WO2022052560A1

WO2022052560A1 - Micro-light emitting diode chip, preparation method therefor, and display panel

Info

Publication number: WO2022052560A1
Application number: PCT/CN2021/101526
Authority: WO
Inventors: 姚志博; 盛翠翠; 董小彪; 郭恩卿; 夏继业; 王程功
Original assignee: 成都辰显光电有限公司
Priority date: 2020-09-11
Filing date: 2021-06-22
Publication date: 2022-03-17
Also published as: CN114171648A

Abstract

Disclosed in the present application are a micro-light emitting diode chip, a preparation method therefor, and a display panel. The micro-light emitting diode chip comprises an epitaxial wafer and a first electrode. The epitaxial wafer comprises a first cladding layer and a first current spreading layer that are stacked. The first cladding layer is located on the side of the first current spreading layer away from the first electrode. The first current spreading layer comprises a contact surface that is in contact with the first cladding layer. Along the thickness direction of the micro-light emitting diode chip, the projection of the contact surface is located inside of the projection of the first cladding layer. The first electrode is disposed to be in contact with the first current spreading layer.

Description

Micro light-emitting diode chip, method for making the same, and display panel

This application claims the priority of the Chinese patent application with application number 202010954485.3 filed with the China Patent Office on September 11, 2020, the entire contents of which are incorporated into this application by reference.

technical field

The embodiments of the present application relate to display technology, for example, to a micro light-emitting diode chip, a method for manufacturing the same, and a display panel.

Background technique

With the continuous development of micro-LED chip technology, the application of micro-LED display panels is becoming more and more extensive.

However, a large amount of non-radiative recombination exists in the micro-LED chip during current recombination, so that the luminous efficiency of the micro-LED chip is low, which limits the application of the micro-LED display panel.

SUMMARY OF THE INVENTION

The present application provides a micro-light-emitting diode chip, a preparation method thereof, and a display panel, so as to reduce the non-radiative recombination of the current of the micro-light-emitting diode chip and improve the luminous efficiency.

An embodiment of the present application provides a micro-light-emitting diode chip, the micro-light-emitting diode chip includes: an epitaxial wafer, the epitaxial wafer includes a first cladding layer and a first current spreading layer arranged in layers; a first electrode, the first An electrode is arranged in contact with the first current spreading layer; the first cladding layer is located on the side of the first current spreading layer away from the first electrode; the first current spreading layer includes and the first current spreading layer The contact surface contacted by the cladding layer, along the thickness direction of the micro-LED chip, the projection of the contact surface is located inside the projection of the first cladding layer. The non-radiative recombination of the current on the side wall of the micro light-emitting diode chip is less, thereby reducing the non-radiative recombination of the current and improving the luminous efficiency.

Optionally, the first current spreading layer includes a plurality of block structures, and a gap exists between two adjacent block structures. On the one hand, it makes it easier to separate the micro-LED chip from the transfer head, thereby improving the yield of mass transfer, and on the other hand, it can also improve the bonding strength between the micro-LED chip and the driving backplane.

Optionally, the first current spreading layer further includes a flat structure between the plurality of bulk structures and the first cladding layer. The resistance of current transmission can be reduced, so that the turn-on voltage of the micro-LED chip is lowered, the power consumption of the micro-LED chip is reduced, and the luminous efficiency is further improved.

Optionally, a side of the first cladding layer close to the first current spreading layer includes a plurality of raised structures; the plurality of raised structures correspond to the plurality of block structures one-to-one. On the one hand, it makes it easier to separate the micro-LED chip from the transfer head, improving the yield of mass transfer, and on the other hand, it can also greatly improve the bonding strength between the micro-LED chip and the driving backplane.

Optionally, the plurality of block structures are evenly distributed. The internal current distribution of the active layer can be made more uniform, and the stability of the electrical connection between the micro light emitting diode chip and the driving backplane can be improved at the same time.

Optionally, the shape of the first electrode matches the shape of the first current spreading layer. The contact area between the first electrode and the solder post is large, which effectively reduces the contact resistance, thereby reducing the loss, and can also increase the stability of the electrical connection between the first electrode and the solder post, thereby improving the stability of the light-emitting display of the micro-LED chip.

Optionally, the epitaxial wafer includes a stacked second cladding layer, an active layer, the first cladding layer and the first current spreading layer, the micro-LED chip further includes a second electrode, and the The second electrode is arranged in contact with the second cladding layer.

Optionally, the first electrode is an anode of the micro-LED chip, and the second electrode is a cathode of the micro-LED chip.

Optionally, the second cladding layer includes a plurality of protrusions, and the shape of the second electrode matches the shape of the plurality of protrusions, which can further improve the stability of the connection between the micro-LED chip and the driving backplane. sex.

Embodiments of the present application further provide a method for fabricating a micro-light emitting diode chip, the method comprising: forming an epitaxial wafer, wherein the epitaxial wafer includes a first cladding layer and a first current spreading layer arranged in layers, the first cladding layer and the first current spreading layer. A cladding layer is located on the side of the first current spreading layer away from the first electrode; the first current spreading layer includes a contact surface in contact with the first cladding layer, and along the thickness direction of the micro-LED chip, The projection of the contact surface is located inside the projection of the first cladding layer; the first electrode is formed in contact with the first current spreading layer.

Optionally, the first current spreading layer includes a plurality of block structures, a gap exists between two adjacent block structures, and a side of the first cladding layer close to the first current spreading layer includes a plurality of block structures. Protruding structures; the plurality of protruding structures correspond to the plurality of block structures one-to-one; the plurality of block structures and the plurality of protruding structures are formed by a one-step etching process.

An embodiment of the present application further provides a display panel, comprising: a plurality of micro-LED chips as provided in the above-mentioned embodiments; a driving backplane, the driving backplane includes a plurality of first driving electrodes, each The first driving electrode is bound to the first electrode of a micro light-emitting diode chip.

In this embodiment, the adopted micro-LED chip includes an epitaxial wafer and a first electrode, the epitaxial wafer includes a first cladding layer and a first current spreading layer arranged in layers, and the first cladding layer is located on the first current spreading layer away from the first electrode. On one side, the first current spreading layer includes a contact surface that is in contact with the first cladding layer, and along the thickness direction of the micro-LED chip, the projection of the contact surface is located inside the projection of the first cladding layer; the first electrode and the first current Extended layer contact settings. The amount of current reaching the sidewall of the first cladding layer is very small, that is, the current on the sidewall of the micro-LED chip is very small, and accordingly, the non-radiative recombination current on the sidewall of the micro-LED chip is also less, thereby reducing the current consumption. Non-radiative recombination improves luminous efficiency.

Description of drawings

FIG. 1 is a schematic structural diagram of a micro-LED chip according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a circuit structure of a pixel circuit according to an embodiment of the present application;

FIG. 3 is a schematic structural diagram of another micro-LED chip according to an embodiment of the present application;

Fig. 4 is a partial enlarged view of Fig. 1;

FIG. 5 is a schematic structural diagram of another micro-LED chip according to an embodiment of the present application;

Fig. 6 is a partial enlarged view of Fig. 5;

FIG. 7 is a schematic structural diagram of another micro-LED chip according to an embodiment of the present application;

FIG. 8 is a schematic structural diagram of another micro-LED chip according to an embodiment of the present application;

9 is a flowchart of a method for preparing a micro-LED chip provided by the application;

FIG. 10 is a schematic structural diagram of a display panel according to an embodiment of the present application;

FIG. 11 is a schematic structural diagram of a display device according to an embodiment of the present application.

detailed description

The present application will be described below with reference to the accompanying drawings and embodiments. The embodiments described here are only used to explain the present application, but not to limit the present application. For convenience of description, the drawings only show some but not all structures related to the present application.

There are a lot of non-radiative recombination in micro-LED chips, and the luminous efficiency is low. Micro Light Emitting Diode (MicroLED) generally includes a current spreading layer and a cladding layer. The current spreading layer extends to the edge of the cladding layer. When the Micro Light Emitting Diode chip emits light, the current expanded inside the current spreading layer will reach the cladding layer. The sidewall of the cladding layer is usually also the sidewall of the micro-LED chip, and the sidewall of the micro-LED chip usually has large defects (such as the material of the sidewall residual current spreading layer due to the process), which will lead to current The transmission along the sidewalls results in non-radiative recombination, which makes the luminous efficiency of the micro-LED chips lower.

The present application provides a micro light emitting diode chip. 1 is a schematic structural diagram of a micro-LED chip provided by an embodiment of the present application. Referring to FIG. 1 , the micro-LED chip includes an epitaxial wafer and a first electrode 101 , and the epitaxial wafer includes a stacked first cladding layer 103 and a first electrode 101 . The current spreading layer 102, the first cladding layer 103 is located on the side of the first current spreading layer 102 away from the first electrode 101; the first current spreading layer 102 includes a contact surface with the first cladding layer 103, along the In the thickness direction, the projection of the contact surface is located inside the projection of the first cladding layer 103 ; the first electrode 101 is arranged in contact with the first current spreading layer 102 .

As shown in FIG. 1 , the epitaxial wafer may include a second current spreading layer 106 , a second cladding layer 105 , an active layer 104 , a first cladding layer 103 and a first current spreading layer 102 which are sequentially stacked and formed on a substrate 107 . The substrate 107 may be a dielectric or a semiconductor, for example, the material of the substrate 107 may be sapphire (aluminum oxide (Aluminium Oxide, Al ₂ O ₃ )), silicon (Silicon, Si), silicon carbide (Silicon Carbide, SiC), arsenic One or more mixtures of gallium (Gallium Arsenide, GaAs). For example, a substrate with good lattice matching with the second cladding layer 105 can be selected to facilitate the growth of the second cladding layer 105 . The second cladding layer 105 and the first cladding layer 103 may be formed by metal organic chemical vapor deposition, liquid phase epitaxy, hydride vapor phase epitaxy, molecular beam epitaxy, or metal organic vapor phase epitaxy. The first cladding layer 103 and the second cladding layer 105 may be, for example, gallium nitride (Gallium Nitride, GaN) or gallium phosphide (Gallium Phosphide, GaP). For example, when the light emitted by the micro-LED chip is red light, the material of the first cladding layer 103 and the second cladding layer 105 is GaP, and when the light emitted by the micro-LED chip is blue light or green light, the first cladding layer 103 and the material of the second cladding layer 105 is GaN. The first cladding layer 103 and the second cladding layer 105 have opposite conductivity types. For example, the first cladding layer 103 can be a p-type cladding layer, which can be realized by doping magnesium (Magnesium, Mg), for example; the second cladding layer 105 can be an n-type cladding layer, such as can be realized by doping Si.

The light-emitting principle of the micro-LED chip is as follows: the holes and electrons generated in the first cladding layer 103 and the second cladding layer 105 recombine in the active layer 104 to emit light, that is, radiative recombination, and the light emitted by the radiative recombination can be It is visible light, so as to realize the light-emitting display of the micro light-emitting diode chip. The active layer 104 can be a single quantum well or a multi-quantum well, and the active layer 104 can emit light of different wavelengths (eg, red) by adjusting the characteristics of the active layer 104, such as using different materials or doping different materials. light, green light or blue light).

The first current spreading layer 102 and the second current spreading layer 106 have good electrical conductivity. For example, the conductivity of the first current spreading layer 102 is better than the conductivity of the first cladding layer 103. The first current spreading layer 102 and the first cladding layer 103 may have the same doping type, such as p-type doping. In this case, the doping concentration of the first current spreading layer 102 can be set to be greater than that of the first cladding layer 103 , and the first cladding layer 103 can also be undoped, that is, the first current spreading layer 102 has a higher density than the first cladding layer 103 . The high conductivity facilitates the formation of ohmic contact between the first current spreading layer 102 and the first electrode 101 . The second current spreading layer 106 and the second cladding layer 105 can have the same doping type, for example, both are n-type doped, and the doping concentration of the second current spreading layer 106 can be set to be greater than that of the second cladding layer 105 , the second cladding layer 105 may also be undoped, that is, the second current spreading layer 106 has higher conductivity than the second cladding layer 105, which facilitates the formation of ohmic contact between the second current spreading layer 106 and the corresponding electrode. The material of the first current spreading layer 102 may be Indium Tin Oxide (ITO), Gallium Phosphide (GaP) or Indium Gallium Nitride (InGaN).

The first electrode 101 may be any conductive material or a combination of multiple conductive materials, such as copper (Cuprum, Cu), nickel (Nickel, Ni), silver (Argentum, Ag), aluminum (Aluminium, Al), An alloy of one or more of gold (Aurum, Au) and titanium (Titanium, Ti). The first electrode 101 can optionally be the anode of the micro-LED chip, and this embodiment is described by taking the first electrode 101 as the anode of the micro-LED chip as an example. When the first electrode is an anode, the first electrode is generally used as the reflective surface of the micro-LED chip, and the second current spreading layer 106 corresponds to the light-emitting surface of the micro-LED chip, that is, the light emitted by the active layer needs to pass through the second current After the expansion layer 106 is emitted, the light emitted by the active layer 104 can be reflected to the second current expansion layer 106 after reaching the first electrode 101 to improve the luminous efficiency. The first electrode 101 can be made of a reflective material, such as silver ( An alloy of one or more of Argentum, Ag), aluminum (Aluminium, Al), and platinum (Platinum, Pt).

2 is a schematic diagram of the circuit structure of a pixel circuit provided by an embodiment of the present application. The pixel circuit can be used to drive the micro-LED chip provided by the embodiment of the present application to emit light. The pixel circuit is also called a 2T1C circuit, which includes two transistors and a storage capacitor. When the scanning signal line SCAN is selected, the switching transistor Tsw is turned on, the gray-scale voltage on the data signal line VDATA is transmitted to the storage capacitor C, and the storage capacitor C stores the gray-scale voltage, so that the driving transistor Tdrv can adjust the gray-scale voltage according to the gray-scale voltage. A stable driving current is generated, and then the micro LED chip MicroLED is driven to emit light. In other embodiments, the pixel circuit can also be a driving circuit with a threshold compensation function, such as a 7T1C pixel circuit, so that the generated driving current is independent of the threshold voltage of the driving transistor. Since the anode of the micro-LED chip receives the driving current of the driving transistor, and the cathode is generally a common ground electrode, the state of the current at the anode affects the luminous efficiency of the micro-LED chip, while the state of the current at the cathode has less effect. Therefore, The first electrode in this embodiment can be set as the anode of the micro-LED chip.

Along the thickness direction of the micro-LED chip (X direction in FIG. 1 ), the first current spreading layer 102 includes a contact surface in contact with the first cladding layer 103 , and the projection of the contact surface is located inside the projection of the first cladding layer 103 , meaning that the projected area of the contact surface is smaller than the projected area of the first coating layer 103 , and the projection of the first coating layer 103 completely covers the projection of the contact surface. As shown in Figure 1, along the thickness direction of the micro-LED chip, the part where the projection of the micro-LED chip completely overlaps with the projection of the contact surface can be understood as the current main recombination area Ia, and the rest can be understood as the current sub-recombination area Ib , the current is concentrated in the current main recombination region Ia. The conductivity of the first cladding layer 103 is lower than that of the first current spreading layer 102, the current mainly spreads in the first current spreading layer 102, and the current in the first cladding layer 103 is mainly along the thickness direction of the micro-LED chip X transmission, the amount of expansion along the Y direction is small, that is, the current is mainly located in the part of the first cladding layer 103 located in the current main recombination region Ia, and the amount of current reaching the sidewall of the first cladding layer 103 is very small. That is to say, there is very little current on the sidewall of the micro-LED chip, and correspondingly less current occurs in the sidewall of the micro-LED chip without radiation recombination, thereby reducing the non-radiative recombination of current and improving the luminous efficiency.

In this embodiment, the shape of the first current spreading layer 102 is not limited, and the area of the side of the first current spreading layer 102 away from the first cladding layer 103 may also be larger than that of the first cladding layer 103 . As shown in FIG. 3 , FIG. 3 is a schematic structural diagram of another micro-LED chip according to an embodiment of the present application. Although the thickness direction X of the micro-LED chip is along the thickness direction X of the micro-LED chip, the first current spreading layer 102 is far away from the first cladding layer 103 . The projected area of one side is greater than or equal to the projected area of the first cladding layer 103, but since the projection of the contact surface is still located inside the projection of the first cladding layer 103, the current is still mainly concentrated in the current main recombination area Ia, that is, it can still reach The purpose of reducing the current of non-radiative recombination on the side wall of the micro-LED chip, thereby improving the luminous efficiency. The structure shown in FIG. 3 can be formed by, for example, anisotropic etching or the like.

In this embodiment, the adopted micro-LED chip includes an epitaxial wafer and a first electrode, the epitaxial wafer includes a first cladding layer and a first current spreading layer arranged in layers, and the first cladding layer is located on the first current spreading layer away from the first electrode. On one side, the first current spreading layer includes a contact surface that is in contact with the first cladding layer, and along the thickness direction of the micro-LED chip, the projection of the contact surface is located inside the projection of the first cladding layer; the first electrode and the first current The extension layer is arranged in contact, and the first electrode can be the anode of the micro-LED chip. This arrangement makes the amount of current reaching the sidewall of the first cladding layer very small, that is, the current on the sidewall of the micro-LED chip is very small, correspondingly The non-radiative recombination of the current on the side wall of the micro-LED chip is also less, thereby reducing the non-radiative recombination of the current and improving the luminous efficiency.

A passivation layer 108 may also be included between the first electrode 101 and the first current spreading layer 102 . The passivation layer 108 may be formed to cover the entire surface. The passivation layer 108 may be formed by, for example, growing. The material can be an oxide or a nitride, such as a mixture of one or more of aluminum oxide (Aluminium Oxide, AlO), silicon oxide (Silicon Oxide, SiO), silicon nitride (Silicon Nitride, SiN), And the passivation layer 108 is provided with openings to expose part of the surface of the first current spreading layer 102 .

The shape of the micro-LED chip can be prismatic, cylindrical or other irregular columnar structures, etc., and the shape of the first current spreading layer 102 can also be annular, prismatic or columnar.

The size of the micro-LED chip in this embodiment can be set differently according to different application scenarios. For example, the size of the display used for lighting can be several millimeters, while the size of the micro-LED chip used for display in the display is Can be tens of microns.

Optionally, the first current spreading layer 102 includes a plurality of block structures, and a gap exists between two adjacent block structures.

FIG. 4 is a partial enlarged view of FIG. 1 . In combination with FIG. 1 and FIG. 4 , the first current spreading layer 102 includes a plurality of block structures 1021 (the number of block structures is greater than or equal to 2), and two adjacent block structures A gap is formed between the structures 1021. During the mass transfer process of the micro-LED chip, the solder posts on the driving backplane can fully fill the gap when the micro-LED chip is pressed down, thereby fully wrapping the multiple block structures 1021, on the one hand, it makes it easier to separate the micro-LED chips from the transfer head, thereby improving the yield of mass transfer, and on the other hand, it can also improve the bonding strength between the micro-LED chips and the driving backplane.

Optionally, continuing to combine FIG. 1 and FIG. 4 , the first current spreading layer 102 further includes a flat structure 1022 located between the plurality of bulk structures 1021 and the first cladding layer 103 .

In this embodiment, the block structure 1021 can be understood as a plurality of protrusions formed on the surface of the flat structure 1022 by the first current spreading layer 102 . Along the thickness direction X of the micro-LED chip, the projected area of the flat structure 1022 is larger than the projected area of the plurality of block structures 1021 , and the projection of each block structure 1021 is located inside the flat structure 1022 . After the first current spreading layer 102 is grown, the first current spreading layer 102 may be etched to form a plurality of bulk structures 1021 and a flat structure 1022. The etching method may be dry etching or wet etching, for example. The flat structure 1022 is in contact with the first cladding layer 103 . Compared with the contact between the plurality of block structures 1021 and the first cladding layer 103 , the area of the contact surface between the flat structure 1022 and the first cladding layer 103 is larger, that is, the current The main recombination area Ia is larger, which can reduce the resistance of current transmission, so that the turn-on voltage of the micro-LED chip is decreased, the power consumption of the micro-LED chip is reduced, and the luminous efficiency is improved.

When the light emitted by the micro-LED chip is red light, the thickness of the first current spreading layer 102 is relatively thick. Correspondingly, a plurality of block structures 1021 and flat structures 1022 with a certain thickness may be formed on one side of the first current spreading layer 102 . When the light emitted by the micro-LED chip is light of other colors, the first current spreading layer 102 is relatively thin, and the formed bulk structure 1021 is relatively thin, and the bonding strength between the micro-LED chip and the driving backplane cannot be improved. obvious. Referring to FIG. 5 and FIG. 6 , FIG. 5 is a schematic structural diagram of another micro-LED chip provided by an embodiment of the present application, and FIG. 6 is a partial enlarged view of FIG. One side includes a plurality of protruding structures 1031 ; the plurality of protruding structures 1031 are in one-to-one correspondence with the plurality of block structures 1021 .

In this way, the thickness of the first cladding layer 103 is usually thick, and the thickness of the convex portion formed by the combination of the convex structure 1031 and the corresponding block structure 1021 can be thicker, such as the thickness of the convex structure 1031 and the corresponding block structure 1021 The sum of the thicknesses (that is, the thickness of the protrusions) is greater than 0.3 μm, which on the one hand makes the micro-LED chips easier to separate from the transfer head, improves the yield of mass transfer, and on the other hand enables the micro-LED chips to be separated from the transfer head more easily. The bonding strength with the drive backplane is greatly improved. The bump structures 1031 and the block structures 1021 can be formed by a one-step etching process. After etching to form a plurality of block structures 1021, a plurality of bump structures 1031 can be formed by over-etching. Along the thickness direction of the micro-LED chip, The projection of the first current spreading layer 102 completely coincides with the projection of the plurality of protruding structures 1031 , which can reduce the etching steps and save the process cost. In this embodiment, for example, the etching depth can be adjusted by adjusting the etching time.

Optionally, the plurality of block structures 1021 are evenly distributed.

Exemplarily, the plurality of block structures 1021 may be arranged in an array, for example, may be uniformly distributed on the surface of the first cladding layer 103 . On the one hand, during light-emitting display, the current distribution inside the active layer 104 is also relatively uniform, so that the light-emitting is relatively uniform; It is also uniform. After the welding column fills the gaps between the plurality of protrusions, the multiple parts of the welding column are subjected to relatively uniform force when the transfer head is separated, so as to prevent a part of the dry column from being damaged due to excessive force. Ensure the stability of the electrical connection between the micro-LED chip and the driving backplane.

Optionally, the shape of the first electrode 101 matches the shape of the first current spreading layer 102 .

The first electrode 101 may be disposed along the surface of the first current spreading layer 102, that is, the structure shown in FIG. 1; when the first current spreading layer 102 includes a plurality of block structures, the first cladding layer 103 includes a plurality of protruding structures , the first electrode 101 may be disposed along the convex portion, that is, the structure shown in FIG. 5 . When the micro-LED chip is bound to the driving backplane, the contact area between the first electrode 101 and the solder post is larger, which effectively reduces the contact resistance, thereby reducing loss, and can also increase the stability of the electrical connection between the first electrode 101 and the solder post properties, thereby improving the stability of the light-emitting display of the micro-LED chip.

Optionally, along the thickness direction of the micro-LED chip, the projected area of the first electrode 101 is smaller than the projected area of the first cladding layer 103 , and the projection of the first electrode 101 is within the projection of the first cladding layer 103 .

The edge of the first electrode 101 has a certain distance from the edge of the first cladding layer 103, that is, the edge of the first electrode 101 has a certain distance from the sidewall of the micro-LED chip, and the current in the first electrode 101 will not be transmitted to Non-radiative recombination occurs on the sidewalls of the micro-LED chips, thereby further improving the luminous efficiency of the micro-LED chips.

The micro-LED chip in this embodiment can be either a chip with a vertical structure or a chip with a flip-chip structure. As shown in FIG. 7 , which is a schematic structural diagram of another micro-LED chip provided by an embodiment of the present application, a second electrode 201 can be provided on the surface of the second cladding layer 105 , and the second electrode 201 can be used as a micro-LED chip The cathode of the chip and the material of the second electrode 201 can be any conductive material.

Optionally, as shown in FIG. 8 , which is a schematic structural diagram of another micro-LED chip provided by an embodiment of the present application, a portion of the second cladding layer 105 corresponding to the second electrode 201 may also be provided with a plurality of raised portions 1051, the corresponding second cladding layer 105 may further include a plurality of second current spreading layer block structures 1061, and the shape of the second electrode 201 matches the shape of the plurality of protrusions 1051, for example, the second electrode 201 along the protrusions The arrangement of the portion 1051 and the second current spreading layer block structure 1061 can increase the stability of the electrical connection between the second electrode 201 and the solder post on the driving backplane and reduce the contact resistance, thereby reducing power consumption.

FIG. 9 is a flowchart of a method for preparing a micro-LED chip provided by the present application. Referring to FIG. 9 , the method for preparing a micro-LED chip includes the following steps.

Step S901 , forming an epitaxial wafer, wherein the epitaxial wafer includes a first cladding layer and a first current spreading layer arranged in layers, and the first cladding layer is located on the side of the first current spreading layer away from the first electrode; the first current spreading layer includes For the contact surface in contact with the first cladding layer, along the thickness direction of the micro-LED chip, the projection of the contact surface is located inside the projection of the first cladding layer.

Step S902, forming a first electrode in contact with the first current spreading layer.

The epitaxial wafer may include, for example, a second current spreading layer, a second cladding layer, an active layer, a first cladding layer, and a first current spreading layer, which are sequentially stacked and formed on the substrate by growth. As shown in Figure 1, along the thickness direction of the micro-LED chip, the part where the projection of the micro-LED chip completely overlaps with the projection of the contact surface can be understood as the current main recombination area Ia, and the rest can be understood as the current sub-recombination area Ib , the current is concentrated in the current main recombination region Ia. The conductivity of the first cladding layer is lower than that of the first current spreading layer, the current mainly spreads in the first current spreading layer, and in the first cladding layer, the current is mainly transmitted along the thickness direction X of the micro-LED chip, The amount of extension in the Y direction is less. That is to say, the current is mainly located in the part where the first cladding layer is located in the current main recombination region Ia, and the amount of current reaching the sidewall of the first cladding layer is very small, that is, the current on the sidewall of the micro-LED chip is very small, correspondingly in the micro-LED chip. The non-radiative recombination of the side wall of the diode chip is also less, thereby reducing the non-radiative recombination of the current and improving the luminous efficiency.

Optionally, the first current spreading layer includes a plurality of block structures, a gap exists between two adjacent block structures, and a side of the first cladding layer close to the first current spreading layer includes a plurality of protruding structures; The protruding structures are in one-to-one correspondence with a plurality of block structures. The plurality of raised structures and the plurality of block-like structures can be formed by a one-step etching process. After the plurality of block-like structures are formed by etching, over-etching can be performed to form a plurality of raised structures. Along the thickness direction of the micro-LED chip, The projection of the first current spreading layer completely coincides with the projection of the plurality of protruding structures, which can reduce the etching steps and save the process cost.

10 is a schematic structural diagram of a display panel provided by an embodiment of the present application. Referring to FIG. 10 , the display panel includes a plurality of micro light emitting diode chips (MicroLED) and a driving backplane 301; each micro light emitting diode chip (MicroLED) includes an epitaxial wafer and a first electrode, the epitaxial wafer includes a first cladding layer and a first current spreading layer arranged in contact, the first cladding layer is located on the side of the first current spreading layer away from the first electrode; the first current spreading layer includes and The contact surface contacted by the first cladding layer, along the thickness direction of each micro light-emitting diode chip, the projection of the contact surface is located inside the projection of the first cladding layer; the first electrode is in contact with the first current spreading layer, and the first electrode is in contact with the first current spreading layer. An electrode may be the anode of each of the micro-LED chips; the driving backplane 301 includes a first driving electrode 401, and the first driving electrode 401 is bound to the first electrode.

The driving backplane 301 may be a Thin Film Transistor (TFT) backplane or a Complementary Metal-Oxide-Semiconductor (CMOS) backplane. The interior of the driving backplane 301 may include a pixel circuit. The first driving electrode 401 is used as the first driving electrode 401 of the driving backplane 301 , and the first driving electrode 401 is bound to the first electrode through a solder post 502 , and the solder post 502 may be, for example, indium (Indium, In), tin (Stannum, Sn) or alloy materials, or conductive polymers, etc. In this embodiment, after the micro-LED chip and the driving backplane 301 are pressed and bonded, a planarization layer 501 can be filled in the gap between the micro-LED chip and the driving backplane 301 , and the material of the planarization layer 501 can be, for example, organic matter. In other embodiments, the planarization layer 501 can also be fabricated on the driving backplane 301 first, and then the micro-LED chips and the driving backplane 301 are aligned and pressed together. After the alignment is completed, the substrate of the micro-LED chip can be removed first. If the substrate is silicon carbide (SiC), it can be removed by mechanical thinning or chemical etching; if the substrate is sapphire , it can be removed by laser dissolution or other methods. After the substrate is removed, a second electrode 503 (ie, a common electrode) can be formed on the entire surface of the exposed second current spreading layer, and the second electrode 503 is electrically connected to the second driving electrode 402 on the driving backplane 301 to form Complete current loop. The material of the second electrode 503 can be selected from a conductive material with transparent or translucent properties, such as magnesium-silver alloy, etc., and the formation method of the second electrode 503 can be vapor deposition or the like. Before forming the second electrode 503, the surface of the second current spreading layer can also be roughened to increase the exit angle of the exiting light and increase the viewing angle of the display panel. After the second electrode 503 is formed, quantum dot material can also be fabricated at the position of the micro-LED chip, and the light emitted by the micro-LED chip becomes light of different colors after passing through different quantum dot materials, so that the display panel can achieve full color display.

An embodiment of the present application also provides a display device. As shown in FIG. 11 , FIG. 11 is a schematic structural diagram of a display device provided by an embodiment of the present application. The display device includes a display panel provided by any embodiment of the present application. The display device may be a mobile phone, a tablet, a computer, a display, a smart watch, or other wearable devices.

Claims

A micro light-emitting diode chip, comprising:

an epitaxial wafer, the epitaxial wafer includes a first cladding layer and a first current spreading layer arranged in layers;

a first electrode, which is arranged in contact with the first current spreading layer;

The first cladding layer is located on the side of the first current spreading layer away from the first electrode; the first current spreading layer includes a contact surface contacting with the first cladding layer, along the micro light emitting diode In the thickness direction of the chip, the projection of the contact surface is located inside the projection of the first cladding layer.
The micro-LED chip according to claim 1, wherein the first current spreading layer comprises a plurality of block structures, and a gap exists between two adjacent block structures.
The micro-LED chip of claim 2, wherein the first current spreading layer further comprises a flat structure between the plurality of bulk structures and the first cladding layer.
The micro-LED chip according to claim 2, wherein a side of the first cladding layer close to the first current spreading layer comprises a plurality of protruding structures; the plurality of protruding structures and the plurality of protruding structures The block structures correspond one-to-one.
The micro-LED chip of claim 2, wherein the plurality of bulk structures are uniformly distributed.
The micro-LED chip of claim 1, wherein the shape of the first electrode matches the shape of the first current spreading layer.
The micro light emitting diode chip according to claim 1, wherein the epitaxial wafer comprises a second cladding layer, an active layer, the first cladding layer and the first current spreading layer which are stacked and arranged, and the micro light emitting diode The diode chip further includes a second electrode, and the second electrode is arranged in contact with the second cladding layer.
The micro-LED chip of claim 7, wherein the first electrode is an anode of the micro-LED chip, and the second electrode is a cathode of the micro-LED chip.
The micro-LED chip of claim 7, wherein the second cladding layer comprises a plurality of protrusions, and the shape of the second electrode matches the shape of the plurality of protrusions.
The micro-LED chip according to claim 7, wherein the epitaxial wafer comprises: a second current spreading layer, the second cladding layer, the active layer, the first cladding layer and the The first current spreading layer is stacked.
The micro-LED chip of claim 7, wherein the conductivity type of the first cladding layer is opposite to that of the second cladding layer.
The micro-LED chip of claim 10 , wherein the conductivity of the first current spreading layer is higher than that of the first cladding layer, and the conductivity of the second current spreading layer is higher than that of the first cladding layer. The conductivity of the second cladding layer.
The micro light emitting diode chip according to claim 1, wherein, along the thickness direction of the micro light emitting diode chip, the projected area of the side of the first current spreading layer away from the first cladding layer is greater than or equal to the first The projected area of a cladding.
The micro-LED chip according to claim 1, further comprising: a passivation layer, the passivation layer being disposed between the first electrode and the first current spreading layer.
The micro-LED chip of claim 14, wherein the passivation layer is provided with openings to expose a part of the surface of the first current spreading layer.
The micro light emitting diode chip according to claim 7, wherein, along the thickness direction of the micro light emitting diode chip, the projected area of the first electrode is smaller than the projected area of the first cladding layer, and the first electrode The projection of is within the projection of the first cladding.
A preparation method of a micro light-emitting diode chip, wherein the method comprises:

forming an epitaxial wafer, wherein the epitaxial wafer includes a first cladding layer and a first current spreading layer arranged in layers, the first cladding layer is located on the side of the first current spreading layer away from the first electrode; A current spreading layer includes a contact surface in contact with the first cladding layer, and along the thickness direction of the micro-LED chip, the projection of the contact surface is located inside the projection of the first cladding layer;

The first electrode is formed in contact with the first current spreading layer.
The method of claim 17, wherein the first current spreading layer comprises a plurality of bulk structures, a gap exists between two adjacent bulk structures, and the first cladding layer is close to the first current spreading One side of the layer includes a plurality of raised structures; the plurality of raised structures are in one-to-one correspondence with the plurality of block structures;

The plurality of block structures and the plurality of protruding structures are formed by a one-step etching process.
A display panel, comprising:

A plurality of micro-LED chips according to any one of claims 1-16;

The driving backplane includes a plurality of first driving electrodes, and each first driving electrode is bound to the first electrode of a micro-LED chip.
The display panel of claim 19, further comprising: a planarization layer, the planarization layer filling in the gaps between the plurality of micro-LED chips and the driving backplane.