Abstract:
A light-emitting diode device includes a transparent substrate having an edge side, a peripheral region and a central region surrounded by the peripheral region; and a plurality of light-emitting diode units disposed along the peripheral region and having a first light-emitting diode unit with an edge parallel to the edge side. The central region is devoid of any light-emitting diode unit.

Description:
REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 14/513,810, filed on Oct. 14, 2014, which is a continuation application of U.S. patent application Ser. No. 13/767,217, filed on Feb. 14, 2013, now U.S. Pat. No. 8,860,046 which claims the right of priority based on Taiwan application Serial No. 101105428, filed on Feb. 20, 2012, and the content of which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The disclosure relates to a light-emitting diode device with high light extraction efficiency. 
       DESCRIPTION OF BACKGROUND ART 
       [0003]    The lighting theory and structure of light-emitting diode (LED) is different from that of conventional lighting source. An LED has advantages like low power loss, long life-time, no need for warming time, and fast responsive time. Moreover, it is small, shockproof, suitable for mass production, so LEDs are widely adopted in the market. For example, LEDs can be used in optical display apparatus, laser diodes, traffic lights, data storage devices, communication devices, illumination devices, medical devices, and so on. 
         [0004]    The conventional two dimensional array light emitting diode device  1  shown as  FIGS. 1A and 1B  comprises a transparent substrate  10 , a plurality of light-emitting diode units  12  extending along two dimensions and closely arranged and formed on the transparent substrate  10 . Every light-emitting diode unit  12  comprises one p-type semiconductor layer  121 , one light-emitting layer  122 , and one n-type semiconductor layer  123 . Because the transparent substrate is electrically insulating, after forming the grooves by etching between the light-emitting diode units  12 , each light-emitting diode unit can be insulated to each other. Then, etching part of each light-emitting diode unit  12  to the n-type semiconductor layer  123  and forming a first electrode  18  and a second electrode  16  on the exposed region of the n-type semiconductor layer  123  and the p-type semiconductor  121 , respectively. Furthermore, the first electrodes  18  and the second electrodes  16  of the plurality of the light-emitting diode units  12  are selectively connected by the conductive connecting structures  19  in order to make the plurality of the light-emitting diode units  12  to electrically connect in parallel or in series. Wherein, there can be air under the conductive connecting structure  19 , or an insulating layer  13  can be formed on part surfaces of the epitaxial layers of the light-emitting diode units  12  and the regions between the adjacent light-emitting diode units  12  by chemical vapor deposition method (CVD), physical vapor deposition method (PVD), or sputtering method and so on in order to protect and electrically insulate the epitaxial layers of the adjacent light-emitting diode units  12 . The material of the insulating layer  13  can be aluminum oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ), aluminum nitride (AlN), silicon nitride (SiN x ), titanium oxide (TiO 2 ), and the combination thereof. 
         [0005]    However, because the height difference between the grooves  14  and the light-emitting units  12  is large, the conductive connecting structures  19  electrically connecting the light-emitting diode units  12  is easy to cause the connecting failure and to influence the yield of the device. 
         [0006]    Besides, the aforementioned light emitting diode device  1  can further constitute and connect with other devices to form a light-emitting apparatus  100 .  FIG. 11  illustrates a conventional light-emitting apparatus  100 . As shown in  FIG. 11 , a light-emitting apparatus  100  comprises one submount  110  comprising one circuit  101  thereon; the aforementioned light-emitting diode device  1  attached on the submount  110 ; and an electrical connecting structure  104  electrically connecting the first electrode pad  16 ′ and the second electrode pad  18 ′ of the first light-emitting diode device  1  and the circuit  101  on the lead frame  110 . Wherein, the aforementioned submount  110  can be a lead frame or a large-sized mounting substrate which is advantageous for circuit design of the light-emitting apparatus and heat dissipating. The aforementioned electrical connecting structure  104  can be the bonding wire or other connecting structures. 
       SUMMARY OF THE DISCLOSURE 
       [0007]    In accordance with the description above, the present disclosure provides a light-emitting diode device including a transparent substrate having an edge side, a peripheral region and a central region surrounded by the peripheral region; and a plurality of light-emitting diode units disposed along the peripheral region and having a first light-emitting diode unit with an edge parallel to the edge side. The central region is devoid of any light-emitting diode unit. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1A  illustrates a side-view structure of a conventional two dimensional array light-emitting diode device; 
           [0009]      FIG. 1B  illustrates a top-view structure of a conventional two dimensional array light-emitting diode device; 
           [0010]      FIG. 2A  illustrates a top-view structure of a two dimensional array light-emitting diode device in accordance with an embodiment of the present application; 
           [0011]      FIG. 2B  illustrates a side-view structure of a two dimensional array light-emitting diode device in accordance with an embodiment of the present application; 
           [0012]      FIG. 3  illustrates a top-view structure of a light-emitting diode unit in accordance with an embodiment of the present application; 
           [0013]      FIGS. 4A-4B  illustrate the top-view diagrams of two dimensional array light-emitting diode devices in accordance with the embodiments of the present application; 
           [0014]      FIG. 5  illustrates a top-view diagram of a two dimensional array light-emitting diode device in accordance with another embodiment of the present application; 
           [0015]      FIGS. 6A-6B  illustrate the top-view diagrams of two dimensional array light-emitting diode devices in accordance with the embodiments of the present application; 
           [0016]      FIG. 7  illustrates a comparison chart of the light-emitting efficiency and the light-emitting power of each light-emitting diode unit in accordance with different two dimensional array light emitting diode devices; 
           [0017]      FIGS. 8A-8C  illustrate the top-view diagrams of two dimensional array light-emitting diode devices in accordance with the embodiments of the present application; 
           [0018]      FIGS. 9A-9D  illustrate the top-view diagrams of the single string serially-connected light-emitting diode devices in accordance with the embodiments of the present application; 
           [0019]      FIG. 10  illustrates a top-view diagram of a two dimensional array light-emitting diode device in accordance with another embodiment of the present application; 
           [0020]      FIG. 11  illustrates the top-view diagram of a conventional light-emitting apparatus. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0021]    The following discloses the embodiments of the present application in detail accompanying with the drawings. First,  FIGS. 2A and 2B  illustrate the top-view diagram and the side-view diagram of a two dimensional array light-emitting diode device  2  in accordance with the first embodiment of the present application, respectively. The two dimensional array light-emitting diode device  2  includes a transparent substrate  20  including a first surface  201  and a bottom surface  202  opposite to the first surface  201 . The transparent substrate  20  is not limited to be composed of a single material and can also be composed of a plurality of different materials. For example, the transparent substrate  20  can be composed of two substrates including a first transparent substrate and a second transparent substrate connecting to each other (not shown). In the present embodiment, the material of the transparent substrate  20  is sapphire. In other embodiments, the material of the transparent substrate  20  can also comprise inorganic material such as lithium aluminum oxide (LiAlO 2 ), zinc oxide (ZnO), gallium phosphide (GaP), aluminum nitride (AlN), and glass or organic polymer material. Then, an array including a plurality of light-emitting diode units  22  extending two dimensionally on the first surface  201  of the transparent substrate  20  is formed. In the present embodiment, the manufacturing method discloses as the following: 
         [0022]    First, the n-type semiconductor layer  221 , the light-emitting layer  222 , the p-type semiconductor layer  223  are sequentially formed on a growth substrate (not shown) by the traditional epitaxial growth method. In the present embodiment, the material of the growth substrate is gallium arsenide (GaAs). In other embodiments, the material of the growth substrate can also comprise germanium (Ge), indium phosphide (inP), sapphire, silicon carbide (SiC), silicon (Si), lithium aluminum oxide (LiAlO 2 ), zinc oxide (ZnO), gallium nitride (GaN), and aluminum nitride (AlN). 
         [0023]    Then, a part of epitaxial layers is selectively removed by the photolithography method, and the remained epitaxial layers form a plurality of separated light-emitting diode units  22  on the growth substrate as shown in  FIG. 2B . The light-emitting diode units can further include the exposed region of the n-type semiconductor by photolithography method, and the region can be used as the platform for the electrode to form thereon. 
         [0024]    In order to increase the light extraction efficiency of the whole device, the epitaxial layer structures of the light-emitting diode units  22  can be arranged on the transparent substrate  20  by the substrate transferring method or the substrate bonding method. The light-emitting diode units  22  can be directly bonded to the transparent substrate  20  by heating, pressurizing, or bonding the light-emitting diode units  22  and the transparent substrate  20  with a transparent adhesive layer (not shown). The transparent adhesive layer can be an organic polymer transparent glue layer, such as polyimide, benzocyclobutene (BCB), perfluorocyclobutane (PFCB), Epoxy, Acrylic Resin, and polyethylene terephthalate (PET) or the combination thereof; a transparent conductive metal oxide layer, such as Indium Tin Oxide (ITO), Indium Oxide (InO), Tin Oxide (SnO), Fluoro Tin Oxide (FTO), Antimony Tin Oxide (ATO), Cadmium Tin Oxide (CTO), Aluminum Zinc Oxide (AZO), and Gallium Doped Zinc Oxide (GZO) or the combination thereof; or an inorganic layer, such as aluminum oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ), aluminum nitride (AlN), silicon nitride (SiN x ), titanium oxide (TiO 2 ), and the combination thereof. 
         [0025]    In the present embodiment, the light-emitting diode units  22  are bonded to the transparent substrate  20  by using the benzocyclobutene (BCB) series material as the adhesive layer. In practice, the method of forming the light-emitting diode units  22  on the transparent substrate  20  is not limited to this embodiment; people with ordinary skill in the art can realize that depends on the different structure properties, the light-emitting diode units  22  can also be epitaxially formed on the transparent substrate. Besides, with different transfer frequency, for example, transfer twice, the structure with the p-type semiconductor layer adjacent to the substrate, the n-type semiconductor layer on the p-type semiconductor layer, and the light-emitting layer therebetween can also be formed. 
         [0026]    Then, forming the insulating layer  23  on partial surfaces of the epitaxial layers of the light-emitting diode units  22  and the regions between the adjacent light-emitting diode units  22  by the chemical vapor deposition method (CVD), physical vapor deposition method (PVD), sputtering method, and so on in order to protect and electrically insulate the epitaxial layers of the adjacent light-emitting diode units  22 . The material of the insulating layer  23  can be aluminum oxide (Al 2 O 3 ), silicon dioxide (SiO 2 ), aluminum nitride (AlN), silicon nitride (SiN x ), titanium oxide (TiO 2 ), and the combination thereof. 
         [0027]    Then, forming a first electrode  28  on the n-type semiconductor exposed region of the light-emitting diode unit  22 , forming a second electrode  26  on the surface of the p-type semiconductor layer, and forming a conductive connecting structure  29  by the sputtering method in order to electrically connect the light-emitting diode units  22  therebetween on the first surface  201  of the transparent substrate. Take the embodiment for example, forming a first electrode  28  on the n-type semiconductor layer exposed region of the first light-emitting diode unit  22 , forming a second electrode  26  on the p-type semiconductor layer  223  of the adjacent light-emitting diode unit  22 , and forming a conductive connecting structure  29  between the two electrodes in order to electrically connect the two adjacent light-emitting diode units in series. The material of the conductive connecting structure  29  and the electrodes  26 ,  28  can be metal such as gold (Au), silver (Ag), copper (Cu), chromium (Cr), aluminum (Al), platinum (Pt), nickel (Ni), titanium (Ti), tin (Sn), the alloy or the stacks thereof. The materials of the first electrode  28 , the second electrode  26 , and the conductive connecting structure  29  can be the same or different, and the structures thereof can be made by one-step process or by multi-steps process. 
         [0028]    In order to reduce the influence of the non-transparent metal structure for the light extraction efficiency on the light emitting diode device  2 , as shown in  FIG. 2A , based on different circuit designs, two conductive connecting structures  29  are respectively formed on the surfaces of the p-type semiconductor layer  223  of one light-emitting diode unit  22  and the n-type semiconductor layer  221  of another light-emitting diode unit  22  in the light-emitting diode units chain, and are extended to the first surface  201  of the substrate  20  uncovered by the epitaxial layer to form a first electrode pad  26 ′ and a second electrode pad  28 ′. Through the two electrode pads, the device can electrically connect to external power by wiring or soldering. The process of forming the electrode pads  26 ′ and  28 ′ can proceed in the same process with forming the electrodes  26  and  28  or in multiple processes. The materials of forming the electrode pads  26 ′ and  28 ′ can also be the same with or different from the materials of the electrodes  26  and  28  or the conductive connecting structure  29 . 
         [0029]      FIG. 3  illustrates the enlarged top view of the light-emitting diode unit  22 . In the present embodiment, each light-emitting diode unit  22  is a rectangle having four sides  22   a  (length a),  22   b  (length b),  22   c  (length a), and  22   d  (length b), and the circumference of the light-emitting diode unit  22  are the total lengths of the four sides, that is, 2a+2b. 
         [0030]    In the embodiment of the present application, the arrangement of the light-emitting diode units in the device is proposed to enhance the light extraction efficiency of the light emitting diode device. In the conventional two dimensional array light-emitting diode device, when two light-emitting diode units is too close, the light emitted from the light emitting diode unit is reabsorbed easily by the semiconductor layers which have similar band gap (especially the light-emitting layers) in the neighboring light-emitting diode units, and the total light extraction efficiency of the device can be influenced. In order to reduce the reabsorption, the distance between each light-emitting diode units  22  is enlarged. In the present embodiment, because the band gaps of the light-emitting layers are close, the light reabsorption is more obvious. Therefore, taking the distances between the light-emitting layers as the reference, all the distances between the light-emitting layers of the ten light-emitting diode units is preferred to be larger than 35 μm. Besides, the portion of the sides neighboring with another light-emitting diode unit  22  is preferably reduced. Referring to  FIG. 4A , when the vertical distance x between the sides of neighboring light-emitting diode units  22  is larger than 50 μm, the chance of reabsorption between two adjacent light-emitting diode units is lower. In that case, the two sides of the light-emitting diodes with the distance larger than 50 μm are defined as not being near each other. This definition can be extensively applied to light-emitting diode units  22  with different shapes. As shown in  FIG. 4B , the circular light-emitting diode units  22  can be arranged not near each other on the substrate in a two-dimensional array form in order to reduce the chance of reabsorption between each other and to enhance the light extraction efficiency of the light-emitting diode device. 
         [0031]    In the above embodiments, a “not-near value” a for a light-emitting diode unit  22  is defined as the ratio of the total length of the sides of one light-emitting diode unit  22  not near another light-emitting diode unit to the circumference of one light-emitting diode unit  22 . As shown in  FIG. 5 , the ten light-emitting diode units  22  are numbered and the not-near value α of the light-emitting diode unit  22 - 1  is calculated. The sides of the light-emitting diode unit  22 - 1  and the light-emitting diode unit  22 - 2  thereunder are connected by the conductive connecting structure  29 , and the vertical distance between the side  22 - 1   c  and the side  22 - 2   d  is smaller or equal to 50 μm, that is, the near-each-other length of the sides  22 - 1   c  and  22 - 2   d  is b. Similarly, the distance between the side  22 - 1   d  of the light-emitting diode unit  22 - 1  and the side  22 - 3   b  of the light-emitting diode unit  22 - 3  on the left hand side thereof is smaller than 50 μm. That is, they are also near each other, and the length is b. Besides, the circumference of the light-emitting diode unit  22 - 1  is 2a+2b. In this embodiment, the light-emitting diode unit comprises the sides with the length 2b near other light-emitting diode units, and the total not-near length of the sides is (2a+2b)−2b=2a. Therefore, the not-near value α is 2a/(2a+2b). The same calculation formula can be applied to the light-emitting diode units  22  with different shapes. In that case, the sides of one light-emitting diode unit are divided into a plurality of points, and the tangent line along the side of each point is given. The vertical distance along the tangent line between each point and the nearest side of other light-emitting diode units is then calculated. After determining the distance of each point with the nearest light-emitting diode unit, all the not-near sides are integrated, and the integral value is the total length of the not-near sides. The not-near value α is the ratio of the integral value to the circumference of the light-emitting diode unit. 
         [0032]    Taking  FIGS. 6A and 6B  for example, whether each point of the light-emitting diode unit with irregular shape is near other light-emitting diode units or not can be further determined. If the shape of the light-emitting diode unit is irregular, the vertical distance x of each point is calculated by taking each point on the side of the light-emitting diode unit along the direction vertical to the side. When the side is a curve, a tangent line for each point on the curve is given and the vertical distance of the point along the direction vertical to the tangent line is calculated. In  FIGS. 6A and 6B , light-emitting diode unit  32 - 1  and light-emitting diode unit  42 - 1  are referred to demonstrate the calculation formulas for the vertical distances between different positions of the sides of the light-emitting diode unit and the nearest light-emitting diode units  32 - 2 ,  32 - 3 ,  42 - 2 , and  42 - 3 . 
         [0033]    In accordance with the experiment results, when the not-near value α of the light-emitting diode unit on the two dimensional array diode device is larger than 50%, the light emitting efficiency of the light-emitting diode device  2  is 5% better than that of the conventional closely arranged two dimensional array light-emitting diode device  3 . As shown in the comparison chart of the light-emitting efficiency between different light-emitting diode devices and the light-emitting power of each light-emitting diode unit, when the side length a of each light-emitting diode unit in the light-emitting diode device  2  is 560 μm and the side length b of each light-emitting diode unit in the light-emitting diode device  2  is 290 μm, the not-near value α is about 65%. The light emitting efficiency of the light-emitting diode device  2  can be 10% better than the conventional closely arranged two dimensional array light-emitting diode device  3 . 
         [0034]      FIGS. 8A to 8C  show other embodiments of the two dimensional array light-emitting diode devices to fit the arrangements of the light-emitting diode units with not-near value α larger than 50%. 
         [0035]    Besides, in order to enhance the total light emitting efficiency of the device, the first surface and/or the backside surface can be roughened by wet etching method or dry etching method so the light scattering probability and the light extraction probability are increased. Furthermore, viewing from the top, when the light emitting diode unit  22  is disposed on the transparent substrate  20 , the shortest distance between the position of the light emitting layer of the light emitting diode unit  22  vertically projected on the first surface and any side faces is preferably larger than 20 μm in order to enhance the probability of the light extracted from the transparent substrate  20 . 
         [0036]    Under the similar concept, the single string of serially-connected high voltage light-emitting diode devices on the transparent substrate can be adequately arranged in a two dimensional form to increase the not-near value α of each light emitting diode unit in each serially-connected light-emitting diode device. 
         [0037]      FIGS. 9A to 9D  illustrate different single string of serially-connected high voltage light-emitting diode devices  4 ,  5 ,  6 ,  7 , respectively. Each serially-connected high voltage light-emitting diode device comprises four light emitting diode units  42 ,  52 ,  62 ,  72  formed on the substrate  40 ,  50 ,  60 ,  70  by epitaxy or by bonding, respectively. Similar with the structures mentioned above, forming the first electrodes  46 ,  56 ,  66 ,  76  on exposed regions of the n-type semiconductor of the first light emitting diode units  42 ,  52 ,  62 ,  72 , respectively, extending the conductive connecting structures  49 ,  59 ,  69 ,  79  to another adjacent light emitting diode units  42 ,  52 ,  62 ,  72 , and forming the second electrodes  48 ,  58 ,  68 ,  78  on the p-type semiconductor layer of the adjacent light emitting diode unit  42  in order to electrically connect two adjacent light emitting diode units  42 ,  52 ,  62 ,  72  in series. In each single string of serially-connected high voltage light-emitting diode devices  4 ,  5 ,  6 ,  7 , two light emitting diode units  42 ,  52 ,  62 ,  72  at the two ends in each string further comprise the first electrode pads  46 ′,  56 ′,  66 ′,  76 ′, and the second electrode pads  48 ′,  58 ′,  68 ′,  78 ′, respectively, which are used to electrically connect to the external device or the power source. 
         [0038]    More than one of the single string of the serially-connected high voltage light-emitting diode devices  4 ,  5 ,  6 ,  7  can be attached to a single transparent substrate  80  to a transparent adhesive layer, and the light-emitting diode devices  4 ,  5 ,  6 ,  7  can be electrically connected to each other by the wire-bonding process or forming conductive connecting structures  89  through the photolithography process. With adequate arrangement, it is possible to form a two dimensional array of light-emitting diode device with a not-near value α higher than that of the conventional compact two dimensional array of light-emitting diode device in order to achieve the higher light extraction efficiency as shown in  FIG. 10 . 
         [0039]    The embodiments mentioned above are used to describe the technical thinking and the characteristic of the invention and to make the person with ordinary skill in the art to realize the content of the invention and to practice, which could not be used to limit the claim scope of the present application. Any modification or variation according to the spirit of the present application should also be covered in the claim scope of the present disclosure.