A flexible electronic transfer printing method based on liquid foam stamp

Abstract

The application discloses a flexible electronic transfer printing method based on liquid foam stamp, and belongs to the technical field of micro-nano processing and flexible electronics. First, a flexible electronic film is prepared on the surface of a substrate by means of photolithography technology, and the flexible electronic film is separated from the substrate and floated in water by dissolving a sacrifice layer in water. Second, a surfactant is added to the water, and air is injected into the solution through a nozzle to generate liquid foam composed of dense small bubbles; as the liquid foam increases, the flexible electronic film is lifted above the water surface, and the liquid foam serves as a stamp in the transfer printing process. Finally, the flexible electronic film is rapidly transferred to a complex target surface by means of the liquid foam stamp, and the liquid foam stamp is removed and the surface is cleaned to complete the transfer printing process. The flexible electronic transfer printing method provided by the application uses a liquid foam stamp as an auxiliary to complete the transfer printing process, and can realize self-supporting and adapt to various complex surfaces, and realize conformal effect on multiple concave-convex surfaces at the same time.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of micro-nano processing and flexible electronics, and relates to a flexible electronic transfer printing method based on a liquid foam stamp. BACKGROUND

[0002] Flexible electronic devices are electronic devices that can be stretched or deformed, and have advantages such as light weight, flexibility and conformal attachment compared with traditional silicon-based electronics, which are more conducive to the development of emerging fields such as wearable devices, flexible consumer electronics, implantable bioelectronics, soft robots and optoelectronics. At present, the thickness of flexible electronic devices has been reduced to sub-micron and nanometer levels, and has a wide application prospect. However, it is difficult to transfer ultra-thin flexible electronic devices to a target surface: on the one hand, the devices themselves are fragile and can be easily damaged during operation; on the other hand, without support, the ultra-thin flexible devices are prone to wrinkling or curling. Transfer printing technology using a stamp as a temporary carrier can transfer ultra-thin electronic devices from a rigid substrate to a target surface. The form of the stamp includes: a solid stamp, such as the elastic balloon used by Sim et al. of the University of Houston, which can improve the contact effect with complex surfaces, but the strain force generated during transfer printing of the solid stamp can cause damage to the fragile flexible electronic structure; a liquid stamp, also known as water transfer printing, which has poor transfer printing accuracy, and because the liquid cannot be self-supported, it is affected by gravity, environment and container shape, so it cannot be shaped and fixed, so there are many limitations in the transfer printing process; a reflowable material stamp (such as sugar), which can change its form between solid and liquid. Although there has been progress in shape-preserving transfer printing and precision control, the presence of stress can still cause damage to the device, and the high viscosity and low flowability of liquid sugar also limit the area and geometry of the target surface. SUMMARY

[0003] The application proposes a flexible electronic transfer printing method based on a liquid foam stamp. Compared with the previously reported transfer printing methods, the transfer printing method based on the liquid foam stamp can achieve self-supporting while adapting to various complex surfaces.

[0004] To achieve the above purpose, the technical scheme adopted by the application is:

[0005] A flexible electronic transfer printing method based on a liquid foam stamp, comprising the following steps:

[0006] (1) A flexible electronic film 1 is prepared on a substrate surface 3 by photolithography technology, and a sacrificial layer 2 is between the flexible electronic film 1 and the substrate surface 3; it is placed in water, the sacrificial layer is dissolved by water, the flexible electronic film 1 is separated from the substrate 3, and the flexible electronic film 1 floats in the liquid water.

[0007] Further, the substrate 3 is silicon, glass or polymethyl methacrylate.

[0008] Further, the sacrificial layer 2 is made of water-soluble polyacrylic acid (PAA), polyvinyl alcohol (PVA) or dextran.

[0009] (2) After adding a surfactant to the liquid obtained in step (1), air is injected into the solution through a nozzle to generate a liquid foam consisting of dense small bubbles.

[0010] Further, 3g of surfactant is added per 100ml of water.

[0011] Further, the surfactant includes sodium stearate, sodium oleate or sodium laurate.

[0012] Further, the flow rate of the injected air is 500ml / min.

[0013] Further, the outlet diameter of the nozzle is 100μm.

[0014] (3) As the liquid foam increases, the flexible electronic film 1 is lifted above the liquid surface, at which time the liquid foam serves as a temporary carrier for the flexible electronic film transfer, i.e., as a stamp during the transfer process.

[0015] (4) The flexible electronic film 1 is quickly transferred to a complex target surface using the liquid foam stamp, the liquid foam stamp is removed and the surface is cleaned to complete the transfer process. Because the liquid foam has good fluidity and the shear force between the small bubbles is small, the liquid foam stamp will not damage the flexible electronic film during the transfer process.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] (1) In the flexible electronic transfer method based on the liquid foam stamp, the liquid foam stamp has the characteristics of a liquid stamp: maintaining fluidity to adapt to complex surfaces of various shapes (such as an I-beam structure containing multiple concave-convex surfaces, which can achieve conformal effect with multiple concave-convex surfaces at the same time; wrapping effect on micron-level low-curvature surfaces); and the characteristics of a solid stamp: self-supporting without using containers or other tools, avoiding the wrinkling phenomenon of the flexible electronic film.

[0018] (1) The present application has no pre-stress during the transfer process, maintains the shape of the flexible electronic film, and does not damage the flexible electronic film, so that the flexible electronic film can be transferred to the target surface without damage or with low damage, and the residual liquid during the transfer will not cause the electromagnetic performance of the flexible electronic film to decrease; has good deformability and easy-to-remove characteristics, and can be applied to fragile target surfaces (such as soft animals, plants, and liquid drops); the overall process is simple; the process has good universality and is suitable for a plurality of transfer materials and substrate materials. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of the flexible electronic film freely immersed in water;

[0020] Figure 2 is a schematic diagram of using a nozzle to generate a liquid foam to lift the flexible electronic film to the liquid surface;

[0021] Figure 3 is a schematic diagram of transferring the liquid foam and the flexible electronic film to the target surface;

[0022] Figure 4 is a schematic diagram of the flexible electronic film successfully transferred to the target surface;

[0023] Figure 5 is a schematic diagram of the overall process of transferring the flexible electronic film using the liquid foam stamp;

[0024] Figure 6 is a schematic diagram of the flexible electronic film being lifted by the liquid foam stamp; Figure 6 (a) is a schematic diagram of the liquid foam lifting the flexible electronic film; Figure 6 (b) is a partial enlarged view of the flexible electronic film;

[0025] Figure 7 is a schematic diagram of the flexible electronic film being transferred to a complex surface of a skin model with non-uniform curvature; Figure 7 (a) is a surface diagram of the skin model after transfer; Figure 7 (b) is a partial enlarged view of the skin model;

[0026] Figure 8 is a schematic diagram of the flexible electronic film being transferred to the surface of an I-beam with multiple concave and convex surfaces; Figure 8 (a) is a surface fitting effect diagram of the I-beam after transfer; Figure 8 (b) is a surface fitting effect diagram of the I-beam after transfer;

[0027] Figure 9 is a schematic diagram of the flexible electronic film being transferred to the surface of a fragile and easily damaged stamen; Figure 9 (a) is a surface effect diagram of the flexible electronic film being transferred to the surface of the stamen; Figure 9 (b) is a partial enlarged view of the stamen;

[0028] Figure 10 is a schematic diagram of flexible electronic film transfer to the surface of a moving soft-bodied animal;

[0029] Figure 11 is a schematic diagram of flexible electronic film transfer to the surface of a low-curvature needle;

[0030] In the figure: 1 flexible electronic film, 2 sacrificial layer, 3 substrate, 4 liquid foam stamp, 5 target surface. DETAILED DESCRIPTION

[0031] The embodiments of the present application will be described in detail below with reference to the technical solutions and the accompanying drawings.

[0032] A flexible electronic transfer method based on a liquid foam stamp, comprising the following steps:

[0033] Step 1: Take silicon as the hard substrate 3, water-soluble polyacrylic acid (PAA) as the sacrificial layer 2, and prepare the flexible electronic film 1 on the substrate surface 3 by photolithography technology, such as Figure 1 ; soak it in water until the sacrificial layer 2 is completely dissolved, and the flexible electronic film 1 is detached from the surface of the substrate 3 and floats on the water surface.

[0034] Step 2: Add 3g of sodium stearate powder to 100ml of water to obtain a mixed solution. Use a nozzle to blow gas into the mixed solution to obtain a liquid foam 4 composed of fine bubbles, and the liquid foam 4 will lift up the flexible electronic film 1, such as Figure 2 .

[0035] Step 3: Use the liquid foam 4 as a transfer stamp to take out the flexible electronic film 1 from the mixed solution, and place the liquid foam 4 with the surface attached flexible electronic film 1 close to the transfer target 5, and directly place it to adhere to the target surface 5, which can make the flexible electronic film 1 form conformal contact with the complex surface of the receptor containing multiple concave-convex surfaces, such as Figure 3 .

[0036] Step 4: After the flexible electronic film 1 contacts the target 5, the liquid foam 4 is naturally broken or artificially destroyed, and the flexible electronic film 1 will be in close contact with the target surface, completing the transfer process, such as Figure 4 .

[0037] As shown in Figure 5 , it is a schematic diagram of the transfer process based on the liquid foam stamp.

[0038] As shown in Figure 6 , the liquid foam provided by the embodiment of the present application lifts up the flexible electronic film. In this example, the overall thickness of the flexible electronic film 1 is 150nm, and the length and width of the patterned structure are both 10mm.

[0039] As Figure 7 shown, it is an effect diagram of transferring the flexible electronic film to the artificial skin surface provided by the embodiment of the present application. In this example, the target surface is a skin surface with non-uniform curvature, the overall thickness of the flexible electronic film 1 is 150 nm, and the length and width of the patterned structure are both 10 mm. The flexible electronic film can be well transferred to the skin model surface.

[0040] As Figure 8 shown, it is an effect diagram of transferring the flexible electronic film to the I-beam surface provided by the embodiment of the present application. In this example, the target surface 5 is an I-beam surface with multiple concave-convex surfaces, the overall thickness of the flexible electronic film 1 is 150 nm, and the length and width of the patterned structure are both 10 mm. The flexible electronic film 1 can be well transferred to the I-beam surface, realizing the conformal effect on the multiple concave-convex structures.

[0041] As Figure 9 shown, it is an effect diagram of transferring the flexible electronic film to the flower stigma surface provided by the embodiment of the present application. In this example, the target surface 5 is a fragile and easily damaged flower stigma surface, the overall thickness of the flexible electronic film 1 is 150 nm, and the length and width of the patterned structure are both 10 mm. The flexible electronic film 1 can be well transferred to the fragile flower stigma surface.

[0042] As Figure 10 shown, it is an effect diagram of transferring the flexible electronic film to the soft-bodied animal surface provided by the embodiment of the present application. In this example, the target surface 5 is a soft-bodied animal surface, the overall thickness of the flexible electronic film 1 is 150 nm, and the length and width of the patterned structure are both 10 mm. The flexible electronic film 1 can be well transferred to the soft-bodied animal surface without affecting the normal activity of the animal.

[0043] As Figure 11 shown, it is an effect diagram of transferring the flexible electronic film to the needle tip surface provided by the embodiment of the present application. In this example, the target surface 5 is a needle surface with a curvature of 250 μm, the overall thickness of the flexible electronic film 1 is 150 nm, and the length and width of the patterned structure are both 10 mm. The flexible electronic film 1 can be well transferred to the needle tip surface, realizing the wrapping effect on the low-curvature surface.

[0044] The above-described embodiments only express the implementation of the present application, but cannot be interpreted as a limitation on the scope of the present patent. It should be noted that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application.

Claims

1. A flexible electronic transfer printing method based on liquid foam stamp, characterized in that, The flexible electronic transfer printing method uses a liquid foam stamp as an auxiliary to complete the transfer printing process, which can realize self-supporting while adapting to various complex surfaces and realizing conformal effect with multiple concave-convex surfaces at the same time; the method comprises the following steps: (1) a flexible electronic film is prepared on a substrate surface by photolithography, and a sacrificial layer is between the flexible electronic film and the substrate surface; the flexible electronic film is placed in water, and the sacrificial layer is dissolved by water, so that the flexible electronic film is separated from the substrate and floats in water; (2) a surfactant is added to the water, and air is injected into the solution through a nozzle to generate a liquid foam composed of dense small bubbles; the outlet diameter of the nozzle is 100 μm, and the flow rate of the injected air is 500 ml / min; (3) as the liquid foam increases, the flexible electronic film is lifted above the water surface, at this time, the liquid foam serves as a temporary carrier for the transfer printing of the flexible electronic film and as a stamp in the transfer printing process; (4) the flexible electronic film is quickly transferred to a complex target surface by using the liquid foam stamp, the liquid foam stamp is removed and the surface is cleaned to complete the transfer printing process.

2. A flexible electronic transfer printing method based on liquid foam stamp according to claim 1, characterized in that, The substrate in step (1) is silicon, glass or polymethyl methacrylate.

3. A flexible electronic transfer printing method based on liquid foam stamp according to claim 1, characterized in that, The sacrificial layer material in step (1) is water-soluble polyacrylic acid PAA, polyvinyl alcohol PVA or glucose.

4. The flexible electronic transfer printing method based on liquid foam stamp according to claim 1, characterized in that, In step (2), 3 g of surfactant is added to every 100 ml of water.

5. The flexible electronic transfer printing method based on liquid foam stamp according to claim 1, wherein, In step (2), the surfactant includes sodium stearate, sodium oleate or sodium laurate.

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