CN114858872A - Flexible humidity sensor based on ink-jet printing and preparation process thereof - Google Patents

Flexible humidity sensor based on ink-jet printing and preparation process thereof Download PDF

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Publication number
CN114858872A
CN114858872A CN202210366875.8A CN202210366875A CN114858872A CN 114858872 A CN114858872 A CN 114858872A CN 202210366875 A CN202210366875 A CN 202210366875A CN 114858872 A CN114858872 A CN 114858872A
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China
Prior art keywords
capacitor
electrode plate
flexible
ink
layer
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Pending
Application number
CN202210366875.8A
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Chinese (zh)
Inventor
李辉
张云帆
甄羽飞
申胜男
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Wuhan University WHU
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Wuhan University WHU
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Priority to CN202210366875.8A priority Critical patent/CN114858872A/en
Publication of CN114858872A publication Critical patent/CN114858872A/en
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/223—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity
    • G01N27/225—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance for determining moisture content, e.g. humidity by using hygroscopic materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/0041—Digital printing on surfaces other than ordinary paper
    • B41M5/0047—Digital printing on surfaces other than ordinary paper by ink-jet printing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
    • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
    • B41M5/0041—Digital printing on surfaces other than ordinary paper
    • B41M5/0064—Digital printing on surfaces other than ordinary paper on plastics, horn, rubber, or other organic polymers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/221—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance by investigating the dielectric properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
    • G01N27/22—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating capacitance
    • G01N27/226—Construction of measuring vessels; Electrodes therefor

Abstract

The invention discloses a flexible humidity sensor based on ink-jet printing and a preparation process thereof, wherein a flexible substrate is firstly oxidized to change the hydrophilicity of the flexible substrate, and then an ink-jet printing bottom circuit, namely a capacitor bottom electrode plate and an inductance coil, is carried out on the flexible substrate; after drying the bottom layer circuit, covering an insulating layer on the bottom layer circuit based on an ink-jet printing technology or a coating technology; then preparing a water absorption layer on the insulating layer; and processing a top circuit, namely a capacitor top electrode plate and a lead wire, by an ink-jet printing technology after the surface of the water absorption layer is modified, so that the lead wire is communicated with a bottom circuit, the capacitor bottom electrode plate, the capacitor top electrode plate and the water absorption layer positioned between the capacitor bottom electrode plate and the capacitor top electrode plate form a flat humidity-sensitive capacitor together, the flat humidity-sensitive capacitor and an inductance coil form an LC resonance circuit, and the preparation of the flexible humidity sensor is completed. The wearable patch has the advantages of simple structure, flexibility, application and the like, is simple in preparation process, low in cost, green and environment-friendly in preparation process, and is suitable for large-scale popularization and application.

Description

Flexible humidity sensor based on ink-jet printing and preparation process thereof
Technical Field
The invention belongs to the technical field of humidity sensors, relates to a flexible humidity sensor preparation technology, and particularly relates to a flexible humidity sensor based on ink-jet printing and a preparation process thereof.
Background
The humidity sensor plays an important role in the fields of agriculture, industry, meteorology, military and the like, replaces the traditional wet-dry bulb hygrometer and the traditional hair hygrometer, and can stably and accurately measure the environmental humidity. Common humidity sensors are mainly classified into two types, namely resistance type and capacitance type, and the basic structure of the humidity sensor is that a layer of humidity sensitive material is coated on a substrate by utilizing a semiconductor preparation process (photoetching, sputtering and the like) to form a humidity sensitive film. After the humidity sensing film absorbs water vapor, the impedance, relative dielectric constant and geometric dimension of the element are greatly changed, so that the humidity sensing element is manufactured.
Common resistance-type humidity sensors include metal oxide humidity-sensitive resistors, silicon humidity-sensitive resistors, ceramic humidity-sensitive resistors and the like, have the advantages of high precision and high sensitivity, but have poor linearity and product interchangeability, and are mostly made of rigid materials. Common capacitive humidity sensors are generally made of polymer films (polystyrene, polyimide, etc.), and although the precision is generally lower than that of a humidity-sensitive resistor, the humidity-sensitive capacitor has the characteristics of good sensitivity, linearity, interchangeability, response speed and easiness in realizing miniaturization, integration and flexibility, so that the humidity-sensitive capacitor becomes the mainstream in the wearable market.
Inkjet printing (inkjet printing) is known as digital writing technology and operates on the principle of depositing a large number of tiny droplets of ink generated at a jet directly onto a substrate under digital control. The pattern of the ink-jet printing is defined by a digital file instead of a template set manually, so that the pattern is easy to change, low in setting cost and short in time, and is very suitable for short-term printing. With the increasing technical stability and robustness, inkjet printing has gained an increasingly important share in the printing market and is now widely used for printing variable information in a production environment, even for printing customized products.
In recent years, with the rapid development of flexible electronic devices, how to reduce the manufacturing cost, shorten the development cycle, and reduce environmental pollution while achieving flexibility, ensuring sensitivity and reliability by designing a sensor structure and improving a material preparation process becomes a research field which is receiving much attention, and the introduction of an inkjet printing technology is one of the main solutions at present.
Disclosure of Invention
Aiming at the defects of high cost, incapability of bending a substrate and the like of the existing humidity sensor based on a semiconductor process, the invention provides the flexible humidity sensor based on ink-jet printing and the preparation process thereof, so that the defects of the original product and process are overcome, the flexibility is realized, and the industrial and time costs are saved.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the invention provides a flexible humidity sensor based on ink-jet printing, which sequentially comprises the following structures from bottom to top:
a flexible substrate, using a biocompatible material that is bendable but not extensible;
the bottom layer circuit comprises a capacitor bottom electrode plate printed on the flexible substrate through ink jet and an inductance coil connected with the capacitor bottom electrode plate;
an insulating layer covering the flexible insulating material on the bottom layer circuit;
the water absorption layer is arranged on the insulating layer and is a flexible high polymer film capable of absorbing water and expanding and used for sensing moisture, and the insulating layer and the water absorption layer are exposed out of the lead heads of the induction coil;
the top layer circuit comprises a capacitor top electrode plate printed on the water absorbing layer based on ink jet, and micropores which are convenient for the water absorbing layer to absorb moisture and evaporate are arranged on the capacitor top electrode plate; the capacitor top electrode plate is connected with the inductance coil on the bottom layer circuit through a conductive lead;
the capacitor bottom electrode plate, the capacitor top electrode plate and the water absorption layer positioned between the capacitor bottom electrode plate and the capacitor top electrode plate form a flat-plate humidity-sensitive capacitor together.
The insulating layer is used for separating the capacitor bottom electrode plate from the capacitor top electrode plate and avoiding short circuit breakdown of the capacitor.
The plate humidity sensitive capacitor and the inductance coil form an LC resonance circuit together. When the environmental humidity is increased, the water absorption layer absorbs water and expands, the thickness and the relative dielectric constant of the water absorption layer change, so that the plate capacitor formed by the capacitor bottom electrode plate and the capacitor top electrode plate changes, the resonance frequency change of the LC resonance circuit is detected by the external vector network analyzer, the element humidity response curve is calibrated according to the experimental result, and the humidity measurement function is realized.
Preferably, the capacitor bottom electrode plate and the capacitor top electrode plate are parallel to each other, are opposite in position and have the same size, and therefore stability and symmetry of the sensor structure are improved.
Preferably, the water absorption layer is made of a biodegradable polyvinyl alcohol (PVA) material with good adhesion and film forming property.
Preferably, the thicknesses of the bottom layer circuit and the top layer circuit based on ink jet printing processing are both 100-300nm, and the optimal thickness is 200nm, so that the thicknesses of the bottom layer circuit and the top layer circuit can be ignored in the preparation and packaging process, the adjacent two layers of flexible materials can be directly overlapped to realize packaging, and packaging structures such as other adhesives are not needed.
Preferably, the thickness of the flexible substrate is 50-100 μm, and the thickness of the insulating layer and the water absorption layer is 200-500 nm.
Preferably, the flexible humidity sensor has the overall thickness of 10-100 mu m and the area of 10-100 mm 2 。
Preferably, the biocompatible material is Polyimide (PI), but is not limited thereto.
Preferably, the flexible insulating material is Polydimethylsiloxane (PDMS) and/or polytrimethylene carbonate (PTMC), but is not limited thereto.
Preferably, the insulating layer and the water absorbing layer are prepared by ink jet printing or coating.
Preferably, the capacitor top electrode plate is of a metal film mesh structure, the aperture of the mesh on the metal film is in a micron order, the shape of the metal film is not limited to square, round, triangular and the like, and the size and the distance can be changed according to actual requirements.
Preferably, the bottom layer circuit and the top layer circuit are printed by adopting nano silver ink.
The invention also provides a preparation process of the flexible humidity sensor, which is characterized by comprising the following steps of:
s1, preparing a flexible substrate;
s2, subjecting the flexible substrate to an oxidation treatment to change its hydrophilicity so that inkjet printing can be performed thereon;
s3, processing a bottom layer circuit, namely a capacitor bottom electrode plate and an inductance coil, based on the ink-jet printing technology, and connecting the capacitor bottom electrode plate and the inductance coil;
s4, drying the bottom layer circuit to enable the bottom layer circuit to have the conductive capability after being solidified;
s5, covering an insulating layer on the bottom layer circuit based on an ink-jet printing technology or a coating technology, and exposing the lead heads;
s6, preparing a water absorption layer on the insulating layer based on an ink-jet printing technology or a coating technology, and exposing the lead heads;
s7, oxidizing the water absorbing layer to change its hydrophilicity so that ink-jet printing can be performed thereon;
s8, processing a top layer circuit, namely a capacitor top electrode plate and a lead wire, based on an ink-jet printing technology, and printing the lead wire onto an inductance coil to enable the lead wire to be communicated with a bottom layer circuit;
and S9, drying the top layer circuit to enable the top layer circuit to have the conductive capability after being solidified.
Preferably, the oxidation treatment described in steps S2 and S7 employs an ultraviolet ozone lamp irradiation treatment.
Preferably, the polymer material solution of the insulating layer in step S5 and the water-absorbing layer in step S6 easily blocks the nozzle of the inkjet printing apparatus, and a common coating process in semiconductor manufacturing may be used instead of inkjet printing.
Preferably, a flexible protection layer can be covered on the top layer circuit, and a humidity sensitive window is formed in the corresponding position of the capacitor top electrode plate of the flexible protection layer, so that moisture absorption and evaporation are facilitated.
The invention also provides an application of the flexible humidity sensor, which is characterized in that: the device is matched with a vector network analyzer and used in the fields of organism surface sweat detection, robot electronic skin, radian surface humidity detection and the like.
Compared with the prior art, the invention has the beneficial effects that:
1. the flexible humidity sensor based on ink-jet printing has the advantages of simple structure, flexibility, wearable application and the like, can be processed into various shapes, particularly adopts a high-molecular film material capable of absorbing water and expanding as a water absorbing layer, can realize single response to humidity with high sensitivity, high reliability and long service life, and can be used in the fields of biological sweat detection, robot electronic skin, radian surface humidity detection and the like;
2. the preparation process of the flexible humidity sensor based on ink-jet printing has the advantages of low cost, environmental protection and no toxicity, auxiliary materials are not needed in the preparation process, special processes of large-scale equipment are not needed, toxic reagents (such as photoresist) are not used, all consumables are used on a finished product, and no extra waste is generated;
3. the preparation process of the humidity sensor based on ink-jet printing provided by the invention adopts full-digital manufacturing, the humidity sensor except the flexible substrate is processed by ink-jet printing equipment, the humidity sensor can be continuously manufactured and formed at one time in situ after a substrate is laid, and the pattern printed by ink-jet printing is defined by a digital file, is easy to modify, and has the advantages of editable property and short research and development period.
Drawings
Fig. 1 is a schematic structural diagram of a flexible humidity sensor based on inkjet printing according to an embodiment of the present invention.
Fig. 2 is an exploded view of a flexible humidity sensor based on inkjet printing according to an embodiment of the present invention.
Fig. 3 is a schematic cross-sectional view of a flexible humidity sensor based on inkjet printing according to an embodiment of the present invention.
For convenience of expression, in fig. 1 and 2, the thicknesses of the bottom layer circuit and the top layer circuit are relatively enlarged by many times, and are actually small, and the substrate, the insulating layer and the water absorption layer are flexible, so that the substrate, the insulating layer and the water absorption layer are actually attached together as shown in fig. 3.
1-flexible substrate, 2-bottom circuit, 3-insulating layer, 4-water absorbing layer, 5-top circuit, 21-capacitor bottom electrode plate, 22-inductance coil, 51-capacitor top electrode plate, 52-lead and 53-micropore.
Detailed Description
The device of the present invention will be described in detail below with reference to the accompanying drawings.
As shown in FIG. 1, the present invention provides a flexible humidity sensor based on ink-jet printing, comprising
A flexible substrate 1, made of a biocompatible material that is bendable but not extensible;
a bottom layer circuit 2 including a capacitor bottom electrode plate 21 printed on a flexible substrate by ink-jet printing and an inductance coil 22 connected to the capacitor bottom electrode plate;
an insulating layer 3 covering the flexible insulating material on the bottom layer circuit;
the water absorption layer 4 is arranged on the insulating layer, is a flexible polymer film capable of absorbing water and expanding and is used for sensing moisture, and the insulating layer and the water absorption layer are exposed out of the inductance coil;
the top layer circuit 5 comprises a capacitor top electrode plate 51 printed on the water absorbing layer based on ink jet, and micropores 53 convenient for the water absorbing layer to absorb moisture and evaporate are formed in the capacitor top electrode plate; the top plate of the capacitor is connected to the inductor coil 23 on the bottom layer circuit by a conductive lead 52;
the capacitor bottom electrode plate 21, the capacitor top electrode plate 51 and the water absorption layer 4 positioned between the capacitor bottom electrode plate and the capacitor top electrode plate form a flat-plate humidity-sensitive capacitor together, and the flat-plate humidity-sensitive capacitor and the inductance coil 22 form an LC resonance circuit. When the environmental humidity increases, the water absorption layer 4 absorbs water and expands, the thickness and the relative dielectric constant of the water absorption layer change, so that the plate capacitor formed by the capacitor bottom electrode plate 21 and the capacitor top electrode plate 51 changes, the resonance frequency change of the LC resonance circuit is detected by an external vector network analyzer, the humidity response curve of the element is calibrated according to the experimental result, and the humidity measurement function is realized.
Specifically, this embodiment of the present invention comprises the steps of:
(1) washing and drying 8mm 10mm 74 μm PI-based flexible substrate 1;
(2) carrying out oxidation treatment on the flexible substrate 1 for 2min by using an ultraviolet ozone lamp to change the hydrophilicity thereof, so that inkjet printing can be carried out thereon;
(3) printing a bottom layer circuit 2 with the thickness of 200nm, namely a capacitor bottom electrode plate 21 and an inductance coil 22, on a flexible substrate 1 by using nano silver ink;
(4) drying the bottom layer circuit 2 at 150 ℃ for 30min to enable the cured bottom layer circuit to have the conductive capability;
(5) coating a PDMS film with the thickness of 500nm, namely an insulating layer 3, on the bottom layer circuit 2 by using a spin coater;
(6) coating a layer of PVA solution on the insulating layer 3 by a spin coater, and drying the water in the PVA at a low temperature of 45 ℃ to obtain a PVA film with the thickness of 180nm (about 360nm after complete water absorption and expansion), namely a water absorption layer 4;
(7) carrying out oxidation treatment on the water absorption layer 4 for 10min by using an ultraviolet ozone lamp to change the hydrophilicity of the water absorption layer so as to carry out ink-jet printing on the water absorption layer;
(8) printing a top layer circuit 5 with the thickness of 200nm, namely a capacitor top electrode plate 51 with a mesh structure and a lead 52 on the water absorption layer 4 by using nano silver ink, communicating the lead 52 with the inductance coil 22 to form an LC resonance circuit, and drying the bottom layer circuit 2 at 150 ℃ for 30min to enable the bottom layer circuit 2 to have the conductivity after being solidified;
(9) the obtained flexible humidity sensor is connected with a vector network analyzer, the humidity is changed through a temperature and humidity test box, the resonance frequency change of an LC resonance circuit of the sensor under 10% -90% RH is measured, the humidity response curve of the element is calibrated, and the humidity measurement function is realized.
The flexible humidity sensing device is soft and skin-friendly, convenient to wear and apply, simple in structure, low in cost, environment-friendly and non-toxic, can realize single response to humidity with high sensitivity, high reliability and long service life, has the advantages of being capable of editing in digital manufacturing, short in research and development period, one-step forming and the like due to the fact that the preparation process of the flexible humidity sensing device is integrated with an ink-jet printing technology, is suitable for large-scale industrial production, and can be applied to the fields of biological sweat detection, robot electronic skin, radian surface depth detection and the like.
It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments, which are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention accordingly. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A flexible humidity sensor based on ink-jet printing is characterized by comprising
A flexible substrate, using a biocompatible material that is bendable but not extensible;
the bottom layer circuit comprises a capacitor bottom electrode plate printed on the flexible substrate through ink jet and an inductance coil connected with the capacitor bottom electrode plate;
an insulating layer covering the flexible insulating material on the bottom layer circuit;
the water absorption layer is arranged on the insulating layer and is a flexible high polymer film capable of absorbing water and expanding and used for sensing moisture, and the insulating layer and the water absorption layer are exposed out of the inductance coil;
the top layer circuit comprises a capacitor top electrode plate which is processed on the water absorbing layer based on ink-jet printing, and micropores which are convenient for the water absorbing layer to absorb moisture and evaporate are arranged on the capacitor top electrode plate; the capacitor top electrode plate is connected with the inductance coil on the bottom layer circuit through a conductive lead;
the capacitor bottom electrode plate, the capacitor top electrode plate and the water absorption layer positioned between the capacitor bottom electrode plate and the capacitor top electrode plate form a flat-plate humidity-sensitive capacitor together, and the flat-plate humidity-sensitive capacitor and the inductance coil form an LC resonance circuit.
2. The flexible humidity sensor of claim 1, wherein: the capacitor bottom electrode plate and the capacitor top electrode plate are parallel to each other, opposite in position and identical in size.
3. The flexible humidity sensor of claim 1, wherein: the thicknesses of the bottom layer circuit and the top layer circuit based on the ink-jet printing processing are both 100-300 nm.
4. The flexible humidity sensor of claim 1, wherein: the thickness of the flexible substrate is 50-100 mu m, and the thickness of the insulating layer and the water absorption layer is 200-500 nm.
5. The flexible humidity sensor of claim 1, wherein: the flexible humidity sensor is 10-100 mu m in overall thickness and 10-100 mm in area 2 。
6. The flexible humidity sensor according to any one of claims 1 to 5, wherein: the biocompatible material is polyimide.
7. The flexible humidity sensor according to any one of claims 1 to 5, wherein: the flexible insulating material is polydimethylsiloxane and/or polytrimethylene carbonate.
8. The flexible humidity sensor according to any one of claims 1 to 5, wherein: the insulating layer and the water absorbing layer are prepared by printing or coating.
9. A process for preparing a flexible humidity sensor according to any one of claims 1 to 8, comprising the steps of:
s1, preparing a flexible substrate;
s2, subjecting the flexible substrate to an oxidation treatment to change its hydrophilicity so that inkjet printing can be performed thereon;
s3, processing a bottom layer circuit, namely a capacitor bottom electrode plate and an inductance coil, based on the ink-jet printing technology;
s4, drying the bottom layer circuit to enable the bottom layer circuit to have the conductive capability after being solidified;
s5, covering an insulating layer on the bottom layer circuit based on an ink-jet printing technology or a coating technology;
s6, preparing a water absorbing layer on the insulating layer based on an ink-jet printing technology or a coating technology;
s7, oxidizing the water absorbing layer to change its hydrophilicity so that ink-jet printing can be performed thereon;
and S8, processing the top layer circuit, namely the capacitor top electrode plate and the leads based on the ink-jet printing technology, so that the leads are communicated with the bottom layer circuit.
10. The production process according to claim 9, wherein the oxidation treatment in steps S2 and S7 is ultraviolet ozone lamp irradiation treatment.
CN202210366875.8A 2022-04-08 2022-04-08 Flexible humidity sensor based on ink-jet printing and preparation process thereof Pending CN114858872A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN202210366875.8A CN114858872A (en) 2022-04-08 2022-04-08 Flexible humidity sensor based on ink-jet printing and preparation process thereof

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN202210366875.8A CN114858872A (en) 2022-04-08 2022-04-08 Flexible humidity sensor based on ink-jet printing and preparation process thereof

Publications (1)

Publication Number Publication Date
CN114858872A true CN114858872A (en) 2022-08-05

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