A flexible thin film pressure sensor and a method of manufacturing the same

Abstract

The application discloses a flexible thin film pressure sensor, which comprises a lower flexible substrate, an electrode layer, a double-sided adhesive gasket, a composite sensitive layer and an upper flexible substrate which are sequentially stacked from bottom to top; and a preparation method thereof comprises the following steps: S1, modifying the surfaces of the lower flexible substrate and the upper flexible substrate respectively; S2, printing silver paste, gold paste or copper paste on the upper surface of the lower flexible substrate to form a patterned electrode, i.e., the electrode layer; S3, screen printing conductive composite paste on the lower surface of the upper flexible substrate to form the composite sensitive layer after solidification; and S4, arranging the double-sided adhesive gasket between the electrode layer and the composite sensitive layer, and then bonding together to form the flexible thin film pressure sensor. The flexible thin film pressure sensor has high precision, high stability and high durability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sensors, in particular to a flexible thin film pressure sensor and a preparation method thereof. BACKGROUND

[0002] In recent years, flexible pressure sensors have attracted widespread attention. Flexible pressure sensors are flexible pressure sensor devices that have the characteristics of flexibility, bendability and wearability, and have broad application prospects. Flexible thin film pressure sensors, as a special structure of flexible pressure sensors, have also received extensive attention from the relevant industry at home and abroad.

[0003] In the field of flexible thin film pressure sensors, researchers and related enterprises at home and abroad have carried out a series of innovative research work on the materials, structures and device design of the sensors. Carbon-based materials such as carbon nanotubes (CNTs), graphene and new two-dimensional conductive materials MXene have become the main choice of conductive fillers for pressure resistance type pressure sensors based on percolation theory due to their good conductivity, low percolation concentration and other advantages. However, due to the easy agglomeration of such pressure-sensitive materials, the dispersion of the prepared devices is poor, and the accuracy and stability of such sensors are poor (±15%). SUMMARY

[0004] In view of the above problems existing in the prior art, the present application provides a flexible thin film pressure sensor and a preparation method thereof. The flexible thin film pressure sensor of the present application has high precision, high stability and high durability.

[0005] The technical scheme of the present application is as follows:

[0006] A flexible thin film pressure sensor, the flexible thin film pressure sensor comprising, from bottom to top, a lower flexible substrate, an electrode layer, a double-sided adhesive gasket, a composite sensitive layer and an upper flexible substrate.

[0007] The composite sensitive layer comprises a polymer matrix material and a conductive filler, which is prepared by screen printing.

[0008] As a further improvement of the above technical scheme:

[0009] The surface of the lower flexible substrate and the upper flexible substrate is subjected to a modification treatment, and the modification treatment method is plasma treatment, acid-base treatment or ion beam treatment.

[0010] The lower flexible substrate and the upper flexible substrate are one of polyimide (PI), polyvinyl chloride (PVC), polyethylene terephthalate (PET), thermoplastic polyurethane elastomer rubber (TPU), and polydimethylsiloxane (PDMS).

[0011] The electrode layer is a patterned electrode formed by printing silver paste, gold paste, or copper paste, and the thickness of the electrode layer is 5-10 microns, and the surface resistance is 15-25 ohms.

[0012] Preferably, the electrode layer is an interdigital electrode.

[0013] The double-sided adhesive pad is polyimide (PI) coated with adhesive on the upper and lower surfaces.

[0014] Preferably, the double-sided adhesive pad is a hollow structure with a hollow shape and size identical to the composite sensitive layer.

[0015] Preferably, the thickness of the double-sided adhesive pad is 50-100 microns.

[0016] The high molecular matrix material in the composite sensitive layer is a mixture of epoxy resin and polyphenol resin, and the mass ratio of epoxy resin to polyphenol resin is 1:0.4-0.6.

[0017] Preferably, the epoxy resin is bisphenol A epoxy resin or bisphenol F epoxy resin, and the average molecular weight of the polyphenol resin is 52,000.

[0018] Preferably, the conductive filler is a mixture of graphite and carbon black.

[0019] The thickness of the composite sensitive layer is 5-10 microns, and the surface resistance is 0.4-0.6 MΩ.

[0020] A method for manufacturing the flexible thin film pressure sensor, the method comprising the following steps:

[0021] S1, the surfaces of the lower flexible substrate and the upper flexible substrate are respectively modified;

[0022] S2, silver paste, gold paste, or copper paste is printed on the upper surface of the lower flexible substrate to form a patterned electrode, i.e., an electrode layer.

[0023] S3, the lower surface of the upper flexible substrate is screen printed with conductive composite paste, and the composite material sensitive layer is formed after curing.

[0024] S4, a double-sided adhesive pad is arranged between the electrode layer and the composite material sensitive layer, and then they are bonded together to form the flexible thin film pressure sensor.

[0025] As a further improvement of the above technical solution:

[0026] In step S3, the preparation method of the conductive composite paste is as follows:

[0027] ① mixing graphite and carbon black according to a mass ratio of 1:0.5-0.7 to form a mixed conductive filler;

[0028] ② mixing epoxy resin, polyphenol resin, curing agent and accelerator to prepare a resin mixture, and then dissolving the resin mixture in a solvent to obtain a mixed solution A;

[0029] ③ adding the mixed conductive filler obtained in step ① into the mixed solution A obtained in step ② to perform sufficient stirring and mixing, and then adding a dispersant to uniformly mix to obtain a conductive polymer matrix solution;

[0030] ④ stirring the solution obtained in step ③ at an opening speed of 100-400 rad / min for 0.5-6 h to volatilize the solvent in the paste to obtain a conductive composite paste;

[0031] In step ②, the epoxy resin is bisphenol A epoxy resin or bisphenol F epoxy resin; the average molecular weight of the polyphenol resin is 52,000;

[0032] The mass ratio of the epoxy resin to the polyphenol resin is 1:0.4-0.6;

[0033] The curing agent is methyl tetrahydrophthalic anhydride, and the amount is 50-60% of the mass of the epoxy resin;

[0034] The accelerator is 2,4,6-tris[(dimethylamino)methyl]phenol, and the amount is 10-13% of the mass of the epoxy resin;

[0035] The solvent is acetone or dimethyl nylon acid, and the amount is 2.4-2.8 times of the mass of the resin mixture;

[0036] In step ③, the mass ratio of the mixed conductive filler to the resin mixture in step ② is 1:6-8;

[0037] The dispersant is acrylic block copolymer or propylene glycol methyl ether, and the amount is 2.6% of the mass of the mixed solution A.

[0038] The present application has the beneficial technical effects that:

[0039] The present application improves the sensitive layer material of the composite material, has high strength after curing, and is resistant to crack generation, and has high sensitivity (>3.3 kPa -1 ) and short response time (<1 ms) compared with the existing flexible sensor, and has high durability (>2 million times).

[0040] The flexible thin-film pressure sensor of this invention is located in the midstream of the intelligent sensing application industry chain. Upstream is multi-purpose chemical sensing raw materials, and downstream is the end-user application of the sensor. This invention has wide applications in downstream scenarios such as wearable physiological monitoring, intelligent industrial sensing, and wearable human-computer interaction.

[0041] Based on material properties, this invention employs an integrated screen printing process with high process maturity, enabling the integrated fabrication of flexible sensing materials and electrodes. This effectively improves the mass production capability of materials while ensuring high product yield and significantly reducing production costs. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the present invention;

[0043] In the figure: 1. Lower flexible substrate, 2. Upper flexible substrate, 3. Electrode layer, 4. Double-sided adhesive pad, 5. Composite material sensitive layer.

[0044] Figure 2 This is a schematic diagram of signal detection using a flexible thin-film pressure sensor.

[0045] Figure 3 The curve showing the relative current change versus pressure for the flexible thin-film pressure sensor corresponding to Example 1 is shown.

[0046] Figure 4 The resistance change curve of the flexible thin-film pressure sensor prepared in Example 1 under cyclic pressure testing;

[0047] Figure 5 This is a comparison chart of the sensor sensitivity of Example 1, Comparative Example 1, and Comparative Example 2;

[0048] Figure 6 This is a comparison chart showing the changes in the resistance of the printed electrode layer after multiple bending tests were conducted on the substrate film before and after modification in Example 2. Detailed Implementation

[0049] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0050] Example 1

[0051] like Figure 1 As shown, the flexible thin-film pressure sensor of this embodiment includes a lower flexible substrate 1, an electrode layer 3, a double-sided adhesive pad 4, a composite material sensitive layer 5, and an upper flexible substrate 2, which are stacked sequentially from bottom to top. The composite material sensitive layer 5 includes a polymer matrix material and a conductive filler, which are obtained by screen printing.

[0052] The specific preparation method is as follows:

[0053] (1) Put the 50ml beaker for experiment into the fume hood, add 34.05g of nylon acid dimethyl ester (DBE) into the beaker, heat at 100℃, use the planetary mixer to set the stirring speed at 300rad / min, add 5.85g of bisphenol F epoxy resin (NPEF-170 of Nanya), 3.25g of polyphenol epoxy resin (PKHH of Gabriel, USA), 3.25g of methyl tetrahydrophthalic anhydride and 0.65g of 2,4,6-tris[(dimethylamino)methyl]phenol (DMP-30) into the beaker to mix well to obtain mixed solution A;

[0054] (2) Add 1g of graphite, 0.65g of carbon black (EC-600JD) and 1.3g of acrylic block copolymer (EFKA-4310) into the obtained mixed solution A, stir at 300rad / min in the planetary mixer for 30min, then stir at 100rad / min to evaporate the solvent, until the viscosity of the slurry is >10000mPa·s, to obtain the conductive composite slurry;

[0055] (3) Take two PI film (polyimide) substrates with the same shape and size and a thickness of 75μm, clean them with deionized water, then put the cleaned PI films into a NaOH solution with a concentration of 1mol / L for treatment for 40min, then take out the PI films, wash them with deionized water and dry them for standby;

[0056] (4) Use the conductive silver paste (SINWE 3702) to screen print the silver paste interdigital electrode on one of the PI films treated in step (3) using a screen printing mesh with a mesh number of 300, then place the printed PI film on a heating table at 100℃ to heat and cure for 15min to obtain a 5μm thick electrode layer; the surface resistance is 20Ω;

[0057] (5) Use a screen printing mesh with a mesh number of 300 to print the conductive composite slurry obtained in step (2) on the other PI film treated in step (3), then place the PI film on a heating table at 120℃ to heat and cure for 30min to obtain a 5μm thick composite material sensitive layer; the surface resistance of the composite material sensitive layer is 0.5MΩ; use a material tensile testing machine to test the 90° peeling strength of the PI film printed with the composite material sensitive layer, the peeling strength of the composite material sensitive layer prepared based on the epoxy resin-polyphenol epoxy resin mixed resin system is 0.97N / mm, while the peeling strength of the sensitive layer prepared by the epoxy resin system without adding polyphenol epoxy resin under the same conditions is 0.75N / mm, and the peeling strength is increased by 29%.

[0058] (6) Using double-sided adhesive pads (polyimide PI, upper and lower surfaces coated with adhesive, 50 μm), the two PI films treated in step (4) and step (5) are laminated together, with the electrode layer and the composite material sensitive layer placed opposite each other, to obtain the flexible thin film pressure sensor.

[0059] Figure 3 The force-sensitive curve of the flexible thin film pressure sensor prepared in this example under a voltage of 5.0 V is shown in the figure. As can be seen from the figure, the sensor has relatively obvious linearity in both the small pressure region and the large pressure region, and has very high sensitivity in the small pressure region.

[0060] Figure 4 The resistance change curve of the flexible thin film pressure sensor prepared in this example under a 1.5 kPa pressure cycle is shown in the figure. As can be seen from the figure, the lowest resistance remains stable. This may be because the polyphenol resin has crack resistance, and the sensor can still maintain high accuracy and stability after repeated use.

[0061] Example 2

[0062] The same as example 1, except that the substrate in step (3) is changed to a PET substrate (thickness of 75 μm), and the pretreatment method is to immerse the PET film in the prepared BP solution (5×10 -3 mol / L) for 2 h, and then dry it until the acetone on the surface of the PET film is completely volatilized. The dried PET film is placed in a glass container, nitrogen is introduced to remove oxygen in the container, and the container is sealed and placed under a 1000 W ultraviolet lamp for modification treatment to obtain a modified PET substrate. The comparison of the resistance change of the substrate film before and after treatment after bending is shown in Figure 6 As can be seen from the figure, after the surface-treated substrate film is printed with silver paste electrodes, the adsorption capacity of the silver paste is significantly enhanced. Compared with the substrate film before treatment, the resistance change range of the printed electrode after 300 bending tests is much smaller than that of the substrate film before treatment.

[0063] Example 3

[0064] The same as example 1, except that in step (2), 1 g of graphite is added to the obtained mixed solution A, and 0.65 g of carbon black is replaced by 1 g of graphite and 0.6 g of carbon black.

[0065] Example 4

[0066] The same as example 1, except that in step (2), 1 g of graphite is added to the mixed solution A, and 0.65 g of carbon black is replaced by 1 g of graphite and 0.7 g of carbon black.

[0067] The raw material ratio and some properties in example 1 are shown in table 1:

[0068] Table 1

[0069]

[0070] The ratio of graphite to carbon black in the conductive filler affects the electrical and mechanical properties of the conductive composite paste. When the content of carbon black particles increases, the gaps between the graphite layers can be filled, thereby reducing the tunnel effect and improving the electrical conductivity of the conductive mixed filler. However, due to the large specific surface area and porous structure of carbon black, increasing the content of carbon black will increase the viscosity of the ink, which is not conducive to printing. As shown in the above table, when the mass ratio of graphite to carbon black is between 1:(0.5-0.7), the conductive composite paste can ensure good electrical conductivity and suitable viscosity.

[0071] Meanwhile, the amount of mixed conductive filler of graphite and carbon black in the composite paste is between 10% and 15% of the effective components in the mixed solution A. If the mass ratio of the conductive filler is too low, the electrical conductivity of the prepared composite paste will be poor, and the resistance value will fluctuate greatly during measurement. If the mass ratio of the conductive filler is too high, it will lead to the agglomeration of the prepared paste to form a stable conductive network, resulting in a decrease in sensitivity. As shown in Figure 5 the sensitivity curves of the sensors prepared in Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that in Example 1, the sensitivity of the thin film pressure sensor is the highest when the conductive filler accounts for 12.7%, and the sensitivity of the sensors in the two comparative examples decreases when the conductive filler accounts for 9% and 17%. In particular, in Comparative Example 2, when the conductive filler accounts for 17%, the sensor first enters the saturation region (the resistance change is not obvious with the increase of pressure).

[0072] Comparative Example 1

[0073] The same as Example 1, the difference is that in step (2), 1g of graphite is added to the obtained mixed solution A, and 0.65g of carbon black is replaced by 0.7g of graphite and 0.47g of carbon black. The sensor sensitivity comparison chart is shown in Figure 5 .

[0074] Comparative Example 2

[0075] The same as Example 1, the difference is that in step (2), 1g of graphite is added to the obtained mixed solution A, and 0.65g of carbon black is replaced by 1.33g of graphite and 0.88g of carbon black. The sensor sensitivity comparison chart is shown in Figure 5 .

[0076] Therefore, the flexible thin film pressure sensor provided by the present application can realize accurate and stable pressure detection, and the device has the characteristics of flexibility, ultra-thinness, strong anti-peeling ability and low cost, and has wide application prospects in industrial robot environment perception, intelligent human-computer interaction, wearable physiological monitoring, etc.

Claims

1. A method for fabricating a flexible thin-film pressure sensor, characterized in that, The flexible thin-film pressure sensor includes a lower flexible substrate (1), an electrode layer (3), a double-sided adhesive pad (4), a composite material sensitive layer (5), and an upper flexible substrate (2) stacked from bottom to top. The composite material sensitive layer (5) comprises a polymer matrix material and a conductive filler, which are obtained by screen printing; The method for fabricating the flexible thin-film pressure sensor includes the following steps: S1, the surfaces of the lower flexible substrate (1) and the upper flexible substrate (2) are modified respectively; S2, print silver paste, gold paste or copper paste on the upper surface of the lower flexible substrate (1) to form a patterned electrode, namely the electrode layer (3). S3, conductive composite paste is screen-printed on the lower surface of the upper flexible substrate (2), and then cured to form a composite material sensitive layer (5). S4, a double-sided adhesive pad (4) is placed between the electrode layer (3) and the composite material sensitive layer (5), and then they are bonded together to form the flexible thin film pressure sensor; In step S3, the method for preparing the conductive composite paste is as follows: ① Mix graphite and carbon black at a mass ratio of 1:0.5-0.7 to form a mixed conductive filler; ② Prepare a resin mixture by mixing epoxy resin, polyphenolic resin, curing agent and accelerator, and then dissolve the above resin mixture in a solvent to obtain mixture A; ③ Add the mixed conductive filler obtained in step ① to the mixture A obtained in step ② and stir thoroughly. Then add the dispersant and mix evenly to obtain a composite conductive polymer matrix solution. ④ Stir the solution obtained in step ③ at a speed of 100-400 rad / min in an open manner for 0.5-6 hours to allow the solvent in the slurry to evaporate, thereby obtaining a conductive composite slurry; In step ③, the mass ratio of the mixed conductive filler to the resin mixture in step ② is 1:6-8.

2. The method for fabricating a flexible thin-film pressure sensor according to claim 1, characterized in that, The surfaces of the lower flexible substrate (1) and the upper flexible substrate (2) are modified by plasma treatment, acid-base treatment or ion beam treatment.

3. The method for fabricating a flexible thin-film pressure sensor according to claim 1, characterized in that, The lower flexible substrate (1) and the upper flexible substrate (2) are one of polyimide (PI), polyvinyl chloride (PVC), polyethylene terephthalate (PET), thermoplastic polyurethane elastomer rubber (TPU), and polydimethylsiloxane (PDMS).

4. The method for fabricating a flexible thin-film pressure sensor according to claim 1, characterized in that, The electrode layer (3) is a patterned electrode formed by printing silver paste, gold paste or copper paste; the thickness of the electrode layer (3) is 5-10 μm and the surface resistance is 15-25 Ω. The electrode layer (3) is an interdigitated electrode.

5. The method for fabricating a flexible thin-film pressure sensor according to claim 1, characterized in that, The double-sided adhesive pad (4) is made of polyimide (PI) and has self-adhesive coating on its upper and lower surfaces. The double-sided adhesive pad (4) has a hollow structure, and the shape and size of the hollow in the middle are the same as those of the composite material sensitive layer (5); The thickness of the double-sided adhesive pad (4) is 50-100 μm.

6. The method for fabricating a flexible thin-film pressure sensor according to claim 1, characterized in that, The polymer matrix material in the composite sensitive layer (5) is a mixture of epoxy resin and polyphenolic resin, and the mass ratio of epoxy resin to polyphenolic resin is 1:0.4-0.

6. The epoxy resin is either bisphenol A epoxy resin or bisphenol F epoxy resin; the average molecular weight of the polyphenolic resin is 52,000. The conductive filler is a mixture of graphite and carbon black.

7. The method for fabricating a flexible thin-film pressure sensor according to claim 1, characterized in that, The thickness of the composite material sensitive layer (5) is 5-10 μm, and the surface resistance is 0.4-0.6 MΩ.

8. The method for fabricating a flexible thin-film pressure sensor according to claim 1, characterized in that, In step ②, the epoxy resin is bisphenol A epoxy resin or bisphenol F epoxy resin; the average molecular weight of the polyphenolic resin is 52,000. The mass ratio of epoxy resin to polyphenolic resin is 1:0.4-0.6; The curing agent is methyltetrahydrophthalic anhydride, and its dosage is 50-60% of the epoxy resin mass. The accelerator is 2,4,6-tris[(dimethylamino)methyl]phenol, and its dosage is 10-13% of the epoxy resin mass; The solvent is acetone or dimethyl nylonate, and the amount used is 2.4-2.8 times the mass of the resin mixture; In step ③, the dispersant is an acrylic block copolymer or propylene glycol methyl ether, and the amount used is 2.6% of the mass of mixture A.

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