as follows. 
   First, since the conventional supporting devices are small, the location arranging machine must be highly precise, which makes location of the supporting device very difficult. Second, the supporting device may cause pollution by the attachment of the fixing chemical since the conventional supporting device must touch the fixing chemical to attach to the display panel. The next process is to heat the panel to fix the display panel. But the attachment process may contaminate the display panel. In addition, the sintering process on the display panel may cause the fixing chemical to evaporate and further contaminate the display panel. From the description of these shortcomings of the conventional supporting device, it is evident that a new device should be developed to resolve the above problems and reduce the manufacturing cost. 
   The inventor has developed a new structure by modify the insulating supporting device  38  with coating a reflection layer  44 . The modification provided by the inventor supports between the anode and the cathode and enhances the brightness of the phosphors layer. Additionally, the settling cost of the present invention is low because the process is simple. The conventional machine for the location arrangement of the supporting device is not required. 
   SUMMARY OF THE INVENTION 
   The prior art uses a low actuating power voltage of less than 5 KV. This is the major reason for the low efficiency of the phosphors layer. The conventional technical uses the reflection layer to raise the lighting efficiency, but the manufacturing process is very complex. In addition, in another conventional technique, contamination of the display panel is not easily prevented. The present invention thus provides a new insulating supporting device  38  with the reflection layer to raise the lighting efficiency of an FED. The installation process of the insulating device of the present invention is very easy. The insulating device of the present invention is also easy to manufacture independently with a low failure rate in quality. 
   The major purpose of the present invention is to provide an insulating supporting device  38  to raise the brightness of the FED. 
   Another purpose of the current invention is to provide a manufacturing method of an insulation supporting device  38  with the reflection layer. The insulation supporting device  38  can be manufactured independently and then installed in the FED by packaging. 
   The further purpose of the present invention is to provide a packaging method for an insulation supporting device  38  with the reflection layer. The insulation supporting device  38  can be applied in an FED without affecting the air guiding path and to fit the vacuum packaging process. 
   The structure of the present invention of field emission display with the reflection layer comprises an anode structure having a phosphors layer, a cathode structure having a nano-carbon-tube layer and an insulation supporting device located between the anode structure and cathode structure. The reflection layer faces the phosphors layer to reflect the light emitted from the phosphors layer. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings: 
       FIG. 1  shows a schematic view of the structure of a first prior art for the field emission display with three electrodes; 
       FIG. 2  shows a schematic view of the supporting device of a second prior art for field emission display; 
       FIG. 3  shows a schematic view of the structure of the present invention; 
       FIG. 4  shows a schematic view of the supporting device with the reflection layer according to the present invention; 
       FIG. 5  shows a schematic view of the insulating supporting device in panel shape according to the present invention; 
       FIG. 6  shows a schematic view of the partial anode structure of the present invention; 
       FIG. 7  shows a schematic view of the partial anode structure of the prior art; 
       FIG. 8  shows a schematic view of the holes arrangement of the supporting device of the present invention; and 
       FIG. 9  shows a schematic view of the holes arrangement of another supporting device of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention provides an insulation supporting device  38  with a reflection layer. Reference is made  FIG. 5 , in which the insulation supporting device  38  is made of an insulating material with a thermal expansion modulus similar to that of the anode structure (plate shape) or the cathode structure (plate shape). The said similar thermal expansion property can be useful when the heating process is applied to the FED panel, avoiding an expansion difference that would crack the FED panel surface. The said insulation supporting device  38  has a plurality of holes  42  that is arranged according to the cells of the anode structure or the cathode structure. The holes can act as the tunnels for the electrons from the cathode to pass through to strike the anode. The holes are formed by, for example, etching. For the special feature of the invention, a reflection layer  44  is installed on one side of the insulation supporting device  38 . Reference is also made to  FIG. 4  to illustrate the smooth, mirror-like surface serving as the reflection layer  44 , of which the material is, for example, a conductive material. An alignment mark can be made on the extra side  43  for the vacuum package of the FED display panel and the cells of anode/cathode structure can face the holes  42  of the insulation supporting device  38 . Additionally, a brushing area for the fixing chemical, to bind the anode structure and the cathode structure through the sintering process, can be designated on the extra side  43 . 
   The manufacturing method of the present invention is described as follows. First, the insulation supporting device  38  with a plurality of holes therein is formed by spluttering or evaporating a reflection layer  44  on one side of the insulation supporting device  38 . The main feature of FED of present invention can thus be produced by the above method. 
   The major feature of the present invention is insulation supporting device  38  and its assembly method is not the same as that of the conventional method in which it is directly inserted into the gap between the anode and the cathode. The assembly method according to the present invention adds an interference rib  39  on the side of cathode structure  20  (with the electron emitting layer  36 ) or anode structure  10  (with the phosphors layer  41 ). The interference rib  39  is formed to relate to the connection area between the holes of the insulation supporting device  38  for the function of additional support to provide an air or vacuum-flowing gap for the FED panel package. The air gap allows the residual air to escape from the cells (or the holes of the insulation supporting device  38 ) of the anode or the cathode during the packaging process of the FED. Another important assembly method is to attach the fixing chemical to the extra area  43  of the FED panel. The fixing chemical includes organic glue and binding material. The organic glue is for temporary fixing and the binding material is for binding the FED panel through sintering. The assembly process of the insulation supporting device  38  is to fix it between the anode and the cathode then to perform a heating process for sintering. The binding material can be the general glass glue to be applied in the sintering process for the binding of anode and the cathode. In addition, the alignment mark is designated to be formed on the insulation supporting device  38  to calibrate the position of the anode structure  10 , cathode structure  20 , and the insulation supporting device  38 . The reflection layer  44  of the insulation supporting device  38  is formed on the side to face the phosphors layer  41  of the anode structure  10 . From the application of the alignment mark, the cell in the cathode and the anode can fit the position of the holes on the insulation supporting device  38 . Then the organic glue temporarily secures the calibrated components. Finally, the sintering process is performed on the fixing calibrated components by heating at a high temperature to bind the insulation supporting device  38  to the cathode structure  20  and the anode structure  10 . 
   The electron emitting layer  36  (nano-carbon-tube layer), is described with the following application as the embodiment. 
   The insulation supporting device  38  of the present invention can be made of the glass material with a thermal expansion modulus of 82×10 −7 –86×10 −7 /° C, which is similar in range to that of the expansion modulus of the cathode plate  35  and anode plate  31 . The outline dimension of the insulation supporting device  38  is designated by the FED panel size and multiple alignment marks are usually formed to fit the anode structure  10  and the cathode structure  20  at calibration. The holes in the insulation supporting device  38  are arranged relative to the cells array of anode structure  10  and the cathode structure  20 . Reference is also made to  FIG. 8  and  FIG. 9 , which provide a cross-sectional view of the chemically-etched holes as two types of the hole section.  FIG. 8  shows that the first hole diameter  101  is larger than the second hole diameter  102 .  FIG. 9  illustrates another embodiment for the holes section, in which the third hole diameter  103  and the fifth hole diameter  105  are larger than the fourth hole diameter  104 . In addition, the second hole diameter  102  and the fourth hole diameter are larger than the cell width of the electron emitting layer  36 . Further, the reflection layer is located on the side of first hole in  FIG. 8 . In the embodiment illustrated in  FIG. 9 , however, the reflection layer is located on one of the two sides. The reflection layer of the insulation supporting device  38  can be generated by the evaporation of aluminum or chromium. The thickness of the insulation supporting device  38  is, for example, about 700 μm and the thickness of the reflection layer is, for example, about 80–500 nm. The extra area  43  of the insulation supporting device  38  is designed to have a glue brushing area and the fixing material deposing area. The glue brushing area is brushed with UV glue of the organic type for temporary fixing. Glass glue is deposited as the binding material on the fixing material deposition area. The assembly process for the FED uses the alignment mark to assemble the cathode structure  20 , anode structure  10 , and the insulation supporting device  38 . The reflection layer  44  of the insulation supporting device  38  is located on the side of the anode structure  10  to face the phosphors layer  41 . Additionally, a plurality of interference ribs  39  can be installed on the side of the anode structure  10 . The interference ribs  39  are made of the glass with a thickness of about 50 μm to 150 μm to cause a gas communication area for the FED panel packaging. The interference ribs  39  are thus installed between the holes of the insulation supporting device  38 . Packaging is performed by irradiating the UV glue with UV light to secure temporarily the panel and then sintering the temporarily fixed panel.  FIG. 3  illustrates the whole structure of the present invention and  FIG. 6  provides a partial structure of the anode structure  10  of the FED panel. The anode plate  31  has the phosphors layer  41  on the anode conductive layer  32 . The interference rib  39  can be properly distributed on the side of the phosphors layer  41  to provide support and to let the air (vacuum) flow. The interference ribs  39  are not, however, installed on every cell of the anode structure  10 . The insulation supporting device  38  has the reflection layer  44  on it. As illustrated in  FIG. 3 , the cathode structure  20  also has the dielectric period  33  with the gate electrode layer  37  thereon to provide the ability to accelerate the electrons. The cathode plate  35  has the cathode conductive layer  34  to receive the electrons emitting layer  36  (nano-carbon-tube layer). 
   The basic structure of the present invention is described as comprising an anode structure  10  having a phosphors layer  41 , a cathode structure  20  having the nano-carbon-tube layer  36  (electrons emitting layer  36 ) and an insulation supporting device  38  located between the anode structure  10  and cathode structure  20 . The reflection layer  44  faces the phosphors layer  41  to reflect the light emitted from the phosphors layer  41 . 
   Various embodiments will be described in the following. The cathode structure  20  may comprises the gate electrode layer  37  between the nano-carbon-tube layer  36  and the insulation supporting device  38 . Additionally the phosphors layer  41  can be formed by screen printing or spray coating. The nano-carbon-tube layer  36  is formed by screen printing or spray coating (by spray nozzle) as well. The nano-carbon-tube layer  36  comprises the property-improved (with a high degree of electron emitting efficiency) nano-carbon tube. In addition, the insulation supporting device  38  has a plurality of holes  42  and every nano-carbon-tube layer  36  in cell shape is placed in the holes  42 . The present invention can further comprising an interference rib  39  placed in the insulation supporting device  38  and the anode structure  10 ; the interference rib  39  forms many air (vacuum) communication paths connecting to every of the holes  42 . The reflection layer  44  can also be made of aluminum or chromium. For uniform expansion, the insulation supporting device  38  is made of glass with a thermal expansion modulus of about 82×10 −7 –86×10 −7 /° C. For sintering, a binding material containing glass is used to package the cathode structure  20  and the anode structure  10 . 
   The benefits of the FED structure of the present invention are described in the following. The manufacturing process of the insulation supporting device is simple and can be manufactured independently. Additionally, the structure of the present invention can be manufactured without using the supporting post placing machine. The process is very simple for the insulation supporting machine. Further, the major benefit of the main feature of the reflection layer on the insulation supporting device is to reflect the light (deflected or reversed) emitted from the phosphors layer. The brightness can be raised with an obvious period. 
   Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have suggested in the foregoing description, and other will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended