TW202501843A - Micro-sucker transfer micro-light-emitting diode (micro-led) method - Google Patents

Abstract

The present invention discloses a micro- sucker transfer miniature light-emitting diode (Micro LED) method, the method mainly utilizes an elastic micro- sucker on the impression mold, presented from the carrier substrate The micro-light-emitting diode (Micro LED) is vertically adsorbed and picked up on the first bonding layer of the softened state, and then transferred and combined to the second bonding layer of the softened state of the target substrate, and after the second bonding layer of the target substrate is cooled, the micro-light-emitting diode (Micro LED) can be detached from the elastic micro- sucker, so that the micro-light-emitting diode (Micro LED) is fixed on the target substrate through the second bonding layer to complete the transfer of the micro-light-emitting diode (Micro LED)., forming an ultra-small pitch miniature light-emitting diode (Micro LED) substrate, resulting in a high-resolution display screen.

Description

Micro-suction cup transfer method of micro-light-emitting diodes (Micro LEDs)

The present invention relates to a method in the field of display imaging technology, and in particular to a method for transferring micro LEDs by using a micro suction cup to selectively or comprehensively pick up micro LEDs from a carrier substrate and transfer them to a target substrate.

Micro LED technology refers to small-size LED arrays integrated on a substrate with high density. Currently, Micro LED technology is beginning to develop, and the industry expects high-quality Micro LED products to enter the market. High-quality Micro LED will have a far-reaching impact on traditional display products (such as LCD/OLED) that have already been launched on the market.

Micro LED can replace traditional LCD and OLED as panel displays. It is also suitable for wearable device screens, electronic billboards, head-up displays (HUD), head-mounted displays (HMD), etc. due to its ultra-power-saving advantages. Therefore, Micro LED is regarded as a technology that provides better display images.

The four major challenges that need to be solved in the mass production of Micro LEDs are: (1) mass transfer, (2) bonding, (3) repair, and (4) the luminous efficiency of red Micro LEDs; the most important bottleneck technology is mass transfer technology.

In the prior art, there are electrostatic technology and adhesive technology to perform transfer. Among them: electrostatic technology, such as LuxVue US Patent No. 8,333,860B1 (US2013/0127020A1) discloses a method for transferring micro devices, which discloses applying voltage to the electrodes in the transfer head to generate suction through static electricity to pick up the micro devices. Due to the advantages brought by the miniaturization of micro light-emitting diodes (Micro LEDs), however, the miniaturization of the volume also faces new difficulties and challenges in manufacturing. During the electrostatic transfer process, the electrostatic transfer head array plane must be aligned with the Micro LED array plane before picking up and transferring. Therefore, in manufacturing, the position and height of each Micro LED must be precisely controlled. Any deviation in the position, height difference or contamination of any Micro LED may lead to the failure of the entire Micro LED array transfer, resulting in a reduction in yield and an increase in cost. In addition, in the micro-light-emitting diode (Micro LED) manufacturing process, an additional dielectric layer is required. Therefore, the development of robust inventions that make ESD have strong immunity to process variations is the biggest difficulty and challenge of ESD technology. Adhesion technology, such as Micro-Transfer-Printing (μTP) technology developed by X-Celeprint, uses sacrificial layer wet etching and PDMS transfer technology. X-Celeprint μTP technology, which uses a flexible stamp combined with a high-precision motion control print head to selectively pick up large arrays of micro devices and print (place) them on a replacement substrate. First, a micro device (chip) is made on a source wafer, and then "released" by removing the sacrificial layer underneath the micro device (chip). Then, an elastic stamp picks up the micro device from the source wafer and prints (places) the micro device on the target substrate.

In addition, for example, X-Celeprint US2017173852A1 discloses a microstructure and device, which can transfer microcomponents to a substrate using a microtransfer printing method. The microcomponent is formed on a source substrate, released from the source substrate by contact with a stamp, and adhered to the stamp, which is then pressed onto a target substrate to adhere the microcomponent to the target substrate. The stamp is then removed from the target substrate, leaving the microcomponent on the target substrate. However, the structure of the entire stamp is a "columnar structure with a flat top", and the adhesion between the stamp and the microcomponent mainly depends on the van der Waals force, that is, the faster the stamp approaches, the greater the adhesion, and vice versa. Adjusting the adhesion by adjusting the speed of the stamp approach will lead to difficulties in precision control of the entire process, complexity of the entire equipment control, greater sensitivity to transfer defects, and problems with defect repair.

In addition, Innolux patent No. 107113115 discloses a transfer carrier and a die carrier, which uses a bonding layer (block) under the transfer piece to adhere the driving circuit from the first substrate and then transfer it to the second substrate. The entire text of the patent is incorporated herein by reference.

In addition, for example, X-Celeprint's patent application TW201614860A discloses a micro-transfer technology, including: preparation work before picking up/transferring, picking up/transferring technology, and target substrate assembly technology.

Preparation before picking up/transferring:

(1) Preparation work before picking up/transferring refers to providing a releasable structure and method for micro-LEDs that can be micro-transferred on a large scale, which is different from the current mass production standard of micro-LEDs. X-Celeprint proposed a preparation method before pick-up/transfer in its patent application TW 201614860A, one of which is a method patent for preparing a releasable structure from a silicon substrate, the method comprising: depositing a GaN epitaxial layer on a substrate with a Si<111> lattice structure; using the epitaxial layer to form a micro light-emitting diode (Micro LED); demarcating the micro light-emitting diode (Micro LED) using photolithography technology; and forming an anchoring structure and a tethering structure, and connecting the micro light-emitting diode (Micro LED) device to the substrate by means of the anchoring structure and the tethering structure; and then removing the silicon material under the structure by means of another etchant, thereby forming a printable structure including the micro light-emitting diode (Micro LED) device.

(2) Since the lattice mismatch between the silicon substrate and the GaN crystal that constitutes the Micro LED is high, the performance of the Micro LED is reduced. Therefore, X-Celeprint proposed another method of forming a releasable structure on a sapphire native substrate in its patent application TW 201614860A, and used an intermediate substrate with a controlled adhesive property to operate, wherein the adhesive property can be controlled by cross-linking density, surface chemistry, surface texture, surface composition, elastic layer thickness or surface morphology, and its bonding or release can also be controlled by pressure or temperature.

(ii) Pick up/transfer:

As the preparation work before pick-up/transfer is completed, a Micro LED with a releasable structure is formed, allowing the subsequent pick-up/transfer technology to be executed more smoothly. At the same time, in order to transfer the picked/transferred Micro LED to the target substrate more firmly, a coating polymer layer and a heating plate are added to control the temperature during the pick-up/transfer process to adjust the mold adhesion and promote release.

X-Celeprint Taiwan Patent No. I659475 discloses a stamp that picks up printable micro-light-emitting diodes (Micro LEDs) from a native substrate. The stamp transfers the printable micro-light-emitting diodes (Micro LEDs) to a target substrate. The hot plate is in direct thermal contact with the target substrate and heated to an equilibrium temperature to reduce the adhesion between the stamp and the polymer layer. After removing the polymer layer, the micro-light-emitting diodes (Micro LEDs) are transferred to the target substrate.

Difficulties and challenges in micro-transfer printing technology, such as the method of using a silicon homogeneous substrate to prepare a releasable structure in the preparation scheme before picking up, although this scheme has many advantages, such as the ability to directly form a sacrificial layer on the silicon <111> lattice structure, and the sacrificial layer can be removed by simple KOH solution anisotropic etching, which simplifies the method of preparing a releasable structure. However, there is a yield problem of silicon substrate epitaxy, because the lattice matching between the silicon substrate and the lattice structure of the GaN crystal that constitutes the LED is low, which reduces the performance of the LED. Therefore, the process of preparing a releasable structure from a silicon substrate is not yet mature and has not reached the mass production stage.

In addition, in the method of preparing a releasable structure using sapphire as a native substrate, an intermediate substrate is required as a temporary transfer site. The transfer process also includes making a sacrificial layer on the sapphire native substrate, performing laser stripping to remove the sapphire substrate, and making a sacrificial layer on the intermediate substrate, which increases the complexity. The laser stripping cost is high, and the yield problem needs to be improved.

Since the X-Celeprint patent application TW 201614860A does not mention how to select good Micro LED chips from homogeneous substrates, traditional LED wafers are tested and sorted according to key parameters such as main wavelength, luminous intensity, luminous flux, color temperature, operating voltage, and reverse breakdown voltage. After thinning and cutting, the LEDs are divided into various bins one by one. Micro LEDs are smaller and more numerous than traditional LEDs, so how to use a large number of molds to pick up Micro LEDs from different bins and classify them is a big problem.

In the following invention, the concave arc structure of an elastic micro suction cup is used to solve the problems encountered by the microstructure stamp, so that the invention only needs to change the preload pressure in the micro suction cup stamp, and heat the carrier substrate (or native substrate) and the bonding layer on the target substrate to change the adhesion between the micro light-emitting diode (Micro LED), and then the elastic micro suction cup of the invention can be used to selectively or comprehensively vertically absorb and pick up the transfer of micro light-emitting diodes (Micro LED), so as to achieve the purpose of mass transfer of micro light-emitting diodes (Micro LED).

The main purpose of the present invention is to provide a method for transferring micro LEDs by using a micro suction cup, which utilizes the concave arc structure design of the elastic micro suction cup in the stamp, so that the elastic micro suction cup can easily absorb and pick up the micro LEDs from the carrier substrate and transfer them to the target substrate.

The advantages of the present invention of using the concave arc structure of the elastic micro suction cup to absorb, pick up and transfer are:

(1) Adsorb and pick up micro LEDs without the need for complex mechanical design.

(2) The elastic micro suction cup can absorb and pick up the micro LED without using an adhesive layer between the micro LED and the micro LED.

(3) Using a pre-designed elastic micro suction cup, the Micro LEDs can be selectively or comprehensively transferred to the target substrate in sequence, thus overcoming the sorting problem.

(4) The parallelism between the elastic micro suction cup and the Micro LED array does not need to be strictly controlled.

(5) The height and position of the elastic micro suction cup and the Micro LED do not need to be as strict as the electrostatic adsorption system.

(6) No dielectric layer is required between the elastic micro suction cup and the micro LED array.

In order to achieve the above purpose, the technical means used in the present invention are: providing a method for transferring micro light-emitting diodes (Micro LEDs) using a micro suction cup, comprising the following steps:

(l) providing a carrier substrate, on which there is at least one micro light emitting diode (Micro LED), each micro light emitting diode (Micro LED) being fixed to the carrier substrate via a first bonding layer below, the first bonding layer being allowed to be heated to change from a solid state to a semi-solid state or a liquid state, so that when the first bonding layer is in a solid state and a liquid state, a different bonding force F2 is formed between each micro light emitting diode (Micro LED) and the carrier substrate. For example, when the first bonding layer is in a solid state, the bonding force between each micro light emitting diode (Micro LED) and the carrier substrate is F2, and when the first bonding layer is changed to a liquid state, the bonding force between each micro light emitting diode (Micro LED) and the carrier substrate will drop to F2' (F2>F2');

(2) A stamp is provided for adsorbing and picking up a micro-light-emitting diode (Micro LED) on a carrier substrate. The stamp has at least one elastic micro-suction cup, and the lower end of each elastic micro-suction cup is in a concave arc-shaped structure. When a predetermined pressure is applied to the stamp, each elastic micro-suction cup will vertically contact the top surface of the micro-light-emitting diode (Micro LED) on the carrier substrate. When the concave arc-shaped structure at the lower end of each elastic micro-suction cup is pressed and spread open, the contact area with the top surface of the micro-light-emitting diode (Micro LED) is increased, so that each elastic micro-suction cup and each micro-light-emitting diode (Micro LED) generate a vertical suction force F1. At this time, the vertical suction force F1 is less than the micro-light-emitting diode (Micro LED). The adhesive force F2 between the micro LED and the carrier substrate. For example, when the lower end of each elastic micro suction cup is pushed open by pressure and adsorbed on the top surface of the micro LED, each elastic micro suction cup and each micro LED generate a vertical suction force F1. At this time, the vertical suction force F1 is smaller than the adhesive force F2 between the micro LED and the carrier substrate;

(3) providing a first heat source, which can provide point, local or overall heating to the first bonding layer through the carrier substrate at a predetermined temperature, so that the first bonding layer selected to be heated changes from a solid state to a liquid state. At this time, the adhesive force between each micro light-emitting diode (Micro LED) and the carrier substrate in step (1) decreases by F2, and when the adhesive force F' after the decrease decreases to less than the vertical suction force F1 generated by each elastic micro suction cup and each micro light-emitting diode (Micro LED) in step (2), each micro light-emitting diode (Micro LED) can be adsorbed by each elastic micro suction cup and detached from the carrier substrate, so that the selected micro light-emitting diode (Micro LED) The micro LED can be easily picked up from the carrier substrate. For example, when the first bonding layer on the carrier substrate is heated to turn into a liquid state, the adhesive force between the micro LED and the carrier substrate will decrease from F2 to F2'. When the adhesive force F2' is less than the vertical suction force F1 between the elastic micro suction cup and the micro LED, the micro LED can be adsorbed by the elastic micro suction cup and detached from the carrier substrate, so that the selected micro LED can be easily picked up from the carrier substrate;

(4) Providing a target substrate for receiving the micro light-emitting diode (Micro LED) from the carrier substrate, the target substrate having a solid second bonding layer, the solid second bonding layer having an adhesive force with the target substrate, the second bonding layer being allowed to be heated to change from a solid state to a semi-solid state or a liquid state, and returning to a solid state when not heated;

(5) providing a second heat source, which can provide point, local or overall heating to the second bonding layer through the target substrate at a predetermined temperature, so that the second bonding layer that is selectively heated can be converted from a solid state to a liquid state. For example, when the second bonding layer on the target substrate is not heated to a solid state, the second bonding layer and the target substrate have an adhesion force F3. At this time, the adhesion force F3 is greater than the vertical suction force F1 in step (2), and the second bonding layer is preferably heated to a liquid state. When the second bonding layer is heated, it turns into liquid state, and the bonding force between the second bonding layer and the target substrate decreases from F3 to F3'. At this time, the bonding force F3' is less than the vertical suction force F1 in step (2). When the second bonding layer is cooled to room temperature and returns to a solid state, the bonding force between the second bonding layer and the target substrate can rise from F3' to F3. At this time, the bonding force F3 is greater than (2) the vertical suction force F1;

(6) Each micro-LED adsorbed and picked up by each elastic micro-suction cup in step (3) is transferred and bonded to the second bonding layer in liquid state on the target substrate, and then the second heat source is stopped to heat, so that the second bonding layer on the target substrate returns to a solid state. At this time, the bonding force between the second bonding layer and the target substrate returns to the bonding force F3 in step (4), and when the bonding force F3 is greater than the vertical suction force F1 generated by each elastic micro-suction cup and each micro-LED in step (2), each micro-LED can be detached from each elastic micro-suction cup, so that each micro-LED can be LED) is fixed on the target substrate through the second bonding layer to complete the transfer of micro LED.

In one embodiment of the present invention, the carrier substrate is a silicon substrate or a sapphire substrate. In addition, the first bonding layer on the carrier substrate of the present invention is applicable, such as the bonding layer disclosed in LuxVue patent US 2013/0127020A1, which discloses a micro light-emitting diode (Micro LED) bonding structure with a bonding layer (or stabilizing layer) and a carrier substrate. In addition, the polymer layer of X-Celeprint Taiwan Patent No. I659475 can also be used as the first bonding layer of an embodiment of the present invention.

40℃，液態溫度

70℃。 In one embodiment of the present invention, the first bonding layer on the carrier substrate is a temperature-sensitive crystalline polymer or an inorganic solder, and the solid state temperature of the first bonding layer is

40℃ , liquid temperature

70℃ .

In order to facilitate the release of the micro LED from the carrier substrate, in one embodiment of the present invention, the first heat source is heated by a hot plate or irradiated, and the heating temperature is between 50 and 150°C. The preferred first heat source is hot plate heating.

In one embodiment of the present invention, the target substrate is a drive circuit substrate or other display substrate.

In order to provide a micro light-emitting diode (Micro LED) to be bonded and fixed on a target substrate, in one embodiment of the present invention, the second bonding layer on the target substrate is a temperature-sensitive crystalline polymer or inorganic solder with conductive properties, and the second bonding layer includes a conductive particle, a temperature-sensitive crystalline polymer and an additive.

In one embodiment of the present invention, the conductive particles are selected from metals, metal alloys, anisotropic conductive particles or a combination of at least one of the above. Preferably, the conductive particles are tin, copper or gold.

In one embodiment of the present invention, the aforementioned temperature-sensitive crystalline polymer is composed of a main chain, a plurality of crystallizable side chains, and a plurality of heteroatoms connected to the polymer, wherein the temperature-sensitive crystalline polymer comprises repeating units of the following formula (I)

其中：n為約1至約1000範圍內的整數；R₁為H或CH3；R₂和R₃為具有C1~C12的直鏈烷基鏈、具有C3~C12的支鏈烷基鏈、脂環族環、雜環或芳香族環；R₄為具有C1~C6的直鏈烷基鏈、具有C3~C6的支的支鏈烷基鏈，丙烯酸酯基，甲基丙烯酸酯基或環氧基；A和B是碳、氧或氮。

Wherein: n is an integer in the range of about 1 to about 1000; _R1 is H or CH3; _R2 and _R3 are straight chain alkyl chains with C1~C12, branched chain alkyl chains with C3~C12, alicyclic rings, heterocyclic rings or aromatic rings; _R4 is a straight chain alkyl chain with C1~C6, branched chain alkyl chains with C3~C6, acrylate, methacrylate or epoxide; A and B are carbon, oxygen or nitrogen.

In one embodiment of the present invention, the additive is selected from a polymerization catalyst, a photopolymerization initiator, an antioxidant, or a combination of at least one of the above. The preferred additive is a polymerization catalyst.

In order to facilitate the bonding and fixing of the micro LED on the target substrate, in one embodiment of the present invention, the second heat source is heated by a hot plate or irradiated, and the heating temperature is between 50 and 150° C. The preferred second heat source is hot plate heating.

In order to increase the adsorption force between the elastic micro suction cup and the micro LED, in one embodiment of the present invention, the concave arc structure at the lower end of the elastic micro suction cup is a circular concave arc or an elliptical concave arc. A circular concave arc is preferred. With this concave arc structure design, the adsorption force between the micro LED and the micro LED can be greatly increased, so as to achieve the purpose of adsorbing and picking up the micro LED.

In order to provide better adsorption force for picking up micro light-emitting diodes (Micro LEDs), in one embodiment of the present invention, the width of the concave arc-shaped structure at the lower end of the elastic micro suction cup when stretched open by pressure is not greater than (less than or equal to) the top width of the micro light-emitting diode (Micro LED).

10: Carrier substrate

11: Micro LEDs

12: Electrode

13: First bonding layer

20: Impression

21: Elastic micro suction cup

22: Concave arc structure

30: The first heat source

40: Target substrate

41: Second bonding layer

50: Second heat source

60: Cool down

Figure 1-A is a schematic diagram of the transfer process of the present invention, used to illustrate the bonding force F2 between the first bonding layer 13 and the carrier substrate 10.

FIG1-B is a schematic diagram of the transfer process of the elastic micro suction cup of the present invention, which is used to illustrate the adhesion force F2 between the first bonding layer 13 and the carrier substrate 10 and the elastic micro suction cup 21 and each micro light-emitting diode (Micro LED11) to generate a vertical suction force F1, at which time F2>F1.

FIG1-C is a schematic diagram of the transfer process of the first heat source of the present invention heating the first bonding layer through the carrier substrate, which is used to illustrate the schematic diagram of using the first heat source 30 to heat the first bonding layer 13 through the carrier substrate 10 to transform the first bonding layer 13 from a solid state to a liquid state.

FIG1-D is a schematic diagram of the transfer process of the first bonding layer on the carrier substrate of the present invention being heated and converted into a liquid state, which is used to illustrate that after the first bonding layer 13 is converted into a liquid state, the adhesion force F2 with the carrier substrate 10 decreases to F2', at which time F1>F2', and the micro-LED 11 is sucked by the elastic micro-suction cup 21.

FIG. 1-E is a schematic diagram of the transfer process of the stamp 20 of the present invention to the target substrate 40, which is used to illustrate the bonding force F3 between the solid second bonding layer 41 and the target substrate 40.

FIG1-F is a schematic diagram of the transfer process of pressing down the stamp 20 of the present invention and heating the second bonding layer of the target substrate, which is used to illustrate that after heating the second bonding layer 41 to convert it into liquid, the stamp 20 is pressed down to make the micro-LED 11 contact the second bonding layer 41. At this time, the bonding force F3 between the second bonding layer 41 and the target substrate 40 decreases to F3'.

FIG1-G is a schematic diagram of the transfer process of the second bonding layer 41 of the present invention without heating or cooling, which is used to illustrate that the second heat source 50 stops heating, the temperature drops to room temperature, and the second bonding layer 41 on the target substrate 40 returns to a solid state. At this time, the bonding force between the second bonding layer 41 and the target substrate 40 returns from F3' to F3 (F3>F3').

FIG1-H is a schematic diagram of the transfer process of the second bonding layer 41 of the present invention returning to a solid state, which is used to illustrate that when the second bonding layer 41 returns to a solid state, the bonding force between the second bonding layer 41 and the target substrate 40 returns from F3' to F3 (F3>F3'), and the bonding force F3 is greater than the vertical suction force F1 between the elastic micro suction cup 21 and the micro light-emitting diode (Micro LED) 11 (F3>F1), so that each micro light-emitting diode (Micro LED) 11 is fixed on the target substrate 40 by bonding with the second bonding layer 41 through the electrode 12.

Figure 2-A is a schematic diagram of the downward pressing distance of the elastic micro suction cup 21 of the present invention, which is used to illustrate the design distance h1 between the lower end of the elastic micro suction cup 21 and the top height of the micro light-emitting diode 11.

Figure 2-B is a schematic diagram of the elastic micro suction cup 21 of the present invention being pressed down and adsorbed, which is used to illustrate the design distance h2 of the elastic micro suction cup 21 touching the top surface of the micro light-emitting diode 11 and then pressing down.

Figure 3-A is a schematic diagram of the concave arc-shaped structure at the lower end of the elastic micro suction cup of the present invention, which is used to illustrate the width and position of the concave arc-shaped structure 22 at the lower end of the elastic micro suction cup 21 and the top surface of the micro light-emitting diode 11.

Figure 3-B is a schematic diagram of the elastic micro suction cup downward pressure adsorption structure of the present invention, which is used to illustrate the width and position of the top surface of the micro light-emitting diode when the concave arc-shaped structure 22 at the lower end of the elastic micro suction cup 21 is pressed and stretched open after contact.

In order to clearly illustrate the purpose that the present invention can achieve, a better embodiment is given below to further illustrate the efficacy and features of the micro-suction cup transfer micro-light-emitting diode (Micro LED) method of the present invention.

Please refer to Figures 1-A to 1-H. First, the various equipment, materials and transfer operation settings used in this embodiment are as follows, where: the carrier substrate 10 is a silicon substrate. The micro-light-emitting diode 11 is a Micro LED. The first bonding layer 13 is an inorganic solder. The first heat source 30 is a hot plate, and the temperature of the first heat source 30 is between 50 and 150°C. The target substrate 40 is a display substrate. The second bonding layer 41 is a conductive inorganic solder. The second heat source 50 is a hot plate, and the temperature of the second heat source 50 is between 50 and 150°C. Micro-sucke transmission system:

F1: Suction between Micro-sucker and Micro-LED

F2: Adhesion between Micro-LED and Bonding Layer-1 without heating

F2': Adhesion between Micro-LED and Bonding Layer-1 when heated

F3: Adhesion between Micro-LED and Bonding Layer-2 without heating

F3': Adhesion between Micro-LED and Bonding Layer-2 when heated

As shown in FIG2-A, the designed distance between the lower end of the elastic micro suction cup 21 and the top surface of the micro light-emitting diode 11 is h1, and after the elastic micro suction cup 21 touches the top surface of the micro light-emitting diode 11, the downward pressing distance is h2=1~5mm, as shown in FIG2-B. Therefore, the downward moving distance of the elastic micro suction cup 21 for adsorption and picking up is h1+h2 (1~5mm); for example, when the distance h1=1000mm is set, the designed adsorption moving (downward moving) distance is 1000mm+1~5mm. When using a 3mm×3mm micro-LED, the suction movement (downward movement) distance can be designed to be between 1001 and 1005mm. In another embodiment of the present invention, the suction force F1 between the elastic micro-suction cup 21 and the micro-LED 11 depends on the size of the micro-LED 11. The suction distance of the elastic micro-suction cup of the present invention is 1 to 5mm, and in the preferred embodiment of the present invention, the distance is set to 2mm. Therefore, the design distance for the downward movement of the elastic micro-suction cup 21 is 1002mm.

As shown in FIG3-A , the maximum width L2 of the concave arc-shaped structure 22 at the _{lower end of the elastic micro suction cup 21 is between 5/10} ^{and 6/10} of the top width L1 of the micro light-emitting diode when no pressure is applied, _and the maximum width L2' when stretched out is, as shown in FIG3-B , _{between 80/100 and 95/100} ^{of the} top width L1 of the micro light-emitting diode, for example, the micro light-emitting diode (Micro LED) is 3mm×3mm; the maximum width of the concave arc-shaped structure at the _lower end of the elastic micro suction cup when no pressure is applied is 1.5~1.8mm, and the maximum width when stretched out is 2.4~2.85mm.

The present invention discloses a method for transferring a micro light-emitting diode (Micro LED) by using a micro suction cup. The steps of the method are shown in the process diagrams of FIG. 1-A to FIG. 1-H. The steps include:

(1) Provide a carrier substrate 10, as shown in FIG1-A, on which at least one micro light-emitting diode (Micro LED) 11 is pre-formed, and each micro light-emitting diode (Micro LED) 11 has an electrode 12 below it. The electrode 12 is fixed to the carrier substrate 10 by a solid first bonding layer 13, and a predetermined bonding force F2 is formed between each micro light-emitting diode 11 and the carrier substrate 10.

(2) A stamp 20 is provided, as shown in FIG1-A , and at least one elastic micro suction cup 21 is provided on the stamp 20. The lower end of each elastic micro suction cup 21 is a concave arc-shaped structure 22. A predetermined pressure is applied to the stamp 20, as shown in FIG1-B , and each elastic micro suction cup 21 vertically contacts the top surface of the micro light-emitting diode 11 on the carrier substrate 10, so that the lower end of each elastic micro suction cup 21 is pressed to the same size as the top surface of the micro light-emitting diode 11, and the concave arc-shaped structure 22 of the elastic micro suction cup 21 is stretched to increase the contact area. At this time, each elastic micro suction cup 21 and each micro light-emitting diode (Micro LED) generates a vertical suction force F1, which is less than the adhesive force F2 between the micro LED 11 and the carrier substrate 10; the pressure applied to the elastic micro suction cup 21 in the stamp 20 depends on the downward movement distance of the elastic micro suction cup 21, and the movement distance can also be determined by the size and weight of the micro LED. When implementing the present invention, as long as the elastic micro suction cup 21 moves downward, the width of the concave arc-shaped structure 22 at the lower end of the elastic micro suction cup 21 is not greater than the top width of the micro LED 11, as shown in Figure 1-B.

(3) A first heat source 30 is provided. As shown in FIG. 1-C , the first heat source 30 is used to heat the first bonding layer 13 through the carrier substrate 10. During implementation, a heating method can be selected according to the number of micro LEDs to be transferred. For example, when a single or a unit quantity is selected for transfer, irradiation heating can be selected. When all or a block quantity is selected for transfer, a hot plate heating can be selected. The first heat source 30 is used to heat the first bonding layer 13 selected for heating at a temperature of 70-150° C. to convert the solid state into a liquid state. At this time, each micro LED (Micro LED) The adhesive force between the micro LED 11 and the carrier substrate 10 will decrease from F2 to F2' (F2>F2'). When the adhesive force F2' decreases to less than the vertical suction force F1 generated by each viscoelastic micro suction cup 21 and each micro LED 11 (F1>F2'), as shown in Figure 1-D, each micro LED 11 can be adsorbed by each elastic micro suction cup 21 and detached from the carrier substrate 10, so that the selected micro LED 11 can be easily picked up from the carrier substrate 10.

(4) Provide a target substrate 40, as shown in FIG1-E, on which a solid second bonding layer 41 is provided, and the solid second bonding layer 41 has an adhesive force F3 with the target substrate 40.

(5) Provide a second heat source 50, as shown in FIG1-F, and use the second heat source 50 to heat the selected second bonding layer 41 at a temperature of 70-150°C to convert the second bonding layer 41 from solid to liquid. At this time, the adhesion F3 between the second bonding layer 41 and the target substrate 40 will drop to F3' (F3>F3').

(6) As shown in FIG. 1-G , each micro light-emitting diode (Micro LED) 11 adsorbed and picked up by each elastic micro suction cup 21 is transferred and bonded to the second bonding layer 41 in a liquid state on the target substrate 40, and then the second heat source 50 is stopped to heat and the temperature is allowed to drop to room temperature, so that the second bonding layer 41 on the target substrate 40 returns to a solid state. At this time, the bonding force between the second bonding layer 41 and the target substrate 40 returns from F3′ to F3 (F3>F3′), and the bonding force F3 is greater than the vertical suction force F1 between the elastic micro suction cup 21 and the micro light-emitting diode (Micro LED) 11 (F3>F1), so that each micro light-emitting diode (Micro LED) The micro light-emitting diode (Micro LED) 11 is fixed on the target substrate 40 through the electrode 12 and the second bonding layer 41, and is separated from each elastic micro suction cup 21 to complete the transfer of the micro light-emitting diode (Micro LED) 11, as shown in Figure 1-H.

In the aforementioned preferred embodiment of a micro suction cup transfer method of micro LED, the special concave arc-shaped structure design of the elastic micro suction cup on the stamp can greatly increase the adsorption force between the micro LED and the micro LED, thereby achieving the purpose of adsorption, picking up and transferring the micro LED.

The above-mentioned embodiments are descriptions of the preferred implementation methods of the present invention and do not limit the scope of the present invention. Under the premise of not departing from the design spirit of the present invention, various modifications and improvements made by ordinary technicians in this field to the technical solution of the present invention should fall within the scope of protection determined by the claims of the present invention.

10: Carrier substrate

11: Micro LEDs

12: Electrode

13: First bonding layer

20: Impression

21: Elastic micro suction cup

22: Concave arc structure

30: The first heat source

Claims (8)

A method for transferring micro light-emitting diodes (Micro LEDs) using a micro suction cup, the steps comprising: (1) Providing a carrier substrate, on which there is at least one micro light-emitting diode (Micro LED), each micro light-emitting diode (Micro LED) is fixed to the carrier substrate via a first bonding layer, and an adhesive force F2 is formed between each micro light-emitting diode (Micro LED) and the carrier substrate; (2) A stamp is provided for adsorbing and picking up a micro-light-emitting diode (Micro LED) on a carrier substrate. The stamp has at least one elastic micro-suction cup, and the lower end of each elastic micro-suction cup is in a concave arc-shaped structure. When a predetermined pressure is applied to the stamp, each elastic micro-suction cup will vertically contact the top surface of the micro-light-emitting diode (Micro LED) on the carrier substrate. When the concave arc-shaped structure at the lower end of each elastic micro-suction cup is pressed and spread open, the contact area with the top surface of the micro-light-emitting diode (Micro LED) is increased, so that each elastic micro-suction cup and each micro-light-emitting diode (Micro LED) generate a vertical suction force F1. At this time, the vertical suction force F1 is less than the micro-light-emitting diode (Micro LED). Adhesion force F2 between LED and carrier substrate; (3) Providing a first heat source, which can provide point, local or full heating to the first bonding layer through the carrier substrate at a predetermined temperature, so that the first bonding layer selected to be heated gradually softens from a solid state to a semi-solid state or even turns into a liquid state. At this time, the adhesive force F2 between each micro light-emitting diode (Micro LED) and the carrier substrate in step (1) will decrease, and the decreased adhesive force F2' will be less than the vertical suction force F1 in step (2), and each micro light-emitting diode (Micro LED) can be adsorbed by each elastic micro suction cup and detached from the carrier substrate, so that the selected micro light-emitting diode (Micro LED) can be picked up from the carrier substrate; (4) Providing a target substrate for receiving the micro light-emitting diode (Micro LED) from the carrier substrate, the target substrate having a solid second bonding layer, the solid second bonding layer having an adhesion force F3 with the target substrate; (5) Providing a second heat source, which can provide point, local or overall heating to the second bonding layer through the target substrate at a predetermined temperature, so that the second bonding layer that is selected to be heated can be gradually softened from a solid state to a semi-solid state or even to a liquid state, so that the solid bonding force F3 between the second bonding layer and the target substrate is reduced to a liquid bonding force F3', and the bonding force F3' in the liquid state will be less than the vertical suction force F1 of step (2); (6) Each micro-LED adsorbed and picked up by each elastic micro-suction cup in step (3) is transferred and bonded to the second bonding layer on the target substrate which is in a softened or even liquid state, and then the second heat source is stopped to heat the second bonding layer on the target substrate so that the second bonding layer on the target substrate returns to a solid state. At this time, the bonding force F3′ between the softened or even liquid second bonding layer and the target substrate returns to the bonding force F3 in step (4), and when the bonding force F3 is greater than the vertical suction force F1 generated between each elastic micro-suction cup and each micro-LED in step (2), each micro-LED can be detached from each elastic micro-suction cup, so that each micro-LED can be removed from the second bonding layer. LED) is fixed on the target substrate through the second bonding layer to complete the transfer of micro LED. The micro-suction cup transfer method of micro-light-emitting diode (Micro LED) as claimed in claim 1 is characterized in that the first bonding layer on the carrier substrate is a temperature-sensitive crystalline polymer or inorganic solder, and the solid state temperature of the bonding layer is

40℃, liquid temperature

70℃. The micro suction cup transfer micro light-emitting diode (Micro LED) method as described in claim 1 is characterized in that the heating method of the first heat source is hot plate heating or irradiation heating, and the heating temperature is between 50~150℃ The micro-suction cup transfer method of micro-light-emitting diode (Micro LED) as described in claim 1 is characterized in that the second bonding layer on the target substrate is a temperature-sensitive crystalline polymer or inorganic solder with conductive properties, and the solid state temperature of the bonding layer is

40℃, liquid temperature

70℃. The micro-suction cup transfer method of micro-light-emitting diode (Micro LED) as described in claim 1 is characterized in that the second bonding layer on the target substrate includes a conductive particle, a temperature-sensitive crystalline polymer and an additive; wherein: The conductive particles are selected from metals, metal alloys, anisotropic conductive particles or a combination of at least one of the above; The temperature-sensitive crystalline polymer is composed of a main chain, multiple crystallizable side chains, and multiple heteroatoms connected to the polymer, wherein the temperature-sensitive crystalline polymer contains repeating units of the following formula (I)

in: n is an integer in the range of about 1 to about 1000; _R1 is H or CH3; _R2 and _R3 are linear alkyl chains having C1-C12, branched alkyl chains having C3-C12, alicyclic rings, heterocyclic rings or aromatic rings; _R4 is a C1-C6 straight alkyl chain, a C3-C6 branched alkyl chain, an acrylate group, a methacrylate group or an epoxide group; A and B are carbon, oxygen or nitrogen; The additive is selected from a polymerization catalyst, a photopolymerization initiator, an antioxidant, or a combination of at least one of the above. The method for transferring micro LEDs by using a micro suction cup as described in claim 1 is characterized in that the heating method of the second heat source is hot plate heating or irradiation heating, and the heating temperature is between 50 and 150°C. The method for transferring micro light-emitting diodes (Micro LEDs) by using a micro suction cup as described in claim 1 is characterized in that the concave arc structure at the lower end of the elastic micro suction cup is a circular concave arc or an elliptical concave arc. The method for transferring a micro light-emitting diode (Micro LED) by using a micro suction cup as described in claim 1 is characterized in that the width of the concave arc-shaped structure at the lower end of the elastic micro suction cup when stretched open by pressure is not greater than (less than or equal to) the top width of the micro light-emitting diode (Micro LED).

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