A gas sensor, a method for preparing a gas sensor by laser direct writing

Abstract

The application provides a gas sensor and a method for preparing the gas sensor by laser direct writing. The method comprises the following steps: contacting a metal electrode with laser direct writing ink, wherein the laser direct writing ink comprises a nickel source, a porous structure directing agent and a solvent; irradiating a specified contact area of the metal electrode with the laser direct writing ink with a laser, so that the metal electrode absorbs the laser and generates heat, to form a hydrothermal reaction zone in the specified contact area, and make the laser direct writing ink in the hydrothermal reaction zone undergo a hydrothermal reaction, so as to grow porous nickel hydroxide on the metal electrode and obtain a precursor structure; and performing annealing treatment on the precursor structure, so that the porous nickel hydroxide is converted into porous nickel oxide, thereby obtaining the gas sensor. The gas sensor provided by the application has porous nickel oxide, which has a large specific surface area, can increase the effective contact area of the gas sensor and the target gas, and improve the gas response of the gas sensor.

Description

Technical Field

[0001] This invention belongs to the field of laser processing micro-nano device technology, specifically relating to a gas sensor and a method for preparing a gas sensor by laser direct writing. Background Technology

[0002] Traditional gas sensors generally face challenges such as large size, low responsivity, and complex manufacturing processes. These inherent limitations hinder their widespread adoption in portable, distributed, and real-time applications. To address these challenges, the gas sensor field is rapidly evolving towards miniaturization, integration, low power consumption, and high performance. Miniaturization offers significant advantages, including higher detection accuracy, faster response and recovery times, and lower production costs.

[0003] Nickel oxide is a wide-bandgap p-type semiconductor metal oxide that has attracted increasing attention due to its unique and excellent structure, high chemical stability, high sensitivity, and low cost. However, existing nickel oxide thin films or bulk materials suffer from limited specific surface area, restricting gas adsorption-desorption processes to the surface. Furthermore, current nickel oxide gas sensor manufacturing technologies face several limitations. The main problems are: first, traditional semiconductor-based nickel oxide sensor manufacturing methods require expensive equipment and complex processes such as chemical vapor deposition; second, chemical hydrothermal synthesis-based methods require prolonged hydrothermal synthesis in a reactor, hindering the manufacturing of miniaturized and customized sensor devices. Therefore, there is an urgent need to develop a novel nickel oxide sensor manufacturing technology to overcome these limitations and achieve low-cost, customized manufacturing of miniaturized, integrated, and high-performance nickel oxide sensors. Summary of the Invention

[0004] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions:

[0005] A first aspect of the present invention provides a method for fabricating a gas sensor using laser direct writing, the method comprising:

[0006] The metal electrode is brought into contact with laser direct writing ink, which includes a nickel source, a porous structure guiding agent, and a solvent.

[0007] A laser is used to irradiate a designated contact area between the metal electrode and the laser-written ink, causing the metal electrode to absorb the laser and heat up, thereby forming a hydrothermal reaction zone in the designated contact area. The laser-written ink in the hydrothermal reaction zone undergoes a hydrothermal reaction, thereby growing porous nickel hydroxide on the metal electrode to obtain a precursor structure.

[0008] Furthermore, the precursor structure is annealed to convert the porous nickel hydroxide into porous nickel oxide, thereby obtaining the gas sensor.

[0009] This invention uses the laser direct-writing ink to prepare a gas sensor, which can form porous nickel hydroxide and convert it into porous nickel oxide through annealing. It has a large specific surface area, which can increase the effective contact area between the gas sensor and the target gas, improve the gas response of the gas sensor, and solve the problem that the gas adsorption-desorption process of nickel oxide thin film or nickel oxide bulk materials in the prior art is limited by the surface due to the limited specific surface area.

[0010] In some embodiments, the porosity of the porous nickel oxide is 50-200 pores / µm. 2 The pores contained therein have a diameter of 50-300 nm.

[0011] In some embodiments, the concentration of the nickel source in the laser direct-write ink is 2-3 mol / L. The nickel source may include, for example, nickel nitrate, but is not limited thereto.

[0012] In some embodiments, the porous structure directing agent comprises ethanolamine, and the volume ratio of the solvent to ethanolamine is 10-20:1.

[0013] In some embodiments, the solvent of the laser direct writing ink includes dimethyl sulfoxide and ethanol in a volume ratio of 5-10:5-10.

[0014] In some embodiments, the method specifically includes: focusing a laser on a designated contact area between the metal electrode and the laser-written ink to form the hydrothermal reaction zone.

[0015] In some embodiments, the method specifically includes: growing porous nickel hydroxide on at least two metal electrodes spaced apart from each other, connecting the porous nickel hydroxide on the at least two metal electrodes to each other, and then performing the annealing treatment to obtain the gas sensor.

[0016] In some embodiments, the method specifically includes: forming a metal electrode on a first substrate, the metal electrode having a one-dimensional, two-dimensional, or three-dimensional structure; growing porous nickel hydroxide of a two-dimensional shape on the one-dimensional or two-dimensional metal electrode to obtain a gas sensor with porous nickel oxide of a two-dimensional shape; and / or growing porous nickel hydroxide of a three-dimensional shape on a three-dimensional metal electrode to obtain a gas sensor with porous nickel oxide of a three-dimensional shape.

[0017] Any method for fabricating a metal electrode on a substrate can be used to form the metal electrode described in this invention. This invention does not impose any particular limitation on this method. For example, any laser direct writing technology or other micro-nano fabrication method known in the art can be used to fabricate the electrode.

[0018] In some embodiments, the metal electrodes are fabricated using laser direct writing technology, thereby enabling the fabrication of gas sensors on the same laser platform.

[0019] In some embodiments, the method for preparing the metal electrode includes:

[0020] The first surface of the first substrate and the second surface of the second substrate are positioned opposite each other and spaced apart, and the interlayer space between the first surface of the first substrate and the second surface of the second substrate has a thickness of micrometers. The first substrate and the second substrate are light-transmitting substrates.

[0021] Electrode ink for making metal electrodes is injected into the interlayer space to form a laser-printable three-dimensional ink space layer; a laser is incident on the three-dimensional ink space layer and irradiates a selected contact position between the electrode ink and the first surface of the first substrate, thereby forming the metal electrode with a two-dimensional or three-dimensional structure on the first surface of the first substrate.

[0022] In some embodiments, the method for preparing the metal electrode specifically includes:

[0023] The electrode ink is injected into the interlayer space to form the three-dimensional ink space layer;

[0024] The laser is incident on the three-dimensional ink space layer from the third surface of the first substrate and irradiates a selected contact position between the electrode ink and the first surface of the first substrate, thereby forming a first portion of a metal electrode on the first surface of the first substrate.

[0025] The laser is incident from the fourth surface of the second substrate onto the three-dimensional ink space layer and irradiates a selected contact position between the electrode ink and the first part of the metal electrode, thereby integrally forming the second part of the metal electrode on the first part of the metal electrode;

[0026] The third surface is opposite to the first surface, and the fourth surface is opposite to the second surface.

[0027] In some typical embodiments, for example, the above method can be used to first form a first portion of a one-dimensional metal electrode on a first surface of the first substrate, and then continue to grow a second portion on the first portion of the one-dimensional structure, thereby forming a three-dimensional metal electrode. The first portion of the one-dimensional metal electrode is, for example, linear, and continuing to grow a second portion on the linear first portion can form a protruding metal electrode.

[0028] In some embodiments, when the metal electrode is fabricated using laser direct writing technology, the process parameters for forming a one-dimensional metal electrode may include: a laser power of 1.6-3.67 mW and a scanning speed of 5-50 µm / s; the process parameters for integrally forming a three-dimensional metal electrode on a one-dimensional metal electrode may include: a laser power of 0.9-4.1 mW and a scanning speed of 0.1-2 µm / s.

[0029] In some embodiments, after the metal electrode is fabricated, the laser direct-write ink is injected into the interlayer space, so that the laser is incident on the three-dimensional ink space layer and irradiates the designated contact area between the laser direct-write ink and the metal electrode, thereby obtaining the precursor structure.

[0030] In some embodiments, the focal point of the laser is moved relative to the metal electrode in at least one of the x, y, and z directions in a three-dimensional coordinate space, so that the laser sequentially irradiates multiple designated contact areas of the metal electrode and the laser direct writing ink and / or the distance between the focal point of the laser and the designated contact areas of the metal electrode and the laser direct writing ink is changed, thereby controlling the structure of the precursor structure.

[0031] In some embodiments, at least one or more of the wavelength, power, and scanning speed of the laser are adjusted to control the structure of the precursor structure.

[0032] In some typical embodiments, the one-dimensional metal electrode comprises a metal wire. For example, laser-written ink is brought into contact with at least a portion of the metal wire, and a laser is focused onto the metal wire to grow a porous nickel hydroxide of a two-dimensional shape on the metal wire.

[0033] In some embodiments, the laser parameters for growing porous nickel hydroxide in a two-dimensional shape on a one-dimensional or two-dimensional metal electrode include: the laser power is 3-6mW and the laser scanning speed is 0.5-2µm / s.

[0034] It should be understood that the grown nickel hydroxide has a certain thickness, so the two-dimensional nickel hydroxide here does not represent an absolute plane. The thickness of the two-dimensional porous nickel hydroxide described in this invention is less than 3 µm, for example, the thickness can be 2-3 µm.

[0035] In some embodiments, the metal electrode includes multiple parallel metal lines, on which porous nickel hydroxide is grown, and / or, multiple porous nickel hydroxides are grown on one metal line, and adjacent porous nickel hydroxides are interconnected.

[0036] In some embodiments, the three-dimensional metal electrode includes metal protrusions. For example, the laser-written ink is brought into contact with the metal protrusions, and a laser is focused onto the metal protrusions to grow porous nickel hydroxide with a three-dimensional shape on the metal protrusions.

[0037] In some embodiments, the height of the metal protrusion is 4-6 μm.

[0038] In some embodiments, the diameter of the metal protrusion is 1-3 μm.

[0039] In some embodiments, the metal electrode includes a plurality of metal protrusions spaced apart from each other with a spacing of 2-5 μm.

[0040] In some embodiments, the metal electrode includes a plurality of patterned metal protrusions. The patterned arrangement may be, for example, a linear arrangement or an array arrangement, but is not limited thereto.

[0041] In some embodiments, the method specifically includes: when growing nickel hydroxide on the metal protrusion, increasing the power of a laser focused on the metal protrusion in a stepwise manner, wherein the initial power of the laser is 0.9-1.3 mW, the maximum power is 2.5-4.1 mW, and the power is increased from the initial power to the maximum power through 2-5 power increases, with each power increase increment being 0.4-0.7 mW, and the scanning time at each power level is 2-5 s.

[0042] Through systematic research, this invention has discovered that when a metal electrode has multiple adjacent metal protrusions, and the laser power is gradually increased in a stepwise manner according to the above-described method, nickel hydroxide with a protruding structure can be produced. Furthermore, adjacent protruding structures will form "suspended cavities," meaning that the nickel hydroxide grown on the metal protrusions tends to form a protruding structure with a first part far from the substrate and a second part close to the substrate. The first parts of two adjacent protruding structures are in contact with each other, while the second parts are not in contact, thus forming a suspended cavities at the bottom near the substrate. The formation of suspended cavities can further increase the effective contact area between the gas sensor and the target gas, improve the gas responsivity, and also improve the conductivity of the device.

[0043] In some preferred embodiments, the laser-written ink is brought into contact with a patterned array of metal protrusions. A laser is then applied to a designated contact area between the metal electrode and the laser-written ink, and the laser power is progressively increased in a stepwise manner as described above to form a precursor structure with suspended holes. The precursor structure is then annealed to obtain a gas sensor with suspended holes. For example, nickel hydroxide can be grown on an array of metal protrusions using a stepwise increase in laser power to obtain an array of nickel hydroxide protrusion structures. Adjacent protrusion structures are interconnected to form suspended holes. In an array, multiple interconnected suspended holes form a three-dimensional interconnected suspended network, further improving the conductivity and gas responsiveness of the device.

[0044] In some embodiments with multiple adjacent metal protrusions or a patterned arrangement of metal protrusions, the height of the metal protrusions can be 4-6 μm, the diameter can be 1-3 μm, and the spacing between adjacent metal protrusions can be 2-5 μm. In this case, the nickel hydroxide protrusion structure fabricated using the aforementioned step-wise progressive increase in laser power can have a height of 4-8 μm, a diameter of 3-6 μm, a height of 2-5 μm for the suspended holes, and a spacing of 2-5 μm between the centers of two adjacent suspended holes. Furthermore, because the height of the metal protrusions is uniform, the resulting network of interconnected nickel hydroxide protrusions is possible. If the height of the metal protrusions is not uniform, it will be difficult for adjacent nickel hydroxide protrusions to connect.

[0045] In some embodiments, the annealing temperature is 350-400°C.

[0046] In some embodiments, the annealing process takes 1-3 hours.

[0047] After the annealing treatment, nickel hydroxide is transformed into nickel oxide, but the annealing treatment does not change the porous structure or shape of nickel hydroxide.

[0048] In some embodiments, the metal electrode is made of platinum. When preparing the platinum metal electrode using the aforementioned laser direct writing technology, the electrode ink may include ferric ammonium oxalate trihydrate, ammonium tetrachloroplatinate, and a solvent. The concentration of ferric ammonium oxalate trihydrate may be 400-600 mM, the concentration of ammonium tetrachloroplatinate may be 50-100 mM, and the solvent may include water.

[0049] A second aspect of the present invention provides a gas sensor prepared by the laser direct writing method for preparing a gas sensor as described in any of the above technical solutions.

[0050] A third aspect of the present invention provides a gas sensor, including a substrate and a metal electrode and a gas-sensitive structure disposed on the substrate; the gas-sensitive structure includes a plurality of continuously distributed and mutually contacting porous nickel oxides, the porous nickel oxides being electrically bonded to the metal electrode.

[0051] In some embodiments, the porosity of the porous nickel oxide is 50-200 pores / µm. 2 The pores contained therein have a diameter of 50-300 nm.

[0052] In some embodiments, the porous nickel oxide is a raised structure, the raised structure including a first portion away from the substrate and a second portion close to the substrate, the first portions of at least two adjacent raised structures are in contact with each other, and the second portions are not in contact, so as to form an escalator hole at the bottom close to the substrate.

[0053] In some embodiments, the diameter of the protrusion structure is 3-6 μm, and / or the height of the protrusion structure is 4-8 μm.

[0054] In some embodiments, the height of the overhead opening is 2-5 μm.

[0055] In some embodiments, the gas-sensitive structure includes adjacent overhead holes composed of multiple protruding structures, with a distance of 2-5 μm between the centers of two adjacent overhead holes.

[0056] In some embodiments, the gas-sensitive structure includes a plurality of patterned protrusions. The patterned arrangement may be, for example, a linear arrangement or an array arrangement, but is not limited thereto.

[0057] In some embodiments, the multiple protruding structures constitute multiple interconnected overhead holes to form a three-dimensional interconnected overhead network. For example, when the protruding structures are arranged in an array, multiple overhead holes are formed sequentially in both the horizontal and vertical directions of the array, thereby forming overhead channels in the horizontal and vertical directions. These overhead channels are interconnected, which is the "three-dimensional interconnected overhead network".

[0058] In some embodiments, the metal electrode is made of platinum.

[0059] Compared with the prior art, the present invention has at least the following beneficial effects:

[0060] The gas sensor fabrication method provided by this invention is based on preparing porous nickel hydroxide using laser direct writing ink, and then converting it into porous nickel oxide through annealing. The resulting porous nickel oxide has a large specific surface area, which can increase its effective contact area with the target gas and improve the gas response of the gas sensor.

[0061] The method provided by this invention can achieve rapid customized production of gas sensors of different shapes and sizes by controlling laser power, scanning time and scanning path, providing an excellent solution for small-batch customization of gas sensors;

[0062] The laser direct writing method for fabricating gas sensors provided by this invention can achieve micron-level structural precision and three-dimensional complexity that is difficult to achieve with existing technologies such as hydrothermal methods and simple deposition methods, thereby improving the integration and miniaturization level of gas sensors and making them suitable for the miniaturized and arrayed sensor requirements of modern electronic devices. Attached Figure Description

[0063] To more clearly illustrate the technical solutions in the embodiments of this application 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 recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0064] Figure 1 This is a schematic diagram of the process for preparing the gas sensor in Embodiment 1 of the present invention;

[0065] Figure 2 This is a photograph of the platinum electrode ink used to print the platinum electrode in Example 1;

[0066] Figure 3 This is a photograph of the laser direct-write ink used to grow porous nickel hydroxide in Example 1;

[0067] Figure 4 This is a schematic diagram of the structure of the gas sensor prepared in Example 1;

[0068] Figure 5 This is an electron microscope image of the gas sensor prepared in Example 1;

[0069] Figure 6 This is a schematic diagram of the process for preparing the gas sensor in Embodiment 2 of the present invention;

[0070] Figure 7 These are electron microscope images of the platinum wires and platinum needles printed in Example 2;

[0071] Figure 8 This is a schematic diagram of the structure of the gas sensor prepared in Example 2;

[0072] Figure 9 This is an electron microscope image of the gas sensor prepared in Example 2;

[0073] Figure 10 The image shows the repeatable response curve of the gas sensor prepared in Example 1 to 100 ppm ethanol gas.

[0074] Figure 11 The image shows the repeatable response curve of the gas sensor prepared in Example 2 to 100 ppm ethanol gas.

[0075] Figure 12 This is a comparison chart of the single-response patterns of the gas sensors prepared in Examples 1 and 2 to 100 ppm ethanol gas. Detailed Implementation

[0076] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention. The specific functional details disclosed herein should not be construed as limiting, but are merely intended to form the basis of the claims and to teach those skilled in the art to employ the representative basis of the invention in different ways in any suitable detailed embodiment.

[0077] In addition, unless otherwise specified, all raw materials used in the following embodiments can be purchased from the market or other sources, and all production and testing equipment used are known in the art, as are the methods used.

[0078] Example 1

[0079] This embodiment provides a gas sensor and its preparation method. The gas sensor includes two-dimensional nickel oxide, and its preparation process is as follows: Figure 1 As shown, the specific steps include the following:

[0080] 1. Apply a polyimide tape with a thickness of about 60 µm and a width of 5 mm to both sides of the first glass substrate. Place the second glass substrate parallel to the tape, and then fix the second glass substrate with polyimide tape to form a sandwich space with a thickness of about 60 µm between the two opposing glass substrates.

[0081] 2. Printing platinum electrodes:

[0082] 1) To prepare the platinum electrode ink required for printing platinum electrodes, dissolve ferric ammonium oxalate trihydrate and ammonium tetrachloroplatinate in deionized water to obtain the platinum electrode ink. The concentration of ferric ammonium oxalate trihydrate is approximately 500 mM, and the concentration of tetrachloroplatinate is approximately 70 mM. Figure 2 These are actual photos of platinum electrode ink;

[0083] 2) The platinum electrode ink is injected into the interlayer space between the two glass substrates. A laser is incident from the surface of the first glass substrate facing away from the interlayer space and focused at the junction of the glass substrate and the platinum electrode ink. Platinum lines are printed with a laser power of 2.57 mW and a scanning speed of 30 µm / s, and the spacing between adjacent platinum lines is 4 µm to form platinum lines on the first glass substrate. After printing, the platinum lines are cleaned.

[0084] To facilitate subsequent testing of the gas sensor by testing instruments, a large-area platinum electrode is formed on the first glass substrate using a photolithography mask. The "large area" facilitates the alignment and connection of the probes of the testing instruments and allows the platinum wires to be connected to the large-area platinum electrode. The formation of the large-area platinum electrode using a photolithography mask is an existing technology, so it will not be described in detail here.

[0085] 3. Growth of porous nickel hydroxide:

[0086] 1) Preparation of laser direct writing ink: Dissolve 0.785 g of nickel nitrate hexahydrate in a mixed solution of 0.5 mL dimethyl sulfoxide and 0.5 mL ethanol, then add 90 μL ethanolamine. Stir at room temperature until the solution is homogeneous to obtain the laser direct writing ink. Figure 3 These are actual photos of laser-written ink.

[0087] 2) Inject the laser direct writing ink prepared above into the interlayer space so that it contacts the platinum wire. Use a laser to pass through the glass substrate and focus on the selected contact position between the laser direct writing ink and the platinum wire. Through the thermal effect generated by the absorption of the laser by the metallic platinum, a micro-hydrothermal growth reaction zone is formed on the platinum wire. The laser prints a two-dimensional porous nickel hydroxide with a constant power of 4mW and a scanning speed of 1µm / s.

[0088] 4. Wash the printed sample in deionized water for 10 minutes and air dry it naturally. Then place it in a tube furnace and anneal it at 400°C for 2 hours to convert the porous nickel hydroxide into porous nickel oxide, thus obtaining a gas sensor with two-dimensional nickel oxide.

[0089] Figure 4 This is a schematic diagram of the gas sensor fabricated in this embodiment. Figure 5 This is an electron microscope image of the gas sensor fabricated in this embodiment. Combined with... Figure 4 , Figure 5 As can be seen, the gas sensor fabricated in this embodiment has two large-area platinum electrodes located on the left and right sides, with two-dimensional nickel oxide distributed between the two large-area platinum electrodes and connected by platinum wires. Multiple two-dimensional nickel oxides are arranged sequentially along a first direction (in this embodiment, the first direction is perpendicular to the two-dimensional platinum wires), with adjacent two-dimensional nickel oxides in contact with each other. The customized arrangement of the two-dimensional nickel oxides can be achieved by using a three-dimensional moving platform to precisely move the sample relative to the laser beam in the X, Y, and Z directions. The length of a single two-dimensional nickel oxide fabricated in this embodiment is approximately 20 µm, the width is approximately 4 µm, and the height is approximately 1 µm.

[0090] The laser direct-write ink provided by this invention enables the production of porous nickel hydroxide through laser-induced hydrothermal growth, followed by annealing to form porous nickel oxide. The final nickel oxide has a porosity of approximately 120 porosities / µm. 2 The pores contained therein have a diameter of approximately 50-160 nm, which can effectively increase the contact area between nickel oxide and gas and improve gas responsiveness.

[0091] Example 2

[0092] This embodiment provides a gas sensor and its fabrication method. The gas sensor includes three-dimensional nickel oxide, and its fabrication process is as follows: Figure 6 As shown, the specific steps include the following:

[0093] 1. Preparation of substrate structure: Apply a polyimide tape with a thickness of about 60 µm and a width of 5 mm to both sides of the first glass substrate. Place the second glass substrate parallel to the tape, and then fix the second glass substrate with polyimide tape to form a 60 µm gap between the two glass substrates.

[0094] 2. Printing platinum electrodes:

[0095] 1) To prepare the platinum electrode ink required for printing platinum electrodes, ferric ammonium oxalate trihydrate and ammonium tetrachloroplatinate are dissolved in deionized water to obtain the platinum electrode ink, wherein the concentration of ferric ammonium oxalate trihydrate is about 500 mM and the concentration of tetrachloroplatinate is about 70 mM.

[0096] 2) The platinum electrode ink is injected into the interlayer space between two glass substrates. A laser is incident from the surface of the first glass substrate facing away from the interlayer space and focused on the interface between the glass substrate and the platinum electrode ink. Platinum lines are printed with a laser power of 2.57 mW and a scanning speed of 30 µm / s, and the spacing between adjacent platinum lines is 4 µm. After the platinum lines are printed, the sample is flipped so that the laser is incident from the surface of the second glass substrate facing away from the interlayer space and focused on the selected contact area between the platinum lines and the laser direct-write ink. The laser is printed on the platinum lines with a laser power of 1.6 mW and a scanning speed of 0.4 µm / s to integrally form a three-dimensional platinum needle (i.e., the metal protrusion described in this invention) on the platinum lines.

[0097] To facilitate subsequent testing of the gas sensor by testing instruments, a large-area platinum electrode is formed on the first glass substrate using a photolithography mask. The "large area" facilitates the alignment and connection of the probes of the testing instruments and allows the platinum wires to be connected to the large-area platinum electrode. The formation of the large-area platinum electrode using a photolithography mask is an existing technology, so it will not be described in detail here.

[0098] Figure 7This is an electron microscope image of the platinum wires and platinum needles printed in this embodiment. As can be seen, the three-dimensional platinum needles extend upward from the platinum wires. Based on the interval arrangement of multiple platinum wires, the formed platinum needles are arranged in an array. The height of a single platinum needle printed in this embodiment is about 5µm, the diameter is about 1.5µm, and the spacing between adjacent platinum needles is about 3.5µm.

[0099] 3. Growth of porous nickel hydroxide:

[0100] 1) Preparation of laser direct writing ink: Dissolve 0.785 g of nickel nitrate hexahydrate in a mixed solution of 0.5 mL dimethyl sulfoxide and 0.5 mL ethanol, then add 90 μL ethanolamine, and stir at room temperature until the solution is homogeneous to obtain laser direct writing ink.

[0101] 2) Inject the laser direct writing ink prepared above into the interlayer space so that it contacts the platinum needle. Use a laser to penetrate the glass substrate and focus on the selected contact position between the laser direct writing ink and the platinum needle. Set the laser power to 1.15 mW and hold for 4s, then increase it to 1.8 mW and hold for 4s, and then increase it to 2.5 mW and hold for 4s. Through the thermal effect generated by the absorption of laser by the metallic platinum, a micro-hydrothermal growth reaction zone is formed on the platinum needle to grow a three-dimensional porous nickel hydroxide on the platinum needle.

[0102] 4. Wash the printed sample in deionized water for 10 minutes and air dry it naturally. Then place it in a tube furnace and anneal it at 400°C for 2 hours to convert porous nickel hydroxide into porous nickel oxide, thus obtaining a gas sensor with three-dimensional nickel oxide.

[0103] Figure 8 This is a schematic diagram of the gas sensor fabricated in this embodiment. Figure 9 This is an electron microscope image of the gas sensor fabricated in this embodiment. Combined with... Figure 8 , Figure 9 As can be seen, the gas sensor fabricated in this embodiment has two large-area platinum electrodes located on the left and right sides, with three-dimensional nickel oxide positioned between the two large-area platinum electrodes and connected to them by platinum wires. The three-dimensional nickel oxide has a raised structure, which has a first portion away from the substrate and a second portion close to the substrate. The first portions of two adjacent raised structures are in contact with each other, while the second portions are not in contact, thereby forming an vented cavity at the bottom near the substrate. The formation of the vented cavity can further increase the effective contact area between the nickel oxide and the gas. Figure 9As shown, since the three-dimensional nickel oxide is grown on the basis of platinum needles, multiple three-dimensional nickel oxides are also arranged in an array, and there are overhead holes between adjacent three-dimensional nickel oxides. There are multiple rows of overhead channels in the horizontal and vertical directions of the array. These overhead channels are interconnected, so that the gas sensor has a three-dimensional interconnected overhead network, which further improves the conductivity and gas sensing performance of the device.

[0104] The laser power and duration focused on the three-dimensional platinum needles affect the formation of the suspended holes. This invention enables a stepwise increase in laser power and maintains each power level for an appropriate duration, which facilitates the formation of suspended holes. If the laser power is too low or the duration is too short, the grown individual nickel hydroxides will be too small to effectively connect with adjacent structures, thus hindering the formation of a continuous suspended three-dimensional network. If the laser power is too high or the duration is too long, the nickel hydroxides will overgrow and overlap each other, resulting in smaller or no suspended holes, and the specific surface area of ​​the nickel oxide will decrease. It should be noted that gas sensors based on the porous structure of nickel oxide without suspended holes also have good gas sensing performance, but gas sensors with suspended holes are preferred, and gas sensors with three-dimensional interconnected suspended holes are even more preferred, as the conductivity and gas sensing performance of the device are further improved.

[0105] The present invention tests the relevant performance of the gas sensors prepared in Examples 1 and 2 above, and the test methods are as follows:

[0106] The gas sensor was heated to 300°C in a sealed chamber environment. 1.3 μL of ethanol was injected into a miniature heating container within the 6.4 L chamber, allowing it to fully evaporate and create a 100 ppm ethanol gas environment within the chamber. The responsivity of the gas sensor was then tested. The responsivity was calculated by measuring its resistance in air (Ra) and its resistance in ethanol gas (Rg), and the responsivity (S) was defined as S = Rg / Ra.

[0107] Figure 10 , Figure 11 The images show the repetitive response curves of the gas sensors prepared in Examples 1 and 2 to 100 ppm ethanol gas, respectively. Figure 10 It can be seen that the gas sensor in Example 1 has an average rise response time of approximately 60 seconds and an average fall recovery time of approximately 40.8 seconds; Figure 11 It can be seen that the gas sensor in Example 2 exhibits a faster response and recovery speed, with an average rise response time of about 43.6s and an average fall recovery time of about 30.8s. Figure 12 This is a comparison graph showing the single-response pattern of the gas sensors prepared in Examples 1 and 2 to 100 ppm ethanol gas. Figure 12It can be seen that the responsivity of the gas sensor in Example 1 is approximately 1.75 times, while the responsivity of the gas sensor in Example 2 is significantly improved to approximately 2.69 times. In summary, the gas sensor prepared in Example 2 performs significantly better than that in Example 1 in terms of both responsivity and response / recovery speed.

[0108] Example 3

[0109] Example 3 is basically the same as Example 2, except that the laser direct writing ink in Example 3 is prepared as follows: nickel nitrate hexahydrate is dissolved in a mixed solution of 1 mL dimethyl sulfoxide and 1 mL ethanol, and then 100 μL ethanolamine is added, wherein the concentration of nickel nitrate is 2 mol / L. The solution is stirred at room temperature until homogeneous to obtain the laser direct writing ink. The rest is the same as in Example 2 and will not be repeated here.

[0110] The structure and performance of the gas sensor prepared in Example 3 are comparable to those in Example 2.

[0111] Example 4

[0112] Example 4 is basically the same as Example 2, except that the laser direct writing ink in Example 4 is prepared as follows: nickel nitrate hexahydrate is dissolved in a mixed solution of 0.5 mL dimethyl sulfoxide and 1 mL ethanol, and then 100 μL ethanolamine is added, wherein the concentration of nickel nitrate is 3 mol / L. The solution is stirred at room temperature until homogeneous to obtain the laser direct writing ink. The rest is the same as in Example 2 and will not be repeated here.

[0113] The structure and performance of the gas sensor prepared in Example 4 are comparable to those in Example 2.

[0114] Example 5

[0115] Example 5 is essentially the same as Example 2, except that the steps for growing porous nickel hydroxide in Example 5 are as follows: the laser direct-write ink prepared above is injected into the interlayer space, making it contact the platinum needle. A laser is used to penetrate the glass substrate and focus on the selected contact position between the laser direct-write ink and the platinum needle. The laser power is first set to 1.3 mW and held for 5 seconds, then increased to 1.7 mW and held for 5 seconds, then increased to 2.1 mW and held for 5 seconds, and then increased to 2.5 mW and held for 5 seconds. The rest is the same as in Example 2 and will not be repeated here.

[0116] The gas sensor prepared in Example 5 also has a three-dimensional nickel oxide and vented hole structure similar to that in Example 2, and its performance is comparable to that of Example 2.

[0117] Example 6

[0118] Example 6 is essentially the same as Example 2, except that the step of growing porous nickel hydroxide in Example 6 is as follows: the laser direct-write ink prepared above is injected into the interlayer space, making it contact the platinum needle. A laser is used to penetrate the glass substrate and focus on the selected contact position between the laser direct-write ink and the platinum needle. The laser power is first set to 0.9 mW and held for 5 s, then increased to 1.6 mW and held for 5 s, then increased to 2.3 mW and held for 5 s, then increased to 3.0 mW and held for 2 s, then increased to 3.7 mW and held for 2 s, and then increased to 4.1 mW and held for 2 s. The rest is the same as in Example 2 and will not be repeated here.

[0119] The gas sensor prepared in Example 6 also has a three-dimensional nickel oxide and vented hole structure similar to that in Example 2, and its performance is comparable to that of Example 2.

[0120] Example 7

[0121] The difference between Example 7 and Example 2 is that in Example 7, the step of growing porous nickel hydroxide is as follows: the laser direct-write ink prepared above is injected into the interlayer space, so that it contacts the platinum needle, and a laser is used to penetrate the glass substrate and focus on the selected contact position between the laser direct-write ink and the platinum needle, so that the laser power is kept constant at 2.5mW and the duration is 12s. The rest is the same as in Example 2, and will not be described again here.

[0122] Comparing Examples 2 and 7, it was found that when nickel hydroxide was grown on a three-dimensional platinum needle with constant power, the platinum needle would collapse due to overheating or structural stress. If the laser power increased too quickly or the single increase was too large, it would produce an effect similar to that of constant laser power, that is, the three-dimensional platinum electrode was prone to overheating or collapse due to structural stress, and the effect was worse than that of Example 2.

[0123] Example 8

[0124] The difference between Example 8 and Example 2 is that in Example 8, the holding time at each power level is 20 seconds during the growth of porous nickel hydroxide. The rest of the procedure is the same as in Example 2 and will not be repeated here.

[0125] Comparing Examples 2 and 7, it was found that when the laser duration is too long, the nickel hydroxide structure will overgrow, causing it to cover each other and fill the adjacent voids, which is not conducive to the formation of voids. Compared with Example 2, the specific surface area of ​​the material decreases, and the gas sensor produced is also somewhat inferior to that of Example 2.

[0126] Comparative Example 1

[0127] The only difference between Comparative Example 1 and Example 2 is that ethanolamine is not added to the nickel-based laser direct ink of Comparative Example 1. The rest is the same as that of Example 2, and will not be repeated here.

[0128] Using the ink prepared in Comparative Example 1 to print nickel hydroxide, it was found that the surface of nickel hydroxide was dense with no pore distribution, and the surface area was much smaller than that of porous nickel hydroxide, resulting in poor response of the gas sensor.

[0129] In summary, the gas sensor fabrication method provided by this invention is based on laser-written ink to prepare porous nickel hydroxide, which is then converted into porous nickel oxide through annealing. This porous nickel oxide has a large specific surface area, increasing the effective contact area with the target gas and improving the gas sensor's gas responsivity. Furthermore, this invention obtains three-dimensional porous nickel hydroxide through laser-induced hydrothermal growth, forming three-dimensional nickel oxide after annealing. This three-dimensional nickel oxide not only has high porosity but also the formation of vented pores increases the effective contact area between the nickel oxide and the target gas, further improving gas responsivity. Compared to existing gas sensor fabrication methods using multi-step etching, deposition, or hydrothermal methods, the laser-written ink-based method provided by this invention has simpler process steps. From metal electrode fabrication to nickel hydroxide growth, everything can be achieved on the same laser platform through program control, greatly simplifying the manufacturing process and reducing reliance on cleanroom environments and the use of chemical reagents.

[0130] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0131] All aspects, embodiments, features, and examples of this invention should be considered illustrative and used to explain and illustrate the invention, but not to limit the invention. The scope of the invention is defined only by the claims.

[0132] Although the invention has been described with reference to illustrative embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that elements in the described embodiments can be substituted with substantially equivalents. Furthermore, many modifications can be made without departing from the scope of the invention to adapt particular situations or materials to the teachings of the invention. Therefore, this invention is not intended to be limited to the specific embodiments disclosed, but rather to encompass all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated otherwise, any use of the terms first, second, etc., does not indicate any order or importance, but is used to distinguish one element from another.

Claims

1. A method for fabricating a gas sensor using laser direct writing, characterized in that, include: The metal electrode is brought into contact with laser direct writing ink, which includes a nickel source, a porous structure guiding agent, and a solvent. A laser is used to irradiate a designated contact area between the metal electrode and the laser-written ink, causing the metal electrode to absorb the laser and heat up, thereby forming a hydrothermal reaction zone in the designated contact area. The laser-written ink in the hydrothermal reaction zone undergoes a hydrothermal reaction, thereby growing porous nickel hydroxide on the metal electrode to obtain a precursor structure. Furthermore, the precursor structure is annealed to convert the porous nickel hydroxide into porous nickel oxide, thereby obtaining the gas sensor.

2. The method according to claim 1, characterized in that, Specifically, it includes: The laser is focused on a designated contact area between the metal electrode and the laser-written ink to form the hydrothermal reaction zone.

3. The method according to claim 1, characterized in that, Specifically, it includes: The porous nickel hydroxide is grown on at least two of the metal electrodes spaced apart from each other, and the porous nickel hydroxide on the at least two metal electrodes is interconnected. Then, the annealing process is performed to obtain the gas sensor.

4. The method according to claim 1, characterized in that, Specifically, it includes: A metal electrode is formed on a first substrate, the metal electrode having a one-dimensional, two-dimensional, or three-dimensional structure; a two-dimensional porous nickel hydroxide is grown on the one-dimensional or two-dimensional metal electrode to obtain a gas sensor with a two-dimensional porous nickel oxide; and / or, a three-dimensional porous nickel hydroxide is grown on a three-dimensional metal electrode to obtain a gas sensor with a three-dimensional porous nickel oxide.

5. The method according to claim 4, characterized in that: The first surface of the first substrate and the second surface of the second substrate are positioned opposite each other and spaced apart, and the interlayer space between the first surface of the first substrate and the second surface of the second substrate has a thickness of micrometers. The first substrate and the second substrate are light-transmitting substrates. Electrode ink for making metal electrodes is injected into the interlayer space to form a laser-printable three-dimensional ink space layer. A laser is then incident on the three-dimensional ink space layer and irradiates a selected contact position between the electrode ink and the first surface of the first substrate, thereby forming the metal electrode with a two-dimensional or three-dimensional structure on the first surface of the first substrate.

6. The method according to claim 5, characterized in that: The electrode ink is injected into the interlayer space to form the three-dimensional ink space layer; the laser is incident on the three-dimensional ink space layer from the third surface of the first substrate and irradiates the selected contact position between the electrode ink and the first surface of the first substrate, thereby forming the first part of the metal electrode on the first surface of the first substrate; The laser is incident from the fourth surface of the second substrate onto the three-dimensional ink space layer and irradiates a selected contact position between the electrode ink and the first part of the metal electrode, thereby integrally forming the second part of the metal electrode on the first part of the metal electrode; The third surface is opposite to the first surface, and the fourth surface is opposite to the second surface.

7. The method according to claim 5 or 6, characterized in that: After the metal electrode is fabricated, the laser direct writing ink is injected into the interlayer space, and the designated contact area between the laser direct writing ink and the metal electrode is irradiated to obtain the precursor structure.

8. The method according to claim 4, characterized in that, The laser parameters for growing porous nickel hydroxide in two-dimensional shapes on one-dimensional or two-dimensional metal electrodes include: the laser power is 3-6 mW and the laser scanning speed is 0.5-2 µm / s.

9. The method according to claim 4, characterized in that, The three-dimensional metal electrode includes metal protrusions.

10. The method according to claim 9, characterized in that: The metal protrusion has a height of 4-6 μm and a diameter of 1-3 μm.

11. The method according to claim 9, characterized in that: The metal electrode includes multiple metal protrusions spaced apart from each other with a spacing of 2-5 μm.

12. The method according to claim 9, characterized in that: The metal electrode includes a plurality of patterned metal protrusions.

13. The method according to any one of claims 9-12, characterized in that, include: When growing nickel hydroxide on the metal protrusion, the power of the laser is gradually increased in a stepwise manner. The initial power of the laser is 0.9-1.3 mW, the maximum power is 2.5-4.1 mW, and the power is increased from the initial power to the maximum power through 2-5 power increases. The increment of each power increase is 0.4-0.7 mW, and the scanning time at each power level is 2-5 s.

14. The method according to claim 1, characterized in that: The annealing temperature is 350-400℃, and / or the annealing time is 1-3h.

15. The method according to claim 1, characterized in that: The concentration of nickel source in the laser direct writing ink is 2-3 mol / L.

16. The method according to claim 1, characterized in that: The porous structure directing agent includes ethanolamine, and the volume ratio of the solvent to ethanolamine is 10-20:

1.

17. The method according to claim 1, characterized in that: The solvent comprises dimethyl sulfoxide and ethanol in a volume ratio of 5-10:5-10.

18. The method according to claim 1, characterized in that: The porous nickel oxide has a porosity of 50-200 pores / µm. 2 The pores contained therein have a diameter of 50-300 nm.

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