System and method for coaxial multi-color LED

Abstract

The preparation method of the single-pixel micro LED device for the display panel comprises the steps of providing a substrate with a pixel driver and preparing an LED structure layer stacked on the substrate. The method further comprises the step of bonding the substrate and the LED structural layer together through a bonding layer. The LED structural layer is electrically connected to the pixel driver through the key and layer. In some embodiments, prior to bonding a substrate to an LED structural layer, the method includes coating a reflective layer on the LED structural layer. In some embodiments, the method includes patterning an LED structure layer to form a red LED.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 62 / 863,559, filed on June 19, 2019, entitled “Systems and Methods for Coaxial Multi-Color LEDs,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a light emitting diode (LED) display device, and more particularly to a system and a method for manufacturing an LED semiconductor device capable of emitting light of different colors with high brightness and micrometer-level pixel size. Background Art

[0004] With the development of mini LED and micro LED technology in recent years, consumer devices and applications, such as augmented reality (AR), projection, head-up display (HUD), mobile device display, wearable device display and automotive display, require LED panels with improved resolution and brightness. For example, an AR display integrated into goggles and positioned close to the wearer's eyes can be only the size of a fingernail, while still requiring HD resolution (1280×720 pixels) or higher. Many electronic devices require specific pixel sizes, distances between adjacent pixels, brightness, and viewing angles for LED panels. Typically, when trying to achieve maximum resolution and brightness on a small display, it is challenging to maintain both resolution requirements and brightness requirements. On the contrary, in some cases, pixel size and brightness are difficult to balance at the same time because the two have an approximately opposite relationship. For example, making each pixel obtain high brightness will result in low resolution. And obtaining high resolution will reduce brightness.

[0005] Typically, at least red, green, and blue are superimposed to generate a variety of colors. In some cases, in order to include at least red, green, and blue in a pixel area, separate single-color LEDs are manufactured in different non-overlapping partitions within the pixel area. The prior art faces the challenge of increasing the effective illumination area within each pixel when the distance between adjacent LEDs is determined. On the other hand, when the illumination area of ​​a single LED is determined, further improving the overall resolution of the LED panel is also a difficult task because LEDs of different colors must occupy their designated partitions within a single pixel.

[0006] Active matrix liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays combined with thin film transistor (TFT) technology are becoming increasingly popular in today's commercial electronic devices. These displays are widely used in laptop computers, smart phones and personal digital assistants. Millions of pixels together produce an image on the display. TFTs are used as switches to turn each pixel on and off individually, making the pixel brighter or darker, which allows convenient and efficient control of each pixel and the entire display.

[0007] However, conventional LCD displays suffer from low light efficiency, resulting in high power consumption and limited battery operating time. Although active-matrix organic light-emitting diode (AMOLED) display panels generally consume less power than LCD panels, AMOLED display panels are still the most significant power consuming component in battery-powered devices. To extend battery life, reducing the power consumption of the display panel is a desirable approach.

[0008] Conventional inorganic semiconductor light emitting diodes (LEDs) have demonstrated excellent light efficiency, which makes active matrix LED displays more suitable for battery-powered electronic devices. Arrays of drive circuits and light emitting diodes (LEDs) are used to control millions of pixels to present images on the display. Both monochrome and full-color display panels can be produced according to various manufacturing methods.

[0009] However, integrating thousands or even millions of micro-LEDs with an array of pixel drive circuits is quite challenging. Various different manufacturing methods have been proposed. In one method, the control circuit is assembled on one substrate, and all the LEDs are assembled on another substrate. All the LEDs are transferred to an intermediate substrate and the original substrate is removed. Then, the LEDs on the intermediate substrate are picked up and placed one or a few at a time on the substrate assembled with the control circuit. However, this manufacturing process is inefficient, costly and has poor reliability. In addition, there are currently no ready-made production tools for transferring micro-LEDs in large quantities. Therefore, new tools must be developed.

[0010] In another method, the entire LED array and its original substrate are aligned with the control circuit and bonded to the control circuit using metal bonding. The substrate on which all the LEDs are located will be retained in the finished product, which may cause optical crosstalk. In addition, the thermal mismatch between the two different substrates will generate stress at the bonding interface, which may cause poor reliability problems. Furthermore, compared with monochrome display panels, multi-color display panels generally require more LEDs, and LEDs of different colors are grown on different substrate materials, making the traditional production process more complicated and inefficient.

[0011] Therefore, it would be desirable to provide an LED structure for a display panel that can solve the above-mentioned drawbacks. Summary of the invention

[0012] There is a need to improve the design of multi-color LEDs to improve and address the shortcomings of conventional display systems as described above. In particular, there is a need for an LED device structure that can simultaneously improve brightness and resolution while effectively maintaining low power consumption. The multi-color LED device described herein integrates at least three micro-LED structures that are vertically stacked by being placed in different layers of the device structure and receive control current using the same electrode. By aligning at least three LED structures along the same axis as disclosed herein, the system effectively enhances the light illumination efficiency within a single pixel area while improving the resolution of the LED panel.

[0013] Pitch refers to the distance between the centers of adjacent pixels on a display panel. In some embodiments, the pitch can vary from about 40 microns, to about 20 microns, to about 10 microns, and / or to a more ideal of about 5 microns or less. Many efforts have been made to reduce the pitch. Once the specification of the pitch is determined, the area of ​​a single pixel is fixed.

[0014] The multicolor coaxial LED system described in this article makes it possible to emit light mixed with different colors emitted by a single pixel area without the need for additional areas to accommodate LED structures with different colors. Therefore, the occupied area of ​​a single pixel is significantly reduced, and the resolution of the micro-LED panel can also be improved. At the same time, the concentration of different colors of light from the boundary of a micro-LED device greatly enhances the brightness within a single pixel area.

[0015] Compared with the traditional manufacturing process of micro LED display chips that rely on inefficient pick and place processes or low reliability multi-substrate methods, the multi-color micro LED manufacturing process disclosed in this article effectively improves the efficiency and reliability of micro LED device manufacturing. For example, the LED structure is directly bonded to the substrate with the pixel driver without introducing an intermediate substrate. In addition, the substrate of the micro LED structure is not retained in the final multi-color device, thereby reducing crosstalk and mismatch.

[0016] The multicolor micro-LED devices described in this article can improve both brightness and resolution, making them suitable for modern display panels, especially for high-definition AR devices and virtual reality (VR) glasses.

[0017] In one embodiment, a single-pixel multicolor micro-light-emitting diode (LED) device for a display panel includes: a substrate; two or more LED structure layers, including: a first LED structure layer stacked on top of the substrate; and a second LED structure layer stacked on top of the first LED structure layer. In some cases, the first LED structure layer and the second LED structure layer substantially overlap each other laterally, forming an optical path to mix the light emitted by the first LED structure layer and the second LED structure layer.

[0018] In some embodiments, the two or more LED structure layers in the single-pixel multi-color micro-LED device further include: a third LED structure layer stacked on top of the second LED structure layer. In some cases, the third LED structure layer substantially overlaps the first LED structure layer and the second LED structure layer laterally to form an optical path and then add light emitted by the third LED structure layer.

[0019] In some embodiments, the single-pixel multi-color micro LED device also includes: a first bonding layer located between the substrate and the first LED structure layer; a second bonding layer located between the first LED structure layer and the second LED structure layer; and a third bonding layer located between the second LED structure layer and the third LED structure layer.

[0020] In some embodiments of the single-pixel multicolor micro-LED device, the first bonding layer is approximately 0.1 micron to 3 microns, the second bonding layer is approximately 0.1 micron to 5 microns, and the third bonding layer is approximately 0.1 micron to 5 microns. In some embodiments, the second and third bonding layers are transparent.

[0021] In some embodiments, the substrate of the single-pixel multi-color micro LED device supports a pixel driver, and the first, the second, and the third LED structure layers are electrically connected to the pixel driver, respectively.

[0022] In some embodiments, the pixel driver comprises a thin film transistor pixel driver or a silicon CMOS pixel driver.

[0023] In some embodiments, the single-pixel multi-color micro LED device also includes: a first reflective layer located between the substrate and the first LED structure layer; a second reflective layer located between the first LED structure layer and the second LED structure layer; and a third reflective layer located between the second LED structure layer and the third LED structure layer.

[0024] In some embodiments of the single-pixel multi-color micro-LED device, at least one of the first, second and third reflective layers includes a distributed Bragg reflector (DBR) structure; and each of the first, second and third reflective layers is approximately 0.1 microns to 5 microns.

[0025] In some embodiments of the single-pixel multi-color micro LED device, the first light emitted by the first LED structure layer propagates through the second LED structure layer and the third LED structure layer, and the second light emitted by the second LED structure layer propagates through the third LED structure layer.

[0026] In some embodiments of the single-pixel multi-color micro-LED device, each of the first, second, and third LED structure layers includes: an epitaxial structure forming an LED in the corresponding LED structure layer; a lower conductive layer electrically connected to the bottom of the LED; and an upper conductive layer electrically connected to the top of the LED. In some cases, the lower conductive layer is also electrically connected to the pixel driver, and the upper conductive layer is also electrically connected to a common electrode.

[0027] In some embodiments of the single-pixel multi-color micro-LED device, the epitaxial structure of each of the first, the second and the third LED structure layers is selected from one or more of the following structures: III-V nitride epitaxial structure, III-V arsenide epitaxial structure, III-V phosphide epitaxial structure and III-V antimonide epitaxial structure.

[0028] In some embodiments of the single-pixel multi-color micro-LED device, the lower conductive layer and the upper conductive layer of each of the first, second and third LED structure layers include an indium tin oxide (ITO) layer, and each of the ITO layers is approximately 0.01 microns to 1 micron.

[0029] In some embodiments, the single-pixel multi-color micro LED device also includes: an anode metal contact pad electrically connected to the lower conductive layer of each of the first, second and third LED structure layers; a first cathode metal contact pad electrically connected to the upper conductive layer of the first LED structure layer; a second cathode metal contact pad electrically connected to the upper conductive layer of the second LED structure layer; and a third cathode metal contact pad electrically connected to the upper conductive layer of the third LED structure layer.

[0030] In some embodiments of the single-pixel multi-color micro LED device, the anode metal contact pad and the cathode metal contact pad are composed of one or more of the following metals: aluminum, silver, rhodium, zinc, gold, germanium, nickel, chromium, platinum, tin, copper, tungsten, indium tin oxide, palladium, indium, and titanium.

[0031] In some embodiments of the single-pixel multi-color micro LED device, the epitaxial structure of each of the first, second, and third LED structure layers is approximately 0.3 microns to 5 microns.

[0032] In some embodiments of the single-pixel multi-color micro LED device, the LEDs in the different LED structure layers generate light of different wavelengths.

[0033] In some embodiments of the single-pixel multi-color micro LED device, the LEDs in the different LED structure layers generate visible light of different wavelengths.

[0034] In some embodiments of the single-pixel multi-color micro-LED device, the LEDs in the different LED structure layers are ultraviolet, blue, green, orange, red, or infrared micro-LEDs.

[0035] In some embodiments of the single-pixel multi-color micro LED device, the first LED structure layer forms a red LED; the second LED structure layer forms a green LED; and the third LED structure layer forms a blue LED.

[0036] In some embodiments of the single-pixel multi-color micro-LED device, the longest dimension of the single-pixel multi-color micro-LED device is approximately 1 micron to 500 microns.

[0037] In some embodiments of the single-pixel multi-color micro LED device, the single-pixel multi-color micro LED device has a pyramidal cross-sectional shape with a bottom layer having the longest lateral dimension and a top layer having the shortest lateral dimension.

[0038] In some embodiments of the single-pixel multi-color micro LED device, the single-pixel multi-color micro LED device has an external quantum efficiency of not less than 20%.

[0039] In another embodiment, a micro-LED display chip includes: a substrate supporting a pixel driver array; and a single-pixel multi-color micro-light emitting diode (LED) device array, each of the single-pixel multi-color LED devices including: two or more LED structure layers stacked on top of the substrate and the pixel driver, wherein there is a bonding layer between adjacent LED structure layers, each of the LED structure layers also includes an epitaxial structure for forming a micro-LED, and the micro-LED is configured to generate monochromatic light. In some cases, the single-pixel multi-color LED array is electrically connected to the pixel driver array and a common electrode, two or more of the LED structure layers overlap each other laterally to form a light propagation path through the micro-LEDs directly stacked together, and the micro-LEDs in different LED structure layers generate light of different wavelengths.

[0040] In some embodiments of the micro LED display chip, the common electrode includes separate common electrode structures respectively used for the micro LEDs generating light of the same color in each of the LED structure layers.

[0041] In yet another embodiment, a method for manufacturing a single-pixel three-color micro-light-emitting diode (LED) device for a display panel includes: providing a substrate; manufacturing a first LED structure layer stacked on top of the substrate; manufacturing a second LED structure layer stacked on top of the first LED structure layer; and manufacturing a third LED structure layer stacked on top of the second LED structure layer. In some cases, the first LED structure layer, the second LED structure layer, and the third LED structure layer substantially overlap each other laterally, forming an optical path to mix the light emitted by the first LED structure layer, the second LED structure layer, and the third LED structure layer.

[0042] In some embodiments, the manufacturing method of the single-pixel three-color micro LED device also includes: bonding the substrate and the first LED structure layer together through a first bonding layer; bonding the first LED structure layer and the second LED structure layer together through a second bonding layer; and bonding the second LED structure layer and the third LED structure layer together through a third bonding layer.

[0043] In some embodiments of the method for manufacturing the single-pixel three-color micro LED device, the first bonding layer includes one or more selected from the following bonding structures: Au-Au bonding, Au-Sn bonding, Au-In bonding, Ti-Ti bonding and Cu-Cu bonding.

[0044] In some embodiments of the manufacturing method of the single-pixel three-color micro LED device, the second bonding layer and the third bonding layer both include one or more bonding materials selected from the following: transparent plastic (resin), SiO2, spin-on glass (SOG), and Micro Resist's bonding adhesive BCL-1200.

[0045] In some embodiments of the method for manufacturing a single-pixel three-color micro-LED device, the first bonding layer is approximately 0.1 micron to 3 microns, the second bonding layer is approximately 0.1 micron to 5 microns, and the third bonding layer is approximately 0.1 micron to 5 microns. In some cases, the second bonding layer and the third bonding layer are transparent.

[0046] In some embodiments, the manufacturing method of the single-pixel three-color micro LED device also includes: before the substrate is bonded to the first LED structure layer, coating a first reflective layer on the first LED structure layer; before the first LED structure layer is bonded to the second LED structure layer, coating a second reflective layer on the first LED structure layer; and before the second LED structure layer is bonded to the third LED structure layer, coating a third reflective layer on the second LED structure layer.

[0047] In some embodiments, the method for manufacturing the single-pixel three-color micro-LED device further includes: forming a distributed Bragg reflector (DBR) structure for each of the first, second, and third reflective layers. In some embodiments, the first, second, and third reflective layers are each approximately 0.1 microns to 5 microns.

[0048] In some embodiments of the method for manufacturing the single-pixel three-color micro LED device, the substrate supports the pixel driver, and each of the first, second, and third LED structure layers is electrically connected to the pixel driver.

[0049] In some embodiments, the method for manufacturing the single-pixel three-color micro-LED device further includes: performing the following on each of the first, second, and third LED structure layers including the epitaxial structure: imaging the epitaxial structure to form an LED within the corresponding LED structure layer; coating a lower conductive layer and electrically connecting it to the bottom of the LED; and coating an upper conductive layer and electrically connecting it to the top of the LED. In some cases, the lower conductive layer is also electrically connected to the pixel driver, and the upper conductive layer is also electrically connected to a common electrode.

[0050] In some embodiments of the manufacturing method of the single-pixel three-color micro-LED device, the epitaxial structure of each of the first, the second and the third LED structure layers is selected from one or more of the following structures: III-V nitride epitaxial structure, III-V arsenide epitaxial structure, III-V phosphide epitaxial structure and III-V antimonide epitaxial structure.

[0051] In some embodiments of the manufacturing method of the single-pixel three-color micro-LED device: the lower conductive layer and the upper conductive layer of each of the first, second and third LED structure layers include an indium tin oxide (ITO) layer, and each of the ITO layers is approximately 0.01 microns to 1 micron.

[0052] In some embodiments, the manufacturing method of the single-pixel three-color micro-LED device also includes: coating an anode metal contact pad electrically connected to the lower conductive layer of each of the first, second and third LED structure layers; coating a first cathode metal contact pad electrically connected to the upper conductive layer of the first LED structure layer; coating a second cathode metal contact pad electrically connected to the upper conductive layer of the second LED structure layer; and coating a third cathode metal contact pad electrically connected to the upper conductive layer of the third LED structure layer.

[0053] In some embodiments of the method for manufacturing the single-pixel three-color micro-LED device, the epitaxial structure of each of the first, second, and third LED structure layers is approximately 0.3 microns to 5 microns.

[0054] In some embodiments of the method for manufacturing the single-pixel three-color micro-LED device, the LEDs in different LED structure layers generate light of different wavelengths.

[0055] In some embodiments of the method for manufacturing the single-pixel three-color micro-LED device, the LEDs in different LED structure layers generate visible light of different wavelengths.

[0056] In some embodiments of the method for manufacturing the single-pixel three-color micro-LED device, the LEDs in different LED structure layers are ultraviolet, blue, green, orange, red or infrared micro-LEDs.

[0057] In some embodiments, the manufacturing method of the single-pixel three-color micro LED device also includes: imaging the first LED structure layer to form a red light LED; imaging the second LED structure layer to form a green light LED; and imaging the third LED structure layer to form a blue light LED.

[0058] The compact design of the multicolor LED device and system disclosed herein utilizes the lateral overlap of the light-emitting LED structure, thereby improving the luminous efficiency, resolution, and overall performance of the LED display system. In addition, the manufacture of the multicolor LED display system can reliably and efficiently pattern the LED structure without using or retaining additional substrates. Therefore, compared with the use of traditional LEDs, the implementation of the multicolor LED display system can meet the stringent display requirements of AR and VR, head-up displays (HUD), mobile device displays, wearable device displays, high-definition small projectors, and automotive displays.

[0059] It should be noted that the various embodiments described above may be combined with any other embodiments described herein. The features and advantages described in the specification are not all inclusive, and in particular, many additional features and advantages will be apparent to one of ordinary skill in the art in view of the drawings, the specification, and the claims. Furthermore, it should be noted that the language used in the specification is primarily selected for readability and instructional purposes, and may not be selected to describe or limit the subject matter of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to be able to understand the present disclosure in more detail, a more specific description may be made with reference to the features of various embodiments, some of which are illustrated in the accompanying drawings. However, the accompanying drawings only illustrate the relevant features of the present disclosure and are therefore not to be considered restrictive, as the description may admit other effective features.

[0061] Figure 1 is a cross-sectional view of a single-pixel three-color coaxial LED device 100 according to some embodiments.

[0062] Figure 2A is a cross-sectional view of a multi-layer structure 200 for forming a three-color coaxial LED device according to some embodiments.

[0063] Figure 2B is a cross-sectional view of a tri-color coaxial LED device 250 after the manufacturing process is completed according to some embodiments.

[0064] Figure 3 is a circuit diagram of a matrix of three-color LED devices 300 according to some embodiments.

[0065] Figure 4 is a flow chart of a method 400 of manufacturing a three-color coaxial LED device according to some embodiments.

[0066] Figure 5 is a top view of a micro LED display panel 500 according to some embodiments.

[0067] According to common practice, the various features shown in the drawings may not be drawn to scale. Therefore, for the sake of clarity, the sizes of the various features may be arbitrarily expanded or reduced. In addition, some drawings may not describe all the components of a given system, method or device. Finally, throughout the specification and drawings, the same reference numerals may be used to represent the same features. DETAILED DESCRIPTION

[0068] Numerous details are described herein to provide a thorough understanding of the example embodiments shown in the accompanying drawings. However, some embodiments may be practiced without many of the specific details, and the scope of the claims is limited only by those features and aspects specifically recited in the claims. In addition, well-known processes, components, and materials are not described in detail so as not to unnecessarily obscure the relevant aspects of the embodiments described herein.

[0069] Figure 1 1 is a cross-sectional view of a single-pixel three-color coaxial LED device 100 according to some embodiments. In some embodiments, the three-color coaxial LED device includes a substrate 102. For convenience, "upward" is used to indicate a direction away from the substrate 102, and "downward" is used to indicate a direction toward the substrate 102, and other directional terms such as top, bottom, above, below, under, below, etc. are interpreted accordingly. The supporting substrate 102 is a substrate on which an array of individual drive circuits 104 is mounted. In some embodiments, the drive circuit can also be located in one of the layers above the substrate 102, or above the micro three-color LED structure 100. Each drive circuit is a pixel driver 104. In some cases, the pixel driver is a thin film transistor pixel driver or a silicon CMOS pixel driver. In one embodiment, the substrate 102 is a silicon substrate. In another embodiment, the supporting substrate 102 is a transparent substrate, such as a glass substrate. Examples of other substrates include GaAs substrates, GaP substrates, InP substrates, SiC substrates, ZnO substrates, and sapphire substrates. The driving circuit 104 forms a single pixel driver to control the operation of a single single pixel three-color coaxial LED device 100. The circuit on the substrate 102 includes contacts connected to each individual pixel driver 104 and a ground contact. Each micro three-color LED structure 100 also has two types of contacts: a P electrode or anode connected to the pixel driver, such as 120; and an N electrode or cathode connected to the ground (e.g., a common electrode), such as 122, 124, and 126.

[0070] Although some features are described herein with the term "layer", it should be understood that these features are not limited to a single layer, but may include multiple sub-layers. In some cases, a "structure" may take the form of a "layer".

[0071] In some embodiments, three LED structures including three epitaxial layers 108, 112, and 116 form a stacked structure, for example, the green LED epitaxial layer 112 is directly on top of the red LED epitaxial layer 108, and the blue LED epitaxial layer 112 is directly on top of the green epitaxial layer 112. In some embodiments, light emitted by the red epitaxial layer 108 can propagate through the green epitaxial layer 112, then through the blue epitaxial layer 116, and be emitted from the three-color LED device 100. In some embodiments, light emitted by the green epitaxial layer 112 can propagate through the blue epitaxial layer 116 and be emitted from the three-color LED device 100. In some embodiments, one LED structure includes many epitaxial sub-layers with different compositions. Examples of LED epitaxial structures include III-V nitride epitaxial structures, III-V arsenide epitaxial structures, III-V phosphide epitaxial structures, and III-V antimonide epitaxial structures. Examples of micro-LEDs include GaN-based UV / blue / green micro-LEDs, AlInGaP-based red / orange micro-LEDs, and GaAs or InP-based infrared (IR) micro-LEDs.

[0072] In some embodiments, each layer of the stacked LED structure can be controlled individually to generate its own light. In some embodiments, since all LED epitaxial layers in the tri-color coaxial LED device 100 work simultaneously, the mixed light emitted from the top LED epitaxial layer can change the color of a single pixel on the display panel within a small footprint.

[0073] In some embodiments, according to the design of the coaxial LED device 100, the color of the light emitted by the LED structure in the same device is not limited to red, green and blue. For example, a suitable color can be selected from visible light with a wavelength between 380 nanometers and 700 nanometers. In some embodiments, the LED structure can emit other light belonging to the invisible light range, such as ultraviolet light and infrared light. For example, the three colors from bottom to top can be red, green and blue. In another embodiment, the three color selections from bottom to top can be ultraviolet, orange and infrared. In some embodiments, the wavelength of the light emitted by the LED structure on a certain layer of the device 100 must be longer than the wavelength of the light emitted by the LED structure on the layer at the top of the layer. For example, the wavelength of the light emitted by the bottom epitaxial layer 108 is longer than the wavelength of the light emitted by the middle epitaxial layer 112, and the wavelength of the light emitted by the middle epitaxial layer 112 is longer than the wavelength of the light emitted by the top epitaxial layer 116. In some embodiments, the wavelength of the light emitted by the LED structure on a certain layer of the device 100 must be shorter than the wavelength of the light emitted by the LED structure on the layer at the top of the layer. For example, the wavelength of light emitted by the bottom epitaxial layer 108 is shorter than the wavelength of light emitted by the middle epitaxial layer 112 , and the wavelength of light emitted from the middle epitaxial layer 112 is shorter than the wavelength of light emitted by the top epitaxial layer 116 .

[0074] In some embodiments, the insulating layer 128 covers the top surface and edge sidewalls of the tri-color LED structure. In some embodiments, a P electrode 120 is placed on one side of the tri-color LED device 100 to connect the red LED structure, the green LED structure, and the blue LED structure. In some embodiments, separate N electrodes are placed to connect the red LED structure, the green LED structure, and the blue LED structure, respectively. For example, the N electrode 126 is connected to the red LED structure including the LED epitaxial layer 108. The N electrode 124 is connected to the green LED structure including the LED epitaxial layer 112. The N electrode 122 is connected to the blue LED structure including the LED epitaxial layer 116.

[0075] In some embodiments, the bottom epitaxial layer 108 is bonded to the substrate via a metal bonding layer 106. In some embodiments, the metal bonding layer 106 can also serve as a reflector to reflect light emitted from the upper LED structure. In some embodiments, the middle epitaxial layer 112 is bonded to the bottom epitaxial layer 108 via a first transparent bonding layer 110. In some embodiments, the top epitaxial layer 116 is bonded to the middle epitaxial layer 112 via a second transparent bonding layer 114. In some embodiments, the transparent bonding layer can facilitate the light emitted by the layer below the bonding layer to pass through.

[0076] In some embodiments, a reflective layer is formed between the LED epitaxial layers to improve light emission efficiency, which will be further described below. In some embodiments, a conductive transparent layer is formed between the LED epitaxial layers to improve conductivity and transmittance.

[0077] Figure 2A is a cross-sectional view of a multilayer structure 200 for forming a tri-color coaxial LED device according to some embodiments. More specifically, Figure 2A The multiple layers of a three-color coaxial LED device fabricated on a substrate are shown.

[0078] like Figure 2AAs shown, substrate 202 supports pixel driver 204. In some embodiments, substrate 202 is made of silicon and has a thickness of about 700 microns. In one method, a metal (bonding) layer 206 is grown on substrate 202. Metal (bonding) layer 206 may include an ohmic contact layer and a metal bonding layer. In some embodiments, the thickness of metal (bonding) layer 206 is about 0.1 micron to 3 microns. In some cases, metal (bonding) layer 206 includes two metal layers. One of the metal layers is deposited on epitaxial layer 210 or on reflective layer 208, and the epitaxial layer 210 or reflective layer 208 is directly located above metal (bonding) layer 206. The corresponding metal bonding layer is also deposited on substrate 202 with pixel driver 204. In some embodiments, the composition for metal (bonding) layer 206 includes Au-Au bonding, Au-Sn bonding, Au-In bonding, Ti-Ti bonding, Cu-Cu bonding, or a mixture thereof. For example, if Au-Au bonding is selected, each of the two Au layers requires a Cr coating as an adhesive layer and a Pt coating as an anti-diffusion layer. The Pt coating is located between the Au layer and the Cr layer. The Cr layer and the Pt layer are positioned at the top and bottom of the two bonded Au layers. In some embodiments, when the thickness of the two Au layers is approximately the same, under high pressure and high temperature, the Au on the two layers diffuse mutually to bond the two layers together. Eutectic bonding, thermal compression bonding, and transient liquid phase (TLP) bonding are example techniques that can be used.

[0079] In some embodiments, epitaxial layer 210 is bonded on top of the existing structure of substrate 202 with pixel driver 204 through metal (bonding) layer 206. In one approach, epitaxial layer 210 is grown on another separate substrate (referred to as epitaxial substrate). The epitaxial substrate is removed after bonding, for example by laser lift-off process or wet chemical etching to remove the epitaxial substrate, leaving Figure 2A The structure shown in .

[0080] In some embodiments, the reflective layer 208 is coated on the epitaxial layer 210 before bonding. After bonding, the reflective layer 208 is located between the metal (bonding) layer 206 and the epitaxial layer 210. In some cases, the thickness of the reflective layer 208 is about 0.1 microns to 5 microns. In some embodiments, the reflective layer 208 includes a distributed Bragg reflector (DBR) structure. For example, the reflective layer 208 is formed by a plurality of layers alternately formed by materials with different refractive indices, or a plurality of layers of different materials with different refractive indices. In some cases, the boundary of each layer of the DBR structure causes partial reflection of the light wave. The reflective layer 208 can be used to reflect some selected wavelengths of light, such as red light. In some embodiments, the reflective layer 208 is made of multiple layers of SiO2 and Ti3O5. By changing the thickness and number of each SiO2 and Ti3O5 layer, selective reflection or transmission of light of different wavelengths can be formed. In some embodiments, the reflective layer 208 for red LEDs includes multiple layers of Au or / and indium tin oxide (ITO).

[0081] In some embodiments, the reflective layer 208 for the red LED structure has a low absorbance (e.g., equal to or less than 5%) for the light generated by the different layers of the tri-color LED device. In some embodiments, the reflective layer 208 for the red LED structure has a high reflectivity (e.g., equal to or greater than 95%) for the light generated above the reflective layer, such as red light, green light, and blue light.

[0082] In some embodiments, epitaxial layer 210 is used to form a red micro-LED. Examples of red LED epitaxial structures include III-V nitride epitaxial structures, III-V arsenide epitaxial structures, III-V phosphide epitaxial structures, and III-V antimonide epitaxial structures. In some cases, the film within the red LED epitaxial layer 210 may include a layer of P-type GaP / P-type AlGaInP light-emitting layer / AlGaInP / N-type AlGaInP / N-type GaAs. In some embodiments, the P-type is typically Mg-doped, while the N-type is typically Si-doped. In some examples, the thickness of epitaxial layer 210 is approximately 0.3 microns to 5 microns.

[0083] In some embodiments, an indium tin oxide (ITO) layer 212 and a transparent conductive oxide are provided above the epitaxial layer 210. In some embodiments, the thickness of the ITO layer 212 is about 0.01 microns to 1 micron. In some cases, the ITO layer 212 is deposited on the epitaxial layer 210 before any bonding process with the next epitaxial layer, generally by vapor deposition, such as electron beam evaporation or sputtering deposition. In some examples, the ITO layer is used to maintain good conductivity of the electrode connection, and in some cases, improves the optical properties of the LED device, such as reflectivity or transmittance.

[0084] In some embodiments, before the bonding process with the next epitaxial layer is performed, the second reflective layer 214 is coated on the ITO layer 212. In some cases, the thickness of the reflective layer 214 is about 0.1 microns to 5 microns. In some embodiments, the reflective layer 214 includes a DBR structure. For example, the reflective layer 214 is formed by a plurality of layers alternately formed by materials with different refractive indices, or a plurality of layers of different materials with different refractive indices. In some cases, the boundary of each layer of the DBR structure causes partial reflection of the light wave. The reflective layer 214 can be used to reflect some selected wavelengths of light, such as green light. In some embodiments, the reflective layer 214 is made of a plurality of layers of SiO2 and Ti3O5. By changing the thickness and quantity of each SiO2 and Ti3O5 layer, selective reflection or transmission of light of different wavelengths can be formed.

[0085] In one example, the following DBR structure shown in Table 1 is used to reflect green light emitted by a green LED:

[0086] Table 1: DBR layer structure of green LED reflector layer.

[0087]

[0088]

[0089] In some embodiments, the reflective layer 214 for the green LED structure has a low absorbance (e.g., equal to or less than 5%) for the light generated by different layers of the tri-color LED device. In some embodiments, the reflective layer 214 for the green LED structure has a high reflectance (e.g., equal to or greater than 95%) for the light generated above the reflective layer, such as green light and blue light.

[0090] In some embodiments, the second epitaxial layer 220 is bonded on top of the first epitaxial layer 210 via a transparent bonding layer 216. In one approach, the second epitaxial layer 220 is grown on another separate substrate (referred to as an epitaxial substrate). The epitaxial substrate is removed after bonding, for example, by a laser lift-off process or wet chemical etching to remove the epitaxial substrate, leaving Figure 2A The structure shown in .

[0091] In some embodiments, the transparent bonding layer 216 is made of transparent plastic (resin) or SiO2, such as spin-on glass (SOG), bonding adhesive BCL-1200 from Micro Resist, etc. The thickness of the transparent bonding layer 216 is about 0.1 micrometer to 5 micrometers.

[0092] In some embodiments, the second epitaxial layer 220 is used to form a green micro LED. Examples of green LED epitaxial structures include III-V nitride epitaxial structures, III-V arsenide epitaxial structures, III-V phosphide epitaxial structures, and III-V antimonide epitaxial structures. In some cases, the film within the green LED epitaxial layer 220 may include a layer of P-type GaN / InGaN light-emitting layer / N-type GaN. In some embodiments, the P-type is typically Mg-doped, while the N-type is typically Si-doped. In some examples, the thickness of the second epitaxial layer 220 is approximately 0.3 microns to 5 microns.

[0093] In some embodiments, the ITO layer 218 is deposited on the second epitaxial layer 220 before bonding. After bonding, the ITO layer 218 is located between the transparent bonding layer 216 and the second epitaxial layer 220. In some embodiments, the thickness of the ITO layer 218 is about 0.01 micrometers to 1 micrometers.

[0094] In some embodiments, before the bonding process with the next epitaxial layer, another ITO layer 222 is deposited on top of the second epitaxial layer 220. In some embodiments, the thickness of the ITO layer 218 is about 0.01 micrometers to 1 micrometer.

[0095] In some embodiments, before bonding with the next epitaxial layer, the third reflective layer 224 is coated on the ITO layer 222. In some cases, the thickness of the reflective layer 224 is about 0.1 micron to 5 microns. In some embodiments, the reflective layer 224 includes a DBR structure. For example, the reflective layer 224 is formed by a plurality of layers alternately formed by materials with different refractive indices, or a plurality of layers of different materials with different refractive indices. In some cases, each layer boundary of the DBR structure may cause partial reflection of light waves. The reflective layer 224 may be used to reflect some selected wavelengths of light, such as blue light. In some embodiments, the reflective layer 224 is made of a plurality of layers of SiO2 and Ti3O5. By changing the thickness and quantity of each SiO2 and Ti3O5 layer, selective reflection or transmission of light of different wavelengths may be formed.

[0096] In one example, the following DBR structure shown in Table 2 is used to reflect blue light emitted by a blue LED:

[0097] Table 2: DBR layer structure of blue LED reflector layer.

[0098]

[0099] In some embodiments, the reflective layer 224 for the blue LED structure has a low absorbance (e.g., equal to or less than 5%) for light generated by different layers of the tri-color LED device. In some embodiments, the reflective layer 224 for the blue LED structure has a high reflectance (e.g., equal to or greater than 95%) for light generated above the reflective layer, such as blue light.

[0100] In some embodiments, the third epitaxial layer 230 is bonded on top of the second epitaxial layer 220 via a transparent bonding layer 226. In one approach, the third epitaxial layer 230 is grown on another separate substrate (referred to as an epitaxial substrate). The epitaxial substrate is removed after bonding, for example, by a laser lift-off process or wet chemical etching to remove the epitaxial substrate, leaving Figure 2A The structure shown in .

[0101] In some embodiments, the transparent bonding layer 226 is made of transparent plastic (resin) or SiO2, such as spin-on glass (SOG), bonding adhesive BCL-1200 from Micro Resist, etc. The thickness of the transparent bonding layer 226 is about 0.1 micrometer to 5 micrometers.

[0102] In some embodiments, the third epitaxial layer 230 is used to form a blue micro-LED. Examples of blue LED epitaxial structures include III-V nitride epitaxial structures, III-V arsenide epitaxial structures, III-V phosphide epitaxial structures, and III-V antimonide epitaxial structures. In some cases, the film within the blue LED epitaxial layer 230 may include a layer of P-type GaN / InGaN light-emitting layer / N-type GaN. In some embodiments, the P-type is typically Mg-doped, while the N-type is typically Si-doped. In some examples, the thickness of the third epitaxial layer 230 is approximately 0.3 microns to 5 microns.

[0103] In some embodiments, the ITO layer 228 is deposited on the third epitaxial layer 230 before bonding. After bonding, the ITO layer 228 is located between the transparent bonding layer 226 and the third epitaxial layer 230. In some embodiments, the thickness of the ITO layer 228 is about 0.01 micrometers to 1 micrometers.

[0104] In some embodiments, another ITO layer 232 is deposited on top of the third epitaxial layer 230. In some embodiments, the thickness of the ITO layer 232 is about 0.01 micrometers to about 1 micrometer.

[0105] Figure 2B is a cross-sectional view of a tri-color coaxial LED device 250 after the manufacturing process is completed according to some embodiments. More specifically, Figure 2B Also shown is the three-color coaxial LED device 250 after some additional manufacturing processes, particularly the patterning process of the multilayer structure 200, are completed.

[0106] In some embodiments, a three-color LED structure is formed by dry etching and wet etching, and the axes of the LED structures of different colors are aligned vertically with each other. In some embodiments, LED structures of different colors share the same axis. In some embodiments, LED structures of different colors form a pyramid shape or a trapezoidal cross-section shape, wherein the lateral dimension of the bottom LED structure is the longest and the lateral dimension of the top LED structure is the shortest. Each layer is narrower in width or smaller in area than the layer below it. In this case, the width or area is measured by the size of a plane parallel to the surface of the substrate 202. In some embodiments, the bottom layer, such as the metal (bonding) layer 206, has a lateral dimension of about 1 micron to 500 microns. The pyramid shape will improve the electrical connection between each LED structure and the electrode and simplify the manufacturing process. For example, the electrode connection points in each layer are not blocked, and the connection is convenient.

[0107] In some embodiments, when the lateral dimension of a layer changes, the aspect ratio of the cross section of the layer of the tri-color LED device remains substantially the same. For example, when the lateral dimension of the patterned epitaxial layer is 5 microns, the thickness of the patterned epitaxial layer is less than 1 micron. In another example, when the lateral dimension of a patterned epitaxial layer increases, the thickness of the patterned epitaxial layer is also increased accordingly to maintain the aspect ratio unchanged. In some embodiments, the aspect ratio of the cross section of the epitaxial layer and other layers is thickness / width less than 1 / 5.

[0108] The shape of the LED device is not limited, and in some other embodiments, the cross-sectional shape of the tri-color coaxial LED device can take other shapes, such as an inverted trapezoid, a semi-ellipse, a rectangle, a parallelogram, a triangle or a hexagon, etc.

[0109] In some embodiments, when Figure 2A After the layers are formed, the top ITO layer 232 located above the third epitaxial layer 230 is patterned using photolithography and etching. In some cases, the etching method used for patterning is dry etching, such as inductively coupled plasma (ICP) etching, or wet etching using an ITO etching solution. In some embodiments, the same patterning method can be applied to all other ITO layers, including the ITO layers 212, 218, 222, and 228 within the structure 200.

[0110] In some embodiments, blue LED epitaxial layer 230 and green LED epitaxial layer 220 are patterned using photolithography and etching. In some cases, the etching method used for patterning is dry etching, such as inductively coupled plasma (ICP) etching using Cl2 and BCl3 etching gases.

[0111] In some embodiments, the transparent bonding layer including 216 and 226 is patterned using photolithography and etching. In some cases, the etching method used for patterning is dry etching, such as inductively coupled plasma (ICP) etching using CF4 and O2 etching gases.

[0112] In some embodiments, photolithography and etching are used to pattern the reflective layers including 208, 214, and 224. In some cases, the etching method used to pattern the reflective layer, especially the DBR layer, is dry etching, such as inductively coupled plasma (ICP) etching using CF4 and O2 etching gases, or ion beam etching (IBE) using Ar gas.

[0113] In some embodiments, photolithography and etching are used to pattern the red LED epitaxial layer 210. In some cases, the etching method used for patterning is dry etching, such as inductively coupled plasma (ICP) etching using Cl2 and HBr etching gases.

[0114] In some embodiments, photolithography and etching are used to pattern the metal (bonding) layer 206. In some cases, the etching method used for patterning is dry etching, such as inductively coupled plasma (ICP) etching using Cl2 / BCl3 / Ar etching gas, or ion beam etching (IBE) using Ar gas.

[0115] In some embodiments, after the LED device structure is patterned, an insulating layer 252 is deposited on the surface of the patterned LED device structure, including all patterned layers, sidewalls, and unobstructed substrate. In some embodiments, the insulating layer 252 is made of SiO2 and / or Si3N4. In some embodiments, the insulating layer 252 is made of TiO2. In some embodiments, after curing, for example, a SOG layer at high temperature, the insulating layer 252 is formed of a composition similar to SiO2. In some embodiments, the insulating layer 252 is made of a material having a thermal coefficient similar to that of the layer below it.

[0116] In some embodiments, the insulating layer 252 is patterned using photolithography and etching to expose the electrode contact area. In some cases, the etching method used for patterning is dry etching, such as inductively coupled plasma (ICP) etching using CF4 and O2.

[0117] In some embodiments, anode metal pad 254 is vapor deposited at a suitable position of the patterned LED structure, for example, on one side, to cover the red LED structure, the green LED structure, and the blue LED structure. In some embodiments, anode metal pad 254 is connected to metal (bonding) layer 206 at the bottom of red LED epitaxial layer 210, conductive ITO layer 218 at the bottom of green LED epitaxial layer 220, and conductive ITO layer 228 at the bottom of blue LED epitaxial layer 230. Anode metal pad 254 is also electrically connected to an integrated circuit including pixel driver 204 located on substrate 202 through metal (bonding) layer 206.

[0118] In some embodiments, separate cathode metal pads are placed, each connected to the red LED epitaxial layer, the green LED epitaxial layer, and the blue LED epitaxial layer. For example, cathode metal pad 256 is vapor deposited on one side of the patterned LED structure and connected to the red LED epitaxial layer 210 through the conductive ITO layer 212 on top of the red LED epitaxial layer 210. In some embodiments, cathode metal pad 258 is vapor deposited on one side of the patterned LED structure and connected to the green LED epitaxial layer 220 through the conductive ITO layer 222 on top of the green LED epitaxial layer 220. In some embodiments, cathode metal pad 260 is vapor deposited on one side of the patterned LED structure and connected to the blue LED epitaxial layer 230 through the conductive ITO layer 232 on top of the blue LED epitaxial layer 230.

[0119] In some embodiments, the external quantum efficiency of the red LED structure in the three-color LED device is about 0.5%-5%. In some embodiments, the external quantum efficiency of the green LED structure in the three-color LED device is about 2%-10%. In some embodiments, the external quantum efficiency of the blue LED structure in the three-color LED device is about 5%-15%. In some embodiments, when calculating the external quantum efficiency of each color LED structure, the effects of all relevant layers outside the LED structure, such as the reflective layer, bonding layer, ITO layer, and insulating layer, should be taken into account.

[0120] In some embodiments, the external quantum efficiency of the tricolor LED device 250 is about 20% or higher. In some embodiments, when calculating the external quantum efficiency of the multicolor LED device, the effects of all layers outside the LED structure layer, such as the reflective layer, bonding layer, ITO layer, and insulating layer, should be taken into account.

[0121] In order to obtain the desired LED characteristics, multiple design factors of the tri-color coaxial LED system 250 need to be selected (e.g., optimized using cost or performance functions), such as: the dimensions of the layers (e.g., the width, length, height, and cross-sectional area of ​​each layer); the dimensions of the electrodes; the size, shape, spacing, and arrangement of two or more LED structural layers, bonding layers, reflective layers, and conductive layers; and the configuration between the integrated circuit, pixel driver, and electrical connections. LED characteristics that vary with the above design factors include, for example: size, material, cost, manufacturing efficiency, light emission efficiency, power consumption, directivity, light intensity, luminous flux, color, spectrum, and spatial radiation pattern.

[0122] Figure 3 is a circuit diagram of a matrix of three-color LED devices 300 according to some embodiments. Figure 3 The circuit shown includes three pixel drivers 302 , 304 , and 306 and three tri-color coaxial LED devices 308 , 310 , and 312 .

[0123] In some embodiments, a display panel includes a plurality of pixels, such as millions of pixels, and each pixel includes a three-color LED device structure. In some embodiments, the LED device structure can be a micro-LED. The micro-LED typically has a lateral dimension of 50 micrometers (μm) or less, and can have a lateral dimension of less than 10 μm or even only a few μm.

[0124] In some embodiments, a pixel driver, such as pixel driver 302, includes a plurality of transistors and capacitors ( Figure 3 The transistor includes a driving transistor connected to a voltage source, and a control transistor configured to have its gate connected to a scan signal bus. The capacitor includes a storage capacitor for maintaining a gate voltage of the driving transistor during a period when the scan signal sets other pixels.

[0125] In this example, each tricolor LED device, such as tricolor LED device 308, has its own integrated circuit (IC) pixel driver 302. The tricolor LED device 308 for a single pixel can be viewed as three separate LEDs of different colors connected in parallel. For example, the red LED 318, green LED 316, and blue LED 314 within the same tricolor LED device 308 are connected via a shared P electrode pad or anode, such as Figure 2B Metal pads 254 are shown connected to the same IC pixel driver 302 .

[0126] In some embodiments, the red LED, green LED, and blue LED within the same three-color LED device 308 are each connected to a separate N-electrode pad or cathode. For example, the red LED is connected to N-electrode 336, such as Figure 2BThe green LED is connected to the N electrode 334, as shown in FIG. Figure 2B The blue LED is connected to the N electrode 332, as shown in FIG. Figure 2B Metal pad 260 is shown.

[0127] In some embodiments, all red LEDs in different three-color LED devices, such as 318, 324, and 330, are connected to the same common N electrode 336. All green LEDs in different three-color LED devices, such as 316, 322, and 328, are connected to the same common N electrode 334. All blue LEDs in different three-color LED devices, such as 314, 320, and 326, are connected to the same common N electrode 332. Using a common electrode simplifies the manufacturing process and reduces the area of ​​the LED device, especially the area occupied by the electrode.

[0128] Figure 4 is a flow chart of a method 400 of manufacturing a three-color coaxial LED device according to some embodiments.

[0129] It can correspond to the above Figure 1 , 2A , 2B and 3 to perform the operations (e.g., steps) of method 400.

[0130] The method 400 includes step 402: providing a substrate. In some embodiments, a pixel driver is formed in the substrate.

[0131] Method 400 also includes step 404: manufacturing a first LED structure layer stacked on top of the substrate. In some embodiments, the first LED structure layer includes a first epitaxial structure. In some embodiments, the first LED structure layer is bonded to the substrate via a first bonding layer. In some embodiments, before the substrate is bonded to the first LED structure layer, a first reflective layer is coated on a side of the first LED structure layer facing the substrate. In some cases, after bonding, the first reflective layer is located between the first bonding layer and the first epitaxial structure. In some embodiments, the first bonding layer is a conductive layer located at the bottom of the first LED structure layer, and the first bonding layer is electrically connected to the pixel driver and the bottom of the first LED structure layer, respectively. In some embodiments, a first upper conductive layer is coated on top of the first LED structure layer and is electrically connected to a common electrode at the top of the first LED structure layer, respectively.

[0132] Method 400 also includes step 406: manufacturing a second LED structure layer stacked on top of the first LED structure layer. In some embodiments, the second LED structure layer includes a second epitaxial structure. In some embodiments, the second LED structure is bonded to the first LED structure through a second bonding layer. In some embodiments, before the first LED structure layer is bonded to the second LED structure layer, a second reflective layer is coated on a side of the first LED structure layer facing the second LED structure layer. In some cases, after bonding, the second reflective layer is located between the first upper conductive layer and the second bonding layer. In some embodiments, a second lower conductive layer is coated on the bottom of the second LED structure layer and is electrically connected to the pixel driver and the bottom of the second LED structure layer, respectively. In some embodiments, a second upper conductive layer is coated on top of the second LED structure layer and is electrically connected to the top of the second LED structure layer and a common electrode, respectively.

[0133] Method 400 also includes step 408: manufacturing a third LED structure layer stacked on top of the second LED structure layer. In some embodiments, the third LED structure layer includes a third epitaxial structure. In some embodiments, the third LED structure is bonded to the second LED structure through a third bonding layer. In some embodiments, before the second LED structure layer is bonded to the third LED structure layer, a third reflective layer is coated on a side of the second LED structure layer facing the third LED structure layer. In some cases, after bonding, the third reflective layer is located between the second upper conductive layer and the third bonding layer. In some embodiments, a third lower conductive layer is coated on the bottom of the third LED structure layer and is electrically connected to the pixel driver and the bottom of the third LED structure layer, respectively. In some embodiments, a third upper conductive layer is coated on the top of the third LED structure layer and is electrically connected to the top of the third LED structure layer and a common electrode, respectively.

[0134] In some embodiments, the first LED structure layer, the second LED structure layer, and the third LED structure layer substantially overlap each other laterally, forming an optical path to mix light emitted by the first LED structure layer, the second LED structure layer, and the third LED structure layer.

[0135] The method 400 further includes step 410: patterning each layer formed in the above steps 402-408 by photolithography and etching to form three LEDs directly stacked together.

[0136] The method 400 further includes step 412 of depositing an insulating layer over the unobstructed structure formed in the above steps 402 - 410 , and etching the insulating layer to coat the electrode contact pads.

[0137] Method 400 also includes step 414: coating electrode contact pads on the surface of the structure formed in the above steps 402-412. In some embodiments, an anode metal contact pad is coated for electrical connection to the lower conductive layer and the pixel driver in the first LED structure layer, the second LED structure layer, and the third LED structure layer. In some embodiments, a first cathode metal contact pad is coated for electrical connection to the upper conductive layer of the first LED structure layer. In some embodiments, a second cathode metal contact pad is coated for electrical connection to the upper conductive layer of the second LED structure layer. In some embodiments, a third cathode metal contact pad is coated for electrical connection to the upper conductive layer of the third LED structure layer.

[0138] Additional embodiments also include various subsets of the above embodiments, including combinations or other rearrangements of the above embodiments. Figure 1 , 2A , 2B, 3 and 4.

[0139] Figure 5 5 is a top view of a micro LED display panel 500 according to some embodiments. The display panel 500 includes a data interface 510, a control module 520, and a pixel area 550. The data interface 510 receives data that defines an image to be displayed. The source and format of the data will vary depending on the application. The control module 520 receives input data and converts it into a form suitable for driving pixels in the display panel. The control module 520 may include digital logic and / or a state machine for converting the received format into a format suitable for the pixel area 550, a shift register or other type of cache and memory for storing and transmitting data, a digital-to-analog converter and a level shifter, and a scan controller including a clock circuit.

[0140] The pixel area 550 includes a pixel array. The pixel includes a micro-LED, such as a three-color coaxial LED 534, integrated with a pixel driver, the example of which is as described above. In this example, the display panel 500 is a color RGB display panel. It includes a red pixel, a green pixel, and a blue pixel. In each pixel, the three-color coaxial LED 534 is controlled by a pixel driver. According to the previously shown embodiment, the pixel is connected to a power supply voltage (not shown), grounded via a ground pad 536, and also connected to a control signal. Although Figure 5 Although not shown in the figure, the p-electrode of the tri-color coaxial LED 534 and the output terminal of the driving transistor are placed inside the LED 534, and they are connected to each other through a bonding metal layer, such as Figure 2AThe metal layers 204 shown in FIG. 1 are electrically connected to each other. According to various embodiments, LED current drive signal connections (between the p-electrode of the LED and the pixel driver output), ground (between the n-electrode and the system ground), power supply voltage Vdd connections (between the pixel driver source and the system Vdd), and control signal connections to the pixel driver gate are established.

[0141] Figure 5 This is only a representative diagram. Other designs will be obvious. For example, the colors do not have to be red, green, and blue. Nor do they have to be arranged in columns or strips. As an example, except Figure 5 In addition to the square pixel matrix layout shown, a hexagonal pixel matrix layout can also be used to form the display panel 500.

[0142] In some applications, a fully programmable rectangular pixel array is not necessary. Other designs of display panels with different shapes and displays can also be constructed using the device structure described in this article. One class of examples is professional applications, including signage and automobiles. For example, multiple pixels can be arranged in a star or spiral to form a display panel, and different patterns on the display panel are generated by turning LEDs on and off. Another professional example is automotive headlights and smart lighting, where certain pixels are grouped together to form different lighting shapes, and each group of LED pixels is turned on or off or adjusted by a separate pixel driver.

[0143] Even the lateral layout of devices within each pixel can be different. Figure 1 , 2A As shown in FIG. 2B , the LEDs and pixel drivers are arranged vertically, i.e., each LED is located on top of the corresponding pixel driver circuit. Other layouts are also possible. For example, the pixel driver can also be located "behind", "in front of" or "beside" the LED.

[0144] Different types of display panels can be manufactured. For example, the resolution of a display panel can typically range from 8×8 to 3840×2160. Common display resolutions include QVGA with a resolution of 320×240 and an aspect ratio of 4:3, XGA with a resolution of 1024×768 and an aspect ratio of 4:3, D with a resolution of 1280×720 and an aspect ratio of 16:9, FHD with a resolution of 1920×1080 and an aspect ratio of 16:9, UHD with a resolution of 3840×2160 and an aspect ratio of 16:9, and 4K with a resolution of 4096×2160. There can also be a wide variety of pixel sizes, ranging from sub-micron and below to 10 mm and above. The size of the entire display area can also vary widely, ranging from as small as tens of microns or less on the diagonal to hundreds of inches or more.

[0145] Different applications have different requirements for optical brightness. Example applications include direct-view displays, light engines for home / office projectors and portable electronic devices such as smartphones, laptops, wearable electronics, AR and VR glasses, and retinal projection. Power consumption can range from as low as a few milliwatts for retinal projectors to as high as kilowatts for large-screen outdoor displays, projectors, and smart car headlights. In terms of frame rate, due to the fast response of inorganic LEDs (nanoseconds), the frame rate can be as high as KHz, or even MHz for small resolutions.

[0146] Additional embodiments also include various subsets of the above embodiments, including combinations or other rearrangements of the above embodiments. Figure 1 , 2A , 2B, and embodiments in 3 to 5.

[0147] Although the detailed description contains many details, these details should not be interpreted as limiting the scope of the present invention, but are merely illustrative of different examples and aspects of the present invention. It should be understood that the scope of the present invention includes other embodiments not discussed in detail above. For example, the above method can be applied to the integration of functional devices other than LEDs with control circuits other than pixel drivers. Examples of non-LED devices include vertical cavity surface emitting lasers (VCSELs), photodetectors, microelectromechanical systems (MEMS), silicon photonic devices, power electronic devices, and distributed feedback lasers (DFBs). Examples of other control circuits include current drivers, voltage drivers, transimpedance amplifiers, and logic circuits.

[0148] The foregoing description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the embodiments described herein and variations thereof. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the spirit or scope of the subject matter disclosed herein. Therefore, the present disclosure is not intended to be limited to the embodiments shown herein, but should be consistent with the widest scope consistent with the appended claims and the principles and novel features disclosed herein.

[0149] Features of the present invention can be implemented in, using or by means of a computer program product, such as a storage medium or computer-readable storage medium with instructions stored thereon / therein, which can be used to program a processing system to perform any features presented herein. Storage media can include, but are not limited to, high-speed random access memory such as DRAM, SRAM, DDR RAM or other random access solid-state memory devices, and can include non-volatile memory such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices or other non-volatile solid-state storage devices. Memory optionally includes one or more storage devices located away from the CPU. Memory or alternatively non-volatile memory devices in memory include non-temporary computer-readable storage media.

[0150] Features of the present invention stored on any machine-readable medium may be incorporated in software and / or firmware for controlling the hardware of a processing system and for enabling the processing system to interact with other mechanisms utilizing the results of the present invention. Such software or firmware may include, but is not limited to, application code, device drivers, operating systems, and execution environments / containers.

[0151] It should be understood that, although the terms “first”, “second”, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.

[0152] The terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the claims. As used in the description of the embodiments and the appended claims, the singular forms "one", "an" and "the" are intended to also include plural forms unless the context clearly states otherwise. It will also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms "include" and / or "comprising" specify the presence of the features, integers, steps, operations, elements and / or parts set forth when used herein, but do not exclude the presence or increase of one or more other features, integers, steps, operations, elements, parts and / or their groups.

[0153] As used herein, the term "if" may be interpreted to mean "when" or "at" or "in response to determining" or "according to" or "in response to detecting" that the stated precondition is true, depending on the context. Similarly, the phrase "if it is determined that [the stated precondition is true]" or "if [the stated precondition is true]" or "when [the stated precondition is true]" may be interpreted to mean "upon determining that the stated precondition is true" or "in response to determining that the stated precondition is true" or "according to a determination that the stated precondition is true" or "upon detecting that the stated precondition is true" or "in response to detecting that the stated precondition is true," depending on the context.

[0154] For purposes of explanation, the foregoing description has been described with reference to specific embodiments. However, the above illustrative discussion is not intended to be exhaustive or to limit the claims to the precise forms disclosed. In view of the above teachings, many modifications and variations are possible. The embodiments are chosen and described in order to best explain the operating principles and practical applications, thereby enabling others skilled in the art to realize.

Claims

1. A method for preparing a single-pixel micro light-emitting diode (LED) device for a display panel, comprising: providing a substrate, the substrate comprising a pixel driver; preparing an LED structure layer stacked on the substrate; Bonding the substrate and the LED structure layer together through a bonding layer; The LED structure layer is electrically connected to the pixel driver through the bonding layer.

2. The method for preparing a single-pixel micro LED device according to claim 1, wherein: The bonding layer includes one or more bonding structures selected from the group consisting of Au-Au bonding, Au-Sn bonding, Au-In bonding, Ti-Ti bonding, and Cu-Cu bonding.

3. The method for preparing a single-pixel micro LED device according to claim 2, wherein: The bonding layer is about 0.1 microns to about 3 microns.

4. The method for preparing a single-pixel micro LED device according to any one of claims 2 to 3, further comprising: Before bonding the substrate and the LED structure layer, a reflective layer is coated on the LED structure layer.

5. The method for preparing a single-pixel micro LED device according to claim 4, further comprising: forming a distributed Bragg reflector (DBR) structure for the reflective layer, The reflective layer is about 0.1 micrometers to about 5 micrometers.

6. The method for preparing a single-pixel micro LED device according to claim 1, further comprising: patterning the epitaxial structure of the LED structure layer to form an LED in the LED structure layer; Applying a lower conductive layer to electrically connect to the bottom of the LED; as well as Applying a conductive layer to electrically connect to the top of the LED; Wherein, the lower conductive layer is also electrically connected to the pixel driver and the upper conductive layer is also electrically connected to the common electrode.

7. The method for preparing a single-pixel micro-LED device according to claim 6, wherein the epitaxial structure of the LED structure layer is selected from the group consisting of one or more structures of a III-V nitride epitaxial structure, a III-V arsenide epitaxial structure, a III-V phosphide epitaxial structure, and a III-V antimonide epitaxial structure.

8. The method for preparing a single-pixel micro LED device according to any one of claims 6 and 7, wherein: The lower conductive layer and the upper conductive layer for the LED structure layer include indium tin oxide (ITO) layers, and each of the ITO layers is about 0.01 micrometers to 1 micrometers.

9. The method for preparing a single-pixel micro LED device according to any one of claims 6 and 7, further comprising: applying an anode metal contact pad to electrically connect the lower conductive layer of the LED structure layer; A cathode metal contact pad is applied to electrically connect the upper conductive layer in the LED structure layer. 10 . The method for preparing a single-pixel micro LED device according to claim 6 , wherein the epitaxial structure of the LED structure layer is about 0.3 microns to about 5 microns.

11. The method for preparing a single-pixel micro LED device according to claim 1, further comprising: The LED structure layer is patterned to form a red LED.

12. The method for preparing a single-pixel micro-LED device according to claim 9, wherein the anode and cathode metal contact pads include one or more metals selected from the group consisting of aluminum, silver, rhodium, zinc, gold, germanium, nickel, chromium, platinum, tin, copper, tungsten, indium tin oxide, palladium, indium, and titanium.

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