A humidity sensor and its preparation method

Abstract

This invention discloses a humidity sensor and its fabrication method. The humidity sensor includes a first electrode, a second electrode, and a humidity-sensitive layer covering the first and second electrodes. The first and second electrodes are carbon arrays with porous structures, and the humidity-sensitive material in the humidity-sensitive layer is obtained by cross-linking a conductive polymer material. This invention also provides a method for fabricating the above-mentioned humidity sensor, which utilizes laser direct writing to process a carbonizable polymer film to prepare an electrode with a porous carbon array structure. Then, the cross-linked conductive polymer humidity-sensitive material is coated onto the surface of the polymer film containing the electrodes to obtain the humidity sensor. The above fabrication method is simple to operate and has good process controllability. The prepared humidity sensor, through the synergistic effect between the cross-linked conductive polymer and the porous carbon array, has advantages such as high sensitivity, fast response time, low hysteresis, and good long-term stability.

Description

Technical Field

[0001] This invention relates to the field of humidity sensor fabrication technology, specifically to a humidity sensor and its fabrication method. Background Technology

[0002] Humidity detection and monitoring have wide applications in many social fields such as agriculture and medicine. Traditional humidity sensors are mostly built on rigid substrates. With the increasing demand for humidity sensors in flexible electronics and other fields, there is an urgent need to develop lightweight, low-cost, and easy-to-manufacture flexible wearable humidity sensors. One of the core components of a humidity sensor is the humidity-sensitive material. Furthermore, the structural design of the electrodes, the selection of electrode materials, and their fabrication techniques are also key research issues in the field of humidity sensing.

[0003] Among various humidity-sensitive materials, polymers and polymer composites offer advantages such as low cost, simple synthesis, easy processing, and good compatibility with different manufacturing processes. Conductive polymers such as polyaniline, polystyrene sulfonic acid, and polyethyleneimine are some commonly used humidity-sensitive materials. However, the sensitivity, response / recovery time, and other performance characteristics of existing polymer-based humidity sensors still fall short of the requirements of commercial sensors. More importantly, these linear or branched polymers easily swell and dissolve in water, and are prone to chain segment dissolution / migration / relaxation under high humidity conditions. This severely affects the long-term stability of polymer-based humidity sensors, especially in high-humidity operating environments. For wearable flexible humidity sensors, this problem is particularly pronounced due to the continuous and significant mechanical deformation of the entire sensing system.

[0004] Besides the selection of sensitive materials, the patterning and fabrication of the electrodes, as well as their integration / assembly with the substrate and sensing materials, also play a crucial role. Inkjet printing, vacuum sputtering, screen printing, 3D printing, physical and chemical vapor deposition, and other techniques are commonly used for patterned electrode fabrication; however, they often suffer from drawbacks such as complex processing techniques and printing ink formulations, making it difficult to achieve flexible patterning. Compared to the aforementioned electrode fabrication methods, laser direct-writing carbonization technology can fabricate electrode structures with abundant porosity. Currently, laser direct writing carbonization technology has been preliminarily used in the development of humidity sensors. For example, Delacroix, S. et al. used laser direct writing carbonization to generate porous carbon arrays in situ on the surface of carbonizable polymers, and directly used the porous carbon arrays as humidity-sensitive materials to obtain humidity sensors. They used the change in electrical properties of porous carbon under humid conditions as the detection mechanism of the sensor (Delacroix, S.; Zieleniewska, A.; Ferguson, AJ; Blackburn, JL; Ronneberger, S.; Loeffler, FFACS Applied Electronic Materials, 2020, 2(12): 4146-4154.). In addition, Cai, J. et al. used high-energy lasers to reduce graphene oxide and remove oxygen-containing functional groups on it to prepare interdigitated electrodes as humidity sensors (Cai, JG; Lv, C.; Aoyagi, E.; Ogawa, S.; Watanabe, A. ACS Applied Materials & Interfaces, 2018, 10(28): 23987-23996.). Wang, JJ et al. used carbon materials obtained by laser carbonization of PEEK as electrodes and materials obtained by vacuum sputtering with PEEK as a target as sensing materials to obtain humidity sensors, but there was a hysteresis of ~6.5% (Wang, JJ; Wang, N.; Xu, D.; Tang, L.; Sheng, B. Sensors and Actuators B-Chemical, 2023, 375: 132846.). In summary, the existing technical solutions for preparing humidity sensors using laser processing methods result in sensors with low sensitivity. The sensitivity calculation and summary are detailed in Table 1. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a humidity sensor and its fabrication method. A carbon array with a porous structure is used as the electrode, and a cross-linked conductive polymer material is used as the humidity-sensitive material to prepare a humidity-sensitive layer on the electrode surface. The resulting humidity sensor has advantages such as high sensitivity, fast response time, low hysteresis, and good long-term stability.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] The first aspect of the present invention provides a humidity sensor, comprising:

[0008] The first electrode and the second electrode formed on the substrate; and

[0009] A humidity-sensitive layer covering the first and second electrodes;

[0010] The first electrode and the second electrode are carbon arrays with porous structures, and the humidity-sensitive material in the humidity-sensitive layer is obtained by cross-linking conductive polymer material.

[0011] Furthermore, the substrate is preferably a flexible substrate, and more preferably a carbonizable polymer film, including but not limited to polyimide film, polyacrylonitrile film or polyvinyl chloride film.

[0012] Furthermore, the first electrode and the second electrode form an interdigitated electrode structure or a serpentine electrode structure;

[0013] When the first electrode and the second electrode form an interdigitated electrode structure, the interdigitation distance of the interdigitated electrode structure is 10-600μm, and the width and length of a single interdigitated finger are 20-2000μm and 2-20mm, respectively.

[0014] When the first electrode and the second electrode form a serpentine electrode structure, the spacing between individual electrodes is 10-600 μm, and the width and length of individual electrodes are 20-2000 μm and 3-15 mm, respectively.

[0015] Furthermore, the ratio of the surface area of ​​the pores in the first electrode and / or the second electrode to the area occupied by the corresponding electrode is 20-80:1; the average pore size of the carbon array with porous structure is preferably 1-10 μm.

[0016] Furthermore, the humidity-sensitive layer is a continuous film layer.

[0017] Furthermore, the thickness of the humidity-sensitive layer is preferably 1-10 μm. In the above-mentioned humidity sensor, if the humidity-sensitive layer is too thin, the amount of conductive polymer is insufficient, making it impossible to form a continuous and uniform humidity-sensitive layer, resulting in high impedance and poor stability of the sensor; if the humidity-sensitive layer is too thick, excessive conductive polymer can easily block the pore structure of the electrode, making it difficult for water molecules to be absorbed / diffused into the humidity-sensitive material, thereby causing a decrease in the ionic conductivity of the conductive polymer and affecting the sensitivity of the sensor. Therefore, in order to improve the sensitivity of the humidity-sensitive layer while ensuring the long-term stability of the sensor, the thickness of the humidity-sensitive layer needs to be controlled within a suitable range, such as 1-10 μm.

[0018] Furthermore, the conductive polymer material is preferably one or more of polyethyleneimine and its derivatives, including but not limited to linear or branched polyethyleneimine, polyethyleneimine polylactic acid glycolic acid, and benzoic acid amidated polyethyleneimine.

[0019] Further, the crosslinking treatment specifically involves: chemically crosslinking the conductive polymer material in the presence of a crosslinking agent to obtain the humidity-sensitive material; the ratio of the number of functional groups of the conductive polymer material to the crosslinking agent is preferably 1:0.08-0.67, for example 1:0.08, 1:0.17, 1:0.33, 1:0.42, 1:0.67, including but not limited to the ratios listed above; the crosslinking agent is preferably one or more of tannic acid, glutaraldehyde, and polyacrylic acid.

[0020] This invention pre-crosslinks conductive polymer materials, transforming linear or branched conductive polymers into a network-crosslinked conductive polymer. The resulting humidity-sensitive layer exhibits better structural stability under high humidity conditions, effectively improving the long-term stability of the humidity sensor. However, excessive crosslinking of the conductive polymer material leads to increased impedance and decreased sensitivity in the humidity sensor. Therefore, this invention regulates the crosslinking degree of the conductive polymer material by controlling the ratio of functional groups in the conductive polymer material to the crosslinking agent. To ensure good stability and sensitivity of the humidity sensor, the ratio of functional groups in the conductive polymer material to the crosslinking agent must be controlled within a suitable range, for example, 1:0.08-0.67.

[0021] A second aspect of the present invention provides a method for manufacturing the humidity sensor described in the first aspect, comprising the following steps:

[0022] (1) Using a laser to perform carbonization on a carbonizable polymer film according to a preset electrode pattern, the first electrode and the second electrode are obtained;

[0023] The conductive polymer material is mixed with a crosslinking agent and subjected to crosslinking treatment to obtain the humidity-sensitive material.

[0024] (2) A coating containing the above-mentioned humidity-sensitive material is applied to the surface of the carbonizable polymer film with a porous carbon array, and after drying, a humidity-sensitive layer is formed to obtain the humidity sensor.

[0025] Furthermore, in step (1), the laser process used for carbonization includes carbon dioxide laser carbonization processing technology and ultraviolet laser carbonization processing technology.

[0026] Furthermore, in step (1), the wavelength of the laser used in the carbonization process is 10nm-1mm, and the irradiation power of the laser is 0.2-10W. The pore size and distribution of the porous carbon electrode formed by the above carbonization process can be controlled by adjusting the laser wavelength, irradiation power and other process parameters.

[0027] Further, in step (1), the carbonizable polymer is a natural or synthetic carbonizable polymer material, including but not limited to polyimide, polyacrylonitrile or polyvinyl chloride.

[0028] Furthermore, in step (1), wires are led out from the first electrode and the second electrode by silver paint, silver glue connection method or welding method.

[0029] Further, in step (1), the functional group ratio of the conductive polymer material to the crosslinking agent is preferably 1:0.08-0.67, for example 1:0.08, 1:0.17, 1:0.33, 1:0.42, 1:0.67, including but not limited to the functional group ratios listed above; wherein, the conductive polymer material is preferably linear or branched polyethyleneimine, and the crosslinking agent is preferably one or more of tannic acid, glutaraldehyde, and polyacrylic acid, wherein the amino group of polyethyleneimine and the polyphenol or other functional groups in the crosslinking agent form a crosslinked structure through a chemical reaction.

[0030] In some preferred embodiments, polyethyleneimine is dissolved in water, and an aqueous solution of tannic acid with a pH of 8-9 is added. After mixing evenly, the mixture is stored in the dark for 24 hours to obtain a coating containing moisture-sensitive materials.

[0031] Furthermore, in step (2), before coating with a coating containing a moisture-sensitive material, the surfaces of the carbonizable polymer film containing the first and second electrodes can be subjected to a hydrophilic treatment; the hydrophilic treatment includes silane coupling agent treatment and plasma treatment. By performing a hydrophilic treatment on the surface of the carbonizable polymer film containing the electrodes, the hydrophilicity of the electrode surface is improved, thereby obtaining a surface structure that can form good wetting with the coating.

[0032] Furthermore, in step (2), the coating method includes, but is not limited to, spraying, dripping, and dipping, and the drying method includes, but is not limited to, air drying at room temperature, heating, or vacuuming.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] 1. This invention provides a humidity sensor that uses a porous carbon array as an electrode and a conductive polymer material with a network cross-linked structure as a humidity-sensitive material. The humidity-sensitive material and its cross-linked products still possess abundant hydrophilic functional groups, exhibiting good wettability with the porous electrode surface. After drying, it maintains its affinity for the carbon electrode surface, allowing the polymer to be uniformly coated on the porous carbon electrode surface. This increases the sensing sites of the humidity-sensitive layer and effectively improves the interfacial stability between the humidity-sensitive layer and the electrode. Through the synergistic effect between the porous carbon electrode and the cross-linked humidity-sensitive material, the impedance of the constructed humidity sensor changes rapidly with changes in humidity, exhibiting high sensitivity and fast response. Furthermore, this humidity sensor demonstrates excellent cyclic stability during cyclic testing.

[0035] 2. This invention also provides a method for fabricating the above-mentioned humidity sensor. Electrodes with a predetermined pattern are directly fabricated on a carbonizable polymer film using laser direct writing carbonization technology. Then, a coating containing a pre-crosslinked conductive polymer material is applied to the electrode-bearing side of the carbonizable polymer film to form a humidity-sensitive layer, thereby obtaining the humidity sensor. This fabrication method is simple to operate, has good process controllability, and can be automated. The aforementioned low-cost, high-performance humidity sensor is suitable for industrial mass production. Furthermore, the humidity sensor fabricated directly on a flexible polymer film according to this invention can be integrated into flexible wearable devices. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a porous carbon interdigitated electrode structure.

[0037] Figure 2 This is a schematic diagram of the cross-section of a porous carbon interdigitated electrode, where ① is the substrate, ② is the first electrode, ③ is the second electrode, and ④ is the humidity-sensitive layer.

[0038] Figure 3 The images show the electrode before coating: (a) overall view, (b) surface, and (c) cross-section; and the electrode after coating: (d) overall view, (e) surface, and (f) cross-section.

[0039] Figure 4 (a) Impedance Bode plot when the ratio of functional groups of conductive polymer to crosslinking agent is 1:0.33; (b) Impedance variation with humidity.

[0040] Figure 5 The swelling / dissolution of the cross-linked structure formed by tannic acid and polyethyleneimine under different ratios of functional groups in the feed when immersed in deionized water;

[0041] Figure 6The impedance of humidity sensors fabricated from humidity-sensitive materials with different degrees of cross-linking varies with humidity.

[0042] Figure 7 The change in sensitivity of humidity sensors made of humidity-sensitive materials with different degrees of crosslinking over time at 60% RH;

[0043] Figure 8 The graph shows the change in sensitivity over time for crosslinking agent to conductive polymer functional group ratios of 0:1, 0.17:1, and 0.33:1.

[0044] Figure 9 The humidity sensor's moisture adsorption and desorption curves are shown in the humidity range of 35-90%RH.

[0045] Figure 10 The change in impedance of a humidity sensor under different humidity conditions over time;

[0046] Figure 11 The humidity response and recovery behavior of the humidity sensor when it is alternately placed in humidity environments of 33%RH and 85%RH;

[0047] Figure 12 (a) Impedance Bode plot and (b) Impedance variation with humidity of the humidity sensor prepared for comparison. Detailed Implementation

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0049] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0050] Example 1

[0051] This embodiment relates to the fabrication of a humidity sensor, and the specific operations are as follows:

[0052] A 125 μm thick polyimide film was cut into 20 mm × 15 mm strips, and carbon interdigitated electrodes were fabricated using CO2 laser carbonization technology. The laser processing parameters were: speed 100 mm / s; defocus height 1 mm; operating power 0.35 W; the interdigitated electrode (structural schematic diagram shown) Figure 1The geometric dimensions (as shown) are: interdigital spacing: 0.30 mm, interdigital width: 166 μm, interdigital length: 10 mm, interdigital number: 10, and silver wires are led out from the two poles of the interdigital electrode by dotting conductive silver paste.

[0053] A water-soluble conductive polymer, polyethyleneimine, was dissolved in deionized water (10 wt%), and a tannic acid aqueous solution (pH 8.5, 10 wt%) was prepared separately. The tannic acid and the above conductive polymer polyethyleneimine solution were mixed at a functional group ratio of 0.33:1, shaken for 5 min, and then stored in the dark for 24 h to achieve cross-linking. A carbon interdigitated electrode was treated with plasma, and then the cross-linked polyethyleneimine solution was sprayed onto the carbon interdigitated electrode using a spraying process. The electrode was then dried at room temperature to form a humidity-sensitive layer. The spraying time was controlled to ensure the thickness of the humidity-sensitive layer was approximately 2 μm, thus obtaining a humidity sensor. A schematic diagram of the cross-sectional structure of this humidity sensor is shown below. Figure 2 As shown.

[0054] SEM images of the interdigitated electrodes before and after the fabrication of the humidity-sensitive layer are shown below. Figure 3 As shown in the figures, (b) and (e) are SEM images of the interdigital electrode surface before and after the preparation of the humidity-sensitive layer. As can be seen from the figures, the humidity-sensitive material can enter the pores on the surface of the interdigital electrode to form a humidity-sensitive layer with a large specific surface area. As can be seen from the figures (c) and (f), the preparation of the humidity-sensitive layer did not affect the pore structure inside the interdigital electrode.

[0055] The Bode plots of the AC impedance of the humidity sensor prepared in this embodiment at different humidity levels and the impedance variation with humidity are shown below. Figure 4 As shown, the sensor has a sensitivity of 0.299 under conditions of 60% RH and 30℃.

[0056] Example 2

[0057] To investigate the effect of crosslinking agent content on the solubility / swelling of the crosslinked conductive polymer material in water, this example uses polyethyleneimine as the conductive polymer material and tannic acid as the crosslinking agent, and sets up the following experiment:

[0058] A water-soluble conductive polymer, polyethyleneimine, was dissolved in deionized water (10 wt%) to obtain an aqueous polyethyleneimine solution. A tannic acid aqueous solution (10 wt%) with pH 8.5 was also prepared. The tannic acid aqueous solution and the polyethyleneimine aqueous solution were mixed at functional group ratios of 0:1, 0.17:1, 0.33:1, and 0.67:1, respectively. After shaking for 5 min, the mixture was stored in the dark for 24 h. The mixed solution after 24 h of storage was drop-coated onto a glass slide. After the water evaporated, the resulting polymer film was immersed in deionized water, and its dissolution and swelling behavior over time was monitored at room temperature.

[0059] Figure 5 The figure shows the swelling / dissolution of the cross-linked structure formed by tannic acid and polyethyleneimine under different feed ratios when immersed in deionized water. As can be seen from the figure, the polyethyleneimine film without added tannic acid dissolves immediately when immersed in deionized water. When the functional group ratio of tannic acid to polyethyleneimine is 0.17:1, the film swells significantly after immersion for 5 hours. However, when the tannic acid content is increased to a functional group ratio of tannic acid to polyethyleneimine of 0.33 or 0.67, no significant swelling phenomenon is observed when the film is immersed in deionized water for 24 hours.

[0060] This embodiment further investigates the effects of humidity-sensitive materials with different degrees of cross-linking on the sensitivity and stability of humidity sensors.

[0061] (1) The effect of humidity-sensitive materials with different degrees of cross-linking on the sensitivity of humidity sensors

[0062] A 100 μm thick polysiloxane film was cut into 20 mm × 15 mm strips, and carbon interdigitated electrodes were fabricated using ultraviolet laser carbonization technology. The laser processing parameters were: speed 10 mm / s; defocus height 0.8 mm; operating power 0.15 W. The geometric dimensions of the interdigitated electrodes were: interdigital spacing 0.20 mm, interdigital width 106 μm; interdigital length 10 mm; and 10 interdigitated fingers. Conductive silver paste was applied to the two electrodes, and silver wires were led out from both ends of the interdigitated electrodes.

[0063] A water-soluble conductive polymer, polyethyleneimine, was dissolved in deionized water (10 wt%), and a tannic acid aqueous solution (10 wt%) with pH = 8.5 was prepared separately. The tannic acid and the above conductive polyethyleneimine solution were mixed in functional group ratios of 0:1, 0.08:1, 0.17:1, 0.22:1, 0.33:1, 0.42:1, 0.55:1, and 0.67:1, respectively. After shaking for 5 min, the mixture was stored in the dark for 24 h to achieve cross-linking. A carbon interdigitated electrode was treated with plasma, and then the cross-linked polyethyleneimine solution was sprayed onto the carbon interdigitated electrode using a spraying process. The electrode was then dried at room temperature to form a humidity-sensitive layer. The spraying time was controlled to maintain the thickness of the humidity-sensitive layer at approximately 2 μm, thus preparing a humidity sensor with a measurement temperature of 30 °C.

[0064] Humidity sensing behavior of humidity sensors made from humidity-sensitive materials with different degrees of cross-linking, such as... Figure 6 As shown in the figure, the impedance values ​​|Z| of each sensor are... norm The sensitivity of the sensor decreases monotonically with increasing humidity, and the sensitivity at 60% RH decreases with increasing cross-linking degree. Figure 7 ).

[0065] (2) The influence of humidity-sensitive materials with different degrees of cross-linking on the stability of humidity sensors

[0066] A 100-micrometer-thick polysiloxane film was cut into 20mm × 15mm strips, and carbon interdigitated electrodes were fabricated using ultraviolet laser carbonization technology. The laser processing parameters were: speed 10mm / s; defocus height 0.8mm; operating power 0.15W. The geometric dimensions of the interdigitated electrodes were: interdigital spacing 0.20mm, interdigital width 106μm; interdigital length 10mm; number of interdigitals 10. Conductive silver paste was applied to the two electrodes, and silver wires were led out from both ends of the interdigitated electrodes.

[0067] A water-soluble conductive polymer, polyethyleneimine, was dissolved in deionized water (10 wt%), and a tannic acid aqueous solution (10 wt%) with pH = 8.5 was prepared separately. The tannic acid and the above conductive polyethyleneimine solution were mixed at functional group ratios of 0:1, 0.17:1, and 0.33:1, respectively. After shaking for 5 min, the mixture was stored in the dark for 24 h to achieve cross-linking. A carbon interdigitated electrode was treated with plasma, and then the cross-linked polyethyleneimine solution was sprayed onto the carbon interdigitated electrode using a spraying process. The electrode was then dried at room temperature to form a humidity-sensitive layer. The spraying time was controlled to maintain the thickness of the humidity-sensitive layer at approximately 5 μm, thus obtaining a humidity sensor with a measurement temperature of 30 °C.

[0068] like Figure 8 As shown, the sensitivity of humidity sensors prepared by tannic acid and polyethyleneimine at a functional group ratio of 0:1 or 0.17:1 showed an increasing trend over time. This is because uncrosslinked or poorly crosslinked samples undergo hygroscopic swelling when exposed to humid environments for extended periods, affecting their long-term stability. In contrast, the humidity sensor prepared by tannic acid and polyethyleneimine at a functional group ratio of 0.33:1 showed no significant change in sensitivity under the aforementioned test conditions, demonstrating good stability.

[0069] Example 3

[0070] This embodiment relates to the fabrication of a humidity sensor and further investigates the effect of the thickness of the humidity-sensitive layer on the sensitivity of the humidity sensor. The specific operations are as follows:

[0071] A 125-micron thick polyimide film was cut into 20mm × 15mm strips, and carbon interdigitated electrodes were fabricated using CO2 laser carbonization technology. The laser processing parameters were: speed 100mm / s; defocus height 1.5mm; operating power 0.35W. The geometric dimensions of the interdigitated electrodes were: interdigital spacing 0.30mm, interdigital width 166μm; interdigital length 10mm; number of interdigitals 10. Conductive silver paste was applied to the two electrodes, and silver wires were led out from both ends of the interdigitated electrodes.

[0072] A water-soluble conductive polymer, polyethyleneimine, was dissolved in deionized water (10 wt%), and a tannic acid aqueous solution (pH 8.5, 10 wt%) was prepared separately. The tannic acid and the aforementioned conductive polyethyleneimine solution were mixed at a functional group ratio of 0.33:1, shaken for 5 min, and then stored in the dark for 24 h to achieve cross-linking. A carbon interdigitated electrode was treated with plasma, and then the cross-linked polyethyleneimine solution was sprayed onto the carbon interdigitated electrode using a spraying process. The electrode was then dried at room temperature to form a humidity-sensitive layer. The spraying time was controlled to achieve humidity-sensitive layer thicknesses of approximately 0.5 μm (a thickness less than 1 μm would prevent the formation of a uniform sensing layer, resulting in higher impedance), 5 μm, and 15 μm, respectively, thus preparing a humidity sensor with a measurement temperature of 30 °C.

[0073] The sensitivity of the humidity sensors with different thicknesses of humidity-sensitive layers was tested under 60% RH conditions. The humidity sensor with a humidity-sensitive layer of 0.5 μm had a sensitivity of 0.299 under 60% RH conditions, the humidity sensor with a humidity-sensitive layer of 5 μm had a sensitivity of 0.1 under 60% RH conditions, while the humidity sensor with a humidity-sensitive layer of 15 μm had a sensitivity of only 0.03 under 60% RH conditions.

[0074] Example 4

[0075] This embodiment relates to the fabrication of a humidity sensor, and further studies the hysteresis performance and reversible response recovery capability of the humidity sensor. The specific operations are as follows:

[0076] A 100-micrometer-thick polyvinyl chloride (PVC) film was cut into 20mm × 15mm strips, and carbon interdigitated electrodes were fabricated using laser carbonization technology with a wavelength of 9.64μm. The laser processing parameters were: speed 100mm / s; defocus height 0.5mm; working power 0.35W; the geometric dimensions of the interdigitated electrodes were: interdigital spacing 0.30mm, interdigital width 166μm; interdigital length 10mm; number of interdigitals 10; and silver wires were led out from the two terminals of the interdigitated electrodes by dotting conductive silver paste.

[0077] Water-soluble conductive polymer polyethyleneimine was dissolved in deionized water (10 wt%), and a dopamine (10 wt%) aqueous solution with pH 8.5 was prepared separately. Tannic acid was mixed with the above conductive polymer polyethyleneimine solution at a functional group ratio of 0.33:1, shaken for 5 min, and stored in the dark for 24 h to achieve cross-linking. The carbon interdigitated electrode was treated with plasma, and then the cross-linked polyethyleneimine solution was sprayed onto the carbon interdigitated electrode using a spraying process. It was then dried at room temperature to form a humidity-sensitive layer. The spraying time was controlled to ensure that the thickness of the humidity-sensitive layer was approximately 5 μm, thus preparing a humidity sensor with a measurement temperature of 30 °C.

[0078] (1) Study on wet hysteresis performance

[0079] The study investigated the moisture adsorption and desorption behavior of a humidity sensor within a humidity range of 35-90% RH, such as... Figure 9 As shown, the adsorption and desorption curves of the sensor almost overlap, demonstrating good hygroscopic performance; and when the humidity sensor is placed under different humidity levels for 30 days, its impedance remains relatively stable under the corresponding humidity conditions. Figure 10 (As shown).

[0080] (2) Reversible response capability

[0081] The humidity sensor was alternately placed in humid environments of 33% RH and 85% RH, and the impedance value of the sensor at 10 Hz was recorded simultaneously to examine the transient change of the sensor impedance during humidity switching. Figure 11 As shown, the impedance of the sensor can undergo reversible response and recovery.

[0082] Comparative Example

[0083] This comparative example relates to the fabrication of a humidity sensor, which differs from Example 1 in that the electrode fabrication is as follows:

[0084] A metal mask was covered on the PI film, and gold sputtering was performed for 200s under the conditions of cavity pressure of 4Pa and current of 30mA. After sputtering, the mask was removed to obtain a gold interdigitated electrode supported by the PI film. The structure of the gold interdigitated electrode is the same as that of the carbon interdigitated electrode in Example 1.

[0085] Water-soluble conductive polymer polyethyleneimine was dissolved in deionized water (10 wt%), and a tannic acid aqueous solution (pH 8.5, 10 wt%) was prepared separately. The tannic acid and the above conductive polymer polyethyleneimine solution were mixed at a functional group ratio of 0.33:1, shaken for 5 min, and then stored in the dark for 24 h to achieve cross-linking. A carbon interdigitated electrode was treated with plasma, and then the cross-linked polyethyleneimine solution was sprayed onto the carbon interdigitated electrode using a spraying process. The electrode was then dried at room temperature to form a humidity-sensitive layer. The spraying time was controlled to ensure the thickness of the humidity-sensitive layer was approximately 2 μm, thus obtaining a humidity sensor with a measurement temperature of 30 °C.

[0086] The Bode plots of the humidity sensor prepared in this comparative example at 30℃ and different humidity levels, and the impedance variation with humidity are shown in the figure below. Figure 12 As shown, the sensor's impedance changes little with humidity, and its sensitivity at 60% RH is 0.0032, which is much smaller than that of the humidity sensor prepared in Example 1.

[0087] Furthermore, taking the humidity sensor prepared in Example 1 of this invention as an example, this humidity sensor is compared with the prior art polymer-based humidity sensor and humidity sensor prepared with porous carbon electrode in terms of sensitivity, hysteresis, and response / recovery time. The sensitivity test is calculated using the following formula:

[0088] |Z|=aexp(-b×RH) (1)

[0089]

[0090] Where |Z| is the impedance, and RH is the humidity. This refers to relative sensitivity.

[0091] Using the above formula, the relative sensitivity of the humidity sensor prepared in Example 1, the polymer-based humidity sensor disclosed in the prior art, and the humidity sensor obtained by laser processing technology at 60% RH were calculated.

[0092] The test and calculation results of the above performance are shown in Table 1:

[0093] Table 1

[0094] sample Relative sensitivity at 60% RH Dampness Response / Reply Time Example 1 0.299 ～2％ 28 / 12s <![CDATA[QC-P4VP / PANI [1] ]]> 0.0874 ～3％ 24 / 35s <![CDATA[LiCl / PETMP-DVB [2] ]]> 0.0519 ～1.5％ 3.5 / 63s <![CDATA[POSS-TPPBr / PS [3] ]]> 0.112 ～2.3％ 5.6 / 39.1s <![CDATA[PANI / WGO [4] ]]> 0.0363 NA 8 / 9s <![CDATA[PEEK / SP [5] ]]> 0.0103 ～6.5％ 4.2 / 6.8 <![CDATA[rGO / GO / rGO [6] ]]> 0.0085 NA NA

[0095] NA in the table represents unpublished information;

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[0102] As shown in Table 1, compared with the humidity sensors prepared by polymer-based or porous carbon electrodes in the prior art, the humidity sensor prepared by the present invention not only has relatively small hysteresis and fast response recovery capability, but also has higher sensitivity. This can be attributed to the combination of the high specific surface area of ​​the porous carbon electrode and an appropriate amount of deposited cross-linked conductive humidity-sensitive polymer material, which can create favorable conditions for the adsorption of water molecules, provide more sensing sites, and thus obtain higher sensitivity.

[0103] The embodiments described above are merely preferred examples to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A humidity sensor, characterized by, The humidity sensor includes: The first electrode and the second electrode formed on the substrate; and A humidity-sensitive layer covering the first and second electrodes; The first electrode and the second electrode are carbon arrays with porous structures, and the humidity-sensitive material in the humidity-sensitive layer is obtained by cross-linking conductive polymer material; The preparation of the humidity sensor includes the following steps: (1) A carbonizable polymer film is carbonized using a laser according to a preset electrode pattern to obtain the first electrode and the second electrode; a conductive polymer material is mixed with a crosslinking agent and crosslinked to obtain the humidity-sensitive material; the ratio of the number of functional groups of the conductive polymer material to the crosslinking agent is 1:0.33-0.

67. (2) A coating containing the above-mentioned humidity-sensitive material is applied to the surface of the carbonizable polymer film having the first electrode and the second electrode, and after drying, a humidity-sensitive layer is formed to obtain the humidity sensor; the thickness of the humidity-sensitive layer is 1-10 μm. The conductive polymer material is one or more of polyethyleneimine and its derivatives; The crosslinking agent is selected from one or more of tannic acid, dopamine, polydopamine, and glutaraldehyde.

2. The humidity sensor of claim 1, wherein, The first electrode and the second electrode form an interdigitated electrode structure or a serpentine electrode structure; When the first electrode and the second electrode form an interdigitated electrode structure, the interdigitation distance of the interdigitated electrode structure is 10-600 μm, and the width and length of a single interdigitated finger are 20-2000 μm and 2-20 mm, respectively. When the first electrode and the second electrode form a serpentine electrode structure, the spacing between individual electrodes is 10-600 μm, and the width and length of individual electrodes are 20-2000 μm and 3-15 mm, respectively.

3. The humidity sensor according to claim 1, characterized in that, The ratio of the surface area of ​​the pores in the first electrode and / or the second electrode to the area occupied by the corresponding electrode is 20-80:1; the average pore size of the carbon array with porous structure is 1-10 μm.

4. A method for preparing a humidity sensor according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Using a laser to perform carbonization treatment on a carbonizable polymer film according to a preset electrode pattern, a carbon array with a porous structure is obtained, namely the first electrode and the second electrode. The conductive polymer material is mixed with a crosslinking agent and subjected to crosslinking treatment to obtain the humidity-sensitive material. (2) The coating containing the above-mentioned humidity-sensitive material is applied to the surface of the carbonizable polymer film with the porous carbon array, and after drying, a humidity-sensitive layer is formed to obtain the humidity sensor.

5. The preparation method according to claim 4, characterized in that, In step (1), the wavelength of the laser used in the carbonization process is 10 nm-1 mm, and the irradiation power of the laser is 0.2 W-10 W.

6. The preparation method according to claim 4, characterized in that, In step (1), the carbonizable polymer is polyimide, polyacrylonitrile, or polyvinyl chloride.

7. The preparation method according to claim 4, characterized in that, In step (2), before coating with a coating containing a moisture-sensitive material, the surfaces of the carbonizable polymer film containing the first electrode and the second electrode are first subjected to a hydrophilic treatment; the hydrophilic treatment includes silane coupling agent treatment and plasma treatment.

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