WO2020228253A1

WO2020228253A1 - Flexible sensor and preparation method therefor

Info

Publication number: WO2020228253A1
Application number: PCT/CN2019/114306
Authority: WO
Inventors: 刘宜伟; 李法利; 李润伟
Original assignee: 中国科学院宁波材料技术与工程研究所
Priority date: 2019-05-13
Filing date: 2019-10-30
Publication date: 2020-11-19
Also published as: CN110017923A

Abstract

A flexible sensor and a preparation method therefor. The flexible sensor comprises a flexible substrate (1), electrodes (10), a liquid metal thin film (13), and a flexible encapsulation layer (11); the liquid metal thin film (13) is located on the flexible substrate (1), and is composed of surface oxidized liquid metal particles (8, 9); the flexible encapsulation layer (11) is located on the surface of the liquid metal thin film (13); the electrodes (10) are located on the flexible substrate (1) and are used to monitor electrical signals between certain regions of the liquid metal thin film (13); and under the action of an external force, the resistance between the electrodes (10) changes from high resistance to low resistance, and then the external force is determined to be a harmful external force. The present flexible sensor may sense external harmful action forces, and the integration of the sensor in electronic skin may expand the function of the electronic skin.

Description

Flexible sensor and preparation method thereof

Technical field

The invention relates to the technical field of flexible electronics, in particular to a flexible sensor and a preparation method thereof

Background technique

With the development of industries such as robots and smart prostheses, there is an increasing demand for electronic skins with highly flexible human-like skins. At present, people have developed a series of flexible sensing elements for electronic skin, such as pressure, temperature, stretch and other signal sensing elements. The integration and functional complexity of electronic skin are gradually improving.

People have always imitated human skin to design electronic skins. The external signals received by the human skin can be divided into two categories, innocuous signals that are non-damaging to the skin structure and noxious signals that are damaging to the skin structure. A large number of sensors that detect innocuous signals are distributed in the dermis, and a large number of sensors that monitor noxious signals are distributed in the epidermis to protect the internal sensor system, so that the entire system works stably.

At present, sensors for detecting innocuous signals are developing rapidly, and sensors for sensing innocuous signals are rarely implemented. Therefore, providing a sensor that can sense damage to the skin can further expand the electronic skin function.

Summary of the invention

In view of the foregoing technical status, the present invention aims to provide a flexible sensor capable of sensing external harmful forces, and integrating the sensor into an electronic skin can expand the function of the electronic skin.

In order to achieve the above technical objectives, the technical solution provided by the present invention is: a flexible sensor including a flexible substrate, an electrode, a liquid metal film, and a flexible packaging layer;

The liquid metal film is located on a flexible substrate and is composed of liquid metal particles oxidized on the surface;

The flexible packaging layer is located on the surface of the liquid metal film;

The electrode is located on the flexible substrate and is used to monitor the electrical signal between a certain area of the liquid metal film;

Under the action of an external force, the resistance between the electrodes changes from a high resistance to a low resistance, and the external force is judged to be a harmful external force.

The flexible substrate is flexible and can be deformed such as bending, stretching, twisting, etc. In addition, the flexible substrate does not infiltrate the liquid metal, that is, the contact angle of the liquid metal on the surface of the flexible substrate is relatively large, and the liquid metal particles are island-shaped on the surface of the flexible substrate, that is, they cannot be spread out to form a covering layer.

The flexible substrate material is not limited, including polydimethylsiloxane (PDMS), PU, PI, PET, PVC, etc.

The liquid metal includes, but is not limited to, gallium (Ga), gallium (Ga)-indium (In) alloy, gallium (Ga)-indium (In)-tin (Sn) alloy, and transition metals, solid non-metallic elements One or more doped gallium, gallium indium alloy, gallium indium tin alloy, etc.

The electrode has good conductivity. The electrode material is not limited and includes liquid metal and solid metal.

Preferably, in the liquid metal film, the liquid metal particles oxidized on the surface are connected to each other.

Preferably, the electrode is a flexible electrode, which can undergo deformation such as bending, stretching, twisting, etc., and is an excellent conductor under deformation conditions.

In order to improve the detection sensitivity to harmful external forces, the electrodes are distributed in an array to increase the electrode distribution density, thereby improving the conductivity monitoring of the electrodes to each area of the liquid metal film. The electrode array material is not limited, including liquid metal, silver nanowires, copper nanowires, graphene, carbon nanotubes, etc.

The flexible packaging layer is flexible and can be deformed such as bending, stretching, twisting, etc. The material of the flexible encapsulation layer is not limited, including polydimethylsiloxane (PDMS), PU, PI, PET, PVC, etc. Preferably, the flexible packaging layer material adopts a flexible material with modified self-healing, such as modified self-healing PDMS, and modified self-healing PI.

The action form of the external force is not limited, and may be mechanical force, pressure, gravity, etc.

The present invention also provides a method for preparing the above-mentioned flexible sensor, which includes the following steps:

(1) Prepare electrodes on the surface of the flexible substrate;

(2) Put the flexible substrate in the cavity, use physical vapor deposition technology after vacuuming, deposit liquid metal particles on the surface of the flexible substrate, and then let air enter the cavity, and the liquid metal particles are oxidized;

In this step (2), the liquid metal particles are deposited on the surface of the flexible substrate and grow in an island shape to obtain discrete liquid metal particles. After oxidation, a nano-scale oxide film is formed on the surface of the liquid metal particles, so that the liquid metal particles are in an insulating state. ；

In this step (2), the physical vapor deposition method is not limited, including resistance thermal evaporation coating technology, electron beam evaporation coating technology, magnetron sputtering coating technology, etc.

(3) A flexible packaging layer is prepared on the surface of the liquid metal film prepared in step (2).

Preferably, the step (2) is followed by the following step (2-1), and then the step (3):

(2-1) Repeat step (2) at least once;

In this step (2-1), the liquid metal particle film is grown again on the surface of the liquid metal particle film obtained in step (2), and the oxidized liquid metal particles obtained in the previous step can be connected to obtain a multilayer stack The liquid metal film can improve the connectivity of the oxidized liquid metal particles, thereby facilitating the formation of a conductive connection with the electrode due to the rupture of the oxide film on the surface of the liquid metal under the action of external force.

By adjusting the parameters of physical vapor deposition in step (2) and step (2-1), the resistance between the electrodes can be adjusted.

In the step (1), the method for preparing the electrode on the surface of the flexible substrate is not limited, including printing, coating, deposition and the like.

In the step (3), the method for preparing the flexible encapsulation layer is not limited, including printing, coating, deposition and the like.

The flexible sensor provided by the present invention utilizes the characteristics of island-like growth of liquid metal particles on the surface of the flexible substrate to obtain a liquid metal film composed of discrete surface-oxidized liquid metal particles, and measures the resistance between certain areas of the liquid metal film through electrodes In the initial state, the resistance between the electrodes is in a high resistance state. When an external force is applied, the flexible packaging layer is damaged under the external force, and the surface oxide film of the liquid metal particles is broken by the external force, and the liquid metal particles are connected to the electrodes to form a conductive state. During the passage, the resistance between the electrodes changes to a low resistance state, that is, the damage of the external force can be judged according to the change of the resistance state between the electrodes: when the flexible sensor is under the action of an external force, the resistance between the electrodes changes from a high resistance state When it is in a low resistance state, the external force is judged to be a harmful external force, and when the resistance remains in a high resistance state, the external force is judged to be a non-harmful external force. Compared with the prior art, the present invention has the following beneficial effects:

(1) The flexible sensor of the present invention can sense harmful external forces from the outside, and integrating the sensor into the electronic skin can expand the function of the electronic skin.

(2) Through the adjustment of the preparation process of the liquid metal film, the resistance between the electrodes before and after the external force is the insulating resistance value and the metal resistance value, so the resistance changes before and after the external force is large, and it has a higher switching ratio. Improve detection sensitivity.

(3) When the resistance between the electrodes is in a low resistance state, a voltage is applied across the electrodes. When the current exceeds a certain threshold, the liquid metal particles undergo electromigration, which disconnects the conductive path and the resistance between the electrodes can be restored To high impedance state. In this case, when the flexible packaging layer material is selected as a material with self-healing function, that is, the "wound" of the flexible packaging layer damaged by external force has self-healing properties, and the flexible sensor has functional and structural repair Ability, can be used multiple times.

(4) The flexible sensor of the present invention can be used in conjunction with an ordinary tactile sensor. The latter monitors the pressure strength and provides early warning before the skin is damaged, and the former is responsible for positioning and monitoring after the injury.

Description of the drawings

Fig. 1 is a schematic structural diagram of a flexible sensor in Embodiment 1 of the present invention.

Figure 2 is a schematic diagram of step (1) in the process of preparing a flexible sensor in Example 1 of the present invention.

Fig. 3 is a schematic diagram of step (2) in the process of preparing a flexible sensor in Example 1 of the present invention.

4 is a schematic diagram of step (3) in the process of preparing a flexible sensor in Example 1 of the present invention.

Fig. 5 is a schematic diagram of the sample structure obtained in step (3) in the process of preparing the flexible sensor in Example 1 of the present invention.

6 is a schematic diagram of step (4) in the process of preparing a flexible sensor in Example 1 of the present invention.

Fig. 7 is a schematic diagram of step (5) in the process of preparing a flexible sensor in Example 1 of the present invention.

FIG. 8 is a schematic diagram of the sample structure obtained in step (5) in the process of preparing the flexible sensor in Example 1 of the present invention.

Fig. 9 is a schematic structural diagram of a flexible sensor in which an external force is applied in the first embodiment of the present invention.

FIG. 10 is a schematic structural diagram of a flexible sensor in Embodiment 2 of the present invention.

Fig. 11 shows the resistance change of the flexible sensor in Example 1 of the present invention before and after the harmful external force is applied, and the resistance change under the applied current condition after the harmful external force is applied.

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the drawings. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on it.

The reference signs are: flexible substrate 1, evaporation boat 2, intake valve 3, vacuum pump solenoid valve 4, liquid metal droplets 5, cavity 6, liquid metal vapor 7, liquid metal particles 8, liquid metal particles 9, Electrode 10, encapsulation layer 11, blade 12, liquid metal film 13.

Example 1:

In this embodiment, the flexible sensor structure is shown in FIG. 1 and includes a flexible substrate 1, an electrode 10, a liquid metal film 13, and an encapsulation layer 11.

The liquid metal film 13 is located on the flexible substrate 1 and is composed of liquid metal particles whose surface is oxidized.

The packaging layer 11 is located on the surface of the liquid metal film.

The electrode is located on the flexible substrate and is used to monitor the electrical signal between a certain area of the liquid metal film.

The flexible substrate 1 uses a self-healing PU material. The packaging layer 11 is made of self-repairing PU material.

The electrode is a strip liquid metal/copper electrode formed by the combination of liquid metal and micron copper powder. The liquid metal is a gallium indium tin alloy. The weight percentage of each element is: Ga 67.5%, In 22.5%, Sn 10% .

The preparation method of the flexible sensor is as follows:

(1) As shown in FIG. 2, two rows of strip-shaped liquid metal/copper electrodes 10 are formed on the flexible substrate 1 by stencil printing.

(2) As shown in Figure 3, the flexible substrate processed in step (1) is placed in the cavity 6 of the thermal evaporation device. The cavity 6 is also provided with an evaporation boat 2, and 3ml of liquid metal droplets 5 are weighed and placed in In the evaporation boat 2, the liquid metal in this embodiment is gallium indium tin alloy, and the vacuum pump solenoid valve 4 is turned on to vacuum the cavity to a pressure of less than 3×10 ⁴ Pa.

(3) As shown in Figure 4, the evaporation power is turned on, the liquid metal droplets 5 in the evaporation boat 2 evaporate to form steam 7, and a thin film composed of liquid metal particles 8 is deposited on the surface of the flexible substrate 1. The surface of the substrate 1 grows as discrete islands, and the evaporation time is controlled to be 5 minutes, and the diameter of the liquid metal particles can reach 10 microns; then, the evaporation is stopped, the vacuum pump solenoid valve 4 is closed, the intake valve 3 is opened, and air is released into the cavity to make liquid An oxide layer about 3 nm thick is formed on the metal surface, and the sample structure shown in FIG. 5 is obtained.

(4) As shown in Figure 6, put the sample obtained in step (3) into the cavity 6 again, replenish the liquid metal droplets 5 in the evaporation boat 2 to 3ml, turn on the vacuum pump solenoid valve 4 to vacuum the cavity to The air pressure is less than 3×10 ⁴ Pa.

(5) As shown in Figure 7, the evaporation power is turned on, the liquid metal droplets 5 in the evaporation boat 2 evaporate to form steam 7, and liquid metal particles 9 are deposited on the film surface of the flexible substrate 1, and the evaporation time is controlled to 2 minutes. The diameter of the particles 9 can reach about 4 microns; then, stop evaporation, close the vacuum pump solenoid valve 4, open the intake valve 3, and release air into the cavity, so that a layer of about 3nm thick oxide layer is formed on the surface of the liquid metal particles 9 to obtain The sample structure is shown in Figure 8.

(6) Using coating technology, the encapsulation layer material is coated on the surface of the liquid metal film of the sample obtained in step (5), and then cured to obtain the encapsulation layer 11, and the sample structure shown in FIG. 1 is obtained.

When an external force acts on the encapsulation layer of the sample prepared above, it can be judged whether the external force is a harmful external force according to the resistance change between the electrodes. For example, as shown in FIG. 1, since the surface of the liquid metal particles in the liquid metal film 13 is an oxide film, the liquid metal film 13 is in an insulating state, and the resistance between the two ends of the electrode is in a high resistance state. As shown in Figure 9, an external force is applied to the packaging layer 11 with a knife 12. Under the external force, if the flexible packaging layer 11 is damaged and the surface oxide film of the liquid metal particles of the liquid metal particle film is broken by the external force, the liquid metal particles When a conductive path is formed with the electrode, the resistance between the electrodes changes to a low resistance state, as shown in Figure 11; if the liquid metal particles do not form a conductive path with the electrode, the resistance between the electrodes maintains a high resistance state. That is, before and after applying an external force with a knife, according to the change in the resistance state between the electrodes, it can be judged whether the external force is a harmful external force: when the resistance between the electrodes changes from a high resistance state to a low resistance state under the action of the external force, it is judged The external force is a harmful external force; when the resistance maintains a high resistance state, the external force is judged to be a non-damaging external force.

In addition, when the resistance between the electrodes changes to a low resistance state under the action of the external force, a voltage can be applied across the electrodes to control the current increase. As shown in Figure 11, when the current reaches 31mA, the resistance returns to a high resistance state, that is , The liquid metal particles undergo electromigration, so that the conductive path is disconnected, and the resistance between the electrodes is restored to a high resistance state. In addition, because the flexible packaging layer material PU has a self-repairing function, after 12 hours at room temperature, the "wound" of the flexible packaging layer damaged by the external force will heal naturally, so the flexible sensor has functional and structural repair Ability, can be used multiple times.

The flexible sensor in this embodiment is integrated in the electronic skin to expand the function of the electronic skin, and can sense, locate, and monitor harmful external forces.

Example 2:

In this embodiment, the structure of the flexible sensor is basically the same as that of the first embodiment. The difference is to improve the detection sensitivity of noxious external forces. It can detect not only lateral external forces but also longitudinal external forces. This embodiment The flexible sensor in Example 1 is composed of two parts. The structure of the first part is exactly the same as the structure of the flexible sensor in Example 1. The second part of the structure is obtained by rotating the flexible sensor structure in Example 1 clockwise by 90°. Partially laminated to obtain a flexible sensor.

The above-mentioned embodiments describe the technical solutions of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Anything done within the scope of the principles of the present invention Any modification, supplement or substitution in a similar manner shall be included in the protection scope of the present invention.

Claims

A flexible sensor, which is characterized by: comprising a flexible substrate, an electrode, a liquid metal film, and a flexible packaging layer;

The liquid metal film is located on a flexible substrate and is composed of liquid metal particles oxidized on the surface;

The flexible packaging layer is located on the surface of the liquid metal film;

The electrode is located on the flexible substrate and is used to monitor the electrical signal between a certain area of the liquid metal film;

Under the action of an external force, the resistance between the electrodes changes from a high resistance to a low resistance, and the external force is judged to be a harmful external force.
The flexible sensor according to claim 1, wherein the flexible base material includes PDMS, PU, PI, PET, PVC.
The flexible sensor according to claim 1, wherein the liquid metal includes gallium, gallium-indium-alloy, gallium-indium-tin alloy, and one or more of transition metals and solid non-metallic elements. Mixed gallium, gallium indium alloy, gallium indium tin alloy.
The flexible sensor according to claim 1, wherein the liquid metal particles on the surface of the liquid metal film are connected to each other.
The flexible sensor according to claim 1, wherein the electrode is a flexible electrode.
The flexible sensor according to claim 1, wherein the electrodes are distributed in an array.
The flexible sensor according to claim 1, characterized in that: the material of the flexible packaging layer includes one or more of PDMS, PU, PI, PET, and PVC.
The flexible sensor according to claim 1, wherein the material of the flexible packaging layer is a flexible material with modified self-repair.
The flexible sensor according to claim 1, wherein the flexible base material is a flexible material with modified self-repair.
The flexible sensor according to claim 1, wherein when the resistance between the electrodes is low resistance, a voltage is applied across the electrodes, and when the current exceeds a certain threshold, the resistance between the electrodes returns to a high resistance state.
The method for preparing a flexible sensor according to any one of claims 1 to 10, characterized in that it comprises the following steps:

(1) Prepare electrodes on the surface of the flexible substrate;

(2) Put the flexible substrate in the cavity, use physical vapor deposition technology after vacuuming, deposit liquid metal particles on the surface of the flexible substrate, and then let air enter the cavity, and the liquid metal particles are oxidized;

(3) A flexible packaging layer is prepared on the surface of the liquid metal film prepared in step (2).
The method for preparing a flexible sensor according to claim 11, characterized in that: in the step (2), the physical vapor deposition method includes resistance thermal evaporation coating technology, electron beam evaporation coating technology, and magnetron sputtering coating technology. One or more.
The method for preparing a flexible sensor according to claim 11, characterized in that: after the step (2), the following step (2-1) is performed, and then the step (3) is performed:

(2-1) Repeat step (2) at least once.
The method for preparing a flexible sensor according to claim 13, wherein the resistance between the electrodes can be adjusted by adjusting the parameters of physical vapor deposition in step (2) and step (2-1).
The method for preparing a flexible sensor according to claim 11, characterized in that: in the step (1), the method for preparing electrodes on the surface of the flexible substrate includes printing, coating, and deposition.
The method for preparing a flexible sensor according to claim 11, wherein in the step (3), the method for preparing the flexible encapsulation layer includes printing, coating, and deposition.