Piezoelectric vibrator and piezoelectric device
The piezoelectric vibrator employs a lower-diffusion-coefficient surface film to mitigate interdiffusion and adhesion of metallic foreign matter, ensuring stable vibration and frequency in piezoelectric devices.
Patent Information
- Application Number
- JP2025022209
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-02-14
- Publication Date
- 2026-08-26
AI Technical Summary
Foreign matter, particularly metallic fragments, adheres firmly to the main electrode film of piezoelectric devices due to interdiffusion, leading to vibration inhibition and frequency deviation, which conventional cleaning methods fail to effectively address.
A piezoelectric vibrator with a surface film on the main electrode made of a material with a lower diffusion coefficient than the main electrode, such as tungsten, tantalum, or molybdenum, to reduce interdiffusion and adhesion of metallic foreign matter.
The surface film effectively minimizes the risk of interdiffusion and adhesion of foreign matter, maintaining the vibration characteristics and target frequency of the piezoelectric device.
Smart Images
Figure 2026136610000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a piezoelectric vibrating piece having an electrode structure excellent in the effect of reducing foreign matter adhesion, and a piezoelectric device using the same.
Background Art
[0002] As a representative example of a piezoelectric device, there is one using a piezoelectric vibrating piece that vibrates in thickness shear. This device has excitation electrodes on the front and back of the piezoelectric vibrating piece. The excitation electrode is composed of an underlayer film and a main electrode film laminated thereon. A typical example of the underlayer film is a chromium thin film, and typical examples of the main electrode film are a gold thin film or a silver thin film.
[0003] In the case of a piezoelectric device that vibrates in thickness shear, when foreign matter adheres to the excitation electrode, the thickness shear vibration is inhibited by this foreign matter and the vibration characteristics deteriorate, and this foreign matter comes off during the use of the piezoelectric device and the frequency deviates from the target frequency, and various problems such as this occur. To prevent this, screening processes such as cleaning the manufacturing environment of the piezoelectric device and blowing ionized gas onto the excitation electrode while strongly exciting the piezoelectric device during the manufacturing process of the piezoelectric device to remove foreign matter are performed.
Summary of the Invention
Problems to be Solved by the Invention
[0004] Foreign matter can be made of various materials. Furthermore, there are various mechanisms for the adhesion of foreign matter to the main electrode film. The inventors of this application have diligently studied the mechanisms of foreign matter adhesion. As a result of this study, it was found that, in the case of metallic foreign matter, as explained with reference to the plan view of the piezoelectric device in Figure 2(A) and the enlarged view (SEM photograph) of portion M in Figure 2(A) shown in Figure 2(B), there exists foreign matter X that adheres relatively firmly to the main electrode film 13b of the piezoelectric device 10 through interdiffusion with the main electrode film 13b. Typical examples of foreign matter X include fragments of gold or silver thin films remaining in the deposition apparatus used to deposit metal thin films for excitation electrodes. In Figure 2, 10 represents a quartz crystal oscillator as a piezoelectric device, 11 represents an AT-cut quartz crystal diaphragm, and 15 represents a container housing the quartz crystal diaphragm as a piezoelectric diaphragm. Further details will be explained in the section on embodiments.
[0005] Foreign matter X, which adheres relatively firmly to the main electrode film due to interdiffusion, is difficult to remove by the screening described above and enters the market as incorporated into the completed piezoelectric device. Furthermore, foreign matter X may detach from the main electrode film for some reason during use, leading to malfunctions. Therefore, relatively firmly adhering foreign matter can cause serious problems, and some kind of countermeasure is desirable. This application has been made in view of the above points, and therefore, the object of this application is to provide a piezoelectric vibrator having an electrode structure that is superior to conventional ones in reducing foreign matter adhesion, and a piezoelectric device using the same. [Means for solving the problem]
[0006] To achieve this objective, according to the first invention of this application, a piezoelectric vibrating piece comprising a base film and a main electrode film formed on the base film, The present invention is characterized by comprising a surface film on the main electrode film, which is made of a material having a smaller diffusion coefficient than the main electrode film and reduces the interdiffusion between the main electrode film and metallic foreign matter. According to the second invention of this application, in a piezoelectric device including a piezoelectric vibrating piece, excitation electrodes including a base film provided on the front and back surfaces of the piezoelectric vibrating piece and a main electrode film laminated thereon, and a container containing the piezoelectric vibrating piece having the excitation electrodes, On the main electrode film, a surface film made of a material having a smaller diffusion coefficient than the main electrode film and reducing the mutual diffusion between the main electrode film and metallic foreign matter is provided, which is characterized in that.
[0007] In carrying out each of the above inventions, the main electrode film is preferably a thin film of gold or a thin film of silver, and the surface film is preferably selected from a thin film of tungsten, a thin film of tantalum, and a thin film of molybdenum. In carrying out each of the above inventions, if the film thickness of the surface film is too thin, the effect of reducing foreign matter cannot be obtained, and if it is too thick, it will cause the characteristics of the piezoelectric device to deteriorate, so it is determined in consideration of these. Specifically, when the film thickness of the surface film is represented as t and the film thickness of the main electrode film is represented as T, the film thickness t of the surface film is preferably t < T, preferably 0.05T ≤ t ≤ 0.3T, more preferably 0.05T ≤ t ≤ 0.2T, and even more preferably 0.05T ≤ t < 0.1T. Specifically, the film thickness of the surface film is preferably 20 nm to 100 nm, and more preferably 20 nm to 50 nm.
[0008] In the manufacturing process of the piezoelectric device, there is a process for adjusting the frequency of the piezoelectric device to the target frequency. The current main frequency adjustment method for a piezoelectric device vibrating in thickness shear is a method of shaving the surface of the excitation electrode with an ion gun to adjust the frequency to the target frequency. Therefore, when the object to which the present invention is applied is a piezoelectric device that performs frequency adjustment by an ion gun, the film thickness t of the surface film should be such that it can remain after being removed by the ion gun. Alternatively, as a frequency adjustment method, there is also a method of attaching a predetermined metal to the excitation electrode by vapor deposition or the like to adjust the frequency to the target frequency. In the case of this method, the material to be attached is preferably the same material as the surface film or another material that satisfies the conditions for preventing diffusion as referred to in the present invention for frequency adjustment.
[0009] In carrying out each of the above inventions, it is preferable that the piezoelectric vibrator vibrates through thickness sliding vibration. This is because, since thickness sliding vibration is greatly affected by the adhesion of foreign matter, it is preferable to apply the present invention to it. As a thickness sliding vibration, it is preferable to have an AT-cut quartz vibrator. This is because AT-cut quartz vibrators are widely used as reference signal sources in electronic devices, and reducing the adhesion of foreign matter to them would be industrially useful.
[0010] In carrying out the above inventions, it is preferable to provide the surface film on the excitation electrodes on both the front and back surfaces of the piezoelectric vibrator. However, it is also possible to provide it only on the excitation electrode on one side of the piezoelectric vibrator. Furthermore, the piezoelectric device comprises an electrode portion corresponding to the vibrating part, i.e., an excitation electrode, and an electrode portion corresponding to the lead-out wiring drawn out from there to the end of the piezoelectric vibrating piece. It is preferable to provide the surface film on both the electrode portion corresponding to the vibrating part and the portion corresponding to the lead-out wiring, but in some cases, the surface film may be provided only on the electrode portion corresponding to the vibrating part. [Effects of the Invention]
[0011] According to the piezoelectric vibrator and piezoelectric device of this invention, since the excitation electrode is provided with a predetermined surface film, the risk of metallic foreign matter that easily interdiffuses with the main electrode film interdiffusing and adhering to the excitation electrode can be reduced. Therefore, it is possible to provide a piezoelectric vibrator having an electrode structure that is superior to conventional ones in reducing foreign matter adhesion, and a piezoelectric device using the same. [Brief explanation of the drawing]
[0012] [Figure 1] This is a diagram illustrating the piezoelectric vibrator and piezoelectric device of the embodiment. [Figure 2] These figures illustrate the problem and the key features of the present invention. In particular, Figure (A) is a plan view showing the relationship between the foreign substance X and the piezoelectric device 10 to illustrate the problem, and Figure (B) is a diagram (SEM observation photograph) illustrating the adhesion of the foreign substance X. [Modes for carrying out the invention]
[0013] Embodiments of the piezoelectric vibrator and piezoelectric device of this invention will be described below with reference to the drawings. Note that the figures used in this description are only schematic representations to the extent necessary to understand the invention. Furthermore, in the figures used in this description, similar components are indicated with the same number, and their descriptions may be omitted. Also, the structural examples and materials used described below are merely preferred examples within the scope of this invention. Therefore, the present invention is not limited to the embodiments described below.
[0014] Figure 1 is a diagram illustrating the piezoelectric vibrator and piezoelectric device of the embodiment. Specifically, (A) is a plan view of the piezoelectric device 10, (B) is a cross-sectional view of the piezoelectric device along the PP line in (A), and (C) is an enlarged cross-sectional view of the electrode structure showing the N portion in (B). The piezoelectric device 10 of this embodiment comprises a piezoelectric vibrating piece 11, an excitation electrode 13 including a base film 13a and a main electrode film 13b laminated thereon, which are provided on the front and back surfaces of the piezoelectric vibrating piece 11, a container 15 enclosing the piezoelectric vibrating piece 11 equipped with the excitation electrode 13, and a lid member 17. Furthermore, a feature of the present invention is that the main electrode film 13b is provided with a surface film 13c made of a material with a smaller diffusion coefficient than the main electrode film, which reduces the mutual diffusion between the main electrode film 13b and metallic foreign matter (such as foreign matter X shown in Figure 2). The surface film 13c may also be considered as one of the components of the excitation electrode 13.
[0015] In this case, the piezoelectric vibrator 11 is an AT-cut quartz crystal vibrator with a rectangular shape in plan view. However, the piezoelectric vibrator can be of any other vibrating configuration, and can be various types that reduce the problem of foreign matter adhesion. Its shape is not limited to a rectangle. In this case, the excitation electrode 13 is rectangular in shape when viewed from above. However, the shape of the excitation electrode may of any other shape. The base film 13a of the excitation electrode 13 is made of an arbitrary metal film, for example, a chromium thin film, and the main electrode film 13b is made of an arbitrary metal film, for example, a gold thin film or a silver thin film. The chromium thin film as the base film and the gold thin film and silver thin film as the main electrode film are preferable based on the achievements in the field of piezoelectric devices. However, the base film may be other materials such as a titanium thin film, and the main electrode film may be other materials such as an aluminum thin film. The film thickness of the base film 13a is, for example, several nm to several tens of nm. The film thickness of the main electrode film 13b is, for example, several hundred nm.
[0016] In addition, a lead-out wiring 19 is provided from one end of the excitation electrode 13 to one short side of the piezoelectric vibrating piece 11. The lead-out wiring 19 may have the same configuration as the excitation electrode 13. The surface film 13c is preferably composed of, for example, a thin film selected from a tungsten thin film, a tantalum thin film, and a molybdenum thin film. Tungsten, tantalum, and molybdenum each have a considerably smaller diffusion coefficient compared to gold and silver, which are frequently used as main electrode film materials, so they are preferable for achieving the object of the present invention.
[0017] The diffusion coefficients of the above-mentioned metals that can form the surface film 13c and the main electrode film 13b are shown below. The source is the database DICE of the National Institute for Materials Science, a National Research and Development Agency. The data is at a temperature of 1273K. Diffusion coefficient of W: 2.20E-29 / m^2 / sec Diffusion coefficient of Ta: 2.85E-11 / m^2 / sec Diffusion coefficient of Mo: 1.06E-19 / m^2 / sec Diffusion coefficient of Au: 1.77E-13 / m^2 / sec Diffusion coefficient of Ag: 2.15E-12 / m^2 / sec
[0018] In this case, the container 15 is composed of a well-known ceramic package including a concave portion 15a, a main body portion 15b, a flange portion 15c, an adhesive pad 15d, and an external connection terminal 15e. The specific structure of each part is as follows, for example. The recess 15a is rectangular in plan view enclosing the piezoelectric vibrating piece 11. The main body portion 15b is made of ceramic and rectangular in plan view including the recess 15a. The flange portion 15c is formed of a metal ring surrounding the recess 15a and also serving as a part of the sealing member. Two bonding pads 15d are provided at one end of the bottom surface of the recess 15a. A predetermined number of external connection terminals 15e are provided on the outer bottom surface of the container 15 for connecting the piezoelectric device 10 to an arbitrary electronic device (not shown). The bonding pads 15d and the external connection terminals 15e are connected to each other by vias or castellations not shown. The piezoelectric vibrating piece 11 is connected and fixed to the bonding pads 15d of the container 15 via a conductive adhesive 21 at the position of the lead-out wiring 19. Therefore, in this case, it has a cantilever support structure. The lid member 17 is joined to the flange portion 15c by a method according to the sealing method. Therefore, the piezoelectric vibrating piece 11 is hermetically sealed in an arbitrary atmosphere in the container 15.
[0019] Next, the operation and effects of this invention will be described below. In the case of a conventional structure without a surface film, foreign substances made of metal such as Au fragments and Ag fragments are in a state of directly contacting the Au electrode or Ag electrode which is the main electrode film 13b. That is, the foreign substances are typically attached to the Au electrode or Ag electrode by van der Waals force. In this state, when some high heat is applied to the piezoelectric device in the manufacturing process of the piezoelectric device, for example, the heat during the curing of the conductive adhesive or the heat for degassing the piezoelectric device before sealing, the foreign substances adhere (diffusion bonding) to the main electrode film by mutual diffusion. As a result, a foreign substance X (see FIG. 2) that adheres (diffusion bonds) relatively firmly to the main electrode is generated. On the other hand, in this embodiment, since the surface film 13c composed of a material selected from a tungsten thin film, a tantalum thin film, and a molybdenum thin film is provided on the main electrode film 13b, the risk of the above mutual diffusion can be reduced, so the risk of generating the foreign substance X can be reduced.
[0020] In the embodiments described above, piezoelectric resonators, specifically quartz crystal resonators, were given as examples of applications of the present invention. However, the piezoelectric device referred to in the present invention is not limited to piezoelectric resonators, but can be various devices such as piezoelectric oscillators, where the adhesion of foreign matter is a problem. Furthermore, the container structure described above is just one example; a piezoelectric device having a cylindrical metal container, a piezoelectric device comprising a flat plate-shaped base and a cap-shaped lid member enclosing a piezoelectric vibrator, etc., are also possible. [Explanation of Symbols]
[0021] 10: Piezoelectric device of the embodiment 11: Piezoelectric vibrator 13: Excitation electrode 13a: Base film 13b: Main electrode film 13c: Surface film 15: Container 15a: Recess 15b: Main body 15c: Embankment 15d: Adhesive pad 15e: External connection terminal 17: Lid component 19: Wiring pull-out 21: Conductive adhesive
Claims
1. A piezoelectric vibrating piece comprising a base film and a main electrode film formed on the base film, A piezoelectric vibrating piece characterized by comprising a surface film on the main electrode film, the surface film being made of a material having a smaller diffusion coefficient than the main electrode film and reducing the interdiffusion between the main electrode film and metallic foreign matter.
2. The piezoelectric vibrating piece according to claim 1, characterized in that the piezoelectric vibrating piece vibrates through thickness sliding vibration, the main electrode film is a thin film of gold or a thin film of silver, and the surface film is selected from a thin film of tungsten, a thin film of tantalum, and a thin film of molybdenum.
3. The piezoelectric vibrating piece according to claim 1 or 2, characterized in that, when the thickness of the surface film is denoted as t and the thickness of the main electrode film is denoted as T, the thickness of the surface film t is 0.05T ≤ t ≤ 0.3T.
4. The piezoelectric vibrating piece according to claim 1 or 2, characterized in that, when the thickness of the surface film is denoted as t and the thickness of the main electrode film is denoted as T, the thickness of the surface film t is 0.05T ≤ t ≤ 0.2T.
5. A piezoelectric device comprising a piezoelectric vibrator, excitation electrodes including a base film and a main electrode film laminated thereon, provided on the front and back surfaces of the piezoelectric vibrator, respectively, and a container enclosing the piezoelectric vibrator having the excitation electrodes, A piezoelectric device characterized by comprising a surface film on the main electrode film, the surface film being made of a material having a smaller diffusion coefficient than the main electrode film and reducing interdiffusion between the main electrode film and metallic foreign matter.
6. The piezoelectric device according to claim 5, characterized in that the piezoelectric vibrating piece vibrates through thickness sliding vibration, the main electrode film is a thin film of gold or a thin film of silver, and the surface film is selected from a thin film of tungsten, a thin film of tantalum, and a thin film of molybdenum.
7. The piezoelectric device according to claim 5 or 6, characterized in that, when the thickness of the surface film is denoted as t and the thickness of the main electrode film as T, the thickness of the surface film t is 0.05T ≤ t ≤ 0.3T.
8. The piezoelectric device according to claim 5 or 6, characterized in that, when the thickness of the surface film is denoted as t and the thickness of the main electrode film is denoted as T, the thickness of the surface film t is 0.05T ≤ t ≤ 0.2T.