CN112945429A - High-sensitivity flexible pressure sensor and manufacturing method thereof - Google Patents
High-sensitivity flexible pressure sensor and manufacturing method thereof Download PDFInfo
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- G01L1/00—Measuring force or stress, in general
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- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/02—Detecting, measuring or recording pulse, heart rate, blood pressure or blood flow; Combined pulse/heart-rate/blood pressure determination; Evaluating a cardiovascular condition not otherwise provided for, e.g. using combinations of techniques provided for in this group with electrocardiography or electroauscultation; Heart catheters for measuring blood pressure
Abstract
A high-sensitivity flexible pressure sensor comprises a first metal electrode layer, a first electret layer, a second electret layer and a second metal electrode layer which are sequentially laminated together, wherein an air cavity is arranged between the first electret layer and the second electret layer, positive and negative charges ionized by air in the air cavity through corona polarization are respectively captured by the first electret layer and the second electret layer to form a charge dipole, the charge dipole and induced charges on the first metal electrode layer and the second metal electrode layer form electric field balance in an initial state, when the sensor is compressed and deformed, dipole moment is changed, the induced charges are transferred to form current on an external circuit, and when pressure is released, the sensor can form reverse current on the external circuit and restore electric field balance due to self elasticity. The sensor has the advantages of long service life, high sensitivity and stability, short process period and low manufacturing cost, and can realize mass production.
Description
Technical Field
The invention relates to a wearable device technology, in particular to a high-sensitivity flexible pressure sensor and a manufacturing method thereof.
Background
With the development of micro-nano processing technology and the development and utilization of various new materials, the pressure sensor has good effects in the aspects of human-computer interfaces, electronic skins, health monitoring, medical diagnosis and the like, and is widely applied. In recent years, pressure sensors have become one of the areas of intense interest to researchers, and are widely used to detect various physiological signals of the human body, such as pulse, blood pressure, and the like. In the previously disclosed documents or patents, various pressure sensors of piezoresistive type, strain type, capacitive type, piezoelectric type, and triboelectric type have been proposed. In summary, researchers hope to improve the performance of sensors and reduce the complexity and cost of their fabrication process by developing new processes (low cost, large scale fabrication processes such as self-assembly, full solution processing, etc.), new materials (graphene, carbon nanotubes, conductive polymers, etc.), and new structural designs (structural designs such as micro-pyramids, micro-pillars, etc. and integration with thin film transistors, TFTs), and new sensing mechanisms (visualization of pressure distribution, multi-directional force sensing, etc.).
However, the existing pressure sensor has insufficient flexibility and large thickness, is difficult to completely fit with the skin, cannot accurately measure the pulse with high signal to noise ratio, and can affect the comfort of a user when being worn for a long time. Most of the existing flexible pressure sensors have low sensitivity and poor stability, and clear and stable pulse waveforms are difficult to obtain; to improve the signal-to-noise ratio of the output signal, existing flexible pressure sensors tend to be large in area, which is disadvantageous for some applications requiring small area sensors, such as measuring fingertip pulses. And most flexible pressure sensors have complex process and long manufacturing period, or need to use dangerous toxic chemical reagents, and are difficult to meet the requirements of mass production and rapid manufacturing and forming in practical application.
It is to be noted that the information disclosed in the above background section is only for understanding the background of the present application and thus may include information that does not constitute prior art known to a person of ordinary skill in the art.
Disclosure of Invention
The main objective of the present invention is to overcome the above problems in the background art, and to provide a high-sensitivity flexible pressure sensor and a manufacturing method thereof.
In order to achieve the purpose, the invention adopts the following technical scheme:
a high-sensitivity flexible pressure sensor comprises a first metal electrode layer, a first electret layer, a second electret layer and a second metal electrode layer which are sequentially laminated together, wherein an air cavity is formed between the first electret layer and the second electret layer, positive and negative charges ionized by air in the air cavity through corona polarization are respectively captured by the first electret layer and the second electret layer to form a charge dipole, the charge dipole and induced charges on the first metal electrode layer and the second metal electrode layer form electric field balance in an initial state, when the sensor is deformed under pressure, dipole moment is changed, the induced charges are transferred to form current on an external circuit, and when pressure is released, the sensor can form reverse current on the external circuit and restore the electric field balance due to the fact that the sensor elastically restores to the original state.
Further:
the first electret layer and/or the second electret layer have a groove on an inner surface thereof.
The inner surface of the first electret layer is provided with a plurality of first strip-shaped grooves which are parallel to each other, the inner surface of the second electret layer is provided with a plurality of second strip-shaped grooves which are parallel to each other, and the first strip-shaped grooves and the second strip-shaped grooves are opposite to each other and are preferably vertical to each other.
The material of the first electret layer and/or the second electret layer is selected from fluorinated ethylene propylene copolymer (FEP), polypropylene (PP), polyvinylidene fluoride (PVDF).
The material of the first metal electrode layer and/or the second metal electrode layer is selected from gold (Au), silver (Ag), copper (Cu), aluminum (Al) and chromium (Cr).
The first metal electrode layer and/or the second metal electrode layer are formed by metal plating films, screen printing or metal adhesive tape bonding.
An enclosed air cavity is formed by the first electret layer and the second electret layer together.
A method of making the high sensitivity flexible pressure sensor, comprising the steps of:
manufacturing a first electret layer and a second electret layer, and oppositely bonding the first electret layer and the second electret layer together to form an air cavity between the first electret layer and the second electret layer;
forming a first metal electrode layer on the outer surface of the first electret layer, and forming a second metal electrode layer on the outer surface of the second electret layer;
wherein positive and negative charges ionized from the air in the air cavity by corona polarization are respectively captured by the first electret layer and the second electret layer to form a charge dipole.
The fabricating the first electret layer and the second electret layer includes: forming grooves on opposing surfaces of the first electret layer and/or the second electret layer.
The first electret layer and the second electret layer are bonded by hot-pressing bonding, chemical agent bonding or glue bonding.
Compared with the prior art, the invention has the following beneficial effects:
in the flexible pressure sensor provided by the invention, an air cavity is arranged between the first electret layer and the second electret layer, positive and negative charges are ionized by corona polarization of the air in the air cavity and are respectively captured by the first electret layer and the second electret layer to form a charge dipole, the charge dipole and induced charges on the metal electrode layer form electric field balance in an initial state, when the sensor is compressed and deformed, dipole moment is changed, the induced charges are transferred to form current on an external circuit, and when pressure is released, the sensor is restored due to elasticity of the sensor, reverse current is formed on the external circuit and the electric field balance is restored, so that the flexible pressure sensor has the capability of stably storing charges for a long time, and the sensor can be used for a long time without performance attenuation, namely, the pressure measuring device has excellent stability and can stably measure weak pressure signals such as pulse for a long time. In addition, the sensor has high sensitivity and can measure a pulse in a small area, which is very advantageous for measuring a fingertip pulse and a vein pulse. The sensor disclosed by the invention can be very light and thin, has good flexibility, can be well contacted with the surface of the skin to obtain a clearer pulse signal, and cannot cause discomfort to a user when being worn for a long time. The sensor is convenient to manufacture a plurality of sensors simultaneously, and the requirements of practical application on mass production and rapid manufacturing and forming are met. The flexible pressure sensor has wide application prospect in the fields of pulse and other physiological signal measurement, electronic skin, human-computer interaction interface and the like.
The advantages of the invention mainly include:
(1) the flexible pressure sensor can realize self-driven measurement of dynamic pressure signals, and can be used for a long time without performance attenuation;
(2) the ultra-thin flexible pressure sensor with high sensitivity and high stability is provided;
(3) the manufacturing process flow with short process period and low manufacturing cost is provided;
(4) by utilizing the sensor structure and the manufacturing process flow thereof, the effects of mass production and convenient size adjustment can be realized.
Drawings
FIG. 1 is a flow chart of a sensor manufacturing process according to an embodiment of the present invention.
Fig. 2a is a schematic structural diagram of a sensor according to an embodiment of the present invention.
Fig. 2b is a cross-sectional view of the sensor of fig. 2a along line I-I.
Fig. 2c is an exploded view of the sensor of fig. 2 a.
Fig. 3 illustrates the working principle of the sensor according to an embodiment of the present invention.
Detailed Description
The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary in nature and is not intended to limit the scope of the invention or its application.
It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element. In addition, the connection may be for either a fixed or coupled or communicating function.
It is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in an orientation or positional relationship indicated in the drawings for convenience in describing the embodiments of the present invention and to simplify the description, and are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed in a particular orientation, and be in any way limiting of the present invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of the present invention, "a plurality" means two or more unless specifically limited otherwise.
Referring to fig. 1 to 3, in an embodiment, a high-sensitivity flexible pressure sensor includes a first metal electrode layer 101, a first electret layer 102, a second electret layer 103, and a second metal electrode layer 104, which are sequentially laminated together, an air cavity 105 is provided between the first electret layer 102 and the second electret layer 103, positive and negative charges ionized by corona polarization in the air cavity 105 are respectively captured by the first electret layer 102 and the second electret layer 103 to form a charge dipole, the charge dipole forms an electric field balance with induced charges on the first metal layer 101 and the second metal layer 104 in an initial state, when the sensor is deformed by pressure, the induced charges are transferred to form a current on an external circuit, when the pressure is released, the sensor is restored due to its elasticity, a reverse current is formed on the external circuit and the electric field balance is restored.
In a preferred embodiment, the first electret layer 102 and/or the second electret layer 103 have grooves on their inner surfaces. The groove pattern can be a periodic line groove pattern, a triangular pyramid groove pattern, a rectangular parallelepiped groove pattern, or the like, or a non-periodic, irregular groove pattern.
In a particularly preferred embodiment, the first electret layer 102 has a plurality of first strip-shaped grooves on its inner surface parallel to each other, and the second electret layer 103 has a plurality of second strip-shaped grooves on its inner surface parallel to each other, the first and second strip-shaped grooves being opposite to each other, and preferably also perpendicular to each other.
In various embodiments, the material of the first electret layer 102 and/or the second electret layer 103 may be selected from fluorinated ethylene propylene copolymer (FEP), polypropylene (PP), polyvinylidene fluoride (PVDF).
In various embodiments, the material of the first metal electrode layer 101 and/or the second metal electrode layer 104 may be selected from gold (Au), silver (Ag), copper (Cu), aluminum (Al), chromium (Cr).
In different embodiments, the first metal electrode layer 101 and/or the second metal electrode layer 104 may be formed by metal plating (such as metal vapor deposition), screen printing, or metal tape bonding.
In a preferred embodiment, an enclosed air cavity 105 is formed by the first electret layer 102 and the second electret layer 103.
Referring to fig. 1 to 3, in another embodiment, a method for manufacturing the high-sensitivity flexible pressure sensor includes the following steps:
manufacturing a first electret layer 102 and a second electret layer 103, and oppositely bonding the first electret layer 102 and the second electret layer 103 together, wherein an air cavity 105 is formed between the first electret layer 102 and the second electret layer 103;
forming a first metal electrode layer 101 on an outer surface of the first electret layer 102, and forming a second metal electrode layer 104 on an outer surface of the second electret layer 103;
wherein positive and negative charges ionized by corona polarization of the air in the air cavity 105 are respectively trapped by the first electret layer 102 and the second electret layer 103 to form a charge dipole.
In a preferred embodiment, said fabricating the first electret layer 102 and the second electret layer 103 comprises: grooves are formed on the opposing surfaces of the first electret layer 102 and/or the second electret layer 103. The grooves can be formed by manual engraving, laser engraving, chemical etching based on a mask (such as a photoetching process, a silk screen mold and the like) and the like.
In various embodiments, the first electret layer 102 and the second electret layer 103 may be bonded by thermocompression bonding, chemical bonding, or glue bonding.
In the flexible pressure sensor provided by the embodiment of the invention, the air cavity 105 is arranged between the first electret layer 102 and the second electret layer 103, positive and negative charges are ionized by corona polarization of the air in the air cavity 105, the positive and negative charges are respectively captured by the first electret layer 102 and the second electret layer 103 to form a charge dipole, the charge dipole and induced charges on the metal electrode layers 101 and 104 form electric field balance in an initial state, when the sensor is pressed and deformed, dipole moment is changed, the induced charges are transferred to form current on an external circuit, and when pressure is released, the sensor is restored due to elasticity of the sensor, reverse current is formed on the external circuit and the electric field balance is restored, so that the flexible pressure sensor can sense pulse of pulse, output corresponding current and realize pulse measurement.
Due to the capability of storing electric charge stably, the electret material enables the sensor to be used for a long time without performance attenuation, namely, the electret material has excellent stability and can stably measure weak pressure signals such as pulse for a long time. In addition, the sensor has high sensitivity and can measure a pulse in a small area, which is very advantageous for measuring a fingertip pulse and a vein pulse. The sensor provided by the embodiment of the invention can be very light and thin (50-100 mu m), has good flexibility, can be in good contact with the surface of the skin to obtain a clearer pulse signal, and does not cause discomfort to a user when being worn for a long time. A plurality of sensors can be manufactured simultaneously, and the requirements of practical application on mass production and rapid manufacturing and forming are met. The flexible pressure sensor provided by the embodiment of the invention has wide application prospects in the fields of pulse and other physiological signal measurement, electronic skin, human-computer interaction interfaces and the like.
Specific embodiments of the present invention are described further below by way of example.
In one embodiment, the flexible piezoelectric electret sensor is fabricated based on laser engraving and thermocompression bonding processes. Using a laser to cut line grooves in two electret films (FEP films are used as an example), placing the line grooves on the two FEP films perpendicular to each other, and thermocompression bonding to form a closed air cavity. After a metal electrode is evaporated on one side of the sensor, the sensor is charged by corona through a high-voltage power supply, and finally, a metal adhesive tape is attached to the other side of the sensor to be used as an electrode on the other side. In an alternative embodiment, the metal electrode subjected to vapor deposition can be replaced by an attached metal tape, so that the cost can be further reduced, the manufacturing period can be shortened, and the robustness of the sensor in long-term use can be improved.
FIG. 1 illustrates an example of a sensor fabrication flow. 101 denotes a first metal electrode layer; 102 denotes a first electret layer; 103 denotes a second electret layer; and 104 a second metal electrode layer. The material of the electret film used may be fluorinated ethylene propylene copolymer (FEP), polypropylene (PP), polyvinylidene fluoride (PVDF), etc., and here, FEP film is preferable; the metal electrode used may be gold (Au), silver (Ag), copper (Cu), aluminum (Al), chromium (Cr), or the like, and is preferably a Cu electrode. In order to achieve the effect of flexibility, the thickness of the electret film can be 10-100 μm, and is preferably 25 μm; the thickness of the metal electrode is 0.1 μm to 10 μm, and preferably 10 μm.
Since the electret film is thin, it is placed on a hard substrate in order to make the film flat and convenient for further processing. The selected hard substrate is flat and smooth, the surface energy is low, and the electret film can be torn off smoothly after subsequent treatment. The material of the hard substrate may be a copper plate, preferably 1mm thick. The electret film was laid flat on a hard substrate and wiped several times with a soft paper to remove dust from the electret film and make the electret film adhere to the hard substrate. A pattern of grooves is then engraved in the electret film. The engraving method used may be manual engraving, laser engraving, chemical agent etching based on a mask (e.g. a photolithography process, a screen mold, etc.), etc., where a laser engraving process is preferred. The groove patterns can be periodic line groove patterns, triangular pyramid groove patterns, rectangular parallelepiped groove patterns and the like, or non-periodic and irregular groove patterns. A line groove pattern is preferred here. Preferably, the depth of the grooves is as deep as possible without punching through the electret film.
Such groove delineation is performed on the two electret films 102, 103, respectively. Line grooves are preferred here, and are made perpendicular to one another on both films. Such two films are then placed against each other so that they bond together to form a closed air cavity. The bonding method used may be thermal compression bonding, chemical bonding, glue bonding, etc., and here thermal compression bonding is preferred. For the preferred FEP electret material, the parameters for thermal compression bonding are thermal compression for 90s at a pressure of 1MPa and a temperature of 250 ℃. After hot pressing, the two electret films form an integral body which can not be divided, and the groove patterns form a sealed air cavity.
A metal electrode layer 101 is then provided on one side of the electret film. The setting mode can be metal coating, screen printing, metal tape bonding and the like. A thinner metal layer can be obtained by metal coating and screen printing so as to obtain better flexible effect; they are expensive and time consuming. The metal tape bonding method is preferable here. Corona polarization was then performed using a dc high voltage power supply, a corona pin and a ground electrode. A specific embodiment is to place the metal electrode layer 101 on the ground electrode and a corona needle above the other side of the sensor (e.g. 3 cm). And applying negative high voltage (18 to 30kV) to the corona needle, and carrying out corona charging for 2-5 min. Finally, a metal electrode layer 104 is disposed on the other side of the electret film to complete the fabrication of the sensor. The arrangement mode can still be metal coating, screen printing, metal tape bonding and the like. Still preferred here is the manner of metal tape bonding.
Fig. 2a and 2b show the complete structure and the cross section along the line I-I of the sensor, respectively. Fig. 2c shows an exploded schematic view of the sensor. Fig. 3 shows the working principle of the sensor. During high voltage corona polarization, the air within the sealed cavity 105 will be broken down, ionizing equal amounts of positive and negative charges. Then, under the action of the electric field, the positive and negative charges move to the upper and lower sides respectively, and are finally captured by the inner walls of the electret films 102 and 103, so that a large number of charge dipoles are formed. In the initial state (i in fig. 3), the charge dipoles captured on the trench wall of the electret thin film and the induced charges on the metal electrode form an electric field balance, and no electric response is generated. When the sensor is compressed and deformed (fig. 3) by sensing external pressure, dipole moment is changed, electric field balance is destroyed, and induced charges on the metal electrode are transferred to form current on an external circuit. When the pressure is released, the sensor elastically restores to its original shape, and an opposite current is generated in the external circuit (fig. 3 c).
The sensor continues to operate for years to date due to the ability of electret materials to stably store charge. In addition, the output property of the sensor is similar to that of a piezoelectric sensor, the sensor also has the characteristic of self-driving, an external power supply is not needed when the sensor works, and the effect of low power consumption is achieved. In addition, in the provided manufacturing process flow, laser cutting, hot-press bonding, corona polarization and metal tape pasting are very simple low-cost processes, are convenient for quick manufacturing and forming, and reduce the cost. In addition, in these processes, multiple sensors can be made simultaneously in the same batch, which facilitates mass production of the sensors; or the sensors with different sizes are produced and manufactured in the same batch, the size can be conveniently adjusted, and the sensors with different sizes and types can be applied to different occasions, so that the application range of the sensors is expanded.
The sensor provided by the embodiment of the invention is light and thin, has good flexibility, can be flexibly attached to various rough surfaces, and further can realize a signal output effect with high signal-to-noise ratio; the sensor has high sensitivity and stable performance, can continuously work for years, has the function of long-time pressure sensing, and is very suitable for sensing weak pressure signals such as pulse and the like; the provided manufacturing process is simple and convenient, has a short manufacturing period and has the capability of rapid molding; the manufacturing process has low cost, mass production and convenient size adjustment.
The background of the present invention may contain background information related to the problem or environment of the present invention and does not necessarily describe the prior art. Accordingly, the inclusion in the background section is not an admission of prior art by the applicant.
The foregoing is a more detailed description of the invention in connection with specific/preferred embodiments and is not intended to limit the practice of the invention to those descriptions. It will be apparent to those skilled in the art that various substitutions and modifications can be made to the described embodiments without departing from the spirit of the invention, and these substitutions and modifications should be considered to fall within the scope of the invention. In the description herein, references to the description of the term "one embodiment," "some embodiments," "preferred embodiments," "an example," "a specific example," or "some examples" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Various embodiments or examples and features of various embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction. Although embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope of the claims.
Claims (10)
1. A high-sensitivity flexible pressure sensor is characterized by comprising a first metal electrode layer, a first electret layer, a second electret layer and a second metal electrode layer which are sequentially laminated together, an air cavity is arranged between the first electret layer and the second electret layer, positive and negative charges ionized by air in the air cavity through corona polarization are respectively captured by the first electret layer and the second electret layer to form a charge dipole, the charge dipole and induced charges on the first metal electrode layer and the second metal electrode layer form electric field balance in an initial state, when the sensor is deformed under pressure, the dipole moment changes, the induced charge is transferred to form a current on an external circuit, when the pressure is released, the sensor is restored to the original state due to the elasticity of the sensor, and reverse current is formed on an external circuit and the electric field balance is restored.
2. The pressure sensor of claim 1, wherein the first electret layer and/or the second electret layer has a groove on an inner surface thereof.
3. A pressure sensor according to claim 2, wherein the first electret layer has a plurality of first strip-shaped grooves on its inner surface parallel to each other, and the second electret layer has a plurality of second strip-shaped grooves on its inner surface parallel to each other, the first and second strip-shaped grooves being opposed to each other and preferably also perpendicular to each other.
4. A pressure sensor according to any of claims 1 to 3, wherein the material of the first electret layer and/or the second electret layer is selected from fluorinated ethylene propylene copolymer (FEP), polypropylene (PP), polyvinylidene fluoride (PVDF).
5. The pressure sensor according to any of claims 1 or 4, wherein the material of the first metal electrode layer and/or the second metal electrode layer is selected from gold (Au), silver (Ag), copper (Cu), aluminum (Al), chromium (Cr).
6. The pressure sensor according to any one of claims 1 to 5, wherein the first metal electrode layer and/or the second metal electrode layer is formed by metal plating, screen printing, or metal tape bonding.
7. A pressure sensor according to any of claims 1 to 6, wherein a closed air cavity is formed by the first electret layer together with the second electret layer.
8. A method of making a high sensitivity flexible pressure sensor according to any of claims 1 to 7, comprising the steps of:
manufacturing a first electret layer and a second electret layer, and oppositely bonding the first electret layer and the second electret layer together to form an air cavity between the first electret layer and the second electret layer;
forming a first metal electrode layer on the outer surface of the first electret layer, and forming a second metal electrode layer on the outer surface of the second electret layer;
wherein positive and negative charges ionized from the air in the air cavity by corona polarization are respectively captured by the first electret layer and the second electret layer to form a charge dipole.
9. The method of claim 8, wherein fabricating the first electret layer and the second electret layer comprises: forming grooves on opposing surfaces of the first electret layer and/or the second electret layer.
10. The method according to claim 8 or 9, wherein the first electret layer and the second electret layer are bonded by thermocompression bonding, chemical bonding, or glue bonding.
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Application publication date: 20210611 |