A micro-transfer stamp based on a thermally controllable adhesion surface of a liquid crystal elastomer and its preparation method

Abstract

This invention belongs to the field of micro-transfer printing technology, and relates to a micro-transfer stamp based on a thermally controllable adhesion surface of a liquid crystal elastomer and its preparation method. The preparation method includes: dissolving a liquid crystal monomer to obtain a liquid crystal monomer solution; firstly mixing pentaerythritol tetra-3-mercaptopropionate, 2,2'-(ethylenedithio)diethanol, and 4,4'-trimethylenedipiperidine to obtain an additive mixture; secondly mixing the additive mixture and the liquid crystal monomer solution to obtain a second mixture; thirdly mixing the second mixture and 2,2-dimethoxy-2-phenylacetophenone, stirring the resulting third mixture at a preheating temperature until viscous, and then molding it to obtain a preform; and finally bonding and pressing the preform with a silicon wafer microstructure mold and photocuring to obtain the micro-transfer stamp. The micro-transfer stamp provided by this invention can solve the technical problems of current micro-transfer stamps, such as high pre-pressure during pickup, which easily damages thin and brittle micro-devices, and the inability to precisely adjust the adhesion force.

Description

Technical Field

[0001] This invention belongs to the field of micro-transfer printing technology, specifically relating to a micro-transfer printing stamp based on a liquid crystal elastomer thermally controllable adhesion surface. Background Technology

[0002] With the rapid iterative development of next-generation semiconductor micro-nano manufacturing, Micro-LED high-definition displays, and flexible electronics industries, the transfer printing of precision microstructure devices is showing a trend towards arraying, high-density integration, and personalized arrangement. However, existing micro-transfer stamps are mainly made of materials such as PDMS (polydimethylsiloxane) and shape memory polymers, relying on surface adhesion or material phase change to achieve adhesion. The surface structure adsorption depends on strong pre-pressure, which has the disadvantages of high pick-up pre-pressure during passive bonding, which can easily damage micro-devices, and the inability to precisely control the adsorption force. Summary of the Invention

[0003] In view of this, the present invention proposes a micro-transfer stamp based on a liquid crystal elastomer thermally controllable adhesion surface and its preparation method. The micro-transfer stamp provided by the present invention can solve the technical problems of current micro-transfer stamps having large pre-pressure for picking up, which easily damages thin and brittle micro-devices, and the adhesion force cannot be precisely adjusted.

[0004] To address the above problems, the present invention provides the following technical solution: This invention discloses a method for preparing a micro-transfer stamp based on a liquid crystal elastomer thermally controllable adhesion surface, comprising the following steps: The liquid crystal monomer is dissolved to obtain a liquid crystal monomer solution; the liquid crystal monomer is RM257 or RM82. Pentaerythritol tetra-3-mercaptopropionate, 2,2'-(ethylenedithio)diethanol and 4,4'-trimethylenedipiperidine were mixed to obtain an additive mixture. The additive mixture and the liquid crystal monomer solution are mixed for the second time to obtain a second mixture; The second mixture and 2,2-dimethoxy-2-phenylacetophenone were mixed in the third mixture. The resulting third mixture was stirred at a preheated temperature until it became viscous, and then molded to obtain a preform. The preform is bonded and imprinted with a silicon wafer microstructure mold and then photocured to obtain a micro-transfer stamp.

[0005] Preferably, the mass ratio of pentaerythritol tetra-3-mercaptopropionate to 2,2'-(ethylenedithio)diethanol is 0.12:0.42~0.18:0.52; and the mass ratio of pentaerythritol tetra-3-mercaptopropionate to 4,4'-trimethylenedipiperidine is 0.12:0.02~0.18:0.0128.

[0006] Preferably, the mass ratio of pentaerythritol tetra-3-mercaptopropionate to liquid crystal monomer is (0.12~0.18):2.

[0007] Preferably, the mass ratio of 2,2-dimethoxy-2-phenylacetophenone to the liquid crystal monomer is (0.004~0.006):2; and the preheating temperature is 50~70℃.

[0008] Preferably, the molding process consists of sequential mold casting, prepolymerization, and drying; the prepolymerization process involves placing the cast mold in the dark for 10-14 hours; the drying temperature is 70-85°C, and the drying time is 8-12 hours.

[0009] Preferably, the bonding and imprinting is performed under a constant load of 200g; the light curing is ultraviolet light curing; and the ultraviolet light curing time is 25~40 min.

[0010] The present invention also provides a micro-transfer stamp prepared by the preparation method described in the above technical solution.

[0011] This invention also provides a method for micro-transfer printing using the micro-transfer stamp described above, comprising the following steps: By combining a conductive substrate with a micro-transfer stamp, a conductive substrate-micro-transfer composite stamp is obtained. Pick-up: The conductive substrate is heated by electricity, and then the heated conductive substrate-micro transfer composite stamp is brought into contact with the arrayed semiconductor device supported by blue glue under a pre-pressure of 20~50mN. Subsequently, the surface temperature of the conductive substrate-micro transfer composite stamp is cooled down to complete the pickup. Transfer and release: After the arrayed semiconductor device carried by the conductive substrate-micro transfer composite stamp is transferred to the designated position above the target receiving substrate, the conductive substrate-micro transfer composite stamp is heated to release the chip to the receiving substrate. Preferably, the conductive substrate is an ITO substrate; during pickup, the heating is achieved by inputting 12~15Vs through the ITO substrate to raise the temperature to 80~90℃; during pickup, the temperature is lowered to ≤50℃.

[0012] Preferably, during the transfer and release, the distance from the point of transfer to the designated position above the target receiving substrate is 20~40µm; The heating method of the conductive substrate-micro transfer composite stamp is either electric heating or laser spot heating. The electric heating is achieved by applying a voltage of 5-6V to the conductive substrate to raise the temperature of the entire area to 80-90°C. The laser spot heating is achieved by using a near-infrared laser with a power of 7~12mW to spot heat the conductive substrate-micro-transfer composite stamp, thereby locally raising the temperature to 80~90℃.

[0013] Compared with the prior art, the present invention has the following advantages: 1. In view of the shortcomings of existing stamps that have high pre-pressure and are prone to damaging micro-devices, this invention adopts an LCE thermal response deformation and array micro-pit negative pressure self-adsorption structure, which can generate stable adsorption without relying on strong pre-pressure. Therefore, it can achieve extremely low pre-pressure picking, fundamentally avoiding damage, chipping, and deformation of thin and brittle micro-devices, and significantly improving the transfer yield.

[0014] 2. To address the shortcomings of existing stamps where the adsorption force cannot be precisely controlled, this invention achieves precise, graded, and reversible control of the adhesion force by controlling the deformation of the LCE microstructure through temperature, changing the negative pressure, and continuously adjusting the adsorption force. This allows it to be adapted to micro-devices of different sizes, weights, and materials, significantly improving the versatility and applicability of stamps.

[0015] 3. To address the shortcomings of existing stamps, such as poor surface adhesion and unstable adsorption, this invention employs a uniform and regular LCE array micro-pit surface, ensuring sufficient interface adhesion and stable negative pressure formation. Therefore, adsorption is reliable, release is clean, there are no residues, and no device dragging, achieving superior adhesion interface effect and transfer stability.

[0016] In summary, this invention achieves uniform and reliable adhesion to the stamp surface, low pre-pickup pressure, and precise and adjustable adsorption force by using the thermally induced reversible deformation of LCE (liquid crystal elastomer) material and the negative pressure self-adsorption structure of arrayed micro-pits. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments will be briefly described below.

[0018] Figure 1 A schematic diagram illustrating the preparation of the LCE stamp provided by this invention; Figure 2 This is a schematic diagram of the LCE stamp micro-transfer process provided by the present invention; Figure 3 A scanning electron microscope image of the array of micropits on the LCE stamp prepared in Example 1; Figure 4 Morphology of the LCE stamp micropit surface at 25°C and 85°C as prepared in Example 1; Figure 5 The morphology data of the LCE stamp micropit surface temperature at 25°C and 85°C for Example 1 are shown in the figure. Figure 6 The image shows the test results of the thermal response cycle of the LCE stamp micropit surface prepared in Example 1. Figure 7The relationship between pre-pressure and adhesion force of the LCE stamp prepared in Example 1; Figure 8 The relationship between the retraction rate and adhesion force of the LCE stamp prepared in Example 1; Figure 9 The results of 50 adhesion repeat experiments on the LCE stamp prepared in Example 1; Figure 10 Temperature gradation response diagram of the LCE stamp prepared in Example 1; Figure 11 The relationship between input voltage, power, and surface temperature rise rate of an ITO substrate; Figure 12 This represents the maximum temperature difference on the surface of the elastomer covering the ITO substrate during the heating process under various input voltages. Figure 13 The temperature response and natural cooling conditions over a 0.2s duration at various laser powers are shown. Figure 14 The effect of duration on temperature response at various laser powers; Figure 15 The shedding response time is 7mW under 808nm near-infrared laser power; Figure 16 This is a schematic diagram of the accuracy evaluation criteria; Figure 17 The relationship between transfer gap height and accuracy under ITO global transfer printing; Figure 18 The relationship between gap height and angle error θ in ITO global transfer printing; Figure 19 The relationship between gap height and precision in laser selective transfer printing; Figure 20 This relates the gap height to the angle error θ in laser selective transfer printing. Detailed Implementation

[0019] This invention provides a method for preparing a micro-transfer stamp based on a liquid crystal elastomer thermally controllable adhesion surface, comprising the following steps: The liquid crystal monomers are dissolved to obtain a liquid crystal monomer solution; Pentaerythritol tetra-3-mercaptopropionate, 2,2'-(ethylenedithio)diethanol and 4,4'-trimethylenedipiperidine were mixed to obtain an additive mixture. The additive mixture and the liquid crystal monomer solution are mixed for the second time to obtain a second mixture; The second mixture and 2,2-dimethoxy-2-phenylacetophenone were mixed in the third mixture. The resulting third mixture was stirred at a preheated temperature until it became viscous, and then molded to obtain a preform. The preform is bonded and imprinted with a silicon wafer microstructure mold and then photocured to obtain a micro-transfer stamp.

[0020] This invention dissolves liquid crystal monomers to obtain a liquid crystal monomer solution.

[0021] In this invention, the liquid crystal monomer is RM257 or RM82; the solvent for dissolution can be toluene. In this invention, the dissolution is carried out under magnetic stirring and heating; the heating temperature can be 80~90℃, specifically 80℃, 85℃, or 90℃; the magnetic stirring speed can be 1000~1500 r / min, specifically 1000 r / min, 1200 r / min, or 1500 r / min; the dissolution time can be 5~10 min, specifically 5 min, 6 min, 7 min, 8 min, 9 min, or 10 min.

[0022] The present invention mixes pentaerythritol tetra-3-mercaptopropionate, 2,2'-(ethylenedithio)diethanol and 4,4'-trimethylenedipiperidine to obtain an additive mixture.

[0023] In this invention, the mass ratio of pentaerythritol tetra-3-mercaptopropionate to 2,2'-(ethylenedithio)diethanol is 0.12:0.42~0.18:0.52, specifically 0.09:0.21; the mass ratio of pentaerythritol tetra-3-mercaptopropionate to 4,4'-trimethylenedipiperidine is 0.12:0.02~0.18:0.0128, specifically 0.09:0.01. In this invention, the mass ratio of pentaerythritol tetra-3-mercaptopropionate to liquid crystal monomer can be (0.12~0.18):2, specifically 0.09:1.

[0024] In this invention, the first mixing method can be magnetic stirring.

[0025] After obtaining the additive mixture, the present invention further mixes the additive mixture with the liquid crystal monomer solution to obtain a second mixture.

[0026] In this invention, the second mixing method is to add the additive mixture to the liquid crystal monomer solution.

[0027] The second mixture and 2,2-dimethoxy-2-phenylacetophenone are mixed in the third mixture. The resulting third mixture is stirred at a preheated temperature until it becomes viscous, and then molded to obtain a preform.

[0028] In this invention, the mass ratio of 2,2-dimethoxy-2-phenylacetophenone to the liquid crystal monomer can be (0.004~0.006):2.

[0029] In this invention, the preheating temperature can be 50~70℃, specifically 55℃. In this invention, the stirring at the preheating temperature can be magnetic stirring; the rotation speed of the magnetic stirring can be 1000~1200 r / min, specifically 1000 r / min, 1100 r / min, or 1200 r / min; the magnetic stirring time can be 5~10 min, specifically 8 min.

[0030] In this invention, the molding process can be sequential mold casting, prepolymerization, and drying. In this invention, the prepolymerization involves placing the cast mold in a dark, stationary position; the time for this dark-protected standing period can be 10-14 hours, specifically 12 hours. In this invention, the drying temperature can be 70-85°C, and the drying time can be 8-12 hours.

[0031] In this invention, the preform has a multi-domain structure with a loosely cross-linked network.

[0032] After obtaining the preform, the present invention applies the preform to a silicon wafer microstructure mold for bonding, imprinting, and photocuring to obtain a micro-transfer stamp.

[0033] In this invention, the bonding and imprinting are performed under a constant load of 200g; the light curing can be ultraviolet light curing; the ultraviolet light curing time can be 25~45min, specifically 40min.

[0034] In this invention, under the synergistic effect of imprinting stress and ultraviolet curing, the liquid crystal units inside the preform undergo secondary orientation under the shearing force of the mold microstructure, thereby achieving precise control of the molecular arrangement direction.

[0035] The present invention also provides a micro-transfer stamp prepared by the preparation method described in the above technical solution.

[0036] This invention also provides a method for micro-transfer printing using the micro-transfer stamp described above, comprising the following steps: By combining a conductive substrate with a micro-transfer stamp, a conductive substrate-micro-transfer composite stamp is obtained. Pick-up: The conductive substrate is heated by electricity, and then the heated conductive substrate-micro transfer composite stamp is brought into contact with the arrayed semiconductor device supported by blue glue under a pre-pressure of 20~50mN. Subsequently, the surface temperature of the conductive substrate-micro transfer composite stamp is cooled down to complete the pickup. Transfer and release: After the arrayed semiconductor device carried by the conductive substrate-micro transfer composite stamp is transferred to the designated position above the target receiving substrate, the conductive substrate-micro transfer composite stamp is heated to release the chip to the receiving substrate. In this invention, the conductive substrate can be an ITO substrate; the heating can be achieved by inputting 12~15V through the ITO substrate to raise the temperature to 80~90℃. Taking 85℃ as an example, when the input voltage is 12V, the time to raise the temperature to 85℃ is 2.28s, and when the input voltage is 15V, the time to raise the temperature to 85℃ is 1.3s; during pickup, the temperature is lowered to ≤50℃.

[0037] In this invention, during the transfer and release, the distance above the designated position on the target receiving substrate can be 20~40µm; the heating method of the conductive substrate-micro transfer composite stamp can be electric heating or laser spot heating; the electric heating can be applying 5~6V to the conductive substrate to raise the temperature to 80~90℃. Taking 85℃ as an example, when the input voltage is 5V, the time to raise the temperature to 85℃ is 35.42s, and when the input voltage is 6V, the time to raise the temperature to 85℃ is 28s.

[0038] In this invention, the laser spot heating can be achieved by using a near-infrared laser (808nm) to spot heat the conductive substrate-micro-transfer composite stamp with a power of 7~12mW to locally raise the temperature to 80~90℃. Taking 85℃ as an example, when the input power is 7mW, the time to raise the temperature to 85℃ is 0.2s, and when the input power is 12mW, the time to raise the temperature to 85℃ is 0.06s.

[0039] This invention employs an integrated molecular orientation and structural forming process involving prepolymerization, imprinting, and UV curing to prepare an LCE array micro-pit adhesion surface structure. This structure relies on temperature-driven deformation to generate controllable negative pressure adsorption, achieving low pre-pressure, high stability, and adjustable adhesion. Furthermore, by utilizing the working mechanism of LCE micro-pit structure's thermally induced deformation-negative pressure change-adhesion force hierarchical control, autonomous pickup and controllable release under low pre-pressure are achieved. Combining the LCE array micro-pit adhesion surface with ITO heating and laser local heating constitutes an integrated micro-transfer stamp structure and working method for both full-area batch transfer and single-point selective transfer.

[0040] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0041] Example 1 Place 1g of RM257 liquid crystal monomer in the first reaction flask and add 0.5g of toluene as a solvent. Add a magnetic stir bar to the first reaction flask and place it in a water bath magnetic stirrer at 85℃ and 1000r / min. Stir at a constant temperature for 10min to ensure that the RM257 monomer is completely dissolved in the toluene system.

[0042] 0.09 g pentaerythritol tetra-3-mercaptopropionate (PETMP), 0.21 g 2,2'-(ethylenedithio)diethanol (EDDT) and 0.01 g 4,4'-trimethylenedipiperidine (HHMP) were added to the second reaction flask, followed by the addition of 0.05 g toluene to thoroughly rinse the flask walls and completely transfer the reagents.

[0043] Take out the completely dissolved RM257 monomer solution, slowly inject the auxiliary agent mixture in the second reaction flask into the first reaction flask, and rinse the second reaction flask twice with 0.1g toluene to transfer all the residual reagents into the first reaction flask, so as to achieve thorough mixing of the reactants.

[0044] Add 0.002 g (approximately 4 μL) of 2,2-dimethoxy-2-phenylacetophenone (DPA) to the mixture in the first reaction flask and continue stirring.

[0045] The mixture was placed in a magnetically stirred water bath at 55℃ and 1000 rpm and stirred for 8 minutes until a uniform viscous state with slight adhesion to the walls was achieved. Then, the reaction flask was placed in a vacuum environment for 2 minutes to remove any dissolved micro-bubbles. The degassed precursor solution was then uniformly poured into the pretreated mold cavity.

[0046] The cast mold was left to stand in the dark for 12 hours to induce a Michael addition prepolymerization reaction and complete the initial crosslinking. After the reaction was complete, the polytetrafluoroethylene (PTFE) film on the surface of the mold was removed, and the preform along with the mold was placed in an 80°C vacuum oven and dried for 10 hours to evaporate the toluene, resulting in a multi-domain LCE preform with a loose crosslinked network.

[0047] (2) Secondary imprinting-photocuring orientation and microstructure forming The LCE preform prepared above was bonded and imprinted onto a pre-fabricated silicon wafer microstructure mold (diameter D: spacing L: pillar height H = D / L / H = 2:3:2) (diameter 50µm, spacing 75µm, pillar height 50µm). A constant load of 200g was applied during the imprinting process to ensure that the preform fully filled the mold microcavity. Simultaneously, the mold and preform system was cured by ultraviolet (UV) irradiation for 40 minutes to obtain the LCE stamp.

[0048] Figure 3 The image shows a scanning electron microscope (SEM) image of the arrayed micropits surface of the LCE stamp prepared in Example 1. Test conditions: dwell time 5µs, accelerating voltage 3kV, beam current 86pA, magnification 56x, working distance 20mm, horizontal field of view 3.72mm, mode SE, detector ETD. Figure 3 It can be seen that the sample is a liquid crystal elastomer array micro-pit surface with a diameter of 50µm, a spacing of 75µm, and a depth of 50µm. The surface is flat and the structure is clear, indicating that the imprinting manufacturing process meets the requirements of subsequent processes.

[0049] Figure 4 The images show the morphology of the LCE stamp micropit surface at 25°C and 85°C, as prepared in Example 1. Test conditions: Samples were photographed using a Keyence VHX-X1 optical microscope, and 3D microscopic morphology was synthesized for observation and analysis. Figure 4 It can be seen that the sample can switch between thermal response states (structured and planarized) at 25℃ and 85℃, indicating that the manufacturing process meets the requirements of subsequent transfer printing.

[0050] Figure 5 The images show the morphology of the LCE stamp micropit surface at 25°C and 85°C, as prepared in Example 1. Test conditions: Samples were photographed using a Keyence VHX-X1 optical microscope, and 3D microscopic morphology was synthesized for observation and analysis. Figure 5 It can be seen that the micro-transfer stamp can switch between thermal response states (structured and planarized) under conditions of 25℃ and 85℃, and the change of micro-pits is about 90 times, indicating that the micro-pits have good deformation ability and the ability to generate negative pressure cavities.

[0051] Figure 6 The image shows the thermal response cycle test results of the LCE stamp micropit surface prepared in Example 1. The test conditions were as follows: the micro-transfer stamp was placed on a heated substrate, and the substrate temperature was increased to 25°C, 45°C, 65°C, 85°C, 90°C, 85°C, 65°C, 45°C, and 25°C. After the micro-transfer stamp temperature stabilized, the surface micropits were optically characterized using a Keyence VHX-X1 optical microscope. Figure 6 It can be seen that micro-transfer stamps can undergo structural deformation under gradual temperature changes and have good cycling ability.

[0052] Figure 7 To investigate the relationship between the pre-pressure and adhesion force of the LCE stamp prepared in Example 1, the test conditions were as follows: A 12V voltage was applied to the ITO substrate, and the temperature was raised to 85°C in 2.28 seconds. The adsorbed surface (glass) was then controlled to move downwards, and a specific pre-pressure (50~1000mN) was applied to bring the two surfaces into contact. After cooling to the test temperature of 50°C, the adsorbed surface (glass) was controlled to move upwards at a retraction rate of 2000µm / s, separating the two adhesive surfaces. The force test curve was then obtained on the testing software. Figure 7 It can be seen that the surface of the micro-transfer stamp generates a stable negative pressure adhesion ability under a pre-pressure of 50mN, and achieves an equivalent negative pressure adsorption force of 75% under strong pre-pressure.

[0053] Figure 8 To investigate the relationship between the retraction rate and adhesion force of the LCE stamp prepared in Example 1, the test conditions were as follows: A 12V voltage was applied to the ITO substrate, and the temperature was raised to 85°C in 2.28 seconds. The adsorbed surface (glass) was then controlled to move downwards, bringing the two surfaces into contact with a 50mN force. After cooling to the test temperature of 50°C, the adsorbed surface (glass) was controlled to move upwards at retraction rates of 20µm / s, 100µm / s, 200µm / s, 500µm / s, 1000µm / s, 2000µm / s, and 2500µm / s, thus separating the two adhesive surfaces. Force test curves were obtained on the testing software. Figure 8 It can be seen that the micro-transfer stamp surface achieves the best adhesion performance at a retraction rate of 2000µm / s. This parameter will be used as a constant condition for subsequent experiments.

[0054] Figure 9 The results of 50 repeated adhesion tests on the LCE stamp prepared in Example 1 were as follows: The test conditions were: after heating to 85°C for 2.28 seconds by inputting a 12V voltage through the ITO substrate, the adsorbed surface (glass) was controlled to move downwards, and a specific pre-pressure of 50mN was applied to bring the two surfaces into contact. After cooling to the test temperature of 50°C, the adsorbed surface (glass) was controlled to move upwards at a retraction rate of 2000µm / s to separate the two adhering surfaces. This process was repeated 50 times, and the force test curve was obtained on the testing software. Figure 9 It can be seen that the sample surface still maintains a high and consistent negative pressure adsorption capacity during 50 adhesion cycles, proving that the surface of the liquid crystal elastomer array micro-pits has the ability to be reused.

[0055] Figure 10 The temperature grading response curve of the LCE stamp prepared in Example 1 was obtained under the following test conditions: A 12V voltage was applied to the ITO substrate, and the temperature was raised to 85°C in 2.28 seconds. The adsorbed surface (glass) was then controlled to move downwards, and a specific pre-pressure of 50mN was applied to bring the two surfaces into contact. The temperature was then allowed to cool to the test temperatures (25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 85°C (without cooling)). The adsorbed surface (glass) was then controlled to move upwards at a retraction rate of 2000µm / s, separating the two adhering surfaces. Force test curves were obtained on the testing software. Figure 10It can be seen that the surface of the micro-transfer stamp exhibits a graded negative pressure adhesion force directly related to temperature after cooling to various temperatures. Specifically, when not cooled (maintaining 85℃), only 24mN of adhesion force is generated; when cooled to 70℃, 561mN of adhesion force is generated; when cooled to 60℃, 568mN of adhesion force is generated; when cooled to 50℃, 700mN of adhesion force is generated; when cooled to 40℃, 736mN of adhesion force is generated; when cooled to 30℃, 873mN of adhesion force is generated; and when cooled to 25℃, 1050mN of adhesion force is generated. The adhesion force gradually increases with the graded temperature difference, proving that the surface of the liquid crystal elastomer array micro-pits has the ability to precisely control the negative pressure adhesion force in a graded manner.

[0056] Figure 11 To investigate the relationship between input voltage, power, and surface temperature rise rate of an ITO substrate, the test conditions were as follows: an ITO substrate and an LCE stamp were composited to obtain an ITO-LCE composite stamp. Different input voltages were applied to the ITO substrate for a certain period of time, followed by heating to 85°C. Line graphs were then plotted on the input voltage, temperature rise rate, and input power. Figure 11 It is known that 12~15V has high efficiency and the temperature rise rate is less than 30℃ / s, which is easy to control. When the input voltage is 18V, the surface temperature of ITO rises too quickly, making it difficult to control the temperature accurately. Therefore, this invention uses 12~15V as the pre-temperature input voltage to avoid damaging the device too quickly. When the input voltage is 5V, 8V, 10V, 12V, 15V, and 18V, the corresponding input power is 1.8W, 4.6W, 7.1W, 10.2W, 15.9W, and 22.7W, respectively. The time to heat up from room temperature to 85℃ is 35.42s, 7.3s, 3.7s, 2.25s, 1.3s, and 0.88s, respectively.

[0057] Figure 12 The maximum temperature difference on the surface of the elastomer covering the ITO substrate during heating under various input voltages is given by [the relevant data source]. Figure 12 It can be seen that the uniformity of ITO heating is best when the input voltage is around 5V.

[0058] Figure 13 To test the temperature response and natural cooling under various laser powers for a duration of 0.2 s, the test procedure was as follows: After applying a 12V voltage to the ITO substrate and heating it to 85°C for 2.28 s, the ITO-LCE composite stamp and the arrayed chip supported by blue adhesive were brought into contact with a pre-pressure of 50 mN. Once the surface temperature cooled to 50°C, the chip was picked up. The stamp carrying the chip was then transported to a position 20 µm above the target receiving substrate, and then irradiated for 0.20 s with an 808 nm near-infrared laser at a power of 3–12 mW to rapidly heat the LCE layer locally. Figure 13It can be seen that: at a power of 7~12mW, the material response temperature can be reached within 0.2s, while at 3~5mW, the material response temperature cannot be reached within 0.2s, and the material basically returns to room temperature within 0.6s.

[0059] Figure 14 To investigate the effect of duration of laser power on temperature response, the test procedure was as follows: After heating the ITO substrate to 85°C for 2.28 seconds using a 12V voltage input, an ITO-LCE composite stamp was brought into contact with the arrayed chip supported by blue adhesive under a pre-pressure of 50mN. Once the surface temperature cooled to 50°C, the chip was picked up. The stamp, carrying the chip, was then transported to a position 20µm above the target receiving substrate and illuminated for 2 seconds using an 808nm near-infrared laser at a power of 3-12mW. Figure 14 It can be seen that 3~5mW cannot reach the material response temperature within 2s.

[0060] Figure 15 The test procedure for the chip removal response time under 808nm near-infrared laser power of 7mW was as follows: After heating the ITO substrate to 85°C for 2.28 seconds with a 12V voltage input, the ITO-LCE composite stamp and the arrayed chip supported by blue adhesive were brought into contact with a pre-pressure of 50mN. Once the surface temperature cooled to 50°C, the chip was successfully removed. The stamp carrying the chip was then transported to a designated position 200µm above the target receiving substrate, where it was irradiated with an 808nm near-infrared laser at 7mW power, causing the LCE layer to locally and rapidly heat up to 85°C. The response was simultaneously captured using a FASTCAM Nova R5-4K high-speed camera. Figure 15 It can be seen that the material response desorbed from the transfer device at 100ms, which is consistent with the simulation results.

[0061] Figure 16 This diagram illustrates the accuracy evaluation criteria. The center error d refers to the deviation between the center position of the microchip on the transfer substrate and the center position of the microchip on the receiving substrate; the x-direction deviation Δx is the x-direction deviation between the position of the microchip on the transfer substrate and the position of the microchip on the receiving substrate; the y-direction deviation Δy is the y-direction deviation between the position of the microchip on the transfer substrate and the position of the microchip on the receiving substrate; and the angle deviation θ is the deviation of the angle through which the microchip rotates on the transfer substrate and the receiving substrate.

[0062] Figure 17 The relationship between transfer gap height and precision under ITO global transfer printing. Figure 18To investigate the relationship between the gap height and angular error θ during ITO global transfer printing, the test procedure was as follows: A 12V voltage was applied to the ITO substrate, and the temperature was raised to 85°C in 2.28 seconds. The ITO-LCE composite stamp and the arrayed chip supported by blue adhesive were then brought into contact with a pre-pressure of 50mN. After the surface temperature cooled to 50°C, the chip was picked up. The stamp, carrying the chip, was then transferred to a position 20-200µm above the target receiving substrate. A 5V voltage was then applied to the ITO layer for 35.42 seconds, causing the LCE layer to rapidly heat up to 85°C. Figures 17-18 It can be seen that with a transfer gap height of 20~40µm, the center error d, x, and y direction errors are <30µm, and the angle error θ is <5°. The center error, x, y direction errors, and angle error θ meet the transfer requirements.

[0063] Figure 19 This relates the gap height to accuracy in laser selective transfer printing. Figure 20 To investigate the relationship between gap height and angular error θ in laser selective transfer printing, the test procedure was as follows: After heating the ITO substrate to 85°C using a 12V voltage for 2.28 seconds, the ITO-LCE composite stamp and the arrayed chip supported by blue adhesive were brought into contact with a pre-pressure of 50mN. Once the surface temperature cooled to 50°C, the chip was picked up. The stamp, carrying the chip, was then transported to a position 20-200µm above the target receiving substrate. An 808nm near-infrared laser at a power of 7mW was then applied for 0.20 seconds, causing the LCE layer to locally and rapidly heat up to 85°C. Figures 19-20 It can be seen that with a transfer gap height of 20~40µm, the center error d, x, and y direction errors are <30µm, the angle error θ is <5°, and the center error d, x, and y direction errors and the angle error θ meet the transfer requirements.

[0064] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a micro-transfer stamp based on a thermally controllable adhesion surface of a liquid crystal elastomer, characterized in that, Includes the following steps: The liquid crystal monomer is dissolved to obtain a liquid crystal monomer solution; the liquid crystal monomer is RM257 or RM82. Pentaerythritol tetra-3-mercaptopropionate, 2,2'-(ethylenedithio)diethanol and 4,4'-trimethylenedipiperidine were mixed to obtain an additive mixture. The additive mixture and the liquid crystal monomer solution are mixed for the second time to obtain a second mixture; The second mixture and 2,2-dimethoxy-2-phenylacetophenone were mixed in the third mixture. The resulting third mixture was stirred at a preheated temperature until it became viscous, and then molded to obtain a preform. The preform is bonded and imprinted with a silicon wafer microstructure mold and then photocured to obtain a micro-transfer stamp.

2. The preparation method according to claim 1, characterized in that, The mass ratio of pentaerythritol tetra-3-mercaptopropionate to 2,2'-(ethylenedithio)diethanol is 0.12:0.42~0.18:0.52; the mass ratio of pentaerythritol tetra-3-mercaptopropionate to 4,4'-trimethylenedipiperidine is 0.12:0.02~0.18:0.0128.

3. The preparation method according to claim 1, characterized in that, The mass ratio of pentaerythritol tetra-3-mercaptopropionate to liquid crystal monomer is (0.12~0.18):

2.

4. The preparation method according to claim 1, characterized in that, The mass ratio of 2,2-dimethoxy-2-phenylacetophenone to the liquid crystal monomer is (0.004~0.006):2; the preheating temperature is 50~70℃.

5. The preparation method according to claim 1, characterized in that, The molding process consists of sequential mold casting, prepolymerization, and drying; the prepolymerization process involves placing the cast mold in the dark for 10-14 hours; the drying temperature is 70-85℃ and the drying time is 8-12 hours.

6. The preparation method according to claim 1, characterized in that, The bonding and imprinting are performed under a constant load of 200g; the light curing is ultraviolet light curing; the ultraviolet light curing time is 25~40 min.

7. The micro-transfer stamp prepared by the preparation method according to any one of claims 1 to 6.

8. A method for micro-transfer printing using the micro-transfer stamp according to claim 7, characterized in that, Includes the following steps: By combining a conductive substrate with a micro-transfer stamp, a conductive substrate-micro-transfer composite stamp is obtained. Pick-up: The conductive substrate is heated by electricity, and then the heated conductive substrate-micro transfer composite stamp is brought into contact with the arrayed semiconductor device supported by blue glue under a pre-pressure of 20~50mN. Subsequently, the surface temperature of the conductive substrate-micro transfer composite stamp is cooled down to complete the pickup. Transfer and release: After transferring the arrayed semiconductor devices carried by the conductive substrate-micro transfer composite stamp to a designated position above the target receiving substrate, the conductive substrate-micro transfer composite stamp is heated to release the chip to the receiving substrate.

9. The method as described in claim 8, characterized in that, The conductive substrate is an ITO substrate; during pickup, the heating is achieved by inputting 12~15V through the ITO substrate to raise the temperature to 80~90℃; during pickup, the temperature is lowered to ≤50℃.

10. The method as described in claim 8, characterized in that, During the transfer and release, the distance from the point of transfer to the designated position above the target receiving substrate is 20~40µm; The heating method of the conductive substrate-micro transfer composite stamp is either electric heating or laser spot heating. The electric heating is achieved by applying a voltage of 5-6V to the conductive substrate to raise the temperature of the entire area to 80-90°C. The laser spot heating is achieved by using a near-infrared laser with a power of 7~12mW to spot heat the conductive substrate-micro-transfer composite stamp, thereby locally raising the temperature to 80~90℃.

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