Infrared sensor and preparation method thereof

Abstract

The present invention relates to an infrared sensor and a preparation method thereof, and belongs to the field of sensor technology. The infrared sensor of the present invention comprises: an elastic substrate, a package body and a sensing element; the package body comprises a connection area and a contact area, the connection area extends into the elastic substrate; a cavity is provided in the contact area, and a notch is provided above the cavity; the cavity is filled with a carbon nano-photothermal composite material; the sensing element is covered on the surface of the elastic substrate; the elastic substrate and the package body are bonded to the sensing element after interface treatment; the notch of the package body is located at the center of the sensing element. The present invention uses a carbon nano-photothermal composite material as a nano-photothermal source, based on a photomechanical braking unit with broad-spectrum absorption characteristics, to realize an infrared sensor device under irradiation from visible light to near-infrared and even mid-infrared wavelength light sources. The infrared sensor of the present invention has an independent flexible support structure, and has the characteristics of high responsiveness and fast response speed.

Description

Technical Field

[0001] The present invention relates to the field of sensor technology, and in particular to an infrared sensor and a preparation method thereof. Background Art

[0002] Infrared detection and sensing technology plays an important role in military and civilian fields, such as night vision, face recognition, intelligent sorting, blood oxygen detection, medical imaging, weather forecasting, molecular chemistry, etc. The mature infrared sensing technology now includes two categories: quantum type and thermal type. Quantum type devices use the photovoltage or photocurrent generated by the photoelectric effect of infrared photons and semiconductor sensing materials to detect infrared signals, and have the advantages of fast response, high sensitivity and high signal-to-noise ratio. However, the materials used in quantum sensing systems are generally semiconductor materials with low band gap energy, and electronic excitation is easily affected by thermal disturbances, which leads to excessive thermal noise of quantum devices at room temperature. It must rely on additional cooling systems to make it work at low temperatures, which greatly increases the weight and cost of the system. Unlike quantum devices, the working mechanism of thermal infrared sensing systems is based on the temperature change caused by the photothermal effect when the photothermal material is subjected to infrared radiation, and the corresponding physical property changes are generated to realize the detection of infrared radiation at room temperature. However, the existing infrared detection technology relies on various rigid semiconductor materials, which are brittle and not resistant to bending, and have poor processing flexibility. In addition, the raw materials used are relatively expensive, and coupled with the demanding and complicated processing and packaging processes, the cost is still too high.

[0003] One of the ideas for developing low-cost infrared sensing technology is to achieve infrared detection based on the photothermal effect of photothermal materials through the photothermal expansion mechanism of solid materials. Yao et al. proposed using polydopamine photothermal nanocomposites as photothermal conversion / photomechanical braking elements, using ultra-high sensitivity piezoresistive sensing units to sense the mechanical deformation of polydopamine photothermal nanocomposites under 808nm infrared light, thereby realizing the preparation of infrared sensors that read with resistance (Materials&Design 230(2023)111968). However, the responsiveness of the prepared infrared sensor to infrared sensing at a wavelength of 808nm is -1.4W. -1 -2.2W -1 , the sensitivity is still poor. In addition, it can only detect infrared light of a single wavelength. Therefore, it is still difficult to realize its application in practical occasions. More importantly, this design requires a piezoresistive sensing unit with a sensitivity far higher than that of commercial piezoresistive sensitive elements to detect the signal, which is still difficult to mass produce. In addition, because the device relies on a hard structural design, the configuration form of a flexible device has not yet been realized. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an infrared sensor and a preparation method and application thereof, and in particular, relates to a flexible infrared sensor for broad-spectrum detection and a preparation method and application thereof. First, the present invention uses a carbon nano-photothermal composite material as a nano-photothermal source to fill it into a package, and uses an elastic substrate to encapsulate the package of the obtained composite material to obtain a photomechanical brake element. Secondly, the present invention uses plasma treatment and silane coupling interface modification to perform interface treatment on the photomechanical brake element and the sensor element to enhance the bonding strength between the two and the stress transmission effect of photothermal deformation. The above process design can effectively transmit the tiny deformation signal generated by the photomechanical brake element during the photothermal braking process to the sensor element; it can significantly improve the responsiveness of the sensor, thereby realizing the detection of the signal using a commercial piezoresistive sensor element, which greatly reduces the difficulty of system integration. In addition, the present invention uses a carbon nano-photothermal source with broad-spectrum absorption ability to give the sensor the ability of broad-spectrum detection. Finally, the present invention adopts the method of elastic substrate packaging and interface bonding treatment, so that the prepared infrared sensor has an independent flexible support structure.

[0005] The infrared sensor of the present invention works in the following way: infrared light is irradiated from below, passes through the hard package and is incident on the carbon nano-photothermal composite material, causing photothermal expansion of the carbon nano-photothermal composite material, triggering mechanical deformation and resistance change of the piezoresistive sensing element, thereby realizing the detection of infrared signals.

[0006] The present invention is achieved through the following technical solutions:

[0007] The first object of the present invention is to provide an infrared sensor, the infrared sensor comprising:

[0008] Elastic substrate (1);

[0009] The package (2) comprises a connection area (21) and a contact area (22), wherein the connection area (21) extends into the elastic substrate (1) to prevent it from falling off the elastic substrate; a cavity is provided in the contact area (22), and a notch is provided above the cavity; the cavity is filled with a carbon nanophotothermal composite material; and the contact area (22) allows infrared light to pass through and be incident on the photothermal composite material in the package.

[0010] A sensing element (3) covering the surface of the elastic substrate (1) and the packaging body (2);

[0011] The elastic substrate and the packaging body are bonded to the sensor element after interface treatment; the notch of the packaging body is located at the center of the sensor element.

[0012] In one embodiment of the present invention, the elastic substrate is selected from one or more of natural rubber, synthetic rubber, silicone rubber, styrene-butadiene rubber and fluororubber.

[0013] In one embodiment of the present invention, the package meets the following conditions:

[0014] 1) The encapsulation body is selected from one or more of infrared transparent crystals, glass and polymers; preferably polymers; the polymers are selected from one or more of polycarbonate, polymethyl methacrylate, polystyrene and polytetrachloroethylene; the encapsulation body has a modulus of >3 GPa and an infrared transmittance of >90%;

[0015] 2) The package is cylindrical or spherical, and the cavity volume of the package is less than 2 mm 2 ;

[0016] 3) The ratio of the notch area of ​​the package to the cavity area of ​​the package is ≤1 / 6; preferably, the ratio of the notch area of ​​the package to the cavity area of ​​the package is ≤1 / 60, so as to concentrate the thermal expansion generated by photothermal energy on the notch.

[0017] In one embodiment of the present invention, the carbon nano-photothermal composite material is prepared by the following method:

[0018] Firstly, the carbon nanomaterial is dispersed in an organic solvent, and then a polymer is added to obtain a carbon nanophotothermal composite material; the doping ratio of the carbon nanomaterial to the polymer is 0.05wt%-5wt%;

[0019] The carbon nanomaterial is selected from one or more of carbon nanotubes, graphene and graphite nanosheets; the polymer is selected from one or more of polyethylene, polypropylene, high temperature silicone rubber, polyimide and polyphenylene sulfide. The thermal expansion coefficient of the polymer is greater than 50ppm / °C, and the modulus is less than 10MPa.

[0020] In one embodiment of the present invention, the dispersion is carried out by milling, ultrasound, stirring or homogenization;

[0021] In one embodiment of the present invention, the sensing element is selected from one or more of a silicon film, a carbon film and a silicon carbide film having piezoresistive properties; the piezoresistive sensitivity coefficient of the sensing element is greater than 200;

[0022] In one embodiment of the present invention, the interface treatment is first plasma treatment and then silane coupling treatment.

[0023] In one embodiment of the present invention, the conditions for the plasma treatment are: using oxygen as the atmosphere, the gas flow rate is 0.2L / min-2L / min, and the plasma treatment time is 1min-20min.

[0024] In one embodiment of the present invention, the silane coupling treatment method is: immersing the elastic substrate and the sensor element in a silane coupling agent with bonding ability. Specifically, the elastic substrate and the sensor element are immersed in two silane coupling agents with bonding ability respectively, and the two silane coupling agents can react with each other; the mass concentration of the silane coupling agent is 0.1%-1%; and the immersion time is 0.5h-12h.

[0025] In one embodiment of the present invention, the bonding conditions are: bonding at 25° C.-100° C. for 1 h-24 h under a pressure of 5 MPa-20 MPa.

[0026] The second object of the present invention is to provide a method for preparing an infrared sensor, comprising the following steps:

[0027] Filling the carbon nano-photothermal composite material into the package to obtain a package filled with the composite material;

[0028] The encapsulation body of the obtained composite material is encapsulated using an elastic substrate to obtain an optomechanical braking element;

[0029] The obtained photomechanical braking element and the sensing element are subjected to interface treatment and bonded to obtain the infrared sensor.

[0030] In the present invention, the micro deformation signal generated by the optomechanical brake element after the interface bonding optimization treatment during the photothermal braking process can be effectively transmitted to the sensing element, so that a highly responsive infrared sensor can be obtained. In the infrared sensing unit without interface treatment, the sensing element and the optomechanical brake element are in physical contact, which limits the stress transmission efficiency between the two, so that the responsiveness of the infrared sensor in the optomechanical sensing mode is low. In addition, the present invention uses an encapsulation body of a composite material obtained by an elastic substrate for encapsulation to obtain an infrared sensor with an independent flexible support structure. In the present invention, the elastic substrate of the flexible support structure plays a heat insulation role on the one hand, effectively reducing the heat diffusion of the optomechanical brake element to the surrounding environment, thereby improving the photothermal conversion efficiency of the carbon nanocomposite material and the responsiveness of the sensor. On the other hand, the stress relaxation phenomenon of the sensing element supported by the elastic substrate is improved, so that the effect of the photothermal expansion at the notch on the sensing element is mainly used to cause the out-of-plane bending deformation of the sensing element, which also leads to the improvement of the responsiveness of the infrared sensor proposed by the present invention. Therefore, the high-performance flexible infrared sensor proposed by the present invention not only depends on the improvement of the bonding strength between the optomechanical brake element and the sensing element, but also has a close relationship with the structural design of the sensor. To this end, in the technical solution of optimizing interface bonding and designing flexible device structure to prepare high-response infrared sensor proposed by the present invention, the piezoresistive sensitivity coefficient of piezoresistive sensor element is greatly reduced, so that the integration and manufacture of infrared sensor can be realized by using commercial piezoresistive sensor element. In addition, the structural design of all-solid-state and resistance reading mode also makes the infrared sensor proposed by the present invention easy to manufacture and assemble.

[0031] The above technical solution of the present invention has the following advantages compared with the prior art:

[0032] (1) The present invention uses carbon nanomaterials as nano-photothermal sources and is based on a photomechanical braking unit with broad-spectrum absorption characteristics, thereby realizing infrared sensing devices under irradiation from visible light to near-infrared and even mid-infrared wavelength light sources.

[0033] (2) The infrared sensor proposed in the present invention has the characteristics of high responsiveness and fast response speed.

[0034] (3) The infrared sensor prepared by the present invention has an independent flexible support structure.

[0035] (4) Since the sensor has high sensitivity, commercial piezoresistive sensing elements can be used to detect the signal, reducing the difficulty and cost of system integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein

[0037] Figure 1 1 is a schematic diagram of the structure of the mid-infrared sensor of the present invention; wherein 1 is an elastic substrate; 2 is a package body; 21 is a connection area; 22 is a contact area; 3 is a sensing element; h1 is 1 mm-10 mm; h2 is 0.5 mm-9 mm; w is 0.5 mm-5 mm;

[0038] Figure 2 is the response behavior of the infrared light power experimentally measured by the flexible infrared sensor prepared in Example 1 under 808nm laser irradiation;

[0039] Figure 3 is the time response behavior of infrared light power experimentally measured by the flexible infrared sensor prepared in Example 1 under 808nm laser irradiation;

[0040] Figure 4 This is the time response behavior of the infrared light power experimentally measured by the flexible infrared sensor prepared in Example 2 under 675nm laser irradiation. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0042] like Figure 1 As shown, the infrared sensor provided by the present invention comprises: 1-elastic substrate; 2-package; 21-connection area; 22-contact area; 3-sensing element. Infrared light passes through the package from the contact area 22 upwards, irradiates the carbon nano-photothermal composite material to cause photothermal expansion, and triggers mechanical deformation and resistance change of the piezoresistive film on the supporting film in the sensing element, thereby realizing the detection of infrared signals.

[0043] Example 1

[0044] This embodiment provides a method for preparing an infrared sensor, and the specific method is as follows:

[0045] Single-walled carbon nanotubes were selected as photothermal nanoparticles. First, they were added to n-hexane and ultrasonically dispersed to form a 1 mg / mL dispersion. After forming a uniform mixture with a polyimide precursor, the n-hexane solution was removed to finally obtain a polymer mixture with a carbon nanotube content of 0.2 wt.%. 3D-printed polycarbonate was used as a packaging structure, with a spherical cavity with a diameter of 2 mm in the packaging structure, and a cylindrical cavity with a diameter of 100 μm and a height of 100 μm directly above the cavity. The above polymer mixture was poured into the cavity structure, and the polyimide prepolymer was cured by heating. The above package was embedded with silicone rubber to form a soft package (i.e., an elastic substrate), and then a photomechanical brake element was prepared; wherein the size of the soft package structure was 20 mm×10 mm×1.6 mm. A 1.5 mm×1.5 mm window was opened at the bottom center of the soft package, so that subsequent infrared light could be directly radiated to the surface of the hard package. A commercially available silicon strain gauge (piezoresistive sensitivity coefficient 200) is used as the sensing element.

[0046] The above-obtained optomechanical brake element and piezoresistive strain gauge film were subjected to interface treatment. First, the two sensor components were treated with O2 plasma for 20 minutes to introduce hydroxyl groups on the surface. Then, the two were immersed in an isopropanol solution of 3-mercaptopropyltrimethoxysilane (1% v / v) and a methanol solution of 3-glycidyloxypropyltrimethoxysilane (1% v / v) for 1 hour. The strain gauge was then covered on the surface of the elastic substrate; so that the notch protrusion structure of the package was in the center of the silicon area in the strain gauge. After that, a pressure of 5MPa was applied to the two and they were left to stand for 12 hours. 3-mercaptopropyltrimethoxysilane and 3-glycidyloxypropyltrimethoxysilane underwent a click reaction to form a thiol-epoxy bond, completing the bonding between the two.

[0047] The infrared sensor obtained in this embodiment detects infrared signals by transmitting infrared light through the package and incident on the carbon nano-photothermal composite material, causing photothermal expansion of the carbon nano-photothermal composite material, inducing mechanical deformation and resistance change of the strain gauge.

[0048] The response behavior of the device under 808nm near-infrared light irradiation was tested. Figure 2 The results show that the relative resistance change of the sensor is linearly related to the infrared light power. The linear fitting calculation shows that the sensor's responsivity is 51.6W. -1 .

[0049] The time response behavior of the flexible sensor was tested using different powers. Figure 3 As shown. Figure 3It can be seen that as the infrared light is turned on, the relative resistance of the mechanical deformation sensing unit rises rapidly and then gradually stabilizes. Taking the time for the resistance change to reach 63.2% of the stable value as the response time, it can be obtained that when the power is 17.1mW, 46.2mW and 72.4mW, the experimentally measured response time of the infrared sensor is 3.2s, 3.1s and 2.6s respectively.

[0050] Example 2

[0051] This embodiment provides a method for preparing an infrared sensor, and the specific method is as follows:

[0052] The infrared sensor of this embodiment uses graphene as a photothermal nanomaterial and is composited with polysiloxane, with a filling amount of 0.5wt.%. The corresponding infrared sensor with bonding and flexible packaging is prepared. The responsiveness of the sensor at different wavelengths is characterized using 455nm, 520nm, 675nm, 808nm, 980nm and 1550nm light sources. The results of the relative resistance change of the sensor at 675nm and the incident light power are shown in Figure 2. Figure 4 As shown, from Figure 4 It can be seen that the two are in a linear relationship. Through linear fitting calculation, the responsivity of the sensor is 54.7W. -1 The responsivity test results at 455nm, 520nm, 808nm, 980nm and 1550nm are 52.7W respectively. -1 , 53.1W -1 、49.7W -1 、58.3W -1 and 51.6W -1 , the response behavior at different wavelengths shows similar sensitivity and does not show wavelength dependence.

[0053] Comparative Example 1

[0054] The structure of the sensor prepared in this comparative example is similar to that in Example 1, except that only the package and the elastic substrate are in physical contact with the strain gauge, and no bonding process is performed. The response behavior of the obtained sensor under 808nm near-infrared light irradiation was tested, and its sensitivity was 1W -1 .

[0055] Comparative Example 2

[0056] The sensor structure prepared in this comparative example is similar to that of Example 2, except that polydopamine is used as a photothermal nanomaterial to be compounded with polysiloxane, and the filling amount is 0.5wt.%. The corresponding infrared sensor with bonding and flexible packaging is prepared. The responsiveness of the sensor at different wavelengths is characterized using light sources of 455nm, 520nm, 675nm, 808nm, 980nm and 1550nm. The responsiveness test results at 455nm, 520nm, 675nm, 808nm, 980nm and 1550nm are 43.7W and 43.7W, respectively. -1 、40.1W -1 , 24.7W -1 , 23.3W -1 and 7.6W -1 , the response behavior at different wavelengths shows dependence on wavelength.

[0057] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. An infrared sensor, characterized in that: The infrared sensor comprises: Elastic substrate (1); The package (2) comprises a connection area (21) and a contact area (22), wherein the connection area (21) extends into the elastic substrate (1); a cavity is provided in the contact area (22), and a notch is provided above the cavity; and the cavity is filled with a carbon nano-photothermal composite material; A sensing element (3) covering the surface of the elastic substrate (1) and the packaging body (2); The elastic substrate and the packaging body are bonded to the sensor element after interface treatment; the notch of the packaging body is located at the center of the sensor element; The carbon nano-photothermal composite material is prepared by the following method: Firstly, the carbon nanomaterial is dispersed in an organic solvent, and then a polymer is added to obtain a carbon nanophotothermal composite material; Infrared light irradiates from below, passes through the hard package and impinges on the carbon nano-photothermal composite material, causing photothermal expansion of the carbon nano-photothermal composite material, triggering mechanical deformation and resistance change of the sensing element, thereby realizing the detection of infrared signals.

2. The infrared sensor according to claim 1, characterized in that: The elastic substrate is selected from one or more of natural rubber, synthetic rubber, silicone rubber, styrene-butadiene rubber and fluororubber.

3. The infrared sensor according to claim 1, characterized in that: The package meets the following conditions: 1) The package is selected from one or more of infrared transparent crystals, glass and polymers; the modulus of the package is greater than 3GPa, and the infrared transmittance is greater than 90%; 2) The package is cylindrical or spherical, and the cavity volume of the package is less than 2 mm 2 ; 3) The ratio of the notch area of ​​the package body to the cavity area of ​​the package body is ≤ 1 / 6.

4. The infrared sensor according to claim 1, characterized in that: The doping ratio of the carbon nanomaterial to the polymer is 0.05 wt%-5 wt%; The carbon nanomaterial is selected from one or more of carbon nanotubes, graphene and graphite nanosheets; the polymer is selected from one or more of polyethylene, polypropylene, high-temperature silicone rubber, polyimide and polyphenylene sulfide; the thermal expansion coefficient of the polymer is greater than 50 ppm / °C and the modulus is less than 10 MPa.

5. The infrared sensor according to claim 1, characterized in that: The sensing element is selected from one or more of a silicon film, a carbon film and a silicon carbide film having piezoresistive properties; the piezoresistive sensitivity coefficient of the sensing element is greater than 200.

6. The infrared sensor according to claim 1, characterized in that: The interface treatment is plasma treatment first, and then silane coupling treatment.

7. The infrared sensor according to claim 6, characterized in that: The conditions of the plasma treatment are: using oxygen as the atmosphere, the gas flow rate is 0.2 L / min-2 L / min; the plasma treatment time is 0.5 min-20 min.

8. The infrared sensor according to claim 6, characterized in that: The silane coupling treatment method is: immersing the elastic substrate and the sensor element in a silane coupling agent having bonding ability with each other respectively; the mass concentration of the silane coupling agent is 0.1%-1%; and the immersion time is 0.5 h-12 h.

9. The infrared sensor according to claim 1, characterized in that: The bonding conditions are: at a pressure of 5 MPa-20 MPa, at 25°C-100°C, for 1 h-24 h.

10. The method for preparing the infrared sensor according to any one of claims 1 to 9, characterized in that: The following steps are involved: Filling the carbon nano-photothermal composite material into the package to obtain a package filled with the composite material; The encapsulation body of the obtained composite material is encapsulated using an elastic substrate to obtain an optomechanical braking element; The obtained photomechanical braking element and the sensing element are subjected to interface treatment and bonded to obtain the infrared sensor.

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