Patent Publication Number: US-9899585-B2

Title: Light emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part application of and claims the priority benefit of U.S. application Ser. No. 14/924,728, filed on Oct. 28, 2015, now allowed. The prior U.S. application Ser. No. 14/924,728 claims the priority benefits of U.S. provisional application Ser. No. 62/081,503, filed on Nov. 18, 2014, U.S. provisional application Ser. No. 62/092,265, filed on Dec. 16, 2014, and Taiwan application serial no. 104114438, filed on May 6, 2015. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a semiconductor device, and more particularly, to a light emitting device. 
     2. Description of Related Art 
     Generally, a light emitting chip is composed of a substrate, an epitaxial structure, N-type electrodes and P-type electrodes, where the N-type electrodes and the P-type electrodes respectively contact an N-type semiconductor layer and a P-type semiconductor layer. In order to expand the application of the light emitting chip, the manufactured light emitting chip is generally disposed on a carrier, and a molding compound is used to package the light emitting chip to form a light emitting package. The carrier is, for example, a printed circuit board or a ceramic substrate, etc., and the carrier has pads corresponding to the N-type electrodes and the P-type electrodes of the light emitting chip. An area of the carrier is greater than an orthogonal projection area of the light emitting chip on the carrier. Namely, an edge of the carrier is larger than an edge of the light emitting chip. Moreover, since the molding compound is, for example, formed on the light emitting chip through dispensing, etc., when the molding compound is used to package the light emitting chip, the molding compound presents an arc shape (for example, a semi-circular or semi-elliptical shape) on the carrier. In this way, the light emitting package has a larger width (i.e. a width of the carrier) and a larger height (i.e. the arc-shaped molding compound). Namely, the light emitting package has a larger volume, which is unable to meet today&#39;s demand of thinning and miniaturization of devices. 
     SUMMARY OF THE INVENTION 
     The invention provides a light emitting device having a smaller volume. 
     A light emitting device of the invention includes a substrate, a conductive electrode connection layer, at least one epitaxial structure and an insulating layer. The substrate had an upper surface and a lower surface opposite to each other. The conductive electrode connection layer is disposed on the upper surface of the substrate and electrically connected with the substrate. The epitaxial structure is disposed on the conductive electrode connection layer and electrically connected with the conductive electrode connection layer, wherein the epitaxial structure has a first peripheral surface. The insulating layer is disposed between the conductive electrode connection layer and the least one epitaxial structure, wherein the insulating layer has a second peripheral surface, and the second peripheral surface is aligned with the first peripheral surface. 
     In an embodiment of the invention, the substrate has a peripheral surface, and the conductive electrode connection layer has a third peripheral surface, and the third peripheral surface is aligned with the peripheral surface. 
     In an embodiment of the invention, the at least one epitaxial structure are a plurality of epitaxial structures, and each of the plurality of epitaxial structures are disposed on the conductive electrode connection layer and separated from each other. 
     In an embodiment of the invention, the plurality of epitaxial structures comprise at least one red light epitaxial structure, at least one blue light epitaxial structure and at least one green light epitaxial structure. 
     In an embodiment of the invention, the conductive electrode connection layer has at least one first electrode, at least one second electrode and a connection layer disposed between the substrate and the first electrode and between the substrate and the second electrode. 
     In an embodiment of the invention, each of the epitaxial structures includes a first type semiconductor layer, a light emitting layer and a second type semiconductor layer. The first type semiconductor layer is disposed on the insulating layer, wherein the first electrode of the conductive electrode connection layer penetrates through the insulating layer so as to be electrically connected with the first type semiconductor layer. The light emitting layer is disposed on the first type semiconductor layer. The second type semiconductor layer is disposed on the light emitting layer, wherein the second electrode of the conductive electrode connection layer penetrates through the insulating layer, the first type semiconductor layer and the light emitting layer so as to be electrically connected with the second type semiconductor layer. 
     In an embodiment of the invention, a thickness of the second type semiconductor layer is 3 times to 15 times of a thickness of the light emitting layer, and the thickness of the second type semiconductor layer is 10 times to 20 times of a thickness of the first type semiconductor layer. 
     In an embodiment of the invention, the light emitting device further includes an ohmic contact layer, disposed between the first type semiconductor layer and the insulating layer. 
     In an embodiment of the invention, the light emitting device further includes a reflection layer, disposed between the ohmic contact layer and the insulating layer. 
     In an embodiment of the invention, the light emitting device further includes a sheet-like wavelength converting layer, disposed on each of the epitaxial structures, wherein the substrate has a peripheral surface, the sheet-like wavelength converting layer has a fourth peripheral surface, and the fourth peripheral surface is aligned with the peripheral surface. 
     In an embodiment of the invention, the light emitting device further includes a color mixing layer, disposed on the sheet-like wavelength converting layer, wherein color mixing layer has a fifth peripheral surface, and the fifth peripheral surface is aligned with the fourth peripheral surface. 
     In an embodiment of the invention, a thickness of each of the plurality of the epitaxial structures is between 3 μm to 15 μm and a width of each of the plurality of the epitaxial structures is between 1 μm to 150 μm. 
     In an embodiment of the invention, the substrate includes a plurality of circuit electrodes and the conductive electrode connection layer is electrically connected to the circuit electrodes. 
     In an embodiment of the invention, the substrate includes a thin film transistor substrate, a complementary metal oxide semiconductor substrate, a printed circuit board substrate or a flexible substrate. 
     In an embodiment of the invention, the light emitting device further includes a plurality of pads disposed on the lower surface of the substrate, wherein the substrate comprises a plurality of conductive through holes penetrating through the substrate and connecting to the upper surface and the lower surface, and the plurality of pads are connected with the conductive through holes, and the conductive electrode connection layer is electrically connected with the conductive through holes. 
     In an embodiment of the invention, each of the conductive through holes and the conductive electrode connection layer have at least one space therebetween. 
     Based on the above, since the edge of the electrode connection layer is aligned with the edge of the substrate, the light emitting device of the invention is readily to be used when power is supplied from an external circuit connected with the pads. As compared to the conventional light emitting device, which can only be used by firstly electrically connecting the light emitting device to the pads of a larger carrier board and then supplying power from an external circuit connected with the pads, the light emitting device of the invention can have a smaller volume. 
     In order to make the aforementioned features and advantages of the present invention more comprehensible, embodiments accompanying figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic cross-sectional view illustrating a light emitting device according to an embodiment of the invention. 
         FIG. 2A  and  FIG. 2B  are schematic cross-sectional views each illustrating light emitting devices according to another two embodiments of the invention. 
         FIG. 3A ,  FIG. 3B  and  FIG. 3C  are schematic cross-sectional views each illustrating light emitting devices according to another three embodiments of the invention. 
         FIG. 4  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 5  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 6  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 7  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 8  is a schematic top view illustrating an electrode connection layer of a light emitting device according to another embodiment of the invention. 
         FIG. 9A  and  FIG. 9B  schematic cross-sectional views each illustrating light emitting devices according to another two embodiments of the invention. 
         FIG. 10  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 11  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 12  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 13  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 14  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
         FIG. 15  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIG. 1  is a schematic cross-sectional view illustrating a light emitting device according to an embodiment of the invention. Referring to  FIG. 1 , in the present embodiment, a light emitting device  100   a  includes a substrate  110   a , an electrode connection layer  120   a , an epitaxial structure E and a plurality of pads  170 . In detail, the substrate  110   a  has an upper surface  112  and a lower surface  114  opposite to each other, and a plurality of conductive through holes  116   a  penetrating through the substrate  110   a  and connecting to the upper surface  112  and the lower surface  114 . The electrode connection layer  120   a  is disposed on the upper surface  112  of the substrate  110   a  and connected with the conductive through holes  116   a . An edge  121  of the electrode connection layer  120   a  is substantially aligned with an edge  111  of the substrate  110   a , wherein the electrode connection layer  120   a  includes at least one first electrode  122   a , at least one second electrode  124   a  and a connection layer  126   a , which is disposed between the substrate  110   a  and the first electrode  122   a  and between the substrate  110   a  and the second electrode  124   a . The epitaxial structure E is disposed on the electrode connection layer  120   a  can electrically connected with the electrode connection layer  120   a . The pads  170  is disposed on the lower surface  114  of the substrate  110   a  and connected with the conductive through holes  116   a.    
     In detail, the light emitting device  100   a  of the present embodiment further includes an insulating layer  130 , which is disposed on the electrode connection layer  120   a  and insulates the first electrode  122   a  and the second electrode  124   a . As shown in  FIG. 1 , the epitaxial structure E of the present embodiment includes a first type semiconductor layer  140 , a light emitting layer  150  and a second type semiconductor layer  160 . The first type semiconductor layer  140  is disposed on the insulating layer  130 , wherein the first electrode  122   a  penetrates through the insulating layer  130  so as to be electrically connected with the first type semiconductor layer  140 . The light emitting layer  150  is disposed on the first type semiconductor layer  140 . The second type semiconductor layer  160  is disposed on the light emitting layer  150 , wherein the second electrode  124   a  penetrates through the insulating layer  130 , the first type semiconductor layer  140  and the light emitting layer  150  so as to be electrically connected with the second type semiconductor layer  160 . 
     More specifically, the substrate  110   a  of the present embodiment may be a substrate, having favorable heat dissipation effect, with a thermal conductivity coefficient greater than 10 W/m-K. The substrate  110   a  may also be an insulating substrate with a resistivity greater than 10 10  Ω·m. Herein, the substrate  110   a  is, for example, a ceramic substrate or a sapphire substrate. Preferably, the substrate  110   a  is a ceramic substrate with favorable heat dissipation effect and insulation effect. A thickness of the substrate  110   a  is, for example, between 100 μm and 700 μm, and preferably, between 100 μm and 300 μm. As shown in  FIG. 1 , the conductive through hole  116   a  of the present embodiment are formed by filling a conductive material, such as copper, gold, etc, into the through holes of the substrate  110   a . Two opposite ends of the conductive through hole  116   a  of the substrate  110   a  are electrically connected with the electrode connection layer  120   a  and the pad  170 , respectively, wherein a cross-sectional profile of the conductive through hole  116   a  may have different shapes depending on the fabrication method thereof. For example, if a mechanical drilling method is adopted, then the resulting cross-sectional profile of the conductive through hole  116   a  is a rectangle (not shown); and if a laser drilling method is adopted, then the resulting cross-sectional profile of the conductive through hole  116   a  is a trapezoid, which is as shown in  FIG. 1 . However, if the laser drilling method is adopted, the cross-sectional profile of the conductive through hole may also be influenced by an ablation direction of laser light. For example, if the laser light irradiates the upper surface  112  of the substrate  110   a , then the cross-sectional profile of the conductive through hole  116   a  would appears to be an inverted trapezoid with a wide opening at top and a narrow opening at bottom (not shown); and if the laser light irradiates the lower surface  114  of the substrate  110   a , then the cross-sectional profile of the conductive through hole  116   a  would appear to be a trapezoid with a narrow opening at top and a wide opening at bottom, which is as shown in  FIG. 1 . The aforementioned cross-sectional profiles of the conductive through hole  116   a  are all within the protection scope of the invention, and the invention is not limited to the cross-sectional profile of the conductive through hole  116   a  as depicted in the present embodiment. 
     Moreover, the first electrode  122   a  of the electrode connection layer  120   a  of the present embodiment is, for example, a P-type electrode, and the second electrode  124   a  is, for example, an N-type electrode, but the invention is not limited thereto. A material of the first electrode  122   a  and the second electrode  124   a  can be chromium, platinum, gold, tin, indium, titanium, an alloy of materials selected from the above, a combination of the above or metal oxide (e.g., indium tin oxide and zinc oxide). However, the connection layer  126   a  is disposed between the substrate  110   a  and the first electrode  122   a  and between the substrate  110   a  and the second electrode  124   a , and a portion of the connection layer  126   a  is connected to the first electrode  122   a  and a portion of the connection layer  126   a  is connected to the second electrode  124   a . A material of the connection layer  126   a  can be titanium, gold, indium, tin, chromium, platinum, an alloy of materials selected from the above, a combination of the above or metal oxide (e.g., indium tin oxide and zinc oxide). It should be noted that, the first electrodes  122   a , the second electrodes  124   a  and the connection layer  126   a  can be made of a same material or different materials, and can be integrally formed or separately formed, which are not limited by the invention. As shown in  FIG. 1 , in the present embodiment, an area of an orthogonal projection of the portion, which is connected to the second electrode  124   a  of the connection layer  126   a , on the substrate  110   a  is greater than an area of an orthogonal projection of the portion, which is connected to the first electrode  122   a  of the connection layer  126   a , on the substrate  110   a . In other words, in the present embodiment, an area of the portion connecting to the second electrode  124   a  of the connection layer  126   a  is greater than an area of the portion connecting to the first electrode  122   a  of the connection layer  126   a . Particularly, the first electrode  122   a  and the second electrode  124   a  of the present embodiment are both located on a same side, which is a side of the first type semiconductor layer  140 . In addition, in the epitaxial structure E of the present embodiment, the first type semiconductor layer  140  is, for example, a P type semiconductor layer, and the second type semiconductor layer  160  is, for example, an N type semiconductor layer, but the invention is not limited thereto. An edge of the epitaxial structure E is smaller than or equal to an edge of the substrate  110   a ; and preferably, an area of an orthogonal projection of the epitaxial structure E on the substrate  110   a  is 0.8 to 1 times an area of the upper surface  112  of the substrate  110   a , so that the overall volume will not be effected during the fabrication of the subsequent protection process and thereby causing too much reduction in the light emitting area. A thickness of the epitaxial structure E is between 3 μm to 15 μm; and preferably, the thickness is between 4 μm to 8 μm. As compared to a thickness of an epitaxial structure of a conventional light emitting device, the thickness of the epitaxial structure E of the invention is thinner and can have a smaller overall thickness. Moreover, since the pads  170  of the present embodiment are located on the lower surface  114  of the substrate  110   a , the light emitting device  100   a  can be electrically connected with an external circuit (not shown) through the pads  170 , and the heat generated by the light emitting device  100   a  can be transferred quickly through the pads  170  to the outside. It should be particularly noted that, an edge of the pad  170  may be aligned with an edge of the substrate  110   a . Namely, an edge of the electrode connection layer  120   a , an edge of the substrate  110   a  and an edge of the pads  170  are located on a same side. 
     In the light emitting device  100   a  of the present embodiment, since an edge  121  of the electrode connection layer  120   a  is substantially aligned with an edge  111  of the substrate  110   a , as compared to the conventional light emitting device, which can only be used by firstly connecting electrodes of an light emitting chip thereof to the pads of a larger carrier board and then supplying power from an external circuit connected with the pads, the light emitting device  100   a  of the present embodiment has a smaller overall width, and thus can have a smaller volume. 
     It should be noted that, reference numerals of the components and a part of contents of the previous embodiment are also used in the following embodiment, wherein the same reference numerals denote the same or similar components, and descriptions of the same technical contents are omitted. The descriptions regarding the omitted parts may be referred to the previous embodiments, and thus are not repeated herein. 
       FIG. 2A  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 1  and  FIG. 2A , the light emitting device  100   b   1  of the present embodiment is similar to the light emitting device  100   a  in  FIG. 1 , and a main difference therebetween lies in that: the light emitting device  100   b   1  of the present embodiment further includes a sheet-like wavelength converting layer  180   a , wherein the sheet-like wavelength converting layer  180   a  is disposed on the epitaxial structure E, an edge  181  of the sheet-like wavelength converting layer  180   a  and the edge  111  of the substrate  110   a  are substantially aligned, and an extending direction of the sheet-like wavelength converting layer  180   a  is the same as an extending direction of the substrate  110   a . As shown in  FIG. 2A , the sheet-like wavelength converting layer  180   a  and the substrate  110   a  of the present embodiment are all laterally extended, and the sheet-like wavelength converting layer  180   a  has two flat surfaces S 1 , S 2  that are opposite to each other. In other words, the sheet-like wavelength converting layer  180   a  of the present embodiment is substantially a planar structure. Moreover, a thickness of the sheet-like wavelength converting layer  180   a  of the present embodiment is, for example, 1.5 times to 25 times the thickness of the epitaxial structure E; if the thickness of the sheet-like wavelength converting layer  180   a  is smaller than 1.5 times the thickness of the epitaxial structure E, then the light emitted from the epitaxial structure E would easily penetrate through the sheet-like wavelength converting layer  180   a , and thereby result in poor conversion efficiency; and if the thickness of the sheet-like wavelength converting layer  180   a  is greater than 25 times the thickness of the epitaxial structure E, then the light emitted from the epitaxial structure E would be blocked. In the present embodiment, the thickness of the sheet-like wavelength converting layer  180   a  is, preferably, between 20 μm to 80 μm; and it should be noted that, the thickness of the sheet-like wavelength converting layer  180   a  in addition with the thickness of the epitaxial structure E is, preferably, smaller than 90 μm, so that the light emitting device  100   a  can have a smaller volume. 
     Since the sheet-like wavelength converting layer  180   a  of the present embodiment is a planar structure, and the edge  181  of the sheet-like wavelength converting layer  180   a  and the edge  111  of the substrate  110   a  are substantially aligned, as compared to the conventional light emitting device, which is formed with an arc-shaped molding compound by using a molding compound to package the light emitting chip, the light emitting device  100   b   1  of the present embodiment can have a smaller volume. Moreover, in order to improve the light emitting efficiency of the overall light emitting device  100   b   1 , diffusing particles or reflecting particles can be added to the sheet-like wavelength converting layer  180   a , so as to achieve a light scattering effect and a light reflecting effect, which still fall within the protection scope of the invention. In addition, since the sheet-like wavelength converting layer  180   a  of the present embodiment is the planar structure, a light emitting angle of the overall light emitting device  100   b   1  is, for example, smaller than 140 degrees, so that the light emitting device  100   b   1  can have a favorable light source collimation property, and can have better application flexibility in subsequent optical design. 
       FIG. 2B  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 2A  and  FIG. 2B , the light emitting device  100   b   2  of the present embodiment is similar to the light emitting device  100   b   1  in  FIG. 2A , and a main difference therebetween lies in that: the epitaxial structure E of the light emitting device  100   b   2  of the present embodiment has a rough surface E 1 , and the rough surface E 1  and the sheet-like wavelength converting layer  180   a  have micron-scale voids therebetween. Namely, a surface of the epitaxial structure E contacting the sheet-like wavelength converting layer  180   a  is a non-flat surface, and the light emitted from the epitaxial structure E has a scattering effect through the micron-scale voids, so that light can enter the sheet-like wavelength converting layer  180   a  more evenly. As a result, under such structural design, the light emitted from the epitaxial structure E can have a better scattering effect, and thereby can effectively improve the light emitting uniformity of the overall light emitting device  100   b   2 . 
     Moreover, the micron-scale voids between the epitaxial structure E and the sheet-like wavelength converting layer  180   a  can also serve as a buffer space between the two different layers, so as to increase a bonding force between the epitaxial structure E and the sheet-like wavelength converting layer  180   a , and thereby improves the reliability of the light emitting device  100   b   2 . It should be further noted that, if the size of the voids between the epitaxial structure E and the sheet-like wavelength converting layer  180   a  is smaller than the micro-scale, for example, smaller than 0.1 μm, then the voids are too small and the scattering effect is poor; and if the size of the voids is greater than micro-scale, such as greater than 10 μm, then the voids are too large and a bonding area between the epitaxial structure E and the sheet-like wavelength converting layer  180   a  is too small, thereby resulting in poor bonding effect. 
       FIG. 3A  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 2A  and  FIG. 3A , the light emitting device  100   c   1  of the present embodiment is similar to the light emitting device  100   b   1  in  FIG. 2A , and a main difference therebetween lies in that: the light emitting device  100   c   1  of the present embodiment further includes an optical coupling layer  190   c   1 , wherein the optical coupling layer  190   c   1  is disposed between the sheet-like wavelength converting layer  180   a  and the second type semiconductor layer  160  of the epitaxial structure E, so as to increase light emitting efficiency of the light emitting device  100   c   1  and increase the bonding between the epitaxial structure E and the sheet-like wavelength converting layer  180   a . Herein, the optical coupling layer  190   c   1  has a thickness smaller than 10 μm, and can serve as a buffer between the epitaxial structure E and the sheet-like wavelength converting layer  180   a  and implement a favorable bonding effect between the epitaxial structure E and the sheet-like wavelength converting layer  180   a . Herein, an edge of the optical coupling layer  190   c   1  is aligned with an edge of the second type semiconductor layer  160  of the epitaxial structure E. 
     More specifically, a material of the optical coupling layer  190   c   1  of the present embodiment is, for example, nitride material, such as gallium nitride; or the material of the optical coupling layer  190   c   1  is the same as the material of the second type semiconductor layer  160 , so as to provide a good bonding effect, but the invention is not limited thereto. Moreover, in order to increase the light emitting efficiency of the overall light emitting device  100   c   1 , the optical coupling layer  190   c   1  can be made of a material having a refractive index similar to that of the second type semiconductor layer  160 ; and by adding diffusing particles, reflective particles, scattering particles, or at least two types of the mentioned particles to the optical coupling layer  190   c   1 , the light generated by the epitaxial structure E can produce scattering, reflection and diffusion effects, and the refractive index of the optical coupling layer  190   c   1  can also be changed, such as being changed to be smaller than the refractive index of the second type semiconductor layer  160  and be greater than the refractive index of the sheet-like wavelength converting layer  180   a , so as to increase the light emitting efficiency, whereby all the above are still within the protection scope of the invention. 
       FIG. 3B  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 3A  and  FIG. 3B , the light emitting device  100   c   2  of the present embodiment is similar to the light emitting device  100   c   1  in  FIG. 3A , and main differences therebetween lie in that: the epitaxial structure E of the light emitting device  100   c   2  of the present embodiment has a rough surface E 1 , and the rough surface E 1  and the optical coupling layer  190   c   1  have micron-scale voids therebetween. Namely, a surface of the epitaxial structure E contacting the optical coupling layer  190   c   1  is a non-flat surface, and the light emitted from the epitaxial structure E has a scattering effect through the micron-scale voids, so that light can enter the optical coupling layer  190   c   1  more evenly. As a result, under such structural design, the light emitted from the epitaxial structure E can have a better scattering effect, and thereby can effectively improve the light emitting uniformity of the overall light emitting device  100   c   2 . In addition, the micron-scale voids between the epitaxial structure E and the optical coupling layer  190   c   1  can also serve as a buffer between the two different layers, so that a favorable bonding effect can be provided between the epitaxial structure E and the optical coupling layer  190   c   1 . It should be noted that, if the size of the voids between the epitaxial structure E and the optical coupling layer  190   c   1  is smaller than micro-scale, such as smaller than 0.1 μm, then the voids are too small and the scattering effect is poor; and if the size of the voids is greater than micro-scale, such as greater than 10 μm, then the voids are too large and a bonding area between the epitaxial structure E and the optical coupling layer  190   c   1  are too smaller, thereby resulting in poor bonding effect. 
       FIG. 3C  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 3C  and  FIG. 3A , the light emitting device  100   c   3  of the present embodiment is similar to the light emitting device  100   c   1  in  FIG. 3A , and main differences therebetween lie in that: the optical coupling layer  190   c   3  of the light emitting device  100   c   3  has a rough surface  191 , and the rough surface  191  and the sheet-like wavelength converting layer  180   a  have micron-scale voids therebetween. Namely, a surface of the optical coupling layer  190   c   3  contacting the sheet-like wavelength converting layer  180   a  is a non-flat surface; and with such structural design, the light emitted from the epitaxial structure E may have a better scattering effect, and thereby can effectively improve the light emitting uniformity of the overall light emitting device  100   c   3 . It should be noted that, an aperture of the voids must be greater than 0.1 μm, and particularly, must be greater than an emission peak wavelength of the light emitting device  100   c   3 , so as to provide a favorable scattering effect; however, the aperture also must be smaller than 10 μm, so as to prevent the generation of a total reflection effect and thus influencing the light emitting output. In addition, the micron-scale voids between the optical coupling layer  190   c   3  and the sheet-like wavelength converting layer  180   a  can also serve as a buffer space between the two different layers, so that a favorable bonding effect can be provided between the optical coupling layer  190   c   3  and the sheet-like wavelength converting layer  180   a , so as to improve a reliability of the light emitting device  100   c   3 . Certainly, in other embodiments (not shown), the micron-scale voids may be formed between the rough surface and the epitaxial structure, which is still within the protection scope of the invention. It should particularly be noted that, the optical coupling layer  190   c   3  can also have two rough surfaces, namely, one having micron-scale voids (not shown) with the sheet-like wavelength converting layer  180   a  while another one having micron-scale voids (not shown) with the epitaxial structure E, so that the optical coupling layer  190   c   3  can have favorable bonding effects with both the sheet-like wavelength converting layer  180   a  and the epitaxial structure E, so as to improve the reliability of the light emitting device  100   c   3 ; and the invention is not limited thereto. 
       FIG. 4  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 4  and  FIG. 2A , the light emitting device  100   d  of the present embodiment is similar to the light emitting device  100   b   1  in  FIG. 2A , and main differences therebetween lie in that: the light emitting device  100   d  of the present embodiment further includes an optical coupling layer  190   d , wherein the optical coupling layer  190   d  is located between the sheet-like wavelength converting layer  180   a  and the epitaxial structure E and has a patterned rough surface  191 , and the optical coupling layer  190   d  and the sheet-like wavelength converting layer  180   a  have at least a gap B therebetween. As shown in  FIG. 4 , the optical coupling layer  190   d  of the present embodiment is, for example, a structure having a cross-sectional pattern constituted by periodic triangular patterns, and the gap B exists between two adjacent triangular patterns; certainly, in other embodiments (not shown), the cross-sectional pattern of the optical coupling layer can also have different shapes, and the shapes can also be arranged non-periodically, which are all still within the protection scope of the invention. Since a contact surface between the optical coupling layer  190   d  and the sheet-like wavelength converting layer  180   a  is non-flat, based on such structural design, the light emitted from the epitaxial structure E can have a better scattering effect, and thereby effectively improve the light emitting uniformity of the overall whole light emitting device  100   d . In addition, the gap between the optical coupling layer  190   d  and the sheet-like wavelength converting layer  180   a  can serve as a buffer space between two different layers, so that the epitaxial structure E and the sheet-like wavelength converting layer  180   a  can have a favorable bonding effect therebetween, so as to improve the reliability of the light emitting device  100   d.    
       FIG. 5  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 5  and  FIG. 2A , the light emitting device  100   e  of the present embodiment is similar to the light emitting device  100   b   1  in  FIG. 2A , and a main difference therebetween lies in that, the sheet-like wavelength converting layer  180   e  of the light emitting device  100   e  includes at least two sheet-like wavelength converting unit layers, and a main emission peak wavelength of each of the sheet-like wavelength converting unit layers gradually decreases towards a direction away from the epitaxial structure E. In the present embodiment, the at least two sheet-like wavelength converting unit layers are three sheet-like wavelength converting unit layers, and the sheet-like wavelength converting unit layers include a first sheet-like wavelength converting unit layer  182   e , a second sheet-like wavelength converting unit layer  184   e  and a third sheet-like wavelength converting unit layer  186   e  that are sequentially stacked. A main emission peak wavelength of the first sheet-like wavelength converting unit layer  182   e  is greater than a main emission peak wavelength of the second sheet-like wavelength converting unit layer  184   e , and the main emission peak wavelength of the second sheet-like wavelength converting unit layer  184   e  is greater than a main emission peak wavelength of the third sheet-like wavelength converting unit layer  186   e . With such an arrangement, the light converted by the first sheet-like wavelength converting unit layer  182   e , which has the greater main emission peak wavelength, can not be absorbed by the second and the third sheet-like wavelength converting unit layers  184   e ,  186   e , which have the shorter main emission peak wavelengths, and so forth. For instance, when the epitaxial structure E emits a blue light, the first sheet-like wavelength converting unit layer  182   e  may, for example, be a red light sheet-like wavelength converting unit layer, the second sheet-like wavelength converting unit layer  184   e  may, for example, be a yellow light sheet-like wavelength converting unit layer, and the third sheet-like wavelength converting unit layer  186   e  may, for example, be a green light sheet-like wavelength converting unit layer, and thus the light emitting uniformity and the color rendering of the overall light emitting device  100   e  can be effectively enhanced. Certainly, in other embodiments, the first sheet-like wavelength converting unit layer  182   e , the second sheet-like wavelength converting unit layer  184   e  and the third sheet-like wavelength converting unit layer  186   e  may also be sheet-like wavelength converting unit layers of other colors, which are not limited by the invention. Particularly, extending directions of the first sheet-like wavelength converting unit layer  182   e , the second sheet-like wavelength converting unit layer  184   e  and the third sheet-like wavelength converting unit layer  186   e  are the same as the extending direction of the substrate  110   a . Herein, the first sheet-like wavelength converting unit layer  182   e , the second sheet-like wavelength converting unit layer  184   e , the third sheet-like wavelength converting unit layer  186   e  and the substrate  110   a  have the same extending direction, and are all being laterally extended planar structures, so that the overall light emitting device  100   e  has a smaller volume. Preferably, a thickness of each of the sheet-like wavelength converting unit layers is between 5 μm to 30 μm. 
       FIG. 6  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 6  and  FIG. 5 , the light emitting device  100   f  of the present embodiment is similar to the light emitting device  100   e  in  FIG. 5 , and a main difference therebetween lies in that: in the sheet-like wavelength converting layer  180   f  of the present embodiment, a thickness of the first sheet-like wavelength converting unit layer  182   f , a thickness of the second sheet-like wavelength converting unit layer  184   f , and a thickness of the third sheet-like wavelength converting unit layer  186   f  are all different from each other. Preferably, the thickness of each of the sheet-like wavelength converting unit layers gradually increases towards the direction away from the epitaxial structure E. With such an arrangement, the light converted by the first sheet-like wavelength converting unit layer  182   f , which has the greater main emission peak wavelength, can not be absorbed by the second and the third sheet-like wavelength converting unit layers  184   f ,  186   f , which have the shorter main emission peak wavelengths, so that an effect of having high color rendering effect and light emitting uniformity can be achieve without requiring every layer to have the same thickness. For instance, when the first sheet-like wavelength converting unit layer  182   f  is a red light sheet-like wavelength converting unit layer and the second sheet-like wavelength converting unit layer  184   f  is a green light sheet-like wavelength converting unit layer, wherein a thickness of the first sheet-like wavelength converting unit layer  182   f  is 0.2 times to 0.4 times a thickness of the second sheet-like wavelength converting unit layer  184   f , a usage amount of red phosphor powder with higher cost can be reduced, and thereby can effectively lower a manufacturing cost of the overall light emitting device  100   f.    
       FIG. 7  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 7  and  FIG. 2A , the light emitting device  100   g  of the present embodiment is similar to the light emitting device  100   b   1  in  FIG. 2A , and a main difference therebetween lies in that: at least one space  117  exits between each of the conductive through holes  116   g  of the substrate  110   g  and the electrode connection layer  120   a  in the present embodiment, wherein the space  117  can serve as a buffer space between layers having different thermal expansion coefficients under processes in different temperatures, such as between the conductive through hole  116   g  and the electrode connection layer  120   a , and between the conductive through hole  116   g  and the pad  170 , so as to improve a reliability of the light emitting device  100   g . Herein, the space  117  in  FIG. 7  may be close to or connect with the upper surface  112  or the lower surface  114  of the substrate  110   g , but not limited thereto. 
       FIG. 8  is a schematic top view illustrating an electrode connection layer of a light emitting device according to another embodiment of the invention. Referring to  FIG. 8 , the electrode connection layer  120   h  of the light emitting device  100   h  of the present embodiment has a plurality of first electrodes  122   h  and a plurality of second electrodes  124   h , wherein a profile of each of the first electrodes  122   h  when viewing from atop is a point shape, and a profile of the second electrodes  124   h  when viewing from atop is a combination of a point shape and a line shape. That is, the second electrodes  124   h  of the present embodiment simultaneously have electrodes with a point-shaped contour and electrodes with a line-shaped contour; and as shown in  FIG. 8 , these electrode patterns are in a condition of being separated from each other. Since the second electrodes  124   h  in the light emitting device  100   h  of the present embodiment have the electrode patterns with point-sharped and line-shaped contours, a current distribution can be more even and a forward voltage can be effectively decreased. 
       FIG. 9A  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 9A  and  FIG. 3A , the light emitting device  100   i   1  of the present embodiment is similar to the light emitting device  100   c   1  in  FIG. 3A , and a main difference therebetween lies in that: the light emitting device  100   i   1  of the present embodiment further includes an ohmic contact layer  210   a  disposed between the first type semiconductor layer  140  and the insulating layer  130 . In addition, the light emitting device  100   i   1  further includes a reflection layer  220  disposed between the ohmic contact layer  210   a  and the insulating layer  130 . Herein, the configuration of the ohmic contact layer  210   a  can effectively enhance an electrical connection between the first type semiconductor layer  140  and the first electrode  122   a , wherein a material of the ohmic contact layer  210   a  is, for example, nickel or nickel oxide. A material of the reflection layer  220  is, for example, silver, aluminium or an alloy thereof, which is adapted to reflect the light emitted from the light emitting layer  150 , so as to achieve a better light emitting efficiency. Moreover, a thickness of the ohmic contact layer  210   a  and a thickness of the reflection layer  220  of the present embodiment are, for example, between 1000 Å and 7000 Å, and preferably, between 1000 Å and 3500 Å. 
       FIG. 9B  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 9B  and  FIG. 9A , the light emitting device  100   i   2  of the present embodiment is similar to the light emitting device  100   i   1  in  FIG. 9A , and a main difference therebetween lies in that: the ohmic contact layer  210   b  is a patterned structure, such as in the light emitting device  100   i   2  shown in  FIG. 9B , a cross-sectional pattern of the ohmic contact layer  210   b  is substantially constituted by periodic island-shaped patterns, and thus the first type semiconductor layer  140 , the first electrode  122   a  and the reflection layer  220  have a larger contact surface area therebetween, so that the electrical connections and bonding between the ohmic contact layer  210   b , the first type semiconductor layer  140 , the first electrode  122   a  and the reflection layer  220  are enhanced. However, the cross-sectional pattern of the ohmic contact layer  210   b  may also be constituted by other periodic or non-periodical patterns, and is not limited thereto. 
       FIG. 10  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 10  and  FIG. 9A , the light emitting device  100   j  of the present embodiment is similar to the light emitting device  100   i   1  in  FIG. 9A , and a main difference therebetween lies in that: the light emitting device  100   j  of the present embodiment further includes an insulation protection layer  230 , which covers an edge of the first type semiconductor layer  140 , an edge of the emitting layer  150  and an edge of the second type semiconductor layer  160 , wherein an edge  231  of the insulation protection layer  230  is substantially aligned with an edge of the insulating layer  130 . Herein, a material of the insulation protection layer can be silicon dioxide, silicon nitride, or a combination thereof. The insulation protection layer  230  is configured to effectively protect the edge of the epitaxial structure E, so as to avoid invasion of vapor and oxygen and effectively improve an overall product reliability of the light emitting device  100   j . It should be particularly noted that, the insulation protection layer  230  in the present embodiment further covers edges of the ohmic contact layer  210   a  and the reflection layer  220 , so as to provide the light emitting device  100   j  with better reliability. Furthermore, the insulation protection layer  230  and insulating layer  130  can be disposed integrally. 
       FIG. 11  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 11  and  FIG. 10 , the light emitting device  100   k  of the present embodiment is similar to the light emitting device  100   j  in  FIG. 10 , and a main difference therebetween lies in that: the light emitting device  100   k  of the present embodiment further includes a color mixing layer  240  disposed on the sheet-like wavelength converting layer  180   a . In the present embodiment, the color mixing layer  240  is made of a transparent material, such as glass, sapphire, epoxy resin or silicon; and a thickness of the color mixing layer  240  is greater than 100 μm. In other words, the thickness of the color mixing layer  240  is greater than the thickness of the epitaxial structure E plus the thickness of the sheet-like wavelength converting layer  180   a . Herein, the color mixing layer  240 , which has the thicker thickness, can be regarded as a light guiding layer, and can uniformly mix the light emitted from the epitaxial structure E and the light converted by the sheet-like wavelength converting layer  180   a , so as to effectively enhance the overall light emitting uniformity of the light emitting device  100   k.    
       FIG. 12  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 12  and  FIG. 1 , the light emitting device  100   m  of the present embodiment is similar to the light emitting device  100   a  in  FIG. 1 , and a main difference therebetween lies in that: there are a plurality of epitaxial structures E 1  disposed on substrate  110   m , located on the conductive electrode connection layer  120   m  and separated from each other. The plurality of epitaxial structures E include at least one red light epitaxial structure E 11 , at least one blue light epitaxial structure E 12  and at least one green light epitaxial structure E 13 . A width of the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) is less than a width of the general epitaxial structure (e.g., the side length in a range from 0.2 millimetres to 1 millimeters). Herein, a width of the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) is between 1 micrometer and 150 micrometers. More preferably, the width of the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) is between 1 micrometer and 40 micrometers. In other words, the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) is a micron grading structure that allows the light emitting device  100   m  to have a smaller volume and better efficiency. 
     In addition, the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) includes a first type semiconductor layer  140   m , a light emitting layer  150   m  and a second type semiconductor layer  160   m , wherein the light emitting layer  150   m  is located between the first type semiconductor layer  140   m  and the second type semiconductor layer  160   m . A thickness of the second type semiconductor layer  160   m  is in a range from 1 micrometer to 6 micrometers, a thickness of the light emitting  150   m  is in a range from 0.1 micrometers to 1 micrometer, and a thickness of the first type semiconductor layer  140   m  is in a range from 0.1 micrometers to 0.5 micrometers. In an exemplary embodiment, the thickness of the second type semiconductor layer  160   m  is 5 micrometers, for example, the thickness of the light emitting layer  150   m  is 0.7 micrometers, for example, and the thickness of the first type semiconductor layer  140   m  is 0.4 micrometers, for example. Moreover, the second type semiconductor layer  160   m  in the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) has the greatest thickness. The thickness of the second type semiconductor layer  160   m  is 3 times to 15 times of the thickness of the light emitting layer  150   m , and the thickness of the second type semiconductor layer  160   m  is 10 times to 20 times of the thickness of the first type semiconductor layer  140   m . Moreover, a highest peak current density of an external quantum efficiency curve of the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) of this embodiment is smaller than the peak current density of the epitaxial structure of the conventional light emitting diode. Preferably, the highest peak current density of the external quantum efficiency curve of the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) of this embodiment is lower than 2 A/cm 2 . More preferably, the highest peak current density of the external quantum efficiency curve of the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) of this embodiment is in a range from 0.5 A/cm 2  to 1.5 A/cm 2 . 
     In the light emitting device  100   m  of the present embodiment, the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) of this embodiment has a first peripheral surface P 1 , and the insulating layer  130   m  has a second peripheral surface P 2 , and the second peripheral surface P 2  is aligned with the first peripheral surface P 1 . That is, the insulating layer  130   m  is not covered with first peripheral surface P 1  of the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ). Therefore, the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ) can have a large light exit area, the insulating layer  130   m  can extended to the periphery to increase the contact area with the red light epitaxial structure E 11  (or the blue light epitaxial structure E 12 ; or the green blue light epitaxial structure E 13 ), and the insulating layer  130   m  can also have a buffer function. Furthermore, the substrate  110   m  has a peripheral surface P 4  and the conductive electrode connection layer P 5  has a third peripheral surface P 5 , and the peripheral surface P 4  is aligned with the third peripheral surface P 5 . 
       FIG. 13  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 13  and  FIG. 12 , the light emitting device  100   n  of the present embodiment is similar to the light emitting device  100   m  in  FIG. 12 , and a main difference therebetween lies in that: the substrate  110   n  has an upper surface  112   n  and a lower surface  114   n  opposite to each other, and a plurality of conductive through holes  116   n  penetrating through the substrate  110   n  and connecting to the upper surface  112   n  and the lower surface  114   n . Furthermore, the light emitting device  100   n  furthermore includes a plurality of pads  170   n  disposed on the lower surface  114   n  of the substrate  110   n , wherein the pads  170   n  are connected with the conductive through holes  116   n , and the conductive electrode connection layer  120   n  is electrically connected with the conductive through holes  116   n.    
       FIG. 14  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 14  and  FIG. 12 , the light emitting device  100   p  of the present embodiment is similar to the light emitting device  100   m  in  FIG. 12 , and a main difference therebetween lies in that: the substrate  110   p  includes a plurality of circuit electrodes  118   p  and the conductive electrode connection layer  120   m  are electrically connected to the circuit electrodes  118   p . Herein, the substrate  110   p  is embodied as a thin film transistor (TFT) substrate, and the circuit electrodes  118   p  are electrically connected to the TFT structures  119   p . However, the substrate  110   p  may also be a complementary metal oxide semiconductor substrate, a printed circuit board substrate, a flexible substrate or a substrate with circuit electrodes, and the invention is not limited thereto. 
       FIG. 15  is a schematic cross-sectional view illustrating a light emitting device according to another embodiment of the invention. Referring to  FIG. 15  and  FIG. 12 , the light emitting device  100   q  of the present embodiment is similar to the light emitting device  100   m  in  FIG. 12 , and a main difference therebetween lies in that: the substrate  110   q  includes a plurality of circuit electrodes  118   q  and the conductive electrode connection layer  120   m  are electrically connected to the circuit electrodes  118   q . Herein, the substrate  110   q  for example, is a TFT substrate, a complementary metal oxide semiconductor substrate, a printed circuit board substrate, a flexible substrate or the substrate with circuit electrodes, and the invention is not limited thereto. In particular, the substrate  110   q  further provided with two through holes  116   q , and the outermost conductive electrode connection layer  120   m  is driven by the external circuit through the through holes  116   q  and the pads  170   q.    
     It should be noted that, in other embodiments (not shown), the aforementioned elements, such as the optical coupling layers  190   c   1 ,  190   c   2 ,  190   c   3 ,  190   d , the sheet-like wavelength converting layers  180   a ,  180   e ,  180   f , the substrate  110   g , the electrode connection layer  120   h , the ohmic contact layer  210   b , the reflection layer  220 , the insulation protection layer  230  and the color mixing layer  240 , can also be used, and those skilled in the art should be able to achieve desirable technical effects by selectively implementing the aforementioned elements based on the descriptions provided in the above embodiments and according to the actual requirements. 
     In summary, in the light emitting device of the invention, since the edge of the electrode connection layer is substantially aligned with the edge of the substrate, as compared to the conventional light emitting device, which electrically connects the electrodes of the light emitting device onto the pads of a larger carrier board, the light emitting device of the invention can have a smaller volume. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.