Laser-driven Micro LED chip mass transfer device and preparation method and application thereof

Abstract

The invention belongs to the related technical field of micro light emitting diode assembly, and discloses a laser-driven micro LED 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 absorption layer and a cavity layer, the glass, the laser sensitive layer and the cavity layer are sequentially connected, a through groove is formed in the laser sensitive layer, the heat absorption layer is arranged in the through groove and connected with the groove wall, and heat homogenization can be achieved through the anisotropic heat conduction characteristic of the heat absorption layer when laser and a chip are subjected to offset irradiation; a plurality of cavities arranged at intervals are formed in the side, away from the glass, of the cavity layer. The heating layer is arranged, photo-thermal conversion is achieved through the heating layer, chip transfer is achieved through the heat effect instead of laser ablation, repeated utilization (namely reversible transfer of the chip) of the transfer seal can be achieved, and therefore the time for repeatedly manufacturing the transfer seal is shortened.

Description

Technical Field

[0001] The present invention belongs to the technical field related to micro light emitting diode assembly, and more specifically, relates to a laser-driven MicroLED chip mass transfer device and a preparation method and application thereof. Background Art

[0002] Micro LED technology is considered to be 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, Micro LED is widely used in the fields of high-resolution and high-pixel density display (smartphones, TVs and automotive displays), virtual reality / augmented reality (AR / VR technology), visible light communication and biomedicine.

[0003] Although MicroLED has many advantages and application fields, how to transfer and assemble it on a large scale onto a display panel is a difficult problem. Since the size of MicroLED is less than 100μm, the difficulty of transfer gradually increases as its size decreases. The traditional Pick&Place technology is difficult to operate, the limit size of vacuum adsorption is about 80μm, 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 required to ensure transfer accuracy, yield and efficiency. Mass transfer technology is to selectively transfer MicroLED from the native 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 (±5μm) and high yield (99.9999%), which also makes mass transfer technology an important challenge for the development of MicroLED.

[0004] Regarding MicroLED mass transfer technology, several technical schools have emerged in academia and industry. According to the forces acting in the chip transfer process and the specific transfer methods, they are mainly divided into: van der Waals force transfer (Meitl MA, Zhu ZT, Kumar V, et al. Transfer printing by kinetic control of adhesion to anelastomeric 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 an elastic stamp and the MicroLED chip to pick up and transfer. It can transfer chips on a large scale, but it also has disadvantages such as inability to transfer selectively, difficulty in picking up and placing modulation, and the need to weaken the device to be transferred. Fluid self-assembly uses fluid to drive MicroLEDs, and uses mechanical force, magnetic force, or capillary force to automatically assemble chips to a designated area. The transfer cost is low, but it is difficult to transfer three-color devices. Roll-to-roll roller transfer uses a roller to pick up MicroLEDs on the native substrate and transfer them to the target substrate. It has problems such as selectivity difficulties and interval picking and transfer of MicroLEDs. Laser-assisted mass transfer technology is a process of selectively transferring MicroLEDs in batches to a receiving substrate using a patterned laser spot. Due to the advantages of fast laser processing speed, good programmability, and easy regulation, laser-assisted mass transfer technology is expected to be used in 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 bubbling-assisted transfer (Saeidpourazar R, Li R, Li Y, et al. Laser-Driven MicroTransfer Placement of Prefabricated Microstructures[J]. Journal of Microelectromechanical Systems, 2012.) uses laser ablation of a dynamic release layer to generate bubbles to achieve chip transfer. It has high requirements on the uniformity and resolution of the laser spot, and cannot achieve reversible transfer of chips and reusable transfer devices. Based on the above problems, Song Jizhou's team from Zhejiang University proposed a laser-driven reversible printing method (Zhang S, Luo H, Wang S, et al. A thermally actuated switchable dry adhesive with high reversibility for transfer printing[J]. International Journal of Extreme Manufacturing, 2021.). A transfer device was made using shape memory polymer (SMP) and a steel ball. The chip transfer was achieved by laser heating the steel ball and deforming the SMP, thus achieving reversible transfer of the chip. However, the chip, steel ball and laser spot need to be strictly aligned to ensure the transfer accuracy. The alignment of the laser spot is required to be high, and there are 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 A Joint 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. The selectivity is mainly achieved by programming the laser path. To achieve rapid selective transfer of the chip, it is necessary to control the laser scanning path or align the laser scanning pattern with the chip. For the transfer of MicroLEDs in the actual production process, it is necessary to transfer the red, green and blue microchips to the display panel. For traditional MicroLED mass transfer, three transfers are required, and the process is complicated and the transfer efficiency is low. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the present invention provides a laser-driven MicroLED chip mass transfer device and a preparation method and application thereof, which aims to solve the problem that existing components cannot be repeatedly transferred.

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

[0008] Furthermore, the thermal conductivity within the heat absorption layer is higher than the thermal conductivity between the layers; there are multiple heat absorption layers, and the light absorption degrees of the multiple heat absorption layers are not all the same.

[0009] Furthermore, the heat absorption layer transfers heat to the cavity by being irradiated by the laser, thereby increasing the air pressure in the cavity. The MicroLED chip in contact with the cavity is pushed away by the force of the air pressure and transferred to the target substrate.

[0010] The present invention also provides a method for preparing the laser-driven MicroLED chip mass transfer device as described above, the method comprising the following steps:

[0011] Step 1, preparing the cavity layer of the transfer stamp by spin coating-curing method;

[0012] Step 2: prepare the heat absorption layer by photolithography-development method, and bond the heat absorption layer and the cavity layer together by bonding method to obtain the transfer stamp, and then obtain the device.

[0013] Furthermore, step one includes the following sub-steps:

[0014] (1) Spin-coating a layer of photoresist on a silicon wafer, pre-baking the photoresist, and then aligning the pre-baked photoresist and a photolithography mask and exposing them under a light source of a photolithography machine, and developing them after exposure to form a photoresist mold containing micro-pillars;

[0015] (2) Spin coating a viscoelastic material on the photoresist mold, and then heat curing it and then reverse molding it to form a cavity layer.

[0016] Furthermore, a laser sensitive layer is spin-coated on the sapphire substrate. After curing, the laser spot is patterned using an optical mask, and the laser is irradiated on the sensitive layer to prepare a heat absorption layer, thereby completing the preparation of the heat absorption layer of the transfer stamp. The heat absorption layer and the cavity layer are then surface treated, and the preparation of a complete transfer stamp is achieved through bonding.

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

[0018] The present invention also provides a laser-driven MicroLED chip mass transfer method, the method comprising the following steps:

[0019] (1) The transfer stamp of the laser-driven MicroLED chip mass transfer device as described above is closely attached to the MicroLED chip on the intermediate substrate, and the intermediate substrate is externally stimulated to reduce the adhesion, and the transfer stamp is heated and then cooled, so that negative pressure is formed in the cavity in contact with the chip, and the transfer stamp is lifted to pick up the chip;

[0020] (2) Aligning the MicroLED chip and the electrode array on the target substrate to adjust the distance between the transfer stamp and the target substrate;

[0021] (3) inputting laser light into the device, the patterned laser light irradiates the heat absorption layer inside the transfer stamp, and the air pressure inside the cavity is increased by heat transfer, thereby pushing and transferring the MicroLED chip array, and the MicroLED chip array contacts the circuit substrate;

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

[0023] Furthermore, before step (1), the following steps are also included: the intermediate substrate is tightly attached to the MicroLED chip on the native substrate, the chip and the adhesive layer of the intermediate substrate are bonded, and the laser peeling technology is used to apply the laser peeling light source to the interface between the MicroLED chip and the native substrate to achieve interface separation. After laser peeling, the native substrate and the MicroLED chip are separated, and the MicroLED array is picked up using the sticky intermediate substrate.

[0024] Furthermore, the selective transfer of the MicroLED chip array is achieved through a laser scanning path or a heat absorption layer with different light absorption levels.

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

[0026] 1. The present invention is provided with a heating layer, which realizes light-to-heat conversion, and utilizes thermal effect instead of laser ablation to realize chip transfer, which can realize multiple reuse of transfer stamps (i.e., reversible transfer of chips), thereby reducing the time for repeated production of transfer stamps 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 MicroLEDs to non-sticky substrates.

[0027] 2. The laser is used to act on the heat absorption layer inside the seal to avoid high temperature damage caused by heat absorption of the chip, thereby solving the subsequent repair problem caused by chip damage, and can transfer MicroLED chips that do not have light absorption characteristics, reducing the requirements for MicroLED. By spatially modulating the laser, the laser can be split and quickly scanned, realizing fast, efficient and highly reliable transfer of MicroLED.

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

[0029] 4. The heat absorption layer is prepared by laser irradiation of the laser sensitive layer. Heat absorption layers with different light absorption degrees can be prepared by using different laser energies and irradiation times. At the same time, the laser sensitive layer is irradiated with high-energy laser using backplane assistance, optical path optical mask and other methods to ensure that the laser sensitive layer is not broken, providing a method for high-energy laser interface ablation of polymers to ensure surface integrity.

[0030] 5. The selective transfer of MicroLED chips can be achieved through heat absorption layers with different light absorption levels. The red, green and blue MicroLED chips can be picked up onto the transfer stamp. The selective transfer of different MicroLED chips can be achieved by scanning the entire transfer stamp with a laser or irradiating the transfer stamp with a flash light, thereby improving the transfer efficiency.

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

[0032] 7. The heat absorption layer can ensure that the thermal conductivity of heat within the layer is higher than the thermal conductivity between layers, realizing anisotropic heat conduction. When there is an offset between the laser and the MicroLED chip, the existence of the heat absorption layer can ensure that the heat distribution within the heat absorption layer is relatively uniform. When the heat is transferred between the layers, the air pressure inside the cavity under the heat absorption layer is also relatively uniform under the uniform heat transfer, which can ensure that the chip has a higher transfer accuracy when the light spot is offset, thereby improving the redundancy of the process. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0036] Figure 4 Schematic diagrams of transferring chips when the light spot is offset by a stamp without a heat absorption layer and a stamp with a heat absorption layer, wherein (a) is a schematic diagram of a chip picked up by a stamp without a heat absorption layer when the infrared laser and the MicroLED chip are offset, and (b) is a schematic diagram of a heat absorption layer on the stamp provided by the present invention when the infrared laser and the MicroLED chip are offset;

[0037] Figure 5 (a) and (b) are schematic diagrams of using heat absorption layers with different light absorption levels to achieve selective transfer of MicroLED chips;

[0038] Figure 6 This is a diagram of the process of using a heat-absorbing layer to achieve the selective transfer of MicroLED chips, which is carried out in a top-down order;

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

[0040] Figure 8(a) and (b) are the offset results of the chip with and without a heat absorption layer when the spot is offset by 300μm, and (c) is the accuracy comparison of the stamp transfer chip with and without a heat absorption layer when the spot is offset by different distances;

[0041] Fig. 9 (a), (b), (c), and (d) are schematic diagrams of ablating the laser-sensitive layer by a high-energy laser and using an optical mask to ensure that the surface is intact;

[0042] Fig.10 (a), (b), and (c) are another result of ablating the laser sensitive layer by high-energy laser and using an optical mask to ensure that the surface is intact;

[0043] Fig.11 (a) and (b) are the characterization diagrams of the adhesion performance of the transfer stamp, respectively;

[0044] Fig.12 (a) and (b) are the results of selective transfer of chips by using heat absorption layers with different light absorption levels.

[0045] In all the drawings, the same reference numerals 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 absorption layer, 531 - first heat absorption layer, 532 - second heat absorption layer, 533 - third heat absorption layer, 54 - cavity layer, 60 - MicroLED chip, 70 - target substrate, 71 - electrode, 80 - photoresist mold, 81 - silicon wafer, 82 - photoresist, 90 - photolithography machine light source, 100 - photolithography mask, 110 - ultraviolet laser, 120 - native 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 purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended 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.

[0047] The present invention provides a laser-driven MicroLED chip mass transfer device. In addition to realizing selective chip transfer by laser scanning, the device can also realize selective chip transfer by setting a heat absorption layer 53 with different light absorption degrees on a transfer stamp 50 and scanning the transfer stamp 50 as a whole with laser of the same power; the laser acts on the heat absorption layer 53 of the transfer stamp 50, and the transfer is realized by absorbing the laser and transferring heat by the heat absorption layer 53, which can effectively avoid high-temperature damage to the chip, and can transfer transparent chips that do not absorb light, thereby reducing the requirements for the chips to be transferred.

[0048] See also Figure 1 The device includes a spatial light modulator 20, a scanning galvanometer 30, a focusing lens 40 and a transfer stamp 50. The chip transfer process is to use an optical mask to act on the heat absorption layer 53 in the transfer stamp 50 with a patterned laser spot, transfer the heat to the inside of the cavity, and the air pressure inside the cavity gradually increases with the temperature, so that 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 splits the infrared laser 10. The laser beam after passing through the spatial light modulator 20 enters the scanning galvanometer 30 to achieve rapid scanning of multiple laser beams and irradiate the transfer stamp 50 to achieve efficient mass transfer.

[0050] See also Figure 2 The transfer stamp 50 includes a glass 51, a laser sensitive layer 52, a heat absorbing 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. The heat absorbing layer 53 is arranged in the through groove and connected to the groove wall. The laser sensitive layer 52 and the heat absorbing layer 53 form a continuous layer. The cavity layer 54 is provided with a plurality of cavities arranged at intervals on a side away from the glass 51.

[0051] After the transfer stamp 50 is heated and then cooled, the cavity contacts the MicroLED chip 60 to form a negative pressure, thereby picking up the MicroLED chip 60 and aligning the MicroLED chip 60 with the electrode 71 on the target substrate 70. By irradiating the transfer stamp 50 with infrared laser 10, the infrared laser 10 acts on the heat absorption layer 53, and heat is transferred to the bottom cavity layer 54 through light-heat conversion. The air pressure inside the cavity increases, generating thrust on the MicroLED chip 60, and transferring the MicroLED chip 60 to the target substrate 70.

[0052] See also Figure 3 The method for preparing the transfer stamp 50 as described above mainly comprises the following steps:

[0053] Step 1: Prepare the cavity layer 54 of the transfer stamp 50 by spin coating-curing. Specifically, a layer of photoresist 82 is spin coated on the silicon wafer 81, and photolithography is performed using an optical mask. After development, a photoresist mold 80 with micro-pillars is prepared. Viscoelastic material is spin coated on the photoresist mold 80, and after curing, the cavity layer 54 is formed by reverse molding. The specific steps are:

[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 photolithography mask 100 are aligned and placed under the light source 90 of the photolithography machine for exposure. After exposure, the photoresist is developed to form a photoresist mold 80 containing micro-columns.

[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 inverting the mold.

[0056] The cavity layer 54 can also be made by double molding of 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, and the cavity layer 54 is made by double molding.

[0057] Step 2: Prepare the heat absorption layer 53 by photolithography-development, and bond the heat absorption layer 53 and the cavity layer 54 together by bonding, and then obtain the transfer stamp 50. Spin-coat a laser sensitive layer 52 on the sapphire substrate, and after curing, pattern the laser spot using an optical mask, irradiate the laser on the sensitive layer to prepare the heat absorption layer 53, and complete the preparation of the heat absorption layer 53 of the transfer stamp 50. Then, perform surface treatment on the heat absorption layer 53 and the cavity layer 54, and complete the preparation of the transfer stamp 50 by bonding.

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

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

[0060] The bonding step can be achieved by treating the surface with an oxygen plasma cleaner, a UV cleaner or a reactive ion etcher. The spin coating parameters of the sensitive layer and the cavity layer 54 need to be strictly controlled to ensure the layer thickness for the subsequent laser scanning transfer.

[0061] See also Figure 7 The present invention also provides a laser-driven MicroLED chip mass transfer method, the transfer method mainly includes the following steps:

[0062] Step 1: Use laser lift-off technology to completely lift off the flip-chip MicroLED chip with the pins facing upward on the native substrate 120.

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

[0064] In one embodiment, the intermediate substrate 150 is closely attached to the MicroLED chip on the native substrate 120, and the chip is bonded to the adhesive layer of the intermediate substrate 150. The laser lift-off technology is used to apply the laser lift-off light source 130 to the interface between the MicroLED chip and the native substrate 120. The gallium nitride (GaN) on the native substrate 120 is ablated and decomposed under the action of the laser to produce nitrogen and metal gallium, thereby achieving interface separation. After laser lift-off, the native substrate 120 and the MicroLED array are easily separated, and the MicroLED array is picked up using the sticky intermediate substrate 150.

[0065] Step 2: Considering the orientation of the pins of the chip, the peeled MicroLED chip is bonded using the intermediate substrate 150 containing an adhesive layer, with the pins of the bonded chip facing the intermediate substrate 150 and the light-emitting surface facing outwards.

[0066] The intermediate substrate 150 containing the adhesive layer may be a thermal release tape or an ultraviolet release tape.

[0067] Step three, the prepared transfer stamp 50 is closely attached to the MicroLED chip on the intermediate substrate 150, and the viscosity is reduced by externally stimulating the intermediate substrate 150 140, and the transfer stamp 50 is heated and then cooled, and the internal cavity and the chip are in contact to form a negative pressure, and the transfer stamp 50 is lifted to pick up the chip. At this time, the light-emitting surface of the MicroLED chip faces the transfer stamp 50, and the pins face outward.

[0068] In one embodiment, the transfer stamp 50 is first heated to increase the temperature inside the cavity, and then the heat absorption layer inside the transfer stamp 50 is aligned and contacted with the MicroLED chip on the intermediate substrate. Now, an external stimulus 140 (heating or ultraviolet light irradiation) is applied to the intermediate substrate to modify the intermediate substrate to significantly reduce its viscosity. Then, the transfer stamp 50 is cooled, and the air pressure inside the cavity decreases as the temperature decreases. The closed cavity formed by the contact between the cavity and the chip forms a negative pressure, which generates a pickup force for the chip. The transfer stamp 50 is slowly lifted, and the MicroLED chip is separated from the modified intermediate substrate 151, so that the transfer stamp 50 picks up the chip.

[0069] Step 4: Place the transfer stamp 50 that picks up the MicroLED chip on the corresponding mass transfer equipment platform, align the chip array and the electrode 71 array on the target substrate 70 through visual observation, and adjust the distance between the transfer stamp 50 and the target substrate 70 through a precise motion platform.

[0070] Step 5: Input the laser into the transfer device. After spot splitting and scanning, the patterned laser irradiates the heat absorption layer inside the transfer stamp 50. The air pressure inside the cavity is increased through heat transfer, and the MicroLED chip array is pushed and transferred, so that the MicroLED chip array contacts the circuit substrate.

[0071] The selective transfer of the MicroLED chip array can be achieved through a laser scanning path, or by preparing the heat absorbing layer with different light absorption levels, and realizing the selective transfer of the MicroLED chip through the different heat absorbing layers. The laser for mass transfer can be an 808nm laser or a 1064nm laser, which is mainly used for radiative heating of the heat absorbing layer.

[0072] In one embodiment, the laser is turned on and an infrared laser is incident on the transfer device. The split laser selectively radiates the heat absorption layer inside the transfer stamp 50. Through photothermal conversion and heat transfer, the temperature and air pressure inside the cavity gradually increase, generating a thrust on the MicroLED chip. When the thrust is sufficient to support the MicroLED chip, it will transfer downward.

[0073] Step 6: slowly lift up the transfer stamp 50, and the MicroLED chip array is peeled off from the transfer stamp 50 and successfully transferred to the target substrate 70 to form a display device.

[0074] See also Figure 4 , Figure 4(a) in the figure shows that the infrared laser is offset from the MicroLED chip and acts directly on the chip picked up on the stamp without a heat absorption layer. The heat absorption of the chip causes uneven heat distribution, resulting in a large offset when the chip is transferred to the target substrate 70, and the transfer accuracy is low. Figure 4 (b) is the infrared laser acting on the heat absorption layer on the transfer stamp 50 proposed by the present invention when the infrared laser is offset from the MicroLED chip. The thermal conductivity within the heat absorption layer is higher than the thermal conductivity between the layers, so the temperature transfer speed within the layer is higher than between the layers. The temperature and air pressure of the bottom cavity are not much different, ensuring that the chip is not offset when transferred to the target substrate 70, thereby improving the transfer accuracy. In addition, the thermal conductivity within the heat absorption layer is higher than the thermal conductivity between the layers. Even when the laser and the chip are not aligned, the heat absorption layer can ensure rapid heat homogenization at the interface between the stamp and the chip, ensure the temperature inside each cavity is consistent, reduce the influence of the alignment error between the laser and the chip, and ensure high-precision transfer of the chip.

[0075] See also Figure 5 , by irradiating the laser sensitive layer 52 with ultraviolet laser 110 of different energies and irradiation times, three heat absorption layers with different light absorption degrees are prepared, and the first heat absorption layer 531, the second heat absorption layer 532 and the third heat absorption layer 533 with high absorbance, medium absorbance and low absorbance are prepared by ultraviolet laser of high energy, medium energy and low energy and multiple scanning times, medium scanning times and few scanning times. All the heat absorption layers are scanned by low-power infrared laser, and the MicroLED chips under the first heat absorption layer 531 with high absorbance are transferred to the target substrate 70 to form the letters "H" and "U", and then all the heat absorption layers are scanned by medium-power infrared laser to transfer the chips to the target substrate 70 to form the letter "S", 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 achieved by using infrared lasers of different powers and the transfer of the "HUST" pattern is formed on the target substrate 70.

[0076] See also Figure 6 , heat absorption layers with different absorption degrees to infrared laser are prepared by different energies and irradiation times: a first heat absorption layer 531 with high absorbance and a second heat absorption layer 532 with low absorbance, and the heat absorption layer on the transfer stamp 50 is scanned as a whole by a low-power infrared laser 11, and the MicroLED chip under the first heat absorption layer 531 with high absorbance is transferred to the target substrate 70 to complete the transfer, and then the transfer stamp 50 is scanned as a whole by a high-power infrared laser 12, and the MicroLED chip under the low-absorbance heat absorption layer is transferred to the target substrate 70, and the selective transfer of chips is achieved by using heat absorption layers with different absorbances.

[0077] Figure 8Figures (a) and (b) are the chip shift results when the light spot is shifted by 300 μm for the transfer stamp 50 with and without a heat absorbing layer. It can be seen that the chip transfer accuracy of the transfer stamp 50 with a heat absorbing layer is higher than that of the stamp without a heat absorbing layer when the light spot is shifted. Figure 8 (c) is a comparison chart of the chip transfer accuracy of the stamp with a heat absorption layer and the stamp without a heat absorption layer when the light spot is offset at different distances. The results show that the chip transfer accuracy of the stamp with a heat absorption layer is higher than that of the transfer stamp without a heat absorption layer at different light spot offset distances. This shows that the heat absorption layer has a chip self-alignment effect.

[0078] See also Fig. 9 Since high-energy laser directly irradiating the laser sensitive layer 52 will cause cracks on the edge of its surface, 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 edge. Fig. 9 (a) is an optical mask (such as ITO material) installed in the ultraviolet laser light path. It has a certain absorbance to the ultraviolet laser. After the optical mask is projected, the light spot at the light outlet of the light path is as follows: Fig. 9 As shown in (b), the ultraviolet energy covered by the mask undergoes a certain attenuation, and a series of ultraviolet lasers with high energy in the middle and low energy at the edge are obtained. The local magnified image and laser energy distribution diagram are shown in Fig. 9 As shown in (c) and (d) in the figure, the edge rupture of the laser sensitive layer 52 caused by the high energy previously occurred can be effectively avoided by using this method because the low energy at the edge (AB and CD parts) can act as a buffer for the UV laser ablation of the sensitive layer.

[0079] See also Fig.10 , Fig.10 (a) is to directly use a flat-top high-energy laser to irradiate polyimide to cause cracks at its edges, eventually causing the polyimide layer to fall off, and then modify its spot to form a laser with high energy in the middle and low energy at the edge, and then irradiate the polyimide to form a high-energy carbonization zone and a low-energy buffer zone ( Fig.10 (b)) in the figure ensures the protection of the polyimide layer under high-energy laser irradiation, and finally prepares Fig.10 The high-quality carbonized layer shown in (c).

[0080] See also Fig.11 , Fig.11(a) is the adhesion strength measured when the transfer stamp 50 picks up and transfers the silicon wafer 81. At room temperature, the adhesion strength between the transfer stamp 50 and the silicon wafer 81 is 0.95 kPa. The adhesion strength measured when the transfer stamp 50 is heated to 80°C and then cooled to room temperature (20°C) reaches 37.96 kPa, achieving a strong pickup capability. When the transfer stamp 50 is heated again to 120°C, the adhesion strength is reduced to 0.058 kPa, and the switchable adhesion ratio reaches 650. Fig.11 (b) is a characterization of the adhesion strength of the repetitive transfer of the transfer stamp 50. The transfer stamp 50 is heated to 60°C, cooled to room temperature, and then heated to 120°C to repeatedly measure the adhesion strength, thereby achieving reversible transfer.

[0081] By using infrared laser to heat the heat absorption layer inside the transfer stamp 50, the non-light-absorbing transparent chip can be transferred, which shows that the transfer method has a high redundancy in the transfer process of the MicroLED chip and does not require pre-processing of the chip.

[0082] See also Fig.12 , Fig.12 The darker heat absorbing layer in (a) is the one that uses 200mJ / cm 2 The light-colored heat-absorbing layer was prepared by scanning 500 times with a high-energy ultraviolet laser. 2 The stamp 50 is prepared by scanning the stamp 50 with a low-energy ultraviolet laser 100 times. According to the different absorbance of the two to the infrared laser, the 100-micron microchip under the high-absorbency heat-absorbing layer is transferred to the substrate, thereby achieving the purpose of selective transfer of the chip by using heat-absorbing layers with different absorbance levels.

[0083] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A laser-driven MicroLED chip mass transfer device, characterized in that: The device includes a transfer stamp, which includes glass, a laser sensitive layer, a heat absorbing layer and a cavity layer. The glass, the laser sensitive layer and the cavity layer are connected in sequence. The laser sensitive layer is provided with a through groove, and the heat absorbing layer is arranged in the through groove and connected to the groove wall; the cavity layer is provided with a plurality of spaced cavities on a side away from the glass.

2. The laser-driven MicroLED chip mass transfer device according to claim 1, characterized in that: The thermal conductivity within the heat absorption layer is higher than the thermal conductivity between the layers; there are multiple heat absorption layers, and the light absorption degrees of the multiple heat absorption layers are not all the same.

3. The laser-driven MicroLED chip mass transfer device according to claim 1, wherein: The heat absorption layer transfers heat to the cavity by being irradiated by the laser, thereby increasing the air pressure in the cavity. The MicroLED chip in contact with the cavity is pushed away by the force of the air pressure and transferred to the target substrate.

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

5. The method for preparing a laser-driven MicroLED chip mass transfer device according to claim 4, characterized in that: Step 1 includes the following sub-steps: (1) Spin-coating a layer of photoresist on a silicon wafer, pre-baking the photoresist, and then aligning the pre-baked photoresist and a photolithography mask and exposing them under a light source of a photolithography machine, and developing them after exposure to form a photoresist mold containing micro-pillars; (2) Spin coating a viscoelastic material on the photoresist mold, and then heat curing it and then reverse molding it to form a cavity layer.

6. The method for preparing a laser-driven MicroLED chip mass transfer device according to claim 5, characterized in that: A laser sensitive layer is spin-coated on the sapphire substrate. After curing, the laser spot is patterned using an optical mask. The laser is irradiated on the sensitive layer to prepare a heat absorption layer, completing the preparation of the heat absorption layer of the transfer stamp. The heat absorption layer and the cavity layer are then surface treated, and the preparation of the complete transfer stamp is achieved through bonding.

7. The method for preparing a laser-driven MicroLED chip mass transfer device according to claim 6, characterized in that: The material of the laser sensitive layer is polyimide; the viscoelastic material is polydimethylsiloxane or Ecoflex.

8. A laser-driven MicroLED chip mass transfer method, 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 to 3 is closely attached to the MicroLED chip on the intermediate substrate, and the intermediate substrate is externally stimulated to reduce the adhesion, and the transfer stamp is heated and then cooled, so that negative pressure is formed in the cavity in contact with the chip, and the transfer stamp is lifted to pick up the chip; (2) Aligning the MicroLED chip and the electrode array on the target substrate to adjust the distance between the transfer stamp and the target substrate; (3) inputting laser light into the device, the patterned laser light irradiates the heat absorption layer inside the transfer stamp, and the air pressure inside the cavity is increased by heat transfer, thereby pushing and transferring the MicroLED chip array, and the MicroLED chip array contacts the circuit substrate; (4) The transfer stamp is lifted, and the MicroLED chip array is peeled off from the transfer stamp and successfully transferred to the target substrate to form a display device.

9. The laser-driven MicroLED chip mass transfer method according to claim 8, characterized in that: Before step (1), the following steps are also included: the intermediate substrate is pressed tightly against the MicroLED chip on the native substrate, the chip is bonded to the adhesive layer of the intermediate substrate, and the laser peeling technology is used to apply the laser peeling light source to the interface between the MicroLED chip and the native substrate to achieve interface separation. After laser peeling, the native substrate and the MicroLED chip are separated, and the MicroLED array is picked up using the sticky intermediate substrate.

10. The laser-driven MicroLED chip mass transfer method according to claim 8, characterized in that: Selective transfer of the MicroLED chip array is achieved through a laser scanning path or a heat absorption layer with different light absorption levels.

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