CN112538182A - Piezoelectric film, preparation method thereof, fingerprint identification module and electronic equipment - Google Patents
Piezoelectric film, preparation method thereof, fingerprint identification module and electronic equipment Download PDFInfo
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- 238000002360 preparation method Methods 0.000 title abstract description 12
- 229920000131 polyvinylidene Polymers 0.000 claims abstract description 236
- 238000000137 annealing Methods 0.000 claims abstract description 48
- 238000000034 method Methods 0.000 claims abstract description 33
- 239000013078 crystal Substances 0.000 claims abstract description 32
- 239000002904 solvent Substances 0.000 claims abstract description 26
- 238000004519 manufacturing process Methods 0.000 claims abstract description 24
- 238000001816 cooling Methods 0.000 claims description 46
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 40
- 238000010438 heat treatment Methods 0.000 claims description 31
- MIZLGWKEZAPEFJ-UHFFFAOYSA-N 1,1,2-trifluoroethene Chemical group FC=C(F)F MIZLGWKEZAPEFJ-UHFFFAOYSA-N 0.000 claims description 26
- 239000007788 liquid Substances 0.000 claims description 20
- 229910052757 nitrogen Inorganic materials 0.000 claims description 20
- BQCIDUSAKPWEOX-UHFFFAOYSA-N 1,1-Difluoroethene Chemical group FC(F)=C BQCIDUSAKPWEOX-UHFFFAOYSA-N 0.000 claims description 14
- 238000002844 melting Methods 0.000 claims description 5
- 230000008018 melting Effects 0.000 claims description 5
- 238000009827 uniform distribution Methods 0.000 claims 1
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- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 19
- 238000002834 transmittance Methods 0.000 description 17
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- G06V40/00—Recognition of biometric, human-related or animal-related patterns in image or video data
- G06V40/10—Human or animal bodies, e.g. vehicle occupants or pedestrians; Body parts, e.g. hands
- G06V40/12—Fingerprints or palmprints
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Abstract
The application relates to a piezoelectric film, a preparation method thereof, a fingerprint identification module and electronic equipment. The method for manufacturing a piezoelectric film of the present application includes: preparing a polyvinylidene fluoride-trifluoroethylene wet film; crystallizing the polyvinylidene fluoride-trifluoroethylene wet film and removing a solvent to obtain a polyvinylidene fluoride-trifluoroethylene film, wherein the polyvinylidene fluoride-trifluoroethylene film comprises a beta-phase crystal form of polyvinylidene fluoride-trifluoroethylene; annealing the polyvinylidene fluoride-tetrafluoroethylene film for one or more times; and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film. The preparation method of the piezoelectric film is prepared from polyvinylidene fluoride-trifluoroethylene, and the prepared piezoelectric film has higher piezoelectric strain coefficient and higher transparency by controlling the process conditions of polyvinylidene fluoride-trifluoroethylene film forming.
Description
Technical Field
The application relates to the field of electronics, in particular to a piezoelectric film, a preparation method thereof, a fingerprint identification module and electronic equipment.
Background
Along with the development of technique, require the fingerprint identification module except discerning the fingerprint, can also discern more detailed biowriting characteristics, for example capillary, blood flow signal, skin acoustic resistance etc.. However, the piezoelectric strain coefficient of the existing piezoelectric film is low, and the light transmittance is not high enough, so that the application of the fingerprint identification module is limited.
Disclosure of Invention
In view of this, it is necessary to provide a piezoelectric film having a higher piezoelectric coefficient and a higher transparency.
The embodiment of the application provides a preparation method of a piezoelectric film, which comprises the following steps:
preparing a polyvinylidene fluoride-trifluoroethylene wet film;
crystallizing the polyvinylidene fluoride-trifluoroethylene wet film and removing a solvent to obtain a polyvinylidene fluoride-trifluoroethylene film, wherein the polyvinylidene fluoride-trifluoroethylene film comprises a beta-phase crystal form of polyvinylidene fluoride-trifluoroethylene;
annealing the polyvinylidene fluoride-tetrafluoroethylene film for one or more times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The preparation method of the piezoelectric film is prepared from polyvinylidene fluoride-trifluoroethylene, and the prepared piezoelectric film has higher piezoelectric strain coefficient and higher transparency by controlling the process conditions of polyvinylidene fluoride-trifluoroethylene film forming.
Optionally, in the polyvinylidene fluoride-trifluoroethylene, the molar ratio of the vinylidene fluoride unit to the trifluoroethylene unit is 7:3 to 9: 2. Therefore, the piezoelectric strain coefficient of the prepared piezoelectric film is larger, and the light transmittance is higher.
Optionally, in the molecular chain of the polyvinylidene fluoride-trifluoroethylene, the vinylidene fluoride units and the trifluoroethylene units are uniformly distributed. The vinylidene fluoride has stronger dipole moment, so that the prepared piezoelectric film has better piezoelectric performance, and the trifluoroethylene has weaker dipole moment, so that a molecular chain is more stable.
Optionally, crystallizing the polyvinylidene fluoride-trifluoroethylene wet film and removing the solvent to obtain a polyvinylidene fluoride-trifluoroethylene film, wherein the polyvinylidene fluoride-trifluoroethylene film comprises a beta-phase crystal form of polyvinylidene fluoride-trifluoroethylene, and the method comprises the following steps:
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling and crystallizing;
placing the cooled and crystallized polyvinylidene fluoride-trifluoroethylene wet film in a vacuum to remove the solvent; and
and heating and baking the polyvinylidene fluoride-trifluoroethylene wet film to obtain the polyvinylidene fluoride-trifluoroethylene film.
When the polyvinylidene fluoride-trifluoroethylene wet film is placed in liquid nitrogen, the wet film is cooled at a high speed, so that the solubility of the polyvinylidene fluoride-trifluoroethylene is reduced rapidly and supersaturation is achieved, beta-phase crystal particles formed by crystallization are finer, more crystal nuclei can be obtained, the particles are finer, the beta-phase crystals are easier to turn over in the subsequent polarization process, and the orientation of the polyvinylidene fluoride-trifluoroethylene beta-phase crystals is facilitated.
Optionally, during the evacuation, the humidity of the vacuum environment is 0 to 6%. The humidity is too high, the polar solvent is easy to absorb water, segregation phenomenon is generated, holes are formed on the surface of the polyvinylidene fluoride-tetrafluoroethylene film, and the transparency is reduced.
Optionally, in the vacuum-pumping process, the vacuum-pumping time is more than 1 min. When the vacuumizing time is too short and the vacuumizing speed is too fast, the solvent in the polyvinylidene fluoride-trifluoroethylene wet film is quickly volatilized, holes are easily formed in the polyvinylidene fluoride-trifluoroethylene film, the orientation of the polyvinylidene fluoride-trifluoroethylene film is influenced, the piezoelectric performance of the prepared piezoelectric film is influenced, in addition, the smoothness of the surface of the polyvinylidene fluoride-trifluoroethylene film is also influenced, and the light transmittance is influenced. The slower the vacuum pumping is, the longer the time is, the more uniform the volatilization of the solvent in the polyvinylidene fluoride-trifluoroethylene wet film is, and the smoother the surface is.
Optionally, the annealing temperature is higher than the curie temperature of the polyvinylidene fluoride-trifluoroethylene and lower than the melting temperature of the polyvinylidene fluoride-trifluoroethylene. Annealing in the temperature range can further grow beta-phase crystals in the polyvinylidene fluoride-trifluoroethylene, and the crystallinity of the polyvinylidene fluoride-trifluoroethylene is increased, so that the piezoelectric property is improved. When the temperature is too low, the Curie temperature of the polyvinylidene fluoride-trifluoroethylene is not crossed, no contribution is made to crystal growth, and when the temperature is higher than the melting temperature of the polyvinylidene fluoride-trifluoroethylene, the polyvinylidene fluoride-trifluoroethylene is melted, so that the thickness of a polyvinylidene fluoride-trifluoroethylene film is changed, and the crystallinity and the crystal size of the polyvinylidene fluoride-trifluoroethylene beta-phase crystal formed after annealing are not well controlled.
Optionally, during annealing, the heating rate and the cooling rate are both 1 ℃/min to 1.2 ℃/min. If the temperature rising rate or the temperature reduction rate is too fast, the beta-phase polyvinylidene fluoride-trifluoroethylene crystal generates more defects when the phase change is carried out above the Curie temperature, so that the piezoelectric property and the light transmittance of the polyvinylidene fluoride-trifluoroethylene film are reduced.
Based on the same inventive concept, the present application also provides a piezoelectric film manufactured by the method of manufacturing a piezoelectric film according to the embodiment of the present application.
Based on the same inventive concept, the application also provides a fingerprint identification module, and the fingerprint identification module comprises the piezoelectric film prepared by the preparation method of the piezoelectric film.
Based on the same inventive concept, the application further provides an electronic device, and the electronic device includes the piezoelectric film or the fingerprint identification module.
Therefore, the preparation method of the piezoelectric film is prepared from polyvinylidene fluoride-trifluoroethylene, and the prepared piezoelectric film has higher piezoelectric strain coefficient and higher transparency by controlling the process conditions of polyvinylidene fluoride-trifluoroethylene film formation.
Drawings
To more clearly illustrate the structural features and effects of the present application, a detailed description is given below in conjunction with the accompanying drawings and specific embodiments.
Fig. 1 is a schematic flow chart of a method for manufacturing a piezoelectric film according to an embodiment of the present disclosure.
Fig. 2 is a schematic structural diagram of an electronic device according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It should be apparent that the described embodiments are only some of the embodiments of the present application, and not all embodiments. All other embodiments that can be derived by a person skilled in the art from the embodiments given herein without making any creative effort shall fall within the protection scope of the present application.
Referring to fig. 1, an embodiment of the present application provides a method for manufacturing a piezoelectric film, including:
s101, preparing a polyvinylidene fluoride-trifluoroethylene wet film;
specifically, polyvinylidene fluoride-trifluoroethylene (Poly (vinylidene fluoride-trifluoroethylene)), PVDF-Trfe (PVDF-Trfe) is dissolved in a solvent to obtain a polyvinylidene fluoride-trifluoroethylene solution, and the polyvinylidene fluoride-trifluoroethylene solution is coated or sprayed to prepare the polyvinylidene fluoride-trifluoroethylene wet film. Specifically, the coating method may be, but is not limited to, slit coating.
Specifically, the solvent may be, but is not limited to, a polar solvent, and the polar solvent may be, but is not limited to, Dimethylformamide (DMF), Dimethylacetamide (DMAC), and the like.
Specifically, the weight fraction of polyvinylidene fluoride-trifluoroethylene in the polyvinylidene fluoride-trifluoroethylene solution is 10 wt% to 20 wt%, and more specifically, may be, but is not limited to, 10 wt%, 12 wt%, 15 wt%, 16 wt%, 18 wt%, 20 wt%, and the like. When the concentration of the polyvinylidene fluoride-trifluoroethylene is lower than 10 wt%, the viscosity is too low, the film is easy to collapse, and the film thickness is not easy to control; when the concentration of the polyvinylidene fluoride-trifluoroethylene is lower than 20 wt%, the viscosity is too high, a film is not easy to form, and bubbles are easy to remain in the obtained film, so that the crystallinity of the prepared piezoelectric film is influenced, and the piezoelectric performance of the prepared piezoelectric film is influenced.
Preferably, the weight fraction of polyvinylidene fluoride-trifluoroethylene in the polyvinylidene fluoride-trifluoroethylene solution is 15 wt%, so that even the solution is more easily slit coated and the residual amount of bubbles in the film obtained is small.
In some embodiments, the polyvinylidene fluoride-trifluoroethylene has a molar ratio of vinylidene fluoride units to trifluoroethylene units of 7:3 to 9: 2. Specifically, the molar ratio of vinylidene fluoride units to trifluoroethylene units may be, but is not limited to, 7:3, 7.5:3, 6: 2. 7:2, 8:2, 9:2, etc. Preferably, the molar ratio of the vinylidene fluoride unit to the trifluoroethylene unit is 8:2, so that the piezoelectric strain coefficient of the prepared piezoelectric film is larger and the light transmittance is higher.
In some embodiments, the vinylidene fluoride units and trifluoroethylene units are uniformly distributed in the molecular chain of the polyvinylidene fluoride-trifluoroethylene. For example: in each molecular chain, every two vinylidene fluoride units and every one trifluoroethylene unit are sequentially and alternately arranged; or, in each molecular chain, every three vinylidene fluoride units and one trifluoroethylene unit are sequentially and alternately arranged; or, in each molecular chain, every four vinylidene fluoride units and one trifluoroethylene unit are alternately arranged in sequence. The vinylidene fluoride has stronger dipole moment, so that the prepared piezoelectric film has better piezoelectric performance, and the trifluoroethylene has weaker dipole moment, so that a molecular chain is more stable.
In some embodiments, the weight average molecular weight of the polyvinylidene fluoride-trifluoroethylene is 30 to 100 ten thousand, and specifically, may be, but is not limited to, 30 ten thousand, 40 ten thousand, 50 ten thousand, 60 ten thousand, 70 ten thousand, 80 ten thousand, 90 ten thousand, or 100 ten thousand, and the like.
S102, crystallizing the polyvinylidene fluoride-trifluoroethylene wet film and removing a solvent to obtain a polyvinylidene fluoride-trifluoroethylene film, wherein the polyvinylidene fluoride-trifluoroethylene film comprises a beta-phase crystal form of polyvinylidene fluoride-trifluoroethylene;
specifically, crystallizing the polyvinylidene fluoride-trifluoroethylene wet film and removing the solvent to obtain the polyvinylidene fluoride-trifluoroethylene film, which comprises the following steps:
s1021, placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling and crystallizing;
specifically, the liquid nitrogen cooling time is 20S to 120S, and specifically, the liquid nitrogen cooling time may be, but is not limited to, 20S, 30S, 40S, 50S, 60S, 80S, 90S, 100S, 110S, 120S, and the like. When the polyvinylidene fluoride-trifluoroethylene wet film is placed in liquid nitrogen, the wet film is cooled at a high speed, so that the solubility of the polyvinylidene fluoride-trifluoroethylene is reduced rapidly and supersaturation is achieved, beta-phase crystal particles formed by crystallization are finer, more crystal nuclei can be obtained, the particles are finer, the beta-phase crystals are easier to turn over in the subsequent polarization process, and the orientation of the polyvinylidene fluoride-trifluoroethylene beta-phase crystals is facilitated.
S1022, placing the cooled and crystallized polyvinylidene fluoride-trifluoroethylene wet film in vacuum to remove the solvent; and
specifically, the cooled and crystallized polyvinylidene fluoride-trifluoroethylene wet film is placed in a vacuum drying oven, and is slowly vacuumized for at least 1min, so that the atmospheric pressure of the vacuum drying oven is lower than 5Pa, and the vacuum holding time is 5min to 15 min.
Alternatively, the evacuation time is 1min or more, specifically, 1min to 20min, more specifically, the evacuation time may be, but is not limited to, 1min, 2min, 3min, 4min, 5min, 6min, 7min, 8min, 9min, 10min, 12min, 15min, 18min, 20min, and the like. The evacuation time is too short and the atmospheric pressure is too high to remove most of the solvent.
Most of the solvent in the polyvinylidene fluoride-trifluoroethylene wet film is removed, and the polyvinylidene fluoride-trifluoroethylene wet film is continuously vacuumized, so that the solvent removal effect is not great.
Optionally, the air humidity of the vacuum drying oven is 0 to 6%, excluding 0. Specifically, the air humidity of the vacuum drying oven (vacuum environment) may be 0.0001%, 1%, 2%, 3%, 4%, 6%. The humidity is too high, the polar solvent is easy to absorb water, segregation phenomenon is generated, holes are formed on the surface of the polyvinylidene fluoride-tetrafluoroethylene film, and the transparency is reduced.
Optionally, the vacuum pumping speed is up to 5Pa or less of atmospheric pressure, which requires at least 1min or more. When the vacuumizing time is too short and the vacuumizing speed is too fast, the solvent in the polyvinylidene fluoride-trifluoroethylene wet film is quickly volatilized, holes are easily formed in the polyvinylidene fluoride-trifluoroethylene film, the orientation of the polyvinylidene fluoride-trifluoroethylene film is influenced, the piezoelectric performance of the prepared piezoelectric film is influenced, in addition, the smoothness of the surface of the polyvinylidene fluoride-trifluoroethylene film is also influenced, and the light transmittance is influenced. The slower the vacuum pumping is, the longer the time is, the more uniform the volatilization of the solvent in the polyvinylidene fluoride-trifluoroethylene wet film is, and the smoother the surface is.
Alternatively, the vacuum hold time may be, but is not limited to, 5min, 6min, 7min, 8min, 10min, 12min, 14min, 15min, and the like. The vacuum holding time is too short to remove most of the solvent, the vacuum holding time is too long, most of the solvent in the polyvinylidene fluoride-trifluoroethylene wet film is removed, the vacuum is continuously pumped, and the solvent removal effect is not great.
The polyvinylidene fluoride-tetrafluoroethylene membrane is gradually vacuumized in a low-temperature and low-humidity environment, the solvent is slowly separated out, the surface of the prepared polyvinylidene fluoride-tetrafluoroethylene membrane is smooth and complete in a mild volatilization process, diffuse reflection is reduced, and light transmittance is improved.
S1023, heating and baking the polyvinylidene fluoride-trifluoroethylene wet film to obtain the polyvinylidene fluoride-trifluoroethylene film.
Optionally, the baking temperature is 80 ℃ to 120 ℃; specifically, the baking temperature may be, but not limited to, 80 ℃, 85 ℃, 90 ℃, 100 ℃, 105 ℃, 110 ℃, 115 ℃, 120 ℃ or the like. The baking temperature is too low, the solvent in the polyvinylidene fluoride-trifluoroethylene wet film cannot be completely removed, crystallization of polyvinylidene fluoride-trifluoroethylene during annealing can be influenced by the existence of the solvent, the baking temperature is too high, beta-phase polyvinylidene fluoride-trifluoroethylene wet film crystals in the polyvinylidene fluoride-trifluoroethylene wet film are easy to melt or undergo phase transition, the subsequent orientation of the polyvinylidene fluoride-trifluoroethylene is not facilitated, and the piezoelectric performance of the prepared polyvinylidene fluoride-trifluoroethylene film is influenced.
Optionally, the baking time is 30min to 240 min. Specifically, the baking time may be, but is not limited to, 30min, 50min, 70min, 100min, 130min, 150min, 180min, 200min, 220min, 240min, etc. The baking time is too short to completely remove the solvent in the polyvinylidene fluoride-trifluoroethylene wet film.
S103, annealing the polyvinylidene fluoride-tetrafluoroethylene film for one or more times; and
specifically, the polyvinylidene fluoride-tetrafluoroethylene membrane is heated to the annealing temperature at the heating rate of 1 ℃/min to 1.2 ℃/min, the heat is preserved for 2 hours to 6 hours, and the polyvinylidene fluoride-tetrafluoroethylene membrane is cooled to the room temperature at the cooling rate of 1 ℃/min to 1.2 ℃/min. RetreatThe number of fires may be, but is not limited to, 2, 3, 4, 5, etc. The temperature is increased and decreased for a long time and at a slow rate for many times, particularly when the Curie temperature is crossed, the beta-phase crystals of the polyvinylidene fluoride-tetrafluoroethylene film further grow, the crystallinity is further improved, the surface layer and the internal defects of the polyvinylidene fluoride-tetrafluoroethylene film are repaired, the piezoelectric property and the light transmittance of the polyvinylidene fluoride-tetrafluoroethylene film are improved, and meanwhile, the size change of the crystals is about
To
Therefore, the light transmittance is not obviously reduced, and the light transmittance reduction caused by the crystal size change is far inferior to the light transmittance improvement caused by defect repair, so that the light transmittance can be improved besides the piezoelectric performance by annealing.
Alternatively, the temperature ramp rate and the temperature ramp rate may each be, but are not limited to, 1 deg.C/min, 1.1 deg.C/min, 1.2 deg.C/min, and the like. If the temperature rising rate or the temperature reduction rate is too fast, the beta-phase polyvinylidene fluoride-trifluoroethylene crystal generates more defects when the phase change is carried out above the Curie temperature, so that the piezoelectric property and the light transmittance of the polyvinylidene fluoride-trifluoroethylene film are reduced.
Optionally, the annealing temperature is higher than the curie temperature of the polyvinylidene fluoride-trifluoroethylene and lower than the melting temperature of the polyvinylidene fluoride-trifluoroethylene. Annealing in the temperature range can further grow beta-phase crystals in the polyvinylidene fluoride-trifluoroethylene, and the crystallinity of the polyvinylidene fluoride-trifluoroethylene is increased, so that the piezoelectric property is improved. When the temperature is too low, the Curie temperature of the polyvinylidene fluoride-trifluoroethylene is not crossed, no contribution is made to crystal growth, and when the temperature is higher than the melting temperature of the polyvinylidene fluoride-trifluoroethylene, the polyvinylidene fluoride-trifluoroethylene is melted, so that the thickness of a polyvinylidene fluoride-trifluoroethylene film is changed, and the crystallinity and the crystal size of the polyvinylidene fluoride-trifluoroethylene beta-phase crystal formed after annealing are not well controlled.
The Curie temperature refers to the temperature at which the phase change of the polyvinylidene fluoride-trifluoroethylene beta-phase crystal occurs and the piezoelectric effect disappears after the temperature of the crystal is raised to a certain temperature.
Specifically, the annealing temperature is 132 ℃ to 148 ℃, and more specifically, the annealing temperature may be, but is not limited to, 132 ℃, 135 ℃, 136 ℃, 140 ℃, 142 ℃, 145 ℃, 146 ℃, 148 ℃ and the like. Furthermore, the annealing temperature is 135 ℃ to 144 ℃, and annealing in the temperature range can ensure that the obtained polyvinylidene fluoride-trifluoroethylene has better crystallinity and better piezoelectric property.
Alternatively, the annealing hold time may be, but is not limited to, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours, and the like.
And S104, polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
Specifically, an in-situ corona polarization method is adopted to carry out corona polarization on the polyvinylidene fluoride-tetrafluoroethylene film so as to obtain the piezoelectric film with the beta-phase crystal in unidirectional orientation.
More specifically, a high voltage of 5KV to 20KV is loaded on the electrode wire, so that air is ionized to generate negative ions, a polarization net which is 3mm to 5mm away from the polyvinylidene fluoride-tetrafluoroethylene membrane generates a high voltage of 1.5KV to 5KV, the generated negative ions converge the surface of the polyvinylidene fluoride-tetrafluoroethylene membrane to move and stay on the surface of a polymer, and therefore beta-phase crystals of the polyvinylidene fluoride-tetrafluoroethylene membrane are turned over in the same direction to realize unidirectional orientation, and a piezoelectric membrane with high voltage performance and light transmittance is formed. The voltage is too low, the polyvinylidene fluoride-tetrafluoroethylene membrane cannot be completely polarized, the piezoelectric performance of the prepared piezoelectric membrane is influenced, and the voltage is too high, so that the polyvinylidene fluoride-tetrafluoroethylene membrane is easy to break down.
Alternatively, the time of corona polarization is 5min to 30min, and specifically, the time of corona polarization may be, but is not limited to, 5min, 10min, 15min, 20min, 25min, 30min, and the like. When the corona polarization time is less than 5min, the polarization of the polyvinylidene fluoride-tetrafluoroethylene film is incomplete, and the piezoelectric performance of the polyvinylidene fluoride-tetrafluoroethylene film is influenced.
In addition, besides corona polarization, the polyvinylidene fluoride-tetrafluoroethylene film of the present application can be polarized by other polarization methods such as contact polarization, and the present application is not limited specifically.
Alternatively, the thickness of the prepared piezoelectric film is 6 μm to 30 μm; specifically, the thickness of the piezoelectric film may be, but is not limited to, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 23 μm, 28 μm, 30 μm, or the like. When the thickness of the piezoelectric film is too thin, the intensity of the emitted ultrasonic wave is insufficient and cannot be used well for fingerprint recognition, and when the thickness of the piezoelectric film is too thick, the conditions required for polarization orientation are too severe, for example, when corona polarization is performed, the voltage required is too high.
Optionally, the piezoelectric film has a piezoelectric strain coefficient (D33) of 28pC/N to 40 pC/N; for example, the piezoelectric film has a piezoelectric strain coefficient of 28pC/N, 30pC/N, 32pC/N, 35C/N, 38pC/N, 40pC/N, or the like.
Optionally, the transmittance of the piezoelectric film is greater than 90%; for example, the light transmittance of the piezoelectric film is 91%, 93%, 95%, 96%, 97%, 98%, or the like.
The preparation method of the piezoelectric film is prepared from polyvinylidene fluoride-trifluoroethylene, and the prepared piezoelectric film has a higher piezoelectric strain coefficient and a higher transparency by controlling the molar ratio of the vinylidene fluoride to the trifluoroethylene in the polyvinylidene fluoride-trifluoroethylene, the humidity during crystallization, the vacuumizing time, the annealing temperature and the like.
The embodiment of the application also provides a piezoelectric film, and the piezoelectric film is prepared by the preparation method of the piezoelectric film. The piezoelectric film can be applied to fingerprint identification, capillary vessel identification, blood flow signal detection, skin acoustic resistance testing, gesture identification, distance measurement and the like.
Referring to fig. 2, an embodiment of the present application further provides a fingerprint identification module 100, where the fingerprint identification module 100 includes a piezoelectric film manufactured by the method for manufacturing a piezoelectric film according to the embodiment of the present application.
Referring to fig. 2, an electronic device 200 is further provided in the embodiment of the present application, where the electronic device 200 includes the fingerprint identification module 100 in the embodiment of the present application.
The electronic device 200 of the present application may be, but is not limited to, an electronic device capable of performing fingerprint recognition, face recognition, gesture recognition, distance measurement, and the like, such as a fingerprint recognition device, a face recognition device, a lock, a mobile phone, a tablet computer, a gesture recognition device, and the like.
The piezoelectric film of the present application is further described below by way of specific embodiments.
Example 1
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 1min in a vacuum drying oven with the air humidity of 0.0001% to ensure that the atmospheric pressure of the vacuum drying oven is 5Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1.2 ℃/min for annealing treatment, preserving the heat for 4h, and then cooling to room temperature at the cooling rate of 1.2 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Example 2
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 5min in a vacuum drying oven with the air humidity of 0.0001% to ensure that the atmospheric pressure of the vacuum drying oven is 4Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1.1 ℃/min for annealing treatment, preserving the heat for 4h, and then cooling to room temperature at the cooling rate of 1.1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Example 3
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying oven with the air humidity of 0.0001% to ensure that the atmospheric pressure of the vacuum drying oven is 3Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Example 4
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 20min in a vacuum drying oven with the air humidity of 0.0001% to enable the atmospheric pressure of the vacuum drying oven to be 1Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Example 5
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying box with the air humidity of 3% to ensure that the atmospheric pressure of the vacuum drying box is 3Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Example 6
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying box with the air humidity of 5%, and keeping the atmospheric pressure of the vacuum drying box at 3Pa for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Comparative example 1
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying box with the air humidity of 7%, and keeping the atmospheric pressure of the vacuum drying box at 3Pa for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Comparative example 2
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by adopting slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying box with the air humidity of 10%, and keeping the atmospheric pressure of the vacuum drying box at 3Pa for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Comparative example 3
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying box with air humidity of 13% to enable the atmospheric pressure of the vacuum drying box to be 3Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
Comparative example 4
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying box with air humidity of 13% to enable the atmospheric pressure of the vacuum drying box to be 3Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 130 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 um.
Comparative example 5
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying box with air humidity of 13% to enable the atmospheric pressure of the vacuum drying box to be 3Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 150 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 um.
Comparative example 6
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 1: 1;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 10min in a vacuum drying box with air humidity of 13% to enable the atmospheric pressure of the vacuum drying box to be 3Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 um.
Comparative example 7
A method of manufacturing a piezoelectric film, comprising:
preparing a DMF (dimethyl formamide) solution of polyvinylidene fluoride-trifluoroethylene with the mass fraction of 15 wt%, and coating by slit coating to obtain a polyvinylidene fluoride-trifluoroethylene wet film with the thickness of 120 mu m, wherein the molar ratio of polyvinylidene fluoride to trifluoroethylene is 8: 2;
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling for 30s, slowly vacuumizing for 0.5min in a vacuum drying oven with the air humidity of 0.0001% to ensure that the atmospheric pressure of the vacuum drying oven is 5Pa, and keeping for 10 min;
taking out the polyvinylidene fluoride-trifluoroethylene wet film, and baking for 30min at 80 ℃ to obtain a polyvinylidene fluoride-trifluoroethylene film;
heating the polyvinylidene fluoride-tetrafluoroethylene membrane to 140 ℃ at the heating rate of 1 ℃/min for annealing treatment, preserving heat for 4h, and then cooling to room temperature at the cooling rate of 1 ℃/min; repeating the annealing process for 3 times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
The thickness of the obtained piezoelectric film was measured to be 10 μm.
The piezoelectric films prepared in the above examples and comparative examples were subjected to performance tests, and the test results are shown in table 1 below:
TABLE 1 preparation conditions of examples 1 to 6 and comparative examples 1 to 7 and performance data of the piezoelectric films obtained
The haze and transmittance measurement method comprises the following steps: the measurement is carried out by adopting the national standard GB/T2410-2008.
The piezoelectric coefficient measuring method comprises the following steps: the position D33 value (pC/N) can be calculated according to software by printing an Ag (thickness is 10um) bottom electrode on one side surface of the piezoelectric film, placing the other side of the piezoelectric film on a platform, pressing the piezoelectric film surface by a metal probe with a charge detection function through a spring mechanism by using a certain pressure F (less than 5N), and receiving a charge signal generated by the surface.
The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the present application, and these modifications or substitutions should be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.
Claims (11)
1. A method of manufacturing a piezoelectric film, comprising:
preparing a polyvinylidene fluoride-trifluoroethylene wet film;
crystallizing the polyvinylidene fluoride-trifluoroethylene wet film and removing a solvent to obtain a polyvinylidene fluoride-trifluoroethylene film, wherein the polyvinylidene fluoride-trifluoroethylene film comprises a beta-phase crystal form of polyvinylidene fluoride-trifluoroethylene;
annealing the polyvinylidene fluoride-tetrafluoroethylene film for one or more times; and
and polarizing the polyvinylidene fluoride-tetrafluoroethylene film to obtain the piezoelectric film.
2. The method according to claim 1, wherein the polyvinylidene fluoride-trifluoroethylene has a molar ratio of vinylidene fluoride units to trifluoroethylene units of 7:3 to 9: 2.
3. A method of manufacturing a piezoelectric film according to claim 2, wherein the molecular chain of the polyvinylidene fluoride-trifluoroethylene has a uniform distribution of the vinylidene fluoride units and the trifluoroethylene units.
4. The method for preparing a piezoelectric film according to claim 1, wherein the polyvinylidene fluoride-trifluoroethylene wet film is crystallized and the solvent is removed to obtain the polyvinylidene fluoride-trifluoroethylene film, wherein the polyvinylidene fluoride-trifluoroethylene film comprises a beta-phase crystal form of polyvinylidene fluoride-trifluoroethylene, and comprises the following steps:
placing the polyvinylidene fluoride-trifluoroethylene wet film in liquid nitrogen for cooling and crystallizing;
placing the cooled and crystallized polyvinylidene fluoride-trifluoroethylene wet film in a vacuum to remove the solvent; and
and heating and baking the polyvinylidene fluoride-trifluoroethylene wet film to obtain the polyvinylidene fluoride-trifluoroethylene film.
5. A method of manufacturing a piezoelectric film according to claim 4, wherein the humidity of the vacuum environment during the evacuation is 0 to 6%.
6. A method of manufacturing a piezoelectric film according to claim 4, wherein the evacuation is performed for 1min or more.
7. The method of claim 1, wherein the annealing temperature is higher than the curie temperature and lower than the melting temperature of the pvdf-trifluoroethylene.
8. The method according to claim 7, wherein the temperature increase rate and the temperature decrease rate are both 1 ℃/min to 1.2 ℃/min during the annealing.
9. A piezoelectric film produced by the production method according to any one of claims 1 to 8.
10. A fingerprint identification module comprising a piezoelectric film produced by the production method according to any one of claims 1 to 8.
11. An electronic device comprising the piezoelectric film of claim 9 or comprising the fingerprint recognition module of claim 10.
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Application publication date: 20210323 |