A graphene-based highly sensitive flexible multifunctional sensor and preparation method thereof

Abstract

The present invention discloses a graphene-based highly sensitive flexible multifunctional sensor and a preparation method thereof. The sensor comprises a temperature sensor layer, a capacitive pressure sensor microstructure dielectric layer, a humidity sensor layer and a PDMS encapsulation layer. The temperature sensor layer is located at the bottom layer, the PDMS encapsulation layer is located at the top layer, and the capacitive pressure sensor microstructure dielectric layer is between the temperature sensor layer and the humidity sensor layer. The humidity sensor silver electrode, the capacitive pressure sensor microstructure dielectric layer and the temperature sensor silver electrode are aligned and superimposed in the vertical direction to form four capacitive pressure sensors with different detection ranges. The present invention has a reasonable structural layout, is safe and reliable, is highly flexible, is comfortable to wear, has high sensitivity, has low crosstalk between array units, has a simple preparation process, has low development cost, has no coupling between the measured environmental signal parameters, and does not require complex algorithms for signal decoupling.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible wearable sensors and system integration, and in particular to a highly sensitive flexible multifunctional sensor prepared from graphene-based materials and PDMS and a preparation method thereof. Background Art

[0002] Flexible wearable sensors are widely used in the fields of electronic skin, wearable medical devices, human-computer interaction and soft robots because they have good mechanical compatibility with human skin or tissue. At present, a large number of wearable flexible sensor devices based on physical signal detection have been successfully used to monitor individual health parameters such as blood pressure, body temperature, humidity and limb activity.

[0003] For example, the invention patent with publication number CN113670465A and application number 202110981870.1 discloses a graphene high-sensitivity temperature sensor. The invention patent includes an antiferromagnetic layer, a pinned layer, a barrier layer, a graphene layer and a free layer, which are prepared by traditional integrated circuit processes such as chemical vapor deposition and thermal evaporation. The invention uses the difference in magnetoresistance of the magnetic tunnel junction to determine the difference in magnetoresistance. Specifically, the part of the graphene layer extending out of the barrier layer and the free layer absorbs heat from the environment to be measured, and the temperature of the barrier layer is changed through the heat transfer of the graphene layer, thereby changing the quantum tunneling characteristics of the barrier layer, and then changing the magnetoresistance of the magnetic tunnel junction. For example, the invention patent with publication number CN112880886B and application number 202110063683.5 discloses a flexible sensor, which is composed of a flexible crown made of superelastic material, a flexible sensitive strip, a first flexible hinge, a second flexible hinge, a third flexible hinge, a metal support plate and a metal base. The flexible sensitive strip is arranged in a cavity, including a superelastic material and a resistance strain gauge embedded in the superelastic material. After pressure is applied, the resistance of the strain gauge changes, and the external pressure can be monitored according to this change. For example, the invention patent with authorization number CN110530931B and application number 201910914225.0 discloses a method for preparing a laser transfer printed graphene oxide humidity sensor, which uses laser full printing to prepare a graphene oxide film in the interdigital region of the interdigital electrode. When the humidity in the environment changes, the capacitance between the difference finger electrodes changes, and the humidity can be monitored according to this change trend. Although these flexible devices can conformally contact with irregular body surfaces and achieve normal detection and diagnosis of individual human health indexes, they all have corresponding disadvantages, such as the single monitoring function of the sensor, the use of a large number of sensitive materials resulting in high cost and complex preparation process, large test signal crosstalk, and the need for complex algorithms for decoupling. Summary of the invention

[0004] In order to solve the problems of single function, high cost and complex preparation process in the above-mentioned existing sensors, the present invention proposes a graphene-based highly sensitive flexible multifunctional sensor and a preparation method thereof.

[0005] In order to achieve the above object, the present invention provides the following scheme:

[0006] A graphene-based highly sensitive flexible multifunctional sensor comprises: a temperature sensor layer, a capacitive pressure sensor microstructure dielectric layer, a humidity sensor layer and a PDMS packaging layer; the temperature sensor layer is located at the bottom layer, the PDMS packaging layer is located at the top layer, the capacitive pressure sensor microstructure dielectric layer is between the temperature sensor layer and the humidity sensor layer, and the PDMS packaging layer is located above the humidity sensor layer.

[0007] Preferably, the temperature sensor layer is mainly composed of a temperature sensor PDMS substrate, four temperature sensor silver electrodes and three rGO temperature sensitive units; the four temperature sensor silver electrodes are made on the temperature sensor PDMS substrate by screen printing; the three rGO temperature sensitive units are made of a single type of graphene-based material, and are formed by masking with a mask plate and spraying with a spray gun to form rGO temperature sensitive units, and their positions span between any two adjacent temperature sensor silver electrodes, wherein the rGO temperature sensitive units are not sprayed between two adjacent temperature sensor silver electrodes.

[0008] Preferably, the humidity sensor layer is mainly composed of a humidity sensor PDMS substrate, four humidity sensor silver electrodes and four GO humidity sensitive units; the four humidity sensor silver electrodes are made on the humidity sensor PDMS substrate by screen printing; the four GO humidity sensitive units are made of a single type of graphene-based material and are prepared by masking with a mask plate and spraying with a spray gun, and are positioned across any two adjacent humidity sensor silver electrodes. Any adjacent humidity sensor silver electrodes and the GO humidity sensitive material can form a lateral capacitor shape to form a humidity sensor, and the GO humidity sensitive units between any two adjacent humidity sensor silver electrodes need to be masked with a mask plate and sprayed with a spray gun.

[0009] The silver electrode of the temperature sensor layer and the silver electrode of the humidity sensor layer are the same in size and shape.

[0010] Preferably, the capacitive pressure sensor microstructure dielectric layer is composed of a capacitive pressure sensor microstructure dielectric layer PDMS substrate and a PDMS conical microstructure on its surface.

[0011] Preferably, every three PDMS conical microstructures form a radial straight line; every ten radial straight lines are arranged in a circular radial pattern to surround an air gap, and there are four air gaps in total. Each air gap is located between two upper and lower temperature and humidity sensor silver electrodes of the same size, and its size is approximately equal to the size of the temperature and humidity sensor silver electrode in the vertical direction.

[0012] The silver electrode of the humidity sensor, the dielectric layer of the capacitive pressure sensor microstructure and the silver electrode of the temperature sensor are aligned and stacked in the vertical direction to form four capacitive pressure sensors with different detection ranges. The four air gaps in the dielectric layer of the capacitive pressure sensor microstructure together with the PDMS substrate above and below it serve as the dielectric of the four capacitive pressure sensors. When pressure is applied, each sensor will work in three linear regions, namely the sensitive region, the working region and the saturation region; the sensitive region is the soft state of the capacitive pressure sensor at the beginning, and once pressure is applied, it will immediately enter the ultra-sensitive rapid response stage, at which time the PDMS conical microstructure has not yet deformed; the working region is the working state when the PDMS conical microstructure begins to deform, at which time the response sensitivity of the capacitive pressure sensor decreases slightly, but the working range will be relatively wide; the saturation region is the PDMS conical microstructure has reached the limit deformation state, and at this time, if pressure is continued to be applied, only the pure PDMS substrate after removing the PDMS conical microstructure in the dielectric layer of the capacitive pressure sensor microstructure will deform as a dielectric alone, thereby causing capacitance changes.

[0013] Preferably, the PDMS encapsulation layer is mainly used to encapsulate the humidity sensor; the PDMS encapsulation layer has 4 windows thereon, and the position and size of each window are the same as those of the GO humidity sensitive unit directly below it.

[0014] A method for preparing a graphene-based highly sensitive flexible multifunctional sensor comprises the following steps:

[0015] Step 1: pre-treat the 4-inch silicon wafer and the silicon mold for preparing the dielectric layer of the microstructure of the capacitive pressure sensor. Use acetone, alcohol and deionized water solution to clean the silicon wafer and the silicon mold in a cleaning machine for 3 minutes each. Use nitrogen to blow dry the moisture on the surface of the silicon wafer and the silicon mold, then soak them in a release agent for 2-10 minutes, and finally dry them at 120 degrees Celsius for 5-10 minutes.

[0016] Step 2, prepare a PDMS mixed solution, wherein the ratio of the PDMS main agent to the curing agent is 10:1; use the PDMS mixed solution to prepare the PDMS substrate and PDMS encapsulation layer of the temperature sensor and the humidity sensor by vacuuming, spin coating and drying.

[0017] Step 3: Prepare a capacitive pressure sensor microstructure dielectric layer by using a silicon mold through injection molding and demolding.

[0018] Step 4: treating the temperature sensor PDMS substrate, humidity sensor PDMS substrate, PDMS packaging layer and capacitive pressure sensor microstructure dielectric layer described in steps 2 and 3 with oxygen plasma.

[0019] Step 5, prepare silver electrodes for temperature and humidity sensors, and the silver electrodes are prepared using a screen printing process.

[0020] Step 6, preparation of temperature and humidity sensors, using a spray gun and a mask to spray rGO temperature sensitive units between the silver electrodes of the temperature sensor in step 5, to prepare 5 temperature sensors, of which no temperature sensitive material is sprayed between two adjacent silver electrodes of the temperature sensors.

[0021] Use a spray gun and a mask to spray GO humidity sensitive units between any adjacent silver electrodes of the humidity sensor in step 5 to prepare 6 humidity sensors, and spraying is required between any two adjacent electrodes.

[0022] Step 7, preparation of the capacitive pressure sensor, vertically align and laminate the temperature sensor silver electrode, capacitive pressure sensor microstructure dielectric layer air gap, and humidity sensor silver electrode prepared in steps 3 and 5 on the experimental alignment table in turn to form four pressure sensors in the vertical direction.

[0023] Step 8, integration and packaging of multifunctional sensors. Use a scalpel to open a window in the PDMS packaging layer in step 2. The window position is opposite to the position of the GO humidity sensitive unit, and its size is equal to the GO humidity sensitive unit. Then, under the experimental alignment table, the PDMS packaging layer with the window is vertically aligned and laminated onto the surface of the humidity sensor. Finally, the temperature, humidity, pressure sensors and PDMS packaging layer are placed in a vacuum box and evacuated for 20 minutes to bond the PDMS substrates of these sensors to each other, and the peripheral edges of each layer of PDMS substrate are bonded with AB glue to complete the preparation of the multifunctional sensor.

[0024] Preferably, the step 2 comprises the following sub-steps:

[0025] Sub-step 21, after the PDMS main agent and the curing agent are prepared in a ratio of 10:1, stir them with a magnetic stirrer for 20-30 minutes;

[0026] Sub-step 22, placing the silicon wafer on a coating machine, setting the speed to 1000 rpm, taking an appropriate amount of PDMS mixed solution and placing it on the silicon wafer, and starting the coating machine to evenly spread the PDMS mixed solution on the silicon wafer;

[0027] Sub-step 23, after the silicon wafer and PDMS mixed solution are allowed to stand for a period of time, they are placed in a drying oven for baking to form a film, the baking temperature is 75° C., and the baking time is 60 min;

[0028] Sub-step 24, using plastic tweezers, tearing the PDMS substrate off the silicon wafer;

[0029] Sub-step 25, repeating the above steps to obtain the PDMS substrate and PDMS packaging layer used by all sensors.

[0030] Preferably, the step 3 comprises the following sub-steps:

[0031] Sub-step 31, placing the silicon mold of the dielectric layer of the capacitive pressure sensor microstructure on a coating machine, setting the speed to 600 rpm, taking an appropriate amount of PDMS mixed solution and placing it on the silicon mold, and starting the coating machine to evenly spread the mixed solution on the silicon mold;

[0032] Sub-step 32, the silicon mold and PDMS mixed solution are allowed to stand for a period of time to allow it to fully enter the conical groove of the mold, and then placed in a drying oven for baking to form a film, the baking temperature is 75° C., and the baking time is 60 minutes;

[0033] Sub-step 33, using plastic tweezers, gently tear off the injection-molded capacitive pressure sensor microstructure dielectric layer from the silicon mold;

[0034] Preferably, the step 5 comprises the following sub-steps:

[0035] Sub-step 51, using AutoCAD software to draw a mask pattern for preparing the silver electrodes of the temperature and humidity sensors, and preparing the mask of the temperature and humidity sensors;

[0036] Sub-step 52, fixing the mask plate to the temperature and humidity sensor PDMS substrate with tape, and then scraping the silver paste with a scraper;

[0037] Sub-step 53, after removing the mask, the PDMS substrate with the silver paste is placed on a heating table at 60° C. for drying.

[0038] Preferably, the step 6 comprises the following sub-steps:

[0039] Sub-step 61, using AutoCAD software to draw a mask template used for spraying the temperature and GO humidity sensitive units, and prepare a mask template;

[0040] Sub-step 62, fixing the mask plate to the PDMS substrate where the silver electrodes of the temperature and humidity sensors are located with adhesive tape;

[0041] Sub-step 63, placing the PDMS substrate with the silver electrode mask of the temperature sensor fixed on a prefabricated heating platform at 100° C., and spraying the rGO solution with a spray gun until an rGO temperature sensitive unit is formed, and the temperature sensor preparation is completed after removing the mask;

[0042] Sub-step 64, placing the PDMS substrate with the humidity sensor silver electrode mask fixed on a prefabricated 100° C. heating table, and spraying GO solution with a spray gun until a GO humidity sensitive unit is formed. After removing the mask, the humidity sensor preparation is completed.

[0043] Beneficial effects of the present invention: The temperature sensor, humidity sensor, capacitive pressure sensor microstructure dielectric layer and PDMS packaging layer described in the present invention all use PDMS with relatively stable physical and chemical properties, good biocompatibility and high flexibility and stretch resistance as the substrate base material. The sensitive materials are rGO and GO, which only produce obvious responses to their own sensitive signals. The entire preparation process does not use traditional complex integrated circuit processing technology, and the preparation of multifunctional sensors can be achieved by simple spraying and vertical lamination.

[0044] The present invention has a reasonable structural layout, is safe and reliable, highly flexible, comfortable to wear, has high sensor sensitivity, low crosstalk between array units, has a simple preparation process, has low development cost, has no coupling between measured environmental signal parameters, does not require complex algorithms for signal decoupling, and can achieve monitoring of three or more physical signals using only a single type of sensitive material and a simple spray coating process. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 Schematic diagram of the vertical three-dimensional structure of the flexible multifunctional sensor;

[0047] Figure 2 Schematic diagram of the cross-sectional structure of the flexible multifunctional sensor;

[0048] Figure 3 This is a front view of the actual flexible multifunctional sensor;

[0049] Figure 4 This is the working principle diagram of the flexible multifunctional sensor. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present invention are clearly and completely described below through specific embodiments in combination with the accompanying drawings.

[0051] The purpose of the present invention is to realize a graphene-based flexible multifunctional sensor which is comfortable to wear, has good stretch resistance, has a simple preparation process, has high detection sensitivity, has no crosstalk, and can simultaneously monitor multiple environmental stimulus signals.

[0052] In order to make the above-mentioned objects, features and advantages of the present invention more distinct and easy to understand, the invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0053] Figure 1 Schematic diagram of the vertical three-dimensional structure of the flexible multifunctional sensor in the embodiment provided by the present invention, which includes a temperature sensor PDMS substrate 1, a capacitive pressure sensor microstructure dielectric layer PDMS substrate 2, a humidity sensor PDMS substrate 3, a PDMS packaging layer 4, a temperature sensor silver electrode 5, an rGO temperature sensitive unit 6, a capacitive pressure sensor microstructure dielectric layer PDMS conical microstructure 7, an air gap 8 formed by an annular radial microstructure, a humidity sensor silver electrode 9, a GO humidity sensitive unit 10 and a PDMS packaging layer window 11.

[0054] like Figure 1 As shown, a graphene-based highly sensitive flexible multifunctional sensor includes: a temperature sensor layer, a capacitive pressure sensor microstructure dielectric layer, a humidity sensor layer and a PDMS packaging layer; the temperature sensor layer is located at the bottom layer, the humidity sensor layer is located at the top layer, the capacitive pressure sensor microstructure dielectric layer is between the temperature sensor layer and the humidity sensor layer, and the PDMS packaging layer is located above the humidity sensor layer.

[0055] Preferably, the temperature sensor layer is located at the lowest layer, and is composed of a temperature sensor PDMS substrate 1, four temperature sensor silver electrodes 5 and three rGO temperature sensitive units 6; the PDMS substrate is 20 μm thick, and the four temperature sensor silver electrodes are made of silver paste on the temperature sensor PDMS substrate by screen printing, and their sizes are 2×2 mm, 2×3 mm, 3×4 mm, and 2×4 mm respectively; the three rGO temperature sensitive units are made of a single type of graphene-based material, and are formed by masking and spraying with a spray gun, spanning between two adjacent temperature sensor silver electrodes, and their area sizes are different. Five temperature sensors with different detection ranges can be formed between any two temperature sensor silver electrodes. The temperature change amount presents a highly linear negative temperature coefficient relationship, so it is a resistive temperature sensor, in which in order to improve the sensitivity of the temperature sensor and make the detection range wider, multiple different detection ranges are provided and adjustable, and rGO temperature sensitive units are not sprayed between two adjacent electrodes to avoid the situation where the resistors of the rGO temperature sensitive units are connected in parallel.

[0056] Specifically, the multiple temperature sensors have a negative temperature sensitivity coefficient, and their resistance decreases linearly with increasing temperature, and they have strong sensitivity and linearity to external temperature stimulus signals.

[0057] Preferably, the humidity sensor layer is located directly above the capacitive pressure sensor microstructure dielectric layer, and is composed of a humidity sensor PDMS substrate 3, four humidity sensor silver electrodes 9 and four GO humidity sensitive units 10; the PDMS substrate is 20 μm thick, and the four humidity sensor silver electrodes are made of silver paste by screen printing technology, and their area size is the same as that of the temperature sensor silver electrode. On one hand, they serve as the vertical upper plate electrode of the capacitive pressure sensor, and on the other hand, they serve as the lateral plate electrode of the capacitive humidity sensor; the capacitance of the four GO humidity sensitive units 10 presents a piecewise linear positive coefficient relationship with the humidity change, which is formed by masking a mask template and spraying with a spray gun, and the position spans between any two adjacent humidity sensor silver electrodes, and the area sizes are different, so that 6 humidity sensors with different detection ranges can be formed. Unlike the number of rGO temperature sensitive units, the humidity sensor unit is sprayed between any two humidity sensor silver electrodes, mainly to prevent the capacitance between any two humidity sensor silver electrodes from forming a series connection, so that the humidity sensor change range is more obvious, the sensitivity is improved, and multiple different detection ranges are provided.

[0058] Specifically, the multiple humidity sensors have a segmented sensitivity response coefficient. As the humidity increases, the GO dielectric constant increases, thereby increasing the sensor capacitance, showing a strong sensitivity to external humidity stimulus signals, and the sensitivity and detection range are adjustable.

[0059] The silver electrodes of the temperature sensor layer and the silver electrodes of the humidity sensor layer are the same in size and shape;

[0060] Preferably, the preparation material of the capacitive pressure sensor microstructure dielectric layer is PDMS, and the surface of the capacitive pressure sensor microstructure dielectric layer PDMS substrate 2 has a large number of PDMS conical microstructures 7, and the bottom diameter and vertical height of the PDMS conical microstructure are 80μm and 50μm respectively. Every three PDMS conical microstructures form a radial straight line; every ten radial straight lines are arranged in a circular radial shape to surround an air gap 8, and there are 4 air gaps 8, and their positions and sizes are the same as the temperature sensor silver electrode 5 and the humidity sensor silver electrode 9 in the vertical direction above and below. Similarly, the positions and sizes of the other air gaps are also the same as the temperature sensor electrode and the humidity sensor electrode in the vertical direction above and below. A radiation channel will be formed between any two radiation lines, and the radiation channel can effectively unload the excess force applied to the capacitive sensor, which is beneficial to reduce the crosstalk between adjacent array units and improve the service life of the sensor.

[0061] Specifically, the air gap 8 together with the PDMS substrate thereunder serves as the dielectric of the vertical capacitive pressure sensor, and together with the silver electrodes of the temperature and humidity sensors in the vertical directions above and below it, constitute a capacitive pressure sensor with different detection ranges. Similarly, other air gaps respectively form three capacitive pressure sensors with different detection ranges with the corresponding electrodes in the vertical directions above and below them. When pressure is applied, each sensor will work in three linear regions, namely the sensitive region, the working region and the saturation region; the sensitive region is when the sensor is initially in a soft state, and once pressure is applied, it will immediately enter the ultra-sensitive rapid response stage, at which time the PDMS conical microstructure has not yet deformed; the working region is the working state when the PDMS conical microstructure begins to deform, at which time the sensor sensitivity decreases slightly, but the working range is relatively wide; the saturation region is when the PDMS conical microstructure has reached the limit deformation state, and at this time, if pressure continues to be applied, only the pure PDMS substrate after removing the conical PDMS microstructure in the dielectric layer of the capacitive pressure sensor microstructure will deform as a dielectric alone, causing a change in capacitance, and the sensitivity is relatively small. Considering the limited pressure resistance of PDMS, further application of pressure may permanently damage the microstructure on the dielectric layer.

[0062] Specifically, the capacitive pressure sensor has a very high sensitivity. Unlike previous studies, when pressure is applied to it, the excess force will be unloaded due to the presence of the conical microstructure and the annular radial grooves, and there is almost no crosstalk between multiple pressure units.

[0063] Preferably, the PDMS encapsulation layer 4 has a thickness of 20 μm and has four windows 11 thereon. The four windows are located vertically opposite to the GO humidity sensitive unit and have the same size as the GO humidity sensitive unit.

[0064] Specifically, the PDMS encapsulation layer is mainly used to encapsulate the humidity sensor, which can effectively protect the humidity sensor electrode, prevent external signals from interfering with the humidity sensor electrode signal, and avoid damaging the humidity sensor sensitive material during pressure monitoring; the position and size of each window 11 are the same as the GO humidity sensitive unit directly below it, in order to ensure that the GO humidity sensitive unit can effectively and fully contact the air humidity, the humidity sensitive material is fully exposed to the surrounding environment of the user object, so as to better respond to the humidity parameters.

[0065] Preferably, the temperature sensor layer, the capacitive pressure sensor microstructure dielectric layer, the humidity sensor layer and the PDMS packaging layer are bonded by vacuuming and using a vertical lamination process, and then bonded with flexible AB glue.

[0066] Figure 2 is a cross-sectional view of a flexible multifunctional sensor according to an embodiment of the present invention, and the numbers in the figure correspond to Figure 1 The numbering in the three-dimensional view shows that in addition to the lateral temperature and humidity sensors, the silver electrodes of the temperature and humidity sensors and the capacitive pressure sensor microstructure dielectric layer can be used in the vertical direction to form pressure sensors with multiple monitoring ranges. The advantage of the capacitive pressure sensor is that the air gap formed by the annular radial microstructure and its upper and lower PDMS substrates are used as dielectrics, rather than directly using the capacitive pressure sensor microstructure as a dielectric. When monitoring pressure, the minimum monitoring force is small and the response is very sensitive. In addition, due to the existence of the microstructure radiation channel, the excess force can be unloaded to avoid mutual crosstalk between pressure sensing units.

[0067] Figure 3 This is a physical picture of the flexible multifunctional sensor in the embodiment provided by the present invention. The multifunctional sensor has a small size, all substrate materials are PDMS, it is comfortable to wear, and has good mechanical compatibility with the human body. The sensitive materials are all made of a single type of graphene-based material. The preparation process is simple, and the mutual interference between signals in a multi-physical field environment is relatively low, and decoupling can be achieved without complex algorithms.

[0068] Figure 4It is a working principle diagram of the flexible multifunctional sensor in the embodiment provided by the present invention. The black single solid line represents the top layer, the gray single dotted line represents the bottom layer, the four capacitors connected to the top layer represent the humidity sensor between adjacent electrodes that changes with humidity, and any combination of the four capacitors can also constitute other capacitors of different sizes. The three resistors connected to the bottom layer represent the temperature sensor between adjacent electrodes that changes with temperature, and any combination of the three resistors can also constitute other resistors of different sizes. The capacitor between the top layer and the bottom layer represents four capacitive pressure sensors in the vertical direction.

[0069] Specifically, the temperature sensor is prepared using rGO sensitive material. When the temperature changes, the conductivity of rGO will show a rapid linear growth trend as the temperature rises. The temperature of the object can be obtained based on this change law.

[0070] Specifically, the humidity sensor is prepared using GO sensitive material. When the humidity changes, GO can adsorb water molecules in the air due to the presence of oxygen-containing functional groups on its surface, especially hydroxyl groups, thereby causing the dielectric constant of the capacitor to change regularly. The humidity of the object can be obtained based on this change pattern.

[0071] A method for preparing a graphene-based high-sensitivity, low-crosstalk flexible multifunctional sensor comprises the following steps:

[0072] Step 1, pre-treat the 4-inch silicon wafer and the silicon mold for preparing the microstructure dielectric layer, use acetone, alcohol and deionized water solution to clean the silicon wafer in a cleaning machine for 3 minutes each, blow dry the moisture on the surface of the silicon wafer with nitrogen, soak it in a release agent for 2-10 minutes, and finally dry it at 120 degrees Celsius for 5-10 minutes to complete the cleaning of the silicon wafer;

[0073] Step 2, preparing a PDMS mixed solution, wherein the ratio of PDMS to curing agent is 10:1; using the PDMS mixed solution, preparing a PDMS substrate and a PDMS encapsulation layer of the temperature sensor and the humidity sensor by vacuuming, spin coating, and drying;

[0074] Step 3, preparing a capacitive pressure sensor microstructure dielectric layer, using a silicon mold to prepare a PDMS microstructure dielectric layer by injection molding and demolding;

[0075] Step 4, treating the temperature sensor PDMS substrate, humidity sensor PDMS substrate, PDMS encapsulation layer and capacitive pressure sensor microstructure dielectric layer described in Step 2 and Step 3 with oxygen plasma to enhance the adsorption of the substrate surface;

[0076] Step 5, preparing silver electrodes for temperature and humidity sensors, wherein the silver electrodes are prepared using a screen printing process;

[0077] Step 6, preparation of temperature and humidity sensors, using a spray gun and a mask to spray rGO temperature sensitive units between the silver electrodes of the temperature sensor in step 5, to prepare 5 temperature sensors. In order to provide temperature sensors with multiple monitoring ranges and improve sensitivity, no spraying is performed between two adjacent electrodes;

[0078] Use a spray gun and a mask to spray GO humidity sensitive units between any silver electrodes of the humidity sensor in step 5 to prepare a humidity sensor. In order to provide humidity sensors with multiple monitoring ranges and improve sensitivity, spraying is required between any adjacent silver electrodes of the humidity sensor. This is because the principle of the temperature sensor is resistive, while the principle of the humidity sensor is capacitive;

[0079] Because the principle of temperature sensor is resistance type, and the principle of capacitance sensor is capacitance type, according to the resistance parallel connection formula and capacitance series connection formula, the purpose of not spraying one unit of temperature sensor is mainly to prevent all temperature sensors between any two electrodes of temperature sensor from forming a loop and causing parallel connection, so as to prevent the resistance change caused by temperature change from being obvious. Similarly, the purpose of spraying all humidity sensors is to avoid the series connection between capacitance sensors, so as to prevent the capacitance change from being obvious when humidity changes.

[0080] Step 7, preparation of the capacitive pressure sensor, vertically aligning and laminating the temperature sensor silver electrode, the capacitive pressure sensor microstructure dielectric layer air gap, and the humidity sensor silver electrode prepared in steps 3 and 5 on the experimental alignment table in turn, to form four pressure sensors in the vertical direction;

[0081] Step 8, integration and packaging of multifunctional sensors. Use a scalpel to open a window in the PDMS packaging layer in step 2. The window position is opposite to the position of the GO humidity sensitive unit, and the size is equal. It is vertically aligned and laminated to the humidity sensor under the experimental alignment table. Finally, the temperature, humidity, pressure sensor and PDMS packaging layer are placed in a vacuum box and evacuated for 20 minutes to bond the PDMS to each other, and the peripheral edges of each layer of PDMS substrate are bonded with AB glue to complete the preparation of the multifunctional sensor.

[0082] Preferably, the step 2 comprises the following sub-steps:

[0083] Sub-step 21, after the PDMS solution and the curing agent are prepared in a ratio of 10:1, they are stirred for 20-30 minutes by a magnetic stirrer to fully mix them;

[0084] Sub-step 22, placing the silicon wafer on a coating machine, setting the speed to 1000 rpm, taking an appropriate amount of PDMS mixed solution and placing it on the silicon wafer, and starting the coating machine to evenly spread the PDMS mixed solution on the silicon wafer;

[0085] Sub-step 23, after the silicon wafer and PDMS mixed solution are allowed to stand for a period of time, they are placed in a drying oven for baking to form a film, the baking temperature is 75° C., and the baking time is 60 min;

[0086] Sub-step 24, using plastic tweezers, gently tear off the PDMS substrate from the silicon wafer;

[0087] Sub-step 25, repeating the above steps to obtain the substrate and packaging layer used by all sensors.

[0088] Preferably, the step 3 comprises the following sub-steps:

[0089] Sub-step 31, placing the silicon mold of the dielectric layer of the capacitive pressure sensor microstructure on a coating machine, setting the speed to 600 rpm, taking the PDMS mixed solution and placing it on the silicon mold, and starting the coating machine to evenly spread the mixed solution on the silicon mold;

[0090] Sub-step 32, the silicon wafer and PDMS mixed solution are allowed to stand for a period of time to allow it to fully enter the conical groove of the mold, and then placed in a drying oven for baking to form a film, the baking temperature is 75°C, and the baking time is 60 minutes;

[0091] Sub-step 33, using plastic tweezers, gently tear off the PDMS substrate from the silicon wafer to obtain a microstructured dielectric layer of the capacitive pressure sensor;

[0092] Preferably, the step 5 comprises the following sub-steps:

[0093] Sub-step 51, using AutoCAD software to draw a mask pattern for preparing the silver electrodes of the temperature and humidity sensors, and preparing the mask of the temperature and humidity sensors;

[0094] Sub-step 52, using tape to fix the temperature sensor mask plate and the humidity sensor mask plate to the temperature sensor PDMS substrate and the humidity sensor PDMS substrate respectively, and then using a scraper to scrape the silver paste;

[0095] Sub-step 53, after removing the mask, all PDMS substrates with silver paste are placed on a heating table at 60°C for drying.

[0096] Preferably, the step 6 comprises the following sub-steps:

[0097] Sub-step 61, using AutoCAD software to draw the mask template layout used for spraying the rGO temperature sensitive unit and the GO humidity sensitive unit of the temperature sensor and the humidity sensor, respectively, to prepare the mask template;

[0098] Sub-step 62, using tape to fix the mask plate to the humidity sensor PDMS substrate where the humidity sensor silver electrode is located, and then using a scraper to gently scrape the silver paste;

[0099] Sub-step 63, placing the temperature sensor PDMS substrate with the temperature sensor silver electrode mask fixed on a prefabricated 100° C. heating table, and spraying rGO solution with a spray gun until an rGO temperature sensitive unit is formed, and the temperature sensor preparation is completed after removing the mask;

[0100] Sub-step 64, placing the PDMS substrate with the humidity sensor silver electrode mask fixed on a prefabricated 100° C. heating table, and spraying GO solution with a spray gun until a GO humidity sensitive unit is formed. After removing the mask, the humidity sensor preparation is completed.

[0101] The present invention uses PDMS, which has relatively stable physical and chemical properties, good biocompatibility, and high flexibility and stretch resistance, as a substrate base material. The sensitive material is graphene and its derivatives, which only produce obvious responses to their own sensitive signals. The preparation process only requires simple spraying and vertical lamination to realize the preparation of multifunctional sensors.

Claims

1. A graphene-based highly sensitive flexible multifunctional sensor, characterized in that include: temperature sensor layer, capacitive pressure sensor microstructure dielectric layer, humidity sensor layer and PDMS encapsulation layer; The temperature sensor layer is located at the bottom layer, the PDMS encapsulation layer is located at the top layer, the capacitive pressure sensor microstructure dielectric layer is between the temperature sensor layer and the humidity sensor layer, and the PDMS encapsulation layer is located above the humidity sensor layer; The temperature sensor layer is composed of a temperature sensor PDMS substrate, four temperature sensor silver electrodes and three rGO temperature sensitive units. The four temperature sensor silver electrodes are made on the temperature sensor PDMS substrate by screen printing; the three rGO temperature sensitive units are made of a single type of graphene-based material, and are formed by masking with a mask plate and spraying with a spray gun to form rGO temperature sensitive units, which are located across any two adjacent temperature sensor silver electrodes, and there are two adjacent temperature sensor adjacent silver electrodes without spraying rGO temperature sensitive units; The humidity sensor layer is composed of a humidity sensor PDMS substrate, four humidity sensor silver electrodes and four GO humidity sensitive units; The four humidity sensor silver electrodes are made on the PDMS substrate by screen printing; The four GO humidity sensitive units are made of a single type of graphene-based material and are prepared by masking with a mask plate and spraying with a spray gun. The positions are across any two adjacent silver electrodes of the humidity sensor. The GO humidity sensitive units between any two adjacent silver electrodes of the humidity sensor need to be masked with a mask plate and sprayed with a spray gun. The silver electrode of the temperature sensor is the same in size and shape as the silver electrode of the humidity sensor; The capacitive pressure sensor is formed by vertically aligning and stacking a temperature sensor silver electrode, a capacitive pressure sensor microstructure dielectric layer, and a humidity sensor silver electrode; The capacitive pressure sensor microstructure dielectric layer is composed of a capacitive pressure sensor microstructure dielectric layer PDMS substrate and a PDMS conical microstructure on its surface; Every three of the PDMS conical microstructures form a radial straight line; Every ten of the radiation lines are arranged in a circular radial shape to form an air gap. There are four air gaps in total. Each air gap is located between two silver electrodes of the temperature sensor and the humidity sensor of the same size above and below it, and its size is equal to the size of the silver electrode in the vertical direction; The four air gaps in the capacitive pressure sensor microstructure dielectric layer together with the PDMS substrates above and below the air gaps serve as dielectrics for the four capacitive pressure sensors; The PDMS encapsulation layer is mainly used to encapsulate the humidity sensor; The PDMS packaging layer has four windows, and the position and size of each window are the same as the GO humidity sensitive unit directly below it.

2. A graphene-based highly sensitive flexible multifunctional sensor according to claim 1, characterized in that: A radiation channel is formed between any two of the radiation lines; the channel is used to effectively unload the excess force applied to the capacitive pressure sensor.

3. The graphene-based highly sensitive flexible multifunctional sensor according to claim 1, characterized in that: When pressure is applied to the capacitive pressure sensor, each capacitive pressure sensor operates in one of three linear regions, wherein the three linear regions are respectively a sensitive region, a working region, and a saturation region; The sensitive area is a capacitive pressure sensor that is in a soft state at the beginning and immediately enters an ultra-sensitive rapid response stage when pressure is applied, at which time the PDMS conical microstructure has not yet deformed; When the PDMS conical microstructure begins to deform, entering the working area; When the PDMS conical microstructure has reached the limit deformation state and entered the saturation zone, if pressure continues to be applied, only the pure PDMS substrate after removing the PDMS conical microstructure in the dielectric layer of the capacitive pressure sensor microstructure will deform as a dielectric, thereby causing a change in capacitance.

4. A method for preparing a graphene-based highly sensitive flexible multifunctional sensor, characterized in that The following steps are involved: Step 1, pre-treat the four-inch silicon wafer and the silicon mold for preparing the dielectric layer of the microstructure of the capacitive pressure sensor: use acetone, alcohol and deionized water solution to clean the silicon wafer and the silicon mold in a cleaning machine in turn, blow dry the moisture on the surface of the silicon wafer and the silicon mold with nitrogen, soak them in a release agent for 2-10 minutes, and dry them at 120 degrees Celsius for 5-10 minutes; Step 2, prepare a PDMS mixed solution, wherein the ratio of PDMS main agent to curing agent is 10:1; Using the PDMS mixed solution, the PDMS substrate and PDMS encapsulation layer of the temperature sensor and humidity sensor are prepared by vacuuming, spin coating and drying. Step 3, using the silicon mold in step 1 to prepare a capacitive pressure sensor microstructure dielectric layer by injection molding and demolding technology; Step 4, performing oxygen plasma treatment on the temperature sensor PDMS substrate, humidity sensor PDMS substrate, PDMS encapsulation layer and capacitive pressure sensor microstructure dielectric layer described in step 2 and step 3; Step 5, preparing the temperature sensor silver electrode and the humidity sensor silver electrode by screen printing process; Step 6, using a spray gun and a mask to spray rGO temperature sensitive units between two silver electrodes of the temperature sensor in step 5, to prepare five temperature sensors, wherein no rGO sensitive material is sprayed between two adjacent electrodes; Use a spray gun and a mask to spray GO humidity sensitive units between the silver electrodes of the humidity sensor in step 5 to prepare six humidity sensors, and spraying is required between any two adjacent electrodes; Step 7, preparation of the capacitive pressure sensor, vertically aligning the temperature sensor silver electrode, the capacitive pressure sensor microstructure dielectric layer air gap, and the humidity sensor silver electrode prepared in steps 3 and 5 on the experimental alignment table, and performing a lamination operation to form four pressure sensors in a vertical direction; Step 8, integration and packaging of the multifunctional sensor, using a scalpel to open a window in the PDMS packaging layer in step 2, the window position is directly opposite to the position of the GO humidity sensitive unit, and its size is equal to the GO humidity sensitive unit, and then the PDMS packaging layer with the window is vertically aligned under the experimental alignment stage and laminated onto the surface of the humidity sensor; Finally, the temperature sensor, humidity sensor, pressure sensor and PDMS packaging layer are placed in a vacuum box to evacuate the vacuum, and the peripheral edges of each layer of PDMS substrate are bonded with AB glue.

5. The method for preparing a graphene-based highly sensitive flexible multifunctional sensor according to claim 4, characterized in that: The step 2 comprises the following sub-steps: Sub-step 21, after the PDMS main agent and the curing agent are prepared in a ratio of 10:1, stir them with a magnetic stirrer for 20-30 minutes; Sub-step 22, placing the silicon wafer on a coating machine, setting the speed to 1000 rpm, taking the PDMS mixed solution and placing it on the silicon wafer, and starting the coating machine to evenly spread the PDMS mixed solution on the silicon wafer; Sub-step 23, after the silicon wafer and PDMS mixed solution are allowed to stand, they are placed in a drying oven for baking to form a film, the baking temperature is 75° C., and the baking time is 60 min; Sub-step 24, using plastic tweezers, tearing the PDMS substrate off the silicon wafer; Sub-step 25, repeating the above steps to obtain the PDMS substrate and PDMS packaging layer used for the temperature sensor and the humidity sensor.

6. The method for preparing a graphene-based highly sensitive flexible multifunctional sensor according to claim 4, characterized in that: The step 3 comprises the following sub-steps: Sub-step 31, placing the silicon mold of the dielectric layer of the capacitive pressure sensor microstructure on a coating machine, setting the speed to 600 rpm, taking the PDMS mixed solution and placing it on the silicon mold, and starting the coating machine to evenly spread the mixed solution on the silicon mold; Sub-step 32, after the silicon mold and the PDMS mixed solution are allowed to stand, the mixed solution is fully absorbed into the conical groove of the mold, and then placed in a drying oven for baking to form a film, the baking temperature is 75° C., and the baking time is 60 min; Sub-step 33, using plastic tweezers, tear off the injection-molded capacitive pressure sensor microstructure dielectric layer from the silicon mold.

7. The method for preparing a graphene-based highly sensitive flexible multifunctional sensor according to claim 4, characterized in that: The step 5 comprises the following sub-steps: Sub-step 51, using AutoCAD software to draw a mask pattern for preparing the temperature sensor silver electrode and the humidity sensor silver electrode, and preparing the temperature sensor mask and the humidity sensor mask; Sub-step 52, using tape to fix the temperature sensor mask plate and the humidity sensor mask plate to the temperature sensor PDMS substrate and the humidity sensor PDMS substrate respectively, and then using a scraper to scrape the silver paste; Sub-step 53, after removing the mask, all PDMS substrates with silver paste are placed on a heating table at 60° C. for drying.

8. The method for preparing a graphene-based highly sensitive flexible multifunctional sensor according to claim 4, characterized in that: The step 6 comprises the following sub-steps: Sub-step 61, using AutoCAD software to draw the mask template layout used for spraying the rGO temperature sensitive unit and the GO humidity sensitive unit of the temperature sensor and the humidity sensor, respectively, to prepare the mask template; Sub-step 62, using adhesive tape to fix the mask plate to the PDMS substrate of the temperature and humidity sensor where the silver electrodes of the temperature and humidity sensor are located; Sub-step 63, placing the temperature sensor PDMS substrate fixed with the temperature sensor silver electrode mask on a preheated platform at 100° C., spraying rGO solution with a spray gun until an rGO temperature sensitive unit is formed, and removing the mask; Sub-step 64, placing the PDMS substrate with the humidity sensor silver electrode mask fixed on a prefabricated 100° C. heating table, and spraying GO solution with a spray gun until a GO humidity sensitive unit is formed, and removing the mask.

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