Micro LED display device

Abstract

The utility model provides a Micro LED display device. 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 utility model relates to the field of semiconductor technology, in particular to a Micro LED display device. 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 higher and higher requirements for the portability and lightness of the equipment, which requires that the size of the Micro LED (micro light emitting diode) used must be further reduced. However, with the reduction of the size of Micro LED pixels, and the usual preparation of a regular trapezoidal light-emitting structure, the luminous efficiency of the LED has dropped significantly. In addition, in projection applications, if the optical collimation of the pixel light is not high enough, it is easy to cause image blur. Therefore, there are higher requirements for the optical collimation of the pixel light to ensure the clarity and brightness of the image. At present, metal walls are generally set 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 rate. Utility Model Content

[0003] In order to overcome the above shortcomings, the utility model 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 LED.

[0004] The technical solution provided by the utility model is:

[0005] On the one hand, the utility model provides a Micro LED display device, comprising:

[0006] A driving substrate, a driving circuit being formed on a surface of the driving substrate;

[0007] At least two mutually 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 groove penetrating the semiconductor multilayer structure is formed between the pixel units, and the sidewall of the groove is inclined and the opening width gradually decreases from bottom to top;

[0008] A first reflective structure is formed on the sidewall of the groove 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;

[0009] A bonding metal layer, formed in a conductive opening corresponding to each pixel unit, for bonding the corresponding pixel unit to a driving circuit on the surface of the driving substrate;

[0010] A bonding adhesive layer is formed around the bonding metal layer, and the upper surface of the bonding adhesive layer is flush with the upper surface of the bonding metal layer;

[0011] 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.

[0012] On the other hand, the utility model provides a method for preparing a Micro LED display device, comprising:

[0013] 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;

[0014] Etching the semiconductor multilayer structure to the first semiconductor layer along the edge of each pixel unit to form a groove between the pixel units, wherein the groove sidewall is inclined and the opening width gradually decreases from top to bottom, and the first semiconductor layer is partially etched;

[0015] Forming a first reflective structure on the sidewall of the groove of each pixel unit and the edge of the second semiconductor layer, and forming a conductive opening on the surface of the second reflective structure;

[0016] 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;

[0017] The pixel unit is flipped and bonded to the surface of the driving circuit on the driving substrate through the bonding metal layer;

[0018] Removing the growth substrate and etching the exposed first semiconductor layer to obtain mutually independent pixel units;

[0019] A metal wall is formed on the surface of the first semiconductor layer along the grooves of each pixel unit to obtain a mesh-like ohmic contact structure. The joints of adjacent pixel units share a metal wall, which is conductively connected to the first semiconductor layers of two adjacent pixel units.

[0020] The Micro LED display device and the preparation method thereof provided by the present utility model can at least bring the following beneficial effects:

[0021] 1) The ohmic contact structure with a mesh structure formed by the metal wall is used to reflect the light emitted by the pixel unit back to achieve the purpose of light collimation. The special design of the grooves between the pixel units enables the ohmic contact structure to be directly conductively connected to the first semiconductor layer of the pixel unit, realizing the N-type electrical contact of each pixel unit, achieving the purpose of common cathode design and saving process, while increasing the overall light output area of ​​the Micro LED display device, thereby improving the light efficiency.

[0022] 2) While the first reflective structure is formed on the sidewall of the groove, 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.

[0023] 3) It has expanded the application areas of Micro LED display devices and achieved better application effects in the fields of AR projection display and automotive matrix headlights. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a cross-sectional schematic diagram of forming a semiconductor multilayer structure on the surface of a growth substrate in one embodiment of the utility model;

[0025] Figure 2 It is a cross-sectional schematic diagram of etching a semiconductor multilayer structure to form a groove in one embodiment of the utility model;

[0026] Figure 3 It 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 utility model;

[0027] Figure 4 It is a cross-sectional schematic diagram of forming a passivation layer on the surface of a semiconductor multilayer structure in one embodiment of the utility model;

[0028] Figure 5 It is a cross-sectional schematic diagram of forming a reflective layer on the surface of a semiconductor multilayer structure in one embodiment of the utility model;

[0029] Figure 6 It is a cross-sectional schematic diagram of forming a bonding metal layer in the first opening in one embodiment of the utility model;

[0030] Figure 7 It is a cross-sectional schematic diagram of bonding each pixel unit to a driving substrate through a bonding metal layer in one embodiment of the utility model;

[0031] Figure 8 It is a cross-sectional schematic diagram of removing the growth substrate in one embodiment of the utility model;

[0032] Fig. 9 It is a cross-sectional schematic diagram of etching the first semiconductor layer in one embodiment of the utility model;

[0033] Fig.10 It is a cross-sectional schematic diagram of forming an ohmic contact structure on the surface of the first semiconductor layer in one embodiment of the utility model;

[0034] Fig.11 It 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 utility model;

[0035] Fig.12 It is a cross-sectional schematic diagram of a microlens structure formed on the surface of the first semiconductor layer in one embodiment of the utility model;

[0036] Fig.13 It is a cross-sectional schematic diagram of a microlens structure formed on the surface of the first semiconductor layer in another embodiment of the utility model.

[0037] Reference numerals:

[0038] 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

[0039] In order to more clearly illustrate the implementation cases of the utility model or the technical solutions in the prior art, the specific implementation methods of the utility model will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the utility model. For ordinary technicians in this field, other drawings and other implementation methods can be obtained based on these drawings without creative work.

[0040] An embodiment of the utility model provides a Micro LED display device, comprising: a driving substrate, a driving circuit formed on the 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 groove penetrating the semiconductor multilayer structure is formed between the pixel units, the sidewall of the groove is inclined and the opening width gradually decreases from bottom to top; a first reflective structure is formed at the sidewall of the groove of each pixel unit and the edge position 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 at 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 is formed around the bonding metal layer, and the upper surface of the bonding adhesive layer is flush with the upper surface of the bonding metal layer; an ohmic contact structure is a mesh structure formed by interconnecting metal walls of each pixel unit; the metal wall is formed on the surface of the first semiconductor layer along the groove 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.

[0041] In this embodiment, the semiconductor multilayer structure includes a first semiconductor layer, a light-emitting layer and a second semiconductor layer grown on the surface of a substrate such as silicon, sapphire, silicon carbide, gallium arsenide, etc. in sequence; usually, the first semiconductor layer is prepared from an N-type semiconductor material, and the second semiconductor layer is prepared from a P-type semiconductor material, but this embodiment is not limited to this, and the semiconductor layer can be doped GaN, or can be made of other binary or ternary materials; in a specific application scenario, 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. In theory, 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 and release energy in the light-emitting layer, thereby generating photon light emission.

[0042] The groove runs through the semiconductor multilayer structure between each pixel unit, isolating the light-emitting material of each pixel unit to make it independent of each other. The shape of the pixel unit isolated by the groove can be circular, square, polygonal, etc., and the corresponding groove can be designed as a criss-cross grid, etc. This embodiment does not limit this, and it can be designed according to the actual application requirements. Generally speaking, the pixel unit in the Micro LED display device is a square structure and is less than 100µm*100µm (micrometer). Since there is no light-emitting material in the groove area, photon light emission cannot be generated. In order to improve the light-emitting efficiency, the maximum width of the groove can be designed as small as possible without affecting the photoelectric performance. In this embodiment, in order to facilitate the formation of the first reflective structure and the contact between the first semiconductor layer and the ohmic contact structure, the groove is formed with an inclined sidewall, that is, the opening width of the groove gradually decreases from bottom to top, and correspondingly, the cross-section of the pixel unit is an inverted trapezoid to increase the light-emitting surface area of ​​the pixel unit. For the shape of the groove, in order to further improve the overall light-emitting efficiency of the Micro LED display device, the width of the bottom of the groove can be designed to be zero, that is, the groove is designed to be V-shaped (opening downward). This design not only reduces the distance between adjacent pixel units and increases the light-emitting area, but also because the distance between adjacent pixel units is close, the width of the metal wall formed above the adjacent pixel units can be further reduced, thereby reducing the area ratio of the metal wall on the light-emitting surface and increasing the overall light-emitting area of ​​the Micro LED display device. In order to achieve better reflection effect and better ohmic contact with the metal wall, the angle between the groove sidewall and the horizontal direction is designed to be 20°~80° (degrees).

[0043] The first reflective structure covers the sidewalls of the grooves of each pixel unit and the edge of the surface of the second semiconductor layer, and only forms a conductive opening on the surface of the second semiconductor layer (usually designed at the center of the surface of the second semiconductor layer). The first reflective structure contains a metal material with high reflectivity, which reflects the light emitted from the light-emitting layer to the first reflective structure; at the same time, the first reflective structure is not conductively connected to the surface of the second semiconductor, so a conductive opening is formed to facilitate the conduction of current to the second semiconductor layer. The shape of the conductive opening can be arbitrarily designed according to needs, such as circular, square, etc.

[0044] The bonding metal layer is made of Au, Cu, Sn, In or their alloys, filled in the conductive opening, and conductively connected to the surface of the second semiconductor layer of the pixel unit. It is a conductive connection bridge between the pixel unit and the driving substrate. The thickness is generally higher than the thickness of the conductive opening, ranging from 0.2µm to 20µm. In order to facilitate alignment and bonding with the driving substrate, SiO2, SU8 photoresist or other polymers are filled between the bonding metal layers of each pixel unit to form a bonding adhesive layer, and the surface is made flush with the surface of the bonding metal layer by CMP (chemical mechanical polishing) technology. Each pixel unit is bonded to the driving circuit on the surface of the driving substrate through the bonding metal layer, and the driving circuit drives the pixel unit conductively 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. A driving circuit is formed on the driving surface, and the pixel unit is conductively driven by the internal circuit control design after the power is turned on. 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.

[0045] The ohmic contact structure is a mesh structure formed by interconnecting the metal walls of each pixel unit; the metal walls of each pixel unit in the Micro LED display device are interconnected as a whole, and the metal wall conducts current to each pixel unit to realize the common cathode design, and the height of the metal wall is 0.5µm~50µm. Before preparing the metal wall, the growth substrate on the surface of the semiconductor multilayer structure has been removed to expose the surface of the first semiconductor layer. The metal wall is in ohmic contact and conductive with the first semiconductor layer of two adjacent pixel units at the same time, and is formed on the surface of the first semiconductor layer along the groove of each pixel unit. The bottom surface of the metal wall is in contact with the first semiconductor layer of the two adjacent pixel units, and the metal wall is arranged around each pixel unit. In this embodiment, the metal wall directly contacts the first semiconductor layer, realizes the N-face contact of the pixel unit, plays the role of optical isolation, avoids optical crosstalk between adjacent pixel units, and saves processes. In the example where the pixel unit is a square structure, the ohmic contact structure is a square mesh structure, and the adjacent pixel units share a metal wall at the junction, 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 light isolation and ohmic contact at the same time.

[0046] The above embodiment is improved to obtain the present embodiment. In the present 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. At this time, 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 (the reflective material of the first reflective structure at least wraps the edge of the second reflective structure, and the two reflective structures complement each other and are formed on the entire light-emitting surface), and a conductive opening is formed on the surface of the second reflective structure, and the bonding metal layer in the conductive opening is conductively connected to the second reflective structure, and the 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 a multilayer, 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, and the area range of the second reflective structure is at least larger than the area of ​​the conductive opening. In order to realize the 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 only formed on the surface of the second semiconductor layer. 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 there is a certain distance between the second reflective structures of each pixel unit and they do not touch each other. The function of the second reflective structure is not only to reflect the light emitted from the light-emitting layer to the second semiconductor layer to 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 perform the function of conducting electricity; 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. Usually, the thickness of the second reflective structure is 10nm~1000nm (nanometers), which can ensure both the reflection effect of light and the conduction effect of current.

[0047] Furthermore, an ohmic contact layer is formed between the second reflective structure and the second semiconductor layer to reduce the contact resistance, and the thickness of the ohmic contact layer is usually 10nm~200nm. The ohmic contact layer can be 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 material of the ohmic contact layer can also be a metal material, such as one or more metals such as Pt and Ag.

[0048] In the above embodiment, the first reflective structure includes a passivation layer and a reflective layer, and 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 the first opening and the second opening at the same time. The width of the second opening is greater than the first opening, and the bonding metal layer does not contact the reflective layer. The passivation layer is formed on the sidewall of the groove of each pixel unit and 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, SiN, etc., which plays a role of insulation isolation, and the thickness is 50nm~1000nm. In order to facilitate the power supply to the second reflective structure, the first opening in the passivation layer is located above the second reflective structure, exposing part of the surface of the second reflective structure; the size and shape of the first opening can achieve the purpose of conducting current to the second reflective structure, and this is not limited in this embodiment, such as a round hole, a square hole, etc.

[0049] The reflective layer can also be a single layer or a multilayer, 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 to the light-emitting surface, and has no conductive function. 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 range of the second reflective structure. In other words, the coverage area of ​​the second opening is larger than the area range of the first opening, and at the same time 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 drive each pixel unit independently 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 other than the light-emitting surface in the Micro LED display device (including the groove surface between the pixel units) are reflective surfaces, reflecting the scattered light back to the light-emitting surface, effectively improving the luminous efficiency.

[0050] The above embodiment is improved to obtain the present embodiment, in which 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 other wavelengths. The internal wavelength conversion material converts the light emitted from the light emitting surface into another wavelength, and 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 different light color 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. This embodiment does not limit this, and 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 emitting requirements.

[0051] The above-mentioned embodiment is improved to obtain the present embodiment, wherein the Micro LED display device further includes a microlens structure, and 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 a 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., and the present 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 it can be designed according to the needs.

[0052] Corresponding to the above utility model concept, another embodiment of the utility model is a method for preparing a Micro LED display device, such as Figures 1 to 13 As shown, including:

[0053] 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 sequence from bottom to top on a surface of the substrate.

[0054] 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 grown on the surface of a growth substrate 10 such as silicon, sapphire, silicon carbide, gallium arsenide, etc. in sequence. Usually, the first semiconductor layer is prepared from an N-type semiconductor material, and the second semiconductor layer is prepared from 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 a specific application scenario, 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 the light emitted by the device, that is, the light color of the display device. In theory, 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 and release energy in the light-emitting layer, thereby generating photon light emission.

[0055] 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.

[0056] In this embodiment, Figure 2As shown, in order to facilitate the transfer of pixel units, the second semiconductor layer 23, the light-emitting layer 22 and part of the second semiconductor layer 21 are etched along the edge of each pixel unit to form a groove 24, the sidewall of the groove is inclined, and the width of the groove opening gradually decreases from top to bottom. In other embodiments, the semiconductor multilayer structure can also be directly etched. A groove that runs through the semiconductor multilayer structure between each pixel unit is formed by etching, and the light-emitting materials of each pixel unit are isolated to make them independent of each other. Etching can be performed by wet etching or dry etching (preferably dry etching). The shape of the pixel unit isolated by the groove can be circular, square, polygonal, etc., and the corresponding groove can be designed to be criss-crossed or independently surrounded. This embodiment does not limit this, and it can be designed according to actual application requirements; generally speaking, the pixel unit in the Micro LED display device is a square structure and is less than 100µm*100µm (micrometer). Since there is no light-emitting material in the groove area, photon light emission cannot be generated. In order to improve the light-emitting efficiency, the width of the groove should be designed to be as small as possible without affecting the photoelectric performance of the chip. As for the shape of the groove, in order to further improve the overall light output efficiency of the Micro LED display device, the width of the bottom of the groove can be designed to be zero, that is, the groove can be designed to be V-shaped. This design method not only reduces the distance between adjacent pixel units and increases the light-emitting area; but also because the distance between adjacent pixel units is close, the width of the metal wall formed above the adjacent pixel units can be further reduced, thereby further reducing the area ratio of the metal wall on the light-emitting surface. In order to achieve better reflection effect and better ohmic contact with the metal wall, the angle between the groove sidewall and the horizontal direction is designed to be 20°~80° (degrees).

[0057] 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.

[0058] The second reflective structure can be a single layer or a multilayer, and the material is selected from one or more of Ag, Al, Cr, Ni, Ti, etc., and is usually prepared by a lift-off method. The second reflective structure is formed on the surface of the second semiconductor layer of each pixel unit, and the area range 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 only formed 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 there is a certain distance between the second reflective structures of each pixel unit and they do not touch each other. The function of the second reflective structure is not only to reflect the light emitted from the light-emitting layer to the second semiconductor layer to 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 perform the function of conducting electricity; 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. Usually, the thickness of the second reflective structure is 10nm~1000nm (nanometers), which can ensure both the reflection effect of light and the conduction effect of current.

[0059] In order to achieve a 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 the contact resistance, and the thickness of the ohmic contact layer is usually 10nm~200nm. The ohmic contact layer can be 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 material of the ohmic contact layer can also be a metal material, such as one or more metals such as Pt and Ag.

[0060] S40 forms a first reflective structure at the groove sidewall of each pixel unit and the edge position of the second reflective structure, and forms a conductive opening on the surface of the second reflective structure. In an embodiment where the second reflective structure is not formed, the step S40 is as follows: forming a first reflective structure at the groove sidewall of each pixel unit and the edge position of the second semiconductor layer, and forming a conductive opening on the surface of the second reflective structure. The first reflective structure covers other surfaces of the Micro LED display device away from the first semiconductor layer, including the groove sidewall of each pixel unit and the surface edge position of the second semiconductor layer / second reflective structure, and only forms a conductive opening on the surface of the second semiconductor layer / second reflective structure (usually designed at the center position of the second semiconductor layer surface). The first reflective structure contains a metal material with high reflectivity, which reflects the light emitted from the light-emitting layer to the first reflective structure; at the same time, the first reflective structure is not conductively connected to the second semiconductor surface / second reflective structure, so a conductive opening is formed to facilitate the conduction of current to the second semiconductor layer. The shape of the conductive opening can be arbitrarily designed according to needs, such as circular, square, etc.

[0061] 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 the first opening and the second opening at the same time, 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:

[0062] S41 deposits a passivation layer on the sidewall of the groove of each pixel unit and the edge of the second reflective structure, and the passivation layer forms a first opening on the surface of the second reflective structure.

[0063] like Figure 4 As shown, the passivation layer 40 is deposited on the surface of the second reflective structure 30 and the side surface of the groove 24 between each pixel unit. The passivation layer can be made of materials such as Al2O3, SiO2, SiN, etc., and plays a role of insulation isolation. The thickness is 50nm~1000nm. In order to facilitate the power supply to the second reflective structure, a first opening 41 is also provided in the passivation layer. The first opening is located above the second reflective structure layer 30, exposing part of the second reflective structure surface; the size and shape of the first opening can be any size and shape as long as it can achieve the purpose of conducting current to the first reflective layer. This embodiment does not limit this, such as a round hole, a square hole, etc.

[0064] S42: depositing 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.

[0065] 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 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 a second opening 51 is formed, 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, and at the same time 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 drive each pixel unit independently 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 (including the groove surface between pixel units) in the Micro LED display device other than the light-emitting surface are reflective surfaces, reflecting scattered light back to the light-emitting surface, effectively improving the luminous efficiency.

[0066] S50: depositing a bonding metal layer in the conductive opening of each pixel unit, and filling a bonding glue layer flush with the surface of the bonding metal layer in the area between the bonding metal layers.

[0067] The bonding metal layer is made of Au, Cu, Sn, In or their alloys, and is filled in the conductive opening by photolithography and evaporation, ion sputtering, chemical plating, etc. It is conductively connected to the surface of the second semiconductor layer of the pixel unit (conducted to the second semiconductor layer through the bonding metal layer flowing through the second reflective structure). It is a conductive connection bridge between the pixel unit and the drive 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, the bonding metal layer 60 is filled in the first opening 41 of each pixel unit and connected to the second reflective structure 30. Since 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 reflective layer is not conductive. SiO2, SU8 photoresist or other polymers are filled between the bonding metal layers of each pixel unit to form a bonding adhesive layer, and the surface is made flush with the surface of the bonding metal layer through CMP (chemical mechanical polishing) technology.

[0068] S60: flipping and bonding the pixel unit to the surface of the driving circuit on the driving substrate through the bonding metal layer.

[0069] like Figure 7 As shown, each pixel unit is bonded to the driving circuit on the surface of the driving substrate through the bonding metal layer 60, and the driving circuit conducts and 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., and can also be formed on the surface of the substrate circuit using metal (corresponding to the bonding metal layer contacts) and dielectric materials (formed between the bonding metal layer contacts) and planarized using CMP technology.

[0070] S70: removing the growth substrate and etching the exposed first semiconductor layer to obtain mutually independent pixel units.

[0071] 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 8As shown, in Figure 8 Lieutenant General Figure 7 In some embodiments, in step S20, the second semiconductor layer, the light emitting layer and part 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 Fig. 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 process of etching to form the trench in step S20, the step of etching the first semiconductor layer can be omitted.

[0072] S80: forming a metal wall on the surface of the first semiconductor layer along the grooves above each pixel unit to obtain a mesh-shaped 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.

[0073] The metal walls of each pixel unit are interconnected to form a mesh to form an ohmic contact structure. The metal walls of each pixel unit in the Micro LED display device are interconnected as a whole. The metal wall conducts current to each pixel unit to achieve 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. Fig.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 directly in contact with the first semiconductor layer, and in addition to realizing the N-face contact of the pixel unit, it also plays 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 adjacent pixel units share a metal wall at the junction, 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.

[0074] 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. Fig.11 As 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 internal wavelength conversion material 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, so as to obtain a display device with a different light color 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. This embodiment does not limit this, and it can be designed according to 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 emitting requirements.

[0075] The present embodiment is obtained by improving the above embodiment. In the present embodiment, after step S80, it further includes: S90 forming a microlens structure above the metal wall on the surface of the first semiconductor layer of each pixel unit, and the microlens structure includes a plurality of microlenses corresponding to the pixel units one by one.

[0076] 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. Fig.12 and Fig.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.

[0077] It should be noted that the above embodiments can be freely combined as needed. The above is only a preferred implementation of the utility model. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the utility model, and these improvements and modifications should also be regarded as the protection scope of the utility model.

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 mutually 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 groove penetrating the semiconductor multilayer structure is formed between the pixel units, and the sidewall of the groove is inclined and the opening width gradually decreases from bottom to top; A first reflective structure is formed on the sidewall of the groove 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, formed in a conductive opening corresponding to each pixel unit, for bonding the corresponding pixel unit to a driving circuit on the surface of the driving substrate; A bonding adhesive layer is formed around the bonding metal layer, and 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, characterized in that: 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, characterized in that: The first reflective structure comprises: A passivation layer is formed on the sidewalls of the grooves 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 in the mesh of the ohmic contact structure.

6. The Micro LED display device according to any one of claims 1 to 5, characterized in that: 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 a metal wall of the corresponding pixel unit.

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