CN113720255B - Amorphous carbon-based flexible sensor based on crack fold structure and preparation method thereof - Google Patents
Amorphous carbon-based flexible sensor based on crack fold structure and preparation method thereof Download PDFInfo
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Classifications
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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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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
- C23C14/0605—Carbon
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
- C23C14/34—Sputtering
- C23C14/3435—Applying energy to the substrate during sputtering
- C23C14/345—Applying energy to the substrate during sputtering using substrate bias
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
- C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
- C23C14/34—Sputtering
- C23C14/35—Sputtering by application of a magnetic field, e.g. magnetron sputtering
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Abstract
The invention discloses an amorphous carbon-based flexible sensor based on a crack fold structure, which comprises: the flexible substrate, the amorphous carbon film and the conductive electrode, wherein the amorphous carbon film is deposited on the surface of the flexible substrate, the conductive electrode is positioned at two ends of the amorphous carbon film, and the amorphous carbon film is of a crack fold structure. The amorphous carbon-based flexible sensor has higher sensitivity in a larger stretching measurement range. The invention also provides a preparation method of the amorphous carbon-based flexible sensor based on the crack fold structure, which comprises the steps of pre-stretching the flexible substrate to deposit the amorphous carbon film on the surface of the amorphous carbon film, releasing the pre-stretching flexible substrate, and enabling the pre-stretching amorphous carbon film on the surface of the pre-stretching flexible substrate after rebound to have the crack fold structure so as to obtain the amorphous carbon-based flexible sensor based on the crack fold structure. The method is simple and efficient in preparation and easy for mass production.
Description
Technical Field
The invention belongs to the technical field of sensor manufacturing, and particularly relates to an amorphous carbon-based flexible sensor based on a crack fold structure and a preparation method thereof.
Background
With the development of electronic science and technology and the continuous improvement of the living standard of people, flexible wearable electronic devices attract more and more attention. Compared with the traditional electronic equipment, the flexible wearable electronic equipment has greater flexibility, and can meet various deformation requirements of people on the equipment. For example, it can be applied to various aspects of daily life, such as flexible touch display screens, electronic skins, wearable computers, flexible robots, flexible pressure monitoring insole pedometers, and the like.
Currently, highly flexible, stretchable wearable sensors have received considerable attention due to the potential applications of artificial robotic skin, advanced prostheses, and continuous health monitoring. In particular, the flexible strain sensor may provide electrical feedback in response to external forces (including pulsatile blood flow, respiration, and human touch/motion), and may be used for continuous health monitoring, thereby providing a true and real-time medical solution. These applications require that the device must make conformal contact with the curved surface and maintain electrical stability under large deformation conditions, and therefore require the design of stretchable electrodes with electrically stable properties.
In order to develop stretchable electrodes, in addition to the intrinsically stretchable conductive polymer as the conductive matrix, structural designs have been used to develop stretchable electrodes including wrinkles, undulations, grids, serpentine patterns, paper cuts, cracks, and the like. These structures allow for high stretchability of the hard metal-based electrode and applications in stretchable and soft electronics. Among them, the fold structure is one of the most commonly used design structures, which can give the wearable device high stretchability, high mechanical stability and comfort between man-machine interaction.
At present, the fold structure is mainly formed by compounding a conductive material with a pre-stretched or pre-stressed substrate, and after the elastic substrate is pre-stretched or pre-stressed and released, the conductive material deforms out of plane or in plane. The substrate shrinkage is achieved by thermally induced (heating or cooling) polymer shrinkage, solvent expansion and de-expansion or directly by mechanical pretension and release. The heat induction method generally deposits a conductive layer on the surface of a shape memory material (PS, PVP, etc.), and the conductive layer is shrunk by heating or cooling to promote the formation of a folded structure in the conductive layer. The solvent swelling/de-swelling method is to soak a thermosetting elastic matrix (such as PDMS) in a solvent (chloroform), the volume of the elastic matrix becomes large, a conductive layer is deposited on the surface thereof, and the matrix contracts when the solvent volatilizes in the swelled thermosetting elastic matrix, thereby obtaining a corrugated structure conductive layer. Both heat-induced shrinkage and solvent expansion can obtain a uniformly shrunk fold structure, but the problems of limited stretchability of the composite electrode, material waste and even environmental pollution caused by limited shrinkage rate of the polymer exist.
The mechanical pre-stretching method is widely applied, namely, pre-stretching an elastic substrate in a single-shaft or double-shaft system, then compounding the elastic substrate with a conductive material, and releasing the pre-stretched elastic substrate to obtain the stretchable electrode with the fold structure. The prestretching method has the advantages of simplicity, easiness in implementation and controllable substrate shrinkage, but a uniformly shrunk fold structure cannot be obtained, and cracks and layering are easy to occur between the elastic substrate and the conductive layer. In addition, the stretchable electronic device manufactured by the uniaxial or biaxial stretching process generally has directionality, resulting in orientation of electrical stability, and external force applied to the stretchable electronic material in practical application is random, so that electrical reliability of multi-angle stretching cannot be ensured.
In summary, due to the limitations of materials and structural design, the existing flexible sensor is difficult to have high sensitivity (GF > 100) and a large tensile measurement range (epsilon > 50%), meanwhile, the preparation of the novel flexible sensor involves a complicated process for transferring sensitive materials, and the wide requirements of the flexible sensor are difficult to meet, so that the development of the novel flexible sensor is urgently needed.
Disclosure of Invention
The invention provides an amorphous carbon-based flexible sensor based on a crack fold structure, which has high sensitivity in a larger tensile measurement range, and a preparation method of the sensor, wherein the preparation method can flexibly regulate and control the crack fold structure of the flexible sensor according to the actual requirement on sensitivity, and is simple and efficient.
An amorphous carbon-based flexible sensor based on a crack-and-fold structure, comprising: the flexible substrate, the amorphous carbon film and the conductive electrode, wherein the amorphous carbon film is deposited on the surface of the flexible substrate, the conductive electrode is positioned at two ends of the amorphous carbon film, and the amorphous carbon film is of a crack fold structure.
The crack density in the crack fold structure is that 10-30 cracks exist in the range of 200 multiplied by 200 mu m, the crack direction is mostly parallel to the stretching direction, and the fold structure is perpendicular to the stretching direction and is rectangular, trapezoidal or triangular. Based on the crack fold structure, the device has high sensitivity, can still recover the original structure after being subjected to larger strain, and has better repeatability.
The amorphous carbon film is a large class of materials formed by mixing sp 2 and sp 3 of carbon, has high piezoresistance sensitivity, corrosion resistance and scratch resistance, and can realize signal sensing under the working conditions of sweat, scratch and the like of a human body. In addition, amorphous carbon can be directly deposited on the flexible matrix to realize flexible sensing. Meanwhile, due to high stress (10 GPa) and high brittleness, when amorphous carbon is directly deposited on a flexible substrate, the mechanical property difference is too large, so that cracks and wrinkles can occur on the amorphous carbon film, large-range deformation detection is obtained based on the mechanical flexibility of a flexible substrate, and a large resistance change response is made to small external force change based on the amorphous carbon cracks, so that the flexible strain sensor with high sensitivity (GF > 100) and a large tensile measurement range (50) is prepared.
The flexible substrate material comprises any one of Polydimethylsiloxane (PDMS), polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), polymethyl methacrylate (PMMA), natural Rubber (NR), styrene-butadiene rubber (SBR), epoxy resin or thermoplastic elastomer (TPU, SBCS and POE). Further, the flexible substrate material is Polydimethylsiloxane (PDMS).
The invention also provides a preparation method of the amorphous carbon-based flexible sensor based on the crack fold structure, which comprises the following steps:
prestretching the flexible substrate, placing the prestretching flexible substrate in a vacuum cavity, continuously introducing Ar gas, rotating the prestretching flexible substrate, starting a solid carbon source target material by adopting a magnetron sputtering technology, depositing an amorphous carbon film on the surface of the prestretching flexible substrate, pasting and solidifying conductive metal to two ends of the amorphous carbon film, and releasing the prestretching flexible substrate, so that the amorphous carbon film on the surface of the prestretching flexible substrate after rebound has a crack fold structure, thereby obtaining the amorphous carbon-based flexible sensor based on the crack fold structure.
Further, the solid carbon source target is a graphite target. Gaseous carbon sources such as methane, acetylene, etc. are not used because hydrogen-containing carbon sources increase and uncontrollable the electrical resistance of the deposited carbon film.
The elongation of the prestretched flexible substrate is 10% -100%. The substrate becomes hard after etching due to the overlong pre-stretching length, and the substrate cannot rebound effectively; the prestretched elongation is too short, and the wrinkling effect is not obvious.
The air flow of Ar gas is 40-100sccm.
The specific steps of the rotary pre-stretching flexible substrate are as follows: the rotation is carried out for 10-80min at a speed of 10-50rpm, and then the rotation is carried out for 10-80min.
And generating an amorphous carbon film with proper thickness at proper rotating speed and deposition time, wherein the forward rotation and reverse rotation time is kept consistent, so that the carbon film can be uniformly deposited.
And etching the rotary pre-stretching flexible substrate before starting the solid carbon source.
Further, the etching process comprises the following steps: the pulse bias voltage is 350-450V, the vacuum degree of the cavity is 1.6X10 -5-2.5×10-5 Torr, and the etching time is 10-60min. Based on the surface cleanliness, the flexible substrate is etched in a proper etching time, so that the surface of the flexible substrate is hardened, and the combination with the subsequent amorphous carbon film is enhanced.
Further, after the rotating pre-stretching flexible substrate is etched, the bias power supply is turned off before the solid carbon source target is turned on, the graphite target is self-cleaned, and the self-cleaning process comprises the following steps: the direct current power is 2-3kW, the pressure in the vacuum cavity is 2-4mTorr, and the cleaning time is 5-20min.
The solid carbon source target sputtering process comprises the following steps: the DC sputtering power is 1.6-4.2kW, the deposition time is 20-160min, the bias voltage is 200-350V, and the pressure in the vacuum cavity is 2-4mTorr.
The curing time is 15-120min, and the curing temperature is 30-150 ℃. Curing is carried out at a proper temperature, so that the curing speed is increased, but the temperature is not too high, otherwise, the PDMS matrix is affected to a certain extent.
The design idea of the invention is as follows: the sensing mechanism of the amorphous carbon-based flexible strain sensor based on the crack and fold structure is researched, and the amorphous carbon-based flexible strain sensor based on the crack and fold structure is obtained: for surface-deposited strain sensors, the crack propagation mechanism may be its primary sensing mechanism, since cracks are very prone to propagate in the brittle conductive layer during stretching. In the critical strain range, the conductivity of the sensor is primarily dependent on the extent of crack propagation, and after removal of the applied strain, the cracks created by the sensitive material re-close, allowing the sensor resistance to recover substantially to its original state. Thus, reversible generation/closure of cracks is a necessary condition for a strain sensor having high sensitivity and good reproducibility. In addition, the method is possibly influenced by conductive sp 2 clusters distributed in the amorphous carbon film, so that the sp 2 and sp 3 content of the film and the size and distribution of the clusters can be changed by regulating and controlling the carbon source type, the matrix pulse bias, the sputtering power, the deposition time and the like, thereby regulating and controlling the GF value of the element; and the thickness of the film can be changed, so that the initial resistance value of the element can be regulated and controlled. Therefore, the flexible strain sensor with high GF value and large stretching range can be obtained according to the requirement by regulating and controlling the technological parameters in the preparation method, and the rapid preparation technology of the flexible strain sensor with strong combination, long service life, high sensitivity and large stretching range is realized. In summary, the invention uses the amorphous carbon film based on the crack fold structure as the sensitive material, directly deposits the amorphous carbon film on the surface of the prestretched flexible substrate, and sets the metal electrode on the surface of the amorphous carbon film to form the flexible strain sensor.
Compared with the prior art, the invention has the beneficial effects that:
(1) In the prior art, the flexible strain sensor has the advantages of smaller sensitivity, high preparation cost, complex preparation process and short service life. The method for presetting the microcrack fold structure on the amorphous carbon film layer is adopted, so that the sensor has the advantages of simple structure, convenience in testing, high sensitivity, good anti-fatigue property and the like in specific use.
(2) The amorphous carbon-based flexible strain sensor based on the crack and fold structure provided by the invention has an ultrahigh GF value and a large stretching range, wherein the GF value is 100-1000, and the maximum elongation can reach more than 50%; and the GF value and the initial resistance value can be further regulated and controlled by changing the process parameters.
(3) Compared with the graphene and carbon nanotube equal-pressure resistance materials, the amorphous carbon film provided by the invention has the advantages of simplicity and convenience in preparation, low production cost, easiness in processing, capability of large-area in-situ deposition, no need of manual transfer, and obvious technological advantages.
(4) The amorphous carbon-based flexible strain sensor based on the crack and fold structure provided by the invention takes the amorphous carbon film as a functional layer, has excellent performances similar to diamond, such as friction resistance, chemical inertness and the like, and also has excellent electrical characteristics, so that the prepared product is low in price and high in cost performance.
(5) The flexible strain sensor with the microcrack fold structure provided by the invention can monitor the strain change in real time through the change of the resistance, and the excellent performance has wide application prospects in the fields of electronic skin, human health monitoring devices and the like.
Drawings
Fig. 1 is a schematic flow chart diagram of an amorphous carbon-based flexible strain sensor based on a crack and wrinkle structure according to an embodiment;
FIG. 2 is a schematic structural picture of an amorphous carbon-based flexible strain sensor based on a crack and wrinkle structure;
FIG. 3 is a microstructure and three-dimensional structure picture of the amorphous carbon-based flexible strain sensor based on a crack and wrinkle structure prepared in example 1;
FIG. 4 is a graph showing the relationship between the resistivity and the sensitivity coefficient of the amorphous carbon-based flexible strain sensor based on the crack and wrinkle structure obtained in example 1 and the strain change at the loading stage;
Fig. 5 is a voltage trend graph of the amorphous carbon-based flexible strain sensor based on the crack and wrinkle structure prepared in example 1, which is cyclically loaded and unloaded 1500 times when the constant current source is 1 nA.
FIG. 6 is a microstructure and three-dimensional structure picture of the amorphous carbon-based flexible strain sensor based on a crack and wrinkle structure prepared in example 5;
FIG. 7 is a graph showing the relationship between the resistivity and the sensitivity coefficient of the amorphous carbon-based flexible strain sensor based on the crack and wrinkle structure obtained in example 5 and the strain;
Fig. 8 is a voltage trend graph of the amorphous carbon-based flexible strain sensor based on the crack and wrinkle structure prepared in example 5, which is cyclically loaded and unloaded 1500 times when the constant current source is 10 nA.
Detailed Description
The invention will be described in further detail below with reference to the embodiments of the accompanying drawings, it being noted that the embodiments described below are intended to facilitate the understanding of the invention and are not meant to be limiting in any way.
As shown in fig. 1, a flexible substrate is fixed first, the flexible substrate is stretched, amorphous carbon is deposited on the stretched flexible substrate, and finally the flexible substrate is rebounded to obtain the amorphous carbon-based flexible strain sensor based on a crack fold structure
Example 1:
in this embodiment, as shown in fig. 2, the flexible strain sensor is composed of a PDMS substrate, an amorphous carbon film with a preset crack fold structure, and conductive silver colloid electrodes, wherein the amorphous carbon film with the preset crack fold structure is located on the surface of the PDMS substrate, and the metal electrodes are located on two ends of the amorphous carbon film with the preset crack fold structure, namely, on the surface of the amorphous carbon film.
The preparation method of the flexible strain sensor comprises the following steps:
(1) The PDMS substrate was pre-stretched with a self-made stretching device according to an elongation of 10%, and tested, the PDMS substrate had a tensile strength of 4MPa, a tear strength of 7kN/m, and an elongation at break of 100%. Leaving an electrode area to be deposited of about 50mm multiplied by 10mm on the surface of the substrate support, covering the rest area by using a mask plate, fixing the mask plate on a substrate support rotating in a vacuum cavity, and pre-vacuumizing to 2.5 multiplied by 10 -5 Torr;
(2) In order to obtain higher bonding strength, ar gas is introduced into the coating cavity, and the Ar gas flow is 100sccm; etching the PDMS substrate for 20min under the conditions that the pulse substrate bias voltage is-400V and the working pressure is 1.1 Pa;
(3) Closing a bias power supply, opening a direct current power supply, and performing self-cleaning on the target material for 10min under the conditions that the direct current power is 2.1kW and the cavity pressure is 3.3 mTorr;
(4) Ar gas is introduced into the cavity, and the Ar gas flow is 65sccm; simultaneously, the bias voltage and the direct current power supply are turned on, and the graphite target is sputtered under the conditions that the working pressure is 0.3Pa, the pulse substrate bias voltage is-200V and the direct current power is 2.1 kW. The deposition time is generally 20min, and the film thickness is controlled to be 110-130nm. In the deposition process, the substrate rotates forward at the speed of 10rpm for 10min and then rotates reversely for 10min so as to improve the uniformity of the film;
(5) Connecting a platinum wire to two ends of the surface of the amorphous carbon film by using conductive silver paste, and curing for 20 minutes at 120 ℃;
(6) The amorphous carbon film on the surface of the pre-stretched flexible substrate after rebound is provided with a crack fold structure so as to obtain the amorphous carbon-based flexible sensor based on the crack fold structure, the surface morphology of the amorphous carbon-based flexible sensor is shown as figure 3, 10-15 cracks are distributed in the visual field range of 200 multiplied by 200 mu m, and the shape of the block fold structure is approximately rectangular and trapezoidal. The crack direction is mostly parallel to the stretching direction and the fold structure is perpendicular to the stretching direction.
The amorphous carbon-based flexible strain sensor prepared by the method is subjected to sensing performance test, namely the sensor is stretched, and the resistance change is observed, as shown in fig. 4, the resistivity is in an ascending trend along with the increase of the strain degree, the linearity is good, and the sensitivity reaches the highest when the stretching rate is in a range of 20% -30%. Applying tensile deformation to the sensing element by using a microstress applying and testing system through a microstress device; the I-V curve of the sensor at room temperature is tested by adopting a four-point method through a nanovoltmeter and a current source, as shown in figure 5, when the constant current source is 1nA, the trend of the voltage curve shows good reproducibility along with the increase of the cyclic loading and unloading times, which shows that the prepared sensor has excellent dynamic cyclic stability. And calculating the resistance value R of the linear contact region by using ohm's law to obtain the relation of the resistance change rate along with the change of the strain, and then passing through the following formula:
(R 0 is the initial resistance, R is the resistance of the film after stretching, epsilon is the corresponding tensile strain) and the maximum GF value is about 155.
Example 2:
In this embodiment, the structure of the flexible strain sensor is exactly the same as that of embodiment 1.
In this example, the method of manufacturing the flexible strain sensor was substantially the same as that of example 1, except that the PDMS substrate selected in step (1) had a tensile strength of 3.5MPa, a tear strength of 15kN/m and an elongation at break of 350%.
And (3) carrying out a sensing performance test on the amorphous carbon-based flexible strain sensor, namely stretching the sensor, and observing the resistance change of the sensor. Applying tensile deformation to the sensing element by using a microstress applying and testing system through a microstress device; the four-point method is adopted, an I-V curve of the sensor at room temperature is tested through a nano-volt meter and a current source, the resistance value R of a linear contact area is calculated through ohm's law, the relation of the resistance change rate along with the change of the strain is obtained, and the following formula is adopted:
(R 0 is the initial resistance, R is the resistance of the film after stretching, epsilon is the corresponding tensile strain), and the maximum GF value is about 105.
Example 3:
In this embodiment, the structure of the flexible strain sensor is exactly the same as that of embodiment 1.
In this example, the method of manufacturing the flexible strain sensor was substantially the same as that of example 1, except that the PDMS substrate was pre-stretched at 20% elongation in step (1).
And (3) carrying out a sensing performance test on the amorphous carbon-based flexible strain sensor, namely stretching the sensor, and observing the resistance change of the sensor. Applying tensile deformation to the sensing element by using a microstress applying and testing system through a microstress device; the four-point method is adopted, an I-V curve of the sensor at room temperature is tested through a nano-volt meter and a current source, the resistance value R of a linear contact area is calculated through ohm's law, the relation of the resistance change rate along with the change of the strain is obtained, and the following formula is adopted:
(R 0 is the initial resistance, R is the resistance of the film after stretching, epsilon is the corresponding tensile strain), and the maximum GF value is about 278.
Example 4:
In this embodiment, the structure of the flexible strain sensor is exactly the same as that of embodiment 1.
In this example, the method of manufacturing the flexible strain sensor was substantially the same as that of example 1, except that the film deposition time in step (5) was 160min.
And (3) carrying out a sensing performance test on the amorphous carbon-based flexible strain sensor, namely stretching the sensor, and observing the resistance change of the sensor. Applying tensile deformation to the sensing element by using a microstress applying and testing system through a microstress device; the four-point method is adopted, an I-V curve of the sensor at room temperature is tested through a nano-volt meter and a current source, the resistance value R of a linear contact area is calculated through ohm's law, the relation of the resistance change rate along with the change of the strain is obtained, and the following formula is adopted:
(R 0 is the initial resistance, R is the resistance of the film after stretching, epsilon is the corresponding tensile strain), and the maximum GF value is about 746.
Example 5:
in this embodiment, the flexible strain sensor is composed of a PDMS substrate, an amorphous carbon film with a preset crack fold structure, and conductive silver colloid electrodes, the amorphous carbon film with the preset crack fold structure is located on the surface of the PDMS substrate, and the silver colloid electrodes are located at two ends of the surface of the amorphous carbon film with the preset crack fold structure.
The preparation method of the flexible strain sensor comprises the following steps:
(1) The two ends of the PDMS substrate are fixed with self-made stretching devices, a cylinder with the diameter of 10mm is inserted in the middle to bend the PDMS substrate, and the stretching strength of the PDMS substrate is 4MPa, the tearing strength is 7kN/m and the elongation at break is 100% after test. Leaving an electrode area to be deposited of about 50mm multiplied by 10mm on the surface of the substrate, covering the rest area by using a mask plate, fixing the mask plate on a substrate support rotating in a vacuum cavity, and pre-vacuumizing to 1.6X10 -5 Pa.
(2) In order to obtain higher bonding strength, ar gas is introduced into the coating cavity, and the Ar gas flow is 40sccm; and etching the PDMS substrate for 60min under the conditions that the pulse substrate bias voltage is minus 350V and the working pressure is 1.5 Pa.
(3) And (3) turning off the bias power supply, turning on the direct current power supply, and performing self-cleaning on the target material for 20min under the conditions that the direct current power is 3kW and the cavity pressure is 2.4 mTorr.
(4) Ar gas is introduced into the cavity, and the Ar gas flow is 80sccm; simultaneously, the bias voltage and the direct current power supply are turned on, and the graphite target is sputtered under the conditions that the working pressure is 0.5Pa, the pulse substrate bias voltage is 320V and the direct current power is 2.8 kW. The deposition time is generally 10min, and the film thickness is controlled to be about 110-130 nm. In the deposition process, the substrate rotates forward at 30rpm for 50min and then rotates reversely for 50min so as to improve the uniformity of the film;
(5) Connecting a platinum wire to two ends of the surface of the amorphous carbon film by using conductive silver paste, and curing for 120 minutes at 30 ℃;
(6) The amorphous carbon film on the surface of the pre-stretched flexible substrate after rebound is provided with a crack fold structure so as to obtain the amorphous carbon-based flexible sensor based on the crack fold structure, a physical diagram is shown in fig. 6, the surface morphology of the amorphous carbon-based flexible sensor is obtained, 20-30 cracks are distributed in the visual field range of 200 multiplied by 200 mu m, and the shape of the block fold structure is approximately rectangular large blocks and triangular small blocks. The crack direction is mostly parallel to the stretching direction and the fold structure is perpendicular to the stretching direction. The amorphous carbon-based flexible strain sensor prepared by the method is subjected to sensing performance test, namely the sensor is stretched, resistance change is observed, as shown in fig. 7, the relative resistance change is in an ascending trend along with the increase of the strain degree, good linearity is achieved, and the sensitivity reaches the highest when the stretching rate is in a range of 20% -30%. Applying tensile deformation to the sensing element by using a microstress applying and testing system through a microstress device; the I-V curve of the sensor at room temperature is tested by adopting a four-point method through a nanovoltmeter and a current source, as shown in fig. 8, when the constant current source is 10nA, the trend of the voltage curve shows good reproducibility along with the increase of the cyclic loading and unloading times, which shows that the prepared sensor has excellent dynamic cyclic stability. And calculating the resistance value R of the linear contact region by using ohm's law to obtain the relation of the resistance change rate along with the change of the strain, and then passing through the following formula:
(R 0 is the initial resistance, R is the resistance of the film after stretching, epsilon is the corresponding tensile strain), and the maximum GF value is about 567;
The foregoing embodiments have been described in some detail by way of illustration of the principles of the invention, and it is to be understood that this invention is not limited to the specific embodiments described herein, but is intended to cover modifications and improvements made within the spirit and scope of the invention.
Claims (4)
1. An amorphous carbon-based flexible sensor based on a crack and wrinkle structure, comprising: the amorphous carbon film is deposited on the surface of the flexible substrate, and the conductive electrodes are positioned at two ends of the amorphous carbon film, and the amorphous carbon film is of a crack fold structure;
The preparation method of the amorphous carbon-based flexible sensor based on the crack fold structure comprises the following steps:
Prestretching the flexible substrate, placing the prestretching flexible substrate in a vacuum cavity, continuously introducing Ar gas, rotating the prestretching flexible substrate, starting a solid carbon source target material by adopting a magnetron sputtering technology, depositing an amorphous carbon film on the surface of the prestretching flexible substrate, pasting and solidifying conductive metal to two ends of the amorphous carbon film, and releasing the prestretching flexible substrate to obtain the amorphous carbon-based flexible sensor based on a crack fold structure;
etching the rotary prestretched flexible substrate before starting the solid carbon source;
The air flow of Ar gas is 40-100sccm;
The specific steps of the rotary pre-stretching flexible substrate are as follows: firstly, forward rotating for 10-80min at the speed of 10-50rpm, and then reverse rotating for 10-80min;
the etching process comprises the following steps: the pulse bias voltage is 350-450V, the cavity vacuum degree is 1.6X10 -5-3×10-5 Torr, and the etching time is 10-60min;
The solid carbon source target sputtering process comprises the following steps: the sputtering power is 1.6-4.2kW, the deposition time is 20-160min, the bias voltage is 200-350V, and the pressure in the vacuum cavity is 2-4mTorr.
2. The amorphous carbon-based flexible sensor based on a crack and wrinkle structure according to claim 1, wherein the crack density in the crack and wrinkle structure is 10-30 pieces/200 x 200 μm, and the wrinkle structure is rectangular, trapezoidal or triangular.
3. The amorphous carbon-based flexible sensor based on a crack and wrinkle structure according to claim 1, wherein the flexible substrate material comprises any one of polydimethylsiloxane, polyvinylidene fluoride, polyethylene terephthalate, polypropylene, polyimide, polymethyl methacrylate, natural rubber, styrene-butadiene rubber, epoxy resin, or thermoplastic elastomer.
4. The amorphous carbon-based flexible sensor based on crack and pucker structure as recited in claim 1, wherein the pre-stretched flexible substrate has an elongation of 10% -100%.
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