MicroLED transfer seal structure based on colloid self-assembly and preparation method and application thereof

Abstract

The invention belongs to the related technical field of micro light emitting diode assembly, and discloses a micro LED transfer seal structure based on colloid self-assembly and a preparation method and application thereof, and the method comprises the steps: transferring a thermal expansion microsphere single layer to a seal, and packaging to obtain a seal structure, the thermal expansion microsphere single layer is prepared on the basis of a colloid self-assembly technology, and the preparation method comprises the following specific steps: taking a colloidal solution containing thermal expansion microspheres as a raw material, and preparing the thermal expansion microsphere single layer by adopting the colloid self-assembly technology. According to the invention, uniform distribution of the thermal expansion microspheres is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field related to the assembly of micro light-emitting diodes, and more specifically, relates to a MicroLED transfer stamp structure based on colloidal self-assembly, a preparation method thereof, and an application thereof. Background Art

[0002] Micro light-emitting diode (MicroLED) technology is regarded as a new display technology in the field of consumer electronics. Compared with traditional liquid crystal display (LCD) technology and organic light-emitting diode (OLED) display technology, it has the advantages of high brightness and contrast, high color saturation, fast response speed, low energy consumption, long service life, and high reliability. Therefore, MicroLEDs are widely used in the fields of high-resolution and high pixel density displays (smartphones, TVs, and automotive displays), virtual reality / augmented reality (AR / VR technology), visible light communication, and biomedicine.

[0003] In the field of microelectronics manufacturing, the efficient and precise transfer technology of chips is one of the key processes for realizing complex integrated circuits and new display devices (such as Micro-LEDs). With the continuous reduction of chip size and the improvement of integration, traditional chip transfer technologies have gradually revealed problems such as low efficiency, insufficient precision, and poor reliability. Flip-chip bonding technology is one of the earliest chip transfer technologies applied in large-scale production. This technology pre-sets solder balls or conductive adhesives at the bottom of the chip, directly flips the chip, and presses it onto the target substrate; although this technology has high reliability, its transfer speed is limited by the mechanical operation precision of the equipment, and usually only about 8,000 chips can be transferred per hour. For applications such as 8K display panels that require the transfer of more than 100 million chips, traditional flip-chip bonding technology obviously cannot meet the efficiency requirements. In addition, this technology also has certain limitations on the size and shape of the chips, and it is difficult to be applicable to the transfer of micron-sized chips. Thus, mass transfer technology has emerged. Mass transfer technology requires selectively batch transferring micron-sized MicroLED chips from the original sapphire substrate to the circuit substrate. Since the size of MicroLEDs is very small, and mass transfer technology requires very high yields (99.9999%), efficiency, and transfer precision, mass transfer technology has also become the biggest challenge in the MicroLED R & D process, hindering the development of MicroLEDs.

[0004] Regarding the MicroLED mass transfer technology, several technical schools have emerged in the academic and industrial circles. According to the acting force and specific transfer method in the chip transfer process, they are mainly divided into: van der Waals force transfer (Meitl M A, Zhu Z T, Kumar V, et al. Transfer printing by kinetic control of adhesion to an elastomeric stamp[J]. Nature Materials, 2005.), fluidic self-assembly (Lee D, Cho S, Park C, et al. Fluidic self-assembly for MicroLED displays by controlled viscosity[J]. Nature, 2023.), roll-to-roll roller transfer (Choi M, Jang B, Lee W, et al. Stretchable Displays: Stretchable Active Matrix Inorganic Light-Emitting Diode Display Enabled by Overlay-Aligned Roll-Transfer Printing[J]. Advanced Functional Materials, 2017.), and laser-assisted transfer technology. The electrostatic adsorption technology uses the action of an electrostatic field to adsorb the chip onto the transfer medium, and then realizes the release of the chip by controlling the electric field strength. The advantages of this technology are simple equipment and low cost, but its disadvantages are also obvious. First, the electrostatic adsorption force is weak, making it difficult to apply to the transfer of large-size or heavy-mass chips. Second, impurity particles are easily introduced during the electrostatic adsorption process, resulting in chip surface contamination and affecting the transfer accuracy. In addition, the electrostatic adsorption technology is sensitive to environmental humidity and temperature, and the process stability is poor. The fluidic self-assembly technology suspends the chips in a liquid and assembles the chips onto the target substrate using capillary force or van der Waals force. This technology has been widely used in the manufacture of early LEDs and optoelectronic devices. However, the fluidic self-assembly technology requires special designs for the shape and size of the chips to ensure the correct orientation and assembly of the chips. This dependence on chip design limits the versatility of this technology. In addition, the randomness of the chips during the fluidic self-assembly process is relatively high, making it difficult to achieve high-precision chip alignment. The thermally expandable microsphere stamp technology uses the characteristic that the volume of thermally expandable microspheres expands when heated to achieve dynamic adhesion regulation by changing the contact area between the stamp and the chip. The core of this technology lies in precisely controlling the distribution and expansion behavior of the thermally expandable microspheres and optimizing the morphology of the microstructures on the stamp surface, thereby realizing the efficient transfer of chips. Although this technology has significant advantages in theory, there are still some key problems in the existing processes.The non-uniformity of microsphere distribution is one of the main problems of the existing thermal expansion microsphere stamping technology. In the existing technology, the distribution of microspheres usually depends on the mixing and stirring process, which is difficult to achieve uniform distribution of microspheres, resulting in random formation of microstructures on the stamping surface. For example, during the mixing and stirring process, microspheres are prone to form aggregates, which lead to non-uniform microstructures on the stamping surface after expansion, affecting the accuracy of chip transfer. Summary of the Invention

[0005] In view of the above defects or improvement requirements of the existing technology, the present invention provides a MicroLED transfer stamping structure based on colloidal self-assembly, its preparation method and application, aiming to solve the problem of non-uniform distribution of microspheres in the existing thermal expansion microsphere stamping.

[0006] To achieve the above object, according to one aspect of the present invention, a preparation method of a MicroLED transfer stamping structure based on colloidal self-assembly is provided, and the method includes the following steps:

[0007] After transferring a monolayer of thermal expansion microspheres onto the stamping and encapsulating it to obtain a stamping structure, wherein the monolayer of thermal expansion microspheres is prepared based on colloidal self-assembly technology. The specific steps are as follows: using a colloidal solution containing thermal expansion microspheres as raw material, and preparing the monolayer of thermal expansion microspheres by colloidal self-assembly technology.

[0008] Further, a surfactant solution is dropped into the colloidal solution to prepare a monolayer of thermal expansion microspheres.

[0009] Further, deionized water and thermal expansion microspheres are used to prepare a colloidal solution with a thermal expansion microsphere content of 2.5 wt%.

[0010] Further, before transferring the thermal expansion microspheres onto the stamping, it also includes stretching an intermediate substrate with a monolayer of thermal expansion microspheres to control the spacing between the thermal expansion microspheres.

[0011] Further, the material of the thermal expansion microspheres is a phase change material.

[0012] The present invention also provides a stamping structure, which is prepared by using the preparation method of the MicroLED transfer stamping structure based on colloidal self-assembly as described above.

[0013] Further, the stamping structure includes a transparent glass, an adhesive layer disposed on the transparent glass, and an encapsulation layer disposed on the adhesive layer, and the thermal expansion microspheres are uniformly embedded in the encapsulation layer.

[0014] Further, both the adhesive layer and the encapsulation layer are made of PDMS.

[0015] The present invention also provides a method for massively transferring MicroLED chips, and the method for massively transferring includes the following steps:

[0016] (1) Using laser lift-off technology to integrally lift off the flip-chip MicroLED chips prepared on the native substrate;

[0017] (2) Transferring the MicroLED chips to an intermediate carrier substrate;

[0018] (3) Pressing the stamp structure as described above on the MicroLED chips, aligning the thermally expandable microspheres with the MicroLEDs, then corresponding the MicroLED chips with the electrodes on the target substrate, and further transferring the MicroLED chips to the target substrate.

[0019] Further, the peeled MicroLED chips are transferred to an intermediate carrier substrate with an adhesive layer. At this time, the electrode contacts of the MicroLED chips are bonded to the adhesive layer, and the other side faces outward.

[0020] Generally speaking, compared with the prior art by the above technical solution conceived by the present invention, the MicroLED transfer stamp structure based on colloidal self-assembly and its preparation method and application provided by the present invention mainly have the following beneficial effects:

[0021] 1. The monolayer of thermally expandable microspheres is prepared based on colloidal self-assembly technology. The specific steps are as follows: Using a colloidal solution containing thermally expandable microspheres as a raw material, the monolayer of thermally expandable microspheres is prepared by colloidal self-assembly technology. Colloidal self-assembly technology is a technology that utilizes colloidal particles to spontaneously organize into an ordered structure under specific conditions, which enables the thermally expandable microspheres to achieve uniform distribution.

[0022] 2. A surfactant solution is dropped into the colloidal solution to prepare a monolayer of thermally expandable microspheres. In this way, by dropping the surfactant solution, the surface tension distribution state at the liquid surface is changed, so that the surface tension at the liquid surface where the surfactant is dropped is reduced. Due to the different surface tension distributions across the entire liquid surface, the thermally expandable microspheres on the liquid surface move from the position with low surface tension to the position with high surface tension, thereby achieving the dense arrangement of the thermally expandable microspheres. Then, the monolayer of thermally expandable microspheres is transferred to an intermediate substrate by the lifting method, realizing the uniform distribution of the thermally expandable microspheres.

[0023] 3. During the heating process, the microspheres can expand independently without obvious agglomeration, forming a uniform surface microstructure, which significantly improves the accuracy of chip transfer and avoids chip transfer failure or damage caused by uneven local adhesion forces. At the same time, it ensures that all areas in the adhesive layer of the stamp are covered by thermally expandable microspheres. During the foaming process, the microspheres in the entire area expand uniformly, forming a continuous surface microstructure, and this full-coverage foaming effect achieves a uniform adhesive reduction effect.

[0024] 4. The stamp prepared by the present invention is not only applicable to contact transfer, but also can be combined with laser technology to achieve non-contact transfer; this versatility enables the present invention to adapt to different application scenarios and process requirements, further enhancing its practicality and market competitiveness.

[0025] 5. Using the stamp of the present invention for MicroLED has a simple process and does not require additional complex process means such as lithography, secondary molding, and bonding, greatly reducing the complexity of the mass transfer operation and improving the transfer rate. Brief Description of the Drawings

[0026] Figure 1 is a flowchart of a preparation method of a MicroLED transfer stamp structure based on colloidal self-assembly provided by the present invention;

[0027] Figure 2 in which (a) and (b) are flowcharts for preparing closely arranged thermally expandable microspheres in the embodiments of the present invention;

[0028] Figure 3 in which (a), (b), and (c) are schematic diagrams of three kinds of closely arranged colloidal particles prepared by colloidal self-assembly in the embodiments of the present invention;

[0029] Figure 4 in which (i), (ii), and (iii) are flowcharts for controlling the microsphere spacing and transferring them to the stamp in the embodiments of the present invention;

[0030] Figure 5 in which (a), (b), (c), and (d) are distribution diagrams of thermally expandable microspheres on the stamp structure before and after stretching;

[0031] Figure 6 is a graph showing the relationship between the encapsulation layer thickness and the spin coating time at different dilution ratios obtained in the embodiments of the present invention;

[0032] Figure 7 in which (a) and (b) are the stamp structure preparation and working principle diagrams proposed by the present invention;

[0033] Figure 8 in which (a) and (b) are microscopic result diagrams of the stamp structure before and after foaming prepared in the embodiments of the present invention;

[0034] Figure 9 It is a schematic diagram of the process of realizing the overall picking and overall releasing of MicroLEDs through a transfer device provided by an embodiment of the present invention;

[0035] Figure 10 It is a schematic diagram of the colloidal monolayer prepared by the present invention. Among them, (a) is the colloidal monolayer prepared under a 1.44 wt% SDS solution, (b) is the colloidal monolayer prepared under a 7.2 wt% SDS solution, (c) is the colloidal monolayer prepared under a 13.4 wt% SDS solution, and (d) is the colloidal monolayer prepared under a 21.6 wt% SDS solution.

[0036] In all the drawings, the same reference numerals are used to represent the same elements or structures, where: 10 - Petri dish, 20 - deionized water, 30 - thermally expandable microspheres, 40 - surfactant solvent, 50 - intermediate substrate, 60 - quartz substrate, 70 - stamp, 71 - transparent glass, 72 - PDMS adhesive layer, 73 - PDMS encapsulation layer, 80 - MicroLED, 90 - receiving substrate, 100 - thermal field, 110 - intermediate carrier substrate, 120 - original substrate, 130 - target substrate. Detailed implementation manners

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] The present invention provides a preparation method for a MicroLED transfer stamp structure based on colloidal self-assembly. The preparation method realizes the uniform distribution of the thermally expandable microspheres 30 in the stamp 70, so that the thermally expandable microspheres 30 can achieve the purpose of uniform foaming after being heated, thereby minimizing the adhesion force between the MicroLED chip 80 and the stamp structure and realizing the high-precision transfer of the MicroLED chip 80.

[0039] The preparation method ensures the uniform distribution of the thermal expansion microspheres 30 in the viscous layer 72 through the colloidal self-assembly process, without obvious agglomeration. During the heating process, the microspheres can expand independently to form a uniform surface microstructure. This uniformly foamed surface microstructure significantly improves the accuracy of chip transfer, avoiding chip transfer failure or damage caused by uneven local adhesion forces. Among them, the colloidal self-assembly technology is a technology that uses colloidal particles to spontaneously organize into an ordered structure under specific conditions, and its driving forces include van der Waals forces, electrostatic interactions, solvent evaporation, and surface tension, etc. A colloid is a system in which tiny particles (usually in the nanometer to micrometer scale) are dispersed in another medium. These particles can be polymers, metals, semiconductors, or biomolecules. Through methods such as the solvent evaporation method, template-assisted method, or electric / magnetic field-assisted method, this technology can achieve two-dimensional or three-dimensional ordered structures of colloids. The colloidal self-assembly technology has the following remarkable advantages: First, this method is easy to operate, does not rely on high-precision instruments, reduces the complexity and cost of experimental equipment, and is suitable for research and application at the laboratory scale. Second, colloidal self-assembly mainly relies on the interfacial tension difference at the interface of the dispersion liquid, so it has strong adaptability to solvents, is applicable to a variety of organic solvent systems, and has wide universality. Finally, the colloidal crystal film obtained by colloidal self-assembly has a single-layer particle thickness and can be transferred to substrates of any material by the dipping method, showing good flexibility.

[0040] The present invention changes the surface tension distribution state at the liquid surface by dropping a surfactant solution, making the surface tension at the liquid surface where the surfactant is dropped decrease. Due to the different distribution of surface tension across the entire liquid surface, the thermal expansion microspheres 30 on the liquid surface move from the position with low surface tension to the position with high surface tension, thereby realizing the dense arrangement of the thermal expansion microspheres 30. Then, the thermal expansion microsphere monolayer is transferred to the intermediate substrate 50 by the dipping method.

[0041] In one embodiment, sodium dodecyl sulfate (SDS) is used as the solute and deionized water 20 is used as the solvent to prepare the surfactant, and irregular silica microspheres are used as colloidal particles and deionized water 20 is used as the solvent to prepare a 2.5 wt% colloidal solution. The monolayer colloidal particles prepared under different SDS ratios are subjected to the colloidal self-assembly process, as shown in Figure 10 .

[0042] Please refer to Figure 1 , the preparation method mainly includes the following steps: After transferring the thermal expansion microsphere monolayer to the stamp 70, it is encapsulated to obtain a stamp structure. Among them, the thermal expansion microsphere monolayer is prepared based on the colloidal self-assembly technology. The specific steps are: using a colloidal solution containing the thermal expansion microspheres 30 as the raw material, and preparing the thermal expansion microsphere monolayer by the colloidal self-assembly technology.

[0043] Please refer toFigure 3 , Figure 4 , Figure 5 and Figure 6 , in one embodiment, a colloidal solution with a thermal expansion microsphere content of 2.5 wt% is prepared. Using this colloidal solution as a raw material, a dense monolayer of thermal expansion microspheres is prepared by colloidal self-assembly technology, and the monolayer of thermal expansion microspheres is transferred onto an intermediate substrate 50. Specifically, a surfactant solution is dropped into the colloidal solution to prepare a monolayer of thermal expansion microspheres, and the monolayer of thermal expansion is transferred onto the intermediate substrate 50. In addition, a quartz substrate 60 is provided on a side of the intermediate substrate 50 away from the thermal expansion microspheres 30.

[0044] Before transferring the thermal expansion microspheres onto the stamp, the intermediate substrate 50 is stretched to control the spacing between the thermal expansion microspheres, so that the monolayer of thermal expansion microspheres corresponds to the MicroLED chips 80 to be transferred, achieving a more precise transfer effect.

[0045] Please refer to Figure 2 , in one embodiment, the preparation steps of the monolayer of thermal expansion microspheres are as follows:

[0046] First, a surfactant solution is dropped into a petri dish 10. The thermal expansion microspheres in the petri dish 10 are closely arranged at the interface between deionized water 20 and the air liquid surface, and then the thermal expansion microspheres at the liquid surface are transferred onto the intermediate substrate 50 by the lifting method. Among them, the material of the thermal expansion microspheres is a phase change material, so that the thermal expansion microspheres can be reused.

[0047] After that, the intermediate substrate 50 with closely arranged thermal expansion microspheres is clamped onto a stretching machine, and then forces in two directions are applied to the intermediate substrate 50 to control the transfer spacing of the thermal expansion microspheres.

[0048] Please refer to Figure 7 , the stamp structure includes a transparent glass 71, an adhesive layer 72 provided on the transparent glass 71, and a packaging layer 73 provided on the adhesive layer 72. The thermal expansion microspheres are uniformly embedded in the packaging layer 73. Among them, both the adhesive layer 72 and the packaging layer 73 are made of PDMS.

[0049] Please refer to Figure 8 and Figure 9 , the present invention also provides a method for massively transferring MicroLED chips. The method for massively transferring mainly includes the following steps:

[0050] Step 1, using laser lift-off technology to integrally peel off the flip-chip MicroLED chips 80 prepared on a native substrate 120.

[0051] Step 2: Transfer the MicroLED chip 80 onto the intermediate carrier substrate 110.

[0052] Considering the pin orientation, the peeled MicroLED chip 80 needs to be transferred onto the intermediate carrier substrate 110 with an adhesive layer first. At this time, the electrode contacts of the MicroLED chip 80 are bonded to the adhesive layer, and the other side faces outward. The adhesive layer can significantly reduce its viscosity until it disappears through ultraviolet light irradiation.

[0053] In one embodiment, the MicroLED chip 80 is pressed onto the intermediate carrier substrate 110, and the ultraviolet laser is transmitted through the native substrate 120 and irradiated at the interface between the MicroLED chip and the native substrate 120. Since the substrate of the MicroLED chip is composed of gallium nitride material, gallium nitride can absorb the ultraviolet laser and undergo thermal decomposition to form liquid gallium and nitrogen. Therefore, the adhesion strength at the interface between the MicroLED chip and the native substrate 120 is significantly reduced after being irradiated by the laser, and the MicroLED chip can be separated from the native substrate 120.

[0054] Step 3: Press the stamp structure onto the MicroLED chip, and align the thermally expandable microspheres with the MicroLED.

[0055] Step 4: Align the MicroLED chip with the electrodes on the target substrate 130, and then transfer the MicroLED chip onto the target substrate 130.

[0056] In one embodiment, the stamp structure with the MicroLED chip is placed on the transfer driving platform, and the MicroLED chip on the stamp structure is aligned with the electrode array of the circuit substrate through methods such as visual positioning. Then, the distance between the stamp structure and the target substrate is adjusted through a precision motion platform. After that, the stamp structure is heated as a whole by the thermal field 100, so that the thermally expandable microspheres in the stamp structure uniformly foam and expand, realizing the pushing and transfer of the MicroLED chip, and reducing the adhesion force between the MicroLED chip and the stamp structure. Then, the stamp structure is slowly lifted, so that the MicroLED chip is peeled off from the stamp structure and transferred onto the target substrate 130, that is, the receiving substrate 90.

[0057] In another embodiment, the stamp structure is pressed onto the intermediate carrier substrate 110 of the MicroLED chip, with strict one-to-one correspondence. Since the temporary intermediate carrier substrate 110 serves a temporary transitional role, the interfacial adhesion force between the MicroLED array and the temporary intermediate carrier substrate 110 (such as a UV glue substrate) can be reduced until it disappears under certain conditions, enabling the release of the MicroLED chip. At this time, the stamp structure can peel off the MicroLED chip as a whole.

[0058] Among them, the material of the intermediate substrate 50 can be elastic materials such as polydimethylsiloxane (PDMS), ECOFLEX, etc.; for encapsulation, polydimethylsiloxane (PDMS) diluted with cyclohexane can be used, and cyclohexane can be replaced with non-polar solvents such as acetone; for the laser in the laser lift-off technology, 308nm / 248nm / 266nm excimer lasers, 355nm femtosecond lasers, etc. can be used; the intermediate transparent carrier substrate can be a UV release layer adhesive layer; the heating method can be a hot plate / laser, etc.

[0059] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A preparation method of a MicroLED transfer stamp structure based on colloidal self-assembly, characterized in that, The method includes the following steps: After transferring a single layer of thermally expandable microspheres onto a stamp, encapsulation is performed to obtain a stamp structure. The single layer of thermally expandable microspheres is prepared based on colloidal self-assembly technology. The specific steps are as follows: Using a colloidal solution containing thermally expandable microspheres as a raw material, the single layer of thermally expandable microspheres is prepared by colloidal self-assembly technology.

2. The preparation method of the MicroLED transfer stamp structure based on colloidal self-assembly according to claim 1, characterized in that: A surfactant solution is dropped into the colloidal solution to prepare a single layer of thermally expandable microspheres.

3. The preparation method of the MicroLED transfer stamp structure based on colloidal self-assembly according to claim 1, wherein: A colloidal solution with a thermally expandable microsphere content of 2.5 wt% is prepared using deionized water and thermally expandable microspheres.

4. The preparation method of the MicroLED transfer stamp structure based on colloidal self-assembly according to claim 1, wherein: Before transferring the thermally expandable microspheres onto the stamp, it also includes stretching an intermediate substrate with a single layer of thermally expandable microspheres to control the spacing between the thermally expandable microspheres.

5. The preparation method of the MicroLED transfer stamp structure based on colloidal self-assembly according to claim 1, wherein: The material of the thermally expandable microspheres is a phase change material.

6. A seal structure, characterized in that: The stamp structure is prepared by the preparation method of the MicroLED transfer stamp structure based on colloidal self-assembly described in any one of claims 1-5.

7. The seal structure according to claim 6, characterized in that: The stamp structure includes a transparent glass, an adhesive layer provided on the transparent glass, and an encapsulation layer provided on the adhesive layer. The thermally expandable microspheres are uniformly embedded in the encapsulation layer.

8. The seal structure according to claim 7, characterized in that: Both the adhesive layer and the encapsulation layer are prepared using PDMS.

9. A method for mass transfer of MicroLED chips, characterized in that, The mass transfer method includes the following steps: (1) Using laser lift-off technology to integrally lift off the flip-chip MicroLED chips prepared on a native substrate; (2) Transferring the MicroLED chips to an intermediate carrier substrate; (3) Pressing the stamp structure described in any one of claims 6-8 on the MicroLED chips, aligning the thermally expandable microspheres with the MicroLEDs, and then corresponding the MicroLED chips with the electrodes on the target substrate, and further transferring the MicroLED chips to the target substrate.

10. The method for massive transfer of MicroLED chips according to claim 9, wherein: The peeled MicroLED chips are transferred to an intermediate carrier substrate with an adhesive layer. At this time, the electrode contacts of the MicroLED chips are bonded to the adhesive layer, and the other side faces outward.

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