Use of a polymer thin film as an electret thin film

Abstract

The invention relates to the use of a polymer thin film as an electret thin film (3), which polymer thin film is formed from monomers (21) by deposition by means of a chemical vapour deposition process, wherein at least some of the monomers (21) have at least two terminal acrylate and / or methacrylate groups, and wherein the electret thin layer (3) is formed from the polymer thin layer during the vapour deposition process.

Description

[0001] USE OF A POLYMER THIN FILM AS ELECTRET THIN FILM

[0002] The invention relates to the use of a polymer thin film formed from monomers by chemical vapor deposition as an electret thin film.

[0003] Electrets are dielectric layers that have a (quasi-)permanent surface potential and thus, analogous to a permanent magnet, provide a permanent electric field. Due to this special property, electrets are used in a wide variety of applications today and have become indispensable in our daily lives. The best-known example is certainly the electret microphone, produced in the millions. Other examples of devices based on the electret transducer principle include energy converters that, for example, harvest energy from vibrations, acceleration sensors and structure-borne sound measurements, as well as magnetic field sensors. In addition to the electret transducers mentioned above, electrets are also used in respiratory masks as air filters, to reduce the threshold voltage in organic field-effect transistors (OFETs), and in many other applications.

[0004] According to the current state of the art, a dielectric material is charged by irradiation with charge carriers (e.g., corona discharge). The charge carriers are trapped in so-called trap states within the material, and a surface potential is created by the excess charge. Fluoropolymers, such as PTFE, Teflon AF, Cytop, or Teflon FEP, are currently the starting materials of choice in industry and science for producing electrets. They provide numerous trap states, have high dielectric strength, and, due to their hydrophobic nature, are less susceptible to charge decay due to atmospheric moisture.

[0005] Ethylene glycol dimethacrylate (EGDMA) is a monomer typically used as a cross-linker in initiated chemical vapor deposition. Christian, P. et al., report in "Controlling indomethacin Release through Vapor-Phase Deposited Hydrogel Films by Adjusting the Cross-linker Density" (Science Rep. 2018, 8, 7134) on the use of tert-butyl peroxide (TBPO) as an initiator and also in combination with hydrogels (e.g., P(HEMA-co-EDGMA)).

[0006] Another possibility for producing electrets is the use of ferroelectric materials, which enter a polarized state when exposed to an electric field and retain this state even after the field is removed. Polymers that exhibit this state, also known as spontaneous polarization, can also be used as electrets because they exhibit a surface potential. An example of such a polymer is ferroelectric polyvinylidene fluoride (PVDF).

[0007] Furthermore, for some molecules, such as water, which exhibit a high dipole moment, it was reported as early as 1972 that surface potentials can be measured under vacuum conditions and surface temperatures of T < 100 K (Kutzner, K. "Spontaneous photonization of condensing carbon monoxide and other gases with an electrical dipole moment" Thin solid films 1972, 14, 49; Balog, Richard et al. "Spontaneous dipole alignment in films of N2O". Physical review letters, 2009, 102.073003). However, these surface potentials are not suitable for applications because they are not stable under normal conditions.

[0008] In addition to small gas molecules, it has also been demonstrated that aluminum tris(8-hydroxyquinoline) (Alq3), which is used, for example, in organic light-emitting diodes (LEDs), exhibits a surface potential after thermal vapor deposition onto a substrate (Ito, Eisuke et al., "Spontaneous buildup of giant surface potential by vacuum deposition of Alq3 and its removal by visible light irradiation," Journal of Applied Physics, 2002, 92, 7306). However, this resulting surface potential is also not stable under normal conditions, as the potential decays under light in the visible range. 1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene also shows polarization and a first energy generator / electret converter has been shown to work with this molecule (Tanaka, Y., Matsuura, N. & Ishii, H. “Self-Assembled Electret for Vibration-Based Power Generator” Sei Rep 2020, 10, 6648; NOGUCHI, Yutaka, et al.“Understanding spontaneous orientation polarization of amorphous organic semiconducting films and its application to devices” Synthetic Metals, 2022, 288, 117101). However, here too, the surface potential disappears after only about 24 hours in the atmosphere under visible light, making the molecules unsuitable for devices intended to function for longer than a day.

[0009] US Pat. No. 7,431,969 B2 discloses the use of various acrylate and methacrylate monomers, also in combination with the initiator di-tert-butyl peroxide (TBPO), in an initiated chemical vapor deposition (iCVD) process. The formation of permanently charged electret layers is not described.

[0010] In addition, the document KR 102153808 B1 discloses an iCVD process for producing a blocking dielectric insulation layer made of acrylate monomers and initiators, in which a thin layer of fluoropolymer is applied to the produced layer and charged separately to act as an electret layer.

[0011] From the document US 2018 / 0 164245 A1, a method for depositing a polymer layer is known, which comprises the following: providing a substrate with a sensor structure arranged on the substrate on a substrate carrier within a hot wire chemical vapor deposition (HWCVD) chamber; providing a process gas comprising an initiator gas and a monomer gas as well as a carrier gas in the HWCVD chamber; heating a plurality of filaments arranged in the HWCVD chamber to a first temperature sufficient to activate the initiator gas without decomposing the monomer gas; and exposing the substrate to initiator radicals from the activated initiator gas and the monomer gas in order to deposit a polymer layer on the sensor structure.

[0012] In addition, the document US 2018 / 0 009 001 A1 describes methods for forming thin polymer films on a surface of an article by vapor deposition. The method for depositing a coating comprises the following steps: providing an article, the article comprising an internal volume, an internal surface, and an external surface; introducing a gaseous mixture of reagents into the internal volume of the article, wherein the gaseous mixture comes into contact with the internal surface and the gaseous mixture comprises an unsaturated monomer; temporarily entrapping the gaseous mixture of reagents in the internal volume of the article; and applying heat to the gaseous mixture of reagents temporarily entrapped in the internal volume of the article, thereby depositing a coating on the internal surface.

[0013] The document US 2014 / 0 186620 A1 discloses a method for passivating a substrate, comprising: exposing a surface of a substrate comprising silicon hydride groups to a vapor phase initiator species under conditions that facilitate a radical reaction between at least a portion of the silicon hydride groups and the vapor phase initiator species.

[0014] Furthermore, the document US 2014 / 0 030 165 A1 discloses a method for coating a substrate, such as a microfluidic device with an inner surface, which method comprises heating a gas containing a perfluoroacrylate, a crosslinker and an initiator to a first temperature, maintaining the substrate at a second temperature which is lower than the first temperature in a reaction chamber, exposing the heated gas to the substrate in the reaction chamber and reacting the perfluoroacrylate with the initiator and the crosslinker to form a polymer coating on the surface of the substrate.

[0015] Methods and devices for manufacturing energy storage devices are known from US 2011 / 0 045 349 A1. In one embodiment, a method for manufacturing an energy storage device is provided.The method comprises positioning an anodic current collector in a processing area, depositing one or more three-dimensional electrodes separated by a finite distance on a surface of the anodic current collector such that portions of the surface of the anodic current collector remain exposed, depositing a conformal polymer layer over the anodic current collector and the one or more three-dimensional electrodes using iCVD techniques comprising flowing a gaseous monomer into the processing area, flowing a gaseous initiator into the processing area through a heated filament to form a reactive gas mixture of the gaseous monomer and the gaseous initiator, wherein the heated filament is heated to a temperature between about 300°C and about 600°C.heated, and depositing a conformal layer of cathodic material over the conformal polymeric layer.

[0016] US 2009 / 0 087 562 A1 describes a method for forming a polymer film on a surface of a substrate. The method comprises placing a substrate on a substrate holder in a vapor deposition system and introducing a process gas into the vapor deposition system, wherein the process gas comprises a monomer, a crosslinking monomer, and an initiator. The substrate is then exposed to the process gas to form a polymer film on the substrate, wherein the polymer film thermally decomposes at a decomposition temperature.

[0017] Furthermore, US 2007 / 0 104 860 A1 discloses a completely dry encapsulation method that enables the coating of well-defined polymers around particles with sizes down to the nanoscale. In certain embodiments, the processes are modified forms of initiated chemical vapor deposition (iCVD) using thermally initiated radical polymerization to create conformal coatings around individual particles while avoiding agglomeration. The present invention also enables the coating of particle surfaces with a range of functional groups by directly incorporating the functionality into the monomers used or indirectly by subsequently modifying the surface of a coated particle. In certain embodiments, the process leads to high-quality functional polymer coatings.

[0018] The main problems with the current state of the art are that known electret thin films must be charged in separate process steps, and there are no ways to apply charges in a truly homogeneous and reproducible manner. Precise potential control is not feasible. The corona discharge method, for example, achieves very high electric field strengths, which can lead to dielectric breakdown in the thin films and produce inhomogeneous surface charges or surface potentials.

[0019] Electrets typically use polymers that are initially uncharged and then subjected to a subsequent polarization process. Polymers used for this purpose are hydrophobic, exhibit high electrical resistance, and are particularly suitable for permanently storing applied charge. Examples include polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), polypropylene (PP), polyvinylidene fluoride (PVDF), polytetrafluoroethylene propylene (PTFEP), and their copolymers.

[0020] The present invention is based on several objects: to provide an electret or a manufacturing method therefor that enables precise potential control. It should be possible to use electrets with a homogeneously and reproducibly distributed surface potential without requiring a separate downstream charging step, thus simplifying the manufacturing process.

[0021] These tasks are solved by using a polymer thin film as an electret thin film according to the main claim.

[0022] A polymer thin film formed from monomers by chemical vapor deposition is used as an electret thin film, wherein at least a portion of the monomers has at least two terminal acrylate and / or methacrylate groups and wherein the electret thin film is formed from the polymer thin film during the vapor deposition process.

[0023] In particular, the polymer thin film can be used as an electret thin film due to spontaneous polarization from the polymer thin film.

[0024] In addition, the polymer thin film can be deposited by chemical vapor deposition from monomers with

[0025] - an initiator as a radical starter and / or

[0026] - a broken monomer / dimer as radical initiator and / or

[0027] - an oxidizing agent and / or

[0028] - a reactant and / or

[0029] - ions are formed,

[0030] Preferably, the surface potential of the electret thin film can be adjusted with the initiator, with the surface potential being either positive or negative. A positive surface potential of the electret thin film can also be adjusted with the initiator di-tert-butyl peroxide (TBPO), and a negative surface potential of the electret thin film can be adjusted with the initiator perfluorobutanesulfonyl fluoride (PFBSF).

[0031] The level of surface potential per layer thickness can be adjusted by the combination of initiator and monomer.

[0032] In particular, a higher surface potential per layer thickness can be formed by a higher dipole moment of the produced polymer.

[0033] Furthermore, by using polyethylene glycol dimethacrylate (PEGDMA), polydimethylpropanediol methacrylate (PDPDMA) or polyglyceryl trimethacrylate (PGTMA) as monomers, different potentials per nanometer layer thickness can be formed when they are prepared with di-tert-butyl peroxide (TBPO), with PDPDMA having a higher potential than PEGDMA and PGTMA a lower potential than PEGDMA per layer thickness.

[0034] The polymer thin film can also be used as an electret thin film in vacuum, atmospheric pressure or overpressure.

[0035] The polymer thin film usable as an electret thin film can be produced by a self-charging polymer electret manufacturing process for producing an electret formed from monomers with an initiator (not required if the monomer is used self-initiating) comprising the step of:

[0036] Depositing a polymer thin film via initiated chemical vapor deposition, wherein

[0037] - at least some of the monomers have at least two terminal acrylate and / or methacrylate groups,

[0038] - the initiator is a radical initiator and / or the monomer is self-initiating and

[0039] - spontaneous polarization to an electret thin film occurs in the formed polymer thin film without the application of an electric field.

[0040] The monomers can be formed as either homo- or co-monomers.

[0041] In particular, at least some of the monomers may be formed as dimethacrylates and / or as trimethacrylates.

[0042] In addition, the surface potential of the electret thin film resulting from polarization increases linearly with the layer thickness.

[0043] The surface potential of the electret thin film can be adjusted with the initiator, whereby the surface potential can be either positive or negative. The initiator di-tert-butyl peroxide (TBPO) can be used to adjust a positive surface potential of the electret thin film, and the initiator perfluorobutanesulfonyl fluoride (PFBSF) can be used to adjust a negative surface potential of the electret thin film.

[0044] The monomers used may preferably have a dipole moment of at least 1 Debye and a vapor pressure of at least 16 Pa at 25 °C (at ambient pressure 1 atm, 12766.95 Pa).

[0045] In particular, the surface potential of the formed electret thin films is stable under standard conditions and the electret thin film can be easily used in electret transducers and other devices.

[0046] Initiators that form radicals with an electronegativity of more than 3 on the Pauling scale after their activation can in particular lead to negative surface potentials in the formed electret layers, and initiators that form radicals with an electronegativity of less than 3 on the Pauling scale after their activation can lead to positive surface potentials in the formed electret layers.

[0047] Because the monomers can also be formed as comonomers, it is possible to combine monomers with at least two terminal acrylate and / or methacrylate groups with monomers without these end groups. Monomers with a vinyl group are also possible as comonomers if at least one comonomer has at least two acrylate or methacrylate groups. The resulting polymer layer is formed as an electret layer, making it possible to combine different functionalities of monomers or to adjust a desired charge / surface potential at a desired film thickness.

[0048] In the self-charging polymer electret manufacturing process, the surface potential can be adjusted extremely precisely in the millivolt range, which is not possible with conventional electrets, which currently require charging during production. The effect is substrate-independent for various substrates such as gold, silicon (conductive, heavily n-doped), copper, titanium oxide, and silicon. The applications of the films are extremely promising both scientifically and industrially (e.g., electret microphones, MEMS devices). Some of the polymers exhibiting the effect have indeed been deposited in the past using the same method, but the effect of self-charging has not yet been documented.

[0049] Compared to conventional electrets, the charging process is eliminated. Furthermore, since the charges scale linearly with layer thickness (as previously observed), they can be applied with extreme precision, opening up entirely new applications for electret thin films. As already discussed, the disadvantage of currently used electret materials is that a charging or poling process is always necessary to generate a surface potential.

[0050] Polyacrylates and polymethacrylates are not suitable for a downstream charging process because they have difficulty storing separately applied charge and have therefore not typically been used as electret materials to date.

[0051] In polymer thin films deposited via the gas phase, particularly with dimethacrylates or trimethacrylates as homomonomers or comonomers, spontaneous polarization can be observed immediately after deposition, without the application of an electric field. This observation forms the basis for the self-charging polymer electret manufacturing process according to the invention. Deposition takes place via initiated chemical vapor deposition (iCVD). The surface potential of the thin films resulting from polarization increases linearly with film thickness.

[0052] This represents a significant advantage for use in industrial applications, as an entire process step (the charging step) is eliminated. This reduces costs, particularly in industrial applications. Another advantage is the highly precise control over the resulting surface potential. This opens up entirely new possibilities, especially for small applications and micro-electro-mechanical systems (MEMS). Furthermore, the layers can also be applied homogeneously to large-area substrates using the typical CVD growth process.

[0053] The potential precision, reproducibility, and homogeneity of the electrets produced using the inventive method are unparalleled. The substrate independence opens up the possibility of using electrets on materials that make traditional charging impossible. Since iCVD is already industrialized, self-charged electret thin films can be mass-produced.

[0054] This is particularly interesting because electrets are already used in large quantities today, for example as membranes in sound transducers (electret microphones, headphones), in filter technology, as ultrasonic transducers in medical technology, as infrared sensor elements in security technology and to reduce the threshold voltage in organic field-effect transistors.

[0055] Due to the highly precise potential control of the self-charged layers, for example, deposited on a field-effect transistor (FET), the threshold voltage of the FET can be virtually compensated, which was previously impossible. The lower the threshold voltage in the FET, the more sensitive the component becomes and thus also the respective sensor connected to the FET. The energy consumption of the FET is also reduced, resulting in enormous energy savings for the multitude of transistors in modern electronic devices ("low-power electronics").

[0056] In one variant, an electric field can be applied during deposition to enhance the effect.

[0057] Furthermore, the polymer thin film used as an electret thin film can be used to change the threshold voltage in transistor applications, especially OFETs.

[0058] In another application, the polymer thin film used as an electret thin film can be used in an energy harvester.

[0059] In addition, the polymer thin film that can be used as an electret thin film can be used in an electret microphone.

[0060] Furthermore, the electret thin film can be used in a variant as a usable polymer thin film in a solar cell.

[0061] The invention is described below with reference to the accompanying figures in the

[0062] The description of the figures is intended to illustrate the invention and is not to be considered limiting. They show:

[0063] Figure 1 shows an exemplary schematic representation of a simple electret transducer according to the state of the art;

[0064] Figure 2 shows an exemplary graphical representation of the polarization curve in an electric field with a dielectric (Fig. 2a)) and a ferroelectric

[0065] (Fig. 2b));

[0066] Figure 3 exemplary test results of selected electrets produced by CVD with a plot of surface potential against the

[0067] Film thickness for different compositions (Fig. 3a)), different process parameters (Fig. 3b)) and a plot of charge stability versus temperature (Fig. 3c));

[0068] Figure 4 shows an exemplary schematic representation of the processes in the iCVD process (Fig. 4a), an exemplary schematic representation of the reaction processes in the iCVD process (Fig. 4b)) and a plot of transmittance against the wavenumber in the IR range for the polymer films resulting from the exemplary reactions from Fig. 4b) (Fig. 4c));

[0069] Figure 5 shows an exemplary tabular representation of the electrical voltage of electret films produced by CVD process on different substrates at different exemplary times after storage in atmosphere under aluminum foil cover.

[0070] Fig. 1 shows an exemplary schematic representation of a simple electret transducer 1 according to the prior art. The electret transducer 1 consists of a plate capacitor in which the position of the counter electrode 11 is variable. On the other electrode 12 is an electret thin film, foil, or plate 3, from which an electric field emanates. If the counter electrode 11 is now set into vibration by an external signal, for example, by sound waves, mechanical vibrations, or magnetic fields, a signal can be measured at the signal output 13. In the case of the electret microphone, an acoustic signal, such as speech, is converted into an electrical signal.

[0071] Fig. 2 shows an exemplary graphical representation of the polarization curve in an electric field with a dielectric (Fig. 2a)) and a ferroelectric (Fig. 2b)), where the polarization is plotted as a function of the electric field.

[0072] The ferroelectric effect has been known for a long time and is used in sensors, memory devices, and actuators. Originally observed in ceramics, it quickly became clear over time that some polymers, such as PVDF, PLLA, PLG, and nylon, also exhibit this effect. Normally, linear polarization occurs in a dielectric when an electric field is applied (Fig. 2a). In the ferroelectric effect, the electric polarization is nonlinear when an electric field is applied and follows a hysteresis curve, as shown schematically in Fig. 2b. If an electric field is applied to the ferroelectric, the electric polarization follows the recurve and the material saturates. After the electric field is reduced to zero, a polarization remains in the material, which is called spontaneous polarization.Only an electric field of opposite sign can reduce the polarization and, with sufficient strength, even reverse it. This creates the hysteresis curve typical of ferroelectrics.

[0073] Fig. 3 shows exemplary test results of selected electrets 3 produced by the CVD process with a plot of surface potential versus film thickness for different compositions (Fig. 3a)), different process parameters (Fig. 3b)) and a plot of charge stability versus temperature (Fig. 3c)).

[0074] Fig. 3a) shows the surface potential of PEGDMA with various initiators 22, as well as of PV3D3, which has no surface potential. When using the combination of PEGDMA and the initiator TBPO, positive surface potentials are always produced. Instead of applying an external electric field of reversed polarity, as is known from ferroelectric materials, a reversed polarity can be achieved in the electret layers 3 manufactured using the self-charging polymer electret manufacturing process by selecting the initiator 22. The application of an external electric field is not necessary. As can be seen in Fig. 3a), the combination of PEGDMA with the initiator PFBSF produces negative surface potentials instead of TBPO.Other iCVD monomers that do not have at least two terminal acrylate and / or methacrylate groups are represented here by V3D3 as an example and do not show surface potentials at all layer thicknesses.

[0075] For example, the straight line for PEGDMA+TBPO in Figure 3a has a slope of 20 mV / nm.

[0076] Figure 3b shows the surface potential of PEGDMA+TBPO when varying the process parameters (heating power and gas flow). It is clear that the charge per film thickness remains constant despite changing the process parameters.

[0077] In Fig. 3c) it can be seen that charge stability is given for the exemplary electret thin film 3 formed from PEGDMA+TBPO up to a temperature of approximately 90 °C and the surface potential only begins to decrease at higher temperatures until at approximately 160 °C no surface potential is present anymore.

[0078] Fig. 4 shows an exemplary schematic representation of the processes in the initiated chemical vapor deposition (iCVD) process 2 (Fig. 4a), an exemplary schematic representation of the reaction processes in the iCVD process 2 according to the self-charging polymer electret manufacturing process (Fig. 4b)) and an FTIR plot of transmittance versus wavenumber for the exemplary reactions from Fig. 4b) (Fig. 4c)).

[0079] In the exemplary iCVD process 2 shown in Fig. 4a), a thin polymer layer is created by free radical polymerization. Process 2 takes place under vacuum conditions (process pressure approximately 40-50 Pa). Typically, one or more monomers 21 and an initiator 22 are introduced into the reactor in the form of vapors. To prevent condensation on the reactor walls, the reactor and all inlet and outlet lines are heated to approximately 90-130°C (depending on the monomer 21 used). To start the process, for example, a filament / filament arrangement located above the substrate holder is heated (approximately 250-400°C), causing the initiator molecules 22 to decompose into free radicals 23. This can also occur in other ways, for example, by UV, plasma, thermally, or chemically. The monomer molecules 21 do not decompose and adsorb onto the substrate holder. In order for the monomer molecules 21 to adsorb, the substrate holder must be heated to approx.The reactor is cooled to 20-35 °C. The free radicals 23 then collide with the adsorbed monomer molecules 21 and initiate free radical polymerization on the cooled substrate holder. The process is typically carried out in a flow-through mode. New (co-)monomer 21 and initiator molecules are continuously added to the reactor, while byproducts and unreacted molecules are simultaneously pumped out. A batch process is also possible.

[0080] For the exemplary schematic representation of the reaction processes in iCVD process 2 according to the self-charging polymer electret manufacturing process shown in Fig. 4b), the same monomers 21 and initiators 22 as in Fig. 3a were used. Using the combination of PEGDMA and the initiator TBPO results in positive surface potentials. Combining PEGDMA with the initiator PFBSF instead of TBPO results in negative surface potentials. Other iCVD monomers 21 that do not have at least two terminal acrylate and / or methacrylate groups, represented here as an example by V3D3, do not exhibit surface potentials at all layer thicknesses.

[0081] Fig. 4c) shows the differences in transmittance plotted against wavenumber in the FTIR spectrum for the exemplary reactions from Fig. 4b).

[0082] Figure 5 shows an example tabular representation of the electrical potential of electret films 3 produced using the self-charging polymer electret manufacturing process on various substrates at various exemplary times, thus demonstrating their long-term stability. It shows that a charge loss occurs during storage in the open atmosphere, as the surface is polar and attracts polar molecules from the environment (e.g., H2O). For the experimental measurements, the samples were simply wrapped in aluminum foil and stored. Encapsulation or storage in a protective gas atmosphere should result in no charge loss at all. The charge is long-term stable.

[0083] To achieve a long-term stable electret thin film 3, a thin hydrophobic layer can be applied to the polymer.

[0084] In addition, electret thin films produced using the self-charging polymer electret manufacturing process have proven to be stable with respect to their charge against mechanical influences.

[0085] If a polymer thin film formed from monomers by chemical vapor deposition is used as an electret thin film, wherein at least some of the monomers have at least two terminal acrylate and / or methacrylate groups, and wherein the electret thin film can be formed from the polymer thin film without applying an electric field to the polymer thin film, the surface potential of the electret thin film can be influenced by appropriate parameter selection during the polymer thin film manufacturing process. The surface potential of the electret thin film can be specifically influenced by the initiator selection, the monomer selection, the comonomer selection, and also the deposition kinetics during chemical vapor deposition. The production of polymer layers according to the production of the polymer thin films used here is considered state of the art.However, the knowledge of being able to use these layers as electret layers without any further subsequent process steps is new and represents an inventive step. In addition, it will also be possible to precisely adjust the surface potential of the layers by selecting parameters prior to production.

[0086] List of reference symbols

[0087] 1 electret converter

[0088] 11 Variable counter electrode

[0089] 12 Electrode

[0090] 13 Signal output

[0091] 2 initiated chemical vapor deposition process (iCVD process)

[0092] 21 Monomer

[0093] 22 Initiator

[0094] 23 free radical

[0095] 3 Electret, electret thin film, foil, plate, film

Claims

CLAIMS 1. Use of a polymer thin film formed by deposition via chemical vapor deposition from monomers (21) as an electret thin film (3), wherein at least some of the monomers (21) have at least two terminal acrylate and / or methacrylate groups and wherein the electret thin film (3) is formed from the polymer thin film during the vapor deposition process.

2. Use according to claim 1, wherein the polymer thin film can be used as an electret thin film (3) by spontaneous polarization from the polymer thin film.

3. Use according to claim 1 or 2, characterized in that the polymer thin layer is deposited by chemical vapor deposition from monomers with - an initiator (22) as a radical starter and / or - a broken monomer / dimer as radical initiator and / or - an oxidizing agent and / or - a reactant and / or - ions are formed, 4. Use according to one of the preceding claims, characterized in that the surface potential of the electret thin film (3) is adjustable with the initiator (22), wherein the surface potential is positive or negative.

5. Use according to the preceding claim, characterized in that a positive surface potential of the electret thin film (3) is set with the initiator di-tert-butyl peroxide (TBPO) and a negative surface potential of the electret thin film (3) is set with the initiator perfluorobutanesulfonyl fluoride (PFBSF).

6. Use according to one of the preceding claims, characterized in that the level of the surface potential per layer thickness is adjustable via the combination of initiator (22) and monomer (21).

7. Use according to the preceding claim, characterized in that a higher surface potential per layer thickness can be formed by a higher dipole moment of the polymer produced.

8. Use according to the preceding claim, characterized in that by using polyethylene glycol dimethacrylate (PEGDMA), polydimethylpropanediol methacrylate (PDPDMA) or polyglyceryl trimethacrylate (PGTMA) as monomers (21), different potentials per nanometer layer thickness can be formed when they are prepared with di-tert-butyl peroxide (TBPO), PDPDMA having a higher potential than PEGDMA and PGTMA a lower potential than PEGDMA per layer thickness.

9. Use according to one of the preceding claims, characterized in that the polymer thin film can be used as an electret thin film (3) in vacuum, atmospheric pressure or overpressure.

10. Use according to one of the preceding claims, characterized in that the polymer thin film usable as electret thin film (3) is produced by a self-charging polymer electret production process for producing an electret formed from monomers (21) with an initiator (22) with the step: depositing a polymer thin film via an initiated chemical vapor deposition (2), wherein - at least some of the monomers (21) have at least two terminal acrylate and / or methacrylate groups, - the initiator (22) is a radical initiator and - spontaneous polarization to an electret thin layer (3) takes place in the polymer thin layer formed without the application of an electric field.

11. Use according to one of the preceding claims, characterized in that the polymer thin film usable as an electret thin film (3) is used to change the threshold voltage in transistor applications and / or OFETs.

12. Use according to one of the preceding claims, characterized in that the polymer thin film usable as an electret thin film (3) is used in an energy harvester.

13. Use according to one of the preceding claims, characterized in that the polymer thin film usable as an electret thin film (3) is used in an electret microphone.

14. Use according to one of the preceding claims, characterized in that the polymer thin film usable as an electret thin film (3) is used in a solar cell.

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