MICRO LIGHT-EMITTING DIODE PIXEL STRUCTURE AND METHOD FOR FORMING THE SAME

A micro light-emitting diode pixel structure and a method for forming the same are provided. The micro light emitting diode pixel structure includes micro light emitting diode chips, redistribution layers, bonding pads, an insulating layer, a flexible material layer and a first hard mask pattern. The redistribution layers are electrically connected to electrode surfaces of the micro light-emitting diode chips. The bonding pads are disposed under the redistribution layers. The insulation layer is disposed between the redistribution layers and the bonding pads. The flexible material layer disposed on the insulating layer to cover the micro light-emitting diode chips, the redistribution layers and insulation layer. The first hard mask pattern is disposed under or above the flexible material layers. In a cross-sectional view, the first hard mask pattern has a first edge and the flexible material layer has a second edge flush with the first edge.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of Taiwan Patent Application No. 112109939, filed on Mar. 17, 2023, and the content of which is incorporated by reference herein in its entireties.

BACKGROUND OF THE DISCLOSURE

Field of the Disclosure

The present disclosure relates to a micro light-emitting diode pixel structure and a method for forming the same, and, in particular, to a micro light-emitting diode pixel structure having high cutting efficiency and a method for forming the same.

Description of the Related Art

Since light-emitting diodes (LEDs) have the advantage of low power consumption, light-emitting diode displays have become the mainstream in the field of display technology. However, during the manufacturing process of light-emitting diode displays, the size of the pixel structure composed of red, green and blue (three primary colors) light-emitting diodes cannot be further reduced due to the fixed thickness and size of the light-emitting diodes. Therefore, it is difficult for the current pixel structure of the light-emitting diode to achieve the goals of small spacing, large light-emitting area, high process yield and low cost.

BRIEF SUMMARY OF THE DISCLOSURE

An embodiment of the present disclosure provides a micro light-emitting diode pixel device structure. The micro light-emitting diode pixel structure includes micro light-emitting diode chips, redistribution layers, bonding pads, an insulating layer, a flexible material layer and a first hard mask pattern. The micro light-emitting diode chips are arranged side by side. Each of the micro-light-emitting diode chips includes an electrode surface and a light-emitting surface. The redistribution layers are arranged at the electrode surfaces of the micro light-emitting diode chips and electrically connected to the micro light-emitting diode chips respectively. The bonding pads are disposed under the redistribution layers. The insulation layer is disposed between the redistribution layers and the bonding pads. The redistribution layers pass through the insulating layer to electrically connect to the bonding pads. The flexible material layer disposed on the insulating layer to covers the light-emitting surfaces of the micro light-emitting diode chips, the redistribution layers, and the insulating layer. The first hard mask pattern is disposed under or above the flexible material layer. In a cross-sectional view, the first hard mask pattern has a first edge and the flexible material layer has a second edge, and the first edge is flush with the second edge.

In addition, an embodiment of the present disclosure provides a method for forming a micro light-emitting diode pixel device structure. The method for forming the micro light-emitting diode pixel structure includes providing a first carrier. The method further includes forming a first adhesive layer on a surface of the first carrier. The method further includes forming a first hard mask pattern on the first adhesive layer. The first hard mask pattern has openings to expose the first adhesive layer. The method further includes forming bonding pads on the first hard mask pattern. The bonding pads are in contact with the first adhesive layer through the openings. The method further includes forming an insulating layer on the first hard mask pattern and the bonding pads. The insulating layer has via holes to expose the bonding pads. The method further includes forming redistribution layers on the insulating layer. The redistribution layers are electrically connected to the bonding pads through the via holes. The method further includes providing micro light-emitting diode chips on the first carrier. The micro light-emitting diode chips are electrically connected to the redistribution layers. The method further includes forming a flexible material layer on the first carrier to cover the micro light-emitting diode chips, the redistribution layers, and the insulating layer. The method further includes attaching a second carrier to the flexible material layer. The second carrier has a second adhesive layer, and the flexible material layer is in contact with the second adhesive layer. The method further includes removing the first carrier and the first adhesive layer. The method further includes performing an anisotropic etching process to remove a portion of the flexible material layer at the periphery which is not overlapped with the first hard mask pattern in a vertical direction. After performing the anisotropic etching process, in a cross-sectional view, the first hard mask pattern has a first edge and the flexible material layer has a second edge, and the first edge is flush with the second edge. The method further includes removing the second carrier and the second adhesive layer.

Moreover, an embodiment of the present disclosure provides a method for forming a micro light-emitting diode pixel structure. The method for forming the micro light-emitting diode pixel structure includes providing a carrier. The method further includes forming an adhesive layer on a surface of the carrier. The method further includes forming bonding pads on the adhesive layer. The method further includes forming an insulating layer on the adhesive layer and the bonding pads. The insulation layer has via holes to expose the bonding pads. The method further includes forming redistribution layers on the insulating layer. The redistribution layers are electrically connected to the bonding pads through the via holes. The method further includes providing micro light-emitting diode chips on the carrier. The micro light-emitting diode chips are electrically connected to the redistribution layers. The method further includes forming a flexible material layer on the carrier to cover the micro light-emitting diode chips, the redistribution layers, and the insulating layer. The method further includes forming a hard mask pattern on the flexible material layer. The method further includes performing an anisotropic etching process to remove a portion of the flexible material layer at the periphery which is not overlapped with the hard mask pattern in a vertical direction. After performing the anisotropic etching process, in a cross-sectional view, the hard mask pattern has a first edge and the flexible material layer has a second edge, and the first edge is flush with the second edge. The method further includes removing the carrier and the adhesive layer

DETAILED DESCRIPTION OF THE DISCLOSURE

The following description is made for the purpose of illustrating the general principles of the disclosure and should not be taken in a limiting sense. The scope of the disclosure is best determined by reference to the appended claims.

The embodiments of the present disclosure are described fully hereinafter with reference to the accompanying drawings, and the advantages and features of the present disclosure and methods of achieving them will be apparent from the following exemplary embodiments that will be described in more detail with reference to the accompanying drawings. It should be noted, however, that the present disclosure is not limited to the following exemplary embodiments, and may be implemented in various forms. Accordingly, the exemplary embodiments are provided only to disclose the present disclosure and let those skilled in the art know the category of the present disclosure. Also, the drawings as illustrated are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated for illustrative purposes and not drawn to scale. The dimensions and the relative dimensions do not correspond to actual dimensions in the practice of the disclosure. The micro light-emitting diode pixel structure provided in some embodiments of the present disclosure includes a hard mask pattern disposed under or above a flexible material layer, and is fabricated by an anisotropic etching process to improve the precision and accuracy of the dicing process and the flatness of the sidewall profile of the micro light-emitting diode pixel structure after performing the dicing process. Therefore, the process yield of the micro light-emitting diode pixel structure is further improved. Because the dicing loss is reduced, the yield of the micro light-emitting diode pixel structure is increased.

FIG.1is a schematic top view of micro light-emitting diode pixel structures500A,500B, or500C in accordance with some embodiments of the disclosure.FIG.2Ais a schematic cross-sectional view along the line A-A′ of the micro light-emitting diode pixel structure500A in accordance with some embodiments of the disclosure shown inFIG.1. The micro light-emitting diode pixel structure500A includes micro light-emitting diode chips230(including electrodes230P1and230P2), a redistribution layer220, a flexible material layer250P, a first hard mask pattern210, an insulating layer212and bonding pads206P1,206P2,206P3, and206P4. For illustration,FIG.1only shows the micro light-emitting diode chip230, the electrodes230P1and230P2, the bonding pads206P1,206P2,206P3and206P4, the redistribution layer220and the first hard mask pattern210. The flexible material layer250P, the insulating layer212and other features can be seen in the schematic cross-sectional view ofFIG.2A.

As shown inFIG.1andFIG.2A, the micro light-emitting diode chips230are arranged side by side on the insulating layer212, and each of the micro light-emitting diode chips230includes an electrode surface230T and a light-emitting surface230B opposite to each other. Each of the micro light-emitting diode chips230includes the electrodes230P1and230P2disposed at the electrode surface230T. In some embodiments, the electrodes230P1and230P2have different or opposite polarities. For example, the electrode230P1is a cathode, and the electrode230P2is an anode. In some embodiments, the micro light-emitting diode chips230respectively emit lights of different wavelengths to form a pixel unit. For example, the micro light-emitting diode chips230emitting lights of different colors may include the micro light-emitting diode chip emitting red light, the micro light-emitting diode chip emitting green light, and the micro light-emitting diode chip emitting blue light. However, embodiments of the disclosure are not limited thereto. In some embodiments, the micro light-emitting diode chips230include the micro light-emitting diode chips that emit light of the same wavelength, such as blue light or ultraviolet (UV) light, and are respectively coated with phosphors or quantum dot materials in different compositions to absorb the light emitted from the micro light-emitting diode chips and convert them into red light, green light or blue light, to form a pixel unit. In some embodiments, the light-emitting surface230B of the micro light-emitting diode chip230may be a rough surface, so as to increase the luminous efficiency of the micro light-emitting diode pixel structure500A. In some embodiments, the electrodes230P1and230P2include a conductive material such as chromium (Cr), aluminum (Al), nickel (Ni), gold (Au), platinum (Pt), tin (Sn), copper (Cu), or combinations thereof. In addition, the electrodes230P1and230P2can be formed by a plating process, such as evaporation or electroplating and a subsequent patterning process.

The redistribution layer220is disposed at the electrode surface230T of each of the micro light-emitting diode chips230and is electrically connected to the corresponding micro light-emitting diode chip230. In some embodiments, the redistribution layer220electrically connected to the corresponding micro light-emitting diode chip230includes redistribution layers220-1and220-2. Specifically, the redistribution layer220-1has a first side220-1S1and a second side220-1S2opposite to each other; the redistribution layer220-2has a first side220-2S1and a second side220-2S2opposite to each other; the second side220-1S2of the redistribution layer220-1is in contact with the electrode230P1of the corresponding micro light-emitting diode chip230, and the second side220-2S2of the redistribution layer220-2is in contact with the electrode230P2of the corresponding micro light-emitting diode chip230. The redistribution layer220is used as the interconnection structure of the micro light-emitting diode pixel structure500A to reroute (e.g. fan out) the electrical contact position from the original positions of the electrical nodes of the micro light-emitting diode chip230to the designated positions of the micro light-emitting diode pixel structure500A. In some embodiments, the redistribution layer220includes a stack of conductive materials layers formed of, for example, chromium (Cr), aluminum (Al), nickel (Ni), gold (Au), platinum (Pt), tin (Sn), indium (In), copper (Cu), nickel-cobalt-aluminum (NCA), anisotropic conductive film (ACF) or a combination thereof. In addition, the redistribution layer220may be formed by a plating process, such as evaporation or electroplating.

In addition to the redistribution layer220, the interconnect structure of the micro light-emitting diode pixel structure500A further includes an insulating layer212and bonding pads206P1,206P2,206P3and206P4. As shown inFIG.2A, the insulating layer212is disposed under the redistribution layer220-1and220-2to face the first sides220-1S1and220-2S1of the redistribution layers220-1and220-2. The bonding pads206P1,206P2,206P3and206P4are disposed under the insulating layer212and electrically connected to the redistribution layer220-1and220-2passing through the insulating layer212respectively. The bonding pads206P1,206P2,206P3and206P4can electrically connect to an external circuit (not shown). For example, in the embodiment shown inFIG.1, the bonding pads206P1,206P2,206P3and206P4are located at the lower left corner, the upper right corner, the lower right corner and the upper left corner of the micro light-emitting diode pixel structure500A respectively; the bonding pad206P1is electrically connected to three micro light-emitting diode chips230, and the bonding pads206P2,206P3and206P4are electrically connected to the corresponding one of the three micro light-emitting diode chips230respectively. Specifically, the electrodes230P1(such as the cathodes) of the three micro light-emitting diode chips230are electrically connected to the bonding pad206P1by one redistribution layer220-1, and the electrodes230P2(such as the anodes) of the three micro light-emitting diode chips230are electrically connected respectively to the corresponding bonding pads206P2,206P3and206P4by three different redistribution layers220-2. That is, the micro light-emitting diode chips230of the micro light-emitting diode pixel structure500A are electrically connected to each other by three anodes and one common-cathode. In other embodiments, the micro light-emitting diode chips230of the micro light-emitting diode pixel structure500A are electrically connected to each other by three cathodes and one common-anode. In some embodiments, a distributed Bragg reflector (DBR) layer can be disposed on the redistribution layer220and the insulating layer212to increase the luminous efficiency of the micro light-emitting diode pixel structure500A. In some embodiments, the insulating layer212includes polyimide (PI), epoxy resin (epoxy), benzocyclobutene (BCB) and other insulating materials with low dielectric constant and good step coverage, and can be formed by a coating process, for example, spin coating or spray coating. In some embodiments, the bonding pads206P1,206P2,206P3and206P4and the redistribution layers220-1and220-2may have the same or similar materials and formation processes.

As shown inFIG.2A, the flexible material layer250P covers and is in contact with the light-emitting surface230B of the micro light-emitting diode chip230and the second sides220-1S2and220-2S2of the redistribution layers220-1and220-2. In addition, the flexible material layer250P may surround the micro light-emitting diode chip230and the insulating layer212. In some embodiments, the flexible material layer250P includes a flexible material with good light transmittance (for example, the light transmittance is greater than 90%), such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polystyrene (PS), polypropylene (PP), polyamide (PA), polycarbonate (PC), polyimide (PI), epoxy, silicone, polydimethylsiloxane (PDMS) or a combination of any two or more of the above materials, and can be formed by, for example, film pasting, spray coating, or molding.

As shown inFIG.2A, the micro light-emitting diode pixel structure500A further includes an insulating layer224disposed between the micro light-emitting diode chip230and the insulating layer212. Specifically, the insulating layer224is disposed under the electrode surface230T of the micro light-emitting diode chip230and covers a portion of the surface of the insulating layer212right below the electrode surface230T of the micro light-emitting diode chip230. In addition, the insulating layer224further covers a portion of the second sides220-1S2and220-2S2of the redistribution layers220-1and220-2right below the electrode surface230T. The insulating layer224is in contact with the redistribution layer220and the flexible material layer250P. Moreover, the insulating layer224may surround the electrodes230P1and230P2of the micro light-emitting diode chip230to provide electrical insulation between the electrodes230P1and230P2. In some embodiments, the insulating layers212and224may have the same or similar materials and formation processes.

The first hard mask pattern210is disposed under the insulating layer212so that the insulating layer212is disposed between the redistribution layer220and the first hard mask pattern210. In the cross-sectional view shown inFIG.2A, an edge210E of the first hard mask pattern210is flush with an edge250E of the flexible material layer250P, and an edge212E of the insulating layer212is located closer to the micro light-emitting diode chip230than the edge210E of the first hard mask pattern210. That is, a part of the first hard mask pattern210around the edge210E is not covered by the insulating layer212so that the flexible material layer250P surrounds the insulating layer212and is in contact with the first hard mask pattern210. Moreover, the first hard mask pattern210may surround the bonding pads206P1and206P2. In this embodiment, the first hard mask pattern210is the bottommost layer of the micro light-emitting diode pixel structure500A, and the flexible material layer250P is the topmost layer of the micro light-emitting diode pixel structure500A. As shown inFIG.2A, the first hard mask pattern210has a bottom surface210B away from the flexible material layer250P. The bonding pads206P1and206P2respectively have bottom surfaces206P1B and206P2B away from the redistribution layer220. The bottom surface210B of the first hard mask pattern210and the bottom surfaces206P1B,206P2B of the bonding pads206P1,206P2are flush with each other and collectively form the bottom surface of the micro light-emitting diode pixel structure500A. Moreover, the top surface250T of the flexible material layer250P forms the top surface of the micro light-emitting diode pixel structure500A.

The first hard mask pattern210may serve as a mask during the dicing process (e.g., the anisotropic etching process such as plasma dicing) for forming the micro light-emitting diode pixel structure500A, so as to improve the dicing efficiency of the dicing process of the micro light-emitting diode pixel structure. In some embodiments, the first hard mask pattern210includes a material with good light transmittance, and the material of the first hard mask pattern210is different from that of the insulating layer212. For example, when the insulating layer212includes polyimide (PI), epoxy, and/or benzocyclobutene (BCB), the first hard mask pattern210may include silicon dioxide (SiO2). In addition, in some embodiments, the etching selectivity ratio of the first hard mask pattern210to the flexible material layer250P is between 1:10 and 1:1000. Furthermore, the etching selectivity ratio of the bonding pads206P1and206P2to the flexible material layer250P may be between 1:10 and 1:200. In the dicing process of forming the micro light-emitting diode pixel structure500A, due to the high etching selectivity between the first hard mask pattern210and the flexible material layer250P, the geometric shape and dimensions of the micro light-emitting diode pixel structure500A in the top view can be formed by using the first hard mask pattern210(and the bonding pads206P1and206P2) as a mask. In some embodiments, the top view shape of the first hard mask pattern210, such as polygon, circle, ellipse or other geometric shapes, is determined according to the predetermined geometry of the micro light-emitting diode pixel structure. In addition, the edge of the micro light-emitting diode pixel structure (composed of the edge250E of the flexible material layer250P and the edge210E of the first hard mask pattern210) can be etched to have a concave-convex profile by the design of the first hard mask pattern210. In some embodiment, the contour line of the micro light-emitting diode pixel structure in the top view may have a concave-convex shape, for example, stamp, wavy or jagged shape. In some embodiments, the first hard mask pattern210is formed using a deposition process such as plasma enhanced chemical vapor deposition (PECVD) and a subsequent patterning process.

FIG.2Bis a schematic cross-sectional view along the line A-A′ of the micro light-emitting diode pixel structure500B in accordance with some embodiments of the disclosure shown inFIG.1, and the reference numbers the same or similar as those previously described with reference toFIGS.1and2Adenote the same or similar elements. In some embodiments, the hard mask patterns used to form the geometric shape and dimensions of the micro light-emitting diode pixel structure are provided on both the top side and bottom side of the micro light-emitting diode pixel structure. As shown inFIG.2B, the difference between the micro light-emitting diode pixel structure500B and the micro light-emitting diode pixel structure500A is that the micro light-emitting diode pixel structure500B further includes a second hard mask pattern310disposed over the flexible material layer250P, so that the second hard mask pattern310is arranged as the topmost layer of the micro light-emitting diode pixel structure500B. In addition, the first hard mask pattern210and the bonding pads206P1and206P2are arranged as the bottommost layer of the micro light-emitting diode pixel structure500B. As shown inFIG.2B, the flexible material layer250P has the top surface250T away from the first hard mask pattern210, and the second hard mask pattern310covers and is in contact with the top surface250T of the flexible material layer250P, so that the top surface310T of the second hard mask pattern310constitutes the top surface of the micro light-emitting diode pixel structure500B. Moreover, the bottom surface210B of the first hard mask pattern210and the bottom surfaces206P1B and206P2B of the bonding pads206P1and206P2are flush with each other and collectively form the bottom surface of the micro light-emitting diode pixel structure500B. As shown inFIG.2B, the edge210E of the first hard mask pattern210may be flush with the edge310E of the second hard mask pattern310and the edge250E of the flexible material layer250P. In some embodiments, the first hard mask pattern210and the second hard mask pattern310in the micro light-emitting diode pixel structure500B may have the same or similar material, fabrication process and top-view shape.

FIG.2Cis a schematic cross-sectional view along the line A-A′ of the micro light-emitting diode pixel structure500C in accordance with some embodiments of the disclosure shown inFIG.1, and the reference numbers the same or similar as those previously described with reference toFIGS.1,2A and2Bdenote the same or similar element. In some embodiments, the hard mask pattern used to form the geometric shape and dimensions of the micro light-emitting diode pixel structure is provided on the top side of the micro light-emitting diode pixel structure. In this embodiment, since only the second hard mask pattern310is provided, the marks of the first hard mask pattern210and the openings211aland211a2of the first hard mask pattern210denoted inFIG.1can be omitted. As shown inFIG.2C, the difference between the micro light-emitting diode pixel structure500C and the micro light-emitting diode pixel structure500A is that the micro light-emitting diode pixel structure500C includes a second hard mask pattern310disposed on the flexible material layer250P so that the second hard mask pattern310is the topmost layer of the micro light-emitting diode pixel structure500C. In other words, the top surface310T of the second hard mask pattern310may constitute the top surface of the micro light-emitting diode pixel structure500C. In addition, the insulating layer212may have the bottom surface212B away from the micro light-emitting diode chip230. The bottom surface212B is flush with the bottom surfaces206P1B and206P2B of the bonding pads206P1and206P2and collectively form the bottom surface of the micro light-emitting diode pixel structure500C. Also, the edge310E of the second hard mask pattern310is flush with the edge250E of the flexible material layer250P.

FIG.3is a schematic top view of micro light-emitting diode pixel structures in accordance with some embodiments of the disclosure, which includes micro light-emitting diode pixel structures500D,500E, and500F. Similar toFIG.1, since there are no openings of the hard mask pattern in some embodiments (e.g. the micro light-emitting diode pixel structure500F), the marks of the openings (e.g.211aland211a2) denoted inFIG.3can be omitted when the aforementioned embodiments are considered.FIG.4is an equivalent circuit diagram of the micro light-emitting diode pixel structures500D,500E, and500F in accordance with some embodiments of the disclosure shown inFIG.3.FIGS.5A,5B, and5Care schematic cross-sectional views along the line A-A′ of the micro light-emitting diode pixel structures500D,500E, and500F in accordance with some embodiments of the disclosure shown inFIG.3, and the reference numbers the same or similar as those previously described with reference toFIGS.1,2A,2B and2Cdenote the same or similar element. The micro light-emitting diode pixel structures500D,500E, and500F may integrate a control device and micro light-emitting diodes into a pixel package so that the micro light-emitting diodes can be individually/independently controlled. The difference between the micro light-emitting diode pixel structures500D,500E, and500F shown inFIGS.5A,5B, and5Cand the micro light-emitting diode pixel structures500A,500B, and500C shown inFIGS.2A,2B, and2C is that the micro light-emitting diode pixel structures500D,500E, and500F include micro light-emitting diode chips330, a control device340, and redistribution layers320(including redistribution layers320-1,320-2,320-3,320-4and320-5).

As shown inFIGS.3, each of the micro light-emitting diode chips330includes electrodes330P1and330P2. In some embodiments, the micro light-emitting diode chips330may include the same or similar structures to the micro light-emitting diode chips230, and the dimensions of the micro light-emitting diode chips330may be the same or different to those of the micro light-emitting diode chips220. For example, the micro light-emitting diode chips230and330may have the same structure. In addition, the dimension of the micro light-emitting diode chip330may be smaller than that of the micro light-emitting diode chip230.

As shown inFIGS.5A,5B, and5C, the control device340is disposed between the micro light-emitting diode chip330and the bonding pads206P1and206P2. In addition, the control device340may be fixed on the first hard mask pattern210by an adhesive layer304. The control device340is electrically connected to the micro light-emitting diode chip330for driving the micro light-emitting diode chip330to emit light. In some embodiments, the control device340includes a 2TIC circuit composed of two thin film transistors (TFT, T) and one capacitor(C). As shown inFIG.4, the 2TIC circuit is electrically connected between a power supply terminal VDD and a ground terminal VSS, and controlled by a select line SL and a data line DL which may control the input of the scanning voltage signal and the data voltage signal. Therefore, the control device340may control the light emission of the micro light-emitting diode chip330.

In some embodiments, the control device340includes contact pads, such as contact pads340P1,340P2,340P3,340P4and340P5. The contact pad340P1of the control device340may be electrically connected to the corresponding electrode330P2of the micro light-emitting diode chip330. Moreover, the contact pads340P2,340P3,340P4, and340P5of the control device340may be electrically connected to the ground terminal VSS, the power supply terminal VDD, the data voltage signal source, and the scanning voltage signal source of the external circuit, respectively.

As shown inFIG.3, in some embodiments, the electrode330P1(cathode) of each of the micro light-emitting diode chips330and the contact pad340P2of the control device340may be electrically connected to the bonding pad206P1by the redistribution layer320-1, and further electrically connected to the ground terminal VSS of the external circuit by the bonding pad206P1. The electrode330P2(anode) of each of the micro light-emitting diode chips330may be electrically connected individually to the corresponding contact pad340P1of the control device340by the redistribution layer320-2, so that the control device340may electrically control the micro light-emitting diode chips330. The control device340may be further electrically connected to the bonding pad206P2by the redistribution layer320-3. Specifically, the contact pad340P3of the control device340may be electrically connected to the bonding pad206P2by the redistribution layer320-3and further electrically connected to the power supply terminal VDD of the external circuit by the bonding pad206P2. The contact pad340P4of the control device340may be electrically connected to the bonding pad206P3by the redistribution layer320-4, and further electrically connected to the data voltage signal source of the external circuit by the bonding pad206P3. The contact pad340P5of the control device340may be electrically connected to the bonding pad206P4by the redistribution layer320-5, and further electrically connected to the scanning voltage signal source of the external circuit by the bonding pad206P4.

The method for forming the micro light-emitting diode pixel structure is described below.FIGS.6A-6J,7A-7D,8A-8C, and9A-9Gillustrate methods for forming a micro light-emitting diode pixel structure (single pixel unit) for the sake of the convenience, though the embodiments of the present disclosure are not limited thereto. In some other embodiments, the methods for forming the micro light-emitting diode pixel structure may form periodically arranged micro light-emitting diode pixel structures.

FIGS.6A,6B,6C,6D,6E,6F,6G,6H,6I and6Jare schematic cross-sectional views at different stages of forming the micro light-emitting diode pixel structure500A in accordance with some embodiments of the disclosure as shown inFIG.2A. As shown inFIG.6A, first, a first carrier200is provided. The first carrier200is used to carry the micro light-emitting diode chips subsequently transferred onto a surface201of the first carrier200. In some embodiments, the material of the first carrier200includes glass, sapphire, transparent polymer or a combination thereof. Next, the adhesive layer204is formed, by coating for example, on the surface201of the first carrier200. In some embodiments, the adhesive layer204includes polymer materials having adhesive force and easily to be dissociated and destroyed at the interface with the first carrier200in the subsequent removal process (such as laser lift-off (LLO)), for example, polyimide (PI), epoxy, or silicone.

Next, as shown inFIG.6B, a deposition process and a subsequent patterning process are performed to form the first hard mask pattern210on the first carrier200. The first hard mask pattern210has openings211aland211a2to expose the adhesive layer204. In some embodiments, the edge210E of the first hard mask pattern210may be located inward relatively to the edge200E of the first carrier200. In other words, the edge210E of the first hard mask pattern210may be closer to the center of the first carrier200than the edge200E of the first carrier200, therefore a portion of the first carrier200, e.g. around the edge200E, is not covered by the first hard mask pattern210.

Next, as shown inFIG.6C, a plating process and a subsequent patterning process are performed to form the bonding pads206P1and206P2on the first carrier200. The bonding pads206P1and206P2are surrounded by the first hard mask pattern210. The bonding pads206P1and206P2are in contact with the adhesive layer204through the openings211aland211a2of the first hard mask pattern210. In other words, the bonding pads206P1and206P2are attached to the first carrier200by the adhesive layer204.

In some embodiments, the sequence of the process shown inFIG.6BandFIG.6Ccan be changed. That is, after coating the adhesive layer204, the bonding pads206P1and206P2are formed on the adhesive layer204, and then the first hard mask pattern210is formed on the adhesive layer204and the bonding pads206P1and206P2. The first hard mask pattern210has openings211aland211a2to respectively expose the bonding pads206P1and206P2.

Next, as shown inFIG.6D, a coating process and a subsequent patterning process are performed to form the insulating layer212on the first hard mask pattern210and the bonding pads206P1and206P2. The insulation layer212has via holes214a1and214a2to expose the bonding pads206P1and206P2. In some embodiments, the edge212E of the insulating layer212may be located inward relatively to the edge210E of the first hard mask pattern210. In other words, the edge212E of the insulating layer212may be closer to the center of the first carrier200than the edge210E of the first hard mask pattern210, therefore a portion of the first hard mask pattern210, e.g. around the edge210E, is not covered by the insulating layer212. Alternatively, in some embodiments, the edge212E of the insulating layer212may be not located inward relatively to the edge210E of the first hard mask pattern210, and may be connected with the insulating layer212of the intermediate structure of the adjacent micro light-emitting diode pixel structure.

Next, as shown inFIG.6E, a plating process and a subsequent patterning process are performed to form the redistribution layers220-1and220-2on the insulating layer212. The redistribution layers220-1and220-2cover a portion of the insulation layer212. Moreover, the redistribution layers220-1and220-2are electrically connected to the corresponding bonding pads206P1and206P2through the via holes214a1and214a2.

Next, as shown inFIG.6F, the micro light-emitting diode chip230may be transferred onto the first carrier200by transfer processes such as stamp transferring and/or laser transferring. The electrodes230P1and230P2of the micro light-emitting diode chip230are electrically connected to the redistribution layers220-1and220-2. Furthermore, the insulating layer224is filled in the gap between the micro light-emitting diode chip230and the redistribution layers220-1and220-2.

Next, as shown inFIG.6G, a film pasting, coating or molding process is performed to form a flexible material layer250covering the micro light-emitting diode chip230and the redistribution layers220-1and220-2. In some embodiments, the flexible material layer250further covers the insulating layer212, the first hard mask pattern210and the adhesive layer204, and surrounds the edge210E of the first hard mask pattern210.

Next, as shown inFIG.6H, an attaching process may be performed to attach the second carrier260to the flexible material layer250by a film-pasting machine. In some embodiments, the second carrier260has an adhesive layer264, and the flexible material layer250is in contact with the adhesive layer264. In some embodiments, the first carrier200and the second carrier260include the same or similar materials. The adhesive layer264includes polymer materials having adhesive force and easily to be dissociated and destroyed at the interface with the second carrier260in the subsequent removal process (such as, laser lift-off (LLO)), for example, UV tape, polyimide (PI), epoxy or silicone. Next, a removal process is performed to remove the first carrier200to expose the adhesive layer204. In some embodiments, the removal process of the first carrier200includes laser debonding or other suitable removal processes.

Next, as shown inFIG.6I, another removal process is performed to remove the adhesive layer204, so that the bottom surface210B of the first hard mask pattern210, the bottom surfaces206PB1and206P2B of the bonding pads206P1and206P2, and the bottom surface of a portion of the flexible material250not covered by the first hard mask pattern210and the bonding pads206P1and206P2are exposed. In some embodiments, the removal process of the adhesive layer204includes chemical etching, plasma etching or other suitable removal processes.

Next, as shown inFIG.6J, an anisotropic etching process (the dicing process)400is performed to remove the portion of the flexible material layer250at the periphery which is not covered by the first hard mask pattern210and the bonding pads206P1and206P2until the adhesive layer264is exposed to form the flexible material layer250P. In some embodiments, the anisotropic etching process includes a dry etching process such as plasma etching, and oxygen may be used as an etchant for the plasma etching. During the plasma etching process using oxygen as an etchant, an anisotropic etching process may be performed on the flexible material layer250using the first hard mask pattern210(and the bonding pads206P1,206P2) as an etching mask due to the high etching selectivity (between 1:10 and 1:1000) between the first hard mask pattern210and the flexible material layer250. After the anisotropic etching process, the edge210E of the first hard mask pattern210is flush with the edge250E of the flexible material layer250P in the cross-sectional view shown inFIG.6J.

Finally, a removal process is performed to remove the second carrier260and the adhesive layer264from the flexible material layer250P to form the micro light-emitting diode pixel structure500A as shown inFIG.2A. In some embodiments, the first carrier200and the second carrier260are removed using the same or similar removal process, and the adhesive layers204and264are removed using the same or similar removal process.

FIGS.7A,7B,7C and7Dare schematic cross-sectional views at different stages of forming the micro light-emitting diode pixel structure500B in accordance with some embodiments of the disclosure as shown inFIG.2B, and the reference numbers the same or similar as those previously described with reference toFIGS.1,2A-2C,3,4,5A-5C and6A-6Jdenote the same or similar element.

In some embodiments, after performing the processes shown inFIGS.6A to6Gin sequence, the second hard mask pattern310is formed on the flexible material layer250by the deposition and patterning processes, as shown inFIG.7A. In some embodiments, the second hard mask pattern310covers a portion of the flexible material layer250. In this embodiment, the edge310E of the second hard mask pattern310may be flush with the edge210E of the first hard mask pattern210.

Next, as shown inFIG.7B, the processes similar to those shown inFIG.6Hare performed to attach the second carrier260to the second hard mask pattern310and the flexible material layer250. In some embodiments, the adhesive layer264is in contact with both the second hard mask pattern310and the flexible material layer250. Afterwards, the first carrier200is removed to expose the adhesive layer204.

Next, as shown inFIGS.7C and7D, the processes similar to those shown inFIGS.61and6Jare sequentially performed to remove the adhesive layer204, and then the anisotropic etching process (the dicing process)400is performed to remove a portion of the flexible material layer250at the periphery which is not covered by the first hard mask pattern210until the adhesive layer264is exposed, so as to form the flexible material layer250P. After performing the anisotropic etching process, the edge250E of the flexible material layer250P is flush with the edge210E of the first hard mask pattern210and the edge310E of the second hard mask pattern310in the cross-sectional view shown inFIG.7D.

Finally, a removal process is performed to remove the second carrier260and the adhesive layer264from the second hard mask pattern310to form the micro light-emitting diode pixel structure500B as shown inFIG.2B.

In some embodiments, the anisotropic etching process may be performed from the side of the flexible material layer away from the bonding pads.FIGS.8A,8B and8Care schematic cross-sectional views at different stages of forming the micro light-emitting diode pixel structure500B in accordance with some embodiments of the disclosure as shown inFIG.2B, and the reference numbers the same or similar as those previously described with reference toFIGS.1,2A-2C,3,4,5A-5C,6A-6J and7A-7Ddenote the same or similar element.

As shown inFIG.8A, after performing the processes shown inFIGS.6A-6G and7Ain sequence, the anisotropic etching process (the dicing process)400is performed to remove a portion of the flexible material layer250at the periphery which is not covered by the second hard mask pattern310until the adhesive layer204is exposed, so as to form the flexible material layer250P. After performing the anisotropic etching process, the edge250E of the flexible material layer250P is flush with the edge310E of the second hard mask pattern310and the edge210E of the first hard mask pattern210in the cross-sectional view shown inFIG.8A.

Next, as shown inFIGS.8B and8C, the processes similar to those shown inFIGS.7B and7Care performed to attach the second carrier260to the second hard mask pattern310, and then remove the first carrier200and adhesive layer204.

Finally, a removal process is performed to remove the second carrier260and the adhesive layer264from the second hard mask pattern310to form the micro light-emitting diode pixel structure500B as shown inFIG.2B.

FIGS.9A,9B,9C,9D,9E,9F and9Gare schematic cross-sectional views at different stages of forming the micro light-emitting diode pixel structure500C in accordance with some embodiments of the disclosure as shown inFIG.2C, and the reference numbers the same or similar as those previously described with reference toFIGS.1,2A-2C,3,4,5A-5C,6A-6J,7A-7D and8A-8Cdenote the same or similar element.

As shown inFIG.9A, after performing the processes shown inFIG.6Ain sequence, a plating process and a subsequent patterning process are performed to form the bonding pads206P1and206P2on the first carrier200. In addition, the bonding pads206P1and206P2are in contact with the adhesive layer204.

Next, as shown inFIG.9B, the processes similar to those shown inFIG.6Dare performed to form the insulating layer212on the adhesive layer204and the bonding pads206P1and206P2. The insulation layer212may have the via holes214a1and214a2to expose the bonding pads206P1and206P2.

Next, as shown inFIG.9C, the processes similar to those shown inFIG.6Eare performed to form the redistribution layers220-1and220-2on the insulating layer212. The redistribution layers220-1and220-2may cover a portion of the insulation layers212. Moreover, the redistribution layers220-1and220-2are electrically connected to the corresponding bonding pads206P1and206P2through the via holes214a1and214a2.

Next, as shown inFIG.9D, the processes similar to those shown inFIG.6Fare performed to transfer the micro light-emitting diode chip230onto the first carrier200, so that the micro light-emitting diode chip230are electrically connected to the corresponding redistribution layers220-1and220-2.

Next, as shown inFIG.9E, the processes similar to those shown inFIG.6GandFIG.7Ain sequence are performed to form the flexible material layer250covering the micro light-emitting diode chip230and the redistribution layers220-1and220-2, and then, the second hard mask pattern310is formed on the flexible material layer250. In some embodiments, the edge212E of the insulating layer212may be located inward relatively to the edge310E of the second hard mask pattern310. Alternatively, the edge212E of the insulating layer212may be not located inward relatively to the edge310E of the second hard mask pattern310, and may be connected with the insulating layer212of the intermediate structure of the adjacent micro light-emitting diode pixel structure.

Next, as shown inFIG.9F, the processes similar to those shown inFIG.8Aare performed. The anisotropic etching process400is performed to remove a portion of the flexible material layer250at the periphery which is not covered by the second hard mask pattern310to form the flexible material layer250P. After performing the anisotropic etching process, the edge310E of the second hard mask pattern310is flush with the edge250E of the flexible material layer250P in the cross-sectional view shown inFIG.9F.

Next, as shown inFIG.9G, a removal process is performed to remove the first carrier200to expose the adhesive layer204.

Finally, another removal process is performed to remove the adhesive layer204and thereby forming the micro light-emitting diode pixel structure500C shown inFIG.2C.

In some embodiments, the method of forming the micro light-emitting diode pixel structures500D and500E shown inFIGS.5A and5Bare similar to that of forming the micro light-emitting diode pixel structures500A and500B shown inFIGS.2A and2B, which are shown inFIGS.6A-6J,7A-7D, and8A-8C. The differences are described below. For example, after performing the processes similar to those shown inFIGS.6A-6Cto form the bonding pads206P1and206P2, the adhesive layer304may be coated on the first hard mask pattern210between the bonding pads206P1and206P2. Next, the control device340is disposed on the first carrier200by transfer processes such as stamp transferring or laser transferring so that the bonding pads206P1and206P2are located at a side of the control device340opposite to the contact pads340P1and340P3of the control device340. In addition, after performing the processes similar to those shown inFIG.6Dto form the insulating layer212, the control device340is also covered by the insulating layer212and the contact pads340P1and340P3of the control device340are exposed from the insulating layer212. Furthermore, after performing the processes similar to those shown inFIGS.6Eand6F, the redistribution layers320-1,320-2and320-3are formed on the insulating layer212, so that the control device340is electrically connected to the micro light-emitting diode chip330by the redistribution layers320. The processes similar to those shown inFIGS.6F to6Jare sequentially performed to form the micro light-emitting diode pixel structure500D. Alternatively, the processes similar to those shown inFIGS.6F,6G, and7A-7D(orFIGS.6F,6G,7A, and8A-8C) are sequentially performed to form the micro light-emitting diode pixel structure500E.

In some embodiments, the method of forming the micro light-emitting diode pixel structure500F shown inFIG.5Cis similar to that of forming the micro light-emitting diode pixel structure500C shown inFIGS.2C, which is shown inFIGS.9A-9G. The differences are described below. For example, after performing the processes similar to those shown inFIG.9A, the adhesive layer304may be coated on the adhesive layer204between the bonding pads206P1and206P2. Next, the control device340is disposed on the adhesive layer304by transfer processes such as stamp transferring and laser transferring so that the bonding pads206P1and206P2are located on a side of the control device340opposite to the contact pads340P1and340P3of the control device340. In other embodiments, the control device340may be disposed on the first carrier200between the bonding pads206P1and206P2by the adhesive layer204without using the coated adhesive layer304. In addition, after performing the processes similar to those shown inFIG.9Bto form the insulating layer212, the control device340is also covered by the insulating layer212and the contact pads340P1and340P3of the control device340are exposed from the insulating layer212. Furthermore, after performing the processes similar to those shown inFIGS.9C and9D, the redistribution layers320-1,320-2and320-3are formed on the insulating layer212, so that the control device340is electrically connected to the micro light-emitting diode chip330by the redistribution layers320. The processes similar to those shown inFIGS.9E to9Gis sequentially performed to form the micro light-emitting diode pixel structure500F.

Embodiments of the disclosure provide a micro light-emitting diode pixel structure and a method for forming the same. Compared with the singulation process (such as laser cutting, dicing saw cutting, or other conventional dicing process) of the conventional light-emitting diode pixel structure, the micro light-emitting diode pixel structure in accordance with some embodiments of the disclosure has a hard mask pattern serving as the bottommost and/or topmost layer of the pixel structure and as an etching mask. Therefore, the anisotropic etching process such as plasma etching may be performed from the bottom and/or top surface of the pixel structure for singulation. Because of the high etching selectivity between the hard mask pattern and the flexible material layer, the top-view shape and dimension of the micro light-emitting diode pixel structure may be formed with better precision/accuracy and without destroying the sidewall profile of the micro light-emitting diode pixel structure. Therefore, the process yield of micro light-emitting diode pixel structure can be improved.