CN112834086A - Ultra-sensitive capacitive flexible pressure sensor and preparation method thereof - Google Patents
Ultra-sensitive capacitive flexible pressure sensor and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the field of capacitive sensors, and particularly discloses an ultra-sensitive capacitive flexible pressure sensor and a preparation method thereof. The ultra-sensitive capacitive flexible pressure sensor comprises an upper electrode layer, a middle dielectric layer and a lower electrode layer, wherein: the upper electrode layer and the lower electrode layer have the same structure and both comprise a flexible base material and a conductive material embedded on the surface of the flexible base material; the surface of the middle dielectric layer is provided with a micro-groove structure, and a micro-cone structure is arranged in the micro-groove structure, so that the contact area between the middle dielectric layer and the upper electrode layer or the lower electrode layer is increased, and the sensitivity of the ultra-sensitive capacitive flexible pressure sensor is improved. According to the invention, the micro-groove structure is arranged on the surface of the dielectric layer, so that the dielectric layer can show larger deformation and compressibility in a wider pressure range, and meanwhile, the micro-cone structure is arranged in the micro-groove structure, so that the dielectric layer has higher sensitivity in a wider pressure range.
Description
Technical Field
The invention belongs to the field of capacitive sensors, and particularly relates to an ultra-sensitive capacitive flexible pressure sensor and a preparation method thereof.
Background
As one of the current research hotspots, intelligent robots are increasingly applied to daily life. Robots are well developed and widely used in these fields, thanks to their ability to perceive the external environment and their good adaptability. The sensing system is a main window for information exchange between the robot and the outside, and is the basis of the sensing capability of the robot, the robot senses the state of the surrounding environment according to different sensing elements arranged on the robot body, transmits sensing signals to the central processing system through the internal system for analysis and processing, and controls the actuator to execute corresponding actions through corresponding instructions, so that the whole loop for executing the actions by the robot is completed. For a robot, the sense of touch provides it with information about physical contact, which is one of the important perception abilities of the robot, assisting it in manipulating unknown objects in an unknown environment.
The tactile sensors currently used on robots include: piezoelectric sensors, triboelectric sensors, resistive sensors, capacitive sensors, and the like. Compared with other types of sensors, the capacitive sensor has the advantages of simple structure, easiness in manufacturing, higher sensitivity, good dynamic response, higher resolution and the like, and is widely applied to measuring physical parameters such as displacement, acceleration, pressure and the like. However, the traditional capacitive sensor can not meet the requirements in the aspects of shape retention, flexibility, stretchability and the like. The flexible capacitive sensor not only has the advantages, but also has good stretchability, shape retention and flexibility, can be used for detecting on a complex surface, and is widely applied to the fields of electronic skin, contact measurement, flexible antennas, biosensors and the like.
The high sensitivity is a hotspot of research on flexible capacitive sensors, and the preparation of an electrode layer or a dielectric layer with a microstructure on the surface can improve the sensitivity and response speed of the sensor, such as a micro pyramid array, a micro column array, a fingerprint structure, a microstructure copied from plants (such as lotus leaves and roses), and the like. Besides introducing the microstructure into the sensor structure, the sensor can also utilize the super-capacitance principle and adopt the ionic gel as a dielectric layer to enable the interface between the dielectric layer and the electrode to form an electric double layer capacitance to improve the interface capacitance density, thereby further improving the sensitivity of the sensor. In order to achieve increased sensitivity and pressure resolution at higher pressures, the dielectric layer is of a multi-level microstructure, such that further compressive deformation of the intermediate dielectric layer can also increase sensitivity using the microstructure. In the manufacture of multilevel microstructures, flexible electronic technology is not used in solid electronic technology, so that the traditional semiconductor technology is also adopted in a large quantity, but some flexible materials have poor adaptability to the traditional technology, so that improvement of the preparation technology is necessary.
Disclosure of Invention
In view of the above-mentioned drawbacks and/or needs for improvement of the prior art, the present invention provides an ultra-sensitive capacitive flexible pressure sensor and a method for manufacturing the same, in which a micro-groove structure is formed on a surface of a dielectric layer, and a micro-cone structure is formed inside the micro-groove structure, so that the dielectric layer can exhibit large deformation and compressibility in a wide pressure range and has high sensitivity.
To achieve the above object, according to one aspect of the present invention, there is provided an ultra-sensitive capacitive flexible pressure sensor including an upper electrode layer, an intermediate dielectric layer, and a lower electrode layer, wherein: the upper electrode layer and the lower electrode layer have the same structure and both comprise a flexible base material and a conductive material embedded on the surface of the flexible base material; the surface of the middle dielectric layer is provided with a micro-groove structure, and a micro-cone structure is arranged in the micro-groove structure, so that the contact area between the middle dielectric layer and the upper electrode layer or the lower electrode layer is increased, and the sensitivity of the ultra-sensitive capacitive flexible pressure sensor is improved.
As a further preference, the intermediate dielectric layer is prepared from a biomimetic template having a micro-cone structure.
More preferably, the distance between the upper electrode layer and the lower electrode layer is 150 to 350 μm, the thickness of the upper electrode layer and the lower electrode layer is 100 to 200 μm, and the thickness of the middle dielectric layer is 150 to 350 μm.
More preferably, the average radius of the micro-groove structure in the middle dielectric layer is 40 to 80 μm, the average height of the micro-cone structure is 5 to 25 μm, and the line pitch of the micro-cone structure is 10 to 35 μm.
As a further preference, the flexible matrix material is PDMS, PI, PTFE, PET or ecoflex; the conductive material is a flexible conductive polymer, the viscosity of the flexible conductive polymer is between 10 Pa.s and 100 Pa.s, and the conductivity is higher than 1 x 105S/cm, and the curing temperature is between 100 and 180 ℃.
According to another aspect of the present invention, a method for manufacturing an ultra-sensitive capacitive flexible pressure sensor is provided, the method comprising the steps of:
s1, preparing an upper electrode layer and a lower electrode layer;
s2, the elastic material with the surface provided with the micro-cone structure is soaked in the ionic gel solution, the heating is carried out at 26-28 ℃ to volatilize the solvent in the ionic gel solution, so that a groove is formed on the surface of the elastic material with the micro-cone structure, and the ionic gel film is peeled off to obtain the intermediate dielectric layer;
and S3, bonding the upper electrode layer, the middle dielectric layer and the lower electrode layer together to obtain the ultra-sensitive capacitive flexible pressure sensor.
As a further preference, step S1 specifically includes the following sub-steps:
s11, spin-coating a sacrificial layer solution on a hard substrate, and forming a sacrificial layer on the hard substrate after the sacrificial layer solution is solidified;
s12, adhering a mask plate containing an electrode pattern on the surface of the sacrificial layer, coating a flexible conductive polymer on the mask plate, tearing off the mask plate, heating to cure, and thus obtaining a flexible conductive polymer with a preset pattern on the surface of the sacrificial layer;
s13, spin-coating a flexible matrix layer solution on the sacrificial layer containing the flexible conductive polymer, embedding the flexible conductive polymer on the surface of the flexible matrix layer after curing, putting the substrate into hot water to dissolve the sacrificial layer, and obtaining the flexible matrix layer containing the flexible conductive polymer, so as to obtain the upper electrode layer or the lower electrode layer.
Further preferably, in step S11, the hard substrate is a glass sheet, an epitaxial wafer, a monocrystalline silicon wafer, a polycrystalline silicon wafer, a glass slide or a quartz sheet; the sacrificial layer solution is a polyvinyl alcohol solution; in step S12, the mask is a PVC film, wallpaper, or scotch tape.
As further preferred, in step S2, the ionic gel employs polyvinylidene fluoride-hexafluoropropylene and/or 1-ethyl-3-methylimidazolium bistrifluoromethylsulfonyl imide; the elastic material is a copolyester compound, a silicon-based polymer, a silica gel compound or a rubber compound.
As a further preferable method, the method for preparing the elastic material having the surface with the micro-cone structure in step S2 is: sticking leaves with the surface of the microcone structure on a substrate, pouring an elastic material on the leaf surface, standing until the elastic material is solidified, and peeling the elastic material from the leaf surface to obtain the elastic material with the microcone structure.
Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:
1. according to the invention, the micro-groove structure is arranged on the surface of the dielectric layer, so that the dielectric layer can show larger deformation and compressibility in a wider pressure range, meanwhile, the micro-cone structure is arranged in the micro-groove structure, so that the dielectric layer has higher sensitivity in a wider pressure range, and the dielectric layer applied to the ultra-sensitive capacitive flexible pressure sensor can ensure that the ultra-sensitive capacitive flexible pressure sensor has the advantages of high sensitivity, low detection limit, large pressure range, high pressure resolution, high stability, quick response time and the like; compared with a sensor without an intermediate dielectric layer, the sensitivity of a low-pressure stage (0 kPa-10 kPa) is obviously improved, four orders of magnitude can be improved, and the integral linearity is obviously improved; the linearity of a capacitance change curve is improved in a medium-pressure stage (10 kPa-30 kPa); higher sensitivity is shown in the high pressure stage (30 kPa-200 kPa);
2. meanwhile, the thicknesses of the upper electrode layer, the lower electrode layer and the middle dielectric layer and the specific parameters of the micro-groove structure and the micro-cone structure in the middle dielectric layer are optimized, so that the sensor can be tightly attached to the surface of the robot under the condition of good performance, the gap between the sensor and the surface of the robot is reduced, the conformal contact with the surface of the robot is realized, and the measurement accuracy of the sensor in a high-voltage area and a low-voltage area is improved;
3. in addition, the invention provides a preparation method of the ultra-sensitive capacitive flexible pressure sensor, which comprises the steps of pouring an elastic material with a micro-cone structure on the surface into an ionic gel solution, heating at 26-28 ℃ to volatilize a solvent in the ionic gel solution, so that a groove is formed on the surface of the elastic material with the micro-cone structure, obtaining the groove only by changing the ambient temperature, and not needing to carry out etching and other steps on a primary structure, thereby greatly simplifying the process, effectively reducing the process cost and shortening the process time.
Drawings
FIG. 1 is a schematic diagram of the construction of an ultra-sensitive capacitive flexible pressure sensor constructed in accordance with a preferred embodiment of the present invention;
FIG. 2 is a flow chart of the fabrication of upper and lower electrode layers constructed in accordance with a preferred embodiment of the present invention;
FIG. 3 is a flow chart of the fabrication of an inter-dielectric layer constructed in accordance with a preferred embodiment of the present invention;
FIG. 4 is an SEM image of an inter-dielectric layer prepared in example 1 of the present invention;
FIG. 5 is a pressure test chart of the ultra-sensitive capacitive flexible pressure sensor prepared in example 1 of the present invention at 1 kHz;
FIG. 6 is a pressure test chart of the ultra-sensitive capacitive flexible pressure sensor prepared in example 1 of the present invention at 300 kHz.
The same reference numbers will be used throughout the drawings to refer to the same or like elements or structures, wherein:
1-silicon chip, 2-polyvinyl alcohol sacrificial layer, 3-mask, 4-flexible conductive polymer, 5-polydimethylsiloxane membrane, 6-crystallizing dish, 7-electrode layer, 8-velvet arrowroot leaf, 9-polydimethylsiloxane membrane, 10-ionic gel solution, 11-ionic gel film and 12-oven.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
As shown in fig. 1, an ultra-sensitive capacitive flexible pressure sensor according to an embodiment of the present invention includes an upper electrode layer, a middle dielectric layer, and a lower electrode layer, where:
the upper electrode layer and the lower electrode layer have the same structure and both comprise a flexible base material and a conductive material embedded on the surface of the flexible base material; the upper electrode layer and the lower electrode layer are made of conductive materials with certain stretchability, so that the tensile property of the electrode layers is improved, the stability of the sensor is improved, and the durability of the sensor is improved; the surface of the middle dielectric layer is provided with a micro-groove structure, and a micro-cone structure is arranged in the micro-groove structure, so that the contact area between the middle dielectric layer and the upper electrode layer or the lower electrode layer is increased, the sensitivity of the ultra-sensitive capacitive flexible pressure sensor is improved, when the flexible sensor is subjected to pressure or tensile force, the capacitance between the upper electrode layer and the lower electrode layer is changed, and the pressure or tensile force applied to the flexible sensor is obtained by measuring the change of the capacitance of the flexible sensor.
When the sensor is subjected to pressure or tensile force, the surface micro-cone structure of the middle dielectric layer increases the contact area between the dielectric layer and the electrode layer, so that the sensitivity of the sensor is increased, and the sensor has a lower detection limit; the dielectric layer shows larger deformation and compressibility in a wider pressure range by utilizing the micro-groove structure on the surface of the dielectric layer; the sensor has high sensitivity in a wide pressure range by utilizing a micro-cone structure in a dielectric surface micro-groove structure.
Further, the intermediate dielectric layer is prepared by adopting ionic gel to prepare a bionic template with a micro-cone structure, and preferably, the bionic template is prepared by adopting velvet arrowroot as a template. The distance between the upper electrode layer and the lower electrode layer is 150-350 microns, the thickness of the upper electrode layer and the lower electrode layer is 100-200 microns, so that a large capacitance is ensured, the anti-interference capability of the ultra-sensitive capacitive flexible pressure sensor is improved, and the small pressure range is avoided while the surface adhesion of the ultra-sensitive capacitive flexible pressure sensor is ensured. The thickness of the middle dielectric layer is 150-350 μm, so that the rigidity of the middle dielectric layer of the ultra-sensitive capacitive flexible pressure sensor is reduced, the sensitivity of the sensor is improved, and the stability of the sensor is ensured. Too high a density of the micro-cone structure can reduce the sensitivity of the low-voltage area of the sensor, while too low a density can reduce the sensitivity of the high-voltage area; meanwhile, the average radius of the micro grooves is too large, so that the micro cone structures are not arranged in the micro grooves, the overall sensitivity of the sensor is reduced, and the average radius of the micro grooves is too small, so that the number of the micro cone structures contained in each micro groove structure is too small, the sensitivity of a high-voltage area of the sensor is reduced, therefore, in order to ensure that the sensor has higher sensitivity in a low-voltage area and a high-voltage area, the average radius of the micro groove structures in the middle dielectric layer is 40-80 mu m, the average height of the micro cone structures is 5-25 mu m, and the line spacing of the micro cone structures is 10-35 mu m.
Further, the flexible base material is a flexible and stretchable high polymer material such as PDMS, PI, PTFE, PET or ecoflex, and is used as a support layer of the sensor; the material has good stretchability to ensure the effectiveness of the electrode in operation in a stretchable state. The conductive material is a flexible conductive polymer, the viscosity of the flexible conductive polymer is between 10 Pa.s and 100 Pa.s, and the conductivity is higher than 1 x 105S/cm, and the curing temperature is between 100 and 180 ℃.
According to another aspect of the present invention, a method for manufacturing an ultra-sensitive capacitive flexible pressure sensor is provided, the method comprising the steps of:
s1, preparing an upper electrode layer and a lower electrode layer, specifically comprising the following substeps:
s11, spin-coating the sacrificial layer solution on the hard substrate at a spin-coating speed of 200-800 rpm for 30-60 seconds, and then heating the printed substrate at 80-100 ℃ for 5-15 minutes to form a sacrificial layer on the hard substrate after the sacrificial layer solution is cured;
s12, adhering a mask plate containing an electrode pattern on the surface of the sacrificial layer, coating a flexible conductive polymer on the mask plate, tearing off the mask plate, and heating and curing at 100-180 ℃ for 60-90 minutes to obtain the flexible conductive polymer with the preset pattern on the surface of the sacrificial layer;
s13, spin-coating a flexible matrix layer solution on a sacrificial layer containing a flexible conductive polymer, wherein the spin-coating speed is 350-1000 rpm and the time is 50-120S, then heating at 80-100 ℃ for 30-60 minutes, embedding the cured flexible conductive polymer on the surface of the flexible matrix layer, putting the substrate into hot water to dissolve the sacrificial layer, and obtaining a flexible matrix layer containing the flexible conductive polymer to obtain an upper electrode layer or a lower electrode layer;
s2, the elastic material with the surface provided with the micro-cone structure is soaked in the ionic gel solution, the heating is carried out at 26-28 ℃ to volatilize the solvent in the ionic gel solution, so that a groove is formed on the surface of the elastic material with the micro-cone structure, and the ionic gel film is peeled off to obtain the intermediate dielectric layer;
and S3, bonding the upper electrode layer, the middle dielectric layer and the lower electrode layer together to obtain the ultra-sensitive capacitive flexible pressure sensor.
Further, in step S11, the hard substrate is a glass sheet, an epitaxial wafer, a monocrystalline silicon wafer, a polycrystalline silicon wafer, a glass slide or a quartz wafer. In step S11, the sacrificial layer solution is a polyvinyl alcohol solution, which is an organic high polymer material dissolved in water, and is colorless, transparent, non-toxic, harmless, and has good film-forming properties. The solvent for dissolving the polyvinyl alcohol sacrificial layer is water, so that the silicon chip and the sensor cannot be damaged, and the environment cannot be polluted. In step S12, the mask is a PVC film, wallpaper, or scotch tape.
Further, in step S2, the solute of the ionic gel solution is mixed with poly (vinylidene fluoride-hexafluoropropylene) P (VDF-HFP) and/or 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [ EMIM ] [ TFSI ] in a mixing mass ratio of 1: 3; the elastic material is copolyester compound, silicon-based polymer (polydimethylsiloxane), silica gel compound or rubber compound, and the solvent of the ionic gel solution is preferably acetone or DMF solution.
Further, the preparation method of the elastic material having the surface with the micro-cone structure in the step S2 includes: sticking the leaves with the micro-cone structures on the surface of the leaf to a substrate, pouring the elastic material on the surface of the leaves, standing for 36-48 hours until the elastic material is solidified, and then stripping the elastic material from the surface of the leaves to obtain the elastic material with the micro-cone structures.
The method for manufacturing the ultra-sensitive capacitive flexible pressure sensor according to the present invention is described in detail below according to an embodiment.
Example 1
As shown in fig. 2, the upper and lower electrode layers are first prepared.
(1) Washing a clean 2-inch silicon wafer 1 by using acetone, isopropanol and deionized water in sequence, and then drying by using nitrogen;
(2) spin-coating a sacrificial layer solution, namely a 10% polyvinyl alcohol aqueous solution, on the polished surface of the silicon wafer 1 at a spin-coating speed of 200 rpm for 60 seconds, then placing the silicon wafer 1 on a hot plate to be heated at a heating temperature of 80 ℃ for 15 minutes, so that water is heated and evaporated, and polyvinyl alcohol is cured into a film, thereby obtaining a polyvinyl alcohol sacrificial layer 2 with a smooth surface and close adhesion to the silicon wafer 1;
(3) cutting electrode patterns on the mask 3 by using a laser cutting machine, and adhering the mask 3 with the electrode patterns on the polyvinyl alcohol sacrificial layer 2;
(4) after the flexible conductive polymer 4 is uniformly coated and covers the electrode pattern on the mask 3, the mask 3 is carefully torn off, thereby completing patterning of the flexible conductive polymer 4, wherein the coated conductive material is about 50 μm thick;
(5) putting the silicon wafer 1 subjected to the steps into an oven 12 for curing, wherein the curing temperature is 100 ℃, and the curing time is 90 minutes;
(6) spin coating polydimethylsiloxane again on the silicon wafer 1 subjected to the steps, wherein the spin coating speed is 350 revolutions per minute and the spin coating time is 120s, then placing the silicon wafer on a hot plate and heating the silicon wafer at the heating temperature of 90 ℃ for 30 minutes, and curing the polydimethylsiloxane into a film, wherein the thickness of the polydimethylsiloxane film 5 is 200 microns;
(7) putting the silicon wafer 1 into a crystallizing dish 6 filled with deionized water for water bath heating, and dissolving the polyvinyl alcohol sacrificial layer 2 to finish the preparation of an electrode layer 7 with the thickness of 200 mu m;
fig. 3 is a flow chart for preparing an intermediate dielectric layer constructed in accordance with a preferred embodiment of the present invention.
(8) Cutting a clean 2-inch silicon wafer 1 into a shape of the size of the silicon wafer 1, sticking the back of the velvet arrowroot leaves 8 to the surface of a glass slide by using a double-sided adhesive, and blowing off dust on the surfaces of the leaves by using nitrogen;
(9) inverting the polydimethylsiloxane on the surface of the leaves, standing at normal temperature for 48 hours, and curing the polydimethylsiloxane into a film, wherein the thickness of the polydimethylsiloxane film 9 is 2mm, so as to form the polydimethylsiloxane film 9 with the leaf surface microstructure;
(10) taking a clean 2-inch silicon wafer 1 as a substrate, adhering a polydimethylsiloxane membrane 9 to the surface of a glass slide, spin-coating a layer of polydimethylsiloxane on the surface of the glass slide at a spin-coating speed of 1000 rpm for 60s, adhering the back surface of the membrane with a leaf microstructure to the surface coated with the polydimethylsiloxane, and then heating the silicon wafer on a hot plate at a heating temperature of 80 ℃ for 20 min to finish the adhesion of the polydimethylsiloxane membrane 9 and the silicon wafer;
(11) mixing 2g of poly (vinylidene fluoride-hexafluoropropylene) P (VDF-HFP) and 20g of acetone, stirring the mixture for 2 hours by using a magnetic stirrer to fully dissolve the poly (vinylidene fluoride-hexafluoropropylene) P (VDF-HFP) in the acetone, dropwise adding 6g of 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [ EMIM ] [ TFSI ], and continuously stirring the mixture for 40 minutes to prepare an ionic gel solution;
(12) taking a clean dropper, and dripping the ionic gel solution on the surface of the polydimethylsiloxane membrane 9 with the leaf surface microstructure until the surface of the polydimethylsiloxane membrane 9 is filled with the ionic gel solution to form an ionic gel solution 10 full of the microstructure;
(13) putting the silicon wafer 1 subjected to the steps into an oven, heating at 28 ℃ to accelerate the volatilization of solvent acetone, wherein the acetone enables grooves with different sizes to be formed on the surface of a micro-cone structure just formed in the volatilization process, and after a multi-stage bionic structure is formed, peeling off the ionic gel film to form an ionic gel film 11 with a multi-stage bionic microstructure, wherein the average height of the micro-cone structure on the surface is 15 microns, the linear spacing is 23 microns, the average radius of the micro-groove structure is 80 microns, and the thickness of an intermediate dielectric layer is 350 microns;
(14) and finally, packaging the upper electrode layer, the middle dielectric layer and the lower electrode layer by using transparent adhesive tapes, wherein the distance between the upper electrode layer and the lower electrode layer is 350 mu m, so that the preparation of the sensor is completed.
Example 2:
as shown in fig. 2, the upper and lower electrode layers are first prepared.
(1) Washing a clean 2-inch silicon wafer 1 by using acetone, isopropanol and deionized water in sequence, and then drying by using nitrogen;
(2) spin-coating a sacrificial layer solution, namely a 10% polyvinyl alcohol aqueous solution, on the polished surface of the silicon wafer 1 at a spin-coating speed of 500 rpm for 45 seconds, then placing the silicon wafer 1 on a hot plate to be heated at a heating temperature of 80 ℃ for 10 minutes, so that water is heated and evaporated, and polyvinyl alcohol is cured into a film, thereby obtaining a polyvinyl alcohol sacrificial layer 2 with a smooth surface and close adhesion to the silicon wafer 1;
(3) cutting electrode patterns on the mask 3 by using a laser cutting machine, and adhering the mask 3 with the electrode patterns on the polyvinyl alcohol sacrificial layer 2;
(4) after the flexible conductive polymer 4 is uniformly coated and the electrode pattern is covered on the mask 3, the mask 3 is carefully torn off, thereby completing the patterning of the flexible conductive polymer 4, wherein the coated conductive material is about 50 μm thick;
(5) putting the silicon wafer 1 subjected to the steps into an oven 12 for curing, wherein the curing temperature is 140 ℃, and the curing time is 75 minutes;
(6) spin coating polydimethylsiloxane again on the silicon wafer 1 subjected to the steps at the spin coating speed of 675 revolutions per minute for 85s, then placing the silicon wafer on a hot plate for heating at the heating temperature of 90 ℃ for 45 minutes, and curing the polydimethylsiloxane into a film, wherein the thickness of the polydimethylsiloxane film 5 is 150 micrometers;
(7) putting the silicon wafer into a crystallizing dish 6 filled with deionized water for water bath heating, and dissolving the polyvinyl alcohol sacrificial layer 2 to finish the preparation of an electrode layer 7 with the thickness of 150 mu m;
fig. 2 is a flow chart for preparing an inter-dielectric layer constructed in accordance with a preferred embodiment of the present invention, as shown in fig. 2.
(8) Cutting a clean 2-inch silicon wafer 1 into a shape of the size of the silicon wafer 1, sticking the back of the velvet arrowroot leaves 8 to the surface of a glass slide by using a double-sided adhesive, and blowing off dust on the surfaces of the leaves by using nitrogen;
(9) inverting the polydimethylsiloxane on the surface of the leaves, standing at normal temperature for 36 hours, solidifying the polydimethylsiloxane into a film 9, wherein the thickness of the polydimethylsiloxane film 9 is 1.5mm, and forming the polydimethylsiloxane film 9 with the leaf surface microstructure;
(10) taking a clean 2-inch silicon wafer 1 as a substrate, adhering a polydimethylsiloxane membrane 9 to the surface of a glass slide, spin-coating a layer of polydimethylsiloxane on the surface of the glass slide at a spin-coating speed of 1500 rpm for 40s, adhering the back surface of the membrane with a leaf microstructure to the surface coated with the polydimethylsiloxane, and then heating the silicon wafer on a hot plate at a heating temperature of 90 ℃ for 17.5 min to finish the adhesion of the polydimethylsiloxane membrane 9 and the silicon wafer;
(11) mixing 1g of poly (vinylidene fluoride-hexafluoropropylene) P (VDF-HFP) and 10g of acetone, stirring for 3 hours by using a magnetic stirrer to fully dissolve the poly (vinylidene fluoride-hexafluoropropylene) P (VDF-HFP) in the acetone, dropwise adding 3g of 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [ EMIM ] [ TFSI ], and continuously stirring for 20 minutes to prepare an ionic gel solution;
(12) taking a clean dropper, and dripping the ionic gel solution on the surface of the polydimethylsiloxane membrane 9 with the leaf surface microstructure until the surface of the polydimethylsiloxane membrane 9 is filled with the ionic gel solution to form an ionic gel solution 10 full of the microstructure;
(13) putting the silicon wafer 1 subjected to the steps into an oven, heating at 26 ℃ to accelerate the volatilization of solvent acetone, wherein the acetone enables grooves with different sizes to be formed on the surface of a micro-cone structure just formed in the volatilization process, and after a multi-stage bionic structure is formed, peeling off the ionic gel film to form the ionic gel film 11 with the multi-stage bionic microstructure, wherein the average height of the micro-cone structure on the surface is 25 micrometers, the linear spacing is 35 micrometers, the average radius of the micro-groove structure is 40 micrometers, and the thickness of the middle dielectric layer is 250 micrometers;
(14) and finally, packaging the upper electrode layer, the middle dielectric layer and the lower electrode layer by using transparent adhesive tapes, wherein the distance between the upper electrode layer and the lower electrode layer is 250 mu m, thereby completing the preparation of the sensor.
Example 3:
as shown in fig. 2, the upper and lower electrode layers are first prepared.
(1) Washing a clean 2-inch silicon wafer 1 by using acetone, isopropanol and deionized water in sequence, and then drying by using nitrogen;
(2) spin-coating a sacrificial layer solution, namely a 10% polyvinyl alcohol aqueous solution, on the polished surface of the silicon wafer 1 at a spin-coating speed of 800 rpm for 30 seconds, then placing the silicon wafer 1 on a hot plate to be heated at a heating temperature of 100 ℃ for 5 minutes, so that water is heated and evaporated, and polyvinyl alcohol is cured into a film, thereby obtaining a polyvinyl alcohol sacrificial layer 2 with a smooth surface and close adhesion to the silicon wafer 1;
(3) cutting electrode patterns on the mask 3 by using a laser cutting machine, and adhering the mask 3 with the electrode patterns on the polyvinyl alcohol sacrificial layer 2;
(4) after the flexible conductive polymer 4 is uniformly coated and covers the electrode pattern on the mask 3, carefully tearing off the mask 3 to complete the patterning of the flexible conductive polymer 4;
(5) putting the silicon wafer 1 subjected to the steps into an oven 12 for curing, wherein the curing temperature is 180 ℃, and the curing time is 60 minutes;
(6) spin coating polydimethylsiloxane again on the silicon wafer 1 subjected to the steps, wherein the spin coating speed is 1000 revolutions per minute and the spin coating time is 50s, then placing the silicon wafer 1 on a hot plate to be heated, the heating temperature is 100 ℃, the heating time is 30 minutes, the polydimethylsiloxane is solidified into a film, and the thickness of the polydimethylsiloxane film 5 is 100 micrometers;
(7) putting the silicon wafer into a crystallizing dish 6 filled with deionized water for water bath heating, and dissolving the polyvinyl alcohol sacrificial layer 2 to finish the preparation of an electrode layer 7 with the thickness of 100 mu m;
fig. 2 is a flow chart for preparing an intermediate dielectric layer, constructed in accordance with a preferred embodiment of the present invention, as shown in fig. 2.
(8) Cutting a clean 2-inch silicon wafer 1 into a shape of the size of the silicon wafer 1, sticking the back of the velvet arrowroot leaves 8 to the surface of a glass slide by using a double-sided adhesive, and blowing off dust on the surfaces of the leaves by using nitrogen;
(9) inverting the polydimethylsiloxane on the surface of the leaves, standing at normal temperature for 42 hours, and curing the polydimethylsiloxane into a film 9, wherein the thickness of the polydimethylsiloxane film 9 is 3mm to form the polydimethylsiloxane film 9 with the leaf surface microstructure;
(10) taking a clean 2-inch silicon wafer 1 as a substrate, adhering a polydimethylsiloxane membrane 9 to the surface of a glass slide, spin-coating a layer of polydimethylsiloxane on the surface of the glass slide at a spin-coating speed of 1250 revolutions per minute for 50s, adhering the back surface of the membrane with a leaf microstructure to the surface coated with the polydimethylsiloxane, and then heating the silicon wafer on a hot plate at the heating temperature of 100 ℃ for 15 minutes to finish the adhesion of the polydimethylsiloxane membrane 9 and the silicon wafer;
(11) mixing 1.5g of poly (vinylidene fluoride-hexafluoropropylene) P (VDF-HFP) and 15g of acetone, stirring for 4 hours by using a magnetic stirrer to fully dissolve the poly (vinylidene fluoride-hexafluoropropylene) P (VDF-HFP) in the acetone, dropwise adding 4.5g of 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide [ EMIM ] [ TFSI ], and continuing stirring for 30 minutes to prepare an ionic gel solution; (ii) a
(12) Taking a clean dropper, and dripping the ionic gel solution on the surface of the polydimethylsiloxane membrane 9 with the leaf surface microstructure until the surface of the polydimethylsiloxane membrane 9 is filled with the ionic gel solution to form an ionic gel solution 10 full of the microstructure;
(13) putting the silicon wafer 1 subjected to the steps into an oven, heating at 27 ℃ to accelerate the volatilization of solvent acetone, wherein the acetone enables grooves with different sizes to be formed on the surface of a micro-cone structure just formed in the volatilization process, and after a multi-stage bionic structure is formed, peeling off the ionic gel film to form an ionic gel film 11 with a multi-stage bionic microstructure, wherein the average height of the micro-cone structure on the surface is 5 microns, the linear spacing is 10 microns, the average radius of the micro-groove structure is 50 microns, and the thickness of an intermediate dielectric layer is 150 microns;
(14) and finally, packaging the upper electrode layer, the middle dielectric layer and the lower electrode layer by using transparent adhesive tapes, wherein the distance between the upper electrode layer and the lower electrode layer is 150 mu m, thereby completing the preparation of the sensor.
Fig. 4 is an SEM image of an interlayer dielectric layer prepared in example 1 of the present invention, and the secondary microstructure of the interlayer dielectric layer is shown.
Fig. 5 and 6 are pressure tests of the ultra-sensitive capacitive flexible pressure sensor prepared in embodiment 1 of the present invention at 1kHz and 300kHz, respectively, and the test results prove that the ultra-sensitive capacitive flexible pressure sensor provided by the present invention has ultra-high pressure sensitivity.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. An ultra-sensitive capacitive flexible pressure sensor, comprising an upper electrode layer, an intermediate dielectric layer and a lower electrode layer, wherein: the upper electrode layer and the lower electrode layer have the same structure and both comprise a flexible base material and a conductive material embedded on the surface of the flexible base material; the surface of the middle dielectric layer is provided with a micro-groove structure, and a micro-cone structure is arranged in the micro-groove structure, so that the contact area between the middle dielectric layer and the upper electrode layer or the lower electrode layer is increased, and the sensitivity of the ultra-sensitive capacitive flexible pressure sensor is improved.
2. The ultra-sensitive capacitive flexible pressure sensor of claim 1, wherein the intermediate dielectric layer is fabricated from a biomimetic template having a micro-cone structure.
3. The ultra-sensitive capacitive flexible pressure sensor according to claim 1, wherein the distance between the upper electrode layer and the lower electrode layer is 150 μm to 350 μm, the thickness of the upper electrode layer and the lower electrode layer is 100 μm to 200 μm, and the thickness of the middle dielectric layer is 150 μm to 350 μm.
4. The ultra-sensitive capacitive flexible pressure sensor of claim 1, wherein the average radius of the micro-groove structures in the middle dielectric layer is 40 μm to 80 μm, the average height of the micro-cone structures is 5 μm to 25 μm, and the line pitch of the micro-cone structures is 10 μm to 35 μm.
5. The ultra-sensitive capacitive flexible pressure sensor according to any of claims 1 to 4, wherein the flexible matrix material is PDMS, PI, PTFE, PET or ecoflex; the conductive material is a flexible conductive polymer, the viscosity of the flexible conductive polymer is between 10 Pa.s and 100 Pa.s, and the conductivity is higher than 1 x 105S/cm, and the curing temperature is between 100 and 180 ℃.
6. A preparation method of an ultra-sensitive capacitive flexible pressure sensor is characterized by comprising the following steps:
s1, preparing an upper electrode layer and a lower electrode layer;
s2, the elastic material with the surface provided with the micro-cone structure is soaked in the ionic gel solution, the heating is carried out at 26-28 ℃ to volatilize the solvent in the ionic gel solution, so that a groove is formed on the surface of the elastic material with the micro-cone structure, and the ionic gel film is peeled off to obtain the intermediate dielectric layer;
and S3, bonding the upper electrode layer, the middle dielectric layer and the lower electrode layer together to obtain the ultra-sensitive capacitive flexible pressure sensor.
7. The method for preparing the ultra-sensitive capacitive flexible pressure sensor as claimed in claim 6, wherein the step S1 comprises the following steps:
s11, spin-coating a sacrificial layer solution on a hard substrate, and forming a sacrificial layer on the hard substrate after the sacrificial layer solution is solidified;
s12, adhering a mask plate containing an electrode pattern on the surface of the sacrificial layer, coating a flexible conductive polymer on the mask plate, tearing off the mask plate, heating to cure, and thus obtaining a flexible conductive polymer with a preset pattern on the surface of the sacrificial layer;
s13, spin-coating a flexible matrix layer solution on the sacrificial layer containing the flexible conductive polymer, embedding the flexible conductive polymer on the surface of the flexible matrix layer after curing, putting the substrate into water to dissolve the sacrificial layer, and obtaining the flexible matrix layer containing the flexible conductive polymer, so as to obtain the upper electrode layer or the lower electrode layer.
8. The method according to claim 6, wherein in step S11, the hard substrate is a glass plate, an epitaxial wafer, a monocrystalline silicon plate, a polycrystalline silicon plate, a glass slide or a quartz plate; the sacrificial layer solution is a polyvinyl alcohol solution; in step S12, the mask is a PVC film, wallpaper, or scotch tape.
9. The method of claim 6, wherein in step S2, the ionic gel is polyvinylidene fluoride-hexafluoropropylene and/or 1-ethyl-3-methylimidazolium bistrifluoromethylsulfonyl imide; the elastic material is a copolyester compound, a silicon-based polymer, a silica gel compound or a rubber compound.
10. The method for preparing an ultrasensitive capacitive flexible pressure sensor according to any one of claims 6 to 9, wherein the method for preparing the elastic material having the surface with the micro-cone structure in step S2 comprises: sticking leaves with the surface of the microcone structure on a substrate, pouring an elastic material on the leaf surface, standing until the elastic material is solidified, and peeling the elastic material from the leaf surface to obtain the elastic material with the microcone structure.
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