LED DISPLAY DEVICE AND METHOD FOR MANUFACTURING SAME

Abstract

The present invention relates to an LED display device and a method for manufacturing the same. A manufacturing method, according to one embodiment of the present invention, comprises the steps of: growing a semiconductor layer on a growth substrate; forming an LED element in an asymmetrical shape from which the semiconductor layer is separated; separating the LED element from the growth substrate; forming a bonding electrode, to which the LED element is bonded, on a display substrate comprising a TFT; forming a groove by patterning the display substrate in the same shape as the LED element formed asymmetrically; seating the LED element in a pattern having the groove in the same shape as the LED element by means of a physical force; and electrically connecting by the bonding electrode of the display substrate or an adhesive conductive material formed on a bonding electrode of the LED element.

Claims

1. A method for manufacturing an LED display device, the method comprising: growing a semiconductor layer on a growth substrate; forming a plurality of LED elements, which are asymmetric with mutually different shapes and in which the semiconductor layer is separated; separating the LED elements from the growth substrate; forming a bonding electrode, to which the LED element is bonded, on a display substrate including a thin film transistor (TFT); forming a groove on the display substrate by patterning the display substrate in a shape identical to the shape of the LED elements which are asymmetric; seating the LED element in a pattern, which has the groove having a shape identical to the shape of the LED element, by a physical force; and establishing electrical connection by the bonding electrode of the display substrate or an adhesive conductive material formed on a bonding electrode of the LED element.

2. The method of claim 1, wherein the growth substrate includes a material selected from the group consisting of sapphire, Si, SiC, MgAl.sub.2O.sub.4, MgO, LiAlO.sub.2, LiGaO.sub.2, GaN, glass, and GaAs.

3. The method of claim 1, further comprising: etching to a level of a first semiconductor layer; forming a second semiconductor layer and an ohmic contact layer by using a metal or a transparent conductive oxide; etching the semiconductor layer to a level of the growth substrate to form the LED element in an asymmetric shape; depositing an insulating layer on a surface of the LED element in which an electrode is formed and on a side surface of the LED element; etching a portion of an insulator to a level of the ohmic contact layer of the second semiconductor layer and the first semiconductor layer; forming a second bonding electrode electrically connected to the ohmic contact layer of the second semiconductor layer and a first bonding electrode making ohmic contact with the first semiconductor layer; and separating the growth substrate and the LED element from each other.

4. The method of claim 1, wherein when etching the semiconductor layer to a level of the growth substrate, the LED element has an asymmetric shape such that a shape of the LED element viewed from a bonding electrode side or an opposite side of the bonding electrode side is asymmetric.

5. The method of claim 3, wherein the insulating layer includes a material selected from the group consisting of SiO.sub.2, SiN, TiO.sub.2, Si.sub.3N.sub.4, Al.sub.2O.sub.3, TiN, AlN, ZrO.sub.2, TiAlN, and TiSiN.

6. The method of claim 3, wherein the second bonding electrode and the first bonding electrode of the LED element bonded to the display substrate include an ohmic contact layer, an under bump metallurgy (UBM) layer, and a solder layer, the ohmic contact layer on a first semiconductor includes a material selected from the group consisting of Ti, Cr, Al, Ag, Rh, Ni, Cu, and a transparent conductive oxide, the UBM layer includes a material selected from the group consisting of Ti, Cr, Ni, Cu, Pd, and Ag, and the solder layer includes a material selected from the group consisting of Sn, Ag, Cu, Ni, In, Bi, Zn, Al, Au, and Ga.

7. The method of claim 1, further comprising: coating a photoresist onto the LED element formed on the growth substrate, baking the photoresist, and wax-bonding the photoresist to a support substrate; or bonding the LED element formed on the growth substrate to an adhesive UV tape or polydimethylsiloxane (PDMS).

8. The method of claim 1, further comprising separating the semiconductor layer and the growth substrate from each other, wherein the growth substrate is removed through laser lift off (LLO), chemical lift off (CLO), or dry etching.

9. The method of claim 1, further comprising removing a foreign substance, which remains after separating the semiconductor layer and the growth substrate from each other, by using HCl.

10. The method of claim 1, further comprising providing a surface concavo-convex portion to a surface of the semiconductor layer separated from the growth substrate by using KOH.

11. The method of claim 3, further comprising etching a portion of the insulator layer from the semiconductor layer and the insulator layer which are exposed after being separated from the growth substrate.

12. The method of claim 1, further comprising: separating the LED element from a support substrate by using a photoresist remover to individually separate the LED elements disposed on the support substrate; or separating the LED element bonded to the adhesive UV tape or the PDMS.

13. The method of claim 1, wherein the display substrate includes glass, a semiconductor substrate, or a flexible polymer material.

14. The method of claim 1, further comprising: forming the bonding electrode, which respectively bonds a plurality of TFTs to the LED elements through an electrical wire, on the display substrate; and forming the groove having the shape identical to the shape of the LED element, which is asymmetric and has the bonding electrode that is exposed.

15. The method of claim 1, wherein when the LED element is inserted into the groove, a clearance is formed between the groove and the LED element.

16. The method of claim 1, wherein the groove is formed by applying a photosensitive material and patterning the photosensitive material through photolithography, or formed by applying glass, spin on glass (SOG), silicon, or a polymer material through coating, and patterning the glass, the SOG, the silicon, or the polymer material.

17. The method of claim 1, wherein the groove is formed by using a mask having a hole which has a shape identical to the shape of the LED element.

18. The method of claim 1, wherein the seating of the LED element in the pattern, which has the groove having the shape identical to the shape of the LED element, by the physical force includes: distributing the LED elements, which are individually separated, on the display substrate having the groove; applying the physical force of vibration, rotation, or tilting to the display substrate; inserting and aligning the LED element in the groove; and separating remaining LED elements, which are not inserted into the groove, from the display substrate.

19. The method of claim 1, further comprising establishing the electrical connection by applying heat or a pressure onto the bonding electrode of the display substrate or the adhesive conductive material formed on the bonding electrode of the LED element.

20. The method of claim 1, wherein after the LED element is bonded to the display substrate, a pattern material for forming the groove is removed or left.

Description

DESCRIPTION OF DRAWINGS

[0035] FIG. 1 is a sectional view showing a structure in which an LED element and a growth substrate 10 are attached to each other.

[0036] FIG. 2 is a sectional view showing the LED element.

[0037] FIGS. 3A, 3B, and 3C are perspective views showing a symmetric LED element.

[0038] FIGS. 4A, 4B, and 4C are sectional views showing a state in which the symmetric LED element is inserted into a groove formed in a display substrate.

[0039] FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, and 5H are plan views showing axisymmetric shapes.

[0040] FIGS. 6A and 6B are plan views showing point-symmetric shapes.

[0041] FIGS. 7A, 7B, 7C, 7D, 7E, 7F, 7G, and 7H are plan views showing asymmetric shapes.

[0042] FIG. 8 is a perspective view showing a state in which bonding electrodes 41 and 42 are formed on the display substrate.

[0043] FIG. 9 is a perspective view showing a state in which a groove having the same shape as the symmetric LED element is formed in the display substrate.

[0044] FIG. 10 is a perspective view showing a state in which the symmetric LED element is inserted into the groove of the display substrate.

[0045] FIGS. 11A, 11B, and 11C are perspective views showing an asymmetric LED element.

[0046] FIG. 12 is a perspective view showing a state in which a groove having the same shape as the asymmetric LED element is formed in the display substrate.

[0047] FIG. 13 is a perspective view showing a state in which the asymmetric LED element (FIG. 11A) having one type of shape is aligned and inserted in the groove of the display substrate.

[0048] FIG. 14 shows a blue LED element (FIGS. 14A, 14D, and 14G), a green LED element (FIGS. 14B, 14E, and 14H), and a red LED element (FIGS. 14C, 14F, and 14I) required to constitute a full-color display device.

[0049] FIG. 15 is a perspective view showing a state in which grooves respectively having the same shapes as the asymmetric blue LED element (FIG. 14A), the asymmetric green LED element (FIG. 14B), and the asymmetric red LED element (FIG. 14C) are formed on the display substrate.

[0050] FIG. 16 is a perspective view showing states 301, 401, and 501 in which the asymmetric blue LED element (FIG. 14A), the asymmetric green LED element (FIG. 14B), and the asymmetric red LED element (FIG. 14C) are aligned and inserted in the grooves of the display substrate, respectively.

[0051] FIG. 17A is a perspective view showing an LED element having an asymmetric shape and formed by perforating a semiconductor layer, FIG. 17B is a perspective view showing a display substrate formed with a groove 101 having the same shape as the LED element, and FIG. 17C is a perspective view showing a state in which an LED element 601 (FIG. 17A) is aligned and inserted in the groove 101.

MODE FOR INVENTION

Best Mode

[0052] Hereinafter, the present invention will be described in detail with reference to the drawings.

[0053] FIG. 1 is a sectional view showing a structure of an LED element to be used to implement a full-color LED display device.

[0054] Referring to FIG. 1, a sapphire substrate may be used as a growth substrate 10. In this case, the growth substrate may effectively withstand a high-temperature condition and the like, which are required when manufacturing the LED element, and the growth substrate refers to a substrate that assists epitaxial growth of a semiconductor layer. For example, sapphire, Si, SiC, MgAl.sub.2O.sub.4, MgO, LiAlO.sub.2, LiGaO.sub.2, GaN, glass, and GaAs substrates may be used as a semiconductor growth substrate.

[0055] Referring to FIG. 1, a first-conductivity type semiconductor layer 11, an active layer 12, and a second-conductivity type semiconductor layer 13 may be grown on the growth substrate 10 by using metal organic chemical vapor deposition (MOCVD). In order to form an LED element, first, dry etching may be performed to a level of a first semiconductor layer 11. Thereafter, a second semiconductor layer 13 and an ohmic contact layer 14 may be formed of a metal or a transparent conductive oxide. Thereafter, etching may be performed to a level of the growth substrate 10. At this time, the growth substrate may be partially etched. In this case, the LED element may be etched to have an asymmetric shape when viewed from an electrode side of the LED element or an opposite side of the electrode side. An electrical insulating film 15 may be formed in each LED element, the electrical insulating film 15 may be etched to a level of the ohmic contact layer 14 and the first semiconductor layer to form a contact hole, and bonding metal layers 16 and 17 may be formed.

[0056] In FIG. 1, n-GaN 11, the active layer 12, and p-GaN, which are semiconductor layers, may represent only the most essential layers of the element.

[0057] In FIG. 1, the bonding metal layer 17 may be electrically connected to the ohmic contact layer 14, and the bonding metal layer 16 may make ohmic contact with the first semiconductor layer. The bonding metal layers 16 and 17 may include an ohmic contact layer, an under bump metallurgy (UBM) layer, and a solder layer; the metal layer making ohmic contact with the first semiconductor may have a single-layer or multilayer structure formed of a material including at least one of a material such as Ti, Cr, Al, Ag, Rh, Ni, Cu, and a transparent conductive oxide, and an alloy thereof; the UBM layer may have a single-layer or multilayer structure formed of a material including at least one of a material such as Ti, Cr, Ni, Cu, Pd, and Ag, and an alloy thereof; and the solder layer may be formed of various chemical compositions including one or a plurality of metals among Sn, Ag, Cu, Ni, In, Bi, Zn, Al, Au, and Ga.

[0058] A photoresist (PR) may be coated onto the LED element to cover the LED element, and the PR may be bonded to another support substrate by using wax.

[0059] As shown in FIG. 2, the LED element may be separated from the growth substrate 10 by a laser lift off (LLO) scheme.

[0060] Depending on a type of the growth substrate, the growth substrate may be separated by a scheme such as laser lift off (LLO), chemical lift off (CLO), polishing, and dry etching.

[0061] After the LLO, a gallium molten droplet (Ga droplet) and foreign substances remaining on the semiconductor layer may be removed by using HCl. In order to further increase light extraction efficiency, a concavo-convex portion may be generally formed on an n-GaN surface by using KOH. Although not shown in the drawing, if undoped GaN is present under the n-GaN, KOH may be used to form a concavo-convex portion similarly to the above configuration. Since the electrical insulating film 15 of FIG. 1 connects the LED elements to each other, only the connected portion may be cut by the dry etching.

[0062] In addition, when the PR and the wax are removed, the LED elements of FIG. 2 may be separated. Then, the PR and the wax remaining on the LED element may be removed by using isopropyl alcohol (IPA) and deionized water (DI water), and moisture may be dried out. If the PR and the wax are not sufficiently removed, the PR and the wax may be additionally removed by a descum or asking scheme.

[0063] Another scheme is to attach the LED element to an UV tape, PDMS, or the like. Thereafter, the LED element and the growth substrate may be separated from each other by the LLO scheme, and the LED element may be separated from the UV tape or the PDMS.

[0064] FIGS. 2 and 3 schematically show the LED element manufactured through the above processes.

[0065] A reference numeral 21 of FIG. 3, which includes all of reference numerals 11, 12, 13, 14, and 15 of FIG. 2, is schematically shown. The bonding metal layer of FIG. 3 may include the bonding metal layer 17 electrically connected to the second semiconductor layer and the bonding metal layer 16 electrically connected to the first semiconductor layer.

[0066] Reference numerals 41 and 42 of FIG. 8 represent a plurality of bonding electrodes which may bond the bonding electrodes 16 and 17 of the LED element to a display substrate 31 on which a thin film transistor (TFT) is formed. The bonding electrodes 41 and 42 may be connected to TFTs, respectively. The bonding electrodes 41 and 42 may have a typical under bump metallurgy (UBM) so that a solder material may excellently form an inter-metallic compound (IMC). A reference numeral 31 represents the display substrate including the TFT.

[0067] A groove having the same shape as the LED element may be formed so that the LED element may be aligned on the substrate in a predetermined direction by a physical force. The groove may have a suitable clearance so that the LED element may be inserted into the groove. Each groove may have a depth that allows only one LED element to be inserted into the groove.

[0068] The groove may be formed by applying a photosensitive material through coating in a photolithography scheme. Alternatively, glass, spin on glass (SOG), or a polymer material may be coated onto the display substrate, and the photosensitive material may be applied through the coating to form a pattern in the photolithography scheme. In addition, dry or wet etching may be performed, and the photosensitive material may be removed.

[0069] The technology of moving numerous LED elements to a desired position within a short time may take a long process time, or requires a facility capable of aligning the LED elements with high precision while placing the LED elements at the desired position. In addition, in most of the technologies, the LED elements arranged on the growth substrate may be transferred on the display substrate as they are. The present invention proposes a method of moving and bonding hundreds of thousands to millions of LED elements or more to a desired position. To achieve the above object, the LED elements have to be individually separated from each other, and the display substrate has to be formed with the groove having the same shape as the LED.

[0070] Sequentially, the display substrate may be fixedly placed on a mechanical device capable of applying a physical force such as vibration, rotation, and tilting, the LED element may be distributed on the display substrate, and the physical force may be applied by the mechanical device. As a result, the LED elements may be aligned and inserted in grooves, respectively.

[0071] FIG. 3 is a perspective view showing a symmetric LED element.

[0072] FIG. 4 is a plan view showing axisymmetric shapes.

[0073] FIG. 5 is a plan view showing point-symmetric shapes.

[0074] FIG. 6 is a plan view showing asymmetric shapes.

[0075] FIG. 4 is a sectional view showing a state in which the symmetric LED element is inserted into a groove on an LED substrate.

[0076] FIG. 9 is a perspective view showing a state in which a groove is patterned on a display substrate.

[0077] FIG. 10 is a perspective view showing a state in which the symmetric LED element is inserted into the groove of the display substrate.

[0078] Referring to FIGS. 3, 4, 9, and 10, if the LED element is formed to be symmetric when viewed from the electrode side or the opposite side thereof, there may be many cases such as a case where the LED elements are normally inserted into grooves, respectively, a case where a positive electrode and a negative electrode are inversely inserted, and a case where the element is inserted upside down.

[0079] Therefore, the LED element is manufactured to be asymmetric when viewed from the electrode side or the opposite side thereof. When the LED element has an asymmetric shape, the first bonding electrode 16 and the second bonding electrode 17 of the LED element may be aligned so as to be bonded to a first bonding electrode 41 and a second bonding electrode of the display substrate, respectively.

[0080] FIG. 11 is a perspective view showing an asymmetric LED element.

[0081] FIG. 12 is a perspective view showing a state in which a groove having the same shape as the asymmetric LED element is formed in the display substrate.

[0082] FIG. 13 is a perspective view showing a state in which the asymmetric LED element (FIG. 11A) having one type of shape is aligned and inserted in the groove of the display substrate.

[0083] FIG. 14 shows a blue LED element (FIG. 14A), a green LED element (FIG. 14B), and a red LED element (FIG. 14C) required to constitute a full-color display device.

[0084] Referring to FIG. 14, the blue, green, and red LED elements may have asymmetric shapes which are slightly different from each other, and the shapes on the electrode sides (FIGS. 14D, 14E, and 14F) and the shapes on the opposite sides (FIGS. 14G, 14H, and 14I) of the blue, green, and red LED elements have to be different from each other. Grooves having shapes identical to the shapes of the opposite sides (FIGS. 14G, 14H, and 14I) of the electrode sides of the blue, green, and red LED elements may be formed on the display substrate on which the TFT is formed. The groove may have a clearance to allow the LED element to be inserted into the groove. As a result, the blue, green, and red LED elements may be aligned and inserted in the grooves that fit the shapes of the LED elements, respectively.

[0085] In more detail, for example, when the blue LED element and the green LED element have mutually different shapes when viewed from the electrode side while the shape viewed from the electrode side of the blue LED element is the same as the shape viewed from the opposite side of the electrode side of the green LED element, the green LED element may be aligned upside down such that the electrode faces upward in the groove of the substrate into which the blue LED element is to be inserted. Similarly, the blue LED element may be aligned upside down such that the electrode faces upward in the groove of the substrate into which the green LED element is to be inserted.

[0086] FIG. 15 is a perspective view showing a state in which grooves 71, 81, and 91 respectively having the same shapes as the asymmetric blue, green, and red LED elements are formed on the display substrate.

[0087] FIG. 16 is a perspective view showing states 301, 401, and 501 in which the asymmetric blue LED element (FIG. 14A), the asymmetric green LED element (FIG. 14B), and the asymmetric red LED element (FIG. 14C) are aligned and inserted in the grooves of the display substrate, respectively.

[0088] The blue, green, and red LED elements may be distributed on the display substrate formed with the grooves, which respectively have the same shapes as the LED elements, and the TFT such that the number of the blue, green, and red LED elements of which the number is larger than the number of the grooves in the substrate. The blue, green, and red LED elements may be distributed at a ratio that allows the numbers of the blue, green, and red LED elements to be similar to each other such that approximately an entire area of the substrate may be covered. When the LED elements are simply distributed, the probability of the LED elements being inserted into the grooves may be very low. Therefore, the present invention provides a method including: forming the LED element and the groove of the display substrate in asymmetric shapes; placing the display substrate on a plate that may be subjected to the physical force such as vibration, rotation, and tilting; and seating the LED element in the grooves, respectively.

[0089] The LED element may be located at the desired position as described above, and the display substrate may be reflowed so that a solder provided on a surface of the LED element or a solder provided on the electrode of the display substrate may be melted.

[0090] In addition, when the reflow is performed, press-bonding may be performed by using a pressing roll so that the LED element and the display substrate may be excellently bonded to each other.

[0091] In order to prevent the moisture from penetrating into the LED element, a front surface of the display substrate to which the LED element is bonded may be coated.

[0092] In FIG. 17, FIG. 17A is a perspective view showing an LED element having an asymmetric shape and formed by perforating a semiconductor layer, FIG. 17B is a perspective view showing a display substrate formed with a groove 101 having the same shape as the LED element, and FIG. 17C is a perspective view showing a state in which an LED element 601 (FIG. 17A) is aligned and inserted in the groove 101.

INDUSTRIAL APPLICABILITY

[0093] The full-color LED display device and the method for manufacturing the same according to the present invention can be widely used in the display industry.