CN113358016A - Flexible strain sensor based on piezoelectric effect and preparation method thereof - Google Patents
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/16—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring the deformation in a solid, e.g. by resistance strain gauge
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
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- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/30—Piezoelectric or electrostrictive devices with mechanical input and electrical output, e.g. functioning as generators or sensors
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Abstract
The invention provides a flexible strain sensor based on a piezoelectric effect and a preparation method thereof, belonging to the technical field of electronic devices. According to the flexible strain sensor with the zigzag structure, by carrying out secondary patterning design on the electrode layer for outputting signals, the isolation of opposite stress regions is realized, the strain offset effect existing in the device is improved, the effective strain level in the region area is improved, and the electrical output characteristic of the device is greatly improved while the device has high tensile rate.
Description
Technical Field
The invention belongs to the technical field of electronic devices, and particularly relates to a flexible strain sensor based on a piezoelectric effect and a preparation method thereof.
Background
The flexible strain sensor, which is an important component of a flexible electronic device, has been widely applied to the fields of intelligent electronics, health monitoring, industrial production, aerospace, environmental monitoring and the like, and particularly, the application in the fields of medical treatment, health monitoring and the like is attracting more and more attention. The flexible strain sensor can convert deformation signals of a human body into visible electric signals, and has great application potential in the aspects of human-computer interaction and medical detection for medical purposes. At present, the common strain sensor mainly has 3 sensing conversion modes of converting a strain signal into an electric signal and outputting the electric signal, namely a capacitance effect, a piezoresistive effect and a piezoelectric effect. Compared with resistance and capacitance signals, the piezoelectric signal is used as a detection signal, which is mainly reflected in the principle that the piezoelectric strain sensor generates an output voltage or current signal based on strain, so that the piezoelectric strain sensor does not need an external power supply to maintain the working state, the self-powered characteristic can reduce the size of the sensor, and the reliability of the sensor can be improved. However, for the piezoelectric strain sensor for detecting the micro-motion of the human body, the strain which can be detected is small, and if a strong electric signal is generated, the sensor is required to have high sensitivity, i.e. the piezoelectric material used has a large piezoelectric coefficient. However, many piezoelectric materials with high piezoelectric coefficients, such as polyvinylidene fluoride (PVDF), have high young's modulus, which makes them difficult to directly apply to the fabrication of flexible ductile strain sensors. Therefore, if the piezoelectric film with high Young modulus and large piezoelectric coefficient can be flexibly achieved, the sensitivity and response speed of the sensor can be guaranteed, good fit with the surface of a human body can be achieved, and the piezoelectric film has great application potential in the aspect of wearable electronic equipment such as electronic skin.
At present, the methods for making the high young modulus film flexible are mainly divided into two methods: firstly, by introducing pre-strain, the high modulus material is deformed, so that ductility is obtained; secondly, the high Young modulus film is patterned through structural design, so that the high Young modulus film has certain ductility. Obviously, the former method for introducing strain is not suitable for the design and preparation of piezoelectric strain sensors, and the latter method can better solve the problem of flexibility of high-modulus piezoelectric materials. This has been well documented in recent studies on the use of flexible network topologies in flexible electronic devices, Hongjie Hu et al (Hu H, Zhu X, Wang C, et al, linear ultrasonic transducer arrays for three-dimensional imaging on complex surfaces [ J ]. Science Advances,2018,4(3): ear 3979.) have successfully constructed a generating transducer array with a tensile rate of up to 49% by using serpentine as an interconnection structure; ZHenLong Huang et al (ZHenLong Huang, Yifei Hao, Yang Li, et al, three-dimensional integrated compact electronics [ J ]. Nature electronics, 2018, 1, 473-480.) also achieve 50%, 35% and 20% stretchability in the vertical, horizontal and equi-biaxial directions, respectively, by constructing an island-bridge structure in a complex circuit using serpentine as an interconnect structure.
The network structure composed of the serpentine units can be formed by patterning the piezoelectric film, so that the piezoelectric film can obtain certain ductility while maintaining excellent piezoelectric characteristics. However, previous research on serpentine network structure applications in flexible electronics focused mainly on the analysis and optimization of ductility, such as Lepton of Yanshan university, Tonghue, etc. (Lepton, Tonghue, Zhao, etc.. the influence of the pre-strain of the flexible device substrate and various parameters on the ductility of the serpentine structure [ J ] applied mechanics reports, 2015(2): 251-. Yung-Yu Hsu, Mario Gonzalez et al (Hsu Y, Gonzalez M, Bossuyt F, et al, Polymer-Enhanced structural Interconnects: Design, contamination, and characteristics [ J ]. IEEE Transactions on Electron Devices,2011,58(8): 2680-; in order to improve the stretchability of the structure, the stress (strain) of the serpentine network structure during stretching should be designed to avoid concentrated distribution as much as possible, and should be at a low level as possible, so as not to destroy the mechanical reliability of the structure. However, for piezoelectric materials, their output characteristics are largely dependent on the strain property and strain level in the material, and in order to obtain higher electrical output, a method is usually used that a flexible structure with a larger area is used, but when detecting deformation signals of some small regions of the human body, such as finger bending signals, the attachable area of the sensor is limited, which requires that we need to increase the effective strain level in the region area as much as possible, and thus, the electrical output characteristics of the sensor.
Disclosure of Invention
In view of the problems in the background art, the present invention is directed to a flexible strain sensor based on piezoelectric effect and a method for manufacturing the same. According to the flexible strain sensor with the zigzag structure, the secondary patterning design is carried out on the electrode for outputting signals, so that the strain offset effect existing in the device is improved, the effective strain level in the area of the region is improved, the device has high tensile rate, and the electrical output characteristic of the device is greatly improved.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a flexible strain sensor based on piezoelectric effect comprises a flexible piezoelectric structure, two electrode lead structures and two insulating packaging layers, wherein the flexible piezoelectric structure sequentially comprises a metal electrode layer (4-1), a piezoelectric thin film layer (5) and a metal electrode layer (4-2) from top to bottom, the two metal electrode layers (4-1, 4-2) and the piezoelectric thin film layer (5) are provided with the same zigzag structure pattern, different sides of the two electrode lead structures (2-1, 2-2) and the two metal electrode layers (4-1, 4-2) are connected and used for outputting electrical signals, the two insulating packaging layers (1-1,1-2) are used for packaging the flexible piezoelectric structure and the electrode lead structures, and the flexible strain sensor is characterized in that the metal electrode layers are required to be subjected to secondary patterning treatment, the secondary pattern is used to isolate the metal electrode regions corresponding to the opposite type of strain.
Further, the secondary pattern is determined according to a simulation result of the finite element mechanical analysis simulation model.
Further, the secondary patterning process is to form a channel on the metal electrode layer with the zigzag structure pattern by laser cutting, and the channel isolates the metal electrode region corresponding to the strain region of the opposite type.
Further, the distance between the channel and the edge of the zigzag structure pattern is closely related to the improvement of the electrical output characteristics, and preferably, the electrical output characteristics are optimal when the channel is arranged to exactly and completely isolate the electric charges with opposite electrical properties.
Further, the zigzag structure pattern is a hollow snake-shaped network structure or a zigzag network structure.
Further, the electrode lead structure is formed by three metal serpentine wires connected in parallel.
Further, the material of the piezoelectric thin film layer is a piezoelectric material with a high young modulus (i.e. young modulus greater than 2Gpa), preferably a piezoelectric ceramic and an organic piezoelectric material, specifically, lead zirconate titanate (PZT) and polyvinylidene fluoride (PVDF).
The material of the sealing film is a polymer material having a low young's modulus (10kPa to 20MPa), good ductility and insulation properties, and includes PU (polyurethane), PDMS (polydimethylsiloxane), and the like.
A preparation method of secondary patterning of a metal electrode layer comprises the following steps:
and 4, forming secondary patterning on the metal electrode layer by adopting a laser cutting mode according to the secondary patterning structure in the step 3.
The application of the flexible strain sensor based on the piezoelectric effect is characterized in that the flexible strain sensor is fixed on the surface of a human body (such as fingers, wrists, elbows, knees and the like) to be tested or the surface of a mechanical device, when the surface of the human body or the surface of the mechanical device generates motion deformation, the flexible piezoelectric structure is driven to generate deformation to generate an electric signal, and the electric signal is output through an electrode lead structure to realize the detection of micro motion.
The mechanism of the invention is as follows:
when the zigzag structure is deformed under the action of external force, stress with opposite properties can be generated at different positions in the zigzag structure, so that polarization with opposite directions can exist in different areas, charges with opposite properties are induced on two sides of the film, the charges with opposite properties are neutralized in the surface electrode and then output, namely, the output electrical signal is the result of charge neutralization. Therefore, the charge neutralization problem has become one of the bottlenecks to further improve the sensitivity of the flexible piezoelectric strain sensor. According to the invention, the metal electrode for collecting the polarization induced charge of the piezoelectric material is subjected to secondary patterning treatment, the insulating channel is arranged between the induced charge areas with opposite properties, neutralization is avoided, the electrical signal of one strain area in the structure is selectively output, the piezoelectric offset effect caused by opposite stress is effectively reduced, and the electrical output characteristic of the sensor is greatly improved.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
1. according to the invention, the surface electrode in the flexible strain sensor is subjected to secondary patterning treatment according to the result of finite element analysis, so that the isolation of the opposite stress region is realized, the piezoelectric offset effect caused by the opposite stress is effectively reduced, the sensor has good bidirectional ductility, the electrical output characteristic of the sensor is greatly improved, and the sensor has higher sensitivity and interference resistance.
2. Compared with the same strain sensor which is not subjected to secondary patterning treatment, the strain sensor subjected to secondary patterning treatment has the advantages that the electrical output performance is greatly improved, the peak value of the output voltage is improved by 80-100%, namely the strain degree is larger, and the difference of the output electrical signals is more obvious.
3. The flexible strain sensor based on the piezoelectric film has good adhesion and can form good conformal contact with complex planes such as the surface of a human body; and the device has simple preparation process and low manufacturing cost, and is easy to realize large-scale industrial production.
Drawings
FIG. 1 is a schematic view of a meandering configuration in a flexible strain sensor of the invention.
FIG. 2 is a schematic structural diagram of a piezoelectric film-based flexible strain sensor according to an embodiment of the present invention;
wherein, 1-1 is an upper side packaging film (PU film), 1-2 is a lower side packaging film (PU film), 2-1 is an upper side metal interconnection structure (copper), 2-2 is a lower side metal interconnection structure (copper), 3-1 is an upper side conductive adhesive tape (copper nickel), 3-2 is a lower side conductive adhesive tape (copper nickel), 4-1 is an upper metal layer (aluminum), 4-2 is a lower metal layer (aluminum), and 5 is a piezoelectric film layer (polyvinylidene fluoride).
Fig. 3 is a schematic diagram of the piezoelectric effect of the piezoelectric material based on the serpentine structure under the stretching condition.
Fig. 4 is a schematic diagram of stress distribution in the direction of S11 when the piezoelectric material based on the serpentine structure is stretched.
Fig. 5 is a schematic diagram of basic units of secondary patterns with serpentine structures used in embodiments 1 and 2 of the present invention.
Fig. 6 is a schematic view of the surface electrode secondary patterning process proposed in embodiment 1 of the present invention.
Fig. 7 is a schematic view of the surface electrode secondary patterning process proposed in embodiment 2 of the present invention.
Fig. 8 is a graph showing output voltages of the flexible strain sensors prepared in example 1 of the present invention and comparative example 1 at different stretching ratios.
Fig. 9 is a diagram of an actual detection signal of the flexible strain sensor applied to a finger movement signal according to embodiment 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the following embodiments and accompanying drawings.
Fig. 1 is a schematic view of a zigzag structure in the flexible strain sensor of the present invention, wherein the left figure is a schematic view of a snake-shaped network structure, and the right figure is a schematic view of a zigzag network structure. By adopting a similar flexible structure, the piezoelectric material which has a larger Young modulus and is difficult to directly stretch has certain extensibility, and simultaneously, the good electrical characteristics of the piezoelectric material are kept. The two examples are shown in the figure, and as long as the patterned thin film with the zigzag structure is provided, in the application process of the strain field, the method can be adopted to carry out secondary patterning treatment on the metal electrode layer, so that different stress type areas of the device are separated in the use process, and the sensitivity of the device is further improved.
Example 1
A flexible strain sensor based on piezoelectric effect, the structural schematic diagram of which is shown in fig. 2, specifically comprising: the flexible piezoelectric structure comprises a flexible piezoelectric structure, two electrode lead structures (2-1, 2-2) formed by connecting three metal serpentine lines in parallel and two insulating packaging layers (1-1,1-2), wherein the flexible piezoelectric structure sequentially comprises a first metal electrode layer (4-1), a piezoelectric film (5) and a second metal electrode layer (4-2) from top to bottom, the first metal electrode layer, the piezoelectric film and the second metal electrode layer form a sandwich structure, and the three layers of the flexible piezoelectric structure are identical in pattern; the first metal electrode layer (4-1) is connected with one side of the first electrode lead structure (2-1) through a first conductive adhesive tape (3-1), the second metal electrode layer (4-2) is connected with one side of the second electrode lead structure (2-2) through a second conductive adhesive tape (3-2), the other sides of the two electrode lead structures (2-1, 2-2) are respectively connected with an external data acquisition and analysis system, and the data acquisition and analysis system filters and reduces the noise of an electrical signal output by the flexible piezoelectric structure and then outputs the electrical signal; the flexible piezoelectric structure and the electrode lead structure are packaged by upper and lower insulating material layers (1-1, 1-2); and the first metal electrode layer and the second metal electrode layer are subjected to secondary patterning treatment, so that the electrodes in different stress type areas are separated.
The piezoelectric film of the present embodiment adopts a serpentine network structure as shown in the left diagram of fig. 1, the piezoelectric material is polyvinylidene fluoride (PVDF) and has a thickness of about 100 μm, and a layer of aluminum (Al) film is deposited on each of the upper and lower layers as a metal electrode layer by vacuum sputtering, and the thickness is about 3 nm; the snakelike interconnecting wire in the electrode lead structure is made of copper (Cu) and has the thickness of about 17 mu m, and the double-sided conductive adhesive tape is made of copper-nickel double-sided conductive adhesive tape and has the thickness of about 50 mu m.
Fig. 3 is a schematic diagram of the piezoelectric effect of the piezoelectric material based on the serpentine structure under the stretching condition. As can be seen from the figure, when the piezoelectric material with the serpentine structure is subjected to tensile stress, the charges induced at the outwardly convex side and the charges induced at the inwardly concave side are opposite in nature, that is, when the charge signals are collected, there is a charge neutralization problem, so that the sensitivity of the device is not high. Therefore, it is necessary to perform a secondary patterning process on the metal electrode layer for collecting charges, so as to reduce the piezoelectric cancellation effect caused by the opposite stress.
The specific process of carrying out secondary patterning treatment on the metal electrode layer comprises the following steps:
and 4, forming a secondary patterning channel on the metal electrode layer by adopting a laser cutting mode according to the secondary patterning structure in the step 3.
The secondary pattern in this embodiment is merely an example as long as the pattern can achieve isolation of strained regions of opposite properties.
One side of the sensor prepared by the embodiment is fixed on a stretching machine, the other side of the sensor is fixed on a bracket, and the stretching machine is used for simulating micro deformation. The sensor was subjected to a cyclic tensile test at tensile distances of 1.3mm (elongation 10%), 2.6mm (elongation 20%) and 3.9mm (elongation 30%), respectively, and the measured output voltages were as shown in fig. 8.
The flexible strain sensor prepared by the embodiment is applied to detecting the bending of the finger, and the specific process is as follows: the sensor was attached to the finger joint and the voltage outputs of 45 ° and 90 ° finger bending were detected, respectively, with the results shown in fig. 9.
Example 2
The metal electrode layer was patterned according to the procedure of example 1, and only the position of the secondary patterning in step 3 was adjusted, i.e., W/L was made 0.25, as shown in fig. 7.
This embodiment does not completely isolate the corresponding force-reaction regions, and therefore there will still be some piezoelectric cancellation, but the sensitivity of the device with the designed quadratic pattern is still improved compared to the comparative example.
If the isolation area is too large, although there is no piezoelectric cancellation, the same charge collection is reduced, and the sensitivity of the fabricated device is improved to a slightly lower degree than that of example 1.
Comparative example 1
A sensor was prepared according to the structure of example 1, with no secondary patterning process being performed on the metal electrode layer.
The sensor prepared in this comparative example was also subjected to a cyclic tensile test, and the measured output voltage was as shown in fig. 8.
Fig. 8 is a graph showing output voltages of the flexible strain sensors prepared in example 1 of the present invention and comparative example 1 at different stretching ratios. It can be seen from the graph that the voltage output has high repeatability, the voltage output is stable after multiple times of stretching, the peak-to-peak output voltage value is increased from 3.34V to 6.9V when the stretching ratio is 10%, the peak-to-peak output voltage value is increased from 7.22V to 14V when the stretching ratio is 20%, and the peak-to-peak output voltage value is increased from 10.85V to 22.46V when the stretching ratio is 30%, i.e. the voltage output has very stable and high sensitivity. By carrying out cyclic tensile tests on the flexible piezoelectric strain sensor with the electrodeless patterning treatment under different tensile rates, the electrode patterning design can effectively reduce the piezoelectric offset effect in the broken line structure under different tensile rates, and the output voltage of the sensor is improved by 80-100% while the stretchability of the sensor is ensured.
Fig. 9 is a diagram of an actual detection signal of the flexible strain sensor applied to a finger movement signal according to embodiment 1 of the present invention. It can be seen from the figure that the sensor prepared by the invention can detect stable and high-sensitivity voltage output signals, and the larger the bending degree of the finger is, the larger the amplitude of the output voltage is. By detecting the output voltage, the finger bending degree and the bending frequency can be detected. The sensor can also be applied to detection of human motion deformation signals such as elbow bending, knee bending, muscle contraction and the like, so that the sensor has great application potential in the field of flexible strain sensors based on piezoelectric films.
While the invention has been described with reference to specific embodiments, any feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise; all of the disclosed features, or all of the method or process steps, may be combined in any combination, except mutually exclusive features and/or steps.
Claims (9)
1. A flexible strain sensor based on piezoelectric effect comprises a flexible piezoelectric structure, two electrode lead structures and two insulating packaging layers, wherein the flexible piezoelectric structure sequentially comprises a metal electrode layer (4-1), a piezoelectric thin film layer (5) and a metal electrode layer (4-2) from top to bottom, the two metal electrode layers (4-1, 4-2) and the piezoelectric thin film layer (5) are provided with the same zigzag structure pattern, different sides of the two electrode lead structures (2-1, 2-2) and the two metal electrode layers (4-1, 4-2) are connected and used for outputting electrical signals, and the two insulating packaging layers (1-1,1-2) are used for packaging the flexible piezoelectric structure and the electrode lead structures; the method is characterized in that the two metal electrode layers also need secondary patterning treatment, and secondary patterns are used for isolating metal electrode areas corresponding to opposite types of strain.
2. The flexible strain sensor of claim 1, wherein the secondary pattern is determined from simulation results of a finite element mechanical analysis simulation model.
3. The flexible strain sensor of claim 1, wherein the secondary patterning process is laser cutting to form channels in the metal electrode layer having the meander pattern, the channels isolating charges generated by metal electrode regions corresponding to strain regions of opposite type.
4. The flexible strain sensor of claim 3, wherein the channel is configured to completely isolate the electrically opposite charges.
5. The flexible strain sensor according to any of claims 1 to 4, wherein the meandering structure pattern is a hollow serpentine network structure or a zigzag network structure.
6. A flexible strain sensor according to any of claims 1 to 4 wherein the electrode lead structure is formed from three metal serpentine wires connected in parallel.
7. The flexible strain sensor according to any one of claims 1 to 4, wherein the material of the piezoelectric thin film layer is a piezoelectric ceramic or an organic piezoelectric material; the packaging film is made of polyurethane or PDMS.
8. A preparation method of secondary patterning of a metal electrode layer is characterized by comprising the following steps:
step 1, determining a zigzag structure pattern of a piezoelectric film layer;
step 2, applying external force to the piezoelectric film layer with the zigzag structural pattern in the step 1, and analyzing the stress of the piezoelectric film layer under deformation by adopting finite element software to obtain the stress distribution condition;
step 3, designing a secondary patterning structure according to the stress distribution condition of the step 2 so as to realize the isolation of the strain regions with opposite properties;
and 4, forming secondary patterning on the metal electrode layer by adopting a laser cutting mode according to the secondary patterning structure in the step 3.
9. The application of the flexible strain sensor as claimed in any one of claims 1 to 4, wherein the flexible strain sensor is fixed on the surface of a human body or the surface of a mechanical device to be tested, and when the surface of the human body or the surface of the mechanical device is deformed by motion, the flexible piezoelectric structure is driven to be deformed to generate an electric signal, and the electric signal is output through the electrode lead structure, so that the detection of micro motion is realized.
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| CN116242245A (en) * | 2023-03-28 | 2023-06-09 | 山东中科智能设备有限公司 | Contact detection device of 3D printing flexible circuit board |
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