Unit pixel and display device

Abstract

A unit pixel according to one embodiment of the present disclosure includes a transparent substrate; a plurality of light-emitting elements aligned on the transparent substrate; connection layers electrically connected to each of the light-emitting elements; and bonding pads disposed on top of each of the connection layers and electrically connected to each of the connection layers; and each of the bonding pads partially overlaps vertically with at least one of the light-emitting elements.

Description

[Technical Field]

[0001] Each exemplary embodiment relates to a unit pixel having a light-emitting element and a display device having the same. [Background technology]

[0002] Light emitting devices are semiconductor devices that use light emitting diodes, which are inorganic light sources, and are used in a variety of fields, such as display devices, vehicle lamps, general lighting, etc. Light emitting diodes have advantages such as long life, low power consumption, and fast response speed, and are rapidly replacing existing light sources.

[0003] Meanwhile, conventional light emitting diodes (LEDs) have been mainly used as backlight sources in display devices, but in recent years, display devices that directly display images using LEDs have been developed, and these displays are sometimes called micro LED displays.

[0004] A display device generally realizes various colors using a mixture of blue, green, and red colors. The display device includes a plurality of pixels to realize various images, and each pixel includes blue, green, and red sub-pixels. The color of a particular pixel is determined by the color of these sub-pixels, and an image is realized by combining these pixels.

[0005] In the case of a micro LED display, micro LEDs are arranged on a two-dimensional plane corresponding to each sub-pixel, which requires a large number of micro LEDs to be arranged on one substrate. However, micro LEDs are very small, for example, less than 200 microns or even less than 100 microns, and such small size causes various problems. In particular, it is difficult to handle small light emitting diodes, so it is not easy to directly mount light emitting diodes on a display panel. Summary of the Invention [Problem to be solved by the invention]

[0006] Each exemplary embodiment provides a unit pixel suitable for mounting on a circuit board and a display device having the same.

[0007] Each exemplary embodiment provides a highly reliable unit pixel and a display device having the same.

[0008] Each exemplary embodiment provides a unit pixel capable of increasing the contact area of a bump pad in a small unit pixel, and a display device having the same. [Means for solving the problem]

[0009] An exemplary embodiment provides a unit pixel, which includes: a transparent substrate; a plurality of light-emitting elements aligned on the transparent substrate; connection layers electrically connected to each of the light-emitting elements; and bonding pads disposed on top of each of the connection layers and electrically connected to each of the connection layers; and each of the bonding pads partially overlaps vertically with at least one of the light-emitting elements.

[0010] An exemplary embodiment provides a display device, the display device including: a circuit board having pads; a plurality of unit pixels arranged on the circuit board; and bonding materials bonding the unit pixels to the pads, each of the unit pixels including a transparent substrate; a plurality of light-emitting elements aligned on the transparent substrate; connection layers electrically connected to the light-emitting elements; and bonding pads arranged on top of the contact layers and electrically connected to the connection layers, each of the bonding pads partially overlapping vertically with at least one of the light-emitting elements, and each of the bonding materials bonding the bonding pads to a respective pad on the circuit board. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic plan view illustrating a display device according to an embodiment; [Figure 2A] 1 is a schematic plan view illustrating a light emitting device according to an embodiment; [Figure 2B] FIG. 2B is a schematic cross-sectional view taken along line AA in FIG. 2A. [Figure 3A] FIG. 2 is a schematic plan view illustrating a unit pixel according to the first embodiment. [Figure 3B] FIG. 3B is a schematic cross-sectional view taken along line BB in FIG. 3A. [Figure 4A] FIG. 2 is a schematic plan view illustrating a pixel module according to an embodiment. [Figure 4B] FIG. 4B is a schematic cross-sectional view taken along line CC in FIG. 4A. [Figure 4C] FIG. 2 is a schematic rear view illustrating a pixel module according to an embodiment. [Figure 4D] FIG. 2 is a schematic circuit diagram illustrating a pixel module according to an embodiment. [Figure 4E] FIG. 2 is a schematic circuit diagram illustrating a pixel module according to an embodiment. [Figure 5A] FIG. 2 is a schematic diagram for explaining a problem that occurs when implementing the unit pixel according to the first embodiment. [Figure 5B] 10 is an image showing a defect that occurs when mounting a unit pixel according to the first embodiment. [Figure 6A] FIG. 10 is a schematic plan view illustrating a unit pixel according to a second embodiment. [Figure 6B] FIG. 6B is a schematic cross-sectional view taken along line DD in FIG. 6A. [Figure 7] FIG. 10 is a schematic cross-sectional view illustrating a display device in which a unit pixel according to a second embodiment is mounted. [Figure 8] 10A and 10B are images showing several display screens of a display device formed using unit pixels according to a second embodiment of the present invention; [Figure 9A] FIG. 10 is a schematic plan view illustrating a unit pixel according to a third embodiment. [Figure 9B] FIG. 9B is a schematic cross-sectional view taken along line EE of FIG. 9A. [Figure 10A] 10A to 10C are schematic cross-sectional views illustrating a method for manufacturing a unit pixel according to a third embodiment. [Figure 10B] 10A to 10C are schematic cross-sectional views illustrating a method for manufacturing a unit pixel according to a third embodiment. [Figure 10C] 10A to 10C are schematic cross-sectional views illustrating a method for manufacturing a unit pixel according to a third embodiment. [Figure 10D] 10A to 10C are schematic cross-sectional views illustrating a method for manufacturing a unit pixel according to a third embodiment. [Figure 10E] 10A to 10C are schematic cross-sectional views illustrating a method for manufacturing a unit pixel according to a third embodiment. [Figure 10F] 10A to 10C are schematic cross-sectional views illustrating a method for manufacturing a unit pixel according to a third embodiment. [Figure 11A] 1 is a schematic plan view illustrating a light emitting device according to an embodiment; [Figure 11B] FIG. 11B is a schematic cross-sectional view taken along line FF in FIG. 11A. [Figure 12] 2 is a schematic cross-sectional view illustrating a surface unevenness pattern of a light emitting device according to an embodiment. [Figure 13] 1 is an SEM image showing the surface unevenness pattern of a light-emitting element. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, each embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. The following embodiments are provided as examples to fully convey the concept of the present disclosure to those skilled in the art. Therefore, the present disclosure is not limited to the embodiments described below and may be embodied in other forms. In the drawings, the width, length, thickness, etc. of components may be exaggerated for convenience. Furthermore, when a component is described as being "on top of" or "on" another component, this includes not only the case where each component is "directly on top of" or "directly above" the other component, but also the case where another component is interposed between the other component and the other component. The same reference numerals refer to the same components throughout the specification.

[0013] A unit pixel according to an exemplary embodiment includes a transparent substrate; a plurality of light-emitting elements aligned on the transparent substrate; connection layers electrically connected to each of the light-emitting elements; and bonding pads disposed on top of each of the connection layers and electrically connected to each of the connection layers; and each of the bonding pads partially overlaps at least one of the light-emitting elements in the vertical direction.

[0014] By arranging each bonding pad so that it overlaps with each light emitting element, the area of each bonding pad can be increased, and the unit pixel can be stably mounted on the circuit board using a reflow process or the like.

[0015] At least one of the bonding pads may partially overlap two of the light emitting devices in a vertical direction.

[0016] The transparent substrate may have a concave-convex pattern on a surface facing each of the light emitting elements, which makes it possible to make the directivity angle of light emitted from each of the light emitting elements uniform.

[0017] Each of the light emitting devices may have a first uneven pattern formed on a surface facing the transparent substrate and a second uneven pattern formed on the first uneven pattern, and the first and second uneven patterns may improve light extraction efficiency and make the directivity angle of each light emitting device uniform.

[0018] The plurality of light emitting elements may include at least three light emitting elements emitting light of different colors, and the at least three light emitting elements may be arranged in a row.

[0019] The unit pixel may further include a light-blocking layer disposed between the transparent substrate and the light-emitting element; and an adhesive layer disposed between the light-blocking layer and each of the light-emitting elements; the light-blocking layer may have windows through which light generated by each of the light-emitting elements passes, and each of the light-emitting elements may be disposed corresponding to each of the windows.

[0020] The unit pixel may further include a surface layer disposed between the transparent substrate and the light-blocking layer.

[0021] The surface layer improves the adhesive strength of the light-blocking layer and prevents the light-blocking layer from peeling off from the transparent substrate.

[0022] The unit pixel may further include a step adjustment layer covering the light emitting device, the step adjustment layer may have openings exposing the light emitting devices, and the connection layers may be disposed on the step adjustment layer and electrically connected to the light emitting devices through the openings of the step adjustment layer.

[0023] The unit pixel may further include an insulating material layer covering the connection layers, the insulating material layer may have openings exposing the connection layers, and the bonding pads may be electrically connected to the connection layers through the openings in the insulating material layer.

[0024] The insulating material layer may cover a side surface of the step adjusting layer as well as a side surface of each of the connection layers.

[0025] In an embodiment, the insulating material layer may have a thickness less than that of the step adjusting layer.

[0026] In one embodiment, the step adjusting layer and the insulating material layer may be formed of polyimide.

[0027] Each of the light emitting elements may include a light emitting structure including a first conductive type semiconductor layer, a second conductive type semiconductor layer, and an active layer interposed between the first conductive type semiconductor layer and the second conductive type semiconductor layer; and a first electrode pad and a second electrode pad disposed on the light emitting structure; and each opening of the step adjusting layer may expose the first and second electrode pads.

[0028] Each of the light emitting devices may further include an insulating layer disposed between the light emitting structure and the first and second electrode pads, and the insulating layer may include a distributed Bragg reflector.

[0029] The light emitting devices may include a red light emitting device, a green light emitting device, and a blue light emitting device, and an insulating layer of the blue light emitting device may have a lower reflectance than the insulating layers of the red and green light emitting devices. By reducing the reflectance of the insulating layer of the blue light emitting device, it is possible to easily adjust the color mixing ratio of the red, green, and blue lights.

[0030] In one embodiment, the transparent substrate may have an area of less than 300 μm×300 μm, and even less than 200 μm×200 μm.

[0031] A display device according to an exemplary embodiment includes a circuit board having pads; a plurality of unit pixels arranged on the circuit board; and bonding materials bonding each of the unit pixels to each of the pads; each of the unit pixels includes a transparent substrate; a plurality of light-emitting elements aligned on the transparent substrate; connection layers electrically connected to each of the light-emitting elements; and bonding pads arranged on top of each of the connection layers and electrically connected to each of the connection layers; each of the bonding pads partially overlaps at least one of the light-emitting elements in the vertical direction, and each of the bonding materials bonds each of the bonding pads to each of the pads on the circuit board.

[0032] Each of the bonding materials may be solder.

[0033] The unit pixel may further include a light-blocking layer disposed between the transparent substrate and each of the light-emitting elements; and an adhesive layer disposed between the light-blocking layer and each of the light-emitting elements; the light-blocking layer may have windows through which light generated by each of the light-emitting elements passes, and each of the light-emitting elements may be disposed corresponding to each of the windows.

[0034] The transparent substrate may have an area of less than 300 μm×300 μm, and even less than or equal to 200 μm×200 μm.

[0035] Hereinafter, embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings.

[0036] FIG. 1 is a schematic plan view illustrating a display device according to an embodiment of the present disclosure.

[0037] Referring to FIG. 1, a display device 10000 includes a panel substrate 2100 and a plurality of pixel modules 1000 .

[0038] The display device 10000 may include, but is not limited to, a micro LED TV, a smart watch, a VR display device such as a VR headset, or an AR display device such as augmented reality glasses.

[0039] The panel substrate 2100 may include circuits for passive matrix driving or active matrix driving. In one embodiment, the panel substrate 2100 may include wiring and resistors therein, and in another embodiment, the panel substrate 2100 may include wiring, transistors, and capacitors. The panel substrate 2100 may also have pads on its top surface that can be electrically connected to arranged circuits.

[0040] In one embodiment, a plurality of pixel modules 1000 are arranged on a panel substrate 2100. Each pixel module 1000 may include a circuit substrate 1001 and a plurality of unit pixels 100 disposed on the circuit substrate 1001. In another embodiment, a plurality of unit pixels 100 may be arranged directly on the panel substrate 2100.

[0041] Each unit pixel 100 includes a plurality of light-emitting elements 10a, 10b, and 10c. Each of the light-emitting elements 10a, 10b, and 10c can emit light of a different color. The light-emitting elements 10a, 10b, and 10c in each unit pixel 100 may be arranged in a row as shown in FIG. 1. In one embodiment, the light-emitting elements 10a, 10b, and 10c may be arranged in a vertical direction with respect to a display screen on which an image is displayed. However, the present disclosure is not limited thereto, and the light-emitting elements 10a, 10b, and 10c may be arranged in a horizontal direction with respect to a display screen on which an image is displayed.

[0042] Hereinafter, each component of the display device 10000 will be described in detail in the order of the light emitting elements 10a, 10b, and 10c, the unit pixel 100, and the pixel module 1000 arranged in the display device 10000.

[0043] 2A is a schematic plan view illustrating a light emitting device 10a according to an embodiment of the present disclosure, and FIG. 2B is a schematic cross-sectional view taken along line AA in FIG. 2A. Here, the light emitting device 10a will be described as an example, but since the light emitting devices 10b and 10c have substantially similar structures, overlapping descriptions will be omitted.

[0044] 2A and 2B, the light emitting device 10a includes a light emitting structure including a first conductive type semiconductor layer 21, an active layer 23, and a second conductive type semiconductor layer 25. The light emitting device 10a may also include an ohmic contact layer 27, an insulating layer 29, a first electrode pad 31, and a second electrode pad 33.

[0045] The light emitting structure, i.e., the first conductivity type semiconductor layer 21, the active layer 23, and the second conductivity type semiconductor layer 25, may be grown on a substrate. The substrate may be any of a variety of substrates that can be used for semiconductor growth, such as a gallium nitride substrate, a GaAs substrate, a Si substrate, or a sapphire substrate, particularly a patterned sapphire substrate. The growth substrate may be separated from each semiconductor layer using techniques such as mechanical polishing, laser lift-off, or chemical lift-off. However, the present invention is not limited thereto, and a portion of the substrate may remain and constitute at least a portion of the first conductivity type semiconductor layer 21.

[0046] In one embodiment, in the case of the light-emitting element 10a that emits red light, each semiconductor layer may include aluminum gallium arsenide (AlGaAs), gallium arsenide phosphide (GaAsP), aluminum gallium indium phosphide (AlGaInP), or gallium phosphide (GaP).

[0047] In the case of the light-emitting element 10b that emits green light, each semiconductor layer may include indium gallium nitride (InGaN), gallium nitride (GaN), gallium phosphide (GaP), aluminum gallium indium phosphide (AlGaInP), or aluminum gallium phosphide (AlGaP).

[0048] In one embodiment, for the light emitting element 10c that emits blue light, the semiconductor layer may include gallium nitride (GaN), indium gallium nitride (InGaN), or zinc selenide (ZnSe).

[0049] The first conductivity type and the second conductivity type are of opposite polarity, and when the first conductivity type is n-type, the second conductivity type is p-type, and when the first conductivity type is p-type, the second conductivity type is n-type.

[0050] The first conductivity type semiconductor layer 21, the active layer 23, and the second conductivity type semiconductor layer 25 may be grown on a substrate in a chamber using a known method such as metal organic chemical vapor deposition (MOCVD). The first conductivity type semiconductor layer 21 contains n-type impurities (e.g., Si, Ge, Sn), and the second conductivity type semiconductor layer 25 contains p-type impurities (e.g., Mg, Sr, Ba). In one embodiment, the first conductivity type semiconductor layer 21 may contain GaN or AlGaN containing Si as a dopant, and the second conductivity type semiconductor layer 25 may contain GaN or AlGaN containing Mg as a dopant.

[0051] Although the first conductive type semiconductor layer 21 and the second conductive type semiconductor layer 25 are each shown as a single layer in the drawings, these layers may be multiple layers or may include a superlattice layer. The active layer 23 may include a single quantum well structure or a multiple quantum well structure, and the composition ratio of the nitride-based semiconductor is adjusted to emit a desired wavelength. For example, the active layer 23 may emit blue light, green light, red light, or ultraviolet light.

[0052] The second conductivity type semiconductor layer 25 and the active layer 23 may have a mesa M structure and be disposed on the first conductivity type semiconductor layer 21. The mesa M includes the second conductivity type semiconductor layer 25 and the active layer 23, and may also include a portion of the first conductivity type semiconductor layer 21, as shown in FIG. 2B . The mesa M may be located on a partial region of the first conductivity type semiconductor layer 21, and the top surface of the first conductivity type semiconductor layer 21 may be exposed around the mesa M.

[0053] Meanwhile, the first conductive type semiconductor layer 21 may have a concave-convex pattern 21p formed by surface texturing. The surface texturing may be performed by patterning using, for example, a dry or wet etching process. For example, cone-shaped protrusions may be formed, with the height of the cones being 2 μm to 3 μm, the spacing between the cones being 1.5 μm to 2 μm, and the diameter of the bottom of the cones being approximately 3 μm to 5 μm. The cones may also be truncated, with the diameter of the top of the cones being approximately 2 μm to 3 μm. Furthermore, fine concave-convex patterns 21p may be further formed. The fine concave-convex patterns may be formed using, for example, wet etching. Forming the concave-convex pattern 21p on the surface of the first conductive type semiconductor layer 21 can reduce total internal reflection and increase light extraction efficiency. In any of the first to third light emitting devices 10a, 10b, and 10c, the first conductive type semiconductor layer may be surface-textured, but is not limited thereto, and some light emitting devices may not be surface-textured.

[0054] The mesa M may have a through-hole 25a exposing the first conductive type semiconductor layer 21. The through-hole 25a may be disposed near one side edge of the mesa M, but is not limited thereto, and may also be disposed in the center of the mesa M.

[0055] The ohmic contact layer 27 is disposed on the second conductive type semiconductor layer 25 and makes ohmic contact with the second conductive type semiconductor layer 25. The ohmic contact layer 27 may be formed as a single layer or multiple layers, and may be formed of a transparent conductive oxide film or a metal film. Examples of transparent conductive oxide films include ITO and ZnO, and examples of metal films include metals such as Al, Ti, Cr, Ni, and Au, and alloys thereof.

[0056] The insulating layer 29 covers the mesa M and the ohmic contact layer 27. Furthermore, the insulating layer 29 may cover the top and side surfaces of the first conductive type semiconductor layer 21 exposed around the mesa M. Meanwhile, the insulating layer 29 may have an opening 29a exposing the ohmic contact layer 27 and an opening 29b exposing the first conductive type semiconductor layer 21 in the through-hole 25a. The insulating layer 29 may be formed of a single layer or multiple layers of a silicon oxide film or a silicon nitride film. The insulating layer 29 may also include an insulating reflector such as a distributed Bragg reflector.

[0057] The first electrode pad 31 and the second electrode pad 33 are disposed on the insulating layer 29. The second electrode pad 33 may be electrically connected to the ohmic contact layer 27 through an opening 29a, and the first electrode pad 31 may be electrically connected to the first conductivity type semiconductor layer 21 through an opening 29b.

[0058] The first and / or second electrode pads 31, 33 may be formed of a single layer or multi-layer metal, and may be made of metals such as Al, Ti, Cr, Ni, Au, and alloys thereof.

[0059] Although the light emitting device 10a according to one embodiment of the present disclosure has been briefly described with reference to the drawings, the light emitting device 10a may further include layers having additional functions in addition to the layers described above. For example, various layers may further be included, such as a reflective layer that reflects light, an additional insulating layer that insulates certain components, and a solder barrier layer that prevents solder diffusion.

[0060] Furthermore, in forming a flip-chip type light emitting device, mesas may be formed in various shapes, and the positions and shapes of the first and second electrode pads 31 and 33 may also be variously changed. Furthermore, the ohmic contact layer 27 may be omitted, and the second electrode pad 33 may be in direct contact with the second conductive type semiconductor layer 25. Furthermore, although the first electrode pad 31 is shown to be directly connected to the first conductive type semiconductor layer 21, a contact layer may be first formed on the first conductive type semiconductor layer 21 exposed in the through-hole 25a, and the first electrode pad 31 may then be connected to the contact layer.

[0061] FIG. 3A is a schematic plan view illustrating a unit pixel 100 according to a first embodiment of the present disclosure, and FIG. 3B is a schematic cross-sectional view taken along line BB in FIG. 3A.

[0062] Referring to Figures 3A and 3B, the unit pixel 100 may include a transparent substrate 121, first to third light-emitting elements 10a, 10b, and 10c, a surface layer 122, a light-blocking layer 123, an adhesive layer 125, a step adjusting layer 127, each connection layer 129a, 129b, 129c, and 129d, each bump 133a, 133b, 133c, and 133d, and a protective layer 131.

[0063] The unit pixel 100 includes first to third light emitting elements 10a, 10b, and 10c, which emit light of different colors and correspond to sub-pixels, respectively.

[0064] The transparent substrate 121 is a light-transmitting substrate such as a PET substrate, a glass substrate, a quartz substrate, or a sapphire substrate. The transparent substrate 121 is disposed on the light-emitting surface of the display device (10000 in FIG. 1), and light emitted from each of the light emitting devices 10a, 10b, and 10c is emitted to the outside through the transparent substrate 121. The transparent substrate 121 may include a concave-convex pattern 121p on the surface facing each of the light emitting devices 10a, 10b, and 10c. The concave-convex pattern 121p scatters the light emitted from each of the light emitting devices 10a, 10b, and 10c, increasing the directivity angle. In addition, the concave-convex pattern 121p allows the light emitted from each of the light emitting devices 10a, 10b, and 10c, which have different directivity angle characteristics, to be emitted at a uniform directivity angle. This prevents color differences depending on the viewing angle.

[0065] The uneven pattern 121p may be regular or irregular. For example, the uneven pattern 121p may have a pitch of 3 μm, a diameter of 2.8 μm, and a height of 1.8 μm. The uneven pattern 121p may be, but is not limited to, a pattern generally applied to a patterned sapphire substrate.

[0066] Furthermore, the transparent substrate 121 may include an anti-reflection coating, or may include an anti-glare layer or be anti-glare treated. The transparent substrate 121 may have a thickness of, for example, 50 μm to 300 μm.

[0067] Since the transparent substrate 121 is disposed on the light emitting surface, the transparent substrate 121 does not include a circuit, but the present disclosure is not limited thereto and may include a circuit.

[0068] Meanwhile, although one unit pixel 100 is formed on one transparent substrate 121, a plurality of unit pixels 100 may be formed on one transparent substrate 121.

[0069] The surface layer 122 covers the uneven pattern 121p of the transparent substrate 121. The surface layer 122 may be formed to follow the shape of the uneven pattern 121p. The surface layer 122 is formed to improve the adhesive strength of the light-blocking layer 123 formed thereon. For example, the surface layer 122 may be formed of a silicon oxide film. The surface layer 122 may be omitted depending on the type of transparent substrate 121.

[0070] The light-blocking layer 123 may include a light-absorbing material such as carbon black, which prevents light generated by the light emitting elements 10a, 10b, and 10c from leaking out to the sides from the region between the transparent substrate 121 and the light emitting elements 10a, 10b, and 10c, thereby improving the contrast of the display device.

[0071] The light-blocking layer 123 may have windows 123a for light propagation paths so that light generated from each of the light emitting elements 10a, 10b, and 10c can be incident on the transparent substrate 121. For this purpose, the light-blocking layer 123 may be patterned on the transparent substrate 121 to expose the transparent substrate 121. The width of the windows 123a may be narrower than the width of the light emitting elements, but is not limited thereto, and may be greater than or equal to the width of the light emitting elements.

[0072] In addition, the windows 123a of the light-blocking layer 123 define the alignment positions of the light-emitting elements 10a, 10b, and 10c. Therefore, separate alignment markers for defining the alignment positions of the light-emitting elements 10a, 10b, and 10c can be omitted. However, the present disclosure is not limited thereto, and alignment markers may be provided on the transparent substrate 121, the light-blocking layer 123, or the adhesive layer 125 to provide positions for aligning the light-emitting elements 10a, 10b, and 10c.

[0073] The adhesive layer 125 is attached to the transparent substrate 121. The adhesive layer 125 can cover the light-blocking layer 123. The adhesive layer 125 can be attached to the entire surface of the transparent substrate 121, but is not limited to this. The adhesive layer 125 can also be attached to a portion of the transparent substrate 121 so as to expose an area near the edge of the transparent substrate 121. The adhesive layer 125 is used to attach each of the light-emitting elements 10a, 10b, and 10c to the transparent substrate 121. The adhesive layer 125 can fill the window 123a formed in the light-blocking layer 123.

[0074] The adhesive layer 125 may be formed of a light-transmitting layer and transmits light emitted from each of the light-emitting elements 10a, 10b, and 10c. The adhesive layer 125 may be formed using an organic adhesive. For example, the adhesive layer 125 may be formed using transparent epoxy. The adhesive layer 125 may also include a diffuser, such as SiO2, TiO2, or ZnO, to diffuse light. The light-diffusing material prevents each of the light-emitting elements 10a, 10b, and 10c from being observed through the light-emitting surface.

[0075] Meanwhile, the first to third light emitting elements 10a, 10b, and 10c are disposed on a transparent substrate 121. The first to third light emitting elements 10a, 10b, and 10c may be attached to the transparent substrate 121 by an adhesive layer 125. The first to third light emitting elements 10a, 10b, and 10c may be disposed corresponding to each window 123a of the light blocking layer 123. If the light blocking layer 123 is omitted, each alignment marker may be added to provide an alignment position for each light emitting element 10a, 10b, and 10c.

[0076] The first to third light emitting elements 10a, 10b, and 10c may be, for example, red, green, and blue light emitting elements. The specific configurations of the first to third light emitting elements 10a, 10b, and 10c are the same as those described with reference to Figures 2A and 2B, and therefore will not be described in detail again.

[0077] The first to third light-emitting elements 10a, 10b, and 10c may be arranged in a row, as shown in FIG. 3A. In particular, when the transparent substrate 121 is a sapphire substrate, the sapphire substrate may include clean cut surfaces (e.g., m-planes) along the cutting direction, along which crystal planes are aligned, and clean cut surfaces (e.g., a-planes). For example, when the sapphire substrate is cut into a square shape, the two cut surfaces (e.g., m-planes) on both sides may be cleanly cut along the crystal planes, while the other two cut surfaces (e.g., a-planes) perpendicular to the clean cut surfaces may not be cleanly cut along the crystal planes. In this case, the clean cut surfaces of the sapphire substrate 121 may be aligned in the alignment direction of the light-emitting elements 10a, 10b, and 10c. For example, as shown in FIG. 3A, the clean cut surfaces (e.g., m-planes) may be arranged vertically, and the other two cut surfaces (e.g., a-planes) may be arranged horizontally.

[0078] The first to third light emitting elements 10a, 10b, and 10c may be those described with reference to FIGS. 2A and 2B, but are not limited thereto, and various light emitting elements having a horizontal or flip-chip structure may be used.

[0079] The step adjusting layer 127 covers the first to third light emitting elements 10a, 10b, and 10c. The step adjusting layer 127 has openings 127a that expose the first and second electrode pads 31 and 33 of the light emitting elements 10a, 10b, and 10c. The step adjusting layer 127 adjusts the height of the surfaces on which the connection layers 129a, 129b, 129c, and 129d are formed to be uniform, thereby helping to ensure safe formation of the connection layers. Furthermore, the step adjusting layer 127 can uniformly adjust the height of the positions on which the bumps 133a, 133b, 133c, and 133d are formed. The step adjusting layer 127 may be formed of, for example, photosensitive polyimide.

[0080] The step adjustment layer 127 may be, but is not limited to, disposed within a region surrounded by the edge of the adhesive layer 125. For example, the step adjustment layer 127 may be formed so as to partially expose the edge of the adhesive layer 125.

[0081] The first to fourth connection layers 129a, 129b, 129c, and 129d are formed on the step adjusting layer 127. The connection layers 129a, 129b, 129c, and 129d may be connected to the first and second electrode pads 31 and 33 of the first to third light emitting elements 10a, 10b, and 10c through the openings 127a of the step adjusting layer 127.

[0082] 3A and 3B, the first connection layer 129a may be electrically connected to the second conductive type semiconductor layer of the first light emitting element 10a, the second connection layer 129b may be electrically connected to the second conductive type semiconductor layer of the second light emitting element 10b, the third connection layer 129c may be electrically connected to the second conductive type semiconductor layer of the third light emitting element 10c, and the fourth connection layer 129d may be electrically connected in common to the first conductive type semiconductor layers of the first to third light emitting elements 10a, 10b, and 10c. The first to fourth connection layers 129a, 129b, 129c, and 129d may be formed together on the step adjustment layer 127 and may include, for example, Au.

[0083] The bumps 133a, 133b, 133c, and 133d are formed on the connection layers 129a, 129b, 129c, and 129d, respectively. For example, the first bump 133a may be electrically connected to the second conductive type semiconductor layer of the first light-emitting element 10a via the first connection layer 129a, the second bump 133b may be electrically connected to the second conductive type semiconductor layer of the second light-emitting element 10b via the second connection layer 129b, and the third bump 133c may be electrically connected to the second conductive type semiconductor layer of the third light-emitting element 10c via the third connection layer 129c. Meanwhile, the fourth bump 133d may be electrically connected in common to the first conductive type semiconductor layers of the first to third light-emitting elements 10a, 10b, and 10c via the fourth connection layer 129d. Each of the bumps 133a, 133b, 133c, 133d may be formed of a metal and / or a metal alloy, such as, for example, AuSn, SnAg, Sn, CuSn, CuN, CuAg, Sb, Ni, Zn, Mo, Co, solder, etc.

[0084] In another embodiment, the first connection layer 129a may be electrically connected to the first conductive type semiconductor layer of the first light emitting element 10a, the second connection layer 129b may be electrically connected to the first conductive type semiconductor layer of the second light emitting element 10b, the third connection layer 129c may be electrically connected to the first conductive type semiconductor layer of the third light emitting element 10c, and the fourth connection layer 129d may be electrically connected in common to the second conductive type semiconductor layers of the first to third light emitting elements 10a, 10b, and 10c. The first to fourth connection layers 129a, 129b, 129c, and 129d may be formed together on the step adjustment layer 127.

[0085] Furthermore, the bumps 133a, 133b, 133c, and 133d are formed on the connection layers 129a, 129b, 129c, and 129d, respectively. For example, the first bump 133a may be electrically connected to the first conductive type semiconductor layer of the first light-emitting element 10a via the first connection layer 129a, the second bump 133b may be electrically connected to the first conductive type semiconductor layer of the second light-emitting element 10b via the second connection layer 129b, and the third bump 133c may be electrically connected to the first conductive type semiconductor layer of the third light-emitting element 10c via the third connection layer 129c. Meanwhile, the fourth bump 133d may be electrically connected in common to the second conductive type semiconductor layers of the first to third light-emitting elements 10a, 10b, and 10c via the fourth connection layer 129d.

[0086] Meanwhile, the protective layer 131 may cover the side surfaces of the bumps 133a, 133b, 133c, and 133d and may also cover the step adjusting layer 127. The protective layer 131 may also cover the adhesive layer 125 exposed around the step adjusting layer 127. The protective layer 131 may be formed of, for example, a photosensitive solder resist (PSR). As a result, the bumps 133a, 133b, 133c, and 133d may be formed after the protective layer 131 is first patterned using photography and development. To this end, the protective layer 131 may be formed to have openings exposing the connection layers 129a, 129b, 129c, and 129d, and the bumps 133a, 133b, 133c, and 133d may be formed in the openings of the protective layer 131. Each of the bumps 133a, 133b, 133c, and 133d may be omitted.

[0087] The protective layer 131 may be made of a white reflective material or a light absorbing material such as black epoxy to prevent light leakage.

[0088] In this embodiment, the light-emitting elements 10a, 10b, and 10c are attached to the transparent substrate 121 by the adhesive layer 125. However, instead of the adhesive layer 125, other couplers may be used to couple the light-emitting elements 10a, 10b, and 10c to the transparent substrate 121. For example, the light-emitting elements 10a, 10b, and 10c may be coupled to the transparent substrate 121 using spacers, thereby filling the space between the light-emitting elements 10a, 10b, and 10c and the transparent substrate 121 with a gas or liquid. This gas or liquid may form an optical layer that transmits light emitted from the light-emitting elements 10a, 10b, and 10c. The adhesive layer 125 is also an example of an optical layer. Here, the optical layer may be formed of a material different from the light-emitting elements 10a, 10b, and 10c, such as a gas, liquid, or solid, and thus be distinct from the material of the semiconductor layers in the light-emitting elements 10a, 10b, and 10c.

[0089] FIG. 4A is a schematic plan view illustrating a pixel module 1000 according to one embodiment of the present disclosure, FIG. 4B is a schematic cross-sectional view taken along line CC in FIG. 4A, FIG. 4C is a rear view of the pixel module 1000, and FIG. 4D is a circuit diagram of the pixel module 1000.

[0090] 4A and 4B, the pixel module 1000 includes a circuit board 1001 and unit pixels 100 arranged on the circuit board 1001. In addition, the pixel module 1000 may further include a cover layer 1010 covering each unit pixel 100.

[0091] The circuit board 1001 may have circuits for electrically connecting the panel substrate 2100 and the light-emitting elements 10a, 10b, and 10c. The circuits in the circuit board 1001 may be formed in a multi-layer structure. The circuit board 1001 may also include passive circuits for driving the light-emitting elements 10a, 10b, and 10c using a passive matrix driving method or active circuits for driving the light-emitting elements 10a, 10b, and 10c using an active matrix driving method. The circuit board 1001 may include pads 1003 exposed on its surface. The pads 1003 may be arranged to correspond to bumps in the unit pixels 100 mounted thereon.

[0092] 3A and 3B, a detailed description thereof will be omitted to avoid redundancy. The unit pixels 100 may be arranged on a circuit board 1001. The unit pixels 100 may be arranged in a 2×2 matrix as shown in FIG. 4A, but may also be arranged in various other matrixes such as 2×3, 3×3, 4×4, 5×5, etc.

[0093] Each unit pixel 100 is bonded to the circuit board 1001 by a bonding material 1005. For example, the bonding material 1005 can bond each of the bumps 133a, 133b, 133c, and 133d to each of the pads 1003. The bonding material 1005 may be formed of, for example, solder. If each of the bumps 133a, 133b, 133c, and 133d is formed of solder, the bonding material 1005 may be omitted.

[0094] The cover layer 1010 covers the plurality of unit pixels 100. The cover layer 1010 can prevent optical interference between the unit pixels 100 and improve the contrast of the display device.

[0095] The cover layer 1010 may be formed of, for example, dry-film type solder resist (DFSR), photoimageable solder resist (PSR), black material (BM), epoxy molding compound (EMC), etc. The cover layer 1010 may be formed using techniques such as lamination, spin coating, slit coating, printing, etc.

[0096] A display device 10000 may be provided by mounting the pixel modules 1000 shown in Figures 4A and 4B on the panel substrate 2100 of Figure 1. The circuit board 1001 has bottom pads connected to the pads 1003. The bottom pads may be arranged in one-to-one correspondence with the pads 1003, but the number of bottom pads may be reduced through common connections. In contrast, a pixel module 1000 having unit pixels 100 arranged in a 2x2 matrix will be described with reference to Figures 4C and 4D, for example.

[0097] 4C shows a rear view of the pixel module 1000, illustrating bottom pads C1, C2, R1, R2, G1, G2, B1, and B2 on the circuit board 1001. The pixel modules 1000 are arranged in a 2×2 matrix, so that a total of four pixel modules are arranged on the circuit board 1001. Three light-emitting elements 10a, 10b, and 10c are arranged on each pixel module 1000, and four bumps 133a, 133b, 133c, and 133d are arranged on each pixel module 1000. Thus, 16 pads 1003 corresponding to the bumps of the four unit pixels 100 are provided on the circuit board 1001. Alternatively, only eight bottom pads may be arranged, and these eight bottom pads may be connected to the panel substrate 2100 to individually drive the light-emitting elements 10a, 10b, and 10c.

[0098] FIG. 4D shows a schematic circuit diagram in which, in one embodiment, each light emitting element 10a, 10b, 10c is coupled to a respective bottom pad C1, C2, R1, R2, G1, G2, B1 and B2.

[0099] Referring to FIG. 4D, bottom pad C1 is commonly connected to the cathodes of the light-emitting elements 10a, 10b, and 10c arranged in the left column, and bottom pad C2 is commonly connected to the cathodes of the light-emitting elements 10a, 10b, and 10c arranged in the right column.

[0100] Meanwhile, in each unit pixel 100 arranged in the upper row, a bottom pad R1 may be connected to each anode of the first light-emitting element 10a, a bottom pad G1 may be connected to each anode of the second light-emitting element 10b, and a bottom pad B1 may be connected to each anode of the third light-emitting element 10c.

[0101] In addition, in each unit pixel 100 arranged in the lower row, a bottom pad R2 may be connected to each anode of the first light-emitting element 10a, a bottom pad G2 may be connected to each anode of the second light-emitting element 10b, and a bottom pad B2 may be connected to each anode of the third light-emitting element 10c.

[0102] Here, bottom pads R1, G1, B1, R2, G2, and B2 are intended to represent pads connected to red, green, and blue light emitting elements, respectively. However, the arrangement of the red, green, and blue light emitting elements may be changed, and accordingly, the positions to which each bottom pad R1, G1, B1, R2, G2, and B2 is connected may also be changed. For example, the circuit diagram of FIG. 4D shows each bottom pad assuming that the first light emitting element 10a is a red light emitting element, the second light emitting element 10b is a green light emitting element, and the third light emitting element 10c is a blue light emitting element. Alternatively, the first light emitting element 10a may be a blue light emitting element, and the third light emitting element 10c may be a red light emitting element. In this case, the positions of bottom pads R1, R2, and bottom pads B1 and B2 may be interchanged.

[0103] According to this embodiment, each bottom pad C1, C2 is commonly connected to each cathode of each light-emitting element in each column, and each bottom pad R1, G1, B1, R2, B2, G2 is commonly connected to each anode of two light-emitting elements, thereby reducing the total number of bottom pads while allowing each light-emitting element 10a, 10b, 10c to be driven independently.

[0104] Meanwhile, in this embodiment, it is illustrated and described that each bottom pad C1, C2 is connected to each cathode of each light-emitting element, and each bottom pad R1, G1, B1, R2, B2, G2 is connected to each anode of each light-emitting element, but as shown in Figure 4E, each bottom pad C1, C2 may be connected to each anode of each light-emitting element, and each bottom pad R1, G1, B1, R2, B2, G2 may be connected to each cathode of each light-emitting element.

[0105] Here, we will describe a pixel module 1000 in which each unit pixel 100 is arranged in a 2x2 matrix, but even if each unit pixel 100 is arranged in other matrices such as 3x3 or 5x5, the number of bottom pads can be reduced by using a common connection circuit.

[0106] Each light emitting element 10a, 10b, 10c in the pixel module 1000 may be individually driven by a driving IC disposed on the panel substrate 2100, and an image may be realized by a plurality of pixel modules 1000.

[0107] In this embodiment, each unit pixel 100 is formed of a pixel module 1000, and each pixel module 1000 is mounted on a panel substrate 2100 to provide a display device, thereby improving the process yield of the display device. However, the present invention is not limited to this, and each unit pixel 100 can also be mounted directly on the panel substrate 2100.

[0108] FIG. 5A is a schematic diagram illustrating a problem that occurs when implementing the unit pixel 100 according to the first embodiment, and FIG. 5B is an image showing a defect that occurs when implementing the unit pixel 100 according to the first embodiment.

[0109] 5A, the unit pixel 100 may include a protective layer 131 formed using photosensitive PSR to define regions for forming the bumps 133a, 133b, 133c, and 133d. The protective layer 131 generally has a thickness corresponding to the height of the bumps 133a, 133b, 133c, and 133d.

[0110] The unit pixel 100 undergoes multiple transfer processes before being disposed on the panel substrate 2100, and in this case, pressure may be applied to the protective layer 131 by an ejector pin 150. If the ejector pin 150 presses the protective layer 131, which is made of a relatively thick PSR, an indentation may remain in the protective layer 131, which may result in a defective appearance inspection and may also cause defects 151 such as cracks. As shown in FIG. 5B , defects 151, particularly cracks, may occur in the protective layer 131 due to the ejector pin 150.

[0111] Furthermore, since the protective layer 131 made of PSR is relatively thick, it may induce a large stress on the unit pixel 100. This may cause cracks or peeling in the light emitting elements 10a, 10b, and 10c and various thin films.

[0112] Hereinafter, various embodiments for solving the problems that arise when forming the protective layer 131 by PSR as described above will be described.

[0113] FIG. 6A is a schematic plan view illustrating a unit pixel 200 according to a second embodiment, and FIG. 6B is a schematic cross-sectional view taken along line DD in FIG. 6A.

[0114] 6A and 6B, the unit pixel 200 according to this embodiment may include a transparent substrate 221, first to third light emitting elements 10a, 10b, and 10c, a surface layer 222, a light-blocking layer 223, an adhesive layer 225, a step adjusting layer 227, connection layers 229a, 229b, 229c, and 229d, and an insulating material layer 231. In addition, the transparent substrate 221 may have a concave-convex pattern 221p.

[0115] The transparent substrate 221, the first to third light emitting elements 10a, 10b, and 10c, the surface layer 222, the light blocking layer 223, the adhesive layer 225, and the step adjusting layer 227 are the same as those described for the unit pixel 100 of the first embodiment, and therefore detailed descriptions thereof will be omitted to avoid duplication.

[0116] Meanwhile, each of the connection layers 229a, 229b, 229c, and 229d is substantially similar to each of the connection layers 129a, 129b, 129c, and 129d described above except for the position and shape, and therefore detailed description thereof will be omitted.

[0117] The insulating material layer 231 is formed to be relatively thinner than the protective layer 131 of the first embodiment. For example, the insulating material layer 231 may be formed to be thinner than the step adjusting layer 227. The sum of the thicknesses of the insulating material layer 231 and the step adjusting layer 227 may be, but is not limited to, 1 μm to 50 μm.

[0118] The insulating material layer 231 covers the side surfaces of the step adjusting layer 227 and the connecting layers 229a, 229b, 229c, and 229d. The insulating material layer 231 may also cover a portion of the adhesive layer 225. The insulating material layer 231 has openings 231a, 231b, 231c, and 231d that expose the connecting layers 229a, 229b, 229c, and 229d, thereby defining pad regions of the unit pixel 200.

[0119] In one embodiment, the insulating material layer 231 may be a semi-transparent material and may be formed of an organic or inorganic material. The insulating material layer 231 may be formed of, for example, polyimide. When the insulating material layer 231 and the step adjustment layer 227 are formed of polyimide, the bottom surface, side surface, and top surface of each of the connection layers 229a, 229b, 229c, and 229d may all be surrounded by polyimide except for the pad regions.

[0120] 3A and 3B, the unit pixel 200 is substantially similar to the unit pixel 100 described with reference to FIGS. 3A and 3B, but differs in that it does not include the bumps 133a, 133b, 133c, and 133d, and that a relatively thin insulating material layer 231 is used instead of the PSR protective layer 131. This prevents defects from occurring in the unit pixel 200 during transfer of the unit pixel 200.

[0121] On the other hand, the unit pixel 200 may be mounted on a circuit board using a bonding material such as solder, and the bonding material can bond each of the connection layers 229a, 229b, 229c, and 229d exposed in each of the openings 231a, 231b, 231c, and 231d of the insulating material layer 231 to each of the pads on the circuit board.

[0122] FIG. 7 is a schematic cross-sectional view illustrating a display device in which a unit pixel 200 according to the second embodiment is mounted.

[0123] 7, each unit pixel 200 is mounted on a circuit board 210 using a bonding material 250. The circuit board 210 may be the panel board 2100 described above, or may be the circuit board 1001 of the pixel module 1000.

[0124] 6A and 6B, the connection layers 229a, 229b, 229c, and 229d exposed through the openings 231a, 231b, 231c, and 231d of the insulating material layer 231 are bonded to the pads 230 on the circuit board 210. The bonding material 250 may be, for example, solder, and the unit pixel 200 and the circuit board 210 may be bonded by disposing a solder paste on the pads 230 using a technique such as screen printing, and then performing a reflow process.

[0125] In this embodiment, unlike the unit pixel 100, bumps are not used, and instead a single-structure bonding material 250 is disposed between each connection layer 229a, 229b, 229c, 229d and each pad 230, and the bonding material 250 directly connects each connection layer 229a, 229b, 229c, 229d and each pad 230.

[0126] FIG. 8 is a diagram showing images of several display screens of a display device formed using the unit pixels 200 according to the second embodiment.

[0127] 8, various color images can be realized by driving each of the light emitting elements 10a, 10b, and 10c in each unit pixel 200. The image on the left is realized by driving all of the light emitting elements 10a, 10b, and 10c in each unit pixel 200. Meanwhile, images realized by driving each of the red light emitting elements 10a, green light emitting elements 10b, and blue light emitting elements 10c in each unit pixel 200, and images realized by driving any two types of light emitting elements in combination, are shown in small size on the right. The display device according to this embodiment can realize various color images using each unit pixel 200.

[0128] FIG. 9A is a schematic plan view illustrating a unit pixel 300 according to a third embodiment, and FIG. 9B is a schematic cross-sectional view taken along line EE in FIG. 9A.

[0129] 9A and 9B, the unit pixel 300 according to this embodiment may include a transparent substrate 321, first to third light emitting elements 10a, 10b, and 10c, a surface layer 322, a light-blocking layer 323, an adhesive layer 325, a step adjusting layer 327, connection layers 329a, 329b, 329c, and 329d, an insulating material layer 331, and bonding pads 333a, 333b, 333c, and 333d. The transparent substrate 321 may have a concave-convex pattern 321p.

[0130] The transparent substrate 321, the first to third light emitting elements 10a, 10b, and 10c, the surface layer 322, the light blocking layer 323, the adhesive layer 325, the step adjusting layer 327, the connection layers 329a, 329b, 329c, and 329d, and the insulating material layer 331 are similar to those described for the unit pixel 200 of the second embodiment, and therefore detailed descriptions thereof will be omitted to avoid duplication.

[0131] However, the outer size of the transparent substrate 321 may be relatively small compared to the outer size of the transparent substrate 221. For example, the transparent substrate 221 may have an area greater than about 300 μm×300 μm, but the transparent substrate 321 may be smaller. In one example, the transparent substrate 321 may have an area of about 200 μm×200 μm or less.

[0132] In the case of the unit pixel 200, if the transparent substrate 221 is small, the exposed areas of the connection layers 229a, 229b, 229c, and 229d exposed through the openings 231a, 231b, 231c, and 231d of the insulating material layer 231 become relatively small. As a result, when the unit pixel 200 is mounted on the circuit board 210, the areas of the connection layers 229a, 229b, 229c, and 229d that come into contact with the bonding material 250 become small, which makes it difficult to stably mount the unit pixel 200 on the circuit board 210.

[0133] To solve this problem, in the unit pixel 300 according to this embodiment, bonding pads 333a, 333b, 333c, and 333d are formed on an insulating material layer 331. The insulating material layer 331 has openings 331a, 331b, 331c, and 331d that expose the connection layers 329a, 329b, 329c, and 329d, respectively, and the bonding pads 333a, 333b, 333c, and 333d are electrically connected to the connection layers 329a, 329b, 329c, and 329d through the openings 331a, 331b, 331c, and 331d in the insulating material layer 331, respectively.

[0134] Meanwhile, each of the bonding pads 333a, 333b, 333c, and 333d may have a larger area than each of the connection layers 329a, 329b, 329c, and 329d. In particular, each of the bonding pads 333a, 333b, 333c, and 333d may partially cover at least one of the light emitting elements 10a, 10b, and 10c. That is, each of the bonding pads 333a, 333b, 333c, and 333d may partially overlap at least one of the light emitting elements 10a, 10b, and 10c in the vertical direction. Furthermore, each of the bonding pads 333a, 333b, 333c, and 333d may partially overlap two adjacent light emitting elements. 9A, the first bonding pad 333a partially covers the red light emitting element 10a and the green light emitting element 10b, the second bonding pad 333b partially covers the green light emitting element 10b and the blue light emitting element 10c, and the third bonding pad 333c partially covers the green light emitting element 10b and the blue light emitting element 10c. Although the fourth bonding pad 333d is shown partially covering only the red light emitting element 10a, it can also partially cover the green light emitting element 10b.

[0135] The first to fourth bonding pads 333a, 333b, 333c, and 333d are separated from the light emitting devices 10a, 10b, and 10c by the step adjusting layer 327 and the insulating material layer 331, and can be electrically connected to the light emitting devices 10a, 10b, and 10c only through the connection layers 329a, 329b, 329c, and 329d, thereby preventing electrical shorts between the first to fourth bonding pads 333a, 333b, 333c, and 333d and the light emitting devices 10a, 10b, and 10c.

[0136] According to this embodiment, even if the transparent substrate 321 is relatively small, each bonding pad 333a, 333b, 333c, and 333d can be formed relatively large, and each unit pixel 300 can be stably mounted on a circuit board using a bonding material such as solder.

[0137] 10A to 10F are schematic cross-sectional views illustrating a method for manufacturing a unit pixel 300 according to the third embodiment.

[0138] 10A, a concave-convex pattern 321p is formed on the surface of a transparent substrate 321. The transparent substrate 321 is a light-transmitting substrate such as a PET substrate, a glass substrate, a quartz substrate, a sapphire substrate, etc. In one embodiment, the concave-convex pattern 321p can be formed by etching the surface of the transparent substrate 321 using a dry or wet etching technique.

[0139] A surface layer 322 may be formed on the transparent substrate 321. The surface layer 322 may be formed along the concave-convex pattern 321p. The surface layer 322 may be formed of, for example, a silicon oxide film. The surface layer 322 is formed to modify the surface of the transparent substrate 321 and may be omitted.

[0140] 10B, a light-blocking layer 323 is formed on the surface layer 322. The light-blocking layer 323 may be formed of a light-absorbing material layer, for example, a black matrix containing a light-absorbing material such as carbon black. Alternatively, the light-blocking layer 323 may be formed of a photosensitive material layer and patterned by exposure and development. Windows 323a may be formed by patterning the light-blocking layer 323. A plurality of windows 323a may be formed corresponding to the light-emitting elements 10a, 10b, and 10c, and these windows 323a may be spaced apart from one another.

[0141] Subsequently, an adhesive layer 325 may be formed on the light-blocking layer 323. The adhesive layer 325 may cover the light-blocking layer 323, and may also cover the surface layer 322 or the transparent substrate 321 exposed through each window 323a formed in the light-blocking layer 323.

[0142] The adhesive layer 325 may be formed on the entire surface of the transparent substrate 321, but is not limited thereto. It may also be formed on a portion of the transparent substrate 321 to expose an area near the edge of the transparent substrate 321. The adhesive layer 325 is used to attach the light emitting elements 10a, 10b, and 10c to the transparent substrate 321. The adhesive layer 325 may be formed of a light-transmitting layer and transmits light emitted from the light emitting elements 10a, 10b, and 10c. The adhesive layer 325 may be formed using an adhesive sheet or an organic adhesive. For example, the adhesive layer 325 may be formed using transparent epoxy. In one embodiment, the adhesive layer 325 may include a diffuser, such as SiO2, TiO2, or ZnO, to diffuse light. The light diffuser prevents the light emitting elements 10a, 10b, and 10c from being observed through the light emission surface.

[0143] 9A and 10C, the light-emitting element 10a is disposed on the adhesive layer 325. The light-emitting element 10a may be disposed corresponding to the window 323a. The light-emitting element 10a may have a size smaller than the window 323a and may be located within the upper region of the window 323a, but is not limited to this. The light-emitting element 10a may also have an area larger than the window 323a.

[0144] 10C shows only the light-emitting element 10a, but each of the light-emitting elements 10b, 10c may also be disposed above each corresponding window 323a. In one embodiment, each of the light-emitting elements 10a, 10b, 10c may be transferred together to the adhesive layer 325 using a transfer process.

[0145] 9A and 10D, a step adjustment layer 327 is formed to cover each of the light emitting elements 10a, 10b, and 10c. The step adjustment layer 327 may be formed of, for example, photosensitive polyimide and may be patterned using an exposure and development technique.

[0146] For example, the step adjusting layer 327 may have openings 327a exposing the light emitting elements 10a, 10b, and 10c. For example, the openings 327a of the step adjusting layer 327 may expose the first and second electrode pads 31 and 33 of the light emitting elements 10a, 10b, and 10c. Furthermore, the step adjusting layer 327 may be removed along the edge of the transparent substrate 321 to expose the adhesive layer 325.

[0147] 9A and 10E, first to fourth connection layers 329a, 329b, 329c, and 329d are formed on the step adjustment layer 327. For example, the first to fourth connection layers 329a, 329b, 329c, and 329d may be formed using a lift-off technique.

[0148] The first to fourth connection layers 329a, 329b, 329c, and 329d may be electrically connected to the light emitting elements 10a, 10b, and 10c through the openings 327a of the step adjusting layer 327. For example, the first to third connection layers 329a, 329b, and 329c may be electrically connected to the first conductive type semiconductor layers of the light emitting elements 10a, 10b, and 10c, respectively, and the fourth connection layer 329d may be electrically connected in common to the second conductive type semiconductor layers of the light emitting elements 10a, 10b, and 10c.

[0149] 9A and 10F, an insulating material layer 331 is formed to cover the first to fourth connection layers 329a, 329b, 329c, and 329d. The insulating material layer 331 may cover the side surfaces of the step adjustment layer 327 and partially cover the adhesive layer 325. For example, the insulating material layer 331 may be formed of photosensitive polyimide. The insulating material layer 331 may be patterned to have openings 331a, 331b, 331c, and 331d that expose the first to fourth connection layers 329a, 329b, 329c, and 329d, respectively.

[0150] Thereafter, bonding pads 333a, 333b, 333c, and 333d may be formed on the insulating material layer 331, thereby forming the unit pixel 300 described with reference to FIGS. 9A and 9B.

[0151] The bonding pads 333a, 333b, 333c, and 333d may be formed to extend beyond the upper regions of the first to fourth connection layers 329a, 329b, 329c, and 329d and partially cover the light emitting elements 10a, 10b, and 10c, respectively.

[0152] Fig. 11A is a schematic plan view illustrating a light emitting device 20a according to one embodiment, and Fig. 11B is a schematic cross-sectional view taken along line FF in Fig. 11A. Here, the red light emitting device 20a will be described, but since the green and blue light emitting devices 20b and 20c have similar structures, overlapping descriptions will be omitted.

[0153] 11A and 11B, the light emitting device 20a according to this embodiment is substantially similar to the light emitting device 10a described with reference to FIGS. 2A and 2B, but differs in the shape of the mesa M. Below, the overlapping points between the light emitting device 20a and the light emitting device 10a will be briefly described, and the differences will be described in detail.

[0154] The light emitting device 20a includes a light emitting structure including a first conductive type semiconductor layer 21, an active layer 23, and a second conductive type semiconductor layer 25, an ohmic contact layer 27, a first contact pad 53, a second contact pad 55, an insulating layer 59, a first electrode pad 61, and a second electrode pad 63. Specific materials and characteristics of the light emitting structure and the ohmic contact layer 27 are the same as those described for the light emitting device 10a, and therefore will not be described in detail again.

[0155] On the other hand, in this embodiment, the mesa M is formed so as to expose the first conductivity type semiconductor layer 21 at its periphery. That is, in this embodiment, the first conductivity type semiconductor layer 21 is exposed outside the mesa M instead of through-hole 25a.

[0156] The first contact pad 53 is disposed on the exposed first conductive type semiconductor layer 21. The first contact pad 53 can be in ohmic contact with the first conductive type semiconductor layer 21. For example, the first contact pad 53 may be formed of an ohmic metal layer that is in ohmic contact with the first conductive type semiconductor layer 21. The ohmic metal layer of the first contact pad 53 can be appropriately selected depending on the semiconductor material of the first conductive type semiconductor layer 21.

[0157] The second contact pad 55 may be disposed on the ohmic contact layer 27. The second contact pad 55 is electrically connected to the ohmic contact layer 27. The second contact pad 55 may be omitted.

[0158] The insulating layer 59 covers the mesa M, the ohmic contact layer 27, the first contact pad 53, and the second contact pad 55. The insulating layer 59 has openings 59a and 59b that expose the first contact pad 53 and the second contact pad 55, respectively. The insulating layer 59 may be formed of a single layer or multiple layers. Furthermore, the insulating layer 59 may include a distributed Bragg reflector formed by stacking insulating layers having different refractive indices. For example, the distributed Bragg reflector may include at least two insulating layers selected from SiO2, Si3N4, SiON, TiO2, Ta2O5, and Nb2O5.

[0159] The distributed Bragg reflector reflects light emitted from the active layer 23. The distributed Bragg reflector can exhibit high reflectivity over a relatively wide wavelength range, including the peak wavelength of light emitted from the active layer 23, and can be designed taking into account the angle of incidence of light. In one embodiment, the distributed Bragg reflector can have a higher reflectivity for light incident at an incident angle of 0 degrees than for light incident at other incident angles. In another embodiment, the distributed Bragg reflector can have a higher reflectivity for light incident at another specific incident angle than for light incident at an incident angle of 0 degrees. For example, the distributed Bragg reflector can have a higher reflectivity for light incident at an incident angle of 10 degrees than for light incident at an incident angle of 0 degrees.

[0160] On the other hand, the light emitting structure of the blue light emitting element 10c has a higher internal quantum efficiency than the light emitting structures of the red light emitting element 10a and the green light emitting element 10b. As a result, the blue light emitting element 10c can exhibit a higher light extraction efficiency than the red and green light emitting elements 10a and 10b. This can make it difficult to maintain an appropriate color mixing ratio of red, green, and blue light.

[0161] In order to adjust the color mixing ratio of red, green, and blue light, the distributed Bragg reflectors applied to each of the light emitting devices 10a, 10b, and 10c may be formed to have different reflectivities. For example, the blue light emitting device 10c may have a distributed Bragg reflector with a relatively lower reflectivity than the red and green light emitting devices 10a and 10b. For example, the distributed Bragg reflector formed in the blue light emitting device 10c may have a reflectivity of less than about 95% or even less than 90% for blue light generated in the active layer 23 at an incident angle of 0 degrees. The green light emitting device 10b may have a reflectivity of between about 95% and 99% for green light at an incident angle of 0 degrees. The red light emitting device 10a may have a reflectivity of 99% or more for red light at an incident angle of 0 degrees.

[0162] In one embodiment, the distributed Bragg reflectors applied to the red, green, and blue light-emitting elements 10a, 10b, and 10c may have substantially similar thicknesses. For example, the difference in thickness between the distributed Bragg reflectors applied to the light-emitting elements 10a, 10b, and 10c may be less than 10% of the thickness of the thickest distributed Bragg reflector. By reducing the difference in thickness between the distributed Bragg reflectors, the process conditions applied to the red, green, and blue light-emitting elements 10a, 10b, and 10c, such as the process of patterning the insulating layer 59, can be set to similar forms, further reducing the complexity of the unit pixel manufacturing process. Furthermore, the distributed Bragg reflectors applied to the red, green, and blue light-emitting elements 10a, 10b, and 10c may have substantially similar numbers of stacked layers. However, the present invention is not limited thereto.

[0163] The first electrode pad 61 and the second electrode pad 63 are disposed on the insulating layer 59. The first electrode pad 61 may extend from the top of the first contact pad 53 to the top of the mesa M, and the second electrode pad 63 may be disposed within the upper region of the mesa M. The first electrode pad 61 may be connected to the first contact pad 53 through the opening 59a, and the second electrode pad 63 may be electrically connected to the second contact pad 55. The first electrode pad 61 may be in direct ohmic contact with the first conductive type semiconductor layer 21, in which case the first contact pad 53 may be omitted. Alternatively, if the second contact pad 55 is omitted, the second electrode pad 63 may be directly connected to the ohmic contact layer 27.

[0164] Meanwhile, the first conductive type semiconductor layer 21 may include a concave-convex pattern 21p on the light emitting surface side. In one embodiment, the concave-convex pattern 21p may include a first concave-convex pattern 21p1 and a second concave-convex pattern 21p2 further formed on the first concave-convex pattern, as shown in FIG.

[0165] Each protrusion of the first uneven pattern 21p1 may have a height of about 2 μm to 3 μm, a spacing of 1.5 μm to 2 μm, and a bottom diameter of about 3 μm to 5 μm. Meanwhile, the second uneven pattern 21p2 may be formed on each protrusion of the first uneven pattern 21p1 and in the areas between the protrusions. Figure 13 shows an SEM image of the uneven pattern actually formed on the surface of the first conductivity type semiconductor layer 21.

[0166] Although various embodiments of the present disclosure have been described above, the present disclosure is not limited to these embodiments, and matters and elements described in one embodiment may also be applied to other embodiments without departing from the technical spirit of the present disclosure. [Explanation of symbols]

[0167] 10a, 10b, 10c Light-emitting element 21 First conductivity type semiconductor layer 23 Active layer 25 Second conductivity type semiconductor layer 27 Ohmic contact layer 29 Insulating layer 31 First electrode pad 33 Second electrode pad 53 First contact pad 55 Second contact pad 59 Insulating layer 61 First electrode pad 63 Second electrode pad 100 unit pixels 121 Transparent substrate 122 Surface layer 123 Light-shielding layer 125 Adhesive layer 127 Step Adjustment Layer 129 Fourth Connection Layer 129 Third Connection Layer 129 Second Connection Layer 129 First Connection Layer 129 First to fourth connection layers 129a, 129b, 129c, 129d Connecting layers 131 PSR protection layer 131 Protective layer 133a, 133b, 133c, 133d bumps 150 Ejector pin 151 Defects 200 unit pixels 210 Circuit Board 221 Transparent substrate 222 Surface layer 223 Light-shielding layer 225 Adhesive layer 227 Step Adjustment Layer 229 Connection Layer 230 pads 231 Insulating material layer 250 Bonding material 300 unit pixels 321 Transparent substrate 322 Surface layer 323 Light-shielding layer 325 Adhesive layer 327 Opening 327 Step Adjustment Layer 329a, 329b, 329c, 329d Connecting layers 331 Insulating material layer 333a, 333b, 333c, 333d Bonding pads 1000 pixel module 1001 Circuit Board 1003 Pad 1005 Bonding material 1010 Cover layer 2100 panel board 10000 display devices

Claims

1. transparent substrate; a plurality of light-emitting elements arranged on the transparent substrate; each connection layer electrically connected to each of the light-emitting elements; Each bonding pad is disposed on the top of each connection layer and electrically connected to each connection layer; and an insulating material layer covering each of the connecting layers; Including, each of the bonding pads partially overlaps with at least one of the light emitting elements in a vertical direction; the insulating material layer has openings exposing the connection layers; the bonding pads are electrically connected to the connection layers through the openings in the insulating material layer; A portion of each of the bonding pads is on the insulating material layer, forming a unit pixel.

2. The unit pixel of claim 1 , wherein at least one of the bonding pads partially overlaps two of the light emitting elements in a vertical direction.

3. The unit pixel according to claim 1 , wherein the transparent substrate has an uneven pattern on a surface facing the light emitting elements.

4. The unit pixel of claim 1 , wherein each of the light-emitting elements has a first uneven pattern formed on a surface facing the transparent substrate, and a second uneven pattern formed on the first uneven pattern.

5. the plurality of light emitting elements include at least three light emitting elements emitting light of different hues; The unit pixel according to claim 1 , wherein the at least three light-emitting elements are arranged in a row.

6. a light-blocking layer disposed between the transparent substrate and each of the light-emitting elements; and an adhesive layer disposed between the light-blocking layer and each of the light-emitting elements; further comprising the light-blocking layer has windows through which light generated by the light-emitting elements passes; The unit pixel according to claim 1 , wherein each of the light-emitting elements is disposed corresponding to each of the windows.

7. The unit pixel of claim 6 , further comprising a surface layer disposed between the transparent substrate and the light-blocking layer.

8. The light emitting device further includes a step adjusting layer covering the light emitting device, the step adjusting layer has openings exposing the light emitting elements; The unit pixel according to claim 6 , wherein each of the connection layers is disposed on the step adjustment layer and electrically connected to each of the light emitting elements through each of the openings in the step adjustment layer.

9. The unit pixel of claim 8 , wherein the insulating material layer covers a side surface of the step adjusting layer as well as a side surface of each of the connection layers.

10. The unit pixel of claim 9 , wherein the insulating material layer has a thickness thinner than a thickness of the step adjustment layer.

11. The unit pixel of claim 9 , wherein the step adjusting layer and the insulating material layer are made of polyimide.

12. Each of the light-emitting elements is a light-emitting structure including a first conductivity type semiconductor layer, a second conductivity type semiconductor layer, and an active layer interposed between the first conductivity type semiconductor layer and the second conductivity type semiconductor layer; and a first electrode pad and a second electrode pad disposed on the light emitting structure; Including, The unit pixel of claim 8 , wherein each opening in the step adjusting layer exposes the first and second electrode pads.

13. Each of the light emitting devices further includes an insulating layer disposed between the light emitting structure and the first and second electrode pads, The unit pixel of claim 12 , wherein the insulating layer includes a distributed Bragg reflector.

14. The light emitting elements include a red light emitting element, a green light emitting element, and a blue light emitting element, The unit pixel of claim 13 , wherein the insulating layer of the blue light-emitting element has a lower reflectance than the insulating layers of the red light-emitting element and the green light-emitting element.

15. The unit pixel according to claim 1 , wherein the transparent substrate has an area of less than 300 μm×300 μm.

16. a circuit board having pads; a plurality of unit pixels disposed on the circuit board; and each bonding material bonding each of the unit pixels to each of the pads; Including, Each of the unit pixels is transparent substrate; a plurality of light-emitting elements arranged on the transparent substrate; Each connection layer electrically connected to each of the light-emitting elements; and Each bonding pad is disposed on the top of each connection layer and electrically connected to each connection layer; and an insulating material layer covering each of the connecting layers; Including, each of the bonding pads partially overlaps with at least one of the light emitting elements in a vertical direction; The bonding materials bond the bonding pads to the pads on the circuit board, the insulating material layer has openings exposing the connection layers; the bonding pads are electrically connected to the connection layers through the openings in the insulating material layer; A portion of each of the bonding pads is on the insulating material layer.

17. 17. The display device of claim 16, wherein each of the bonding materials is solder.

18. The unit pixel is a light-blocking layer disposed between the transparent substrate and each of the light-emitting elements; and an adhesive layer disposed between the light-blocking layer and each of the light-emitting elements; further comprising the light-blocking layer has windows through which light generated by the light-emitting elements passes; The display device according to claim 16, wherein each of the light-emitting elements is disposed corresponding to each of the windows.

19. 17. The display device of claim 16, wherein the transparent substrate has an area of less than 300 μm×300 μm.

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