CN115873375A - Low dielectric gel and preparation method thereof - Google Patents
Low dielectric gel and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a preparation method and application of a low-dielectric organic/inorganic aerogel composite material formed by impregnating low-dielectric gel into a high-molecular solution. The preparation method comprises the following steps: mixing, (2) hydrolysis, (3) condensation, (4) aging, (5) drying, (6) impregnation of a polymer solution, (7) curing and phase separation, and (8) drying and crosslinking. The invention prepares the organic/inorganic aerogel composite material with high strength and low dielectric constant. The low dielectric gel has a porous structure, a porosity higher than 70%, and a density of about 0.12-0.42 g/cm 3 Dielectric properties decrease with increasing porosity, wherein the dielectric constant is 1.28 to 1.93 and the dielectric loss is 0.0026 to 0.014, can be used in dielectric layers, semi-dielectric layers in high frequency circuitsInsulating layers in conductor devices, or microwave circuits in communication integrated circuits.
Description
Technical Field
The invention relates to a preparation technology of a low dielectric organic/inorganic aerogel composite material formed by directly preparing inorganic aerogel and soaking the inorganic aerogel into a high molecular dilute solution, wherein the low dielectric organic/inorganic aerogel composite material is of a porous structure.
Background
The dielectric properties of the materials known at present gradually decrease with the increase of the internal porosity of the materials, so that the aerogel materials and the related composite materials thereof will become low dielectric related products required by the 5G industry in the future. Aerogel is known as a porous material having a three-dimensional network structure, with a porosity higher than 80% (and even higher than 95%), making the aerogel material have a low density (about 0.005 to 0.2 g/cm) 3 ) High specific surface area (500-2000 m) 2 (k =15 to 40 mW/mk), low thermal conductivity (k =0.1 to 2.5), low dielectric loss (Df)<Below 0.001). The aerogel is a material containing a large amount of porosity and extremely low density, so that the aerogel can be applied to high heat insulation, cold insulation, sound insulation, low dielectric and other applications. The low dielectric constant (Dk) is urgently needed in the future 5G high-frequency transmission application<2.5 And low signal loss (Df)<0.005 ) dielectric material. Since porosity causes lower electron hole transport properties, the higher the porosity in the structure of an inorganic material or an organic material, the lower the dielectric properties. Therefore, in the future, the porous material is required to be used as the main substrate for 5G high-frequency application. Japanese laid-open patent publication No. 8-228105 discloses a method of manufacturing a semiconductor device. In the method, a wet glue film is formed on a substrate, and a solvent impregnated in the wet glue film is evaporated by supercritical and subcritical drying procedures to form an aerogel film. The prepared dry aerogel film still maintains the network structure of the wet glue film and is a porous material with high porosity and low dielectric constant. Accordingly, the aerogel can be used as a new material for dielectric layers and insulating inner layers. However, the use of supercritical or subcritical drying process may lead to the disadvantages of complicated process and expensive equipment investment in the fabrication of transistor structures. "supercritical drying" meansThe water and the organic solvent are in a supercritical state at high temperature and high pressure, so that the organic solvent and the water have gas-liquid mixing properties at the same time, and the solvent is directly vaporized and dried in the supercritical state. Thus removing the remaining solvent from the network under supercritical conditions without causing shrinkage of the wet glue. However, in the fabrication of transistor structures, the low dielectric films are not prepared from solution until they are coated. In addition, during the condensation of the aerogel solution, the silica gel molecules are immediately aggregated and coagulated, so that the viscosity of the aerogel solution increases with time. When spin coating is performed at a fixed rate, the thickness of the coating film on the substrate also increases. Similarly, the thickness of the transistor thin film structure coating will vary with the increase of the process time, and thus a high quality transistor thin film structure cannot be prepared.
The traditional aerogel preparing method is sol-gel synthesis, which is mainly to mix precursors such as silicon alkoxides (alkoxysilanes), methyl orthosilicate or water glass and the like with an organic solvent, and then add an acid catalyst to carry out hydrolysis reaction (hydrosis). After the hydrolysis reaction is carried out for a certain period of time, an alkali catalyst is added to carry out condensation reaction (condensation), sol is gradually formed in the condensation reaction process, and molecules in the sol continue to react and bond to gradually form semi-solid polymer gel. And curing (aging) for a period of time to form a three-dimensional network structure with stable structure. And finally, carrying out solvent replacement by using solvents such as n-butanol, n-hexanol, n-hexane or cyclohexane, and the like, and then extracting and drying the solvent of the aerogel system by using a supercritical drying technology.
The preparation method of the hydrophobic aerogel is a sol-gel synthesis method, and mainly comprises the steps of mixing a silicon alkoxide precursor such as methyltrimethoxysilane (MTMS) or Methyltriethoxysilane (MTES) and the like with an organic solvent, and then adding an alkali catalyst for hydrolysis reaction. After the hydrolysis reaction is carried out for a certain time, condensation reaction is carried out, sol is gradually formed in the condensation reaction process, and molecules in the sol are continuously subjected to reaction bonding to gradually form semisolid polymer gel. After a period of aging (aging), the solvent is replaced by isopropanol, acetone, normal hexane or cyclohexane for two to three days, so that the hydrophobic gel forms a stable three-dimensional network structure. And finally, drying the solvent of the aerogel system by using a normal pressure drying technology to obtain the porous dry aerogel block.
Because the drying technology adopted by the aerogel preparation method is a supercritical drying technology or repeated solvent replacement for two to three days, the aerogel can be prevented from being cracked under the influence of the surface tension of moisture in the normal pressure drying process. However, since supercritical drying techniques are carried out under high pressure, they are suitable only for very small amounts of aerogel; multiple solvent replacements also take a considerable amount of time, which is detrimental to mass production and reduces the production cost of aerogels.
U.S. patent No. 8,945,677b2, "fabrication of electronic devices using low K dielectric materials", relates to materials and methods for fabricating electronic devices and semiconductor devices using low dielectric materials, including polyimide aerogels. This patent prior art further provides methods for manipulating dielectric material properties and affecting the overall dielectric properties of the system. Specifically, a polyurethane pre-sol, a catalyst and a polar solvent are mixed into a sol mixture layer, then the sol components are crosslinked to form a wet gel material, and the solvent is removed by using a supercritical fluid to form a polyimide aerogel film. This technique was used to combine a polyimide aerogel film on a non-porous, low-k template substrate surface. The prior art, which uses low-K dielectric materials to manufacture electronic devices and utilizes supercritical fluid technology to remove solvent in multiple steps by means of pressure cycling, is time-consuming and costly, requires too long processing time, and is not cost-effective.
The invention discloses a low-K dielectric layer structure, a semiconductor device structure and a forming method thereof in Chinese patent publication No. CN102044525A, and mainly uses silicon dioxide aerogel to form the low-K dielectric layer structure. This patent application also provides a semiconductor device structure and a method for forming the same, wherein the method for forming the semiconductor device structure comprises: providing a substrate, wherein a first dielectric layer and an etching barrier layer are formed on the substrate, openings are formed in the first dielectric layer and the etching barrier layer, and metal is filled in the openings to be used as plugs; forming a sacrificial oxide layer on the etching barrier layer and the plug; forming an opening in the sacrificial oxide layer, and filling the opening with a metal to form an interconnect structure, wherein the interconnect structure is electrically connected to the plug; selectively removing the sacrificial oxide layer to form gaps among the interconnection structures; and forming silicon dioxide aerogel in the gaps between the interconnection structures to serve as the low-K dielectric layer. This patent prior art uses a low-K dielectric layer structure and utilizes Tetraethoxysilane (TEOS) or tetramethyl silicate (TMOS) as a material structure. In addition, the drying process utilizes the normal temperature or supercritical fluid technology to prepare the low dielectric film in multiple steps, the overall technology is time-consuming and high in cost, and the time required by the process is too long, so that the low dielectric film is not in accordance with the cost benefit.
The aerogel insulation panel and the preparation method thereof of the Chinese patent publication No. CN105189104A mainly use polyimide aerogel to prepare the insulation panel, and the insulation panel can be applied to aerospace application laminated panels. The panel comprises a polyimide aerogel surface layer and a reflective protection layer on the surface layer. The process of the polyimide aerogel in the prior art includes: (a) Polymerizing a mixture of dianhydride and diamine monomers in a bipolar basic solvent (DMAc or NMP) to form a polyamic acid solution; (b) casting a polyamide acid solution gel into the fiber batt; (c) Using acetic anhydride and pyridine to gel polyamide acid solution by chemical imidization reaction; (d) Using supercritical or sub-supercritical CO 2 The drying technique removes the solvent from the gel to form a fiber/polyimide aerogel composite.
The "aerogel/polymer composite" of U.S. patent publication No. us9,777,126b2, comprises an aerogel and a thermoplastic polymer material, and the weight ratio of aerogel to thermoplastic polymer is less than 20:100. the composite material has excellent insulating property, better soft property and lower brittleness in low-temperature environment.
The Chinese patent publication No. CN108203516A, "method for preparing cross-linked polyimide aerogel", mainly adopts sol-gel method, it includes: (a) The mixture of dianhydride and diamine monomers is polymerized in a bipolar basic solvent (DMAc or NMP) to form a polyamic acid solutionLiquid; (b) casting a polyamic acid solution into the fiber batt; (c) Using acetic anhydride and pyridine gel polyamic acid solution by chemical imidization reaction; (d) Using supercritical or sub-supercritical CO 2 The drying technique removes the solvent from the gel to form a fiber/polyimide aerogel composite.
In the manufacture of nanoporous dielectrics, the wet gel film is preferably subjected to conventional aging processes. At the gel point, the hydrolysis and condensation reactions do not stop, but continue to change the gel structure (or age) until the reaction is deliberately terminated. During aging, portions of the solid structure are preferentially dissolved and redeposited, which can produce favorable results, such as: higher strength, better pore uniformity, and better resistance to shrinkage of the micropores during the drying period.
Disclosure of Invention
According to the prior art of producing block aerogel of the present applicant, the linear shrinkage rate of the block aerogel is reduced to below 7% by using the rapid condensation technique, and the preparation of the crystal structure can be rapidly performed without soaking the wet aerogel in a solvent for solvent replacement. This prior art technique utilizes a fast gel technique to rapidly form a gel structure, which is rinsed in deionized water to remove ions from the structure to reduce ion accumulation during subsequent applications. In addition, the removal of wet gel films in a liquid soak and solvent removal using supercritical fluid technology during the overall process surprisingly results in porous low dielectric films that can be aged in a matter of minutes.
Therefore, in order to improve the disadvantages associated with the application of low dielectric polymer aerogel and the like in the optical or electronic devices, such as: the invention provides a method for preparing low dielectric inorganic aerogel or low dielectric organic/inorganic aerogel composite board or low dielectric inorganic aerogel film with thickness ranging from tens of millimeters to hundreds of millimeters by combining sol-gel synthesis technology, which comprises the following steps: (1) a mixing step: mixing a siloxane compound or a hydrophobically modified siloxane compound with an organic mixed solvent to form a mixed solution; (2) a hydrolysis step: adding an acid catalyst into the mixed solution to perform hydrolysis reaction; (3) condensation step: adding an alkali catalyst into the hydrolyzed mixed solution to perform condensation reaction, and adding a trace amount of surfactant in the condensation reaction process to reduce the interfacial tension of the aerogel and avoid the crack of the aerogel structure; (4) an aging step: aging the formed aerogel board at a specific temperature to promote the aerogel structure to be further condensed and to be stable in structure; and (5) a drying step: after the aerogel plate structure is gelled and stabilized, high-temperature drying is carried out under normal pressure and high temperature environment to obtain the low dielectric inorganic aerogel plate with uniform structure, high porosity and high specific surface area, in particular to a silicon-based aerogel plate. In addition, the preparation method for preparing the low dielectric organic/inorganic aerogel composite board further comprises the following steps: (6) polymer solution impregnation step: soaking the prepared low dielectric silicon-based aerogel plate in a polymer dilute solution to enable polymer chains to uniformly penetrate into the silicon-based aerogel plate to form a wet-type polymer/silicon-based composite material; (7) phase separation and drying steps: evaporating the solvent in the polymer dilute solution at a specific temperature, and performing liquid-solid phase separation on the polymer in the wet polymer/silicon-based composite material at the stage to coat the polymer chains on the low-dielectric silicon-based aerogel net-shaped framework structure and gradually dry the polymer chains; and (8) a crosslinking and curing step: and (2) subjecting the dried polymer/silicon-based composite material to crosslinking reaction of polymer chains coated on the low-dielectric silicon-based aerogel reticular framework structure in a specific high-temperature environment, and carrying out chemical reaction combination between the polymer chains in the crosslinking reaction and between the polymer chains and the silicon-based aerogel molecules, so that the porous, light-weight and low-dielectric organic/inorganic aerogel composite material is obtained after the high-temperature crosslinking. The method can quickly produce the low-dielectric inorganic aerogel or organic/inorganic aerogel composite board, is simple and easy to integrally prepare, and can prepare the aerogel board with a film of dozens of millimeters to hundreds of millimeters or a size of several millimeters to centimeters. The overall preparation speed can be rapidly shortened to be completed within 12 to 36 hours, thereby improving the production efficiency of preparing the low-dielectric inorganic aerogel or organic/inorganic aerogel composite board.
Further, the siloxane compound (alkoxysilane) is one or more selected from the group consisting of: tetramethoxysilane (TMOS) and Tetraethoxysilane (TEOS), the hydrophobically modified siloxane compound being one or more selected from the group consisting of: methyltrimethoxysilane (MTMS) and Methyltriethoxysilane (MTES). The hydrophobic modified siloxane is added mainly to reduce the cracking phenomenon of the aerogel system in the drying process; the siloxane is added mainly to regulate the internal fine structure of the aerogel system and increase the pore content in the structure.
Further, the organic mixed solvent is one or more selected from the group consisting of: water, pure water, deionized water, alcohols, acids, ketones, alkanes, and aromatics.
Further, in the hydrolysis step, the higher the content ratio of the acid catalyst in the mixed solution, the faster the hydrolysis rate. But relatively, the higher the content ratio of the acid catalyst, the larger the ion content in the whole aerogel structure, and the higher the dielectric loss of the aerogel, so that the aerogel can be prepared by deionized water in the preparation process to reduce the dielectric property in the aerogel structure.
Further, the purpose of adding a trace amount of surfactant during the condensation reaction is to reduce the interfacial tension of the aerogel structure after condensation and reduce cracks of the aerogel caused by the interfacial tension during drying.
Further, the drying step can evaporate the aqueous solvent in the system of the aged and stabilized inorganic aerogel under the environment of normal pressure and high temperature. In addition, because the invention adds a trace amount of surfactant, the cracking behavior of the inorganic aerogel can be obviously inhibited in the drying process, and the low dielectric inorganic aerogel plate with low density and high porosity, in particular to the low dielectric silicon-based aerogel plate, can be prepared.
Furthermore, the invention can also be further prepared low dielectric organic/inorganic aerogel composite board, especially by using the step of impregnating the prepared low dielectric silica-based aerogel board with the polymer solution, so that the polymer chains uniformly permeate into the holes inside the silica-based aerogel board along with the solvent to form the wet polymer impregnated silica-based aerogel composite material. In addition, the lower the polymer concentration is, the better the efficiency of the polymer to penetrate into the inner holes of the silica-based aerogel is. On the contrary, the higher the polymer concentration is, the higher the content of the polymer coating in the silicon-based aerogel is, and the better the strength of the prepared low dielectric organic/silicon-based aerogel composite board is.
Furthermore, in the phase separation and drying steps, the polymer dilute solution inside the wet polymer impregnated silica-based aerogel composite material is firstly subjected to phase separation, so that the polymer molecular chains are coated on the aerogel skeleton structure inside the high-porosity silica-based aerogel, and meanwhile, the organic solvent inside the high-porosity silica-based aerogel is vaporized, so that the wet polymer impregnated silica-based aerogel composite material is gradually dried.
Further, in the process, a low dielectric gel structure is prepared, and then the prepared low dielectric gel is further contacted with the polymer dilute solution in the manners of impregnation, spraying, curtain coating or soaking, so that the polymer chains uniformly permeate into the inner holes of the low dielectric gel plate along with the solvent and are mixed with the inorganic aerogel structure to form the wet polymer impregnated silicon-based aerogel composite material. And then, the organic/inorganic aerogel composite material with high strength, high porosity and low dielectric constant, in particular to the low dielectric polymer/silicon-based aerogel composite material, can be obtained by normal-pressure high-temperature drying and high-temperature crosslinking. Overall, the process is simple, the manufacturing cost is low, the process speed is fast, and complicated preparation methods such as supercritical drying and the like are not needed. The batch processing speed of the organic/inorganic aerogel composite board can be rapidly reduced to be within 24 to 36 hours, or the organic/inorganic aerogel film is prepared in a continuous production mode, so that the production efficiency is improved.
The invention has the following effects:
1. the preparation method of the invention uses the traditional sol-gel reaction process to simply prepare the inorganic aerogel material with high porosity and low dielectric constant. In addition, factors such as the proportion of siloxane compounds or hydrophobic modified siloxane compounds, the content of organic solvents containing water, the content and proportion of acid catalysts and alkali catalysts and the like in different proportions are used in the preparation process, so that the porosity and the pore size of the aerogel structure and the compact property of the aerogel structure can be easily regulated and controlled, the dielectric property of the prepared aerogel is further regulated and controlled, and the practical property of the aerogel is improved.
2. The preparation method can be used for preparing pure inorganic aerogel materials, and can also be used for preparing organic/inorganic aerogel composite materials with high strength, high porosity and low dielectric constant by further utilizing various high polymer dilute solutions for impregnation, in particular to low dielectric polymer/silicon-based aerogel composite materials.
3. The step of impregnating the silicon-based aerogel plate with the polymer dilute solution in the preparation method of the invention is to impregnate the silicon-based aerogel plate with the polymer dilute solution, so that the related polymer chains uniformly permeate into the holes in the silicon-based aerogel plate along with the solvent to form the wet-type polymer impregnated silicon-based aerogel composite material. Wherein, the lower the polymer concentration is, the better the efficiency of the polymer permeating into the inner holes of the silicon-based aerogel is; on the contrary, the higher the polymer concentration is, the higher the content of the polymer coating in the silica-based aerogel is, and the better the strength of the prepared low dielectric organic/silica-based aerogel composite board is. Therefore, the dielectric coefficient and the strength of the prepared low dielectric organic/silicon-based aerogel composite board can be regulated and controlled by the concentration of the high polymer dilute solution.
4. The polymer thin solution in the preparation method of the present invention may be composed of one of the following polymers or a mixture thereof: thermosetting polymer (thermo set polymer), liquid crystal polymer (liquid crystal polymer), and general thermoplastic polymer (thermal plastic polymer). Specifically, for example: epoxy resin (epoxy), polyimide resin (polyimide), phenolic resin (phenoolic resin), melamine-formaldehyde resin (melamine resin), polyether ketone liquid crystal Polymer (PEK), polyether ether ketone liquid crystal Polymer (PEEK), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polyamide (PA), polyamide Ester (PEA), polyester (PET), or Polytetrafluoroethylene (PTFE). The method can mix various polymer solutions to prepare various low-k polymer/silicon-based aerogel composite materials with different properties, so as to adjust and control the strength, the durable temperature, the bonding property with other materials, the dielectric constant (about 1.23 to 1.89) and the dielectric loss (0.0052 to 0.023) of the low-k polymer/silicon-based aerogel composite material.
5. The acid catalyst and the alkali catalyst added in the preparation method can accelerate the hydrolysis and condensation reaction of siloxane and hydrophobic modified siloxane. Wherein the acid catalyst is added in the reaction system in a molar ratio of the total content of the siloxane and the hydrophobic modified siloxane mixture to the content of the acid catalyst of 1:0.05 to 1:0.00001; and the molar ratio of the acid catalyst to the base catalyst in the condensation reaction is 1:0.8 to 1:1.05. when the contents of the acid catalyst and the alkali catalyst in the mixed solution are higher, the reaction rate is higher; in contrast, the higher the acid and base catalyst content, the higher the ion content in the overall aerogel structure, and the greater the dielectric loss of the aerogel. Thereby regulating the process rate and product properties.
6. The low dielectric polymer/silicon-based aerogel composite material has the advantages of simple overall process, low manufacturing cost, high processing speed and no need of using supercritical drying and other complex preparation methods. The batch processing speed of the organic/inorganic aerogel composite board can be rapidly reduced to 24 to 36 hours, or the organic/inorganic aerogel composite board can be prepared in a continuous production mode, so that the production efficiency is improved.
Drawings
FIG. 1 is a flow chart illustrating steps of a low dielectric gel process according to an embodiment of the invention.
FIG. 2 is a photograph showing the appearance of the low dielectric silicon-based aerogel panel prepared according to the present invention.
FIG. 3 is a scanning electron microscope photograph of a cross-section of a low dielectric silicon-based aerogel panel prepared according to the present invention.
FIG. 4 is a flow chart illustrating the steps of a process for manufacturing a low dielectric organo/silicon based aerogel composite panel according to an embodiment of the present invention.
FIG. 5 is a photograph showing the appearance of the low dielectric polyimide/silica-based aerogel composite panel prepared according to the present invention.
FIG. 6 is a scanning electron microscope photograph of a low dielectric polyimide/silica-based aerogel composite panel prepared according to the present invention.
FIG. 7 is a photograph of the appearance of the low dielectric epoxy plastic ester/silicon-based aerogel composite panel prepared according to the present invention.
FIG. 8 is a scanning electron microscope photograph of the low dielectric epoxy plastic ester/silicon-based aerogel composite panel prepared according to the present invention.
Detailed Description
Referring to fig. 1, a method for preparing a low dielectric silicon-based aerogel plate according to a first embodiment of the present invention is disclosed, which comprises the following steps: a mixing step (S1), a hydrolysis step (S2), a condensation step (S3), an aging step (S4), and a drying step (S5), wherein:
the mixing step (S1): the silicone compound or hydrophobically modified silicone compound is mixed with an organic solvent to form a mixed solution. Wherein the siloxane compound (alkoxysilane) is one or more selected from the group consisting of: tetramethoxysilane (TMOS) and Tetraethoxysilane (TEOS), and the hydrophobically modified siloxane compound is one or more selected from the group consisting of: hydrophobic methyltrimethoxysilane (MTMS) and Methyltriethoxysilane (MTES). The purpose of adding the hydrophobic modified siloxane is to reduce the cracking phenomenon of the aerogel system in the drying process; the purpose of adding the siloxane is to regulate and control the internal fine structure of the aerogel system and increase the content of holes in the structure. The total content mole percentage of siloxane and hydrophobic modified siloxane in the whole mixed solution is between 3.0mol% and 60mol%, and the content mole ratio of the organic solvent is between 97mol% and 40 mol%. Wherein the molar ratio of the siloxane compound to the hydrophobically modified siloxane compound is from 0:100 to 35:65; the preferred ratio is 22:78.
the organic mixed solvent in the mixing step (S1) may be water, treated water, deionized water, C1-C16 alcohols, C3-C16 ketones, C3-C16 alkanes, or C3-C16 aromatics, etc. Specifically, for example, water, treated water, deionized water, ethanol, acetone, cyclohexane, toluene, or the like may be used alone or in combination.
The hydrolysis step (S2): an acid catalyst is added to the mixed solution to perform a hydrolysis reaction (hydrolysis). Wherein the molar ratio of the total content of the siloxane and the hydrophobic modified siloxane mixture to the content of the acid catalyst is 1:0.05 to 1:0.00001, when the content ratio of the acid catalyst in the mixed solution of the siloxane and the hydrophobic modified siloxane is higher, the hydrolysis rate is faster; that is, the higher the acid catalyst content ratio, the greater the ionic content in the overall aerogel structure, and the greater the dielectric loss of the aerogel will be. In this example, the preferred conditions are that the molar ratio of the total siloxane and hydrophobically modified siloxane mixture content to the acid catalyst content is 1:0.0075.
the condensation step (S3): adding an alkali catalyst to the mixed solution, and performing condensation reaction (condensation reaction) at a specific temperature. In addition, a trace amount of surfactant was added during the condensation reaction. The weight ratio of the content of the added trace surfactant to the total content of the siloxane and the hydrophobically modified siloxane mixture is 1:100 to 1:3000; in this embodiment, the preferred conditions are that the weight ratio of the contents is 1:1000. the purpose of adding a trace amount of the surfactant is to reduce the interfacial tension of the condensed aerogel structure and reduce the cracking phenomenon of the aerogel in the drying process. Mixing an alkali catalyst with a mixed solution of water and ethanol, and adding the mixture to perform a condensation reaction, wherein the molar ratio of the water to the ethanol is, for example, 100:0.1 to 4:1, in the present embodiment, the preferable conditions are, for example, 50:1.
the increase in temperature during this condensation step contributes to a significant reduction in the condensation reaction time (i.e., gelation time of the aerogel), wherein the gelation time is about 220 minutes at room temperature of 25 ℃ and about 10 minutes at a condensation reaction temperature of 70 ℃ at a weight ratio of the alkali catalyst to the acid catalyst of 1.0. In addition, in the mixed solution of alkali catalyst, water and ethanol, the condensation reaction time is also shortened obviously by increasing the content of alkali catalyst. When the content volume ratio of the 1M base catalyst to the 1M acid catalyst is 0.8; when the content ratio of the 1M base catalyst to the 1M acid catalyst is 1.2 to 1.0, the gelation time decreases to about 15 minutes.
The aging step (S4): the formed low dielectric silicon-based aerogel board is aged at a specific temperature, so that the aerogel wet glue structure is stable, and the preferable aging temperature is 70 ℃.
The drying step (S5): after the low-dielectric silicon-based aerogel plate structure is aged and stabilized, the water-containing solvent in the aerogel system is evaporated under the environment of normal pressure and high temperature. Because the material contains the surfactant, the cracking behavior in gel drying is quickly reduced through the binding action force of the surfactant in the drying process, so that the low-dielectric-silicon-based aerogel plate with low density and high porosity is prepared. Referring to fig. 2 and 3, the appearance and inner fine structure of the low dielectric silicon-based aerogel board prepared by the present invention are utilized, fig. 3 shows that aerogel particles with uniform appearance structure are combined into a three-dimensional network structure in the prepared low dielectric silicon-based aerogel board, and the size of the aerogel particles ranges from several micrometers to several micrometers, and the particle size can be adjusted and controlled by the ratio of the acid catalyst to the alkali catalyst.
Referring to fig. 4, a method for preparing a low dielectric organic/silicon-based aerogel composite panel according to a second embodiment of the present invention is disclosed, which comprises the following steps: a mixing step (S1), a hydrolysis step (S2), a condensation step (S3), an aging step (S4), a drying step (S5), a polymer solution impregnation step (S6), a phase separation and drying step (S7), and a crosslinking and curing step (S8), wherein:
the mixing step (S1): mixing a siloxane compound or a hydrophobically modified siloxane compound, wherein (alkoxysilane) is one or more selected from the group consisting of: tetramethoxysilane (TMOS) and Tetraethoxysilane (TEOS), and the hydrophobically modified siloxane compound is one or more selected from the group consisting of: hydrophobic methyltrimethoxysilane (MTMS) and Methyltriethoxysilane (MTES). The hydrophobic modified siloxane is added to mainly reduce the cracking phenomenon of the aerogel system in the drying process; however, the addition of the siloxane primarily controls the internal microstructure of the aerogel system and increases the pore content in the structure. The total content molar ratio of the siloxane and the hydrophobic modified siloxane mixture in the whole mixed solution is between 3.0mol% and 60mol%, and the content molar ratio of the organic solvent is between 97mol% and 40 mol%. Wherein the molar ratio of the siloxane compound to the hydrophobic modified siloxane compound is from 0:100 to 35:65, preferably 5:95.
the organic mixed solvent used in the mixing step (S1) may be water, treated water, deionized water, C1-C16 alcohols, C3-C16 ketones, C3-C16 alkanes, or C3-C16 aromatics, etc. Specifically, for example, one or a mixture of different compositions of water, treated water, deionized water, ethanol, acetone, cyclohexane, toluene, and the like may be used.
The hydrolysis step (S2): an acid catalyst is added to the mixed solution to perform hydrolysis (hydrolysis). Wherein the molar ratio of the total content of the siloxane and the hydrophobic modified siloxane mixture to the content of the acid catalyst is 1:0.05 to 1:0.00001, when the content ratio of the acid catalyst in the mixed solution of the siloxane and the hydrophobic modified siloxane is higher, the hydrolysis rate is faster; that is, the higher the acid catalyst content ratio, the greater the ionic content in the overall aerogel structure, and the greater the dielectric loss of the aerogel will be. In this example, the preferred conditions are that the molar ratio of the total siloxane and hydrophobically modified siloxane mixture content to the acid catalyst content is 1:0.0075.
the condensation step (S3): adding an alkali catalyst into the mixed solution, and performing condensation reaction (condensation reaction) at a specific temperature. A trace amount of surfactant is added during the condensation reaction to reduce the interfacial tension of the aerogel structure after condensation and to avoid cracking during drying. In the mixed solution containing the acid catalyst, the base catalyst, and the surfactant, the content of the surfactant is 0.01mol% to 0.5mol%, and preferably 0.2mol%. In addition, the weight ratio of the content of the added trace surfactant to the total content of the siloxane and the hydrophobically modified siloxane mixture is 1:100 to 1: 3000A; in this embodiment, the preferred condition is that the weight ratio of the contents is 1:1000. furthermore, the alkali catalyst is mixed with the mixed solution of water and ethanol, and then added for condensation reaction, wherein the molar ratio of water to ethanol is, for example, 100:0.1 to 4:1, in the present embodiment, the preferable conditions are, for example, 50:1.
the increase in temperature during this condensation step contributes to a significant reduction in the condensation reaction time (i.e., the gelation time of the aerogel), wherein the gelation time is about 220 minutes at room temperature (25 ℃) and about 10 minutes at 70 ℃ when the weight ratio of the alkali catalyst to the acid catalyst is 1.0. In addition, the alkali catalyst content in the mixed solution of water and ethanol is increased, which also significantly shortens the condensation reaction time. When the content volume ratio of the 1M base catalyst to the 1M acid catalyst is 0.8; when the content ratio of the 1M base catalyst to the 1M acid catalyst is 1.2.
The aging step (S4): the formed silicon-based aerogel board is aged at a specific temperature, so that the aerogel wet glue structure is stable, and the preferred temperature is 70 ℃ in the embodiment.
The drying step (S5): after the silicon-based aerogel plate structure is aged and stabilized, the water-containing solvent in the aerogel system is evaporated under the normal-pressure high-temperature environment. Because the material contains the surfactant, the cracking behavior in the drying process of the gel is quickly reduced through the combination acting force of the surfactant in the drying process, and then the low-dielectric silicon-based aerogel plate with low density and high porosity is prepared.
The step (S6) of impregnating a polymer solution: when the silicon-based aerogel plate structure is dried, a silicon-based aerogel plate with a complete structure and proper strength is formed, and then the silicon-based aerogel plate is soaked in a high-molecular dilute solution, so that a high-molecular chain uniformly permeates holes in the silicon-based aerogel plate along with a solvent to form a wet-type high-molecular impregnated silicon-based aerogel composite material. Herein, the concentration of the polymer dilute solution can be 0.01wt% to 60wt%, preferably 0.05wt% to 60wt%, wherein the lower the polymer concentration, the better the efficiency of the polymer penetrating into the pores inside the silica-based aerogel; on the contrary, the higher the polymer concentration is, the higher the content of the polymer coating in the silicon-based aerogel is, and the better the strength of the prepared low dielectric organic/silicon-based aerogel composite board is. That is, the dielectric coefficient and strength of the prepared low dielectric organic/silicon-based aerogel composite board can be regulated and controlled by the concentration of the polymer dilute solution. Wherein the concentration of the polymer dilute solution is more preferably 3.0wt% to 8.5wt%.
The phase separation and drying step (S7): after the wet polymer impregnated silica-based aerogel composite material is impregnated, the solvent in the wet polymer impregnated silica-based aerogel composite material is evaporated under the normal-pressure high-temperature environment. In the drying process, liquid-solid phase separation (liquid-solid phase separation) is firstly carried out on the polymer dilute solution in the wet polymer impregnated silicon-based aerogel composite material, so that polymer molecular chains are coated on an aerogel skeleton structure in the high-porosity silicon-based aerogel, and meanwhile, an organic solvent in the high-porosity silicon-based aerogel is vaporized, so that the wet polymer impregnated silicon-based aerogel composite material is gradually dried, wherein the drying temperature is determined according to the boiling point of the organic solvent, and if the solvent is ethanol, the drying temperature is 60-65 ℃; if the solvent is butanone, the drying temperature is 80-85 ℃, so that the dry macromolecule impregnated silica-based aerogel composite material can be prepared.
The crosslinking and curing step (S8): the method comprises the steps of enabling polymer chains coated on a silicon-based aerogel network framework to carry out cross-linking reaction in a specific high-temperature environment of a dried polymer impregnated silicon-based aerogel composite material, and in the cross-linking reaction, carrying out cross-linking reaction among the polymer chains coated on the silicon-based aerogel network framework and between the polymer chains and silicon-based aerogel molecules to combine the polymer chains and the silicon-based aerogel molecules, so that the porous, light-weight and low-dielectric polymer/silicon-based aerogel composite material can be obtained after the polymer is cross-linked in the high-temperature environment. Referring to fig. 5 and 6, the general appearance and fine structure of the cross section of the prepared low dielectric polyimide/silicon-based aerogel composite board show that the high molecular weight inside the prepared low dielectric polyimide/silicon-based aerogel composite board is coated on the network structure of the aerogel particles to form a porous aerogel structure with uniform appearance structure. Overall, the structural uniformity, shrinkage and strength of the polymer/silica-based aerogel composite material can be regulated and controlled along with the following factors: the content of the siloxane compound or the hydrophobically modified siloxane compound, the total solvent content, the hydrolysis conditions, the condensation rate, the surfactant content, the aging rate, the drying rate, the concentration of the polymer thin solution, the uniformity of polymer chain penetration, and the degree of polymer chain crosslinking.
Referring to fig. 7 and 8, the general appearance and the fine structure of the cross section of the low dielectric epoxy resin/silicon-based aerogel composite board prepared by the present invention show that the high molecules in the prepared low dielectric epoxy resin/silicon-based aerogel composite board are coated on the network structure of the aerogel particles to form a porous aerogel structure with a uniform appearance structure.
Referring to table 1, the basic physical properties of the low dielectric silicon aerogel board, the low dielectric polyimide/silicon-based aerogel composite board, and the low dielectric epoxy resin/silicon-based aerogel composite board prepared according to the present invention are shown, wherein a water-soluble natural adhesive is added in the condensation process of the embodiment. It can be seen from the table that the density of the dielectric silicon-based aerogel plates prepared according to the present invention is about 0.178g/cm as the content of the hydrophobically modified silicone compound in the mixture of the silicone compound and the hydrophobically modified silicone compound is increased 3 The concentration is reduced to 0.123g/cm 3 . In addition, the dielectric constant and dielectric loss were measured by conducting a 10GHz frequency test using an SPDR dielectric resonator for measuring the dielectric constant of Agilent substrate (test standard: IPC TM6502.5.5.13). The dielectric coefficient of the hydrophobic modified siloxane compound gradually decreases from 1.526 to 1.276 along with the increase of the content of the hydrophobic modified siloxane compound in the mixture of the siloxane compound and the hydrophobic modified siloxane compound. On the other hand, it can be seen from the table that the density of the prepared low dielectric polyimide/silicon-based aerogel composite board increases with the polyimide content by about 0.178g/cm 3 Rising to 0.456g/cm 3 . In addition, the dielectric constant was measured at a frequency of 10GHzThe polyimide content gradually increased from about 1.526 to about 1.987. Finally, it can be seen from the table that the density of the prepared low dielectric epoxy resin/silicon-based aerogel composite board increases from about 0.178g/cm along with the content of the epoxy resin 3 Rising to 0.461g/cm 3 . In addition, the dielectric constant of the epoxy resin-modified polycarbonate resin gradually increases from 1.526 to 1.821 with the increase of the content of the epoxy resin when the epoxy resin-modified polycarbonate resin is tested at a frequency of 10 GHz. The low dielectric silicon-based aerogel plate and the low dielectric polymer silicon-based aerogel composite plate prepared by the invention have excellent dielectric properties.
TABLE 1
Please refer to table 2, which shows the basic physical properties of the low dielectric silicon-based aerogel board, the low dielectric polyimide/silicon-based aerogel composite board, and the low dielectric epoxy resin/silicon-based aerogel composite board prepared according to the present invention, wherein no water-soluble natural adhesive is added in the condensation process of the embodiment. As can be seen from the table, the density of the dielectric silicon-based aerogel plate prepared by the invention is about 0.178g/cm as the content of the hydrophobically modified siloxane compound in the mixture of the siloxane compound and the hydrophobically modified siloxane compound is increased 3 The concentration is reduced to 0.123g/cm 3 . In addition, the dielectric constant and the dielectric loss were measured by conducting a 10GHz frequency test on an Agilent substrate dielectric constant measuring SPDR dielectric resonator (test standard: IPC TM6502.5.5.13). The dielectric coefficient of the hydrophobic modified siloxane compound gradually decreases from 1.526 to 1.276 along with the increase of the content of the hydrophobic modified siloxane compound in the mixture of the siloxane compound and the hydrophobic modified siloxane compound. On the other hand, it can be seen from the table that the density of the prepared low dielectric polyimide/silicon-based aerogel composite board increases with the polyimide content by about 0.178g/cm 3 Rising to 0.652g/cm 3 . In addition, the dielectric coefficient of the polyimide gradually increases from about 1.350 to 1 along with the increase of the content of the polyimide.821. Finally, it can be seen from the table that the density of the prepared low dielectric epoxy resin/silicon-based aerogel composite board increases from about 0.178g/cm along with the content of the epoxy resin 3 Rising to 0.421g/cm 3 . In addition, the dielectric coefficient of the epoxy resin gradually rises from 1.526 to 1.933 along with the increase of the content of the epoxy resin. The low dielectric silicon-based aerogel plate and the low dielectric polymer silicon-based aerogel composite plate prepared by the invention have excellent dielectric properties.
TABLE 2
Firstly mixing siloxane compounds, and then preparing the inorganic aerogel material by a sol-gel preparation method under normal pressure, wherein the inorganic aerogel material is mainly silicon-based aerogel, the porosity of the silicon-based aerogel is higher than 70%, and the density of the silicon-based aerogel is about 0.12g/cm 3 To 0.18g/cm 3 . The dielectric property of the product is reduced along with the increase of the porosity, wherein the dielectric constant is 1.28 to 1.53, and the dielectric loss is 0.0026 to 0.0087, so the product has low dielectric constant and low dielectric loss property. The related products can be used as dielectric layers in future 5G high-frequency circuits or insulating layers in high-frequency devices. Then, the inorganic aerogel material is directly impregnated with thermosetting polymer such as polyimide (polyimide) or epoxy resin (epoxy) or other liquid crystal polymer solution (poly semi-aromatic liquid crystal polymer and poly wholly aromatic liquid crystal polymer), and then dried and cross-linked or cured in a high temperature environment to form an organic/inorganic aerogel composite material with a porosity of more than 60% and a density of about 0.12g/cm 3 To 0.42g/cm 3 (preferably 0.2 g/cm) 3 To 0.32g/cm 3 ) The dielectric constant is about 1.35 to 1.93 and the dielectric loss is 0.0033 to 0.0144, so it has low dielectric constant and low dielectric loss properties. The invention can firstly quickly prepare the inorganic aerogel with high porosity and low dielectric constant under normal pressure and then prepare the organic/inorganic aerogelAnd (4) mechanically compounding the aerogel. The invention does not need to carry out long solvent replacement and use supercritical drying equipment, and has simple, convenient and quick whole process and low cost. After the polymer such as polyimide is coated, the strength can be obviously improved. In addition, the low dielectric product can be applied to dielectric layers in high-frequency circuits or insulating layers in semiconductor devices; furthermore, the method can also be applied to microwave circuits in 5G communication circuits and related low dielectric materials.
While the invention has been described with reference to specific embodiments, it will be understood by those skilled in the art that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A method for preparing a low dielectric organic/inorganic aerogel composite, comprising the steps of:
mixing: mixing a siloxane compound or a hydrophobically modified siloxane compound with an organic mixed solvent to form a mixed solution;
a hydrolysis step: adding an acid catalyst into the mixed solution to perform hydrolysis reaction;
condensation step: adding an alkali catalyst into the hydrolyzed mixed solution to perform condensation reaction, and adding a trace amount of surfactant in the condensation reaction process;
and (3) aging: aging the aerogel board formed in the condensation step at a specific temperature to promote the aerogel structure to be further condensed so as to achieve stable structure;
and (3) drying: after the aerogel plate structure is gelled and stabilized, high-temperature drying is carried out in a normal-pressure high-temperature environment to obtain a low-dielectric silicon-based aerogel plate which is uniform in structure and has high porosity and high specific surface area;
impregnating polymer solution: soaking the prepared low dielectric silicon-based aerogel board in a polymer dilute solution to enable polymer chains to uniformly permeate into the silicon-based aerogel board to form a wet-type polymer/silicon-based composite material;
phase separation and drying steps: evaporating the solvent in the polymer dilute solution at a specific temperature, and performing liquid-solid phase separation on the polymer in the wet polymer/silicon-based composite material to coat the polymer chains on the low-dielectric silicon-based aerogel reticular framework structure and gradually dry the polymer chains; and
and (3) crosslinking and curing: and (3) subjecting the dried polymer/silicon-based composite material to a crosslinking reaction under a specific high-temperature environment to coat polymer chains of a low-dielectric silicon-based aerogel reticular framework structure, and carrying out chemical reaction combination among the polymer chains and between the polymer chains and silicon-based aerogel molecules in the crosslinking reaction, so as to obtain the porous, light-weight and low-dielectric polymer/silicon-based aerogel composite material after the crosslinking reaction.
2. The method of claim 1, wherein: wherein the siloxane compound is tetramethoxysilane or tetraethoxysilane, the hydrophobically modified siloxane compound is methyltrimethoxysilane or methyltriethoxysilane, and the molar ratio of the siloxane compound to the hydrophobically modified siloxane compound is from 0:100 to 35:65.
3. the method of claim 1, wherein: wherein the weight ratio of the content of the trace surfactant to the total content of the siloxane compound and the hydrophobically modified siloxane compound mixture is 1:100 to 1:3000.
4. the method of claim 1, wherein: wherein the polymer concentration of the polymer dilute solution used in the step of impregnating the polymer solution is from 0.01wt% to 60wt%, and the lower the polymer concentration is, the faster and more uniform the polymer penetrates into the interior of the aerogel, so that the polymer chains uniformly penetrate into the interior of the silicon-based aerogel board to form the wet-type polymer/silicon-based composite material.
5. The production method according to any one of claims 1 to 4, characterized in that: wherein the polymer in the polymer dilute solution comprises thermosetting polymer, thermoplastic polymer and liquid crystal polymer.
6. The method of claim 5, wherein: wherein the thermosetting polymer is selected from one or a mixture of the following: epoxy resins, polyimide resins, phenolic resins, and polytriacyanamide-formaldehyde resins.
7. The method of claim 5, wherein: wherein the thermoplastic polymer is selected from one or a mixture of the following: polyethylene, polypropylene, polytetrafluoroethylene, polycarbonate, polyamide, polyesteramide, and polyester.
8. The method of claim 5, wherein: wherein the liquid crystal polymer is selected from one or a mixture of the following: a poly-semi-aromatic liquid crystal polymer and a poly-wholly aromatic liquid crystal polymer.
9. The method of claim 1, wherein: wherein the structural uniformity, shrinkage and strength of the polymer/silicon-based aerogel composite material can be regulated and controlled along with the following preparation factors: the content of the siloxane compound or the hydrophobically modified siloxane compound, the total solvent content, the hydrolysis conditions, the condensation rate, the surfactant content, the aging rate, the drying rate, the concentration of the polymer thin solution, the uniformity of polymer chain penetration, and the degree of polymer chain crosslinking.
10. The method of claim 1, wherein: wherein the porosity of the low dielectric polymer/silicon-based aerogel composite material is more than 60 percent, and the density is 0.12 to 0.42g/cm 3 And its dielectric properties decrease with increasing porosity, wherein its dielectric constant is 1.28 to 1.93 and its dielectric loss is 0.0026 to 0.014, and as in high frequency circuitsDielectric layers, insulating layers in semiconductor devices, or microwave circuits in communication integrated circuits.
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