Integrated flexible piezoresistive sensor based on laser direct writing and preparation method thereof

Abstract

The invention relates to a preparation method of an integrated flexible piezoresistive sensor based on laser direct writing, and the preparation method comprises the following steps: mixing a metal salt and a reducing ligand in a solvent to obtain a metal precursor solution; coating a flexible substrate with the obtained metal precursor solution, and drying; carrying out laser direct writing on the obtained flexible substrate according to a preset laser scanning track, and respectively preparing a sensing layer and an electrode layer; and adding glue between the sensing layer and the electrode layer, and pressing to obtain the integrated flexible piezoresistive sensor based on laser direct writing. The laser direct writing method provided by the invention has the characteristics of low cost, high efficiency, controllability and the like, and the sensing layer and the electrode layer of the piezoresistive sensor can be manufactured as required. The assembled piezoresistive sensor is excellent in sensitivity, monitoring range and stability, and can provide powerful support for wearable bioelectronics development; meanwhile, the integrated piezoresistive sensor provided by the invention can realize industrial batch production.

Description

Technical Field

[0001] The present invention relates to the technical field of pressure sensors, and in particular to an integrated flexible piezoresistive sensor based on laser direct writing and a preparation method thereof. Background Art

[0002] Flexible pressure sensors are devices or apparatuses that can sense pressure signals and convert them into electrical signals according to certain rules. The preparation of traditional pressure sensors mainly relies on silicon-based rigid substrates. The resulting devices are not only bulky in size and mass, but also difficult to directly integrate on the surface of the device (especially complex curved surfaces). Emerging flexible pressure sensors have the advantages of being light, portable, and bendable, and show broad application prospects in aerospace, medical health, consumer electronics and other fields. At present, flexible stress sensors can be divided into resistive, capacitive and piezoelectric types according to their sensing mechanism. Among them, resistive pressure sensors have the advantages of simple design, high sensitivity, fast response speed and low noise, and are one of the most widely used flexible sensors today.

[0003] A typical flexible resistive pressure sensor (piezoresistive sensor for short) consists of two parts: a sensing layer and an electrode layer, which are prepared on the surface of a polymer substrate and assembled face to face. The variable resistance characteristic of the former reflects the magnitude of the applied force, and the corresponding signal is further transmitted to the back-end processing system by the latter. The latest research shows that a porous structure formed by doping with metal nanomaterials (such as gold, silver, and copper) based on graphite-based materials with excellent mechanical properties such as graphene and carbon nanotubes can meet the high sensitivity and wide range performance requirements of flexible sensors and is an ideal sensing layer structure. The electrode layer is usually a dense structure formed by sintering metal nanomaterials to ensure stable signal transmission. The development of efficient, fast, and low-cost high-performance piezoresistive sensor manufacturing technology has become one of the research hotspots in this field.

[0004] Due to the complex process and high cost of traditional subtractive methods, the commonly used construction method for flexible pressure sensors is currently the printed electronics approach. For the nano-metal-doped graphite-based sensing layer, nanoparticles are first prepared by wet chemical methods (such as hydrothermal methods), and carbon-based materials are prepared by CVD / chemical stripping methods. The mixture is then mixed by physical methods and stabilizers, dispersants, and viscosity modifiers are added to form a mixture. Subsequently, it is patterned on the target substrate surface using methods such as screen printing, inkjet printing, and ink direct writing. The ligands are removed by post-processing drying to obtain the sensing layer. For the flexible electrode layer, after the nanomaterials are synthesized, they are purified, stabilized, and viscosity modifiers are added to prepare a printable ink. Subsequently, the printing method mentioned above is used for patterning, and the metallurgical connection between the nanoparticles in the ink is achieved through sintering post-processing techniques (such as thermal sintering, chemical sintering, laser sintering, etc.) to form the final dense conductive structure.

[0005] Laser direct writing technology is an emerging technology that uses focused laser to selectively irradiate flexible substrates or materials coated on their surfaces to achieve additive and conversion processes. It has the advantages of low cost, strong controllability, and high flexibility. By irradiating a flexible substrate with laser, its near-surface layer can be induced to transform into porous graphene, which can be used to manufacture the sensing layer of a piezoresistive sensor; at the same time, doped graphene can be formed by adding nanomaterials to its surface. In addition, by applying printable ink to the surface of a flexible substrate, it can be sintered by laser direct writing to form a dense conductive circuit, which can be used to prepare the electrode layer of a piezoresistive sensor. There are also reports of cases where metal sensing layers were prepared directly by laser direct writing, such as reported in CN 107702829 A, but the performance of this sensing layer is poor (only a few hundred Pa). -1 ) does not meet the usage requirements.

[0006] At present, the raw materials, manufacturing processes, and required final structural characteristics involved in the sensing layer and electrode layer of flexible piezoresistive sensors are all completely different, and different technical routes must be adopted, resulting in a relatively complicated preparation process for existing devices; therefore, there is also a lack of industrial production equipment that can be efficiently integrated in one step; on the other hand, nanometals with high specific surface areas are prone to agglomeration and oxidation during storage and processing, which poses a great challenge to the manufacture of high-performance sensors. Summary of the Invention

[0007] In response to the shortcomings of the existing technology, the present invention proposes an integrated flexible piezoresistive sensor based on laser direct writing and a preparation method thereof. The method of the present invention is specifically a low-cost, efficient, and controllable laser direct writing method. It does not require the pre-synthesis of graphene, metal nanoparticles and other materials. The metal-doped graphene sensing layer and metal electrode layer of the piezoresistive sensor can be manufactured on demand directly by controlling the parameters of the irradiated laser. It is convenient and fast. At the same time, thanks to avoiding the problems encountered during the storage of nanometals, the assembled device has very excellent sensing performance. Based on this method, a one-step manufacturing device for an integrated piezoresistive sensor is also disclosed, which can be used for industrial production.

[0008] The present invention is achieved through the following technical solutions:

[0009] The first object of the present invention is to provide a method for preparing an integrated flexible piezoresistive sensor based on laser direct writing, comprising the following steps:

[0010] S1, mixing a metal salt and a reducing ligand in a solvent to obtain a metal precursor solution;

[0011] S2, coating the metal precursor solution obtained in step S1 on a flexible substrate and drying;

[0012] S3, performing laser direct writing on the flexible substrate obtained in step S2 according to a preset laser scanning trajectory to prepare a sensing layer and an electrode layer respectively;

[0013] S4. Add glue between the sensing layer and the electrode layer obtained in step S3 and press them together to obtain an integrated flexible piezoresistive sensor based on laser direct writing.

[0014] In one embodiment of the present invention, in step S1, the metal salt is selected from one or more of copper nitrate, copper acetate, silver nitrate and chloroauric acid.

[0015] In one embodiment of the present invention, in step S1, the reducing ligand is selected from one or more of polyvinyl pyrrolidone, formic acid, ethylene glycol, and methanol. The reducing ligand used in the present invention decomposes to form carboxyl or hydroxyl groups, which, when oxidized by light, donate electrons to the metal salt, reducing the metal salt to a zero-valent element.

[0016] In one embodiment of the present invention, in step S1, the mass ratio of the metal salt to the reducing ligand is 3:1-5:1.

[0017] In one embodiment of the present invention, in step S2, the flexible substrate is selected from one or more of PI, PEN, CPI and PET.

[0018] In one embodiment of the present invention, in step S2, the coating amount of the metal precursor solution is 0.1 μL / mm 2 -1μL / mm 2 .

[0019] In one embodiment of the present invention, in step S2, the drying temperature is 50°C-80°C.

[0020] In one embodiment of the present invention, in step S3, the wavelength of the laser is 800 nm-10.6 μm;

[0021] And / or, the scanning speed of the laser is 50 mm / s-200 mm / s; the scanning interval is 0.01 mm-0.1 mm.

[0022] In one embodiment of the present invention, in step S3, the laser input energy density of the laser direct writing of the sensing layer is 300 J / cm 2 -500 J / cm 2 ;

[0023] And / or, the laser input energy density of the laser direct writing of the electrode layer is 50 J / cm 2 -200 J / cm 2 .

[0024] The second object of the present invention is to provide an integrated flexible piezoresistive sensor based on laser direct writing obtained by the preparation method.

[0025] The above technical solution of the present invention has the following advantages over the prior art:

[0026] The present invention provides an integrated flexible piezoresistive sensor based on laser direct writing and a method for preparing the same. The laser direct writing method proposed in the present invention has the characteristics of low cost, high efficiency, and controllability, and can manufacture the sensing layer and electrode layer of the piezoresistive sensor on demand. The typical electrode layer is a metal copper wire with a square resistance as low as 0.5Ω / sq; the typical sensing layer is a copper-graphene composite structure composed of laser-induced graphene and metal copper nanoparticles, which can achieve 60.2kPa in the range of 0-400kPa. -1 The assembled piezoresistive sensor has excellent sensitivity, monitoring range, and stability, providing strong support for the development of wearable bioelectronics. Furthermore, the integrated piezoresistive sensor of the present invention can be industrialized and mass-produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 Figure 1 shows the schematic diagram of the device for preparing an integrated sensor by laser direct writing. Explanation of reference numerals: 1, 2 - feeding conveyor assembly; 3 - pressing conveyor assembly; 4 - sensor collection conveyor assembly; 5 - slit coating assembly; 6 - heating assembly; 7 - laser assembly; 8 - cleaning assembly; 9 - dispensing assembly; 10 - housing.

[0029] Figure 2 This is a macroscopic photograph of the integrated sensor prepared in Example 2;

[0030] Figure 3 This is a SEM microscopic photograph of the sensing layer in the performance test of the present invention;

[0031] Figure 4 This is a SEM microscopic photograph of the electrode layer in the performance test of the present invention;

[0032] Figure 5 is the XRD spectrum of the sensing layer in the performance test of the present invention;

[0033] Figure 6 This is the XRD spectrum of the electrode layer in the performance test of the present invention;

[0034] Figure 7 is the pressure response IV curve of the sensor in the performance test of the present invention;

[0035] Figure 8 is the sensitivity curve of the sensor in the performance test of the present invention;

[0036] Figure 9 is the response speed of the sensor in the performance test of the present invention;

[0037] Figure 10 It is the long-term stability of the sensor in the performance test of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0039] like Figure 1 As shown, the transmission part of the preparation device of the integrated flexible piezoresistive sensor based on laser direct writing of the present invention is composed of 9 roll-to-roll conveying components, which are fixed to the side wall of the box 10 for continuous operation. Among them, 1 and 2-conveyor components are used for feeding, 3-conveyor component is used for pressing the sensing layer and the electrode layer, 4-conveyor component is used for collecting the prepared sensors, and the remaining conveyor components are used to change the transmission direction; 5-slit coating component is filled with precursor solution for coating on the surface of the flexible substrate, 6-heating component is used to dry the precursor, 7-laser direct writing component is used for laser processing; 8-cleaning component is filled with water or other cleaning agents for removing residual precursor on the surface of the flexible substrate after laser processing; 9-glue dispensing component is used to add adhesive glue. All of the above components are connected to a computer to achieve automation and operation status monitoring.

[0040] The present invention provides a method for manufacturing an integrated flexible piezoresistive sensor based on laser direct writing, comprising the following steps:

[0041] Step 1: Mixing a metal salt solution and a reducing ligand to prepare a precursor solution.

[0042] Furthermore, the metal salt solution uses soluble transition metals and noble metal salts such as copper nitrate, copper acetate, silver nitrate, and chloroauric acid.

[0043] Furthermore, the reducing ligand is a carboxyl or hydroxyl-containing organic / inorganic substance such as polyvinyl pyrrolidone, formic acid, ethylene glycol, methanol, etc.

[0044] Furthermore, the mass ratio of the metal salt solution to the reducing ligand is 3:1-5:1.

[0045] Step 2: Load the flexible substrate into the roll-to-roll conveyor assembly.

[0046] Furthermore, the flexible substrate is made of any carbon-containing polymer such as PI, PEN, CPI, PET, etc.

[0047] Step 3: Load the prepared metal precursor solution into the slit coating assembly and adjust the required precursor coating amount.

[0048] Furthermore, the coating amount of the metal precursor is 0.1 μL / mm 2 -1μL / mm 2 .

[0049] Step 4: Heat the heating component to dry the metal precursor solution to form a uniform precursor film.

[0050] Furthermore, the drying temperature is 50°C-80°C.

[0051] Step 5: Use a laser component to selectively irradiate the flexible substrate containing the precursor film. The laser scanning trajectory can be drawn and imported by a computer to manufacture the sensing layer and the electrode layer respectively.

[0052] Furthermore, the wavelength range of the laser component used is 800nm-10.6μm.

[0053] Furthermore, the laser input energy density during the fabrication of the sensing layer was 300 J / cm 2 -500 J / cm 2 .

[0054] Furthermore, the laser input energy density during the manufacture of the electrode layer is 50 J / cm 2 -200 J / cm 2 .

[0055] Furthermore, the laser scanning speed is 50 mm / s-200 mm / s, and the scanning interval is 0.01 mm-0.1 mm.

[0056] Step 6: Add water or other cleaning agents to the cleaning component to rinse the film to remove residual precursors in areas not irradiated by the laser.

[0057] Step 7: Add acrylic glue through the dispensing component and assemble it through the press-fit component to obtain an integrated flexible piezoresistive sensor.

[0058] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0059] Example 1:

[0060] This embodiment provides a method for preparing an integrated flexible piezoresistive sensor based on laser direct writing, and the specific steps are as follows:

[0061] (1) Copper nitrate and polyvinyl pyrrolidone aqueous solution are mixed to obtain a copper precursor solution; wherein the mass ratio of copper nitrate to polyvinyl pyrrolidone is 4:1; wherein polyvinyl pyrrolidone has a long chain characteristic, which not only acts as a reducing agent but also improves the uniformity of the precursor film after drying.

[0062] (2) The obtained copper precursor was coated on the surface of the PET substrate with a coating amount of 0.1 μL / mm 2 .

[0063] (3) Drying the substrate obtained in step (2) at 60° C. to form a uniform thin film on the surface of the substrate.

[0064] (4) Select a laser component with a wavelength of 1064nm, import the scanning path diagram drawn by the computer into the laser direct writing, and prepare an area of 1cm 2 Sensing layer; wherein the laser input energy density is 400J / cm 2 ; The laser scanning speed is 100 mm / s and the scanning interval is 0.1 mm.

[0065] (5) Using a laser component with a wavelength of 1064 nm, the scanning path diagram drawn by the computer was imported into the laser direct writing to prepare a 1 cm 2 Interdigitated electrode layer; wherein the width and spacing of the interdigitated film are both 500 μm; the laser input energy density is 80 J / cm 2 ; The laser scanning speed is 100 mm / s and the scanning interval is 0.1 mm.

[0066] (6) After laser direct writing, the film is rinsed with deionized water to remove residual precursor.

[0067] (7) The obtained sensing layer and electrode layer are assembled face to face with acrylic glue, pressed together and naturally air-dried to obtain an integrated flexible piezoresistive sensor.

[0068] Example 2

[0069] This embodiment provides a method for preparing an integrated flexible piezoresistive sensor based on laser direct writing, and the specific steps are as follows:

[0070] (1) Mixing silver nitrate and an ethylene glycol aqueous solution to obtain a silver precursor solution; wherein the mass ratio of silver nitrate to ethylene glycol is 3:1.

[0071] (2) The obtained silver precursor was coated on the surface of the PET substrate with a coating amount of 0.5 μL / mm 2 .

[0072] (3) Drying the substrate obtained in step (2) at 60° C. to form a uniform thin film on the surface of the substrate.

[0073] (4) Select a laser component with a wavelength of 808nm, import the scanning path diagram drawn by the computer into the laser direct writing, and prepare an area of 1cm 2 Sensing layer; wherein the laser input energy density is 400J / cm 2 ; The laser scanning speed is 100 mm / s and the scanning interval is 0.1 mm.

[0074] (5) Using a laser component with a wavelength of 808 nm, the scanning path diagram drawn by the computer was imported into the laser direct writing to prepare a 1 cm 2 Interdigitated electrode layer; wherein the width and spacing of the interdigitated film are both 200 μm; the laser input energy density is 50 J / cm 2 ; The laser scanning speed is 200 mm / s and the scanning interval is 0.1 mm.

[0075] (6) After laser direct writing, the film is rinsed with deionized water to remove residual precursor.

[0076] (7) The obtained sensing layer and electrode layer were assembled face to face with acrylic glue, pressed together and naturally air-dried. The macroscopic photograph of the obtained integrated flexible piezoresistive sensor is shown in the figure. Figure 2 shown.

[0077] Performance Testing

[0078] 1) Figure 3 and Figure 4 The scanning electron microscope (SEM) micromorphologies of the sensing layer and electrode layer of Example 1 are shown respectively. Figure 3 and Figure 4 The sensing layer is composed of lamellar porous graphene doped with copper particles. This is because high-energy laser input converts the near-surface layer of the flexible substrate into graphene. Simultaneously, the metal salts provided by the precursor are reduced to form nanoparticles, forming a metal-doped graphene sensing layer. The electrode layer is a continuous copper network. Low-energy laser input does not introduce graphene, but instead in-situ sintering of the synthesized nanoparticles to form metal conductors, resulting in the electrode layer. The morphology of the sensing and electrode layers is uniform and well-formed. The sheet resistance of the electrode layer, measured using a Keithley 2450 meter, is as low as 0.5 Ω / sq.

[0079] 2) Figure 5 and Figure 6 The components of the sensing layer and the electrode layer were analyzed using X-ray diffractometer (XRD) (Example 1). Figure 5 As can be seen, diffraction peaks at 43.4°, 50.6° and 74.3° can be observed in the electrode layer, indicating that the main component is copper. Figure 6As shown, a diffraction peak at 26° can be observed in the sensing layer, indicating the formation of a graphene-like material, with a faint copper diffraction peak. This confirms the successful preparation of the nano-copper-doped graphene sensing layer and the copper electrode layer.

[0080] 3) Connect both sides of the interdigital electrode layer of the integrated flexible piezoresistive sensor prepared in Example 1 to an external test meter (Keithley 2450). A universal tensile / compression / bending tester (ZQ-950) was used to apply pressure to the device and evaluate its performance. Figure 7 The IV curves of the sensor under different pressures show that the sensor output resistance decreases with increasing pressure, and all curves exhibit good linearity. This indicates that the electrode layer and the sensing layer exhibit ohmic contact characteristics, and that the microscopic deformation of the sensing layer can convert the force into a resistance signal output, demonstrating the successful implementation of piezoresistive sensing.

[0081] 4) Using the test method in 3), apply a 0.1V bias voltage to the device and detect the relative current change in the pressure range of 0-400kPa. The results are as follows Figure 8 As shown, the device still responds to pressures up to 500 kPa, indicating that it has an excellent detection range; within the range, the device exhibits two-stage linear changes of 0-100 kPa and 100-400 kPa, with sensitivities of S1=60.2 kPa and S2=60.2 kPa, respectively. -1 , S2=3.4kPa -1 , indicating that the device has excellent sensitivity.

[0082] 5) Using the test method in 3), a 0.1V bias voltage was applied to the device, and a pulse with a load of 100g was applied to the sensor to evaluate the dynamic response. Figure 9 As shown, the response / recovery time obtained under a pulse load of 100 g is 610 / 90 ms, indicating that the sensor prepared in the present invention responds quickly.

[0083] 6) Using the test method in 3), a bias voltage of 0.1 V was applied to the device, and a squeeze / release test was repeated 10,000 times at a pressure of 1 kPa to test the durability of the sensor during long-term use. Figure 10 The figure shows the current signal obtained under 10,000 compression-recovery cycles. It can be seen that the current change can be stably restored, indicating that the sensor prepared by the present invention has excellent stability.

[0084] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing an integrated flexible piezoresistive sensor based on laser direct writing, characterized in that: The following steps are involved: S1, mixing a metal salt and a reducing ligand in a solvent to obtain a metal precursor solution; S2, coating the metal precursor solution obtained in step S1 on a flexible substrate and drying; S3, performing laser direct writing on the flexible substrate obtained in step S2 according to a preset laser scanning trajectory to prepare a sensing layer and an electrode layer respectively; S4. Add glue between the sensing layer and the electrode layer obtained in step S3 and press them together to obtain an integrated flexible piezoresistive sensor based on laser direct writing.

2. The preparation method according to claim 1, characterized in that In step S1, the metal salt is selected from one or more of copper nitrate, copper acetate, silver nitrate and chloroauric acid.

3. The preparation method according to claim 1, characterized in that In step S1, the reducing ligand is selected from one or more of polyvinyl pyrrolidone, formic acid, ethylene glycol and methanol.

4. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of the metal salt to the reducing ligand is 3:1-5:

1.

5. The preparation method according to claim 1, characterized in that In step S2, the flexible substrate is selected from one or more of PI, PEN, CPI and PET.

6. The preparation method according to claim 1, characterized in that In step S2, the coating amount of the metal precursor solution is 0.1 μL / mm 2 -1μL / mm 2 .

7. The preparation method according to claim 1, characterized in that In step S2, the drying temperature is 50°C-80°C.

8. The preparation method according to claim 1, characterized in that In step S3, the wavelength of the laser is 800nm-10.6μm; And / or, the scanning speed of the laser is 50 mm / s-200 mm / s; the scanning interval is 0.01 mm-0.1 mm.

9. The preparation method according to claim 1, characterized in that In step S3, the laser input energy density of the laser direct writing of the sensing layer is 300 J / cm 2 -500 J / cm 2 ; And / or, the laser input energy density of the laser direct writing of the electrode layer is 50 J / cm 2 -200 J / cm 2 .

10. An integrated flexible piezoresistive sensor based on laser direct writing obtained by the preparation method according to any one of claims 1 to 9.

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