CN114883476A - Method for improving adhesion of piezoelectric element - Google Patents

Abstract

A method for improving adhesion of a piezoelectric element, comprising: fully mixing solute particles, a low boiling point solvent and a high boiling point solvent to form a slurry, wherein the solute particles are piezoelectric materials; coating the slurry on a substrate to form a wet film; carrying out a vacuum drying step on the wet film under different vacuum degrees to reduce the thickness of the wet film; carrying out soft baking on the wet film to shape the surface of the wet film; and carrying out a hard baking step on the wet film to solidify the wet film to form the piezoelectric element.

Description

Methods for improving the adhesion of piezoelectric elements

technical field

The present invention relates to a fingerprint identification element, in particular to a method for improving the adhesion of piezoelectric elements in the fingerprint identification element.

Background technique

Generally speaking, the fabrication of the fingerprint identification element on the TFT array substrate usually adopts a wet coating process to complete the film layer of the entire element. At present, there is an ultrasonic fingerprint identification technology that adopts the signal mode of ultrasonic conduction, and the transmission rate and energy attenuation constant of the sound wave in each medium material determine the image comparison of the entire fingerprint identification element. Ultrasonic waves conduct sound waves in inhomogeneous materials, and the signals will absorb and reflect to reduce the total energy. Therefore, high specifications are required to require the physical form of the entire fingerprint identification film structure.

The piezoelectric layer structure of the fingerprint identification device mainly adopts the slot die coating technology, and the cost of the device is reduced through the wet printing process. As for the thickness requirements, there are basic film thickness requirements according to the electromechanical conversion coefficient of the piezoelectric layer material.

Next, please refer to FIGS. 1 to 2 . FIGS. 1 to 2 are schematic diagrams illustrating the piezoelectric layer structure of the fingerprint identification element in the prior art. As shown in FIG. 1 to FIG. 2 , the fingerprint identification element 100 includes a touch layer 30 , a silver layer 20 , and a piezoelectric layer 10 or a piezoelectric layer 10 a , wherein the material of the piezoelectric layer 10 or the piezoelectric layer 10 a is, for example, a copolymer Copolymer. When a corresponding conductive layer (eg Ag) and insulating protective material are stacked on the surface of the piezoelectric layer 10 or the piezoelectric layer 10a, the adhesion between the coating of the piezoelectric layer 10 or the piezoelectric layer 10a and the adjacent layers will be affected. Affects the energy transfer of ultrasonic waves. For example, FIG. 1 shows that the piezoelectric layer 10 has voids (as indicated by circles) inside or at the interface, which will cause ultrasonic reflection and affect signal transmission. In addition, FIG. 2 shows that the surface of the piezoelectric layer 10a is not flat, so that the piezoelectric layer 10a cannot be in close contact with the adjacent silver layer 20, which will also affect the signal transmission.

Therefore, how to provide a device and method that can solve the above problems is an important issue that the industry needs to think about.

SUMMARY OF THE INVENTION

In view of the above, one aspect of the present disclosure provides a method for improving the adhesion of piezoelectric elements, comprising: fully mixing solute particles, a low-boiling point solvent and a high-boiling point solvent to form a slurry, wherein the solute The particles are piezoelectric materials; the slurry is coated on a substrate to form a wet film; a vacuum drying step is performed on the wet film under different vacuum degrees to reduce the thickness of the wet film; A first baking step is performed to shape the surface of the wet film; and a second baking step is performed on the wet film to solidify the wet film to form a piezoelectric element.

According to one or more embodiments of the present disclosure, the high boiling point solvent is a material with high solubility.

According to one or more embodiments of the present disclosure, the solute particles are copolymers of vinylidene fluoride and trifluoroethylene.

According to one or more embodiments of the present disclosure, the low-boiling point solvent and the high-boiling point solvent are independent systems with each other, and neither chemically reacts with the solute particles.

According to one or more embodiments of the present disclosure, the low boiling point solvent and the high boiling point solvent have different vapor pressures.

According to one or more embodiments of the present disclosure, the slurry further comprises other solvents having different vapor pressures.

According to one or more embodiments of the present disclosure, the boiling point of the low boiling point solvent is less than 100°C, and the boiling point of the high boiling point solvent is greater than 140°C.

According to one or more embodiments of the present disclosure, the low boiling point solvent is methyl ethyl ketone (MEK), and the high boiling point solvent is dimethylacetamide (DMAC).

According to one or more embodiments of the present disclosure, the weight percent of the solute particles ranges from 8 to 35 wt %, and the sum of the weight percent of the low boiling point solvent and the high boiling point solvent ranges from 65 to 92 wt %.

According to one or more embodiments of the present disclosure, in a solvent mixture composed of the low-boiling point solvent and the high-boiling-point solvent, the weight percent of the low-boiling-point solvent is 37-46 wt %, and the high-boiling-point solvent has a weight percentage of 37-46 wt %. The weight percentage is between 63 and 54 wt %.

To sum up, in the embodiment of the present invention, by adding a solvent with a high boiling point, other low boiling point solvents in the corresponding slurry can reduce the drying rate of piezoelectric molecules, and in the process of gas-liquid equilibrium, the volume of low boiling point will be reduced. Restricted by the existence of high boiling point molecules, the change rate of the solvent system volume is reduced, and the continuous and stable change of molecular volatilization makes the dried overall structure more continuous to improve the surface roughness of the fingerprint identification element.

Description of drawings

In order to make the above-mentioned and other objects, features, advantages and embodiments of the present invention more easily understood, the descriptions of the accompanying drawings are as follows:

1 to 2 are schematic diagrams illustrating the piezoelectric layer structure of the fingerprint identification element in the prior art.

FIG. 3 is a schematic diagram illustrating a method for improving the adhesion of piezoelectric elements according to an embodiment of the present invention.

FIG. 4 is a schematic diagram illustrating the solvent volatilization rate during vacuum drying according to an embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating the solvent volatilization rate during vacuum drying according to another embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating the solvent volatilization rate during vacuum drying according to another embodiment of the present invention.

In accordance with common practice, the various features and elements in the drawings are not drawn to scale, but are drawn in order to best represent specific features and elements relevant to the present invention. Furthermore, the same or similar reference numerals are used to refer to similar elements and parts among the different figures.

Reference number:

10, 10a: Piezoelectric layer

20: Silver Layer

30: touch layer

100: Fingerprint recognition element

110, 110’, 110”: wet film

110"': Piezoelectric element

120: Solute Particles

130: Solvent mixture

I to VIII: Curves

Detailed ways

In order to facilitate your reviewers to have a further understanding and understanding of the purpose, shape, structure and device features of the present invention and their effects, the following examples are given in conjunction with the drawings.

The following disclosure provides different embodiments or examples for implementing different features of the provided subject matter. The specific examples of components and arrangements described below are for the purpose of simplifying the present disclosure and are not intended to be limiting; the size and shape of the components are not limited by the disclosed ranges or values, but may depend on the processing conditions of the components or the desired characteristic. For example, technical features of the invention are described using cross-sectional illustrations that are schematic illustrations of idealized embodiments. Thus, variations in the shapes of the illustrations due to manufacturing processes and/or tolerances are foreseeable and should not be limited thereto.

Furthermore, spatially relative terms such as "below", "below", "below", "above" and "above" are used to facilitate the description of the elements depicted in the drawings or relationship between features; further, spatially relative terms encompass different orientations of elements in use or operation in addition to the orientation depicted in the illustrations.

First of all, it should be noted that for a copolymer that has been cured by heat treatment (such as the piezoelectric layer 10 or the piezoelectric layer 10a in FIG. 1 or FIG. 2 ), the surface treatment of the polymer by plasma can improve the microstructure . That is to say, with the addition of plasma, the roughness of the copolymer surface will be reduced, so that the water contact angle (WCA) will become smaller, so that the material laid on the copolymer surface can better adhere to it. , the intermolecular forces of the material can be closer to each other, and the Van der Waals force can be exerted to achieve sufficient bonding strength. If the surface of the copolymer is very rough, the effective area where the silver (Ag) atoms can contact the copolymer will be reduced, which will cause the silver layer (such as the silver layer 20 in FIG. 1 or FIG. 2 ) to easily peel off (peeling). question.

Therefore, the embodiments of the present invention provide a method for improving the adhesion of piezoelectric elements to solve the above problems. Hereinafter, the method for improving the adhesion of the piezoelectric element according to the embodiment of the present application will be described with reference to the drawings.

First, please refer to FIG. 3 , which is a schematic diagram illustrating a method for improving the adhesion of piezoelectric elements according to an embodiment of the present invention. As shown in FIG. 3 , in the method for improving the adhesion of piezoelectric elements according to an embodiment of the present invention, the solute particles 120 and a solvent mixture 130 are firstly mixed sufficiently, that is, the solute particles 120 are uniformly dissolved in the solvent mixture 130 . A slurry is formed; wherein, the solute particles 120 are piezoelectric materials, such as vinylidene fluoride and trifluoroethylene copolymer. In the embodiment of the present invention, the solvent mixture 130 is formed by uniformly mixing a low boiling point solvent and a high boiling point solvent. In addition, the high boiling point solvent is a material having high solubility. The low-boiling-point solvent and the high-boiling-point solvent are independent systems with each other, and neither chemically reacts with the solute particles 120 . The low boiling point solvent and the high boiling point solvent have different vapor pressures.

Next, as shown in FIG. 3 , a slurry obtained by fully mixing the solute particles 120 and the solvent mixture 130 is coated on a substrate (not shown) to form a wet film 110 . Then, a vacuum pump (not shown) can be used to perform a vacuum drying step on the wet film 110 under different vacuum degrees (or vacuum values), so that a large amount of solvent in the wet film 110 is volatilized to reduce the thickness of the wet film 110 . It should be noted here that the thickness of the wet film 110' in the figure is constantly changing during the vacuum drying step. For example, in the vacuum drying step, the volatilization rate of the solvent is affected by the boiling point. With the increase of the vacuum value, the solvent easily reaches the vapor pressure at a low temperature and volatilizes. Therefore, the low-boiling point solvent and the high-boiling point solvent in the wet film 110 are partially After escaping, it becomes a thin wet film 110'. That is to say, the overall film thickness of the wet film 110 will be greatly reduced, because the saturated vapor pressure of the solvent causes a large amount of solvent to be spilled by the pump, and the remaining wet film 110 ′ has a higher density of solute particles 120 distributed .

In addition, as shown in Figure 3, the volatilization rate of the solvent will be affected by the boiling point. With the increase of the vacuum value, the solvent can easily reach the vapor pressure at low temperature and volatilize. The rate at which the solvent detaches from the solute particles 120 will affect the surface roughness of the vacuum drying. If it is fast dried, the surface of the wet film 110 ′ will have obvious rough undulation characteristics, that is, the solute particles 120 are exposed on the surface of the wet film 110 ′. , causing the surface of the wet film 110 ′ to have obvious rough undulations, which will form a larger water contact angle, and the surface needs to be repaired by atmospheric atmospheric plasma subsequently. In order to avoid such a problem, the embodiment of the present invention reduces the amount of piezoelectric particles (ie, piezoelectric particles) during the drying process by changing the type and quantity of the solvent in the piezoelectric coating of the fingerprint identification element (ie, the “piezoelectric element” herein). The surface roughness formed by the "solute particles 120" herein). Through this physical property, the surface structure after film formation is improved, the adhesion between layers is improved, and the interface loss of ultrasonic transmission is reduced.

Further, the inventor of the present case found that under the same unit volume, the solute particles are uniformly dispersed in the wet film layer formed by the solution system, and the solvent molecules will gradually escape and escape as the vacuum degree increases during the drying process. Run to the outside of the wet film layer. The establishment of a vacuum system is limited by its rate. At the beginning, the desorption is caused by a large number of solvent molecules participating in the desorption process, which gradually tends to be saturated and stable. This process means that the process of vacuum drying is not a process of continuous movement at the same rate. For the solute molecules, there will be a process that cannot catch up with the arrangement, resulting in discontinuous fluctuations in the liquid-gas interface closer to the environment, resulting in high roughness. the surface of the wet film layer. If a solvent with a high boiling point is introduced, the rapid volatilization of the solvent with a low boiling point in the initial stage can be suppressed, and the fast dry mechanism can be reduced to form a more continuous wet film surface in the initial stage to obtain a smaller water contact angle. However, only using high-boiling point solvent alone will cause a large amount of solvent molecules to volatilize in the later stage of vacuum drying, and there will be a significant difference in the escape between the two periods. Gas-liquid movement balance. In addition, with the high boiling point solvent system representing a heavier molecular weight, the solvent system and the copolymer will have too high bonding characteristics, and cannot meet the film thickness requirements under the specific solid content requirements, so a low boiling point solvent system is required. to adjust the wet printing characteristics.

Therefore, in order to achieve the effect of fast drying of the wet film 110 and avoid the defect of surface roughness caused by fast drying, the inventor further proposes other embodiments and describes them as follows.

In other embodiments of the present invention, the solute particles 120 are made of vinylidene fluoride and trifluoroethylene copolymer; the low boiling point solvent is butanone (MEK) with a boiling point of 80° C.; DMAC). When the weight percentage of the solute particles 120 is X wt %; the weight percentage of the low boiling point solvent is Y wt %; the weight percentage of the high boiling point solvent is Z wt %, X+Y+Z=100% and X ranges from 8 to 35 wt % %, while (Y+Z) ranges from 65 to 92 wt%. In addition, if the proportion of Y is higher than Z, the volatilization rate of the system will be too fast; on the contrary, if the proportion of Z is higher than Y, the volatilization rate of the system will be too slow, so in the solvent mixture composed of low boiling point solvent and high boiling point solvent In 130, the weight percentage of the low boiling point solvent is between 37 and 46 wt %, while the weight percentage of the high boiling point solvent is between 63 and 54 wt % (refer to FIG. 4 ). ) can form a lower roughness surface structure.

In other embodiments, the high and low boiling point solvents may also be in different proportions, and the higher the boiling point of the solvent, the higher the proportion will show a more stable volatilization effect. This can refer to FIG. 4, which is a schematic diagram of the solvent volatilization rate during vacuum drying according to an embodiment of the present invention, illustrating the solvent volatilization rate during vacuum drying, wherein curve I represents a high boiling point solvent; curve II represents a low boiling point solvent; curve III represents the mixed solvent. It can be seen from Figure 4 that, compared with the case of only high or low boiling point solvent, the mixed solvent has a relatively stable volatilization rate and can form a surface structure with lower roughness. In addition, FIG. 5 is a schematic diagram illustrating the volatilization rate of the solvent during vacuum drying according to another embodiment of the present invention. In the embodiment of FIG. 5, curve IV represents the high boiling point solvent; curve V represents the low boiling point solvent; curve VI represents the mixed solvent; in the solvent mixture 130 composed of the low boiling point solvent and the high boiling point solvent, the proportion of Y is 55-67 wt%, while the proportion of Z is 45-33 wt%. It can also be seen from FIG. 5 that, compared with the case of only high or low boiling point solvent, the mixed solvent has a relatively stable volatilization rate and can form a surface structure with lower roughness. In addition, FIG. 6 is a schematic diagram illustrating the solvent volatilization rate during vacuum drying according to another embodiment of the present invention. As the low boiling point solvent, ethylene glycol monoethyl ether with a boiling point of 135°C is used; as the high boiling point solvent, dimethylacetamide (DMAC) with a boiling point of 166°C is used. In the embodiment of FIG. 6, the curve VII represents the high boiling point solvent; the curve VIII represents the low boiling point solvent; the curve VIIII represents the mixed solvent; in the solvent mixture 130 composed of the low boiling point solvent and the high boiling point solvent, the proportion of Y is 15-85wt%, while the proportion of Z is 85-15wt%. It can also be seen from Figure 6 that it is found that the volatilization rate has little difference under different ratio conditions, and the formed surface structure roughness does not change significantly.

In addition, the generation state of hydrogen bonds between the solute particles 120 and the polar solvents such as the high and low boiling point solvents is also an influencing factor for determining the ratio of the three.

Next, referring to FIG. 3 again, after vacuum drying, a first baking step is subsequently performed on the wet film 110 ′ to shape the surface of the wet film 110 ′ to form the wet film 110 ″. Finally, the wet film 110 ″ is subjected to A second baking step cures the wet film '' to form a piezoelectric element 110'''. It should be noted here that the baking steps referred to in this embodiment include soft baking and hard baking. In other feasible solutions, a multi-stage baking program can also be used, wherein, in the soft baking step, It is mainly used to preform the material or wet film, for example, it is provided to bake in the environment of 70℃～80℃ for 40～60 minutes. For example, baking is provided in an environment of 130° C. to 150° C. for 3 hours to 5 hours. In any solution that can be implemented accordingly, those skilled in the art can make equal modifications or adjustments, and the present invention is not limited here.

Additionally, in other embodiments, the slurry further includes other solvents with different vapor pressures.

In addition, in other embodiments, the boiling point of the low boiling point solvent is less than 100°C, and the boiling point of the high boiling point solvent is greater than 140°C.

To sum up, in the embodiment of the present invention, by adding a high boiling point solvent, other low boiling point solvents in the corresponding slurry can reduce the drying rate of piezoelectric molecules, and in the process of gas-liquid equilibrium, the low boiling point solvent can be reduced. The volume will be restricted by the existence of high boiling point molecules, reducing the rate of change of the volume of the solvent system, and through the continuous and stable change of molecular volatilization, the overall structure after drying is made more continuous, which is used to improve the surface roughness of the fingerprint identification element. .

The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced. Without departing from the spirit and scope of the technical solutions of the present invention.

Claims (10)

1. A method for improving the adhesion of a piezoelectric element, comprising: fully mixing the solute particles, the low boiling point solvent and the high boiling point solvent to form a slurry, wherein the solute particles are piezoelectric materials; coating the slurry on the substrate to form a wet film; performing a vacuum drying step on the wet film under different vacuum degrees to reduce the thickness of the wet film; subjecting the wet film to a first baking step to shape the surface of the wet film; and A second baking step is performed on the wet film to cure the wet film to form a piezoelectric element. 2 . The method for improving the adhesion of piezoelectric elements according to claim 1 , wherein the high-boiling point solvent is a material with high solubility. 3 . 3 . The method for improving the adhesion of piezoelectric elements according to claim 1 , wherein the solute particles are copolymers of vinylidene fluoride and trifluoroethylene. 4 . 4 . The method for improving the adhesion of piezoelectric elements according to claim 3 , wherein the low-boiling point solvent and the high-boiling point solvent are independent systems, and neither of them chemically interacts with the solute particles. 5 . reaction. 5 . The method for improving the adhesion of piezoelectric elements according to claim 1 , wherein the low-boiling point solvent and the high-boiling point solvent have different vapor pressures. 6 . 6 . The method for improving the adhesion of piezoelectric elements according to claim 5 , wherein the paste further comprises other solvents with different vapor pressures. 7 . 7 . The method for improving the adhesion of piezoelectric elements according to claim 1 , wherein the boiling point of the low boiling point solvent is less than 100° C., and the boiling point of the high boiling point solvent is greater than 140° C. 8 . 8. The method for improving the adhesion of piezoelectric elements according to claim 2 or 7, wherein the low-boiling solvent is methyl ethyl ketone (MEK), and the high-boiling solvent is dimethylacetamide ( DMAC). 9 . The method for improving the adhesion of piezoelectric elements according to claim 1 , wherein the weight percentage of the solute particles is between 8 and 35 wt %, and the ratio of the low-boiling point solvent and the high-boiling point solvent is between 8 and 35 wt %. The sum of the weight percentages is between 65 and 92 wt %. 10 . The method for improving the adhesion of piezoelectric elements according to claim 9 , wherein in a solvent mixture composed of the low boiling point solvent and the high boiling point solvent, the weight of the low boiling point solvent is 10 . The percentage is 37-46 wt %, and the weight percentage of the high boiling point solvent is 54-63 wt %.

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