Micro LED display device and preparation method thereof

Abstract

The invention provides a Micro LED display device and a preparation method thereof. The Micro LED display device comprises a driving substrate; each pixel unit comprises a semiconductor multilayer structure in which a second semiconductor layer, a light-emitting layer and a first semiconductor layer are sequentially stacked from bottom to top, and a groove penetrating through the semiconductor multilayer structure is formed between the pixel units; the first reflection structure is formed on the side wall of the groove of each pixel unit and the edge position of the second semiconductor layer, and a conductive opening is formed in the surface of the second semiconductor layer; the bonding metal layer is formed on the conductive opening corresponding to each pixel unit; the bonding glue layer is formed on the periphery of the bonding metal layer; and the ohmic contact structure is of a net structure formed by mutually connecting the metal walls formed on the surfaces of the pixel units and is formed along the grooves between the pixel units, and one metal wall is shared at the joint of every two adjacent pixel units. The problems that a Micro LED is low in luminous efficiency and insufficient in optical collimation are effectively solved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a Micro LED display device and a method for preparing the same. Background Art

[0002] In recent years, semiconductor display technology has developed rapidly. In the field of projection display technology such as augmented reality (AR) and virtual reality (VR), users have increasingly high demands for device portability and lightness. This requires that the size of the Micro LED (micro light-emitting diode) used must be further reduced. However, as the size of Micro LED pixels decreases, and the light-emitting structure is usually prepared with a regular trapezoidal shape, the luminous efficiency of the LED decreases significantly. In addition, in projection applications, if the optical collimation of the pixel light is not high enough, it can easily lead to image blur. Therefore, higher requirements are placed on the optical collimation of the pixel light to ensure image clarity and brightness. Currently, metal walls are generally installed between the light-emitting structures to prevent light crosstalk between pixels. Although this structural design can improve the optical collimation of the pixel light to a certain extent, it still loses a large proportion of the light output efficiency. Summary of the Invention

[0003] In order to overcome the above shortcomings, the present invention provides a Micro LED display device and a preparation method thereof, which effectively solves the problems of low luminous efficiency and insufficient optical collimation of Micro LEDs.

[0004] The technical solution provided by the present invention is: In one aspect, the present invention provides a Micro LED display device, comprising: A driving substrate, a driving circuit being formed on a surface of the driving substrate; At least two independent pixel units, each pixel unit comprising a semiconductor multilayer structure in which a second semiconductor layer, a light-emitting layer, and a first semiconductor layer are stacked in sequence from bottom to top, and a trench is formed between the pixel units, penetrating the semiconductor multilayer structure, with inclined sidewalls and an opening width gradually decreasing from bottom to top; A first reflective structure is formed on the sidewall of the trench of each pixel unit and the edge of the second semiconductor layer, and a conductive opening is formed on the surface of the second semiconductor layer; A bonding metal layer is formed in the conductive opening corresponding to each pixel unit and is used to bond the corresponding pixel unit to the driving circuit on the surface of the driving substrate; a bonding adhesive layer formed around the bonding metal layer, wherein the upper surface of the bonding adhesive layer is flush with the upper surface of the bonding metal layer; The ohmic contact structure is a mesh structure formed by interconnected metal walls formed on the surface of each pixel unit; the metal walls are formed on the surface of the first semiconductor layer along the grooves between the pixel units, and the junctions of adjacent pixel units share a metal wall, which is also conductively connected to the first semiconductor layers of two adjacent pixel units.

[0005] In another aspect, the present invention provides a method for preparing a Micro LED display device, comprising: Providing a growth substrate, and growing a semiconductor multilayer structure including a first semiconductor layer, a light-emitting layer, and a second semiconductor layer in order from bottom to top on the surface of the substrate; Etching the semiconductor multilayer structure along the edge of each pixel unit to the first semiconductor layer to form a trench between the pixel units, wherein the trench sidewalls are inclined and the opening width gradually decreases from top to bottom, and the first semiconductor layer is partially etched; forming a first reflective structure at the edge of the second semiconductor layer and the sidewall of the trench of each pixel unit, and forming a conductive opening on the surface of the second reflective structure; Depositing a bonding metal layer in the conductive opening of each pixel unit, and filling the area between each bonding metal layer with a bonding glue layer flush with the surface of the bonding metal layer; flipping and bonding the pixel unit to the driving circuit surface on the driving substrate through the bonding metal layer; removing the growth substrate and etching the exposed first semiconductor layer to obtain mutually independent pixel units; A metal wall is formed on the surface of the first semiconductor layer along the grooves above each pixel unit to obtain a mesh-like ohmic contact structure. The junctions of adjacent pixel units share a metal wall, which is also conductively connected to the first semiconductor layers of two adjacent pixel units.

[0006] The Micro LED display device and its manufacturing method provided by the present invention can bring at least the following beneficial effects: 1) The ohmic contact structure, a mesh of metal walls, reflects light emitted from the pixel units, achieving light collimation. The special design of the grooves between the pixel units enables the ohmic contact structure to directly connect to the first semiconductor layer of the pixel unit, achieving N-type electrical contact for each pixel unit. This achieves a common cathode design and saves process steps, while increasing the overall light output area of ​​the Micro LED display device, thereby improving light efficiency.

[0007] 2) While the first reflective structure is formed on the sidewall of the trench, a second reflective structure is further formed on the surface of the second semiconductor layer. The two reflective structures complement each other to form a complete reflective surface, further improving the luminous efficiency.

[0008] 3) It expands the application areas of Micro LED display devices and achieves better application effects in AR projection display and automotive matrix headlights. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a cross-sectional schematic diagram of forming a semiconductor multilayer structure on a growth substrate surface in one embodiment of the present invention; Figure 2 Schematic cross-sectional view of etching a semiconductor multilayer structure to form a trench in one embodiment of the present invention; Figure 3 is a cross-sectional schematic diagram of forming a second reflective structure on the surface of the second semiconductor layer in one embodiment of the present invention; Figure 4 is a cross-sectional schematic diagram of forming a passivation layer on the surface of a semiconductor multilayer structure in one embodiment of the present invention; Figure 5 is a cross-sectional schematic diagram of forming a reflective layer on the surface of a semiconductor multilayer structure in one embodiment of the present invention; Figure 6 is a schematic cross-sectional view of forming a bonding metal layer in a first opening according to an embodiment of the present invention; Figure 7 is a cross-sectional schematic diagram of bonding each pixel unit to a driving substrate via a bonding metal layer in one embodiment of the present invention; Figure 8 is a cross-sectional schematic diagram of removing the growth substrate in one embodiment of the present invention; Figure 9 is a cross-sectional schematic diagram of etching the first semiconductor layer in one embodiment of the present invention; Figure 10 is a cross-sectional schematic diagram of an ohmic contact structure formed on the surface of the first semiconductor layer in one embodiment of the present invention; Figure 11 is a cross-sectional schematic diagram of forming a light conversion layer on the surface of the first semiconductor layer in another embodiment of the present invention; Figure 12 is a cross-sectional schematic diagram of a microlens structure formed on the surface of the first semiconductor layer in one embodiment of the present invention; Figure 13 FIG. 4 is a cross-sectional schematic diagram of a microlens structure formed on the surface of the first semiconductor layer in another embodiment of the present invention.

[0010] Reference numerals: 10-growth substrate, 20-semiconductor multilayer structure, 21-first semiconductor layer, 22-light-emitting layer, 23-second semiconductor layer, 24-groove, 30-second reflective structure, 31-ohmic contact layer, 40-passivation layer, 41-first opening, 50-reflective layer, 51-second opening, 60-bonding metal layer, 70-metal wall, 71-light conversion layer, 80-microlens. DETAILED DESCRIPTION

[0011] In order to more clearly illustrate the implementation cases of the present invention or the technical solutions in the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings and other embodiments can be obtained based on these drawings without inventive work.

[0012] One embodiment of the present invention provides a Micro LED display device, comprising: a driving substrate having a driving circuit formed on its surface; at least two independent pixel units, each pixel unit comprising a semiconductor multilayer structure in which a second semiconductor layer, a light-emitting layer, and a first semiconductor layer are stacked sequentially from bottom to top, and a trench penetrating the semiconductor multilayer structure is formed between the pixel units, with the trench sidewalls inclined and the opening width gradually decreasing from bottom to top; a first reflective structure formed on the trench sidewalls of each pixel unit and at an edge of the second semiconductor layer, and a conductive opening formed on the surface of the second semiconductor layer; a bonding metal layer formed in the conductive opening corresponding to each pixel unit and used to bond the corresponding pixel unit to the driving circuit on the surface of the driving substrate; a bonding adhesive layer formed around the bonding metal layer, with the upper surface of the bonding adhesive layer flush with the upper surface of the bonding metal layer; an ohmic contact structure, which is a mesh structure formed by interconnecting metal walls of each pixel unit; the metal walls are formed on the surface of the first semiconductor layer along the trenches between the pixel units, and adjacent pixel units share a metal wall, and the metal wall is conductively connected to the first semiconductor layers of two adjacent pixel units at the same time.

[0013] In this embodiment, the semiconductor multilayer structure includes a first semiconductor layer, a light-emitting layer, and a second semiconductor layer grown sequentially on the surface of a substrate such as silicon, sapphire, silicon carbide, gallium arsenide, etc.; typically, the first semiconductor layer is made of an N-type semiconductor material, and the second semiconductor layer is made of a P-type semiconductor material, but this embodiment is not limited to this. The semiconductor layer can be doped GaN, or can be made of other binary or ternary materials; in specific application scenarios, the first semiconductor layer can also be a P-type semiconductor material, and the second semiconductor layer can be an N-type semiconductor material; the light-emitting layer is usually composed of a semiconductor material with a specific energy band gap, which determines the wavelength of light emitted by the device, that is, the light color of the display device. Theoretically, as long as a voltage is applied to the materials and structures of the first semiconductor layer, the light-emitting layer, and the second semiconductor layer, the electrons and holes in the first semiconductor layer and the second semiconductor layer can recombine in the light-emitting layer to release energy, thereby generating photon light emission.

[0014] The trenches extend through the semiconductor multilayer structure between each pixel unit, isolating the light-emitting material of each pixel unit and making them independent of each other. The pixel units separated by the trenches can be circular, square, polygonal, or other shapes. The corresponding trenches can be designed in a crisscrossing grid pattern, etc. This embodiment does not impose any restrictions on this, and the design can be based on actual application requirements. Generally speaking, the pixel units in Micro LED displays are square in structure and smaller than 100µm by 100µm (micrometers). Since there is no light-emitting material in the trench area, no photons can be generated. To improve luminous efficiency, the maximum width of the trench can be designed to be as small as possible without affecting photoelectric performance. In this embodiment, to facilitate the formation of the first reflective structure and the contact between the first semiconductor layer and the ohmic contact structure, the trenches have inclined sidewalls. That is, the width of the trench opening gradually decreases from bottom to top. Correspondingly, the cross-section of the pixel unit is an inverted trapezoid, which increases the light-emitting surface area of ​​the pixel unit. Regarding the trench shape, to further improve the overall light extraction efficiency of the Micro LED display device, the width of the trench bottom can be designed to be zero, that is, the trench is designed to be V-shaped (opening downward). This design not only reduces the distance between adjacent pixel units, increasing the light-emitting area, but also, due to the close distance between adjacent pixel units, further reduces the width of the metal wall formed above the adjacent pixel units, thereby reducing the metal wall's area share on the light-emitting surface and increasing the overall light-emitting area of ​​the Micro LED display device. To achieve better reflection and better ohmic contact with the metal wall, the angle between the trench sidewall and the horizontal direction is designed to be 20° to 80°.

[0015] The first reflective structure covers the trench sidewalls of each pixel unit and the edge of the second semiconductor layer, forming only a conductive opening on the surface of the second semiconductor layer (typically located at the center of the second semiconductor layer surface). The first reflective structure comprises a highly reflective metal material that reflects light from the light-emitting layer toward the first reflective structure. Simultaneously, the first reflective structure is not electrically connected to the second semiconductor surface, thus forming a conductive opening that facilitates current conduction to the second semiconductor layer. The shape of the conductive opening can be arbitrarily designed, such as circular or square.

[0016] The bonding metal layer, made of Au, Cu, Sn, In, or their alloys, fills the conductive openings and electrically connects to the surface of the second semiconductor layer of the pixel unit, serving as a conductive bridge between the pixel unit and the driver substrate. Its thickness is generally higher than the conductive opening, ranging from 0.2µm to 20µm. To facilitate alignment and bonding with the driver substrate, a bonding adhesive layer is formed between the bonding metal layers of each pixel unit using SiO2, SU8 photoresist, or other polymers. Chemical mechanical polishing (CMP) is used to level the surface of the bonding metal layer. Each pixel unit is bonded to the driver circuitry on the driver substrate's surface via the bonding metal layer, which then electrically drives the pixel unit through the bonding metal layer. The driver substrate can be a printed circuit board (PCB), a thin-film transistor (TFT), or a complementary metal oxide semiconductor (CMOS) substrate. The driver circuitry is formed on the driver surface, and when powered on, the internal circuitry controls the pixel unit's electrical drive. Metal (corresponding to the bonding metal layer contacts) and dielectric material (formed between the bonding metal layer contacts) may also be formed on the surface of the driving substrate circuit and planarized using CMP technology.

[0017] The ohmic contact structure is a mesh structure formed by interconnecting metal walls of each pixel unit. In a Micro LED display device, the metal walls of each pixel unit are interconnected as a single unit. The metal walls conduct current to each pixel unit, thus achieving a common cathode design. The height of the metal walls ranges from 0.5µm to 50µm. Before forming the metal walls, the growth substrate on the surface of the semiconductor multilayer structure is removed, exposing the surface of the first semiconductor layer. The metal walls simultaneously make ohmic contact with and conduct electricity to the first semiconductor layers of two adjacent pixel units. They are formed on the surface of the first semiconductor layer above each pixel unit's trench. The bottom surface of the metal walls contacts the first semiconductor layers of two adjacent pixel units, and the metal walls are positioned around each pixel unit. In this embodiment, the metal walls directly contact the first semiconductor layer, achieving N-side contact of the pixel units and providing optical isolation to prevent optical crosstalk between adjacent pixel units, while also saving process steps. In the example of a square pixel unit structure, the ohmic contact structure is a square mesh structure. Adjacent pixel units share a common metal wall at their junctions. The two opposing surfaces of the shared metal wall reflect light from within the corresponding pixel units. In other embodiments, the shape of the ohmic contact structure is determined by the shape of the pixel unit, as long as it can achieve the purposes of optical isolation and ohmic contact at the same time.

[0018] The present embodiment is an improvement to the above embodiment. In this embodiment, in addition to the first reflective structure formed in the Micro LED display device, a second reflective structure is also formed on the surface of the second semiconductor layer. The first reflective structure is formed on the sidewalls of the groove of each pixel unit and at the edge of the second reflective structure (the reflective material of the first reflective structure at least wraps around the edge of the second reflective structure, and the two reflective structures complement each other and form the entire light-emitting surface). A conductive opening is formed on the surface of the second reflective structure. The bonding metal layer in the conductive opening is conductively connected to the second reflective structure, and current flows through the bonding metal layer through the second reflective structure and is conducted to the second semiconductor layer. The second reflective structure can be a single layer or multiple layers, and the material is selected from one or more of Ag, Al, Cr, Ni, Ti, etc. The second reflective structure is formed on the surface of the second semiconductor layer of each pixel unit. The area of ​​the second reflective structure is at least larger than the area of ​​the conductive opening. To achieve independent driving of each pixel unit, the second reflective structures of adjacent pixel units do not contact each other. In this embodiment, the second reflective structure is formed only on the surface of the second semiconductor layer. In other embodiments, the second reflective structure may be formed not only on the surface of the second semiconductor layer but also partially on the side surfaces of the second semiconductor layer and the light-emitting layer in the grooves, as long as the second reflective structures of each pixel unit are spaced apart and do not contact each other. The function of the second reflective structure is not only to reflect light emitted from the light-emitting layer toward the second semiconductor layer toward the light-emitting surface (in this embodiment, the light-emitting surface is the surface of the first semiconductor layer away from the light-emitting layer), but also to provide electrical conductivity. When a voltage is applied to the pixel unit, the bonding metal layer conducts electricity to the second semiconductor layer through the second reflective structure. The second reflective structure typically has a thickness of 10nm to 1000nm (nanometers), ensuring both light reflection and current conduction.

[0019] Furthermore, an ohmic contact layer is formed between the second reflective structure and the second semiconductor layer to reduce contact resistance. The thickness of the ohmic contact layer is typically between 10 nm and 200 nm. The ohmic contact layer can be made of a transparent, highly conductive, low-contact-resistance oxide material, such as indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO), cadmium tin oxide (CTO), indium oxide (InO), indium (In)-doped zinc oxide (ZnO), aluminum (Al)-doped zinc oxide (ZnO), gallium (Ga)-doped zinc oxide (ZnO), or any combination thereof. The ohmic contact layer can also be made of a metal material, such as one or more metals such as Pt and Ag.

[0020] In the above embodiment, the first reflective structure includes a passivation layer and a reflective layer. The conductive openings in the first reflective structure include a first opening in the passivation layer and a second opening in the reflective layer. In each pixel unit, the bonding metal layer has a width consistent with the width of the first opening and simultaneously fills the first and second openings. The second opening is wider than the first opening, and the bonding metal layer does not contact the reflective layer. The passivation layer is formed on the sidewalls of the trench of each pixel unit and at the edge of the second reflective structure. A first opening is formed on the surface of the second reflective structure and can be made of materials such as Al2O3, SiO2, or SiN to provide insulation and isolation. The thickness ranges from 50 nm to 1000 nm. To facilitate electrical conduction to the second reflective structure, the first opening in the passivation layer is located above the second reflective structure, exposing a portion of the surface of the second reflective structure. The size and shape of the first opening are not limited in this embodiment, as long as they can conduct current to the second reflective structure, such as a round hole or a square hole.

[0021] The reflective layer can also be a single layer or multiple layers, made of one or more materials selected from Ag, Al, Cr, Ni, Ti, etc. Its sole function is to reflect light emitted by the light-emitting layer toward other surfaces, returning it to the light-emitting surface. It does not provide electrical conductivity. The reflective layer covers the surface of the passivation layer in each pixel unit and is formed with a second opening. The second opening at least covers the first opening, and the boundary of the second opening is within the area of ​​the second reflective structure. In other words, the coverage area of ​​the second opening is larger than the area of ​​the first opening, but smaller than the area of ​​the second reflective structure. It should be understood that this design of small openings stacked on large openings ensures that the reflective layer in the first reflective structure of each pixel unit is not in conductive contact with the bonding metal layer filled in the smaller first opening, allowing the bonding metal layer to independently drive each pixel unit through the bonding metal layer. Furthermore, the second reflective structure complements the first reflective structure, ensuring that all surfaces other than the light-emitting surface (including the groove surfaces between pixel units) in the Micro LED display device are reflective surfaces, reflecting scattered light back to the light-emitting surface, effectively improving luminous efficiency.

[0022] The present embodiment is an improvement to the above embodiment. A light conversion layer is formed on the surface of the first semiconductor layer in each pixel unit to convert the light emitted by the pixel unit into another wavelength. An internal wavelength conversion material converts light emitted from the light-emitting surface into another wavelength. The wavelength conversion material is a phosphor that can be excited by the light emitted by the semiconductor multilayer structure, thereby obtaining a display device with a light color different from that emitted by the semiconductor multilayer structure. The wavelength conversion material can be composed of at least one or more of the following: garnet-type phosphors, oxynitride phosphors, aluminate phosphors, nitride phosphors, sulfide phosphors, KSF phosphors, quantum dots, etc. The wavelength conversion materials of each pixel unit in the same Micro LED display device can be the same or different. When the Micro LED display device emits uniform white light, the wavelength conversion material of each pixel unit is the same; when the Micro LED display device is a full-color display, the wavelength conversion materials of each pixel unit are different. This embodiment does not impose any restrictions on this, and the design can be based on the application requirements. In this embodiment, the light conversion layer is formed on the surface of the first semiconductor layer between the grids of the ohmic contact structure. The thickness of the light conversion layer can be the same as or different from the thickness of the ohmic contact structure, depending on the light emission requirements.

[0023] The above embodiment is improved to obtain the present embodiment, in which the Micro LED display device further includes a microlens structure. The materials for preparing the microlens structure include photoresist, hot melt adhesive, SiO2, etc., and include a plurality of microlenses, each of which corresponds to the metal wall covering the surface of the first semiconductor layer of each pixel unit. Generally speaking, the microlens completely covers the light-emitting surface of the pixel unit, and the plane projection is consistent with the plane projection shape of each pixel unit. In the present embodiment, the microlens is a spherical convex lens, in which a bulge is formed outward from the light-emitting surface, and the light emitted from the light-emitting surface is focused to achieve collimation. In other embodiments, it can also be a cylindrical lens, a triangular prism, an ellipsoidal lens, etc. This embodiment does not limit this, as long as the purpose of light collimation can be achieved. In this embodiment, the microlens structure can be formed above the light conversion layer of the previous embodiment, or it can be directly formed above the first semiconductor layer of the pixel unit, and can be designed according to needs.

[0024] Corresponding to the above-mentioned inventive concept, another embodiment of the present invention is a method for preparing a Micro LED display device, as follows: Figures 1 to 13 Shown, including: S10 provides a growth substrate, and grows a semiconductor multilayer structure including a first semiconductor layer, a light emitting layer, and a second semiconductor layer in order from bottom to top on a surface of the substrate.

[0025] In this embodiment, Figure 1As shown, the semiconductor multilayer structure 20 includes a first semiconductor layer 21, a light-emitting layer 22, and a second semiconductor layer 23, which are sequentially grown on the surface of a growth substrate 10 such as silicon, sapphire, silicon carbide, or gallium arsenide. Typically, the first semiconductor layer is made of an N-type semiconductor material, and the second semiconductor layer is made of a P-type semiconductor material, but this embodiment is not limited to this. The semiconductor layers can be doped GaN, or made of other binary or ternary materials. In specific application scenarios, the first semiconductor layer can also be a P-type semiconductor material, and the second semiconductor layer can be an N-type semiconductor material. The light-emitting layer is usually composed of a semiconductor material with a specific energy band gap, which determines the wavelength of light emitted by the device, that is, the color of the light emitted by the display device. Theoretically, as long as a voltage is applied to the materials and structures of the first semiconductor layer, the light-emitting layer, and the second semiconductor layer, the electrons and holes in the first semiconductor layer and the second semiconductor layer can recombine in the light-emitting layer to release energy, thereby generating photon light emission.

[0026] S20 etches the semiconductor multilayer structure along the edge of each pixel unit to the first semiconductor layer, forming grooves between the pixel units, wherein the groove sidewalls are inclined and the opening width gradually decreases from top to bottom, and the first semiconductor layer is partially etched.

[0027] In this embodiment, Figure 2As shown, to facilitate the transfer of pixel units, trenches 24 are formed by etching the second semiconductor layer 23, the light-emitting layer 22, and a portion of the second semiconductor layer 21 along the edges of each pixel unit. The trench sidewalls are inclined, and the width of the trench opening gradually decreases from top to bottom. In other embodiments, the semiconductor multilayer structure can also be directly etched through. Trenches are formed by etching through the semiconductor multilayer structure between the pixel units to isolate the light-emitting materials of each pixel unit and make them independent of each other. Etching can be performed using wet or dry etching (preferably dry etching). The pixel units separated by the trenches can be circular, square, polygonal, etc., and the corresponding trenches can be designed to crisscross or independently surround each other. This embodiment does not impose any restrictions on this and can be designed according to actual application requirements. Generally speaking, the pixel units in Micro LED display devices are square in structure and are smaller than 100µm by 100µm (micrometers). Since there is no light-emitting material in the trench area, no photons can be generated. To improve luminous efficiency, the width of the trench should be as small as possible without affecting the optoelectronic performance of the chip. Regarding the groove shape, to further improve the overall light extraction efficiency of the Micro LED display device, the width of the groove bottom can be designed to be zero, that is, the groove can be designed into a V-shape. This design not only reduces the distance between adjacent pixel units, increasing the light-emitting area; but also, due to the close distance between adjacent pixel units, the width of the metal wall formed above the adjacent pixel units can be further reduced, thereby further reducing the area of ​​the metal wall on the light-emitting surface. To achieve better reflection and better ohmic contact with the metal wall, the angle between the groove sidewall and the horizontal direction is designed to be 20° to 80°.

[0028] In this embodiment, after step S20 , the step S30 is included to deposit a second reflective structure on the surface of the second semiconductor layer of each pixel unit.

[0029] The second reflective structure can be a single layer or multiple layers, and the material is selected from one or more of Ag, Al, Cr, Ni, Ti, etc., and is usually prepared by the lift-off method. The second reflective structure is formed on the surface of the second semiconductor layer of each pixel unit. The area of ​​the second reflective structure is at least larger than the area of ​​the conductive opening. In order to achieve independent driving of each pixel unit, the second reflective structures of adjacent pixel units do not contact each other. In this embodiment, Figure 3As shown, the second reflective structure 30 is formed only on the surface of the second semiconductor layer 23. In other embodiments, in addition to being formed on the surface of the second semiconductor layer, the second reflective structure can also be partially formed on the side surfaces of the second semiconductor layer and the light-emitting layer in the groove, as long as the second reflective structures of each pixel unit are spaced a certain distance apart and do not contact each other. The function of the second reflective structure is not only to reflect light emitted from the light-emitting layer toward the second semiconductor layer toward the light-emitting surface (in this embodiment, the light-emitting surface is the surface of the first semiconductor layer away from the light-emitting layer), but also to provide electrical conductivity. When a voltage is applied to the pixel unit, the bonding metal layer conducts electricity to the second semiconductor layer through the second reflective structure. The thickness of the second reflective structure is typically between 10nm and 1000nm (nanometers), which ensures both light reflection and current conduction.

[0030] In order to achieve better conductive effect, in this embodiment, Figure 3 As shown, an ohmic contact layer 31 is further provided between the second reflective structure 30 and the second semiconductor layer 23 to reduce contact resistance. The thickness of the ohmic contact layer is typically between 10 nm and 200 nm. The ohmic contact layer can be made of a transparent, highly conductive, low-contact-resistance oxide material, such as indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), zinc oxide (ZnO), cadmium tin oxide (CTO), indium oxide (InO), indium (In)-doped zinc oxide (ZnO), aluminum (Al)-doped zinc oxide (ZnO), gallium (Ga)-doped zinc oxide (ZnO), or any combination thereof. The ohmic contact layer can also be made of a metal material, such as one or more metals such as Pt and Ag.

[0031] S40 forms a first reflective structure on the sidewalls of the trench of each pixel unit and at the edge of the second reflective structure, and forms a conductive opening on the surface of the second reflective structure. In embodiments where a second reflective structure is not formed, step S40 is as follows: forming a first reflective structure on the sidewalls of the trench of each pixel unit and at the edge of the second semiconductor layer, and forming a conductive opening on the surface of the second reflective structure. The first reflective structure covers all other surfaces of the Micro LED display device away from the first semiconductor layer, including the sidewalls of the trench of each pixel unit and the edge of the second semiconductor layer / second reflective structure. Only one conductive opening is formed on the surface of the second semiconductor layer / second reflective structure (typically located at the center of the second semiconductor layer surface). The first reflective structure contains a high-reflectivity metal material that reflects light from the light-emitting layer toward the first reflective structure. At the same time, the first reflective structure is not electrically connected to the second semiconductor surface / second reflective structure, thereby forming a conductive opening that facilitates current conduction to the second semiconductor layer. The shape of the conductive opening can be arbitrarily designed as required, such as circular or square.

[0032] In the above embodiment, the first reflective structure includes a passivation layer and a reflective layer. The conductive opening in the first reflective structure includes a first opening in the passivation layer and a second opening in the reflective layer. In each pixel unit, the width of the bonding metal layer is consistent with the width of the first opening and is filled in both the first opening and the second opening. The width of the second opening is greater than the first opening, and the bonding metal layer does not contact the reflective layer. Step S40 includes the following steps S41 and S42: S41 deposits a passivation layer on the sidewall of the trench of each pixel unit and the edge of the second reflective structure, wherein the passivation layer forms a first opening on the surface of the second reflective structure.

[0033] like Figure 4 As shown, a passivation layer 40 is deposited on the surface of the second reflective structure 30 and the side surfaces of the trenches 24 between each pixel unit. The passivation layer can be made of materials such as Al2O3, SiO2, and SiN, and serves as an insulating barrier. Its thickness ranges from 50nm to 1000nm. To facilitate electrical conduction to the second reflective structure, a first opening 41 is provided in the passivation layer. The first opening is located above the second reflective structure layer 30, exposing a portion of the second reflective structure surface. The size and shape of the first opening are not limited in this embodiment, as long as they can conduct current to the first reflective layer, and can be, for example, a circular hole or a square hole.

[0034] S42 deposits a reflective layer on the surface of the passivation layer of each pixel unit, wherein the reflective layer forms a second opening on the surface of the second reflective structure, and the second opening at least covers the first opening, and the boundary of the second opening is within the area of ​​the second reflective structure.

[0035] The reflective layer can also be a single layer or multiple layers, and the material is selected from one or more of Ag, Al, Cr, Ni, Ti, etc. The reflective layer only reflects the light emitted by the light-emitting layer to other surfaces and reflects it to the light-emitting surface, and has no conductive function. Figure 4 As shown, the reflective layer 50 covers the surface of the passivation layer 40 in each pixel unit and is formed with a second opening 51. The second opening at least covers the first opening 41, and the boundary of the second opening is within the area of ​​the second reflective structure 30. In other words, the coverage area of ​​the second opening is larger than the area range of the first opening, but smaller than the area range of the second reflective structure. It should be understood that through this design of small openings superimposed on large openings, the reflective layer in the first reflective structure of each pixel unit is not in conductive contact with the bonding metal layer filled in the smaller first opening, and the bonding metal layer can independently drive each pixel unit through the bonding metal layer. At the same time, the second reflective structure and the first reflective structure complement each other, ensuring that all other surfaces of the Micro LED display device other than the light-emitting surface (including the groove surface between pixel units) are reflective surfaces, reflecting scattered light back to the light-emitting surface, effectively improving the luminous efficiency.

[0036] S50 deposits a bonding metal layer in the conductive opening of each pixel unit, and fills the area between each bonding metal layer with a bonding glue layer flush with the surface of the bonding metal layer.

[0037] The bonding metal layer is made of Au, Cu, Sn, In, etc. or their alloys, and is filled in the conductive opening by photolithography and evaporation, ion sputtering, chemical plating, etc., and is conductively connected to the surface of the second semiconductor layer of the pixel unit (through the bonding metal layer flowing through the second reflective structure to the second semiconductor layer). It is a conductive connection bridge between the pixel unit and the driving substrate. The thickness is higher than the thickness of the first opening, generally 0.2µm ~ 20µm. In this embodiment, the bonding metal layer is only filled in the first opening of the conductive opening, and does not contact the second opening, to avoid connection with the reflective layer. Figure 6 As shown, a bonding metal layer 60 fills the first opening 41 of each pixel unit and connects to the second reflective structure 30. Because the second opening 51 of the reflective layer 50 is larger than the first opening, there is a certain distance between the bonding metal layer and the reflective layer, and the bonding metal layer does not conduct electricity to the reflective layer. SiO2, SU8 photoresist, or other polymers are filled between the bonding metal layers of each pixel unit to form a bonding adhesive layer, and CMP (chemical mechanical polishing) technology is used to make the surface flush with the bonding metal layer surface.

[0038] S60: flipping and bonding the pixel unit to the surface of the driving circuit on the driving substrate through the bonding metal layer.

[0039] like Figure 7 As shown, each pixel unit is bonded to the driving circuit on the surface of the driving substrate via a bonding metal layer 60. The driving circuit electrically drives the pixel unit through the bonding metal layer. The driving substrate can be a printed circuit board (PCB), a thin film transistor (TFT) substrate, a complementary metal oxide semiconductor (CMOS) substrate, etc. Metal (corresponding to the bonding metal layer contacts) and dielectric material (formed between the bonding metal layer contacts) can also be formed on the substrate circuit surface and planarized using CMP technology.

[0040] S70: removing the growth substrate and etching the exposed first semiconductor layer to obtain independent pixel units.

[0041] In this embodiment, the method of removing the substrate can be selected according to the actual situation. For example, the silicon or GaAs substrate can be removed by dry etching or wet etching, and the sapphire substrate can be removed by laser stripping. Figure 7 and Figure 8 As shown, in Figure 8Lieutenant General Figure 7 In some embodiments, in step S20, the second semiconductor layer, the light-emitting layer, and a portion of the second semiconductor layer are etched along the edge of each pixel unit to form a groove, the groove sidewall is inclined, and the groove opening width gradually decreases from top to bottom; since the semiconductor multilayer structure is not etched through, in order to form an independent pixel unit, after the growth substrate is removed, the first semiconductor layer is further etched until it is flush with the bottom surface of the groove, such as Figure 9 As shown, the first semiconductor layer 21 is flush with the bottom surface of the trench 24. In other embodiments, if the semiconductor multilayer structure has been etched through during the trench formation process in step S20, the step of etching the first semiconductor layer can be omitted.

[0042] S80 forms a metal wall on the surface of the first semiconductor layer along the upper portion of each pixel unit groove to obtain a mesh-like ohmic contact structure. Adjacent pixel units share a metal wall at their junctions, and the metal wall is conductively connected to the first semiconductor layers of two adjacent pixel units.

[0043] The metal walls of each pixel unit are interconnected to form a mesh-like ohmic contact structure. The metal walls of each pixel unit in the Micro LED display device are interconnected as a whole. The metal walls conduct current to each pixel unit, thereby realizing a common cathode design. The height of the metal wall is 0.5µm~50µm. The metal wall is in ohmic contact and conductive with the first semiconductor layer of two adjacent pixel units at the same time. It is formed on the surface of the first semiconductor layer above the groove of each pixel unit. The bottom surface of the metal wall is in contact with the first semiconductor layer of two adjacent pixel units. The metal wall is set around each pixel unit. Figure 10 As shown, the metal wall 70 is formed on the surface of the first semiconductor layer 21 above each pixel unit groove 24 by photolithography and evaporation, ion sputtering, chemical plating, etc. The metal wall in this embodiment is in direct contact with the first semiconductor layer, realizing the N-side contact of the pixel unit and playing the role of optical isolation and avoiding optical crosstalk between adjacent pixel units, while saving processes. At the same time, the metal wall can also reflect the light emitted from the light surface to other adjacent pixel areas, playing the role of optical isolation and avoiding optical crosstalk between adjacent pixel units. In the example where the pixel unit is a square structure, the ohmic contact structure is a square mesh structure, and the junctions of adjacent pixel units share a metal wall, and the two opposite surfaces of the shared metal wall respectively reflect the light inside the corresponding pixel unit. In other embodiments, the shape of the ohmic contact structure is determined by the shape of the pixel unit, as long as it can achieve the purposes of optical isolation and ohmic contact at the same time.

[0044] In another embodiment, after completing step S80, a step S81 is further included: forming a light conversion layer on the surface of the first semiconductor layer between the metal walls in each pixel unit to convert the light emitted by the pixel unit into other wavelengths. Figure 11As shown, the light conversion layer 71 is formed on the surface of the first semiconductor layer 21 of each pixel unit, inside the area surrounded by the metal wall 70. The wavelength conversion material inside converts the light emitted from the light-emitting surface into another wavelength. The wavelength conversion material is a phosphor that can be excited by the light emitted by the semiconductor multilayer structure, thereby obtaining a display device with a light color different from that emitted by the semiconductor multilayer structure. The composition of the wavelength conversion material can be at least one or more of the following: garnet-type phosphor, nitrogen oxide phosphor, aluminate phosphor, nitride phosphor, sulfide phosphor, KSF phosphor, quantum dot, etc. The wavelength conversion materials of each pixel unit in the same Micro LED display device can be the same or different; when the light emitted by the Micro LED display device is uniformly white light, the wavelength conversion materials of each pixel unit are the same; when the Micro LED display device is a full-color display, the wavelength conversion materials of each pixel unit are different. While this embodiment does not limit this, it can be designed according to the implementation application requirements. In this embodiment, the light conversion layer is formed on the surface of the first semiconductor layer between the grids of the ohmic contact structure. The thickness of the light conversion layer can be the same as or different from the thickness of the ohmic contact structure, depending on the light emission requirements.

[0045] The present embodiment is obtained by improving the above embodiment. In this embodiment, after step S80, the following step is further included: S90 forms a microlens structure above the metal wall on the surface of the first semiconductor layer of each pixel unit, and the microlens structure includes multiple microlenses corresponding to the pixel units one by one.

[0046] The materials used to prepare the microlens structure include photoresist, hot melt adhesive, SiO2, etc., which are prepared by photolithography or lamination and contain multiple microlenses. Figure 12 and Figure 13 As shown, each microlens 80 is correspondingly arranged above the first semiconductor layer 21 of each pixel unit and in the area surrounded by the metal wall 70. Generally speaking, the microlens completely covers the light-emitting surface of the pixel unit, and the plane projection is consistent with the plane projection shape of each pixel unit. In this embodiment, the microlens is a spherical convex lens, which forms a bulge outward from the light-emitting surface to focus the light emitted from the light-emitting surface to achieve collimation. In other embodiments, it can also be a cylindrical lens, a triangular prism, an ellipsoidal lens, etc. This embodiment is not limited to this, as long as the purpose of light collimation can be achieved.

[0047] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of the present invention. It should be pointed out that those skilled in the art can make several improvements and modifications without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A Micro LED display device, characterized in that: include: A driving substrate, a driving circuit being formed on a surface of the driving substrate; At least two independent pixel units, each pixel unit comprising a semiconductor multilayer structure in which a second semiconductor layer, a light-emitting layer, and a first semiconductor layer are stacked in sequence from bottom to top, and a trench is formed between the pixel units, penetrating the semiconductor multilayer structure, with inclined sidewalls and an opening width gradually decreasing from bottom to top; A first reflective structure is formed on the sidewall of the trench of each pixel unit and the edge of the second semiconductor layer, and a conductive opening is formed on the surface of the second semiconductor layer; A bonding metal layer is formed in the conductive opening corresponding to each pixel unit and is used to bond the corresponding pixel unit to the driving circuit on the surface of the driving substrate; a bonding adhesive layer formed around the bonding metal layer, wherein the upper surface of the bonding adhesive layer is flush with the upper surface of the bonding metal layer; The ohmic contact structure is a mesh structure formed by interconnected metal walls formed on the surface of each pixel unit; the metal walls are formed on the surface of the first semiconductor layer along the grooves between the pixel units, and the junctions of adjacent pixel units share a metal wall, which is also conductively connected to the first semiconductor layers of two adjacent pixel units.

2. The Micro LED display device according to claim 1, wherein: The Micro LED display device also includes a second reflective structure formed on the surface of the second semiconductor layer in each pixel unit. The first reflective structure is formed on the sidewall of the groove of each pixel unit and the edge position of the second reflective structure, and the conductive opening is formed on the surface of the second reflective structure.

3. The Micro LED display device according to claim 2, wherein: The first reflective structure includes: A passivation layer is formed on the sidewalls of the groove of each pixel unit and at the edge of the second reflective structure, and a first opening is formed on the surface of the second reflective structure; A reflective layer is formed on the surface of the passivation layer, and a second opening is formed on the surface of the second reflective structure. The second opening at least covers the first opening, and an edge of the second opening is located on the upper surface of the second reflective structure.

4. The Micro LED display device according to claim 1, wherein: The grooves formed between the pixel units are V-shaped grooves, and / or the angle between the sidewalls of the grooves between the pixel units and the horizontal direction is 20° to 80°.

5. The Micro LED display device according to claim 1, wherein: In each of the pixel units, a light conversion layer is formed on the surface of the first semiconductor layer within the mesh of the ohmic contact structure.

6. The Micro LED display device according to any one of claims 1 to 5, wherein: The Micro LED display device also includes a microlens structure, which includes a plurality of microlenses corresponding to the pixel units one by one, and each of the microlenses is formed above the metal wall of the corresponding pixel unit.

7. A method for preparing a Micro LED display device, characterized in that: include: Providing a growth substrate, and growing a semiconductor multilayer structure including a first semiconductor layer, a light-emitting layer, and a second semiconductor layer in order from bottom to top on the surface of the substrate; Etching the semiconductor multilayer structure along the edge of each pixel unit to the first semiconductor layer to form a trench between the pixel units, wherein the trench sidewalls are inclined and the opening width gradually decreases from top to bottom, and the first semiconductor layer is partially etched; forming a first reflective structure at the edge of the second semiconductor layer and the sidewall of the trench of each pixel unit, and forming a conductive opening on the surface of the second reflective structure; Depositing a bonding metal layer in the conductive opening of each pixel unit, and filling the area between each bonding metal layer with a bonding glue layer flush with the surface of the bonding metal layer; flipping and bonding the pixel unit to the driving circuit surface on the driving substrate through the bonding metal layer; removing the growth substrate and etching the exposed first semiconductor layer to obtain mutually independent pixel units; A metal wall is formed on the surface of the first semiconductor layer along the grooves above each pixel unit to obtain a mesh-like ohmic contact structure. The junctions of adjacent pixel units share a metal wall, which is also conductively connected to the first semiconductor layers of two adjacent pixel units.

8. The method for preparing a Micro LED display device according to claim 7, wherein: The semiconductor multilayer structure is etched along the edge of each pixel unit to the first semiconductor layer, and after forming grooves between the pixel units, it includes: depositing a second reflective structure on the surface of the second semiconductor layer of each pixel unit, the first reflective structure is formed on the sidewall of the groove of each pixel unit and the edge position of the second reflective structure, and the conductive opening is formed on the surface of the second reflective structure.

9. The method for preparing a Micro LED display device according to claim 8, wherein: The first reflective structure is formed at the edge of the trench sidewall of each pixel unit and the edge of the second semiconductor layer, and a conductive opening is formed on the surface of the second reflective structure, including: Depositing a passivation layer on the sidewall of the trench of each pixel unit and the edge of the second reflective structure, wherein the passivation layer forms a first opening on the surface of the second reflective structure; A reflective layer is deposited on the surface of the passivation layer of each pixel unit. The reflective layer forms a second opening on the surface of the second reflective structure. The second opening at least covers the first opening, and the boundary of the second opening is within the area of ​​the second reflective structure.

10. The method for preparing a Micro LED display device according to claim 7, wherein: The grooves formed between the pixel units are V-shaped grooves, and / or the angle between the sidewalls of the grooves between the pixel units and the horizontal direction is 20° to 80°.

11. The method for preparing a Micro LED display device according to claim 7, wherein: After forming metal walls on the surface of the first semiconductor layer along the grooves above each pixel unit to obtain a mesh-shaped ohmic contact structure, the method further includes forming a light conversion layer on the surface of the first semiconductor layer within the mesh of the ohmic contact structure.

12. The method for preparing a Micro LED display device according to any one of claims 7 to 11, wherein: After forming a metal wall above the grooves of each pixel unit along the surface of the first semiconductor layer to obtain an ohmic contact structure with a mesh structure, the method further includes: forming a microlens structure above the metal wall on the surface of the first semiconductor layer of each pixel unit, wherein the microlens structure includes multiple microlenses corresponding to the pixel units one by one.

Images