JP2016054363A - Piezoelectric element and method of manufacturing piezoelectric device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element in which generation of swelling of a metal film is suppressed, and also to provide a method of manufacturing a piezoelectric device.SOLUTION: Frequency adjustment films 23a, 23b comprise: a first chrome layer formed on tip sides of two vibration arm parts 12a, 12b extended from a base part of a crystal piece 15; a silver layer formed on the first chrome layer; a second chrome layer formed on the silver layer; and a chromium oxidized film formed on the surface of the second chrome layer. Invasion of oxygen is inhibited by the oxidized film, and oxygen is prevented from reaching the first chrome layer through grain boundary of the silver layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piezoelectric element including a crystal piece and a metal film on the crystal piece, and a method for manufacturing a piezoelectric device including the piezoelectric element as a main component. Hereinafter, a tuning fork-type bending quartz crystal vibrating element (hereinafter abbreviated as “vibrating element”) will be described as an example of a piezoelectric element, and a quartz crystal resonator will be described as an example of a piezoelectric device.

  The vibration element is used, for example, as a reference signal source or a clock signal source. A typical vibration element includes a crystal piece and a metal film formed on the crystal piece. The crystal piece has a portion that becomes a base portion and a portion that becomes two vibrating arm portions extending from the base portion. A frequency adjustment film made of a metal film is formed on the tip side of the two vibrating arm portions (see, for example, Patent Document 1). The resonance frequency of the vibration element is adjusted by cutting the frequency adjustment film with a laser or an ion gun.

  As shown in FIG. 6A, the frequency adjustment film 80 in the related technique 1 includes a chrome layer 81 formed on the crystal piece 85 and a silver layer 82 formed on the chrome layer 81. The reason why the silver layer 82 is used is that the frequency adjusting film 80 also serves as a wiring between the electrodes, so that good conductivity is required. The reason for using the chromium layer 81 is to improve the adhesion between the silver layer 82 and the crystal piece 85.

JP 2014-045255 A (FIG. 7) JP-A-2005-136575 (paragraphs 0005 to 0006)

  However, the vibration element of Related Art 1 has the following problems.

  The vibration element is mounted on the element mounting member via a conductive adhesive made of a thermosetting resin. The conductive adhesive is cured by heating the vibration element mounted on the element mounting member in, for example, a nitrogen atmosphere. At this time, as shown in FIG. 6B, when oxygen slightly contained in the nitrogen atmosphere reaches the chromium layer 81 through the grain boundary of the silver layer 82, chromium oxide is generated (for example, Patent Documents). 2). As a result, since chromium oxide has poor adhesion to the silver layer 82, so-called “bulges 83” are generated at the interface between the silver layer 82 and the chromium layer 81. The swelling 83 causes the frequency adjustment film 80 to peel off, and when the frequency adjustment film 80 peels off, the frequency of the vibration element becomes defective. Here, “fluff” is not limited to the actually convex shape, and includes discoloration that is a precursor of blistering.

  Therefore, an object of the present invention is to provide a piezoelectric element or the like that can suppress the occurrence of blistering of a metal film.

The piezoelectric element according to the present invention is
In a piezoelectric element comprising a crystal piece and a metal film formed on the crystal piece,
The metal film includes a first chromium layer formed on the crystal piece, a silver or gold layer formed on the first chromium layer, a second chromium layer formed on the silver or gold layer, It consists of a chromium oxide film formed on the surface of this second chromium layer,
It is characterized by that.

  According to the present invention, since the surface of the second chromium layer on the silver or gold layer is covered with the chromium oxide film, the entry of oxygen is blocked by the chromium oxide film. Therefore, oxygen can be prevented from reaching the first chromium layer through the grain boundary of the silver or gold layer, so that the blistering of the metal film can be suppressed.

FIG. 3 is a plan view showing the resonator element according to the first embodiment. 2A is a cross-sectional view taken along line IIa-IIa in FIG. 1, and FIG. 2B is a part of a cross-sectional view taken along line IIb-IIb in FIG. 3A is a schematic cross-sectional view showing a state in which the vibration element of FIG. 1 is mounted on an element mounting member, and FIG. 3B is a vacuum seal of the element mounting member of FIG. 3A with a lid member. It is a schematic sectional drawing which shows a state. FIG. 6 is a process diagram illustrating a method for manufacturing the resonator element according to the first embodiment and a method for manufacturing a crystal resonator having the resonator element according to the first embodiment as a main component. The frequency adjustment film | membrane in the vibration element of Embodiment 2 is shown, FIG. 5 [A] is a top view, FIG. 5 [B] is the Vb-Vb sectional view taken on the line in FIG. FIG. 6A is a cross-sectional view at the time of normality, and FIG. 6B is a cross-sectional view at the time of abnormality.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the accompanying drawings. In the present specification and drawings, the same reference numerals are used for substantially the same components. The shapes depicted in the drawings are drawn so as to be easily understood by those skilled in the art, and thus do not necessarily match the actual dimensions and ratios.

  FIG. 1 is a plan view of the resonator element according to the first embodiment. 2A is a cross-sectional view taken along line IIa-IIa in FIG. 1, and FIG. 2B is a part of a cross-sectional view taken along line IIb-IIb in FIG. 3A is a schematic cross-sectional view showing a state in which the vibration element of FIG. 1 is mounted on an element mounting member, and FIG. 3B is a vacuum seal of the element mounting member of FIG. 3A with a lid member. It is a schematic sectional drawing which shows a state. Hereinafter, description will be given with reference to FIGS.

  The vibration element 10 according to the first embodiment includes a crystal piece 15 and frequency adjustment films 23 a and 23 b as metal films formed on the crystal piece 15. As shown in FIG. 2B, the frequency adjusting films 23a and 23b include a first chromium layer 31 formed on the crystal piece 15, a silver layer 32 formed on the first chromium layer 31, and a silver layer. The second chromium layer 33 formed on the second chromium layer 33 and the chromium oxide film 34 formed on the surface of the second chromium layer 33.

  The crystal piece 15 has a portion that becomes the base portion 11 and a portion that becomes the two vibrating arm portions 12 a and 12 b extending from the base portion 11. The frequency adjustment films 23a and 23b are formed on the distal end sides of the two vibrating arm portions 12a and 12b, respectively.

  Next, the configuration of the vibration element 10 will be described in more detail.

  As shown in FIGS. 1 and 2, the resonator element 10 includes a crystal piece 15, excitation electrodes 21a and 21b, pad electrodes 22a and 22b provided on the crystal piece 15, frequency adjustment films 23a and 23b, and a wiring pattern 24a. 24b.

  The crystal piece 15 is configured in a tuning fork shape from a portion that becomes the base portion 11 and a portion that becomes the vibrating arm portions 12a and 12b.

  Quartz is trigonal. A crystal axis passing through the crystal apex is defined as a Z axis, three crystal axes connecting ridge lines in a plane perpendicular to the Z axis are defined as an X axis, and a coordinate axis orthogonal to the X axis and the Z axis is defined as a Y axis. Here, when the coordinate system consisting of these X, Y, and Z axes is rotated within a range of ± 5 degrees around the X axis, the rotated Y axis and Z axis are respectively represented as Y ′ axis and Z axis. 'As axis. In this case, in the first embodiment, the extending direction of the two vibrating arm portions 12a and 12b is the Y′-axis direction, and the direction in which the two vibrating arm portions 12a and 12b are arranged is the X-axis direction. .

  Groove portions 13a and 13b are provided in the longitudinal direction of the vibrating arm portions 12a and 12b, respectively. The number of the groove portions 13a and 13b is not particularly limited. For example, two grooves may be provided on the front and back surfaces of the vibrating arm portion 12a and two grooves on the front and back surfaces of the vibrating arm portion 12b. May be provided one by one and one on the front and back surfaces of the vibrating arm portion 12b. The groove portions 13a and 13b may be provided only on either the front or back surface of the vibrating arm portion 12a, or may be provided only on either the front or back surface of the vibrating arm portion 12b.

  Excitation electrodes 21a and 21b are respectively provided on the vibrating arm portions 12a and 12b so as to have the same polarity on the planes facing each other across the crystal. The excitation electrode 21a is provided in the groove part 13a of the both sides | surfaces of the vibration arm part 12a, and the front and back of the vibration arm part 12b. The excitation electrode 21b is provided in the groove part 13b of the both sides | surfaces of the vibration arm part 12b, and the front and back of the vibration arm part 12a.

  The base 11 is provided with pad electrodes 22a and 22b and wiring patterns 24a and 24b. The wiring pattern 24a electrically connects the pad electrode 22a and the excitation electrode 21a, and the wiring pattern 24b electrically connects the pad electrode 22b and the excitation electrode 21b. The excitation electrode 21a, the pad electrode 22a, the frequency adjustment film 23a, and the wiring pattern 24a are electrically connected to each other, and the excitation electrode 21b, the pad electrode 22b, the frequency adjustment film 23b, and the wiring pattern 24b are electrically connected to each other.

  The excitation electrodes 21a and 21b, the pad electrodes 22a and 22b, and the wiring patterns 24a and 24b have a laminated structure in which, for example, a palladium or gold layer is provided on a titanium layer. The frequency adjustment films 23a and 23b have a laminated structure as described above.

  Explaining in detail with reference to FIG. 2A, the vibrating arm 12a is provided with excitation electrodes 21a on both side surfaces so that the planes facing each other across the crystal have the same polarity, and in the groove 13a on the front and back surfaces. Excitation electrode 21b is provided. Similarly, the vibrating arm portion 12b is provided with excitation electrodes 21b on both side surfaces so as to have the same polarity on opposite surfaces across the quartz, and excitation electrodes 21a are provided in the groove portions 13b on the front and back surfaces. Therefore, in the vibrating arm portion 12a, the excitation electrode 21a provided on both sides and the excitation electrode 21b provided in the groove 13a have different polarities, and in the vibrating arm portion 12b, the excitation electrode 21b provided on both sides. The excitation electrodes 21a provided in the groove 13b have different polarities. At this time, in the vibrating arm 12a, the excitation electrodes 21a on both sides and the excitation electrodes 21b in the groove 13a become parallel plate electrodes, and a large electric field strength is obtained between these electrodes. The same applies to the vibrating arm 12b.

  As shown in FIG. 3A, the vibration element 10 is fixed to the pad electrode 43 on the element mounting member 42 side and electrically connected via the pad electrodes 22a and 22b. The As shown in FIG. 3B, the crystal resonator 40 is obtained by vacuum-sealing the element mounting member 42 with the lid member 44. Although not shown, the element mounting member 42 is provided with an external connection terminal that conducts to the pad electrode 43.

  Next, the operation of the vibration element 10 will be described.

  In order to operate the vibration element 10, an alternating voltage is applied to the pad electrodes 22a and 22b. When an electrical state after application is instantaneously captured, the excitation electrodes 21b provided in the groove portions 13a on the front and back surfaces of the vibrating arm portion 12a have a positive potential, and the excitation electrodes provided on both side surfaces of the vibrating arm portion 12a. 21a becomes a negative potential, and an electric field is generated from positive to negative between the excitation electrode 21b and the excitation electrode 21a facing each other. At this time, the excitation electrode 21a provided in the groove 13b on the front and back surfaces of the vibrating arm portion 12b has a negative potential, and the excitation electrodes 21b provided on both side surfaces of the vibrating arm portion 12b have a positive potential. The polarity is opposite to the generated polarity, and an electric field is generated from plus to minus between the excitation electrode 21b and the excitation electrode 21a facing each other. The electric field generated by the alternating voltage causes a stretching phenomenon in the vibrating arm portions 12a and 12b, and a flexural vibration mode having a resonance frequency set in the shape of the vibrating arm portions 12a and 12b is obtained.

  Further, the resonance frequency of the vibration element 10 can be adjusted by cutting the frequency adjustment films 23a and 23b with a laser or an ion gun. That is, the resonance frequency increases as the frequency adjustment films 23a and 23b are cut.

  Next, a method for manufacturing the vibration element 10 and a method for manufacturing the crystal unit 40 will be described with reference to FIGS. FIG. 4 is a process diagram showing a method for manufacturing the resonator element 10 and a method for manufacturing the crystal resonator 40 having the resonator element 10 as a main component.

  The method for manufacturing the vibration element 10 includes the following steps S1 to S3.

  In step S1, a large number of crystal pieces 15 are formed from a crystal wafer. For example, the tuning fork-shaped crystal piece 15 is formed from the Z plate by a film forming technique, a photolithography technique, and an etching technique. In steps S1 to S3, one crystal wafer is processed into a frame shape, and the process proceeds with a large number of crystal pieces 15 connected in the frame.

  In step S <b> 2, an electrode is formed on the crystal piece 15. For example, the excitation electrodes 21a and 21b, the pad electrodes 22a and 22b, and the wiring patterns 24a and 24b are formed by a film formation technique, a photolithography technique, and an etching technique. Lift-off may be used instead of etching the electrode film.

In step S3, frequency adjustment films 23a and 23b are formed on the crystal piece 15. First, in a film forming apparatus such as sputtering or vapor deposition, the crystal piece 15 is covered with a metal mask in which regions to be frequency adjusting films 23a and 23b are openings. And the 1st chromium layer 31, the silver layer 32, and the 2nd chromium layer 33 are formed into a film in order. Thereafter, when the surface of the second chromium layer 33 is exposed to the atmosphere, an oxide film 34 is naturally formed on the surface of the second chromium layer 33 by oxygen in the atmosphere. The oxide film 34 is also called a “passive film” and is a very dense film having a self-repairing function, and therefore acts as a barrier that prevents the entry of oxygen or the like. The composition formula of the oxide film 34 is, for example, Cr ₂ O ₃ . In addition, you may form the thicker oxide film 34 by heating the surface of the 2nd chromium layer 33 in air | atmosphere, or processing with nitric acid.

  For example, the film thickness of the first chromium layer 31 is 6 to 10 nm, the film thickness of the silver layer 32 is 2 to 3 μm, the film thickness of the second chromium layer 33 is 2 to 20 nm, and the film thickness of the oxide film 34 is 1 to 3 nm. is there. The silver layer 32 is formed to be relatively thick because it is premised on that a part of the silver layer 32 is removed for frequency adjustment. Further, instead of the silver layer 32, a gold layer having similar properties may be used. If the film thickness of the second chromium layer 33 is 2 nm or more, the oxide film 34 can be made sufficiently thick and the step coverage can be improved, and if it is 20 nm or less, removal with a laser or an ion gun can be facilitated. Is 3-5 nm, most preferably 4 nm.

  The vibration element 10 is completed by the above steps S1 to S3. The manufacturing method of the crystal unit 40 includes the following steps S4 to S7.

  In step S4, the vibration element 10 is separated from the crystal wafer, and the vibration element 10 is mounted on the element mounting member 42 via the conductive adhesive 41 made of a thermosetting resin. The conductive adhesive 41 is a commercially available product in which a conductive filler such as silver powder is dispersed in, for example, a thermosetting resin binder.

  Step S5 includes curing annealing for curing the conductive adhesive 41 and vacuum annealing performed thereafter. In the curing annealing, the conductive adhesive 41 is cured by heating the vibration element 10 mounted on the element mounting member 42 via the conductive adhesive 41 in a gas containing oxygen. The heating conditions at this time are, for example, about 290 ° C. and about 15 minutes. As for the gas containing oxygen, oxygen is about 1 vol% and the remainder is nitrogen. That is, even if the atmosphere in the heating device is replaced with nitrogen, a certain amount of oxygen remains, or oxygen attached to the vibration element 10 and the jig / tool is separated by heating. It is impractical from a cost standpoint to completely remove the oxygen. However, oxygen at the time of hardening annealing is blocked by the above-described oxide film 34, and therefore does not cause the frequency adjustment films 23a and 23b to bulge. Subsequent vacuum annealing is performed at 330 ° C. for about 20 minutes, for example, for the purpose of degassing the conductive adhesive 41 and stress relaxation of the excitation electrodes 21a and 21b and the frequency adjustment films 23a and 23b.

  In step S6, the resonance frequency of the vibration element 10 is adjusted to a design value by scraping the frequency adjustment films 23a and 23b with a laser or an ion gun while operating the vibration element 10. Step S6 may be performed at the wafer stage as a rough adjustment of the frequency.

  In step S7, the element mounting member 42 on which the vibration element 10 is mounted is sealed with a lid member 44 in a vacuum, whereby the vacuum-sealed crystal resonator 40 is completed. For example, the element mounting member 42 is made of laminated ceramics, the lid member 44 is made of metal, and the element mounting member 42 and the lid member 44 are joined by electric welding or glass sealing.

  Next, effects of the vibration element 10 and the crystal resonator 40 will be described.

  According to the first embodiment, since the surface of the second chromium layer 33 on the silver layer 32 is covered with the oxide film 34, entry of oxygen is prevented by the oxide film 34. For this reason, oxygen can be prevented from reaching the first chromium layer 31 through the grain boundary of the silver layer 32, and thus the swelling of the frequency adjusting films 23a and 23b can be suppressed.

  In particular, the crystal resonator 40 includes a step of mounting the vibration element 10 on the element mounting member 42 via the conductive adhesive 41 and a step of heating and curing the conductive adhesive 41 in a gas containing oxygen. In the manufacturing method, oxygen can be prevented from entering by the oxide film 34 when the conductive adhesive 41 is cured, so that swelling of the frequency adjustment films 23 a and 23 b caused by the curing annealing of the conductive adhesive 41 can be suppressed.

  At this time, the defect rate due to the occurrence of blistering increases with the related art 1 as the oxygen concentration increases, the heating temperature increases, and the heating time increases. Not receive. Therefore, according to the first embodiment, when the gas containing oxygen is 0.5 vol% or more remaining nitrogen and the heating conditions are 250 ° C. or more and 10 minutes or more, a remarkable effect is obtained and oxygen is contained. The effect is more remarkable when the gas is 1 vol% or more of remaining nitrogen and the heating conditions are 290 ° C. or more and 15 minutes or more.

  Next, Embodiment 2 will be described. 5 shows a frequency adjustment film in the resonator element according to the second embodiment, FIG. 5A is a plan view, and FIG. 5B is a cross-sectional view taken along the line Vb-Vb in FIG. 5A.

  In the frequency adjusting film 23 a, the areas of the second chromium layer 33 and the oxide film 34 are formed larger than the areas of the first chromium layer 31 and the silver layer 32 so as to enclose the entire first chromium layer 31 and the silver layer 32. Has been. In FIG. 5B, the thickness direction of the frequency adjustment film 23a is shown enlarged in comparison with the thickness direction of the crystal piece 15.

  In the laminated structure of the frequency adjustment film 23a in the second embodiment, for example, in step S3 shown in FIG. 4, the opening of the metal mask is used for forming the first chromium layer 31 and the silver layer 32 and for forming the second chromium layer 33. Obtained by dividing.

  According to the second embodiment, the oxide film 34 is formed so as to wrap the entire first chrome layer 31 and the silver layer 32, so that it enters from the peripheral ends 35 of the first chrome layer 31 and the silver layer 32. Since oxygen can also be blocked, swelling of the frequency adjustment film 23a can be further suppressed.

  Other configurations, operations, and effects of the second embodiment are the same as those of the first embodiment. For example, the frequency adjustment film 23b (FIG. 1) also has the same configuration as the frequency adjustment film 23a in the second embodiment.

  Although the present invention has been described with reference to the above embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention. Further, the present invention includes a combination of some or all of the configurations of the above-described embodiments as appropriate.

  For example, the laminated structure of the frequency adjustment films 23a and 23b is not limited to the frequency adjustment films 23a and 23b, and may be applied to at least one of the excitation electrodes 21a and 21b, the pad electrodes 22a and 22b, and the wiring patterns 24a and 24b. . The element mounting member is not limited to the one that mounts only the vibration element, and may be an element that mounts an IC chip or the like together with the vibration element. The piezoelectric element is not limited to a tuning fork type bending vibration element, and may be a thickness shear vibration element, a contour slip vibration element, a SAW (Surface Acoustic Wave) element, or the like.

<Embodiment 1>
DESCRIPTION OF SYMBOLS 10 Vibration element 11 Base part 12a, 12b Vibration arm part 13a, 13b Groove part 15 Crystal piece 21a, 21b Excitation electrode 22a, 22b Pad electrode 23a, 23b Frequency adjustment film | membrane 24a, 24b Wiring pattern 31 1st chromium layer 32 Silver layer 33 2nd Chromium layer 34 Oxide film 35 Peripheral edge 40 Crystal resonator 41 Conductive adhesive 42 Element mounting member 43 Pad electrode 44 Lid member <Related art 1>
80 Frequency adjustment film 81 Chrome layer 82 Silver layer 83 Blister 85 Crystal fragment

Claims (5)

In a piezoelectric element comprising a crystal piece and a metal film formed on the crystal piece,
The metal film includes a first chromium layer formed on the crystal piece, a silver or gold layer formed on the first chromium layer, a second chromium layer formed on the silver or gold layer, It consists of a chromium oxide film formed on the surface of this second chromium layer,
A piezoelectric element characterized by that. A crystal resonator element,
The crystal piece has a portion that becomes a base portion and a portion that becomes two vibrating arm portions extending from the base portion,
The metal film is a frequency adjustment film formed on the tip side of the two vibrating arms.
The piezoelectric element according to claim 1. The areas of the second chromium layer and the oxide film were formed larger than the areas of the first chromium layer and the silver or gold layer so as to enclose the entire first chromium layer and the silver or gold layer. ,
The piezoelectric element according to claim 1 or 2, wherein Mounting a piezoelectric element including a crystal piece and a metal film formed on the crystal piece on an element mounting member via a thermosetting resin;
Curing the thermosetting resin by heating the piezoelectric element mounted on the element mounting member via the thermosetting resin in a gas containing oxygen, and
The metal film includes a first chromium layer formed on the crystal piece, a silver or gold layer formed on the first chromium layer, a second chromium layer formed on the silver or gold layer, It consists of a chromium oxide film formed on the surface of this second chromium layer,
A method for manufacturing a piezoelectric device. The oxygen-containing gas is oxygen of 0.5 vol% or more and the rest is nitrogen, and the heating conditions are 250 ° C. or more and 10 minutes or more.
The method for manufacturing a piezoelectric device according to claim 4.

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