A capacitive-piezoresistive dual-mode flexible pressure sensor and a method for manufacturing the same

Abstract

The present invention provides a capacitive-piezoresistive dual-mode flexible pressure sensor and a preparation method thereof, wherein the sensor comprises: an upper packaging layer, an upper electrode layer, an intermediate dielectric layer, a lower electrode layer and a lower packaging layer arranged from top to bottom, wherein the upper electrode layer has a protruding structure on one side relative to the intermediate dielectric layer, and the intermediate dielectric layer has a groove structure adapted to the protruding structure on one side relative to the upper electrode layer, and the lowest point of the protruding structure is at a certain distance from the bottom of the groove structure, and the sensor further comprises wires respectively fixed to the outer surfaces of the upper and lower electrode layers. The technical solution of the present invention overcomes the problem of limited range of flexible sensors in the prior art.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible pressure sensors, and in particular to a capacitive-piezoresistive dual-mode flexible pressure sensor and a preparation method thereof. Background Art

[0002] As an important component of wearable smart devices, flexible sensors have overcome the rigidity defects of traditional sensors. They not only have the ability to convert various external stimuli into detectable electrical signals, but also have good flexibility, stretchability and biocompatibility. Highly sensitive flexible pressure sensors can more accurately sense physiological information such as human breathing and pulse beats, and play an extremely important role in the fields of electronic skin, medical care and intelligent robots.

[0003] In the prior art, flexible sensors are basically single-mode, such as a single capacitive flexible sensor or a piezoresistive flexible sensor, which performs data detection and collection according to their respective characteristics. Due to their own characteristics, the data collection range is limited, and sufficient and comprehensive data cannot be obtained in some situations.

[0004] Therefore, there is a need for a large-range capacitive-piezoresistive dual-mode flexible pressure sensor and a preparation method thereof. Summary of the invention

[0005] The main purpose of the present invention is to provide a capacitive-piezoresistive dual-mode flexible pressure sensor and a preparation method thereof, so as to solve the problem of limited range of flexible sensors in the prior art.

[0006] To achieve the above-mentioned objectives, the present invention provides a capacitive-piezoresistive dual-modal flexible pressure sensor, comprising: an upper packaging layer, an upper electrode layer, an intermediate dielectric layer, a lower electrode layer and a lower packaging layer arranged from top to bottom, the upper electrode layer having a protruding structure on one side relative to the intermediate dielectric layer, the intermediate dielectric layer having a groove structure matching the protruding structure on one side relative to the upper electrode layer, and the lowest point of the protruding structure has a certain distance from the bottom of the groove structure, and the sensor also includes wires fixed to the outer surfaces of the upper and lower electrode layers, respectively.

[0007] Furthermore, the protrusion structure includes but is not limited to a semicircular protrusion, a cylindrical protrusion, a triangular protrusion, a trapezoidal protrusion, a rectangular protrusion or an irregular protrusion structure.

[0008] Furthermore, the number of the protruding structures is at least 2.

[0009] Furthermore, the upper and lower packaging layers are both made of PI polyimide film material, the upper electrode layer is made of a composite material obtained by combining PU polyurethane solution, DMF dimethylformamide solution and carbon black; the middle dielectric layer is made of Ecoflex material; and the lower electrode layer is made of conductive copper sheet.

[0010] Furthermore, the thickness H of the upper electrode layer ranges from 4.0 to 4.5 mm.

[0011] The present invention also provides a method for preparing a capacitive-piezoresistive dual-mode flexible pressure sensor, comprising the following steps:

[0012] S1, prepare the upper electrode layer, first use Solidworks software to draw a mold, the mold is square, and the inner wall length is 19.5mm, the mold has at least two semicircular grooves, the radius r1 is 3mm, the maximum depth h1 is 3mm, the spacing between the two grooves and the distance d1 of each groove from the inner wall of the mold are both 2.5mm, use 3D printing technology to print the mold, PU solution and DMF solution are mixed in a mass ratio of 1:1, and then add carbon black with a mass fraction of 7% of the total mass of the mixed solution of PU and DMF, magnetically stir the mixed solution for 1h20min~1h30min until it is fully uniform, pour the stirred preform into the mold with semicircular grooves, first put it in water for 3min, and then heat and dry it in an oven at 60℃~70℃ for 15min to obtain an upper electrode layer with a semicircular convex structure;

[0013] S2, the lower electrode layer is made of conductive copper sheet;

[0014] S3, prepare the intermediate dielectric layer, use Solidworks software to draw the mold, the mold is square, the inner wall length is 19.5mm, the mold has at least two cylindrical structures, the radius r2 is 3mm, the height h2 is 2.5mm, the spacing between the two cylindrical structures and the distance d2 between each cylindrical structure and the inner wall of the mold are both 2.5mm, use 3D printing technology to print the mold, glue A and glue B should be mixed in a mass ratio of 1:1 and put into a vacuum drying oven for degassing for 5min to remove bubbles in ecoflex to form a preform, pour the prepared ecoflex preform evenly on the mold with a cylindrical structure, and then heat and dry it in an oven at 60℃~70℃ for 30min to obtain an intermediate dielectric layer with a groove structure;

[0015] S4, encapsulating the sensor, assemble the prepared upper and lower electrode layers and dielectric layers with a size of 1.95cm×1.95cm in the order from inside to outside, namely the middle dielectric layer, the upper and lower electrode layers, and the upper and lower packaging layers. Finally, use conductive silver paste to fix the wires on the outside of the upper and lower electrode layers to lead out the electrodes, and use PI polyimide film for encapsulation and protection.

[0016] The present invention has the following beneficial effects:

[0017] 1. The present invention combines the structures of capacitive and piezoresistive flexible sensors, greatly improving the performance and measurement range of the capacitive flexible pressure sensor. The non-contact structure of the upper and lower electrode layers can make it have the characteristics of the capacitive flexible pressure sensor, such as contact sensing function, while the contact structure of the upper and lower electrode layers turns it into a piezoresistive flexible sensor, which can detect an increase in the linear range of measurement, and the selected flexible material enables it to maintain good repetitive stability.

[0018] 2. The present invention uses a 3D printing mold as a template for the protruding structure, which has a simple manufacturing process and extremely low cost, greatly improving production efficiency, and can mass-produce sensors with different performances by controlling the size and shape of the protruding structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the specific implementation or the prior art description. Obviously, the drawings described below are some implementations of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0020] Figure 1 A partial structural schematic diagram of a capacitive-piezoresistive dual-mode flexible pressure sensor of the present invention is shown;

[0021] Figure 2 Shows the preparation Figure 1 Schematic diagram of the overall structure of the mold used for the upper electrode layer;

[0022] Figure 3 Shows the preparation Figure 1 Schematic diagram of the overall structure of the mold used for the intermediate dielectric layer.

[0023] Among them, the reference numerals in the above drawings are:

[0024] 1. Upper electrode layer; 11. Protruding structure; 2. Intermediate dielectric layer; 21. Grooved structure; 3. Lower electrode layer; 4. Grooved structure; 5. Cylindrical structure. DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] like Figure 1A capacitive-piezoresistive dual-mode flexible pressure sensor is shown, comprising: an upper packaging layer, an upper electrode layer 1, an intermediate dielectric layer 2, a lower electrode layer 3 and a lower packaging layer arranged from top to bottom, the upper electrode layer 1 having a protruding structure 11 on the side opposite to the intermediate dielectric layer 2, the intermediate dielectric layer 2 having a groove structure 21 matching the protruding structure 11 on the side opposite to the upper electrode layer 1, and the lowest point of the protruding structure 11 is at a certain distance from the bottom of the groove structure 21, and the sensor also includes wires fixed to the outer surfaces of the upper and lower electrode layers respectively.

[0027] Further, the protrusion structure 11 includes but is not limited to semicircular protrusions, cylindrical protrusions, triangular protrusions, trapezoidal protrusions, rectangular protrusions or irregular protrusion structures 11. Protrusion structures 11 of different shapes can be generated according to actual needs to meet the mass production of sensors with different performances.

[0028] Furthermore, the number of the protruding structures 11 is at least two.

[0029] Furthermore, the upper and lower packaging layers are both made of PI polyimide film material, the upper electrode layer 1 is made of a composite material obtained by combining PU polyurethane solution, DMF dimethylformamide solution and carbon black; the middle dielectric layer 2 is made of Ecoflex material; and the lower electrode layer 3 is made of conductive copper sheet.

[0030] Furthermore, the thickness H of the upper electrode layer 1 is in the range of 4.0 to 4.5 mm.

[0031] Taking the preparation of a sensor with a semicircular protruding structure 11 as an example, the present invention also provides a method for preparing a capacitive-piezoresistive dual-mode flexible pressure sensor, comprising the following steps:

[0032] S1, prepare the upper electrode layer 1, first use Solidworks software to draw the mold, such as Figure 2 As shown, the mold is square and has an inner wall length of 19.5 mm. The mold has at least two semicircular grooves 4, whose radius r1 is 3 mm, the maximum depth h1 is 3 mm, the spacing between the two grooves 4 and the distance d1 of each groove 4 from the inner wall of the mold are both 2.5 mm. The mold is printed using 3D printing technology, PU solution and DMF solution are mixed in a mass ratio of 1:1, and then carbon black is added with a mass fraction of 7% of the total mass of the mixed solution of PU and DMF. The mixed solution is magnetically stirred for 1h20min~1h30min until it is fully uniform, and the stirred preform is poured into the mold with semicircular grooves 4, first placed in water for 3min, and then placed in an oven at 60℃~70℃ for heating and drying for 15min to obtain an upper electrode layer 1 with a semicircular convex structure 11; wherein the specific heating and drying temperature is 70℃.

[0033] S2, the lower electrode layer 3 is made of conductive copper sheet;

[0034] S3, prepare the intermediate dielectric layer 2, and use Solidworks software to draw the mold, such as Figure 3 As shown, the mold is square, the inner wall length is 19.5mm, and there are at least two cylindrical structures 5 inside the mold, whose radius r2 is 3mm, the height h2 is 2.5mm, the spacing between the two cylindrical structures 5 and the distance d2 between each cylindrical structure 5 and the inner wall of the mold are both 2.5mm. The mold is printed out using 3D printing technology, glue A and glue B should be mixed in a mass ratio of 1:1 and placed in a vacuum drying oven for degassing for 5 minutes to remove bubbles in ecoflex to form a preform, and the prepared ecolfex preform is evenly poured onto the mold with the cylindrical structure 5, and then placed in an oven at 60°C to 70°C for heating and drying for 30 minutes to obtain an intermediate dielectric layer 2 with a groove structure 21; wherein the specific heating and drying temperature is 70°C.

[0035] S4, encapsulating the sensor, assembling the prepared upper and lower electrode layers and dielectric layer 2 with a size of 1.95cm×1.95cm in the order from inside to outside, namely the middle dielectric layer 2, the upper and lower electrode layers and the upper and lower packaging layers, and finally fixing the wires on the outside of the upper and lower electrode layers with conductive silver paste to lead out the electrodes, and encapsulating and protecting them with PI polyimide film.

[0036] When the device is used, the detection circuit is connected to the upper electrode layer 1 and the lower electrode layer 3 to detect the values ​​collected by the capacitive or piezoresistive sensor. When the sensor provided by the present invention is subjected to continuous external pressure, the semicircular protrusion structure 11 of the upper electrode layer is initially blocked by the inner wall of the groove structure 21 of the intermediate dielectric layer 2 and does not contact the lower electrode layer 3. At this time, the device is a capacitive flexible sensor; as the external pressure increases, the semicircular protrusion structure 11 of the upper electrode layer squeezes into the groove structure 21 of the intermediate dielectric layer 2 and contacts the lower electrode layer 3. At this time, the device is a piezoresistive flexible sensor. The device realizes the function of capacitive-piezoresistive dual-mode detection and achieves the purpose of increasing the range of traditional flexible sensors.

[0037] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a capacitive-piezoresistive dual-mode flexible pressure sensor, characterized in that: A capacitive-piezoresistive dual-mode flexible pressure sensor, comprising: an upper packaging layer, an upper electrode layer, an intermediate dielectric layer, a lower electrode layer and a lower packaging layer arranged from top to bottom, wherein the upper electrode layer has a convex structure on one side relative to the intermediate dielectric layer, and the intermediate dielectric layer has a groove structure adapted to the convex structure on one side relative to the upper electrode layer, and the lowest point of the convex structure is at a certain distance from the bottom of the groove structure, and the sensor also includes wires fixed to the outer surfaces of the upper and lower electrode layers respectively; The preparation method of the capacitive-piezoresistive dual-mode flexible pressure sensor comprises the following steps: S1, prepare the upper electrode layer, first use Solidworks software to draw a mold, the mold is square, and the inner wall length is 19.5mm, the mold has at least two semicircular grooves, the radius r1 is 3mm, the maximum depth h1 is 3mm, the spacing between the two grooves and the distance d1 of each groove from the inner wall of the mold are both 2.5mm, use 3D printing technology to print the mold, PU solution and DMF solution are mixed in a mass ratio of 1:1, and then add carbon black with a mass fraction of 7% of the total mass of the mixed solution of PU and DMF, magnetically stir the mixed solution for 1h20min~1h30min until it is fully uniform, pour the stirred preform into the mold with semicircular grooves, first put it in water for 3min, and then heat and dry it in an oven at 60℃~70℃ for 15min to obtain an upper electrode layer with a semicircular convex structure; S2, the lower electrode layer is made of conductive copper sheet; S3, prepare the intermediate dielectric layer, use Solidworks software to draw the mold, the mold is square, the inner wall length is 19.5mm, the mold has at least two cylindrical structures, the radius r2 is 3mm, the height h2 is 2.5mm, the spacing between the two cylindrical structures and the distance d2 between each cylindrical structure and the inner wall of the mold are both 2.5mm, use 3D printing technology to print the mold, glue A and glue B should be mixed in a mass ratio of 1:1 and put into a vacuum drying oven for degassing for 5min to remove bubbles in ecoflex to form a preform, pour the prepared ecoflex preform evenly on the mold with a cylindrical structure, and then heat and dry it in an oven at 60℃~70℃ for 30min to obtain an intermediate dielectric layer with a groove structure; S4, encapsulating the sensor, assemble the prepared upper and lower electrode layers and dielectric layers with a size of 1.95cm×1.95cm in the order from inside to outside, i.e., the middle dielectric layer, the upper and lower electrode layers, and the upper and lower encapsulation layers. Finally, use conductive silver paste to fix the wires on the outside of the upper and lower electrode layers to lead out the electrodes, and encapsulate and protect them with PI polyimide film.

2. The method for preparing a capacitive-piezoresistive dual-mode flexible pressure sensor according to claim 1, characterized in that: The protrusion structure includes but is not limited to a semicircular protrusion, a cylindrical protrusion, a triangular protrusion, a trapezoidal protrusion, a rectangular protrusion or an irregular protrusion structure.

3. The method for preparing a capacitive-piezoresistive dual-mode flexible pressure sensor according to claim 1, characterized in that: The number of the protruding structures is at least 2.

4. The method for preparing a capacitive-piezoresistive dual-mode flexible pressure sensor according to claim 1, characterized in that: The upper and lower packaging layers are both made of PI polyimide film material, the upper electrode layer is made of a composite material obtained by combining PU polyurethane solution, DMF dimethylformamide solution and carbon black; the middle dielectric layer is made of Ecoflex material; and the lower electrode layer is made of conductive copper sheet.

5. The method for preparing a capacitive-piezoresistive dual-mode flexible pressure sensor according to claim 1, characterized in that: The thickness H of the upper electrode layer ranges from 4.0 to 4.5 mm.

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