Patent Application
20240021769
This application claims the benefit and priority of Korean Patent Application No. 10-2022-0086123 filed Jul. 13, 2022. The entire disclosure of the above application is incorporated herein by reference.
The present invention relates to a full-color LED display and a manufacturing method thereof.
Micro-LEDs and nano-LEDs can implement an excellent feeling of color and high efficiency and are eco-friendly materials, thereby being used as core materials for various light sources and displays. In line with such market conditions, recently, research is being conducted to develop a new nanorod LED structure or a nanocable LED having a shell coated by a new manufacturing process. In addition, research on a protective film material to achieve high efficiency and high stability of a protective film covering an outer surface of nanorods, and research and development on a ligand material that is advantageous for a subsequent process are also being conducted.
In line with the research in the field of these materials, recently, even display TVs using red, green, and blue micro-LEDs have been commercialized. Displays and various light sources using micro-LEDs have advantages of high-performance characteristics, very long theoretical lifetime, and very high efficiency, but micro-LEDs should be placed individually on miniaturized electrodes in a limited area. Thus, with electrode assembly implemented by placing the micro-LED on the electrode using pick and place technology, it is difficult to manufacture true high-resolution commercial displays ranging from smartphones to TVs or light sources with various sizes, shapes and brightness due to the limitations of process technology in view of high unit price, high process defect rate, and low productivity. In addition, it is more difficult to individually place nano-LEDs, which are smaller than micro-LEDs, on electrodes using the pick and place technology as in micro-LEDs.
In order to overcome these difficulties, Korean Patent Registration No. 10-1436123 discloses a display manufactured through a method of dropping a solution mixed with nanorod-type LEDs on subpixels and then forming an electric field between two alignment electrodes to self-align nanorod-type LED devices on the electrodes, thereby forming the subpixels. However, in the used nanorod-type LED devices, since a major axis of the LED device coincides with a stack direction of the layers constituting the device, that is, a stack direction of each layer in a p-GaN/InGaN multi-quantum well (MQW)/n-GaN stacked structure, an emission area is narrow. In addition, when manufacturing a nanorod-type LED device by etching a commercially available wafer, it is necessary to etch the wafer as much as the length of the major axis, so surface defects are highly likely to occur as a lot of etchings is performed. Further, since the emission area is narrow, surface defects have a relatively large effect on the degradation in efficiency. In addition, since it is difficult to optimize the electron-hole recombination rate, there is a problem that the luminous efficiency is significantly lower than that of an original wafer. Accordingly, there is a problem in that a large number of LEDs must be mounted in order for an apparatus to which such a nanorod-type LED device is mounted to express a desired level of luminous efficiency.
Therefore, in order to solve these problems, a structural change may be considered so that the major axis of the rod-type LED device is perpendicular to the stacking direction of each layer. In this case, the major axis should be the length and/or width of the LED device, and the thickness of the device becomes thinner compared to the length or width. Thus, the possibility of surface defects is low due to the shallow etching depth when the wafer is etched, but after etching, the area of the lower surface of the etched LED structure connected to the wafer is large, so it is not easy to separate the etched LED structure. In addition, it may be difficult to obtain an LED device having a desired size and efficiency because the separated LED device cannot be completely separated during separation. In addition, in the case of a rod-type LED device in which the stacking directions of the n-type semiconductor layer and p-type semiconductor layer are perpendicular to the major axis of the device, when the LED device is mounted on an electrode through dielectrophoresis by applying an electric field, the surface of the p-type semiconductor layer or n-type semiconductor layer must be self-aligned to be placed on the electrode. When the side surface of the device is self-aligned so as to be in contact with the electrode, there is a problem in that an electric short occurs when driving power is applied, and light is not emitted. In addition, even when self-aligned such that the surface of the p-type semiconductor layer or the n-type semiconductor layer of the LED device, rather than the side surface, is placed on the electrode, the layer placed on the electrode is not dominantly one of the p-type semiconductor layer and the n-type semiconductor layer, but is random or has only a slight difference. Thus, in terms of selecting a driving power source, there is a limitation that DC power cannot be selected as the driving power source.
The present invention has been devised to solve the above-mentioned problems, and an aspect of the present invention is to provide a full-color LED display and a manufacturing method thereof, wherein the full-color LED display uses an LED device which can increase an emission area while reducing the thickness of a photoactive layer exposed to a surface to prevent a degradation in efficiency due to surface defect, and maintain high efficiency in light extraction efficiency and thus improve luminance by minimizing a decrease in electron-hole recombination efficiency due to non-uniformity of electron and hole velocities and the resulting decrease in luminous efficiency, and wherein the full-color LED display is capable of increasing drivable mounting efficiency by minimizing side contact that may cause an electrical short during self-alignment on a lower electrode through dielectrophoresis.
In addition, another aspect of the present invention is to provide a full-color LED display and a manufacturing method thereof, wherein the full-color LED display is capable of increasing drivable mounting ratio of the arranged LED devices while allowing a specific surface of the LED devices to selectively contact a lower electrode, thereby extending the range of selection of driving power sources to DC power, and can achieve higher luminous efficiency.
In order to achieve the aboveaspects, a first embodiment of the present invention provides a method for manufacturing a full-color LED display, the method comprising the steps of: (1) inputting a solution containing ultra-thin pin LED devices onto a lower electrode line in which a plurality of sub-pixel sites are formed, wherein the ultra-thin pin LED devices includes, based on mutually perpendicular x-axis, y-axis and z-axis wherein the x-axis direction is a major axis and a plurality of layers are stacked in the z-axis direction, a first surface and a second surface opposite to each other in the z-axis direction, and other side surfaces, and wherein the ultra-thin pin LED devices have substantially the same light color; (2) applying assembly power to the lower electrode line to self-align each of the ultra-thin pin LED devices input into each of the sub-pixel sites on the lower electrode line so that the first or second surface among the various surfaces of the device becomes the mounting surface more dominantly than the side surface; (3) forming an upper electrode line on the plurality of self-aligned ultra-thin pin LED devices; and (4) patterning a color conversion layer on the upper electrode line corresponding to the sub-pixel sites so that each of the plurality of sub-pixel sites becomes a sub-pixel site emitting any one color among blue, green, and red.
In addition, a second embodiment of the present invention provides a method for manufacturing a full-color LED display, the method comprising the steps of: (a) inputting solutions containing blue ultra-thin pin LED devices, green ultra-thin pin LED devices and red ultra-thin pin LED devices, respectively, onto a lower electrode line in which a plurality of sub-pixel sites are formed so that each sub-pixel site emits the same light color, wherein each of the blue ultra-thin pin LED devices, the green ultra-thin pin LED devices and the red ultra-thin pin LED devices includes, based on mutually perpendicular x-axis, y-axis and z-axis wherein the x-axis direction is a major axis and a plurality of layers are stacked in the z-axis direction, a first surface and a second surface opposite to each other in the z-axis direction, and other side surfaces; (b) applying assembly power to the lower electrode line to self-align each of the ultra-thin pin LED devices input into each of the sub-pixel sites on the lower electrode line so that the first or second surface among the various surfaces of the device becomes the mounting surface more dominantly than the side surface; and (c) forming an upper electrode line on the plurality of self-aligned ultra-thin pin LED devices.
According to the first embodiment or the second embodiment of the present invention, the plurality of layers in the ultra-thin fin LED device may include an n-type conductive semiconductor layer, a photoactive layer, and a p-type conductive semiconductor layer.
In addition, the lowermost layer having the first surface in the ultra-thin fin LED device may contain a plurality of pores in a region ranging from the first surface to a predetermined thickness.
In addition, the uppermost layer having the second surface in the ultra-thin pin LED device may have a higher electrical conductivity than that of the lowermost layer having the first surface, more preferably, the electrical conductivity of the uppermost layer may be 10 times or more than that of the lowermost layer.
In addition, in order to generate rotational torque based on an imaginary rotation axis passing through the center of the device in the x-axis direction under an electric field formed by applying the assembly power in the self-aligning step, the ultra-thin pin LED device may further include a rotation induction film surrounding the side surface of the device.
In addition, the rotation induction film may have a real part of a K(ω) value according to Equation 1 below that satisfies more than 0 and up to 0.72, and more preferably more than 0 and up to 0.62 in at least a part of frequency range within a frequency range of 10 GHz or less.
wherein K(ω) is an equation between εp*, the complex permittivity of the spherical core-shell particle composed of GaN as a core part and a rotation induction film as a shell part, and εm*, the complex permittivity of the solvent at an angular frequency ω, wherein the εp* is according to Equation 2 below:
In Equation 2, R1 is a radius of the core part, R2 is a radius of the core-shell particle, and ε1* and ε2* are the complex permittivity of the core part and the shell part, respectively.
In addition, the assembly power has a frequency of 1 kHz to 100 MHz and a voltage of 5 to 100 Vpp.
In addition, the first embodiment of the present invention provides a full-color LED display comprising: a lower electrode line in which a plurality of sub-pixel sites are formed; a plurality of ultra-thin pin LED devices including, based on mutually perpendicular x-axis, y-axis and z-axis wherein the x-axis direction is a major axis and a plurality of layers are stacked in the z-axis direction, a first surface and a second surface opposite to each other in the z-axis direction, and other side surfaces, wherein the ultra-thin pin LED devices are mounted so that one surface thereof is in contact with the lower electrode line in each sub-pixel site, and emit substantially the same light color; an upper electrode line disposed on the plurality of ultra-thin pin LED devices; and a color conversion layer patterned on the upper electrode line so that each of the plurality of sub-pixel sites becomes a sub-pixel site emitting any one color among blue, green, and red, wherein the plurality of ultra-thin pin LED devices mounted have a drivable mounting ratio of 55% or more in which the first surface or the second surface of each device is mounted so as to contact the lower electrode line.
In addition, the second embodiment of the present invention provides a full-color LED display capable of DC driving, comprising: a lower electrode line in which a plurality of sub-pixel sites are formed, wherein the plurality of sub-pixel sites include all of blue, green, and red, and each site is designated with one of these light colors; a plurality of ultra-thin pin LED devices including, based on mutually perpendicular x-axis, y-axis and z-axis wherein the x-axis direction is a major axis and a plurality of layers are stacked in the z-axis direction, a first surface and a second surface opposite to each other in the z-axis direction, and other side surfaces, wherein each of the plurality of ultra-thin pin LED devices independently emits light of any one of blue, green and red, and wherein the plurality of ultra-thin pin LED devices are mounted so that one surface thereof is in contact with the lower electrode line in each sub-pixel site designated to have substantially the same light color for each light color of the device; and an upper electrode line disposed on the plurality of ultra-thin pin LED devices, wherein the plurality of ultra-thin pin LED devices mounted have a drivable mounting ratio of 55% or more in which the first surface or the second surface of each device is mounted so as to contact the lower electrode line.
According to the first embodiment and the second embodiment of the present invention, the ultra-thin pin LED device may have a thickness, a distance in the z-axis direction, of 0.1 to 3 μm and a length in the x-axis direction of 1 to 10 μm.
Further, the width of the ultra-thin pin LED device, which is the length in the y-axis direction, may be smaller than the thickness, which is the length in the z-axis direction.
In addition, the drivable mounting ratio of the plurality of ultra-thin pin LED devices mounted may be 70% or more.
In addition, a selective mounting ratio, which is a ratio of the number of devices mounted such that any one of the first and second surfaces thereof is in contact with the lower electrode line among the plurality of ultra-thin pin LED devices mounted, may satisfy 70% or more, more preferably 85% or more.
In addition, the light color of the ultra-thin pin LED device included in the first embodiment may be blue, white, or UV.
Hereinafter, terms used in the present invention will be defined.
In the description of the embodiments according to the present invention, when being described as being formed “on”, “above”, “upper”, “under”, “lower” or “below” each layer, region, line, or substrate, the meaning of the terms “on”, “above”, “over”, “under”, “below”, or “beneath includes both cases of “directly” and “indirectly”.
In addition, as used in the present invention, the term ‘drivable mounting ratio’ means a ratio of the number of devices mounted in a drivable form among all LED devices mounted on the lower electrode line. For example, when the total number of LED devices mounted on the lower electrode line is L, and among them, the number of LED devices mounted so that the first surface (B) is in contact with the upper surface of the lower electrode is M, and the number of LED devices mounted such that the second surface (T) is in contact with the upper surface of the lower electrode is N, the drivable mounting ratio is calculated by the formula [(M+N)/L]×100.
In addition, the term ‘selective mounting ratio’ refers to a ratio of the number of devices mounted such that one surface selected from the first surface (B) and the second surface (T) of the device is in contact with the upper surface of the lower electrode line among all LED devices mounted on the lower electrode line. For example, when the total number of LED devices mounted on the lower electrode line is L, and among them, the number of LED devices mounted so that the first surface (B) is in contact with the upper surface of the lower electrode is M, and the number of LED devices mounted such that the second surface (T) is in contact with the upper surface of the lower electrode is N, the selective mounting ratio means the larger of the ratios calculated by the formula [M/L]×100 and [N/L]×100.
The present invention has been researched under support of National Research and Development Project, and specific information of National Research and Development Project is as follow:
The full-color LED display according to the present invention is advantageous in achieving higher luminance and light efficiency by minimizing efficiency degradation due to emission area and surface defects of the device compared to a display using a conventional rod-type LED device. In addition, the drivable mounting ratio of the input LED devices can be increased by self-aligning so that the surface of the LED devices in contact with the electrode through dielectrophoresis becomes the surface on which the LED devices can be driven. In addition, the surface in contact with the electrode is the surface on which the LED device can be driven as described above, and further the surfaces mounted on the electrodes can be selectively adjusted so that driving is possible even when DC power is selected as the driving power, so that the range of selection of driving power can be extended to DC power. Therefore, a higher luminance full-color LED display is advantageously achieved.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that the present invention can be easily implemented by one of ordinary skill in the art to which the present invention pertains. The present invention may be embodied in a variety of forms and is not limited to the embodiments described herein.
First, as a display according to a first embodiment of the present invention, a full-color LED display implemented with LED devices emitting substantially the same light color will be described.
Referring to
The full-color LED display 1000 according to the first embodiment of the present invention can be manufactured using a manufacturing method in which the ultra-thin pin LED devices 101 are self-aligned on the lower electrode line 200 through dielectrophoretic force by using an electric field formed by the assembly power applied to the lower electrode line 200. Here, each of the ultra-thin pin LED devices 101 has, based on mutually perpendicular x-axis, y-axis and z-axis wherein a plurality of layers are stacked in the z-axis direction, a first surface and a second surface opposite to each other in the z-axis direction, and other side surfaces, wherein as the ultra-thin pin LED devices 101 positioned in the electric field are attracted toward the lower electrode line 200 in each sub-pixel site, specifically the lower electrodes 211, 212, 213 and 214 constituting the lower electrode line 200 in each sub-pixel site by dielectrophoretic force, they are self-aligned such that the first or second surface among the various surfaces of each of the ultra-thin pin LED devices 101 contacts the upper surfaces of the lower electrodes 211, 212, 213 and 214 more dominantly than the side surfaces, and specifically, can be manufactured through the following manufacturing method.
Specifically, the full-color LED display according to the first embodiment can be manufactured through the steps of: (1) inputting a solution containing a plurality of ultra-thin pin LED devices 101 emitting substantially the same light color onto a lower electrode line in which a plurality of sub-pixel sites S1 and S2 are formed; (2) applying assembly power to the lower electrode line 200 to self-align the ultra-thin pin LED devices 101 input into each sub-pixel site S1 and S2 on the lower electrode line 200; (3) forming an upper electrode line 300 on a plurality of self-aligned ultra-thin pin LED devices 101; and (4) forming a color conversion layer 700 on the upper electrode line 300 corresponding to the sub-pixel sites S1 and S2 so that the plurality of sub-pixel sites S1 and S2 become sub-pixel sites S1 and S2 emitting any one color among blue, green, and red, respectively.
First, as step (1) according to the present invention, a step is performed in which a solution containing a plurality of ultra-thin pin LED devices 101 emitting substantially the same light color is input onto a lower electrode line 200 in which a plurality of sub-pixel sites S1 and S2 are formed.
Referring to
Meanwhile, as known, the rod-type LED device can be self-aligned on the lower electrodes 211, 212, 213 and 214 by dielectrophoretic force within an electric field formed by the power applied to the lower electrode line 200 corresponding to the mounting electrode, wherein each of ends in the direction of the major axis of the rod-type LED device is generally disposed to contact two adjacent lower electrodes 211/212 and 213/214 to which power is applied.
In this case, when several layers constituting the device are stacked in the x-axis direction, which is the major axis of the rod-type LED device, one end of the rod-type LED device in the direction of the major axis becomes one conductive semiconductor layer or a layer adjacent thereto, and the other end in the direction of the major axis becomes another conductive semiconductor layer or a layer adjacent thereto. When these rod-type LED devices are mounted on lower electrodes spaced apart from each other through dielectrophoretic force, it is mounted so that one end of the rod-type LED device in the direction of the major axis is in contact with one lower electrode, and the other end in the major axis direction is in contact with another spaced apart lower electrode. Therefore, there is no case where the mounted rod-type LED device is not driven. In addition, in the case of a rod-type LED device having such a laminated structure, even if the shape is a polyhedron, for example, a rectangular parallelepiped, any of the side surfaces whose plane direction is parallel to the major axis direction can be driven even in contact with the lower electrode.
However, as shown in
Referring to
Therefore, in the case of the ultra-thin pin LED devices 100, 101 and 102 having a first surface (B) and a second surface (T), and other side surfaces (S) based on mutually perpendicular x-axis, y-axis and z-axis wherein the first surface (B) and second surface (T) are opposite to each other in the z-axis direction in which the layers 10, 20, 30, 40 and 60 are stacked, and the x-axis direction becomes the major axis of the device, as in the LED device employed in the present invention, in order to be mounted on the two lower electrodes 211, 212, 213 and 214 by dielectrophoresis and to further emit light (be driven), they should be mounted such that the first surface (B) or the second surface (T) among the various surfaces constituting the ultra-thin pin LED devices 100, 101 and 102 is in contact with the lower electrodes 211, 212, 213 and 214. Furthermore, in order to use DC power as a driving power source, a selective alignment should be increased in which many of the ultra-thin LED devices 100, 101 and 102 mounted on the lower electrodes 211, 212, 213 and 214 are mounted so that a specific one of the first surface (B) and the second surface (T) selectively contacts the upper surface of the lower electrodes 211, 212, 213 and 214.
Accordingly, for a rod-type LED device in which the stacking direction of the layers constituting the LED device is perpendicular to the major axis direction of the device as described above, the present inventors have continuously studied the structure, shape and the like of the ultra-thin pin LED device in which a specific surface among several surfaces constituting the ultra-thin pin LED devices 100, 101 and 102 can selectively contact a lower electrode so that the device can be driven or driven with a DC power. As a result, the present inventors have found that a full-color LED display can be implemented by performing dielectrophoresis such that the first surface (B) or the second surface (T) of the device comes into contact with the upper surface of the lower electrode more dominantly than the side surfaces (S) through the design of the material, structure and the like of the layers constituting the LED device, and power conditions that can give attraction by dielectrophoretic force to the desired direction and position corresponding to the designed LED device, and have reached the present invention.
Specifically, the movement of particles in a medium during dielectrophoresis can be explained through a dielectrophoresis mechanism, wherein the dielectrophoresis refers to a phenomenon in which a directional force is applied to a particle by a dipole induced in the particle when the particle is placed in a non-uniform electric field. Here, the strength of the force may vary depending on the electrical characteristics of the particles and the medium, the dielectric characteristics, the frequency of the alternating electric field, etc., and the time average force (FDEP) applied to the particles during the dielectrophoresis is shown in Equation 3 below.
F
DEP=2πr3εmRe[K(ω)]∇|E|2 [Equation 3]
In Equation 3, r, εm, and E represent the radius of the particle, the permittivity of the medium, and the magnitude of the mean square root of the applied alternating current electric field, respectively. In addition, Re[K(ω)] is a factor that determines the direction in which the near-spherical particles move, and means a real part of the value according to Equation 1 below.
Here, εp* and εm* are the complex permittivity of the particle and the medium, respectively, and ε* is determined by Equation 4 below.
Here, σ refers to an electrical conductivity coefficient, ε refers to a dielectric constant, ω refers to an angular frequency (ω=2πf), and j refers to an imaginary part (j=√{square root over (−1)})
The movement of the particles during dielectrophoresis greatly depends on the change of the factor according to Equation 1. In other words, the sign change according to the frequency of Re[K(ω)] is the most important factor in determining the direction for the phenomenon in which particles move toward or away from a high electric field region. In this case, if Re[K(ω)] has a positive value, the particles move toward a high electric field region, which is called positive dielectrophoresis (pDEP), whereas if Re[K(ω)] has a negative value, the particles move away from the high electric field region, which is called negative dielectrophoresis (nDEP).
The ultra-thin pin LED devices 100, 101 and 102 are subjected to dielectrophoretic force while being dispersed in a solvent as a medium. Table 1 below shows the electrical conductivity and dielectric constant for each kind of materials that may be included in the solvent and the ultra-thin pin LED devices 100, 101 and 102.
In addition, referring to
Therefore, the dielectrophoretic force received by the ultra-thin pin LED device is also determined by the dielectric constant and electrical conductivity of the materials constituting the ultra-thin pin LED device and the solvent as the medium in which the ultra-thin pin LED device is placed, and the frequency of the applied power, whereby the sign (positive/negative) and level of the value of Re[K(ω)] acting on each surface of the ultra-thin pin LED device can be adjusted to control the movement so that the desired surface of the device is selectively placed on the lower electrodes. However, since the ultra-thin pin LED device is not a single device made of one material, it is almost impossible to predict the movement of the ultra-thin pin LED device in which layers of various materials are stacked by using the experimental results based on a single material as shown in
In Equation 2, R1 is a radius of the core part, R2 is a radius of the core-shell particle, and ε1* and ε2* are the complex permittivity of the core part and the shell part, respectively.
Referring to
Through these results, by materially and/or structurally adjusting the electrical conductivity and dielectric constant characteristics of the layers (or surfaces) constituting the ultra-thin pin LED device input in step (1) (or step (a) in the second embodiment), and adjusting the frequency and power of the power applied in step (2) (or step (a) in the second embodiment) corresponding to the material/structural characteristics to be adjusted, it is possible to implement a mounting form in which the ultra-thin pin LED device is led toward the lower electrode, and further the first surface (B) or the second surface (T) of the device is directed toward and contacts the upper surface of the lower electrode more dominantly than the side surfaces (S). In the ultra-thin pin LED devices mounted in the full-color LED display implemented as described above, a drivable mounting ratio can be increased, and eventually increased luminance can be achieved. In addition, electrical short circuit and leakage caused by the side surface of the ultra-thin pin LED device contacting the lower electrode can be minimized.
Hereinafter, described are the ultra-thin pin LED devices 100, 101 and 102 input in step (1), which are configured so that the first surface (B) or the second surface (T) among the various surfaces of the ultra-thin pin LED device 101 is dominantly attracted to and contacted with the upper surface of the lower electrode line through step (2) as described above.
Specifically, the ultra-thin pin LED devices 100, 101 and 102 may generally include minimum layers to function as LED devices. An example of the minimum layers may include conductive semiconductor layers 10 and 30 and a photoactive layer 20.
As the conductive semiconductor layers 10 and 30, any conductive semiconductor layer employed in a conventional LED device used for display may be used without limitation. According to a preferred embodiment of the present invention, the ultra-thin fin LED devices 100, 101 and 102 may include a first conductive semiconductor layer 10 and a second conductive semiconductor layer 30, wherein any one of the first conductive semiconductor layer 10 and the second conductive semiconductor layer 30 may include at least one n-type semiconductor layer, and the other conductive semiconductor layer may include at least one p-type semiconductor layer.
When the first conductive semiconductor layer 10 includes an n-type semiconductor layer, the n-type semiconductor layer may be at least one selected from semiconductor materials having an empirical formula of InxAlyGa1-x-yN(0≤x≤1, 0≤y≤1, 0≤x+y≤1), for example, InAlGaN, GaN, AlGaN, InGaN, AN, InN, and the like, and may be doped with a first conductive dopant (e.g., Si, Ge, Sn, etc.). According to a preferred embodiment of the present invention, the thickness of the first conductive semiconductor layer 10 including an n-type semiconductor layer may be 0.2 to 3 μm, but is not limited thereto.
In addition, when the second conductive semiconductor layer 30 includes an p-type semiconductor layer, the p-type semiconductor layer may be at least one selected from semiconductor materials having an empirical formula of InxAlyGa1-x-yN(0≤x≤1, 0≤y≤1, 0≤x+y≤1), for example, InAlGaN, GaN, AlGaN, InGaN, AN, InN, and the like, and may be doped with a second conductive dopant (e.g.,Mg). According to a preferred embodiment of the present invention, the thickness of the second conductive semiconductor layer 30 including an p-type semiconductor layer may be 0.01 to 0.35 μm, but is not limited thereto.
Next, the photoactive layer 20 may be formed between the first conductive semiconductor layer 10 and the second conductive semiconductor layer 30, and may be formed in a single or multiple quantum well structure. As the photoactive layer 20, any photoactive layer included in a conventional LED device used for lighting, display, etc. may be used without limitation. A clad layer (not shown) doped with a conductive dopant may be formed above and/or below the photoactive layer 20, wherein the clad layer doped with a conductive dopant may be implemented as an AlGaN layer or an InAlGaN layer. In addition, materials such as AlGaN and AlInGaN may also be used as the photoactive layer 20. In the photoactive layer 20, when an electric field is applied to the device, electrons and holes respectively moving from the conductive semiconductor layers positioned above and below the photoactive layer to the photoactive layer are coupled to generate electron-hole pairs in the photoactive layer, thereby emitting light. According to a preferred embodiment of the present invention, the photoactive layer 20 may have a thickness of 30 to 300 nm, but is not limited thereto.
In addition, the ultra-thin fin LED devices 100, 101 and 102 are illustrated as including the first conductive semiconductor layer 10, the photoactive layer 20, and the second conductive photoactive layer 30 as minimum components, but may further other active layers, conductive semiconductor layers, phosphor layers, hole blocking layers, and/or electrode layers above/below each of the above layers.
Meanwhile, with only the above-described conductive semiconductor layers 10 and 30 and the photoactive layer 20, it may be difficult for the first surface (B) or the second surface (T) among the various surfaces of the ultra-thin pin LED device to be dominantly attracted to and contacted with the upper surface of the lower electrode. Accordingly, in order to increase the ratio of drivably mounted devices among the ultra-thin pin LED devices in contact with the lower electrode line through step (2) described later, and the selective mounting ratio in which the LED devices can be driven (emitted) even by DC power, the ultra-thin pin LED devices 100, 101 and 102 may be configured to have different materials and/or structures depending on positions within the device.
For example, as shown in
Alternatively, according to another embodiment of the present invention, in the ultra-thin pin LED devices 102 and 103 used in step (1), the lowermost layer having the first surface (B) and the uppermost layer having the second surface (T) may be made of materials that differ in at least one of electrical conductivity and dielectric constant from each other. Preferably, they may differ in the electrical conductivity, and for example, the electrical conductivity of the uppermost layer having the second surface (T) may be greater than that of the lowermost layer having the first surface (B). More preferably, the electrical conductivity of the uppermost layer may be 10 times or more, more preferably 100 times or more of that of the lowermost layer, whereby it may be advantageous to achieve a further increased selective mounting ratio.
Referring to
The selective alignment-directing layer 40 may be made of a material having higher electrical conductivity than that of the first conductive semiconductor layer 10, and may be an electrode layer as a specific example. As the electrode layer, any conventional electrode layer provided in an LED device may be used without limitation, and as non-limiting examples, Cr, Ti, Al, Au, Ni, ZnO, AZO, ITO, and oxides or alloys thereof may be used alone or in combination. Preferably, in order to increase the selective mounting ratio in which the second surface (T) contacts the upper surface of the mounting electrode compared to other electrode layer materials, the electrical conductivity of the selective alignment-directing layer 40 may be 10 times or more, more preferably 100 times or more, of that of the first conductive semiconductor layer 10, whereby, it may be advantageous to achieve a further increased selective mounting ratio. In addition, when the selective alignment-directing layer 40 is an electrode layer, the thickness may be 10 to 500 nm, but is not limited thereto.
Alternatively, the selective alignment-retarding layer 60 may be made of a material having lower electrical conductivity than that of the second conductive semiconductor layer 30, and may be, for example, an electronic delay layer having an electronic delay function. That is, as the ultra-thin fin LED device 102 is implemented such that the thickness in the stacking direction of each layer is smaller than the length thereof, the thickness of the n-type GaN layer is bound to be relatively thin. In contrast, since the movement speed of electrons is greater than that of holes, the coupling position of the electrons and the holes may be made in the second conductive semiconductor layer 30 rather than in the photoactive layer 20, thereby reducing luminous efficiency. The selective alignment-retarding layer 60, which is the electron delay layer, balances the number of recombined holes and electrons in the photoactive layer 20, thereby increasing the probability that the second surface (T) among several surfaces selectively contacts the lower electrodes 211, 212, 213 and 214 while preventing a decrease in luminous efficiency. Preferably, the electrical conductivity of the uppermost layer, for example, the second conductive semiconductor layer 30, may be 10 times or more, more preferably 100 times or more, of that of the selective alignment-retarding layer 60, whereby it may be advantageous to further improve the selective mounting ratio in which the second conductive semiconductor layer 30 contacts the upper surface of the lower electrodes 211, 212, 213 and 214.
The electronic delay layer may contain, for example, at least one selected from the group consisting of CdS, GaS, ZnS, CdSe, CaSe, ZnSe, CdTe, GaTe, SiC, ZnO, ZnMgO, SnO2, TiO2, In2O3, Ga2O3, Si, polyparaphenylene vinylene and its derivatives, polyaniline, poly(3-alkylthiophene), and poly(paraphenylene). Alternatively, when the electronic delay layer is an n-type III-nitride semiconductor layer doped with the first conductive semiconductor layer 10, it may be composed of a III-nitride semiconductor having a lower doping concentration than that of the first conductive semiconductor layer 10. In addition, the thickness of the electronic delay layer may be 1 to 100 nm, but is not limited thereto, and may be appropriately changed in consideration of the material of the n-type conductive semiconductor layer, the material of the electronic delay layer, and the like.
Alternatively, according to another embodiment of the present invention, in order to generate rotational torque (Tx) based on an imaginary axis of rotation passing through the center of the device in the x-axis direction, which is the major axis of the ultra-thin pin LED device, under an electric field formed by the assembly power applied to the lower electrode line 200 in step (2) described later, the ultra-thin pin LED devices 100, 101 and 102 may further include a rotation induction film 50 surrounding the side surface thereof. More preferably, in order for any specific one of the first surface (B) and the second surface (T), for example, the second surface (T) to be selectively directed toward the upper surface of the lower electrode, the rotation induction film 50 covering the side surfaces S of the device may be formed of a material that satisfies the real part of the K(ω) value according to Equation 1 greater than 0 and up to 0.72, more preferably greater than 0 and up to 0.62, as calculated in at least a part of the frequency range within the range where the frequency of the power applied in consideration of the permittivity of the solvent is 10 GHz or less, assuming that the particles in Equation 1 above are spherical core-shell particles composed of GaN as the core and the rotation induction film as the shell (see
Referring to
In addition, the rotation induction film 50 has a positive number exceeding 0 as the real part of the K(ω) value according to Equation 1 for the spherical core-shell particle in which the lowermost layer having the first surface (B) is a GaN core part and the rotation induction film 50 is disposed as a shell part, and thus, does not hinder the movement of the ultra-thin pin LED devices 100, 101 and 102 being led toward the lower electrodes 211, 212, 213 and 214. Further, the rotation induction film 50 may adopt a material having the value of 0.72 or less, thereby significantly improving the drivable mounting ratio in which the LED devices are mounted so that they can be driven (emitted) through step (2) described later among all ultra-thin pin LED devices 100, 101 and 102 input on the lower electrode line 200, and the selective mounting ratio in which a specific one of the first surface (B) and the second surface (T) is arranged to contact the mounting electrode surface. If the side surfaces of the ultra-thin pin LED device are provided with the rotation induction film 50 having the real part of the K(ω) value according to Equation 1 which is 0 or a negative number or exceeds 0.72, the drivable mounting ratio of the ultra-thin pin LED devices mounted through step (2) described later, and the selective mounting ratio in which a specific one of the first surface (B) and the second surface (T) becomes the mounting surface (or contact surface) are reduced, and in particular, the selective mounting ratio may be greatly reduced (see Table 2).
In addition, the ultra-thin pin LED devices 100, 101 and 102 may have a different electrical conductivity and/or dielectric constant between the lowermost layer having the first surface (B) and the uppermost layer having the second surface (T) due to material and/or structural adjustment while at the same time having the side surfaces provided with the rotation induction film 50 having the real part of the K(ω) value greater than 0 and up to 0.72, thereby further increasing the drivable mounting ratio and selective mounting ratio of the ultra-thin pin LED devices in step (2) described later (see Table 2).
Meanwhile, the ultra-thin pin LED device input in the step (1) may be provided with the rotation induction film 50 satisfying the real part of the K(ω) value according to Equation 1 greater than 0 and up to 0.62 under the same conditions as described above, thereby increasing the drivable mounting ratio of the ultra-thin pin LED device, and the selective mounting ratio in which a specific one of the first surface (B) and the second surface (T) selectively contacts, while at the same time exhibiting the effect of increasing the good-quality mounting ratio, which is the mounting ratio of the ultra-thin pin LED device that enables the realization of the full-color LED display having good quality when the upper electrode line 300 is formed on the top of the ultra-thin pin LED device self-aligned on the lower electrodes 211, 212, 213 and 214 through step (2) described later and then self-aligned through step (3). Specifically, referring to
In addition, the ultra-thin fin LED devices 100, 101 and 102 input in step (1) can have a more improved emission area by stacking several layers such as the conductive semiconductor layers 10 and 30 and the photoactive layer 20 in the thickness direction and implementing the length longer than the thickness. In addition, even if the area of the photoactive layer 20 exposed as the length increases is slightly increased, since the thickness of the layers to be implemented in the process of manufacturing the ultra-thin pin LED device is thin, the depth to be etched is shallow, whereby eventually defects occurring on the exposed surfaces of the photoactive layer 20 and the conductive semiconductor layers 10 and 30 in the etching process are reduced, which is advantageous for minimizing or preventing a decrease in luminous efficiency due to surface defects.
In addition, the ultra-thin pin LED devices 100, 101 and 102 may have a longer length than a thickness such that the ratio of the total length to the thickness is, for example, 3:1 or more, more preferably 6:1 or more, which has the advantage that the ultra-thin pin LED devices 100, 101 and 102 input can be more easily self-aligned on the lower electrode line 200, specifically the lower electrodes 211, 212, 213 and 214 by dielectrophoretic force through an electric field formed by the assembly power applied in step (2) described below. If the length of the ultra-thin pin LED devices 100, 101 and 102 is reduced so that the ratio of the overall length to the thickness is less than 3:1, it may be difficult to self-align the ultra-thin pin LED devices 100, 101 and 102 on the lower electrode by the dielectrophoretic force through the electric field, and it is difficult for the device to be fixed on the lower electrode, resulting in process defects, which may lead to an electrical contact short circuit. However, the ratio of the length to the thickness of the device may be 15:1 or less, which can be advantageous in achieving the aspect of the present invention, such as optimization of the turning force that can be self-aligned using an electric field.
Meanwhile, the x-y plane in the ultra-thin pin LED devices 100, 101 and 102 is shown as a rectangle in
In addition, the ultra-thin pin LED devices 100, 101 and 102 have a micro or nano size in length and width. For example, the length of the ultra-thin pin LED devices 100, 101 and 102 may be 1 to 10 μm, and the width thereof may be 0.25 to 1.5 μm. In addition, the thickness may be 0.1 to 3 μm. The length and width may have different bases depending on the shapes of the plane, and for example, when the x-y plane is a rhombus or a parallelogram, one of the two diagonals may be the length and the other may be the width, and in the case of a trapezoid, the longer of the height, upper side, and lower side may be the length, and the shorter side perpendicular to the longer side may be the width. Alternatively, when the shape of the plane is an ellipse, the major axis of the ellipse may be the length, and the minor axis may be the width.
The above-described ultra-thin pin LED devices 100, 101 and 102 are input on the lower electrode line 200 in a state of a solution dispersed in a solvent, wherein the dispersed ultra-thin pin LED devices 100, 101 and 102 may be comprised of those emitting substantially the same light color. Here, the term “substantially the same light color” does not mean that the emitted lights have completely the same wavelength, but refers to light belonging to a wavelength region that can be generally referred to as the same light color. For example, when the light color is blue, ultra-thin fin LED devices emitting light belonging to a wavelength range of 420 to 470 nm can all be regarded as emitting substantially the same light color. The light color emitted by the ultra-thin pin LED device provided in the display according to the first embodiment of the present invention may be, for example, blue, white, or UV.
In addition, the solvent performs a function of a dispersion medium to disperse the ultra-thin pin LED devices 100, 101 and 102, and also a function of moving the ultra-thin pin LED devices 100, 101 and 102 to facilitate self-alignment on the lower electrodes 211, 212, 213 and 214. As the solvent, any solvent capable of increasing the dispersibility of the ultra-thin pin LED device without causing physical and chemical damage to the ultra-thin pin LED device can be used without limitation. In addition, the solvent may have an appropriate dielectric constant so as to have dielectrophoretic force such that the ultra-thin pin LED device dispersed in the solvent is attracted toward the lower electrode during dielectrophoresis. Preferably, the solvent may have a dielectric constant of 10.0 or more, as another example, 30 or less, and as still another example, 28 or less, which may be more advantageous to achieve the aspect of the present invention. Meanwhile, the solvent satisfying the above dielectric constant may be, for example, acetone, isopropyl alcohol, or the like. In addition, in the solution containing the ultra-thin pin LED device, the ultra-thin pin LED device may be contained in 0.01 to 99.99% by weight in the solution, but the present invention is not particularly limited thereto. In addition, the solution may be in the form of ink or paste.
Meanwhile, in step (1), the solution may be processed on the lower electrode line 200 through a known method, and a printer device such as an inkjet printer may be used for application to mass production. In addition, to be suitable for the printer apparatus and method for use in the printer apparatus or the like, the solution containing the ultra-thin pin LED device may be implemented as an ink composition. In this case, the type of solvent may be appropriately selected in consideration of physical properties such as viscosity of the solvent, and additives generally added to the composition used in the apparatus may be further included in consideration of the printing method and apparatus, but the present invention is not particularly limited thereto.
Meanwhile, although step (1) has been described as inputting the ultra-thin pin LED device in a state of a solution mixed with a solvent, the ultra-thin pin LED device may be first input on the lower electrode line 200 and then the solvent may be added, or conversely, the solvent may be first input and then the ultra-thin LED device may be input. That is, it should be noted that step (1) also includes a case in which the result is the same as that of the input of the solution.
Next, the lower electrode line 200 including the lower electrodes 211, 212, 213 and 214 functioning as one of the driving electrodes while being the mounting electrodes for mounting the above-described ultra-thin pin LED devices 100, 101 and 102 will be described. As shown in
In addition, the lower electrodes 211, 212, 213 and 214 serve as the mounting electrodes and also as one of the driving electrodes, wherein different types of power (for example, (+) and (−) power) are applied to the adjacent lower electrodes 211, 212, 213 and 214 only in step (2) (and step (b) in the second embodiment), and during driving, the same type of power (for example, (+) or (−) power) is applied. Therefore, there is an advantage in that there is less concern about an electrical short between adjacent lower electrodes 211, 212, 213 and 214, compared to a conventional LED electrode assembly that uses the lower electrodes 211, 212, 213 and 214 as the mounting electrodes and driving electrodes so that different types of power are applied during both step (2) (and step (b) in the second embodiment) and driving.
In addition, the lower electrodes 211, 212, 213 and 214 may be formed on the base substrate 400. The base substrate 400 can serve as a support for supporting the lower electrode line 200, the upper electrode line 300, and the ultra-thin pin LED device mounted between the lower electrode line 200 and the upper electrode line 300. The base substrate 400 may be any one selected from the group consisting of glass, plastic, ceramic, and metal, but is not limited thereto. In addition, the base substrate 400 may preferably be made of a transparent material in order to minimize loss of light emitted from the device. In addition, the base substrate 400 may be preferably a flexible material. In addition, the size and thickness of the base substrate 400 may be appropriately changed in consideration of the size and number of the ultra-thin pin LED devices provided, the specific design of the lower electrode line 200, and the like.
In addition, the lower electrode line 200 may have the material, shape, width, and thickness of an electrode used in a conventional display, and may be manufactured using a known method, so the present invention is not specifically limited thereto. For example, the lower electrodes 211, 212, 213 and 214 may be made of aluminum, chromium, gold, silver, copper, graphene, ITO, or an alloy thereof, and may have a width of 2 to 50 μm and a thickness of 0.1 to 100 μm, which may be appropriately changed in consideration of the size of the desired LED electrode assembly, and the like.
Meanwhile, electrode arrangements such as data electrodes and gate electrodes provided in a conventional display are not shown in
Meanwhile, the sub-pixel sites S1 and S2 are imaginary regions partitioning the upper part of the lower electrode line 200, and may have a unit area of 100 μm×100 μm or less, as another example, 30 μm×30 μm or less, and as still another example 20 μm×20 μm or less. The unit area of this size is smaller than the unit subpixel site of a display using LEDs, and it is possible to achieve a large area while minimizing the area ratio occupied by LEDs, whereby it may be advantageous to implement a high-resolution display. Meanwhile, the unit areas of the respective subpixel sites S1 and S2 may be different from each other. In addition, the surfaces of the sub-pixel sites S1 and S2 may be subjected to a separate surface treatment or may be provided with grooves.
Meanwhile, in order to prevent the input ultra-thin pin LED devices 100, 101 and 102 from flowing out of the target area, that is, each sub-pixel sites S1 and S2 that is not physically partitioned, and to intensively place the ultra-thin pin LED devices 100, 101 and 102 on the respective sub-pixel sites S1 and S2, a barrier (not shown) made of sidewalls may be further included on the lower electrode line 200 to surround each of the sub-pixel sites S1 and S2 at a certain height, wherein the solution including the ultra-thin pin LED devices 100, 101 and 102 may be input into the barrier. The barrier may be formed of an insulating material so as not to be electrically affected when the ultra-thin pin LED device is mounted and driven in the final display implemented. Preferably, the insulating material may be any one or more selected from inorganic insulating materials such as silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O3), hafnium oxide (HfO2), yttrium oxide (Y2O3) and titanium dioxide (TiO2) and various transparent polymer insulating materials. In addition, the barrier may be manufactured by forming the insulating material on the lower electrode line 200 to a certain height and then going through a patterning and etching process to form a sidewall surrounding each of the sub-pixel sites S1 and S2.
In this case, when the barrier is made of an inorganic insulating material, it may be formed by any one of chemical vapor deposition, atomic layer deposition, vacuum deposition, e-beam deposition, and spin coating. In addition, when the barrier is made of a polymer insulating material, it may be formed using a coating method such as spin coating, spray coating, and screen printing. In addition, the patterning may be formed through photolithography using a photosensitive material or by a known nanoimprinting method, laser interference lithography, electron beam lithography, or the like. The height of the formed barrier may be more than ½ of the thickness of the ultra-thin pin LED devices, and may be typically a thickness that may not affect subsequent processes, preferably 0.1 to 100 μm, more preferably 0.3 to 10 μm. If the above range is not satisfied, it may be difficult to form an upper electrode line or make it difficult to manufacture a final display. In particular, when the thickness of the insulator is too thin compared to the thickness of the ultra-thin pin LED devices 100, 101 and 102, there is a concern that a solution such as an ink composition containing the ultra-thin pin LED devices may overflow out of the barrier, and thus, it may be difficult to prevent the ultra-thin pin LED devices from spreading out of the barrier.
In addition, for the etching, an appropriate etching method may be adopted in consideration of the material of the insulator, and for example, a wet etching method or a dry etching method may be performed, and preferably, one or more dry etching methods of plasma etching, sputter etching, reactive ion etching, and reactive ion beam etching may be used.
Next, step (2) according to the present invention is performed in which assembly power is applied to the lower electrode line 200 to self-align each of the ultra-thin pin LED devices 100, 101 and 102 on the lower electrode line 200 so that the first surface (B) or the second surface (T) among the various surfaces of the device becomes the mounting surface more dominantly than the side surface (S).
Here, the voltage and frequency of the assembly power applied to the lower electrode line 200 may be set to generate dielectrophoretic force having magnitude and direction such that the ultra-thin pin LED devices 100, 101 and 102 flowing in the solvent input in step (1) can be attracted to the lower electrodes 211, 212, 213 and 214, and the first surface (B) or second surface (T) of each device can dominantly contact the lower electrodes 211, 212, 213 and 214. Specifically, the assembly power may be determined in consideration of the electrical conductivity and dielectric constant of the solvent input in step (1), the size of the ultra-thin pin LED devices 100, 101 and 102, and the material and/or structure of each layer constituting the ultra-thin pin LED device.
Preferably, as can be seen from the above-described
As described above, the ultra-thin pin LED devices 100, 101 and 102 are self-aligned in step (2) through the application of assembly power so that the first surface (B) or the second surface (T) among the various surfaces of the device comes into contact with the lower electrode line 200, specifically, with the upper surface of the lower electrodes 211, 212, 213 and 214 more dominantly than the side surface (S), wherein the term ‘dominantly’ means that for example, when 120 substantially identical ultra-thin pin LED devices are input in step (1) and self-aligned through dielectrophoretic force in step (2), the number of ultra-thin pin LED devices mounted so that the first surface (B) or the second surface (T), rather than the side surface (S), of each device independently comes into contact with the upper surface of the lower electrode exceeds 50% of the total number of input devices, and in another example, the number ratio is 55%, 60%, 65%, or 70% or more.
Meanwhile, the number of ultra-thin pin LED devices 100, 101 and 102 provided in each of the sub-pixel sites S1 and S2 in step (2) may be at least two, and as another example, 2 to 100,000, but is not limited thereto. When the number of ultra-thin pin LED devices 100, 101 and 102 provided in each of sub-pixel sites S1 and S2 is two or more as described above, even if a defect occurs in some of the ultra-thin pin LED devices disposed in a certain sub-pixel site, the corresponding sub-pixel can emit a predetermined light, so that the generation of defective pixels in the display can be minimized or prevented.
Next, step (3) according to the present invention is performed in which the upper electrode line 300 is formed on the plurality of self-aligned ultra-thin pin LED devices 100, 101 and 102.
The upper electrode line 300 is not limited in number, arrangement, shape, etc., as long as it is designed to electrically contact the top of the ultra-thin pin LED devices 100, 101 and 102 mounted on the lower electrode line 200 described above. However, as shown in
Meanwhile,
Meanwhile, the upper electrode may have the material, shape, width, and thickness of an electrode used in a conventional display, and may be manufactured using a known method, so the present invention is not specifically limited thereto. For example, the upper electrodes may be made of aluminum, chromium, gold, silver, copper, graphene, ITO, or an alloy thereof, and may have a width of 2 to 50 μm and a thickness of 0.1 to 100 μm, which may be appropriately changed in consideration of the size of the desired display, and the like.
In addition, the upper electrode line 300 may be implemented by performing electrode line patterning using known photolithography, and then depositing an electrode material or depositing an electrode material followed by dry and/or wet etching, but a detailed description of the formation method is omitted.
Meanwhile, between steps (2) and (3) described above, it may further include a step of forming a conductive metal layer 500 connecting the lower electrode line 200 and the side surface of the selective directing layer 40, which is the uppermost layer having a specific surface of each ultra-thin pin LED device 101, for example, the second surface (T), in contact with the lower electrode line 200; and a step of forming an insulating layer 600 on the lower electrode line 200 without covering the upper surface of the self-aligned ultra-thin pin LED device 101.
The conductive metal layer 500 can be manufactured by applying a photolithography process using a photosensitive material to pattern a line where the conductive metal layer is to be deposited, and then depositing the conductive metal layer, or patterning the deposited metal layer and then etching it. This process may be performed by appropriately employing a known method, and reference may be made to Korean Patent Application No. 10-2016-0181410 by the present inventors, which is incorporated herein by reference.
After the conductive metal layer 500 is formed, the insulating layer 600 may be formed on the lower electrode line 200 so as not to cover the first surface (B) of the lowermost layer corresponding to the upper surface of the self-aligned ultra-thin fin LED device 101. The insulating layer 600 prevents electrical contact between the two vertically opposed electrode lines 200 and 300, and performs a function of facilitating the implementation of the upper electrode line 300. For the insulating layer 600, any insulating material commonly used in electrical and electronic components may be used without limitation. For example, the insulating layer 600 may be formed by depositing an insulating material such as SiO2 and SiNx through a PECVD method, by depositing an insulating material such as AlN and GaN through the MOCVD method, or by depositing an insulating material such as Al2O, HfO2, and ZrO2 through the ALD method. Meanwhile, the insulating layer 600 may be formed so as not to cover the upper surface of the self-aligned ultra-thin pin LED device 101. To this end, an insulating layer 600 may be formed through deposition to a thickness that does not cover the upper surface, or may be deposited to cover the upper surface and then dry etching may be performed until the upper surface of the device is exposed.
Next, as step (4) according to the present invention, a step is performed in which a color conversion layer 700 is patterned on the upper electrode line 300 so that each of the plurality of sub-pixel sites S1 and S2 becomes one of sub-pixel sites S1 and S2 that emits any one color of blue, green, and red.
The ultra-thin pin LED devices 101 provided in the sub-pixel sites S1 and S2 emit substantially the same type of light color, wherein the light color may be, for example, blue, white, or UV. In this case, in this step, in order to display a color image, a color conversion layer capable of converting light into light of a color different from that of the emitted light is provided on top of the upper electrode line 300 corresponding to the sub-pixel sites S1 and S2. Preferably, in order to improve color reproducibility by further increasing color purity and to improve front emission efficiency of color-converted light, for example, green/red, so that the back emission in the color conversion layer becomes the front, a short wavelength transmission filter (not shown) may be formed on the sub-pixel sites S1 and S2, and a color conversion layer 700 may be formed on one region of the upper portion of the short wavelength transmission filter.
In this case, the color conversion layer 700 may include a blue color conversion layer 711, a green color conversion layer 712, and a red color conversion layer 713 so that each of the plurality of sub-pixel sites S1 and S2 is a sub-pixel site independently emitting any one color among blue, green, and red. The blue color conversion layer 711, the green color conversion layer 712, and the red color conversion layer 713 may be known color conversion layers which convert the light passing through the color conversion layer into blue, green, and red colors in consideration of the wavelength of light emitted by the ultra-thin pin LED device 101 provided in the sub-pixel sites. Meanwhile, when the ultra-thin pin LED device 101 emits blue light, the blue color conversion layer 711 is unnecessary, and thus, the color conversion layer 700 may include a green color conversion layer 712 and a red color conversion layer 713.
Meanwhile, referring to a case where the ultra-thin pin LED device 101 is a blue light emitting LED device, a short wavelength transmission filter may be formed on the upper electrode line 300, and if the plane on which the upper electrode line is formed is not flat, a planarization layer (not shown) is further formed to flatten the plane on which the upper electrode line is formed, and then the short wavelength transmission filter may be formed on the planarization layer. The short-wavelength transmission filter may be a multilayer film in which thin films of high refractive/low refractive index material are repeated, wherein the multilayer film may be composed of [(0.125)SiO2/(0.25)TiO2/(0.125)SiO2]m to transmit blue light and reflect light of a longer wavelength than blue. In addition, the short wavelength transmission filter may have a thickness of 0.5 to 10 μm, but is not limited thereto. A method of forming the short wavelength transmission filter may be any one of e-beam, sputtering, and atomic deposition, but is not limited thereto.
Next, a color conversion layer 700 may be formed on the short wavelength transmission filter. Specifically, the color conversion layer 700 may be formed by patterning a green color conversion layer 712 on the short-wavelength transmission filter corresponding to some selected subpixels determined to be green among the subpixel sites S1 and S2, and patterning a red color conversion layer 713 on the short-wavelength transmission filter corresponding to some selected subpixel sites determined to be red among the remaining subpixel sites S1 and S2. A method of forming the patterning may be at least one method selected from the group consisting of a screen printing method, photolithography, and dispensing. Meanwhile, the patterning order of the green color conversion layer 712 and the red color conversion layer 713 is not limited and may be formed simultaneously or in reverse order. In addition, the green color conversion layer 712 and the red color conversion layer 713 may be color conversion layers known in the display field, and may include, for example, a color conversion material such as a phosphor that can be excited by a color filter or a blue LED device and converted into a desired light color, and a known color conversion material may be used.
As an example, the green color conversion layer 712 may be a fluorescent layer including a green fluorescent material, specifically may include one or more phosphors selected from the group consisting of SrGa2S4:Eu, (Sr,Ca)3SiO5:Eu, (Sr,Ba,Ca)SiO4:Eu, Li2SrSiO4:Eu, Sr3SiO4:Ce,Li, β-SiALON:Eu, CaSc2O4:Ce, Ca3Sc2Si3O12:Ce, Caα-SiALON:Yb, Caα-SiALON:Eu, Liα-SiALON:Eu, Ta3Al5O12:Ce, Sr2Si5N8:Ce, (Ca,Sr,Ba)Si2O2N2:Eu, Ba3Si6O12N2:Eu, γ-AlON:Mn and γ-AlON:Mn,Mg, but is not limited thereto. In addition, the green color conversion layer 712 may be a fluorescent layer containing a green quantum dot material, specifically may include one or more quantum dots selected from the group consisting of CdSe/ZnS, InP/ZnS, InP/GaP/ZnS, InP/ZnSe/ZnS, Peroviskite green nanocrystals, but is not limited thereto.
In addition, the red color conversion layer 713 may be a fluorescent layer containing a red fluorescent material, specifically may include one or more phosphors selected from the group consisting of (Sr,Ca)AlSiN3:Eu, CaAlSiN3:Eu, (Sr,Ca)S:Eu, CaSiN2:Ce, SrSiN2:Eu, Ba2Si5N8: Eu, CaS:Eu, CaS:Eu,Ce, SrS:Eu, SrS:Eu,Ce and Sr2Si5N8: Eu, but is not limited thereto. In addition, the red color conversion layer 713 may be a fluorescent layer containing a red quantum dot material, specifically may include one or more quantum dots selected from the group consisting of CdSe/ZnS, InP/ZnS, InP/GaP/ZnS, InP/ZnSe/ZnS, Peroviskite red nanocrystals, but is not limited thereto.
In some sub-pixel sites, only the short-wavelength transmission filter is disposed on the uppermost layer, and the green color conversion layer and the red color conversion layer are not formed on the vertical upper part. In this site, however, the color of light emitted by the ultra-thin pin LED device, for example, blue light may be irradiated. On the other hand, some sub-pixel spatial sites in which the green color conversion layer 712 is formed above the short wavelength transmission filter may be irradiated with green light through the green conversion layer. In addition, as the red color conversion layer 713 is formed on the short wavelength transmission filter, the remaining sub-pixel spatial sites may be irradiated with red light, whereby a color-by-blue LED display may be implemented.
In addition, preferably, a long-wavelength transmission filter (not shown) may be further formed on the green color conversion layer 712 and the red color conversion layer 713, wherein the long-wavelength transmission filter functions as a filter for preventing color purity from deteriorating due to mixing of blue light emitted from the device and color-converted green/red light. The long-wavelength transmission filter may be formed on part or all of the color conversion layer 700, and preferably may be formed only on the green color conversion layer 712 and the red color conversion layer 713. In this case, the usable long-wavelength transmission filter may be a multilayer film in which thin films of high/low refractive index materials that can achieve the purpose of long-wavelength transmission and short-wavelength reflection that reflect blue are repeated, and may be composed of [(0.125)TiO2/(0.25)SiO2/(0.125)TiO2]m m=number of repeated layers, where m is 5 or more). In addition, the long wavelength transmission filter may have a thickness of 0.5 to 10 μm, but is not limited thereto. A method of forming the long-wavelength transmission filter may be any one of e-beam, sputtering, and atomic deposition, but is not limited thereto. In addition, in order to form the long-wavelength transmission filter only on the top of the green/red color conversion layer, the long wavelength transmission filter may be formed only in the desired region by using a metal mask capable of exposing the green/red color conversion layer and masking other regions.
Meanwhile, after the color conversion layer 700 is formed, a protective layer 800 may be further formed to flatten an upper surface step due to the color conversion layer 700 and to protect the color conversion layer. Since the protective layer 800 may be appropriately formed by a suitable forming method in consideration of the material of the protective layer used in a conventional display in which the color conversion layer 700 is provided, the present invention is not particularly limited in this regard.
The full-color LED display 1000 manufactured according to the first embodiment of the present invention described above includes: a lower electrode line 200 in which a plurality of sub-pixel sites Si and S2 are formed; a plurality of ultra-thin pin LED devices 101 including, based on mutually perpendicular x-axis, y-axis and z-axis wherein the x-axis direction is a major axis and a plurality of layers 10, 20, 30 and 40 are stacked in the z-axis direction, a first surface (B) and a second surface (T) opposite to each other in the z-axis direction, and other side surfaces (S), wherein the ultra-thin pin LED devices are mounted so that one surface thereof is in contact with the lower electrode line 200 in each of sub-pixel sites S1 and S2, and emit substantially the same light color; an upper electrode line 300 disposed on the plurality of ultra-thin pin LED devices 101; and a color conversion layer 700 patterned on the upper electrode line 300 so that each of the plurality of sub-pixel sites S1 and S2 becomes a sub-pixel site emitting any one color among blue, green, and red.
In addition, the plurality of ultra-thin pin LED devices 101 mounted on the full-color LED display 1000 have a drivable mounting ratio of 55% or more in which the first surface (B) or the second surface (T) of each device is mounted so as to contact the lower electrode line 200.
As described in the manufacturing method for the first embodiment, each of the ultra-thin LED devices 101 input into the process is mounted so that the first surface (B) or the second surface (T) among the various surfaces of the device dominantly contacts the lower electrode line 200, specifically the upper surface of the lower electrodes 211, 212, 213 and 214, whereby a full-color LED display 1000 satisfying a drivable mounting ratio of 55% or more can be implemented. In addition, preferably, the full-color LED display 1000 can satisfy the drivable mounting ratio of 70% or more, more preferably 75% or more, still more preferably 80% or more, 90% or more, or 95% or more, whereby the implemented display can achieve excellent luminance by minimizing the case where the input ultra-thin pin LED devices are not mounted or the side surface is mounted, and the manufacturing cost can be lowered by reducing the number of wasted ultra-thin pin LED devices. If the drivable mounting ratio is less than 55%, the manufacturing cost may greatly increase, and the luminance characteristics of the display may be greatly deteriorated as there are many ultra-thin pin LED devices that are mounted but are not driven (emitted) and are wasted.
In addition, according to one embodiment of the present invention, the full-color LED display 1000 may be configured such that the selective mounting ratio, which is a ratio mounted selectively so that the mounting surface of the mounted ultra-thin pin LED devices 101 is any one of the first surface (B) and the second surface (T), satisfies 70% or more, more preferably 85% or more, even more preferably 90% or more, and even more preferably 93% or more. Thereby, it is possible to increase the driving rate and luminance of the mounted ultra-thin pin LED devices, and in particular, the range of applications that can select DC power instead of AC as the driving power source can be expanded. Further, it may be advantageous for the display to implement increased luminance due to the use of DC power.
In addition, in the full-color LED display 1000, the unit area of the subpixel sites that can be driven independently may be, for example, 1 μm2 to 100 cm2, more preferably 10 μm2 to 100 mm2, but is limited thereto. In addition, the full-color LED display 1000 may include, for example, 2 to 100,000 ultra-thin pin LED devices 101 per unit area of 100×100 μm2 in the sub-pixel site, but is limited thereto.
Meanwhile, as described above, the ultra-thin pin LED device 101 provided in the full-color LED display 1000 may be mounted so that some of the mounted ultra-thin pin LED devices have side surfaces (S) in contact with the upper surface of the lower electrode, as long as the drivable mounting ratio does not reach 100%. In this case, if the width, which is the length in the y-axis direction, and the thickness, which is the length in the z-axis direction, of the ultra-thin pin LED device are the same, heights from the upper surface of the lower electrode to the opposite surface facing the mounting surface of the mounted ultra-thin pin LED device may all be the same when the full-color LED display 1000 is viewed from the side. In this case, the ultra-thin pin LED device mounted so that the side surface (S) contacts the upper surface of the lower electrode is also electrically contacted with the upper electrode, which may cause electrical leakage or electrical short circuit.
Accordingly, according to one embodiment of the present invention, the width of the ultra-thin pin LED device may be smaller than the thickness, whereby it is possible to prevent electrical short circuit or leakage caused by contact of the side surface of the device with the lower electrode. Referring to
Next, as a display according to the second embodiment of the present invention, a full-color LED display 2000 capable of implementing colors without a separate color conversion layer because a plurality of ultra-thin pin LED devices 101 are composed of those capable of emitting blue, green and red lights will be described.
Referring to
As in the first embodiment described above, the full-color LED display 2000 according to the second embodiment of the present invention can be manufactured using a manufacturing method in which the ultra-thin pin LED devices 101 are self-aligned on the lower electrode line 200 through dielectrophoretic force by using an electric field formed by the power applied to the lower electrode line 200. In this case, among all the ultra-thin pin LED devices 101 mounted to be in contact with the lower electrode line 200 in each of the sub-pixel sites S3, and S4 and S5, specifically, the upper surfaces of the lower electrodes 201, 202, 203 and 204 constituting the lower electrode line 200 in each of sub-pixel sites S3, and S4 and S5, the first surface (B) or the second surface (T) of each ultra-thin pin LED device 101 may be mounted more dominantly than the side surfaces (S).
Meanwhile, the full-color LED display 2000 according to the second embodiment may be manufactured by a method including the steps of: (a) inputting solutions containing blue ultra-thin pin LED devices, green ultra-thin pin LED devices and red ultra-thin pin LED devices, respectively, onto a lower electrode line 200 in which a plurality of sub-pixel sites S3, and S4 and S5 are formed so that each sub-pixel site emits the same light color, wherein each of the blue ultra-thin pin LED devices, the green ultra-thin pin LED devices and the red ultra-thin pin LED devices includes, based on mutually perpendicular x-axis, y-axis and z-axis wherein the x-axis direction is a major axis and a plurality of layers are stacked in the z-axis direction, a first surface (B) and a second surface (T) opposite to each other in the z-axis direction, and other side surfaces (S); (b) applying assembly power to the lower electrode line 200 to self-align each of the ultra-thin pin LED devices 101 input into each of the sub-pixel sites S3, and S4 and S5 on the lower electrode line 200 so that the first surface (B) or second surface (T) among the various surfaces of the device becomes the mounting surface more dominantly than the side surface (S); and (c) forming an upper electrode line 300 on the plurality of self-aligned ultra-thin pin LED devices 101.
Steps (a), (b) and (c) in the display manufacturing method according to the second embodiment correspond to steps (1), (2) and (3) described in the display manufacturing method according to the above-described first embodiment, respectively, and thus, a detailed description of each step is omitted below.
Differences from the manufacturing method according to the first embodiment will be mainly described. In step (1) of the first embodiment, the ultra-thin pin LED devices emitting substantially the same light color are used, and the solution containing them is input to the plurality of sub-pixel sites, whereas in step (a) of the second embodiment, a solution including an ultra-thin pin LED device capable of emitting a light color corresponding to a color set to appear in each of the plurality of subpixel sites set to show three kinds of blue, green and red is input on the lower electrode line 200, and the ultra-thin pin LED devices themselves emit three colors. Therefore, in the second embodiment, the step of forming the color conversion layer performed to implement color in step (4) of the first embodiment is omitted.
In addition, the LED device having a green light color and the LED device having a red light color used in the second embodiment may be implemented by using an LED wafer used in a conventional display or the like and adjusting the shape and size of the ultra-thin pin LED device according to the present invention, and the electrical conductivity and dielectric constant of materials forming the uppermost and/or lowermost layers.
Meanwhile, as described in the manufacturing method for the first embodiment, each of the ultra-thin LED devices 101 input in the second embodiment is mounted so that the first surface (B) or the second surface (T) among the various surfaces of the device dominantly contacts the lower electrode line 200, specifically the upper surface of the lower electrodes 211, 212, 213 and 214, whereby a full-color LED display 2000 satisfying a drivable mounting ratio of 55% or more can be implemented. In addition, preferably, the full-color LED display 2000 can satisfy the drivable mounting ratio of 70% or more, more preferably 75% or more, still more preferablyb 80% or more, 90% or more, or 95% or more, whereby the implemented display can achieve excellent luminance by minimizing the case where the input ultra-thin pin LED devices are not mounted or the side surface is mounted, and the manufacturing cost can be lowered by reducing the number of wasted ultra-thin pin LED devices. If the drivable mounting ratio is less than 55%, the manufacturing cost may greatly increase, and the luminance characteristics of the display may be greatly deteriorated as there are many ultra-thin pin LED devices that are mounted but are not driven (emitted) and are wasted.
In addition, the full-color LED display 2000 may be configured such that the selective mounting ratio, which is a ratio mounted selectively so that the mounting surface of the mounted ultra-thin pin LED devices 101 is any one of the first surface (B) and the second surface (T), satisfies 70% or more, more preferably 85% or more, even more preferably 90% or more, and even more preferably 93% or more. Thereby, it is possible to increase the driving rate and luminance of the mounted ultra-thin pin LED devices, and in particular, the range of applications that can select DC power instead of AC as the driving power source can be expanded. Further, it may be advantageous for the display to implement increased luminance due to the use of DC power.
In addition, in the full-color LED display 2000, the unit area of the subpixel sites that can be driven independently may be, for example, 1 μm2 to 100 cm2, more preferably 10 μm2 to 100 mm2, but is limited thereto. In addition, the full-color LED display 1000 may include, for example, 2 to 100,000 ultra-thin pin LED devices 101 per unit area of 100×100 μm2 in the sub-pixel site, but is limited thereto.
Hereinafter, the present invention will be described in more detail by way of the following examples, but it should be understood that the examples are not intended to limit the scope of the present invention, but to aid understanding of the present invention.
First, an ultra-thin pin LED device was prepared as follows. Specifically, a conventional LED wafer (Epistar) was prepared in which an undoped n-type III-nitride semiconductor layer, a Si-doped n-type III-nitride semiconductor layer (thickness: 4 μm), a photoactive layer (thickness: 0.15 μm), and a p-type III-nitride semiconductor layer (thickness: 0.05 μm) are sequentially stacked on a substrate. On the prepared LED wafer, ITO (thickness: 0.15 μm) as a selective alignment-directing layer, SiO2 (thickness: 1.2 μm) as a first mask layer, and Ni (thickness: 80.6 nm) as a second mask layer were sequentially deposited, and then a rectangular pattern-transferred SOG resin layer was transferred onto the second mask layer using nanoimprint equipment. Then, the SOG resin layer was cured using RIE, and the remaining resin portion of the resin layer was etched through RIE to form a resin pattern layer. Thereafter, the second mask layer was etched using ICP along the pattern, and the first mask layer was etched using RIE. Thereafter, the first electrode layer, the p-type III-nitride semiconductor layer, and the photoactive layer were etched using ICP, and then the doped n-type III-nitride semiconductor layer was etched to a thickness of 0.5 μm, and an LED wafer having a plurality of LED structures (long side 4 μm, short side 750 nm, height 850 nm) from which the mask pattern layer was removed by KOH wet etching was manufactured.
Afterwards, a temporary protective film of Al2O3 was deposited on the LED wafer having the plurality of LED structures formed therein (deposition thickness of 72 nm based on the side surface of the LED structure), and then the temporary protective film material formed between the plurality of LED structures was removed through RIE to expose the top surface of the doped n-type III-nitride semiconductor layer between the LED structures.
Thereafter, the LED wafer having the temporary protective film formed was immersed in an electrolyte, which is an aqueous solution of 0.3 M oxalic acid, and then connected to an anode terminal of the power supply. A cathode terminal was connected to a platinum electrode immersed in the electrolyte, and then a 15V voltage was applied for 5 minutes to form a plurality of pores in the thickness direction from the surface of the doped n-type III-nitride semiconductor layer between the LED structures. Thereafter, the temporary protective film was removed through ICP, and then a rotation induction film of SiO2 was deposited with a thickness of 60 nm based on the side surface of the LED structure, wherein the rotation induction film of SiO2 has a real part of the K(ω) value according to Equation 1 of 0.336 when the solvent is acetone with a dielectric constant of 20.7 and the frequency of the applied power is in the frequency band of 10 kHz to 10 GHz, assuming that the particles in Equation 1 above are spherical core-shell particles having a radius of 430 nm and composed of GaN with a radius of 400 nm as the core part and a rotational induction film with a thickness of 30 nm as the shell part. Thereafter, the rotation induction film material formed between the LED structures is removed through RIE to expose an upper surface of the doped n-type III-nitride semiconductor layer between the LED structures. Then, the LED wafer was immersed in a 100% gamma-butyrolactone bubble-forming solution, and ultrasonic waves were irradiated thereto at an intensity of 160 W and 40 kHz for 10 minutes to generate bubbles. The generated bubbles were used to collapse the pores formed in the doped n-type III-nitride semiconductor layer, thereby manufacturing a plurality of ultra-thin fin LED devices emitting blue light as shown in the SEM picture of
Thereafter, a lower electrode line was prepared in which a first lower electrode and a second lower electrode extending in a first direction are alternately formed on a base substrate made of quartz and having a thickness of 500 μm so that the interval is 3 μm in a second direction perpendicular to the first direction. Here, the first lower electrode and the second lower electrode each have a width of 10 μm and a thickness of 0.2 μm, the material of the first lower electrode and the second lower electrode is gold, and the area of sub-pixel site in the lower electrode line on which the ultra-thin pin LED device is mounted was set to 1 mm2. In addition, an insulating barrier made of SiO2 was formed on the base substrate to a height of 0.5 μm to surround the mounted region.
Thereafter, 120 prepared ultra-thin fin LED devices are mixed with acetone having a dielectric constant of 20.7 to prepare a solution. 9 μl of the prepared solution was dropped twice in each sub-pixel site, and then a sine wave AC power of 10 kHz and 40 Vpp as an assembly power was applied to the first lower electrode and the second lower electrode to mount the ultra-thin pin LED device on the lower electrode through dielectrophoresis.
Thereafter, a passivation material of SiO2 was deposited using the PECVD method at a height corresponding to the thickness of the ultra-thin pin LED devices in the sub-pixel site where the ultra-thin pin LED devices were mounted, and then extended in a second direction perpendicular to the first direction. A plurality of upper electrodes (width: 10 μm, thickness: 0.2 μm, inter-electrode spacing: 3 μm, and material: gold) spaced apart from each other in the first direction were formed on the upper surface of the mounted ultra-thin pin LED device. Thereafter, a color-by-blue type full-color LED display was implemented by patterning a color conversion layer on the upper electrode line corresponding to the sub-pixel site so that each of the plurality of sub-pixel sites becomes a sub-pixel site emitting any one color among blue, green and red.
An ultra-thin pin LED device was manufactured in the same manner as in Example 1, except that the rotation induction film was changed to a rotation induction film of SiNX having a value of the real part of K(ω) according to Equation 1 of 0.501 under the same conditions, and used to implement a full-color LED display.
An ultra-thin pin LED device was manufactured in the same manner as in Example 1, except that the rotation induction film was changed to a rotation induction film of TiO2 having a value of the real part of K(ω) according to Equation 1 of 0.944 under the same conditions, and used to implement a full-color LED display.
An ultra-thin pin LED device as shown in the SEM picture of
An ultra-thin pin LED device as shown in the SEM picture of
An ultra-thin pin LED device was manufactured in the same manner as in Example 3, except that ITO as a selective alignment-directing layer was not formed, and used to implement a full-color LED display.
An ultra-thin pin LED device was manufactured in the same manner as in Example 1, except that the rotation induction film was deposited without forming a temporary protective film and a plural of pores, and then the rotation induction film material formed on the top of the LED structure was removed through etching, and the LED structure was separated from the wafer using a diamond cutter, and used to implement a full-color LED display.
An ultra-thin pin LED device was manufactured in the same manner as in Example 7, except that the rotation induction film was changed to a rotation induction film of A1203 having a value of the real part of K(w) according to Equation 1 of 0.616 under the same conditions, and used to implement a full-color LED display.
An ultra-thin pin LED device was manufactured in the same manner as in Example 7, except that the rotation induction film was changed to a rotation induction film of TiO2 having a value of the real part of K(w) according to Equation 1 of 0.944, and used to implement a full-color LED display.
An ultra-thin pin LED device was manufactured in the same manner as in Example 7, except that the rotation induction film was not formed, and used to implement a full-color LED display.
An ultra-thin pin LED device was manufactured in the same manner as in Example 7, except that ITO as a selective alignment-directing layer was not formed, and used to implement a full-color LED display.
An ultra-thin pin LED device as shown in the SEM picture of
An ultra-thin pin LED device was manufactured in the same manner as in Example 7, except that ITO as a selective alignment-directing layer and a rotation induction film was not formed, and used to prepare a full-color LED display.
A full-color LED display was implemented using an ultra-thin pin LED device in the same manner as in Example 1, except that the ultra-thin pin LED device was manufactured as follows.
Specifically, for the ultra-thin pin LED device, a conventional LED wafer (Epistar) was prepared in which an undoped n-type III-nitride semiconductor layer, a Si-doped n-type III-nitride semiconductor layer (thickness: 4 μm), a photoactive layer (thickness: 0.45 μm), and a p-type III-nitride semiconductor layer (thickness: 0.05 μm) are sequentially stacked on a substrate. On the prepared LED wafer, SiO2 (thickness: 1.2 μm) as a first mask layer, and Ni (thickness: 80.6 nm) as a second mask layer were sequentially deposited, and then an SOG resin layer having a rectangular pattern transferred in the same size as in Example 1 was transferred onto the second mask layer using nanoimprint equipment. Then, the SOG resin layer was cured using RIE, and the remaining resin portion of the resin layer was etched through RIE to form a resin pattern layer. Thereafter, the second mask layer was etched using ICP along the pattern, and the first mask layer was etched using RIE. Thereafter, the first electrode layer, the p-type III-nitride semiconductor layer, and the photoactive layer were etched using ICP, and then the doped n-type III-nitride semiconductor layer was etched to a thickness of 0.6 μm, and then an LED wafer having a plurality of LED structures from which the mask pattern layer was removed by KOH wet etching was manufactured. Afterwards, Al2O3 as a temporary protective film was deposited on the LED wafer having the plurality of LED structures formed therein (deposition thickness of 72 nm based on the side surface of the LED structure), and then the temporary protective film material formed between the plurality of LED structures was removed through RIE to expose the top surface of the doped n-type III-nitride semiconductor layer between the LED structures. Thereafter, the doped n-type III-nitride semiconductor layer between the LED structures was further etched to a thickness of 0.2 μm to expose the doped n-type III-nitride semiconductor layer without the temporary protective film formed on the side surface. Then, the doped n-type III-nitride semiconductor layer exposed on the side surface of the LED structure was etched using ICP so that the doped n-type III-nitride semiconductor layer was etched in the width direction from both sides to the center. Afterwards, the temporary protective film formed on the side surface of each LED structure was removed through RIE, and a plurality of LED structures were separated by applying ultrasonic waves to the wafer. The separated LED structure was implemented to have a protrusion extending in the longitudinal direction with a predetermined width and protruding in the thickness direction on the lower surface of the doped n-type III-nitride semiconductor layer due to etching in the width direction. In this case, the ultra-thin pin LED device was manufactured so that the height from the p-type III-nitride semiconductor layer to the protrusion, and the length and width of the device were identical to those of the ultra-thin device in Example 1.
For the full-color LED displays according to Examples 1 to 12 and Comparative Examples 1 to 2, the mounting surface of the ultra-thin pin LED device was evaluated as follows, and the results are shown in Table 2 below.
Specifically, SEM pictures were taken in a state in which the ultra-thin pin LED device was self-aligned after applying an assembly voltage during the manufacturing process of the full-color LED display, and the mounting surface of each of the ultra-thin pin LED devices in contact with the upper surface of the lower electrode on the above region was observed and counted. The results are shown in Table 2 below as a percentage of the number of ultra-thin pin LED devices input.
In addition, Table 2 also shows the drivable mounting ratio in which the mounting surface of the ultra-thin pin LED device is the first surface (B) or the second surface (T), and the selective mounting ratio in which a specific one of the first surface (B) and the second surface (T) becomes the mounting surface for each example or comparative example.
As can be seen from Table 2, in the ultra-thin pin LED devices used in the full-color LED display according to Comparative Examples 1 and 2, the ratio of drivably mounted devices among all the ultra-thin pin LED devices input is less than 50%, and thus, the ratio of the first surface (B) or the second surface (T) in contact with the upper surface of the lower electrode is small, whereby the luminous efficiency is lower than that of the mounted device during driving. In contrast, in the case of the full-color LED display using the ultra-thin pin LED device according to the examples, the ratio of drivably mounted devices among all the ultra-thin pin LED devices input is 56% or more, and thus, the first surface (B) or the second surface (T) dominantly contacts the upper surface of the mounting electrode, whereby it can be expected that the luminous efficiency is significantly improved.
Full-color LED displays were manufactured in the same manner as in Examples 1 to 3, respectively, except that the assembly power was changed to 10 kHz and 20 Vpp conditions.
SEM pictures were taken in a state in which the ultra-thin pin LED device was self-aligned after applying an assembly voltage during the manufacturing process of the full-color LED display according to Examples 13 to 15, and the mounting form of the ultra-thin pin LED devices in contact with the upper surface of the lower electrode was analyzed based on
As can be seen from Table 3, in the case of the full-color LED display of Examples 13 and 14 employing an ultra-thin pin LED device including the rotation induction film having a real value of K(ω) of 0.6 or less, the ratio of mounting in a form in which both ends are mounted on two adjacent mounting electrodes is significantly higher than that of Example 15. Therefore, it can be expected that examples 13 and 14 have a more advantageous mounting form compared to example 15 in forming the driving electrode on the top of the ultra-thin pin LED device.
Full-color LED displays were manufactured in the same manner as in Example 1, except that the frequency and voltage of the assembly power were changed as shown in Table 4 below.
For the full-color LED displays according to Examples 1, 13 and 16 to 17, the mounting surface was analyzed in the same manner as in Experimental Example 1, and the results are shown in Table 4 below.
As can be seen from Table 4, it can be confirmed that in the ultra-thin pin LED devices of the full-color LED display according to the examples, each of the ultra-thin pin LED devices is mounted such that the first or second surface thereof contacts the upper surface of the lower electrode more dominantly than the side surface under an electric field formed through the applied assembly power. In addition, in the case of the full-color LED display according to the examples, the selective mounting ratio in which the second surface of the ultra-thin pin LED devices becomes the mounting surface is also 92% or more, so that it can be driven by DC power. Accordingly, high luminance is expected to be expressed.
Although an embodiment of the present invention have been described above, the spirit of the present invention is not limited to the embodiment presented in the subject specification; and those skilled in the art who understands the spirit of the present invention will be able to easily suggest other embodiments through addition, changes, elimination, and the like of elements without departing from the scope of the same spirit, and such other embodiments will also fall within the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0086123 | Jul 2022 | KR | national |
