TWI798087B - Method for improving the adhesion of piezoelectric elements - Google Patents

Abstract

Disclosed is 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 particles are piezoelectric materials; coating the slurry on a substrate to form a wet film; performing a vacuum drying step on the wet film under different vacuum degree to reduce the thickness of the wet film; performing a soft baking step on the wet film until the surface is shaped; and performing a hard baking step on the wet film to solidify the wet film to form a piezoelectric element.

Description

Method for Improving Adhesion of Piezoelectric Elements

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

Generally speaking, the fabrication of the fingerprint recognition 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 uses the signal mode of ultrasonic transmission, and the transmission rate and energy attenuation constant of sound waves in various dielectric materials determine the image contrast of the entire fingerprint identification component. Ultrasound conducts sound waves in heterogeneous substances, and the signal will produce behaviors such as absorption and reflection that reduce the total energy. Therefore, high specifications are required to identify the physical form of the entire fingerprint identification film structure.

The piezoelectric layer structure of the fingerprint identification element mainly adopts the slot die coating technology, and the component cost is reduced through the wet printing process. As for the thickness requirement, the basic film thickness requirement depends on the electromechanical conversion coefficient of the piezoelectric layer material.

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

In view of the above, an 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 particles It is a piezoelectric material; the slurry is coated on a substrate to form a wet film; the wet film is subjected to a vacuum drying step under different vacuum degrees to reduce the thickness of the wet film; the wet film is subjected to a The first baking step is to shape the surface of the wet film; and the 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 particle is a copolymer of difluoroethylene and trifluoroethylene.

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

According to one or more embodiments of the present disclosure, wherein 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 includes other solvents with different vapor pressures.

According to one or more embodiments of the present disclosure, 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.

According to one or more embodiments of the present disclosure, wherein 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 percentage of the solute particles is 8-35 wt%, and the sum of the weight percentages of the low boiling point solvent and the high boiling point solvent is 65-92 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 percentage of the low boiling point solvent is 37-46wt%, and the high boiling point solvent The weight percentage is between 63~54wt%.

To sum up, the embodiment of the present invention adds a solvent with a high boiling point, so that other low boiling point solvents in the corresponding slurry can reduce the drying rate of the piezoelectric molecules, and the volume of the low boiling point will be reduced due to the high The existence of boiling point molecules is restricted to reduce the volume change rate of the solvent system, and through the continuous and stable change of molecular volatilization, the overall structure after drying is more continuous, which is used to improve the surface roughness of fingerprint recognition components.

In order to facilitate your review committee to further understand and understand the purpose, shape, structure, device features and effects of the present invention, the following examples are given in conjunction with the drawings, and the detailed description is as follows.

The following disclosure provides different embodiments or examples to implement different features of the provided subject matter. The specific examples of the 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 elements are not limited by the disclosed range or numerical values, but may depend on the process conditions or required requirements of the elements. characteristic. For example, the technical features of the present invention are described using sectional views, which are schematic diagrams of idealized embodiments. Thus, variations in the shapes shown as a result of manufacturing processes and/or tolerances are foreseeable and should not be limiting.

Furthermore, spatial relative terms such as "below", "below", "below", "above" and "above" are for ease of description of the elements depicted in the drawings or the relationship between features; moreover, 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 the copolymer (copolymer) (such as the piezoelectric layer 10 or piezoelectric layer 10a in FIG. 1 or FIG. 2 ) that has been cured by heat treatment, the surface treatment of the polymer by using plasma can improve the microstructure. . That is to say, with the addition of plasma, the roughness of the copolymer surface will be reduced, making the water contact angle (water contact angle, WCA) smaller, so that the materials spread on the surface of the copolymer can be better attached to it , the force between the material molecules 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, causing the silver layer (Ag layer) (such as the silver layer 20 in FIG. 1 or FIG. 2 ) to easily peel off (peeling). question.

Therefore, 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 . FIG. 3 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 fully mixed first, that is, the solute particles 120 are uniformly dissolved in the solvent mixture 130, so that A slurry is formed; wherein, the solute particles 120 are piezoelectric materials, such as ethylene difluoride and ethylene trifluoride copolymer. In an embodiment of the present invention, the solvent mixture 130 is uniformly mixed with a low boiling point solvent and a high boiling point solvent. In addition, the high boiling point solvent is a material with high solubility. The low-boiling-point solvent and the high-boiling-point solvent are independent systems, neither of which reacts with the solute particles 120 . The low boiling point solvent has a different vapor pressure than the high boiling point solvent.

Next, as shown in FIG. 3 , the slurry obtained by fully mixing the solute particles 120 and the solvent mixture 130 is coated on a substrate (not shown in the figure) to form a wet film 110 . Then, a vacuum pump (not shown) can be utilized to carry out a vacuum drying step to the wet film 110 at different vacuum degrees (or vacuum values), so that a large amount of solvent in the wet film 110 evaporates to reduce the thickness of the wet film 110 . It should be particularly noted here that the thickness of the wet film 110' in the figure is in the process of 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 is easy to reach the vapor pressure at a low temperature and volatilizes, so the low boiling point solvent and the high boiling point solvent in the wet film 110 After dissipating, it becomes a thinner 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 distribution. .

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 speed at which the solvent leaves the solute particles 120 will affect the surface roughness of the vacuum drying. If it is dried quickly (fast dry), the surface of the wet film 110' will have obvious rough undulating characteristics, that is, the solute particles 120 are exposed on the surface of the wet film 110' , leading to obvious rough undulations on the surface of the wet film 110 ′, which will form a large water contact angle, and the surface needs to be repaired by atmospheric normal pressure plasma. In order to avoid such problems, the embodiment of the present invention is to reduce the piezoelectric particles in the drying process (ie, the "piezoelectric element" herein) by changing the type and quantity of the solvent on the piezoelectric coating of the fingerprint recognition element (ie, the "piezoelectric element" herein). The so-called "solute particles 120") form the surface roughness. Through this physical property, the surface structure after film formation can be improved, the adhesion between layers can be improved, and the interface loss of ultrasonic transmission can be reduced.

Furthermore, the inventors of this case found that under the same unit volume, the solute particles are evenly dispersed in the wet film layer formed by the solution system, and the solvent molecules will gradually overflow and detach as the vacuum degree increases during the drying process. Run out of the wet film layer. The establishment of a vacuum system has its speed limit. At the beginning of desorption, a large number of solvent molecules participate in the desorption process, and gradually tend to be saturated and stable. This process represents that the process of vacuum drying is not a process of continuous movement at a constant rate. For solute molecules, there will be a process that cannot catch up with the arrangement, resulting in discontinuous fluctuations and high roughness at the liquid-gas interface that is closer to the environment. 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 early stage can be suppressed, and the fast drying mechanism can be reduced to form a relatively continuous wet film surface in the early stage to obtain a smaller water contact angle. However, only using high-boiling-point solvents alone will still cause a large number of solvent molecules to volatilize in the later stage of vacuum drying, and there will be obvious differences in the dissipation between the two periods before and after, so it is necessary to use two solvent systems with high and low boiling points to achieve a balanced atmosphere. fluid balance. In addition, the solvent system with a high boiling point represents a heavy molecular weight. This solvent system and the copolymer will have excessively high bonding characteristics, and cannot meet the film thickness requirements under a specific solid content requirement, so a low boiling point solvent system is required. To adjust the wet printing characteristics.

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

In other embodiments of the present invention, the solute particle 120 is a copolymer of difluoroethylene and trifluoroethylene; the low boiling point solvent is methyl ethyl ketone (MEK) with a boiling point of 80°C; the high boiling point solvent is dimethylacetamide with a boiling point of 166°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 is between 8~35wt %, while (Y+Z) is between 65~92wt%. 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 percent of low boiling point solvent is between 37~46wt%, and the weight percent of high boiling point solvent is between 63~54wt% (referring to Fig. 4), with respect to solute particle 120 (difluoroethylene and trifluoroethylene copolymer ) can form a surface structure with lower roughness.

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

In addition, the generation 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 determining the ratio of the three.

Then, please refer to Fig. 3 again, after vacuum drying, the wet film 110' is subsequently subjected to a first baking step to shape the surface of the wet film 110' to form a wet film 110 ". Finally, the wet film 110 "is A second baking step to cure the wet film "to form a piezoelectric element 110"'. What needs to be explained here is that the baking steps referred to in this embodiment include soft baking and hard baking. It is mainly used to preform materials or wet films, such as providing an environment of 70ﾟC ~ 80ﾟC for 40 to 60 minutes of baking. In the step of hard baking, it is mainly used to cure materials or wet films or to preform For example, bake in an environment of 130ﾟC～150ﾟC for 3 hours～5 hours. In any scheme that can be implemented, those skilled in the art can make equal modifications or adjustments. The present invention does not include Without limitation.

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

Additionally, 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, the embodiments of the present invention add a solvent with a high boiling point, so that other low-boiling point solvents in the corresponding slurry can reduce the drying rate of piezoelectric molecules, and the volume of the low-boiling point will be reduced during the process of gas-liquid equilibrium. Due to the existence of high boiling point molecules, it is restricted to reduce the volume change rate of the solvent system, and through the continuous and stable change of molecular volatilization, the overall structure after drying is more continuous, which is used to improve the surface roughness of fingerprint recognition components.

The above embodiments are only used to illustrate the technical solutions of the present invention without limitation. Although the present invention has been described in detail with reference to preferred embodiments, those skilled 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 solution of the present invention.

10, 10a: Piezoelectric layer 20: silver layer 30: Touch layer 100:Fingerprint identification component 110, 110’, 110”: wet film 110"': piezoelectric element 120: solute particles 130: solvent mixture I~VIII: Curve

In order to make the above and other objects, features, advantages and embodiments of the present invention more understandable, the accompanying drawings are described as follows: 1 to 2 are schematic diagrams illustrating the piezoelectric layer structure of the fingerprint recognition 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 showing the solvent evaporation rate during vacuum drying according to an embodiment of the present invention. FIG. 5 is a schematic diagram showing the solvent evaporation rate during vacuum drying according to another embodiment of the present invention. FIG. 6 is a schematic diagram showing the solvent evaporation 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 the specific features and elements relevant to the invention. In addition, the same or similar reference symbols refer to similar elements and parts in different drawings.

110, 110’, 110”: wet film

110''': piezoelectric element

120: solute particles

130: solvent mixture

Claims (10)

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 particles are piezoelectric materials; coating the slurry on A wet film is formed on a substrate; a vacuum drying step is carried out on the wet film under different vacuum degrees to reduce the thickness of the wet film; a first baking step is carried out on the wet film, and the surface of the wet film is shaping; and performing a second baking step on the wet film to solidify the wet film to form a piezoelectric element. 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. The method for improving the adhesion of piezoelectric elements according to claim 1, wherein the solute particles are copolymers of difluoroethylene and trifluoroethylene. 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 chemically reacts with the solute particles. 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. The method for improving the adhesion of piezoelectric elements according to claim 5, wherein the slurry further includes other solvents with different vapor pressures. 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. The method for improving the adhesion of piezoelectric elements according to claim 2 or 7, wherein the low boiling point solvent is methyl ethyl ketone (MEK), and the high boiling point solvent is dimethylacetamide (DMAC). The method for improving the adhesion of piezoelectric elements as described in Claim 1, wherein in the slurry, the weight percentage of the solute particles is between 8 and 35 wt%, and the weight percentage of the low boiling point solvent and the high boiling point solvent is And between 65~92wt%. The method for improving the adhesion of piezoelectric elements as described in Claim 9, wherein in a solvent mixture composed of the low boiling point solvent and the high boiling point solvent, the weight percentage of the low boiling point solvent is between 37 and 46 wt%, and The weight percent of the high boiling point solvent is between 54-63wt%.

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