Patent Publication Number: US-2022223437-A1

Title: Self-assembly apparatus and method for semiconductor light-emitting devices

Description:
TECHNICAL FIELD 
     The present disclosure relates to a display device and a method for manufacturing the same, and more particularly, to a self-assembly apparatus and method for a semiconductor light-emitting device with a size of several to several tens of μm. 
     BACKGROUND 
     The current competing technologies for large area display are liquid crystal displays (LCDs), organic light-emitting diode (OLED) displays, micro-LED displays, and the like. 
     However, there exist problems such as not-so-fast response time and low efficiency of light generated by backlight in the case of the LCDs, and there exist drawbacks such as a short lifespan, not-so-good yield, and low efficiency in the case of the OLEDs. 
     The use of semiconductor light-emitting diodes (micro-LEDs (pLEDs)) with a diameter or cross-sectional area of 100 microns or less in a display may provide very high efficiency because the display does not use a polarizer to absorb light. However, since a large display requires millions of LEDs, it has difficulty in transferring the LEDs compared to other technologies. 
     Pick and place, laser lift-off (LLO), self-assembly, and the like have been developed for transfer techniques. Among them, the self-assembly technique, which is a method in which semiconductor light-emitting diodes are self-organized in a fluid, is the most suitable method for realizing a large screen display device. 
     In relation to the self-assembly technique, various methods for improving the assembly speed and accuracy by controlling distribution and movement of semiconductor light-emitting diodes in a fluid have been discussed recently. 
     SUMMARY 
     The present disclosure is directed to solving the above-described problems. The present disclosure describes a self-assembly apparatus and method for semiconductor light-emitting devices capable of separating semiconductor light-emitting devices adhered to each other during the self-assembly, and generating a flow of fluid according to a movement direction of a magnet. 
     According to one aspect of the subject matter described in this application, a self-assembly apparatus for semiconductor light-emitting devices includes: a chamber in which a plurality of semiconductor light-emitting devices each including a magnetic material, and a fluid are accommodated; a transfer unit configured to transfer a substrate on which the semiconductor light-emitting devices are assembled to an assembly position; a magnet disposed to be spaced apart from the chamber to apply a magnetic force to the semiconductor light-emitting devices; a position controller connected to the magnet and configured to control a position of the magnet; and a vibration generator disposed such that at least a portion thereof is in contact with the fluid to generate vibration in the fluid, so as to separate the semiconductor light-emitting devices from each other. An electric field may be produced in the substrate to allow the semiconductor light-emitting devices to be assembled at predetermined positions of the substrate while moving according to a change of the position of the magnet. 
     Implementations according to this aspect may include one or more of the following features. For example, the substrate may be disposed at the chamber such that an assembly surface thereof on which the semiconductor light-emitting devices are assembled faces downward, and at least a portion of the substrate may be immersed in the fluid. 
     In some implementations, the substrate may include a plurality of electrodes extending in one direction, and an electric field may be produced in the substrate when power is applied to the plurality of electrodes. 
     In some implementations, the vibration generator may be provided at each of both sides of the substrate to be adjacent to the substrate. 
     In some implementations, the vibration generator may generate vibration in the fluid before the substrate is transferred to the assembly position. 
     In some implementations, the chamber may accommodate a fluid to which a surfactant is added. 
     In some implementations, a channel communicating with a space in the chamber may be formed, and the channel may generate a flow of the fluid in the chamber in association with movement of the magnet. 
     According to another aspect, a method for self-assembling semiconductor light-emitting devices is provided. The method may include the steps of: putting a plurality of semiconductor light-emitting devices each including a magnetic material into a chamber in which a fluid is accommodated; transferring a substrate on which the semiconductor light-emitting devices are assembled to an assembly position; applying a magnetic force to the semiconductor light-emitting devices to allow the semiconductor light-emitting devices to move in the chamber along one direction; applying an electric field to the substrate to guide the semiconductor light-emitting devices to predetermined positions such that the semiconductor light-emitting devices are assembled at the predetermined positions of the substrate while moving; and generating vibration in the fluid to separate the semiconductor light-emitting devices from each other before the substrate is transferred to the assembly position. 
     Implementations according to this aspect may include one or more following features. For example, the substrate may be disposed at the chamber such that an assembly surface thereof on which the semiconductor light-emitting devices are assembled faces downward, and at least a portion of the substrate may be immersed in the fluid. 
     In some implementations, the semiconductor light-emitting devices may move in a direction in which the magnetic force is applied, and the method may further include generating a flow of the fluid in the chamber in a direction in which the magnetic force is applied. 
     In a self-assembly apparatus and method for semiconductor light-emitting devices according to implementations of the present disclosure, as a vibration generator disposed to be in contact with a fluid generates vibration in a fluid, semiconductor light-emitting devices adhered to each other in the fluid can be separated from each other, thereby preventing two or more semiconductors from being assembled into one cell. 
     In particular, as the vibration generator generates vibration before an assembly substrate is transferred to an assembly position, the semiconductor light-emitting devices can be present while being separated from each other in the fluid before the self-assembly, and minimize the influence of vibration during the self-assembly. 
     In addition, a flow of the fluid can be generated in a direction in which the magnet moves through a channel communicating with a space in the chamber in which the fluid is accommodated to thereby assist the movement of the semiconductor light-emitting devices. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual view illustrating a display device using a semiconductor light-emitting device (diode) according to one implementation of the present disclosure. 
         FIG. 2  is an enlarged view illustrating a portion “A” of the display device in  FIG. 1 . 
         FIG. 3  is an enlarged view of a semiconductor light-emitting device of  FIG. 2 . 
         FIG. 4  is an enlarged view illustrating another example of a semiconductor light-emitting device of  FIG. 2 . 
         FIGS. 5A to 5E  are conceptual views illustrating a new process of fabricating the semiconductor light-emitting device. 
         FIG. 6  illustrates a self-assembly apparatus for semiconductor light-emitting devices according to one implementation of the present disclosure. 
         FIG. 7  illustrates an assembly surface of a substrate submerged in a fluid according to the present disclosure. 
         FIGS. 8A to 8C  illustrate a self-assembly apparatus for semiconductor light-emitting devices according to another implementation of the present disclosure. 
         FIG. 9  is a conceptual view illustrating a semiconductor light-emitting device used for the self-assembly according to the present disclosure. 
         FIGS. 10A to 10G  illustrate a process of self-assembling semiconductor light-emitting devices to a substrate using the self-assembly apparatus of  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Description will now be given in detail according to exemplary implementations disclosed herein, with reference to the accompanying drawings. For the sake of brief description with reference to the drawings, the same or equivalent components may be provided with the same or similar reference numbers, and description thereof will not be repeated. In general, a suffix such as “module” and “unit” may be used to refer to elements or components. Use of such a suffix herein is merely intended to facilitate description of the specification, and the suffix itself is not intended to give any special meaning or function. In describing the present disclosure, if a detailed explanation for a related known function or construction is considered to unnecessarily divert the main point of the present disclosure, such explanation has been omitted but would be understood by those skilled in the art. The accompanying drawings are used to help easily understand the technical idea of the present disclosure and it should be understood that the idea of the present disclosure is not limited by the accompanying drawings. It will be understood that when an element such as a layer, area or substrate is referred to as being “on” another element, it can be directly on the element, or one or more intervening elements may also be present. 
     A display device disclosed herein may include a mobile phone, a smart phone, a laptop computer, a digital broadcast terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigator, a slate PC, a tablet PC, an ultrabook, a digital TV, a desktop computer, and the like. However, it would be readily apparent to those skilled in the art that the configuration according to the implementations described herein may also be applied to a new product type of display device that will be developed later. 
       FIG. 1  is a conceptual view illustrating a display device using a semiconductor light-emitting device according to one implementation of the present disclosure,  FIG. 2  is an enlarged view of a portion “A” of the display device in  FIG. 1 ,  FIG. 3  is an enlarged view of a semiconductor light-emitting device of  FIG. 2 , and  FIG. 4  is an enlarged view illustrating another example of the semiconductor light-emitting device of  FIG. 2 . 
     As illustrated, information processed in a control unit (or controller) of a display device  100  may be displayed on a display module  140 . A case with a closed-loop shape surrounding an edge of the display module  140  may form a bezel of the display device  100 . 
     The display module  140  may include a panel  141  on which an image is displayed, and the panel  141  may include semiconductor light-emitting devices  150  with a micro size and a wiring substrate (or board)  110  on which the semiconductor light-emitting devices  150  are mounted. 
     A wiring is formed on the wiring substrate  110  so as to be connected to an n-type electrode  152  and a p-type electrode  156  of the semiconductor light-emitting device  150 . This may allow the semiconductor light-emitting devices  150  to be provided on the wiring substrate  110  as self-emitting individual pixels. 
     An image displayed on the panel  141  is visual information, which is achieved by independently controlling light emission of sub-pixels arranged in the form of matrix through the wiring. 
     The present disclosure exemplarily illustrates a micro light-emitting diode (micro-LED) as one type of the semiconductor light-emitting device  150  that converts current into light. The micro-LED may be a light-emitting diode with a small size of 100 microns or less. The semiconductor light-emitting devices  150  may be provided in blue, red, and green light-emitting regions, respectively, to define a sub-pixel by a combination thereof. That is, the sub-pixel denotes a minimum unit for realizing one color, and at least three micro-LEDs may be provided in the sub-pixel. 
     More specifically, the semiconductor light-emitting device  150  may have a vertical structure as illustrated in  FIG. 3 . 
     For example, each of the semiconductor light-emitting devices  150  may be implemented as a high-power light-emitting device that emits various light colors including blue in a manner that gallium nitride (GaN) is mostly used, and indium (In) and/or aluminum (Al) are added thereto. 
     The vertical type semiconductor light-emitting device may include a p-type electrode  156 , a p-type semiconductor layer  155  formed on the p-type electrode  156 , an active layer  154  formed on the p-type semiconductor layer  155 , an n-type semiconductor layer  153  formed on the active layer  154 , and an n-type electrode  152  formed on the n-type semiconductor layer  153 . Here, the p-type electrode  156  located at the bottom may be electrically connected to a p-electrode of the wiring substrate  110 , and the n-type electrode  152  located at the top may be electrically connected to an n-electrode at an upper side of the semiconductor light-emitting device. The electrodes may be disposed in an up and down direction in the vertical type semiconductor light-emitting device  150  to thereby provide a great advantage of reducing the chip size. 
     Alternatively, referring to  FIG. 4 , the semiconductor light-emitting device may be a flip chip type light-emitting device. 
     For example, a semiconductor light-emitting device  200  may include a p-type electrode  256 , a p-type semiconductor layer  255  on which the p-type electrode  256  is formed, an active layer  254  formed on the p-type semiconductor layer  255 , an n-type semiconductor layer  253  formed on the active layer  254 , and an n-type electrode  252  disposed on the n-type semiconductor layer  253  with being spaced apart from the p-type electrode  256  in a horizontal direction. Here, both the p-type electrode  256  and the n-type electrode  252  may be electrically connected to the p-electrode and the n-electrode of the wiring substrate  110  at the bottom of the semiconductor light-emitting device  250 . 
     Each of the vertical type semiconductor light-emitting device and the horizontal type semiconductor light-emitting device may be a green semiconductor light-emitting device, a blue semiconductor light-emitting device, or a red semiconductor light-emitting device. The green semiconductor light-emitting device and the blue semiconductor light-emitting device may each be implemented as a high-power light-emitting device that emits green or blue light in a manner that gallium nitride (GaN) is mostly used, and indium (In) and/or aluminum (Al) are added thereto. As an example, the semiconductor light-emitting device may be a gallium nitride thin film consisting of various layers such as n-Gan, p-Gan, AlGaN, InGan, and the like. More specifically, the p-type semiconductor layer may be P-type GaN, and the n-type semiconductor layer may be N-type GaN. In the case of the red semiconductor light-emitting device, the p-type semiconductor layer may be P-type GaAs, and the n-type semiconductor layer may be N-type GaAs. 
     In addition, the p-type semiconductor layer may be P-type GaN doped with Mg on the p-electrode side, and the n-type semiconductor layer may be N-type GaN doped with Si on the n-electrode side. In this case, the semiconductor light-emitting devices described above may be semiconductor light-emitting devices without an active layer. 
     Referring to  FIGS. 1 to 4 , since the light-emitting diode is very small, the display panel may be configured such that self-emitting sub-pixels are arranged at fine pitch, thereby achieving a high-definition display device. 
     In a display device using the semiconductor light-emitting devices of the present disclosure, a semiconductor light-emitting device grown on a wafer and formed by mesa and isolation is used as an individual pixel. Here, the semiconductor light-emitting device  150  with the micro size should be transferred onto the wafer at a predetermined position on the substrate of the display panel. Pick and place is one example of those transfer techniques, which has a low success rate and requires much time. As another example, a technique of transferring several devices at once using a stamp or a roll can be used, which is poor in yield and is not suitable for a large screen display. Therefore, the present disclosure provides a new method for manufacturing a display device that can solve these problems and a manufacturing device therefor. 
     A new method for manufacturing a display device will be described first.  FIGS. 5A to 5E  are conceptual views illustrating a new process of fabricating the semiconductor light-emitting device. 
     The present disclosure exemplarily illustrates a display device using a passive matrix (PM) type semiconductor light-emitting device. However, an example described hereinafter may also be applied to an active matrix (AM) type semiconductor light-emitting device. In addition, the present disclosure exemplarily illustrates self-assembly of horizontal semiconductor light-emitting devices, but it is equally applicable to self-assembly of vertical semiconductor light-emitting devices. 
     According to a manufacturing method, a first conductive semiconductor layer  153 , an active layer  154 , and a second conductive semiconductor layer  155  are grown on a growth substrate  159  ( FIG. 5A ). 
     When the first conductive semiconductor layer  153  is grown, the active layer  154  is grown on the first conductive semiconductor layer  253 , then the second conductive semiconductor layer  155  is grown on the active layer  154 . As such, when the first conductive semiconductor layer  153 , the active layer  154 , and the second conductive semiconductor layer  155  are sequentially grown, the first conductive semiconductor layer  153 , the active layer  154 , and the second conductive semiconductor layer  155  form a layered structure as illustrated in  FIG. 5A . 
     Here, the first conductive semiconductor layer  153  may be a p-type semiconductor layer, and the second conductive semiconductor layer  155  may be an n-type semiconductor layer. However, the present disclosure is not necessarily limited thereto, and the first conductive semiconductor layer  153  may be an n-type semiconductor layer, and the second conductive semiconductor layer  155  may be a p-type semiconductor layer. 
     In addition, this implementation exemplarily illustrates a case in which the active layer  154  is present. However, in some cases, a structure without the active layer  154  is also possible as described above. For example, the p-type semiconductor layer may be P-type GaN doped with Mg, and the n-type semiconductor layer may be N-type GaN doped with Si. 
     The growth substrate (wafer)  159  may be made of a material having optical transparency, such as sapphire (Al 2 O 3 ), GaN, ZnO, and AlO, but the present disclosure is not limited thereto. In addition, the growth substrate  159  may be made of a material suitable for growing a semiconductor material, namely, a carrier wafer. The growth substrate  159  may be formed of a material having high thermal conductivity, and use, for example, a SiC substrate having higher thermal conductivity than a sapphire (Al 2 O 3 ) substrate, or Si, GaAs, GaP, and InP, in addition to a conductive substrate or an insulating substrate. 
     Next, at least portions or parts of the first conductive semiconductor layer  153 , the active layer  154 , and the second conductive semiconductor layer  155  are removed to form a plurality of semiconductor light-emitting devices ( FIG. 5B ). 
     More specifically, isolation is carried out such that the plurality of light-emitting devices form an array of semiconductor light-emitting devices. That is, the first conductive semiconductor layer  153 , the active layer  154 , and the second conductive semiconductor layer  155  are etched in a vertical direction to form a plurality of semiconductor light-emitting devices. 
     In case the horizontal type semiconductor light-emitting device is formed in this step, the active layer  154  and the second conductive semiconductor layer  155  may be partially removed in the vertical direction to perform a mesa process in which the first conductive semiconductor layer  153  is exposed to the outside, and then an isolation process in which the first conductive semiconductor layer  153  is etched to form a plurality of semiconductor light-emitting device arrays. 
     Next, a second conductive electrode  156  or p-type electrode is formed on one surface of each of the second conductive semiconductor layers  155  ( FIG. 5C ). The second conductive electrode  156  may be formed by a deposition method such as sputtering, but the present disclosure is not limited thereto. However, when the first conductive semiconductor layer  153  and the second conductive semiconductor layer  155  are an n-type semiconductor layer and a p-type semiconductor layer, respectively, the second conductive electrode  156  may be an n-type electrode. 
     Then, the growth substrate  159  is removed to have the plurality of semiconductor devices. For example, the growth substrate  159  may be removed using a laser lift-off (LLO) or chemical lift-off (CLO) method ( FIG. 5D ). 
     After that, a step of placing the plurality of semiconductor light-emitting devices  150  onto a substrate in a chamber filled with a fluid is performed ( FIG. 5E ). 
     For example, the semiconductor light-emitting devices  150  and a substrate  161  are put into a chamber filled with a fluid, such that the semiconductor light-emitting devices  150  are self-assembled onto the substrate  161  using the flow, gravity, surface tension, and the like. Here, the substrate  161  may be an assembly substrate. 
     As another example, a wiring substrate, instead of the assembly substrate, may be put into the fluid chamber to allow the semiconductor light-emitting devices  150  to be directly seated on the wiring substrate. In this case, the substrate may be a wiring substrate. However, for the sake of convenience of explanation, the present disclosure exemplarily illustrates the case in which the substrate  161  is an assembly substrate on which the semiconductor light-emitting devices  150  are seated. 
     In order to allow the semiconductor light-emitting devices  150  to be easily placed onto the substrate  161 , the substrate  161  may be provided with cells (not shown) to which the semiconductor light-emitting devices  150  are fitted. In detail, the cells on which the semiconductor light-emitting devices  150  are placed are formed at the substrate  161  in positions where the semiconductor light-emitting devices  150  are aligned with wiring electrodes. The semiconductor light-emitting devices  150  are assembled to the cells while moving in the fluid. 
     After the plurality of semiconductor light-emitting devices  150  are arrayed on the assembly substrate  161 , the semiconductor light-emitting devices  150  of the assembly substrate  161  are transferred onto a wiring substrate, enabling large-area transfer. Therefore, the assembly substrate  161  may be referred to as a temporary substrate. 
     Meanwhile, the self-assembly described above requires increased transfer efficiency and transfer yield to be applied to the manufacture of a large screen display. The present disclosure provides a self-assembly device and method for semiconductor light-emitting devices that can improve the assembly speed and assembly accuracy by controlling distribution and movement of semiconductor light-emitting devices in a fluid. 
     According to the present disclosure, semiconductor light-emitting devices including magnetic materials are used to cause the light-emitting devices to be moved by a magnetic force, and are placed at predetermined positions on a substrate by using an electric field while moving. Hereinafter, an apparatus and a method used for the self-assembly will be described in detail with reference to the accompanying drawings. 
       FIG. 6  illustrates a self-assembly apparatus for semiconductor light-emitting devices according to one implementation of the present disclosure,  FIG. 7  illustrates an assembly surface of a substrate submerged in a fluid according to the present disclosure, and  FIGS. 8A to 8C  illustrate a self-assembly apparatus for semiconductor light-emitting devices according to another implementation of the present disclosure, and  FIG. 9  is a conceptual view illustrating a semiconductor light-emitting device used for self-assembly according to the present disclosure. 
     A self-assembly apparatus or device (hereinafter, ‘self-assembly apparatus’)  200  according to one implementation of the present disclosure may include a chamber  210 , a transfer unit  220 , a magnet  230 , a position controller (or location control unit)  240 , and vibration generators (or vibration control units)  270 . 
     The chamber  210  may be configured to accommodate a plurality of semiconductor light-emitting devices  250  including a magnetic material (or substance)  255   a , and a fluid therein. For example, the chamber  210  may be a water tank with one side open, but is not limited thereto. 
     The fluid accommodated in the chamber  210  is an assembly solution, and may contain de-ionized water or a fluid to which a surfactant is added (or deionized water to which a surfactant is added), and a type of surfactant added to the fluid is not specifically limited. When a fluid containing a surfactant is used as the assembly solution, it is possible to prevent the semiconductor light-emitting devices  250  put into the chamber  210  from adhering or sticking to each other. 
     Meanwhile, a substrate  260  to which the semiconductor light-emitting devices  250  are assembled may be disposed at the one open side of the chamber  210 . According to the implementation of the present disclosure, the substrate  260  may be disposed such that its assembly surface on which the semiconductor light-emitting devices  250  are assembled faces downward, namely, toward a bottom surface of the chamber  210 . Also, as illustrated in  FIG. 7 , at least a portion of the substrate  260  may be submerged in the fluid, and the degree of submersion may vary according to the degree of bending of the substrate  260 . However, for the self-assembly of the semiconductor light-emitting devices  250 , cells  265  on which the semiconductor light-emitting devices  250  are seated may be completely immersed in the fluid. 
     The substrate  260  may be transferred to the assembly position by the transfer unit  220 , and the position may be adjusted by the control unit (not shown). The transfer unit  220  may include a stage on which the substrate  260  is mounted and supported as shown in  FIG. 7 , and the substrate  260  may be fixed to the assembly position by the stage during the self-assembly. 
     Referring to  FIG. 7 , the substrate  260  may be an assembly substrate in which an electric field is produced, and may include a base portion  261 , a plurality of electrodes  262 , and a dielectric layer  263 . 
     The base portion  261  is made of an insulating material, and the plurality of electrodes  262  may be thin films or bi-planar electrodes patterned on one surface of the base portion  261 . The electrodes  262  may each extend in one direction, and be formed of a stack of Ti/Cu/Ti, silver (Ag) paste, indium tin oxide (ITO), or the like. Power may be applied to the plurality of electrodes  262  through a power supply unit  280 . When power is applied to the plurality of electrodes  262 , an electric field may be generated in the substrate  260 . 
     The dielectric layer  263  may be configured to cover the plurality of electrodes  262 , and be made of an inorganic material such as SiO 2 , SiN x , SiON, Al 2 O 3 , TiO 2 , HfO 2 , and the like. Alternatively, the dielectric layer  263  may be formed of a single-layer or multi-layered organic insulator. The dielectric layer  263  may have a thickness of several tens of nm to several μm. 
     Further, the substrate  260 , which is a region in which the semiconductor light-emitting devices  250  are assembled, may include a plurality of cells  265  partitioned by partition walls  264 . The cells  265  are sequentially disposed in one direction, and neighboring cells  265  may share a partition wall  264 . The partition walls  264  may be provided on the dielectric layer  263 . Therefore, the dielectric layer  263  may correspond to a bottom surface of the cells  265 . The cells  265  divided by the partition walls  264  may form a matrix arrangement. 
     The semiconductor light-emitting devices  250  may be assembled into the plurality of cells  265 , and one semiconductor light-emitting device  250  may be assembled into one cell  265 . The cell  265  may have the same or similar shape as the semiconductor light-emitting device  250 . 
     Meanwhile, a plurality of electrodes  262  may be provided below the cells  265 , such that an electric field may be produced in the cells  265  when power is applied to the electrodes  262 . More specifically, one cell  265  may overlap two electrodes  262 , and different polarities may be applied to the electrodes  262  to thereby produce an electric field in the cell  265 . The semiconductor light-emitting devices  250  may be assembled into the cell  265  by a magnetic field to be described later and the electric field produced in the cell  265 . 
     The self-assembly apparatus  200  according to the present disclosure may include the magnet  230  that applies a magnetic force to the semiconductor light-emitting devices  250 . The magnet  230  may be spaced apart from the chamber  210  to apply a magnetic force to the semiconductor light-emitting devices  250  in the fluid. The magnet  230  may be disposed at an opposite side of the assembly surface of the substrate  260 , and its position may be controlled by the position controller  240  that is connected thereto. A position of the position controller  240  may be adjusted by the control unit (not shown) like the transfer unit  220 . 
     More specifically, the magnet  230  may be moved horizontally and vertically from above the chamber  210  by the position controller  240 , and rotate clockwise or counterclockwise in a direction horizontal to the substrate  260  during the movement. 
     Meanwhile, the semiconductor light-emitting devices  250  may move within the fluid along a magnetic field region according to a change of the position of the magnet  230 . For this purpose, the semiconductor light-emitting devices  250  may include magnetic materials. 
     Referring to  FIG. 9 , the semiconductor light-emitting device  250  may include a first conductive electrode  251 , a second conductive electrode  255 , a first conductive semiconductor layer  252  on which the first conductive electrode  251  is disposed, a second conductive semiconductor layer  254  overlapping the first conductive semiconductor layer  252  and beneath which the second conductive electrode  255  is disposed, and an active layer  253  disposed between the first and second conductive semiconductor layers  252  and  254 . 
     Here, the first conductive type may be a p-type and the second conductive type may be an n-type, and vice versa is also possible. Also, as described above, the semiconductor light-emitting device  250  may not include an active layer. 
     In the present disclosure, the first conductive electrode  251  may be formed after the semiconductor light-emitting device  250  is self-assembled onto the substrate  260 . Also, in the present disclosure, the second conductive electrode  255  may include a magnetic material. The magnetic material may be a magnetic metal, and include a material corresponding to any one of Ni, SmCo, Gd-based, La-based, and Mn-based material, for example. 
     The magnetic material may be provided on the second conductive electrode  255  in the form of particles, or may form one layer of the second conductive electrode  255  as shown in  FIG. 9 . Referring to  FIG. 9 , the second conductive electrode  255  may include a first layer  255   a  and a second layer  255   b . The first layer  255   a  may be a layer including a magnetic material, and the second layer  255   b  may be a layer made of a non-magnetic metal material. 
     In this implementation, the first layer  255   a  including the magnetic material may be disposed to be in contact with the second conductive semiconductor layer  254 , and the second layer  255   b  may be a contact metal connected to the electrode of the substrate  260 . However, this structure is merely illustrative, and the magnetic material may be disposed on one surface of the first conductive semiconductor layer  252 . 
     Meanwhile, some of the semiconductor light-emitting devices  250  move together in the fluid according to a change in position of the magnet  230  while being adhered to each other by an attractive force between magnetic materials, which causes two or more semiconductor light-emitting devices  250  to be assembled into one cell  255 . 
     In order to prevent this, the self-assembly apparatus  200  according to an implementation of the present disclosure may include vibration generators  270 , and the vibration generators  270  may apply vibration to the fluid to separate the semiconductor light-emitting devices  250  from each other. For example, the vibration generator  270  may be provided with a sonicator, an acoustic field generator, or the like, and generate vibration of a predetermined intensity in the fluid at a predetermined interval. 
     The vibration generators  270  may be provided such that at least portions thereof are in contact with the fluid. The vibration generators  270  may be disposed adjacent to both sides of the substrate  260  ( FIGS. 8B and 8C ), respectively, or the vibration generators  270  may be integrally formed with the chamber  210  ( FIG. 8A ). In the latter case, additional vibration generators may be further provided to be located adjacent to both sides of the substrate  260  separately from the chamber  210 . 
     As the vibration generators  270  are provided at both sides of the substrate  260  or employed entirely in the chamber  210 , vibration can be applied to the entire fluid. A shape or position of the vibration generator  270  is not particularly limited as long as at least a portion thereof is disposed to be in contact with the fluid. 
     Also, the vibration generator  270  may generate vibration in the fluid before the substrate  260  is transferred to the assembly position. In detail, vibration of the fluid by the vibration generator  270  may be produced after the semiconductor light-emitting devices  250  are put into the chamber  210  and before the substrate  260  is transferred to the assembly position. Alternatively, vibration may be generated before a magnetic force is applied to the semiconductor light-emitting devices  250  even after the substrate  260  is transferred to the assembly position. The semiconductor light-emitting devices  250  put into the chamber  210  can be initially inhibited from adhering to each other by a surfactant component contained in the fluid. Vibration generated by the vibration generators  270  can prevent the semiconductor light-emitting devices  250  from adhering to each other, and simultaneously separate semiconductor light-emitting devices  250  in a state of being adhered to each other. 
     The vibration generator  270  may not produce vibration in the fluid during the self-assembly induced by the magnetic field and the electric field. Accordingly, the self-assembly of the semiconductor light-emitting devices  250  on the substrate  260  may not be disturbed or interrupted by the vibration. 
     According to the present disclosure, the chamber  210  may include channels  211  communicating with a space of the chamber  210  in which the fluid is accommodated. The channels  211  may generate a flow of fluid in the chamber  210  in association or cooperation with movement of the magnet  230 . That is, the channels  211  may form a main flow of the fluid in a direction the same as a movement direction of the magnet  230 . 
     In one implementation, the channels  211  may be formed at positions corresponding to both sides of the chamber  210 , as illustrated in  FIG. 8C , to generate a flow of fluid. For example, the channels  211  may be defined in a direction parallel to an extension direction of the plurality of electrodes  262  formed on the substrate  260 . More specifically, as the cells  265  on which the semiconductor light-emitting devices  250  are placed are formed along the extension direction of the plurality of electrodes  262 , the magnet  230  may mainly move along the extension direction of the plurality of electrodes  262 . Here, the semiconductor light-emitting devices  250  on the fluid move together with the magnet  230  by a magnetic field, and the channels  211  may form the flow of the fluid in the same direction as the movement direction of the magnet  230  to assist the movement of the semiconductor light-emitting devices  250 . 
     Although not illustrated in the drawings, the bottom surface of the chamber  210  may be made of a light transparent material to allow an inside of the chamber  210  to be monitored therethrough. In one implementation, an image sensor (not shown) may be disposed at an outside of the bottom surface of the chamber  210  to observe the assembly surface of the substrate  260 . The image sensor (not shown) may be controlled by the control unit, and an inverted type lens, a CCD, or the like may be provided as the image sensor. 
     The self-assembly apparatus  200  is configured such that the plurality of semiconductor devices  250  can be placed at predetermined positions of the substrate  260  while horizontally and vertically moving by the magnetic field generated by the magnet  230  and the electric field produced by the plurality of electrodes  262  electrically connected to the power supply unit  280 . Hereinafter, the assembly process of the semiconductor light-emitting devices  250  using the self-assembly apparatus  200  will be described in more detail. 
       FIGS. 10A to 10G  are views illustrating a process of self-assembling semiconductor light-emitting devices to a substrate using the self-assembly apparatus of  FIG. 6 . 
     First, a plurality of semiconductor light-emitting devices  250  each including a magnetic material may be formed through the process described with reference to  FIG. 5  before the steps illustrated in  FIG. 10 . 
     Next, after putting the plurality of semiconductor light-emitting devices  250  including the magnetic materials into the fluid of the chamber  210 , vibration may be generated in the fluid ( FIGS. 10A and 10B ). 
     The semiconductor light-emitting devices  250  put into the chamber  210  may sink to the bottom of the chamber  210  or some of them may float in the fluid. Some of the semiconductor light-emitting devices  250  may present in the fluid in a state of being adhered to each other ( FIG. 10A ). 
     Therefore, after the semiconductor light-emitting devices  250  are put into the chamber  210 , vibration is applied before the substrate  260  is transferred to the assembly position to separate the semiconductor light-emitting devices  250  being adhered to each other so as to prepare the next step ( FIG. 10B ). As long as a magnetic force has not been applied to the semiconductor light-emitting devices  250 , vibration can be applied to the fluid even after the substrate  260  is transferred to the assembly position. 
     For example, a distribution state of the semiconductor light-emitting devices  250  put through the bottom surface of the chamber  210  may be checked, and the intensity of vibration applied to the fluid may be adjusted according to the distribution state. Vibration of a predetermined intensity may be applied to the fluid at a predetermined interval, and the vibration may be applied until the semiconductor light-emitting devices  250  adhered to each other are completely separated. 
     Next, the substrate  260  on which the semiconductor light-emitting devices  250  are assembled may be transferred to the assembly position ( FIG. 100 ). As described above, the substrate  260  may be disposed such that the assembly surface on which the semiconductor light-emitting devices  250  are assembled faces downward, namely, the bottom surface of the chamber  210 . In addition, at least a portion of the substrate  260  may be submerged in the fluid, and the degree of submersion may vary depending on the degree of bending of the substrate  260 , however, at least the assembly surface of the substrate  260  on which the semiconductor light-emitting devices  250  are assembled is disposed to be immersed in the fluid. 
     Then, a magnetic force may be applied to the semiconductor light-emitting devices  250  to make them vertically float in the chamber  210  ( FIG. 10D ). In the self-assembly apparatus  200 , when the magnet  230  moves adjacent to an opposite side of the assembly surface of the substrate  260 , the semiconductor light-emitting devices  250  in the fluid may float toward the substrate  260 . 
     Meanwhile, a separation distance between the assembly surface of the substrate  260  and the semiconductor light-emitting devices  250  may be controlled by adjusting the magnitude of a magnetic force by the magnet  230 , and the separation distance from the outermost surface of the substrate  260  may be several mm to several μm. 
     Next, a magnetic force may be applied to the semiconductor light-emitting devices  250 , such that the semiconductor light-emitting devices  250  can move along one direction in the chamber  210 . The magnetic force may be produced by the magnet  230 , and the semiconductor light-emitting devices  250  may move in a direction parallel to the substrate  260  by the magnetic force from a position distant from the substrate  260  ( FIG. 10E ). 
     Here, the channels  211  may generate a flow of fluid in association with the movement of the magnet  230 . The channels  211  may generate the flow of fluid in the chamber  210  in a direction to which a magnetic force is applied, thereby assisting the movement of the semiconductor light-emitting devices  230 . As a result, the assembly speed of the semiconductor light-emitting devices  250  can be improved. 
     Next, an electric field may be applied to guide the semiconductor light-emitting devices  250  to predetermined positions while moving, such that the semiconductor light-emitting devices  250  can be seated at the predetermined positions of the substrate  260 . For example, the semiconductor light-emitting devices  250  moving in a direction horizontal to the substrate  260  by the magnetic force may move in a direction perpendicular to the substrate  260  by the electric field to be placed at the predetermined positions of the substrate  260 . 
     More specifically, power may be selectively supplied to the plurality of electrodes  262  of the substrate  260  to induce or enable the semiconductor light-emitting devices  250  to be assembled only at the predetermined positions. The predetermined positions at which the semiconductor light-emitting devices  250  are seated may be the cells  265  formed on the substrate  260 . 
     When the substrate  260  is a wiring substrate, unloading of the substrate  260  may proceed after the above-described steps to complete the assembly process. If the substrate  260  is an assembly substrate, as described above, a post-process may be performed for transferring the semiconductor light-emitting devices  250  arrayed in the cells  265  of the substrate  260  onto a wiring substrate to achieve a final display device. 
     Meanwhile, after guiding the semiconductor light-emitting devices  250  to the predetermined positions of the substrate  260 , the magnet  230  may be moved in a direction away from the substrate  260  to drop the remaining semiconductor light-emitting devices  250  to the bottom of the chamber  210  ( FIG. 10F ). 
     Then, the semiconductor light-emitting devices  250  left at the bottom of the chamber  210  are collected, and the collected semiconductor light-emitting devices  250  may be reused in another self-assembly process later. 
     As described above, according to the self-assembly apparatus and method according to the present disclosure, the assembly speed and assembly accuracy can be improved by controlling the distribution and movement of the semiconductor light-emitting devices  250  self-assembled on the substrate  260 . 
     More specifically, the semiconductor light-emitting devices  250  adhered to each other can be separated by vibration generated in the fluid by the vibration generators  270  to thereby prevent two or more semiconductor light-emitting devices  250  from being assembled into one cell  265  formed on the substrate  260 . In addition, the channels  211  may generate the flow of fluid along a movement direction of the magnetic force by the magnet  230  to thereby facilitate the movement of the semiconductor light-emitting devices  250 . 
     The present disclosure is not limited to the configuration and the method of the implementations described above, but the implementations may be configured such that all or some of the implementations are selectively combined so that various modifications can be made.