Method for local polarization of piezoelectric thin films

Abstract

The application discloses a piezoelectric film local polarization method, comprising the following steps: preparing metal electrodes on both sides of the target polarization area of the film; and performing polarization on the target polarization area of the film after the metal electrodes are prepared, wherein the area of a polarization pressure head of a polarization device is smaller than the area of the target polarization area during the polarization. When the metal electrodes are prepared, a chromium metal layer is first prepared, and then a gold metal layer is prepared on the chromium metal layer. The application has the beneficial effects that: through the method of preparing the metal electrodes on the film first and then performing polarization, and in combination with the setting that the polarization pressure head is slightly smaller than the target polarization area, the area control precision of the polarization area is improved, the application and measurement of the PVDF film in the fields of piezoelectric sensing, sound pickup and thermal reaction are more accurate, and the application field of the PVDF is widened.

Description

Technical Field

[0001] This application relates to the field of thin film local polarization technology, and in particular to a method for local polarization of piezoelectric thin films. Background Technology

[0002] Polyvinylidene fluoride (PVDF) piezoelectric films are a promising smart material with excellent piezoelectric and pyroelectric properties. Utilizing its piezoelectric properties, PVDF films can be used as record player pickups; based on the calibration relationship between its piezoelectric characteristics and applied pressure, it can be used as a pressure sensor for testing flexible surfaces; due to the good electrical output characteristics of piezoelectric films under pressure, this material can also be used as a self-powered functional material for some low-power electronic products. Furthermore, PVDF films have excellent pyroelectric properties; by fabricating PVDF films into temperature sensors, the relationship between its electrical output and temperature can be used to measure ambient temperature or the surface temperature of objects.

[0003] The performance of piezoelectric thin films depends on the level of polarization. Existing local polarization processes for piezoelectric thin films generally use a circular indenter to directly polarize the target area. This type of targeted polarization is prone to producing an outer halo: that is, while the target polarized area achieves good piezoelectric performance, a certain area outside the target polarized area is also polarized. An excessively large polarization halo area interferes with the polarization area of ​​the thin film, seriously affecting the calibration and testing results of the thin film. Summary of the Invention

[0004] This application provides a method for local polarization of piezoelectric thin films to improve the accuracy of polarization area control. The technical solution of this application is as follows:

[0005] A first aspect of this application provides a method for local polarization of a piezoelectric thin film, comprising the following steps:

[0006] Metal electrodes were fabricated in the target polarization regions on both sides of the PVDF thin film;

[0007] The target polarization region after the metal electrode is prepared is polarized by a polarization pressure head of a polarization device, wherein the area of ​​the polarization pressure head is smaller than the area of ​​the target polarization region, and the edge of the polarization pressure head is 0.3 mm to 1 mm away from the edge of the metal electrode on the PVDF film.

[0008] In some embodiments of this application, when preparing the metal electrode, a chromium metal layer is first prepared, and then a gold metal layer is prepared on the chromium metal layer.

[0009] In some embodiments of this application, the thickness of the chromium metal layer ranges from 5 to 20 nm, and the thickness of the gold metal layer ranges from 40 to 100 nm.

[0010] In some embodiments of this application, magnetron sputtering is used to prepare the metal electrode, and the magnetron sputtering parameters for preparing the chromium metal layer are set as follows: gas pressure is 1 Pa, and sputtering power is 10 W / cm². 2 The magnetron sputtering time is 2 minutes.

[0011] In some embodiments of this application, magnetron sputtering is used to prepare the metal electrode, and the magnetron sputtering parameters for preparing the gold metal layer are set as follows: gas pressure is 10 Pa, and sputtering power is 40 W / cm². 2 The magnetron sputtering time is 8 minutes.

[0012] In some embodiments of this application, the thickness of the PVDF film ranges from 9 micrometers to 100 micrometers.

[0013] In some embodiments of this application, the target polarization region is more than 7 mm away from the edge of the PVDF film.

[0014] In some embodiments of this application, when an array of electrodes is fabricated on both sides of a thin film, the polarization method provides uniform control over the polarization of multiple target polarization regions.

[0015] In some embodiments of this application, the polarization method can control the polarization of a single target polarization region individually.

[0016] In a second aspect of this application, an array-type piezoelectric sensor is provided, comprising a polarized PVDF piezoelectric film, wherein the PVDF piezoelectric film is obtained by polarization via the piezoelectric film local polarization method described in the first aspect above.

[0017] The technical solutions provided by the embodiments of this application have at least the following beneficial effects:

[0018] By first preparing a metal electrode bonded to a thin film and then polarizing it, and by setting the polarization pressure head to be slightly smaller than the target polarization region, better accuracy in controlling the polarization region area can be obtained.

[0019] The local polarization method proposed in this application improves the area control accuracy of the polarization region, making the measurement of PVDF thin films in piezoelectric sensing, sound pickup and thermal reaction more accurate, and broadening the application fields of PVDF.

[0020] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application, and do not constitute an undue limitation of this application.

[0022] Figure 1 This is a diagram showing the electric field distribution during polarization.

[0023] Figure 2 This is a flowchart illustrating a piezoelectric thin film local polarization method according to an exemplary embodiment.

[0024] Figure 3 This is a schematic diagram of a structure in which a metal electrode is disposed in a circular target polarization region according to an exemplary embodiment.

[0025] Figure 4 This is a schematic diagram of a structure in which a metal electrode is disposed in the target polarization region of an array, according to an exemplary embodiment. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solutions of this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0027] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0028] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In the description of this application, it should be noted that unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two elements. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0029] The excellent electrical properties of piezoelectric thin films enable them to have a wide range of applications. In the initial stages of film preparation, the interior is mostly α-phase and lacks electrical properties. By applying a high-voltage electric field to polarize the film, the α-phase is transformed into the β-phase, thus giving the film its superior electrical properties. Therefore, the performance of PVDF piezoelectric thin films depends on the level of polarization.

[0030] In existing piezoelectric thin film local polarization processes, the target polarization region is prone to developing an outer halo. The reason for this is that if the pressure head squeezes the thin film too tightly during polarization, it will cause the thin film to deform, reduce the breakdown voltage threshold, and have an adverse effect on the polarization performance.

[0031] However, without forceful compression, a gap can easily exist between the film and the pressure head. After connecting the high-voltage power supply, because the lower region is a bare film with uniform conductivity, the pressure head area experiences a scattering discharge, such as... Figure 1 As shown, therefore, significant polarization also occurs around the target polarization region. Furthermore, the greater the distance between the pressure head and the thin film, the greater the distance the arc travels outward, and the more pronounced the halo region becomes, making it impossible to guarantee the accuracy of the target polarization region.

[0032] Figure 2 This is a flowchart illustrating a local polarization method for a piezoelectric thin film according to an exemplary embodiment. Figure 2 As shown, the piezoelectric thin film local polarization method includes the following steps:

[0033] Step S100: Metal electrodes are fabricated in the target polarization regions on both sides of the PVDF film;

[0034] First, the specifications of the PVDF film need to be selected. The thickness of the PVDF film can range from 9 micrometers to 100 micrometers. In one embodiment of this application, a PVDF film with a length of 100 mm, a width of 20 mm, and a thickness of 25 micrometers is selected for polarization. When setting the target polarization region on the PVDF film, the target polarization region is more than 7 mm away from the edge of the PVDF film to prevent the electrode edge from connecting with the lower electrode and causing leakage from the edge.

[0035] For example, taking a circular polarization region as an example, such as Figure 3 As shown, a target polarization region is selected, and a metal electrode is prepared in the target polarization region. The preparation of the metal electrode requires the preparation of metal electrodes on both sides of the film. The alignment of the upper and lower metal electrodes is determined according to the actual application scenario. The alignment accuracy requirement of this scheme is <5%. The alignment accuracy refers to the percentage of the overlapping area of ​​the upper and lower metal electrodes to the area of ​​a single metal electrode (the upper and lower metal electrodes have the same area).

[0036] Furthermore, the surface of the thin film may have some minor unevenness. After passing through the coated metal electrode, the flatness is better, so during polarization, the polarization pressure head makes better contact with the metal electrode and will not squeeze it.

[0037] The electrodes for the target polarization region can be prepared using either magnetron sputtering or screen printing.

[0038] Optionally, in some embodiments, when preparing the metal electrode, a chromium metal layer is first prepared; then a gold metal layer is prepared on the chromium metal layer.

[0039] The chromium metal layer is primarily used to enhance adhesion to the thin film and to protect the flexible film. Because a certain level of adhesion is required between the metal electrode and the thin film to prevent detachment during high-voltage polarization, chromium can improve the adhesion between the metal and the thin film, thus enhancing bonding strength. Therefore, it is preferable to first deposit the chromium metal layer.

[0040] To ensure the continuity and uniformity of the metal electrode, a certain thickness is required. The thickness cannot be too small; the metal electrode needs to have a certain thickness to prevent cracking under high-voltage polarization. Optionally, the thickness of the metal electrode can be greater than 50 nm, depending on the specific circumstances.

[0041] In one embodiment of this application, the thickness of the chromium metal layer ranges from 5 to 20 nm, and the thickness of the gold metal layer ranges from 40 to 100 nm. As an example, a 50 nm metal electrode is selected, wherein the chromium metal layer is 10 nm and the gold metal layer is 40 nm.

[0042] In some embodiments, magnetron sputtering is used to fabricate the metal electrode. The parameters for magnetron sputtering are typically a gas pressure range of 0.1–10 Pa and a sputtering power range of 1–40 W / cm². 2 The deposition thickness of the electrode is mainly determined by the sputtering time. Higher sputtering power results in higher ion energy, a denser film, and a higher deposition rate. However, excessively high sputtering power can damage the flexible thin film substrate. This application requires obtaining a highly dense metal film without damaging the flexible thin film substrate; therefore, a suitable magnetron sputtering deposition method must be selected.

[0043] Preferably, the magnetron sputtering parameters for preparing the chromium metal layer are set as follows: gas pressure of 1 Pa and sputtering power of 10 W / cm². 2 The magnetron sputtering time is 2 minutes.

[0044] Preferably, the magnetron sputtering parameters for preparing the gold metal layer are set as follows: gas pressure of 10 Pa and sputtering power of 40 W / cm². 2The magnetron sputtering time was 2 minutes. Compared with the settings for preparing the chromium metal layer, the gas pressure and sputtering power were increased when preparing the gold metal layer in order to improve the density of the gold metal layer, thereby improving its conductivity.

[0045] The local polarization method of this application directly prepares metal electrodes on both sides of the thin film. The electrode region where the metal electrodes are prepared has a significant difference in conductivity compared to the surrounding polymer thin film. Therefore, the current mainly flows through the electrode region, ensuring the stability of the target polarization area. In addition, since the metal electrodes have good conductivity and the distance between the metal electrodes is fixed, the polarization pressure head does not need to press the thin film tightly, thus preventing the thin film from deforming.

[0046] The polarized indenter does not require separate control of the distance to the film. It is placed on the film by the gravity of the polarized indenter, which can ensure effective contact between the indenter and the film. Furthermore, since the polarized indenter is very small, its weight will not cause deformation of the film.

[0047] Step S200: Polarize the target polarization region of the thin film after the metal electrode is prepared;

[0048] During polarization, the area of ​​the polarization pressure head of the selected polarization device is smaller than the area of ​​the target polarization region.

[0049] The thin film material with the prepared metal electrode is polarized, and the area of ​​the polarization head of the polarization device is selected to be slightly smaller than the area of ​​the target polarization region.

[0050] Because the polarization indenter is concentric with the target polarization region and the metal electrode, the edge of the polarization indenter and the edge of the electrode on the thin film can be selected to differ in edge size by 0.3-1 mm, preferably 0.5 mm, depending on the electrode's shape and area. This ensures uniform polarization and avoids creepage between the electrode and the thin film. A difference of 0.5 mm in polarization size provides even better uniformity.

[0051] For example, if the target polarization region is circular, the diameter of the polarization indenter needs to be slightly smaller than the diameter of the target polarization region. In one embodiment of this application, the diameter of the target polarization region is 5 mm, the diameter of the polarization indenter is 4 mm, and the edge size difference is 0.5 mm. That is, the diameter of the polarization indenter is preferably 0.8 times the diameter of the target polarization region.

[0052] This is because, even with the same diameter, current can still penetrate from the edge of the target polarization region, expanding the outer halo area. Furthermore, having the same diameter requires very high alignment precision, reducing fabrication efficiency.

[0053] Multiple experiments have confirmed that a polarization indenter slightly smaller than the target polarization region yields better area control. However, if it is too small, it can easily cause local compression, which is detrimental to polarization uniformity. Therefore, the diameter of the polarization indenter needs to be slightly smaller than the diameter of the target polarization region, and the size ratio should be controlled within a certain range.

[0054] The local polarization method of this application improves the area control accuracy of the polarization region, enabling precise control of both the polarization region and its area. This allows for the fabrication of patterned electrodes of arbitrary shapes, such as S-shaped, square-shaped, and irregularly shaped electrodes, meeting the polarization region requirements for complex patterns. Therefore, the method of this application can achieve the polarization region requirements for many simple and complex patterns.

[0055] The local polarization method of this application allows for individual control of the polarization performance of a single polarization region. Optionally, a method of polarizing each target polarization region individually can be adopted, with different parameters set for different target polarization regions. Therefore, polarization units with different performance can be fabricated according to requirements to meet the needs of various operating conditions. It can also realize complex electrode shapes and combinations of different shapes to meet the application needs under different operating conditions.

[0056] Meanwhile, since the polarization region can be precisely controlled, the polarization method of this application can be used to fabricate array electrodes, such as... Figure 3 As shown, a structural design for fabricating multiple polarization units on a single thin film is realized. Since each unit in the array is identical, the polarization method provides unified control over the polarization of multiple target polarization regions during the fabrication of the array electrode.

[0057] An array of piezoelectric sensors can be fabricated by preparing an array of electrodes on a PVDF thin film and then polarizing them.

[0058] Array-type sensing units output the electrical signal of each unit. For microphone applications, this can be achieved by fabricating them on a single thin film. For devices, array-type polarization units on a single thin film offer better performance consistency. Furthermore, by outputting the electrical signal of each unit, array-type sensing units can be used in pressure and temperature sensor applications to monitor pressure / temperature in different areas.

[0059] Based on the wide range of applications for piezoelectric thin films, the local polarization method proposed in this application improves the area control accuracy of the polarization region. This enables more precise measurements of PVDF thin films in piezoelectric sensing, sound pickup, and thermodynamic applications, broadening the application areas of PVDF and accelerating the development of the PVDF industry.

[0060] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A method for local polarization of a piezoelectric thin film, characterized in that, Includes the following steps: Metal electrodes were fabricated in the target polarization regions on both sides of the PVDF thin film; The target polarization region after the metal electrode is prepared is polarized by the polarization pressure head of the polarization device, wherein the area of ​​the polarization pressure head is smaller than the area of ​​the target polarization region, and the edge of the polarization pressure head is 0.3mm-1mm away from the edge of the metal electrode on the PVDF film; When preparing the metal electrode, a chromium metal layer is first prepared, and then a gold metal layer is prepared on the chromium metal layer. The metal electrode was prepared using magnetron sputtering. The magnetron sputtering parameters for preparing the chromium metal layer were set as follows: gas pressure of 1 PA and sputtering power of 10 W / cm². 2 The magnetron sputtering time is 2 minutes; The metal electrode was prepared using magnetron sputtering. The magnetron sputtering parameters for preparing the gold metal layer were set as follows: gas pressure 10 Pa, sputtering power 40 W / cm². 2 The magnetron sputtering time is 8 minutes; The target polarization region is more than 7 mm away from the edge of the PVDF film; The thickness of the chromium metal layer ranges from 5 to 20 nm, and the thickness of the gold metal layer ranges from 40 to 100 nm. The thickness of the PVDF film ranges from 9 micrometers to 100 micrometers.

2. The method according to claim 1, characterized in that, When fabricating array electrodes on both sides of a thin film, the polarization method provides unified control over the polarization of multiple target polarization regions.

3. The method according to claim 1, characterized in that, The polarization method allows for individual control of the polarization of a single target polarization region.

4. An array-type piezoelectric sensor, characterized in that, The invention includes a polarized PVDF piezoelectric film, which is obtained by polarization using the piezoelectric film local polarization method according to any one of claims 1-3.

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