Piezoelectric vibrator and method for manufacturing the same

Abstract

According to the present invention, changes over time in a resonant frequency are suppressed.　A crystal resonator 1 comprises a base member 30, and a crystal resonating element 10 which is held on one surface of the base member 30 and which includes a crystal piece 11, and a first excitation electrode 14a and a second excitation electrode 14b provided on both main surfaces of the crystal piece 11, wherein: the first excitation electrode 14a and the second excitation electrode 14b each include a first metal layer 141 and a second metal layer 142 disposed between the first metal layer 141 and the crystal piece 11; and the weight ratio of the second metal layer 142 with respect to the first metal layer 141 is 0.1% to 1.1% inclusive.

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric vibrator and a method for manufacturing a piezoelectric vibrator. [Background technology]

[0002] Piezoelectric vibrators are generally known as electronic components and are used as signal sources for reference signals used in oscillators, bandpass filters, etc. A piezoelectric vibrator includes, for example, a piezoelectric vibrating element, a lid member and a base member that form a housing that houses the piezoelectric vibrating element, and a bonding material that bonds the lid member and the base member. The piezoelectric vibrating element also includes a vibrating reed that is a piezoelectric body, and an excitation electrode provided on a vibrating portion of the vibrating reed.

[0003] Cited Document 1 discloses a frequency adjustment method for a vibrating element, which comprises performing an oxidation treatment on a vibrating element having a piezoelectric substrate, a pair of conductive electrode layers provided on the upper surface of the piezoelectric substrate, and a mass portion including an oxidizable material provided on the surface of the electrode layer, thereby increasing the mass of the mass portion through oxidation and adjusting the resonant frequency of the vibrating element. This method allows for delicate adjustment of the mass of the oxidizable layer, making it easy to fine-tune the resonant frequency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-200040 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even when an oxidation treatment is performed on a piezoelectric piece (vibration piece) as in the frequency adjustment method of Patent Document 1, if the piezoelectric vibration element is sealed in a housing and then placed in a high-temperature environment or a high-temperature, constant-temperature, high-humidity environment, the unoxidized material in the mass portion may oxidize over time, causing a change in the mass of the vibration portion of the piezoelectric piece. As a result, there is a risk that the resonant frequency of the piezoelectric vibration element may change over time.

[0006] The present invention has been made in view of the above circumstances, and one of its objects is to provide a piezoelectric vibrator and a method for manufacturing a piezoelectric vibrator that can suppress changes in resonant frequency over time. [Means for solving the problem]

[0007] A piezoelectric vibrator according to one aspect of the present invention comprises a base member and a piezoelectric vibration element held on one surface of the base member and having a piezoelectric piece and an excitation electrode provided on each of both main surfaces of the piezoelectric piece, wherein the excitation electrode includes a first metal layer and a second metal layer arranged between the first metal layer and the piezoelectric piece, and the weight ratio of the second metal layer to the first metal layer is 0.1% or more and 1.1% or less.

[0008] A method for manufacturing a piezoelectric vibrator according to one aspect of the present invention includes the steps of preparing a piezoelectric piece, forming a first metal layer primarily composed of gold on each of both main surfaces of the piezoelectric piece, and a second metal layer primarily composed of chromium and disposed between the first metal layer and the piezoelectric piece, and trimming away a portion of the first metal layer formed on one of the main surfaces, wherein the thickness ratio of the second metal layer to the first metal layer is 0.4% or more and 2.9% or less. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the change in the resonant frequency over time. [Brief explanation of the drawings]

[0010] [Figure 1]FIG. 1 is an exploded perspective view schematically illustrating the configuration of a quartz crystal resonator according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically showing the cross-sectional configuration of the crystal resonator shown in FIG. 1 taken along line II-II. [Figure 3] FIG. 3 is an enlarged view of a main part, schematically illustrating an example of the configuration of the side surface of the quartz crystal vibrating element shown in FIGS. 1 and 2, taken along the X-axis. [Figure 4] FIG. 4 is a graph showing the change over time in the resonant frequency of the resonant resonator of this embodiment and a conventional crystal resonator. [Figure 5] FIG. 5 is a graph showing the relationship between the weight ratio of the second metal layer to the first metal layer and the rate of change of the resonant frequency. [Figure 6] FIG. 6 is a flowchart showing a method for manufacturing a crystal resonator according to the first embodiment. [Figure 7] FIG. 7 is a graph showing the relationship between the thickness of the second metal layer and the rate of change of the resonant frequency. [Figure 8] FIG. 8 is a graph showing the relationship between the ratio of the thickness of the second metal layer to the thickness of the first metal layer and the rate of change of the resonant frequency. [Figure 9] FIG. 9 is a cross-sectional view schematically illustrating a cross-sectional configuration of a quartz crystal resonator according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described. In the following description of the drawings, the same or similar components are denoted by the same or similar reference numerals. The drawings are illustrative, and the dimensions and shapes of each part are schematic. The technical scope of the present invention should not be interpreted as being limited to the embodiment.

[0012] For the sake of clarity, each drawing may be accompanied by a Cartesian coordinate system consisting of an X-axis, a Y'-axis, and a Z'-axis to clarify the relationship between the drawings and to aid in understanding the positional relationship of each component. The X-axis, Y'-axis, and Z'-axis correspond to each other in each drawing. The X-axis, Y'-axis, and Z'-axis correspond to the crystallographic axes of the quartz blank 11, which will be described later. The X-axis corresponds to the electrical axis (polarity axis) of the quartz, the Y-axis corresponds to the mechanical axis of the quartz, and the Z-axis corresponds to the optical axis of the quartz. The Y'-axis and Z'-axis are axes obtained by rotating the Y-axis and Z-axis around the X-axis by 35 degrees 15 minutes ± 1 minute 30 seconds in the direction from the Y-axis to the Z-axis.

[0013] In the following description, the direction parallel to the X-axis is referred to as the "X-axis direction," the direction parallel to the Y'-axis as the "Y'-axis direction," and the direction parallel to the Z'-axis as the "Z'-axis direction." The directions of the arrows on the X-axis, Y'-axis, and Z'-axis are referred to as "positive" or "+ (plus)," and the directions opposite the arrows are referred to as "negative" or "- (minus)." For convenience, the +Y'-axis direction will be described as the upward direction, and the -Y'-axis direction will be described as the downward direction, but the up-down orientation of the quartz crystal vibrating element 10 and the quartz crystal unit 1 is not limited to this. The plane defined by the X-axis and Z'-axis will be referred to as the Z'X plane, and the same applies to planes defined by the other axes.

[0014] In the following description, a quartz crystal resonator unit equipped with a quartz crystal resonator element will be used as an example of the piezoelectric vibrator. A quartz crystal blank will be used as an example of the piezoelectric vibrator. A quartz crystal blank is a type of piezoelectric material (piezoelectric piece) that vibrates in response to an applied voltage. The piezoelectric vibrator is not limited to a quartz crystal resonator, but may use other piezoelectric materials such as ceramic, lithium tantalate, or lithium niobate. Similarly, the piezoelectric vibrator is not limited to a quartz crystal resonator, but may use other piezoelectric materials such as ceramic, lithium tantalate, or lithium niobate.

[0015] First Embodiment A quartz crystal resonator according to a first embodiment will be described with reference to Figures 1 and 2. Figure 1 is an exploded perspective view schematically showing the configuration of a quartz crystal resonator 1 according to the first embodiment. Figure 2 is a cross-sectional view schematically showing the configuration of a cross section taken along line II-II of the quartz crystal resonator 1 shown in Figure 1.

[0016] 1, the quartz crystal resonator 1 includes a quartz crystal resonator element 10, a lid member 20, a base member 30, and a bonding material 40. The lid member 20 and the base member 30 are part of a holder that houses the quartz crystal resonator element 10. The quartz crystal resonator 1 is a small quartz crystal resonator with external dimensions smaller than, for example, 2.0 × 1.6 mm (2016 size), such as 1.6 × 1.2 mm (1612 size) or 1.0 × 0.8 mm (1008 size).

[0017] The quartz crystal vibrating element 10 is an element that vibrates a quartz crystal by the piezoelectric effect and converts electrical energy into mechanical energy. The quartz crystal vibrating element 10 includes, for example, an AT-cut quartz crystal blank 11. The AT-cut quartz crystal blank 11 is cut out with the XZ' plane, defined by the X-axis and Z'-axis, as the principal surface, when the Y-axis and Z-axis are respectively rotated 35 degrees 15 minutes ± 1 minute 30 seconds from the Y-axis to the Z-axis around the X-axis.

[0018] The rotation angle of the Y'-axis and Z'-axis in AT-cut crystal blank 11 may be in the range of -5 degrees to +15 degrees from 35 degrees 15 minutes. Also, the cut angle of crystal blank 11 may be a cut other than AT-cut, such as BT-cut, GT-cut, or SC-cut.

[0019] Quartz crystal vibration elements using AT-cut quartz crystal blanks have high frequency stability over a wide temperature range. They also have excellent aging characteristics and can be manufactured at low cost. Furthermore, AT-cut quartz crystal vibration elements use the thickness shear vibration mode as their primary vibration mode.

[0020] The quartz crystal vibrating element 10 further includes a pair of excitation electrodes. An alternating electric field is applied between the pair of excitation electrodes. This causes the vibrating portion of the quartz crystal blank 11 to vibrate at a predetermined oscillation frequency in thickness-shear vibration mode, resulting in resonance characteristics associated with this vibration.

[0021] In this way, since the main vibration of the quartz crystal vibrating element 10 is thickness-shear vibration mode, by using, for example, an AT-cut quartz crystal piece 11, it is possible to easily realize a quartz crystal vibrator 1 that performs thickness-shear vibration at vibration frequencies in the MHz range.

[0022] Crystal blank 11 has first and second principal surfaces 12a and 12b that are opposed to each other and are in the XZ' plane. Crystal blank 11 has a flat plate shape. Therefore, first and second principal surfaces 12a and 12b of crystal blank 11 are each flat surfaces. Note that crystal blank 11 is not limited to a flat plate shape, and may have, for example, a convex or concave central portion.

[0023] AT-cut crystal blank 11 has a long side direction in which the long sides extend parallel to the X-axis direction, a short side direction in which the short sides extend parallel to the Z'-axis direction, and a thickness direction in which the thickness extends parallel to the Y'-axis direction. Crystal blank 11 has a rectangular shape when first main surface 12a of crystal blank 11 is viewed in a plan view (hereinafter simply referred to as "plan view").

[0024] The planar shape of crystal blank 11 is not limited to a rectangular shape, but may be a polygonal shape, a circular shape, an elliptical shape, or a combination thereof.

[0025] The quartz crystal vibrating element 10 includes a first excitation electrode 14a and a second excitation electrode 14b that form a pair of electrodes. The first excitation electrode 14a is provided on the first main surface 12a. The second excitation electrode 14b is provided on the second main surface 12b. The first excitation electrode 14a and the second excitation electrode 14b are provided opposite each other across the quartz crystal blank 11 in an area including the center of each main surface. The first excitation electrode 14a and the second excitation electrode 14b are arranged so that they overlap substantially entirely in the XZ' plane. The area where the first excitation electrode 14a and the second excitation electrode 14b are provided becomes the vibrating portion of the quartz crystal blank 11.

[0026] The first excitation electrode 14a and the second excitation electrode 14b each have a long side parallel to the X-axis direction, a short side parallel to the Z'-axis direction, and a thickness parallel to the Y'-axis direction. In the example shown in FIG. 1, in the XZ' plane, the long sides of the first excitation electrode 14a and the second excitation electrode 14b are each parallel to the long sides of the crystal blank 11. Similarly, the short sides of the first excitation electrode 14a and the second excitation electrode 14b are each parallel to the short sides of the crystal blank 11. Furthermore, the long sides of the first excitation electrode 14a and the second excitation electrode 14b are each spaced apart from the long sides of the crystal blank 11. Similarly, the short sides of the first excitation electrode 14a and the second excitation electrode 14b are each spaced apart from the short sides of the crystal blank 11.

[0027] The quartz crystal vibrating element 10 includes lead electrodes 15a and 15b and connection electrodes 16a and 16b. The connection electrode 16a is electrically connected to the first excitation electrode 14a via the lead electrode 15a. The connection electrode 16b is electrically connected to the second excitation electrode 14b via the lead electrode 15b. The connection electrodes 16a and 16b are each terminals for electrical connection to the base member 30. The connection electrodes 16a and 16b are each provided on the second principal surface 12b of the quartz crystal blank 11. The connection electrodes 16a and 16b are each arranged near the short side of the quartz crystal blank 11 on the negative side of the X-axis, along the short side.

[0028] The extraction electrode 15a electrically connects the first excitation electrode 14a and the connection electrode 16a. Specifically, the extraction electrode 15a extends from the first excitation electrode 14a on the first principal surface 12a in the positive direction of the Z'-axis and the negative direction of the X-axis, extends from the first principal surface 12a through each side surface of the crystal blank 11 to the second principal surface 12b, and is electrically connected to the connection electrode 16a on the second principal surface 12b. The extraction electrode 15b electrically connects the second excitation electrode 14b and the connection electrode 16b. Specifically, the extraction electrode 15b extends from the second excitation electrode 14b on the second principal surface 12b in the negative direction of the X-axis, and is electrically connected to the connection electrode 16b on the second principal surface 12b. In this way, by extending the extraction electrodes 15a, 15b, the connection electrodes 16a, 16b electrically connected to the first excitation electrode 14a and the second excitation electrode 14b provided on both the first main surface 12a and the second main surface 12b can be arranged on one of the second main surfaces 12b.

[0029] The connection electrodes 16a and 16b are electrically connected to electrodes of the base member 30, which will be described later, via the conductive holding members 36a and 36b.

[0030] The materials of the extraction electrodes 15a, 15b and the connection electrodes 16a, 16b are not particularly limited, but may be, for example, a chromium (Cr) layer as a base and a gold (Au) layer on the surface of the chromium layer. Details of the first excitation electrode 14a and the second excitation electrode 14b will be described later.

[0031] In this embodiment, the quartz crystal vibrating element 10 includes a flat, plate-shaped quartz crystal blank 11. However, this is not limiting. The quartz crystal blank may have a mesa structure in which the vibrating portion, including the center of the main surface, is thicker than the peripheral portion, or an inverted mesa structure in which the vibrating portion is thinner than the peripheral portion. Alternatively, the quartz crystal blank may have a convex or bevel shape in which the thickness (step) between the vibrating portion and the peripheral portion changes continuously. The cut angle of the quartz crystal blank may be a cut other than the AT cut, such as a BT cut. Furthermore, the quartz crystal vibrating element may be a tuning-fork quartz crystal vibrating element, which uses a quartz crystal plate cut at a predetermined angle relative to the X-axis, Y-axis, and Z-axis, which are orthogonal to each other as the crystal axes of the quartz crystal, as a base material. The quartz crystal blank has a base and at least one vibrating arm extending from the base, and excitation electrodes are provided on the vibrating arm to cause flexural vibration.

[0032] In this way, since the quartz crystal vibration element 10 includes a set of first excitation electrode 14a and second excitation electrode 14b provided on both main surfaces of the quartz crystal blank 11, it is possible to easily configure (realize) a quartz crystal vibration element 10 in which the vibration part vibrates in a predetermined vibration mode.

[0033] The lid member 20 and the base member 30 form an internal space 26 that accommodates the quartz crystal vibrating element 10. The lid member 20 and the base member 30 are bonded together by a bonding material 40, which will be described later.

[0034] The lid member 20 has a concave shape, specifically a box shape including an opening, and has an inner surface 24 and an outer surface 25. The lid member 20 includes a top surface 21 facing the first main surface 32a of the base member 30, and a sidewall 22 connected to the outer edge of the top surface 21 and extending in a direction normal to the main surface of the top surface 21. The lid member 20 has, for example, a long side direction in which the long sides extend parallel to the X-axis direction, a short side direction in which the short sides extend parallel to the Z'-axis direction, and a height direction in which the Y'-axis direction. The lid member 20 also has an opposing surface 23 that faces the first main surface 32a of the base member 30 at the edge of the concave opening. The opposing surface 23 has a frame shape and extends to surround the periphery of the quartz crystal vibrating element 10.

[0035] The lid member 20 is, for example, a metal member. Specifically, the lid member 20 is made of 42 alloy, which is an alloy containing iron (Fe) and nickel (Ni), or kovar, which is an alloy containing iron (Fe), nickel (Ni), and cobalt (Co). 42 alloy and kovar are both known as metals with low thermal expansion coefficients. A nickel (Ni) layer or the like formed by plating may be provided on the innermost surface (surface including the inner surface 24) of the lid member 20. A gold (Au) layer or the like for the purpose of preventing oxidation may be provided on the outermost surface (surface including the outer surface 25) of the lid member 20. Furthermore, a nickel (Ni) layer and a gold (Au) layer or the like formed by plating may be provided on the opposing surface 23 of the lid member 20. However, the material of the lid member 20 is not limited to metal and may be other materials.

[0036] In this way, by providing the cover member 20 that houses the crystal vibrating element 10 in the internal space 26 formed between the cover member 20 and the base member 30, the crystal vibrating element 10 can be protected from the external environment.

[0037] The base member 30 supports the quartz crystal vibrating element 10 so that it can vibrate. Specifically, the quartz crystal vibrating element 10 is held in a vibrating manner on a first main surface 32a of the base member 30 via conductive holding members 36a and 36b.

[0038] The base member 30 has a flat plate shape and has a long side direction in which the long sides extend parallel to the X-axis direction, a short side direction in which the short sides extend parallel to the Z'-axis direction, and a thickness direction in which the thickness extends parallel to the Y'-axis direction.

[0039] The base member 30 includes a substrate 31. The substrate 31 has a first main surface 32a and a second main surface 32b, which are XZ' planes facing each other. The substrate 31 is a sintered material such as insulating ceramic (alumina). In this case, the substrate 31 may be formed by stacking and sintering multiple insulating ceramic sheets. Alternatively, the substrate 31 may be formed of a glass material (e.g., silicate glass or a material containing a non-silicate as its main component and exhibiting a glass transition phenomenon upon heating), a quartz material (e.g., AT-cut quartz), or a glass epoxy resin. The substrate 31 is preferably made of a heat-resistant material. The substrate 31 may be a single layer or multiple layers. If the substrate 31 is a multiple layer, it includes an insulating layer formed on the outermost layer of the first main surface 32a.

[0040] The base member 30 includes electrode pads 33a and 33b provided on the first main surface 32a and external electrodes 35a, 35b, 35c, and 35d provided on the second main surface 32b. The electrode pads 33a and 33b are terminals for electrically connecting to the quartz crystal vibrating element 10. The external electrodes 35a, 35b, 35c, and 35d are terminals for electrically connecting to a circuit board (not shown). The electrode pad 33a is electrically connected to the external electrode 35a through a via electrode 34a extending in the Y'-axis direction, and the electrode pad 33b is electrically connected to the external electrode 35b through a via electrode 34b extending in the Y'-axis direction. The via electrodes 34a and 34b are formed in via holes (not shown) that penetrate the base 31 in the Y'-axis direction.

[0041] The electrode pads 33a and 33b are provided on the first main surface 32a near the short side of the base member 30 on the negative side of the X-axis. In the example shown in Fig. 1, the electrode pads 33a and 33b are arranged apart from the short side of the base member 30 and along the short side. The electrode pad 33a is connected to the connection electrode 16a of the quartz vibrating element 10 via a conductive holding member 36a. The electrode pad 33b is connected to the connection electrode 16b of the quartz vibrating element 10 via a conductive holding member 36b.

[0042] Multiple external electrodes 35a, 35b, 35c, and 35d are provided near each corner of the second main surface 32b. In the example shown in Fig. 1, the external electrodes 35a and 35b are arranged directly below the electrode pads 33a and 33b. This allows the external electrodes 35a and 35b to be electrically connected to the electrode pads 33a and 33b by via electrodes 34a and 34b extending in the Y'-axis direction.

[0043] 1, of the four external electrodes 35a, 35b, 35c, and 35d, the external electrodes 35a and 35b arranged near the short side of the base member 30 on the negative side of the X-axis are input / output electrodes to which input / output signals of the quartz-crystal vibrating element 10 are supplied. The external electrodes 35c and 35d arranged near the short side of the base member 30 on the positive side of the X-axis are dummy electrodes to which input / output signals of the quartz-crystal vibrating element 10 are not supplied.

[0044] The positional relationship between the electrode pads 33a and 33b and the external electrodes 35a, 35b, 35c, and 35d is not limited to the example described above.

[0045] For example, two external electrodes serving as input / output electrodes may be provided on diagonal corners of the second main surface 32b. Alternatively, four external electrodes may be arranged near the centers of each side of the second main surface 32b rather than at the corners. Furthermore, the number of external electrodes is not limited to four, and there may be only two external electrodes serving as input / output electrodes, for example.

[0046] Furthermore, the manner of electrical connection between the electrode pads and external electrodes is not limited to via electrodes. For example, electrical connection between the electrode pads or internal electrodes and external electrodes may be achieved by extending lead electrodes onto the first main surface 32a or the second main surface 32b. Alternatively, electrical connection between the electrode pads or internal electrodes and external electrodes may be achieved by forming the base 31 of the base member 30 in multiple layers, extending via electrodes to intermediate layers, and extending lead electrodes from the intermediate layers.

[0047] A sealing frame 37 is provided on the first main surface 32a of the base member 31. The sealing frame 37 has a frame shape when the first main surface 32a of the base member 30 is viewed in plan view. Electrode pads 33a and 33b are respectively arranged inside the sealing frame 37 and are provided to surround the quartz crystal vibrating element 10.

[0048] The electrode pads 33a and 33b of the base member 30, the external electrodes 35a, 35b, 35c, and 35d, and the sealing frame 37 are all made of metal films. For example, the electrode pads 33a and 33b, the external electrodes 35a, 35b, 35c, and 35d, and the sealing frame 37 are each made of a molybdenum (Mo) layer, a nickel (Ni) layer, and a gold (Au) layer stacked from bottom to top. The via electrodes 34a and 34b can be formed by filling via holes in the base 31 with a metal material such as molybdenum (Mo).

[0049] The lid member 20 and the base member 30 are bonded together via the bonding material 40, thereby sealing the quartz crystal vibrating element 10 in an internal space 26 surrounded by the lid member 20 and the base member 30. In this case, the pressure in the internal space 26 is preferably a vacuum state lower than atmospheric pressure. This can reduce deterioration over time due to oxidation of the first excitation electrode 14a and the second excitation electrode 14b.

[0050] The bonding material 40 is provided around the entire periphery of the lid member 20 and the base member 30. Specifically, the bonding material 40 is provided on the sealing frame 37. The sealing frame 37 and the bonding material 40 are interposed between the opposing surface 23 of the side wall portion 22 of the lid member 20 and the first main surface 32a of the base member 30, thereby sealing the quartz-crystal vibrating element 10 to the lid member 20 and the base member 30.

[0051] The bonding material 40 is made of a metal material. The bonding material 40 is made of an alloy made of a plurality of metals, for example, a gold (Au)-tin (Sn) eutectic alloy.

[0052] In this way, by providing the bonding material 40 that bonds the base member 30 and the lid member 20 together, the crystal vibrating element 10 can be sealed in the internal space 26 between the base member 30 and the lid member 20.

[0053] In the quartz crystal resonator 1 of this configuration example, an alternating electric field is applied between a pair of first excitation electrode 14a and second excitation electrode 14b in the quartz crystal resonator element 10 via the external electrodes 35a, 35b of the base member 30. This causes the vibrating portion of the quartz crystal blank 11 to vibrate in a predetermined vibration mode such as a thickness-shear vibration mode, and resonance characteristics associated with this vibration are obtained.

[0054] As shown in FIG. 2, the quartz crystal vibrating element 10 is held so that one end of the long side of the quartz crystal blank 11 (the end on which the electrode pads 33a and 33b are arranged) is a fixed end, and the other end is a free end.

[0055] More specifically, the conductive holding members 36a, 36b are formed on one surface of the electrode pads 33a, 33b (the surface on the positive Y'-axis side in Figure 2), and the conductive holding members 36a, 36b hold one end of the quartz vibrating element 10 on the surface of the electrode pads 33a, 33b.

[0056] This structure can be obtained, for example, by applying a conductive adhesive to one surface of the electrode pads 33a, 33b, and then heating and solidifying the conductive adhesive with the quartz-crystal vibrating element 10 mounted thereon. The solidified conductive holding members 36a, 36b electrically connect the connection electrodes 16a, 16b of the quartz-crystal vibrating element 10 to the electrode pads 33a, 33b of the base member 30. The quartz-crystal vibrating element 10 is mounted such that the second excitation electrode 14b faces the first main surface 32a of the base member 30.

[0057] The position of the fixed end of the quartz crystal vibrating element 10 is not particularly limited. As a modified example, the quartz crystal vibrating element 10 may be fixed to the base member 30 at both ends of the long side of the quartz crystal blank 11. In this case, the electrodes of the quartz crystal vibrating element 10 and the base member 30 may be formed in such a manner that the quartz crystal vibrating element 10 is fixed at both ends of the long side of the quartz crystal blank 11.

[0058] As described above, the material of the conductive holding members 36a, 36b is preferably a conductive adhesive, which makes it possible to easily configure (achieve) the quartz crystal resonator 1 that holds one end of the quartz crystal resonator element 10 on one surface of the electrode pads 33a, 33b while electrically connecting the electrode pads 33a, 33b and the quartz crystal resonator element 10.

[0059] Next, the layered structure of the quartz crystal vibrating element according to the first embodiment will be described with reference to Fig. 3. Fig. 3 is an enlarged view of a main part that schematically illustrates an example of the configuration of the side surface of the quartz crystal vibrating element 10 shown in Figs. 1 and 2 along the X-axis.

[0060] 3, the quartz crystal vibrating element 10 includes a quartz crystal blank 11, a first excitation electrode 14a provided on a first main surface 12a of the quartz crystal blank 11, and a second excitation electrode 14b provided on a second main surface 12b of the quartz crystal blank 11. The first excitation electrode 14a and the second excitation electrode 14b include a first metal layer 141 and a second metal layer 142, respectively.

[0061] The first metal layer 141 is a layer exposed on the surfaces of the first excitation electrode 14a and the second excitation electrode 14b, and serves as an electrode. Therefore, the first metal layer 141 is preferably a metal with high electrical conductivity. The material of the first metal layer 141 is, for example, a metal such as gold (Au) or silver (Ag), and the first metal layer 141 contains one of these metals as a main component. That is, the first metal layer 141 may contain, for example, a metal from the second metal layer 142 diffused therein, or may contain a metal oxide, a compound bonded with other elements, or the like.

[0062] The second metal layer 142 is a layer that serves as a base for the first metal layer 141, and the first metal layer 141 is laminated on top of the second metal layer 142. That is, the second metal layer 142 is disposed between the first metal layer 141 and the crystal blank 11, and serves to fix the first metal layer 141 to the crystal blank 11, which is a piezoelectric body. The material of the second metal layer 142 is a metal such as chromium (Cr) or titanium (Ti), and the second metal layer 142 contains one of these metals as a main component. That is, the second metal layer 142 may contain, for example, the metal of the first metal layer 141 diffused therein, or may contain a metal oxide or a compound bonded with other elements.

[0063] Furthermore, it is preferable that the thermal expansion coefficient of second metal layer 142 is close to that of the piezoelectric piece with which it comes into contact. In other words, it is preferable that the difference in thermal expansion coefficient between second metal layer 142 and crystal blank 11 is smaller than the difference in thermal expansion coefficient between first metal layer 141 and crystal blank 11. This allows second metal layer 142 to function (play the role) as an adhesive layer that adheres first metal layer 141 to crystal blank 11.

[0064] In conventional quartz crystal units, the metal in the second metal layer below the excitation electrode would sometimes diffuse into the first metal layer and become exposed on the surface. Therefore, even when the quartz crystal unit is sealed in a housing, if it is placed in a high-temperature or high-humidity environment, the metal in the second metal layer exposed on the surface of the excitation electrode would oxidize over time, causing a change in the mass of the vibrating part of the quartz crystal blank. As a result, there was a risk that the resonant frequency of the quartz crystal unit would change over time.

[0065] In response to this, the inventors of the present invention have discovered that when the ratio (proportion) of the first metal layer and the second metal layer in the excitation electrode is within a predetermined range, diffusion of the metal from the second metal layer into the first metal layer can be suppressed.

[0066] In the quartz crystal resonator 1 of this embodiment, the ratio of the weight of the second metal layer 142 to the weight of the first metal layer 141 (hereinafter simply referred to as the "weight ratio of the second metal layer 142") is 0.1% or more and 1.1% or less.

[0067] Furthermore, it is preferable that the thickness of the second metal layer 142 is smaller than the thickness of the first metal layer 141. More specifically, it is even more preferable that the thickness of the second metal layer 142 is less than a few percent of the thickness of the first metal layer 141, specifically less than about 3%.

[0068] In the following description, unless otherwise specified, the material of first metal layer 141 is assumed to be gold (Au), and the material of second metal layer 142 is assumed to be chromium (Cr). Furthermore, unless otherwise specified, the piezoelectric body (piezoelectric piece) will be described using the above-described crystal piece 11.

[0069] Next, the relationship between the weight ratio of the second metal layer to the first metal layer and the frequency change rate of the resonant frequency will be described with reference to FIGS. 4 and 5. FIG. 4 is a graph showing the time change in the resonant frequency of the crystal unit 1 of this embodiment and a conventional crystal unit. FIG. 5 is a graph showing the relationship between the weight ratio of the second metal layer to the first metal layer and the frequency change rate of the resonant frequency. In FIG. 4, the horizontal axis represents time in [h]. The vertical axis represents the frequency change rate of the resonant frequency (dF / F) in [ppm]. In FIG. 5, the horizontal axis represents the weight ratio of the second metal layer to the first metal layer in [%]. The vertical axis represents the frequency change rate of the resonant frequency (dF / F) in [ppm].

[0070] As shown on the right side of Figure 4, when a conventional quartz crystal unit is placed in an environment with a temperature of 85°C and a humidity of 85% RH, the average frequency change rate of the resonant frequency after 500 hours is approximately -14 ppm. Immediately after manufacture, i.e., at time 0, the conventional quartz crystal unit has a thickness of 1820 nm at the vibrating portion of the quartz crystal blank, a thickness of 125 nm at the first metal layer on each excitation electrode, and a thickness of 5 nm at the second metal layer on each excitation electrode. At this time, the weight ratio of the second metal layer to the first metal layer is 1.5%.

[0071] In contrast, as shown on the left side of Figure 4, when the quartz crystal unit 1 of this embodiment is placed in an environment with a temperature of 85°C and a humidity of 85% RH, the average frequency change rate of the resonant frequency after 500 hours is approximately -4 ppm. Immediately after manufacture, i.e., at time 0, the quartz crystal unit 1 of this embodiment has a thickness of 1820 nm at the vibrating portion of the quartz crystal blank 11, a thickness of 125 nm for the first metal layer 141 on each of the first excitation electrode 14a and the second excitation electrode 14b, and a thickness of 1 nm for the second metal layer 142 on each excitation electrode. At this time, the weight ratio of the second metal layer 142 to the first metal layer 141 is 0.3%.

[0072] Furthermore, as shown by the white circle plot in Figure 5, a conventional quartz crystal unit with a weight ratio of 1.5% exhibits an average frequency change rate of about -14 ppm after 500 hours under the above-mentioned environment.

[0073] In contrast, as shown by the black dots in FIG. 5 , after 500 hours under the above-described environment, the crystal unit 1 exhibited an average frequency change rate of approximately −4 ppm when the weight ratio of the second metal layer 142 to the first metal layer 141 was 0.3%. Furthermore, when the weights of the first metal layer 141 and the second metal layer 142 were changed to a value of 1.1%, the average frequency change rate of the resonant frequency was also approximately −4 ppm. Furthermore, although not shown, we found that the smaller the weight ratio of the second metal layer 142 to the first metal layer 141, the more saturated the frequency change rate of the resonant frequency becomes. Therefore, a similar frequency change rate of the resonant frequency can be obtained even when the weight ratio of the second metal layer 142 to the first metal layer 141 is 0.1%, which is the thinnest possible thickness for stable manufacturing of the second metal layer.

[0074] As described above, first excitation electrode 14a and second excitation electrode 14b each include first metal layer 141 and second metal layer 142 disposed between first metal layer 141 and crystal blank 11, and the weight ratio of second metal layer 142 to first metal layer 141 is 0.1% or more and 1.1% or less, so that the weight of second metal layer 142 relative to first metal layer 141 is smaller than that of conventional crystal resonators, thereby suppressing diffusion of metal from second metal layer 142 into first metal layer 141. This reduces the possibility that the metal from second metal layer 142 will be exposed to the surface and oxidized, and suppresses changes in resonant frequency over time.

[0075] Furthermore, since the thickness of the second metal layer 142 is smaller than the thickness of the first metal layer 141, the second metal layer 142 having a smaller weight ratio to the first metal layer 141 can be easily formed.

[0076] Next, a method for manufacturing a quartz crystal resonator according to the first embodiment will be described with reference to Fig. 6. Fig. 6 is a flowchart showing the method S150 for manufacturing the quartz crystal resonator 1 according to the first embodiment.

[0077] 6, first, crystal blank 11 is prepared (S151). As described above, crystal blank 11 is, for example, an AT-cut crystal blank obtained by cutting synthetic crystal at a predetermined angle.

[0078] Next, a first metal layer 141 and a second metal layer 142 are formed on the first principal surface 12a and the second principal surface 12b of the crystal blank 11, respectively (S152). Specifically, on each of the first principal surface 12a and the second principal surface 12b, a chromium (Cr) film is first formed on the crystal blank 11 by vapor deposition such as sputtering to form the second metal layer 142. Next, a gold (Au) film is formed on the chromium (Cr) by vapor deposition or sputtering to form the first metal layer 141. At this time, for example, the first metal layer 141 formed on the first principal surface 12a side is formed thicker than the first metal layer 141 formed on the second principal surface 12b side, taking into account removal by trimming, which will be described later.

[0079] After the first metal layer 141 is formed, the positions, shapes, dimensions, etc. of the first metal layer 141 and the second metal layer 142 are adjusted by etching or the like. This results in the formation of the first excitation electrode 14a and the second excitation electrode 14b on both main surfaces of the crystal blank 11. At the same time, the extraction electrodes 15a, 15b and the connection electrodes 16a, 16b, etc. are also formed, and the crystal vibrating element 10 is manufactured.

[0080] Next, the quartz crystal vibrating element 10, which includes the quartz crystal blank 11 and the first and second excitation electrodes 14a and 14b, is mounted on the base member 30 (S153). Specifically, electrode pads 33a and 33b are formed on the first main surface 32a of the base member 30. Connection electrodes 16a and 16b formed on one end of the second main surface 12b of the quartz crystal blank 11 are mounted on the electrode pads 33a and 33b via conductive holding members 36a and 36b. As a result, the quartz crystal vibrating element 10 is held in a cantilevered state on the first main surface 32a of the base member 30. The second excitation electrode 14b of the quartz crystal vibrating element 10 is disposed facing the first main surface 32a of the base member 30.

[0081] The process for processing the base member 30 and the process for forming the various electrodes are common, and the configuration of the base member 30 has already been described. Therefore, the description of the process for preparing the base member 30 will be omitted.

[0082] Next, a portion of the first excitation electrode 14a formed on the first principal surface 12a of the quartz crystal blank 11 is removed by trimming (S154). Specifically, an argon (Ar) ion beam is irradiated onto the entire surface of the first excitation electrode 14a from above the base member 30 on which the quartz crystal vibrating element 10 is provided. As a result, atoms of the first metal layer 141 exposed on the surface of the first excitation electrode 14a are sputtered away, and a portion of the first metal layer 141 is removed. After step S154, the initial thickness of the first metal layer 141 of the first excitation electrode 14a and the thickness to be removed by trimming are adjusted so that the thickness of the first excitation electrode 14a and the thickness of the second excitation electrode 14b are approximately the same.

[0083] In this case, for example, when the thickness of the crystal blank 11 is 1820 [nm], the first metal layer 141 in the first excitation electrode 14a and the second excitation electrode 14b is formed to have a thickness of approximately 125 [nm], and the second metal layer 142 is formed to have a thickness of approximately 1 [nm].

[0084] In a small quartz crystal resonator such as the quartz crystal resonator 1 of this embodiment, the thickness of the quartz crystal blank 11 typically ranges from a maximum of approximately 2000 nm to a minimum of approximately 1000 nm. When the thickness of the quartz crystal blank 11 is 1000 nm, the first metal layer 141 in the first excitation electrode 14a and the second excitation electrode 14b is approximately 68.5 nm thick, and the second metal layer 142 is approximately 2 nm thick. When the thickness of the quartz crystal blank 11 is 2000 nm, the first metal layer 141 in the first excitation electrode 14a and the second excitation electrode 14b is approximately 137 nm thick, and the second metal layer 142 is approximately 0.5 nm thick.

[0085] Therefore, the ratio of the thickness of the second metal layer 142 to the thickness of the first metal layer 141 (hereinafter simply referred to as the "thickness ratio of the second metal layer 142") is 0.4% or more and 2.9% or less.

[0086] Next, the base member 30 and the lid member 20 are bonded together using the sealing frame 37 and the bonding material 40 (S155). Specifically, the sealing frame 37 is provided around the entire periphery of the first main surface 32a of the base member 30. The sealing frame 37 is provided by screen printing, and then heated to solidify (pre-solidify). Then, the bonding material 40, which is a glass adhesive, and the lid member 20 are placed on the sealing frame 37 of the base member 30, and heated again to melt the sealing frame 37 and the bonding material 40, followed by firing (main firing). As a result, the base member 30 and the lid member 20 are bonded together. In this manner, a quartz crystal resonator 1 having improved airtightness between the lid member 20 and the base member 30 is manufactured.

[0087] The process for processing the lid member 20 is common, and the configuration of the lid member 20 has already been explained. Therefore, the explanation of the process for preparing the lid member 20 will be omitted.

[0088] Next, with reference to FIGS. 7 and 8, the relationship between the thickness of the second metal layer or the thickness ratio of the second metal layer to the first metal layer and the frequency change rate of the resonant frequency will be described. FIG. 7 is a graph showing the relationship between the thickness of the second metal layer and the frequency change rate of the resonant frequency. FIG. 8 is a graph showing the relationship between the thickness ratio of the second metal layer to the first metal layer and the frequency change rate of the resonant frequency. In FIG. 7, the horizontal axis represents the thickness of the second metal layer in [nm]. The vertical axis represents the frequency change rate of the resonant frequency (dF / F) in [ppm]. Note that the thickness of the second metal layer in FIG. 7 is the sum of the thicknesses of the second metal layer in both the first excitation electrode and the second excitation electrode. In FIG. 8, the horizontal axis represents the thickness ratio of the second metal layer to the first metal layer in [%]. The vertical axis represents the frequency change rate of the resonant frequency (dF / F) in [ppm].

[0089] As shown by the white circle plots in Figure 7, a conventional quartz crystal unit with a total thickness of the second metal layer of approximately 10 nm exhibits an average frequency change rate of approximately -14 ppm after 500 hours in an environment with a temperature of 85°C and a humidity of 85% RH.

[0090] In contrast, as shown by the black dots in Figure 7, after 500 hours under the above-mentioned environment, the crystal unit 1 exhibited an average frequency change rate of approximately -4 ppm when the total thickness of the second metal layer 142 was 2 nm. Furthermore, when the thickness of the second metal layer 142 was changed to 4 nm, the frequency change rate of the resonant frequency was also approximately -4 ppm on average. Furthermore, although not shown in the figure, it was found that the frequency change rate of the resonant frequency tends to saturate as the total thickness of the second metal layer 142 becomes smaller. Therefore, a similar frequency change rate of the resonant frequency can be obtained even when the total thickness of the second metal layer is 1 nm, which is the smallest (thinnest) thickness that can be stably manufactured.

[0091] Looking at a different indicator, as shown by the white circle plot in Figure 8, a conventional quartz crystal unit in which the thickness ratio of the second metal layer to the first metal layer is about 4% has an average frequency change rate of about -14 ppm after 500 hours under the above-mentioned environment.

[0092] In contrast, as shown by the black dots in Figure 8, the crystal unit 1 after 500 hours under the above-mentioned environment exhibited an average frequency change rate of approximately -4 ppm when the thickness ratio of the second metal layer 142 to the first metal layer 141 was 0.8%. Furthermore, when the thicknesses of the first metal layer 141 and the second metal layer 142 were varied and the thickness ratio of the second metal layer 142 to the first metal layer 141 was 2.9%, the frequency change rate of the resonant frequency was also approximately -4 ppm on average. Furthermore, although not shown, we found that the frequency change rate of the resonant frequency tends to saturate as the thickness ratio decreases. Therefore, a similar frequency change rate of the resonant frequency can be obtained even when the thickness ratio of the second metal layer 142 to the first metal layer 141 is 0.4%, which is the smallest (thinnest) thickness at which the second metal layer 142 can be stably manufactured.

[0093] In this way, by setting the thickness ratio of second metal layer 142 to first metal layer 141 to be equal to or greater than 0.4% and equal to or less than 2.9%, the thickness of second metal layer 142 relative to first metal layer 141 is smaller than in conventional quartz crystal resonators, and this makes it possible to suppress diffusion of the metal of second metal layer 142 into first metal layer 141. Therefore, it is possible to reduce the possibility that the metal of second metal layer 142 will be exposed to the surface and oxidized, and it is possible to suppress changes in the resonant frequency over time.

[0094] Second Embodiment Next, a resonator device according to a second embodiment of the present invention will be described with reference to Fig. 9. In the following embodiments, the same or similar components as those in the first embodiment will be denoted by the same or similar reference numerals, and only the differences from the first embodiment will be described. Furthermore, similar effects and advantages resulting from similar components will not be mentioned in detail.

[0095] Fig. 9 is a cross-sectional view that schematically illustrates the cross-sectional configuration of a quartz crystal resonator 201 according to the second embodiment. Fig. 9 is a cross-sectional view that corresponds to Fig. 2 in the first embodiment.

[0096] The configuration example of the second embodiment shown in FIG. 9 differs from the configuration example of the quartz crystal resonator 1 of the first embodiment shown in FIG. 2 in that the cover member 220 is a flat plate-like member and the base member 230 has a box shape including an opening.

[0097] The base member 230 has an inner bottom surface 238a, an opposing surface 238b, and an inner side surface 238c on the lid member 220 side. The inner bottom surface 238a and the opposing surface 238b face the first main surface 222a of the lid member 220. The inner bottom surface 238a is located in the center of the lid member 220 side. An electrode pad 233a is provided on the inner bottom surface 238a. The inner side surface 238c is a surface that connects the inner bottom surface 238a and the opposing surface 238b. The opposing surface 238b is located outside the inner bottom surface 238a when the inner bottom surface 238a is viewed in plan, and has a frame shape. A sealing frame 237 is provided on the opposing surface 238b around the entire periphery.

[0098] The lid member 220 has a first main surface 222a and a second main surface 222b facing each other. A bonding material 240 is provided around the entire outer periphery of the second main surface 222b. The bonding material 240 bonds the base member 230 and the lid member 220 together, sealing the internal space 226. The quartz crystal vibrating element 210 is housed in the internal space 226.

[0099] A conductive holding member 236a is formed on one surface of the electrode pad 233a (the surface on the positive Y'-axis direction side in Figure 4), and one end of the quartz vibrating element 210 is held on the surface of the electrode pad 233a by the conductive holding member 236a.

[0100] The quartz crystal vibrating element 210 includes a quartz crystal blank 211, and a first excitation electrode 214a and a second excitation electrode 214b provided on both main surfaces of the quartz crystal blank 211. The first excitation electrode 214a and the second excitation electrode 214b each include a first metal layer 141 and a second metal layer 142 (not shown), similar to the first embodiment.

[0101] The method for manufacturing the quartz crystal vibrating element 210 is substantially the same as the method for manufacturing the quartz crystal vibrating element 1 in the first embodiment described above, and therefore illustrations and explanations thereof will be omitted.

[0102] An exemplary embodiment of the present invention has been described above. In a quartz crystal unit according to one embodiment, the first excitation electrode and the second excitation electrode each include a first metal layer and a second metal layer disposed between the first metal layer and the quartz crystal blank, and the weight ratio of the second metal layer to the first metal layer is 0.1% to 1.1%. This reduces the weight of the second metal layer relative to the first metal layer compared to conventional quartz crystal units, thereby suppressing diffusion of the metal from the second metal layer into the first metal layer. This reduces the possibility of the metal from the second metal layer being exposed to the surface and oxidized, thereby suppressing changes in the resonant frequency over time.

[0103] In the above-described crystal unit, the thickness of the second metal layer is smaller than the thickness of the first metal layer, which makes it easy to form the second metal layer with a smaller weight ratio than the first metal layer.

[0104] In addition, in the above-mentioned quartz crystal unit, the difference in thermal expansion coefficient between the second metal layer and the quartz crystal blank is smaller than the difference in thermal expansion coefficient between the first metal layer and the quartz crystal blank, which allows the second metal layer to function as an adhesive layer that adheres the first metal layer to the quartz crystal blank.

[0105] In addition, in the above-mentioned quartz crystal unit, the first metal layer is made of gold (Au) and the second metal layer is made of chromium (Cr), which makes it easy to configure (realize) a quartz crystal unit that suppresses changes in resonance frequency over time.

[0106] Furthermore, in the above-described crystal resonator, the material of the piezoelectric piece is crystal, which makes it possible to easily configure (realize) a crystal resonator that suppresses changes in the resonant frequency over time.

[0107] The above-described crystal unit further includes a cover member that houses the crystal vibrating element in the internal space formed between the cover member and the base member, thereby protecting the crystal vibrating element from the external environment.

[0108] Furthermore, by further providing a bonding material that bonds the base member and the lid member to each other in the above-described quartz crystal resonator, the quartz crystal resonator element can be sealed in the internal space between the base member and the lid member.

[0109] In one embodiment of the method for manufacturing a quartz crystal unit, the ratio of the thickness of the second metal layer to the thickness of the first metal layer is 0.4% or more and 2.9% or less. This reduces the thickness of the second metal layer relative to the first metal layer compared to conventional quartz crystal units, thereby suppressing diffusion of the metal of the second metal layer into the first metal layer. This reduces the possibility of the metal of the second metal layer being exposed to the surface and oxidized, thereby suppressing changes in the resonant frequency over time.

[0110] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the scope of the present invention. The present invention may be modified or improved without departing from its spirit, and equivalents are also encompassed within the scope of the present invention. In other words, designs modified by those skilled in the art as appropriate to the embodiments and / or modifications are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention. For example, the elements and their arrangements, materials, conditions, shapes, sizes, etc. of the embodiments and / or modifications are not limited to those illustrated and can be modified as appropriate. Furthermore, the embodiments and modifications are merely examples, and it goes without saying that partial substitutions or combinations of the configurations shown in different embodiments and / or modifications are possible. These are also encompassed within the scope of the present invention as long as they incorporate the characteristics of the present invention. [Explanation of symbols]

[0111] 1...quartz crystal resonator, 10...quartz crystal resonator element, 11...quartz crystal blank, 12a...first main surface, 12b...second main surface, 14a...first excitation electrode, 14b...second excitation electrode, 15a, 15b...lead-out electrode, 16a, 16b...connection electrode, 20...lid member, 21...top surface, 22...side wall, 23...opposing surface, 24...inner surface, 25...outer surface, 26...internal space, 30...base member, 31...substrate, 32a...first main surface, 32b...second main surface, 33a, 33b...electrode pads, 34a, 34b...via electrodes, 35a, 35b, 35c, 35d...external electrodes, 36a ,36b...conductive holding member, 37...sealing frame, 40...bonding material, 141...first metal layer, 142...second metal layer, 201...quartz crystal oscillator, 210...quartz crystal oscillator element, 211...quartz crystal blank, 214a...first excitation electrode, 214b...second excitation electrode, 220...lid member, 222a...first main surface, 222b...second main surface, 226...internal space, 230...base member, 233a...electrode pad, 236a...conductive holding member, 237...sealing frame, 238a...inner bottom surface, 238b...opposing surface, 238c...inner surface, 240...bonding material, S150...manufacturing method.

Claims

1. A base member; a piezoelectric vibration element held on one surface of the base member, the piezoelectric vibration element having a piezoelectric piece made of quartz crystal with a thickness of 1000 nm to 2000 nm and excitation electrodes provided on both main surfaces of the piezoelectric piece; the excitation electrode includes a first metal layer made of gold and a second metal layer made of chromium disposed between the first metal layer and the piezoelectric piece, and a weight ratio of the second metal layer to the first metal layer is 0.1% or more and 1.1% or less; a total thickness of the first metal layers in the excitation electrodes on both main surfaces is 137 nm or more and 274 nm or less, and a total thickness of the second metal layers is 1 nm or more and 4 nm or less; Piezoelectric vibrator.

2. a difference in thermal expansion coefficient between the second metal layer and the piezoelectric piece is smaller than a difference in thermal expansion coefficient between the first metal layer and the piezoelectric piece; The piezoelectric vibrator according to claim 1 .

3. a cover member that houses the piezoelectric vibration element in a space formed between the cover member and the base member; 3. The piezoelectric vibrator according to claim 1 or 2.

4. Further provided is a bonding material that bonds the base member and the lid member. The piezoelectric vibrator according to claim 3 .

5. A step of preparing a piezoelectric piece made of quartz crystal having a thickness of 1000 nm or more and 2000 nm or less; forming excitation electrodes on both main surfaces of the piezoelectric piece, the excitation electrodes including a first metal layer mainly made of gold and a second metal layer mainly made of chromium, the second metal layer being disposed between the first metal layer and the piezoelectric piece; and removing a portion of the first metal layer formed on one of the two main surfaces by trimming, a thickness ratio of the second metal layer to the first metal layer is 0.4% or more and 2.9% or less; the total thickness of the first metal layer is equal to or greater than 137 nm and equal to or less than 274 nm; a total thickness of the second metal layer in the excitation electrodes on both main surfaces is 1 nm or more and 4 nm or less; A method for manufacturing a piezoelectric vibrator.

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