Preparation method and application of a surface pyramid multi-level ordered piezoresistive sensor

Abstract

The present invention provides a method for preparing a surface pyramid multi-level ordered piezoresistive sensor and its application. First, a Si substrate with a surface covered with a SiO2 film is obtained. The crystal orientation of the Si substrate is <100> The surface of the SiO2 film is covered with a photoresist layer, on which several groups of dots are exposed, each group consisting of three rows of dots arranged in parallel; after development with a developer, the exposed SiO2 is plasma etched to expose the Si substrate; after removing the photoresist, the exposed Si is wet-etched with a NaOH solution to obtain a silicon template; a conductive material is poured on the silicon template, heated and cured, and then peeled off from the silicon template to obtain a sensing layer of a surface pyramid multi-level ordered piezoresistive sensor. The present invention improves the sensor's dependence on the electrode contact area and compressibility, thereby improving sensitivity and sensing range.

Description

Technical Field

[0001] The present invention belongs to the field of micro-nano structures and relates to a surface pyramid multi-level ordered piezoresistive sensor and a preparation method and application thereof. Background Art

[0002] A piezoresistive sensor utilizes the piezoresistive effect, converting pressure changes into resistance changes. Piezoresistive sensors are widely used due to their small size, ease of integration, simple structure, ease of manufacturing, and excellent frequency response, enabling them to measure high-speed pulse pressure. Their primary application areas include human motion detection, electronic skin, and human-computer interaction. In human motion detection, piezoresistive sensors can adapt to the bending pressure of varying joint sizes, and can display bending pressure changes through changes in current and resistance. They are therefore suitable for applications such as finger movement function assessment and rehabilitation training.

[0003] The performance of piezoresistive sensors is primarily reflected in their high sensitivity and wide detection range. High sensitivity allows the sensor to distinguish subtle pressure stimuli, while a wide detection range allows the sensor to discern between low and high pressures. Sensor performance depends primarily on two factors: first, the change in contact between the functional layer and the electrode. This occurs primarily when an external force increases the contact area between the piezoresistive layer and the electrode, widening the conductive path. Second, the change in resistance within the functional layer. In most cases, when an external force is applied, the piezoresistive material deforms, shortening the conductive path. Therefore, piezoresistive sensors require a positive correlation between pressure and the contact area between the piezoresistive material and the electrode, as well as high compressibility of the piezoresistive material.

[0004] Research has shown that the surface microstructure of the functional layer can significantly improve the sensor's dependence on electrode contact area and compressibility, and can also enhance sensitivity to a certain extent. Surface microstructures primarily include single micro-protrusion structures, such as pillars, hemispherical shapes, and pyramids; composite micro-protrusion structures, such as porous pyramids, interlocking structures, and multi-level pillars; and three-dimensional porous structures. Compared to other structures, composite micro-protrusion structures can enhance deformation capacity, increase specific surface area, and improve overload resistance.

[0005] The current problem with piezoresistive sensors is how to balance sensitivity and sensing range. Summary of the Invention

[0006] In view of the above problems, the present invention aims to propose a method for preparing a surface pyramid multi-level ordered piezoresistive sensor:

[0007] In order to achieve the above objectives, this application is implemented through the following technical solutions:

[0008] A surface pyramid multi-level ordered piezoresistive sensor comprises: two silver electrodes with pins, and a piezoresistive functional layer located between the pins. The surface of the piezoresistive functional layer is distributed with a multi-level and ordered micro-pyramid structure, and the functional layer contains multi-walled carbon nanotubes and graphene.

[0009] To achieve the above objectives, the present invention adopts the following scheme: a method for preparing a surface pyramid multi-level ordered piezoresistive sensor, comprising the following steps:

[0010] S1. Obtain a Si substrate with a SiO2 film on its surface, wherein the crystal orientation of the Si substrate is <100> ;

[0011] The surface of the SiO2 film is covered with a photoresist layer, and a plurality of groups of dots are exposed on the photoresist layer, each group consisting of three rows of dots arranged in parallel; the number of dots in each row is not less than three;

[0012] In the three rows of dots, the dots in each row have the same diameter, and the dots in different rows have different diameters. The dots with three different diameters are named circle one, circle two, and circle three from smallest to largest. The three rows of dots are composed of circle one, circle two, and circle three in order.

[0013] For any row of the three rows of dots, the dots are spaced equally, denoted by d; and the spacing between adjacent rows is also d;

[0014] After developing with a developer, the exposed SiO2 is plasma etched to expose the Si substrate. After removing the photoresist, the exposed Si is wet-etched with a NaOH solution to obtain three rows of pyramid-shaped pits with equal spacing on the Si substrate. Finally, the SiO2 is removed to obtain a silicon template.

[0015] S2, preparing PDMS-based conductive material by mixing multi-walled carbon nanotubes, graphene and n-hexane;

[0016] S3. Pour the conductive material onto the silicon template, heat and solidify it, and then peel it off from the silicon template to obtain a sensing layer of a surface pyramid multi-level ordered piezoresistive sensor.

[0017] Preferably, after step S3, the following steps are further included:

[0018] S4, printing silver paste electrodes and silver paste pins on a polyethylene terephthalate (PET) film, and then heating and curing the film to obtain electrodes;

[0019] S5. Assemble the electrode obtained in S4 and the sensing layer obtained in step S3 to obtain a surface pyramid multi-level ordered piezoresistive sensor.

[0020] Preferably, the diameters of circle 1, circle 2 and circle 3 in S1 are 10 μm, 20 μm and 30 μm respectively.

[0021] Preferably, the distance between the dots is d=10 μm.

[0022] Preferably, the wet etching of the exposed Si using a NaOH solution specifically includes: etching the Si substrate with a 6.0 M in H2O NaOH solution for 3 hours and 30 minutes.

[0023] Preferably, the thickness of the SiO2 film is 700nm, and the specific process of plasma etching the exposed SiO2 includes: etching power of 125W, SF6 of 65SCCM, pressure of 20Pa, and etching time of 18min.

[0024] Preferably, S2 specifically includes the following steps:

[0025] S2.1. Mix multi-walled carbon nanotubes and graphene in a mass ratio of 1:1, then mix the mixture with n-hexane in a mass ratio of 1:20, sonicate for 10 minutes, and magnetically stir for 10 minutes;

[0026] S2.2. Add PDMS solution A in a certain proportion and stir magnetically for 2 hours; the mass ratio of PDMS solution A to multi-walled carbon nanotube graphene mixture is 50:3;

[0027] S2.3. Heat in a water bath at 75°C with stirring for 15 minutes;

[0028] S2.4. Add PDMS solution B and stir magnetically for 10 minutes to obtain a conductive material; the mass ratio of the PDMS solution A to the PDMS solution B is 10:1.

[0029] Preferably, S3 specifically includes the following steps: pouring the conductive material onto the silicon template, first rotating the silicon template at a speed of 500 rpm for 30 seconds, then rotating the silicon template at a speed of 1000 rpm for 60 seconds, heating the conductive film at 90°C for 10 minutes to solidify, and peeling it off from the silicon template after cooling to obtain the sensing layer of the surface pyramid multi-level ordered piezoresistive sensor.

[0030] Preferably, S4 specifically includes the following steps: using screen printing to print 1 cm×1 cm silver paste electrodes and 3 mm×3 cm silver paste pins on a 50 μm thick polyethylene terephthalate (PET) film, and finally heating at 120°C for 20 minutes to solidify the silver paste to obtain the electrodes.

[0031] The present invention also provides the sensitivity and sensing range of the silicon template after film inversion and subpackaging under different wet etching times.

[0032] In this paper, a piezoresistive sensor with a multi-level ordered surface pyramid structure was fabricated. The sensor comprises two electrodes and a piezoresistive functional layer located between the electrodes. The surface of the piezoresistive functional layer is covered with a multi-level, ordered micro-pyramid structure and contains multi-walled carbon nanotubes and graphene.

[0033] The piezoresistive functional layer with a multi-level ordered micro-pyramid structure proposed in this invention changes its contact area with the electrode under the influence of external force, altering its internal conduction path and causing a change in internal resistance. This multi-level ordered micro-pyramid structure significantly reduces the sensor's dependence on electrode contact area and compressibility.

[0034] The sensor's piezoresistive functional layer has a multi-level, ordered micro-pyramid structure. This multi-level, ordered micro-pyramid structure improves the sensor's reliance on electrode contact area and compressibility, and to a certain extent, can increase sensitivity and extend its sensing range.

[0035] The present invention also provides an application of a surface pyramid multi-level ordered piezoresistive sensor prepared by the preparation method in measuring joint bending angles, comprising the following steps: attaching the surface pyramid multi-level ordered piezoresistive sensor to a joint, measuring the corresponding relationship between the joint bending angle and the current; and inferring the joint bending angle based on the corresponding relationship by measuring the sensor output current.

[0036] Beneficial effects of the present invention:

[0037] The present invention proposes a novel three-level ordered micro-pyramid structure, with the functional layer containing multi-walled carbon nanotubes and graphene. When applied to sensors, it can improve the sensor's dependence on electrode contact area and compressibility, while also increasing sensitivity and sensing range.

[0038] The three-level ordered micro-pyramid structure proposed in the present invention has a sensing effect that is significantly better than similar products of level 1 or 2.

[0039] After encapsulating the three-level ordered micro-pyramid structure, the current change test was carried out at different finger bending angles. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the silicon template preparation process of the present invention.

[0041] Figure 2 Schematic diagram of a surface pyramid multi-level ordered piezoresistive sensor.

[0042] Figure 3 Schematic diagram of the microstructure of the functional layer of a surface pyramid multi-level ordered piezoresistive sensor.

[0043] Figure 4This is the SEM image of a silicon wafer wet-etched with NaOH analytical solution for 2h10min.

[0044] Figure 5 This is the SEM image of a silicon wafer wet-etched with NaOH analytical solution for 2h50min.

[0045] Figure 6 This is the SEM image of the silicon wafer wet-etched with NaOH analytical solution for 3h30min.

[0046] Figure 7 This is a detailed SEM image of the silicon wafer after wet etching with NaOH analytical solution for 2h10min.

[0047] Figure 8 This is a detailed SEM image of the silicon wafer after wet etching with NaOH analytical solution for 2h50min.

[0048] Figure 9 This is a detailed SEM image of the silicon wafer after wet etching with NaOH analytical solution for 3h30min.

[0049] Figure 10 When using laser direct writing, an array of circles with a diameter of 30 μm and a spacing of 10 μm is exposed on the photoresist. The wet etching time is 3 hours and 30 minutes. The detailed SEM image after film inversion is shown.

[0050] Figure 11 When laser direct writing is used, an array of circles with diameters of 10μm and 30μm and a spacing of 10μm is cross-exposed on the photoresist. The wet etching time is 3h30min. Detailed SEM image after film inversion.

[0051] Figure 12 This is a local SEM image of the silicon wafer after wet etching with NaOH analytical solution for 2h10min.

[0052] Figure 13 This is a local SEM image of the silicon wafer after wet etching with NaOH analytical solution for 2h50min.

[0053] Figure 14 This is a local SEM image of the silicon wafer after wet etching with NaOH analytical solution for 3h30min.

[0054] Figure 15 When laser direct writing is used, an array of circles with a diameter of 10 μm and a spacing of 10 μm is exposed on the photoresist. This is a local SEM image after the film is inverted.

[0055] Figure 16 When using laser direct writing, an array of circles with a diameter of 30 μm and a spacing of 10 μm is exposed on the photoresist. The wet etching time is 3 hours and 30 minutes. The local SEM image after the film is inverted.

[0056] Figure 17 When laser direct writing is used, an array of circles with diameters of 10μm and 30μm and a spacing of 10μm is cross-exposed on the photoresist. The wet etching time is 3h30min. Local SEM image after film inversion.

[0057] Figure 18 The sensitivity and sensing range of the sensor after wet etching the silicon wafer for 2h10min and then packaging.

[0058] Figure 19 The sensitivity and sensing range of the sensor after wet etching the silicon wafer for 2h50min and then packaging.

[0059] Figure 20 The sensitivity and sensing range of the sensor after wet etching the silicon wafer for 3h30min and then packaging.

[0060] Figure 21 When laser direct writing is used, an array with a diameter of 10μm and a spacing of 10μm is exposed on the photoresist, wet-etched for 2h10min, and the sensitivity and sensing range of the sensor after film inversion and packaging.

[0061] Figure 22 When laser direct writing is used, an array with a diameter of 30μm and a spacing of 10μm is exposed on the photoresist. The wet etching time is 3h30min. The sensitivity and sensing range of the sensor after inverted film packaging.

[0062] Figure 23 When laser direct writing is used, an array of circles with diameters of 10μm and 30μm and a spacing of 10μm is cross-exposed on the photoresist. The wet etching time is 3h30min. The sensitivity and sensing range of the sensor after inverted film packaging are shown.

[0063] Figure 24 The current variation curve when the finger is bent at different angles for human motion detection. DETAILED DESCRIPTION Example

[0064] S1. Preparation of silicon template

[0065] Schematic diagram of the silicon template preparation process Figure 1 As shown;

[0066] S1.1. Electron beam evaporation is used to deposit a layer of SiO2 thin film on a clean Si substrate; the Si substrate has a crystal orientation of <100> Silicon wafer, Si02 film thickness is 700nm;

[0067] S1.2. Spin-coat a layer of photoresist on the uniform SiO2, and expose circles of different diameters and arranged evenly on the photoresist, and then develop with a developer:

[0068] Positive photoresist was spin-coated on SiO2 at 1000 rpm for 30 s and 4000 rpm for 60 s;

[0069] The photoresist layer is exposed with a plurality of groups of dots, each group consisting of three rows of dots arranged in parallel; the number of dots in each row is not less than three;

[0070] The dots of three different diameters are named circle one, circle two, and circle three in ascending order of diameter. The three rows of dots are composed of circle one, circle two, and circle three in sequence.

[0071] For any of the three rows of dots, the spacing between the dots is fixed, denoted as d; and the spacing between adjacent rows is also d;

[0072] The diameters of circles 1, 2, and 3 are 10 μm, 20 μm, and 30 μm, respectively, and the spacing is d = 10 μm. After exposure, the silicon wafer is placed in a developer for 1 minute.

[0073] S1.3, plasma etching the exposed SiO2; the etching power is 125W, SF6 is 65SCCM, the pressure is 20Pa, and the etching time is 18min;

[0074] S1.4. Wash off the photoresist with isopropyl alcohol;

[0075] S1.5, wet-etch the exposed Si with 6.0M in H2O NaOH titrant for 2h10min to obtain a cone-shaped structure with a depth of 5μm. Figure 4 As shown;

[0076] S1.6, wash away SiO2 with HF;

[0077] S2. Preparation of conductive materials

[0078] S2.1. Mix multi-walled carbon nanotubes and graphene in a mass ratio of 1:1, then mix the mixture with n-hexane in a mass ratio of 1:20, sonicate for 10 minutes, and magnetically stir for 10 minutes;

[0079] S2.2. Add PDMS solution A in a certain proportion and stir magnetically for 2 hours; the mass ratio of PDMS solution A to multi-walled carbon nanotube graphene mixture is 50:3;

[0080] S2.3. Heat in a water bath at 75°C with stirring for 15 minutes;

[0081] S2.4. Add PDMS solution B and stir magnetically for 10 minutes. The ratio of PDMS solution A to solution B is 10:1.

[0082] S3. Pour the conductive material onto the silicon template with different wet etching times, rotate at 500 rpm for 30 s and 1000 rpm for 60 s, heat the conductive film at 90°C for 10 minutes to solidify, and peel it from the silicon template after cooling to obtain a 5 μm high cone detail SEM. Figure 7 As shown, the local SEM Figure 12 shown.

[0083] S4. Electrode preparation: 1 cm × 1 cm silver paste electrodes and 3 mm × 3 cm silver paste pins were printed on a 50 μm thick polyethylene terephthalate (PET) film using screen printing. Finally, the silver paste was cured by heating at 120°C for 20 minutes.

[0084] S5. Assemble the flexible pressure sensing unit and stick the sensing layer with microstructure on the surface and the electrode together with tape to complete the preparation of the surface pyramid multi-level ordered piezoresistive sensor. The schematic diagram is shown in the figure. Figure 2 shown.

[0085] The sensitivity and sensing range of the assembled sensor are tested, and the final results are as follows: Figure 18 shown. Example

[0086] The difference from Example 1 is that the exposed Si is wet-etched with NaOH solution for 2h50min to obtain a pyramidal structure with a depth of 10μm. Figure 5 As shown; the etched silicon wafer was inverted to obtain a 10μm high cone detail SEM as shown Figure 8 As shown, the local SEM Figure 13 The sensitivity and sensing range of the assembled sensor were tested, and the final results are shown as follows. Figure 19 shown. Example

[0087] The difference from Example 1 is that the exposed Si is wet-etched with NaOH solution for 3h30min to obtain a pyramidal structure with a depth of 15μm. Figure 6 As shown; the etched silicon wafer was inverted to obtain a 15μm high cone detail SEM as shown Figure 9 As shown, the local SEM Figure 14 The sensitivity and sensing range of the assembled sensor were tested, and the final results are shown as follows. Figure 20 shown. Example

[0088] The difference from Example 1 is that the array of circles with a diameter of 10 μm and a spacing of 10 μm is exposed on the photoresist, and the single-stage cone after etching is as follows: Figure 15 The sensitivity and sensing range of the assembled sensor were tested, and the final results are shown as follows. Figure 21shown. Example

[0089] The difference from Example 1 is that the array of 30 μm diameter circles and 10 μm spacing is exposed on the photoresist, the wet etching time is 3 hours and 30 minutes, and the single-stage cone after the film is turned over is as follows: Figure 10 As shown, the local SEM Figure 16 The sensitivity and sensing range of the assembled sensor were tested, and the final results are shown as follows. Figure 22 shown. Example

[0090] The difference from Example 1 is that the array of circles with diameters of 10 μm and 30 μm and a spacing of 10 μm is cross-exposed on the photoresist, the wet etching time is 3 hours and 30 minutes, and the double-stage cone after the film is turned over is as follows: Figure 11 As shown, the local SEM Figure 17 The sensitivity and sensing range of the assembled sensor were tested, and the final results are shown as follows. Figure 23 shown.

[0091] like Figure 18 、 19 As shown in the figure, when the Si wet etching time is short, the microstructure after film inversion presents a pillar-shaped structure. Because the top of the pillar is large, the contact area between the functional layer and the electrode is limited, resulting in low sensitivity.

[0092] like Figure 21 As shown in the figure, when the size of the laser direct writing is 10μm and the microstructure on the functional layer is single-level, after the film is inverted, due to its low cone height and small deformation, its test range is narrow and can only test the sensitivity under 0-300kPa pressure. Figure 22 As shown in the figure, when the size of the laser direct writing is 30μm and the microstructure on the functional layer is single-level, the microstructure of the functional layer has a certain height after the film is inverted, which can test the sensitivity under 0-800kPa pressure, but the sensitivity is relatively small. Figure 23 As shown in the figure, when the size of the laser direct writing is 10μm and 30μm and the microstructure on the functional layer is double-level, after the film is inverted, the final relative height difference is large, the test results are unstable and the linearity is poor.

[0093] like Figure 20 As shown in the figure, the sensitivity of the sensor changes under different pressures. The overall current change rate has experienced a process of rapid increase to slow and gentle. Under the pressure of 0-300kPa, the sensitivity is 6.93kPa -1 The micro-pyramid structure gradually deforms and has a certain degree of deformation capacity. Under a pressure of 325-525kPa, the deformation of the micro-pyramid structure gradually reaches saturation, with a sensitivity of 1.53kPa. -1, significantly reduced. Under the pressure of 550-800kPa, the microstructure deformation reaches the limit, almost no deformation, and the sensitivity is 0.233kPa -1 Whether in terms of sensitivity, test range or linearity, the three-level functional layer microstructure is superior to other structures. Example

[0094] The surface pyramid multi-level ordered piezoresistive sensor prepared by the above preparation method is attached to the finger joint, and the current signal output by the sensor is collected when the finger is bent at 0°, 30°, 45°, 90°, and 120° to obtain the corresponding relationship between the finger bending angle and the current; based on the corresponding relationship, the finger bending angle is inferred by measuring the current output by the sensor. Figure 24 As shown in Figure 3, the sensor output current changes significantly at different bending angles.

[0095] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a surface pyramid multi-level ordered piezoresistive sensor, characterized in that: The following steps are involved: S1. Obtain a Si substrate with a SiO2 film on its surface, wherein the crystal orientation of the Si substrate is <100> ; The surface of the SiO2 film is covered with a photoresist layer. During laser direct writing, a plurality of groups of dots are exposed on the photoresist layer, each group consisting of three rows of dots arranged in parallel; the number of dots in each row is not less than three; The dots of three different diameters are named circle one, circle two, and circle three from small to large. The three rows of dots are composed of circle one, circle two, and circle three in sequence and are named row one, row two, and row three respectively. The distance between circles 1, 2, and 3 in each row is fixed, denoted as d; and the distance between adjacent rows is also d; After developing with a developer, the exposed SiO2 is plasma etched to expose the Si substrate; After removing the photoresist, the exposed Si substrate is wet-etched with a NaOH solution to obtain three rows of equally spaced pyramid-shaped pits on the Si substrate. Finally, the SiO2 is removed to obtain a silicon template. S2, preparing PDMS-based conductive material by mixing multi-walled carbon nanotubes, graphene and n-hexane; S3. Pour the conductive material onto the silicon template, heat and solidify it, and then peel it off from the silicon template to obtain a sensing layer of a surface pyramid multi-level ordered piezoresistive sensor.

2. The method for preparing a surface pyramid multi-level ordered piezoresistive sensor according to claim 1, characterized in that: After step S3, the following steps are also included: S4, printing silver paste electrodes and silver paste pins on a polyethylene terephthalate (PET) film, and then heating and curing the film to obtain electrodes; S5. Assemble the electrode obtained in S4 and the sensing layer obtained in step S3 to obtain a surface pyramid multi-level ordered piezoresistive sensor.

3. The method for preparing a surface pyramid multi-level ordered piezoresistive sensor according to claim 1, characterized in that: The diameters of circle 1, circle 2, and circle 3 in S1 are 10 μm, 20 μm, and 30 μm, respectively.

4. The method for preparing a surface pyramid multi-level ordered piezoresistive sensor according to claim 3, characterized in that: The distance between the three circles is d=10 μm.

5. The method for preparing a surface pyramid multi-level ordered piezoresistive sensor according to claim 4, characterized in that: The wet etching of the exposed Si using the NaOH solution specifically includes: etching the Si substrate with a 6.0M NaOH solution for 3 hours and 30 minutes.

6. The method for preparing a surface pyramid multi-level ordered piezoresistive sensor according to claim 5, characterized in that: The thickness of the SiO2 film is 700nm, and the specific process of plasma etching the exposed SiO2 includes: etching power of 125W, SF6 of 65SCCM, pressure of 20Pa, and etching time of 18min.

7. The method for preparing a surface pyramid multi-level ordered piezoresistive sensor according to claim 5, characterized in that: S2 specifically includes the following steps: S2.

1. Mix multi-walled carbon nanotubes and graphene in a mass ratio of 1:1, then mix the mixture with n-hexane in a mass ratio of 1:20, sonicate for 10 minutes, and magnetically stir for 10 minutes; S2.

2. Add PDMS solution A in a certain proportion and stir magnetically for 2 hours; the mass ratio of PDMS solution A to multi-walled carbon nanotube graphene mixture is 50:3; S2.

3. Heat in a water bath at 75°C with stirring for 15 minutes; S2.

4. Add PDMS solution B and stir magnetically for 10 minutes to obtain a conductive material; the mass ratio of the PDMS solution A to the PDMS solution B is 10:

1.

8. The method for preparing a surface pyramid multi-level ordered piezoresistive sensor according to claim 5, characterized in that: S3 specifically includes the following steps: pouring the conductive material onto the silicon template, first rotating the silicon template at a speed of 500 rpm for 30 seconds, then rotating the silicon template at a speed of 1000 rpm for 60 seconds, heating the conductive film at 90°C for 10 minutes to solidify it, and then peeling it off from the silicon template after cooling to obtain the sensing layer of the surface pyramid multi-level ordered piezoresistive sensor.

9. The method for preparing a surface pyramid multi-level ordered piezoresistive sensor according to claim 2, characterized in that: S4 specifically includes the following steps: using screen printing, printing 1cm×1cm silver paste electrodes and 3mm×3cm silver paste pins on a 50μm thick polyethylene terephthalate (PET) film, and finally heating at 120℃ for 20 minutes to cure the silver paste to obtain the electrode.

10. Application of the surface pyramid multi-level ordered piezoresistive sensor prepared by the preparation method according to any one of claims 1 to 9 in measuring joint bending angle, characterized in that: The method comprises the following steps: attaching a surface pyramid multi-level ordered piezoresistive sensor to a joint to measure the corresponding relationship between the joint bending angle and the current; Based on the corresponding relationship, the joint bending angle is inferred by measuring the sensor output current.

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