A flexible dielectric film preparation method for millimeter wave terahertz frequency band

Abstract

This invention discloses a method for preparing flexible dielectric thin films for the millimeter-wave terahertz band, belonging to the field of high-frequency electronic materials technology. The method includes the following steps: 1. Under nitrogen protection, a photosensitive resin solution is spin-coated onto a glass substrate using a spin coater to obtain a uniform wet film; 2. Under nitrogen protection, ultraviolet light initiates a thiol-ene click reaction based on a linearly gradient transmittance mask to obtain a film with a continuous gradient crosslinking density; 3. The film with the continuous gradient crosslinking density is cured and annealed to obtain a gradient crosslinked thermotropic liquid crystal polyester film; 4. The gradient crosslinked thermotropic liquid crystal polyester film is peeled off and subjected to supercritical treatment to obtain a flexible dielectric thin film for the millimeter-wave terahertz band. This invention not only avoids the doping of any inorganic fillers, thus reducing interfacial losses and preventing a significant increase in the high-frequency loss factor, but also achieves a continuous gradient in crosslinking density through optical field gradient modulation, facilitating precise control of the dielectric constant.

Description

Technical Field

[0001] This invention belongs to the field of high-frequency electronic materials technology, specifically relating to a method for preparing flexible dielectric thin films for the millimeter-wave terahertz band. Background Technology

[0002] Millimeter-wave terahertz bands are widely used in mobile communications due to their ample bandwidth, high transmission rate, and excellent time-domain resolution.

[0003] Flexible dielectric films are the core functional substrates for millimeter-wave terahertz devices, serving functions such as signal transmission, impedance matching, and structural support.

[0004] Currently, the method for preparing flexible dielectric films for millimeter-wave and terahertz bands generally involves compositing inorganic fillers with thermotropic liquid crystal polyester films. Although this method can adjust the dielectric constant, the interface between the inorganic filler and the substrate introduces severe interfacial polarization loss, resulting in a significant increase in the high-frequency loss factor. Moreover, it is difficult to control the dispersion uniformity of the inorganic filler.

[0005] In view of this, a method for preparing flexible dielectric thin films for the millimeter-wave terahertz band is designed to solve the above problems. Summary of the Invention

[0006] To address the problems mentioned in the background section, this invention provides a method for preparing flexible dielectric thin films in the millimeter-wave terahertz band. This method not only enables continuous and gradual spatial variation of crosslinking density through optical field gradient modulation, allowing for precise control of the dielectric constant, but also reduces the loss of the liquid crystal polyester by eliminating the need for any inorganic dielectric fillers.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing flexible dielectric thin films for the millimeter-wave terahertz frequency band, comprising the following steps: 1. Nitrogen gas is introduced at room temperature. The pretreated glass substrate is placed on the spin coating platform. Under nitrogen protection, the photosensitive resin solution is spin-coated to obtain a uniform wet film. 2. A glass substrate coated with a uniform wet film is placed on an ultraviolet curing platform. A linear gradient transmittance mask is placed on top of the glass substrate coated with a uniform wet film. Under nitrogen protection, a crosslinking density gradient film is prepared by triggering a thiol-ene click reaction based on ultraviolet light. III. Gradient crosslinked thermotropic liquid crystal polyester film was prepared by curing and annealing of the film with a continuous gradient crosslinking density. IV. A flexible dielectric film for millimeter-wave terahertz frequency band is prepared by peeling a gradient cross-linked thermotropic liquid crystal polyester film from a glass substrate and subjecting it to supercritical treatment.

[0008] Further, in step one, the preparation steps of the photosensitive resin solution include: A transparent compound solvent was prepared by stirring cyclopentanone and γ-butyrolactone in a volume ratio of 2:1 at 300 r / min for 10 min at room temperature. A thiol-modified thermotropic liquid crystal polyester prepolymer with a solid-liquid mass-to-volume ratio of 1:6 was added to a compound solvent, and stirred at 400 r / min for 3 h in the dark to obtain a thiol-modified thermotropic liquid crystal polyester solution. A thiol-modified thermotropic liquid crystal polyester solution was prepared by adding pentaerythritol triallyl ether with a thiol molar ratio of 1:1 to a thiol-modified thermotropic liquid crystal polyester solution, and stirring at 400 r / min for 1 h in the dark. A mixture of 1.2 wt% phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and 0.04 wt% hydroquinone was sequentially added to a thiol-modified thermotropic liquid crystal polyester-crosslinking agent solution. The mixture was kept in the dark, heated to 30°C, and stirred at a constant speed of 350 r / min for 3 h to obtain a photosensitive resin mixture solution. The photosensitive resin mixture was degassed by ultrasonication in the dark for 30 minutes, and then allowed to stand for 15 minutes to remove air bubbles. The photosensitive resin mixture solution was filtered under pressure using a polytetrafluoroethylene needle filter to remove trace impurities, thus obtaining the photosensitive resin solution.

[0009] Further, in step one, the preparation steps of the thiol-modified thermotropic liquid crystal polyester prepolymer include: Nitrogen gas was introduced at room temperature, and pentafluorophenol and p-chlorophenol in a volume ratio of 3:1 were stirred at 350 r / min for 15 min under nitrogen protection to obtain a transparent compound solvent. A thermotropic liquid crystal polyester with a solid-liquid mass-to-volume ratio of 1:6 was added to a compound solvent, heated to 130°C, and stirred at 450 r / min for 5 h under nitrogen protection to obtain a transparent viscous liquid. 3-Mercaptopropionic acid with a molar ratio of 1:35 to repeating units of thermotropic liquid crystal polyester was added to a viscous liquid. The temperature was maintained at 130℃, and the mixture was stirred at 450 r / min for 5 h under nitrogen protection. Thiol groups were grafted onto the end and side groups of the thermotropic liquid crystal polyester molecular chain. After the reaction was completed, the mixture was cooled to room temperature to obtain a transparent crude product solution of thiol-modified thermotropic liquid crystal polyester prepolymer. The crude product solution of thiol-modified thermotropic liquid crystal polyester prepolymer was slowly added to anhydrous ethanol and stirred at 350 r / min for 15 min to precipitate thiol-modified thermotropic liquid crystal polyester prepolymer. The precipitate was collected by vacuum filtration. The precipitate of the thiol-modified thermotropic liquid crystal polyester prepolymer was washed three times with anhydrous ethanol to remove residual solvent and unreacted modifier. The thiol-modified thermotropic liquid crystal polyester prepolymer precipitate was placed in a vacuum drying oven, heated to 80°C, and vacuum dried at a constant temperature for 12 hours to obtain the thiol-modified thermotropic liquid crystal polyester prepolymer.

[0010] Furthermore, in step three, the curing and annealing process includes: The cross-linked density continuous gradient film was placed in an oven, heated to 70°C, and pre-dried at a constant temperature for 15 minutes to evaporate the free solvent. A crosslinked density gradient film was placed in a vacuum oven, and nitrogen gas was introduced at a flow rate of 0.1 L / min. Under nitrogen protection, the temperature was raised to 80 °C and held for 1 h to evaporate the residual solvent. The temperature was then raised to 120 °C and held for 2 h to promote the complete crosslinking reaction. The temperature was then raised to 150 °C and held for 1 h to eliminate internal stress and stabilize the liquid crystal phase structure. The film was then cooled to room temperature to obtain a gradient crosslinked thermotropic liquid crystal polyester film.

[0011] Furthermore, in step four, the supercritical treatment step includes: The gradient crosslinked thermotropic liquid crystal polyester film was laid flat in the extraction chamber, and carbon dioxide was introduced at a flow rate of 0.1 L / min to replace the air. The pressure was increased to 7.4 MPa, and the temperature was increased to 31 °C to reach the supercritical state. The extraction was carried out at constant temperature and pressure for 30 min to remove residual solvent, unreacted small molecule monomers and auxiliary impurities. After the extraction was completed, the pressure was released to atmospheric pressure to obtain the purified gradient crosslinked thermotropic liquid crystal polyester film.

[0012] Compared with the prior art, the beneficial effects of the present invention are: This invention prepares gradient crosslinked thermotropic liquid crystal polyester films based on ultraviolet gradient light-induced thiol-ene click reaction. Compared with the prior art, it not only does not contain any inorganic fillers, thus reducing interface loss and avoiding a significant increase in high-frequency loss factor, but also enables continuous and gradual spatial variation of crosslinking density through light field gradient control, facilitating precise control of dielectric constant. Attached Figure Description

[0013] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0015] I. Preparation of Thiol-Modified Thermotropic Liquid Crystal Polyester Prepolymer Nitrogen gas was introduced at a flow rate of 0.1 L / min at room temperature, and 45.0 mL of pentafluorophenol and 15.0 mL of p-chlorophenol were stirred at 350 r / min for 15 min under nitrogen protection to obtain a transparent compound solvent. 10.0g of thermotropic liquid crystal polyester was added to the compound solvent, heated to 130℃, and stirred at 450r / min for 5h under nitrogen protection to obtain a transparent viscous liquid. 0.32g of 3-mercaptopropionic acid was added to a viscous liquid, and the temperature was maintained at 130℃. The mixture was stirred at 450r / min for 5h under nitrogen protection. Thiol groups were grafted onto the end and side groups of the thermotropic liquid crystal polyester molecular chain. After the reaction was completed, the mixture was cooled to room temperature to obtain a transparent crude product solution of thiol-modified thermotropic liquid crystal polyester prepolymer. The crude product solution of thiol-modified thermotropic liquid crystal polyester prepolymer was slowly added to 500.0 mL of anhydrous ethanol and stirred at 350 r / min for 15 min. The thiol-modified thermotropic liquid crystal polyester prepolymer precipitate was precipitated. The precipitate was collected by vacuum filtration. The precipitate of the thiol-modified thermotropic liquid crystal polyester prepolymer was washed three times with anhydrous ethanol to remove residual solvent and unreacted modifier. The thiol-modified thermotropic liquid crystal polyester prepolymer precipitate was placed in a vacuum drying oven, heated to 80°C, and vacuum dried at a constant temperature for 12 hours to obtain the thiol-modified thermotropic liquid crystal polyester prepolymer.

[0016] II. Preparation of Photosensitive Resin Solution At room temperature, 32.0 mL of cyclopentanone and 16.0 mL of γ-butyrolactone were stirred at 300 r / min for 10 min to obtain a transparent compound solvent. 8.0g of thiol-modified thermotropic liquid crystal polyester prepolymer was added to a compound solvent, protected from light, and stirred at 400r / min for 3h to obtain a thiol-modified thermotropic liquid crystal polyester solution. 1.05 g of pentaerythritol triallyl ether was added to a thiol-modified thermotropic liquid crystal polyester solution, and stirred at 400 r / min for 1 h in the dark to obtain a thiol-modified thermotropic liquid crystal polyester-crosslinking agent mixed solution. 0.135g of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide and 0.0045g of hydroquinone were sequentially added to a thiol-modified thermotropic liquid crystal polyester-crosslinking agent mixed solution. The solution was kept in the dark, heated to 30°C, and stirred at a constant temperature of 350r / min for 3h to obtain a photosensitive resin mixed solution. The photosensitive resin mixture was degassed by ultrasonication in the dark for 30 minutes, and then allowed to stand for 15 minutes to remove air bubbles. The photosensitive resin mixture solution was filtered under pressure using a polytetrafluoroethylene needle filter to remove trace impurities, thus obtaining the photosensitive resin solution.

[0017] III. Preparation of Flexible Dielectric Thin Films Nitrogen gas was introduced at a flow rate of 0.1 L / min at room temperature. The pretreated glass substrate was placed on the spin coating platform. Under nitrogen protection, the spin coater first spin-coated the photosensitive resin solution at a speed of 300 r / min for 10 s, and then spin-coated the photosensitive resin solution at a speed of 2000 r / min for 45 s to obtain a uniform wet film with a thickness of 25 μm. A glass substrate coated with a uniform wet film is placed on a UV curing platform. A mask with a linear gradient transmittance of 10%-90% is placed 120μm above the glass substrate coated with the uniform wet film. Under nitrogen protection, a 365nm UV light source is turned on, the light intensity gradient is adjusted to 15-85mW / cm², the temperature is raised to 25℃, and the exposure is kept at a constant temperature for 90s to initiate a thiol-olefin click reaction, thus obtaining a film with a continuous gradient of crosslinking density. The cross-linked density continuous gradient film was placed in an oven, heated to 70°C, and pre-dried at a constant temperature for 15 minutes to evaporate the free solvent. A crosslinked density gradient film was placed in a vacuum oven and nitrogen gas was introduced at a flow rate of 0.1 L / min. Under nitrogen protection, the temperature was raised to 80 °C and held for 1 h to evaporate the residual solvent. The temperature was then raised to 120 °C and held for 2 h to promote the complete crosslinking reaction. The temperature was then raised to 150 °C and held for 1 h to eliminate internal stress and stabilize the liquid crystal phase structure. The film was then cooled to room temperature to obtain a gradient crosslinked thermotropic liquid crystal polyester film. The gradient crosslinked thermotropic liquid crystal polyester film was peeled off from the glass substrate; The gradient crosslinked thermotropic liquid crystal polyester film was laid flat in the extraction chamber, and carbon dioxide was introduced at a flow rate of 0.1 L / min to replace the air. The pressure was increased to 7.4 MPa, and the temperature was increased to 31 °C to reach the supercritical state. The extraction was carried out at constant temperature and pressure for 30 min to remove residual solvent, unreacted small molecule monomers and auxiliary impurities. After the extraction was completed, the pressure was released to atmospheric pressure to obtain the purified gradient crosslinked thermotropic liquid crystal polyester film. The purified gradient crosslinked thermotropic liquid crystal polyester film was placed in a vacuum drying oven, heated to 80°C, and vacuum dried for 4 hours to obtain a flexible dielectric film for the millimeter-wave terahertz band.

[0018] Comparative Example 1 The difference between this comparative example and Example 1 is that: A glass substrate coated with a uniform wet film was placed on an ultraviolet curing platform. Under nitrogen protection, a 365nm ultraviolet light source was turned on, the light intensity gradient was adjusted to 40mW / cm², the temperature was raised to 25℃, and the exposure was kept at a constant temperature for 90s to initiate a thiol-olefin click reaction, thus obtaining a film with a continuous gradient of crosslinking density.

[0019] Comparative Example 2 I. Preparation of Thermotropic Liquid Crystal Polyester Prepolymer Nitrogen gas was introduced at a flow rate of 0.1 L / min at room temperature, and 45.0 mL of pentafluorophenol and 15.0 mL of p-chlorophenol were stirred at 350 r / min for 15 min under nitrogen protection to obtain a transparent compound solvent. 10.0g of thermotropic liquid crystal polyester was added to the compound solvent, heated to 130℃, and stirred at 450r / min for 5h under nitrogen protection to obtain a transparent viscous liquid. The viscous liquid was slowly added to 500.0 mL of anhydrous ethanol and stirred at 350 r / min for 15 min. The thermotropic liquid crystal polyester prepolymer precipitate was precipitated. The precipitate was collected by vacuum filtration. The thermotropic liquid crystal polyester prepolymer precipitate was washed three times with anhydrous ethanol to remove residual solvent and unreacted modifier; The thermotropic liquid crystal polyester prepolymer precipitate was placed in a vacuum drying oven, heated to 80°C, and vacuum dried at a constant temperature for 12 hours to obtain the thermotropic liquid crystal polyester prepolymer.

[0020] II. Preparation of Thermotropic Liquid Crystal Polyester Solution At room temperature, 32.0 mL of cyclopentanone and 16.0 mL of γ-butyrolactone were stirred at 300 r / min for 10 min to obtain a transparent compound solvent. 8.0 g of thermotropic liquid crystal polyester prepolymer was added to a compound solvent, protected from light, and stirred at 400 r / min for 3 h to obtain a thermotropic liquid crystal polyester solution. Thermotropic liquid crystal polyester solution was ultrasonically degassed in the dark for 30 minutes, then allowed to stand for 15 minutes to remove air bubbles. Thermotropic liquid crystal polyester solution is obtained by pressure filtration using a polytetrafluoroethylene needle filter to remove trace impurities.

[0021] III. Preparation of Flexible Dielectric Thin Films Nitrogen gas was introduced at a flow rate of 0.1 L / min at room temperature. The pretreated glass substrate was placed on the spin coating platform. Under nitrogen protection, the spin coater first spin-coated the photosensitive resin solution at a speed of 300 r / min for 10 s, and then spin-coated the photosensitive resin solution at a speed of 2000 r / min for 45 s to obtain a uniform wet film with a thickness of 25 μm. A glass substrate coated with a uniform wet film is placed in an oven and heated to 70°C. It is then pre-dried at this constant temperature for 15 minutes to evaporate the free solvent. A glass substrate coated with a uniform wet film was placed in a vacuum oven, and nitrogen gas was introduced at a flow rate of 0.1 L / min. Under nitrogen protection, the temperature was raised to 80°C and held for 1 hour to evaporate the residual solvent. The temperature was raised to 120°C and held for 2 hours to promote the complete crosslinking reaction. The temperature was raised to 150°C and held for 1 hour to eliminate internal stress and stabilize the liquid crystal phase structure. The temperature was then cooled to room temperature to obtain a thermotropic liquid crystal polyester film. The thermotropic liquid crystal polyester film is peeled off from the glass substrate; The thermotropic liquid crystal polyester film was laid flat in the extraction chamber, and carbon dioxide was introduced at a flow rate of 0.1 L / min to replace the air. The pressure was increased to 7.4 MPa, and the temperature was increased to 31 °C to reach the supercritical state. The extraction was carried out at constant temperature and pressure for 30 min to remove residual solvent, unreacted small molecule monomers and auxiliary impurities. After the extraction was completed, the pressure was released to atmospheric pressure to obtain the purified thermotropic liquid crystal polyester film. The purified thermotropic liquid crystal polyester film was placed in a vacuum drying oven, heated to 80°C, and vacuum dried for 4 hours to obtain a flexible dielectric film for the millimeter-wave terahertz band.

[0022] The flexible dielectric thin film samples of Example 1, Comparative Example 1, and Comparative Example 2 were tested, and the results are as follows:

[0023] As shown in the table above, this application combines the characteristics of low loss, gradient dielectric, and high stability.

[0024] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing flexible dielectric thin films for millimeter-wave terahertz frequency bands, characterized in that, Includes the following steps:

1. Nitrogen gas is introduced at room temperature. The pretreated glass substrate is placed on the spin coating platform. Under nitrogen protection, the photosensitive resin solution is spin-coated to obtain a uniform wet film.

2. A glass substrate coated with a uniform wet film is placed on an ultraviolet curing platform. A linear gradient transmittance mask is placed on top of the glass substrate coated with a uniform wet film. Under nitrogen protection, a crosslinking density gradient film is prepared by triggering a thiol-ene click reaction based on ultraviolet light. III. Gradient crosslinked thermotropic liquid crystal polyester film was prepared by curing and annealing of the film with a continuous gradient crosslinking density. IV. A flexible dielectric film for millimeter-wave terahertz frequency band is prepared by peeling a gradient cross-linked thermotropic liquid crystal polyester film from a glass substrate and subjecting it to supercritical treatment.

2. The method for preparing a flexible dielectric thin film for the millimeter-wave terahertz band according to claim 1, characterized in that: In step one, the preparation steps of the photosensitive resin solution include: A transparent compound solvent was prepared by stirring cyclopentanone and γ-butyrolactone in a volume ratio of 2:1 at 300 r / min for 10 min at room temperature. A thiol-modified thermotropic liquid crystal polyester prepolymer with a solid-liquid mass-to-volume ratio of 1:6 was added to a compound solvent, and stirred at 400 r / min for 3 h in the dark to obtain a thiol-modified thermotropic liquid crystal polyester solution. A thiol-modified thermotropic liquid crystal polyester solution was prepared by adding pentaerythritol triallyl ether with a thiol molar ratio of 1:1 to a thiol-modified thermotropic liquid crystal polyester solution, and stirring at 400 r / min for 1 h in the dark. A mixture of 1.2 wt% phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and 0.04 wt% hydroquinone was sequentially added to a thiol-modified thermotropic liquid crystal polyester-crosslinking agent solution. The mixture was kept in the dark, heated to 30°C, and stirred at a constant speed of 350 r / min for 3 h to obtain a photosensitive resin mixture solution. The photosensitive resin mixture was degassed by ultrasonication in the dark for 30 minutes, and then allowed to stand for 15 minutes to remove air bubbles. The photosensitive resin mixture solution was filtered under pressure using a polytetrafluoroethylene needle filter to remove trace impurities, thus obtaining the photosensitive resin solution.

3. The method for preparing a flexible dielectric thin film for the millimeter-wave terahertz band according to claim 2, characterized in that: Step one, the preparation steps of the thiol-modified thermotropic liquid crystal polyester prepolymer include: Nitrogen gas was introduced at room temperature, and pentafluorophenol and p-chlorophenol in a volume ratio of 3:1 were stirred at 350 r / min for 15 min under nitrogen protection to obtain a transparent compound solvent. A thermotropic liquid crystal polyester with a solid-liquid mass-to-volume ratio of 1:6 was added to a compound solvent, heated to 130°C, and stirred at 450 r / min for 5 h under nitrogen protection to obtain a transparent viscous liquid. 3-Mercaptopropionic acid with a molar ratio of 1:35 to repeating units of thermotropic liquid crystal polyester was added to a viscous liquid. The temperature was maintained at 130℃, and the mixture was stirred at 450 r / min for 5 h under nitrogen protection. Thiol groups were grafted onto the end and side groups of the thermotropic liquid crystal polyester molecular chain. After the reaction was completed, the mixture was cooled to room temperature to obtain a transparent crude product solution of thiol-modified thermotropic liquid crystal polyester prepolymer. The crude product solution of thiol-modified thermotropic liquid crystal polyester prepolymer was slowly added to anhydrous ethanol and stirred at 350 r / min for 15 min to precipitate thiol-modified thermotropic liquid crystal polyester prepolymer. The precipitate was collected by vacuum filtration. The precipitate of the thiol-modified thermotropic liquid crystal polyester prepolymer was washed three times with anhydrous ethanol to remove residual solvent and unreacted modifier. The thiol-modified thermotropic liquid crystal polyester prepolymer precipitate was placed in a vacuum drying oven, heated to 80°C, and vacuum dried at a constant temperature for 12 hours to obtain the thiol-modified thermotropic liquid crystal polyester prepolymer.

4. The method for preparing a flexible dielectric thin film for the millimeter-wave terahertz band according to claim 3, characterized in that: Step three, the curing and annealing process includes: The cross-linked density continuous gradient film was placed in an oven, heated to 70°C, and pre-dried at a constant temperature for 15 minutes to evaporate the free solvent. A crosslinked density gradient film was placed in a vacuum oven, and nitrogen gas was introduced at a flow rate of 0.1 L / min. Under nitrogen protection, the temperature was raised to 80 °C and held for 1 h to evaporate the residual solvent. The temperature was then raised to 120 °C and held for 2 h to promote the complete crosslinking reaction. The temperature was then raised to 150 °C and held for 1 h to eliminate internal stress and stabilize the liquid crystal phase structure. The film was then cooled to room temperature to obtain a gradient crosslinked thermotropic liquid crystal polyester film.

5. The method for preparing a flexible dielectric thin film for the millimeter-wave terahertz band according to claim 4, characterized in that: Step four, the supercritical treatment step includes: The gradient crosslinked thermotropic liquid crystal polyester film was laid flat in the extraction chamber, and carbon dioxide was introduced at a flow rate of 0.1 L / min to replace the air. The pressure was increased to 7.4 MPa, and the temperature was increased to 31 °C to reach the supercritical state. The extraction was carried out at constant temperature and pressure for 30 min to remove residual solvent, unreacted small molecule monomers and auxiliary impurities. After the extraction was completed, the pressure was released to atmospheric pressure to obtain the purified gradient crosslinked thermotropic liquid crystal polyester film.

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