Micro light emitting diode layout structure and manufacturing method thereof

Abstract

A micro-LED layout structure for augmented reality and mixed reality and a manufacturing method thereof are disclosed. The micro-LED layout structure for augmented reality and mixed reality includes a plurality of display units arranged into a unit array on a transparent substrate, a plurality of micro-LEDs disposed at an edge region of each display unit and exposing a light-transmitting region surrounded by the edge region, and a pixel driving circuit disposed on the edge region directly below the micro-LEDs.

Description

TECHNICAL FIELD

[0001] The present application relates to a micro light emitting diode (micro LED) layout structure, and more particularly to a micro light emitting diode layout structure for augmented reality (AR) and mixed reality (MR) and a related manufacturing process thereof. BACKGROUND

[0002] Micro light emitting diode (micro LED) is a display technology that has been developed in recent years. The micro LED has a micro LED array structure and a self-emitting display characteristic. Each pixel can be independently driven, and the micro LED has high brightness, high contrast, low power consumption, high resolution, and high color saturation. Compared with an organic light emitting diode (OLED) display, which is also a self-emitting display, the micro LED has the advantages of high efficiency, long service life, and good environmental tolerance. The unique low power consumption and high brightness characteristics of the micro LED make it very suitable for use in wearable watches, mobile phones, vehicle displays, augmented reality (AR) / virtual reality (VR), displays, and televisions. The micro LED has been regarded as the most promising next-generation display technology after the transitional mini light emitting diode (mini LED).

[0003] Based on the characteristics and advantages of low power consumption and high resolution of the micro light emitting diode, the industry is currently working on researching and developing new micro light emitting diode structures and related manufacturing processes in order to apply them to small-sized wearable devices and augmented / mixed reality (AR / MR, Mixed Reality) devices, such as smart glasses with augmented / mixed reality functions. However, there are still many technical bottlenecks to be overcome in order to apply micro light emitting diodes to wearable devices for augmented / mixed reality, such as mass transfer technical challenges, improvement of light transmittance, micro light emitting diode lenses, and integration with existing CMOS manufacturing processes. SUMMARY

[0004] In order to research and develop the application of micro light emitting diodes (micro LED) in augmented reality (AR) / mixed reality (MR), the present application proposes a novel micro light emitting diode layout structure. The micro light emitting diode is designed to be arranged at the edges of each display unit and to leave a transparent area in the middle. This achieves a high light transmittance and at the same time has high resolution and high light efficiency display quality.

[0005] One aspect of the present application is to provide a micro-LED layout structure for augmented reality and mixed reality, comprising a transparent substrate, a plurality of display units arranged in a unit array defined on the transparent substrate, a plurality of micro-LEDs disposed at the edge region of each display unit and exposed as a light transmission region surrounded by the edge region, and a pixel driving circuit disposed on the edge region directly below the micro-LEDs.

[0006] Another aspect of the present application is to provide a manufacturing method of a micro-LED layout structure for augmented reality and mixed reality, comprising the steps of providing a substrate, wherein a plurality of display units arranged in a unit array are defined on the substrate, each of the display units comprising an edge region and a light transmission region surrounded by the edge region, forming a pixel driving circuit and a first light transmission layer on the edge region of each display unit on the substrate, and disposing a plurality of micro-LEDs on the first light transmission layer of the edge regions, the micro-LEDs being connected with the pixel driving circuit below.

[0007] These and other objects of the present application will no doubt become obvious to one of ordinary skill in the art after having read the following detailed description of the preferred embodiment of the present application, illustrated in the various figures and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0008] The present application is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which:

[0009] Figure 1 A schematic diagram of a smart glass equipped with a lens having a micro-LED layout structure of the present application;

[0010] Figure 2 A schematic diagram of a display unit having a micro-LED of a preferred embodiment of the present application;

[0011] Figure 3 A schematic diagram of a unit array having a micro-LED of a preferred embodiment of the present application;

[0012] Figure 4 A schematic diagram of a unit array having a micro-LED of another embodiment of the present application;

[0013] Figure 5 A schematic diagram of a unit array having a micro-LED of yet another embodiment of the present application; and

[0014] Figures 6 to 10 A schematic diagram of a manufacturing process of a micro-LED layout structure of a preferred embodiment of the present application.

[0015] It is to be understood that all drawings included herein are for illustrative purposes only, that the devices shown are examples of exemplary devices that can be implemented according to various embodiments and thus are not intended to limit the scope of the disclosure. When the description of the drawings discloses positioning of elements relative to one another and / or relative to an axis or plane, such descriptions are not intended to be specific as to relative position, unless specifically so stated. It is also to be understood that the figures can not be to scale.

[0016] Main element symbol explanation

[0017] 100 smartglasses

[0018] 102 lens

[0019] 102a intermediate region

[0020] 102b peripheral region

[0021] 104 frame

[0022] 106 temple

[0023] 108 cell array

[0024] 109 pitch

[0025] 110 display cell

[0026] 110a light transmissive region

[0027] 110b edge region

[0028] 114 micro light emitting diode

[0029] 116 mini array

[0030] 120 substrate

[0031] 122 first light transmissive layer

[0032] 124 pixel drive circuit

[0033] 126 metal interconnect structure

[0034] 128 second light transmissive layer

[0035] 130, 132 recess

[0036] 134 lens layer

[0037] 136, 138 microlens structure

[0038] 140 protective layer DETAILED DESCRIPTION

[0039] Now the exemplary embodiments of the present application will be described in detail below, which will show the described features with reference to the accompanying drawings in order for the reader to understand and realize the technical effects. It should be understood by the reader that the description herein is only by way of example, and is not intended to limit the present application. Various embodiments of the present application and various features in the embodiments that are not in conflict with each other can be combined or rearranged in various manners. Modifications, equivalents or improvements of the present application that are not departing from the spirit and scope of the present application can be understood by those skilled in the art, and are intended to be included in the scope of the present application.

[0040] It should be readily understood by the reader that the meanings of "on", "over", and "above" in the present application should be interpreted in a broad manner, such that "on" not only means "directly on" but also includes the meaning of "on" with intervening features or layers therebetween, and "over" or "above" not only means "over" or "above" but also can include the meaning of "over" or "above" without intervening features or layers therebetween (i.e., directly on).

[0041] In addition, spatially relative terms such as "beneath", "below", "lower", "above", "upper", and the like can be used herein for ease of description to describe one element's or feature's relationship to another element(s) or feature(s) as illustrated in the figures.

[0042] As used herein, the term "substrate" refers to a material to which a subsequent material is added. The substrate itself can be patterned. The material added on top of the substrate can be patterned or can remain unpatterned. In addition, the substrate can include a wide range of semiconductor materials, such as silicon, germanium, gallium arsenide, indium phosphide, etc. Alternatively, the substrate can be made of a non-conductive material such as glass, plastic, or sapphire wafer.

[0043] Reference will now be made to Figure 1, which is a schematic diagram of a smart glasses 100 with micro light emitting diode (micro LED) layout structure. The smart glasses 100 is composed of three parts, which are a lens 102, a frame 104 and a temple 106. Each lens 102 is defined with a peripheral region 102b at the edge of the lens and a middle region 102a surrounded by the peripheral region 102b. The middle region 102a is the transparent part of the lens, through which the wearer can receive the image light from the outside world. In the embodiment of the present application, the middle region 102a of the lens 102 is provided with an array of display units arranged by micro light emitting diodes, which can provide images or information that can be combined with and interacted with the real world scene in the operation of augmented reality (AR) or mixed reality (MR) on the lens. The peripheral region 102b of the lens 102 can be a non-transparent non-visible part, on which a light emitting diode driving circuit and a main logic circuit for the operation of the micro light emitting diodes can be arranged. Designing the light emitting diode driving circuit and the logic circuit on the periphery of the lens 102 can avoid these circuit elements from blocking the visible middle region 102a, thereby improving the overall light transmittance and visual experience of the lens.

[0044] Referring back to Figure 1 , the frame 104 of the smart glasses 100 is connected with the lens 102, and a small circuit board can be arranged inside the frame 104, such as a circuit board including a wireless communication module, a sensing module and a microphone component. A main circuit board can be arranged in the space of the temple 106 of the smart glasses 100, such as a circuit board including a microprocessor, a microsystem module and a speaker component, and can accommodate a relatively large energy supply battery component. The functional circuits or modules described above can be connected with the circuits on the peripheral region 102b of the lens 102 through the wiring in the frame 104, so as to display the images and information to be conveyed through the array of display units arranged by micro light emitting diodes on the lens 102. Furthermore, designing the functional circuits or modules on the frame 104 or the temple 106 parts with weight support can provide a good wearing experience.

[0045] Next, please refer to Figure 2 , which is a schematic diagram of a display unit with micro light emitting diodes according to a preferred embodiment of the present application. In the embodiment of the present application, the AR / MR interactive images or information are displayed on the lens by emitting image light through a plurality of display units 110. Each display unit 110 preferably has the same and regular shape, such as Figure 2square. In other embodiments, the display units 110 can also be rectangular or polygonal, as long as they can be arranged in a regular array of units on the middle region 102a of the lens 102. In embodiments of the present application, each display unit 110 has an edge region 110b at the edge and a light-transmissive region 110a surrounded by the edge region 110b. The light-transmissive region 110a of the display unit 110 is free of any components and can be considered as the body of the lens 102. The edge region 110b of the display unit 110 is provided with a plurality of micro-LEDs 114, which preferably surround the light-transmissive region 110a of the display unit 110. In preferred embodiments of the present application, the micro-LEDs 114 include red (R), green (G) and blue (B) micro-LEDs, each of which serves as a sub-pixel, and each group of adjacent red (R), green (G) and blue (B) micro-LEDs 114 forms a pixel, i.e. a full-color image point. The image light emitted by the pixels combines together to form the output image presented on the lens.

[0046] Next, please refer to Figure 3 which is a schematic diagram of an array of display units with micro-LEDs according to a preferred embodiment of the present application. In embodiments of the present application, a plurality of the aforementioned display units 110 are arranged in an array of units 108 on the middle region 102a of the lens 102. As Figure 3 shown, the array of units 108 is closely arranged with a small spacing 109 between each other. With such an arrangement, the micro-LEDs 114 are arranged in a mesh-like pattern on the lens, which forms an image output screen on the lens and can output AR / MR interactive images or information. On the other hand, the parts not provided with micro-LEDs 114, i.e. the light-transmissive regions 110a, serve as the light-transmissive parts of the lens, through which the person wearing the smart glasses can receive the image light from the outside.

[0047] According to the above features of the present application, the present application has the following advantages over the prior art. First, the micro-LEDs 114 of the present application are directly fabricated on the light-transmissive / visible region of the lens, unlike the prior art which mostly uses an interference waveguide to guide the image from an image output device provided outside the lens to the lens surface. The direct output of the image on the lens has a higher image resolution, no distortion, a wider field of view, and is more power-efficient. Furthermore, the design of the display unit 110 described above can leave a uniform and large area of light-transmissive region on the lens surface, so that the arrangement of the micro-LEDs does not affect the original light-transmissive property of the lens. The light transmittance can be greater than 50%, even up to 70%, while maintaining excellent image output quality.

[0048] Next, please refer to Figure 4Fig. 8 is a schematic diagram of a unit array with micro-LEDs according to another embodiment of the present application. The unit array 108 of this embodiment is similar to the aforementioned embodiments, except that the display units 110 in this embodiment are adjacent to each other without any gap therebetween.

[0049] Referring next to Figure 5 Fig. 9 is a schematic diagram of a unit array with micro-LEDs according to yet another embodiment of the present application. In this embodiment, the display units 110 are similar to the aforementioned embodiments, except that the micro-LEDs 114 are not arranged around the entire light-transmissive region 110a, but instead are arranged in a square mini-array 116 of four micro-LEDs 114 (e.g., a configuration of red (R), green (G), red (R), and blue (B)) on the edge region 110b of each display unit 110. Such a mini-array 116 of micro-LEDs 114 has the advantage that the micro-LEDs 114 are picked up and placed in groups of four during the mass transfer step, which improves the yield of the mass transfer step and reduces the time required for the mass transfer.

[0050] Referring next to Figures 6 to 10 Fig. 10 is a schematic diagram of a fabrication flow of a micro-LED layout structure according to a preferred embodiment of the present application. The fabrication process of the micro-LED layout structure of the present application can be integrated with the conventional complementary metal-oxide-semiconductor (CMOS) fabrication process. More specifically, the micro-LED layout structure of the present application can be formed on the lens together with the peripheral driving circuit and logic circuit in the same CMOS fabrication process, without the need to develop a new additional fabrication process or to affect the existing fabrication process, thereby saving a large amount of fabrication cost and development time.

[0051] Referring first to Figure 6 A substrate 120 is provided as the foundation for the entire fabrication process, such as a substrate composed of a semiconductor material suitable for the CMOS fabrication process, wherein the semiconductor material can be selected from the group consisting of silicon, germanium, silicon-germanium compound, silicon-carbon compound, and gallium arsenide. In the embodiment of the present application, the substrate 120 is defined with the aforementioned light-transmissive region 110a of the display unit 110 and the edge region 110b, wherein the light-transmissive region 110a will not have any elements disposed thereon, and the edge region 110b will be used to dispose the micro-LEDs and driving circuit of the present application, and the like. Next, the pixel driving circuit 124 and the metal interconnection structure 126, and the like, are fabricated on the edge region 110b of the substrate 120 by the conventional CMOS fabrication process. It is noted that in the embodiment of the present application, the pixel driving circuit 124 (including the gate element) can be fabricated on the peripheral region 102b (see Fig. 1) of the lens together with the pixel driving circuit 124 of the display unit 110, and the like, by the conventional CMOS fabrication process. Figure 1) and logic circuits are formed in the front-end-of-line (FEOL) of the CMOS process, and the pixel driving circuit 124 is electrically connected to the micro-LED driving circuits and logic circuits to receive and transmit the required image signals. Similarly, the metal interconnection structure 126 on the edge region 100b is formed in the back-end-of-line (BEOL) of the CMOS process simultaneously with the metal interconnection structure on the lens peripheral region 102b. The pixel driving circuit 124 can adopt a common cathode design, which is connected to the metal interconnection structure 126 through a contact. Both the pixel driving circuit 124 and the metal interconnection structure 126 can be formed in a first light-transmissive layer 122 on the substrate 120. The first light-transmissive layer 122 can include inter-layer dielectric (ILD) and inter-metal dielectric (IMD) layers on general logic elements, which can be formed on the substrate by a deposition process such as chemical vapor deposition (CVD) using an ultra low-k (ULK) material or tetraethoxysilane (TEOS). The material of the metal interconnection structure 126 can be selected from, but not limited to, tungsten (W), copper (Cu), aluminum (Al), titanium aluminum (TiAl), cobalt tungsten phosphide (CoWP), and the like.

[0052] Please refer to Figure 7 After the pixel driving circuit 124 and the metal interconnection structure 126 are formed on the edge region 110b, the micro-LED 114 is disposed on the first light-transmissive layer 122 and electrically connected to the metal interconnection structure 126 therein. In the embodiment of the present application, the micro-LED 114 is first fabricated on an LED substrate. Then, the individual micro-LED 114 is separated from the source substrate by a mass transfer fabrication process and placed on the substrate 120 to be connected to the corresponding metal interconnection structure 126, for example, by flip-chip bonding. In this way, the pixel driving circuit 124 can control the light emission of the micro-LED 114 through the metal interconnection structure 126.

[0053] Please refer to Figure 8After the micro-LEDs 114 are bonded, the fabrication of the microlens array is performed. A second transparent layer 128 is formed on the top surface of the micro-LEDs 114 and the first transparent layer 122. The second transparent layer 128 can be the same material as the first transparent layer 122, which can be a low dielectric constant material or tetraethoxysilane, formed on the first transparent layer 122 by a CVD process. The second transparent layer 128 covers and protects the micro-LEDs 114, and the subsequent fabrication process will fabricate the microlens structure on the second transparent layer 128. Then, a plurality of grooves 130, 132 are formed on the second transparent layer 128 by a photolithography process. In the embodiment of the present application, the grooves 130, 132 are arranged in an array on the surface of the transparent layer, and because the required microlens structure size of the micro-LEDs 114 and the transparent area 110a is different, the width and depth of the grooves 130, 132 formed on the transparent area 110a and the edge area 110b are also different. In the preferred embodiment of the present application, each groove 132 on the edge area 110b overlaps and corresponds to a micro-LED 114 arranged thereon.

[0054] Please refer to Figure 9 After the grooves 130, 132 are formed, a lens layer 134 is then formed on the second transparent layer 128. The material of the lens layer 134 can be a commonly used plastic optical material such as polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), cycloolefin polymer (COP), cyclic olefin copolymer (COC), etc., with a light transmittance of more than 90%, which covers the surface of the entire second transparent layer 128 and fills the grooves 130, 132. Then, an ultraviolet curing process is performed to cure and shrink the deposited lens layer 134, thereby forming the microlens structures 136, 138 as shown in the figure. In the embodiment of the present application, because the lens layer 134 forming the microlens structures 136, 138 is deposited in grooves 130, 132 with different widths and depths, the microlens structures 136, 138 formed after shrinkage have different curvatures, which can provide better visual balance. In the preferred embodiment of the present application, each microlens structure 138 on the edge area 110b corresponds to a micro-LED 114 (sub-pixel) below it. In other embodiments, it is also possible for one microlens structure 138 to correspond to multiple micro-LEDs 114, and the microlens structure 138 can also be a convex lens shape instead of a concave lens shape, depending on the requirements of the application.

[0055] Please refer to Figure 10After the microlens array is completed, a backgrinding process, such as a chemical mechanical planarization (CMP) process, is performed to thin the non-transparent substrate 120 to reduce its thickness and weight to suit the final lens product. Next, a photolithography process is performed to remove the substrate 120 of the transparent region 110a so that the front and back surfaces of the transparent region 110a are transparent. Finally, a protective layer 140, such as a transparent silicon oxide or silicon nitride layer, is coated on the back surface of the substrate 120 and the exposed first transparent layer 122, and the fabrication of the micro-LED layout structure of the present application is completed. The micro-LED layout structure described above can be directly used as the lens of smart glasses or attached to an additional transparent substrate for use.

[0056] The above description is only the preferred embodiments of the present application, and any equivalent changes and modifications made according to the claims of the present application shall be within the scope of the present application.

Claims

1. A micro-LED layout structure for augmented reality and mixed reality, comprising: a transparent substrate, the transparent substrate having a plurality of display units defined thereon arranged in a unit array; a plurality of micro-LEDs disposed at an edge region of each display unit and exposing a light-transmissive region surrounded by the edge region; and a pixel driving circuit disposed on the edge region directly below the micro-LEDs. 2.The micro-LED layout structure for augmented reality and mixed reality of claim 1, wherein the micro-LEDs enclose the entire light-transmissive region. 3.The micro-LED layout structure for augmented reality and mixed reality of claim 1, wherein the display units are adjacent to each other. 4.The micro-LED layout structure for augmented reality and mixed reality of claim 1, wherein the display units are spaced apart from each other by a distance. 5.The micro-LED layout structure for augmented reality and mixed reality of claim 1, wherein four of the micro-LEDs are arranged in a square mini-array, and the mini-arrays are disposed on the edge region of each display unit with a spacing between them. 6.The micro-LED layout structure for augmented reality and mixed reality of claim 1, wherein the transparent substrate is a lens having a peripheral region and a central region surrounded by the peripheral region, and the unit array is disposed on the central region. 7.The micro-LED layout structure for augmented reality and mixed reality of claim 6, further comprising a light-emitting diode driving circuit and a logic circuit disposed on the peripheral region and connected to the pixel driving circuit. 8.The micro-LED layout structure for augmented reality and mixed reality of claim 1, wherein the micro-LEDs comprise red (R), green (G), and blue (B) micro-LEDs, each of which serves as a sub-pixel, and each group of red (R), green (G), and blue (B) micro-LEDs constitutes a pixel. 9.A method for manufacturing a micro-LED layout structure for augmented reality and mixed reality, comprising: providing a substrate, wherein the substrate has a plurality of display units defined thereon arranged in a unit array, each of the display units comprising an edge region and a light-transmissive region surrounded by the edge region; forming a pixel driving circuit and a first light-transmissive layer on the edge region of each display unit on the substrate; and disposing a plurality of micro-LEDs on the first light-transmissive layer of the edge regions, the micro-LEDs being connected to the pixel driving circuit below. 10.The method for manufacturing a micro-LED layout structure for augmented reality and mixed reality of claim 9, further comprising: forming a second light-transmissive layer on the front surface of the micro-LEDs and the first light-transmissive layer; forming a plurality of recesses in the second light-transmissive layer, each of the micro-LEDs overlapping one of the recesses; forming a lens layer on the second light-transmissive layer, wherein the lens layer fills the recesses; and performing a curing manufacturing process on the lens layer to form a microlens structure on the lens layer in each of the recesses.

11. The method of claim 10, wherein the width and depth of the recesses on the light transmission region are different from the width and depth of the recesses on the edge region.

12. The method of claim 10, further comprising: thinning the substrate; removing the substrate on the light transmission region; and forming a protective layer on the back of the substrate and the light transmission layer.

13. The method of claim 12, wherein the first light transmission layer, the second light transmission layer, the microlens structure, and the protective layer form a lens having a peripheral region and a central region surrounded by the peripheral region, the micro-LEDs and the pixel driving circuit are located in the lens, and the unit array is disposed on the central region.

14. The method of claim 13, further comprising fabricating light-emitting diode driving circuits and logic circuits connected to the pixel driving circuit on the peripheral region.

15. The method of claim 14, wherein the light-emitting diode driving circuits and the logic circuits are formed in the same complementary metal-oxide-semiconductor fabrication process as the pixel driving circuit.

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