JP2005318477A - Piezoelectric vibrating piece, electrode forming method thereof, and piezoelectric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element piece having a thickness-shear vibration capable of exhibiting a high vibration energy confinement effect without processing a piezoelectric substrate into a convex shape.
A quartz crystal resonator element has a convex cross section in which excitation electrodes provided on main surfaces of a flat AT-cut quartz crystal substrate are thinned from a central portion toward an end portion. Thus, it has a structure in which three electrode films 6 to 8 are laminated. Each electrode film is formed in a desired pattern by discharging droplets 20 in which conductive metal fine particles are dispersed from the inkjet head 19 onto the main surface of the crystal substrate.
[Selection] Figure 1

Description

  The present invention relates to a piezoelectric vibration piece such as a quartz crystal having a thickness-shear vibration mode as a main vibration, and a piezoelectric device such as a piezoelectric vibrator on which the piezoelectric vibration piece is mounted, and further relates to a method of forming electrodes of the piezoelectric vibration piece.

  In general, piezoelectric devices such as piezoelectric vibrators that can be mounted on a circuit board that meet the demands for miniaturization and thickness reduction are cantilevered at the base end. Many supporting structures are used. In particular, in a thickness-shear vibration mode piezoelectric vibrator, when a rectangular thin piezoelectric vibrating piece is formed into a convex shape in which the thickness gradually decreases from the center to the end, the amount of attenuation of vibration displacement at the end is reduced. Since it becomes large, the effect of confining vibration energy in the central part of the resonator element is enhanced. Therefore, the piezoelectric vibrator can improve the frequency characteristics such as the CI value and the Q value, and the size of the piezoelectric vibrating piece is smaller than a normal one even at a relatively high frequency, and thus the piezoelectric device can be miniaturized. There is an advantage (see, for example, Patent Document 1).

  Conventionally, such a convex-shaped piezoelectric element piece is formed by, for example, mechanical polishing using a barrel polishing apparatus, or a chemical processing method by wet etching using an etching solution is known (for example, (See Patent Document 2). In addition, we proposed a processing method in which the main surface of the piezoelectric element piece is wet-etched stepwise to process it into a staircase shape that approximates a convex shape, and this staircase shape is further processed into a convex shape by sandblasting or a polishing machine. (For example, see Patent Document 3).

  The electrode of the piezoelectric vibrator is usually formed by depositing an electrode material on the surface of the piezoelectric element piece by vacuum vapor deposition or sputtering (see, for example, Patent Document 4), or an electrode material film using photolithography technology. It can also be formed by patterning. Recently, a liquid in which metal nanoparticles composed of fine conductive metal particles such as gold and silver having a particle size of nano level are dispersed in a dispersion medium such as an organic solvent is used as an ink on the surface of a substrate by an inkjet method. A method of directly applying and forming electrodes and wiring patterns has been developed (see, for example, Patent Documents 5 and 6).

Japanese Patent Laid-Open No. 11-355094 JP 2001-285000 A JP 2003-168941 A JP 2002-344281 A Japanese Patent Laid-Open No. 2003-136991 JP 2003-231306 A

  However, the above-described methods using vacuum deposition and sputtering require expensive and large-sized machinery and equipment for using a vacuum pump, a vacuum chamber, etc., which requires many man-hours, complicated operations, lowers productivity, and reduces manufacturing costs. Is high. The patterning method using the photolithography technique also requires many steps such as exposure / development of the resist film, etching / cleaning of the electrode material film, and as a result, the productivity is lowered and the manufacturing cost is increased.

  Furthermore, both of these methods require exposure masks and vapor deposition masks, and electrode / circuit pattern masters to produce them, which not only requires much time and cost, but also a slight design change. It cannot be easily dealt with. Moreover, a metal mask used for vacuum deposition or sputtering has technical problems that it is difficult to design a complicated or fine electrode pattern and a floating electrode cannot be formed.

  In addition, if the surface is uniformly flat, it is easy to accurately form the electrode film in a desired pattern using these methods, but the convex curved surface of the piezoelectric vibrating piece processed into a convex shape is easy. When there is such a height difference, it is difficult to form the electrode film in a desired pattern accurately and uniformly. In particular, the smaller and smaller the piezoelectric vibrating piece, the more difficult it is to maintain and improve shape accuracy and dimensional accuracy.

  Therefore, the present invention has been made in view of the above-described conventional problems, and its purpose is to confine high vibration energy without processing the piezoelectric vibrating piece into a convex shape in which it is difficult to form an accurate pattern of the electrode film. An object of the present invention is to provide a piezoelectric vibrating piece of thickness-shear vibration that can exert an effect.

  Furthermore, an object of the present invention is to provide a piezoelectric device that can improve frequency characteristics particularly in terms of CI value, Q value, and the like, and can be made smaller than before by providing such a piezoelectric element piece. .

  Another object of the present invention is that the electrode of the piezoelectric vibrating piece of the thickness-shear vibration can be formed in a desired pattern, and the man-hour is reduced without using an expensive and large vacuum apparatus / equipment or mask means. It is an object of the present invention to provide a method that can reduce and simplify the work.

  According to the present invention, in order to achieve the above object, a piezoelectric substrate having flat front and back main surfaces and excitation electrodes formed on the front and back main surfaces of the piezoelectric substrate are provided. There is provided a piezoelectric vibrating piece having a convex cross section that becomes thinner from a central portion toward an end portion.

  In this way, by making the excitation electrode into a convex shape cross section, the amount of vibration displacement attenuation at the end of the piezoelectric vibrating piece is increased and vibration is caused at the center as in the case where the piezoelectric substrate has a convex shape cross section. It has been confirmed by the present inventor that the effect of confining energy can be enhanced as will be described later. Further, since the piezoelectric substrate is a flat plate, its processing is easy and inexpensive, and it can be manufactured with high dimensional and shape accuracy at low cost.

  In one embodiment, the excitation electrode has a laminated structure composed of a plurality of electrode films, and the plurality of electrode films are laminated so that the outer dimension of the upper electrode film is smaller than that of the lower electrode film. Thus, an excitation electrode having a convex cross section that becomes thinner from the central portion toward the end portion can be obtained.

  Furthermore, according to the present invention, by mounting this piezoelectric vibrating piece on a package, the frequency characteristics such as the Q value can be improved, and the size of the piezoelectric vibrating piece can be reduced even at a relatively high frequency. Since it can be made smaller than a normal one, a piezoelectric device that can be miniaturized can be realized.

  According to another aspect of the present invention, a first electrode film having a predetermined electrode pattern is formed by discharging droplets in which conductive metal fine particles are dispersed to the front and back main surfaces of a flat piezoelectric substrate, The droplets are ejected onto the first electrode film, and one or more second electrode films are laminated so that the outer dimension of the upper electrode film is smaller than that of the lower electrode film. Thus, there is provided a method for forming an electrode of a piezoelectric vibrating piece in which excitation electrodes having a convex cross section that becomes thinner from the central portion toward the end portion are formed on the front and back main surfaces of the piezoelectric substrate.

  Since the ink-jet method is used to form a film on a flat substrate surface, each electrode film can be formed in a desired pattern with a desired pattern accurately and with high accuracy. A piezoelectric vibrating piece having an excitation electrode that can be made uniform and thicker than the prior art and has a desired convex cross section can be manufactured. Moreover, since the film can be formed in the atmosphere, each electrode film can be formed more easily and with less man-hours without the need for an expensive and large vacuum apparatus / equipment and mask as in the conventional method described above. Improvement of productivity and reduction of manufacturing cost can be realized.

  As the conductive metal fine particles, various conventionally known metal nanoparticles such as gold and silver can be used. In particular, the silver fine particles exhibit good adhesion when the piezoelectric substrate is quartz, so that the water repellent treatment and the base film on the substrate surface as in the conventional method are not required.

  In one embodiment, each electrode film is formed by ejecting droplets according to bit map format pattern data, so that even a fine-sized electrode can be precisely formed.

  In another embodiment, in the step of discharging droplets to the front and back main surfaces of the piezoelectric substrate to form the first electrode film, the extraction electrode from the excitation electrode is simultaneously formed at the same time as the first electrode film. And the wiring which connects them can be formed in the front and back main surface of a piezoelectric substrate. Of course, the film thickness of the extraction electrode and the wiring can be adjusted, and in the process of forming the second electrode film, it can be made thick by laminating an additional electrode film thereon.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
1A and 1B show an embodiment of a quartz crystal resonator element according to the present invention in which the thickness shear vibration mode is a main vibration. The quartz crystal resonator element 1 of the present embodiment has excitation electrodes 3 and 3 at substantially the center of each main surface of the front and back surfaces of a rectangular AT-cut quartz crystal substrate 2. A pair of extraction electrodes 4, 4 are provided at one longitudinal end of the quartz crystal vibrating piece 1, and are connected to corresponding excitation electrodes 3, 3 via wirings 5, 5, respectively.

  Each of the excitation electrodes 3 and 3 has a three-layer structure in which three electrode films 6 to 8 are stacked. The lowermost first electrode film 6 has an external pattern of a desired excitation electrode, and is disposed substantially at the center of each main surface of the quartz substrate 2. The second electrode film 7 of the intermediate layer provided thereon is smaller in outer dimension than the first electrode film 6 and is disposed at the approximate center. Furthermore, the third electrode film 8 of the uppermost layer provided thereon is smaller in outer dimension than the second electrode film 7 and is arranged at the approximate center. Due to the laminated structure of these electrode films, the excitation electrodes 3 and 3 have a convex cross section that becomes thinner from the center to the end.

  FIG. 2 shows a crystal resonator 9 as an example of a piezoelectric device on which the crystal resonator element 1 of FIG. 1 is mounted. Similarly to the conventional crystal resonator, the quartz crystal resonator element 1 has, for example, connection electrodes 12 on the bottom surface of the cavity corresponding to the lead electrodes 4 and 4 in the cavity 11 of the rectangular box package 10 made of a ceramic material. It is fixed and supported in a cantilever manner by bonding with a conductive adhesive 13. The package 10 is hermetically sealed with a metal lid 14 bonded to the top thereof.

  The excitation electrodes 3 and 3 are formed by a film forming method using an ink jet method, as will be described below with reference to FIGS. 3 and 4 show a preferred embodiment of the electrode forming method according to the present invention in the order of its steps. In the present embodiment, the case where the first to third electrode films 6 to 8 are formed on one main surface 15 of the quartz substrate 2 will be described.

  In advance, image data is created for each of the first to third film forming regions 16 to 18 corresponding to the respective electrode films to be formed on the main surface 15 of the quartz crystal substrate 2, and these are converted into binary data, and then converted into bits. Creates dot pattern data for the map method. As shown in FIG. 3A, the first film formation region 16 includes film formation regions of the extraction electrode 4 and the wiring 5 that are formed simultaneously with the first electrode film 6.

  On the other hand, a metal particle dispersion is prepared by dispersing conventionally known conductive metal fine particles such as fine gold and silver having a nano-size particle size in an appropriate dispersion medium. As the conductive metal fine particles, silver is particularly good in adhesion to quartz, and when used for a quartz substrate as in this embodiment, it is advantageous because the liquid repellency of the substrate surface does not need to be modified in advance. As the dispersion medium, an organic solvent having low volatility such as tetradecane is preferable. In addition, if the surface of the conductive metal fine particles is previously coated with an appropriate dispersant, aggregation in the metal particle dispersion can be prevented, and stable dispersion can always be achieved.

  First, the first electrode film 6 is formed in the first film formation region 16. As shown in FIG. 4A, an inkjet head 19 is arranged above the quartz substrate 2, and the fine droplets 20 of the metal particle dispersion are ejected based on the dot pattern data and dropped onto the first film formation region 16. To do. In the present embodiment, the first electrode film 6 is formed in a uniform film thickness by applying the droplets repeatedly through a three-stage ejection process. The ink jet head 19 may be either a piezo type or a thermal type used in a normal ink jet printer.

  In the first ejection step, as shown in FIGS. 3-1 (B) and 4 (B), the droplets L1 are formed on the quartz substrate 2 so as not to contact or overlap each other after landing on the quartz substrate main surface 15. It discharges with the fixed pitch larger than the diameter after each landing along the width direction and a longitudinal direction. After the droplet L1 is discharged over the entire first film formation region 16, the dispersion medium is removed by performing a drying process using, for example, a hot plate, an electric furnace, or lamp annealing. At this stage, it is not necessary to completely remove the dispersion medium. Therefore, it is sufficient that the drying process is carried out in the atmosphere at about 100 ° C. for several minutes. Further, the drying process can be omitted.

  Next, in the second ejection step, the respective droplets L2 are ejected at the same pitch and the same ejection amount as in the first ejection step so that they do not contact or overlap each other after landing on the quartz substrate main surface 15. As shown in FIGS. 3A and 4C, each droplet L2 is in the same position as each droplet L1 in the first ejection step in the width direction of the quartz substrate 2 and in the longitudinal direction. Drops to fill the gap in the middle position of each droplet L1. After the droplet L2 is discharged to the entire first film formation region 16, a drying process is similarly performed to remove the dispersion medium.

  Next, in the third ejection step, each droplet L3 is positioned between the droplets L1 and L2 in the width direction of the quartz substrate 2 as shown in FIGS. 3-1D and 4D. The droplets are dropped at a constant pitch and with the same discharge amount as in the first and second discharge steps so as to fill the gap and overlap each other in the longitudinal direction. After the droplet L3 is discharged over the entire first film formation region 16, a drying process is similarly performed to remove the dispersion medium.

  Thus, after apply | coating the said metal-particle dispersion liquid to the 1st film-forming area | region 16 whole, heat processing and / or light processing are performed, and as shown to FIGS. 3-1 (E) and FIG. The electrode film 6 is baked. The heat treatment and light treatment are performed in the atmosphere using, for example, a hot plate, an electric furnace, lamp annealing, etc., as in the case of the drying treatment, thereby completely removing the dispersion medium. When the surface of the conductive metal fine particles is coated with a dispersant, the dispersant can also be completely removed simultaneously by firing at a temperature of about 300 ° C., for example.

  Next, the second electrode film 7 is formed in the second film formation region 17 on the first electrode film 6. As in the case of the first electrode film 6 described above, the droplets L1 to L3 are overcoated as shown in FIGS. 3-1 (F) and FIG. Alternatively, light treatment is performed and baking is performed. As a result, as shown in FIGS. 3-1 (G) and 4 (G), the second electrode film 7 is laminated on the first electrode film 6 with a uniform film thickness.

  Further, the third electrode film 8 is formed in the third film formation region 18 on the second electrode film 7. As in the case of the first and second electrode films 6 and 7, the droplets L1 to L3 are overcoated as shown in FIGS. 3-1 (H) and 4 (H) by a three-stage ejection process, and Firing is performed by heat treatment and / or light treatment. As a result, the second electrode film 8 is laminated on the second electrode film 7 with a uniform thickness, and the excitation electrode 3 shown in FIG. 1 is formed on the main surface 15 of the crystal substrate 2.

  According to the present invention, the excitation electrode 3 is similarly formed on the opposite main surface of the quartz substrate 2 by the ink jet method. Thereby, the crystal vibrating piece 1 of the present invention shown in FIG. 1 is obtained.

  The preferred embodiments of the present invention have been described in detail above. However, as will be apparent to those skilled in the art, the present invention can be implemented with various modifications and changes within the technical scope thereof. .

Using the electrode forming method of the above example, the quartz crystal resonator element of the present invention was manufactured under the following conditions, and its vibration energy confinement effect was tested. As a comparative example, a quartz crystal vibrating piece in which a conventional flat excitation electrode was formed on the same quartz crystal substrate was manufactured.
AT cut quartz substrate dimensions: 1.0 x 2.0 mm
Electrode pattern: 0.5 x 1.0 mm
Metal particle dispersion: 60% by weight of ULVAC silver ink
Dispersion medium: Tetradecane droplet discharge amount: 7.5 pl
Droplet size after landing: Diameter 100μm
Minimum bitmap: 10 μm
Firing conditions: 300 ° C x 30 minutes in air

  Each quartz crystal vibrating piece was excited by applying a predetermined voltage, and the amount of displacement of the surface of each quartz vibrating piece caused by the excitation was measured in relation to the distance from the base end where the extraction electrode was formed. The measurement results are shown in FIG. In the figure, the quartz crystal resonator element of the present invention indicated by the solid line has a significantly larger displacement than the quartz crystal resonator element of the comparative example indicated by the broken line, particularly in the central region where the excitation electrode is formed. It can be seen that the confinement effect is improved.

FIG. 4A is a plan view showing a quartz crystal resonator element according to the present invention, and FIG. FIG. 2 is a cross-sectional view of a crystal resonator on which the crystal resonator element of FIG. (A)-(D) figure is a top view which shows the process of forming the 1st electrode film of the electrode for excitation of FIG. 1 in order of a process, respectively. FIGS. 4E to 4H are plan views showing a process of forming second and third electrode films of the excitation electrode in FIG. (A)-(H) figure is sectional drawing of FIG. 3 (A)-(H), respectively. The diagram which shows the displacement amount at the time of excitation in the surface of the quartz crystal vibrating piece by this invention by the relationship with the distance from a base end part compared with the conventional quartz crystal vibrating piece.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Crystal vibrating piece, 2 ... Crystal board, 3 ... Excitation electrode, 4 ... Extraction electrode, 5 ... Wiring, 6 ... 1st electrode film, 7 ... 2nd electrode film, 8 ... 3rd electrode film, 9 ... Crystal Vibrator, 10 ... Package, 11 ... Empty, 12 ... Connection electrode, 13 ... Conductive adhesive, 14 ... Lid, 15 ... Main surface, 16 ... First film formation region, 17 ... Second film formation region, 18 ... 3rd film-forming area | region, 19 ... Inkjet head, 20 ... Micro droplet.

Claims (8)

  A piezoelectric substrate having a flat front and back main surface and excitation electrodes formed on the front and back main surfaces of the piezoelectric substrate, wherein the excitation electrode is thinned from the center to the end. A piezoelectric vibrating piece having a cross section.   2. The piezoelectric device according to claim 1, wherein the excitation electrode is formed by laminating a plurality of electrode films so that an outer dimension of the electrode film on the upper side is smaller than that on the lower side of the electrode film. Vibrating piece. Droplets in which conductive metal fine particles are dispersed are ejected onto the front and back main surfaces of a flat piezoelectric substrate to form a first electrode film having a predetermined electrode pattern;
The droplets are ejected onto the first electrode film to stack one or more second electrode films so that the outer dimension of the upper electrode film is smaller than that of the lower electrode film. By doing
A method for forming an electrode of a piezoelectric vibrating piece, comprising forming excitation electrodes having a convex cross section that becomes thinner from a central portion toward an end portion on each of the front and back main surfaces of the piezoelectric substrate.   4. The method for forming an electrode of a piezoelectric vibrating piece according to claim 3, wherein each of the electrode films is formed by discharging the droplets according to pattern data in a bitmap format.   By discharging the droplets onto the main surfaces of the front and back surfaces of the piezoelectric substrate, the first electrode film is formed, and at the same time, the lead electrodes from the excitation electrodes and the wirings connecting them are connected to the main and front surfaces of the piezoelectric substrate. The method of forming an electrode of a piezoelectric vibrating piece according to claim 3 or 4, wherein the electrode is formed on a surface.   6. The method for forming an electrode of a piezoelectric vibrating piece according to claim 3, wherein the conductive metal fine particles are silver and the piezoelectric substrate is quartz.   A piezoelectric vibrating piece, comprising: a piezoelectric substrate having a flat front and back main surface; and an excitation electrode formed by the method according to claim 3 on each of the front and back main surfaces of the piezoelectric substrate.   A piezoelectric device comprising: the piezoelectric vibrating piece according to claim 1; and a package on which the piezoelectric vibrating piece is mounted.

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