Preparation process of array type flexible capacitive pressure sensor

Abstract

The invention relates to the technical field of flexible electronics, in particular to a method for preparing a dielectric layer of a capacitive sensor, which comprises the following main steps of: preparing an ITO / PET (indium tin oxide / polyethylene terephthalate) electrode; spontaneously forming a flexible dielectric layer; a flexible dielectric layer dispersion process; and packaging the device. The array type flexible pressure sensor prepared by the invention has the advantages of high-sensitivity feedback, stable work, good signal transmission, good flexibility and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and specifically designs a preparation process of an array-type flexible capacitive pressure sensor. Background Art

[0002] In today's era of rapid technological advancement, sensor technology, as a key means of acquiring information, plays a vital role in numerous fields. With the booming development of emerging fields such as smart wearable devices, health monitoring systems, intelligent robotics, and the Internet of Things, the demand for flexible sensors is becoming increasingly urgent. Due to their unique flexibility, bendability, and excellent conformability, flexible sensors can adapt to various complex surfaces, enabling more accurate, convenient, and comfortable human-computer interaction and environmental perception.

[0003] Among the many types of flexible sensors, capacitive pressure sensors have attracted widespread attention due to their high sensitivity, fast response, low power consumption, and good linearity. Traditional capacitive pressure sensors typically use rigid substrates, which limits their use in flexible applications. Flexible capacitive pressure sensors, however, overcome this limitation. By using flexible substrate materials such as polydimethylsiloxane (PDMS) and polyethylene terephthalate (PET), they enable the sensor to operate normally in complex mechanical environments such as bending and stretching, greatly expanding its application range.

[0004] However, the preparation of flexible capacitive pressure sensors still faces many challenges. On the one hand, how to achieve high-precision and high-stability electrode patterning on a flexible substrate is a key issue. Although traditional micro-nano processing technologies such as photolithography and etching can achieve high-precision patterning, these technologies usually require complex equipment and process flows, are costly, and are difficult to be compatible with flexible substrate materials. On the other hand, the balance between the sensitivity and range of the sensor is also an urgent problem to be solved. In order to improve the sensitivity of the sensor, it is usually necessary to reduce the electrode spacing, but this may result in a smaller range of the sensor, limiting its scope of use in practical applications. In addition, how to improve the durability and reliability of the sensor so that it can maintain stable performance during long-term use is also one of the current research focuses.

[0005] To address these challenges, the present invention proposes a process for fabricating an array of flexible capacitive pressure sensors. Through innovative process design and material selection, the present invention aims to efficiently fabricate flexible capacitive pressure sensors with high precision, high sensitivity, and high stability, providing an effective solution to meet the growing market demand for flexible sensors. Summary of the Invention

[0006] This invention addresses the shortcomings of existing flexible capacitive pressure sensors, such as complex manufacturing processes, imbalanced sensitivity and range, and high costs. Based on the nanomaterial MWCNT and a microstructured flexible substrate, this new sensor is simplified through material self-assembly, template formation, and magnetron sputtering. This approach maintains sensor performance while simplifying the manufacturing process.

[0007] The technical solution adopted by the present invention is a preparation process of an array-type flexible capacitive pressure sensor, comprising the following steps:

[0008] Step 1: Prepare MWCNT dispersion using isopropyl alcohol by ultrasonic dispersion method, and prepare PDMS / MWCNT mixed slurry by magnetic stirring;

[0009] Step 2: preparing a flexible substrate using a template method;

[0010] Step 3: Control the dielectric layer thickness through custom molds;

[0011] Step 4: Control the spontaneously formed microstructure on the surface by controlling the weight ratio of MWCNTs;

[0012] Step 5: solidify the mixed slurry in a vacuum drying oven;

[0013] Step 6: ITO film is deposited on the PET substrate by magnetron sputtering;

[0014] Step 7: For the ITO-PET electrode obtained in the above step, vertically plane-laminate in the order of encapsulation layer-ITO / PET conductive film-PDMS / MWCNT dielectric layer-ITO / PET conductive film-encapsulation layer, and lead out the wires.

[0015] Furthermore, the preparation method of the MWCNT / PDMS mixed slurry is specifically as follows:

[0016] 1) Mix the PDMS prepolymer and curing agent in a mass ratio of 10:1, stir continuously for 10 minutes to ensure uniform mixing, and then remove bubbles in the PDMS using a vacuum of less than 10 Pa;

[0017] 2) Using ultrasonic dispersion, mix isopropyl alcohol with MWCNTs and disperse the MWCNT powder in the isopropyl alcohol solution by ultrasonication for half an hour. The application of ultrasound helps to disperse the MWCNT powder into a liquid state, improving its subsequent dispersibility in PDMS.

[0018] 3) Next, the ultrasonically treated mixed solution was poured into the PDMS colloid and magnetically stirred for half an hour to mix the three solutions evenly to obtain a PDMS / MWCNT / isopropanol slurry. The slurry was then allowed to stand for half an hour to allow the isopropanol to evaporate.

[0019] Furthermore, the preparation method of the curing mold and the packaging mold is specifically as follows:

[0020] 1) Use a high-precision milling cutter for milling, set the milling cutter parameters according to the design requirements, and after milling, clean the substrate with deionized water and check whether the size and shape meet the requirements.

[0021] 2) Preheat the milled glass substrate to about 30°C above the transition point temperature, use a flame gun to polish it at about 150°C above the softening point, polish the edges and corners evenly, and then anneal it to slowly drop the temperature below 100°C. Finally, cool it naturally to room temperature and perform quality inspection to ensure that there are no defects and the thickness difference meets the requirements.

[0022] 3) Using 3D printing, the material is Future R4600 resin, and the pre-designed structure is printed.

[0023] Furthermore, the method for preparing the ITO / PET thin film flexible electrode prepared by magnetron sputtering is specifically as follows:

[0024] 1) The PET film was ultrasonically cleaned with deionized water, ethanol and acetone in sequence to remove surface impurities, and then dried for later use.

[0025] 2) Place the PET film in a vacuum sputtering device and evacuate to 10 -4 -10 -6 Pa, fill with argon, set sputtering parameters (power 100-300W, gas pressure 0.01-1Pa), ITO target atoms are sputtered and deposited on the surface of the PET film to form an ITO film.

[0026] 3) Allow the PET film to cool naturally to room temperature, take it out and conduct performance testing and subsequent applications.

[0027] Furthermore, the MWCNT / PDMS mixed solution is cured in a vacuum drying oven, and the encapsulation preparation method is specifically as follows:

[0028] 1) Evacuate the vacuum drying oven and heat it to 40°C to allow the isopropyl alcohol to evaporate better. Keep it at this temperature for half an hour.

[0029] 2) Heat the vacuum drying oven to 80°C and keep it for 4 hours.

[0030] 3) Prepare the prepared dielectric layer and ITO / PET film into 1*1cm 2 , placed in a prepared packaging container, surrounded by a layer of sponge wrapped around the prepared sensor, using a high conductivity cable to connect to the electrode through conductive silver paste, lead out the cable to connect to the external circuit,

[0031] 4) Use jelly glue to encapsulate the entire structure, and adhere the layers vertically in the order of encapsulation layer-ITO / PET conductive film-PDMS / MWCNT dielectric layer-ITO / PET conductive film-encapsulation layer.

[0032] Furthermore, the encapsulation layer is RTVS6100 highly transparent potting glue.

[0033] The purpose of the present invention is to solve the shortcomings of existing flexible capacitive pressure sensors, such as complex preparation process, unbalanced sensitivity and range, and high cost, and to provide a preparation process of a flexible capacitive pressure sensor.

[0034] Compared with existing achievements, the beneficial effects of the present invention are:

[0035] 1) Through structural innovation, the present invention has a simple sensing structure, high stability and reliability, and uses a variety of excellent performance materials such as MWCNT and PDMS to achieve improved mechanical strength and sensing performance of flexible tactile electronic skin;

[0036] 2) At the same time, the randomly distributed sensing structure of the flexible capacitive pressure sensor of the present invention can also maintain the sensitive tactile sensing capability of the flexible tactile electronic skin;

[0037] 3) The use of material self-assembly method, template method, magnetron sputtering method and other processes has achieved the optimization of the preparation process and improved the performance of the sensor. It has low processing technology requirements and low cost, and is suitable for large-scale manufacturing;

[0038] 4) The structure is designed in a vertical stacking style to achieve the purpose of lightweight and miniaturization.

[0039] Other advantages, objectives and features of the present invention will be reflected in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 : A schematic diagram of the overall structure of the array flexible capacitive pressure sensor of the present invention;

[0041] Figure 2 Schematic diagram of the process of preparation to packaging of the present invention;

[0042] Figure 3 : A schematic diagram of the response / recovery time of the flexible capacitive pressure sensor prepared by the present invention;

[0043] Figure 4 Schematic diagram of sensitivity and linear range of the flexible capacitive pressure sensor prepared by the present invention; DETAILED DESCRIPTION

[0044] The present invention is further explained below with reference to the accompanying drawings and embodiments to facilitate understanding by those skilled in the art.

[0045] like Figure 1 As shown in the figure, the array-type flexible capacitive pressure sensor of the present invention is composed of a five-layer vertical packaging structure, which is, from top to bottom, a packaging layer, an ITO / PET film, a PDMS / MWCNT dielectric layer, an ITO / PET film, and a packaging layer.

[0046] After packaging the array of flexible capacitive pressure sensors, the micro-spine-like protrusions on the dielectric substrate contact the ITO / PET film, forming a conductive path and generating a primary signal response. When pressure is applied to the structure, the stress on the flexible substrate further causes the ITO / PET film to contact the microstructure of the PDMS / MWCNT dielectric layer. This further increases the contact area and capacitance due to the capacitive effect. Simultaneously, the partially stacked PDMS / MWCNT dielectric layers further contact each other, resulting in a highly sensitive response under pressure. After the load is removed, the deformed structure, supported by the PDMS substrate, quickly recovers, improving the overall signal response and force stability of the flexible tactile electronic skin system.

[0047] The following describes the preparation process of the array type flexible capacitive pressure sensor of the present invention. Figure 2 , including the following steps:

[0048] In step 1, the PDMS prepolymer and curing agent are mixed in a mass ratio of 10:1, and stirring is continued for 10 minutes to ensure uniform mixing. Then, a vacuum below 10 Pa is used to remove bubbles in the PDMS. An ultrasonic dispersion method is used to prepare a MWCNT dispersion using isopropyl alcohol. Next, the ultrasonically treated mixed solution is poured into the PDMS colloid and magnetically stirred for half an hour to mix the three solutions evenly to obtain a PDMS / MWCNT / isopropyl alcohol slurry, which is then left to stand for half an hour to allow the isopropyl alcohol to evaporate.

[0049] In step two, the mixed slurry is evenly applied to a custom curing template to form a 20 x 20 x 0.6 mm dielectric layer. Due to the evaporation of the isopropyl alcohol and the subsequent curing and drying, the final dielectric layer without wrinkles is only 0.3 mm thick. The vacuum drying oven is evacuated and heated to 40°C for half an hour to allow for better evaporation of the isopropyl alcohol and prevent bubbles from forming in the mixed solution. The vacuum drying oven is then heated to 80°C and held for four hours. The surface of the prepared dielectric layer exhibits a spontaneously wrinkled microstructure.

[0050] Step 3: Use ultrasonic cleaning to immerse the PET film in deionized water, ethanol and acetone solutions in turn for cleaning, and then blow it dry with nitrogen. The cleaned PET film needs to be preheated, usually between 100-300°C, to remove volatile substances such as water adsorbed on the surface, and at the same time adjust the substrate temperature to a range suitable for film growth. Place the cleaned and preheated PET film in the vacuum sputtering equipment, start the vacuum pump, and reduce the air pressure in the vacuum chamber to 10 -4 -10 - 6 The ion source is then activated, using high-purity argon as the working gas. The sputtering parameters, such as sputtering power, pressure, and sputtering time, are adjusted. Typically, the sputtering power is set between 100-300W, the pressure is controlled between 0.01-1Pa, and the sputtering time is determined by the desired film thickness. During the sputtering process, the ITO target is bombarded by argon ions, and the target atoms are sputtered and deposited on the surface of the PET film, forming an ITO film.

[0051] Step 3: Prepare the prepared dielectric layer and ITO / PET film into 1*1cm 2 , placed in a prepared packaging container, and a layer of sponge is placed around the prepared sensor to offset the pressure of the potting glue and prevent the potting glue from entering between the electrode layer and the dielectric layer and affecting the sensor performance; use high conductivity cables to connect to the electrodes through conductive silver paste, lead out cables to connect to the external circuit, and use jelly glue to encapsulate the whole, in the order of encapsulation layer-ITO / PET conductive film-PDMS / MWCNT dielectric layer-ITO / PET conductive film-encapsulation layer, and fit vertically on the plane.

[0052] Furthermore, the thickness of the dielectric layer is 0.3 mm.

[0053] Furthermore, the performance of the array-type flexible capacitive pressure sensor was tested, such as Figure 3 As shown, it can clearly detect and record response and recovery times.

[0054] Furthermore, the performance of the array-type flexible capacitive pressure sensor was tested, such as Figure 4 As shown, it can be clearly seen that within the pressure range, the sensitivity and linearity are close to linear.

[0055] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. The technical solution adopted by the present invention is a preparation process of an array-type flexible capacitive pressure sensor, characterized in that: The following steps are involved: Step 1: Prepare MWCNT dispersion using isopropyl alcohol by ultrasonic dispersion method, and prepare PDMS-MWCNT mixed slurry by magnetic stirring; Step 2: preparing a flexible substrate using a template method; Step 3: Control the dielectric layer thickness through custom molds; Step 4: Control the spontaneously formed microstructure on the surface by controlling the weight ratio of MWCNTs; Step 5: solidify the mixed slurry in a vacuum drying oven; Step 6: ITO film is deposited on the PET substrate by magnetron sputtering; Step 7: For the ITO-PET electrode obtained in the above step, vertically plane-laminate in the order of encapsulation layer-ITO / PET conductive film-PDMS / MWCNT dielectric layer-ITO / PET conductive film-encapsulation layer, and lead out the wires.

2. The preparation process of an array-type flexible capacitive pressure sensor according to claim 1, characterized in that: The preparation method of the PDMS / MWCNT mixed slurry is specifically as follows: using an ultrasonic dispersion method to mix isopropyl alcohol and MWCNT, so that the MWCNT powder is dispersed in the isopropyl alcohol solution.

3. The preparation process of an array-type flexible capacitive pressure sensor according to claim 1, characterized in that: The preparation method of the PDMS / MWCNT mixed slurry is specifically as follows: pouring the MWCNT solution into the PDMS colloid, and using magnetic stirring to mix the two solutions evenly to obtain the PDMS / MWCNT slurry.

4. The preparation process of an array-type flexible capacitive pressure sensor according to claim 1, characterized in that: The specific preparation method of the template method is: the template is a glass substrate, and the sinking surface is made smoother by milling + fire polishing, and the sensor dielectric layer is solidified with a customized thickness.

5. The preparation process of an array-type flexible capacitive pressure sensor according to claim 1, characterized in that: The specific preparation method of controlling the microstructure spontaneously formed on the surface by controlling the weight ratio of MWCNT is: controlling the weight ratio of MWCNT and PDMS, so as to explore the optimal performance.

6. The preparation process of an array-type flexible capacitive pressure sensor according to claim 1, characterized in that: The method for preparing the vacuum drying oven-cured mixed slurry is specifically as follows: firstly, the temperature is heated to 40° C. for 1 hour to volatilize the isopropyl alcohol without generating bubbles, and then the drying oven temperature is heated to 80° C. for curing for 3 hours.

7. The preparation process of an array-type flexible capacitive pressure sensor according to claim 1, characterized in that: The specific method of coating ITO thin film on PET substrate by magnetron sputtering is: by precisely controlling the sputtering parameters, high-quality deposition of ITO thin film on PET flexible substrate is achieved, ensuring that the film has good conductivity, transparency and adhesion.

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