Preparation strategy of stretchable three-dimensional integrated circuit

Abstract

The invention discloses a preparation strategy of a stretchable three-dimensional integrated circuit, and relates to the technical field of flexible electronics. The method includes preparing a silver-based circuit structure on a substrate; forming a liquid metal-based circuit; carrying out curing treatment on the Soft-IBA precursor solution, and then stripping the substrate to obtain a single-layer stretchable circuit; a plurality of single-layer stretchable circuits are arranged in a laminated mode, and corresponding through holes are formed between layers in a physical punching mode; and depositing conductive layers in the through holes, so that the layers are conducted, and the stretchable three-dimensional integrated circuit is obtained. According to the stretchable three-dimensional integrated circuit and the manufacturing method thereof, stable conduction between layers is achieved through design of vertical interconnection paths (through holes) and metallization of the through holes, various inorganic electronic elements are combined through the liquid metal three-dimensional integrated circuit, and therefore the feasibility and stability of the stretchable three-dimensional integrated circuit are verified.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronic technology, and in particular to a preparation strategy for a stretchable three-dimensional integrated circuit. Background Art

[0002] Soft and stretchable electronic systems have potential applications in critical care, large-scale physiological monitoring, real-time analysis of health status, and local treatment. Intrinsically stretchable electronic systems are usually prepared by composites of functional materials, polymer elastomer materials, conductive fillers, etc. Compared with the shortcomings of traditional functional materials that cannot maintain effective connection of active materials when stretched, these intrinsically stretchable electronic composites can maintain their complete functional properties under applied strain, but these materials have poor mechanical properties and limited ability to withstand large strains. In order to effectively protect the functional devices in stretchable electronic systems, they can be constructed into rigid island structures. However, the performance of rigid island structure stretchable electronic systems is challenged by the stiffness and interface engineering of rigid and flexible components. Therefore, how to simultaneously enhance the difference in Young's modulus ratio between the rigid island and the flexible substrate and the interface stability between the two is still a problem that restricts the large-scale development of stretchable electronic systems.

[0003] Technicians in this field have developed a rigid island structure substrate with high modulus ratio and high stretch rate (stiff-&soft-IBA rigid island structure substrate). By using different ratios of the same material, two parts with a large difference in Young's modulus ratio (7880) were created - a rigid island (stiff-IBA) and a flexible substrate (soft-IBA). The rigid island (stiff-IBA) is formed in situ in the flexible matrix (soft-IBA), and its Young's modulus differs by nearly four orders of magnitude, which means that the rigid area will not deform under large stretching, effectively protecting the functional devices and active substances above it. At the same time, there are carbon-carbon double bonds at the interface between the two, which polymerize into long molecular chains shuttling between the rigid island (stiff-IBA) and the flexible substrate (soft-IBA) under ultraviolet light irradiation, which will greatly enhance the mechanical strength at the interface, so that the prepared two-dimensional stretchable electronic system has a high stretch rate of 560%, and still maintains stable performance during up to 1000 cycles, effectively solving the above problems and providing a feasible and high-performance material type for the production of rigid island structure substrates.

[0004] However, in order to realize high-density and multifunctional stretchable electronic products, it is necessary to develop three-dimensional (3D) stretchable integrated electronic systems. However, the development of three-dimensional stretchable electronic products is still in its early stages. At present, it is not possible to prepare high-resolution stretchable three-dimensional integrated circuits on a large scale based on this material, which greatly restricts the development of three-dimensional stretchable electronic products.

[0005] In summary, the technical problem that needs to be solved is: how to print high-resolution stretchable three-dimensional integrated circuits on a large scale based on this high modulus ratio, high stretch rate rigid island structure substrate (stiff-&soft-IBA), and make the prepared three-dimensional integrated circuits able to produce large deformations synchronously with the flexible substrate and stably conduct. Summary of the invention

[0006] In view of the deficiencies in the above-mentioned background technology, the main technical problem solved by the present invention is: how to print high-resolution stretchable three-dimensional integrated circuits on a large scale based on such a high modulus ratio, high stretch rate rigid island structure substrate (stiff-&soft-IBA), and make the prepared three-dimensional integrated circuits able to produce large deformation synchronously with the flexible substrate and stably conduct.

[0007] The present invention provides a preparation strategy for stretchable three-dimensional integrated circuits. The strategy uses photolithography to prepare stretchable three-dimensional integrated circuits on stiff-&soft-IBA rigid island structure substrates. Liquid metal (LM) gallium indium alloy (EGaIn) with high conductivity and stretchability is used as a stretchable conductor, and the liquid metal is patterned with a high resolution as low as 5 microns. These liquid metal circuits show excellent electronic properties. When the liquid metal circuit line width is 500 μm, it still has excellent conductivity when stretched to 380% strain, and the resistance only increases by 1.4 times. At the same time, we achieve stable conduction between layers by designing vertical interconnection paths (through holes) and metallization of through holes, and use liquid metal three-dimensional integrated circuits to combine multiple inorganic electronic components to verify the feasibility and stability of stretchable three-dimensional integrated circuits.

[0008] The first object of the present invention is to provide a method for preparing a stretchable three-dimensional integrated circuit, comprising the following steps: preparing a silver-based circuit structure on a substrate; selectively wetting a silver-based circuit structure using liquid metal to form a liquid metal-based circuit; The Soft-IBA precursor liquid is directly poured onto the liquid metal circuit, and the Soft-IBA precursor liquid is cured, and then the substrate is peeled off to obtain a single-layer stretchable circuit; Multiple single-layer stretchable circuits are stacked and corresponding through holes are set between the layers by physical punching; then a conductive layer is deposited in the through holes to make the layers conductive, thus obtaining a stretchable three-dimensional integrated circuit.

[0009] Preferably, a silver-based circuit structure is prepared on a substrate, comprising: preparing a sacrificial layer on a substrate; Coating photoresist on the sacrificial layer and baking to obtain a photoresist layer; The photoresist layer is exposed to UV light with the assistance of a mask. After UV exposure, it is immersed in a developer. After washing and drying, chromium and silver are sequentially deposited on the surface of the immersed sample by thermal evaporation coating, and then it is stripped in an acetone solvent, thereby preparing a silver-based circuit structure on the substrate.

[0010] Preferably, the sacrificial layer is formed by spin coating an aqueous solution of dextran on the substrate; the mass percentage of the aqueous solution of dextran is 10-30 wt%.

[0011] Preferably, the substrate is peeled off by immersing the cured sample in deionized water to dissolve the sacrificial layer, thereby peeling off the substrate.

[0012] Preferably, the baking temperature is 110-120° C. and the baking time is 60-80 s; The UV exposure time is 8~12 s, and the development time is 20~30 s.

[0013] Preferably, the liquid metal is a gallium-indium alloy.

[0014] Preferably, the Soft-IBA precursor solution is prepared by mixing isobornyl acrylate, benzyl acrylate and polyurethane acrylate in a mass ratio of 2: 5: 3, adding 1-2% of the total mass of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator, and then stirring for 6-8 h to obtain the soft-IBA precursor solution.

[0015] Preferably, between the stacked single-layer stretchable circuits, the contacts of the circuits are cured using Stiff-IBA precursor liquid; The Stiff-IBA precursor solution is prepared by mixing isobornyl acrylate, benzyl acrylate and polyurethane acrylate in a mass ratio of 5: 2: 3, adding 1-2% of the total mass of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator, and stirring for 6-8 hours to obtain the Stiff-IBA precursor solution.

[0016] The second object of the present invention is to provide a stretchable three-dimensional integrated circuit.

[0017] The third object of the present invention is to provide a stretchable three-dimensional integrated circuit for use in flexible electronic devices.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a preparation strategy for stretchable three-dimensional integrated circuits. Based on a rigid island structure substrate (stiff-&soft-IBA) with a high modulus ratio and high stretch rate, the present invention develops a method for large-scale printing of high-resolution stretchable three-dimensional integrated circuits. The liquid metal circuit (line width 500 μm) produced by the present invention still has excellent conductivity when stretched to 380% strain, and the resistance is only increased by 1.4 times. The present invention solves the problem of how to conduct between different layers of the three-dimensional circuit, and realizes stable conduction between layers by designing vertical interconnection paths (through holes) and metallization of through holes. The present invention uses liquid metal three-dimensional integrated circuits to combine a variety of inorganic electronic components, and prepares a multi-module integrated device based on the above-mentioned rigid island structure substrate and printed liquid metal interconnection technology, demonstrating its functional application in various complex strain environments, and verifying the feasibility and stability of stretchable three-dimensional integrated circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Optical microscope image of liquid metal selectively wetting the silver-covered area to form a liquid metal circuit; Figure 2 Optical microscope image of liquid metal circuit transferred onto flexible substrate (soft-IBA); Figure 3 The stretching conductivity curves of liquid metal circuits with different widths on a flexible substrate (soft-IBA); Figure 4 Optical photograph of a receiving coil based on liquid metal on a flexible substrate (soft-IBA); Figure 5 The waveform of the voltage applied to the transmitting coil, the waveform of the voltage received by the liquid metal receiving coil, and the curve of the rectified DC voltage; Figure 6 Optical microscope image of a cross-section of a three-dimensional via after a layer of copper was deposited in the via using electroless plating; Figure 7 It is a circuit diagram of a multi-module three-dimensional integrated device of a wireless charging / rectifier module / photosensitive sensor module; Figure 8 It is a physical display of a wireless charging / rectifier module / photosensitive sensor module multi-module three-dimensional integrated device, and a physical picture of the device under complex strains of biaxial stretching and torsion is shown; Fig. 9 The wireless charging function curve diagram of the wireless charging / rectifier module / photosensitive sensor module multi-module three-dimensional integrated device; Fig.10 This is a curve diagram of the voltage and current changes at both ends of the battery and the LED lamp when the wireless charging / rectifier module / photosensitive sensor module multi-module three-dimensional integrated device demonstrates its functions in a dark environment. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0021] The purpose of the present invention is to provide a method for preparing a stretchable three-dimensional integrated circuit on a stiff-&soft-IBA rigid island structure substrate by photolithography. Liquid metal (LM) gallium indium alloy (EGaIn) with high conductivity and stretchability is used as a stretchable conductor, and the liquid metal is patterned with a high resolution as low as 5 microns. These liquid metal circuits show excellent electronic properties. When the liquid metal circuit line width is 500 μm, it still has excellent conductivity when stretched to 380% strain, and the resistance only increases by 1.4 times. At the same time, we achieve stable conduction between layers by designing vertical interconnection paths (through holes) and metallization of through holes, and use liquid metal three-dimensional integrated circuits to combine multiple inorganic electronic components to verify the feasibility and stability of stretchable three-dimensional integrated circuits.

[0022] In order to achieve the above object, the present invention provides a method for preparing a stretchable three-dimensional integrated circuit in a first aspect, comprising the following steps: preparing a silver-based circuit structure on a substrate; selectively wetting a silver-based circuit structure using liquid metal to form a liquid metal-based circuit; The Soft-IBA precursor liquid is directly poured onto the liquid metal circuit, and the Soft-IBA precursor liquid is cured, and then the substrate is peeled off to obtain a single-layer stretchable circuit; Multiple single-layer stretchable circuits are stacked and corresponding through holes are set between the layers by physical punching; then a conductive layer is deposited in the through holes to make the layers conductive, thus obtaining a stretchable three-dimensional integrated circuit.

[0023] The substrate is Si or SiO 2 Chip.

[0024] In the present invention, a silver-based circuit structure is prepared on a substrate, comprising: preparing a sacrificial layer on a substrate; Coating photoresist on the sacrificial layer and baking to obtain a photoresist layer; The photoresist layer is exposed to UV light with the assistance of a mask. After UV exposure, it is immersed in a developer. After washing and drying, chromium and silver are sequentially deposited on the surface of the immersed sample by thermal evaporation coating, and then it is stripped in an acetone solvent, thereby preparing a silver-based circuit structure on the substrate.

[0025] Among them, the baking temperature is 110~120℃, and the baking time is 60~80 s; the UV exposure treatment time is 8~12 s, and the development time is 20~30 s.

[0026] The sacrificial layer is formed by spin coating an aqueous solution of dextran on a substrate; the mass percentage of the aqueous solution of dextran is 10-30 wt%.

[0027] The substrate is peeled off by immersing the cured sample in deionized water to dissolve the sacrificial layer, thereby peeling off the substrate.

[0028] The liquid metal is a gallium-indium alloy.

[0029] The Soft-IBA precursor solution is prepared by mixing isobornyl acrylate, benzyl acrylate, and polyurethane acrylate in a mass ratio of 2: 5: 3, adding 1-2% of the total mass of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator, and then stirring for 6-8 hours to obtain the soft-IBA precursor solution.

[0030] Between the stacked single-layer stretchable circuits, the contacts of the circuits are cured using a Stiff-IBA precursor solution; wherein the Stiff-IBA precursor solution is prepared by mixing isobornyl acrylate, benzyl acrylate, and polyurethane acrylate in a mass ratio of 5: 2: 3, and then adding 1-2% of the total mass of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator, and stirring for 6-8 hours to obtain the Stiff-IBA precursor solution.

[0031] Exemplarily, a preparation strategy of a stretchable three-dimensional integrated circuit includes the following specific steps: Step 1: Si or SiO 2 The wafer was ultrasonically treated in acetone, isopropanol and deionized water, then dried and treated with a plasma cleaner. 2 The wafers were ultrasonically treated in acetone, isopropanol and deionized water for fifteen minutes each and in a plasma cleaner for five minutes to make the surface of the silicon wafer hydrophilic.

[0032] Step 2: Spin-coat the aqueous solution of dextran on the silicon wafer to form a sacrificial layer, and then bake it on a hot plate. In step 2, the mass percentage of the aqueous solution of dextran is 20 wt%, the spin-coating speed is 4000 rpm, and the time is 40 s; during the baking process, first heat at 80 ° C for one minute, and then heat at 180 ° C for 30 min.

[0033] Step 3: Spin-coat the photoresist S1813 on the dextran-coated silicon wafer, and then bake it on a hot plate. In step 3, the spin-coating speed of the S1813 photoresist is 4000 rpm, the time is 60 s, and the temperature during baking on the hot plate is 115 °C.

[0034] Step 4: UV exposure was performed on S1813 with the help of a mask. After UV exposure, the sample was immersed in a developer for a certain period of time, then rinsed with deionized water and dried with nitrogen. In step 4, the UV exposure time was 10 s and the development time was 25 s.

[0035] Step 5: Deposit chromium and silver on the sample surface by thermal evaporation, and then lift off in acetone solvent to form a silver-based circuit structure on the silicon wafer. In step 5, the thickness of chromium deposited on the sample is 20 nm, the thickness of silver is 400 nm, and the thermal evaporation coating speed is 0.8 Å / s. Then the sample needs to be lifted off in acetone solution with the assistance of ultrasound.

[0036] Step 6: In a glove box filled with argon, liquid metal is used to selectively wet the silver-based circuit structure to form a liquid metal-based circuit. In step 6, the liquid metal uses gallium-indium alloy with a melting point of 16°C. It needs to be treated with a 5 wt% sodium hydroxide aqueous solution in advance to remove the oxide layer on the surface of the liquid metal.

[0037] Step 7: Pour the Soft-IBA precursor directly onto the liquid metal circuit, and then irradiate with ultraviolet light to solidify the Soft-IBA precursor. In step 7, the Soft-IBA precursor is prepared by adding isobornyl acrylate (IBOA), benzyl acrylate (BA), and polyurethane acrylate (AUD) into a beaker at a ratio of 2: 5: 3, and then adding 1% of the total mass of diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide (TPO) as a photoinitiator, and stirring the mixture for 6-8 hours using a mechanical stirrer to obtain the soft-IBA precursor; the ultraviolet irradiation time is 5 seconds.

[0038] Step 8: By immersing the sample in deionized water at room temperature, the sacrificial layer between the silicon wafer and the liquid metal circuit is dissolved, thereby peeling the Soft-IBA film from the silicon wafer and transferring the liquid metal circuit to the Soft-IBA film to obtain a single-layer stretchable circuit. In step 8, the time for dissolving the sacrificial layer is more than 6 hours, waiting for the Soft-IBA film to automatically fall off the silicon wafer.

[0039] Step 9: Prepare multiple single-layer stretchable circuits in the same way, use Stiff-IBA to cure at the contacts of the circuit, and design through holes between layers by physical punching. In step 9, the Stiff-IBA precursor is isobornyl acrylate (IBOA), benzyl acrylate (BA), and polyurethane acrylate (AUD) added to a beaker in a ratio of 5: 2: 3, and then 1% of the total mass of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide (TPO) is added as a photoinitiator. The mixture is stirred for 6-8 hours using a mechanical stirrer to obtain the Stiff-IBA precursor. The punching position is on the Stiff-IBA hard island, aiming to prevent the three-dimensional circuit from breaking due to stress concentration caused by the presence of through holes during the stretching process.

[0040] Step 10: Roughen, sensitize and activate the through-holes, and then immerse them in a chemical copper plating solution at room temperature to deposit a layer of copper in the through-holes to achieve the purpose of conduction between layers. Finally, multiple single-layer stretchable circuits with through-holes are aligned, bonded, and packaged to obtain a stretchable three-dimensional integrated circuit.

[0041] In step ten, the roughening is to immerse the sample in a 30 ml / L sulfuric acid solution for 10 h; the sensitizing solution is prepared using 10 ml of deionized water, 0.2 g of stannous chloride, and 0.2 ml of hydrochloric acid, and the sensitization time is 30 min; the activation solution is prepared using 10 ml of deionized water, 0.01 g of palladium chloride, and 0.2 ml of hydrochloric acid, and the activation time is 30 min; the chemical copper plating time is 10 h.

[0042] A second aspect of the present invention provides a stretchable three-dimensional integrated circuit.

[0043] A third aspect of the present invention provides an application of a stretchable three-dimensional integrated circuit in a flexible electronic device.

[0044] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0045] Example 1 A preparation strategy for a stretchable three-dimensional integrated circuit, the specific steps of which are as follows: Step 1: The Si wafer was ultrasonically treated in acetone, isopropanol and deionized water, then blown dry and treated with a plasma cleaner. In step 1, the Si wafer was ultrasonically treated in acetone, isopropanol and deionized water for 15 minutes each, and the plasma cleaner was used for 5 minutes to make the surface of the silicon wafer hydrophilic.

[0046] Step 2: Spin-coat the aqueous solution of dextran on the silicon wafer to form a sacrificial layer, and then bake it on a hot plate. In step 2, the mass percentage of the aqueous solution of dextran is 20 wt%, the spin-coating speed is 4000 rpm, and the time is 40 s; during the baking process, first heat at 80 ° C for 1 minute, and then heat at 180 ° C for 30 min.

[0047] Step 3: Spin-coat the photoresist S1813 on the dextran-coated silicon wafer, and then bake it on a hot plate. In step 3, the spin-coating speed of the S1813 photoresist is 4000 rpm, the time is 60 s, and the temperature during baking on the hot plate is 115 °C.

[0048] Step 4: UV exposure was performed on the photoresist S1813 with the help of a mask. After UV exposure, the sample was immersed in positive photoresist developer ZX-238 for 25 s, then rinsed with deionized water and dried with nitrogen. In step 4, the UV exposure time was 10 s and the development time was 25 s.

[0049] Step 5: Deposit chromium and silver on the sample surface by thermal evaporation, and then lift off in acetone solvent to form a silver-based circuit structure on the silicon wafer. In step 5, the thickness of chromium deposited on the sample is 20 nm, the thickness of silver is 400 nm, and the thermal evaporation coating speed is 0.8 Å / s. Then the sample needs to be lifted off in acetone solution with the assistance of ultrasound.

[0050] Step 6: In a glove box filled with argon, liquid metal is used to selectively wet the silver-based circuit structure, where the liquid metal selectively wets the surface of the silver and does not wet areas other than the silver. Based on this principle, a circuit structure based on liquid metal can be formed. In step 6, the liquid metal uses gallium-indium alloy with a melting point of 16°C. It needs to be treated with a 5 wt% sodium hydroxide aqueous solution in advance to remove the oxide layer on the surface of the liquid metal.

[0051] Step 7: Pour the Soft-IBA precursor directly onto the liquid metal circuit, and then irradiate with ultraviolet light to solidify the Soft-IBA precursor. In step 7, the Soft-IBA precursor is prepared by adding isobornyl acrylate (IBOA), benzyl acrylate (BA), and polyurethane acrylate (AUD) into a beaker at a ratio of 2: 5: 3, and then adding 1% of the total mass of diphenyl (2,4, 6-trimethylbenzoyl) phosphine oxide (TPO) as a photoinitiator, and stirring the mixture for 7 hours using a mechanical stirrer to obtain the soft-IBA precursor; the ultraviolet irradiation time is 5 s.

[0052] Step 8: The sacrificial layer between the silicon wafer and the liquid metal circuit is dissolved by immersing the sample in deionized water at room temperature, thereby peeling off the Soft-IBA film from the silicon wafer to obtain a single-layer stretchable circuit. In step 8, the sacrificial layer is dissolved for more than 6 hours, waiting for the liquid metal circuit and the Soft-IBA film to automatically fall off the silicon wafer.

[0053] Step 9: Prepare multiple single-layer stretchable circuits in the same way, use Stiff-IBA to cure at the connection points of the three-dimensional circuits between layers, and make three-dimensional vertical interconnection through holes between layers by physical punching.

[0054] In step nine, the Stiff-IBA precursor solution is prepared by adding isobornyl acrylate (IBOA), benzyl acrylate (BA), and polyurethane acrylate (AUD) into a beaker at a ratio of 5:2:3, and then adding 1% of the total mass of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide (TPO) as a photoinitiator. The mixture is stirred for 7 hours using a mechanical stirrer to obtain the Stiff-IBA precursor solution. The holes are punched on the Stiff-IBA hard island, so that the three-dimensional circuit will not break due to stress concentration caused by the presence of the through-holes during the stretching process.

[0055] Step 10: Roughen, sensitize and activate the area around the through hole, and then immerse it in a chemical copper plating solution at room temperature to deposit a layer of copper in the through hole to achieve the purpose of conducting electricity between layers. Finally, multiple single-layer stretchable circuits with through holes are aligned, bonded, and packaged to obtain a stretchable three-dimensional integrated circuit.

[0056] In step ten, the roughening is to immerse the sample in a 30 ml / L sulfuric acid solution for 10 h; the sensitizing solution is prepared using 10 ml of deionized water, 0.2 g of stannous chloride, and 0.2 ml of hydrochloric acid, and the sensitization time is 30 min; the activation solution is prepared using 10 ml of deionized water, 0.01 g of palladium chloride, and 0.2 ml of hydrochloric acid, and the activation time is 30 min; the chemical copper plating time is 10 h.

[0057] In order to illustrate the relevant performance of a stretchable three-dimensional integrated circuit obtained by a preparation strategy of a stretchable three-dimensional integrated circuit provided in this embodiment 1, it is described in conjunction with the accompanying drawings.

[0058] like Figure 1 As shown in Figure 2, the minimum size of the silver surface selectively wetted by liquid metal is shown. The width of the silver line is Figure 1 The left image in (a) and the left image in (b) are both 25 μm; Figure 1 The distance between the two silver wires is 50 μm. Figure 1The left image in (a) is 10 μm; Figure 1 The left image in (b) is 50 μm; Figure 1 The left image in (c) is 25 μm; Figure 1 The left picture in (d) is 50 μm. Its size did not change significantly after selective wetting by liquid metal (ad right). Among them, gallium indium alloy (EGaIn) was selected as the liquid metal. EGaIn has a low melting temperature of 16 °C and stable conductive properties. We deposited 400 nm thick silver wires on silicon wafers with line widths of 25 μm and 50 μm. The distance between lines ranged from 10 μm to 50 μm. The surface of the silicon wafer was pre-spin-coated with a smooth surface of dextran layer. After drying, EGaIn was applied to the silver wire. Due to its poor affinity for dextran and high reactivity with silver, EGaIn selectively fell off the dextran surface and wetted on the silver-covered area, forming a liquid metal-based circuit.

[0059] like Figure 2 As shown in the figure, a circuit based on liquid metal is displayed on a Soft-IBA substrate. The line widths are (a) 5 μm, (b) 30 μm, (c) 100 μm, and (d) 200 μm, respectively. After the liquid metal circuit is formed on the surface of the dextran layer, a 500 μm thick soft-IBA precursor liquid is covered on the circuit and solidified in situ to form a flexible substrate. The entire sample is then immersed in deionized water, and the water immediately dissolves the dextran layer, causing the flexible substrate and the liquid metal circuit to automatically fall off. The minimum width of the transferred liquid metal circuit can reach 5 μm.

[0060] like Figure 3 As shown in the figure, the resistance change rate of liquid metal stretchable circuits with different line widths under different strains. The liquid metal circuit on the flexible substrate (soft-IBA) can form a continuous conductive path. Under a tensile strain of 300%, the resistance of the 100 μm liquid metal circuit increases by about 3.9 times. When the line width increases to 200 μm and 500 μm, the liquid metal circuit can show electrical stability under higher tensile strains. Under a tensile strain of 380%, the resistance only increases by 2.7 times and 1.4 times, respectively, showing excellent stretchability and electrical stability.

[0061] like Figure 4 As shown in the figure, the physical display of the stretchable wireless charging receiving coil based on liquid metal. The wireless charging receiving coil based on liquid metal is transferred to a flexible substrate (soft-IBA). The receiving coil has a regular shape and is stably conductive, with a resistance of about 12 Ω. Circular contacts are designed at both ends of the receiving coil to facilitate its stable conduction in the three-dimensional stretchable circuit.

[0062] like Figure 5 As shown in the figure, the voltage waveform applied to the transmitting coil is received by the liquid metal receiving coil and rectified to perform DC charging on the battery. A wireless charging device is used to apply a sine wave voltage with a peak value of 20 Vpp to the transmitting coil to generate AC power, which induces an alternating magnetic flux and an alternating current with a peak value of 12.32 Vpp in the liquid metal receiving coil. The AC power is then rectified into DC power with a voltage of about 6.1 V, which can be used to charge the battery for energy storage.

[0063] like Figure 6 As shown, Figure 6 (a) Optical microscope image of a through-hole cross section after electroless copper plating. Figure 6 (bc) A partial enlarged view of the through-hole cross section. The metallization of the through-hole is based on a chemical copper plating process, in which a layer of copper can be deposited in the through-hole at room temperature and pressure without applying any conditions. The copper plating rate is 3 μm / h, and the thickness of the copper layer in the through-hole is 30 μm. Considering that stress concentration will occur at the through-hole when the integrated device is stretched and deformed, which may cause the integrated device to break under tension, stiff-IBA precursor liquid is used to solidify the through-hole when making a three-dimensional stretchable integrated device, which can effectively isolate stress and enhance the mechanical stability of the stretchable three-dimensional integrated circuit.

[0064] like Figure 7 As shown, the circuit diagram of the wireless charging / rectifier module / photosensitive sensor module multi-module integrated device. In order to verify the reliability of the stretchable three-dimensional integrated circuit, the circuit diagram of the wireless charging / rectifier module / photosensitive sensor module multi-module integrated device was designed. A wireless charging device is used to apply a sinusoidal voltage to the transmitting coil to generate alternating current, which induces alternating magnetic flux and alternating current in the liquid metal receiving coil. The alternating current is converted into direct current through a rectifier bridge to charge the battery and store energy. In the photosensitive sensor module, the transistor is NPN type, model 8050, the resistor R has a resistance of 100 K, and the photoresistor R G The resistance value is 2.6 K in a bright environment and 0.44 M in a dark environment. The base potential of the transistor is adjusted by changing the resistance of the photoresistor. When the base potential of the transistor is 0.7 V higher than the emitter potential, the transistor is in the on state and the LED is lit, demonstrating the function of light sensitivity.

[0065] like Figure 8As shown, the physical picture of the wireless charging / rectifier module / photosensitive sensor module multi-module three-dimensional integrated device (a) is shown, and its working state in a dark environment (b) and the integrated device can still work normally under tension (c) and torsion (d) conditions are shown. The physical picture of the multi-module three-dimensional integrated device is shown. The rigid island array is made using stiff-&soft-IBA substrate. Functional devices are placed on each rigid island to isolate the stress concentration generated during the stretching process, so that the functional devices are effectively protected. The figure shows the physical picture of the sample in a bright environment and a dark environment (a, b). The device is divided into two layers. The lower layer is a liquid metal receiving coil and the upper layer is a rectifier module / photosensitive sensor module circuit. The layers are stably connected through metalized through holes. In a bright environment, the LED does not emit light (a), and in a dark environment, the LED is lit (b), proving that the three-dimensional circuit can normally realize its function. And the physical picture of the device under biaxial tension and torsion is shown, in which the LED still maintains the same brightness even under various deformation conditions, proving the feasibility of the prepared three-dimensional integrated circuit.

[0066] like Fig. 9 As shown, the voltage and current change curves at both ends of the battery when the integrated device performs the wireless charging function, where the voltage gradually increases during the charging process and the current stabilizes at around 0.55 mA, proving that the integrated device can effectively collect energy from long radio waves and demonstrates the potential for electronic skin with energy autonomy and long-term continuous operation.

[0067] like Fig.10 As shown, the voltage and current change curves across the battery (a) and the LED (b) when the integrated device performs the light-sensitive sensing function and lights up the LED. Fig.10 (a) is the curve of voltage and current variation across the battery of the integrated device in bright and dark environments. In a bright environment, the transistor in the integrated device cannot be turned on, and the resistance in the circuit is extremely large, so the current is almost zero and the voltage remains at 3 V; in a dark environment, due to the increase in the resistance of the photoresistor, the base potential of the transistor increases, and the transistor is turned on, so the current in the entire circuit increases sharply to about 3.8 mA, and the voltage decreases. This is a voltage drop phenomenon caused by the battery. Fig.10 (b) shows the voltage and current curves of the LED in bright and dark environments. In bright environments, the transistors in the integrated device cannot be turned on, and the LED is in the off state, so its current and voltage are both zero; in dark environments, the LED is in the on state, and its voltage is 1.9 V and its current is 3.6 mA, which is consistent with the voltage and current changes of the battery. This proves that the modules of the integrated device can function normally, successfully verifying the reliability of the stretchable three-dimensional integrated circuit.

[0068] Example 2 Same as Example 1, except that In step 2, the mass percentage of the aqueous solution of dextran is 10 wt %; In step 4, the UV exposure treatment time is 8 s and the development time is 30 s.

[0069] In step seven, 2% by weight of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide (TPO) is added as a photoinitiator.

[0070] Example 3 Same as Example 1, except that In step 2, the mass percentage of the aqueous solution of dextran is 30wt%; In step 4, the UV exposure treatment time is 12 s and the development time is 20 s.

[0071] The present invention describes preferred embodiments and their effects. However, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0072] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a stretchable three-dimensional integrated circuit, characterized in that: The following steps are involved: preparing a silver-based circuit structure on a substrate; selectively wetting a silver-based circuit structure using liquid metal to form a liquid metal-based circuit; The Soft-IBA precursor liquid is directly poured onto the liquid metal circuit, and the Soft-IBA precursor liquid is cured, and then the substrate is peeled off to obtain a single-layer stretchable circuit; Multiple single-layer stretchable circuits are stacked and corresponding through holes are set between the layers by physical punching; then a conductive layer is deposited in the through holes to make the layers conductive, thus obtaining a stretchable three-dimensional integrated circuit.

2. The method for preparing a stretchable three-dimensional integrated circuit according to claim 1, characterized in that: A silver-based circuit structure is prepared on a substrate, comprising: preparing a sacrificial layer on a substrate; Coating photoresist on the sacrificial layer and baking to obtain a photoresist layer; The photoresist layer is exposed to UV light with the assistance of a mask. After UV exposure, it is immersed in a developer. After washing and drying, chromium and silver are sequentially deposited on the surface of the immersed sample by thermal evaporation coating, and then it is stripped in an acetone solvent, thereby preparing a silver-based circuit structure on the substrate.

3. The method for preparing a stretchable three-dimensional integrated circuit according to claim 2, characterized in that: The sacrificial layer is formed by spin coating an aqueous solution of dextran on a substrate; the mass percentage of the aqueous solution of dextran is 10-30 wt%.

4. The method for preparing a stretchable three-dimensional integrated circuit according to claim 3, characterized in that: The substrate is peeled off by immersing the cured sample in deionized water to dissolve the sacrificial layer, thereby peeling off the substrate.

5. The method for preparing a stretchable three-dimensional integrated circuit according to claim 2, characterized in that: The baking temperature is 110-120°C and the baking time is 60-80 seconds. The UV exposure time is 8~12 s, and the development time is 20~30 s.

6. The method for preparing a stretchable three-dimensional integrated circuit according to claim 1, characterized in that: The liquid metal is a gallium-indium alloy.

7. The method for preparing a stretchable three-dimensional integrated circuit according to claim 1, characterized in that: The Soft-IBA precursor solution is prepared by mixing isobornyl acrylate, benzyl acrylate, and polyurethane acrylate in a mass ratio of 2: 5: 3, adding 1-2% of the total mass of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator, and then stirring for 6-8 hours to obtain the soft-IBA precursor solution.

8. The method for preparing a stretchable three-dimensional integrated circuit according to claim 1, characterized in that: Between the single-layer stretchable circuits in the stacked arrangement, the contacts of the circuits are cured using Stiff-IBA precursor liquid; The Stiff-IBA precursor solution is prepared by mixing isobornyl acrylate, benzyl acrylate and polyurethane acrylate in a mass ratio of 5: 2: 3, adding 1-2% of the total mass of diphenyl (2, 4, 6-trimethylbenzoyl) phosphine oxide as a photoinitiator, and stirring for 6-8 hours to obtain the Stiff-IBA precursor solution.

9. A stretchable three-dimensional integrated circuit made by the method according to any one of claims 1 to 8.

10. Application of the stretchable three-dimensional integrated circuit according to claim 9 in flexible electronic devices.

Images