CN115507979A - Flexible pressure sensor based on bionic gradient microstructure and preparation method thereof - Google Patents
Flexible pressure sensor based on bionic gradient microstructure and preparation method thereof Download PDFInfo
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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
- G01L1/18—Measuring force or stress, in general using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
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Abstract
The invention discloses a flexible pressure sensor based on a bionic gradient microstructure and a preparation method thereof, wherein the flexible pressure sensor comprises a flexible substrate layer, a force-sensitive structure layer and a flexible packaging layer; the patterned electrode is arranged on the inner side of the flexible substrate layer, a plurality of flexible bulges with different heights are arranged on one side of the force-sensitive structure layer opposite to the flexible substrate layer, and the surfaces of the flexible bulges are coated with the conductive layers; the flexible packaging layer is positioned on the other side of the flexible substrate layer and packages the flexible substrate layer and the force-sensitive structure layer. The flexible pressure sensor based on the bionic gradient structure breaks through the design concept of the conventional uniform microstructure, and the response range and sensitivity of the pressure sensor are improved by using the gradient structure. The sensor is prepared by stacking from bottom to top layer by layer, and has the advantages of ultrathin property, ultralight property, high precision, strong applicability and easy large-area large-scale manufacturing.
Description
Technical Field
The invention belongs to the technical field of sensors, and particularly relates to a flexible pressure sensor based on a bionic gradient microstructure and a preparation method thereof.
Background
The skin surface has the fine hair and the epidermis layer, and the fine hair and the epidermis layer have important effects on inducing external stimulation to human beings. For human beings, long hairs tend to transmit this signal to skin neurons and react when receiving slight vibration, while short hairs are touched during further touch, and touch the human epidermis when external contact or force stimulation is larger. Therefore, it is proposed to design a structure with gradient similar to human long and short fine hairs to realize the purpose of identifying external small stimulation and large stimulation.
For this reason, many types of pressure sensors have been proposed, and mainly include several types, such as a piezoresistive type, a piezoelectric type, a pressure-capacitive type, and a triboelectric type, according to their operation mechanisms. Although self-powered piezoelectric and triboelectric sensors can be self-powered, the sensor has poor reducibility to key information such as pressure and the like and has large interference. The flexible piezoresistive sensor has a simple working principle, can easily acquire a plurality of signals similar to compression, bending, distortion and other deformations, and converts the signals into electric signals, so that the flexible piezoresistive sensor is greatly developed and is expected to become the future electronic skin.
In recent years, many studies have been reported to pursue a wide range and high sensitivity of piezoresistive pressure sensors. At present, a macroscopic structure based on a device can be divided into a two-dimensional film and a three-dimensional state, and for the three-dimensional state, a carbon-based conductive material (carbon nano tube and graphene) and some porous materials are usually mixed or soaked, so that the carbon-based conductive material has compressibility and conductivity, and further, the change of electrical properties after compression is realized. However, the thickness of the three-dimensional state in the thickness direction is too thick, usually several centimeters, and the three-dimensional state is not suitable for shape-retaining fit with human skin. Therefore, thin film based sensors have been greatly developed because they are thin overall. Common film materials such as polyethylene terephthalate (PET), polyurethane (PU), polyvinylidene fluoride (PVDF), styrene thermoplastic elastomer (SBS), polydimethylsiloxane (PDMS), and the like, which endow the sensor with special properties such as flexibility, stretchability, water resistance, and the like, are generally compounded with graphene, carbon tubes, and the like, and pressure sensing is realized in combination with the microstructure of the film, however, the current microstructure is generally difficult to prepare in a large area due to the limitation of the photolithography technique or poor in performance reproducibility due to the non-uniform structure caused by the non-photolithography system, and is difficult to be commercially applied.
Disclosure of Invention
Aiming at the prior art, the invention provides a flexible pressure sensor based on a bionic gradient microstructure and a preparation method thereof, and aims to solve the problems that the pressure sensor in the prior art is low in sensitivity, narrow in range, incapable of being produced in large batch, complex in process and the like.
In order to achieve the purpose, the invention adopts the technical scheme that: the flexible pressure sensor based on the bionic gradient microstructure comprises a flexible substrate layer, a force-sensitive structure layer and a flexible packaging layer; the patterned electrode is arranged on the inner side of the flexible substrate layer, a plurality of flexible bulges with different heights are arranged on one side of the force-sensitive structure layer relative to the flexible substrate layer, and the surfaces of the flexible bulges are coated with the conductive layers; the flexible packaging layer is positioned on the other side of the flexible substrate layer and packages the flexible substrate layer and the force-sensitive structural layer.
The force-sensitive structure layer in the pressure sensor is designed by imitating the structure of the length of human sweat hair, the force-sensitive structure layer is provided with the flexible bulges with higher height and the flexible bulges with lower height, under the condition of small acting force, only the flexible bulges with higher height are contacted with the electrode, and under the condition of large force, the microspheres with lower height are contacted with the electrode, and at the moment, the flexible bulges with higher height and the flexible bulges with lower height play a synergistic effect. The advantage of such a gradient structure is that compared to a uniform structure of the same height as is conventional, the initial contact area is small, the current at the same voltage is small, and after a larger force, the change in contact area is more rapid compared to a structure of uniform height, and after a larger force, the shorter flexible protrusions start to take on a part of the stress and cooperate together to act as a sensing unit.
On the basis of the technical scheme, the invention can be further improved as follows.
Further, the patterned electrode is an interdigital electrode.
Furthermore, the interdigital electrode is an interdigital gold electrode.
Further, the flexible protrusions comprise high-flexibility protrusions and low-flexibility protrusions, and the height ratio of the high-flexibility protrusions to the low-flexibility protrusions is (2).
The areas of the bottom surfaces of the high-flexibility bulges and the low-flexibility bulges are consistent, and the heights of the high-flexibility bulges and the low-flexibility bulges are different. When the areas of the bottom surfaces of the flexible protrusions are consistent, the height ratio has a serious influence on the performance of the flexible protrusions. When the height of the high-flexibility bulge exceeds 3 times of the height of the low-flexibility bulge, the high-flexibility bulge can be broken due to the lateral bending of the high-flexibility bulge under the action of pressure, and accordingly the performance of the sensor is unstable.
Further, the flexible protrusions are distributed in rows, the height of the flexible protrusions in each row being the same.
Further, the high-flexibility protrusions and the low-flexibility protrusions are arranged in a staggered mode according to the row ratio of 1.
Furthermore, the conductive layer is made of carbon nanotubes or MXene nanosheets.
Further, the MXene nanosheet is prepared through the following steps:
s1: dissolving lithium salt in acid with the concentration of 8-10M according to the material-liquid ratio of 1g;
s2: will be mixed with lithium salt of equal mass of MAX-Ti 3 AlC 2 Adding the mixture into the reactant obtained in the S1, and continuously reacting for 20-30 h at the temperature of 35-45 ℃; then centrifuging and vacuum drying to obtain the product.
The flexible substrate layer is made of PI (polyimide) or PET (polyethylene terephthalate); the material of the force-sensitive structure layer is PU (polyurethane) or PDMS (polydimethylsiloxane); the flexible packaging layer is made of PU.
The invention also discloses a preparation method of the flexible pressure sensor based on the bionic gradient microstructure, which comprises the following steps:
(1) Preparing a flexible substrate layer
Taking a flexible substrate, forming a patterned electrode on one side of the flexible substrate in a magnetron sputtering mode, and extracting the electrode from the patterned electrode by using conductive carbon cloth; the magnetron sputtering conditions are as follows: vacuum degree of 1X 10 -5 Pa below, the magnetron sputtering power is 40W, the ratio of argon to oxygen is 40, and the sputtering time is 5min;
(2) Preparation of force-sensitive structural layer
Etching pits with different depths on the surface of a silicon wafer with the thickness of 100-1000 mu m; then coating the material for preparing the force-sensitive structure layer on a silicon wafer in a spin coating mode, baking for 50-120 min at the temperature of 60-150 ℃, then removing the film from the silicon wafer, and then coating the conductive material according to the ratio of 0.05-0.4 mg/cm 2 Spraying the spraying amount of the water-based paint on the convex surface of the film to obtain the paint;
(3) Device packaging conductive layer
And (3) oppositely placing the side of the flexible substrate layer with the patterned electrode and the side of the force-sensitive structure layer with the protrusions, and then packaging the side with the flexible packaging layer to obtain the flexible packaging film.
The invention has the beneficial effects that:
1. the flexible pressure sensor based on the bionic gradient structure breaks through the design concept of the conventional uniform microstructure, and the response range and sensitivity of the pressure sensor are improved by using the gradient structure.
2. The sensor is prepared by stacking from bottom to top layer by layer, and has the advantages of ultrathin property, ultralight property, high precision, strong applicability and easiness for large-area large-scale manufacturing.
Drawings
FIG. 1 is an exploded view of a flexible pressure sensor with a bionic gradient microstructure;
FIG. 2 is an SEM image of a silicon wafer template after etching;
FIG. 3 is an SEM image of the diaphragm after repeated etching;
FIG. 4 is an SEM image of the membrane after spraying the conductive material;
FIG. 5 is a force-bearing simulation diagram of the flexible pressure sensor;
FIG. 6 shows the electrical performance test results of the flexible pressure sensor;
wherein, 1, a flexible substrate layer; 2. patterning the electrode; 3. a force sensitive structural layer; 4. a high flexibility protrusion; 5. a low flexibility bulge; 6. a flexible encapsulation layer.
Detailed Description
The following examples are provided to illustrate specific embodiments of the present invention.
Example 1
A flexible pressure sensor based on a bionic gradient microstructure is disclosed, as shown in figure 1, the flexible pressure sensor comprises a flexible substrate layer 1, a force-sensitive structure layer 3 and a flexible packaging layer 6; the flexible substrate layer 1 is made of PI, and a patterned electrode 2 is arranged on the inner side of the flexible substrate layer, wherein the patterned electrode 2 in the embodiment is an interdigital gold electrode; the force-sensitive structure layer 3 is provided with a plurality of flexible protrusions with different heights on one side relative to the flexible substrate layer 1, as can be seen from fig. 1, the flexible protrusions comprise high flexible protrusions 4 and low flexible protrusions 5 which are distributed in staggered rows, and the ratio of the heights of the high flexible protrusions 4 to the low flexible protrusions 5 is 2. The surface of the flexible bulge is coated with MXene nanosheet conductive material, and the coating amount of the MXene nanosheet is 0.1mg/cm 2 (ii) a The flexible encapsulating layer 6 is located on the other side of the flexible substrate layer 3 and forms an encapsulation for the flexible substrate layer 3 and the force sensitive structural layer 1.
The flexible pressure sensor based on the bionic gradient microstructure in the embodiment is prepared by the following steps:
(1) Preparing a flexible substrate layer
Forming an interdigital gold electrode (a patterned electrode 2) on one side of a PI flexible substrate by taking PI as the flexible substrate and gold as a sputtering source in a magnetron sputtering mode, and leading out the electrode from the patterned electrode 2 by using conductive carbon cloth to obtain a flexible substrate layer 1; the magnetron sputtering conditions are as follows: vacuum degree of 1X 10 -5 Pa below, the magnetron sputtering power is 40W, the ratio of argon to oxygen is 40, and the sputtering time is 5min;
(2) Preparation of force-sensitive structural layer
Taking a polished silicon wafer with the thickness of 500 microns as a template material, and etching the silicon wafer by an ultraviolet laser marking machine; the specific process is to draw a point on CAD software, then draw a plurality of points through an array tool, set the distance between each point and the point to be 110 μm, and set marking machine parameters: marking times are one, marking speed is 100mm/s, and marking current is 6A; after marking the silicon chip, moving the marking pattern to the left and downwards by 55 microns, and then setting the parameters of a marking machine: the marking frequency is 2 times, the marking speed is 100mm/s, and the marking current is 6A. Thus, since the place marked once is etched once and the place marked 2 times is etched 2 times, pits with different etching depths (the depth of the pit with the deeper depth is 40 μm, and the depth of the pit with the shallower depth is 20 μm) are formed on the surface of the silicon wafer, and the pits with different depths are arranged in rows and in a staggered manner, and the etched silicon wafer is as shown in fig. 2.
The double etching was performed using PU (polyurethane). And (3) spin-coating the polyurethane aqueous emulsion with the solid content of 30% on a silicon wafer at the spin-coating speed of 500r/min for 30 seconds, and then baking the silicon wafer for 5min by adopting a 120 ℃ oven. And forming a film on the silicon wafer after baking, taking down the film by using tweezers, re-etching the structure on the silicon wafer on the surface of the film corresponding to the silicon wafer template in the curing process, forming high-flexibility bulges 4 and low-flexibility bulges 5 which are arranged in rows in a staggered manner on the film, and forming the re-etched film structure as shown in figure 3.
Spraying conductive material MXene nanosheets on the side of the membrane with the flexible protrusions, wherein the spraying amount of the MXene nanosheets is 0.1mg/cm 2 And obtaining the force sensitive structure layer 3. The preparation method of the MXene nanosheet spraying liquid comprises the following steps:
s1: dissolving lithium fluoride into 9M hydrochloric acid according to a material-liquid ratio of 1g;
s2: MAX-Ti with the same mass as lithium fluoride 3 AlC 2 Adding the mixture into the reactant obtained in the S1, and continuously stirring and reacting for 24 hours at the temperature of 40 ℃; centrifuging the reactant at the rotating speed of 4000r/min for 5 times, each time for 5min, performing suction filtration, and baking the material subjected to suction filtration in a vacuum oven at 45 ℃ for 24h to obtain MXene nanosheets;
s3: dispersing the MXene nanosheets in water according to a material-liquid ratio of 1g to 400mL, then crushing for one hour by using an ultrasonic crusher, then centrifuging for 1 hour in a centrifuge at a rotating speed of 3500r/min, and finally taking supernatant liquid to obtain the MXene nanosheet spraying liquid.
Adding the prepared MXene nanosheet spraying liquid into a spray gun, adjusting the air pressure of the spray gun to be 3Mpa, and spraying the MXene nanosheet spraying liquid onto a film with flexible protrusions, wherein the spraying amount of the MXene nanosheets is 0.1g/cm 2 . The force-sensitive structure layer 3 is prepared as shown in fig. 4, MXene nanosheets are seen to be bonded on the PU film, and the conductive material and the gradient microstructure ensure the condition of the force-sensitive structure layer as a sensing layer.
(3) Device packaging conductive layer
And (3) oppositely placing the patterned electrode 2 on the flexible substrate layer 1 and the side, with the flexible bulge, of the force-sensitive structure layer 3, and then packaging the flexible substrate layer 1 and the force-sensitive structure layer 3 by using Polyurethane (PU) as a flexible packaging layer 6 to obtain the flexible force-sensitive structure.
Example 2
Example 2 compared with example 1, the height ratio of the high flexibility projections 4 to the low flexibility projections 5 was adjusted to 3.
Example 3
Example 3 compared with example 1, the height ratio of the high flexibility projections 4 to the low flexibility projections 5 was adjusted to 1, and the rest conditions were the same.
Example 4
Example 4 the material of the flexible substrate layer 1 was changed to PET compared to example 1, and the rest of the conditions were exactly the same.
Example 5
In example 5, the material of the force-sensitive structure layer 3 was changed to PDMS, and the other conditions were completely the same as in example 1.
Examples of the experiments
Since the performance of the pressure sensors obtained in examples 4 and 5 is substantially similar to that of the pressure sensor in example 1, the electrical performance of the pressure sensors will be described by taking examples 1 to 3 as examples. Specific electrical properties were tested as follows.
The pressure simulation test was performed on the pressure sensors of examples 1 to 3, and the results are shown in fig. 5. As can be seen from fig. 5, when the gradient height ratio of the flexible bump on the force-sensitive structure layer exceeds 1.
In order to verify the electrical properties of the pressure sensor with the bionic gradient microstructure, three flexible pressure sensors with gradient height ratios of 1. The test method comprises the following steps:
and 2, enabling the linear motor to impact the piezoresistive pressure sensor back and forth, recording the magnitude of force through a dynamometer arranged at the front end of the linear motor, connecting conductive carbon cloth led out of the pressure sensor with SR-570, applying a constant bias voltage of 0.1V to a device by the SR-570, acquiring a current signal by using the SR-570, and recording the output of the current signal by using LabVIEW and a data acquisition system.
The test results are shown in fig. 5. It can be seen that the pressure sensor of uniform height (gradient height ratio of 1) has a low sensitivity due to its large initial contact area and moreover its sensitivity is saturated at about 50 kPa; the sensor with the gradient height ratio of 1; the sensor with the height ratio of 1.
While the present invention has been described in detail with reference to the embodiments, it should not be construed as limited to the scope of the patent. Various modifications and changes may be made by those skilled in the art without inventive step within the scope of the appended claims.
Claims (10)
1. The utility model provides a flexible pressure sensor based on bionical gradient microstructure which characterized in that: the flexible packaging film comprises a flexible substrate layer, a force-sensitive structural layer and a flexible packaging layer; the inner side of the flexible substrate layer is provided with a patterned electrode, one side of the force-sensitive structure layer, which is opposite to the flexible substrate layer, is provided with a plurality of flexible bulges with different heights, and the surfaces of the flexible bulges are coated with conductive layers; the flexible packaging layer is located on the other side of the flexible substrate layer and packages the flexible substrate layer and the force-sensitive structure layer.
2. The flexible pressure sensor based on bionic gradient microstructure according to claim 1, wherein: the patterned electrodes are interdigitated electrodes.
3. The flexible pressure sensor based on bionic gradient microstructure according to claim 2, wherein: the interdigital electrode is an interdigital gold electrode.
4. The flexible pressure sensor based on bionic gradient microstructure according to claim 1, wherein: the flexible protrusions comprise high-flexibility protrusions and low-flexibility protrusions, and the height ratio of the high-flexibility protrusions to the low-flexibility protrusions is (2).
5. The flexible pressure sensor based on bionic gradient microstructure according to claim 4, wherein: the flexible projections are distributed in rows, and the height of the flexible projections in each row is the same.
6. The flexible pressure sensor based on bionic gradient microstructure according to claim 5, wherein: the high-flexibility bulges and the low-flexibility bulges are arranged in a staggered mode according to the row ratio of 1.
7. The flexible pressure sensor based on bionic gradient microstructure according to claim 1, wherein the flexible pressure sensor comprises: the conducting layer is made of carbon nano tubes or MXene nano sheets.
8. The flexible pressure sensor based on bionic gradient microstructure according to claim 7, wherein the MXene nanosheets are prepared by:
s1: dissolving lithium salt in acid with the concentration of 8-10M according to the material-liquid ratio of 1g;
s2: will be mixed with lithium salt of equal mass of MAX-Ti 3 AlC 2 Adding the mixture into the reactant obtained in the S1, and continuously reacting for 20-30 h at 35-45 ℃; then centrifuging and vacuum drying to obtain the product.
9. The flexible pressure sensor based on bionic gradient microstructure according to claim 1, wherein: the flexible substrate layer is made of PI or PET; the force-sensitive structure layer is made of PU or PDMS; the flexible packaging layer is made of PU.
10. The method for preparing the bionic gradient microstructure-based flexible pressure sensor as claimed in any one of claims 1 to 9, characterized by comprising the following steps:
(1) Preparing a flexible substrate layer
Taking a flexible substrate, forming a patterned electrode on one side of the flexible substrate in a magnetron sputtering mode, and extracting the electrode from the patterned electrode by using conductive carbon cloth; magnetron sputteringThe conditions are as follows: vacuum degree of 1X 10 -5 Pa below, the magnetron sputtering power is 40W, the ratio of argon to oxygen is 40, and the sputtering time is 5min;
(2) Preparation of force-sensitive structural layer
Etching pits with different depths on the surface of a silicon wafer with the thickness of 100-1000 mu m; then coating the force-sensitive structure layer preparation material on a silicon wafer in a spin coating mode, baking for 50-120 min at 60-150 ℃, then removing the film from the silicon wafer, and then coating the conductive material according to the ratio of 0.05-0.4 mg/cm 2 Spraying the spraying amount of the water-based paint on the convex surface of the film to obtain the paint;
(3) Device packaging conductive layer
And (3) oppositely placing the side of the flexible substrate layer with the patterned electrode and the side of the force-sensitive structural layer with the flexible protrusions, and then packaging the flexible substrate layer with the flexible packaging layer.
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