Semiconductor fiber gas sensor as well as preparation method and application thereof

Abstract

The invention provides a semiconductor fiber gas sensor. The semiconductor fiber gas sensor comprises a silicon dioxide composite fiber, a gas detection electrode, a metal oxide semiconductor gas sensitive layer, a heating electrode and a breathable film, the gas detection electrodes are formed at two ends of the silicon dioxide coating layer; the surface of the silicon dioxide composite fiber is coated with the metal oxide semiconductor gas sensitive layer; the heating electrodes are formed at the two ends of the alloy fiber; the surface of the metal oxide semiconductor gas-sensitive layer is coated with the breathable film. The invention further provides a preparation method and application of the semiconductor fiber gas sensor. The gas sensor provided by the invention is high in heat source utilization rate, high in flexibility and small in size, an additional heating wire is not needed to provide heat energy for the sensor, and the alloy fiber of the composite fiber can generate enough Joule heat to provide heat energy for the gas-sensitive material when current passes through, so that high-sensitivity response is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of gas sensors, and in particular to a semiconductor fiber gas sensor, a preparation method thereof and applications thereof. Background Art

[0002] A gas sensor is a device that can detect the type and concentration of a target gas and output it as an electrical signal. Gas sensors can be divided into semiconductor gas sensors, solid electrolyte gas sensors, contact combustion gas sensors, electrochemical gas sensors, and optical gas sensors. Metal oxide semiconductor gas sensors are a type of semiconductor gas sensor. Due to their unique electrical properties and large specific surface area, they are very suitable for NO x Chemical gas sensing of toxic gases such as NH3, SO2 and H2S has attracted widespread attention.

[0003] The gas-sensitive materials in metal oxide semiconductor gas sensors will have electron depletion zones of different widths in different environments. When the gas-sensitive materials are in the air, the oxygen on the surface of the material will exchange electrons with the gas-sensitive layer, and the electrons of the gas-sensitive material will transfer to the oxygen around the material, so that the oxygen around the material is converted into oxygen anions and adsorbed on the surface of the gas-sensitive material, causing the electron depletion zone of the gas-sensitive material to change, and the resistance will also change accordingly. When the gas-sensitive material is in a certain concentration of response gas, the response gas will react with the oxygen anions adsorbed on the surface of the gas-sensitive material, so that the electrons are released back to the gas-sensitive layer, causing the electron depletion zone to change, and the resistance will change accordingly. Therefore, the nanostructure of metal oxide gas-sensitive materials has many advantages in gas sensing, such as strong controllability and low cost, but there are a lot of problems in wearable applications, such as poor flexibility, the need to provide sufficient thermal energy to achieve the best response, and low thermal utilization, which limits the development of metal oxide semiconductor gas sensors in wearable applications.

[0004] At present, common metal oxide semiconductor gas sensors usually coat gas-sensitive materials on ceramic tubes and grow them directly on hard substrates such as microelectromechanical systems (MEMS): For gas sensors with ceramic tube structures, the process of built-in heating wires in ceramic tubes is generally used to provide the required thermal energy for the gas-sensitive layer. The heating layer prepared by this method has a large space and fast air flow, which will also cause heat dissipation faster, affecting the thermal insulation effect, thereby greatly increasing power consumption. For MEMS sensors, the commonly used structure is to deposit a silicon nitride film layer on the upper surface of a single-crystal silicon substrate as a lower insulating layer, and prepare an insulating groove on the lower surface of the single-crystal silicon substrate. The insulating groove can prevent heat loss to reduce power consumption. The back wet etching process can be used to prepare the insulating groove, or a cantilever beam can be etched out of the lower insulating layer first, and then an inverted pyramid insulating groove can be wet-etched downward; a platinum heating wire layer is processed above the lower insulating layer by a lift-off process, and heat can be generated by energizing the heating wire to form the temperature required for the gas sensor to work, and a silicon nitride layer is deposited on the surface of the platinum heating wire as an upper insulating layer, and finally a temperature sensitive layer and a gas sensitive layer are deposited. However, after the insulation groove is etched out by this method, the heating layer and the gas sensitive layer are supported by only a silicon nitride layer of a thin film structure, and the thin film is supported only at two ends by the supporting substrate of the cantilever structure. The insulating layer of this thin film structure has poor mechanical properties and is prone to cracking when the device is vibrated or collided, resulting in device failure; in addition, due to the difference in thermal expansion coefficients between the insulation layer and the heating wire, the insulation layer is prone to warping at high temperatures, making it easy for the heating wire to fall off the insulation layer, also resulting in device failure; the insulation groove of the cantilever structure uses the air between the cantilevers for thermal insulation. Due to the large space and fast air flow, heat dissipation will also be caused quickly, affecting the insulation effect; moreover, the preparation process of this insulation groove is complicated and requires high control conditions, which increases the processing difficulty.

[0005] Therefore, in order to broaden the application field of metal oxide semiconductor gas sensors, it is of great significance to provide a gas sensor with high heat source utilization, good flexibility and small size. Summary of the invention

[0006] The technical problem solved by the present invention is to provide a semiconductor fiber gas sensor. The gas sensor provided by the present application has the advantages of high heat source utilization, good flexibility and small size.

[0007] In view of this, the present application provides a semiconductor fiber gas sensor, including a silica composite fiber, a gas detection electrode, a metal oxide semiconductor gas sensitive layer, a heating electrode and a breathable film; the silica composite fiber is a composite fiber having a silica coating layer on the surface of the alloy fiber except for the two ends;

[0008] The gas detection electrodes are formed at both ends of the silicon dioxide coating layer;

[0009] The metal oxide semiconductor gas-sensitive layer is coated on the surface of the silicon dioxide composite fiber;

[0010] The heating electrodes are formed at both ends of the alloy fiber;

[0011] The air-permeable film is coated on the surface of the metal oxide semiconductor gas-sensitive layer.

[0012] Preferably, the alloy fiber includes molybdenum wire, nickel-chromium alloy, chromium-aluminum alloy, copper-nickel alloy, iron-chromium-aluminum alloy or iron-chromium-aluminum-tungsten alloy.

[0013] Preferably, the outer diameter of the silica composite fiber is ≥30 μm, and the inner diameter is ≥1 μm.

[0014] Preferably, the gas detection electrode comprises a silver wire, a platinum wire or a gold wire, and the heating electrode comprises a silver wire, a platinum wire or a gold wire.

[0015] Preferably, the metal oxide in the metal oxide semiconductor gas sensing layer includes one or more of ZnO, SnO2, Fe2O3, In2O3, WO3, TiO2, Co3O4, the above metal oxides doped with metals and / or metal oxides, and the above metal oxides modified with metals and / or metal oxides; the thickness of the metal oxide semiconductor gas sensing layer is ≥10nm; the microscopic morphology of the metal oxide in the metal oxide semiconductor gas sensing layer is one or more of nanoparticles, nanorods, nanowires, nanobelts, nanotubes, nanocombs, nanosheets, nano-ization and nanoclusters.

[0016] The present application also provides a method for preparing the semiconductor fiber gas sensor, comprising the following steps:

[0017] S1) placing a metal powder raw material in a hollow silica preform rod with one end closed, heating the metal powder raw material until it melts, and drawing the softened silica to obtain a silica composite fiber; the melting temperature of the metal powder raw material is lower than the melting temperature of silica, and the silica composite fiber is a composite fiber having a silica coating layer on the surface of the alloy fiber except for the two ends;

[0018] S2) forming gas detection electrodes at both ends of the silica coating layer of the silica composite fiber;

[0019] forming a metal oxide semiconductor gas-sensitive layer on the surface of the silica composite fiber;

[0020] forming heating electrodes at both ends of the alloy fiber of the silica composite fiber;

[0021] S3) forming a breathable film on the surface of the metal oxide semiconductor gas sensitive layer.

[0022] Preferably, the drawing speed is 1-10 mm / min.

[0023] Preferably, the preparation method of the metal oxide semiconductor gas sensitive layer includes one or more of vapor deposition, atomic layer deposition, template method, solvent thermal method, solid phase reaction method, sol-gel method, electrospinning and microwave assisted method.

[0024] The present application also provides a flexible substrate sensor, comprising a flexible substrate and a plurality of gas sensors formed on the flexible substrate, wherein the gas sensor is the semiconductor fiber gas sensor or the semiconductor fiber gas sensor prepared by the preparation method.

[0025] The present application also provides a sensor system, including the semiconductor fiber gas sensor or the semiconductor fiber gas sensor prepared by the preparation method.

[0026] The present application provides a semiconductor fiber gas sensor, which includes a silica composite fiber, a gas detection electrode, a metal oxide semiconductor gas sensitive layer, a heating electrode and a breathable film, wherein the silica composite fiber is a composite fiber having a silica coating layer on the surface of the alloy fiber except for the two ends, the gas detection electrodes are formed at the two ends of the silica coating layer, the metal oxide semiconductor gas sensitive layer is coated on the surface of the silica composite fiber, the heating electrodes are formed at the two ends of the alloy fiber, and the breathable film is coated on the surface of the metal oxide semiconductor gas sensitive layer; the semiconductor fiber gas sensor provided by the present application uses the alloy fiber as a heat source and silica as an insulating substrate. The Joule heat generated by the alloy fiber in the silica composite fiber after being energized can directly provide heat for the gas sensitive response of the gas sensitive material in the metal oxide semiconductor gas sensitive layer by heat conduction, thereby realizing the great utilization of electric thermal energy and solving the problem of large heat transfer loss of the existing metal oxide semiconductor gas sensor; at the same time, the alloy fiber as a substrate material can significantly reduce the overall volume of the gas sensor compared with the traditional ceramic tube and MEMS substrate, and can make the gas sensor have a certain flexibility, thereby expanding the application of the semiconductor fiber gas sensor of the present application in the field of flexible wearables.

[0027] On the other hand, the silica coating layer in the silica composite fiber provided in the present application can directly grow the metal oxide semiconductor gas-sensitive layer in situ, reducing the technical difficulty of setting the gas-sensitive layer on the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of the process of preparing the semiconductor fiber gas sensor of the present invention;

[0029] Figure 2 It is a schematic diagram of the structure of the semiconductor fiber gas sensor of the present invention;

[0030] Figure 3 Schematic diagram of the preparation of the alloy fiber of the present invention;

[0031] Figure 4 This is a SEM photo of a gas sensor including a metal oxide semiconductor gas-sensitive layer prepared in Example 1 of the present invention;

[0032] Figure 5 This is a SEM photograph of the metal oxide of the metal oxide semiconductor gas sensing layer prepared in Example 1 of the present invention;

[0033] Figure 6 This is a gas-sensitive response curve diagram of the semiconductor fiber gas sensor prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0035] In order to make the application of metal oxide semiconductor gas sensors in wearable devices more flexible, the present application provides a semiconductor fiber gas sensor, which introduces silica composite fiber, and the fiber core is an alloy fiber, so that the gas sensor is a self-heating sensor, and the Joule heat generated by the fiber core provides thermal energy for the gas sensitive layer grown on the surface of the silica coating layer of the fiber shell, and no additional heating wire is required to provide thermal energy for the sensor. The alloy fiber can generate the thermal energy required for the gas sensitive layer to be in the best working state when powered on, achieving the purposes of high thermal energy utilization, high response, high flexibility, simple preparation process, and lightness to wear. Specifically, the embodiment of the present invention discloses a semiconductor fiber gas sensor, including silica composite fiber, gas detection electrode, metal oxide semiconductor gas sensitive layer, heating electrode and breathable film; the silica composite fiber is a composite fiber having a silica coating layer on the surface of the alloy fiber except for the two ends;

[0036] The gas detection electrodes are formed at both ends of the silicon dioxide coating layer;

[0037] The metal oxide semiconductor gas-sensitive layer is coated on the surface of the silicon dioxide composite fiber;

[0038] The heating electrodes are formed at both ends of the alloy fiber;

[0039] The air-permeable film is coated on the surface of the metal oxide semiconductor gas-sensitive layer.

[0040] like Figure 3 As shown, Figure 3This is a schematic diagram of the structure of the semiconductor fiber gas sensor provided in the present application, in which 6 is an alloy fiber, 7 is a silicon dioxide coating layer, 8 is a metal oxide semiconductor gas sensitive layer, 9 is a breathable film, 10 is a gas detection electrode, and 11 is a heating electrode.

[0041] In the semiconductor fiber gas sensor provided in the present application, the alloy fiber is used as the fiber core, and the silica coating layer is used as the fiber shell, which together constitutes a silica composite fiber; the alloy fiber includes molybdenum wire, nickel-chromium alloy, chromium-aluminum alloy, copper-nickel alloy, iron-chromium-aluminum alloy or iron-chromium-aluminum-tungsten alloy; the ratio of the raw materials in the above alloy fibers is well known to those skilled in the art. The outer diameter of the silica composite fiber is ≥30μm, and the inner diameter is ≥1μm. Specifically, the outer diameter of the silica composite fiber is 80-120μm, and the inner diameter is 20-50μm; more specifically, the outer diameter of the silica composite fiber is 90-100μm, and the inner diameter is 30-40μm. The silica composite fiber uses the alloy fiber as a heat source. The Joule heat generated by the alloy fiber after applying an external current provides heat for the gas-sensitive response process of the gas-sensitive layer through heat conduction. The silica coating layer serves as an insulating substrate, and metal oxide semiconductor gas-sensitive materials can also be directly grown in situ. Both ends of the alloy fiber of the silica composite fiber are not coated with a silica coating layer. The silica composite fiber is prepared by a hot drawing method, and the alloy fiber and the silica coating layer are composited together.

[0042] A metal oxide semiconductor gas-sensitive layer is formed on the surface of the silica composite fiber. The metal oxide in the metal oxide semiconductor gas-sensitive layer serves as a gas-sensitive material and provides a site for the adsorption of the target gas to achieve the purpose of detecting the target gas. The metal oxide in the metal oxide semiconductor gas-sensitive layer includes one or more of ZnO, SnO2, Fe2O3, In2O3, WO3, TiO2, Co3O4, the above metal oxides doped with metals and / or metal oxides, and the above metal oxides modified with metals and / or metal oxides; in a specific embodiment, the metal oxide is yttrium-doped zinc oxide. The thickness of the metal oxide semiconductor gas-sensitive layer is ≥10nm. Specifically, the thickness of the metal oxide semiconductor gas-sensitive layer is 1 to 5μm; for example, the thickness of the metal oxide semiconductor gas-sensitive layer is 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm. The microscopic morphology of the metal oxide in the metal oxide semiconductor gas sensing layer is one or more of nanoparticles, nanorods, nanowires, nanobelts, nanotubes, nanocombs, nanosheets, nano-nization and nanoclusters; in a specific embodiment, the microscopic morphology of the metal oxide in the metal oxide semiconductor gas sensing layer is nanorods.

[0043] The gas detection electrodes are formed at both ends of the silicon dioxide coating layer, and are used to detect the resistance of the metal oxide semiconductor gas-sensitive layer, convert the interaction between the target gas and the metal oxide in the gas-sensitive layer into a change in resistance, and realize gas detection. The gas detection electrodes include silver wires, platinum wires or gold wires.

[0044] The heating electrodes are arranged at both ends of the alloy fiber to apply current to the alloy fiber so that the alloy fiber generates Joule heat. The heating electrodes include silver wire, platinum wire or gold wire; the materials of the gas detection electrode and the heating electrode can be the same or different, and this application does not impose any special restrictions on this.

[0045] A permeable film is formed on the surface of the metal oxide semiconductor gas-sensitive layer, which can prevent the semiconductor gas-sensitive layer from falling off. The permeable film specifically includes: polytetrafluoroethylene (PTFE), polypropylene (PP), PDMS and Teflon AF2400.

[0046] In the semiconductor fiber gas sensor provided in the present application, the above-mentioned two ends are relative to the middle part, and there is no special restriction on the specific positions of the two ends.

[0047] The present application provides a method for preparing the semiconductor fiber gas sensor, comprising the following steps:

[0048] S1) placing a metal powder raw material in a hollow silica preform rod with one end closed, heating the metal powder raw material until it melts, and drawing the softened silica to obtain a silica composite fiber; the melting temperature of the metal powder raw material is lower than the melting temperature of silica, and the silica composite fiber is a composite fiber having a silica coating layer on the surface of the alloy fiber except for the two ends;

[0049] S2) forming gas detection electrodes at both ends of the silica coating layer of the silica composite fiber;

[0050] forming a metal oxide semiconductor gas-sensitive layer on the surface of the silica composite fiber;

[0051] forming heating electrodes at both ends of the alloy fiber of the silica composite fiber;

[0052] S3) forming a breathable film on the surface of the metal oxide semiconductor gas sensitive layer.

[0053] In the method for preparing the semiconductor fiber gas sensor provided in the present application, the present application first prepares the silica composite fiber, specifically as follows: Figure 2As shown, 1 is a hollow silica preform rod, 2 is a metal powder raw material, 3 is a high-frequency induction heater, 4 is a capstan, and 5 is a composite fiber; that is, the metal powder raw material is placed in a hollow silica preform rod with one end closed, heated until the metal powder raw material melts, and the softened silica is drawn to obtain a silica composite fiber; the melting temperature of the metal powder raw material is lower than the melting temperature of silica. In the above preparation process, in order to improve the heating efficiency, the heating equipment preferably uses a high-frequency induction heater; since the melting temperature of the metal powder raw material is lower than the melting temperature of silica, when the metal powder raw material melts, the part of the hollow silica preform rod capping near the molten metal powder raw material softens and wraps the metal droplets. In order to form a composite fiber of appropriate size, it is preferred to use a glass rod to lead the fiber down from the softened silica capping, and then draw it after cooling, so as to obtain a composite fiber with an alloy fiber as the core and silica as the fiber shell; the drawing speed is 1 to 10 mm / min, and specifically, the drawing speed is 3 to 8 mm / min.

[0054] The present application further forms gas detection electrodes at both ends of the silica coating of the silica composite fiber, and the formation method is not particularly limited in the present application; in a specific embodiment, the gas detection electrodes are respectively wound around the two ends of the silica coating, and then the conductive metal paste is coated on the connection between the gas detection electrode and the silica coating, and then annealed to sinter it with the gas detection electrode; in the above process, the material selection of the gas detection electrode and the conductive metal paste can be the same or different. In some specific embodiments, the gas detection electrode is a platinum wire and the conductive metal paste is a silver paste. The annealing temperature is 400-500°C and the time is 10-30min; specifically, the annealing temperature is 420-480°C and the time is 15-25min.

[0055] According to the present invention, a metal oxide semiconductor gas-sensitive layer is then formed on the surface of the silica composite fiber; the preparation method of the metal oxide semiconductor gas-sensitive layer includes one or more of vapor deposition, atomic layer deposition, template method, solvent thermal method, solid phase reaction method, sol-gel method, electrospinning and microwave-assisted method; in a specific embodiment, the preparation method of the metal oxide semiconductor gas-sensitive layer is a sol-gel method, more specifically, Y-doped ZnO nanorods can be in-situ grown on the surface of the silica coating layer using a hydrothermal method, firstly, ZnO nanoparticles are coated on the surface of the silica coating layer using a sol-gel method to form a seed layer, and then Y-doped ZnO nanorods are grown using a hydrothermal method.

[0056] The present application then connects heating electrodes at both ends of the alloy fiber, and applies a thermal conductive slurry to the connection between the heating electrode and the alloy fiber, and sintering the alloy fiber and the heating electrode together after annealing; in this step, it is preferred to soak both ends of the silica composite fiber in an organic solution to remove the gas-sensitive layer and the silica coating layer at both ends of the composite fiber to prevent the heating electrode and the gas-sensitive material from being connected in series; the annealing temperature is 100-200°C, and the time is 10-30 minutes; specifically, the annealing temperature is 120-180°C, and the time is 15-25 minutes.

[0057] According to the present invention, a breathable film is finally formed on the surface of the gas-sensitive layer to form a protective layer on the surface of the gas-sensitive layer to prevent the gas-sensitive layer from falling off; the method for forming the breathable film is not particularly limited in this application. In a specific embodiment, the formation method is an immersion pulling method.

[0058] Figure 1 FIG. 1 is a schematic diagram of a specific process of the semiconductor fiber gas sensor of the present invention, which includes sequentially preparing silica composite fibers by thermal drawing, in-situ growing a gas sensitive layer, and preparing a sensor, as shown in FIG. Figure 1 shown.

[0059] The present invention provides a semiconductor fiber gas sensor and a preparation method and application thereof; the gas sensor provided by the present invention comprises: a composite fiber with an alloy fiber as a fiber core and silicon dioxide as a fiber shell; a gas detection electrode formed on the surface of the composite fiber; a metal oxide semiconductor gas-sensitive layer coated on the surface of the composite fiber, the free end of the gas detection electrode passing through the metal oxide semiconductor layer; and heating electrodes arranged at both ends of the alloy fiber; the alloy fiber is used as a heat source and the silicon dioxide coating layer is used as an insulating substrate, and the Joule heat generated after the fiber core is energized can provide heat for the gas-sensitive response process of the metal oxide semiconductor gas-sensitive material by heat conduction. It realizes the maximum utilization of electrothermal energy and solves the problem of large heat transfer loss when the existing metal oxide semiconductor gas sensor is heated; moreover, the insulating substrate material (silicon dioxide) in the present application can directly grow the metal oxide semiconductor material in situ, reducing the technical difficulty of setting the gas sensitive material layer on the substrate, and the process implementation threshold is low, which is more conducive to commercial promotion; in addition, since the present application adopts a fibrous substrate material, compared with the traditional ceramic tube and MEMS substrate, the overall volume of the gas sensor can be significantly reduced, and the gas sensor can have a certain flexibility, making the flexible wearable application of the metal oxide semiconductor gas sensor possible.

[0060] The present application also provides a flexible substrate sensor, comprising a flexible substrate and a plurality of gas sensors formed on the flexible substrate, wherein the gas sensor is the gas sensor described in the above scheme; and the number of gas sensors among the plurality of gas sensors is ≥1, so as to realize the detection of multiple gases at the same time.

[0061] The present application also provides a sensor system, which includes the metal oxide semiconductor gas sensor to which the above-mentioned solution belongs.

[0062] The semiconductor fiber gas sensor provided in this application can be used alone to detect the concentration of gas, and can also be integrated with other components to still play its own role, while other components can play their respective roles to form a sensor system with multiple functions.

[0063] The present invention provides a semiconductor fiber gas sensor and a preparation method and application thereof. The gas sensor provided by the present invention has high heat source utilization, high flexibility and small size, and does not require additional heating wires to provide thermal energy for the sensor. The alloy core of the fiber itself will generate sufficient Joule heat to provide thermal energy for the gas-sensitive material when current passes through, so as to achieve high-sensitivity response.

[0064] In order to further improve the gas-sensitive response of the metal oxide semiconductor gas-sensitive layer, the metal oxide gas-sensitive layer can be doped and / or modified, including but not limited to the doping of metals and / or metal oxides. Doping and / or modification may form a heterojunction or cause a change in the lattice, thereby causing a change in the electron depletion layer, an increase in the oxygen content adsorbed on the surface of the gas-sensitive layer, and improving the gas-sensitive response of the sensor. The methods of doping and / or modification include: sol-gel method, reduction method, sputtering method and flame spray pyrolysis, etc.

[0065] In order to further understand the present invention, the semiconductor fiber gas sensor and the preparation method thereof provided by the present invention are described in detail below in conjunction with the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0066] Example 1

[0067] This embodiment provides a fiber-based metal oxide semiconductor gas sensor, and the specific preparation process is as follows:

[0068] (1) Preparation of composite fibers with nickel-chromium alloy as core and silica as shell

[0069] The nickel-chromium master alloy is placed in a silica preform rod with one end sealed, and then placed in a high-frequency induction heater, and the temperature is adjusted to 1550°C. Under high-temperature heating, the nickel-chromium master alloy gradually becomes a molten state, and the end of the preform rod close to the molten nickel-chromium alloy gradually softens. At this time, it is led down by a glass rod, and the condensed water is condensed and then wound onto a capstan. The capstan applies tension to form a coaxial fiber, with the nickel-chromium alloy at the fiber core and the silica at the fiber shell. During the hot drawing process, the diameter of the preform rod is reduced from 30 mm to 1 mm, and the diameter of the fiber core is reduced from 4 mm to 130 μm, and the hot drawing speed is 1 m / min. The nickel-chromium composite fiber with a diameter of 1 mm prepared above is loaded into a new silica preform rod, heated with a hydrogen-oxygen flame, and hot-drawn again until a nickel-chromium composite fiber with an outer diameter of 90 μm and an inner diameter of 40 μm is obtained.

[0070] The nickel-chromium composite fiber prepared above was cut into 5 cm lengths for flexibility test. The specific test process and test results are as follows:

[0071] A compressive force was applied to both ends of the fiber axially to make it bend, and the limit radius of curvature before the fiber was bent and broken was tested, and the result was about 1 cm; thus, it can be proved that the composite fiber prepared in this embodiment has good flexibility;

[0072] (2) Preparation of sensor gas detection electrodes

[0073] The nickel-chromium composite fiber prepared in step (1) is cut into 2 cm lengths using an optical fiber cutter, and then the cut nickel-chromium composite fiber is ultrasonically cleaned in acetone, ethanol and deionized water solution for 10 min respectively to remove surface pollutants and dried in air at 60° C.; platinum wires with a diameter of 100 μm are respectively wound around both ends of the nickel-chromium composite fiber as gas detection electrodes, silver paste is applied to the connection between the platinum wire and the nickel-chromium composite fiber, and annealed at 450° C. for 15 min to sinter the fiber and the platinum wire together;

[0074] (3) Growth of Metal Oxide Semiconductor Gas Sensing Materials

[0075] A zinc oxide seed layer is grown on the surface of the nickel-chromium composite fiber connected with the gas detection electrode prepared in step (2) by a sol-gel method, and the specific operation steps are as follows:

[0076] ① The composite fiber prepared above was subjected to air plasma treatment for 120s to improve the hydrophilicity of the fiber and make the seed layer solution more easily adhere to the surface of the fiber; ② A Zn(CH3COO)2·2H2O ethanol solution with a concentration of 0.03 mol / L was prepared, and the seed layer solution was evenly dispersed on the surface of the fiber by a pulling method to form a film, and then dried, and the pulling and drying were repeated 5 times; ③ Annealing treatment was performed at 350°C for 30min to thermally decompose Zn(CH3COO)2·2H2O to form ZnO nanoparticles, and a uniform and dense ZnO seed layer with high crystallinity was formed on the fiber surface, so that the zinc oxide nanorods grown later had better orientation;

[0077] On the basis of the zinc oxide seed layer, yttrium-doped zinc oxide nanorods were in situ grown on the fiber surface by a hydrothermal method. The specific operation steps are as follows:

[0078] ① Prepare a 0.025 mol / L Zn(NO3)2·6H2O aqueous solution, an equal molar ratio of HMTA aqueous solution and a 0.01 mol / L Y(NO3)3·6H2O solution, then mix the three solutions and stir at room temperature for 1 hour to mix them evenly; ② Transfer the mixed solution to a reactor, place the fiber with the grown seed layer obliquely in the reactor, react at 95°C for 8 hours, take out the fiber after the reactor temperature drops to room temperature, wash with deionized water to remove excess material on the surface, and dry at 60°C; ③ Anneal at 500°C for 2 hours to remove impurities in the nanorods and reduce structural defects; finally, a metal oxide semiconductor gas sensing layer with a thickness of about 5 μm is obtained on the surface of the composite fiber;

[0079] Figure 4 , Figure 5 The electron microscope images of the composite fiber and the gas-sensitive layer obtained after the above steps are shown. The core-shell structure of the composite fiber and the nanorod-shaped gas-sensitive material can be clearly shown from the above two images.

[0080] (4) Preparation of sensor heating electrode

[0081] The two ends of the composite fiber on which the metal oxide semiconductor has been uniformly grown prepared in step (3) are immersed in a dilute hydrochloric acid solution to remove the gas-sensitive layer at the two ends of the fiber, so as to prevent the heating electrode and the gas-sensitive material from being connected in series; then, platinum wires with a diameter of 100 μm are connected to the cross sections at the two ends of the fiber, and silver paste is coated on the connection between the platinum wire and the fiber, and annealed at 150° C. for 15 min in a tubular furnace to sinter the fiber and the platinum wire together; by sintering the silver paste at high temperature, the solid particles are bonded to each other, the grains grow, the gaps and grain boundaries gradually decrease, and through the transfer of matter, the total volume shrinks, the density increases, the silver element crystallizes, the contact resistance is reduced, and an ideal ohmic contact is formed;

[0082] The gas sensor prepared in this embodiment was subjected to a thermal effect test. The specific test process included: connecting the heating electrode of the fiber to the circuit, applying current to examine its heat generation; the results showed that: when different currents were applied at both ends of the fiber, the temperature of the fiber could reach 500°C, which fully met the thermal energy required for gas-sensitive response; this proved that the nickel-chromium composite fiber prepared in this embodiment had a good thermal effect.

[0083] (5) Preparation of breathable film: Prepare PDMS solution, apply PDMS solution to the composite fiber prepared in step (4) through immersion pulling method, so that PDMS is evenly covered on the surface of the fiber, and heat and cure to form a breathable film. The presence of the breathable film can prevent the gas sensitive layer from falling off, thereby obtaining a semiconductor fiber gas sensor.

[0084] The gas sensor prepared in this embodiment was subjected to a gas sensitivity test. The specific test process includes: placing the sensor in a gas chamber, connecting a heating electrode and a detection electrode, and passing acetone gas of different concentrations to perform a gas sensitivity test; the experimental results are shown in FIG. Figure 6 As shown: When 10 ppm of acetone is introduced, the response of the sensor is 1.81.

[0085] The metal oxide semiconductor gas sensor provided in this embodiment uses fiber material as a substrate, has good flexibility, and can be woven onto a flexible substrate such as clothing.

[0086] Example 2

[0087] (1) Preparation of composite fibers with iron-chromium-aluminum alloy as the core and silicon dioxide as the shell:

[0088] First, an iron (75.4%), chromium (20%), and aluminum (4.5%) master alloy is placed in a silicon dioxide preform rod with one end sealed, and then placed in a high-frequency induction heater and the temperature is adjusted to 1500°C. Under high-temperature heating, the iron-chromium-aluminum master alloy gradually turns into a molten state, and the end of the preform rod close to the molten alloy gradually softens. At this time, it is led down by a glass rod, and the condensed water is condensed and wound onto a capstan. The capstan applies a tensile force, and the stretching speed is 1m / min. The fiber is pulled and stretched to form a coaxial fiber with an iron-chromium-aluminum alloy as a fiber core and silicon dioxide as a fiber shell. During the hot drawing process, fibers of different sizes can be prepared by multiple stretching.

[0089] The iron-chromium-aluminum composite fiber prepared above was cut into 5 cm lengths for flexibility testing. The specific test process and test results are as follows:

[0090] Axially, squeezing force was applied to both ends of the fiber to make it bend, and the limiting radius of curvature before the fiber broke was tested, and the result was about 1 cm; thus, it can be proved that the composite fiber prepared in this embodiment has good flexibility.

[0091] (2) Preparation of the sensor: A metal oxide semiconductor gas-sensitive layer is grown in situ by the same method as in Example 1, and a heating electrode and a detection electrode are prepared by sintering a silver paste. A breathable film is then prepared on the fiber surface by dipping and pulling to prevent the gas-sensitive layer from falling off, thereby forming the desired sensor.

[0092] The heating electrode of the fiber was connected to the circuit, and current was applied to examine its heat generation. The result was that at a current of 100 mA, the temperature of the alloy fiber could reach 300° C. This proves that the iron-chromium-aluminum composite fiber prepared in this embodiment has a good thermal effect.

[0093] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0094] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A semiconductor fiber gas sensor, comprising a silica composite fiber, a gas detection electrode, a metal oxide semiconductor gas sensitive layer, a heating electrode and a breathable film; the silica composite fiber is a composite fiber having a silica coating layer on the surface of the alloy fiber except for the two ends; The gas detection electrodes are formed at both ends of the silicon dioxide coating layer; The metal oxide semiconductor gas-sensitive layer is coated on the surface of the silicon dioxide composite fiber; The heating electrodes are formed at both ends of the alloy fiber; The air-permeable film is coated on the surface of the metal oxide semiconductor gas-sensitive layer.

2. The gas sensor according to claim 1, characterized in that The alloy fiber includes molybdenum wire, nickel-chromium alloy, chromium-aluminum alloy, copper-nickel alloy, iron-chromium-aluminum alloy or iron-chromium-aluminum-tungsten alloy.

3. The gas sensor according to claim 1, characterized in that: The outer diameter of the silica composite fiber is ≥30 μm, and the inner diameter is ≥1 μm.

4. The gas sensor according to claim 1, characterized in that: The gas detection electrode includes a silver wire, a platinum wire or a gold wire, and the heating electrode includes a silver wire, a platinum wire or a gold wire.

5. The gas sensor according to claim 1, characterized in that: The metal oxide in the metal oxide semiconductor gas sensing layer includes one or more of ZnO, SnO2, Fe2O3, In2O3, WO3, TiO2, Co3O4, the above metal oxides doped with metals and / or metal oxides, and the above metal oxides modified with metals and / or metal oxides; the thickness of the metal oxide semiconductor gas sensing layer is ≥10nm; the microscopic morphology of the metal oxide in the metal oxide semiconductor gas sensing layer is one or more of nanoparticles, nanorods, nanowires, nanobelts, nanotubes, nanocombs, nanosheets, nano-clustering and nanoclusters.

6. The method for preparing the semiconductor fiber gas sensor according to claim 1, comprising the following steps: S1) placing a metal powder raw material in a hollow silica preform rod with one end closed, heating the metal powder raw material until it melts, and drawing the softened silica to obtain a silica composite fiber; the melting temperature of the metal powder raw material is lower than the melting temperature of silica, and the silica composite fiber is a composite fiber having a silica coating layer on the surface of the alloy fiber except for the two ends; S2) forming gas detection electrodes at both ends of the silica coating layer of the silica composite fiber; forming a metal oxide semiconductor gas-sensitive layer on the surface of the silica composite fiber; forming heating electrodes at both ends of the alloy fiber of the silica composite fiber; S3) forming a breathable film on the surface of the metal oxide semiconductor gas sensitive layer.

7. The preparation method according to claim 6, characterized in that: The drawing speed is 1-10 mm / min.

8. The preparation method according to claim 6, characterized in that: The preparation method of the metal oxide semiconductor gas sensitive layer includes one or more of vapor deposition method, atomic layer deposition method, template method, solvent thermal method, solid phase reaction method, sol-gel method, electrostatic spinning and microwave assisted method.

9. A flexible substrate sensor, comprising a flexible substrate and a plurality of gas sensors formed on the flexible substrate, wherein the gas sensor is a semiconductor fiber gas sensor as described in any one of claims 1 to 5 or a semiconductor fiber gas sensor prepared by the preparation method as described in any one of claims 6 to 8.

10. A sensor system, comprising the semiconductor fiber gas sensor according to any one of claims 1 to 5 or the semiconductor fiber gas sensor prepared by the preparation method according to any one of claims 6 to 8.

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