CN114107940B - Discontinuous carbon film preparation and respiration sensor application based on aluminum-nickel metal layer - Google Patents
Discontinuous carbon film preparation and respiration sensor application based on aluminum-nickel metal layer Download PDFInfo
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Abstract
Discontinuous carbon film preparation and breath sensor application based on aluminum nickel metal layer belong to carbon film preparation technical field. In the preparation process of the carbon film, firstly, aluminum-nickel metal layers with different components are sputtered on the surface of a silicon-based substrate by a magnetron sputtering method, and partial nickel catalytic active sites are passivated by adding aluminum, so that the carbon film with a discontinuous structure is obtained after the carbon film grows by a CVD method; and then removing the aluminum-nickel catalytic metal layer on the silicon-based substrate by adopting a wet etching method to obtain the discontinuous carbon film directly falling on the substrate. The carbon film has sensitive response to respiration through conducting test of evaporating titanium electrode, and the device changes from non-conducting state to conducting state when respiration is changed from outside humidity, and has good response sensitivity, so that the carbon film can be used for developing and preparing wearable respiration monitoring device with high sensitivity and low power consumption.
Description
Technical Field
According to the invention, an aluminum nickel metal layer is used as a growth catalyst, a discontinuous carbon film with respiratory responsiveness is grown on a silicon-based chip by a CVD method, and a metal electrode is evaporated on the surface of the discontinuous carbon film to prepare a simple respiratory sensor for electrical performance test. The conductivity test shows that the carbon film has sensitive response to respiration, and has great practical significance in researching the growth mechanism of the discontinuous carbon film catalyzed by the aluminum nickel metal, preparing the simple low-power consumption high-sensitivity respiration sensor, optimizing the technological process of the respiration device, improving the quality of the device and the like.
Background
Carbon is located in the sixth position of the periodic table, is widely distributed in the crust, and is one of the elements that humans earlier contact and use. Nickel is a common catalytic metal for graphene growth, has higher carbon solubility, and can absorb a cracked carbon source at a high temperature, and then is precipitated and nucleated in the cooling process. Aluminum is a common nonferrous metal and has the advantages of CMOS compatibility, low melting point, low cost, extremely low carbon solubility at low temperature and the like. Aluminum does not have growth catalysis performance on carbon substances, is not generally used as a growth substrate material, but carbon substance growth can be carried out on an aluminum substrate under certain special conditions, for example, 2011 Yamada, T.et Al successfully synthesizes graphene on a non-catalytic material aluminum substrate at a low temperature by adopting a surface microwave plasma chemical vapor deposition method, and the research shows that compared with Cu, graphene films D and D' on Al have stronger peaks and fewer defects. According to the invention, aluminum without catalysis and nickel with better catalysis are combined to prepare aluminum-nickel metal layers with different thicknesses, so that discontinuous carbon films are grown catalytically. The main reason is that the addition of aluminum reduces the catalytic property of nickel, passivates the original active sites of part of the nickel metal layer, and is beneficial to generating the carbon film with a discontinuous structure. The discontinuous carbon film is in a non-conductive state before absorbing the vapor, and is changed from the non-conductive state to a conductive state after absorbing the vapor in respiration, thereby realizing the response to the respiration change of the human body.
Respiration is one of the most important physiological indexes of human body, and many diseases can cause the change of respiratory rate and depth, so that the real-time detection of respiration is helpful for diagnosing some potential diseases and preventing the risk of sudden cardiopulmonary arrest. In the past, different methods have been devised to monitor human respiration: traditional methods of respiratory rate measurement are to detect expansion and contraction of the chest by pressure sensors, or to detect airflow from the nasal cavity. However, these conventional methods cannot realize real-time and portable monitoring, and there are methods of monitoring respiration by detecting a temperature change between inhalation and exhalation by a thermal sensor. In fact, the biggest feature of respiration is that the local humidity around the mouth and nose changes due to the change of the respiration state, and the respiration state can be directly obtained by analyzing the resistance or capacitance parameters of the humidity sensitive material. By utilizing the characteristic, yu Luo et al adopts silk fibroin with good biocompatibility as a sensing film, and develop a transparent and ultra-sensitive humidity sensor which shows good response to vapor penetration during human respiration and is used for wearable respiration monitoring. In addition, graphene Oxide (GO), which is a derivative of graphene, contains various active oxygen functional groups such as epoxy, hydroxyl, carboxyl, etc., has extremely strong hydrophilicity and humidity sensitivity, and is also a common humidity sensitive material, and Li et al have prepared a capacitive humidity sensor based on graphene oxide by a direct drop casting process, but the bonding between a graphene oxide film and a substrate is weak, and thus the adsorption capacity on a substrate is poor. In recent years, emerging flexible and wearable electronic products show great potential application value in medical care monitoring, and are attracting great attention in various communities, and developing a respiratory monitoring device with biocompatibility, wearable performance, transparency and high sensitivity is also becoming a research hotspot.
According to the invention, the aluminum-nickel metal layers with different thicknesses are used as growth substrates, and the growth attempt is carried out at 800 ℃ through a CVD method, so that finally, the aluminum-nickel metal layer with a certain thickness ratio can be found to grow a discontinuous carbon film which can be used for human respiration monitoring. The respiratory responsiveness of the device is shown as that the respiratory dynamics of a human body can be reflected in real time through the change of current, and the device has the advantages of low power consumption, high reaction speed, good repeatability and stability and the like, and can be used for manufacturing human respiratory monitoring equipment in future.
Disclosure of Invention
The invention aims at: a discontinuous carbon film preparation method based on aluminum nickel metal layers with different thicknesses and application of the discontinuous carbon film as a respiration sensor are provided.
Nickel is a commonly used graphene growth catalyst, has high carbon solubility, is absorbed in the heating process, is separated out in the cooling process, and is easy to form graphene with uneven layers and quality. Nickel has certain growth catalysis on carbon substances, while aluminum is a common metal, and has the advantages of low melting point, good conductivity, low cost and the like, but has no catalysis on the growth of the carbon substances. According to the invention, aluminum nickel metal layers with different thicknesses are used as growth substrates, certain methane is introduced at different temperatures for CVD growth attempt, and the addition of aluminum covers part of nickel catalytic active sites, so that the catalytic performance of the nickel catalytic active sites is reduced. As a result, it was found that an aluminum-nickel metal layer with a certain thickness ratio can be grown as a substrate at 800 ℃ to obtain a special discontinuous carbon film, and the carbon film has good respiratory responsiveness, can detect respiratory rate, and is changed from a non-conductive state to a conductive state after absorbing water vapor in the outside or respiration. Therefore, aiming at the existing market vacancy and technical defect of the existing respiratory sensor, the discontinuous carbon film preparation and respiratory sensor application based on the aluminum nickel metal layers with different thicknesses are provided, and the problems of complex preparation, low sensitivity, high power consumption and the like of the existing respiratory sensor are solved, so that the range of respiratory sensor materials is widened.
The technical scheme adopted by the invention is as follows:
the invention discloses a discontinuous carbon film preparation method based on an aluminum-nickel metal layer, which is characterized by comprising the following steps of:
(1) Removing impurities and organic pollutants from the surface of the silicon-based substrate;
(2) Then sputtering a metal Al layer on the silicon-based substrate, and then sputtering a metal Ni layer, wherein the thickness of the Al layer is 30-60nm, preferably 50nm, and the thickness of the Ni layer is 30-60nm, preferably 50nm; obtaining a silicon-based substrate with an aluminum-nickel metal layer; preferably, the Ni sputtering power is 400w,2.5A/s; the sputtering power of Al is 250w,1.5A/s;
(3) Introducing methane into the silicon-based substrate subjected to metal sputtering at 800 ℃ for CVD growth; the pressure is controlled to 25mbar during the growth process, the temperature is firstly increased to 800 ℃, and after the temperature is stabilized, the temperature is firstly increased to 1000sccm H 2 Annealing for 7min, and then introducing carbonSource CH 4 Three gases Ar and H in the growth process 2 、CH 4 The flux of (2) is 960sccm, 40sccm, 5sccm, respectively; and after the growth is finished, cooling to a temperature lower than 200 ℃ in Ar atmosphere, wherein the cooling rate is 15 ℃/min.
(4) After CVD growth, a discontinuous carbon film is obtained on the surface, a wet etching method is adopted to soak a sample in the solution to remove the aluminum nickel metal layer, and the discontinuous carbon film directly falling on the silicon-based substrate is obtained;
the wet etching is specifically as follows: after a polymer supporting layer, namely polymethyl methacrylate (PMMA), is spin-coated on the surface of the carbon film, the prepared corrosive liquid reacts with the metal layer below through the layer to corrode the two metal layers without damaging the PMMA layer on the surface, so that the carbon film and the PMMA layer are left to directly fall on a silicon-based substrate, finally, the PMMA layer on the carbon film is dissolved by using the principle of mutual solubility of organic solvents, and the carbon film and a substrate are better in adhesiveness and are not easy to fall off in the process, so that the discontinuous carbon film directly falling on the silicon-based substrate can be obtained.
Etching solution: the components of the corrosion solution are CuSO 4 HCl and H 2 O, in a molar ratio of about 1: (5.0-5.5): (65-70), such as 1:5.4:69.8.
spin-coating PMMA: spin-coating a layer of PMMA on the surface of the grown silicon-based substrate by using a spin coater, wherein the spin-coating step is that 800r is firstly carried out for 6s, and then 2000r is carried out for 20s; after spin coating, PMMA was cured by baking at 100deg.C for 2 min. The rotating speed is not too high, otherwise, the PMMA film is too thin, the mechanical strength is low, the PMMA film is easy to damage, and the function of protecting the carbon film is not realized.
And (3) adopting a mode of soaking in corrosive liquid, and completely corroding the metal part after soaking for about 3 hours, so that the PMMA and the carbon film layer are left to directly fall on the silicon-based substrate.
And (3) drying, namely taking out the flakes, washing with ionized water, naturally air-drying, and then drying on a heating table at 150 ℃ for 10min to firmly bond the surface PMMA and the carbon film layer with the substrate and prevent the carbon film from falling off in the next PMMA removal step.
(5) Acetone soaking to remove PMMA: soaking the dried sample in acetone for about 8 hours, and removing PMMA on the surface; then soaking and cleaning sequentially by using ethanol and deionized water; the ethanol is mainly used for removing residual acetone, and deionized water is used for removing residual ethanol. And finally, naturally air-drying the sample to obtain a discontinuous carbon film directly falling on the silicon-based substrate, so that subsequent Raman spectrum, optical microscope, SEM characterization and respiratory conductivity test are facilitated.
Electrodes, such as titanium gold electrodes, are prepared on the discontinuous carbon film for use in a respiratory sensor.
In order to obtain larger breath responsiveness, before testing the responsiveness of the grown carbon film to breath, a titanium electrode with the thickness of 10nm/150nm is prepared by applying a hard mask plate on the surface of the carbon film for evaporation. During conductivity test, a probe is pricked on a pair of evaporated titanium electrodes, a fixed voltage is applied, and the change condition of current with time under the condition of simulating artificial respiration is tested. As shown in FIG. 8, the carbon film current I grown on different metal substrates has different time variation, wherein 50nmAl/50nmNi is not conductive under the condition of no breathing, when artificial respiration is simulated, the exhaled water vapor changes the discontinuous state into the continuous state to realize conduction, and the carbon films grown on the other two metal substrates 50nmNi/50nmAl and 25nmNi/50nmAl/25nmNi are thicker (as shown in FIG. 5), have conductivity when artificial respiration is not simulated, and after artificial respiration is simulated, the current is increased
The invention mainly comprises the steps of sputtering an aluminum nickel metal layer with a certain thickness proportion on a silicon substrate as a catalyst, growing to obtain a discontinuous carbon film by CVD, and sputtering a titanium gold electrode on the grown discontinuous carbon film to prepare the simple respiration sensor. The simple respiration sensor provided by the invention comprises the following structures: the technical route of the three parts of the silicon-based substrate, the discontinuous carbon film on the substrate and the titanium-gold electrode on the carbon film is shown in figure 2.
Drawings
FIG. 1 is a schematic diagram of a low power consumption breath sensor based on a discontinuous carbon film in the present invention.
FIG. 2 is a flow chart of experimental techniques in the present invention.
FIG. 3 is a schematic diagram of the respiratory responsiveness principle of the discontinuous carbon film structure in the present invention.
FIG. 4 is an optical microscope image of a different metal substrate of the present invention after CVD growth at 800 ℃.
Fig. 5 is an SEM image of a different metal substrate of the present invention after CVD growth at 800 ℃.
Fig. 6 is a graph showing raman curves of different metal substrates according to the present invention after CVD growth at 800 ℃.
FIG. 7 is an optical micrograph of the device of the present invention after evaporating a titanium electrode.
Fig. 8 is a plot of current I versus time for a device under simulated respiratory conditions in the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. In addition, the technical features described in the embodiments of the present invention described below may be combined with each other as long as they do not collide with each other.
The invention discloses a respiratory sensor based on a discontinuous carbon film and a preparation method thereof. The respiratory sensing device comprises three parts: a silicon-based substrate, a discontinuous carbon film on the silicon-based substrate, and a titanium-gold electrode on the discontinuous carbon film.
The specific implementation method comprises the following steps: firstly, a large round silicon wafer (300 nm SiO) 2 ) Scribing, namely scribing the small silicon-based substrate with the size of 1cm, soaking the small silicon-based substrate in acetone for 10min, then soaking in ethanol and deionized water for 10min in sequence, and cleaning, and drying by a nitrogen gun, wherein the aim is to remove surface impurities and organic pollutants; then heating for 3min on a heating table at 100 ℃, and drying the flakes. Then sputtering metal layers on the silicon-based substrate in sequence: 50nmAl/50nmNi, 50nmNi/50nmAl, 25nmNi/50nmAl/25nmNi (Ni sputtering power 400w,2.5A/s; al sputtering power 250w, 1.5A/s) to obtain silicon-based substrates with metal layers of different thicknesses composed of AlNi.
And introducing methane into the silicon-based substrate after metal sputtering at 800 ℃ to carry out CVD growth. The growth equipment is a vertical cold wall type CVD system with the model of Black Magic manufactured by Aixtron corporation, england, and mainly comprises an equipment main body, a vacuum oil pump and a circulating water cooler, wherein the equipment main body is the core of the whole equipment: the center of the cavity is provided with a graphite heater, the two ends of the graphite heater are electrified to realize heating according to the Joule heat principle, and the temperature of the graphite heater is detected by a thermocouple and is led into the system; below the heater is a plasma electrode, which is in a loop with the entire chamber metal wall, for providing a plasma electric field. The top of the cavity is provided with a gas nozzle, and when the growth is carried out, methane, hydrogen and other gases are mixed outside the cavity and then enter the cavity from the top nozzle; the bottom of the cavity is provided with an exhaust system which is communicated with a vacuum pump to control the air pressure in the cavity; the metal walls around the chamber are kept at a low temperature by means of a water-cooled circulation system.
The growth process is as follows: the pressure is controlled to 25mbar during the growth process, the temperature is raised to 800 ℃ first, and the temperature raising rate is 20 ℃/min. After the temperature is stable, the temperature is firstly set at 1000sccm H 2 Annealing for 7min, introducing carbon source, and growing for 10min, wherein three gases Ar and H are used in the growing process 2 、CH 4 The flux of (C) was 960sccm, 40sccm, and 5sccm, respectively. And after the growth is finished, cooling to a temperature lower than 200 ℃ in Ar atmosphere, wherein the cooling rate is 15 ℃/min.
After CVD growth, a discontinuous carbon film is obtained on the surface, a wet etching method is adopted to soak a sample in the solution to remove the aluminum-nickel metal layer, and the discontinuous carbon film directly falling on the silicon-based substrate is obtained. The wet etching principle is that after a polymer supporting layer-polymethyl methacrylate (PMMA) is spin-coated on the surface of a carbon film, the prepared etching solution can etch away two metal layers through the reaction of the polymer supporting layer and the metal below without damaging the PMMA layer on the surface, so that the carbon film and the PMMA layer are left to directly fall on a silicon-based substrate, finally, the PMMA layer on the carbon film is dissolved by using the principle of mutual dissolution of organic solvents, and the adhesion between the carbon film and a substrate is better in the process and is not easy to fall off, so that the discontinuous carbon film directly falling on the silicon-based substrate can be obtained.
The wet etching method comprises the following specific steps:
(1) and (5) preparing an etching solution. The components of the corrosion solution are CuSO 4 HCl and H 2 O, in a molar ratio of about 1:5.4:69.8.
(2) and (5) spin-coating PMMA. Spin-coating a layer of PMMA on the surface of the silicon-based substrate after growth by using a spin coater, wherein the spin-coating step is that 800r is firstly carried out for 6s, and then 2000r is carried out for 20s. After spin coating, PMMA was cured by baking at 100deg.C for 2 min. The rotating speed is not too high, otherwise, the PMMA film is too thin, the mechanical strength is low, the PMMA film is easy to damage, and the function of protecting the carbon film is not realized.
(3) And (5) soaking in a corrosive liquid. After soaking for about 3 hours, the metal part is completely corroded away, leaving the PMMA and carbon film layer directly on the silicon-based substrate.
(4) And (5) drying. Taking out the flakes, washing with ionized water, naturally air-drying, and drying in a heating table at 150deg.C for 10min to firmly bond the PMMA and carbon film layer on the surface with the substrate, so as to prevent the carbon film from falling off in the next PMMA removal step.
(5) And (5) soaking in acetone to remove PMMA. And immersing the dried sample in acetone for about 8 hours, and removing PMMA on the surface. Then soaking and cleaning by using ethanol and deionized water in sequence. The ethanol is mainly used for removing residual acetone, and deionized water is used for removing residual ethanol. And finally, naturally air-drying the sample to obtain a discontinuous carbon film directly falling on the silicon-based substrate, so that subsequent Raman spectrum, optical microscope, SEM characterization and respiratory conductivity test are facilitated.
In order to obtain larger breath responsiveness, before testing the responsiveness of the grown carbon film to breath, a titanium electrode with the thickness of 10nm/150nm is prepared by applying a hard mask plate on the surface of the carbon film for evaporation. During conductivity test, a probe is pricked on a pair of evaporated titanium electrodes, a fixed voltage is applied, and the change condition of current with time under the condition of simulating artificial respiration is tested. As shown in FIG. 8, the carbon film current I grown on different metal substrates is different in time change condition, wherein 50nmAl/50nmNi is not conductive under the non-breathing condition, the exhaled water vapor changes the discontinuous state into the continuous state to realize conduction in artificial respiration simulation, and carbon films grown on the other two metal substrates 50nmNi/50nmAl and 25nmNi/50nmAl/25nmNi are thicker (as shown in FIG. 5), have conductivity in artificial respiration simulation, and have insignificant current increase and poor responsiveness than 50nmAl/50nmNi after artificial respiration is added.
It will be readily appreciated by those skilled in the art that the foregoing description is merely a preferred embodiment of the invention and is not intended to limit the invention, but any modifications, equivalents, improvements or alternatives falling within the spirit and principles of the invention are intended to be included within the scope of the invention.
Claims (7)
1. The preparation method of the discontinuous carbon film based on the aluminum-nickel metal layer is characterized by comprising the following steps of:
(1) Removing impurities and organic pollutants from the surface of the silicon-based substrate;
(2) Then sputtering a metal Al layer on the silicon-based substrate, and then sputtering a metal Ni layer, wherein the thickness of the Al layer is 30-60nm, and the thickness of the Ni layer is 30-60nm; obtaining a silicon-based substrate with an aluminum-nickel metal layer; ni sputtering power is 400w,2.5A/s; the sputtering power of Al is 250w,1.5A/s;
(3) Introducing methane into the silicon-based substrate subjected to metal sputtering at 800 ℃ for CVD growth; the pressure is controlled to 25mbar during the growth process, the temperature is firstly increased to 800 ℃, and after the temperature is stabilized, the temperature is firstly increased to 1000sccm H 2 Annealing for 7min, and then introducing a carbon source CH 4 Three gases Ar and H in the growth process 2 、CH 4 The flux of (2) is 960sccm, 40sccm, 5sccm, respectively; after the growth is finished, cooling to a temperature lower than 200 ℃ in Ar atmosphere, wherein the cooling rate is 15 ℃/min;
(4) After CVD growth, a discontinuous carbon film is obtained on the surface, a wet etching method is adopted to soak a sample in the solution to remove the aluminum nickel metal layer, and the discontinuous carbon film directly falling on the silicon-based substrate is obtained; the wet etching is specifically as follows: after a polymer supporting layer-polymethyl methacrylate (PMMA) is spin-coated on the surface of a carbon film, the prepared corrosive liquid reacts with the metal layer below through the layer to corrode the two metal layers without damaging the PMMA layer on the surface, so that the carbon film and the PMMA layer are left to directly fall on a silicon-based substrate, finally, the PMMA layer on the carbon film is dissolved by using the principle of mutual dissolution of organic solvents, and the carbon film and a substrate are better in adhesiveness and are not easy to fall off in the process, so that a discontinuous carbon film directly falling on the silicon-based substrate is obtained;
(5) Acetone soaking to remove PMMA: soaking the dried sample in acetone to remove PMMA on the surface; then soaking and cleaning by using ethanol and deionized water in sequence.
2. The method for producing a discontinuous carbon film based on an aluminum-nickel metal layer according to claim 1, wherein the etching solution: the components of the corrosion solution are CuSO 4 HCl and H 2 O, its mole ratio is 1: (5.0-5.5): (65-70).
3. A method for producing a discontinuous carbon film based on an aluminum-nickel metal layer according to claim 2, wherein CuSO 4 HCl and H 2 O, its mole ratio is 1:5.4:69.8.
4. the method for preparing the discontinuous carbon film based on the aluminum-nickel metal layer according to claim 1, wherein PMMA is spin-coated: spin-coating a layer of PMMA on the surface of the grown silicon-based substrate by using a spin coater, wherein the spin-coating step is that 800r is firstly carried out for 6s, and then 2000r is carried out for 20s; after spin coating, PMMA was cured by baking at 100deg.C for 2 min.
5. The preparation method of the discontinuous carbon film based on the aluminum-nickel metal layer, which is characterized in that a corrosive liquid soaking mode is adopted, the metal part is completely corroded after soaking, and PMMA and the carbon film layer are left to directly fall on a silicon-based substrate;
and (3) drying, namely taking out the flakes, washing with ionized water, naturally air-drying, and then drying on a heating table at 150 ℃ for 10min to firmly bond the surface PMMA and the carbon film layer with the substrate and prevent the carbon film from falling off in the next PMMA removal step.
6. The method for producing a discontinuous carbon film based on an aluminum-nickel metal layer according to claim 1, wherein the thickness of the Al layer is 50nm and the thickness of the Ni layer is 50nm.
7. Use of a discontinuous carbon film based on an alnico metal layer, prepared according to the method of any one of claims 1-6, for preparing electrodes on a discontinuous carbon film for use in a respiration sensor.
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| CN102994976A (en) * | 2011-09-08 | 2013-03-27 | 中国科学院上海硅酸盐研究所 | Multi-element substrate, graphene capable of continuously adjusting layer number based on multi-element substrate and preparation method |
| CN108660430A (en) * | 2018-05-14 | 2018-10-16 | 北京工业大学 | The process of the direct growing large-area graphene of class on insulated by oxide substrate |
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| CN102134067A (en) * | 2011-04-18 | 2011-07-27 | 北京大学 | Method for preparing single-layer graphene |
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