A pressure sensor of ITO nanocrystal-plant fiber composite material and preparation method thereof

Abstract

The present invention belongs to the field of sensor technology, specifically a pressure sensor made of ITO nanocrystal-plant fiber composite material and a preparation method thereof. The pressure sensor made of ITO nanocrystal-plant fiber composite material of the present invention is composed of an interdigitated electrode layer, an ITO nanocrystal-plant fiber composite material elastic layer, and a flexible encapsulation layer; the ITO nanocrystal-plant fiber composite material elastic layer is a composite material mixed with plant fibers and ITO nanocrystals; the encapsulation layer covers the elastic layer of the pressure sensor and the interdigitated electrode interdigitated area of ​​the ITO nanocrystal-plant fiber composite material. The pressure sensor made of ITO nanocrystal-plant fiber composite material of the present invention has high sensitivity, simple structure and process, wide sensing pressure range and flexibility, and has application prospects in robot tactile sensors, pulse sensors, or wearable devices.

Description

Technical Field

[0001] The invention relates to a pressure sensor of an ITO nanocrystal-plant fiber composite material and a preparation method thereof. Background Art

[0002] The manipulators used in current engineering equipment and robots are only capable of rudimentary gripping, simply grasping and opening. A drawback of these manipulators is that they typically lack the ability to sense the amount of pressure applied to the object. This ability to sense pressure would prevent damage to the object caused by excessive pressure.

[0003] Currently, flexible sensors typically utilize conductive polymer ultra-thin films on flexible substrates. However, the poor conductivity of polymer materials results in small currents and current variations, resulting in low signal strength and the need for frequent signal amplification. While some highly sensitive pressure sensors exist, these typically utilize metal oxide nanowire arrays as sensing elements. However, these sensors remain insensitive, are sensitive to acid and alkali conditions, and exhibit poor stability.

[0004] Currently, wearable devices and electronic skins with application prospects have high requirements for sensor array density. However, most of the current graphene pressure sensor arrays are not easy to stretch, and the area of ​​some individual sensors cannot be made very small. When individual sensors are arranged to form an array, the high-density requirements cannot be met.

[0005] Patent CN206114156U discloses a graphene pressure sensor array system. The sensor array includes an array circuit board and an array circuit arranged on the array circuit board. The array circuit board is provided with a plurality of graphene pressure sensing units connected to the array circuit. Although this sensor can be manufactured with densely packed graphene sensing units as needed, the circuit board of this sensor is rigid and cannot meet the flexibility requirements of wearable devices and electronic skin.

[0006] Most of the current graphene pressure sensors have complex processes and structures and are composed of multiple components.

[0007] Patent CN105300574A discloses a graphene pressure sensor consisting of at least an elastic substrate layer, a graphene pressure-sensing layer, and an encapsulation layer. The elastic substrate layer includes a sensing region, an overlap region, and an electrode region. The graphene pressure-sensing layer is attached to the sensing region. When subjected to compression or other external forces, the graphene with the etched sensing pattern contacts the surrounding graphene pressure-sensing layer, or the contact area changes, causing a change in contact resistance. The graphene pressure-sensing layer in this sensor requires multiple steps to prepare graphene powder into a graphene film, which also requires laser etching. This process is complex and expensive. Summary of the Invention

[0008] The object of the present invention is to provide an ITO nanocrystal-plant fiber pressure sensor with high sensitivity, simple structure, low cost and flexibility, and a preparation method thereof.

[0009] The present invention proposes an ITO nanocrystal-plant fiber composite pressure sensor, which consists of an interdigital electrode layer, an ITO nanocrystal-plant fiber composite elastic layer, a flexible film layer, and a flexible packaging layer; wherein:

[0010] The interdigitated electrode layer is divided into an interdigitated electrode interdigital region and an interdigitated electrode plane region;

[0011] The ITO nanocrystal-plant fiber composite elastic layer is a composite material formed by mixing plant fibers and ITO nanocrystals; the thickness of the ITO nanocrystal-plant fiber composite elastic layer is 0.2 to 1 mm, wherein the particle size of the ITO nanocrystals is approximately 10 to 50 nm, and the weight ratio of the plant fibers to the ITO nanocrystals is 1:4 to 1:10; the ITO nanocrystal-plant fiber composite elastic layer covers the interdigital region of the interdigital electrode and overlaps with the interdigital region of the interdigital electrode;

[0012] The flexible film layer covers the interdigitated electrode plane area;

[0013] The flexible packaging layer is formed by packaging the ITO nanocrystal-plant fiber composite elastic layer and the interdigital electrodes.

[0014] In the present invention, the sensible pressure range of the ITO nanocrystal-plant fiber composite pressure sensor is 10-100 kPa, which is related to the thickness of the elastic layer of the ITO nanocrystal-plant fiber composite material.

[0015] In the present invention, the interdigital electrode layer is an etched circuit composed of indium tin oxide or a conductive metal film and a polymer film or glass, and the interdigital electrode circuit is etched or evaporated into a finger-cross shape.

[0016] In the present invention, the flexible film layer is a polyimide or polypropylene flexible film.

[0017] In the present invention, the flexible encapsulation layer is made of elastic organic silicone or thermoplastic elastomer, such as elastic organic silicone (such as polydimethylsiloxane (PDMS)) or thermoplastic elastomer (such as hydrogenated styrene isoprene copolymer (SEPS)), but not limited thereto.

[0018] The present invention proposes a method for preparing a pressure sensor made of an ITO nanocrystal-plant fiber composite material, and the specific steps are as follows:

[0019] (1) Preparation of the elastic layer of ITO nanocrystal-plant fiber composite material: Add 0.02 g of qualitative filter paper fragments to 3 ml of deionized water and stir for 4 hours until the paper fragments become pulpy; add 0.08-0.2 g of ITO nanocrystals and continue stirring for 1 hour; pipette 1 ml of the mixed solution into the mold and place it in a 100°C oven to dry into a film;

[0020] (2) transferring the ITO nanocrystal-plant fiber composite elastic layer obtained in step (1) onto the interdigital electrode layer, and ensuring that the size of the ITO nanocrystal-plant fiber composite elastic layer coincides with the interdigital region of the interdigital electrode layer;

[0021] (3) Covering the back of the interdigital region of the interdigital electrode layer with a flexible film layer;

[0022] (4) trimming the ITO nanocrystal-plant fiber composite elastic layer and the flexible film layer on both sides of the interdigital region of the interdigital electrode layer;

[0023] (5) Encapsulating the ITO nanocrystal-plant fiber composite elastic layer and the flexible film layer on both sides of the interdigital region of the interdigital electrode layer to form a flexible encapsulation layer.

[0024] In the present invention, the flexible packaging layer is formed in step (5), and its operation steps are as follows: coating the packaging material on the surface and surrounding interfaces of the ITO nanocrystal-plant fiber elastic layer and the flexible film layer located on both sides of the interdigital area of ​​the interdigital electrode layer, and drying to form a flexible packaging layer, or vertically immersing the portion covering the ITO nanocrystal-plant fiber elastic layer and the flexible film layer into the packaging material, drying and solidifying, digging out the ITO nanocrystal-plant fiber pressure sensor together with a portion of the solidified packaging material, and cutting off the excess packaging material according to the packaging thickness.

[0025] The uses of the ITO nanocrystal-plant fiber pressure sensor proposed in the present invention include: being used as a pulse sensor in the form of a sensor array; being used as a tactile sensor for a manipulator; and being used as a force or deformation sensor in wearable electronic devices.

[0026] In the present invention, the interdigitated electrode layer is an etched circuit composed of indium tin oxide (ITO) or a conductive metal film (such as Au, Ag or Cu) and a polymer film (such as polyethylene terephthalate, PET) or glass. The interdigitated electrode circuit is etched or evaporated into a finger-cross shape, so it is called an interdigitated electrode; the shape of the interdigitated fingers can be square, arc, cone, etc.; the number of interdigitated fingers can be 1 to 50 pairs (two interdigitated fingers are considered one pair); see Figure 2 shown.

[0027] In the present invention, the interdigitated electrode layer has an interdigitated region with a gap width of about 10-50 μm.

[0028] In the present invention, the thickness of the flexible film layer is preferably 10 to 100 μm.

[0029] The ITO nanocrystal-plant fiber pressure sensor of the present invention has high sensitivity, simple structure, easy process, low production cost, small size and flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the overall structure of an ITO nanocrystal-plant fiber pressure sensor.

[0031] Figure 2 2 is a top view of the interdigitated electrode layer structure.

[0032] Figure 3 This is the waveform of the wrist pulse wave measured by the ITO nanocrystal-plant fiber pressure sensor at a voltage of 3V.

[0033] Numbers in the figure: 1-flexible encapsulation layer; 2-ITO nanocrystal-plant fiber composite elastic layer; 3-interdigitated electrode conductive surface; 4-interdigitated electrode non-conductive surface; 5-interdigitated electrode layer. DETAILED DESCRIPTION

[0034] The following will further describe the technical solution of the present invention in detail with reference to the embodiments of the present invention and the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention and are only used to explain the present invention, not all embodiments, and should not be understood as limiting the present invention.

[0035] The ITO nanocrystal-plant fiber pressure sensor provided by the present invention consists of an interdigital electrode layer, an ITO nanocrystal-plant fiber composite material elastic layer and a flexible packaging layer; wherein the ITO nanocrystal-plant fiber composite material elastic layer is a composite material mixed with plant fibers and ITO nanocrystals; the packaging layer covers the ITO nanocrystal-plant fiber composite material elastic layer and the interdigital electrode interdigital area.

[0036] In the present invention, the interdigital electrode layer is an etched circuit composed of ITO and PET polymer films, and the interdigital region electrode circuit is etched into a finger-cross shape.

[0037] In the present invention, the circuit of the interdigitated electrode layer is deposited on a layer of PET film and etched into the required pattern. It is integrated and does not require the process of binding the two electrodes. Moreover, the integrated structure of the interdigitated electrode layer is also beneficial to protecting the ITO nanocrystal-plant fiber composite material elastic layer between the interdigitated electrode layer and the flexible film layer.

[0038] The encapsulation layer covers the ITO nanocrystal-plant fiber composite elastic layer and the interdigital electrode interdigital area, which helps to stabilize and protect the final product and ensure the long-term use of the product.

[0039] The present invention provides a method for preparing an ITO nanocrystal-plant fiber pressure sensor, and the specific steps are as follows:

[0040] (1) Prepare the elastic layer of ITO nanocrystal-plant fiber composite material. Add 0.02 g of qualitative filter paper fragments to 3 ml of deionized water and stir for 4 hours until the paper fragments become pulpy. Add 0.08-0.2 g of ITO nanocrystals and continue stirring for 1 hour. Use a pipette to draw 1 ml of the mixed solution into the mold and place it in a 100°C oven to dry into a film.

[0041] (2) Transferring the ITO nanocrystal-plant fiber composite elastic layer to the interdigital electrode layer, and ensuring that the size of the ITO nanocrystal-plant fiber composite elastic layer coincides with the interdigital range of the interdigital electrode layer;

[0042] (3) Covering the back of the interdigital region of the interdigital electrode layer with a flexible film layer;

[0043] (4) trimming the ITO nanocrystal-plant fiber composite elastic layer and the flexible film layer on both sides of the interdigital region of the interdigital electrode layer;

[0044] (5) Encapsulating the ITO nanocrystal-plant fiber elastic substrate layer and the flexible film layer on both sides of the interdigital region of the interdigital electrode layer to form a flexible encapsulation layer.

[0045] In a preferred embodiment, in step (1), the ITO nanocrystal-plant fiber sensing layer is formed by compounding ITO nanocrystals and plant fibers into a thin film, and the thin film is cut into the same size as the interdigital region.

[0046] In step (2), the thickness of the elastic layer of the ITO nanocrystal-plant fiber composite material is 0.2-1 mm.

[0047] In step (3), the flexible film layer may be a flexible film such as PI (polyimide) or PP (polypropylene) with a thickness of 10 to 100 μm.

[0048] In step (3), the interdigitated electrode has an interdigitated region where the interdigitated gap width is approximately 10 to 50 μm.

[0049] In step (4), the flexible film layer covers the back side of the electrode corresponding to the interdigital region of the interdigital electrode, so that the ITO nanocrystal-plant fiber composite elastic layer is located between the flexible film layer and the interdigital region of the interdigital electrode and the substrate layer.

[0050] In a preferred embodiment, in step (5), the packaging material is coated on the surfaces and surrounding interfaces of the ITO nanocrystal-plant fiber composite elastic layer and the flexible film layer on both sides of the interdigital region of the interdigital electrode layer, and dried to form a packaging layer.

[0051] In another preferred embodiment, in step (5), part of the elastic layer and the flexible film layer of the ITO nanocrystal-plant fiber composite material are vertically immersed in the packaging material. After drying and solidification, the ITO nanocrystal-plant fiber pressure sensor is dug out together with a part of the solidified packaging material, and the excess packaging material is cut off according to the packaging thickness.

[0052] The present invention will be further described below with reference to the accompanying drawings, but is not intended to limit the present invention.

[0053] Example 1

[0054] In this embodiment, an interdigital electrode 4 with an interdigital area of ​​5×5 mm is used as an example. The protective films on both sides of the ITO interdigital electrode 5 are removed, and a multimeter is used to distinguish the conductive surface 3 and non-conductive surface 4 of the ITO interdigital electrode, that is, the ITO surface 3 and non-ITO surface 4 of the ITO interdigital electrode.

[0055] To prepare the elastic layer of an ITO nanocrystal-plant fiber composite, add 0.02 g of qualitative filter paper fragments to 3 ml of deionized water and stir for 4 hours until the paper fragments become a pulp. Then add 0.2 g of ITO nanocrystals and continue stirring for 1 hour. Use a pipette to transfer 1 ml of the mixed solution into a mold and dry it in a 100°C oven to form a film.

[0056] The basic components of Corning SYLGARD 184 are thoroughly mixed with its curing agent in a weight ratio of 10:1. The bubbles can be removed by vacuuming.

[0057] The ITO nanocrystal-plant fiber film is cut into the same size as the interdigital region to obtain the ITO nanocrystal-plant fiber composite elastic layer 2 .

[0058] The ITO nanocrystal-plant fiber composite elastic layer 2 is placed on the experimental table with the substrate layer facing upward, and the interdigitated electrode layer 5 is placed on the ITO nanocrystal-plant fiber composite elastic layer 2 so that the interdigitated area of ​​the interdigitated electrode conductive surface 3 overlaps with the ITO nanocrystal-plant fiber composite elastic layer 2.

[0059] Apply a flexible film layer (PI film) to the corresponding locations on the non-conductive surface 4 of the interdigital electrode interdigital region, ensuring it overlaps with the PI film (i.e., the flexible film layer) on the conductive surface of the interdigital electrode. Remove any excess PI film along the edges of the interdigital electrode layer 5 and trim it. Gently pinch the edges of the PI film on both sides of the interdigital electrode layer 5 to secure it.

[0060] The interdigital electrode interdigital area is completely immersed in the prepared Dow Corning SYLGARD184 silicone. After taking it out, the excess flow is scraped off and the silicone adhered to the two sides of the PI film is made uniform, thereby forming a flexible packaging layer 1 around the ITO nanocrystal-plant fiber composite elastic layer 2, the interdigital electrode layer 5 and the PI film.

[0061] The prepared ITO nanocrystal-plant fiber sensor is hung in an oven at a temperature of 25-105°C and can be taken out after the flexible encapsulation layer 1 is solidified.

[0062] The working principle of the ITO nanocrystal-plant fiber pressure sensor is as follows:

[0063] When pressure is applied to the ITO nanocrystal-plant fiber pressure sensor, the elastic layer 2 of the ITO nanocrystal-plant fiber composite material is squeezed by the interdigitated electrode layer 5 and the flexible packaging layer 1, and the contact area between the elastic layer 2 of the ITO nanocrystal-plant fiber composite material and the interdigitated electrode increases. The contact area between the ITO nanocrystal particles also increases, and the number of grains that are conductive to each other increases, resulting in an increase in the number of micro-conductive paths between the two interdigitated fingers on the interdigitated electrode layer 5, and the resistance of the ITO nanocrystal-plant fiber pressure sensor decreases.

[0064] like Figure 3 Shown is the wrist pulse waveform measured by the ITO nanocrystal-plant fiber pressure sensor at a voltage of 3 V.

Claims

1. A pressure sensor of ITO nanocrystal-plant fiber composite material, characterized in that: It consists of an interdigital electrode layer, an ITO nanocrystal-plant fiber composite elastic layer, a flexible film layer and a flexible packaging layer; wherein: The interdigitated electrode layer is divided into an interdigitated electrode interdigital region and an interdigitated electrode plane region; The ITO nanocrystal-plant fiber composite elastic layer is a composite material formed by mixing plant fibers and ITO nanocrystals; the thickness of the ITO nanocrystal-plant fiber composite elastic layer is 0.2 to 1 mm, wherein the particle size of the ITO nanocrystals is 10 to 50 nm, and the weight ratio of the plant fibers to the ITO nanocrystals is 1:4 to 1:10; the ITO nanocrystal-plant fiber composite elastic layer covers the interdigital region of the interdigital electrode and overlaps with the interdigital region of the interdigital electrode; The flexible film layer covers the interdigitated electrode plane area; The flexible encapsulation layer is formed by encapsulating the ITO nanocrystal-plant fiber composite elastic layer and the interdigital electrodes; The sensible pressure range of the ITO nanocrystal-plant fiber composite material pressure sensor is 10-100 kPa, which is related to the thickness of the elastic layer of the ITO nanocrystal-plant fiber composite material.

2. The pressure sensor of the ITO nanocrystal-plant fiber composite material according to claim 1, characterized in that: The interdigital electrode layer is an etched circuit composed of indium tin oxide or a conductive metal film and a polymer film or glass. The interdigital electrode circuit is etched or evaporated into a finger-cross shape.

3. The pressure sensor of the ITO nanocrystal-plant fiber composite material according to claim 1, characterized in that: The flexible film layer is a polyimide or polypropylene flexible film.

4. The pressure sensor of the ITO nanocrystal-plant fiber composite material according to claim 1, characterized in that: The flexible packaging layer is elastic organic silicone or thermoplastic elastomer.

5. A method for preparing a pressure sensor of the ITO nanocrystal-plant fiber composite material according to claim 1, comprising the following steps: (1) Preparation of the elastic layer of ITO nanocrystal-plant fiber composite material: Add 0.02 g of qualitative filter paper fragments to 3 ml of deionized water and stir for 4 hours until the paper fragments become pulp-like; add 0.08-0.2 g of ITO nanocrystals and continue stirring for 1 hour; pipette 1 ml of the mixed solution into the mold and place it in a 100°C oven to dry to form a film; (2) transferring the ITO nanocrystal-plant fiber composite elastic layer obtained in step (1) onto the interdigital electrode layer, and ensuring that the size of the ITO nanocrystal-plant fiber composite elastic layer coincides with the interdigital region of the interdigital electrode layer; (3) Covering the back of the interdigital region of the interdigital electrode layer with a flexible film layer; (4) trimming the ITO nanocrystal-plant fiber composite elastic layer and the flexible film layer on both sides of the interdigital region of the interdigital electrode layer; (5) Encapsulating the ITO nanocrystal-plant fiber composite elastic layer and the flexible film layer on both sides of the interdigital region of the interdigital electrode layer to form a flexible encapsulation layer.

6. The preparation method according to claim 5, characterized in that The flexible packaging layer is formed as described in step (5), and its operation steps are as follows: coating the packaging material on the surface and surrounding interfaces of the ITO nanocrystal-plant fiber elastic layer and the flexible film layer on both sides of the interdigital area of ​​the interdigital electrode layer, and drying to form a flexible packaging layer, or vertically immersing the portion covering the ITO nanocrystal-plant fiber elastic layer and the flexible film layer into the packaging material, and after drying and solidification, digging out the ITO nanocrystal-plant fiber pressure sensor together with a portion of the solidified packaging material, and cutting off the excess packaging material according to the packaging thickness.

7. A use of the ITO nanocrystal-plant fiber pressure sensor according to claim 1, characterized in that: include: In the form of a sensor array, used as a pulse sensor; Tactile sensors for robotic arms; Force or deformation sensors used in wearable electronic devices.

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