A laser-driven micro-led chip mass transfer device, a preparation method thereof and application thereof

Abstract

The application belongs to the technical field of micro light emitting diode assembly, and discloses a laser-driven MicroLED chip mass transfer device and a preparation method and application thereof. The device comprises a transfer stamp, the transfer stamp comprises glass, a laser-sensitive layer, a heat-absorbing layer and a cavity layer, the glass, the laser-sensitive layer and the cavity layer are sequentially connected, the laser-sensitive layer is provided with a through groove, the heat-absorbing layer is arranged in the through groove and connected with the groove wall, and the anisotropic heat conduction characteristics of the heat-absorbing layer can realize heat homogenization when laser and chip offset irradiation. A plurality of cavities are arranged on the side of the cavity layer away from the glass. The application is provided with a heating layer, realizes photo-thermal conversion through the heating layer, realizes chip transfer by using thermal effect instead of laser ablation, can realize repeated use of the transfer stamp (i.e. reversible transfer of the chip), and thus reduces the time for repeatedly producing the transfer stamp.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of micro light emitting diode assembly, and more particularly relates to a laser-driven MicroLED chip mass transfer device, a preparation method thereof and an application thereof. BACKGROUND

[0002] Micro light emitting diode (MicroLED) technology is considered to be a new display technology in the field of consumer electronics. It has the advantages of high brightness and contrast, high color saturation, fast response speed, low energy consumption, long service life, and high reliability compared to traditional liquid crystal display (LCD) technology and organic light emitting diode (OLED) display technology. Therefore, MicroLED is widely used in high-resolution and high-pixel-density display fields (smartphones, televisions, and car displays), virtual reality / augmented reality (AR / VR technology), visible light communication, and biomedical fields.

[0003] Although MicroLED has many advantages and application fields, it is a difficult problem to transfer and assemble it on a display panel on a large scale. Since the size of MicroLED is less than 100 μm, as its size decreases, the difficulty of transfer also gradually increases. The traditional Pick&Place technology is difficult to operate, the limit size of vacuum adsorption is about 80 μm, and the transfer efficiency is low (25,000 pieces / hour). Therefore, this transfer method is not suitable for actual mass production, and mass transfer technology is needed to ensure transfer precision, yield, and efficiency. Mass transfer technology is to selectively transfer MicroLED from the original substrate to the display panel. Due to the size effect of MicroLED, the difficulty of mass transfer technology lies in high efficiency (20,000 pieces / second), high precision (±5 μm), and high yield (99.9999%). This also makes mass transfer technology an important challenge for the development of MicroLED.

[0004] For the MicroLED mass transfer technology, several technical schools have emerged in the academic and industrial communities. According to the force and specific transfer method in the chip transfer process, it is 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.), fluid 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. Van der Waals force transfer technology uses the intermolecular force between the elastic stamp and the MicroLED chip for picking up and transferring, which can transfer a large number of chips, but also has the shortcomings of non-selective transfer, difficulty in pick-and-place modulation and the need to weaken the transferred device. Fluid self-assembly is to drive MicroLED by fluid, and realize automatic assembly of chips to the specified area through mechanical force, magnetic force or capillary force, which has low transfer cost, but it is difficult to transfer three-color devices. Roll-to-roll roller transfer is to pick up MicroLED on the original substrate by roller and transfer it to the target substrate, which has the problems of difficulty in selectivity and interval pick-up and transfer of MicroLED. Laser-assisted mass transfer technology is a process of using patterned laser spots to selectively transfer MicroLED to the receiving substrate in batches. Due to the advantages of fast laser processing speed, good programmability and easy control, laser-assisted mass transfer technology is expected to be used for the manufacture of ultra-large size high-resolution MicroLED displays.

[0005] Although laser-assisted mass transfer technology has the advantages of high transfer efficiency and good selectivity, it also has many limitations. For example, laser-induced bubble-assisted transfer (Saeidpourazar R, Li R, Li Y, et al. Laser-Driven Micro Transfer Placement of Prefabricated Microstructures[J]. Journal of Microelectromechanical Systems, 2012.) uses laser ablation to dynamically release the layer to generate bubbles to achieve chip transfer, which has high requirements for laser spot uniformity and resolution, and cannot achieve reversible chip transfer and reusable transfer device. Based on the above problems, Song Jizhou team of Zhejiang University proposed a laser-driven reversible transfer method (Zhang S, Luo H, Wang S, et al. A thermal actuated switchable dry adhesive with high reversibility for transfer printing[J]. International Journal of Extreme Manufacturing, 2021.), which uses shape memory polymer (SMP) and steel balls to make a transfer device. By heating the steel ball with a laser, the SMP deforms to transfer the chip, achieving reversible chip transfer. However, the chip, steel ball, and laser spot need to be strictly aligned to ensure transfer accuracy, which requires high alignment of the laser spot and has certain limitations. Laser thermal stress-assisted chip transfer technology (Saeidpourazar, R, Li, et al. Laser-Driven Micro Transfer Placement of Prefabricated Microstructures[J]. Journal of Microelectromechanical Systems AJoint IEEE&Asme Publication on Microstructures Microactuators Microsensors&Microsystems, 2012.) uses the chip to absorb laser heat and the thermal stress mismatch at the interface to achieve chip transfer. Selectivity is mainly achieved by programming the laser path. For fast and selective chip transfer, the laser scanning path or laser scanning pattern needs to be aligned with the chip. For actual production process of MicroLED transfer, red, green, and blue micro-chips need to be transferred to the display panel. Traditional MicroLED mass transfer requires three transfers, which is a complex process with low transfer efficiency. SUMMARY

[0006] In view of the above defects or improvement needs of the prior art, the present application provides a laser-driven MicroLED chip mass transfer device and a preparation method and application thereof, which aims to solve the problem of non-reproducible transfer of existing components.

[0007] To achieve the above-mentioned purpose, according to one aspect of the present application, a laser-driven MicroLED chip mass transfer device is provided, which comprises a transfer stamp, the transfer stamp comprising glass, a laser-sensitive layer, a heat-absorbing layer and a cavity layer, the glass, the laser-sensitive layer and the cavity layer being connected in sequence, the laser-sensitive layer being provided with a through slot, and the heat-absorbing layer being arranged in the through slot and connected with the slot wall; a plurality of cavities are arranged on the side of the cavity layer away from the glass.

[0008] Further, the in-layer thermal conductivity of the heat-absorbing layer is higher than the inter-layer thermal conductivity; the number of the heat-absorbing layers is multiple, and the light absorption degrees of the multiple heat-absorbing layers are not all the same.

[0009] Further, the heat-absorbing layer transmits heat to the cavities by being irradiated by laser, thereby increasing the air pressure in the cavities, and the MicroLED chips in contact with the cavities are pushed away and transferred to the target substrate by the force of air pressure.

[0010] The present application also provides a preparation method of the laser-driven MicroLED chip mass transfer device as described above, which comprises the following steps:

[0011] Step one: the cavity layer of the transfer stamp is prepared by spin coating and curing;

[0012] Step two: the heat-absorbing layer is prepared by photolithography and development, and the heat-absorbing layer and the cavity layer are bonded together by bonding to obtain the transfer stamp, and then the device is obtained.

[0013] Further, step one comprises the following sub-steps:

[0014] (1) spin coating a layer of photoresist on a silicon wafer, pre-baking the photoresist, then aligning the pre-baked photoresist and a photomask and placing them under the light source of a photoetching machine for exposure, developing after exposure, and forming a photoresist mold containing micro columns;

[0015] (2) spin coating a viscoelastic material on the photoresist mold, and after heating and curing, forming a cavity layer by inverse molding.

[0016] Further, a laser sensitive layer is spin-coated on the sapphire substrate, after solidification, the laser spot is patterned by using an optical mask, the laser is irradiated on the sensitive layer to prepare the heat absorption layer, the preparation of the heat absorption layer of the transfer stamp is completed, and the surface treatment of the heat absorption layer and the cavity layer is carried out, and the complete transfer stamp is prepared by bonding.

[0017] Further, the material of the laser sensitive layer is polyimide, and the viscoelastic material is polydimethylsiloxane or Ecoflex.

[0018] The application also provides a laser-driven MicroLED chip mass transfer method, which comprises the following steps:

[0019] (1) The transfer stamp of the laser-driven MicroLED chip mass transfer device is tightly attached to the MicroLED chip on the intermediate substrate, the adhesion is reduced by external stimulation to the intermediate substrate, the transfer stamp is heated and then cooled, the negative pressure is formed in the cavity and the chip is contacted, the transfer stamp is lifted to realize the pickup of the chip;

[0020] (2) The MicroLED chip and the electrode array on the target substrate are aligned, and the distance between the transfer stamp and the target substrate is adjusted;

[0021] (3) The laser is input into the device, the patterned laser irradiates the heat absorption layer in the transfer stamp, the air pressure in the cavity is increased by heat transfer, the MicroLED chip array is pushed and transferred, and the MicroLED chip array is contacted with the circuit substrate;

[0022] (4) The transfer stamp is lifted, the MicroLED chip array is peeled off from the transfer stamp, and is successfully transferred to the target substrate to form a display device.

[0023] Further, before step (1), the following steps are further included: the intermediate substrate is tightly attached to the MicroLED chip on the original substrate, the chip is bonded to the adhesive layer of the intermediate substrate, and the laser peeling source is used to act on the interface between the MicroLED chip and the original substrate by using laser peeling technology, so that the interface is separated, after laser peeling, the original substrate and the MicroLED chip are separated, and the MicroLED array is picked up by using the adhesive intermediate substrate.

[0024] Further, the selective transfer of the MicroLED chip array is realized by laser scanning path or different light absorption degree of the heat absorption layer.

[0025] Overall, compared with the prior art, the laser-driven MicroLED chip mass transfer device and its preparation method and application provided by the present application mainly have the following beneficial effects:

[0026] 1. The present application is provided with a heating layer, which realizes photo-thermal conversion and realizes chip transfer by using thermal effect instead of laser ablation, so that the transfer of the transfer stamp can be repeated multiple times (i.e. reversible transfer of the chip), thereby reducing the time for repeatedly producing the transfer stamp and improving the efficiency of mass transfer. At the same time, this transfer method has the advantages of parallelism, programmability, non-contact, etc., and can transfer MicroLED to a non-adhesive substrate.

[0027] 2. The laser acts on the heat-absorbing layer inside the stamp, avoiding high-temperature damage caused by chip heat absorption, thereby solving the repair problem caused by chip damage and enabling the transfer of MicroLED chips without light absorption characteristics, reducing the requirements for MicroLED, and enabling beam splitting and rapid scanning of the laser through spatial modulation of the laser, thereby realizing rapid, efficient and reliable transfer of MicroLED.

[0028] 3. The mass transfer method of the present application can ensure high precision of chip transfer when the light spot and the chip are offset. When the laser is offset, the heat-absorbing layer absorbs laser radiation and converts light into heat. Since the thermal conductivity of the heat-absorbing layer is higher than that of the cavity layer, the heat transfer speed inside the heat-absorbing layer is higher than that between layers, ensuring that the temperature difference inside the cavity is small, thereby ensuring that the air pressure of each cavity is small, improving the transfer precision of the chip and the redundancy of the process, and ensuring the transfer precision of the chip even when the laser and the chip are not aligned during transfer.

[0029] 4. The heat-absorbing layer is prepared by irradiating the laser-sensitive layer with laser, which can prepare heat-absorbing layers with different light absorption levels by using different laser energies and irradiation times. Meanwhile, the laser-sensitive layer is not broken by using backplate assistance, optical mask and other methods for high-energy laser irradiation, providing a method for high-energy laser interface ablation of polymers to ensure surface integrity.

[0030] 5. The heat-absorbing layer with different light absorption levels is used to realize selective transfer of MicroLED chips, which can pick up red, green and blue MicroLED chips on the transfer stamp, and realize selective transfer of different MicroLED chips by scanning the transfer stamp with laser or irradiating the transfer stamp with a flash lamp, thereby improving the transfer efficiency.

[0031] 6. Laser input transfer device, the shaping, homogenization and beam splitting of laser are realized through a spatial light modulator, a scanning galvanometer scans multiple laser beams, and irradiates on a transfer stamp to realize high-efficiency chip transfer.

[0032] 7. The heat absorption layer can ensure that the thermal conductivity of heat in the layer is higher than that between the layers, realizing anisotropic conduction of heat, and when there is an offset between the laser and the MicroLED chip, the heat distribution in the heat absorption layer can be ensured to be relatively uniform due to the presence of the heat absorption layer, and when the heat is transferred between the layers, the air pressure in the cavity below the heat absorption layer is also relatively uniform under uniform heat transfer, so that the chip has high transfer precision in the case of spot offset, and the process redundancy is improved. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a schematic diagram of a laser-driven MicroLED chip mass transfer device provided by the present application;

[0034] Figure 2 (a) and (b) in (a) and (b) are schematic diagrams of chip self-alignment mass transfer;

[0035] Figure 3 is a process schematic diagram of preparing a transfer stamp, wherein (a) is a schematic diagram of preparing a cavity layer inside the transfer stamp, and (b) is a schematic diagram of preparing and bonding a heat absorption layer of the transfer stamp;

[0036] Figure 4 is a schematic diagram of transferring chips when the spot of the stamp without a heat absorption layer and the stamp with a heat absorption layer is offset, wherein (a) is a schematic diagram of picking up a chip when the infrared laser is directly acted on the stamp without a heat absorption layer when the infrared laser and the MicroLED chip are offset, and (b) is a schematic diagram of the heat absorption layer of the stamp when the infrared laser and the MicroLED chip are offset;

[0037] Figure 5 (a) and (b) in (a) and (b) are schematic diagrams of selectively transferring MicroLED chips by using heat absorption layers with different light absorption degrees;

[0038] Figure 6 is a process diagram of selectively transferring MicroLED chips by using a heat absorption layer, which is in the order from top to bottom;

[0039] Figure 7 (a), (b), (c), (d) and (e) in (a), (b), (c), (d) and (e) are process schematic diagrams of transferring MicroLED chips from a native substrate to a target substrate;

[0040] Figure 8(a), (b) in FIG. 4 are the offset results of the chips with and without the heat-absorbing layer when the light spot is offset by 300 μm, (c) is a comparison chart of the accuracy of the stamp transfer chips with and without the heat-absorbing layer when the light spot is offset by different distances;

[0041] Figure 9 (a), (b), (c), (d) in FIG. 5 are schematic diagrams of ablation of the laser sensitive layer by high-energy laser and use of an optical mask to ensure surface damage-free;

[0042] Figure 10 (a), (b), (c) in FIG. 6 are another result diagrams of ablation of the laser sensitive layer by high-energy laser and use of an optical mask to ensure surface damage-free;

[0043] Figure 11 (a), (b) in FIG. 7 are respectively a characterization diagram of the adhesion performance of the transferred stamp;

[0044] Figure 12 (a), (b) in FIG. 8 are respectively result diagrams of selective transfer of the chips by using heat-absorbing layers with different light absorption degrees.

[0045] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein: 10 - infrared laser, 11 - low-power infrared laser, 12 - high-power infrared laser, 20 - spatial light modulator, 30 - scanning galvanometer, 40 - focusing lens, 50 - transfer stamp, 51 - glass, 52 - laser sensitive layer, 53 - heat-absorbing layer, 531 - first heat-absorbing layer, 532 - second heat-absorbing layer, 533 - third heat-absorbing layer, 54 - cavity layer, 60 - MicroLED chip, 70 - target substrate, 71 - electrode, 80 - photoresist mold, 81 - silicon wafer, 82 - photoresist, 90 - photoetching machine light source, 100 - photoetching mask, 110 - ultraviolet laser, 120 - original substrate, 130 - laser lift-off light source, 140 - external stimulus, 150 - intermediate substrate, 151 - modified intermediate substrate. DETAILED DESCRIPTION

[0046] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application 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 application and should not be used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0047] The application provides a laser-driven MicroLED chip mass transfer device, which can realize selective transfer of chips by scanning of laser, and can realize selective transfer of chips by overall scanning of the transfer stamp 50 by the laser with different light absorption degrees of the heat absorption layer 53 on the transfer stamp 50; the laser acts on the heat absorption layer 53 of the transfer stamp 50, and the heat absorption layer 53 absorbs the laser and transfers heat to realize transfer, which can effectively avoid high-temperature damage of the chip and can transfer transparent chips without light absorption, and the requirement of the chip to be transferred is reduced.

[0048] Please refer to Figure 1 The device comprises a spatial light modulator 20, a scanning galvanometer 30, a focusing lens 40 and a transfer stamp 50, and the transfer process of the chip is realized by using an optical mask to make a patterned laser spot act on the heat absorption layer 53 in the transfer stamp 50, so that heat is transferred to the inside of the cavity, the air pressure in the cavity gradually increases with the increase of the temperature, and the MicroLED chip 60 picked up on the transfer stamp 50 is selectively transferred to the target substrate 70.

[0049] When the incident laser enters the device, the spatial light modulator 20 shapes, homogenizes and divides the infrared laser 10, and the laser beam after the spatial light modulator 20 enters the scanning galvanometer 30 to realize rapid scanning of multiple laser beams, and is irradiated on the transfer stamp 50 to realize efficient mass transfer.

[0050] Please refer to Figure 2 The transfer stamp 50 comprises glass 51, a laser-sensitive layer 52, a heat absorption layer 53 and a cavity layer 54, the glass 51, the laser-sensitive layer 52 and the cavity layer 54 are connected in sequence, the laser-sensitive layer 52 is provided with a through groove, and the heat absorption layer 53 is arranged in the through groove and connected with the groove wall. The laser-sensitive layer 52 and the heat absorption layer 53 form a continuous layer. The cavity layer 54 is provided with a plurality of cavities arranged at intervals away from one side of the glass 51.

[0051] After the transfer stamp 50 is heated and then cooled, the cavities contact the MicroLED chip 60 to form negative pressure, so that the MicroLED chip 60 is picked up, and the MicroLED chip 60 is aligned with the electrode 71 on the target substrate 70. By irradiating the infrared laser 10 on the transfer stamp 50, the infrared laser 10 acts on the heat absorption layer 53, heat is transferred to the bottom cavity layer 54 through photo-thermal conversion, the air pressure in the cavity increases, a pushing force is generated on the MicroLED chip 60, and the MicroLED chip 60 is transferred to the target substrate 70.

[0052] Please refer to Figure 3 The preparation method of the transfer stamp 50 mainly comprises the following steps:

[0053] Step one, the cavity layer 54 of the transfer stamp 50 is prepared by spin-coating and curing. Specifically, a layer of photoresist 82 is spin-coated on a silicon wafer 81, and a photoresist mold 80 with micro-pillars is prepared by photoetching using an optical mask and developing, and the cavity layer 54 is formed by spin-coating a viscoelastic material on the photoresist mold 80 and then reverse-molding after curing. The specific steps are as follows:

[0054] (1) A layer of photoresist is spin-coated on the silicon wafer 81, and the photoresist is pre-baked, then the pre-baked photoresist and the photoetching mask 100 are aligned and placed under the light source 90 of the photoetching machine for exposure, and then developed to form a photoresist mold 80 containing micro-pillars.

[0055] (2) A viscoelastic material is spin-coated on the photoresist mold 80, and after heating and curing, the cavity layer 54 is formed by reverse-molding.

[0056] The cavity layer 54 can also be made by twice reverse-molding using a silicon wafer 81 mold made by deep silicon etching, sandpaper, or a 3D printing mold. The viscoelastic material can be polydimethylsiloxane (PDMS) or Ecoflex, which is used to make the cavity layer 54 by reverse-molding.

[0057] Step two, the heat-absorbing layer 53 is prepared by photoetching and developing, and the heat-absorbing layer 53 is bonded to the cavity layer 54 to obtain the transfer stamp 50. A layer of laser-sensitive layer 52 is spin-coated on a sapphire substrate, and after curing, the laser spot is patterned using an optical mask, and the heat-absorbing layer 53 is prepared by laser irradiation on the sensitive layer, and the heat-absorbing layer 53 of the transfer stamp 50 is completed. The surface treatment of the heat-absorbing layer 53 and the cavity layer 54 is carried out, and the complete transfer stamp 50 is prepared by bonding.

[0058] The specific steps are as follows: First, spin-coat the laser-sensitive layer 52 material on the glass 51, and form the laser-sensitive layer 52 after heating and curing, then use the ultraviolet laser 110 to act on the laser-sensitive layer 52 to generate a patterned heat-absorbing layer 53, and then perform surface modification treatment on the cavity layer 54 and the laser-sensitive layer 52 with the heat-absorbing layer 53, and bond them to form the complete transfer stamp 50.

[0059] The material of the laser-sensitive layer 52 can be polyimide, and the laser can be 308nm excimer laser, femtosecond 355nm laser, 808nm infrared solid-state laser, 1064nm infrared laser, etc. The heat-absorbing layer is a light-absorbing material such as carbonized layer, graphene, etc. produced by laser ablation of polymers.

[0060] The bonding step can be achieved by treating the surface on an oxygen plasma cleaning machine, a UV cleaning machine or a reactive ion etching machine. The sensitive layer and the cavity layer 54 need to strictly control the spin coating parameters to ensure the layer thickness for the later laser scanning transfer.

[0061] Referring to Figure 7 The application also provides a laser-driven MicroLED chip mass transfer method, which mainly includes the following steps:

[0062] Step one, using laser lift-off technology, the flip-chip MicroLED chip on the original substrate 120 is peeled off as a whole.

[0063] The laser used in the laser lift-off technology can be 308nm, 248nm excimer laser or 266nm, 355nm solid-state laser.

[0064] In one embodiment, the intermediate substrate 150 is attached to the MicroLED chip on the original substrate 120, and the chip is bonded to the adhesive layer of the intermediate substrate 150. The laser lift-off light source 130 is used to act on the interface between the MicroLED chip and the original substrate 120 by using laser lift-off technology. The gallium nitride (GaN) on the original substrate 120 will ablate and decompose under the action of laser, generating nitrogen and metallic gallium, realizing the separation of the interface. After laser lift-off, the original substrate 120 and the MicroLED array can be easily separated, and the MicroLED array can be picked up by using the adhesive intermediate substrate 150.

[0065] Step two, considering the direction of the chip pins, the peeled MicroLED chip is bonded by using the intermediate substrate 150 with an adhesive layer. The chip pins after bonding are directed to the intermediate substrate 150, and the light-emitting surface is directed outward.

[0066] The intermediate substrate 150 with an adhesive layer can be a heat-releasing adhesive tape or a UV-releasing adhesive tape.

[0067] Step three, the prepared transfer stamp 50 is attached to the MicroLED chip on the intermediate substrate 150, the adhesion of the intermediate substrate 150 is reduced by external stimulation 140, and the transfer stamp 50 is heated and then cooled. The internal cavity and the chip are in contact to form a negative pressure, the transfer stamp 50 is lifted to realize the pickup of the chip. At this time, the light-emitting surface of the MicroLED chip is directed to the transfer stamp 50, and the pins are directed outward.

[0068] In one embodiment, the transfer stamp 50 is first heated to increase the temperature inside the cavity, and then the heat-absorbing layer inside the transfer stamp 50 is aligned and contacted with the Micro LED chip on the intermediate substrate. Then, the intermediate substrate is subjected to external stimulation 140 (heating or ultraviolet light source irradiation) to modify the intermediate substrate and greatly reduce its adhesion. Then, the transfer stamp 50 is cooled, and the internal pressure of the cavity decreases with the decrease of temperature. The closed cavity formed by the cavity and the chip forms a negative pressure, which generates a picking force on the chip. Slowly lift the transfer stamp 50, and the Micro LED chip is separated from the modified intermediate substrate 151, realizing the picking of the chip by the transfer stamp 50.

[0069] Step four, place the transfer stamp 50 picking the Micro LED chip on the corresponding mass transfer equipment platform, and align the chip array and the electrode 71 array on the target substrate 70 through visual observation. Adjust the distance between the transfer stamp 50 and the target substrate 70 through a precise motion platform.

[0070] Step five, input laser into the transfer device, and through beam splitting and scanning, the patterned laser irradiates the heat-absorbing layer inside the transfer stamp 50, increases the internal pressure of the cavity through heat transfer, realizes the pushing and transferring of the Micro LED chip array, and the Micro LED chip array is in contact with the circuit substrate.

[0071] The selective transfer of the Micro LED chip array can be realized by laser scanning path, or by preparing different light absorption degrees of the heat-absorbing layer to realize the selective transfer of the Micro LED chip through the heat-absorbing layer. The laser for mass transfer can be 808 nm laser or 1064 nm laser, which is mainly used for radiation heating of the heat-absorbing layer.

[0072] In one embodiment, the laser is turned on, and infrared laser is incident into the transfer device. The split laser selectively radiates the heat-absorbing layer inside the transfer stamp 50, and through photo-thermal conversion and heat transfer, the temperature and pressure inside the cavity gradually increase, generating a pushing force on the Micro LED chip. When the pushing force is sufficient to support the Micro LED chip, it will be transferred downward.

[0073] Step six, slowly lift the transfer stamp 50, and the Micro LED chip array is peeled off from the transfer stamp 50 and successfully transferred to the target substrate 70, forming a display device.

[0074] Please refer to Figure 4 , Figure 4(a) in the figure is the infrared laser and the MicroLED chip offset directly on the chip picked up by the stamp without the heat-absorbing layer, which causes uneven heat distribution due to chip heat absorption, resulting in a larger offset when the chip is transferred to the target substrate 70, and lower transfer precision. Figure 4 (b) in the figure is the infrared laser and the MicroLED chip offset acting on the heat-absorbing layer of the transfer stamp 50 proposed by the application, and the in-layer thermal conductivity of the heat-absorbing layer is higher than the inter-layer thermal conductivity, so the in-layer temperature transfer speed is higher than the inter-layer, and the bottom cavity temperature and air pressure difference are not large, which ensures that the chip offset is not large when transferred to the target substrate 70, and improves the transfer precision. In addition, the in-layer thermal conductivity of the heat-absorbing layer is higher than the inter-layer thermal conductivity, so even in the case of laser and chip misalignment, the heat-absorbing layer can ensure rapid heat homogenization at the interface between the stamp and the chip, ensure the internal temperature of each cavity is consistent, reduce the influence of laser and chip alignment error, and ensure high-precision transfer of the chip.

[0075] Please refer to Figure 5 , by using different energy and irradiation times of ultraviolet laser 110 to irradiate the laser-sensitive layer 52, three different light-absorbing heat-absorbing layers are prepared, high light-absorbing, medium light-absorbing and low light-absorbing first heat-absorbing layer 531, second heat-absorbing layer 532 and third heat-absorbing layer 533 are prepared by using high-energy, medium-energy and low-energy ultraviolet laser and multiple scanning times, medium scanning times and few scanning times, all heat-absorbing layers are scanned by low-power infrared laser, the MicroLED chip below the high light-absorbing first heat-absorbing layer 531 is transferred to the target substrate 70 to form the letters "H" and "U", then the chips are transferred to the target substrate 70 to form the letter "S" by scanning all the heat-absorbing layers with medium-power infrared laser, and finally the remaining MicroLED chips are selectively scanned by high-power infrared laser to form the letter "T", and finally the selective transfer of MicroLED chips is realized by using different power infrared laser, and the "HUST" pattern transfer is formed on the target substrate 70.

[0076] Please refer to Figure 6 , by using different energy and irradiation times, heat-absorbing layers with different absorption degrees to infrared laser are prepared: high light-absorbing first heat-absorbing layer 531 and low light-absorbing second heat-absorbing layer 532, the heat-absorbing layers on the transfer stamp 50 are scanned by low-power infrared laser 11, the MicroLED chip below the high light-absorbing first heat-absorbing layer 531 is transferred to the target substrate 70 to complete the transfer, then the transfer stamp 50 is scanned by high-power infrared laser 12, and the MicroLED chip below the low light-absorbing heat-absorbing layer is transferred to the target substrate 70, and the selective transfer of the chip is realized by using heat-absorbing layers with different light-absorbing degrees.

[0077] Figure 8Figures (a) and (b) show the chip transfer results with and without a heat-absorbing layer when the light spot shifts by 300 μm. It can be seen that the transfer stamp 50 with a heat-absorbing layer has higher chip transfer accuracy than the stamp without a heat-absorbing layer when the light spot shifts. Figure 8 (c) is a comparison of the chip transfer accuracy of the stamp with and without the heat-absorbing layer when the light spot is offset by different distances. The results show that the chip transfer accuracy of the stamp with the heat-absorbing layer is higher than that of the stamp without the heat-absorbing layer at different light spot offset distances, indicating that the heat-absorbing layer has a chip self-alignment function.

[0078] Please see Figure 9 Since direct irradiation of high-energy laser onto the laser-sensitive layer 52 will cause cracks at its surface edges, an optical mask can be used to modify the laser spot to form a laser with high energy in the middle and low energy at the edges. Figure 9 (a) in the image is an optical mask (e.g., made of ITO material) installed in the ultraviolet laser path. It has a certain absorbance for ultraviolet laser light. After projection through the optical mask, the light spot at the exit of the optical path is as shown in the image. Figure 9 As shown in (b), the ultraviolet energy covered by the mask undergoes a certain attenuation, resulting in a series of ultraviolet lasers with high energy in the middle and low energy at the edges. The magnified view and laser energy distribution diagram are shown below. Figure 9 As shown in (c) and (d), for the high energy that previously caused the laser-sensitive layer 52 to crack at the edge, the low energy at the edge (parts AB and CD) can act as a buffer against the ultraviolet laser ablation of the sensitive layer. This method can effectively avoid this.

[0079] Please see Figure 10 , Figure 10 (a) involves directly irradiating polyimide with a flat-top high-energy laser, causing cracks at its edges and ultimately leading to the peeling of the polyimide layer. The laser spot is then modified to create a laser with high energy in the middle and low energy at the edges. This modified laser is then used to irradiate the polyimide, forming a high-energy carbonization zone and a low-energy buffer zone. Figure 10 (b) in the figure ensures the protection of the polyimide layer under high-energy laser irradiation, and ultimately prepares the material as shown in the figure. Figure 10 The high-quality carbonized layer shown in (c) is shown in the image.

[0080] Please see Figure 11 , Figure 11The (a) in the above table is the adhesion strength measured when the transfer stamp 50 picks up and transfers the silicon wafer 81. The adhesion strength between the transfer stamp 50 and the silicon wafer 81 at room temperature is 0.95 kPa. After the transfer stamp 50 is heated to 80℃ and then cooled to room temperature (20℃), the adhesion strength is measured to be 37.96 kPa, achieving a very strong picking-up capability. After the transfer stamp 50 is heated again, the adhesion strength is reduced to 0.058 kPa when the temperature reaches 120℃, and the switchable adhesion ratio reaches 650, Figure 11 The (b) in the above table is the adhesion strength of the repeated transfer of the transfer stamp 50. After the transfer stamp 50 is heated to 60℃ and then cooled to room temperature, the adhesion strength is repeatedly measured after being heated to 120℃, achieving reversible transfer.

[0081] The heat-absorbing layer inside the transfer stamp 50 is heated by infrared laser, which can realize the transfer of transparent chips that do not absorb light, and the transfer method has high redundancy for the transfer process of MicroLED chips, without the need for pretreatment of the chips.

[0082] Please refer to Figure 12 , Figure 12 The dark heat-absorbing layer in the (a) above is prepared by scanning 500 times with a high-energy ultraviolet laser of 200 mJ / cm 2 , and the light heat-absorbing layer is prepared by scanning 100 times with a low-energy ultraviolet laser of 133 mJ / cm 2 . According to the different absorbance of infrared laser of the two, the transfer stamp 50 is scanned by low-power infrared laser, and the 100-micron microchips under the high-absorbance heat-absorbing layer are transferred to the substrate, achieving the purpose of selective transfer of chips by heat-absorbing layers with different absorbance.

[0083] It is easy for those skilled in the art to understand that the above description is only a preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A laser-driven MicroLED chip mass transfer device, characterized in that: the device comprises a transfer stamp, the transfer stamp comprises glass, a laser-sensitive layer, a heat-absorbing layer and a cavity layer, the glass, the laser-sensitive layer and the cavity layer are sequentially connected, the laser-sensitive layer is provided with a through groove, the heat-absorbing layer is arranged in the through groove and connected with the groove wall; a plurality of cavities are arranged on the side of the cavity layer away from the glass; the heat conductivity of the heat-absorbing layer is higher than the interlayer thermal conductivity; the number of the heat-absorbing layer is multiple, and the light absorption degrees of the multiple heat-absorbing layers are not all the same. 2.The laser-driven Micro LED chip mass transfer device of claim 1, wherein: The heat-absorbing layer transmits heat to the cavity by being irradiated by laser, and then the air pressure in the cavity is increased, the MicroLED chip in contact with the cavity is pushed away and transferred to the target substrate by the force of air pressure.

3. A method for preparing the laser-driven MicroLED chip mass transfer device according to any one of claims 1-2, characterized in that, The method comprises the following steps: Step 1: the cavity layer of the transfer stamp is prepared by spin coating-curing; Step 2: the heat-absorbing layer is prepared by photolithography-development, and the heat-absorbing layer and the cavity layer are bonded together by bonding to obtain the transfer stamp, and then the device is obtained.

4. The preparation method of the laser-driven MicroLED chip mass transfer device according to claim 3, characterized in that: Step 1 comprises the following substeps: (1) spin coating a layer of photoresist on a silicon wafer, pre-baking the photoresist, then aligning the pre-baked photoresist and a photomask and placing them under the light source of a photoetching machine for exposure, developing after exposure, and forming a photoresist mold containing micro columns; (2) spin coating a viscoelastic material on the photoresist mold, and after heating and curing, forming a cavity layer by inverse molding.

5. The preparation method of the laser-driven MicroLED chip mass transfer device according to claim 4, characterized in that: A layer of laser-sensitive layer is spin coated on a sapphire substrate, after curing, the laser spot is patterned by using an optical mask, and the heat-absorbing layer is prepared by laser irradiation on the sensitive layer, the preparation of the heat-absorbing layer of the transfer stamp is completed, and then the heat-absorbing layer and the cavity layer are surface treated to realize the preparation of the complete transfer stamp by bonding.

6. The preparation method of the laser-driven MicroLED chip mass transfer device according to claim 5, characterized in that: The material of the laser-sensitive layer is polyimide; the viscoelastic material is polydimethylsiloxane or Ecoflex. 7.A method for laser-driven mass transfer of MicroLED chips, characterized in that, The method comprises the following steps: (1) the transfer stamp of the laser-driven MicroLED chip mass transfer device according to any one of claims 1-2 is tightly attached to the MicroLED chip on the intermediate substrate, the adhesion is reduced by external stimulation to the intermediate substrate, the transfer stamp is heated and then cooled, a negative pressure is formed in the cavity in contact with the chip, the transfer stamp is lifted to realize the pickup of the chip; (2) aligning the MicroLED chip and the electrode array on the target substrate, and adjusting the distance between the transfer stamp and the target substrate; (3) inputting laser to the device, the patterned laser irradiates the heat-absorbing layer inside the transfer stamp, the air pressure in the cavity is increased by heat transfer, the MicroLED chip array is pushed and transferred, and the MicroLED chip array is in contact with the circuit substrate; (4) lifting the transfer stamp, the MicroLED chip array is peeled off from the transfer stamp and successfully transferred to the target substrate to form a display device. 8.The laser-driven Micro LED chip mass transfer method of claim 7, wherein: Before step (1), the following steps are further included: the intermediate substrate is attached to the MicroLED chip on the native substrate, the chip is bonded to the adhesive layer of the intermediate substrate, and a laser ablation light source is used to act on the interface between the MicroLED chip and the native substrate by using a laser ablation technology, so that the interface is separated, and after laser ablation, the native substrate and the MicroLED chip are separated, and the MicroLED array is picked up by using the adhesive intermediate substrate.

9. The laser-driven MicroLED chip mass transfer method of claim 7, wherein: The selective transfer of the MicroLED chip array is realized by a laser scanning path or a heat absorption layer with different light absorption degrees.

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