A liquid metal-based multi-modal flexible sensor and a preparation method thereof

Abstract

This invention relates to the field of flexible electronics technology, and in particular to a multimodal flexible sensor based on liquid metal and its fabrication method. The flexible sensor comprises, from bottom to top: a Y-axis strain sensing layer, an X-axis strain sensing layer, a lower electrode array layer, a micropillar dielectric layer, and an upper electrode array layer; wherein the lower electrode array layer, the micropillar dielectric layer, and the upper electrode array layer together form a capacitive pressure sensor. This invention combines an X-axis strain sensor, a Y-axis strain sensor, and a pressure sensor to form a multimodal flexible sensor, effectively expanding the sensor's application range. Furthermore, the use of a vertical stacking method makes the multimodal sensor structure compact. Simultaneously, the sensor of this invention has high sensitivity and detection accuracy, and also possesses good portability and flexibility.

Description

Technical Field

[0001] This invention relates to the field of flexible electronics technology, and in particular to a multimodal flexible sensor based on liquid metal and its fabrication method. Background Technology

[0002] In recent years, flexible strain sensors and flexible pressure sensors have received widespread attention due to their applications in flexible electronic skin, wearable devices, and soft robots. Currently, several manufacturing methods for flexible strain sensors have been proposed, but the flexible strain sensors produced by current processes and technologies generally exhibit limited tensile strength and significant hysteresis. Pressure sensors include piezoelectric, resistive, and capacitive types. Compared to piezoelectric and resistive pressure sensors, capacitive pressure sensors have advantages such as lower temperature sensitivity, simpler structure, faster dynamic response, and higher accuracy, leading to their widespread use. Flexible capacitive pressure sensors change capacitance by applying pressure, altering the distance between electrodes and their relative permittivity. However, the constant volume of the polymer dielectric layer in flexible capacitive sensors limits the improvement of sensor sensitivity, and most polymer elastomers exhibit severe viscoelasticity and interfacial adhesion forces, which exacerbate the hysteresis effect. Simultaneously, multimodal sensors integrating flexible strain and pressure sensors have also been applied; however, integrated multimodal sensors still suffer from the drawbacks of single-unit sensors.

[0003] In current technologies, it is of great significance to improve the hysteresis of flexible strain sensors and the sensitivity of flexible pressure sensors, and to manufacture flexible multimodal sensors that can simultaneously perform strain sensing and pressure sensing. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the background technology by proposing a multimodal flexible sensor based on liquid metal and its fabrication method.

[0005] The technical solution of the present invention is a multimodal flexible sensor based on liquid metal, comprising a Y-axis strain sensing layer, an X-axis strain sensing layer, a lower electrode array layer, a micropillar dielectric layer and an upper electrode array layer arranged sequentially from bottom to top;

[0006] The Y-axis strain sensing layer is provided with a first inlet, a first outlet and a first flow channel;

[0007] The X-axis strain sensing layer is provided with a second inlet, a second outlet, and a second flow channel;

[0008] The lower electrode array layer is provided with a third inlet, a third outlet, and a first matrix electrode array;

[0009] A micro-pillar array is disposed on the micro-pillar dielectric layer;

[0010] The upper electrode array layer is provided with a fourth inlet, a fourth outlet, and a second matrix electrode array;

[0011] The first exit is connected to the second entrance, and the second exit is connected to the third entrance;

[0012] Positioning holes for positioning and installation are provided around the Y-axis strain sensing layer, X-axis strain sensing layer, lower electrode array layer, micropillar dielectric layer, and upper electrode array layer.

[0013] Preferably, the liquid metal enters through the first inlet, flows through the first flow channel and exits from the first outlet into the X-axis strain sensing layer;

[0014] After the liquid metal enters through the second inlet, it flows out through the second outlet via the second flow channel and enters the lower electrode array layer.

[0015] Liquid metal enters through the third inlet, passes through the first matrix electrode array, and flows out through the third outlet.

[0016] Liquid metal enters from the fourth inlet, passes through the second matrix electrode array, and flows out from the fourth outlet.

[0017] Preferably, the first flow channel on the Y-axis strain sensor layer and the second flow channel on the X-axis strain sensor layer are both wavy; and the central angle of the wavy flow channel is in the range of 60-180°.

[0018] Preferably, the electrode array structures on the lower electrode array layer and the upper electrode array layer are rectangular or circular structures.

[0019] Preferably, the micro-pillar array on the micropillar dielectric layer is a pyramid structure, a pillar structure, or an arch structure.

[0020] Preferably, the micropillar dielectric layer, the lower electrode array layer, and the upper electrode array together constitute a capacitive pressure sensor.

[0021] Preferably, the liquid metal is one of gallium, gallium-indium alloy, or gallium-indium-tin alloy.

[0022] Preferably, the materials used for the Y-axis strain sensing layer, X-axis strain sensing layer, lower electrode array layer, and upper electrode array layer are all silicone rubber polymers; the material used for the micropillar dielectric layer is PDMS.

[0023] A method for fabricating a multimodal flexible sensor based on liquid metal includes the following specific steps:

[0024] S1. Using laser cutting, liquid metal inlets, outlets, and corrugated channels are processed on the Y-axis strain sensing layer and X-axis strain sensing layer of silicone rubber. Liquid metal inlets, outlets, and matrix arrays are also processed on the lower electrode array layer and upper electrode array layer. The positions of the first liquid outlet and the second inlet are aligned, and the positions of the second outlet and the third inlet are aligned.

[0025] S2. The structure of a micro-pillar array in a micro-pillar dielectric layer is fabricated using soft photolithography.

[0026] S3. The processed silicone rubber film and PDMS are placed in a plasma cleaner for surface modification. After removal, the Y-axis strain sensing layer, X-axis strain sensing layer and lower electrode array layer are bonded from bottom to top using positioning holes. Then, the micropillar dielectric layer and upper electrode array layer are bonded.

[0027] S4. Liquid metal is injected through the first inlet, and the liquid metal will sequentially fill the Y-axis strain sensing layer, X-axis strain sensing layer 2 and the lower electrode array layer, and then flow out from the third outlet; liquid metal is injected through the fourth inlet, and after filling the upper electrode array layer, it flows out from the fourth outlet.

[0028] S5. After filling the two parts with liquid metal, put them into a plasma cleaner for surface modification, and then bond them together after taking them out.

[0029] S6. Lead the wires out from the corresponding liquid metal inlet and outlet, and encapsulate them to obtain a multimodal flexible sensor.

[0030] Preferably, each of the Y-axis strain sensing layer, X-axis strain sensing layer, lower electrode array layer, micropillar dielectric layer and upper electrode array layer is connected to each other through a modified silicone rubber film.

[0031] Compared with the prior art, the present invention has the following beneficial technical effects:

[0032] This invention combines Y-axis strain sensing, X-axis strain sensing, and pressure sensing to form a flexible multimodal sensor. It realizes strain sensing functions in the X and Y directions and pressure sensing functions in the Z direction through a single sensor, which greatly expands the application range of the sensor.

[0033] The flexible strain sensor in the X and Y axes employs a wave-shaped flow channel structure, which differs from the existing straight flow channel structure. This wave-shaped flow channel structure effectively reduces hysteresis and provides high resolution and fast response time. The dielectric layer of the flexible pressure sensor uses a micropillar structure, unlike capacitive sensors without microstructures. The use of a microstructure in the pressure sensor not only improves sensitivity but also expands the pressure measurement range. Liquid metal is used as the active material, which has lower viscosity, thus improving the sensor's ductility.

[0034] Furthermore, by utilizing laser cutting and soft lithography processes and employing a vertical stacking method, the flexible multimodal sensor can achieve a compact structure, making it widely applicable in wearable devices, health monitoring, soft robots, and other fields. Attached Figure Description

[0035] Figure 1 This is an exploded view of the present invention;

[0036] Figure 2 This is a schematic diagram of the Y-axis strain sensing layer.

[0037] Figure 3 This is a schematic diagram of the X-axis strain sensing layer.

[0038] Figure 4 This is a schematic diagram of the lower electrode array layer;

[0039] Figure 5 This is a schematic diagram of the micropillar dielectric layer structure;

[0040] Figure 6 This is a schematic diagram of the upper electrode array layer;

[0041] Figure 7 This is a schematic diagram of the principle of a flexible capacitive sensor.

[0042] Reference numerals: 1. Y-axis strain sensing layer; 11. First inlet; 12. First outlet; 13. First flow channel; 2. X-axis strain sensing layer; 21. Second inlet; 22. Second outlet; 23. Second flow channel; 3. Lower electrode array layer; 31. Third inlet; 32. First matrix electrode array; 33. Third outlet; 4. Micropillar dielectric layer; 41. Micropillar array; 5. Upper electrode array layer; 51. Fourth inlet; 52. Second matrix electrode array; 53. Fourth outlet. Detailed Implementation

[0043] Example 1

[0044] like Figure 1As shown, an embodiment of the present invention provides a multimodal flexible sensor based on liquid metal, comprising, from bottom to top, a Y-axis strain sensing layer 1, an X-axis strain sensing layer 2, a lower electrode array layer 3, a micropillar dielectric layer 4, and an upper electrode array layer 5.

[0045] like Figure 2 As shown, the Y-axis strain sensing layer 1 is provided with a first inlet 11, a first outlet 12 and a first flow channel 13;

[0046] like Figure 3 As shown, the X-axis strain sensing layer 2 is provided with a second inlet 21, a second outlet 22, and a second flow channel 23;

[0047] like Figure 4 As shown, the lower electrode array layer 3 is provided with a third inlet 31, a third outlet 33 and a first matrix electrode array 32;

[0048] like Figure 5 As shown, a micro-pillar array 41 is disposed on the micro-pillar dielectric layer 4;

[0049] like Figure 6 As shown, a fourth inlet 51, a fourth outlet 53, and a second matrix electrode array 52 are provided on the upper electrode array layer 5.

[0050] The first exit 12 is connected to the second entrance 21, and the second exit 22 is connected to the third entrance 31;

[0051] Positioning holes for positioning and installation are provided around the Y-axis strain sensing layer 1, X-axis strain sensing layer 2, lower electrode array layer 3, micropillar dielectric layer 4, and upper electrode array layer 5.

[0052] like Figure 1 As shown, an embodiment of the present invention discloses a multimodal flexible sensor based on liquid metal, which is assembled from bottom to top using four positioning holes on each layer. First, the Y-axis strain sensing layer 1, the X-axis strain sensing layer 2, and the lower electrode array layer 3 are assembled into one module. Next, the micropillar dielectric layer 4 and the upper electrode array layer 5 are assembled into another module. Finally, the two modules are assembled together. The first outlet 12 is connected to the second inlet 21, and the second outlet 22 is connected to the third inlet 31.

[0053] like Figure 2The diagram shows the structure of the Y-axis strain sensing layer. A first inlet 11, a first outlet 12, and a first flow channel 13 are fabricated using laser cutting. Liquid metal is injected from the inlet and flows out through the wavy flow channel to the next stage. When a tensile force along the Y-direction is applied to the sensor, the microchannels within the sensor are stretched along the direction of the force. Due to the tensile force, the length L and cross-sectional area S of the microchannels change, and the liquid metal changes shape along with the microchannels, causing changes in the length and cross-sectional area of ​​the liquid metal, thus resulting in a change in the output resistance.

[0054] In this embodiment of the invention, the microchannel structure is designed as a wave shape. Compared with the straight channel structure, under the same deformation, the wave-shaped channel will generate uneven stress. The maximum stress is concentrated inside and around the wave-shaped channel, which will produce uneven lateral contraction. Furthermore, since the axial stress of the shear stress will suppress viscoelasticity during unloading, the hysteresis effect of the strain sensor will be reduced.

[0055] like Figure 7 The diagram shows the principle of a flexible capacitive sensor. The lower electrode array layer 3, the micropillar dielectric layer 4, and the upper electrode array layer 5 constitute a capacitive flexible pressure sensor. When the sensor is subjected to pressure, the capacitive pressure sensor converts the effect of external pressure into a change in capacitance in the sensing area. Generally, the change in capacitance is controlled by changing the electrode area, changing the dielectric constant, and changing the distance between the electrodes.

[0056] In this embodiment of the invention, a dielectric layer with a micropillar structure is fabricated using soft photolithography. When subjected to pressure, on the one hand, the presence of the micropillar structure increases the voids in the dielectric layer, allowing for greater deformation under external pressure, resulting in a more significant change in the distance between the two electrodes. On the other hand, since the dielectric constant of PDMS is greater than that of air, the micropillar structure is compressed under external pressure, and the air between the micropillars is occupied by the PDMS matrix, which is equivalent to increasing the dielectric constant of the dielectric layer. Compared with a dielectric layer without a microstructure, the sensitivity of the flexible capacitive sensor using a micropillar structure is significantly improved, and the pressure measurement range of the sensor is also expanded.

[0057] In this embodiment of the invention, the electrode layers of the flexible capacitive sensor are a lower electrode array layer 3 and an upper electrode array layer 5, both of which are designed as array electrodes. Figure 6 The area shown in Figure 55 is subjected to pressure. The distance between the electrodes in this area changes more significantly than in other areas, resulting in a more pronounced change in capacitance. By utilizing the advantages of the array electrodes, the sensor can not only measure the magnitude of the pressure but also determine the area on the sensor where the pressure is applied. This facilitates the application of the sensor in a wider range of fields.

[0058] Example 2

[0059] like Figure 1 As shown, this invention proposes a method for fabricating a multimodal flexible sensor based on liquid metal, comprising the following steps:

[0060] Step S1: Using laser cutting, liquid metal inlets, outlets, and wavy flow channels are processed on the silicone rubber for the Y-axis strain sensing layer 1 and X-axis strain sensing layer 2. Liquid metal inlets, outlets, and matrix arrays are also processed on the lower electrode array layer 3 and upper electrode array layer 5. The positions of the first outlet 12 and the second inlet 21 are aligned, and the positions of the second outlet 22 and the third inlet 31 are aligned.

[0061] Step S2: The structure of the micro-pillar array 41 in the micro-pillar dielectric layer 4 is fabricated using soft photolithography.

[0062] Step S3: The processed silicone rubber film and PDMS are placed in a plasma cleaner for surface modification. After removal, the Y-axis strain sensing layer 1, X-axis strain sensing layer 2 and lower electrode array layer 3 are bonded sequentially from bottom to top using positioning holes. Then, the micropillar dielectric layer 4 and upper electrode array layer 5 are bonded. Each layer is connected to the other through the modified silicone rubber film.

[0063] Step S4: Inject liquid metal through the first inlet 11. The liquid metal will sequentially fill the Y-axis strain sensing layer 1, the X-axis strain sensing layer 2 and the lower electrode array layer 3, and then flow out from the third outlet 33. Inject liquid metal through the fourth inlet 51. After filling the upper electrode array layer 5, it will flow out from the fourth outlet 53.

[0064] Step S5: After filling the two parts with liquid metal, put them into a plasma cleaner for surface modification, and then bond them together after taking them out.

[0065] Step S6: Lead the wires out from the corresponding liquid metal inlet and outlet, and encapsulate them to obtain a multimodal flexible sensor.

[0066] This invention utilizes laser cutting and soft lithography processes and employs a vertical stacking method to make the flexible multimodal sensor compact in structure, which can be widely used in wearable devices, health monitoring, soft robots and other fields.

[0067] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A liquid metal based multi-modal flexible sensor, characterized in that, It includes a Y-axis strain sensing layer (1), an X-axis strain sensing layer (2), a lower electrode array layer (3), a micropillar dielectric layer (4), and an upper electrode array layer (5) arranged sequentially from bottom to top. The Y-axis strain sensing layer (1) is provided with a first inlet (11), a first outlet (12) and a first flow channel (13). The X-axis strain sensing layer (2) is provided with a second inlet (21), a second outlet (22), and a second flow channel (23); The lower electrode array layer (3) is provided with a third inlet (31), a third outlet (33) and a first matrix electrode array (32). A micro-pillar array (41) is disposed on the micro-pillar dielectric layer (4); The upper electrode array layer (5) is provided with a fourth inlet (51), a fourth outlet (53), and a second matrix electrode array (52); The first exit (12) is connected to the second entrance (21), and the second exit (22) is connected to the third entrance (31); Positioning holes for positioning and installation are provided around the Y-axis strain sensing layer (1), X-axis strain sensing layer (2), lower electrode array layer (3), micropillar dielectric layer (4) and upper electrode array layer (5). The state metal enters through the first inlet (11), flows out through the first flow channel (13) and exits through the first outlet (12) into the X-axis strain sensing layer (2); After the liquid metal enters through the second inlet (21), it flows out through the second outlet (22) through the second flow channel (23) and enters the lower electrode array layer (3); After the liquid metal enters through the third inlet (31), it flows out through the first matrix electrode array and exits through the third outlet (33); Liquid metal enters from the fourth inlet (51), passes through the second matrix electrode array (52), and flows out from the fourth outlet (53).

2. The liquid metal based multi-modal flexible sensor of claim 1, wherein: The first flow channel (13) on the Y-axis strain sensor layer (1) and the second flow channel (23) on the X-axis strain sensor layer (2) are both wavy; and the central angle of the wavy flow channel is in the range of 60-180°.

3. The multimodal flexible sensor based on liquid metal according to claim 1, characterized in that: The electrode array structures on the lower electrode array layer (3) and the upper electrode array layer (5) are rectangular or circular.

4. The multimodal flexible sensor based on liquid metal according to claim 1, characterized in that: The micro-pillar array (41) on the micro-pillar dielectric layer (4) is a pyramid structure, a pillar structure or an arch structure.

5. The multimodal flexible sensor based on liquid metal according to claim 1, characterized in that: The micropillar dielectric layer (4), the lower electrode array layer (3), and the upper electrode array (5) together constitute a capacitive pressure sensor.

6. The multimodal flexible sensor based on liquid metal according to claim 1, characterized in that: Liquid metal is one of gallium, gallium-indium alloy, or gallium-indium-tin alloy.

7. The multimodal flexible sensor based on liquid metal according to claim 1, characterized in that: The materials used for the Y-axis strain sensing layer (1), X-axis strain sensing layer (2), lower electrode array layer (3) and upper electrode array layer (5) are all silicone rubber polymers; the material used for the micropillar dielectric layer (4) is PDMS.

8. A method for fabricating a multimodal flexible sensor based on liquid metal, characterized in that: The specific steps include the following: S1. Using laser cutting, liquid metal inlet, outlet and wave-shaped flow channel are processed on the Y-axis strain sensing layer (1) and X-axis strain sensing layer (2) on silicone rubber. Liquid metal inlet, outlet and matrix array are processed on the lower electrode array layer (3) and upper electrode array layer (5). The positions of the first liquid outlet (12) and the second inlet (21) are aligned, and the positions of the second outlet (22) and the third inlet (31) are aligned; S2. The structure of the micro-pillar array (41) in the micro-pillar dielectric layer (4) is fabricated using soft photolithography. S3. The processed silicone rubber film and PDMS are placed in a plasma cleaner for surface modification. After taking them out, the Y-axis strain sensing layer (1), X-axis strain sensing layer (2) and lower electrode array layer (3) are bonded from bottom to top using positioning holes. Then, the micropillar dielectric layer (4) and upper electrode array layer (5) are bonded. S4. Liquid metal is injected through the first inlet (11). The liquid metal will sequentially fill the Y-axis strain sensing layer (1), the X-axis strain sensing layer (2) and the lower electrode array layer (3), and flow out from the third outlet (33). Liquid metal is injected through the fourth inlet (51). After filling the upper electrode array layer (5), it flows out from the fourth outlet (53). S5. After filling the two parts with liquid metal, put them into a plasma cleaner for surface modification, and then bond them together after taking them out. S6. Lead the wires out from the corresponding liquid metal inlet and outlet, and encapsulate them to obtain a multimodal flexible sensor.

9. The method for fabricating a multimodal flexible sensor based on liquid metal according to claim 8, characterized in that: The Y-axis strain sensing layer (1), X-axis strain sensing layer (2), lower electrode array layer (3), micropillar dielectric layer (4) and upper electrode array layer (5) are connected in pairs through a modified silicone rubber film.

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