Highly selective acetone gas sensor and method of making same

Abstract

The application discloses a high-selectivity acetone gas sensor and a preparation method thereof, and comprises the following steps: providing a MEMS micro-hotplate substrate with a defined active window as a working substrate, in-situ growing an epsilon-WO3 nanostructure array in the active window, sequentially constructing a super-thin NiO continuous shell layer and a discrete CuO catalytic island on the surface of the epsilon-WO3 nanostructure array to form a radial p-n-p heterojunction sensitive structure with epsilon-WO3 as the core and NiO / CuO as the shell, performing a thermal stabilization treatment on the heterojunction sensitive structure, constructing a ZIF-8 molecular sieve film or a ring-shaped fluorinated ionomer selective layer on the surface of the heterojunction sensitive structure to obtain a high-selectivity sensor device, effectively blocking the passage of interfering molecules, and significantly improving the selectivity ratio and the anti-cross interference capability of the sensor device; meanwhile, based on the MEMS micro-hotplate substrate and the thermal stabilization treatment process, the device has good structural stability, low power consumption characteristics and compatibility with a standard semiconductor process, and high selectivity for acetone is realized while high sensitivity is ensured.

Description

Technical Field

[0001] This invention relates to the field of sensors, and more particularly to a highly selective acetone gas sensor and its preparation method. Background Technology

[0002] Acetone, a key indicator of human metabolism, has a direct correlation between its exhaled concentration and blood glucose levels, making highly selective acetone gas sensors a promising candidate for non-invasive diabetes screening. Furthermore, there is an urgent need for accurate and reliable detection of acetone gas in fields such as chemical production and environmental monitoring. However, real-world applications are often complex and variable. High concentrations of water vapor in exhaled breath and common interfering substances (such as ethanol) can easily cause cross-sensitivity in sensors, leading to false alarms. This places extremely high demands on the selectivity of the sensors.

[0003] Currently, metal-oxide-semiconductor (MOS) based gas sensors are one of the mainstream technologies. To improve the selectivity for acetone, a common preparation method typically employs a bulk doping strategy. This involves mechanically mixing and ball milling metal oxide powders with different functions to form a slurry, which is then coated onto a ceramic tube or MEMS hotplate, and finally sintered at high temperature for an extended period to form a sensitive film. However, this method has a significant drawback: the heterojunction interface formed by this "mix-sintering" process is random, sparse, and unstable, limiting its intrinsic selectivity improvement capability. More importantly, because these organic framework materials cannot withstand high-temperature processes, the sensors struggle to fundamentally address the interference resistance issues of gases such as ethanol and water vapor, making it difficult to achieve a breakthrough in selectivity improvement.

[0004] Therefore, it is necessary to improve the existing technology to solve the technical problems of poor selectivity of traditional metal oxide gas sensors for acetone gas and their susceptibility to environmental interference molecules. Summary of the Invention

[0005] The purpose of this invention is to provide a highly selective acetone gas sensor and its preparation method, thereby solving the above-mentioned technical problems.

[0006] To achieve this objective, the present invention adopts the following technical solution: A method for preparing a highly selective acetone gas sensor includes the following steps: S1 provides a MEMS micro hot plate substrate with a defined active window as a working substrate, and grows an ε-WO3 nanostructure array in situ within the active window. S2, on the surface of the ε-WO3 nanoarray, an ultrathin NiO continuous shell and a discrete CuO catalytic island are sequentially constructed to form a radial p–n–p heterojunction sensitive structure with ε-WO3 as the core and NiO / CuO as the shell. The heterojunction sensitive structure is then thermally stabilized. S3. Construct ZIF-8 molecular sieve films or annular fluorinated ionomer selective layers on the surface of heterojunction sensitive structures to obtain highly selective sensor devices.

[0007] Optionally, the MEMS micro-hot plate substrate is prefabricated with a Pt heating electrode and a detection electrode, and the active window is defined at a preset position of the detection electrode.

[0008] Optionally, the process of defining the active window is as follows: S101 provides a silicon-based MEMS micro-hot plate substrate, on which Pt heating electrodes, detection electrodes and insulating layers are prefabricated on the surface. S102, spin-coating photoresist onto the surface of the MEMS micro hot plate substrate, and defining an active window pattern in the area of ​​the detection electrode through mask exposure and development process; S103 involves treating the active window area after development with oxygen plasma to remove organic residues and activate the surface.

[0009] Optionally, the process of in-situ growing the ε-WO3 nanostructure array within the active window specifically involves: S104 uses the sol-gel method to coat the first precursor solution of tungsten source within the active window, and forms a uniform wet film by low-speed spin coating. S15, the coated MEMS micro-hot plate substrate undergoes the first stage of heat treatment, holding at 250-350°C for 10-30 minutes to transform the uniform wet film into an amorphous WO. 3-x Seed layer; S106, the obtained substrate is placed in a high-pressure reactor, a tungstate solution containing an organic acid regulator is added, and a hydrothermal reaction is carried out at 120-180°C for 1-4 hours. 3-x In-situ growth of oriented ε-WO3 nanostructure arrays on seed layer; S107. After the reaction is complete, remove the substrate, rinse it with deionized water and dry it at low temperature to remove residual reactants on the surface. S108 undergoes a second-stage heat treatment in an oxygen-containing atmosphere, annealing at 300-400°C for 20-60 minutes to achieve ε-WO3 phase stabilization and crystallinity enhancement.

[0010] Optionally, step S2 specifically includes: S21, a low-temperature atomic layer deposition process is used on the MEMS micro hot plate substrate with ε-WO3 nanoarray, using bis(cyclopentadiene) nickel and ozone as reaction precursors, to cyclically deposit a 5-20 nm thick NiO continuous shell on the surface of the ε-WO3 nanoarray at 80-150°C. S22, the device after NiO deposition is immersed in a low-concentration copper organic salt ethanol solution. By controlling the immersion time and the pulling speed, the copper source is confined and adsorbed on the outer surface of the NiO shell. S23. The impregnated device undergoes the first stage of heat treatment under an inert atmosphere, decomposing the organic ligands at 200-280°C and initially forming CuO. x Crystal nucleus; S24, undergo a second-stage low-temperature annealing in an oxygen-containing atmosphere, treated at 300-350°C for 5-15 minutes, to allow CuO to anneal. x The crystal nuclei are oxidized and discretized into CuO catalytic islands with a particle size of 1-5 nm, forming an ε-WO3 / NiO / CuO radial p–n–p heterojunction sensitive structure.

[0011] Optionally, step S3 specifically includes: S31, devices with radial p–n–p heterojunction sensitive structures are subjected to hydrophilic pretreatment by oxygen plasma or ultraviolet ozone treatment for 5-20 minutes to improve surface energy and introduce hydroxyl functional groups. S32, depending on the target selection layer type, construct the selection layer of ZIF-8 molecular sieve film on the surface of the heterojunction sensitive structure using scheme A, or use the selection layer of cyclic fluorinated ionomer using scheme B. S33, the device with the selective layer is subjected to low-temperature curing treatment, which involves heating at 80-120°C for 10-30 minutes to remove residual solvent and enhance the adhesion and density of the selective layer; S35 involves performing performance activation treatment on the cured selective layer. For ZIF-8 molecular sieve films, low-temperature vacuum degassing is used, or for annular ionomer bands, acid treatment and ion exchange processes are used to finally obtain highly selective acetone sensor devices.

[0012] Optionally, Scheme A is: immersing the pretreated device in a ZIF-8 second precursor solution containing 2-methylimidazole and zinc salt, allowing it to stand at room temperature for 10-60 minutes to grow a 30-100 nm thick ZIF-8 molecular sieve film in situ on the surface of the heterojunction sensitive structure. Option B involves using precision screen printing technology to pattern a perfluorosulfonic acid resin solution around the active window, forming an annular ionomer band with a width of 50-200 μm.

[0013] Optionally, step S3 may be followed by: S4. The obtained sensor device is laser-trimmed, electrode wire bonded, and encapsulated to complete the sensor fabrication.

[0014] Optionally, step S4 includes the following steps: S41, perform pattern trimming on the sensor device to remove sensitive material and selection layer overflowing from the periphery of the active window; S42, wire bonding is performed on the Pt heating electrode solder joint using a gold wire ball bonding process, with the bonding temperature controlled at 150-250°C and the pressure at 0.5–1.2 N, to form a stable electrical connection; S43, the bonded chip is assembled onto a TO-type or ceramic package base, and hermetic sealing is achieved by laser welding or epoxy resin bonding process. S44. Cover the top of the package base with a dust cover with a microporous structure to complete the assembly of the acetone gas sensor.

[0015] The present invention also provides a highly selective acetone gas sensor, which is prepared by the method described above. The highly selective acetone gas sensor includes a MEMS hot plate substrate, the MEMS hot plate substrate having a Pt heating electrode and a detection electrode, and the detection electrode having an active window. An ε-WO3 nanostructure array is grown within the active window, and a radial p–n–p heterojunction sensitive structure is formed on the surface of the ε-WO3 nanostructure array. A selection layer is provided covering the heterojunction sensitive structure, as well as an encapsulation structure for electrical connection and gas permeation.

[0016] Compared with existing technologies, this invention has the following advantages: By constructing a synergistic mechanism between a radial p–n–p heterojunction and a surface molecular sieve selective layer, high selectivity for acetone gas detection is achieved. The internal ε-WO3 / NiO / CuO heterojunction structure provides high sensitivity and signal amplification for acetone, while the external ZIF-8 molecular sieve membrane or fluorinated ionomer selective layer effectively blocks the passage of common interfering molecules such as ethanol and water vapor due to their molecular size sieving or differences in hydrophilicity and hydrophobicity, thereby significantly improving the selectivity and anti-cross-interference capability of the sensor. At the same time, based on the MEMS micro-hot plate substrate and thermal stabilization process, the device has good structural stability, low power consumption characteristics, and compatibility with standard semiconductor processes, achieving high selectivity for acetone while ensuring high sensitivity. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0019] Figure 1 This is one of the flowcharts illustrating the preparation method of the highly selective acetone gas sensor in this embodiment. Figure 2 This is the second schematic diagram of the preparation method of the highly selective acetone gas sensor in this embodiment one; Figure 3 This is a schematic diagram of the structure of the high-selectivity acetone gas sensor in this embodiment 2. Detailed Implementation

[0020] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0022] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1: Combination Figures 1 to 3 As shown in the figure, this invention provides a method for preparing a highly selective acetone gas sensor, comprising the following steps: S1 provides a MEMS micro-hot plate substrate with a defined active window as a working substrate, and grows an ε-WO3 nanostructure array in situ within the active window.

[0024] First, a MEMS micro-hot plate substrate with pre-fabricated active windows is provided. By directly growing an array of ε-WO3 nanostructures within the active windows, the resulting ε-phase WO3 has abundant surface active sites and good electron transport channels, providing the sensor with a high specific surface area and a stable sensitive basis, significantly improving initial sensitivity and substrate compatibility.

[0025] S2, on the surface of the ε-WO3 nanoarray, an ultrathin NiO continuous shell and a discrete CuO catalytic island are sequentially constructed to form a radial p–n–p heterojunction sensitive structure with ε-WO3 as the core and NiO / CuO as the shell. The heterojunction sensitive structure is then thermally stabilized.

[0026] A unique radial p–n–p heterojunction sensing structure was formed by sequentially constructing an ultrathin continuous NiO shell and discretely distributed CuO catalytic islands. The NiO shell and WO3 core form a pn junction, expanding the space charge region and enhancing carrier separation efficiency in the gas-sensing process. The introduction of CuO islands further improves the selective catalytic ability for acetone oxidation. Subsequent thermal stabilization treatment promotes electronic coupling and structural stability between the heterojunctions, effectively improving the sensor's response amplitude and response recovery characteristics.

[0027] S3. Construct ZIF-8 molecular sieve films or annular fluorinated ionomer selective layers on the surface of heterojunction sensitive structures to obtain highly selective sensor devices.

[0028] ZIF-8 achieves size-selective permeability of acetone molecules through its regular microporous structure, effectively blocking interfering molecules such as ethanol and water vapor. The annular fluorinated ionomer band utilizes its hydrophobicity and proton migration properties to selectively separate small molecule gases. This selective layer significantly improves the sensor's selectivity for acetone from both physical and chemical perspectives and greatly suppresses signal drift caused by changes in ambient humidity.

[0029] S4. The obtained sensor device undergoes laser trimming, electrode wire bonding, and encapsulation to complete sensor fabrication. The functionalized sensor device is laser trimmed to precisely define the sensitive area and maintain the integrity of the thermal isolation structure. Reliable electrical connections are then achieved through wire bonding, and finally, a microporous vented cover plate is added to complete the encapsulation. This process ensures that the sensitive element operates under mechanical protection and a controlled atmosphere, maintaining gas diffusion efficiency while improving the device's mechanical strength and stability.

[0030] The working principle of this invention is as follows: By constructing a synergistic mechanism between a radial p–n–p heterojunction and a surface molecular sieve selective layer, highly selective detection of acetone gas is achieved. The internal ε-WO3 / NiO / CuO heterojunction structure provides a highly sensitive response and signal amplification for acetone, while the external ZIF-8 molecular sieve membrane or fluorinated ionomer selective layer effectively blocks the passage of common interfering molecules such as ethanol and water vapor due to their molecular size sieving or differences in hydrophilicity and hydrophobicity, thereby significantly improving the selectivity and anti-cross-interference capability of the sensor. At the same time, based on the MEMS micro-hot plate substrate and thermal stabilization process, the device has good structural stability, low power consumption characteristics, and compatibility with standard semiconductor processes, achieving high selectivity for acetone while ensuring high sensitivity.

[0031] In this embodiment, the MEMS micro hot plate substrate is prefabricated with a Pt heating electrode and a detection electrode, and the active window is defined at a preset position of the detection electrode.

[0032] It should be noted that the substrate is fabricated using silicon-based micromachining technology, with Pt heating electrodes and interdigitated Pt detection electrodes pre-fabricated on its surface, and covered with a silicon nitride or silicon oxide insulating layer. The active window is confined to a predetermined area of ​​the detection electrode, ensuring that the sensitive material can be directionally grown in the electrode gap region where the electric field distribution is strongest, which is beneficial for the efficient collection of gas response signals. Simultaneously, the micro-hotplate structure enables rapid local heating and cooling, significantly reducing sensor power consumption and providing dimensionally stable and thermally controllable substrate conditions for the subsequent orderly growth of the sensitive material and the construction of heterogeneous structures.

[0033] In this embodiment, the process of defining the active window is specifically described as follows: S101 provides a silicon-based MEMS micro-hot plate substrate, on which Pt heating electrodes, detection electrodes and insulating layers are prefabricated on the surface. A silicon-based MEMS micro-hotplate substrate is provided, on which Pt heating electrodes and interdigitated detection electrodes are integrated using semiconductor micromachining processes and covered with an insulating layer. This structure provides the sensor with a stable and precisely temperature-controlled micro-heating platform, while ensuring good insulation between the electrodes and reliable signal readout.

[0034] S102 involves spin-coating photoresist onto the surface of a MEMS micro-hot plate substrate, and then using a mask exposure and development process to define an active window pattern in the area of ​​the detection electrode. This ensures that the sensitive material grows only within the designed electrode area, avoiding material waste and the risk of electrical short circuits, and improving the consistency and yield of device fabrication.

[0035] S103 involves treating the active window area after development with oxygen plasma to remove organic residues and activate the surface.

[0036] It should be noted that oxygen plasma is used to treat the active window area after development. This treatment effectively removes residual organic contaminants from the photolithography and development processes, and activates the surface of the insulating layer through plasma bombardment, increasing its surface energy and hydrophilicity. This cleaning and activation treatment provides an ideal surface condition for the subsequent uniform deposition of the seed layer, enhances the adhesion between the sensitive material and the substrate, and improves the uniformity and stability of the final sensitive film.

[0037] In this embodiment, the process of in-situ growing an ε-WO3 nanostructure array within the active window is further described as follows: S104 uses a sol-gel method to coat the first precursor solution of tungsten source within the active window, and then forms a uniform wet film by low-speed spin coating.

[0038] A sol-gel method was used to coat a precursor solution containing a tungsten source onto the active window region, and then a uniform wet film was formed by low-speed spin coating. This process confines the precursor material within a micrometer-scale window region, ensuring uniform coating distribution and facilitating the formation of a stable seed layer during subsequent heat treatment.

[0039] S15, the coated MEMS micro hot plate substrate is subjected to the first stage of heat treatment, and is kept at 250-350°C for 10-30 minutes to transform the uniform wet film into an amorphous WO3-x seed layer; the seed layer serves as the substrate for the directional growth of nanostructures in the subsequent hydrothermal reaction, which can improve the nucleation density and improve the uniformity of crystal growth.

[0040] S106, the obtained substrate is placed in a high-pressure reactor, a tungstate solution containing an organic acid regulator is added, and a hydrothermal reaction is carried out at 120-180°C for 1-4 hours to grow an oriented ε-WO3 nanostructure array in situ on the WO3-x seed layer. The treated substrate was placed in a high-pressure reactor, and a tungstate solution containing an organic acid regulator was added. A hydrothermal reaction was then carried out at 120-180°C. Through the synergistic effect of the temperature and acidic conditions of the hydrothermal environment, an ε-WO3 nanostructure array with good orientation could be grown in situ on the WO3-x seed layer, thereby effectively increasing the specific surface area and the number of active sites of the gas-sensitive layer.

[0041] S107. After the reaction is complete, remove the substrate, rinse it with deionized water and dry it at low temperature to remove residual reactants on the surface and ensure the surface cleanliness and integrity of the obtained nanostructure.

[0042] S108 undergoes a second-stage heat treatment in an oxygen-containing atmosphere, annealing at 300-400°C for 20-60 minutes to achieve ε-WO3 phase stabilization and crystallinity enhancement.

[0043] It should be noted that the second stage of oxygen atmosphere heat treatment, annealing at 300-400°C, on the obtained nanostructure array can further stabilize the ε-WO3 crystal phase and improve its crystallinity. This annealing process not only helps to improve the electrical properties of the nanostructure, but also enhances its structural stability under high-temperature conditions, thus providing support for the long-term reliable operation of the gas sensor.

[0044] In this embodiment, step S2 specifically includes: S21, a low-temperature atomic layer deposition process is used on the MEMS micro hot plate substrate with ε-WO3 nanoarray, using bis(cyclopentadiene) nickel and ozone as reaction precursors, to cyclically deposit a 5-20 nm thick NiO continuous shell on the surface of the ε-WO3 nanoarray at 80-150°C. Using ALD (Alternating Deposition) with bis(cyclopentadiene) nickel and ozone as precursors, NiO can be cyclically deposited at relatively low temperatures (80–150°C), achieving atomic-level coating uniformity and thickness control on complex three-dimensional surfaces of ε-WO3 nanopillars / nanowires. The self-confined growth mechanism of the ALD process results in a continuous and ultrathin NiO coating layer (5–20 nm). This continuous shell can form a good electrical contact interface and also serve as a p-type coating to modulate the band structure of the ε-WO3 (n-type) surface, thus providing a consistent and repeatable interface basis for the subsequent formation of radial p–n–p heterojunctions.

[0045] S22, the device after NiO deposition is immersed in a low-concentration copper organic salt ethanol solution. By controlling the immersion time and the pulling speed, the copper source is confined and adsorbed on the outer surface of the NiO shell.

[0046] By immersing the NiO-coated sheet in a low-concentration copper organic salt ethanol solution and controlling the immersion time and uniform pulling speed to limit the adsorption amount and distribution of copper ions / complexes on the device surface, the copper source can be mainly concentrated on the NiO surface rather than being deposited in large quantities on the overall substrate. This confined adsorption method is beneficial for subsequent heat treatment to transform the copper precursor into dispersed oxide nuclei rather than forming a continuous thick film, thus creating a prerequisite for the formation of discrete, microscale catalytic islands.

[0047] S23, the impregnated device undergoes the first stage of heat treatment under an inert atmosphere, decomposing the organic ligands at 200-280°C and initially forming CuOx crystal nuclei.

[0048] The low-temperature heat treatment (200-280°C) of the impregnated device under an inert atmosphere (e.g., nitrogen or argon) is primarily used to decompose the copper organic ligands and transform them into amorphous or low-crystallinity CuOx precursors / nuclei, while simultaneously preventing premature reactions with oxygen at this stage that could lead to uncontrolled oxidation and coarsening. The inert atmosphere treatment helps control the initial morphology and distribution of the nuclei, allowing for more controlled generation of small, dispersed CuO catalytic islands in subsequent controlled oxidation steps. Furthermore, this treatment balances the thermal tolerance of both the MEMS device and the metal electrodes, reducing the impact of thermal stress on the substrate structure.

[0049] S24, a second-stage low-temperature annealing is carried out in an oxygen-containing atmosphere, and the process is carried out at 300-350°C for 5-15 minutes to oxidize and discretize CuOx crystal nuclei into CuO catalytic islands with a particle size of 1-5nm, forming an ε-WO3 / NiO / CuO radial p–n–p heterojunction sensitive structure.

[0050] By transferring the inert-pretreated device into an oxygen-containing atmosphere and briefly annealing it at a relatively mild temperature (300-350°C), the CuOx precursor can be fully oxidized and redistributed as discrete small particles at the NiO / ε-WO3 interface, forming CuO catalytic islands on the order of 1–5 nm. Oxidation annealing not only completes the chemical morphological transformation of the catalytic islands but also achieves particle discretization and interface passivation through thermal energy, avoiding large particle agglomeration. The resulting ε-WO3 / NiO / CuO radial p–n–p heterojunction, under the combined effect of space charge and band mismatch, can enhance the modulation of electrical signals caused by surface adsorption / reaction. The two-stage thermal treatment synergistically balances catalytic activity, interfacial contact, and thermal compatibility with the MEMS substrate, which is beneficial to device stability and mass production consistency.

[0051] In this embodiment, step S3 specifically includes: S31, devices with radial p–n–p heterojunction sensitive structures are subjected to hydrophilic pretreatment by oxygen plasma or ultraviolet ozone treatment for 5-20 minutes to improve surface energy and introduce hydroxyl functional groups. Before constructing the selective layer on a device with a radial p–n–p heterojunction sensitive structure, a hydrophilic pretreatment (e.g., oxygen plasma or ultraviolet ozone treatment, with the treatment duration selected within the range of 5–20 minutes according to process requirements) is preferentially applied to the active region. This pretreatment primarily removes surface organic residues, increases surface energy, and introduces polar functional groups such as hydroxyl groups onto the sensitive layer surface, thereby improving the wettability and interaction of subsequent solution phase materials (such as ZIF-8 precursors or perfluorosulfonic acid resin solutions) in the sensitive region.

[0052] S32, depending on the target selection layer type, construct the selection layer of ZIF-8 molecular sieve film on the surface of the heterojunction sensitive structure using scheme A, or use the selection layer of cyclic fluorinated ionomer using scheme B. Scheme A involves immersing the pretreated device in a ZIF-8 second precursor solution containing 2-methylimidazole and zinc salt, allowing it to stand at room temperature for 10-60 minutes, and then growing a 30-100 nm thick ZIF-8 molecular sieve film in situ on the surface of the heterojunction sensitive structure. The resulting ZIF-8 film achieves molecular sieving and enrichment of target small molecules (such as acetone) through its pore size and adsorption characteristics. At the same time, it has a certain repulsive ability for interfering molecules with strong polarity or mismatched size, which helps to improve the selectivity of the sensor and its stability under wet disturbance.

[0053] Option B involves using precision screen printing technology to pattern a perfluorosulfonic acid resin solution around the active window, forming an annular ionomer band with a width of 50-200 μm.

[0054] The toroidal ionomer band, by providing a combination of hydrophobic / ionic barriers and localized selective channels, suppresses the direct intrusion of polar interfering substances such as water vapor into the sensitive region, while preserving the diffusion pathway of the target gas, thereby improving the baseline stability and selective response of the device in high-humidity environments. Both approaches can be used individually or in combination to balance response rate and selectivity requirements.

[0055] S33 involves low-temperature curing of devices with selective layers, heating at 80-120°C for 10-30 minutes to remove residual solvents and enhance the adhesion and density of the selective layer.

[0056] It should be noted that the curing process gently removes volatile components and induces densification of the microstructure within the film, which helps reduce the impact of residual solvent in the pores on the sensing baseline, while enhancing the structural stability and resistance to moisture swelling of the film. The low-temperature setting can meet the requirements for film densification while also taking into account the thermal compatibility of the MEMS substrate and electrode materials.

[0057] S35 involves performing performance activation treatment on the cured selective layer. For ZIF-8 molecular sieve films, low-temperature vacuum degassing is used, or for annular ionomer bands, acid treatment and ion exchange processes are used to finally obtain highly selective acetone sensor devices.

[0058] For ZIF-8 molecular sieve films, low-temperature vacuum degassing (reduced pressure and gentle heating) can be used to remove solvent or guest molecules adsorbed in the pores, thereby reopening the pores and restoring the adsorption / diffusion properties. For annular ionomer bands (such as perfluorosulfonic acid resins), acid treatment and ion exchange processes can be used to place the functional groups in the desired ionic state and optimize their hydrophobic / hydrophilic balance, thereby adjusting the shielding ability against polar interferences and the permeation rate of target molecules.

[0059] In this embodiment, step S4 specifically includes the following steps: S41 involves pattern trimming of the sensor device, removing excess sensitive material and selector layer overflowing from the periphery of the active window. This is typically achieved using non-contact or minimally invasive methods such as laser micromachining, plasma etching, or microblading / microbrush cleaning. These methods precisely remove excess coating around the active window, redefine the sensitive area boundary, and eliminate potential short circuits or parasitic conductive paths. Removing this overflow reduces batch-to-batch electrical differences and noise sources caused by edge residue. It also improves the flatness of contact surfaces and the bonding / soldering quality in subsequent bonding and packaging processes, thereby enhancing overall chip consistency and yield.

[0060] S42, wire bonding is performed on the Pt heating electrode solder joint using a gold wire ball bonding process, with the bonding temperature controlled at 150-250°C and the pressure at 0.5–1.2N, to form a stable electrical connection; To balance solder joint reliability with the thermomechanical effects on the sensitive layer and substrate, bonding parameters should be controlled within a given range (e.g., temperature approximately 150–250°C, pressure 0.5–1.2 N) and appropriate solder / wire and soldering sequence should be used. Controlled bonding temperature and pressure can form a strong electrical connection to ensure stable signal transmission, while avoiding thermal damage or mechanical stress to adjacent functional thin films or selective layers.

[0061] S43, the bonded chip is assembled onto a TO-type or ceramic package base, and hermetic sealing is achieved by laser welding or epoxy resin bonding process. During assembly, the chip and package substrate are hermetically sealed using laser welding or a suitable epoxy resin bonding process to prevent external particles, moisture, or chemical contaminants from directly entering the device, while maintaining the designed gas channels and diffusion paths. Laser welding provides locally high-strength, low-residual-stress metal seals, while epoxy bonding offers advantages in low-temperature operation and process simplicity, thus benefiting the thermal compatibility of sensitive devices.

[0062] S44. Cover the package base with a dust cover with a microporous structure to complete the assembly of the acetone gas sensor. Covering the package base with a dust cover with a microporous structure serves as the first physical barrier to the outside of the device, preventing dust and larger particles from entering the sensitive area, while retaining gas diffusion channels through micropores or porous films to allow the target gas to reach the sensitive layer.

[0063] Example 2 Combination Figure 3 As shown, the present invention also provides a high-selectivity acetone gas sensor, which is prepared by the same method as in Example 1. The high-selectivity acetone gas sensor includes a MEMS hot plate substrate 100, which has a Pt heating electrode 101, an insulating support layer 102 and a detection electrode 103. The detection electrode is provided with an active window 110. An ε-WO3 nanostructure array 120 is grown within the active window 110. A radial p–n–p heterojunction sensitive structure is formed on the surface of the ε-WO3 nanostructure array. The radial p–n–p heterojunction sensitive structure includes a continuous NiO shell 131 and a discrete CuO catalytic island 132. A selection layer 200 is provided covering the heterojunction sensitive structure, as well as an encapsulation structure 300 for electrical connection and gas permeation.

[0064] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a highly selective acetone gas sensor, characterized in that, Includes the following steps: S1, a MEMS micro hot plate substrate with a defined active window is provided as a working substrate, and an ε-WO3 nanostructure array is grown in situ within the active window; the MEMS micro hot plate substrate is prefabricated with a Pt heating electrode and a detection electrode, and the active window is defined at a preset position of the detection electrode. S2, on the surface of the ε-WO3 nanoarray, an ultrathin NiO continuous shell and a discrete CuO catalytic island are sequentially constructed to form a radial p–n–p heterojunction sensitive structure with ε-WO3 as the core and NiO / CuO as the shell. The heterojunction sensitive structure is then thermally stabilized. Specifically, step S2 includes: S21, a low-temperature atomic layer deposition process is used on the MEMS micro hot plate substrate with ε-WO3 nanoarray, using bis(cyclopentadiene) nickel and ozone as reaction precursors, to cyclically deposit a 5-20 nm thick NiO continuous shell on the surface of the ε-WO3 nanoarray at 80-150°C. S22, the device after NiO deposition is immersed in a low-concentration copper organic salt ethanol solution. By controlling the immersion time and the pulling speed, the copper source is confined and adsorbed on the outer surface of the NiO shell. S23, the impregnated device is subjected to the first stage of heat treatment under the protection of an inert atmosphere, and the organic ligands are decomposed at 200-280°C to initially form CuOx crystal nuclei; S24, the second stage of low-temperature annealing is carried out in an oxygen-containing atmosphere, and the process is carried out at 300-350°C for 5-15 minutes to oxidize and discretize CuOx crystal nuclei into CuO catalytic islands with a particle size of 1-5nm, forming an ε-WO3 / NiO / CuO radial p–n–p heterojunction sensitive structure. S3, Constructing a ZIF-8 molecular sieve film or a ring-shaped fluorinated ionomer selective layer on the surface of the heterojunction sensitive structure to obtain a highly selective sensor device; specifically including: Devices with radial p–n–p heterojunction sensitive structures undergo hydrophilic pretreatment by oxygen plasma or ultraviolet ozone treatment for 5–20 minutes to improve surface energy and introduce hydroxyl functional groups. The pretreated device is immersed in a ZIF-8 second precursor solution containing 2-methylimidazole and zinc salt. The reaction is allowed to proceed at room temperature for 10-60 minutes to form a 30-100 nm thick ZIF-8 molecular sieve film in situ on the surface of the heterojunction sensitive structure. A perfluorosulfonic acid resin solution is patterned and printed around the active window using precision screen printing technology to form an annular ionomer band with a width of 50-200 μm. The ZIF-8 molecular sieve film is used in combination with the annular ionomer band. Devices with selective layers are subjected to low-temperature curing treatment, which involves heating at 80-120°C for 10-30 minutes to remove residual solvents and enhance the adhesion and density of the selective layer. The selected layer after curing is subjected to performance activation treatment. Low temperature vacuum degassing is used for ZIF-8 molecular sieve film, and acid treatment and ion exchange process are used for annular ionomer band to finally obtain a highly selective acetone sensor device.

2. The method for preparing a highly selective acetone gas sensor according to claim 1, characterized in that, The process of defining the active window is as follows: S101 provides a silicon-based MEMS micro-hot plate substrate, on which Pt heating electrodes, detection electrodes and insulating layers are prefabricated on the surface. S102, spin-coating photoresist onto the surface of the MEMS micro hot plate substrate, and defining an active window pattern in the area of ​​the detection electrode through mask exposure and development process; S103 involves treating the active window area after development with oxygen plasma to remove organic residues and activate the surface.

3. The method for preparing a highly selective acetone gas sensor according to claim 2, characterized in that, The process of in-situ growth of ε-WO3 nanostructure arrays within the active window is specifically as follows: S104 uses the sol-gel method to coat the first precursor solution of tungsten source within the active window, and forms a uniform wet film by low-speed spin coating. S15, the coated MEMS micro-hot plate substrate undergoes the first stage of heat treatment, holding at 250-350°C for 10-30 minutes to transform the uniform wet film into an amorphous WO. 3-x Seed layer; S106, the obtained substrate is placed in a high-pressure reactor, a tungstate solution containing an organic acid regulator is added, and a hydrothermal reaction is carried out at 120-180°C for 1-4 hours. 3-x In-situ growth of oriented ε-WO3 nanostructure arrays on seed layer; S107. After the reaction is complete, remove the substrate, rinse it with deionized water and dry it at low temperature to remove residual reactants on the surface. S108 undergoes a second-stage heat treatment in an oxygen-containing atmosphere, annealing at 300-400°C for 20-60 minutes to achieve ε-WO3 phase stabilization and crystallinity enhancement.

4. The method for preparing a highly selective acetone gas sensor according to claim 1, characterized in that, The step S3 is followed by: S4. The obtained sensor device is laser-trimmed, electrode wire bonded, and encapsulated to complete the sensor fabrication.

5. The method for preparing a highly selective acetone gas sensor according to claim 4, characterized in that, Step S4 includes the following steps: S41, perform pattern trimming on the sensor device to remove sensitive material and selection layer overflowing from the periphery of the active window; S42, wire bonding is performed on the Pt heating electrode solder joint using a gold wire ball bonding process, with the bonding temperature controlled at 150-250°C and the pressure at 0.5–1.2 N, to form a stable electrical connection; S43, the bonded chip is assembled onto a TO-type or ceramic package base, and hermetic sealing is achieved by laser welding or epoxy resin bonding process. S44. Cover the top of the package base with a dust cover with a microporous structure to complete the assembly of the acetone gas sensor.

6. A highly selective acetone gas sensor, characterized in that, The high-selectivity acetone gas sensor is prepared by the preparation method of any one of claims 1 to 5. The high-selectivity acetone gas sensor includes a MEMS micro hot plate substrate, the MEMS micro hot plate substrate has a Pt heating electrode and a detection electrode, and the detection electrode is provided with an active window. An ε-WO3 nanostructure array is grown within the active window, and a radial p–n–p heterojunction sensitive structure is formed on the surface of the ε-WO3 nanostructure array. A selection layer is provided covering the heterojunction sensitive structure, as well as an encapsulation structure for electrical connection and gas permeation.

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