High-temperature and high-humidity resistant humidity sensor and preparation method thereof

Abstract

The application discloses a high-temperature and high-humidity resistant humidity sensor, which comprises a silicon wafer and a humidity-sensitive film; the silicon wafer comprises a silicon substrate and a metal electrode formed on the silicon substrate; the humidity-sensitive film is formed on the surface of the metal electrode; the humidity-sensitive film is a cross-linked polyamic acid film obtained by introducing a photosensitive group and a multifunctional amine into a reaction system. The application further discloses a preparation method of the high-temperature and high-humidity resistant humidity sensor. The high-temperature and high-humidity resistant humidity sensor has a fluorine-containing cross-linked polyimide film as the humidity-sensitive film, so that the moisture absorption rate and the dielectric constant of the humidity-sensitive film are reduced, the humidity-sensitive film has the properties of heat resistance, stability and hydrolysis resistance, and the humidity deviation of the humidity sensor is reduced, and the measurement precision is improved.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, specifically to a high-temperature and high-humidity resistant sensor and its preparation method. Background Technology

[0002] Humidity generally refers to the amount of water vapor in the environment being measured, reflecting the degree of dryness or wetness. Humidity sensors are indispensable not only in traditional industries, agriculture, medicine, and meteorology, but also occupy an important position in cutting-edge technology fields such as military, aviation, aerospace, and microelectronic devices. However, compared to parameters such as temperature, humidity detection is much more difficult, mainly because the water vapor content in the air is relatively low. Impurities in the air react chemically with water vapor to produce substances such as acids and alkalis, causing irreversible damage to the sensitive materials of humidity sensors and accelerating their corrosion and aging. Furthermore, the humidity-sensitive materials of humidity sensors must be in direct contact with the environment being measured to undergo changes, which reduces the lifespan of the humidity sensor.

[0003] Dew point meters and wet-bulb and dry-bulb thermometers are relatively traditional humidity tools. Their principles and structures are relatively simple, but they have disadvantages such as large size, need to add water regularly, and need to be calibrated frequently. Therefore, they have been gradually replaced by humidity sensors with modern measurement methods.

[0004] Modern micro-humidity sensors are typically based on MEMS technology and combined with semiconductor processes to manufacture intelligent devices that output resistance or capacitance. Among them, capacitive sensors manufactured based on MEMS (Micro-Electro-Mechanical Systems) technology are favored by users for their advantages of low price, small size, wide testing range, good linearity, high sensitivity, low hysteresis, fast response speed, and good stability.

[0005] The commonly used materials for current humidity detectors mainly include three categories: ceramics, polymers, and porous silicon. In recent years, with the rapid development of methods combining polymers with semiconductor processes, coupled with the advantages of this type of material such as high sensitivity, low cost, and simple manufacturing, polymer humidity sensors have been widely and rapidly developed.

[0006] Commonly used moisture-sensing polymers include polymethyl methacrylate, polyimide, polyacetylenoid, polysulfone, cellulose acetate, and silicone resin. The moisture-sensing mechanism of these polymers is as follows: the dielectric constant of the moisture-sensing polymer is ε = 2 to 7, while the dielectric constant of water molecules is ε ≈ 80. When the ambient humidity changes, the moisture-sensing polymer adsorbs or releases a corresponding proportion of water molecules, and the dipole moment of the moisture-sensing film changes, which is macroscopically manifested as a change in the dielectric constant. After making a capacitive sensor from a moisture-sensing polymer with these properties, the relative humidity of the environment can be obtained by measuring the capacitive response of the humidity sensor.

[0007] As a widely used humidity detection tool, humidity sensors with advantages such as high range, high precision, high stability, fast response speed, low hysteresis effect, moisture resistance, dirt resistance and low manufacturing cost are the goal that people are constantly pursuing.

[0008] Polyimide (PI) is an organic polymer material containing aromatic heterocyclic structures. It is one of the most heat-resistant polymers with moisture-sensing properties. The dielectric constant of polyimide changes with the relative humidity, and its dielectric constant is proportional to the relative humidity. Therefore, it can be used to monitor ambient humidity.

[0009] Humidity sensors made of polyimide material have excellent performance, high mechanical strength, high elastic modulus, are stable at high temperatures and not easily decomposed, have good corrosion resistance, are safe and non-toxic, and have good linearity. In addition, since polyimide is compatible with mature CMOS technology, it can be mass-produced using mature integrated circuit technology, which greatly improves product consistency and reduces product cost.

[0010] Polyimide is prone to ring-opening hydrolysis at high temperatures, especially in the presence of oxygen and moisture. This results in some defects in the practical application of capacitive polyimide sensors, such as moisture hysteresis, temperature drift, and long-term stability issues, which limit the commercialization and application scope of capacitive polyimide humidity sensors. Summary of the Invention

[0011] To overcome the shortcomings of the prior art, the purpose of this application is to provide a high-temperature and high-humidity resistant humidity sensor, which uses a fluorinated cross-linked polyimide film as the humidity-sensitive film, reduces the moisture absorption rate and dielectric constant of the humidity-sensitive film, and endows the humidity-sensitive film with heat resistance, stability, and hydrolysis resistance, thereby reducing the humidity deviation of the humidity sensor and improving the measurement accuracy.

[0012] To solve the above problems, the technical solution adopted in this application is as follows:

[0013] A high-temperature and high-humidity resistant sensor, including

[0014] A silicon wafer and a humidity-sensitive film; the silicon wafer includes a silicon substrate, a passivation layer formed on the silicon substrate, and a metal electrode formed on the passivation layer; the humidity-sensitive film is formed on the surface of the metal electrode;

[0015] The humidity-sensitive membrane is a cross-linked polyimide film obtained by introducing photosensitive groups and polyfunctional amines into the reaction system.

[0016] The photosensitive group comes from a photosensitive compound containing a double bond.

[0017] As a further option, the photosensitive compound containing double bonds described in this application is one or two of hydroxypropyl methacrylate, β-hydroxyethyl acrylate, and pentaerythritol triacrylate.

[0018] As a further embodiment, the cross-linked polyimide film described in this application is a cross-linked polyimide film with fluorine-containing groups introduced.

[0019] As a further embodiment, the thickness of the cross-linked polyimide film described in this application is 2-4 μm.

[0020] Another objective of this application is to provide a method for preparing a high-temperature and high-humidity sensor, which uses dianhydride and diamine precursors and introduces multifunctional amine precursors and photosensitive groups to obtain a capacitive humidity sensor with a cross-linked polyimide thin film humidity-sensitive membrane.

[0021] The method for manufacturing the high-temperature and high-humidity resistant sensor described in this application includes:

[0022] Using dianhydride and diamine as precursors, at least one of the precursors having fluorine-containing functional groups, a carboxyl-terminated polyamic acid solution is prepared by introducing a multifunctional amine precursor into the reaction system. A photosensitive compound is added to the carboxyl-terminated polyamic acid to obtain a photosensitive polyimide precursor solution.

[0023] A photoinitiator is added to the precursor solution, stirred evenly, and then coated onto a silicon substrate on which metal electrodes have been prepared. The substrate is then transferred to a hot plate for baking, which imidizes the precursor coated on the silicon substrate, forming a photosensitive cross-linked polyimide film on the silicon substrate.

[0024] A silicon substrate with a photosensitive cross-linked polyimide film is exposed and then immersed in a developing solution. The developing solution is used to treat the substrate to obtain a patterned photosensitive cross-linked polyimide film.

[0025] Patterned photosensitive cross-linked polyimide films, along with silicon substrates, are transferred into a nitrogen oven for segmented baking to achieve complete imidization, resulting in fully imidized photosensitive cross-linked polyimide film silicon wafers.

[0026] A fully imidized photosensitive cross-linked polyimide thin-film silicon wafer is fabricated into a high-temperature and high-humidity sensor.

[0027] As a further solution, the method for obtaining the prepolymer solution in this application is as follows:

[0028] Step 1: Place the diamine precursor, the multifunctional amine precursor, and the solvent into the reaction apparatus, stir to dissolve, and introduce nitrogen gas.

[0029] Step 2: Add dianhydride precursor and solvent to the above reaction apparatus, adjust the solid content of the solution to 20%~25%, react at room temperature, add end-capping agent, and continue the reaction to obtain carboxyl-terminated polyamic acid solution;

[0030] Step 3: Add a catalyst, a dehydrating agent, and a photosensitizing compound to the above polyamic acid solution. After the reaction is complete, a photosensitive polyamic acid solution is obtained.

[0031] As a further embodiment, the diamine precursor described in this application is one or two of 2,2-bis[4-(4-aminophenoxyphenyl)]hexafluoropropane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, and 4,4'-diaminodiphenyl ether; the polyfunctional amine precursor is one or more of tri(4-aminophenyl)amine and tetra-(4-aminophenyl)ethylene; and the dianhydride is one or more of 4,4'-(hexafluoroisopropene)phthalic anhydride, 4,4'-(2-(3'-trifluoromethyl-phenyl)-1,4-phenoxy)-phthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0032] As a further embodiment, the total molar ratio of amine to anhydride described in this application is amine: anhydride = (1.02~1.08):1.

[0033] As a further embodiment, the organic solvent described in this application is N,N'-dimethylformamide; the end-capping agent is one or more of 2,3-anthracite anhydride, phthalic anhydride, glutaric anhydride, and maleic anhydride; and the photosensitive compound is one or more of hydroxypropyl methacrylate (HPMA), β-hydroxyethyl acrylate (HEA), and pentaerythritol triacrylate (PETA).

[0034] As a further embodiment, in this application, the prepolymer solution is coated using a spin coating method, and the baking temperature is 60-110°C, with a baking time of 3-5 minutes.

[0035] As a further embodiment, the developer described in this application is one or a mixture of two of the following: 0.01% to 0.1% sodium hydroxide and 2% to 3% tetramethylammonium hydroxide.

[0036] As a further solution, the heating procedure for segmented baking described in this application is as follows:

[0037] The first stage involves raising the temperature from room temperature to 80°C and baking for 1 hour.

[0038] The second stage involves increasing the temperature from 80°C to 150°C and baking for 1 hour.

[0039] The third stage involves increasing the temperature from 150°C to 250°C and baking for 1 hour.

[0040] The third stage involves increasing the temperature from 250°C to 300°C and baking for 1 hour.

[0041] The fifth stage involves heating from 300°C to 350°C and baking for 0.5 hours.

[0042] The heating rate for each stage is 0.5-3℃ / min.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] 1. The humidity sensor described in this application uses a fluorinated cross-linked polyimide film as the humidity-sensitive film. Due to the presence of fluorine atoms in the humidity-sensitive film, the humidity hysteresis of the humidity sensor is reduced, the humidity deviation is lowered, and the stability and measurement accuracy of the humidity sensor are improved.

[0045] 2. The method for preparing the high-temperature and high-humidity resistant humidity sensor described in this application uses fluorinated dianhydride and diamine monomers. Introducing fluorinated groups into the polyimide film effectively reduces the moisture absorption rate and dielectric constant of the humidity sensor. A multifunctional amine precursor is added to the reaction system to achieve cross-linking in the polycondensation reaction, resulting in a cross-linked polyimide acid. Photosensitive groups are introduced into the polyimide acid, and after photocuring under the action of a photoinitiator, secondary cross-linking is performed. The heat resistance, stability, and hydrolysis resistance of the obtained fluorinated cross-linked polyimide film are greatly improved, thus improving the heat and humidity resistance of the humidity sensor.

[0046] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a schematic diagram of the structure of a capacitive humidity sensor described in one embodiment of this application;

[0049] Figure 2 This is a process flow diagram of the fabrication process of the capacitive humidity sensor in Embodiment 1 of this application;

[0050] Figure 3 The humidity deviation after high-temperature reflow soldering (260°C) of the capacitive humidity sensor described in Examples 1-3;

[0051] Figure 4 The humidity deviation of the capacitive humidity sensor described in Examples 1-3 after passing through double 85.

[0052] The figures are labeled as follows: 1. Silicon substrate; 2. Passivation layer; 3. Metal electrode; 4. Humidity-sensitive film. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0054] Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0055] The term "comprising" and other equivalent descriptive terms used in the specification and claims of this application are intended to cover a non-exclusive inclusion, which includes both the contents explicitly described in the specification and claims and steps or units that are not described in the specification and claims but are inherent in the product, method or structure.

[0056] This application provides a high-temperature and high-humidity resistant humidity sensor, which uses a fluorinated cross-linked polyimide film as the humidity-sensitive film to solve the problems of humidity hysteresis and reduce humidity deviation, thereby improving the stability and measurement accuracy of the humidity sensor.

[0057] The high-temperature and high-humidity resistant sensor includes

[0058] A silicon wafer and a humidity-sensitive film; the silicon wafer includes a silicon substrate and a metal electrode formed on the silicon substrate; the humidity-sensitive film is formed on the surface of the metal electrode;

[0059] The humidity-sensitive membrane is a cross-linked polyimide film obtained by introducing photosensitive groups and polyfunctional amines into the reaction system. The glass transition temperature of the fluorinated cross-linked polyimide film is ≥350℃ but not more than 430℃.

[0060] Cross-linked polyimide film

[0061] This application uses cross-linked polyimide film.

[0062] In the embodiments of this application, a multifunctional amine is introduced into the reaction system for preparing the cross-linked polyimide film. During the reaction, the proportion of rigid structures in the polyimide film can be increased through cross-linking, resulting in a glass transition temperature Tg ≥ 350℃ and a thermal decomposition temperature Tg ≥ 350℃. 5%≥530℃; at the same time, it improves the hydrolysis resistance and stability of polyimide film.

[0063] Furthermore, the high-temperature and high-humidity sensor described in this application preferably uses a fluorinated cross-linked polyimide film with introduced fluorine groups. Fluorine atoms are introduced into the structure of the polyimide film. Fluorine atoms have high electronegativity. In the structure of the polyimide polymer, on the one hand, due to the high bond energy of the C-F3 elements, the fluorinated polyimide film has high thermal and thermo-oxidative stability, and the large volume of the C-F3 groups results in a low packing density of the macromolecules. The fluorinated polyimide film has high air permeability and low dielectric constant. On the other hand, due to the low electronic polarization of fluorine, it has low cohesive energy and surface free energy, which makes the material have low water absorption, making it both hydrophobic and oleophobic.

[0064] Therefore, in the embodiments of this application, the introduction of fluorine into the polyimide humidity-sensitive film can reduce the hysteresis of the humidity sensor, reduce humidity deviation, and improve the stability and measurement accuracy of the humidity sensor.

[0065] Compared to conventional polyimide films, cross-linked polyimide films with fluorine-containing groups exhibit significantly lower moisture absorption and moisture expansion coefficients.

[0066] As mentioned above, fluorinated cross-linked polyimide films can effectively improve the stability, measurement accuracy, and heat resistance of humidity sensors. However, during the research process, it was found that the thickness of the fluorinated cross-linked polyimide film also affects the performance of the humidity sensor. Specifically, when the thickness of the fluorinated cross-linked polyimide film is too thin, two problems will occur: small capacitance change and decreased accuracy and poor consistency of the humidity sensor. When the polyimide film is too thick, the moisture inside the film is difficult to remove, resulting in increased moisture hysteresis.

[0067] Therefore, in the embodiments of this application, the thickness of the fluorinated cross-linked polyimide film is set to 2-4 μm, which can further ensure the measurement accuracy and consistency of the humidity sensor and reduce moisture hysteresis.

[0068] Preferably, the thickness can be 2μm, 2.5μm, 3μm, 3.5μm, or 4μm.

[0069] [Photosensitive group]

[0070] In the reaction, unsaturated photosensitive groups are introduced through photosensitive compounds, which can undergo both addition polymerization and condensation polymerization. During photocuring, the curing rate is fast, and polymerization can easily occur with only a small amount of initiator.

[0071] In this application, in order to achieve rapid crosslinking polymerization through photocuring, the photosensitive group used is derived from a photosensitive compound containing double bonds.

[0072] Specifically, the photosensitive compound containing double bonds described in this application is one or two of hydroxypropyl methacrylate, β-hydroxyethyl acrylate, and pentaerythritol triacrylate.

[0073] Another objective of this application is to provide a method for preparing a high-temperature and high-humidity sensor, which uses fluorinated dianhydride and fluorinated diamine precursors, and introduces multifunctional amine precursors and photosensitive groups to obtain a capacitive humidity sensor with a fluorinated cross-linked polyimide thin film humidity-sensitive membrane.

[0074] The method for manufacturing the high-temperature and high-humidity resistant sensor described in this application includes:

[0075] Using dianhydride and diamine as precursors, at least one of which has a fluorine-containing functional group, a carboxyl-terminated polyamic acid solution is prepared by introducing a multifunctional amine precursor into the reaction system. A photosensitive compound is added to the carboxyl-terminated polyamic acid to obtain a photosensitive fluorine-containing polyimide precursor solution.

[0076] A photoinitiator is added to the precursor solution, stirred evenly, and then coated onto a silicon substrate on which metal electrodes have been prepared. The substrate is then transferred to a hot plate for baking, which imidizes the precursor coated on the silicon substrate, forming a photosensitive fluorinated cross-linked polyimide film on the silicon substrate.

[0077] After exposing the silicon substrate with the photosensitive cross-linked polyimide film, it is treated with a developing solution to obtain a patterned photosensitive cross-linked polyimide film.

[0078] Patterned photosensitive cross-linked polyimide films, along with silicon substrates, are transferred into a nitrogen oven for segmented baking to achieve complete imidization, resulting in fully imidized photosensitive cross-linked polyimide film silicon wafers.

[0079] A fully imidized photosensitive cross-linked polyimide thin-film silicon wafer is fabricated into a high-temperature and high-humidity sensor.

[0080] Diamine, dianhydride

[0081] In order to obtain fluorinated polyimide films, at least one of the dianhydride and diamine precursors used in this application has a fluorinated group.

[0082] Specifically, the diamine precursor used in this application is selected from, but not limited to, one or more of 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, and 4,4'-diaminodiphenyl ether.

[0083] The dianhydride is one or more of the following: 4,4′-(hexafluoroisopropenyl)phthalic anhydride, 4,4′-(2-(3′-trifluoromethyl-phenyl)-1,4-phenoxy)-phthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic anhydride, and 3,3′,4,4′-biphenyltetracarboxylic dianhydride.

[0084] Polyfunctional amines

[0085] Multifunctional amine precursors were also introduced into the reaction system. The introduction of multifunctional amines into the crosslinking structure can increase the proportion of rigid structures in the polyimide film, thereby imparting a high glass transition temperature (Tg≥350℃) and thermal decomposition temperature (Tg≥350℃) to the polyimide film. 5% With properties such as ≥530℃, it has excellent resistance to hydrolysis, which can improve the stability of the humidity sensor. After being treated under double 85 (85℃, 85%RH) conditions, the degree of hydrolysis of the humidity sensor is reduced; after being placed under high humidity conditions (90%RH) for half a year, the measured humidity deviation is still ≤2%.

[0086] Preferably, in the embodiments of this application, the multifunctional amine precursor is selected from, but is not limited to, one or more of tris(4-aminophenyl)amine and tetra-(4-aminophenyl)ethylene.

[0087] The ratio of amine to anhydride

[0088] Since an anhydride capping agent is introduced during the reaction, the capping agent will react with the diamine. In order to ensure that the diamine and dianhydride react completely, in this application, as a further solution, the ratio of the total moles of amine and anhydride is amine: anhydride = (1.02~1.08):1.

[0089] Other reagents

[0090] Preferably, the dehydrating agent used in the embodiments of this application is N,N'-dicyclohexylcarboimide (DCC), and the catalyst used is 4-diaminopyridine (DMAP).

[0091] The organic solvent used in the embodiments of this application is, but is not limited to, N,N'-dimethylformamide (DMF); the end-capping agent used in the embodiments of this application is selected from, but is not limited to, one or more of 2,3-anthracite anhydride, phthalic anhydride, glutaric anhydride, and maleic anhydride; the photosensitive compound used in the embodiments of this application is selected from, but is not limited to, one or more of hydroxypropyl methacrylate (HPMA), β-hydroxyethyl acrylate (HEA), and pentaerythritol triacrylate (PETA).

[0092]

Preparation Process

[0093] In the embodiments of this application, the method for obtaining the prepolymer solution is as follows:

[0094] Step 1: The ratio of total moles of amine to anhydride is 1.02~1.08:1 (anhydride is calculated as 100, and the amine precursor is slightly in excess). Add the fluorinated diamine precursor, the multifunctional amine precursor and the solvent N,N'-dimethylformamide (DMF) to the reaction flask, dissolve them with stirring at room temperature, and purge with nitrogen for 30 min.

[0095] Step 2: Add a fluorinated dianhydride precursor, then add an appropriate amount of N,N'-dimethylformamide (DMF) to make the solid content of the solution 20%~25%, react at room temperature for 5 hours, then add 1~5 parts of anhydride end-capping agent, react at room temperature for 3 hours to obtain a carboxyl-terminated polyamic acid (PAA) solution.

[0096] Step 3: Add 5-10 parts of N,N'-dicyclohexylcarbodiimide, 0.5-1 parts of 4-dimethylaminopyridine, and 5-10 parts of a compound containing a photosensitive group to the above fluorinated polyamic acid solution, and react at room temperature for 8 hours to obtain a photosensitive polyimide (PSPI) precursor solution.

[0097] In the embodiments of this application, the photosensitive polyimide (PSPI) precursor solution is mixed with 1-2 parts by weight of initiator and then coated by spin coating. The baking temperature is 60-110°C and the baking time is 3-5 minutes.

[0098] Preferably, the baking temperature is 80-100℃. In addition, the baking temperature can also be selected as 60-65℃, 65-70℃, 70-75℃, 75-80℃, 80-85℃, 85-90℃, 90-95℃, 95-100℃, 100-105℃, or 105-110℃.

[0099] In the embodiments of this application, the developing solution is one or a mixture of two of the following: 0.01% to 0.1% sodium hydroxide and 2% to 3% tetramethylammonium hydroxide.

[0100] Since polyamic acid readily forms certain complexes with polar aprotic solvents, making solvent removal more difficult, a segmented stepwise imidization process is employed to create sufficient conditions for the completion of imidization and the removal of residual solvents.

[0101] Therefore, in the embodiments of this application, the baking process of the patterned polyimide film adopts segmented baking. Specifically, the heating procedure for segmented baking is as follows:

[0102] The first stage involves raising the temperature from room temperature to 80°C and baking for 1 hour.

[0103] The second stage involves increasing the temperature from 80°C to 150°C and baking for 1 hour.

[0104] The third stage involves increasing the temperature from 150°C to 250°C and baking for 1 hour.

[0105] The third stage involves increasing the temperature from 250°C to 300°C and baking for 1 hour.

[0106] The fifth stage involves heating from 300°C to 350°C and baking for 0.5 hours.

[0107] During the segmented baking process, the heating rate affects the quality and performance of the polyimide film. If the heating rate is too fast, pores are likely to appear on the film surface and the solvent residue rate will be high; if the heating rate is slow, it will take a long time and consume more electricity.

[0108] Furthermore, both excessively fast and excessively slow heating rates are detrimental to the formation of a regular crystalline structure in thin films.

[0109] Therefore, in order to improve the quality of the polyimide film and meet its performance requirements as a humidity-sensitive film, in this application, the heating rate of each stage of the above-mentioned segmented baking is 0.5-3℃ / min.

[0110] Example 1:

[0111] like Figure 1 As shown, the high-temperature and high-humidity resistant sensor described in this embodiment includes...

[0112] A silicon wafer and a humidity-sensitive film; the silicon wafer includes a silicon substrate 1, a passivation layer 2 formed on the silicon substrate 1, and a metal electrode 3 formed on the passivation layer 2; the humidity-sensitive film 4 is formed on the surface of the metal electrode 3;

[0113] The humidity-sensitive film is a fluorinated cross-linked polyimide film with photosensitive groups introduced into it, and the glass transition temperature of the cross-linked polyimide film is 371.5℃.

[0114] The method for preparing the high temperature and high humidity resistant sensor is as follows:

[0115] Raw materials: The diamine is 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane; the polyfunctional amine is tetra-(4-aminophenyl)ethylene; the dianhydrides are 4,4′-(hexafluoroisopropene)diphthalic anhydride and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride; the photosensitive compound is hydroxypropyl methacrylate; the photoinitiator is commercially known as Photoinitiator 184; the developer is 0.02% NaOH.

[0116] Method: Weigh 28.51g of 2,2-bis[4-(4-aminophenoxybenzene)]hexafluoropropane and 1.51g of tetra-(4-aminophenyl)ethylene and dissolve them in 180g of N,N-dimethylformamide. Stir thoroughly to completely dissolve the amine monomers. Weigh 8.88g of 4,4′-(hexafluoroisopropenyl)phthalic anhydride and 11.69g of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride and add them to the amine solution in three portions, with an interval of 20min between each addition. Then add 20g of DMF to make the solid content of the solution 20%. React at room temperature for 5h. Then add 0.88g of phthalic anhydride and react at room temperature for 3h to obtain a polyamic acid (PAA) solution.

[0117] 1.23 g N,N'-dicyclohexylcarboimide, 0.07 g 4-dimethylaminopyridine, and 1 g hydroxypropyl methacrylate were added to the PAA solution and reacted at 50 °C for 8 h to obtain a polyimide (PSPI) precursor solution containing photosensitive groups. Then, 0.1 g photoinitiator 184 was added to the polyimide (PSPI) precursor solution and stirred at room temperature for 30 min to mix it evenly. Then, it was coated onto a silicon substrate material with interdigitated gold electrodes by spin coating and baked at 60 °C for 5 min.

[0118] The baked polyimide film is exposed to ultraviolet light for 3-4 minutes, then immersed in 0.02% NaOH developer for 30-40 seconds and removed. The residual NaOH developer is then washed with deionized water and treated at 80-100℃ for 10-20 minutes to remove the residual solvent in the film, thus obtaining a patterned polyimide film.

[0119] Patterned polyimide was placed in a nitrogen oven and imidized according to a programmed temperature sequence: room temperature ~ 80℃ for 1 hour; 150℃ for 1 hour; 250℃ for 1 hour; 300℃ for 1 hour; 350℃ for 0.5 hours, with a heating rate of 1℃ / min. The fully imidized polyimide thin film silicon substrate was then cut, wire-bonded, and encapsulated, and calibrated at room temperature.

[0120] Example 2:

[0121] A high-temperature and high-humidity resistant sensor is disclosed in this embodiment. The raw materials for preparing the high-temperature and high-humidity resistant sensor include: a precursor diamine of 4,4'-diaminodiphenyl ether; a multifunctional polyamine of tetra-(4-aminophenyl)ethylene; a dianhydride of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride; a photosensitive compound of hydroxypropyl methacrylate; a photoinitiator commercially known as photoinitiator 184; and a developer solution of 0.02% NaOH solution.

[0122] The glass transition temperature of the obtained cross-linked polyimide film was 392.4℃.

[0123] In this embodiment, the total molar ratio of amines to anhydrides is 1.05:1; the reaction process is the same as in Example 1.

[0124] Example 3:

[0125] A high-temperature and high-humidity resistant sensor is disclosed in this embodiment. The raw materials used to prepare the sensor include 4,4'-diaminodiphenyl ether as the diamine; 3,3',4,4'-biphenyltetracarboxylic acid dianhydride as the dianhydride; hydroxypropyl methacrylate as the photosensitive compound; photoinitiator commercially known as photoinitiator 184; and 0.02% NaOH solution as the developer.

[0126] The glass transition temperature of the obtained cross-linked polyimide film is 301.9℃.

[0127] In this embodiment, no polyfunctional amines were added, and the total molar ratio of amines to anhydrides was 1.08:1; the reaction process was the same as in Example 1.

[0128] [Performance Testing and Results]

[0129] 1. Properties of Fluorine-Containing Crosslinked Polyimide Films

[0130] The properties of the fluorinated cross-linked polyimide films obtained in Examples 1-3 were tested, and the test results are shown in Table 1.

[0131] Table 1: Performance of Fluorinated Crosslinked Polyimide Films in Examples 1-3

[0132]

[0133] The results in Table 1 show that the dielectric constant is significantly reduced compared to ordinary polyimide, and the glass transition temperature is significantly increased, indicating the presence of a cross-linked structure.

[0134] In addition, other performance aspects have also been significantly improved.

[0135] Comparing Examples 1-3, it can be found that the mechanical strength of the fluorinated cross-linked polyimide film obtained in Example 3, which did not contain polyfunctional amines, was significantly lower than that of Examples 1 and 2, which contained polyfunctional amines. Its dielectric constant was also significantly higher than that of Examples 1 and 2, and its glass transition temperature was lower than that of Examples 1 and 2. This indicates that the mechanical strength of the fluorinated cross-linked polyimide film obtained in Example 3, which had a lower degree of cross-linking than Examples 1 and 2, was significantly lower than that of Examples 1 and 2, which contained polyfunctional amines.

[0136] 2. Capacitance value of the humidity sensor

[0137] The capacitance values ​​of the humidity sensors obtained in Examples 1-3 were tested under different humidity levels. The test results are shown in Table 2.

[0138] Table 2: Capacitance values ​​of humidity sensors in Examples 1-3 under different humidity conditions

[0139]

[0140] 3. Humidity deviation after high-temperature reflow soldering (260℃)

[0141] The humidity deviation of the humidity sensors obtained in Examples 1-3 after high-temperature reflow soldering (260°C) is shown in Table 3. Figure 3 .

[0142] The results show that the humidity deviation of the humidity sensors in Examples 1-2 after high-temperature reflow soldering (260℃) is ≤2%. Relatively speaking, the humidity deviation of Example 3 is greater than that of Examples 1 and 2.

[0143] 4. Humidity deviation before and after 10 days of processing (double 85)

[0144] The humidity sensors obtained in Examples 1-3 were subjected to a dual 85 (85°C, 85% humidity) treatment for 10 days. The humidity deviation of the humidity sensors before and after the treatment is shown in Table 3. Figure 4 .

[0145] The results show that the humidity deviation of the humidity sensors in Examples 1-2 after 10 days of double 85 temperature monitoring is ≤4%. Relatively speaking, the humidity deviation of Example 3 is greater than that of Examples 1 and 2.

[0146] Table 3: Measurement deviations of humidity sensors in different embodiments after different treatments

[0147]

[0148] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A high-temperature and high-humidity resistant sensor, comprising: A silicon wafer and a humidity-sensitive film; the silicon wafer includes a silicon substrate, a passivation layer formed on the silicon substrate, and a metal electrode formed on the passivation layer; the humidity-sensitive film is formed on the surface of the metal electrode; Its features are, The humidity-sensitive membrane is a cross-linked polyimide film obtained by introducing photosensitive groups and polyfunctional amines into the reaction system; the photosensitive groups are derived from photosensitive compounds containing double bonds; the cross-linked polyimide film is a cross-linked polyimide film with introduced fluorine-containing groups; the thickness of the cross-linked polyimide film is 2-4 μm.

2. A method for preparing a high-temperature and high-humidity resistant sensor as described in claim 1, characterized in that, include Using dianhydrides and diamines as precursors, a multifunctional amine precursor was introduced into the reaction system to prepare a carboxyl-terminated polyamic acid solution. A photosensitive compound was added to the carboxyl-terminated polyamic acid to obtain a photosensitive polyimide precursor solution. A photoinitiator is added to the precursor solution, stirred evenly, and then coated onto a silicon substrate with a metal electrode. The substrate is then transferred to a hot plate for baking to imidize the precursor coated on the silicon substrate, forming a photosensitive cross-linked polyimide film on the silicon substrate. A silicon substrate with a photosensitive cross-linked polyimide film is exposed and then immersed in a developing solution. The developing solution is used to treat the substrate to obtain a patterned photosensitive cross-linked polyimide film. Patterned photosensitive cross-linked polyimide films, along with silicon substrates, are transferred into a nitrogen oven for segmented baking to achieve complete imidization, resulting in fully imidized cross-linked polyimide film silicon wafers. A fully imidized photosensitive cross-linked polyimide thin-film silicon wafer is fabricated into a high-temperature and high-humidity sensor.

3. The preparation method according to claim 2, characterized in that, The method for obtaining the prepolymer solution is as follows: Step 1: Place the diamine, polyfunctional amine precursor, and solvent into the reaction apparatus, stir to dissolve, and introduce nitrogen gas. Step 2: Add dianhydride precursor and solvent to the above reaction apparatus, adjust the solid content of the solution to 20%~25%, react at room temperature, add end-capping agent, and continue the reaction to obtain carboxyl-terminated polyamic acid solution; Step 3: Add a catalyst, a dehydrating agent, and a photosensitizing compound to the above polyamic acid solution. After the reaction is complete, a photosensitive polyamic acid solution is obtained.

4. The preparation method according to claim 3, characterized in that, The diamine is one or two of 2,2-bis[4-(4-aminophenoxyphenyl)]hexafluoropropane, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, and 4,4'-diaminodiphenyl ether; the polyfunctional amine precursor is one or more of tri(4-aminophenyl)amine and tetra-(4-aminophenyl)ethylene; the dianhydride is one or more of 4,4'-(hexafluoroisopropene)phthalic anhydride, 4,4'-(2-(3'-trifluoromethyl-phenyl)-1,4-phenoxy)phthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

5. The preparation method according to claim 3, characterized in that, The solvent is N,N'-dimethylformamide; the capping agent is one or more of 2,3-anthracite anhydride, phthalic anhydride, glutaric anhydride, and maleic anhydride; the photosensitive compound is one or more of hydroxypropyl methacrylate (HPMA), β-hydroxyethyl acrylate (HEA), and pentaerythritol triacrylate (PETA).

6. The preparation method according to claim 2, characterized in that, The prepolymer solution is coated using a spin coating method, and the baking temperature is 60-110℃, with a baking time of 3-5 minutes.

7. The preparation method according to claim 2, characterized in that, The developing solution is one or a mixture of two of the following: 0.01% to 0.1% sodium hydroxide and 2% to 3% tetramethylammonium hydroxide.

8. The preparation method according to claim 2, characterized in that, The heating process for the segmented baking is as follows: The first stage involves raising the temperature from room temperature to 80°C and baking for 1 hour. The second stage involves increasing the temperature from 80°C to 150°C and baking for 1 hour. The third stage involves increasing the temperature from 150°C to 250°C and baking for 1 hour. The third stage involves increasing the temperature from 250°C to 300°C and baking for 1 hour. The fifth stage involves heating from 300°C to 350°C and baking for 0.5 hours. The heating rate for each stage is 0.5-5℃ / min.

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