Abstract:
A field emission device comprising a first substrate, a second substrate spaced apart from the first substrate, a first metal layer on the first substrate, the first metal layer including a number of first metal lines, a second metal layer over the first metal layer, the second metal layer including a number of second metal lines, emitters over the first metal layer, the emitters being configured to emit electrons toward the second substrate, a luminescent layer between the first substrate and the second substrate, the luminescent layer being configured to provide light when the electrons impinge thereon, and a third metal layer between the second substrate and the luminescent layer, the third metal layer being configured to reflect the light from the luminescent layer toward the first substrate, wherein the first metal lines are substantially parallel to the second metal lines.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of U.S. patent application Ser. No. 11/110,613, filed Apr. 19, 2005, which is herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to an electron emitting device and, more particularly, to a field emission device able to serve as a light source.  
       BACKGROUND OF THE INVENTION  
       [0003]     In recent years, flat-panel display devices have been developed and widely used in electronic applications. Examples of flat-panel display devices include the liquid crystal display (“LCD”), plasma display panel (“PDP”) and field emission display (“FED”) devices. FEDs have received considerable attention as a next generation display device having the advantages of LCDs and PDPs. FEDs, which operate on the principle of field emission of electrons from microscopic tips, are known to be capable of overcoming some of the limitations and provides significant advantages over conventional LCDs and PDPs. For example, FEDs have higher contrast ratios, wider viewing angles, higher maximum brightness, lower power consumption, shorter response times and broader operating temperature ranges compared to conventional LCDs and PDPs. Consequently, FEDs are used in a wide variety of applications ranging from home televisions to industrial equipment and computers.  
         [0004]     One of the most important differences between an FED and an LCD is that, unlike the LCD, the FED may produce its own light source. The FED does not require complicated, power-consuming backlights and filters. Almost all light generated by an FED is viewable by a user. Thus, the costly light source of an LCD may be eliminated. With the property of self-luminescence, a field emission device may function to serve as an independent light source rather than a display device. The principle of field emission of electrons is briefly discussed below.  FIG. 1  is a schematic cross-sectional diagram of a conventional field emission device  10 . Referring to  FIG. 1 , the field emission device  10 , which may function to serve as a light source, includes a first substrate  12 , a cathode assembly  14 , a second substrate  22 , a transparent electrode  24  and a phosphor layer  26 . The cathode assembly  14  may emit electrons, which are accelerated toward the phosphor layer  26 . The phosphor layer  26  may provide luminescence when the emitted electrons collide with phosphor particles. Light provided from the phosphor layer  26  transmits through the transparent electrode  24 , for example, an indium tin oxide (“ITO”) layer, and the second substrate  22  to a display device (not shown), for example, an LCD device attached to second substrate  22 . However, the field emission device  10  may be disadvantageous in that the temperature at the second substrate  22  may be too high to adversely affect the performance or even lifetime of the attached display device.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     A novel field emission device is disclosed, which may obviate one or more problems resulting from the limitations and disadvantages of the prior art.  
         [0006]     Examples of the present invention may provide a field emission device comprising a first substrate, a second substrate spaced apart from the first substrate, a cathode structure between the first substrate and the second substrate, the cathode structure being configured to emit electrons toward the second substrate, a luminescent layer between the first substrate and the second substrate, the luminescent layer being configured to provide light when the electrons impinge thereon, and a reflecting layer between the second substrate and the luminescent layer, the reflecting layer being configured to reflect the light from the luminescent layer toward the first substrate, wherein the cathode structure includes a first metal layer comprising a number of first metal lines and a second metal layer comprising a number of second metal lines, and wherein the first metal lines and the second metal lines are substantially orthogonal to each other.  
         [0007]     Some examples of the present invention may also provide a field emission device comprising a first substrate, a second substrate spaced apart from the first substrate, a first metal layer on the first substrate, the first metal layer including a number of first metal lines, a second metal layer over the first metal layer, the second metal layer including a number of second metal lines, emitters over the first metal layer, the emitters being configured to emit electrons toward the second substrate, a luminescent layer between the first substrate and the second substrate, the luminescent layer being configured to provide light when the electrons impinge thereon, and a third metal layer between the second substrate and the luminescent layer, the third metal layer being configured to reflect the light from the luminescent layer toward the first substrate, wherein the first metal lines are substantially parallel to the second metal lines.  
         [0008]     Examples of the present invention may further provide a field emission device comprising a number of first metal lines extending in parallel with one another on a substrate; a number of second metal lines extending in parallel with one another on the substrate, the number of second metal lines being interleaved with the number of first metal lines; a number of emitters each of which is arranged over one of the number of first metal lines, the number of emitters being configured to emit electrons toward a second substrate being spaced apart from the first substrate; a luminescent layer between the first substrate and the second substrate, the luminescent layer being configured to provide light when the electrons impinge thereon, and a reflecting layer between the second substrate and the luminescent layer, the reflecting layer being configured to reflect the light from the luminescent layer toward the first substrate.  
         [0009]     Additional features and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The features and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.  
         [0010]     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.  
         [0011]     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one example of the present invention and together with the description, serves to explain the principles of the invention. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0012]     The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings examples which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.  
         [0013]     In the drawings:  
         [0014]      FIG. 1  is a schematic cross-sectional diagram of a conventional field emission device;  
         [0015]      FIG. 2A  is a schematic cross-sectional diagram of a field emission device in accordance with an example of the present invention;  
         [0016]      FIG. 2B  is a schematic cross-sectional diagram of a luminescent layer of the field emission device illustrated in  FIG. 2A ;  
         [0017]      FIG. 2C  is a schematic cross-sectional diagram of a cathode structure of the field emission device illustrated in  FIG. 2A ;  
         [0018]      FIG. 3A  is a schematic cross-sectional diagram of a field emission device in accordance with another example of the present invention;  
         [0019]      FIG. 3B  is a top planar view of a cathode structure of the field emission device illustrated in  FIG. 3A ;  
         [0020]      FIG. 3C  is a top planar view of another cathode structure of the field emission device illustrated in  FIG. 3A ;  
         [0021]      FIG. 4A  is a schematic cross-sectional diagram of a field emission device in accordance with still another example of the present invention;  
         [0022]      FIG. 4B  is a top planar view of a cathode structure of the field emission device illustrated in  FIG. 4A ; and  
         [0023]      FIG. 5  is a schematic cross-sectional diagram of a field emission device in accordance with yet another example of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     In this detailed description, for purposes of explanation, numerous specific details are set forth to illustrate examples of the present invention. One skilled in the art will appreciate, however, that examples of the present invention may be practiced without these specific details. Furthermore, one skilled in the art can readily appreciate that the specific sequences in which methods are presented and performed are illustrative and it is contemplated that the sequences can be varied and still remain within the spirit and scope of embodiments of the present invention.  
         [0025]      FIG. 2A  is a schematic cross-sectional diagram of a field emission device  30  in accordance with an example of the present invention. Referring to  FIG. 2A , the field emission device  30  may include a first substrate  32 , a cathode structure  34 , a second substrate  42 , a reflecting layer  46  and a luminescent layer  44 . The reflecting layer  46  and the luminescent layer  44  may be collectively called an “anode structure”  50 . The first substrate  32  and the second substrate  42  may include, for example, glass substrates. The cathode structure  34  may function to emit electrons toward the luminescent layer  44 , which in turn provides luminescence when the emitted electrons impinge thereon. Light generated from the luminescent layer  44 , as indicated by straight arrow lines, may be reflected by the reflecting layer  46  toward the first substrate  32 , as indicated by curved arrow lines.  
         [0026]     In one example consistent with the present invention, the field emission device  30  may serve as an independent light source. In another example, the field emission device  30  may serve as a light source for a display device, for example, a liquid crystal display (“LCD”) device (not shown). The display device may be attached to the first substrate  32  of the field emission device  30  to receive the light emitted therefrom. The temperature at the first substrate  32  may be substantially equal to room temperature, and therefore does not adversely affect the performance of the attached display device. The field emission device  30  may further include a heat conductor  48 , for example, a heat sink, attached to the second substrate  42 . The heat conductor  48  may be arranged to discharge excessive heat generated at the second substrate  42 .  
         [0027]     The field emission device  30  may further include spacers  47  disposed between the anode structure  50  and the cathode structure  34  to maintain a predetermined spacing therebetween. The spacers  47  may be affixed to the anode structure  50  and the cathode structure  34  by using a glass fit sealant. An inter space region defined by the anode structure  50 , the cathode structure  34  and the spacers  47  may be maintained at a vacuum of approximately 10 −6  Torr to 10 −7  Torr to ensure continued accurate emission of electrons from the cathode structure  34 .  
         [0028]     In addition to reflecting the light from the luminescent layer  44 , the reflecting layer  46  may also serve as an electrode. In one example according to the present invention, the reflecting layer  46  may include a material selected from one of aluminum (Al), silver (Ag), platinum (Pt), gold (Au) and copper (Cu).  
         [0029]      FIG. 2B  is a schematic cross-sectional diagram of the luminescent layer  44  of the field emission device  30  illustrated in  FIG. 2A . Referring to  FIG. 2B , the luminescent layer  44  may include a number of sub-layers (not numbered) of phosphor particles. The sub-layers of phosphor particles may be formed on the reflecting layer  46  by for example, a screen printing process or a spin coating process. When the emitted electrons strike the phosphor particles, the luminescent layer  44  emits light. The thickness of the luminescent layer  44  may be approximately 5 micrometers (μm). Also referring to  FIG. 2A , each of the first substrate  32  and the second substrate  42  may be approximately 1.1 to 2.8 millimeters (mm), the cathode structure  34  may range from approximately 6 μm to 10 μm, and the reflecting layer  46  may range from approximately 0.3 μm to 0.5 μm in thickness. Moreover, the thickness of the heat conductor  48  may be approximately 7 mm to 12 mm, and the height of the spacers  47  may be approximately 1 mm to 4 mm.  
         [0030]      FIG. 2C  is a schematic cross-sectional diagram of the cathode structure  34  of the field emission device  30  illustrated in  FIG. 2A . Referring to  FIG. 2C , the cathode structure  34  may include a first metal layer  341 , an insulating layer  343 , a second metal layer  344  and emitters  345 . The first metal layer  341  may be comprised of a number of first metal lines extending in a first direction. The second metal layer  344  may be comprised of a number of second metal lines extending over the first metal lines in a second direction substantially orthogonal to the first direction.  
         [0031]     The first metal layer  341  may be formed over first substrate  32  with a metal such as chromium (Cr) by, for example, a deposition process followed by a photolithography process. In one example according to the present invention, a resistive layer  342  may optionally be formed over the first metal layer  341  with amorphous silicon in order to ensure uniform emission of electrons. The insulating layer  343  may include a dielectric material such as silicon dioxide (SiO 2 ). The second metal layer  344  may be formed over the first metal layer  341  with a metal such as Cr by, for example, a deposition process followed by a photolithography process. The second metal lines of the second metal layer  344  may be arranged at regular intervals. The emitters  345 , in the form of conical micro-tip formed of a metal such as molybdenum (Mo), may be located on the first metal lines within spaces defined by the intervals. The emitters  345  may be formed by a chemical vapor deposition (“CVD”) process, a plasma-enhanced chemical vapor deposition (“PECVD”) process, or other suitable chemical-physical deposition processes such as reactive sputtering, ion-beam sputtering and dual ion beam sputtering.  
         [0032]     The second metal layer  344  may be electrically connected to a relatively positive voltage source, while the first metal layer  341  may be electrically connected to a relatively negative voltage source. Thus, as a voltage is applied across the first metal layer  341  and the second metal layer  344 , electrons are emitted by the emitters  345 . The emitted electrons are accelerated toward the reflecting layer  46 , to which a voltage of, for example, several hundred to several thousand volts is applied. In one example according to the present invention, the voltage levels at first metal layer  341  and second metal layer  344  are approximately 0 volts and 100 to 200 volts, respectively. The reflecting layer  46  may be electrically connected to a power supply of approximately 1000 volts to 8000 volts.  
         [0033]      FIG. 3A  is a schematic cross-sectional diagram of a field emission device  50  in accordance with another example of the present invention. Referring to  FIG. 3A , the field emission device  50  may be similar to the field emission device  30  described and illustrated with reference to  FIG. 2C  except that, for example, a cathode structure  54  in place of the cathode structure  34 . Specifically, the cathode structure  54  may include a patterned first metal layer  541  on the first substrate  32 , a pedestal layer  543  over the first substrate  32 , a patterned second metal layer  544  on the pedestal layer  543 , and emitters  545 . The patterned second metal layer  544  may serve as a switch for the cathode structure  54  and function to switch on or switch off the emission of electrons from the emitters  545 . To facilitate the switch operation, the patterned second metal layer  544  may be disposed closer to the reflecting layer  46  then the emitters  545 . The pedestal layer  543 , which functions to serve as a pedestal, may raise the level of the patterned second metal layer  544  formed thereon. The pedestal layer  543  may include a number of pedestal units  553  extending over and orthogonal to the patterned first metal layer  541 . In one example, the pedestal layer  543  may include a patterned insulating layer made of, for example, silicon dioxide. The cathode structure  54  may optionally include a resistive layer  542  between the patterned first metal layer  541  and the emitters  545 .  
         [0034]      FIG. 3B  is a top planar view of the cathode structure  54  of the field emission device  50  illustrated in  FIG. 3A . Referring to  FIG. 3B , the patterned first metal layer  541  may include a number of first metal lines  551  extending in parallel with one another in a first direction. The pedestal layer  543  may then be formed over the patterned first metal layer  541 . The number of pedestal units  553  may be arranged one another at a predetermined interval not to interfere with the emission of electrons. Furthermore, the patterned second metal layer  544  may include a number of second metal lines  554  extending in parallel with one another in a second direction substantially orthogonal to the first direction. Each of the number of second metal lines  554  may be arranged on one of the number of pedestal units  553 . Each of the emitters  545  may be arranged on one the number of first metal lines  551  within the intervals defined by the number of pedestal units  553 .  
         [0035]     In one example according to the present invention, the patterned first metal layer  541 , the pedestal layer  543  and the patterned second metal layer  544  may be formed by a screen printing process or other suitable processes such as a photolithography process and an electrophoretic deposition (EPD) process. Furthermore, the optional resistive layer  542  and the emitters  545  may also be formed by one of the screen printing, photolithographic and EPD process. Each of the first metal lines  551  may have a length of approximately 230 mm to 360 mm and a width of approximately 100 to 200 μm. Each of the second metal lines  554  may have a length of approximately 230 to 360 mm and a width of approximately 80 to 160 μm. Furthermore, each of the emitters  545  may have a width ranging from approximately 80 to 180 μm but the width may vary as the size of the first and second metal lines  551  and  554  vary in other applications.  
         [0036]      FIG. 3C  is a top planar view of another cathode structure  54 - 1  of the field emission device  50  illustrated in  FIG. 3A . Referring to  FIG. 3C , the cathode structure  54 - 1  may be similar to the cathode structure  54  described and illustrated with reference to  FIG. 3B  except that, for example, a number of second metal lines  564  in place of the number of second metal lines  554 . Specifically, each of the number of second metal lines  564  may include a number of windows  555 , each of which may expose one of the emitters  545  arranged on (in the absence of the resistive layer  542 ) or over (in the presence of the resistive layer  542 ) the number of first metal lines  541 . The number of windows  555  may be formed in the same photolithographic process for forming the number of second metal lines  544 .  
         [0037]      FIG. 4A  is a schematic cross-sectional diagram of a field emission device  60  in accordance with still another example of the present invention. Referring to  FIG. 4A , the field emission device  60  may be similar to the field emission device  50  described and illustrated with reference to  FIG. 3A  except that, for example, a cathode structure  64  in place of the cathode structure  54 . Specifically, the cathode structure  64  may include a number of first metal lines  641  on the first substrate  32 , a number of pedestal units  643  arranged on the first substrate  32  and interleaved with the number of first metal lines  641 , a number of second metal lines  644  each being arranged on one of the number of pedestal units  643 , and a number of emitters  645  over the first metal lines  641 . The first metal lines  641  and the second metal lines  644  may extend in parallel with each other. Furthermore, the second metal lines  644  may be disposed closer to the reflecting layer  46  then the emitters  645  and in turn the first metal lines. In one example, each of the number of pedestal units  643  may include an insulating material. In another example, each of the number of pedestal units  643  may include a metal material, which may include substantially the same material, for example, Cr, as the first and second metal lines  641  and  644 . The cathode structure  64  may optionally include a number of resistive units  642  each of which may be provided between one of the first metal lines  641  and one of the emitters  645 .  
         [0038]      FIG. 4B  is a top planar view of the cathode structure  64  of the field emission device  60  illustrated in  FIG. 4A . Referring to  FIG. 4B , the second metal lines  644  may extend above and in parallel with the first metal lines  641 . As compared to the cathode structure  54  illustrated in  FIG. 3A , the cathode structure  64  with the first and second lines  641  and  644  extending in substantially the same direction may enhance flux of the reflected light at the first substrate  32 .  
         [0039]      FIG. 5  is a schematic cross-sectional diagram of a field emission device  70  in accordance with yet another example of the present invention. Referring to  FIG. 5 , the field emission device  70  may be similar to the field emission device  60  described and illustrated with reference to  FIG. 4A  except that, for example, a cathode structure  74  in place of the cathode structure  64 . Specifically, the cathode structure  74  may include a number of first metal lines  741  on the first substrate  32 , a number of second metal lines  744  arranged on the first substrate  32  and interleaved with the number of first metal lines  741 , and a number of emitters  745  over the first metal lines  741 . The first metal lines  741  and the second metal lines  744  may extend in parallel with each other. In one example according to the present invention, the number of first metal lines  741  and the number of second metal lines  744  may be fabricated simultaneously by, for example, one of a screen printing, photolithography and EPD process. Furthermore, the cathode structure  74  may optionally include a number of resistive units  742  each of which may be provided between one of the first metal lines  741  and one of the emitters  745 .  
         [0040]     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.  
         [0041]     Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.