Paper-based sensor and its preparation method

Abstract

A novel paper-based sensor with simple preparation process, low cost and high sensitivity, and its preparation method. The paper-based sensor not only selects paper as the substrate and fully utilizes the micro-nano structure on the paper surface to achieve high-sensitivity measurement of the sensor, but also can achieve measurement of large deformations through methods such as folding. The proposed paper-based sensor is mainly used for the detection of mechanical quantities and related signals, and can be divided into capacitive and resistive strain sensors according to the measurement principle. They can be fabricated using very simple methods such as common cutting and bonding, and have the advantages of simple process, low cost, environmental friendliness, and can be made into various shapes and sizes according to the test requirements. In addition, according to the advantages of light weight and easy folding of paper, and the ability to be patterned by methods such as printing, writing, and printing, structures such as electrodes, leads, sensitive units, and deformation units can be fabricated on paper in batches and at low cost.

Description

Technical Field

[0001] The present invention relates to the field of sensors, and particularly to a paper-based sensor and a preparation method thereof. Background Art

[0002] As a precision device or component, a sensor can convert various non-electric signals that are not easily captured or measured into electric signals that are easy to detect and display. It is an essential part of modern industrial production, medical and health care, aerospace, wearable applications, etc. Among them, a mechanical quantity sensor converts the detected force or displacement signal into a corresponding electric signal, and is mainly used for the measurement of various direct forces such as pressure, tension, tensile force, torque, or the conversion of physical quantities such as displacement, acceleration, angle, angular velocity, liquid level, etc. It is also one of the sensors with the widest application range and the largest demand at present. Currently, the commonly used force sensors mainly use materials such as semiconductor silicon, metal, ceramic, polymer, etc. as the sensitive materials or substrates of the sensors. With the development of technologies such as wearable medical care and flexible electronics, as well as the continuous improvement of requirements for green and environmental protection of electronic devices, the research on sensors with high sensitivity, large deformation measurement, low cost, and green environmental protection has become one of the trends in the development of sensors.

[0003] As one of the four great inventions in ancient China, paper has long been used for various purposes such as writing, recording, printing, painting, or packaging. Paper is made from pulp suspended in water, deposited on the forming wire of a paper machine to form a complex fiber layer, and then processed through processes such as pressing and drying. It has the advantages of being inexpensive and easily available, light in weight, can be shaped by simple processes such as cutting, folding, stamping, and laser cutting, can be patterned and processed on the surface by methods such as writing, printing, spraying, and micro-nano processing, and is green and environmentally friendly, easy to recycle and process, etc. Therefore, using paper to prepare sensors can, to a certain extent, reduce the preparation cost of sensors, improve the environmental protection level of sensors, and at the same time, the natural structure on the paper surface or the large-size structure prepared by folding can also greatly improve the sensitivity of the sensors and realize large deformation measurement.

[0004] In recent years, with the development of new technologies such as micro-nano, sensors, and precision manufacturing, some research institutions have used paper to make biochemical sensors for the detection of biochemical parameters, but there is less research on paper-based mechanical quantity sensors. And currently reported paper-based mechanical quantity sensors mainly use paper as a carrier and need to combine nano materials such as graphene and graphite as sensitive units to realize the detection of mechanical signals. There has been no discovery of directly using the micro-nano structure on the paper surface as a sensitive unit to achieve high-sensitivity detection of mechanical signals.

[0005] For example, the Ren Tianling group used paper as a carrier and combined it with graphite to fabricate a graphite-paper based piezoresistive sensor, achieving pressure measurement within 20 kPa. The sensitivity within a 2 kPa measurement range reached 17.2 kPa -1 , which can meet the pressure signal detection in a large range to a certain extent and improve the sensitivity of the sensor. Although this technical solution also uses paper, the paper mainly plays a structural and supporting role, and its force-sensitive function is mainly realized by the graphite fabricated on the paper.

[0006] Zhang Yue et al. constructed a two-dimensional graphite sheet flexible paper-based strain sensor using POP (Pencil-on-Paper). Its response time is 110 ms, the sensitivity is 536, the minimum resolvable strain is 0.13%, and after 10,000 strain tests, the resistance drift is 10%, greatly improving the sensitivity of the sensor and reducing the manufacturing cost of the sensor. This technical solution also uses paper as a carrier, and two-dimensional graphite sheets are drawn on the paper by a pencil. Its force-sensitive unit is mainly realized by the two-dimensional graphite sheets on the paper.

[0007] Related literature: Tao L Q, Zhang K N, Tian H, et al. Graphene-Paper Pressure Sensor for Detecting Human Motions[J]. ACS nano, 2017, 11(9): 8790 - 8795.

[0008] Liao X, Liao Q, Yan X, et al. Flexible and highly sensitive strain sensors fabricated by pencil drawn for wearable monitor[J]. Advanced Functional Materials, 2015, 25(16): 2395 - 2401.

[0009] Related patents: CN 104613860 A, CN 105115414 A.

[0010] Therefore, the present invention provides a novel paper-based sensor with a simple preparation process, low cost and high sensitivity, and a preparation method thereof. The paper-based sensor not only uses paper as a carrier, makes full use of the micro-nano structure on the paper surface to achieve high-sensitivity measurement of the sensor, but also can achieve large-deformation measurement through methods such as folding. The proposed paper-based sensor is mainly used for the detection of mechanical quantities and related signals, and can be divided into capacitive and resistive strain sensors according to the measurement principle. They can be fabricated by very simple methods such as common cutting and bonding, and have the advantages of simple process, low cost, environmental friendliness, and can be made into various shapes and sizes according to test requirements. In addition, according to the advantages of light weight and easy folding of paper, and the ability to be patterned by methods such as printing, writing, and printing, structures such as electrodes, leads, sensitive units, and deformation units can be fabricated on paper in batches and at low cost. Summary of the Invention

[0011] The present invention provides a paper-based sensor, including: a substrate, a conductive layer, and a wire. The conductive layer is formed on the substrate and is connected to an external measuring instrument or circuit through the wire. It is characterized in that: the substrate material of the sensor is paper, and the high-sensitivity measurement of the sensor is realized by using the micro-nano structure on the paper surface.

[0012] Furthermore, the micro-nano structure can be prepared by folding, imprinting, cutting, stamping, laser cutting, micro-nano manufacturing processes or can be the natural micro-nano structure on the paper surface.

[0013] Optionally, conductive layers are respectively formed on two surfaces of the substrate. The substrate can be one layer, two layers or multiple layers. The substrate can be a combination of the same or different types of paper.

[0014] Optionally, the material of the conductive layer can be selected from conductive tape, metal thin film, conductive silver paste or conductive carbon paste. The conductive layer is prepared by pasting, sputtering, evaporation or printing processes.

[0015] Optionally, it further includes a packaging layer, which is formed on the four peripheral edges of the substrate.

[0016] Optionally, the wire is fixed to the conductive layer by a wire fixing unit. The wire fixing unit is conductive tape or conductive glue.

[0017] On the other hand, the present invention provides a preparation method of a paper-based sensor, including: forming a conductive layer on a substrate, forming a wire on the conductive layer, and connecting the wire to an external measuring instrument or circuit. It is characterized in that: the substrate is paper, and the high-sensitivity measurement of the sensor is realized by using the micro-nano structure on the paper surface.

[0018] Furthermore, the micro-nano structure can be formed by folding, imprinting, cutting, stamping, laser cutting, micro-nano manufacturing processes, or the micro-structure is the natural structure on the paper surface.

[0019] Optionally, a wire fixing unit is used to fix the wire to the conductive layer. The wire fixing unit is a conductive tape or conductive glue.

[0020] Advantages of the present invention:

[0021] 1. In the preparation of the paper-based sensor of the present invention, not only is paper selected as the substrate, but the natural structure on the paper surface or micro-nano structures are prepared through processes such as folding and imprinting for the sensitive units of the sensor. On the one hand, the manufacturing cost of the sensor is reduced, the environmental protection level of the sensor is improved and it is easy to recycle; on the other hand, the existence of micro-nano structures and wrinkles greatly improves the sensitivity of the sensor.

[0022] 2. Utilizing the easy-foldable property of paper, a bent and folded structure is prepared. On the one hand, it leaves room for the deformation of the sensor, thus realizing large deformation and flexible deformation of the sensor and improving the use range of the sensor; on the other hand, due to phenomena such as stress concentration in the folded and bent parts, the sensor can generate large changes in capacitance or resistance when subjected to external forces, so the sensitivity of the sensor can be further improved.

[0023] 3. In the entire preparation process of the paper-based sensor of the present invention, including paper cutting, paper surface patterning, production of conductive parts and combination of various structures of the sensor, the advantages of paper such as being cuttable, easy to fold, writable, printable, etc. are fully utilized. Therefore, the preparation process of this paper-based sensor is simple, low-cost, and can also realize batch production of the sensor.

[0024] 4. The capacitive paper-based sensor in the technical solution of the present invention can realize large deformation measurement of pressure and tension. If surface treatment (such as waterproof encapsulation, etc.) is carried out on it, it can also realize the detection of liquid pressure and liquid level. In addition, the resistive strain type paper-based sensor in the present invention can also realize high-sensitivity measurement of pressure and tension and realize large deformation. Description of the drawings

[0025] Figure 1 is a schematic structural diagram of the paper-based sensor of the present invention;

[0026] Figure 2 is a schematic cross-sectional view of the capacitive paper-based sensor of the present invention;

[0027] Figure 3 is a schematic top view of the capacitive paper-based sensor of the present invention;

[0028] Figure 4 is a schematic working principle diagram of the capacitive paper-based sensor of the present invention;

[0029] Figure 5 (a) is a schematic front view of the resistive strain type paper-based sensor of the present invention (utilizing the natural structure on the paper substrate); Figure 5(b) is the front view schematic diagram of the resistive strain paper-based sensor of the present invention (a large-size structure formed by folding the paper base, etc.). Detailed implementation manners

[0030] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific implementations described herein are only used to explain the present invention and are not used to limit the present invention. On the contrary, the present invention covers any alternatives, modifications, equivalent methods and solutions made within the spirit and scope of the present invention defined by the claims. Further, in order to enable the public to have a better understanding of the present invention, the detailed description of the present invention below can also fully understand the present invention.

[0031] Figure 1 Two embodiments of the present invention are shown, that is, two types of paper-based sensors, one is a capacitive paper-based sensor and the other is a resistive strain paper-based sensor.

[0032] Embodiment 1

[0033] Figure 2 Specifically shows the structure of the capacitive paper-based sensing of the present invention. The capacitive paper-based sensor includes a substrate, that is, the dielectric layer 1, and also includes a conductive layer 2, a packaging layer 3, a wire fixing unit 4 and a wire 5. The dielectric layer 1 is arranged in the middle, and the dielectric layer 1 can be selected as two layers or multiple layers. The conductive layer 2 is arranged on the upper and lower surfaces of the dielectric layer 1, the packaging layer 3 is arranged on the four peripheral edges of the dielectric layer 1, and a wire 5 is respectively connected to the body diagonal positions of the two conductive layers 2. The wire 5 is connected to a measuring instrument or a circuit, and the wire 5 is fixed on the conductive layer 2 through the wire fixing unit 4. The dielectric layer 1 and the conductive layer 2 are continuous rectangular structures, and their length and width are not limited and can be selected according to actual needs. The dielectric layer 1 is a paper-based with insulating properties, and its materials include: lens cleaning paper, rice paper, napkin paper and other flexible papers. The paper base can be a combination of one layer, two layers or multiple layers of paper, or a combination of different types of paper. High-sensitivity measurement is realized by using the micro-nano structure on the paper surface. The micro-nano structure can be formed by processes such as folding, embossing, cutting, stamping, laser cutting, micro-nano manufacturing, or can be the natural structure on the paper surface.

[0034] The conductive layer 2 is a conductive tape, a metal thin film, a conductive silver paste or a conductive carbon paste, and can be prepared by processes such as pasting, sputtering, evaporation coating, printing, etc. The material of the packaging layer 3 can be a tape, such as a transparent tape, a high-temperature tape and other tapes with an adhesive function. The wire fixing unit 4 can be a conductive tape or a conductive adhesive, which has good conductivity and good adhesion to the conductive layer.

[0035] Low-cost cutting to achieve the desired shape can be realized by methods such as cutting and shearing; low-cost paper surface patterning and low-cost, large-scale production of conductive parts can be achieved through processes such as writing, printing, pasting conductive tape, and micro-nano manufacturing; the production and assembly of the structure can be realized by processes such as cutting and bonding.

[0036] As Figure 3 shown, when using a capacitive paper-based sensor to detect mechanical signals, the sensor is placed at a position perpendicular to the force direction. When the capacitive sensor is subjected to pressure, the plate spacing between the dielectric layers decreases, thereby increasing the capacitance to sense the change in external pressure.

[0037] A preparation method of a capacitive paper-based sensor, the method steps are as follows:

[0038] (1) Cut the paper into a rectangular shape with a specified size to make the dielectric layer;

[0039] (2) Cut the conductive tape into a rectangle slightly smaller than the paper size and adhere it to the upper and lower surfaces of the dielectric layer to prepare the conductive layer;

[0040] (3) Package the periphery of the dielectric layer with the conductive layer obtained in step (2);

[0041] (4) At the position of the body diagonal of the capacitive paper-based sensor obtained in step (3), connect a wire along the length direction of the conductive layer and fix it with conductive tape.

[0042] Example Two

[0043] A resistive strain paper-based sensor is divided into two types according to the preparation process of its sensitive unit microstructure: a natural structure and a large-size structure formed by processes such as folding and imprinting, as shown in Figure 5 (a), (b) respectively.

[0044] Strain sensor substrate 1, conductive layer 2, wire fixing unit 3 and wire 4. The substrate is located at the bottom, and the conductive layer 2 is above the substrate 1. At both ends of the conductive layer 2, there is a wire 4 connected to a measuring instrument or circuit. The wire 4 is fixed on the conductive layer 2 through the wire fixing unit 3. The wire 4 is arranged along the length direction at both ends of the conductive layer 2. The substrate 1 is a paper substrate, and micro-nano structures are prepared on the surface of the paper substrate by methods such as imprinting and folding. The conductive layer 2 is prepared by processes such as sputtering, evaporation coating, and printing to form a conductive layer such as a metal thin film, conductive silver paste, or conductive carbon paste with conductive properties. For existing strain-type paper-based sensors, the conductive layer 2 is usually made by writing or coating materials such as graphite and conductive ink on the surface of the paper substrate, which cannot achieve mass production of the sensor and the consistency of the sensor is poor. Therefore, the use of common MEMS processes or printing methods can achieve mass preparation of the sensor and combine the micro-nano sensitive structure with the metal thin film, and can further improve the sensitivity of the sensor. Among them, the sensor can not only sense using the micro-nano structure of the paper itself, but also sense through the micro-nano structures formed by processes such as folding, imprinting, cutting, stamping, and laser cutting.

[0045] A preparation method of a paper-based resistive strain sensor, the method steps are as follows:

[0046] (1) Cut the paper into a specific size, and use methods such as imprinting or folding to prepare a specific pattern or structure on its surface.

[0047] (2) Use the DC sputtering process to prepare a metal thin film on the surface of the paper substrate with micro-structures in step (2).

[0048] (3) Lead out wires along both ends in the length direction on the electrode layer surface of the sensor obtained in step (2) with silver glue to obtain the strain-type paper-based sensor as shown in Figure 5 (b).

[0049] Most of the existing paper-based sensors are piezoresistive or strain sensors. Generally, only paper is selected as the carrier, and sensors are prepared by combining nanomaterials. Therefore, the cost of the sensors is relatively high. During the measurement process, due to the poor adhesion between the nanomaterials and the substrate and the creep of the nanomaterials, the cyclic stability of the sensors is relatively poor. In the present invention, the preparation of the paper-based sensor not only selects paper as the matrix, but also makes full use of the natural structure on the paper surface or prepares micro-nano structures for the sensitive units of the sensor through processes such as folding and imprinting. On the one hand, the manufacturing cost of the sensor is reduced, the environmental protection level of the sensor is improved, and it is easy to recycle; on the other hand, the presence of the micro-nano structures greatly improves the sensitivity of the sensor. During the subsequent testing process, due to the presence of the surface micro-nano structures or large-scale structures such as wrinkles formed through processes such as folding and imprinting, a certain space is reserved for the deformation of the sensor, so the measurement range of the sensor is increased, and large-deformation measurement can be realized. In addition, due to the existence of the micro-structures on the paper surface, when the sensor is under the same acting force, the force deformation of the sensor is more obvious, so the sensitivity is higher. When the capacitive paper-based sensor is under pressure, due to the existence of the micro-structures on the paper surface, there is a large amount of air between the dielectric layers. When the sensor is under force, the air is discharged, the distance between the electrodes is reduced, and thus the capacitance is increased to sense the change of the external pressure. When the resistive strain sensor is under tension or pressure, the folded and bent part will deform first. At the same time, the stress concentration phenomenon on the paper surface of the folded and bent part will cause an obvious change in the resistance of the conductive layer. As the external force further increases, the micro-nano structures on the paper surface begin to be deformed by the force, causing a change in the resistance of the conductive layer, so as to realize high-sensitivity measurement of the sensor within a large measurement range and a small measurement range.

[0050] The processing, manufacturing and other methods of the paper-based capacitance or resistance sensor proposed in the present invention can also be used for the processing and manufacturing of paper-based inductive sensors and the like.

Claims

1. A paper-based sensor, comprising: A substrate, a conductive layer, and a wire. The conductive layer is formed on the substrate and is connected to an external measuring instrument or circuit through the wire. It is characterized in that: the substrate material of the sensor is paper. When the capacitive paper-based sensor is subjected to pressure, due to the existence of the micro-structure on the paper surface, there is a large amount of air between the dielectric layers. When the sensor is stressed, the air is discharged, the distance between the electrodes decreases, and thus the capacitance increases, so as to sense the change of the external pressure. When the resistive strain sensor is subjected to tension or pressure, the folded and bent part will deform first, and at the same time, the stress concentration phenomenon on the paper surface of the bent and folded part will cause a significant change in the resistance of the conductive layer. As the external force further increases, the micro-nano structure on the paper surface begins to be stressed and deformed, causing the resistance of the conductive layer to change, thereby realizing high-sensitivity measurement of the sensor in a large range and a small range. The high-sensitivity measurement of the sensor is realized by using the micro-nano structure on the paper surface, and the micro-nano structure is formed by folding, embossing, cutting, stamping or laser cutting.

2. The paper-based sensor according to claim 1, characterized in that: The conductive layers are respectively formed on two surfaces of the substrate.

3. The paper-based sensor according to claim 2, characterized in that: The substrate can be one layer, two layers or multiple layers.

4. The paper-based sensor according to claim 2, characterized in that: The substrate can be a combination of the same or different types of paper.

5. The paper-based sensor according to claim 2, characterized in that: The material of the conductive layer can be selected from conductive tape, metal thin film, conductive silver paste or conductive carbon paste.

6. The paper-based sensor according to claim 5, characterized in that: The conductive layer is prepared by a process of pasting, sputtering, evaporation or printing.

7. The paper-based sensor according to claim 2, characterized in that: It further includes a packaging layer, which is formed on the four peripheral edges of the substrate.

8. The paper-based sensor according to claim 2, characterized in that: The wire is fixed to the conductive layer by a wire fixing unit.

9. The paper-based sensor according to claim 8, characterized in that: The wire fixing unit is conductive tape or conductive glue.

10. The paper-based sensor according to claim 1, characterized in that: The material of the conductive layer can be selected from metal thin film, conductive silver paste or conductive carbon paste.

11. The paper-based sensor according to claim 10, characterized in that: The conductive layer is prepared by a process of sputtering, evaporation or printing.

12. A preparation method of the paper-based sensor based on claim 1, characterized in that: It includes: A conductive layer is formed on the substrate, and a wire is led out on the conductive layer. The wire is connected to an external measuring instrument or circuit. It is characterized in that: the substrate is paper, and the high-sensitivity measurement of the sensor is realized by using the micro-nano structure on the paper surface, and the micro-nano structure is formed by folding, embossing, cutting, stamping or laser cutting.

13. The preparation method of the paper-based sensor according to claim 12, characterized in that: The wire is fixed to the conductive layer by a wire fixing unit.

14. The preparation method of the paper-based sensor according to claim 13, characterized in that: The wire fixing unit is conductive tape or conductive glue.

Images