Method for producing a liquid metal conductive pattern on a substrate

Abstract

The application provides a preparation method of a liquid metal conductive pattern on a substrate, comprising the following steps: preparing a composite material with low thermal expansion coefficient as the substrate; arranging a mask pattern on the substrate according to a target pattern; spin-coating photoresist on the surface of the mask pattern, and exposing and developing the spin-coated photoresist to form a pattern structure layer; depositing liquid metal on the substrate with the pattern structure layer by a thermal evaporation method to form a liquid metal conductive film; and removing the pattern structure layer from the substrate with the liquid metal conductive film to form a liquid metal conductive pattern. By using the application, the problem of the mismatch between the flexible substrate and the thermal expansion coefficient of the photoresist affecting the function of the prepared conductive pattern can be solved, so that a high-precision conductive pattern can be prepared.

Description

Technical Field

[0001] This invention relates to the field of flexible electronics technology, and more specifically, to a method for fabricating room-temperature liquid metal conductive patterns on a substrate. Background Technology

[0002] With the continuous development of flexible electronics, flexible electronic systems are playing an increasingly important role in fields such as smart wearables, human-computer interaction, electronic skin, and implantable medical devices. At the same time, this places higher demands on their multifunctionality and integration.

[0003] Room temperature liquid metals, being liquid at room temperature and possessing the excellent electrical and thermal conductivity of metals, have become one of the core materials for flexible electronic systems. However, due to their high surface tension and the tendency to form an insulating oxide layer on their surface, patterning using traditional printing methods is difficult. Patent document CN112996262A proposes a method of pre-printing silver patterns on a substrate to enhance the wettability between the polymer substrate interface and the liquid metal, thereby achieving patterning. This method cannot obtain conductive liquid metal patterns in one step and requires patterning in an acidic environment, making the preparation process and environment quite complex. Patent document CN109215889A proposes uniformly dispersing magnetic particles into liquid metal and using a magnetic field to control the movement of the magnetic particles to achieve patterning of the liquid metal.

[0004] To address the aforementioned issues, there is an urgent need for a method that can directly fabricate liquid metal conductive patterns on flexible substrates. Summary of the Invention

[0005] In view of the above problems, the purpose of this invention is to provide a method for preparing liquid metal conductive patterns on a substrate, so as to solve the problem that the mismatch of the thermal expansion coefficients of the flexible substrate and the photoresist affects the function of the prepared conductive patterns, and to prepare high-precision conductive patterns.

[0006] This invention provides a method for preparing a liquid metal conductive pattern on a substrate, comprising the following steps:

[0007] S1: Prepare a composite material with a low coefficient of thermal expansion as a substrate;

[0008] S2: Set a mask pattern on the substrate according to the target pattern;

[0009] S3: Spin-coat the photoresist onto the surface of the mask pattern, and expose and develop the spin-coated photoresist to form a pattern structure layer;

[0010] S4: Liquid metal is deposited onto a substrate having the patterned structure layer by thermal evaporation to form a liquid metal conductive film;

[0011] S5: The substrate on which the liquid metal conductive film is deposited is subjected to a process to remove the pattern structure layer to form a liquid metal conductive pattern.

[0012] Preferably, in step S1, a composite material with a low coefficient of thermal expansion is prepared by combining flexible materials and nanomaterials in a preset ratio.

[0013] Preferably, the flexible material includes any one of dimethylsiloxane, polyurethane, polyimide, vinyl chloride, platinum-catalyzed silica gel, styrene-based thermoplastic elastomer, and hydrogenated styrene-based thermoplastic elastomer.

[0014] Preferably, the nanomaterial includes any one of silicon carbide fiber, silicon dioxide nanoparticles, carbon fiber, and graphene.

[0015] Preferably, during the process of setting a mask pattern on the substrate according to the target pattern, a rectangular array pattern is set around the target pattern.

[0016] Preferably, the photoresist includes either positive photoresist or negative photoresist.

[0017] Preferably, before step S4, the substrate having the patterned structure layer is cooled using alcohol or liquid nitrogen, wherein the substrate is cooled to below -30°C at a rate of less than 1.5°C / min.

[0018] Preferably, the substrate is cooled to -30℃ to -80℃ at a rate of 0.8-1.2℃ / min.

[0019] Preferably, the liquid metal is a conductive metallic material that is liquid at room temperature, including one or more of mercury, gallium, indium, tin, gallium-indium alloy, gallium-indium-tin alloy, transition metal, gallium-indium alloy doped with solid non-metallic elements, and gallium-indium-tin alloy.

[0020] Preferably, the liquid metal conductive film is treated with acetone or N-methylpyrrolidone to dissolve the patterned structure layer.

[0021] Preferably, the thickness of the liquid metal conductive pattern is 200nm-2µm, the minimum line width is 200nm, the minimum circle radius is 850nm, and the conductivity is 5×10⁻⁶. 5 S / m-4×10 6 S / m.

[0022] As can be seen from the above technical solution, the method for preparing liquid metal conductive patterns on a substrate provided by the present invention prepares a substrate with a low coefficient of thermal expansion, and then prepares a thin liquid metal conductive pattern on the substrate using a microfabrication method combining low-temperature deposition and photolithography. The thin liquid metal conductive pattern is a high-precision liquid metal pattern with a thickness and linewidth at the sub-micron level. This solves the problem of the mismatch between the thermal expansion coefficients of the flexible substrate and the photoresist affecting the function of the conductive pattern. Moreover, the prepared pattern is a high-precision pattern with initial conductivity, and has good application prospects in the fields of flexible electronics, especially flexible chips and electronic skin.

[0023] To achieve the foregoing and related objectives, one or more aspects of the invention include the features that will be described in detail below. The following description and accompanying drawings illustrate certain exemplary aspects of the invention. However, these aspects indicate only a few of the various ways in which the principles of the invention can be used. Furthermore, the invention is intended to encompass all such aspects and their equivalents. Attached Figure Description

[0024] Other objects and results of the invention will become more apparent and readily understood with reference to the following description taken in conjunction with the accompanying drawings. In the drawings:

[0025] Figure 1 This is a schematic diagram of the photomask pattern used in photolithography in Embodiment 1 of the present invention.

[0026] Figure 2 This refers to the liquid metal dot pattern on the Pi substrate in Embodiment 1 of the present invention.

[0027] Figure 3 This is a liquid metal linear pattern on a Pi substrate in Embodiment 2 of the present invention.

[0028] Figure 4 This is a liquid metal linear pattern on a PDMS@SiO2 elastic substrate in Embodiment 3 of the present invention.

[0029] Figure 5 This is the liquid metal strain sensor on the PDMS@SiO2 elastic substrate in Embodiment 4 of the present invention.

[0030] Figure 6 This is the liquid metal antenna on the PDMS@SiO2 elastic substrate in Embodiment 4 of the present invention.

[0031] Figure 7 This is the liquid metal circuit on the PDMS@SiO2 elastic substrate in Embodiment 4 of the present invention.

[0032] Figure 8 This is a schematic diagram of a method for preparing a liquid metal conductive pattern on a substrate according to an embodiment of the present invention.

[0033] Among them, 1. target shape pattern, 2. stress relief rectangular pattern, and 3. Cr shading area.

[0034] In all the accompanying drawings, the same reference numerals indicate similar or corresponding features or functions. Detailed Implementation

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This application specification and embodiments are merely exemplary.

[0038] To address the aforementioned problem of how to resolve the mismatch in thermal expansion coefficients between flexible substrates and photoresists affecting the functionality of fabricated conductive patterns, this invention proposes a method for fabricating liquid metal conductive patterns on a substrate. By preparing a substrate with a low thermal expansion coefficient, a thin liquid metal conductive pattern is fabricated on the substrate using a microfabrication method combining low-temperature deposition and photolithography. The liquid metal conductive pattern fabricated using this method has a thickness of 200 nm-2 μm, a minimum line width of 200 nm, a minimum circle radius of 850 nm, and a conductivity of 5 × 10⁻⁶. 5 S / m-4×10 6 S / m is a high-precision pattern with initial conductivity, which has good application prospects in flexible electronics, especially flexible chips and electronic skin.

[0039] Figure 8 A method flow diagram for fabricating liquid metal conductive patterns on a substrate according to an embodiment of the present invention is shown.

[0040] like Figure 8 As shown, the method for preparing a liquid metal conductive pattern on a substrate provided by the present invention includes the following steps:

[0041] S1: Prepare a composite material with a low coefficient of thermal expansion as a substrate;

[0042] S2: Set a mask pattern on the substrate according to the target pattern;

[0043] S3: Spin-coat the photoresist onto the surface of the mask pattern, and expose and develop the spin-coated photoresist to form a pattern structure layer;

[0044] S4: Liquid metal is deposited onto a substrate having the patterned structure layer by thermal evaporation to form a liquid metal conductive film;

[0045] S5: The substrate on which the liquid metal conductive film is deposited is subjected to a process to remove the pattern structure layer, thereby forming a liquid metal conductive pattern.

[0046] In step S1, a composite material with a low coefficient of thermal expansion is prepared by combining flexible materials and nanomaterials in a preset ratio. The flexible materials include, but are not limited to, dimethylsiloxane, polyurethane, polyimide, vinyl chloride, platinum-catalyzed silica gel, styrene-based thermoplastic elastomers, and hydrogenated styrene-based thermoplastic elastomers. The nanomaterials include, but are not limited to, silicon carbide fibers, silica nanoparticles, carbon fibers, and graphene. In specific applications, the specific ratio of flexible materials to nanomaterials can be set according to actual conditions to prepare the composite material with a low coefficient of thermal expansion; no specific limitation is made here.

[0047] In step S2, during the process of setting a mask pattern on the substrate according to the target pattern, a rectangular array pattern is set around the target pattern. That is, by designing a suitable pattern to obtain the target pattern and releasing thermal stress in subsequent operations, i.e., the target pattern is drawn according to the subsequently selected photoresist and a rectangular array pattern is placed around it to achieve subsequent thermal stress release.

[0048] In step S3, the photoresist can be any one of the following: positive photoresist AZ5214, AZP4620, AZ9260, AZ50XT, and negative photoresist SU-8, NR1500P. In specific applications, the appropriate photoresist specification can be selected based on the actual situation; no specific limitations are made here.

[0049] Before step S4, the substrate having the patterned structure layer is cooled using alcohol or liquid nitrogen. Specifically, as an example, the substrate is cooled to below -30°C and held for 1 hour, with a cooling rate of less than 1.5°C / min. Preferably, the substrate is cooled to -30°C to -80°C, with a cooling rate of 0.8-1.2°C / min.

[0050] In step S4, a continuous thin film of liquid metal is deposited on the substrate using a thermal evaporation method. During the low-temperature deposition process, the temperature of the substrate is maintained below the liquid-solid transition temperature of the liquid metal (below -30°C, preferably, the substrate is cooled to -30°C to -80°C), and the heating and cooling rate is controlled to be less than 1.5°C / min, thereby avoiding stress and strain accumulation.

[0051] Liquid metals are conductive metallic materials that are liquid at room temperature, including one or more of mercury, gallium, indium, tin, gallium-indium alloys, gallium-indium-tin alloys, transition metals, gallium-indium alloys doped with solid non-metallic elements, and gallium-indium-tin alloys.

[0052] In step S5, the patterned structure layer is dissolved in the liquid metal conductive film using acetone or N-methylpyrrolidone. The thickness of the prepared liquid metal conductive pattern can be controlled between 200 nm and 2 μm by adjusting the evaporation rate and time; the minimum line width of the prepared liquid metal conductive pattern is 200 nm, the minimum circle radius of the prepared liquid metal conductive pattern is 850 nm, and the conductivity of the prepared liquid metal conductive pattern is 5 × 10⁻⁶. 5 S / m-4×10 6 S / m.

[0053] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of the present invention, without departing from the spirit and scope of the technical solutions of the present invention, should all be covered within the protection scope of the present invention.

[0054] Example 1:

[0055] In this embodiment, pure gallium (Ga) is used as the liquid metal, Pi substrate is used as the substrate, and AZ5214 photoresist is used as the photoresist.

[0056] Step 1: Spin coat AZ5214 onto the substrate using a dot-pattern mask with a stress-relieving rectangular array. Figure 1 As shown), the target shape pattern 1, the stress-relieving rectangular pattern 2, and the Cr-plated light-shielding area 3 are exposed and developed after being irradiated with 365nm ultraviolet light for 5.5s to obtain a substrate with a dot array pattern.

[0057] Step 2: Place the substrate and the evaporation boat containing 0.1 ml of liquid Ga into a vacuum chamber, and evacuate to a vacuum level of 1.0 × 10⁻⁶. -3 Pa;

[0058] Step 3: Cool the substrate to -80°C using ethanol at a rate of 1°C / min, hold at that temperature for 1 hour, and then continue evacuating to a vacuum level of 3.0 × 10⁻⁶. -4 Pa;

[0059] Step 4: Electric heating evaporation boat, heating parameters: the current is increased from 30A / min to 175A, and the current is kept constant. The liquid metal is heated and evaporated, and deposited on the low-temperature substrate. Evaporation continues until the liquid metal in the boat is completely evaporated, and a continuous conductive film of liquid metal is obtained on the substrate.

[0060] Step 5: Immerse the obtained film in acetone until the excess liquid metal film on the pattern is peeled off from the substrate, leaving the desired liquid metal pattern;

[0061] The surface morphology of the liquid metal dot array pattern obtained through the above experimental steps is as follows: Figure 2 As shown.

[0062] Example 2:

[0063] In this embodiment, pure gallium is used as the liquid metal, Pi substrate is used as the substrate, and PMMA is used as the photoresist.

[0064] Step 1: Spin-coat PMMA onto the substrate, expose and develop it using an electron beam along a pre-drawn pattern to obtain a substrate with a linear pattern.

[0065] Step 2: Place the substrate and the evaporation boat 2 containing 0.1 ml of liquid Ga into a vacuum chamber, and evacuate to a vacuum level of 1.0 × 10⁻⁶. -3 Pa;

[0066] Step 3: Cool the substrate to -80°C using ethanol at a rate of 1°C / min, hold for 1 hour, and then continue evacuating to a vacuum level of 3.0 × 10⁻⁶. -4 Pa;

[0067] Step 4: Electric heating evaporation boat, heating parameters: the current rate is increased from 30A / min to 175A, and the current is kept constant. The liquid metal is heated and evaporated, and deposited on the low-temperature substrate. Evaporation continues until the liquid metal in the boat is completely evaporated, and a continuous conductive thin film of liquid metal is obtained on the substrate.

[0068] Step 5: Immerse the obtained film with NMP (N-methylpyrrolidone) until the excess liquid metal film on the pattern is peeled off from the substrate, leaving the desired liquid metal line pattern.

[0069] The surface morphology of the liquid metal thin film pattern obtained through the above experimental steps is as follows: Figure 3 As shown.

[0070] Example 3:

[0071] In this embodiment, pure gallium is used as the liquid metal, PDMS@SiO2 substrate is used as the substrate, and AZ5214 photoresist is used as the photoresist.

[0072] Step 1: Spin-coat AZ5214 onto the substrate, use a linear pattern mask, irradiate with 365nm ultraviolet light for 5.5s, and then expose and develop to obtain a substrate with a linear pattern.

[0073] Step 2: Place the substrate and the evaporation boat containing 0.1 ml of liquid Ga into a vacuum chamber, and evacuate to a vacuum level of 1.0 × 10⁻⁶. -3 Pa;

[0074] Step 3: Cool the substrate to -80°C using ethanol at a rate of 1°C / min, hold at that temperature for 1 hour, and then continue evacuating to a vacuum level of 3.0 × 10⁻⁶. -4 Pa;

[0075] Step 4: Electric heating evaporation boat, heating parameters: the current rate is increased from 30A / min to 175A, and the current is kept constant. The liquid metal is heated and evaporated, and deposited on the low-temperature substrate. Evaporation continues until the liquid metal in the boat is completely evaporated, and a continuous conductive thin film of liquid metal is obtained on the substrate.

[0076] Step 5: Immerse the resulting film in acetone until the excess liquid metal film on the pattern is peeled off from the substrate, leaving the desired liquid metal pattern.

[0077] The surface morphology of the liquid metal linear pattern obtained through the above experimental steps is as follows: Figure 4 As shown.

[0078] Example 4:

[0079] In this embodiment, pure gallium is used as the liquid metal, PDMS@SiO2 substrate is used as the substrate, and AZ9260 photoresist is used as the photoresist.

[0080] Step 1: Spin-coat AZ9260 onto the substrate, and use an antenna-shaped, strain gauge and mechanical mask corresponding to the required circuit. Irradiate with 365nm ultraviolet light for 11.5s and then expose and develop to obtain a substrate with a linear pattern.

[0081] Step 2: Place the substrate and the evaporation boat containing 0.1 ml of liquid Ga into a vacuum chamber, and evacuate to a vacuum level of 1.0 × 10⁻⁶. -3 Pa;

[0082] Step 3: Cool the substrate to -80°C using ethanol at a rate of 1°C / min, hold at that temperature for 1 hour, and then continue evacuating to a vacuum level of 3.0 × 10⁻⁶. -4 Pa;

[0083] Step 4: Electrically heated evaporation boat. Heating parameters: The current is increased from 30A / min to 175A, and the current is kept constant. The liquid metal is heated and evaporated, and deposited on the low-temperature substrate. The liquid metal in the evaporation boat is completely evaporated, and a continuous conductive thin film of liquid metal is obtained on the substrate.

[0084] Step 5: Immerse the obtained thin film in acetone until the excess liquid metal film on the pattern is peeled off from the substrate, leaving the desired liquid metal pattern. Antennas (e.g., Figure 5 As shown), strain gauges (such as...) Figure 6 As shown in the diagram, the liquid metal pattern of the required circuit is used to place LED chips in the circuit, resulting in a flexible circuit as shown in the diagram. Figure 7 As shown.

[0085] The embodiments described above provide a detailed explanation of the technical solution of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a liquid metal conductive pattern on a substrate, characterized in that, Includes the following steps: S1: Prepare a composite material with a low coefficient of thermal expansion as a substrate; S2: Set a mask pattern on the substrate according to the target pattern; S3: Spin-coat the photoresist onto the surface of the mask pattern, and expose and develop the spin-coated photoresist to form a pattern structure layer; S4: Liquid metal is deposited onto a substrate having the patterned structure layer by thermal evaporation to form a liquid metal conductive film; S5: The substrate on which the liquid metal conductive film is deposited is subjected to a process to remove the pattern structure layer to form a liquid metal conductive pattern.

2. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 1, characterized in that, In step S1, flexible materials and nanomaterials are combined in a preset ratio to prepare a composite material with a low coefficient of thermal expansion.

3. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 2, characterized in that, The flexible material includes any one of dimethylsiloxane, polyurethane, polyimide, vinyl chloride, platinum-catalyzed silica gel, styrene-based thermoplastic elastomer, and hydrogenated styrene-based thermoplastic elastomer.

4. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 2, characterized in that, The nanomaterials include any one of silicon carbide fibers, silicon dioxide nanoparticles, carbon fibers, and graphene.

5. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 1, characterized in that, During the process of setting a mask pattern on the substrate according to the target pattern, a rectangular array pattern is set around the target pattern.

6. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 1, characterized in that, The photoresist includes either positive photoresist or negative photoresist.

7. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 1, characterized in that, Before step S4, the substrate having the patterned structure layer is cooled using alcohol or liquid nitrogen, wherein the substrate is cooled to below -30°C at a rate of less than 1.5°C / min.

8. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 7, characterized in that, The substrate is cooled to -30℃ to -80℃ at a rate of 0.8-1.2℃ / min.

9. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 1, characterized in that, The liquid metal is a conductive metallic material that is liquid at room temperature, including one or more of mercury, gallium, indium, tin, gallium-indium alloys, gallium-indium-tin alloys, transition metals, gallium-indium alloys doped with solid non-metallic elements, and gallium-indium-tin alloys.

10. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 1, characterized in that, The patterned structure layer of the liquid metal conductive film is dissolved by acetone or N-methylpyrrolidone.

11. The method for preparing a liquid metal conductive pattern on a substrate as described in claim 1, characterized in that, The liquid metal conductive pattern has a thickness of 200nm-2µm, a minimum line width of 200nm, a minimum circle radius of 850nm, and a conductivity of 5×10⁻⁶. 5 S / m-4×10 6 S / m.

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