High-sensitivity fast-recovery ammonia sensor and preparation method thereof

Abstract

The application discloses a high-sensitivity and fast-recovery ammonia sensor and a preparation method thereof, and relates to the field of trace detection. The sensor comprises a silicon substrate and a silicon micro-bridge structure above the silicon substrate. The silicon micro-bridge structure comprises a silicon thin film, a Wheatstone full-bridge piezoresistive circuit and a silicon nitride passivation layer. The Wheatstone full-bridge piezoresistive circuit is arranged in the silicon thin film, and the silicon nitride passivation layer is arranged on the upper surface of the silicon thin film. An ammonia-sensitive film is arranged at the upper end of the silicon micro-bridge structure. The ammonia-sensitive film is arranged to be capable of interacting with ammonia molecules in a to-be-detected environment to produce deformation, so that the output voltage of the Wheatstone full-bridge piezoresistive circuit changes. The application utilizes the expansion characteristics of the sensitive film, mainly the physical adsorption process of ammonia molecules, and can work in a room temperature environment. Meanwhile, the thin film deformation mechanics characteristics of the silicon micro-bridge are utilized, so that the recovery speed of the ammonia sensor is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-detection, in particular to a high-sensitivity and fast-recovery ammonia sensor and a preparation method thereof. BACKGROUND

[0002] Ammonia is a toxic gas, and when a certain amount of ammonia is inhaled by the human body, it can induce poisoning symptoms, and in severe cases, the eyes can be blinded, and even more fatal. In addition, ammonia, as a metabolic product, has been recognized as a biomarker for diagnosing diabetes, asthma, kidney disease, malignant tumors and lung cancer. At present, ammonia sensors have a wide range of applications in light industry, chemical industry, pharmaceutical industry, medical health, environmental protection and biological science experiments. In traditional ammonia sensors, electrochemical and semiconductor ammonia sensors are the most common, such as patent CN119827589A discloses an organic phosphoric acid molecule modified tungsten oxide ammonia sensor and a preparation method and application thereof. The application utilizes the bonding of organic phosphoric acid molecules with the active sites on the surface of tungsten trioxide and the catalytic decomposition ability of ammonia, i.e. increasing the service life of the sensor and enhancing the sensitivity and selectivity of tungsten trioxide to ammonia. Patent CN119804577A discloses an ammonia gas sensor based on layered MoTe2 and TiO2 heterojunction, a preparation process and application, which adopts a drop coating method to coat a gas-sensitive material on the surface of an interdigital electrode plate, and has good sensitivity to ammonia and a low detection limit. At present, this type of ammonia sensor can achieve high ammonia detection sensitivity and a large detection range, but it has high working temperature, low integration, high power consumption and slow response / recovery time, and is easily disturbed by external environment. In the signal processing process, errors are also easily introduced.

[0003] Therefore, it is of great practical significance to develop a room temperature ammonia sensor with simple structure, good stability, high sensitivity, fast response / recovery speed. SUMMARY

[0004] The purpose of the present application is to provide a high-sensitivity and fast-recovery ammonia sensor and a preparation method thereof, which utilizes the mechanical properties of a silicon micro-bridge combined with the expansion properties of a sensitive film to solve the problems of high working temperature and slow response / recovery speed of ammonia sensors in the prior art.

[0005] Firstly, the present application provides a high-sensitivity and fast-recovery ammonia sensor, which comprises a silicon substrate and a silicon micro-bridge structure above the silicon substrate, the silicon micro-bridge structure comprising a silicon thin film, a Wheatstone full-bridge piezoresistive circuit and a silicon nitride passivation layer, the Wheatstone full-bridge piezoresistive circuit being arranged in the silicon thin film, and the silicon nitride passivation layer being arranged on the upper surface of the silicon thin film; an ammonia-sensitive film being arranged at the upper end of the silicon micro-bridge structure.

[0006] The ammonia-sensitive film is arranged to be capable of interacting with ammonia molecules in a to-be-detected environment to produce deformation, so that the output voltage of the Wheatstone full-bridge piezoresistive circuit changes.

[0007] As an optional implementation, the ammonia-sensitive film comprises a porous hydrogen-bond organic framework film and a perfluorosulfonic acid film, the porous hydrogen-bond organic framework film is arranged above the silicon nitride passivation layer, and the perfluorosulfonic acid film is arranged above the porous hydrogen-bond organic framework film.

[0008] The projection of the porous hydrogen-bond organic framework film in the vertical direction falls within the perfluorosulfonic acid film, and the surface area of the perfluorosulfonic acid film is greater than that of the porous hydrogen-bond organic framework film.

[0009] As an optional implementation, the porous hydrogen-bond organic framework film is circular, and the perfluorosulfonic acid film is circular or rectangular.

[0010] As an optional implementation, the perfluorosulfonic acid film is petal-shaped.

[0011] As an optional implementation, the perfluorosulfonic acid film comprises 2 to 20 petals.

[0012] As an optional implementation, the thickness of the silicon film is 10 to 40 microns, and the thickness of the silicon nitride passivation layer is 300 to 500 nanometers.

[0013] As an optional implementation, the projections of the porous hydrogen-bond organic framework film and the perfluorosulfonic acid film in the vertical direction are within the range of the silicon film.

[0014] Secondly, the embodiment of the present application also provides a preparation method of the high-sensitivity fast-recovery ammonia sensor, comprising the following steps:

[0015] S1: dispersing a perfluorosulfonic acid solution in deionized water to obtain a perfluorosulfonic acid dispersion liquid, and dispersing a porous hydrogen-bond organic framework solution to obtain a porous hydrogen-bond organic framework dispersion liquid;

[0016] S2: preparing a silicon micro-bridge structure on the back of a silicon substrate;

[0017] S3: placing a template with a hollow structure on the surface of the silicon micro-bridge structure, coating the porous hydrogen-bond organic framework dispersion liquid on the template with the hollow structure, drying in nitrogen, and removing the template with the hollow structure to obtain a silicon micro-bridge structure covered with a circular porous hydrogen-bond organic framework film;

[0018] S4: placing a template on the silicon micro-bridge structure covered with the circular porous hydrogen-bonded organic framework film, taking the perfluorosulfonic acid dispersion liquid to coat on the template, drying in nitrogen, and obtaining the silicon micro-bridge structure with the sensitive film of the perfluorosulfonic acid-restricted porous hydrogen-bonded organic framework structure after removing the template.

[0019] As an optional implementation, the concentration of the perfluorosulfonic acid dispersion liquid in S1 is 0.5-2.5 wt.%, and the concentration of the porous hydrogen-bonded organic framework dispersion liquid is 0.8-1.2 mg / ml.

[0020] S2 includes preparing a silicon film by using an anisotropic KOH etching technology, forming a Wheatstone full-bridge circuit in the silicon film by an ion implantation process, and preparing a silicon nitride passivation layer on the surface of the silicon film for protecting the silicon film and the pressure-sensitive full-bridge circuit.

[0021] As an optional implementation, the diameter of the circular hole of the template of the hollow structure in S3 is 20-100 microns.

[0022] Compared with the prior art, the embodiment of the present application has the following advantages and beneficial effects:

[0023] 1. Compared with the traditional electrochemical reaction mechanism, the embodiment of the present application utilizes the expansion characteristics of the sensitive film, mainly the physical adsorption process of ammonia molecules, and can work in a room temperature environment. Meanwhile, the film deformation mechanics characteristics of the silicon micro-bridge are utilized to effectively improve the recovery speed of the ammonia sensor.

[0024] 2. The embodiment of the present application embeds a core layer between the single-layer sensitive film and the silicon film to form a restricted structure, so that the expansion behavior of the core layer only occurs in the vertical direction. In combination with the petal-shaped upper film formed by the template method, the sensitivity of the sensor is greatly improved. The silicon micro-bridge is prepared by using the MEMS technology, which effectively improves the integration and compatibility of the ammonia sensor. The ammonia sensor also has the advantages of good linearity, simple structure, easy manufacturing, strong anti-interference ability, and the like. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without paying creative labor. In the drawings:

[0026] Figure 1 Fig. 7 is a top view of the ammonia sensor in the embodiment 7 of the present application;

[0027] Figure 2A cross-sectional structural diagram of the ammonia sensor in Example 7 of the present application;

[0028] Figure 3 A response comparison diagram of the ammonia sensors prepared by the non-constrained structure of the double-layer film and the constrained structure in Example 1;

[0029] Figure 4 A response comparison diagram of the ammonia sensors prepared by the non-petal-shaped structure and the petal-shaped structure in Example 2;

[0030] Figure 5 A response / recovery time comparison diagram of the ammonia sensors prepared by the non-petal-shaped structure and the petal-shaped structure in Example 3;

[0031] Figure 6 A response comparison diagram of the ammonia sensors prepared in Example 4 and Example 3;

[0032] Figure 7 A response comparison diagram of the ammonia sensors prepared in Example 5 and Example 3.

[0033] BRIEF DESCRIPTION OF DRAWINGS

[0034] 1-silicon substrate, 2-silicon film, 3-Wheatstone full-bridge resistance circuit, 4-silicon nitride passivation layer, 5-ammonia sensitive film, 51-perfluorosulfonic acid film, 52-porous hydrogen-bonded organic framework film. DETAILED DESCRIPTION

[0035] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are some but not all of the embodiments of the present application.

[0036] Therefore, the detailed description of the embodiments of the present application provided below is not intended to limit the scope of the claimed application, but only represents selected embodiments of the application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of protection of the present application.

[0037] In order to solve the problems of high working temperature and slow response / recovery speed of the ammonia sensor in the prior art, the embodiments of the present application provide a high-sensitivity and fast-recovery ammonia sensor with perfluorosulfonic acid constrained porous hydrogen-bonded organic framework at room temperature and a preparation method thereof. By using the mechanical properties of the silicon micro-bridge and the constrained structure of the multi-layer film, and combining the expansion properties of the sensitive film, high sensitivity and fast response / recovery gas detection are realized.

[0038] Specifically, the embodiments of the present application provide a preparation method of a high-sensitivity and fast-recovery ammonia sensor, comprising the following steps:

[0039] (1) Dissolve 1 ml of perfluorosulfonic acid solution (concentration of 5 wt.%) in 1-9 ml of deionized water, ultrasonic stirring at room temperature for 40-60 minutes to obtain a uniform dispersion solution with a concentration of 0.5-2.5 wt.%; place 1-10 ml of porous hydrogen-bonded organic framework solution (1 mg / ml) in a container, ultrasonic stirring for 30-60 minutes to obtain a uniformly dispersed porous hydrogen-bonded organic framework dispersion, and keep the dispersion obtained above for further use.

[0040] It should be noted that the preparation method of the porous hydrogen-bonded organic framework solution comprises the following steps:

[0041] Place a porous three-arm monomer single crystal ([TM●3H] 3+ ●3HSO 4- ) sample (~30 mg) in a 20 mL glass bottle, add 1 mL of acetonitrile (MeCN) and 0.02 mL of 1,2-ethanedithiol (EDT) to it, and store it in the dark overnight. After 24 hours, replace the mixture with a fresh portion of 0.02 mL of EDT and 1 mL of MeCN. Irradiate the reaction tube under forced air cooling and UV light (medium pressure 175 watt mercury lamp) for 72 hours, collect the crystal sample and wash it with excess MeCN to remove unreacted EDT, and finally dissolve the filtered and washed porous single crystal hydrogen-bonded organic framework in ethanol to obtain a porous hydrogen-bonded organic framework solution.

[0042] (2) Use anisotropic KOH etching technology to prepare a square micro-bridge structure from the back of an N-type silicon substrate, use an ion implantation process to form a pressure-sensitive full bridge in the silicon thin film of the silicon micro-bridge, then make a silicon nitride passivation layer on the surface of the silicon thin film to obtain a silicon micro-bridge substrate with a pressure-sensitive full bridge circuit, and clean the silicon micro-bridge substrate for further use; the thickness of the silicon thin film of the silicon micro-bridge is 10-40 microns, and the thickness of the silicon nitride passivation layer on the surface of the silicon thin film is 300-500 nanometers.

[0043] (3) Place a silica template with a hollow structure on the surface of the silicon micro-bridge obtained in step (2), then take 0.1-2.0 microliters of the porous hydrogen-bonded organic framework dispersion prepared in step (1) and coat it onto the template, place the silicon micro-bridge coated with the porous hydrogen-bonded organic framework dispersion in a nitrogen atmosphere and dry it for 2-5 hours, and after removing the template, obtain a silicon micro-bridge covered with a circular porous hydrogen-bonded organic framework film; the hollow silica template structure is circular and its diameter is 20-100 microns, which does not exceed the side length of the silicon micro-bridge.

[0044] (4) placing a petal-shaped silica template on the silicon micro-bridge covered with the round porous hydrogen-bonded organic framework film obtained in step (3), then coating 2.0-10.0 microliters of the perfluorosulfonic acid dispersion prepared in step (1) onto the template, and drying the silicon micro-bridge coated with the perfluorosulfonic acid dispersion and the porous hydrogen-bonded organic framework film in nitrogen for 3-10 hours to obtain a silicon micro-bridge with a sensitive film of a perfluorosulfonic acid-restricted porous hydrogen-bonded organic framework structure deposited thereon after removing the template; preferably, the diameter or side length of the petal-shaped silica template structure is not more than the side length of the silicon micro-bridge.

[0045] More preferably, the petal-shaped perfluorosulfonic acid film is located above the round porous hydrogen-bonded organic framework film formed in step (3); and the petal-shaped perfluorosulfonic acid film formed can completely wrap the round porous hydrogen-bonded organic framework film formed in step (3), forming a restriction structure with the silicon film of the silicon micro-bridge.

[0046] (5) measuring the ammonia concentration by measuring the change in the piezoresistive resistance caused by the deformation of the silicon micro-bridge with the sensitive film of the perfluorosulfonic acid-restricted porous hydrogen-bonded organic framework structure deposited thereon in step (4).

[0047] Embodiment 1: The present application provides a preparation method of a high-sensitivity and fast-recovery ammonia sensor, comprising the following steps:

[0048] (1) Dissolving 1 ml of a perfluorosulfonic acid solution (concentration of 5 wt.%) in 1 ml of deionized water, and ultrasonically stirring at room temperature for 40 minutes to obtain a uniform dispersion with a concentration of 2.5 wt.%; placing 1 ml of a porous hydrogen-bonded organic framework solution (1 mg / ml) in a container, and ultrasonically stirring for 30-60 minutes to obtain a uniformly dispersed porous hydrogen-bonded organic framework dispersion, and keeping the dispersion obtained above for further use.

[0049] (2) Using an anisotropic KOH etching technique to prepare a square micro-bridge structure from the back of an N-type silicon substrate, forming a piezoresistive full-bridge in the silicon film of the silicon micro-bridge using an ion implantation process, then fabricating a silicon nitride passivation layer on the surface of the silicon film to obtain a silicon micro-bridge substrate with a piezoresistive full-bridge circuit, and cleaning the silicon micro-bridge substrate for further use; the thickness of the silicon film of the silicon micro-bridge is 10 micrometers, and the thickness of the silicon nitride passivation layer on the surface of the silicon film is 300 nanometers.

[0050] (3) The surface of the silicon micro-bridge obtained in step (2) is placed with a hollow structure of a silica template, then 0.1 microliters of the porous hydrogen-bonded organic framework dispersion prepared in step (1) is coated on the template, the silicon micro-bridge coated with the porous hydrogen-bonded organic framework dispersion is dried in nitrogen for 2 hours, and the silicon micro-bridge with a sensitive film of a porous hydrogen-bonded organic framework structure deposited with perfluorosulfonic acid constraint is obtained after the template is removed; the hollow silica template structure is circular and its diameter is 20 micrometers, which does not exceed the side length of the silicon micro-bridge.

[0051] (4) The silicon micro-bridge with a circular porous hydrogen-bonded organic framework film obtained in step (3) is placed with a petal-shaped silica template, then 2.0 microliters of the perfluorosulfonic acid dispersion prepared in step (1) is coated on the template, the silicon micro-bridge coated with the perfluorosulfonic acid dispersion and the porous hydrogen-bonded organic framework film is dried in nitrogen for 3 hours, and the silicon micro-bridge with a sensitive film of a porous hydrogen-bonded organic framework structure deposited with perfluorosulfonic acid constraint is obtained after the template is removed; the diameter or side length of the petal-shaped silica template structure does not exceed the side length of the silicon micro-bridge;

[0052] The petal-shaped perfluorosulfonic acid film is located above the circular porous hydrogen-bonded organic framework film formed in step (3); and the petal-shaped perfluorosulfonic acid film formed can completely wrap the circular porous hydrogen-bonded organic framework film formed in step (3), and together with the silicon film of the silicon micro-bridge, forms a constraint structure for the circular porous hydrogen-bonded organic framework film.

[0053] (5) The ammonia concentration is measured by measuring the change in the pressure-sensitive resistance caused by the deformation of the silicon micro-bridge with a sensitive film of a porous hydrogen-bonded organic framework structure deposited with perfluorosulfonic acid constraint in step (4).

[0054] Embodiment 2: The embodiment of the present application provides a preparation method of a high-sensitivity and fast-recovery ammonia sensor, which comprises the following steps:

[0055] (1) 1 ml of a perfluorosulfonic acid solution (concentration of 5 wt.%) is dissolved in 9 ml of deionized water, ultrasonic stirring is performed at room temperature for 60 minutes to obtain a uniform dispersion liquid with a concentration of 2.5 wt.%; 10 ml of a porous hydrogen-bonded organic framework solution (1 mg / ml) is placed in a container, ultrasonic stirring is performed for 60 minutes to obtain a uniformly dispersed porous hydrogen-bonded organic framework dispersion, and the dispersion obtained is kept for further use.

[0056] (2) A square micro-bridge structure is prepared from the back of an N-type silicon substrate by using an anisotropic KOH etching technique, a pressure-sensitive full-bridge is formed in the silicon thin film of the silicon micro-bridge by using an ion implantation process, a silicon nitride passivation layer is made on the surface of the silicon thin film to obtain a silicon micro-bridge substrate with a pressure-sensitive full-bridge circuit, and the silicon micro-bridge substrate is cleaned and ready for further use; the thickness of the silicon thin film of the silicon micro-bridge is 40 microns, and the thickness of the silicon nitride passivation layer on the surface of the silicon thin film is 500 nanometers.

[0057] (3) The silicon micro-bridge obtained in step (2) is placed on a hollow structure of a silica template, then 2.0 microliters of the porous hydrogen-bonded organic framework dispersion prepared in step (1) is coated on the template, the silicon micro-bridge coated with the porous hydrogen-bonded organic framework dispersion is dried in nitrogen for 5 hours, and after the template is removed, a silicon micro-bridge covered with a circular porous hydrogen-bonded organic framework thin film is obtained; the hollow silica template structure is circular and its diameter is 100 microns, which does not exceed the side length of the silicon micro-bridge.

[0058] (4) The silicon micro-bridge covered with a circular porous hydrogen-bonded organic framework thin film obtained in step (3) is placed on a petal-shaped silica template, then 10.0 microliters of the perfluorosulfonic acid dispersion prepared in step (1) is coated on the template, the silicon micro-bridge coated with the perfluorosulfonic acid dispersion and the porous hydrogen-bonded organic framework thin film is dried in nitrogen for 10 hours, and after the template is removed, a silicon micro-bridge with a sensitive thin film of a perfluorosulfonic acid constrained porous hydrogen-bonded organic framework structure is obtained; preferably, the diameter or side length of the petal-shaped silica template structure does not exceed the side length of the silicon micro-bridge;

[0059] More preferably, the petal-shaped perfluorosulfonic acid thin film is located above the circular porous hydrogen-bonded organic framework thin film formed in step (3); and the petal-shaped perfluorosulfonic acid thin film can completely wrap the circular porous hydrogen-bonded organic framework thin film formed in step (3), together with the silicon thin film of the silicon micro-bridge, to form a constraint structure for the circular porous hydrogen-bonded organic framework thin film.

[0060] (5) The ammonia concentration is measured by measuring the change in the pressure-sensitive resistance caused by the deformation of the silicon micro-bridge with a sensitive thin film of a perfluorosulfonic acid constrained porous hydrogen-bonded organic framework structure obtained in step (4).

[0061] Embodiment 3: The embodiment of the present application provides a preparation method of a high-sensitivity and fast-recovery ammonia sensor, which comprises the following steps:

[0062] (1) Dissolve 1 ml of perfluorosulfonic acid solution (concentration of 5 wt.%) in 5 ml of deionized water, ultrasonic stirring for 50 minutes at room temperature, to obtain a uniform dispersion solution with a concentration of 1.5 wt.%; place 5 ml of porous hydrogen-bonded organic framework solution (1 mg / ml) in a container, ultrasonic stirring for 45 minutes to obtain a uniformly dispersed porous hydrogen-bonded organic framework dispersion, and keep the dispersion obtained above for further use.

[0063] (2) Use anisotropic KOH etching technology to prepare a square micro-bridge structure from the back of an N-type silicon substrate, use an ion implantation process to form a pressure-sensitive full bridge in the silicon thin film of the silicon micro-bridge, and then make a silicon nitride passivation layer on the surface of the silicon thin film to obtain a silicon micro-bridge substrate with a pressure-sensitive full bridge circuit, and clean the silicon micro-bridge substrate for further use; the thickness of the silicon thin film of the silicon micro-bridge is 10-40 microns, and the thickness of the silicon nitride passivation layer on the surface of the silicon thin film is 400 nanometers.

[0064] (3) Place a silica template with a hollow structure on the surface of the silicon micro-bridge obtained in step (2), and then coat 1 microliter of the porous hydrogen-bonded organic framework dispersion prepared in step (1) onto the template, and dry the silicon micro-bridge coated with the porous hydrogen-bonded organic framework dispersion in nitrogen for 3 hours, and after removing the template, obtain a silicon micro-bridge covered with a circular porous hydrogen-bonded organic framework film; the hollow silica template structure is circular and its diameter is 60 microns, which does not exceed the side length of the silicon micro-bridge.

[0065] (4) Place a petal-shaped silica template on the silicon micro-bridge covered with a circular porous hydrogen-bonded organic framework film obtained in step (3), and then coat 2.0-10.0 microliters of the perfluorosulfonic acid dispersion prepared in step (1) onto the template, and dry the silicon micro-bridge coated with the perfluorosulfonic acid dispersion and the porous hydrogen-bonded organic framework film in nitrogen for 6 hours, and after removing the template, obtain a silicon micro-bridge with a sensitive film of a perfluorosulfonic acid constrained porous hydrogen-bonded organic framework structure deposited thereon; preferably, the diameter or side length of the petal-shaped silica template structure does not exceed the side length of the silicon micro-bridge.

[0066] More preferably, the petal-shaped perfluorosulfonic acid film is located above the circular porous hydrogen-bonded organic framework film formed in step (3); and the petal-shaped perfluorosulfonic acid film formed can completely wrap the circular porous hydrogen-bonded organic framework film formed in step (3), together with the silicon thin film of the silicon micro-bridge, to form a constraint structure for the circular porous hydrogen-bonded organic framework film.

[0067] (5) Measure the ammonia concentration by measuring the change in pressure-sensitive resistance caused by the deformation of the silicon micro-bridge with a sensitive film of a perfluorosulfonic acid constrained porous hydrogen-bonded organic framework structure deposited thereon in step (4).

[0068] Comparative Example 1: A preparation method of an ammonia sensor is provided, which is different from Example 3 in that the petal-shaped perfluorosulfonic acid film does not completely wrap the circular porous hydrogen-bonded organic framework film, and the remaining steps remain unchanged.

[0069] Example 4: The example of the present application provides a preparation method of a high-sensitivity and fast-recovery ammonia sensor, which is different from Example 3 in that the porous hydrogen-bonded organic framework film is replaced by a polyaniline film, and the remaining steps remain unchanged.

[0070] Referring to Figure 6 As shown in the figure, when the core layer is a polyaniline film, although it can adsorb ammonia molecules, the deformation of the polyaniline film after adsorbing ammonia molecules is much smaller than that of the porous hydrogen-bonded organic framework film, so the sensitivity of the ammonia sensor prepared therefrom is relatively low.

[0071] Example 5: The example of the present application provides a preparation method of a high-sensitivity and fast-recovery ammonia sensor, which is different from Example 3 in that the perfluorosulfonic acid film is replaced by a graphene film, and the remaining steps remain unchanged.

[0072] Referring to Figure 7 As shown in the figure, when graphene is used as the top panel, the sensitivity of the sensor is improved to a certain extent, and it also has a constraint characteristic, but as the ammonia concentration increases, the degree of sensitivity improvement will decrease, because the graphene film is composed of single-layer or multi-layer graphene stacked together, when the deformation is large, the sheets will move horizontally, and it is difficult to completely constrain the deformation of the porous organic framework to occur only in the longitudinal direction.

[0073] Example 6: The example of the present application provides a preparation method of a high-sensitivity and fast-recovery ammonia sensor, which is different from Example 3 in that the perfluorosulfonic acid film is a non-petal-shaped circular structure, and the remaining steps remain unchanged.

[0074] Example 7: In combination with referring to Figure 1 and Figure 2 The example of the present application provides a high-sensitivity and fast-recovery ammonia sensor, which includes a silicon substrate at the bottom, a silicon micro-bridge structure made above the silicon substrate, the silicon micro-bridge structure includes a silicon film, the silicon film is provided with a Wheatstone full-bridge piezoresistive circuit, the surface of the silicon film is provided with a silicon nitride passivation layer, and further includes an ammonia-sensitive film prepared on the silicon nitride passivation layer by a template method, the ammonia-sensitive film is a sensitive film of a perfluorosulfonic acid constrained porous hydrogen-bonded organic framework structure; the ammonia-sensitive film covers the entire silicon nitride passivation layer.

[0075] Specifically, the silicon micro-bridge structure is prepared by using a KOH etching technology and an ion implantation process, and the silicon micro-bridge structure comprises a silicon thin film, a Wheatstone full-bridge piezoresistive circuit and a silicon nitride passivation layer, wherein the thickness of the silicon thin film is 10-40 microns, and the thickness of the silicon nitride passivation layer is 300-500 nanometers, the thickness of the above two is negatively correlated with the response of the ammonia sensor, if the thickness is greater than 40 microns, the deformation of the silicon micro-bridge structure caused by the deformation of the ammonia sensitive film is small, and the corresponding sensor response is small, on the contrary, if the thickness is thinner, the sensor response is larger, but the process requirement is higher, the cost increases sharply, and it is not suitable for productization.

[0076] In the embodiment of the present application, the ammonia sensitive film on the silicon nitride passivation layer is prepared by a template method, as shown in Figure 2 The ammonia sensitive film is prepared by using the silicon thin film as a bottom panel, the porous hydrogen-bonded organic framework thin film as a core layer and the perfluorosulfonic acid thin film as a top panel. The template shape of the top panel perfluorosulfonic acid thin film can be circular or square, and the diameter or side length thereof should be smaller than the side length of the silicon nitride passivation layer; the template shape of the core layer porous hydrogen-bonded organic framework thin film is circular, and the diameter thereof is smaller than the diameter or side length of the top panel perfluorosulfonic acid thin film, so that the top panel can completely cover the core layer to form a constraint structure, and the preparation method is referred to Embodiments 1-3, which causes the expansion deformation of the core layer porous organic framework thin film after adsorbing ammonia molecules to basically occur in the vertical direction, compared with the unconstrained structure, the preparation method is referred to Comparative Example 1, which will make the ammonia sensor produce a larger response, as shown in Figure 3 In the embodiment of the present application, the template shape of the top panel perfluorosulfonic acid thin film is circular.

[0077] As a preferred embodiment of the present application, the structure of the top panel perfluorosulfonic acid thin film is petal-shaped, and the preparation method is referred to Embodiments 1-3. The perfluorosulfonic acid thin film has a certain selectivity, and large molecules are difficult to quickly pass through the thin film into the core layer, and the penetration speed of ammonia molecules is slow, but the perfluorosulfonic acid is an organic thin film, which has strong plasticity, so the petal-shaped template is adopted in the embodiment of the present application, which does not affect the constraint characteristics of the top panel, increases the contact area of the sensitive film and ammonia molecules, and improves the response of the sensor, as shown in Figure 4 The more the number of petals of the top panel template is, the larger the contact area is, and the larger the response of the sensor is, and the adsorption and desorption of ammonia molecules can reach equilibrium faster, and the response time is shorter, on the contrary, the smaller the number of petals of the top panel template is, the smaller the response of the sensor is, and the longer the response time is, as shown in Figure 5 The more the number of petals of the top panel template is, the larger the contact area is, and the larger the response of the sensor is, and the adsorption and desorption of ammonia molecules can reach equilibrium faster, and the response time is shorter, on the contrary, the smaller the number of petals of the top panel template is, the smaller the response of the sensor is, and the longer the response time is, as shown in

[0078] Of course, the number of petals of the top layer panel perfluorosulfonic acid film template will also affect the constraint performance of the top layer panel, the more the number of petals, the thinner the connecting layer between the petals, the weaker the constraint ability. Preferably, the number of petals of the top layer panel template is 2-20. In order to facilitate understanding, the number of petals of the top layer panel in the embodiment of the application is 10.

[0079] In operation, the top layer panel perfluorosulfonic acid film and the core layer porous hydrogen-bonded organic framework film of the ammonia-sensitive film interact with ammonia molecules in the environment to be measured, and the ammonia film deforms, resulting in a corresponding change in the output voltage of the Wheatstone full-bridge circuit on the silicon micro-bridge structure. Specifically, when the concentration of ammonia in the environment increases, the deformation of the ammonia-sensitive film increases, and the output voltage of the Wheatstone full-bridge circuit increases; when the concentration of ammonia in the environment decreases, the deformation of the ammonia-sensitive film decreases, and the output voltage of the Wheatstone full-bridge circuit decreases, and the resilience characteristics of the silicon micro-bridge will speed up the recovery speed of the sensor and shorten the recovery time.

[0080] It should be noted that in the embodiment of the application, the ammonia-sensitive performance testing device of the ammonia sensor mainly consists of an electrode tuning ammonia sensor, a phase-locked loop oscillator (PLO-10i, MAXTEK-INFICON), a test cavity, a gas flow control system and a frequency counter (53131A, Agilent Technologies). The standard NH3 (10000 ppm, nitrogen as carrier gas) is adjusted by using a mass flow controller (MFC) to obtain the appropriate concentration of NH3. The gas sensor is placed in the test cavity, and different concentrations of NH3 are introduced to study its gas-sensitive properties. The sensor circuit is driven to resonate by the phase-locked loop oscillator, the resonance signal is collected and displayed in real time by the frequency counter, and the collected frequency data is transmitted to the computer through the GPIB-USB data line for saving and processing. In the present application, all data are measured at room temperature unless otherwise specified.

[0081] Overall, the embodiment of the application prepares a high-sensitivity and fast-recovery ammonia sensor of perfluorosulfonic acid constrained porous hydrogen-bonded organic framework at room temperature. By utilizing the mechanical properties of the silicon micro-bridge and the constraint structure of the multi-layer film, and combining the swelling properties of the sensitive film, high sensitivity and fast response / recovery gas detection are achieved.

[0082] The above specific embodiments further illustrate the purpose, technical solutions and advantages of the application. It should be understood that the above description is only a specific embodiment of the application and is not intended to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A high sensitivity fast recovery ammonia sensor characterized in that, The silicon micro-bridge structure includes a silicon substrate and a silicon micro-bridge structure above the silicon substrate, the silicon micro-bridge structure includes a silicon thin film, a Wheatstone full-bridge piezoresistive circuit and a silicon nitride passivation layer, the Wheatstone full-bridge piezoresistive circuit is arranged in the silicon thin film, and the silicon nitride passivation layer is arranged on the upper surface of the silicon thin film; An ammonia-sensitive film is arranged at the upper end of the silicon micro-bridge structure; The ammonia-sensitive film is arranged to be capable of interacting with ammonia molecules in a to-be-measured environment to produce deformation, so that the output voltage of the Wheatstone full-bridge piezoresistive circuit changes, and the ammonia-sensitive film is a multilayer constraint structure; The ammonia-sensitive film includes a porous hydrogen-bond organic framework thin film and a perfluorosulfonic acid thin film, the porous hydrogen-bond organic framework thin film is arranged above the silicon nitride passivation layer, and the perfluorosulfonic acid thin film is arranged above the porous hydrogen-bond organic framework thin film; The projection of the porous hydrogen-bond organic framework thin film in the vertical direction falls within the perfluorosulfonic acid thin film, and the surface area of the perfluorosulfonic acid thin film is greater than that of the porous hydrogen-bond organic framework thin film.

2. The high sensitivity fast recovery ammonia sensor according to claim 1, wherein The porous hydrogen-bond organic framework thin film is circular, and the perfluorosulfonic acid thin film is circular or rectangular.

3. The high sensitivity fast recovery ammonia sensor according to claim 2, wherein The perfluorosulfonic acid thin film is petal-shaped.

4. The high sensitivity fast recovery ammonia sensor according to claim 3, wherein The perfluorosulfonic acid thin film contains 2 to 20 petals.

5. The high sensitivity fast recovery ammonia sensor according to claim 1, wherein The thickness of the silicon thin film is 10 to 40 microns, and the thickness of the silicon nitride passivation layer is 300 to 500 nanometers.

6. The high sensitivity fast recovery ammonia sensor according to claim 1, wherein The projections of the porous hydrogen-bond organic framework thin film and the perfluorosulfonic acid thin film in the vertical direction are within the range of the silicon thin film.

7. A method for preparing a high-sensitivity fast-recovery ammonia sensor according to any one of claims 1 to 6, characterized by, The method includes the following steps: S1: dispersing a perfluorosulfonic acid solution in deionized water to obtain a perfluorosulfonic acid dispersion liquid, and dispersing a porous hydrogen-bond organic framework solution to obtain a porous hydrogen-bond organic framework dispersion liquid; S2: preparing a silicon micro-bridge structure on the back of a silicon substrate; S3: placing a template with a hollow structure on the surface of the silicon micro-bridge structure, coating the porous hydrogen-bond organic framework dispersion liquid on the template with the hollow structure, drying in nitrogen, and removing the template with the hollow structure to obtain a silicon micro-bridge structure covered with a circular porous hydrogen-bond organic framework thin film; S4: placing a template on the silicon micro-bridge structure covered with the circular porous hydrogen-bond organic framework thin film, coating the perfluorosulfonic acid dispersion liquid on the template, drying in nitrogen, and removing the template to obtain a silicon micro-bridge structure with a sensitive thin film of a perfluorosulfonic acid constrained porous hydrogen-bond organic framework structure deposited thereon.

8. The method of claim 7, wherein the high sensitivity fast recovery ammonia sensor is prepared by the steps of: The concentration of the perfluorosulfonic acid dispersion liquid in S1 is 0.5 to 2.5 wt.%, and the concentration of the porous hydrogen-bond organic framework dispersion liquid is 0.8 to 1.2 mg / ml; S2 includes using an anisotropic KOH etching technology to prepare a silicon thin film, forming a Wheatstone full-bridge circuit in the silicon thin film through an ion implantation process, and preparing a layer of silicon nitride passivation layer on the surface of the silicon thin film for protecting the silicon thin film and the piezoresistive full-bridge circuit.

9. The method for preparing a highly sensitive and fast-recovery ammonia sensor according to claim 7, characterized in that, The diameter of the circular hole of the template with the hollow structure in S3 is 20 to 100 microns.

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