Abstract:
An embodiment of the present application discloses a light-emitting structure, comprising a substrate, a first unit and a second unit separately form on the substrate; a trench formed between the first unit and the second unit, and having a bottom portion exposing the substrate, a less steep sidewall and a steeper sidewall steeper than the less steep sidewall; and an electrical connection connecting the first unit and the second unit and covering the first unit, the second unit and the less steep sidewall; wherein the sidewalls directly connect to the bottom portion, and the steeper sidewall is devoid of the electrical connection covering.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional patent application No. 61/382,451 filed on Sep. 13, 2010, and the content of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present application relates to a light-emitting structure, and more particularly to a light-emitting structure having at least two light-emitting units and an electrical connection for connecting the light-emitting units. 
     DESCRIPTION OF BACKGROUND ART 
     A light-emitting diode array is constructed by electrically connecting several light-emitting diodes in series or parallel. One diode is electrically separated from another by a trench or groove. To connect the separated diodes, metal line(s) or film(s) can be used to span the trench between the diodes. However, the metal line(s) or film(s) can be easily damaged during the manufacturing process due to a high aspect ratio of the trench. 
     SUMMARY OF THE DISCLOSURE 
     An embodiment of the present application discloses a light-emitting structure which includes a first unit; a second unit; a trench, between the first unit and the second unit, having a first sidewall and a second sidewall steeper than the first sidewall; and an electrical connection arranged on the first sidewall. 
     Another embodiment of the present application discloses a light-emitting structure which includes a first unit; a second unit; a trench between the first unit and the second unit; and an electrical connection having a joining portion and a bridging portion arranged over the trench and being wider than the joining portion. 
     Another embodiment of the present application discloses a light-emitting structure which includes a first unit; a second unit; a trench between the first unit and the second unit; an isolation layer arranged on the trench and exposing a portion of the first unit nearby the trench; and an electrical connection contacting the portion of the first unit nearby the trench and the second unit. 
     A further embodiment of the present application discloses a light-emitting structure which includes a substrate; a first unit and a second unit separately form on the substrate; a trench, between the first unit and the second unit, having a bottom portion exposing the substrate, a first sidewall and a second sidewall steeper than the first sidewall; and an electrical connection connecting the first unit and the second unit and covering the first unit, the second unit and the first sidewall; wherein the first sidewall and the second sidewall directly connect to the bottom portion, and the second sidewall is devoid of the electrical connection covering. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a cross-sectional view disclosing a connection between two light-emitting structure units in accordance with an embodiment of the present invention; 
         FIG. 2  illustrates a top view of light-emitting structure units in accordance with an embodiment of the present invention; 
         FIG. 3  illustrates a filling of the trench in accordance with an embodiment of the present invention; 
         FIG. 4  illustrates a top view of an electrical connection over a trench in accordance with an embodiment of the present invention; 
         FIG. 5  illustrates a top view of an electrical connection over a trench between two light-emitting structure units in accordance with another embodiment of the present invention; 
         FIG. 6  illustrates a cross-sectional view of interconnections between light-emitting structure units in accordance with one embodiment of the present invention; 
         FIG. 7  illustrates a cross sectional view of several light-emitting structure units in accordance with an embodiment of the present invention; 
         FIGS. 8A-8F  illustrate steps of forming light-emitting structure unit in accordance with an embodiment of the present invention; and 
         FIG. 9  illustrates a cross sectional view of a light-emitting structure unit in accordance with an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  illustrates a cross-sectional view disclosing a connection between two light-emitting structure units in accordance with an embodiment of the present invention. Each of the left light-emitting structure unit  10 A and the right light-emitting structure unit  10 B includes a lower layer ( 11 A,  11 B), an upper layer ( 12 A,  12 B), a light-emitting junction ( 13 A,  13 B) between the lower layer ( 11 A,  11 B) and the upper layer ( 12 A,  12 B), and a current spreading layer ( 14 A,  14 B), which are sequentially formed on a substrate (not shown) by epitaxial growth or bonding method such as metal boding, fusion bonding, and glue bonding. 
     The left light-emitting structure unit  10 A and the right light-emitting structure unit  10 B can be supported by a common substrate or discrete substrates, and electrically separated by a trench  15 . For example, the light-emitting structure units  10 A and  10 B can be commonly formed on a single bulk substrate, such as sapphire, GaAs, Si, metal, glass, or PCB; or each light-emitting structure unit is formed on its independent bulk substrate as described aforementioned, while each independent bulk substrate can be further integrated together by mechanical gadgets, organic material, metallic material, or any combination thereof. The trench  15  is formed to reach to, enter in, or penetrate the substrate or any layer between the units. The trench  15  has a cross-sectional profile of at least one rounded edge and/or at least one chamfered edge. The rounded edge and/or the chamfered edge can be formed on a single layer or several layers. For example, as shown in the drawing, the rounded edge and/or the chamfered edge can be formed on the lower layer  11 A and/or the lower layer  11 B. However, the rounded edge and/or the chamfered edge can be also formed on both of the upper layer and the lower layer. The rounded edge preferably has a radius R not less than 1 μm. The chamfered edge can have two equal or different bevel lengths (L bevel ). 
     Moreover, a sidewall of the trench is inclined by more than 80 degree against the bottom surface of the lower layer. For example, the angle θ between the sidewall and the bottom surface of the lower layer, as illustrated in the drawing, is smaller than 80 degree, 70 degree, 60 degree, 50 degree, or 40 degree. The angle θ can also fall within a specific range, such as 80 degree˜70 degree, 70 degree˜60 degree, and 60 degree˜40 degree. Besides, the trench may have sidewalls inclined at similar or different angles. For example, one sidewall is inclined at an angle of 50 degree˜40 degrees; the other sidewall is inclined at an angle of 60 degree˜50 degree. Provided one or more sidewalls are inclined, the trench can have a trapezoid cross section having a height, a longer side, and a shorter side parallel to the longer side. The height is close to the thickness of the lower layer or the total thickness of the upper layer and the lower layer. For example, the height is between 1 μm˜10 μm; the longer side has a length of 3 μm˜100 μm; the shorter side has a length of 1 μm˜40 μm; the ratio of the longer side to the short side is between 3:1 and 1.5:1. Specifically, the height is between 4 μm˜9 μm; the length of the longer side is between 5 μm˜40 μm; the length of the shorter side is between 2.5 μm˜20 μm. 
     To build an electrical passage between the units, an electrical connection  18  bridges the trench  15  and electrically connects any two layers, which do not belong to the same unit, of the lower layer  11 A, lower layer  11 B, upper layer  12 A, and upper layer  12 B. For example, the units can be coupled together in series connection by bridging the lower layer  11 A and the upper layer  12 B, or the upper layer  12 A and the lower layer  11 B; the units can be coupled in parallel connection by bridging the upper layer  12 A and upper layer  12 B. 
     To prevent the electrical connection  18  from unintentionally contacting with other layer, an isolation layer  16  can be also provided on the trench  15  and some areas near the trench opening, such as the sidewall(s) of the lower layer  11 A and/or the lower layer  11 B, the edge(s) of the trench  15 , the sidewall(s) of the upper layer  12 A and/or the upper layer  12 B, the top surface(s) of the upper layer  12 A and/or the upper layer  12 B, and/or the bottom surface(s) of the current spreading layer  14 A and/or the current spreading layer  14 B. Optionally, an isolation layer  17  can be further provided between the isolation layer  16  and the electrical connection  18 . The isolation layer  17  can be used to fill the empty space between the isolation layer  16  and the electrical connection  18 , to fill voids on the isolation layer  16 , to smooth the outer surface of the isolation layer  16 , to fill the trench  15 , to form a flat plane for laying the electrical connection  18 , to cover area(s) not under the shade of the isolation layer  16 , to improve ESD protection, and/or to support the electrical connection  18 . 
     The isolation layer  16  can have an edge with an acute angle; the layer laid on the isolation layer  16  therefore can smoothly cover the drop on the edge of the isolation layer  16 . The slope of the edge can release the stress concentrated on the layer over the drop. The acute angle can be less than 90, 80, 70, 60, or 50 degree. Besides the isolation layer  16 , the isolation layer  17  can also have an edge with an acute angle. 
     In addition, to protect the electrical connection  18  from oxidation, erosion, and/or damage, a passivation  19  can be formed on the electrical connection  18 . The passivation  19  can cover not only outer surface(s) of the electrical connection  18  but also the area beyond the outer surface(s). Specifically, the passivation  19  can be further formed on any surfaces of the isolation layer  17 , the current spreading layer  14 A, the current spreading layer  14 B, the upper layer  12 A, the upper layer  12 B, the lower layer  11 A, and/or the lower layer  11 B. 
       FIG. 2  illustrates a top view of light-emitting structure units in accordance with an embodiment of the present invention. In the drawing, four rectangular light-emitting structure units  1 ,  2 ,  3 ,  4  are deployed in a 2×2 array; however, the shape, the number, and the deployment of the light-emitting structure units are only illustrative but not to limit applications and variations of the present invention. 
     The light-emitting structure units  1 ,  2 ,  3 ,  4  are laterally separated by trenches  15 . An electrical connection  18  can bridge the trench  15  from one light-emitting structure unit (for example, unit  3 ) to another light-emitting structure unit (for example, unit  4 ) and couple the two units in series or parallel connection. As shown in cross section AA′, the trench  15  (for example, between units  1  and  4 ) on which no electrical connection  18  is formed has steeper sidewalls, therefore, more volume of the light-emitting structure unit resides nearby the trench  15 . In contrast, as shown in cross section BB′, the trench  15  (for example, between units  3  and  4 ) on which the electrical connection  18  is formed has less steep sidewalls in comparison with the sidewalls in the cross section AA′. In one embodiment, some of the light-emitting structure units are removed to form a trench having a ladder-shaped, and/or inclined sidewall. In other words, the trench has a reversed-trapezoid or quasi-reversed-trapezoid cross-sectional profile. For example, the method for forming the trench can be selected from wet etching, dry etching, laser machining, diamond scribing, and any combination thereof. In general, the steeper the sidewall is, the shorter the processing time is taken. 
     In addition, the less steep sidewall can be formed on either a full length trench L full  or a partial length trench L partial  (as illustrated in  FIG. 2 ). The full length trench L full  herein is defined as a trench having a length similar to the width of the light-emitting structure unit; the partial length trench L partial  is defined as a trench has a length smaller than the width of the light-emitting structure unit. For example, L partial  is between 10 μm˜100 μm; the width of the light-emitting structure unit is between 100 μm˜1000 μm; the ratio of L partial  to width of the light-emitting structure unit is between 1:2˜1:10. Moreover, the electrical connection  18  can be further connected with a current network  20  through which current can come from or flow to a position far away from the electrical connection  18 , as shown in  FIG. 5 . 
       FIG. 3  illustrates a filling of the trench. In step ( 1 ), an isolation layer  21  and a lower electrical connection  22   a  are sequentially provided on a trench  23  which is formed between two light-emitting structure units  24 ,  25 . The isolation layer  21  can separate the lower electrical connection  22   a  from contacting with the light-emitting structure units  24 ,  25 . The lower electrical connection  22   a  can electrically link two light-emitting structure units  24 ,  25 . The lower electrical connection  22   a  can be formed by deposition and etching processes. Because the trench  23  has a tapered cross section, the inclined portion of the lower electrical connection  22   a  therefore usually is thinner than the flat portions thereof, and can be easily damaged during following processes. To reinforce the inclined portion of the lower electrical connection  22   a , an upper electrical connection  22   b  is further provided on the lower electrical connection  22   a . The upper electrical connection  22   b  is preferably provided on the top of the inclined portion or within the trench  23 , as shown in step ( 2 ). 
       FIG. 4  illustrates a top view of an electrical connection over a trench between two light-emitting structure units in accordance with one embodiment of the present invention. The electrical connection  250  has a bridging portion  250   a  over the trench  23  and two joining portions  250   b . Each of the two joining portions  250   b  is electrically connected to an anode or a cathode on each of the two light-emitting structure units  26 . The bridging portion  250   a  has a BB cross section; the joining portion  250   b  has an AA cross section. The BB cross section has a width greater than that of the AA cross section, while the two cross sections can have equal or close area for achieving a constant or even electrical current per cross sectional area. For example, the bridging portion  250   a  has a width of 5 μm-50 μm; the joining portion  250   b  has a width of 3 μm-15 μm while both of them has a thickness close to 8 μm. However, the two cross sections can also have different area according to user&#39;s requirements or practical manufacturing processes. The bridging portion  250   a  can be constructed after the basic electrical connection manufacturing process is completed. For example, the electrical connection  250  over the trench  23  which has inclined sidewalls is firstly formed by depositing metal on specific areas of the trench  23  and the light-emitting structure units  26 . But the deposited metal on the inclined sidewalls of the trench  23  is usually thinner than the deposited metal on the light-emitting structure unit  26 , and the deposited metal bridging the two light-emitting structure units therefore has various cross sectional area. To increase the volume or the cross sectional area of the metal over the trench  23 , an extra-deposition process is further applied on the thinner deposited metal area to form the bridging portion  250   a  as described above. Furthermore, the volume or the cross sectional area of the electrical connection  250  over the trench  23  can be increased by other methods, such as bonding one or more supplement articles on the thinner electrical connection portions, and depositing other material(s). The supplement article is such as metal and ceramic. Moreover, the thicker electrical connection portions can be even thinned down to the level similar to the portions over the trench  23 . 
       FIG. 5  illustrates a top view of an electrical connection  250  over a trench  23  between two light-emitting structure units in accordance with another embodiment of the present invention. Each of the light-emitting structure unit  26  includes a lower layer  27  and an upper layer  28  having a smaller area than that of the lower layer  27 . The lower layer  27  has a mesa area  29  surrounding the upper layer  28 . The light-emitting structure unit  26  can emit light from a light-emitting layer which is positioned within the upper layer  28  or between the upper layer  28  and the lower layer  27 . Provided the light-emitting layer is positioned within the upper layer  28 , the upper layer  28  can include a p-type semiconductor layer and an n-type semiconductor layer, between which the light-emitting layer is sandwiched; and the lower layer  27  can include a carrier for supporting the upper layer  28 . The upper layer  28  can be epitaxially grown on the lower layer  27 , or be integrated with the lower layer  27  by glue bonding, metal bonding, fusion bonding, or eutectic bonding. Provided the light-emitting layer is positioned between the upper layer  28  and the lower layer  27 , either the upper layer  28  or the lower layer  27  can include a p-type semiconductor layer, and the other can include an n-type semiconductor layer. 
     To build a current passage from one light-emitting structure unit to another, an electrical connection  250  is provided on the two light-emitting structure units  26 . As shown in the drawing, one end of the electrical connection  250  is installed on the upper layer  28 , and the other end is installed on the lower layer  27 . However, the two ends of the electrical connection  250  can be also installed on two upper layers  28  or two lower layers  27 . The electrical connection  250  can be constructed by metal, semiconductor, metal oxide, or any combination thereof. Provided a metal oxide, which has higher transparency than that of metal, is used to form the electrical connection  250 , fewer light escaping areas are therefore shaded by the electrical connection  250 . The metal oxide is such as ITO, IZO, and CTO. 
       FIG. 6  illustrates a cross-sectional view of interconnections between light-emitting structure units in accordance with one embodiment of the present invention. Each light-emitting structure unit  26  includes an upper layer  28  and a lower layer  27  formed on a common substrate  30  by epitaxial growth and/or bonding method. The bonding method includes but not limited to metal bonding, eutectic bonding, glue bonding, and fusion bonding. A light-emitting zone  31  is sandwiched by the upper layer  28  and the lower layer  27 . The light-emitting zone  31  can generate light when a bias voltage is imposed on the upper layer  28  and the lower layer  27 . The light from the light-emitting zone  31  radiates isotropically. 
     Two light-emitting structure units  26  are separated by a trench  23 . Provided the two light-emitting structure units  26  are coupled in series connection, an isolation layer  21  is formed on the trench  23  to leave the electrical connection  250  touching the upper layer  28  of one light-emitting structure unit  26  and the lower layer  27  of another light-emitting structure unit  26 . In this embodiment, the isolation layer  21  is formed to expose not only the top surface but a portion of the sidewall of the lower layer  27 . The exposure of the sidewall of the lower layer  27  can increase the contact area between the electrical connection  250  and the lower layer  27 , and accordingly the current density can decrease. 
       FIG. 7  illustrates a cross sectional view of several light-emitting structure units in accordance with an embodiment of the present invention. The several light-emitting structure units  26  are supported by a substrate  30 . Two neighboring light-emitting structure units  26  are separated by a trench  23 . In the present embodiment, the trench  23  is trapezoid-shaped and has a narrower top opening and a wider bottom. The light-emitting structure unit  26  nearby the trench  23  therefore has an undercut sidewall with a degree greater than 90 degree, as shown in the drawing. In other words, the light-emitting structure unit  26  has a reversed trapezoid shape. Provided the light-emitting structure unit  26  can emit light from the middle part, the central part, or the upper part of the reversed trapezoid, the light moving backwards can leave the unit  26  on the benefit of the undercut sidewalls. The trapezoid-shaped trench can be formed by using over etching process. 
     In accordance with one embodiment of the present invention, the light-emitting structure unit can include at least a first conductivity layer (for example, the upper layer), a conversion unit (for example, the light-emitting zone), and a second conductivity layer (for example, the lower layer). Each of the first conductivity layer and the second conductivity layer has a single layer or a group of multiple layers (“multiple layers” means two or more layers), and the two single layers or the two groups of the multiple layers, which are respectively located on the first and the second conductivity layers, have distinct polarities or distinct dopants. For example, the first conductivity layer is a p-type semiconductor layer; the second conductivity layer is an n-type semiconductor layer. The conversion unit disposed between the first conductivity layer and the second conductivity layer is a region where the light energy and the electrical energy could be transferred or induced to transfer. The one that the electrical energy can be transferred to the light energy is such as a light-emitting diode, a liquid crystal display, and an organic light-emitting diode. The one that the light energy can be transferred to the electrical energy is such as a solar cell, and an optoelectronic diode. 
     The transferred light emission spectrum of the light-emitting diode can be controlled by changing the physical or chemical arrangement of one layer or more layers in the light-emitting diode. The light-emitting diode can be composed of several materials, such as the series of aluminum gallium indium phosphide (AlGaInP), the series of aluminum gallium indium nitride (AlGaInN), and/or the series of zinc oxide (ZnO). The conversion unit can be configured to be a single heterostructure (SH), a double heterostructure (DH), a double-side double heterostructure (DDH), or a multi-quantum well (MWQ). Besides, the wavelength of the emitting light could be controlled by changing the number of the pairs of the quantum well. 
     The material of the substrate(s) used for growing or supporting the light-emitting structure unit(s) can include but not limits to germanium (Ge), gallium arsenide (GaAs), indium phosphide (InP), sapphire, silicon carbide (SiC), silicon (Si), lithium aluminium oxide (LiAlO2), zinc oxide (ZnO), gallium nitride (GaN), aluminum nitride (MN), glass, composite, diamond, CVD diamond, diamond-like carbon (DLC) and any combination thereof. 
       FIGS. 8A through 8F  illustrate a method of forming light-emitting structure unit(s), or more specific to light emitting diode structures, in accordance with another embodiment of the present invention. Firstly, referring to  FIG. 8A , a substrate  41  is provided. The material of the substrate  41  can be silicon, silicon carbide, sapphire, arsenide, phosphide, zinc oxide, and magnesium oxide. Then, a 1st semiconductor layer  42  which is an epitaxy layer of first conductivity, an active layer  43 , and a 2nd semiconductor layer  44  which is an epitaxy layer of second conductivity are formed on the substrate  41 . The material of the 1st semiconductor layer  42  and the 2nd semiconductor layer  44  include but not limited to an indium-containing nitride semiconductor, an aluminum-containing nitride semiconductor, and a gallium-containing nitride semiconductor. The material of the active layer  43  include but not limited to indium gallium nitride, indium gallium aluminum phosphide, aluminum gallium nitride, aluminum gallium arsenide, and indium gallium arsenide. 
     Referring to  FIGS. 8B-8D , a multi-step patterning process is performed. Firstly, a first region of the 2nd semiconductor layer  44  is defined so that the 2nd semiconductor layer  44  has a concave portion  45  therein by photolithography and etching technology. Then, as shown in  FIG. 8C , a second etching process is performed to etch away partial of the 2nd semiconductor layer  44  and partial of the active layer  43  until a surface of the 1st semiconductor layer  42  is exposed. Finally, as shown in  FIG. 8D , a third pattern process is performed to divide the 1st semiconductor layer  42  by forming a trench  46  therebetween through the photolithography and etching technology. After the multi-step patterning process, light emitting diode structure are divided with the step-like sidewall profiles as shown in  FIG. 8D . 
     Referring to  FIG. 8E , an insulating layer  47  is further formed between two divided light emitting diode structures  40  to cover the step-like sidewalls of the adjacent light emitting diode structures. Wherein, the insulating layer  47  is made of dielectric material such as silicon nitride, silicon oxide, aluminum oxide, and the combination thereof. Then, as shown in  FIG. 8F , a conductive structure  48  is formed on the insulating layer  47  to electrically connect the 1st semiconductor layer  42  of the left light emitting diode structure and the 2nd semiconductor layer  43  of the right light emitting diode structure in series. In addition, a 1st electrode  49   a  and a 2nd electrode  49   b  can also be formed at the same step or in the different steps while the conductive structure  48  is formed. 
     In addition to the patterning process mentioned above, the step-like sidewalls could also be formed by using a gray-tone mask or by a half-tone mask. Taking advantage of different opening ratio existing on a single mask, the step-like sidewall profile can be formed through a one-step exposure. 
     Referring to  FIG. 9 , through the step-like sidewall structure, light (as indicated by arrows) comes from different angles can be extracted more easily because the light can go out to the sidewall of the light emitting diodes from different angles, and therefore a better light extraction ability of the light emitting diode structure could be achieved. Besides, because the slope of the step-like sidewalls is gentle, the coverage profile of the insulating layer and the conductive structure on the light emitting diode can be more uniform.