Patent Publication Number: US-2023163233-A1

Title: Nanowire led, display module including the nanowire led, and method for manufacturing the display module

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a bypass continuation of International Application No. PCT/KR2021/007210, filed on Jun. 9, 2021, which is based on and claims priority to Korean Patent Application No. 10-2020-0164884, filed on Nov. 30, 2020, and Korean Patent Application No. 10-2020-0083658, filed on Jul. 7, 2020, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     The disclosure relates to a nanowire light emitting diode (LED) and a method for manufacturing the same, and in particular, to a display module to which nanowire LEDs are transferred by a fluidic self-assembly (FSA) method, and a method for manufacturing the same. 
     2. Description of Related Art 
     A display module expresses various colors as it is operated in a pixel unit or a sub-pixel unit. In this case, one sub-pixel includes a plurality of nanowire LEDs. 
     Operations of each pixel or sub-pixel are controlled by a plurality of thin film transistors (TFTs). A TFT substrate may include a flexible substrate, a glass substrate, or a plastic substrate on which a TFT circuit is formed. On a TFT substrate, a plurality of TFTs connected to a TFT circuit are mounted. 
     Recently, a display device having a big screen (a large format display) is being manufactured by connecting a plurality of display modules. 
     SUMMARY 
     Provided is a three-dimensional nanowire light emitting diode (LED) which may secure an n-type contact area without a separate etching process after epitaxial growth, and having a magnetic property so as to be aligned by a magnetic field. 
     Further, provided are a display module to which nanowire LEDs are transferred through a hybrid fluidic self-assembly (FSA) process, and a method for manufacturing the same. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     According to an aspect of the disclosure, a nanowire light emitting diode (LED) may include an n-type GaN-based semiconductor layer having a pillar shape, an active layer provided on a first side of the n-type GaN-based semiconductor layer, a p-type GaN-based semiconductor layer provided on the active layer, and a magnetic layer provided on a second side of the n-type GaN-based semiconductor layer. 
     The magnetic layer may be provided on an end part of the second side of the n-type GaN-based semiconductor layer. 
     The magnetic layer may include a diamagnetic material. 
     The diamagnetic material may include Ge. 
     The magnetic layer may include a material having a magnetic property. 
     The material having the magnetic property may include Cr, Mn, Fe, Co, Ni, or Cu. 
     The magnetic layer may include at least one first thin film layer comprising a diamagnetic material or a material having a magnetic property, and at least one second thin film layer comprising an n-type semiconductor, where the at least one first thin film layer and the at least one second thin film layer are alternatingly stacked. 
     According to an aspect of the disclosure, a display module may include a thin film transistor (TFT) substrate comprising a plurality of anode electrodes and a plurality of cathode electrodes provided on a first surface of the TFT substrate, and a plurality of nanowire LEDs including first end parts respectively connected to each anode electrode and second end parts respectively connected to each cathode electrode, where each of the plurality of nanowire LEDs may have a magnetic property and polarity. 
     The plurality of nanowire LEDs may include an n-type GaN-based semiconductor layer having a pillar shape, an active layer provided on a first side of the n-type GaN-based semiconductor layer, a p-type GaN-based semiconductor layer provided on the active layer, and a magnetic layer provided on a second side of the n-type GaN-based semiconductor layer. 
     The plurality of nanowire LEDs may be provided to the TFT substrate in a form of a unit pixel comprising red, green, and blue sub-pixels, and the unit pixel may include a unit substrate on which the red, green, and blue sub-pixels are provided. 
     According to an aspect of the disclosure, a method for manufacturing a display module may include forming a template layer including a magnetic layer on a silicon substrate, growing a plurality of nanowire LEDs on the template layer, separating the plurality of nanowire LEDs from the template layer by ultrasonic waves, forming a plurality of unit cells in a state in which the plurality of nanowire LEDs are aligned to have a specific directivity, forming a plurality of unit pixels by transferring the plurality of unit cells onto a unit substrate, arranging the plurality of unit pixels on a TFT substrate through an FSA, and bonding the plurality of unit pixels to be connected to an electrode of the TFT substrate. 
     The forming the template layer may include forming a first n-type GaN-based semiconductor layer on the silicon substrate, forming the magnetic layer by alternatingly stacking at least one first thin film layer including an n-type semiconductor and at least one second thin film layer including a diamagnetic material or a material having a magnetic property on the first n-type GaN-based semiconductor layer, and forming a second n-type GaN-based semiconductor layer on the magnetic layer. 
     The diamagnetic material may include Ge, and the material having the magnetic property may include Cr, Mn, Fe, Co, Ni, or Cu. 
     The method may further include, prior to growing the plurality of nanowire LEDs, patterning a filling part on the template layer, and infiltrating a filling material having flexibility into the filling part. 
     The method may further include setting a length of an exposed part of the plurality of nanowire LEDs based on a depth of the filling part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a diagram illustrating a display module according to an embodiment of the disclosure; 
         FIG.  2    is a flowchart illustrating a manufacturing process of a display module according to an embodiment of the disclosure; 
         FIG.  3    is a diagram illustrating an example of forming a GaN-based template layer on a substrate according to an embodiment of the disclosure; 
         FIG.  4    is a diagram illustrating an example of forming a plurality of grooves by etching a part of a GaN-based template layer according to an embodiment of the disclosure; 
         FIG.  5    is a diagram illustrating an example of inserting a filling material into a plurality of grooves formed on a GaN-based template layer according to an embodiment of the disclosure; 
         FIG.  6    is a diagram illustrating an example of growing a plurality of nanowire light emitting diodes (LEDs) in a three-dimensional shape on a GaN-based template layer according to an embodiment of the disclosure; 
         FIG.  7    is a diagram illustrating an example of separating a plurality of nanowire LEDs from a substrate by using ultrasonic waves according to an embodiment of the disclosure; 
         FIG.  8    is a cross-sectional view illustrating nanowire LEDs separated from a substrate according to an embodiment of the disclosure; 
         FIG.  9    is a diagram illustrating an example of introducing a plurality of nanowire LEDs into a tank including a polymer compound according to an embodiment of the disclosure; 
         FIG.  10    is a diagram illustrating an example where a plurality of nanowire LEDs are respectively coupled to a plurality of ring-shaped compounds included in a polymer compound according to an embodiment of the disclosure; 
         FIG.  11    is a diagram illustrating an example of infiltrating nanowire LEDs coupled with a polymer compound into a plurality of molding grooves formed on a mold, and forming a magnetic field around the mold according to an embodiment of the disclosure; 
         FIG.  12    is a diagram illustrating an example wherein a plurality of nanowire LEDs arranged in a unit cell are aligned in a specific direction by a magnetic field according to an embodiment of the disclosure; 
         FIG.  13    is a diagram illustrating an example of transferring red/green/blue nanowire LEDs constituting one pixel to a unit substrate according to an embodiment of the disclosure; 
         FIG.  14    is a diagram illustrating a state where nanowire LEDs in a unit cell form are transferred to the unit substrate illustrated in  FIG.  13    according to an embodiment of the disclosure; 
         FIG.  15    is a diagram illustrating a plurality of nanowire LEDs connected to an anode electrode and a cathode electrode on a unit substrate according to an embodiment of the disclosure; 
         FIG.  16    is a diagram illustrating an example of arranging a plurality of unit pixels on a thin film transistor (TFT) substrate through fluidic self-assembly (FSA) according to an embodiment of the disclosure; 
         FIG.  17    is a diagram illustrating a state where a plurality of unit pixels arranged on a TFT substrate are bonded to electrodes of the TFT substrate according to an embodiment of the disclosure; and 
         FIG.  18    is a diagram illustrating a display module according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, various embodiments will be described in more detail with reference to the accompanying drawings. The embodiments described in this specification may be modified in various ways. Also, specific embodiments may be illustrated in the drawings, and described in detail in the detailed description. However, specific embodiments disclosed in the accompanying drawings are just for making the various embodiments easily understood. Accordingly, the technical idea of the disclosure is not restricted by the specific embodiments disclosed in the accompanying drawings, and the embodiments should be understood as including all equivalents or alternatives included in the idea and the technical scope of the disclosure. 
     Also, terms including ordinal numbers such as “the first” and “the second” may be used to describe various components, but these components are not limited by the aforementioned terms. The aforementioned terms are used only for the purpose of distinguishing one component from another component. 
     In addition, in this specification, terms such as “include” and “have” should be construed as designating that there are such characteristics, numbers, steps, operations, elements, components or a combination thereof described in the specification, but not as excluding in advance the existence or possibility of adding one or more of other characteristics, numbers, steps, operations, elements, components or a combination thereof. Further, the description in the disclosure that an element is “coupled with/to” or “connected to” another element should be interpreted to mean that the one element may be directly coupled with/to or connected to the another element, but still another element may exist between the elements. In contrast, the description that one element is “directly coupled” or “directly connected” to another element may be interpreted to mean that still another element does not exist between the one element and the another element. 
     Also, the expression ‘identical’ not only means that some features perfectly coincide, but also means that the features include a difference in consideration of a machining error range. 
     Other than the above, in describing the disclosure, in case it is determined that detailed explanation of related known functions or components may unnecessarily confuse the gist of the disclosure, the detailed explanation will be abridged or omitted. 
     A display module may be a display panel on which nanowire light emitting diodes (LEDs) (nanowire LEDs or NW LEDs) are mounted. The display module is a kind of flat display panels, and it includes a plurality of inorganic LEDs which are respectively 100 micrometers or smaller. Compared to a liquid crystal display (LCD) panel which needs a backlight, a nanowire LED display module provides better contrast, response time, and energy efficiency. Both of an organic LED (OLED) and a nanowire LED which is an inorganic light emitting element have good energy efficiency, but a nanowire LED has better brightness and light emitting efficiency, and a longer lifespan than an OLED. A nanowire LED may be a semiconductor chip that may emit a light by itself in case power is supplied. A nanowire LED has a fast reaction speed, low power consumption, and high luminance. Specifically, a nanowire LED has higher efficiency in converting electrons to photons compared to a conventional liquid crystal display (LCD) or an OLED. That is, a nanowire LED has higher “brightness per watt” compared to a conventional LCD or an OLED display. Accordingly, a nanowire LED may exert the same brightness even with approximately half the energy compared to a conventional LED (the width, length, and height respectively exceed 100 μm) or an OLED. In addition, a nanowire LED may implement a high resolution, and superior colors, contrast, and brightness, and may thus express colors in a wide range precisely, and may implement a clear screen even in the outdoors where sunlight is bright. Also, a nanowire LED is strong against a burn-in phenomenon and emits a small amount of heat, and thus a long lifespan is guaranteed without deformation. 
     A nanowire LED is a semiconductor self luminous element that was grown in a three-dimensional shape on a silicon substrate, and it may constitute a so-called core/shell structure where different materials in a hetero-j unction diode structure are stacked in a radial form with respect to one another. The size of one nanowire LED may be from scores of nm to scores of μm. In the disclosure, one ‘nanowire LED’ may be used as the same meaning as one sub-pixel. 
     A nanowire LED may include a plurality of nanowires. A nanowire LED may include a part of a template layer for growth where a III-Nitride GaN-based (e.g., the general formula is AlxGayIn1-x-yN) semiconductor layer in a hexagonal crystal structure having polarity is used as a light emitting layer, and a diamagnetic material (e.g., Ge), or a material having a magnetic property (e.g., Cr, Mn, Fe, Co, Ni, and Cu) is used as a buffer layer. 
     A nanowire LED may be epitaxially grown three-dimensionally by a bottom-up method, and constitute a pillar shape in a nano size. As a nanowire LED may include a magnetic material, it may be aligned in a specific direction by a magnetic field in a later process. 
     A nanowire LED grown on a GaN-based template layer may be separated from the GaN-based template layer by using ultrasonic waves. Accordingly, damage exerted on the nanowire LED during a separation process may be minimized. 
     A nanowire LED emitting a red color is epitaxially grown on a GaN-based template layer identical to a nanowire LED emitting a green color or a blue color, and accordingly, the epitaxial growth platform may be unified, and the manufacturing efficiency may be improved. 
     A plurality of nanowires go through a molding processing in a state of being coupled by a super high polymer compound having a cross-linking property in a chain-polymer network form, and are encapsulated. The super high polymer compound may be, for example, polyrotaxane. Unit cells molded in a form as above may be manufactured. 
     If a magnetic field is flown to a unit cell before bonding a p-type semiconductor layer and an n-type semiconductor layer to an anode electrode and a cathode electrode of a thin film transistor (TFT) substrate, a plurality of nanowires included in the unit cell may be arranged to have directivity such that all of the respective p-type semiconductor layers are toward the same direction, and all of the respective n-type semiconductor layers are toward the same direction. 
     If a magnetic field is flown after transferring the unit cell including the plurality of nanowires arranged in a state of having directivity to a predetermined location (e.g., the corresponding sub-pixel area) of the TFT substrate, the plurality of nanowires may be arranged such that the p-type semiconductor layer is toward the anode electrode, and the n-type semiconductor layer is toward the cathode electrode. In the unit cell arranged in each sub-pixel area of the TFT substrate, the polymer compound may be removed through a removing process. In a state where the polymer compound has been removed, in the plurality of nanowires, the p-type semiconductor layer may be electronically and physically connected to the anode electrode, and the n-type semiconductor layer may be electronically and physically connected to the cathode electrode through a bonding process. 
     In the disclosure, one pixel may include at least three sub-pixels. The three sub-pixels may include nanowire LEDs that may express R/G/B full colors. 
     The plurality of sub-pixels may be mounted on a subminiature substrate (e.g., a substrate having a size of a degree corresponding to a pixel area). In this case, the subminiature substrate and the plurality of sub-pixels mounted thereon may together be referred to as one pixel unit as a single unit. A plurality of pixel units may be transferred to another TFT substrate by a fluidic self-assembly (FSA) method. 
     In the disclosure, on the front surface of a glass substrate, a TFT layer where a thin film transistor (TFT) circuit is formed may be arranged, and on the rear surface, a circuit that supplies power to the TFT circuit, and is electronically connected to a separate control substrate may be arranged. The TFT circuit may operate a plurality of pixels arranged on the TFT layer. 
     The front surface of the glass substrate may be divided into an active area and a dummy area. The active area may fall under an area occupied by the TFT layer on the front surface of the glass substrate, and the dummy area may fall under the area excluding the area occupied by the TFT layer on the front surface of the glass substrate. 
     The edge area of the glass substrate may be the outermost part of the glass substrate. Also, the edge area of the glass substrate may be the remaining area of the glass substrate excluding the area where the circuit is formed. Further, the edge area of the glass substrate may include the side surface of the glass substrate, a part of the front surface of the glass substrate adjacent to the side surface, and a part of the rear surface of the glass substrate. The glass substrate may be formed of a quadrangle type. Specifically, the glass substrate may be formed of a rectangle or a square. The edge area of the glass substrate may include at least one side among the four sides of the glass substrate. 
     In the edge area of the glass substrate, a plurality of side surface wirings may be formed at a specific interval from one another. One end part of the plurality of side surface wirings may be electronically connected to a plurality of first connection pads formed in an edge area included in the front surface of the glass substrate, and the other end part may be electronically connected to a plurality of second connection pads formed in an edge area included in the rear surface of the glass substrate. The plurality of first connection pads may be connected to the TFT circuit arranged on the front surface of the glass substrate through the wirings, and the plurality of second connection pads may be connected to a driving circuit arranged on the rear surface of the glass substrate through the wirings. 
     As a plurality of side wirings are formed in the display module, the dummy area is minimized and the active area is maximized on the front surface of the TFT substrate, and accordingly, the display module may become bezel-less, and the mounting density of micro LEDs for the display module may be increased. In case a plurality of such display modules having a bezel-less implementation are connected, a large format display (LFD) device that may maximize the active area may be provided. In this case, as the dummy area of each display module is minimized, pitches among each pixel of adjacent display modules may be formed to be maintained identical to the pitches among each pixel in a single display module. Accordingly, appearance of seams in the connecting portions between each display module may be prevented. 
     An example where a plurality of side surface wirings are formed at a specific interval from one another in the respective edge areas corresponding to two sides facing each other among the edge areas corresponding to the four sides of the glass substrate is suggested. However, the disclosure is not limited thereto, and a plurality of side surface wirings may be formed at a specific interval from one another in the edge areas corresponding to two sides adjacent to each other. Also, a plurality of side surface wirings may be formed at a specific interval from one another only in the edge area corresponding to one side among the edge areas corresponding to the four sides, but a plurality of side surface wirings may also be formed at a specific interval from one another in the edge areas corresponding to three sides, depending on needs. 
     The display module includes a glass substrate on which a plurality of LEDs are mounted, and side surface wirings are formed. Such a display module may be installed and applied in a single unit on wearable devices, portable devices, handheld devices, and various kinds of electronic products or electronic components which need displays. Also, the display module may be applied as a matrix type to display devices such as monitors for personal computers (PCs), high resolution TVs and signage (or, digital signage), and electronic displays through a plurality of assembly arrangements. 
     Hereinafter, the display module according to an embodiment of the disclosure will be described with reference to the drawings. 
       FIG.  1    is a diagram illustrating a display module according to an embodiment of the disclosure. 
     Referring to  FIG.  1   , the display module  290  according to an embodiment of the disclosure may include a plurality of unit pixels  270  arranged on the TFT substrate  280 . The plurality of unit pixels  270  may include a plurality of sub-pixels. Here, one sub-pixel may include a plurality of nanowire LEDs. 
     A nanowire LED is a semiconductor chip consisting of an inorganic light emitting material, and it may emit a light by itself in case power is supplied. A nanowire LED may implement a real high dynamic range (HDR), and may provide improved luminance and representation of a black color, and a higher contrast ratio compared to an OLED. The size of a nanowire LED may be from scores of nm to scores of μm. 
     The plurality of unit pixels  270  may be arranged in a lattice form on the TFT substrate  280 . For example, the plurality of unit pixels  270  may be arranged by a first pitch P 1  in a row direction, and may be arranged by a second pitch P 2  in a column direction. The first pitch P 1  and the second pitch P 2  may be set to be identical or different, in consideration of the size of the display module to be manufactured. 
     The TFT substrate  280  may include a glass substrate, a TFT layer including a TFT circuit on the front surface of the glass substrate, and a plurality of side surface wirings electronically connecting the TFT circuit of the TFT layer and circuits arranged on the rear surface of the glass substrate. The TFT substrate  280  may include an active area expressing an image, and a dummy area that cannot express an image on the front surface. 
     The pixel driving method of the display module  290  according to an embodiment of the disclosure may be an active matrix (AM) driving method or a passive matrix (PM) driving method. The display module  290  may form a pattern of wirings to which each nanowire LED is electronically connected according to the AM driving method or the PM driving method. 
     The dummy area may be included in the edge area of the glass substrate, and a plurality of first connection pads may be arranged at a specific interval from one another. Each of the plurality of first connection pads may be electronically connected to each sub-pixel through a wiring. 
     The number of the first connection pads formed in the dummy area may vary according to the number of pixels implemented on the glass substrate, and it may also vary according to the driving method of the TFT circuit arranged in the active area. For example, compared to the passive matrix (PM) driving method where the TFT circuit arranged in the active area drives a plurality of pixels in a horizontal line and a vertical line, the AM driving method where each pixel is independently driven may need more wirings and connection pads. 
     The display module  290  may include a transparent cover layer for protecting the front surface of the TFT substrate  280  on which the plurality of unit pixels  270  are mounted. In this case, on the front surface of the TFT substrate, a spacer for supporting the transparent cover layer may be arranged. The spacer may have a black tone color so that it may absorb lights emitted from each unit pixel  270  and external lights of the display module  290 . Also, the display module  290  may include a touch screen panel stacked on the front surface of the transparent cover layer. 
     Hereinafter, nanowire LEDs and the structure and the manufacturing process of the display module to which the nanowire LEDs are applied will be described sequentially with reference to the drawings. 
       FIG.  2    is a flowchart illustrating a manufacturing process of a display module according to an embodiment of the disclosure.  FIG.  3    is a diagram illustrating an example of forming a GaN-based template layer on a substrate according to an embodiment of the disclosure. 
     Referring to  FIG.  2    and  FIG.  3   , after a Ge buffer layer  30  is formed on the silicon substrate  10 , an n-GaN-based template layer  40  for growing nanowire LEDs in a three-dimensional shape is formed on the Ge buffer layer  30  in operation S 1 . 
     The Ge buffer layer  30  grown on the silicon substrate  10  may minimize a lattice mismatch between the silicon substrate  10  and the n-GaN-based template layer  40 . On the Ge buffer layer  30 , a Ge layer and a GaN layer may be formed in stack alternatingly in a repeated manner. 
     In the case of applying the Ge buffer  30  as above, the dislocation density between the silicon substrate  10  and the n-GaN-based template layer  40  may be reduced, and the mismatch rate may be maintained to be about 0.08% or lower. Accordingly, the threading dislocation density (TDD) of the n-GaN-based template layer  40  becomes—E7/cm 2 , and thus a basis for growing nanowire LEDs that will proceed in a later process may be provided. 
     The n-GaN-based template layer  40  may include a first GaN layer  50  that is the most adjacent to the Ge buffer layer  30 , a magnetic layer  70  stacked on the first GaN layer  50 , and a second GaN layer  90  stacked on the magnetic layer  70 . 
     The magnetic layer  70  constitutes a part of nanowire LEDs together with the second GaN layer  90 . In such nanowire LEDs having a magnetic property, a plurality of nanowire LEDs included in the unit cells may be aligned in one direction by using a magnetic field in a later process. 
     On the magnetic layer  70 , a plurality of n-GaN-based first thin film layers and a plurality of second thin film layers having a magnetic property may be formed in stack alternatingly in a repeated manner. In this case, the plurality of second film layers may be a diamagnetic material, e.g., Ge, or a material having a magnetic property, e.g., any one of Cr, Mn, Fe, Co, Ni, and Cu. Meanwhile, the magnetic layer  70  may be a thin film superlattice (e.g., a strained-layer superlattice (SLS)) layer that has a magnetic property, and where stress is accumulated. 
       FIG.  4    is a diagram illustrating an example of forming a plurality of grooves by etching a part of a GaN-based template layer according to an embodiment of the disclosure.  FIG.  5    is a diagram illustrating an example of inserting a filling material into a plurality of grooves formed on a GaN-based template layer according to an embodiment of the disclosure.  FIG.  6    is a diagram illustrating an example of growing a plurality of nanowire LEDs in a three-dimensional shape on a GaN-based template layer according to an embodiment of the disclosure. 
     On the n-GaN-based template layer  40 , the nanowire LEDs  200  are grown in operation S 2 . For growth of the nanowire LEDs  200 , the following process may be performed. 
     Referring to  FIG.  4   , a filling part  100  is patterned on the n-GaN-based template layer  40  through an etching process or a photolithography process. 
     The filling part  100  may be formed in a specific depth D by a top-down method toward the Ge buffer layer  30  from the surface of the n-GaN-based template layer  40 . 
     In this case, by adjusting the depth D of the filling part  100 , the length of a part that is not covered by the p-type semiconductor layer  170  (refer to  FIG.  8   ) of the nanowire LEDs  200  and is exposed to the outside (referred to as ‘the exposed part of the nanowire LEDs  200 ’ hereinafter) may be determined. 
     The exposed part of the nanowire LEDs  200  is a part of the n-GaN-based template layer  40  that is integrally formed on the n-type semiconductor layer  130  of the nanowire LEDs  200 , and in a later process, it is electronically and physically connected to the cathode electrode through bonding. 
     Referring to  FIG.  5   , a filling material  110  is infiltrated into the filling part  100  for stably growing the nanowire LEDs  200  on the n-GaN-based template layer  40 , and the surface of the n-GaN-based template layer  40  is made approximately flat. 
     The filling material  110  supports the exposed part of the nanowire LEDs  200 . The nanowire LEDs  200  grown on the n-GaN-based template layer  40  are separated from the n-GaN-based template layer  40  by ultrasonic waves in a later process. In this case, the part separated by the ultrasonic waves is the exposed part of the nanowire LEDs  200 . 
     The filing material  110  may include a synthetic resin having flexibility, e.g., polyimide (PI), so that ultrasonic waves may be stably transmitted to the exposed part of the nanowire LEDs  200 . 
     The exposed part of the nanowire LEDs  200  may be easily cut and separated from the n-GaN-based template layer  40  by ultrasonic waves. 
     Referring to  FIG.  6   , the nanowire LEDs  200  are grown in a three-dimensional shape on the n-GaN-based template layer  40 . 
     The n-type semiconductor layer  130  is grown by the bottom-up method. The n-type semiconductor layer  130  is a cladding layer, and may include n-GaN. 
     Then, an active layer  150  is formed on the surface of the n-type semiconductor layer  130 . The active layer  150  may include a multi quantum wells (MQWs) structure in which well structures, where a very thin light emitting layer (an active layer) and a very thin insulation layer (or a barrier layer) are alternatingly stacked, are formed in multiple layers, for increasing the coupling efficiency of electrons and holes quantum-mechanically. 
     Then, the p-type semiconductor layer  170  is formed on the surface of the active layer  150 . The p-type semiconductor layer  170  is a cladding layer, and may include p-GaN. 
     As described above, the plurality of nanowire LEDs  200  are grown on the n-GaN-based template layer  40 , and then a hydrophilic surface treatment is performed on the surface of the p-type semiconductor layer  170  falling under the end part (refer to the part ‘E’ indicated in  FIG.  6   ) of the plurality of nanowire LEDs  200 . 
     The hydrophilic surface treatment is a preceding measure for coupling the plurality of nanowire LEDs to a bridging point of a polymer compound (refer to the ring-shaped compound  335  in  FIG.  10   ) in a later process. 
     As hydrophilic surface treatment methods for modifying the end part of the plurality of nanowire LEDs  200  to be hydrophilic, there are a chemical treatment method, an ultraviolet ray irradiation method, an oxygen plasma treatment method, etc. 
       FIG.  7    is a diagram illustrating an example of separating a plurality of nanowire LEDs from a substrate by using ultrasonic waves according to an embodiment of the disclosure.  FIG.  8    is a cross-sectional view illustrating nanowire LEDs separated from a substrate according to an embodiment of the disclosure. 
     The plurality of nanowire LEDs  200  grown on the n-GaN-based template layer  40  are separated from the n-GaN-based template layer  40  by using ultrasonic waves in operation S 3 . 
     Referring to  FIG.  7   , the silicon substrate  10  on which the plurality of nanowire LEDs  200  have grown is put into a predetermined tank  300  into which a solution has been loaded, and an ultrasonic wave generator  310  is operated. Ultrasonic waves generated from the ultrasonic wave generator are transmitted to the silicon substrate with the solution as the transmission medium. 
     By vibration due to the ultrasonic waves, the part connecting the n-GaN-based template layer  40  and the plurality of nanowire LEDs  200  is cut. Referring to  FIG.  6   , the cut part may be the boundary surface C 1  of the first GaN layer  50  and the magnetic layer  70 , or between a portion C 2  of the first GaN layer  50  corresponding to the bottom surface of the filling part  110  and the boundary surface C 1 . 
     In this case, the depth D of the filling part  110  may be a standard for determining the length of the exposed part of the nanowire LEDs  200 , as described above. 
     Referring to  FIG.  8   , the plurality of nanowire LEDs  200  separated from the n-GaN-based template layer  40  may include a pillar shape on the whole while including the exposed part of the nanowire LEDs  200 . 
     There is no need to form the exposed part (the part adjacent to the magnetic layer  70 ) which is a portion of the n-type semiconductor layer of the plurality of nanowire LEDs  200  through etching, unlike in the related art technology. Accordingly, no damage is exerted to the nanowire LEDs  200 , and thus degradation of the performance of the nanowire LEDs  200  that may occur in the separation process may be fundamentally prevented. Also, compared to a conventional etching process, a simple ultrasonic process proceeds, and thus the time spent for the process may be reduced, and the cost may be saved. 
       FIG.  9    is a diagram illustrating an example of introducing a plurality of nanowire LEDs into a tank including a polymer compound according to an embodiment of the disclosure.  FIG.  10    is a diagram illustrating an example where a plurality of nanowire LEDs are respectively coupled to a plurality of ring-shaped compounds included in a polymer compound according to an embodiment of the disclosure.  FIG.  11    is a diagram illustrating an example of infiltrating nanowire LEDs coupled with a polymer compound into a plurality of molding grooves formed on a mold, and forming a magnetic field around the mold according to an embodiment of the disclosure.  FIG.  12    is a diagram illustrating an example wherein a plurality of nanowire LEDs arranged in a unit cell are aligned in a specific direction by a magnetic field according to an embodiment of the disclosure. 
     A unit cell  230  is formed through the following process by using the plurality of nanowire LEDs in operation S 4 . For manufacturing the unit cell  230 , the following process may be performed. 
     Referring to  FIG.  9   , the plurality of nanowire LEDs  200  are introduced into a predetermined tank  310  into which a compound solution  311  including a polymer compound and a binder has been loaded. 
     Referring to  FIG.  10   , the polymer compound may be, for example, polyrotaxane which is a compound where dumbbell-shaped molecules and ring-shaped compounds (macrocycles)  335  are structurally fitted. 
     The dumbbell-shaped molecules include regular linear molecules  331  and blocking groups  333  coupled respectively to both ends of the linear molecules  331 . The linear molecules  331  penetrate through the insides of the ring-shaped compounds  335 . The ring-shaped compounds  335  may move along the linear molecules  331 , and their detachment from the linear molecules  331  is prevented by the blocking groups  333 . 
     In the plurality of nanowire LEDs  200  introduced into the compound solution  311 , the end parts that respectively went through a hydrophilic treatment (the part ‘E’ indicated in  FIG.  6   ) are coupled to the ring-shaped compounds  335 . To one ring-shaped compound  335 , one nanowire LED  200  is coupled. 
     The nanowire LEDs  200  coupled to the ring-shaped compounds  335  cannot be detached from the linear molecules  331 . The nanowire LEDs  200  may change their postures freely in various directions. Accordingly, the plurality of nanowire LEDs  200  may be aligned in a specific direction by a magnetic field in a later process. 
     Referring to  FIG.  11   , the plurality of nanowire LEDs  200  are infiltrated into a plurality of molding grooves  410  formed on the mold  400  together with the solution  311 . 
     In this case, as the plurality of nanowire LEDs  200  are in a state of being connected to the respective ring-shaped compounds  335 , the density of the nanowire LEDs  200  infiltrated into each molding groove  410  may be homogenized. 
     In the state where the plurality of nanowire LEDs  200  have been infiltrated into the plurality of molding grooves  410 , a magnetic field generation device  430  arranged adjacently to the mold  400  is operated, and a magnetic field is formed in a specific direction. 
     Referring to  FIG.  12   , the plurality of nanowire LEDs  200  infiltrated into each molding groove  410  include a magnetic layer  70 , and thus all of the nanowire LEDs  200  are aligned in the same direction as they are influenced by the magnetic field generated from the magnetic field generation device  430 . 
     Then, the plurality of nanowire LEDs  200  infiltrated into each molding groove  410  are cooled to approximately 30° C. or lower together with the solution  311 , and a unit cell  230  in a gel state is formed. The plurality of nanowire LEDs  200  included in the unit cell  230  formed in a gel state may be protected from an external shock that is applied during the process. 
     One unit cell  230  may correspond to one sub-pixel. Accordingly, depending on the size of the sub-pixel required through the above process, the size of the unit cell  230  may be changed. In this case, the number of the plurality of nanowire LEDs  200  included in the unit cell  230  is also changed. As described above, the disclosure may provide a unit cell that may respond flexibly to the required size of a sub-pixel. 
       FIG.  13    is a diagram illustrating an example of transferring red/green/blue nanowire LEDs constituting one pixel to a unit substrate according to an embodiment of the disclosure.  FIG.  14    is a diagram illustrating a state where nanowire LEDs in a unit cell form are transferred to the unit substrate illustrated in  FIG.  13    according to an embodiment of the disclosure.  FIG.  15    is a diagram illustrating a plurality of nanowire LEDs connected to an anode electrode and a cathode electrode on a unit substrate according to an embodiment of the disclosure 
     A plurality of unit cells  230  are transferred to a unit substrate  250 , and a unit pixel  270  is formed in operation S 5 . The following process may be performed for manufacturing the unit pixel  270 . 
     The unit substrate  250  falls under some features of the unit pixel  270  constituting one pixel while including a plurality of sub-pixels (nanowire LEDs). 
     Referring to  FIG.  13   , the unit substrate  250  is loaded on a conveyor  500  moving in one direction. On the upper side of the conveyor  500 , a first hopper  510  containing unit cells including a plurality of nanowire LEDs emitting a red color (referred to as ‘red unit cells’ hereinafter), a second hopper  520  containing unit cells including a plurality of nanowire LEDs emitting a green color (referred to as ‘green unit cells’ hereinafter), and a third hopper  530  containing unit cells including a plurality of nanowire LEDs emitting a blue color (referred to as ‘blue unit cells’ hereinafter) may be arranged at a specific interval along the longitudinal direction of the conveyor  500 . 
     Also, on the lower side of the first to third hoppers  510 ,  520 ,  530 , first to third mask devices  511 ,  521 ,  531  may be respectively arranged. 
     Also, on the upper side of the conveyor  500 , first to third magnetic field generation devices  610 ,  620 ,  630  may be arranged. The first magnetic field generation device  610  may be arranged between the first and second hoppers  510 ,  520 , the second magnetic field generation device  620  may be arranged between the second and third hoppers  520 ,  530 , and the third magnetic field generation device  630  may be arranged on one side of the third hopper  530 . 
     The unit substrate  250  that is loaded on the conveyor  500  and moves in one direction passes by the lower side of the mask device  511  including a shutter that is arranged on the lower side of the first hopper  510 . Here, when the unit substrate  250  is detected by a sensor, the red unit cells R 1  discharged from the first hopper  510  may be received in the locations of the red sub-pixels of the unit substrate  250  through the opening of the first mask device  511 , as in  FIG.  13   . 
     Then, the red unit cells R 1 , which are received on the unit substrate  250  and move, pass by the lower side of the first magnetic field generation device  610 , and align their postures such that the p-type semiconductor layer  170  of the plurality of nanowire LEDs  200  is toward the anode electrode  251  side of the unit substrate  250 , and a part  90  of the n-type semiconductor layer  130  is toward the cathode electrode  252 , by the magnetic field generated from the first magnetic field generation device  610 . 
     Then, on the unit substrate  250 , the green unit cells G 1  are received in the locations of the green sub-pixels of the unit substrate  250 , and then their postures are aligned by the magnetic field generated from the second magnetic field generation device  620 . 
     Then, on the unit substrate  250 , the blue unit cells B 1  are received in the locations of the blue sub-pixels of the unit substrate  250 , and then their postures are aligned by the magnetic field generated from the third magnetic field generation device  630 . 
     In this case, all of the numbers of the unit cells discharged at one time from the first to third hoppers  510 ,  520 ,  530  are identical. For example, if one red unit cell is discharged from the first hopper  510 , one green unit cell and one blue unit cell are discharged respectively from the second and third hoppers  520 ,  530  sequentially. 
     On the unit substrate  250 , the postures of the red, green, and blue unit cells R 1 , G 1 , B 1  are aligned to correspond to each electrode. In this state, the unit substrate  250  passes by a section for removing the polymer compound by the conveyor  500 . 
     In the section for removing the polymer compound, a polymer compound removing solution is sprayed to the moving unit substrate  250 . Accordingly, the polymer compound constituting the red, green, and blue unit cells R 1 , G 1 , B 1  is removed, and on the unit substrate  250 , red, green, and blue nanowire LEDs  200 R,  200 G,  200 B remain, as in  FIG.  15   . 
     In this state, both ends of the red, green, and blue nanowire LEDs  200 R,  200 G,  200 B are pre-bonded to the respective corresponding cathode electrodes  251 ,  253 ,  255  and anode electrodes  252 ,  254 ,  256 . 
     In the pre-bonding, contact metal (e.g., Ni/Au, In, ITO, etc.) is bonded to the p-type semiconductor layer of the nanowire LEDs. 
       FIG.  16    is a diagram illustrating an example of arranging a plurality of unit pixels on a TFT substrate through fluidic self-assembly (FSA) according to an embodiment of the disclosure.  FIG.  17    is a diagram illustrating a state where a plurality of unit pixels arranged on a TFT substrate are bonded to electrodes of the TFT substrate according to an embodiment of the disclosure. 
     The plurality of unit substrates  250  on which the red, green, and blue nanowire LEDs  200 R,  200 G,  200 B are arranged are aligned on the TFT substrate  280  through an FSA process in operation S 6 , and the plurality of aligned unit substrates  250  are bonded to the electrodes  281  of the TFT substrate  280  in operation S 7 , and the display module  290  may thereby be manufactured. 
     Before the FSA process, a hydrophilic surface treatment is performed respectively on each unit substrate  250  and the TFT substrate  280 . 
     For example, a hydrophilic surface treatment is performed on the anode electrode formed on the rear surface (the opposite surface of the surface to which sub-pixels are bonded) of each unit substrate  250 , and a hydrophilic surface treatment is performed on the TFT substrate  280  along the column L 1  where a plurality of anode electrodes are located. Alternatively, a hydrophilic surface treatment is performed on the cathode electrode formed on the rear surface (the opposite surface of the surface to which sub-pixels are bonded) of each unit substrate  250 , and a hydrophilic surface treatment is performed on the TFT substrate  280  along the column L 2  where a plurality of cathode electrodes are located. 
     Referring to  FIG.  16   , the TFT substrate  280  that went through a hydrophilic treatment is introduced into a predetermined tank  700  into which a solution for FSA has been loaded, and then the plurality of unit substrates  250  that went through a hydrophilic treatment are introduced into the tank  700 . 
     As the solution inside the tank  700  is circulated, the plurality of unit substrates  250  floating in the solution flow inside the tank  700 , and are then attached to the part that went through a hydrophilic surface treatment of the TFT substrate  280 . Through such a FSA process, the plurality of unit substrates  250  are aligned in each location on the TFT substrate  280 . 
     As in  FIG.  17   , when the plurality of unit substrates  250  are aligned in each location on the TFT substrate  280 , the TFT substrate  280  is withdrawn from the tank, and then heat is applied to the TFT substrate  280 , and through this, a eutectic bonding process proceeds such that the electrodes of the plurality of unit substrates  250  are respectively connected to the electrodes  281  of the TFT substrate  280  electronically and physically. 
     In the eutectic bonding process, the contact metal used in bonding the p-type semiconductor layer of the nanowire LEDs may be Ni/Au, and the contact metal used in bonding the n-type semiconductor layer may be Ti/Au. 
     Before the FSA process, a hydrophilic surface treatment was performed respectively to each unit substrate  250  and the TFT substrate  280 . However, the disclosure is not limited thereto, and a hydrophobic surface treatment may be performed instead of a hydrophilic surface treatment. 
     The display module  290  formed as above may be manufactured in a small size of about 7 inches-10 inches. A plurality of display modules  290  manufactured in small sizes may be connected, and a large format display device having a big screen size (e.g., 100 inches or bigger) may be manufactured. 
       FIG.  18    is a diagram illustrating a display module according to an embodiment of the disclosure. 
     Referring to  FIG.  18   , in a display module  291  according to another embodiment of the disclosure, a unit substrate is not formed, but red, green, and blue unit cells may be received in each location of a TFT substrate  281  directly through the process illustrated in  FIG.  13   , and then a magnetic field may be applied, and the postures of the unit cells may be aligned in a specific direction on the TFT substrate  281 . 
     Then, a polymer compound constituting a part of the unit cells may be removed, and then red, green, and blue nanowire LEDs  200 R,  200 G,  200 B may be electronically and physically connected to the TFT substrate  281  through a eutectic bonding process. 
     While the various embodiments of the disclosure have been described separately from one another, the embodiments do not have to be implemented independently, but the configuration and operation of each embodiment may be implemented in combination with at least one other embodiment. 
     Also, while embodiments of the disclosure have been shown and described, the disclosure is not limited to the aforementioned specific embodiments, and it is apparent that various modifications may be made by those having ordinary skill in the technical field to which the disclosure belongs, without departing from the gist of the disclosure as claimed by the appended claims. Further, it is intended that such modifications are not to be interpreted independently from the technical idea or prospect of the disclosure.