Abstract:
The present invention relates to an AC light emitting diode. An object of the present invention is to provide an AC light emitting diode wherein various designs for enhancement of the intensity of light, prevention of flickering of light or the like become possible, while coming out of a unified method of always using only one metal wire with respect to one electrode when electrodes of adjacent light emitting cells are connected through metal wires. To this end, the present invention provides an AC light emitting diode comprising a substrate; bonding pads positioned on the substrate; a plurality of light emitting cells arranged in a matrix form on the substrate; and a wiring means electrically connecting the bonding pads and the plurality of light emitting cells, wherein the wiring means includes a plurality of metal wires connecting an electrode of one of the light emitting cells with electrodes of other electrodes adjacent to the one of the light emitting cells.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a U.S. national phase application of PCT International Application No. PCT/KR2006/003016, filed Aug. 1, 2006, which claims priority to Korean Patent Application No. 2005-0072828, filed Aug. 9, 2005 and Korean Patent Application No. 2005-0076874, filed Aug. 22, 2005, the contents of which are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to an AC (alternating current) light emitting diode including a plurality of light emitting cells arranged in a matrix form and a method of fabricating the same. 
       BACKGROUND OF THE INVENTION 
       [0003]    A light emitting diode, which is a photoelectric conversion device having a structure in which an N-type semiconductor and a P-type semiconductor are joined together, emits light through recombination of electrons and holes. Such light emitting diodes have been widely used as display devices and backlights. Further, since the light emitting diode has less electric power consumption and a longer lifetime as compared with a conventional light bulb or fluorescent lamp, the light emitting diode is substituted for a conventional incandescent bulb or fluorescent lamp and has been widely used for the purpose of general illumination. 
         [0004]    The light emitting diode is repeatedly turned on/off depending on the direction of a current under an AC power source. Thus, in a case where the light emitting diode is used while connected directly to the AC power source, there is a problem in that the light emitting diode does not continuously light and may easily be damaged by a reverse direction current. 
         [0005]    To solve such a problem of the light emitting diode, a light emitting diode that can be used by connecting it directly to a high-voltage AC power source has been disclosed in PCT No. WO2004/023568(A1), entitled “LIGHT-EMITTING DEVICE HAVING LIGHT-EMITTING ELEMENTS” by SAKAI et al. 
         [0006]    According to disclosed PCT No. WO2004/023568(A1), light emitting cells are two-dimensionally connected in series on an insulation substrate such as a sapphire substrate through metal wires to form LED arrays. Such two LED arrays are in reverse parallel on the substrate. As a result, the arrays are repeatedly turned on/off alternately by an AC power supply to emit light. 
         [0007]    However, since the disclosed conventional technology is implemented through a unified method in which only one metal wire is always used with respect to one electrode when connecting electrodes of the adjacent light emitting cells through metal wires, various designs of AC light emitting diodes for enhancement of the intensity of light, prevention of flickering of light or the like have been limited. 
         [0008]    As an example, if the conventional unified wire connection method is used in a case where the light emitting cells are arranged to constitute a matrix and an additional means for enhancing the intensity of light or the like is added as a portion of the elements of the matrix, there may be many difficulties in connecting the metal wires while avoiding the element added as the element of the matrix. Even though it is possible, there may be caused a problem in that the total length of the metal wires becomes extremely long. 
         [0009]    Further, the disclosed conventional technology is configured such that the light emitting cells in the same line are repeatedly turned on/off at the same time, so that continuous and uniform light is not emitted from the substrate and thus flickering arises. In a case where the light emitting diode is used for a long time, such flickering may be a major cause for making human eyes fatigued although the flickering is not observed with naked eyes. The present inventors have conducted various studies for minimizing the aforementioned flickering, and found that the conventional unified wire connection method of using only one metal wire with respect to one electrode becomes a large obstacle in the implementation of a technique for minimizing the flickering. 
         [0010]    An object of the present invention is to provide an AC light emitting diode wherein adaptable designs for enhancement of the intensity of light, prevention of flickering of light or the like become possible, while breaking from the conventional method of always using only one metal wire with respect to one electrode when electrodes of adjacent light emitting cells are connected through metal wires. 
         [0011]    Another object of the present invention is to provide an AC light emitting diode wherein it is easier to employ a means such as a light guide portion for improvement of the intensity of light, while breaking from the conventional method of always using only one metal wire with respect to one electrode when electrodes of adjacent light emitting cells among light emitting cells arranged as elements of a matrix are connected through metal wires. 
         [0012]    A further object of the present invention is to provide an AC light emitting diode wherein it is possible to solve disadvantages of the conventional technology, such as flickering of light, while breaking from the conventional method of always using only one metal wire with respect to one electrode when at least a pair of arrays are configured with light emitting cells arranged as elements of a matrix. 
         [0013]    According to an aspect of the present invention, there is provided an AC light emitting diode comprising: a substrate; bonding pads positioned on the substrate; a plurality of light emitting cells arranged in a matrix form on the substrate; and a wiring means electrically connecting the bonding pads and the plurality of light emitting cells, wherein the wiring means at least includes a plurality of metal wires connecting an electrode of one of the light emitting cells with electrodes of other light emitting cells adjacent to the one of the light emitting cells. 
         [0014]    Preferably, each of the plurality of light emitting cells has first and second electrodes of a P-type an N-type, a light emitting cell adjacent to two light emitting cells among the plurality of light emitting cells has a first electrode connected to a second electrode of one of the adjacent two light emitting cells through a metal wire, and a second electrode connected to a first electrode of the other of the adjacent two light emitting cells through another metal wire. Wherein, if first electrodes are P-type, then second electrodes are N-type. However, if first electrodes are N-type, then second electrodes are P-type. 
         [0015]    Preferably, each of the plurality of light emitting cells has first and second electrodes of a P-type and an N-type, a light emitting cell adjacent to three light emitting cells among the plurality of light emitting cells has a first electrode connected to a second electrode of one of the adjacent three light emitting cells through a metal wire, and a second electrode connected to first electrodes of the others of the adjacent three light emitting cells through other two metal wires. 
         [0016]    Preferably, each of the plurality of light emitting cells has first and second electrodes of a P-type and an N-type, a light emitting cell adjacent to four light emitting cells among the plurality of light emitting cells has a first electrode connected to first electrodes of two of the adjacent four light emitting cells through two metal wires, and a second electrode connected to second electrodes of the others of the adjacent four light emitting cells through other two metal wires. 
         [0017]    Preferably, the AC light emitting diode according to the aspect of the present invention, further comprises light guide means further formed as an element of the matrix to focus light emitted from the plurality of light emitting cells adjacent to the at least light guide portion and to radiate the light to the outside. More preferably, the light guide means consists of a plurality of light guide portions regularly arranged at a predetermined interval. 
         [0018]    According to another aspect of the present invention, there is provided an AC light emitting diode comprising: a substrate; bonding pads positioned on the substrate; a plurality of light emitting cells arranged as elements of a matrix on the substrate; and a wiring means electrically connecting the bonding pads and the plurality of light emitting cells, wherein the wiring means at least includes two metal wires connecting an electrode of one of the light emitting cells with electrodes of other light emitting cells adjacent to the one of the light emitting cells, and the plurality of light emitting cells include at least a pair of arrays of first and second arrays, and the two metal wires comprise a metal wire connecting the same kinds of electrodes of adjacent two of the light emitting cells provided in the same first or second array and a metal wire connecting first and second electrodes of adjacent two of the light emitting cells respectively provided in the first and second arrays. 
         [0019]    According to the present invention, there is an advantage in that it is possible to design a variety of AC light emitting diodes for enhancing the intensity of light or minimizing flickering of light through a configuration of connecting one electrode of a light emitting cell as an element of a matrix to electrodes of other light emitting cells adjacent to the light emitting cell or to other matrix elements through two metal wires. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0020]      FIGS. 1 to 4  are views illustrating arrangements of metal wiring that can be applied to an AC light emitting diode according to the present invention; 
           [0021]      FIG. 5  is a circuit diagram of an AC light emitting diode according to a first embodiment of the present invention; 
           [0022]      FIG. 6  is a plan view of the AC light emitting diode according to the first embodiment of the present invention; 
           [0023]      FIG. 7  is a sectional view taken along line A-A in  FIG. 6 ; 
           [0024]      FIG. 8  is a sectional view taken along line B-B in  FIG. 6 ; 
           [0025]      FIGS. 9 and 10  are sectional views illustrating various forms of light guide portions that may be used in the first embodiment of the present invention; 
           [0026]      FIGS. 11 to 14  are sectional views illustrating a method of fabricating the AC light emitting diode shown in  FIGS. 5 to 10 ; 
           [0027]      FIG. 15  is a circuit diagram of an AC light emitting diode according to a second embodiment of the present invention; and 
           [0028]      FIG. 16  is a plan view of the AC light emitting diode according to the second embodiment of the present invention. 
       
    
    
       [0029]    Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       DETAILED DESCRIPTION 
       [0030]      FIGS. 1 to 4  are views illustrating arrangements of metal wiring that can be used in connection between electrodes of light emitting cells in an AC light emitting diode according to the present invention. As shown in  FIGS. 1 to 4 , each of light emitting cells  200  is formed with N-type and P-type electrodes  50   a  and  50   b , which are connected to electrodes of other light emitting cells (not shown) adjacent to the light emitting cell  200  through metal wires  400 , respectively. In the descriptions of  FIGS. 1 to 4 , the N-type electrode  50   a  is referred to as a first electrode  50   a  and the P-type electrode  50   b  is referred to as a second electrode  50   b  for convenience of illustration. Further, the term adjacent elements used throughout the specification indicate only elements adjacent left and right or above and below and not elements adjacent diagonally. 
         [0031]    Referring to  FIG. 1 , a metal wire  400  is connected to a first electrode  50   a  of one of the light emitting cells  200 , and another metal wire  400  is also connected to a second electrode  50   b  thereof. The arrangement of such metal wires  400  and  400  are usefully utilized in connecting the first and second electrodes  50   a  and  50   b  of the one of the light emitting cells  200  adjacent to two light emitting cells among the plurality of light emitting cells constituting a matrix to electrodes of the adjacent light emitting cells. At this time, in a case where there is a bonding pad  300   a  or  300   b  (see  FIGS. 5 and 6 ) among the elements of the matrix, which will be described in detail below, one of the metal wires  400  and  400  respectively connected to the first and second electrodes  50   a  and  50   b  can be connected to the bonding pad adjacent to the light emitting cell  200 . 
         [0032]    Referring to  FIG. 2 , a metal wire  400  is connected to a second electrode  50   b  of one of the light emitting cells  200 , while two metal wires  400  and  400  are connected to a first electrode  50   a  thereof. The two metal wires  400  and  400  are used in respectively connecting the first electrode  50   a  provided in the one of the light emitting cells  200  to electrodes of other two light emitting cells adjacent to the one of the light emitting cells  200  or to an electrode of one of the two light emitting cells adjacent to the one of the light emitting cells  200  and a bonding pad. 
         [0033]    Referring to  FIG. 3 , a metal wire  400  is connected to a first electrode  50   a  of one of the light emitting cells  200 , while two metal wire  400  and  400  are connected to a second electrode  50   b  thereof. The two metal wires  400  and  400  are used in respectively connecting the second electrode  50   b  provided in the one of the light emitting cells  200  to electrodes of other two light emitting cells adjacent to the one of the light emitting cells  200  or to an electrode of one of the two light emitting cells adjacent the one of the light emitting cells  200  and a bonding pad. 
         [0034]    Since the arrangements of the metal wiring shown in  FIGS. 2 and 3  are those in which two metal wires  400  and  400  are connected from an electrode (first or second electrode) of the one of the light emitting cells  200  and a metal wire  400  is connected from the other electrode, the arrangements may be preferably used in connection of the metal wiring when the light emitting cells  200  are arranged as elements of a matrix and adjacent to three matrix elements (light emitting cells, or a light emitting cell and a bonding pad). 
         [0035]    Similarly to the arrangements shown  FIGS. 2 and 3 , also in  FIG. 4 , there is shown the arrangement of the metal wiring in which two metal wires  400  and  400  are connected to each electrode of a light emitting cell  200 . In the arrangement of the metal wiring shown in  FIG. 4 , two metal wires are connected to each of two electrodes of one of the light emitting cells  200 , i.e., each of first and second electrodes  50   a  and  50   b . The metal wires of which two are connected to each of the first and second electrodes  50   a  and  50   b , i.e. all four metal wires are connected to matrix elements adjacent to the one of the light emitting cells  200  above, below, left and right, respectively. Further, in a case where the adjacent matrix element is a light emitting cell, the metal wire  400  is connected to an electrode of the light emitting cell, and in a case where the adjacent matrix element is a bonding pad, the metal wire  400  is connected to the bonding pad itself. 
         [0036]    An AC light emitting diode according to a first embodiment of the present invention that can be obtained through the arrangements of the metal wiring shown  FIGS. 1 to 4 , is shown in  FIGS. 5 and 6  respectively as a circuit diagram and a plan view. In  FIG. 6 , the arrangements of the metal wires shown in  FIGS. 1 to 4  are formed in circles C″, D″, E″, and F″ respectively. 
         [0037]    That is, in circle C″ of  FIG. 6  is shown an arrangement in which a metal wire  400  is connected to each of first and second electrodes  50   a  and  50   b  of one of the light emitting cells  200 , and the respective metal wires  400  are connected to second and first electrodes  50   b  and  50   a  of other light emitting cells adjacent to the one of the light emitting cells  200 . In circle D″ of  FIG. 6  is shown an arrangement in which two metal wires  400  and  400  connected to a first electrode  50   a  of one of the light emitting cells  200  are respectively connected to second electrodes  50   b  and  50   b  of two light emitting cells adjacent to the one of the light emitting cells  200 , and a metal wire  400  connected to a second electrode  50   b  of the one of the light emitting cells  200  is connected to a first electrode  50   a  of another light emitting cell adjacent to the one of the light emitting cells  200 . In circle E″ of  FIG. 6  is shown an arrangement in which two metal wires  400  and  400  connected to a second electrode  50   b  of one of the light emitting cells  200  are respectively connected to first electrodes  50   a  and  50   a  of two light emitting cells adjacent to the one of the light emitting cells  200 , and a metal wire  400  connected to a first electrode  50   a  of the one of the light emitting cells  200  is connected to a second electrode  50   b  of another light emitting cell  200  adjacent to the one of the light emitting cells  200 . In circle F″ of  FIG. 6  is shown an arrangement in which two metal wires connected to a second electrode  50   b  of one of the light emitting cells  200  are respectively connected to first electrodes  50   a  and  50   a  of two light emitting cells adjacent to the one of the light emitting cells  200 , and two metal wires connected to a first electrode  50   a  of the one of the light emitting cells  200  are respectively connected to second electrodes  50   b  and  50   b  of other two light emitting cells adjacent to the one of the light emitting cells  200 . At this time, although the first electrode  50   a  is shown as if it is shown as two in F of  FIG. 6 , it should be noted that the first electrode  50   a  is practically one identical electrode. 
         [0038]    As shown in  FIGS. 5 and 6 , the AC light emitting diode according to this embodiment comprises a substrate  100 , light emitting cells  200 , first and second bonding pads  300   a  and  300   b , metal wires  400 , and light guide portions  500 . 
         [0039]    The substrate  100  may be made of a sapphire or material such as SiC with thermal conductivity larger than a sapphire, and the plurality of patterned light emitting cells  200  are formed on the substrate  100 . 
         [0040]      FIG. 7  is a sectional view taken along line A-A in  FIG. 6 . Referring to  FIG. 7 , each of the light emitting cells  200  forms a structure in which an N-type semiconductor layer  31 , an active layer  32  and a P-type semiconductor layer  33  are sequentially laminated. The active layer  32  is formed on a portion of the N-type semiconductor layer  31 , and the P-type semiconductor layer  33  is formed on the active layer  32 . Thus, the portion of a top surface of the N-type semiconductor layer  31  is joined with the active layer  32 , and the other portion of the top surface is exposed to the outside. 
         [0041]    Referring back to  FIGS. 5 and 6 , the light emitting cells  200  are arranged between the first and second bonding pads  300   a  and  300   b  in the form of a matrix, e.g., a square matrix. 
         [0042]    The first and second bonding pads  300   a  and  300   b  are to connect a light emitting diode  1  to an external power source through the metal wires  400 . The first and second bonding pads  300   a  and  300   b  may be connected to the external power source through bonding wires (not shown). 
         [0043]    The metal wires  400  electrically connect the light emitting cells  200 . Each of the metal wires  400  connects a first electrode  50   a  of one of the light emitting cells  200  to a second electrode  50   b  of another light emitting cell  200  adjacent to the corresponding light emitting cell  200 , so that P-type and N-type semiconductor layers  33  and  31  of the adjacent light emitting cells  200  are electrically connected to each other. Also, each of the metal wires  400  electrically connects a first or second electrode  50   a  or  50   b  of one of the light emitting cells  200  to the first or second bonding pad  300   a  or  300   b  adjacent to the corresponding light emitting cell  200  thereby to supply power to the light emitting diode  1 . 
         [0044]    Some of the metal wires  400  connect first and second electrodes  50   a  and  50   b  of one of the light emitting cells  200  positioned at an intersection where a row and a column meet each other to second and first electrodes  50   b  and  50   a  of light emitting cells adjacent to the one of the light emitting cells  200 , respectively. Also, some of the metal wires  400  electrically connect the bonding pad  300   a  or  300   b  positioned at an intersection where a row and a column meet each other to first and second electrodes  50   a  and  50   b  of light emitting cells adjacent to the one of the light emitting cells  200 . 
         [0045]    Particularly, one of the light emitting cells  200  positioned adjacent to two matrix elements among the light emitting cells  200  has a first electrode  50   a  electrically connected to a second electrode  50   b  of a light emitting cell  200  adjacent to the one of the light emitting cells  200  or the bonding pad  300   a  or  300   b , and a second electrode  50   b  electrically connected to a first electrode  50   a  of another light emitting cell  200  adjacent to the one of the light emitting cells  200  or the bonding pad  300   a  or  300   b.    
         [0046]    In the matrix arrangement, two of the metal wires  400  are required in a case where the number of matrix elements (except light guide portions) positioned adjacent to one of the light emitting cells  200  is two. A first electrode  50   a  of one of a light emitting cell  200  should be connected to a second electrode  50   b  of another of the light emitting cells  200  for the purpose of operating a diode. Thus, there is only the same arrangement of the metal wiring as shown in  FIG. 1 . 
         [0047]    In the matrix arrangement, in a case where the number of matrix elements (except light guide portions) positioned adjacent to one of the light emitting cells is three, a first electrode  50   a  of the corresponding light emitting cell  200  may be connected to any one of a second electrode  50   b  of a light emitting cell  200  adjacent to the corresponding light emitting cell  200  and the bonding pad  300   a  or  300   b  through a metal wire  400 , and a second electrode  50   b  of the corresponding light emitting cell  200  may be connected to first electrodes  50   a  of two light emitting cells  200  adjacent to the corresponding light emitting cell  200  or a first electrode  50   a  of a light emitting cell adjacent to the corresponding light emitting cell  200  and the bonding pad  300   a  or  300   b  through two metal wires  400  and  400 . 
         [0048]    Further, in a case where the number of matrix elements (except light guide portions) positioned adjacent to one of the light emitting cells is three as described above, a first electrode  50   a  of the corresponding light emitting cell  200  may be electrically connected to second electrodes  50   b  of two light emitting cells  200  adjacent to the corresponding light emitting cell  200  or a second electrode  50   b  of a light emitting cell adjacent to the corresponding light emitting cell  200  and the bonding pad  300   a  or  300   b  through two metal wires  400  and  400 , and a second electrode  50   a  of the corresponding light emitting cell  200  may be electrically connected to any one of a second electrode  50   b  of another light emitting cell  200  adjacent to the one of the light emitting cells  200  and the bonding pad  300   a  or  300   b  through one metal wire  400 . 
         [0049]    That is, in the matrix arrangement, in a case where the number of matrix elements (except light guide portions) positioned adjacent to a light emitting cell is three, the aforementioned three metal wires  400  for the corresponding light emitting cell are required for the purpose of operating a diode (see  FIGS. 2 and 3 ). 
         [0050]    Also, a first electrode  50   a  of one of the light emitting cells  200  positioned adjacent to four of the light emitting cells  200  is electrically connected to second electrodes  50   b  of two of the four light emitting cells  200  adjacent to the corresponding light emitting cell  200 , and a second electrode  50   b  of the corresponding light emitting cell is electrically connected to first electrodes  50   a  of the other two light emitting cells  200  adjacent thereto. In addition, a first electrode  50   a  of one of the light emitting cells  200  positioned adjacent to three of the light emitting cells  200  and one of the bonding pads  300   a  and  300   b  is electrically connected to second electrodes  50   b  of two of the three light emitting cells  200  adjacent to the corresponding light emitting cell  200 , and a second electrode  50   b  of the corresponding light emitting cell is electrically connected to a first electrode  50   a  of another light emitting cell  200  adjacent thereto and the bonding pad  300   a  or  300   b ; alternatively, the first electrode  50   a  of the corresponding light emitting cell  200  is electrically connected to a second electrode  50   b  of one of the three light emitting cells  200  adjacent to the corresponding light emitting cell  200  and the bonding pad  300   a  or  300   b , and the second electrode  50   b  of the corresponding light emitting cell is electrically connected to first electrodes  50   a  of the other two light emitting cells  200  adjacent to the corresponding light emitting cell  200 . 
         [0051]    In the matrix arrangement, in a case where the number of matrix elements (except light guide portions) positioned adjacent to one of the light emitting cells is four, a pair of metal wires are required for each electrode of the corresponding light emitting cell  200 , that is a total of four metal wires  400  are required, and a first electrode  50   a  of the corresponding light emitting cell  200  should be connected to second electrodes  50   b  of other light emitting cells  200  for the purpose of operating a diode (see  FIG. 4 ). 
         [0052]    The light guide portions  500  are formed to be arranged together with the light emitting cells  200  and the bonding pads  300   a  and  300   b  in a matrix form, and function to guide light emitted from a plurality of the light emitting cells  200 , which are positioned adjacent to the light guide portions  500 , to be focused and radiated to the outside. Particularly, it is preferred that the light guide portions  500  be regularly arranged to be spaced apart from each other at predetermined intervals and thus a fabricating process of the light emitting diode  1  can be simplified and fabricating costs can be reduced. 
         [0053]    It will be apparent that a shape of the light guide portion  500  as viewed from above may have an angled shape such as a quadrangle or pentagon although it is a circle as shown in  FIG. 6 . 
         [0054]    Referring back to  FIG. 7 , the light emitting cells  200  spaced apart from one another are positioned on the substrate  100 . Each of the light emitting cells  200  comprises the N-type semiconductor layer  31 , the P-type semiconductor layer  33  positioned over a portion of the N-type semiconductor layer  31 , and the active layer  32  interposed between the N-type and P-type semiconductor layers  31  and  33 . Here, the N-type semiconductor layer  31  serves as a first electrode  50   a . Meanwhile, a second electrode  50   b  is formed on the P-type semiconductor layer  33 . The second electrode  50   b  may be a transparent electrode layer  40  through which light can be transmitted. The light emitting cells  200  may be formed by forming the respective semiconductor layers  30  and the transparent electrode layer  40  on the substrate  100  and then patterning them using a photo and etching process. An electrode pad  60   b  may be formed on the other portion of the N-type semiconductor layer  31 , and an electrode pad  60   a  may be formed on the second electrode  40 . The electrode pads  60   a  and  60   b  may be formed at a desired position using a lift-off technique. The metal wires  400  may be formed together using an air-bridge or step-cover process. 
         [0055]      FIG. 8  is a partial sectional view taken along line B-B in  FIG. 6 . Referring to  FIG. 8 , the light emitting cells  200  spaced apart from each other are positioned on the substrate  100 , and one of the light guide portions  500  is positioned between the light emitting cells  200 . The light emitting cells  200  have the same configuration as the light emitting cells  200  shown in  FIG. 7 . The light guide portion  500  may be formed by forming the semiconductor layers  30  and the transparent electrode layer  40  and then etching a central portion thereof such that the substrate  100  is exposed. The light guide portion  500  may be etched such that the central portion has a slope with respect to the substrate  100  as shown in  FIG. 9  or becomes vertical to the substrate  100  as shown in  FIG. 10 . The light guide portion  500  serves to guide the collected light in a predetermined direction, e.g., a vertical direction to the substrate, after collecting the light emitted from the light emitting cells  200  adjacent to the light guide portion  500 . 
         [0056]    If only the light emitting cells  200  are arranged without the light guide portions  500  in a case where the light emitting cells  200  are arranged in rows and columns, e.g., a two-dimensional square shape, the luminance of light progressing in the horizontal direction with respect to the substrate  100  among the light emitted from the light emitting cells  200  is decreased as the light passes through the light emitting cells  200  adjacent thereto, so that the entire light emitting efficiency of the light emitting diode  1  is lowered. Accordingly, the light guide portions  500  are arranged at predetermined intervals to collect light incident in the horizontal direction from the light emitting cells  200  adjacent thereto the light guide portions  500  and to radiate the light in the vertical direction as shown in  FIGS. 5 and 6 , thereby enhancing the light emitting efficiency of the light emitting diode  1 . 
         [0057]    In addition, a light reflection prevention layer  70  may be formed in the light guide portion  500  by coating the light guide portion  500  with a light reflection prevention substance for enhancing the light transmittance of the light guide portion  500 . Preferably, the thickness of the light reflection prevention layer is /4n. Here, is a wavelength of light incident from the light emitting cell adjacent to the light guide portion, and n is a refractive index of the light reflection prevention substance. Preferably, the light reflection prevention substance is to have a refractive index of 1.3 to 1.7. For example, the light reflection prevention substance may be SiO 2 , Al 2 O 3  or Si 3 N 4 . The light reflection prevention layer  70  may be formed by sputtering the light reflection prevention substance on the light guide portion  500 . 
         [0058]    A method of fabricating the aforementioned AC light emitting diode will be described below with reference to  FIGS. 11 to 14 . 
         [0059]    Referring to  FIG. 11 , a buffer layer  20  is formed on the substrate  100 , and then the N-type semiconductor layer  31 , the active layer  32 , the P-type semiconductor layer  33  and the transparent electrode  40  are sequentially laminated on the buffer layer  20 . The buffer layer  20  and the semiconductor layers  30  may be formed using a metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) or hydride vapor phase epitaxy (HVPE) technique. Further, the semiconductor layers  30  may be consecutively formed in the same process chamber. Although the buffer layer  20  may be formed of an insulation substance film such as an AlN or semi-insulation GaN layer, it may also be made of a conductive substance film such as an N-type GaN layer if necessary. The transparent electrode layer  40  may be a transparent electrode layer made of Ni/Au or indium tin oxide (ITO). 
         [0060]    Referring to  FIG. 12 , after the transparent electrode layer  40  is formed, the semiconductor and transparent electrode layers  30  and  40  are patterned using photo and etching processes, thereby forming semiconductor patterns  200  and  500  arranged in a matrix form and spaced apart from one another. 
         [0061]    Referring to  FIG. 13 , after the semiconductor patterns  200  and  500  are formed, the P-type semiconductor layer  33  and the active layer  32  are patterned in the form of semiconductor patterns to be fabricated as light emitting cells  200  among the semiconductor patterns  200  and  500  using photo and etching processes such that a portion of a top of the N-type semiconductor layer  31  is exposed. Thereafter, by performing a patterning process on semiconductor patterns to be fabricated as a light guide portion  500  among the semiconductor patterns  200  and  500 , the light guide portion  500  is formed which has an outer circumferential portion on which light is incident from the light emitting cells  200  adjacent to the light guide portion  500  and an inner circumferential portion for guiding the incident light to be radiated in a predetermined direction. Then, an electrode pad  60   b  (see  FIG. 7 ) is formed on the exposed N-type semiconductor layer  31 . The electrode pad  60   b  may be formed using a lift-off method. Thereafter, the electrode pads  60   b  and  60   a  (see  FIG. 7 ) of the light emitting cells adjacent to each other are connected through the metal wires  400 . The metal wires  400  may be formed through an air-bridge or step-cover process. 
         [0062]    Referring to  FIG. 14 , after the light guide portion  500  is formed, a light reflection prevention layer  70  covering the surface of the light guide portion except the outer circumferential portion is formed by sputtering a light reflection prevention substance on the light guide portion  500  in order to increase the light transmittance of light incident on the light guide portion  500 . The light reflection prevention substance may be SiO 2 , Al 2 O 3  or Si 3 N 4 , and the thickness of the light reflection prevention layer  70  may be /4n. Here, is a wavelength of light incident from the light emitting cell  200  adjacent to the light guide portion, and n is a refractive index of the light reflection prevention substance. 
         [0063]    Although it has been described in the aforementioned embodiment that the light guide portion  500  is formed after the transparent electrode layer  40  is formed, it will be apparent that the light guide portion  500  may be formed after the semiconductor layers  30  are formed. 
         [0064]    Hereinafter, an AC light emitting device according to a second embodiment of the present invention will be described with reference to  FIGS. 15 and 16 . The same components as the aforementioned first embodiment of the present invention, i.e., the substrate, the first and second electrodes, and the first and second bonding pads will use like reference numerals used in the aforementioned first embodiment of the present invention. However, the reference numerals of metal wires will be used by dividing them into “ 400   a ” “ 400   b ” “ 400   c ” “ 400   d ” and “ 400   e ” depending on use contrary to the aforementioned embodiment. The second embodiment of the present invention will be completed by employing the configuration in which an electrode of one of the light emitting cells is connected to electrodes of other two light emitting cells adjacent to the one of the light emitting cells  200  through two metal wires as shown in  FIGS. 2 and 3 . 
         [0065]    Referring to  FIGS. 15 and 16 , the AC light emitting diode  1  of this embodiment has at least a pair of first and second arrays  11  and  13  of light emitting cells  200 . Here, two pairs of the arrays  11  and  13  are shown. Such a pair of arrays are aligned to be adjacent to each other. 
         [0066]    Metal wires  400   a  and  400   b  shown in  FIG. 16  electrically connect the light emitting cells  200  arranged between the light emitting cells at both ends of each of the arrays. At this time, the metal wires  400   a  and  400   b  electrically connect first and second electrodes  50   a  and  50   b  of one of the light emitting cells to a first electrode  50   a  of one of two light emitting cells adjacent to the one of the light emitting cells  200  and a second electrode  50   b  of the other of the two light emitting cells adjacent thereto, so that the light emitting cells in each of the arrays are connected to one another. 
         [0067]    The metal wires  400   b  for connecting the second electrodes of the first array  11  are adjacent to the metal wires  400   a  for connecting the first electrodes of the second array  13 , and the metal wires  400   a  for connecting the first electrodes of the first array  11  are adjacent to the metal wires  400   b  for connecting the second electrodes of the second array  13 . 
         [0068]    As well shown in  FIG. 16 , the light emitting cells  200  are arranged so that facing electrodes of adjacent two of the light emitting cells  200  provided in the same array  11  or  13  are the same kind as the first electrode  50   a  or the second electrode  50   b , and facing electrodes of adjacent two of the light emitting cells respectively provided in the first and second arrays  11  and  13  are different kinds from each other as the first and second electrodes  50   a  and  50   b . Such arrangements enable the total length of the metal wires to be reduced and the metal wires to be easily connected. 
         [0069]    For example, in a case where one of the light emitting cells  200  has the second and first electrodes  50   b  and  50   a  sequentially formed along the first array  11 , the two light emitting cells adjacent to the one of the light emitting cells  200  in the same array  11  respectively have the first and second electrodes  50   a  and  50   b  sequentially formed along the first array  11 . Accordingly, the length of the metal wires  400   a  and  400   b  connecting the light emitting cells  200  in the same array can be reduced. Further, the light emitting cells of the second array  13  adjacent to the first array  11  are arranged in the opposite direction of the light emitting cells of the first array  11 . That is, a light emitting cell  200  of the second array  13 , which is adjacent to a light emitting cell  200  of the first array  11  that has the first and second electrodes  50   a  and  50   b  in turn along the first array  11 , are arranged to have the second and first electrodes  50   b  and  50   a  in turn along the second array  13 . 
         [0070]    Meanwhile, metal wires  400   c  and  400   d  electrically connect the wiring connections between the first electrodes  50   a  and  50   a  of the first array  11  to the adjacent wiring connections between the second electrodes  50   b  and  50   b  of the second array  13 , respectively, and electrically connect the wiring connections between the second electrodes  50   b  and  50   b  of the first array  11  to the adjacent wiring connections between the first electrodes  50   a  and  50   a  of the second array  13 , respectively. For the electrical connection between the aforementioned wiring connections, the metal wires  400   c  and  400   d  connect the first and second electrodes  50   a  and  50   b  of each of the light emitting cells  200  of the first array  11  to the adjacent second and first electrodes  50   b  and  50   a  of each of the light emitting cells of the second array  13 , respectively. More specifically, the first electrode  50   a  of one of the light emitting cells of the first array  11  and the second electrode  50   b  of the light emitting cell of the second array  13  adjacent thereto are connected to each other through the metal wire  400   c , and the second electrodes  50   b  of the light emitting cells adjacent to the one of the light emitting cells in the first array  11  the first electrodes  50   a  of the light emitting cells in the second array  13  adjacent thereto are connected to each other through the metal wires  400   d.    
         [0071]    The aforementioned arrangement of the metal wires  400   a ,  400   b ,  400   c  and  400   d  can be performed by connecting two metal wires to one electrode  50   a  or  50   b  of the corresponding light emitting cell  200  and by connecting the two metal wires to electrodes of other light emitting cells adjacent to the corresponding light emitting cell. The connection of such metal wires has been already described in detail in the aforementioned descriptions of  FIGS. 2 and 3 . 
         [0072]    Meanwhile, the bonding pads  300   a  and  300   b  may be arranged on the substrate  100  near both the ends of the arrays  11  and  13 . The bonding pads  300   a  and  300   b  are to connect the AC light emitting diode  1  to an external power source. The bonding pads  300   a  and  300   b  may be connected to the external power source through bonding wires (not shown), or may be flip-chip bonded to a submount to be connected to the external power source. 
         [0073]    Metal wires  400   e  can connect the bonding pads  300   a  and  300   b  and the light emitting cells at both the ends of the first and second arrays  11  and  13 . Accordingly, the light emitting cells in a pair of the arrays  11  and  13  are connected zigzag to each other to be driven under an AC power source. 
         [0074]    According to this embodiment, since the light emitting cells of the first and second arrays  11  and  13  are operates zigzag with each other, the light emitting cells of this embodiment may emit generally uniform light as compared with a prior art operating on a substrate in an array unit. 
         [0075]    Meanwhile, although it has been described in this embodiment that the light emitting cells at both the ends of each of the arrays  11  and  13  are all connected to the bonding pads  300   a  and  300   b  through the metal wires  400   e , it is not limited thereto and the light emitting cells at both ends of the arrays may be connected the bonding pads after a plurality of arrays are connected through metal wires. 
         [0076]    Although the present invention has been described in detail in connection with the specific embodiments, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto within the technical spirit and scope of the present invention. Accordingly, it should be construed that the aforementioned descriptions and drawings do not limit the technical spirit of the present invention but illustrate the present invention.