Flexible piezoresistive sensor based on multilayer microstructure

Abstract

The invention discloses a flexible piezoresistive sensor based on a multi-layer microstructure, and relates to the field of flexible piezoresistive sensor design, and the flexible piezoresistive sensor comprises a multi-layer microstructure piezoresistive sensing unit. The multi-layer microstructure piezoresistive sensing unit comprises a top surface electrode, a middle electrode, a surface electrode and a bottom surface electrode which are compressed in sequence; a conductive elastomer is compressed among the top surface electrode, the middle electrode and the surface electrode; and the conductive elastomer is an elastomer combined with a conductive nano material and an organic elastic polymer. The flexible piezoresistive sensing range and sensitivity are improved.

Description

Technical Field

[0001] The present application relates to the field of piezoresistive sensor design, and in particular to a flexible piezoresistive sensor based on a multi-layer microstructure. Background Art

[0002] As a new type of electronic device, flexible sensors solve the problem that traditional rigid semiconductor sensors cannot adapt to various irregular surfaces. Due to their lightness, flexibility, stretchability and strong biocompatibility, they are regarded as the key core components for the transformation of wearable products from 1.0 to 2.0.

[0003] As a type of flexible sensor, the working mechanism of flexible pressure sensor mainly includes piezoresistive, capacitive and piezoelectric types. These sensors can convert external pressure signals into other physical signals (such as resistance, voltage, capacitance, etc.) that are easy to detect to test absolute pressure values ​​or pressure changes. They have broad application prospects in the fields of tactile perception, fingerprint recognition, medical monitoring, human-computer interface, Internet of Things, etc. So far, people have developed a variety of strategies to improve the comprehensive performance of flexible piezoresistive sensors, including: development of sensitive functional materials and device structure design and construction. Among them, due to the limitations of material selection, especially wearable medical devices for human body have strict requirements on parameters such as material safety and stability, it is generally considered to be an effective means to improve the performance of flexible piezoresistive sensors by microstructuring the functional layer of the device.

[0004] By constructing a microstructure on the functional layer of the flexible piezoresistive sensor, its elastic modulus can be effectively reduced and the deformation rate of the functional layer under stress can be increased, thereby obtaining a greater electrical response; at the same time, the stress concentration brought by the microstructure is also conducive to the device obtaining a faster response time, etc.

[0005] The microstructures that are currently being widely studied include pyramid structures, hemispherical structures, columnar structures, internal porous structures, and irregular structures. Taking the pyramid structure as an example, the principle is that as pressure is applied, the pyramid structure deforms, and the tip of the pyramid changes from a point contact shape to a surface contact structure, thereby increasing the contact area between the active layer and the electrode layer. The pyramid structure causes the stress to be unevenly distributed and concentrated at the tip. For a given applied pressure, a larger local stress concentration can cause a larger change in the contact area relative to a non-structured surface.

[0006] Although the above advantages of the microstructure functional layer can improve the sensitivity and response time of flexible piezoresistive sensors, it is difficult to increase the sensing range by simply changing the contact area. At present, this type of flexible piezoresistive sensors are mostly explored in daily activities below 100kPa. Most of them are based on changing the response resistance by changing the contact area. The effective modulus of the piezoresistive structure increases with the increase of pressure, resulting in a limited sensing range, which makes it difficult to achieve effective application in high-pressure sports. Summary of the invention

[0007] The purpose of this application is to provide a flexible piezoresistive sensor based on a multi-layer microstructure to solve the problem of limited sensor range and improve sensitivity at the same time.

[0008] To achieve the above objectives, this application provides the following solutions:

[0009] In a first aspect, the present application provides a flexible piezoresistive sensor based on a multi-layer microstructure, comprising: a multi-layer microstructure piezoresistive sensing unit;

[0010] The multi-layer microstructure piezoresistive sensing unit comprises a top surface electrode, an intermediate electrode, a surface electrode and a bottom surface electrode which are compressed in sequence;

[0011] A conductive elastomer is compressed between the top surface electrode, the middle electrode and the surface electrode; the conductive elastomer is an elastomer combining conductive nanomaterials and organic elastic polymers.

[0012] According to the specific embodiments provided by the present application, the present application discloses the following technical effects: when the contact area of ​​the multilayer structure is saturated with the increase of pressure, the present application includes a multilayer microstructure piezoresistive sensing unit, which includes a top surface electrode, an intermediate electrode, a surface electrode and a bottom surface electrode compressed in sequence; a conductive elastomer is also compressed between the top surface electrode, the intermediate electrode and the surface electrode, and after the electrode layers are compressed, the contact area between the electrodes changes due to the compression of the multilayer microstructure, and after the electrode layers are subjected to pressure, the tunneling current increases, thereby enhancing the change in conductivity; under compression, the contact of the conductive nanomaterial inside the conductive elastomer increases, and the conductivity is further improved, thereby increasing the pressure sensing range; and the contact area and the tunneling current increase at the same time, which also improves the sensitivity of the device. The flexible piezoresistive sensor based on the multilayer microstructure provided by the present application can be effectively applied in a wide range of pressure sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 This is a schematic diagram of a flexible piezoresistive sensor sensing unit based on a multi-layer microstructure in one embodiment of the present application;

[0015] Figure 2 In one embodiment of the present application, based on Figure 1 Schematic diagram of a flexible piezoresistive sensor with an array of sensing units. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0017] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0018] like Figure 1 As shown, a flexible piezoresistive sensor based on a multi-layer microstructure comprises: a multi-layer microstructure piezoresistive sensing unit; the multi-layer microstructure piezoresistive sensing unit comprises a top surface electrode 1, an intermediate electrode 2, a surface electrode 3 and a bottom surface electrode 4 which are compressed in sequence; a conductive elastomer 5 is compressed between the top surface electrode 1, the intermediate electrode 2 and the surface electrode 3; the conductive elastomer 5 is an elastomer combining conductive nanomaterials and organic elastic polymers.

[0019] In an exemplary embodiment, it further comprises: a top substrate 6 and a bottom substrate 7; the top substrate 6 is arranged on the top of the top surface electrode 1; the bottom substrate 7 is arranged on the bottom of the bottom surface electrode 3. The top substrate 6 and the bottom substrate 7 are flexible substrates.

[0020] Furthermore, the top substrate 6 serves as a substrate for the top support and the top surface electrode 1 , and the bottom substrate 7 and the bottom surface electrode 3 have the same function as the top.

[0021] The top surface electrode 1 is a surface electrode of the whole device and plays a role in current conduction. The top surface electrode 1 is prepared on a flexible substrate, and the substrate material includes but is not limited to various stretchable and bendable flexible organic materials, such as PET, PI, PU, ​​etc.

[0022] The conductive elastomer 5 is formed by combining the conductive nanomaterial with the organic elastic polymer, so that the conductive elastomer 5 has conductive function and elasticity; under compression, the conductivity is improved due to the increased contact of the internal conductive nanomaterial; and the original shape can be restored after the pressure is removed.

[0023] The intermediate electrode 2 enables the device to work as a layered structure. On the one hand, it enhances the current conduction; on the other hand, after compression, the distance with the conductive nanomaterial in the conductive elastomer 5 is close and the contact surface is increased, thereby enhancing the tunneling current. The intermediate electrode 2 is a conductive layer formed by the conductive nanomaterial in the functional layer, and an example is a carbon nanotube layer, which can be prepared by spraying, spin coating or drop coating.

[0024] The microstructure functional layer on the substrate includes an intermediate electrode 2 and a conductive elastomer 5, which is characterized by being an elastic polymer mixed with conductive nanomaterials, and the conductivity can change after being subjected to stress such as compression or stretching. The conductive elastomer 5 and the conductive nanomaterials are not restricted, and an example is PDMS mixed with carbon nanotubes.

[0025] The contact area between the surface electrode 3 and the bottom surface electrode 3 will change under the pressure, so that the current of the device changes under the pressure. The surface electrode 3 can be any conductor, including but not limited to metal.

[0026] A support structure having a height consistent with the height of the entire functional layer is also prepared on the bottom substrate 7 to maintain the stability of the overall structural packaging; the material is not limited and is located at the edge of the entire array active area.

[0027] In an exemplary embodiment, the thickness of the conductive elastomer in the multi-layer microstructure piezoresistive sensing unit varies linearly with the doping content of the conductive nanomaterial in the conductive elastomer 5 .

[0028] In an exemplary embodiment, the multi-layer microstructure piezoresistive sensing unit is in the shape of a triangular pyramid.

[0029] The shape of the multi-layer microstructure piezoresistive sensing unit can be any shape, and can also be spherical or cylindrical, etc. The focus of this application is on the multi-layer design based on the microstructure and the design of the intermediate electrode 2 layers. An example is a triangular pyramid structure, which can be realized by mold inversion and other methods.

[0030] The conductive elastomer 5 located at the top surface electrode 1 can achieve a change in conductivity by compression, and can also achieve a change in the contact area with the bottom surface electrode 3 .

[0031] Since the conductive nanomaterials between the electrode layers, such as carbon nanotubes, are compressed, the distance between the carbon nanotubes decreases and the contact increases, which increases the tunneling current. In addition, the distance between the carbon nanotubes and the electrodes also decreases, and the contact increases, which also increases the current.

[0032] The multi-layer microstructure piezoresistive sensing unit is repeatedly prepared, and the thickness and conductivity of each layer of the multi-layer microstructure piezoresistive sensing unit are designed to change linearly. Since the sensitivity is determined by the current value changed by the unit pressure, after compression, the contact area between the electrodes changes due to the compression of the microstructure, and the tunneling current between the layers changes after being subjected to pressure. The current changes in both aspects will increase the rate of change and achieve high sensitivity in a wide pressure range.

[0033] In an exemplary embodiment, the multilayer microstructure piezoresistive sensing unit includes one or more; Figure 2 As shown, a plurality of multi-layer microstructure piezoresistive sensing units of different heights form a sensing array, which can further improve the sensing range of the sensing array; the number of multi-layer microstructure piezoresistive sensing units in the sensing array is determined according to the actual size of the piezoresistive sensor.

[0034] In an exemplary embodiment, packaging structures are provided at both ends of the sensor array to stabilize the device as a whole.

[0035] Furthermore, the arraying of the active area can form a practical device size, and the device is designed with packaging structures on both sides of the active area with a height equal to or slightly lower than the active area, so that the device as a whole is stable.

[0036] In an exemplary embodiment, the substrate materials of the top substrate 6 and the bottom substrate 7 include stretchable and bendable flexible organic materials.

[0037] In an exemplary embodiment, the intermediate electrode 2 is doped with a conductive layer of conductive nanomaterial.

[0038] In an exemplary embodiment, the intermediate electrode 2 and the conductive elastic body 5 coated on the intermediate electrode 2 are made of the same or different materials.

[0039] Furthermore, a layer of conductive elastomer 5 is prepared on the surface of the intermediate electrode 2. The material of the conductive elastomer 5 can be the same as or different from that of the intermediate electrode 2 at the bottom layer. The materials of each layer of intermediate electrodes 2 can be the same or different.

[0040] In an exemplary embodiment, the intermediate electrode 2 is prepared by spraying, spin coating or drop coating of a conductive nano material.

[0041] Compared with the previous single-layer design, the dual mechanism of intra-layer compression and inter-layer tunneling brought by the flexible piezoresistive sensor based on multi-layer microstructure provided by the present application can solve the problems of monotonous sensing mechanism and easy saturation of microstructure deformation, while achieving high sensitivity and wide pressure detection range performance of the flexible piezoresistive sensor.

[0042] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0043] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A flexible piezoresistive sensor based on a multi-layer microstructure, characterized in that: The flexible piezoresistive sensor based on multi-layer microstructure comprises: a multi-layer microstructure piezoresistive sensing unit; The multi-layer microstructure piezoresistive sensing unit comprises a top surface electrode, an intermediate electrode, a surface electrode and a bottom surface electrode which are compressed in sequence; A conductive elastomer is compressed between the top surface electrode, the middle electrode and the surface electrode; the conductive elastomer is an elastomer combining conductive nanomaterials and organic elastic polymers.

2. The flexible piezoresistive sensor based on multi-layer microstructure according to claim 1, characterized in that: The thickness of the conductive elastomer in the multi-layer microstructure piezoresistive sensing unit varies linearly with the doping content of the conductive nanomaterial in the conductive elastomer.

3. The flexible piezoresistive sensor based on multi-layer microstructure according to claim 2, characterized in that: The single-layer shape of the multi-layer microstructure piezoresistive sensing unit is any structure, including but not limited to a triangular pyramid shape, a sphere or a columnar shape.

4. The flexible piezoresistive sensor based on multi-layer microstructure according to claim 1, characterized in that: Also includes: a top substrate and a bottom substrate; The top substrate is disposed on top of the top surface electrode; The bottom substrate is disposed at the bottom of the bottom surface electrode.

5. The flexible piezoresistive sensor based on a multilayer microstructure according to any one of claims 1 to 4, characterized in that: The multi-layer microstructure piezoresistive sensing unit includes one or more; A plurality of multi-layer microstructure piezoresistive sensing units of different heights form a sensing array; The number of the multi-layer microstructure piezoresistive sensing units in the sensing array is determined according to the actual size of the piezoresistive sensor.

6. The flexible piezoresistive sensor based on multi-layer microstructure according to claim 4, characterized in that: Packaging structures are provided at two ends of the sensor array.

7. The flexible piezoresistive sensor based on multi-layer microstructure according to claim 2, characterized in that: The substrate materials of the top substrate and the bottom substrate include stretchable and bendable flexible organic materials.

8. The flexible piezoresistive sensor based on multi-layer microstructure according to claim 1, characterized in that: The intermediate electrode is doped with a conductive layer of conductive nanomaterial.

9. The flexible piezoresistive sensor based on multi-layer microstructure according to claim 8, characterized in that: The middle electrode and the conductive elastic body coated on the middle electrode may be made of the same material or different material.

10. The flexible piezoresistive sensor based on multi-layer microstructure according to claim 8, characterized in that: The intermediate electrode is prepared by spraying, spin coating or drop coating of conductive nanomaterials.

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