Embedded liquid metal microstructure electrodes, flexible pressure sensor arrays and their fabrication methods

Abstract

This invention discloses an embedded liquid metal microstructure electrode, a flexible pressure sensor array, and a fabrication method thereof, solving the technical problems of low sensitivity and high crosstalk in existing flexible pressure sensor arrays. The embedded liquid metal microstructure electrode includes a first flexible substrate, a first liquid metal layer, and a first encapsulation layer. The lower surface of the first flexible substrate is planar, and the upper surface is evenly distributed with multiple microconical structures arranged in an array. The cone portion of each microconical structure faces upward and is flush with the upper surface of the first flexible substrate. The first liquid metal layer covers the upper surface of the first flexible substrate and all the microconical structures. The first encapsulation layer covers the side of the first liquid metal layer away from the upper surface of the first flexible substrate. Furthermore, this invention provides a fabrication method for this microstructure electrode, a flexible pressure sensor array based on this microstructure electrode, and a fabrication method thereof. This flexible pressure sensor array exhibits high sensitivity and low crosstalk.

Description

Technical Field

[0001] This invention relates to flexible electronics technology, specifically to an embedded liquid metal microstructure electrode, a flexible pressure sensor array, and a fabrication method thereof. Background Technology

[0002] With the development of electronic technology, flexible wearable devices have become a major direction for the future development of electronic devices. Among them, flexible pressure sensors or flexible tactile electronic skin have great potential in robotic tactile perception, wearable electronic devices, and smart healthcare. Flexible pressure sensors or flexible tactile electronic skin can convert external physical stimuli into electrical signals, simulating the mechanical pressure stimulation of the external environment perceived by human skin, thus maintaining the same flexibility and stretchability as natural human skin. Taking flexible pressure sensors as an example, they are composed of a flexible substrate and flexible electrode materials, possessing good ductility and the ability to maintain good conductivity even when subjected to repeated deformation. In recent years, researchers have used a liquid metal material—gallium-based alloys—as flexible electrode materials. Taking gallium-indium alloys as an example, this liquid metal has a melting point below 30°C, is liquid at room temperature, and possesses good electrical and thermal conductivity; furthermore, gallium-indium alloys are non-toxic and harmless to the human body, therefore they can be used to fabricate flexible pressure sensors.

[0003] Among various flexible pressure sensors, capacitive pressure sensors are widely praised for their simple design, excellent stability, low power consumption, and temperature independence. Furthermore, since the fabrication of microstructured electrodes can significantly improve the pressure sensitivity of electrodes, liquid metal-based microstructured electrodes (introducing microstructures onto a flexible substrate and then covering the microstructures with liquid metal to form liquid metal microstructured electrodes) can effectively improve the sensitivity of flexible pressure sensors. However, because liquid metal is an amorphous liquid phase and is encapsulated by external gallium oxide, it is difficult to print liquid metal on micron- or nanon-scale rough structures. Most studies use rigid metals such as metalophilic copper or gold as intermediate layers to improve the affinity between the liquid metal and the substrate; however, because rigid metals affect the inherent tensile properties of liquid metals, this method greatly limits the ductility of flexible pressure sensors.

[0004] Furthermore, to meet the demands of more complex applications, flexible pressure sensors must not only possess high pressure sensitivity but also maintain stable signal output under various deformation conditions. Existing flexible pressure sensors (or electronic skin) typically employ a multi-layered stacked structure; however, during bending, torsion, and stretching, insufficient adhesion strength between interfaces can affect signal stability, making the interface layers prone to separation, leading to relative displacement of pixels and subsequent signal distortion. Therefore, devices corresponding to this type of electronic skin face the challenge of operating effectively under complex mechanical deformation, such as robotic operations that require sensor deformation to achieve conformal contact on the surface, such as recognizing curved patterns.

[0005] Furthermore, for arrayed pressure sensors, it is essential to minimize crosstalk between pixels to ensure accurate measurements. Typically, signal crosstalk occurs between sensing elements due to stress dispersion caused by their shared plane. When a pixel is subjected to external pressure, its deformation inevitably propagates to the surrounding area, causing responses in neighboring pixels. While system calibration is often used to mitigate unwanted signals, it also requires complex circuitry and additional power consumption.

[0006] In summary, existing flexible pressure sensor arrays suffer from problems such as low sensitivity, instability under mechanical deformation, and high crosstalk. Summary of the Invention

[0007] The purpose of this invention is to solve the technical problems of low sensitivity, instability under mechanical deformation, and large crosstalk in existing flexible pressure sensor arrays, and to provide an embedded liquid metal microstructure electrode, a flexible pressure sensor array, and a fabrication method.

[0008] To achieve the above-mentioned objectives, the technical solution provided by this invention is as follows:

[0009] This invention provides an embedded liquid metal microstructure electrode, which is characterized by:

[0010] It includes a first flexible substrate, a first liquid metal layer, and a first encapsulation layer;

[0011] The lower surface of the first flexible substrate is flat, and the upper surface is grooved, with multiple microconical structures arranged in an array in the groove; the cone of each microconical structure faces upward and is flush with the upper surface of the first flexible substrate;

[0012] The first liquid metal layer is located on the upper surface of the first flexible substrate and covers all the microconical structures;

[0013] The first encapsulation layer covers the surface of the first liquid metal layer.

[0014] Furthermore, the height of the microconical structure region is equal to the thickness of the first flexible substrate.

[0015] The first flexible substrate is made of PDMS or silicone material;

[0016] The first liquid metal layer is made of gallium-based alloy.

[0017] The present invention also provides a method for fabricating the above-mentioned embedded liquid metal microstructure electrode, comprising the following steps:

[0018] Step [1] Process a metal mask with a hollowed-out electrode pattern;

[0019] Step [2]: Prepare a first flexible substrate and attach a sacrificial layer to the upper surface of the first flexible substrate;

[0020] Step [3]: Fabricate embedded microcone structures on the surface of the first flexible substrate.

[0021] 3.1) Place the first flexible substrate on the two-dimensional platform of the femtosecond laser lens system;

[0022] 3.2) Place the metal mask obtained in step 1) on top of the first flexible substrate with the attached sacrificial layer, and focus the femtosecond laser onto the sacrificial layer through a lens;

[0023] 3.3) Configure the bow-shaped scanning program for the 2D platform;

[0024] 3.4) Based on the scanning program set in step 3.3), the two-dimensional platform is moved and the femtosecond laser ablates multiple patterned embedded microcone structures extending to the upper surface of the first flexible substrate on the sacrificial layer through the hollowed-out electrode pattern on the metal mask.

[0025] Step [4] Fabrication of embedded liquid metal microstructure electrodes

[0026] 4.1) Perform oxygen plasma surface hydrophilic modification treatment on the first flexible substrate after processing in step 3.4);

[0027] 4.2) Wet the upper surface of the first flexible substrate after hydrophilic modification with deionized water so that the deionized water covers each microcone structure;

[0028] 4.3) Drop liquid metal onto the surface of the deionized water to cover it;

[0029] 4.4) Drop a hydrogel solution onto the upper surface of the liquid metal to completely encapsulate it;

[0030] 4.5) The first flexible substrate with the drop-coated hydrogel solution and liquid metal is dried, the hydrogel solution solidifies, the deionized water evaporates, and the liquid metal covers all the microcone structures to form the first liquid metal layer.

[0031] 4.6) The solidified hydrogel is peeled off in sequence, the excess liquid metal on the surface of the first flexible substrate is absorbed, the sacrificial layer is peeled off, and then the patterned embedded liquid metal microstructure electrode is obtained after encapsulation.

[0032] Furthermore, step [1] specifically involves:

[0033] 1.1) Prepare a thin metal film and place it on the processing platform of the femtosecond laser galvanometer system;

[0034] 1.2) Adjust the height of the processing platform so that the femtosecond laser is focused onto the metal thin film through the galvanometer;

[0035] 1.3) Draw the electrode pattern to be processed in the background program of the femtosecond laser galvanometer system and set the processing program corresponding to the electrode pattern; the scanning speed of the femtosecond laser galvanometer system is 0.1 to 10 mm / s;

[0036] 1.4) Based on the processing program set in step 1.3), the femtosecond laser is controlled to cut electrode patterns on the metal thin film to form a metal mask with hollowed-out electrode patterns; the center wavelength of the femtosecond laser is 325nm~1200nm, the pulse width is 30fs~150fs, the repetition frequency is 10Hz~100KHz, and the laser power is 100mW~1000mW.

[0037] Further, in step [2], the first flexible substrate is made of PDMS or silicone material; the sacrificial layer is polyethylene terephthalate tape with a thickness of 10μm to 50μm;

[0038] In step 3.4), the moving speed of the two-dimensional platform is 0.1 to 10 mm / s; the center wavelength of the femtosecond laser is 325 nm to 1200 nm, the pulse width is 30 fs to 150 fs, the repetition frequency is 10 Hz to 100 kHz, and the laser power is 100 mW to 1000 mW.

[0039] In step 4.3), the liquid metal is a gallium-based alloy, and the thickness of the droplet coating is 2-5 mm;

[0040] In step 4.4), the hydrogel solution is a polyvinyl alcohol solution with a mass ratio of 5-20%, and the thickness of the drop coating is 0.5-2 mm.

[0041] Meanwhile, the present invention also provides a flexible pressure sensor array, which is characterized by including a liquid metal flat plate electrode and the aforementioned embedded liquid metal microstructure electrode.

[0042] The liquid metal flat electrode includes a second flexible substrate, a second liquid metal layer, and a second encapsulation layer;

[0043] The second flexible substrate has the same dimensions as the first flexible substrate, and the upper surface of the second flexible substrate is evenly distributed with multiple protrusions;

[0044] The second liquid metal layer includes multiple liquid metal regions, which are arranged in an array and disposed on the lower surface of the second flexible substrate; the positions of the multiple liquid metal regions correspond one-to-one with the positions of the multiple microcone structures.

[0045] The second encapsulation layer covers the lower surface of the second liquid metal layer and the second flexible substrate;

[0046] The first encapsulation layer and the second encapsulation layer are assembled by plasma bonding.

[0047] Furthermore, anti-adhesion particles are sprayed between the first and second encapsulation layers, located between each liquid metal region and the corresponding microcone structure.

[0048] Meanwhile, the present invention also provides a method for fabricating the above-mentioned flexible pressure sensor array, comprising the following steps:

[0049] Step 1: Fabrication of embedded liquid metal microstructure electrodes

[0050] The corresponding embedded liquid metal microstructure electrode was prepared according to the aforementioned method for preparing embedded liquid metal microstructure electrodes.

[0051] Step 2: Preparation of liquid metal flat plate electrode

[0052] 2.1) Prepare a second flexible substrate and place it on the processing platform of the femtosecond laser galvanometer system;

[0053] 2.2) Adjust the height of the processing platform so that the femtosecond laser is focused onto the upper surface of the second flexible substrate through the galvanometer;

[0054] 2.3) Draw the raised pattern in the background program of the femtosecond laser galvanometer system and set the corresponding processing program for the raised pattern;

[0055] 2.4) According to the processing program set in step 2.3), the processing platform is moved, and the femtosecond laser processes a protruding structure on the upper surface of the flexible substrate.

[0056] 2.5) Using the same metal mask as when fabricating embedded liquid metal microstructure electrodes, liquid metal is applied to the lower surface of the second flexible substrate by template printing, thereby forming a second liquid metal layer;

[0057] 2.6) Encapsulate the lower surface of the second flexible substrate having the second liquid metal layer to obtain a liquid metal flat plate electrode;

[0058] Step 3: Assemble the embedded liquid metal microstructure electrode prepared in Step 1 and the liquid metal plate electrode obtained in Step 2.6) to obtain a flexible pressure sensor array.

[0059] Furthermore, step three specifically involves:

[0060] 3.1) The embedded liquid metal microstructure electrode prepared in step one and the liquid metal plate electrode obtained in step 2.6) are subjected to oxygen plasma surface modification treatment respectively;

[0061] 3.2) Bring the first encapsulation layer and the second encapsulation layer close together and spray anti-adhesion particles between them; the anti-adhesion particles are located between each liquid metal region and the corresponding microcone structure;

[0062] 3.3) The first and second encapsulation layers are bonded together with their sides close to each other to obtain a flexible pressure sensor array with an embedded liquid metal microstructure.

[0063] Further, in step 3.2), the anti-adhesion particles are SiO2 nanoparticles, with a diameter of 10nm to 100nm for each particle.

[0064] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0065] 1. The present invention introduces a microconical structure and a first liquid metal layer on a first flexible substrate to obtain an embedded liquid metal microstructure electrode. Compared with using copper and gold, which are compatible with liquid metal, as intermediate layers to improve the surface affinity between liquid metal and substrate, the introduction of the microconical structure in this application makes the flexibility of the electrode unaffected by rigid metal materials, and significantly improves mechanical stability and pressure sensitivity.

[0066] 2. The present invention is a flexible pressure sensor based on an embedded liquid metal microstructure electrode. Due to the introduction of the microstructure electrode, the sensitivity of the flexible pressure sensor is greatly improved.

[0067] 3. The pressure sensor array prepared by this invention has a robust interface adhesion and can work stably under deformations such as bending, stretching, and torsion, without problems such as delamination and pixel misalignment.

[0068] 4. The pressure sensor array prepared by this invention has low signal crosstalk and does not require additional complex circuit algorithms to process and filter the signal, thereby saving system costs and improving response speed.

[0069] 5. This invention addresses the shortcomings of current flexible sensor arrays in terms of flexibility and stability, which are limited to the recognition of planar patterns. The high-performance pressure sensor array prepared in this invention can achieve accurate recognition of curved surface patterns. Attached Figure Description

[0070] Figure 1 This is a schematic diagram of an embodiment of the embedded liquid metal microstructure electrode of the present invention.

[0071] Figure 2 This is a schematic flowchart illustrating an embodiment of the method for fabricating embedded liquid metal microstructure electrodes according to the present invention.

[0072] Figure 3 The images shown are electron microscope (EM) images and physical images of each layer structure in the embedded liquid metal microstructure electrode embodiment of the present invention, wherein: (a) is an EEM image of PDMS, (b) is a physical image of PDMS; (c) is an EEM image of PDMS with added liquid metal, (d) is a physical image of PDMS with added liquid metal; (e) is an EEM image of PDMS after encapsulation, and (f) is a physical image of PDMS after encapsulation.

[0073] Figure 4 These are physical images of the embedded liquid metal microstructure electrode of the present invention, wherein (a) is a physical image of the embedded PDMS microcone structure, and (b) is a physical image of the embedded liquid metal microstructure electrode.

[0074] Figure 5 This is a schematic diagram of the structure of an embodiment of the flexible pressure sensor array of the present invention.

[0075] Figure 6 This is a schematic flowchart of an embodiment of the flexible pressure sensor array fabrication method of the present invention.

[0076] Figure 7 This is a schematic diagram of the layered structure of an embodiment of the flexible pressure sensor array of the present invention.

[0077] Figure 8 The images shown are actual pictures of the flexible pressure sensor array of the present invention under different deformations, wherein (a) is a flat state picture, (b) is a stretched state picture, and (c) is a bent state picture.

[0078] Figure 9 The diagram shows a comparison of the crosstalk prevention capabilities of the flexible pressure sensor array of the present invention and a traditional sensor array. (a) is a schematic diagram of the crosstalk prevention capability of the traditional sensor array, and (b) is a schematic diagram of the crosstalk prevention capability of the flexible pressure sensor array of the present invention.

[0079] Figure 10 The diagram shows the pressure signal mapping of the flexible pressure sensor array of the present invention onto a 3D printed sphere model; wherein, (a) is a diagram of a 3D printed sphere model with the curved letter "SOFT", and (b) is a diagram of the dynamic process of the pressure signal mapping of the flexible pressure sensor array of the present invention onto the curved letter "S".

[0080] Figure 11 This is a diagram showing the capacitance signal mapping of the flexible pressure sensor array of the present invention to the curved letter "SOFT".

[0081] The attached figures are labeled as follows:

[0082] 1-First flexible substrate, 2-First liquid metal layer, 3-First encapsulation layer, 4-Micro cone structure, 5-Second flexible substrate, 6-Second liquid metal layer, 7-Second encapsulation layer, 8-Protrusion. Detailed Implementation

[0083] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0084] Reference Figure 1 This embodiment provides an embedded liquid metal microstructure electrode, including a first flexible substrate 1, a first liquid metal layer 2, and a first encapsulation layer 3.

[0085] The first flexible substrate 1 is a polymer material with high ductility, such as PDMS (polydimethylsiloxane) or silicone film-type flexible polymers. The lower surface of the first flexible substrate 1 is planar, and the upper surface is grooved. Multiple microcone structures 4 are arranged in an array within the groove, with the cone portion of each microcone structure 4 facing upwards and flush with the upper surface of the first flexible substrate 1. Generally, the height of the microcone structure 4 is a fraction of the thickness of the first flexible substrate 1. The height of the microcone structure 4 can be determined according to actual needs, and the position and number of the microcone structure 4 can be set.

[0086] The first liquid metal layer 2 is a metallic material that can remain liquid at room temperature (melting point below 30°C), and it covers the upper surface of the first flexible substrate 1 and all the microconical structures 4. In this embodiment, the first liquid metal layer 2 is selected from gallium-based alloys, such as gallium-indium alloy, gallium-indium-tin alloy, etc.

[0087] The first encapsulation layer 3 covers the surface of the first liquid metal layer and is used to protect the first liquid metal layer 2.

[0088] Reference Figure 2 , Figure 3 The fabrication method of the above-mentioned embedded liquid metal microstructure electrode is as follows:

[0089] Step [1] Process a metal mask with a hollowed-out electrode pattern.

[0090] 1.1) Prepare a thin metal film and place it on the processing platform of the femtosecond laser galvanometer system.

[0091] 1.2) Adjust the height of the processing platform so that the femtosecond laser is focused onto the metal thin film through the galvanometer.

[0092] 1.3) Draw the electrode pattern to be processed in the background program of the femtosecond laser galvanometer system and set the processing program corresponding to the electrode pattern. The scanning speed of the femtosecond laser galvanometer system is 0.1 to 10 mm / s.

[0093] 1.4) Based on the processing program set in step 1.3), the femtosecond laser is controlled to cut electrode patterns on the metal thin film to form a metal mask with hollowed-out electrode patterns.

[0094] In step 1.4), the center wavelength of the femtosecond laser is 325nm~1200nm, the pulse width is 30fs~150fs, the repetition frequency is 10Hz~100KHz, and the laser power is 100mW~1000mW.

[0095] Step [2] Prepare the first flexible substrate 1 and attach a sacrificial layer to the upper surface of the first flexible substrate 1.

[0096] In this embodiment, the first flexible substrate 1 is made of PDMS or silicone material; the sacrificial layer is PET (polyethylene terephthalate) tape, and its thickness is generally 10μm to 50μm.

[0097] Step [3]: Fabricate embedded microcone structure 4 on the upper surface of the first flexible substrate 1.

[0098] 3.1) Place the first flexible substrate 1 on the two-dimensional platform of the femtosecond laser lens system.

[0099] 3.2) Place the metal mask obtained in step 1.4) on the first flexible substrate 1 with the sacrificial layer attached, and focus the femtosecond laser onto the sacrificial layer through a lens.

[0100] 3.3) Configure the bow-shaped scanning program for the two-dimensional platform.

[0101] 3.4) Based on the scanning program set in step 3.3), the two-dimensional platform is controlled to move. The femtosecond laser ablates multiple patterned embedded microcone structures 4 extending to the upper surface of the first flexible substrate 1 on the sacrificial layer through the hollow electrode pattern on the metal mask.

[0102] In this embodiment, the moving speed of the two-dimensional platform is in the range of 0.1 to 10 mm / s; the center wavelength of the femtosecond laser is 325 nm to 1200 nm, the pulse width is 30 fs to 150 fs, the repetition frequency is 10 Hz to 100 kHz, and the laser power is 100 mW to 1000 mW.

[0103] This embodiment employs laser direct writing, a process in which a femtosecond laser directly scans the surface of a flexible substrate, significantly reducing processing time. The structure after laser direct writing is a microgroove type, which forms a microcone structure 4 through cross-scanning. The moving speed of the two-dimensional platform and the laser power simultaneously affect the height of the microcone structure 4; by adjusting the moving speed and laser power, the height of the microcone can reach 50–500 μm.

[0104] Step [4] Use water / hydrogel-assisted patterning method to prepare embedded liquid metal microstructure electrodes.

[0105] 4.1) Perform oxygen plasma surface hydrophilic modification treatment on the first flexible substrate 1 after processing in step 3.4).

[0106] 4.2) Wet the upper surface of the first flexible substrate 1 after hydrophilic modification with deionized water, so that the deionized water covers each microcone structure 4.

[0107] 4.3) Drop-coat liquid metal onto the surface of the deionized water. The liquid metal is a gallium-based alloy, and the thickness of the drop coating is 2–5 mm.

[0108] 4.4) Apply a hydrogel solution to the upper surface of the liquid metal to completely encapsulate it.

[0109] In this embodiment, the hydrogel solution is a polyvinyl alcohol (PVA) solution with a mass ratio of 5-20%, and the thickness of the drop coating is 0.5-2 mm.

[0110] 4.5) The first flexible substrate 1, on which the hydrogel solution and liquid metal are drop-coated, is placed in an oven to dry. The hydrogel solution solidifies, the deionized water evaporates, and the liquid metal covers all the microcone structures 4 to form the first liquid metal layer 2.

[0111] 4.6) Sequentially peel off the solidified hydrogel, absorb the excess liquid metal on the surface of the first flexible substrate 1, peel off the sacrificial layer, and then encapsulate to obtain a patterned embedded liquid metal microstructure electrode.

[0112] Figure 4 In the figure, (a) is a physical image of the original embedded PDMS microcone substrate, and (b) is a physical image of the embedded microstructure liquid metal electrode after being covered with liquid metal. The liquid metal coverage is relatively uniform.

[0113] This invention induces microstructures on the surface of a flexible substrate using a femtosecond laser, with the femtosecond laser pulse width being extremely short (10⁻⁶). -15 Extremely high peak power density (~10) 15 W / cm 2 Furthermore, the minimum spot size can reach hundreds of nanometers, enabling high-precision processing and the fabrication of highly integrated electrode patterns. This method overcomes the limitation of liquid metal wettability on rough surfaces, fabricating embedded microstructured liquid electrodes with significantly improved mechanical stability and pressure sensitivity. Flexible material substrates with circuit patterns, after surface oxygen plasma modification, can be bonded and assembled to form high-performance capacitive pressure sensing arrays.

[0114] Therefore, refer to Figure 5 This embodiment also provides a flexible pressure sensor array, including a liquid metal plate electrode and an embedded liquid metal microstructure electrode, wherein the liquid metal plate electrode includes a second flexible substrate 5, a second liquid metal layer 6 and a second encapsulation layer 7.

[0115] The material and size of the second flexible substrate 5 are the same as those of the first flexible substrate 1. The upper surface of the second flexible substrate 5 is evenly distributed with multiple protrusions 8 (i.e. bumps).

[0116] The second liquid metal layer 6 includes multiple liquid metal regions arranged in an array on the lower surface of the second flexible substrate 5; the positions of the multiple liquid metal regions correspond one-to-one with the positions of the multiple microcone structures 4. The material of the second liquid metal layer 6 is the same as that of the first liquid metal layer 2.

[0117] The second encapsulation layer 7 covers the lower surface of the second liquid metal layer 6 and the second flexible substrate 5.

[0118] Anti-adhesion particles are sprayed between the first encapsulation layer 3 and the second encapsulation layer 7. These particles are located between each liquid metal region and the corresponding microcone structure 4. Then, the first encapsulation layer 3 and the second encapsulation layer 7 are assembled by plasma bonding to form a flexible pressure sensor array.

[0119] The flexible pressure sensor array in this embodiment uses liquid metal as the flexible electrode material, a thin encapsulation layer flexible substrate material, and silica nanoparticles as the dielectric layer to form a capacitor structure. All materials used in this sensor are highly ductile, thus the sensor itself possesses excellent flexibility and ductility. The upper layer of the sensor structure includes liquid metal planar electrodes, and the lower layer includes embedded liquid metal microstructure electrodes. After the upper and lower layers are bonded together, the interfaces between the sensor array units are bonded together, exhibiting strong interfacial adhesion, thus maintaining stability under various deformation conditions.

[0120] Therefore, in combination Figure 6 , Figure 7 This embodiment provides a method for fabricating a flexible pressure sensor array, including the following steps:

[0121] Step 1: Fabrication of embedded liquid metal microstructure electrodes

[0122] The embedded liquid metal microstructure electrode was prepared according to the aforementioned method, which will not be described in detail here.

[0123] Step 2: Preparation of liquid metal flat plate electrode

[0124] 2.1) Prepare the second flexible substrate 5 and place it on the processing platform of the femtosecond laser galvanometer system.

[0125] 2.2) Adjust the height of the processing platform so that the femtosecond laser is focused onto the upper surface of the second flexible substrate 5 through the galvanometer.

[0126] 2.3) Draw the raised pattern in the background program of the femtosecond laser galvanometer system and set the corresponding processing program for the raised pattern.

[0127] 2.4) The processing platform is moved according to the processing program set in step 2.3), and the femtosecond laser processes a protruding structure on the upper surface of the flexible substrate.

[0128] 2.5) Using the same metal mask as in step [1] for preparing the embedded liquid metal microstructure electrode, liquid metal is applied to the lower surface of the second flexible substrate 5 by template printing, thereby forming the second liquid metal layer 6.

[0129] 2.6) Encapsulate the lower surface of the second flexible substrate 5 having the second liquid metal layer 6 to obtain a liquid metal flat plate electrode.

[0130] Step 3: Assemble the embedded liquid metal microstructure electrode prepared according to the aforementioned method and the liquid metal plate electrode obtained in step 2.6) to obtain a flexible pressure sensor array. Specifically:

[0131] 3.1) Perform oxygen plasma surface modification treatment on the embedded liquid metal microstructure electrode and the liquid metal plate electrode obtained in step 2.6).

[0132] 3.2) Bring the first encapsulation layer 3 and the second encapsulation layer 7 close together and spray anti-adhesion particles between them. The anti-adhesion particles are located between each liquid metal area and the corresponding microcone structure 4.

[0133] In this embodiment, the anti-adhesion particles are SiO2 nanoparticles, with a diameter of 10nm to 100nm for each particle.

[0134] 3.3) The first encapsulation layer 3 and the second encapsulation layer 7 are bonded together on their close sides to obtain a flexible pressure sensor array with an embedded liquid metal microstructure.

[0135] Figure 8 The image shown is of the flexible pressure sensor array of this embodiment and its physical image under tensile and bending deformation, indicating that the prepared liquid metal pressure sensor array has good flexibility and can be effectively applied to flexible electronics fields such as wearable devices, flexible electronic skin, and flexible robots.

[0136] Figure 9 The diagram shows the crosstalk resistance of the pressure sensor array. Compared with the 58% crosstalk between sensor array units without bonding interfaces or surface protrusions, the crosstalk of the sensor array with bonding interfaces and protrusions prepared in this embodiment is reduced to 7.9%, which is a significant improvement.

[0137] Figure 10 The figure shows a 3D printed sphere model with the curved letter "SOFT" and the dynamic process of the flexible pressure sensor array prepared in this embodiment mapping the pressure signal of the curved letter "S". As can be seen from the figure, the flexible pressure sensor array has good flexibility and high accuracy of pressure signal mapping. Figure 11 This is a signal mapping diagram of the letter "SOFT" on a curved surface, and the mapping of each part is relatively clear.

[0138] In summary, the present invention provides an embedded microstructure electrode and a flexible pressure sensor array based on the microstructure electrode. By selectively printing liquid metal onto the embedded microconical structure, the sensor sensitivity is significantly improved and it can work stably under deformation conditions, while reducing crosstalk between sensor arrays.

[0139] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the present invention. Although the above embodiments have described the present invention in detail, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, and such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. An embedded liquid metal microstructure electrode, characterized in that: It includes a first flexible substrate (1), a first liquid metal layer (2), and a first encapsulation layer (3); The lower surface of the first flexible substrate (1) is a plane, and the upper surface is a groove, and a plurality of micro cone structures (4) are arranged in an array in the groove; the cone of each micro cone structure (4) faces upward and is flush with the upper surface of the first flexible substrate (1); The first liquid metal layer (2) is located on the upper surface of the first flexible substrate (1) and covers all the microconical structures (4); The first encapsulation layer (3) covers the surface of the first liquid metal layer (2).

2. The embedded liquid metal microstructure electrode according to claim 1, characterized in that: The height of the microconical structure (4) is equal to the thickness of the first flexible substrate (1). The first flexible substrate (1) is made of PDMS or silicone material; The first liquid metal layer (2) is made of gallium-based alloy.

3. A method for fabricating the embedded liquid metal microstructure electrode according to claim 1 or 2, characterized in that, Includes the following steps: Step [1] Process a metal mask with a hollowed-out electrode pattern; Step [2] Prepare a first flexible substrate (1) and attach a sacrificial layer to the upper surface of the first flexible substrate (1); Step [3]: Fabricate an embedded microcone structure (4) on the upper surface of the first flexible substrate (1); 3.1) Place the first flexible substrate (1) on the two-dimensional platform of the femtosecond laser lens system; 3.2) Place the metal mask obtained in step 1) on top of the first flexible substrate (1) with the attached sacrificial layer, and focus the femtosecond laser onto the sacrificial layer through a lens; 3.3) Configure the bow-shaped scanning program for the 2D platform; 3.4) Based on the scanning program set in step 3.3), the two-dimensional platform is controlled to move. The femtosecond laser ablates multiple patterned embedded microcone structures (4) extending to the upper surface of the first flexible substrate (1) on the sacrificial layer through the hollow electrode pattern on the metal mask. Step [4]: ​​Fabricate embedded liquid metal microstructure electrodes; 4.1) Perform oxygen plasma surface hydrophilic modification treatment on the first flexible substrate (1) after processing in step 3.4); 4.2) Wet the upper surface of the first flexible substrate (1) after hydrophilic modification with deionized water so that the deionized water covers each microcone structure (4); 4.3) Drop liquid metal onto the surface of the deionized water to cover it; 4.4) Drop a hydrogel solution onto the upper surface of the liquid metal to completely encapsulate it; 4.5) The first flexible substrate (1) with drop-coated hydrogel solution and liquid metal is dried, the hydrogel solution is solidified, the deionized water evaporates, and the liquid metal covers all microcone structures (4) to form the first liquid metal layer (2). 4.6) The solidified hydrogel is peeled off in sequence, the excess liquid metal on the surface of the first flexible substrate (1) is absorbed, the sacrificial layer is peeled off, and then the patterned embedded liquid metal microstructure electrode is obtained after encapsulation.

4. The method for fabricating an embedded liquid metal microstructure electrode according to claim 3, characterized in that, Step [1] specifically involves: 1.1) Prepare a thin metal film and place it on the processing platform of the femtosecond laser galvanometer system; 1.2) Adjust the height of the processing platform so that the femtosecond laser is focused onto the metal thin film through the galvanometer; 1.3) Draw the electrode pattern to be processed in the background program of the femtosecond laser galvanometer system and set the processing program corresponding to the electrode pattern; the scanning speed of the femtosecond laser galvanometer system is 0.1 to 10 mm / s; 1.4) Based on the processing program set in step 1.3), the femtosecond laser is controlled to cut electrode patterns on the metal thin film to form a metal mask with hollowed-out electrode patterns; the center wavelength of the femtosecond laser is 325nm~1200nm, the pulse width is 30fs~150fs, the repetition frequency is 10Hz~100KHz, and the laser power is 100mW~1000mW.

5. The method for fabricating an embedded liquid metal microstructure electrode according to claim 3 or 4, characterized in that: In step [2], the first flexible substrate (1) is made of PDMS or silicone material; the sacrificial layer is polyethylene terephthalate tape with a thickness of 10μm to 50μm; In step 3.4), the moving speed of the two-dimensional platform is 0.1 to 10 mm / s; the center wavelength of the femtosecond laser is 325 nm to 1200 nm, the pulse width is 30 fs to 150 fs, the repetition frequency is 10 Hz to 100 kHz, and the laser power is 100 mW to 1000 mW. In step 4.3), the liquid metal is a gallium-based alloy, and the thickness of the droplet coating is 2-5 mm; In step 4.4), the hydrogel solution is a polyvinyl alcohol solution with a mass ratio of 5-20%, and the thickness of the drop coating is 0.5-2 mm.

6. A flexible pressure sensor array, characterized in that: Includes liquid metal flat plate electrodes and embedded liquid metal microstructure electrodes as described in claim 1 or 2; The liquid metal flat plate electrode includes a second flexible substrate (5), a second liquid metal layer (6), and a second encapsulation layer (7); The second flexible substrate (5) has the same dimensions as the first flexible substrate (1), and the upper surface of the second flexible substrate (5) is evenly distributed with multiple protrusions (8); The second liquid metal layer (6) includes multiple liquid metal regions, which are arranged in an array and disposed on the lower surface of the second flexible substrate (5); the positions of the multiple liquid metal regions correspond one-to-one with the positions of the multiple microcone structures (4); The second encapsulation layer (7) covers the lower surface of the second liquid metal layer (6) and the second flexible substrate (5); The first encapsulation layer (3) and the second encapsulation layer (7) are assembled by plasma bonding.

7. The flexible pressure sensor array according to claim 6, characterized in that: Anti-adhesion particles are sprayed between the first encapsulation layer (3) and the second encapsulation layer (7), which are located between each liquid metal region and the corresponding microcone structure (4).

8. A method for fabricating a flexible pressure sensor array, characterized in that, Includes the following steps: Step 1: Prepare the embedded liquid metal microstructure electrode as described in claim 1 or 2 An embedded liquid metal microstructure electrode was prepared according to the preparation method described in claim 3, 4 or 5; Step 2: Preparation of liquid metal flat plate electrode 2.1) Prepare the second flexible substrate (5) and place it on the processing platform of the femtosecond laser galvanometer system; 2.2) Adjust the height of the processing platform so that the femtosecond laser is focused onto the upper surface of the second flexible substrate (5) through the galvanometer; 2.3) Draw the raised pattern in the background program of the femtosecond laser galvanometer system and set the corresponding processing program for the raised pattern; 2.4) According to the processing program set in step 2.3), the processing platform is moved, and the femtosecond laser processes a protruding structure on the upper surface of the flexible substrate. 2.5) Using the same metal mask as when preparing the embedded liquid metal microstructure electrode, liquid metal is applied to the lower surface of the second flexible substrate (5) by template printing, thereby forming the second liquid metal layer (6); 2.6) Encapsulate the lower surface of the second flexible substrate (5) having the second liquid metal layer (6) to obtain a liquid metal plate electrode; Step 3: Assemble the embedded liquid metal microstructure electrode prepared in Step 1 and the liquid metal plate electrode obtained in Step 2.6) to obtain a flexible pressure sensor array.

9. The method for fabricating a flexible pressure sensor array according to claim 8, characterized in that, Step three specifically involves: 3.1) The embedded liquid metal microstructure electrode prepared in step one and the liquid metal plate electrode obtained in step 2.6) are subjected to oxygen plasma surface modification treatment respectively; 3.2) Bring the first encapsulation layer (3) and the second encapsulation layer (7) close together and spray anti-adhesion particles between them; the anti-adhesion particles are located between each liquid metal region and the corresponding microcone structure (4); 3.3) The first encapsulation layer (3) and the second encapsulation layer (7) are bonded together on their sides to obtain a flexible pressure sensor array with an embedded liquid metal microstructure.

10. The method for fabricating a flexible pressure sensor array according to claim 9, characterized in that: In step 3.2), the anti-adhesion particles are SiO2 nanoparticles with a diameter of 10nm to 100nm for each particle.

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