Piezoelectric vibrators and their manufacturing methods

Abstract

The crystal oscillator (1) comprises: a crystal oscillating element (10) having a pair of electrodes (14a, 14b) comprising opposing electrodes, and a holder for housing the crystal oscillating element (10); at least one of the pair of electrodes (14a, 14b) has an upper layer (22) comprising gold and a lower layer (21) comprising chromium disposed between the crystal wafer (11) and the upper layer (22); the surface of at least one electrode has a plurality of grains (23) made of gold and a chromium compound (27) formed along the grain boundaries (24) of the plurality of grains; when viewed from above, the area ratio of the plurality of grains (23) is 35% to 60%.

Description

Technical Field

[0001] This invention relates to piezoelectric vibrators and methods for manufacturing them. Background Technology

[0002] Oscillators are used in various electronic devices such as mobile communication terminals, communication base stations, and home appliances for purposes such as timing devices, sensors, and oscillators. For example, a piezoelectric oscillator consists of a piezoelectric vibrating element having a mechanical vibrating part that converts electrical vibrations into mechanical vibrations using the piezoelectric effect, a holder housing the piezoelectric vibrating element, and a conductive holding member connecting the piezoelectric vibrating element to the holder. The conductive holding member is, for example, a cured product of a conductive adhesive with silicone resin as the main component.

[0003] Patent Document 1 discloses a method for manufacturing an oscillator to improve frequency stability. The method comprises an excitation electrode having a base layer made of chromium and an upper layer made of gold. The method includes: a step of mounting a vibrating plate on a substrate using a bonding material; a step of heating the bonding material and the vibrating plate at a first temperature; a step of adjusting the frequency of the vibrating plate after the step of heating at the first temperature; and a step of heating the bonding material and the vibrating plate at a second temperature after the step of adjusting the frequency. The second temperature is lower than the first temperature, and the difference between the first temperature and the second temperature is 15°C or more.

[0004] Patent Document 2 discloses an excitation electrode structure for a crystal oscillator that significantly improves the electrical characteristics of the oscillator over time. The structure is characterized by using a titanium layer as the base electrode on a crystal blank of the oscillator, and then stacking a main electrode layer composed of a gold (Au) layer on top of it. The grain size of the main electrode layer is 0.01 μm to 0.1 μm. Furthermore, it discloses that by changing the temperature of the crystal substrate during the film formation of the gold layer (the main electrode layer) from the conventional 120°C ± 10°C to a range of room temperature (25°C ± 3°C) to 50°C, the texture of the gold layer as a grain size is refined, resulting in a dense electrode surface with a grain size of 0.01 μm to 0.1 μm.

[0005] Patent document 3 discloses that the adsorption and desorption of gas molecules on the crystal wafer, the oxidation of the vapor-deposited electrode, the recrystallization of the vapor-deposited electrode, and the diffusion of electrode metal into the crystal wafer are the determining factors of the time-varying characteristics of the crystal oscillator.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2016-144091

[0009] Patent Document 2: Japanese Patent Application Publication No. 2006-311337

[0010] Patent Document 3: Japanese Patent Application Publication No. 2006-50508 Summary of the Invention

[0011] However, in the manufacturing method described in Patent Document 1, even if the heat treatment of the excitation electrode is optimized so that chromium does not diffuse after ion milling for frequency adjustment, chromium will diffuse back to the upper layer through heating processes such as reflow, and a chromium oxide layer will form on the surface of the upper layer, thus causing the frequency to change.

[0012] Furthermore, it is known that at the film-forming temperature described in Patent Document 2, the particle size of gold formed by vapor deposition decreases and the frequency changes over time increases.

[0013] Furthermore, while Patent Document 3 discloses the determining factors of time-varying characteristics, it does not mention any countermeasures.

[0014] The present invention was made in view of the following circumstances, and the object of the present invention is to provide a piezoelectric oscillator with improved frequency stability and a method thereof.

[0015] One aspect of the piezoelectric vibrator of the present invention comprises: a piezoelectric sheet and a pair of electrodes comprising electrodes facing each other sandwiching the piezoelectric sheet, and a holder for housing the piezoelectric vibrating element, wherein at least one of the pairs of electrodes has an upper layer comprising gold and a lower layer comprising chromium disposed between the piezoelectric sheet and the upper layer, and the surface of the at least one electrode has a plurality of grains made of gold and a chromium compound formed along the grain boundaries of the plurality of grains, wherein when viewed from above, the area ratio of the plurality of grains is 35% to 60%.

[0016] Another aspect of the present invention provides a method for manufacturing a piezoelectric vibrator comprising: a step of preparing a piezoelectric sheet; a step of setting a pair of electrodes comprising electrodes sandwiching the piezoelectric sheet and facing each other; a step of mounting a piezoelectric vibrating element on a base member using a conductive retaining member; and a step of joining a cover member to the base member using a joining member; the step of setting a pair of electrodes comprises: a step of preheating the piezoelectric sheet to 100°C to 300°C; a step of setting a lower layer comprising chromium on the preheated piezoelectric sheet; and a step of setting an upper layer comprising gold on the lower layer.

[0017] According to the present invention, a piezoelectric oscillator with improved frequency stability and a method thereof can be provided. Attached Figure Description

[0018] Figure 1 This is an exploded perspective view that schematically shows the structure of the crystal oscillator in the first embodiment.

[0019] Figure 2 This is a cross-sectional view that schematically shows the structure of the crystal oscillator in the first embodiment.

[0020] Figure 3 It is a cross-sectional view that roughly shows the configuration of the electrodes of the crystal resonator.

[0021] Figure 4 It is a top view that roughly shows the configuration of the surface of the central part of the first excitation electrode.

[0022] Figure 5 It is a cross-sectional view that roughly shows the structure of the central part of the first excitation electrode.

[0023] Figure 6 This is a flowchart that roughly illustrates the manufacturing method of the crystal oscillator according to the first embodiment.

[0024] Figure 7 This is a simplified cross-sectional view of the first excitation electrode before ion milling.

[0025] Figure 8 This is a cross-sectional view that roughly represents the variation of the first excitation electrode based on ion milling.

[0026] Figure 9 It is a cross-sectional view that roughly represents the changes in the first excitation electrode based on annealing.

[0027] Figure 10 This is a graph showing the relationship between the frequency deviation after sealing and the film formation conditions.

[0028] Figure 11 This is a diagram showing an FE-SEM image obtained by photographing the surface of the first excitation electrode.

[0029] Figure 12 It is a table representing the area ratio of multiple grains.

[0030] Figure 13 This is a graph showing the relationship between the area ratio of multiple grains on the surface of the first excitation electrode and the film formation conditions.

[0031] Figure 14 It is a table representing the atomic composition of the surface of the first excitation electrode.

[0032] Figure 15 This is a graph showing the relationship between the cumulative frequency and area of ​​multiple grains on the surface of the first excitation electrode. Detailed Implementation

[0033] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The drawings for each embodiment are illustrative, and the dimensions and shapes of the parts are schematic and should not be construed as limiting the scope of the technology of the present invention to these embodiments.

[0034] <First Implementation>

[0035] Reference Figure 1 and Figure 2 The structure of the crystal oscillator 1 according to the first embodiment of the present invention will be described. Figure 1 This is an exploded perspective view that schematically shows the structure of the crystal oscillator in the first embodiment. Figure 2 This is a cross-sectional view that schematically shows the structure of the crystal oscillator in the first embodiment.

[0036] In each of the accompanying figures, to clarify the relationships between the figures, to aid in understanding the positional relationships of the components, and for convenience, an orthogonal coordinate system consisting of the X-axis, Y′-axis, and Z′-axis is provided. The X-axis, Y′-axis, and Z′-axis correspond to each other in the accompanying figures. The X-axis, Y′-axis, and Z′-axis correspond to the crystal axes of the wafer 11, which will be described later. The X-axis corresponds to the electrical axis (polarity axis), the Y-axis corresponds to the mechanical axis, and the Z-axis corresponds to the optical axis. The Y′-axis and Z′-axis are obtained by rotating the Y-axis and Z-axis about the X-axis from the Y-axis along the Z-axis direction by 35 degrees 15 minutes ± 1 minute 30 seconds, respectively.

[0037] 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 is referred to as the "Y′-axis direction," and the direction parallel to the Z′-axis is referred to as the "Z′-axis direction." Furthermore, the direction of the arrowheads for the X-axis, Y′-axis, and Z′-axis is referred to as "+ (positive)," and the direction opposite to the arrowhead is referred to as "- (negative)." It should be noted that, for convenience, the +Y′-axis direction is used as the upward direction and the -Y′-axis direction as the downward direction, but the orientation of the crystal oscillator 1 is not limited. For example, in the following description, the side of the crystal oscillator 10 with the +Y′-axis direction is referred to as the upper surface 11A, and the side with the -Y′-axis direction is referred to as the lower surface 11B, but the crystal oscillator 11 can be configured such that the upper surface 11A is located vertically below the lower surface 11B.

[0038] The crystal oscillator 1 includes a crystal vibrating element 10, a base member 30, a cover member 40, and a connecting member 50. The crystal vibrating element 10 is disposed between the base member 30 and the cover member 40. The base member 30 and the cover member 40 constitute a retainer for housing the crystal vibrating element 10. Figure 1 and Figure 2In the example shown, the base member 30 is flat, and the cover member 40 has a bottomed opening on the base member 30 side for receiving the crystal vibrating element 10. The crystal vibrating element 10 is mounted on the base member 30. It should be noted that the shapes of the base member 30 and the cover member 40 are not limited to the above description, as long as at least the excited portion of the crystal vibrating element 10 is received in the holder. Furthermore, the method of holding the crystal vibrating element 10 is not limited to the above description. For example, the base member 30 may have a bottomed opening on the cover member 40 side for receiving the crystal vibrating element 10. Additionally, the base member 30 and the cover member 40 may clamp the periphery of the excited portion of the crystal vibrating element 10.

[0039] First, the crystal resonator 10 will be explained.

[0040] The crystal oscillating element 10 is a component that converts electrical energy into mechanical energy by causing the crystal to vibrate through the piezoelectric effect. The crystal oscillating element 10 includes: a thin crystal plate 11, a first excitation electrode 14a and a second excitation electrode 14b constituting a pair of excitation electrodes, a pair of lead-out electrodes and a first lead-out electrode 15a and a second lead-out electrode 15b constituting a pair of lead-out electrodes, and a first connecting electrode 16a and a second connecting electrode 16b constituting a pair of connecting electrodes.

[0041] The wafer 11 has an upper surface 11A and a lower surface 11B that are opposite to each other. The upper surface 11A is located on the side opposite to the side facing the base member 30, that is, on the side facing the top surface 41 of the cover member 40, which will be described later. The lower surface 11B is located on the side facing the base member 30.

[0042] The crystal wafer 11 is, for example, an AT-cut type crystal wafer. The AT-cut type crystal wafer 11 is formed such that, in an orthogonal coordinate system composed of intersecting X-axis, Y′-axis, and Z′-axis, the plane parallel to the plane defined by the X-axis and Z′-axis (hereinafter referred to as the "XZ′ plane"; the same applies to the plane defined by the other axes) is the principal plane, and the direction parallel to the Y′-axis is the thickness. For example, the AT-cut type crystal wafer 11 is formed by etching a crystal substrate (e.g., a crystal wafer) obtained by cutting and grinding a crystal of synthetic quartz crystal.

[0043] The crystal resonator 10 using an AT-cut crystal wafer 11 exhibits high frequency stability over a wide temperature range. The AT-cut crystal resonator 10 uses a thickness shear vibration mode as the primary vibration. It should be noted that the rotation angles of the Y′ and Z′ axes in the AT-cut crystal wafer 11 can be tilted within a range from 35 degrees 15 minutes to more than -5 degrees and less than 15 degrees. The cutting angle of the crystal wafer 11 can be different from AT cutting. For example, BT cutting, GT cutting, SC cutting, etc., can be used. Alternatively, the crystal resonator can also be a tuning fork type crystal resonator using a crystal wafer with a cutting angle known as a Z-plate.

[0044] The AT-cut wafer 11 is a plate-shaped material having a long side extending parallel to the X-axis, a short side extending parallel to the Z′-axis, and a thickness extending parallel to the Y′-axis. When viewed from above, the upper surface 11A of the wafer 11 has a rectangular shape, with a centrally located excitation section 17 that facilitates excitation, and peripheral sections 18 and 19 adjacent to the excitation section 17. The excitation section 17 and peripheral sections 18 and 19 are formed in a strip-like manner, extending across the entire width of the wafer 11 along the Z′-axis. Peripheral section 18 is located on the -X-axis side of the excitation section 17, and peripheral section 19 is located on the +X-axis side of the excitation section 17.

[0045] It should be noted that the planar shape of the crystal plate 11 when viewed from above the upper surface 11A is not limited to a rectangular shape. The planar shape of the crystal plate 11 can also be polygonal, circular, elliptical, or a combination thereof. The planar shape of the crystal plate 11 can also be a tuning fork shape. In other words, the crystal plate 11 can have a base and a vibrating arm extending parallel to the base. To suppress vibration leakage and stress propagation, slits can be formed in the crystal plate 11. The shapes of the excitation portion 17 and the peripheral portions 18, 19 of the crystal plate 11 are not limited to a strip shape covering the entire width. For example, the planar shape of the excitation portion can also be an island shape that is adjacent to the peripheral portion in the Z′ axis direction, and the planar shape of the peripheral portion can also be formed as a frame shape surrounding the excitation portion.

[0046] The wafer 11 has a so-called mesa-shaped structure in which the thickness of the excitation section 17 is greater than the thickness of the peripheral sections 18 and 19. The mesa-shaped structure of the wafer 11 can suppress vibration leakage from the excitation section 17. The wafer 11 has a two-sided mesa-shaped structure, with the excitation section 17 protruding from the peripheral sections 18 and 19 on both sides of the upper surface 11A and the lower surface 11B. The boundary between the excitation section 17 and the peripheral section 18, and the boundary between the excitation section 17 and the peripheral section 19, form a cone shape with a continuously varying thickness, but it can also form a stepped shape with a discontinuous variation in thickness. This boundary can also be a convex shape with a continuously varying thickness or a sloping shape with a discontinuous variation in thickness. It should be noted that the wafer 11 can also be a single-sided mesa-shaped structure in which the excitation section 17 protrudes from the peripheral sections 18 and 19 on only one side of the upper surface 11A or the lower surface 11B. Alternatively, the wafer 11 can also be a so-called inverted mesa-shaped structure in which the thickness of the excitation section 17 is less than the thickness of the peripheral sections 18 and 19.

[0047] A first excitation electrode 14a and a second excitation electrode 14b are disposed on the excitation section 17. The first excitation electrode 14a is disposed on the upper surface 11A side of the wafer 11, and the second excitation electrode 14b is disposed on the lower surface 11B side of the wafer 11. In other words, the first excitation electrode 14a is disposed on the main surface of the wafer 11 on the side of the cover member 40, and the second excitation electrode 14b is disposed on the main surface of the wafer 11 on the side of the base member 30. The first excitation electrode 14a and the second excitation electrode 14b sandwich the wafer 11 and face each other. When viewed from above on the upper surface 11A of the wafer 11, the first excitation electrode 14a and the second excitation electrode 14b are each rectangular in shape and are arranged to substantially overlap each other. The first excitation electrode 14a and the second excitation electrode 14b are each distributed across the entire width along the Z′ axis of the wafer 11 and are formed in a strip shape. The first excitation electrode 14a and the second excitation electrode 14b are equivalent to a pair of electrodes including each electrode sandwiching the wafer 11 and facing each other.

[0048] It should be noted that the planar shapes of the first excitation electrode 14a and the second excitation electrode 14b when viewed from above the upper surface 11A of the wafer 11 are not limited to rectangular shapes. The planar shapes of the first excitation electrode 14a and the second excitation electrode 14b may also be polygonal, circular, elliptical, or a combination thereof.

[0049] A first lead-out electrode 15a and a second lead-out electrode 15b are disposed on the peripheral portion 18. The first lead-out electrode 15a is disposed on the upper surface 11A side of the wafer 11, and the second lead-out electrode 15b is disposed on the lower surface 11B side of the wafer 11. The first lead-out electrode 15a electrically connects the first excitation electrode 14a and the first connecting electrode 16a. The second lead-out electrode 15b electrically connects the second excitation electrode 14b and the second connecting electrode 16b. For example, as... Figure 1As shown, one end of the first lead-out electrode 15a is connected to the first excitation electrode 14a at the excitation section 17, and the other end of the first lead-out electrode 15a is connected to the first connecting electrode 16a at the peripheral section 18. Similarly, one end of the second lead-out electrode 15b is connected to the second excitation electrode 14b at the excitation section 17, and the other end of the second lead-out electrode 15b is connected to the second connecting electrode 16b at the peripheral section 18. To reduce stray capacitance, the first lead-out electrode 15a and the second lead-out electrode 15b are preferably separated when viewed from above on the upper surface 11A of the wafer 11. For example, when viewed from the second lead-out electrode 15b, the first lead-out electrode 15a is positioned in the +Z′ axis direction.

[0050] The first connecting electrode 16a and the second connecting electrode 16b are electrodes used to electrically connect the first excitation electrode 14a and the second excitation electrode 14b to the base member 30, respectively, and are disposed on the lower surface 11B side of the wafer 11 in the peripheral portion 18. The first connecting electrode 16a is disposed at the corner formed by the end of the wafer 11 in the -X-axis direction and the end in the +Z′-axis direction, and the second connecting electrode 16b is disposed at the corner formed by the end of the wafer 11 in the -X-axis direction and the end in the -Z′-axis direction.

[0051] Next, the basic component 30 will be described.

[0052] The base member 30 can maintain the excitation of the crystal oscillator 10. The base member 30 has a base 31 having an upper surface 31A and a lower surface 31B facing each other. The upper surface 31A is located on one side of the crystal oscillator 10 and the cover member 40, corresponding to the mounting surface of the crystal oscillator 10. The lower surface 31B corresponds, for example, to the mounting surface facing the circuit board when the crystal oscillator 1 is mounted on the outside circuit board. The base 31 is, for example, a sintered material such as insulating ceramic (alumina). From the viewpoint of suppressing the generation of thermal stress, the base 31 is preferably made of a heat-resistant material. From the viewpoint of suppressing the stress exerted on the crystal oscillator 10 due to thermal experience, the base 31 can be provided with a material having a thermal expansion coefficient close to that of the crystal wafer 11, for example, it can be provided with crystal.

[0053] The base component 30 includes a first electrode pad 33a and a second electrode pad 33b forming a pair of electrode pads. The first electrode pad 33a and the second electrode pad 33b are disposed on the upper surface 31A of the substrate 31. The first electrode pad 33a and the second electrode pad 33b are terminals for electrically connecting the crystal oscillating element 10 to the base component 30. From the viewpoint of suppressing the reduction in reliability due to oxidation, the outermost surface of each of the first electrode pad 33a and the second electrode pad 33b preferably contains gold, and more preferably is composed of approximately only gold. For example, the first electrode pad 33a and the second electrode pad 33b can be a two-layer structure having a base layer that improves adhesion to the substrate 31 and a surface layer containing gold to suppress oxidation.

[0054] The base component 30 includes a first external electrode 35a, a second external electrode 35b, a third external electrode 35c, and a fourth external electrode 35d. The first external electrode 35a to the fourth external electrode 35d are disposed on the lower surface 31B of the base 31. The first external electrode 35a and the second external electrode 35b are terminals for electrically connecting an external substrate (not shown) to the crystal oscillator 1. The third external electrode 35c and the fourth external electrode 35d are virtual electrodes that do not input or output electrical signals, but they can also be grounding electrodes to improve the electromagnetic shielding function of the cover component 40 by grounding it. It should be noted that the third external electrode 35c and the fourth external electrode 35d can be omitted.

[0055] The first electrode pad 33a and the second electrode pad 33b are arranged along the Z′ axis at their ends on the -X axis side of the base member 30. The first external electrode 35a and the second external electrode 35b are arranged along the Z′ axis at their ends on the -X axis side of the base member 30. The third external electrode 35c and the fourth external electrode 35d are arranged along the Z′ axis at their ends on the +X axis side of the base member 30. The first electrode pad 33a is electrically connected to the first external electrode 35a via a first through electrode 34a penetrating the substrate 31 along the Y′ axis. The second electrode pad 33b is electrically connected to the second external electrode 35b via a second through electrode 34b penetrating the substrate 31 along the Y′ axis.

[0056] The first electrode pad 33a and the second electrode pad 33b can be electrically connected to the first external electrode 35a and the second external electrode 35b via side electrodes disposed on the side connecting the upper surface 31A and the lower surface 31B of the substrate 31. The first external electrode 35a to the fourth external electrode 35d can be toothed electrodes that are concavely disposed on the side of the substrate 31.

[0057] The base member 30 includes a first conductive retaining member 36a and a second conductive retaining member 36b that constitute a pair of conductive retaining members. The first conductive retaining member 36a and the second conductive retaining member 36b mount the crystal resonator 10 on the base member 30, electrically connecting the crystal resonator 10 to the base member 30. The first conductive retaining member 36a engages with the first electrode pad 33a and the first connecting electrode 16a, electrically connecting the first electrode pad 33a to the first connecting electrode 16a. The second conductive retaining member 36b engages with the second electrode pad 33b and the second connecting electrode 16b, electrically connecting the second electrode pad 33b to the second connecting electrode 16b. The first conductive retaining member 36a and the second conductive retaining member 36b hold the crystal resonator 10 with a gap from the base member 30 so that the excitation unit 17 can be excited.

[0058] The first conductive retaining member 36a and the second conductive retaining member 36b are cured products of conductive adhesives including thermosetting resins, photocurable resins, etc., and the main component of the first conductive retaining member 36a and the second conductive retaining member 36b is, for example, silicone resin. The first conductive retaining member 36a and the second conductive retaining member 36b contain conductive particles, and such conductive particles can be, for example, metal particles containing silver (Ag). The first conductive retaining member 36a bonds the first electrode pad 33a to the first connecting electrode 16a, and the second conductive retaining member 36b bonds the second electrode pad 33b to the second connecting electrode 16b.

[0059] The main components of the first conductive retaining member 36a and the second conductive retaining member 36b are curable resins, not limited to silicone resins; for example, they can also be epoxy resins, acrylic resins, etc. Furthermore, imparting conductivity to the first conductive retaining member 36a and the second conductive retaining member 36b is not limited to using silver particles; other metals, conductive ceramics, conductive organic materials, etc., can also be used. The main components of the first conductive retaining member 36a and the second conductive retaining member 36b can also be conductive polymers.

[0060] The resin composition of the first conductive retaining member 36a and the second conductive retaining member 36b may contain any additives. Additives may include, for example, tackifiers, fillers, thickeners, sensitizers, anti-aging agents, defoamers, etc., for improving the workability and shelf life of the conductive adhesive. Additionally, fillers may be added to increase the strength of the cured product or to maintain the spacing between the base member 30 and the crystal vibrating element 10.

[0061] Next, the cover component 40 will be described.

[0062] The cover member 40 is joined to the base member 30, forming an internal space 49 between them to house the crystal vibrating element 10. The material of the cover member 40 is not particularly limited; for example, it can be made of a conductive material such as metal. By making the cover member 40 a conductive material, it acquires an electromagnetic shielding function that reduces electromagnetic waves entering and exiting the internal space 49.

[0063] The cover member 40 has a flat top surface 41 and a side wall portion 42 connected to the outer edge of the top surface 41 and extending in a direction intersecting the main surface of the top surface 41. The top surface 41, when viewed from the normal direction of the main surface, has a planar shape, for example, rectangular. The top surface 41 sandwiches the crystal vibrating element 10 and faces the base member 30, while the side wall portion 42 surrounds the crystal vibrating element 10 in a direction parallel to the XZ′ plane. The front end of the side wall portion 42 extends in a frame shape closer to the base member 30 than the crystal vibrating element 10.

[0064] The cover component 40 can be made of ceramic material, semiconductor material, resin material, etc. In addition, the planar shape of the top surface 41 can be polygonal, circular, elliptical, or a combination thereof.

[0065] Next, the connecting member 50 will be described.

[0066] The joining member 50 is provided around the entire circumference of both the base member 30 and the cover member 40, forming a rectangular frame. Viewed from above on the upper surface 31A of the base member 30, the first electrode pad 33a and the second electrode pad 33b are disposed inside the joining member 50, which is configured to surround the crystal vibrating element 10. The joining member 50 joins the front end of the sidewall portion 42 of the cover member 40 to the upper surface 31A of the base member 30, sealing the internal space 49. The joining member 50 preferably has high gas barrier properties, and more preferably low moisture permeability. Such a joining member 50 is, for example, a cured product of an adhesive with epoxy resin as the main component. The resin-based adhesive constituting the joining member 50 may include, for example, vinyl compounds, acrylic compounds, urethane compounds, silicone compounds, etc.

[0067] It should be noted that the joining member 50 is not limited to a continuous frame shape in the circumferential direction, but can also be provided discontinuously in the circumferential direction. The joining member 50 can be provided with a cured product of a silicone-based adhesive containing water glass, a cured product of a calcium-based adhesive containing cement, or an Au-Sn alloy-based metal solder. When the joining member 50 is provided with a metal solder, a metallization layer can be provided on the base member 30 to improve the tightness of the fit between the base member 30 and the joining member 50. The joining member 50 can have a cured product of a resin-based adhesive and a coating with lower moisture permeability than the cured product of a resin-based adhesive.

[0068] Next, refer to Figures 3-5 The configuration of the electrodes of the crystal resonator 10 will be described in more detail. Figure 3 It is a cross-sectional view that roughly shows the configuration of the electrodes of the crystal resonator. Figure 4 It is a top view that roughly shows the configuration of the surface of the central part of the first excitation electrode. Figure 5 It is a cross-sectional view that roughly shows the structure of the central part of the first excitation electrode.

[0069] The crystal resonator 10 has a pair of electrodes. Figure 3 In the example shown, one electrode in the pair includes a first excitation electrode 14a, a first lead-out electrode 15a, and a first connection electrode 16a, while the other electrode in the pair includes a second excitation electrode 14b, a second lead-out electrode 15b, and a second connection electrode 16b. These excitation electrodes, lead-out electrodes, and connection electrodes are formed continuously to each other. Alternatively, these excitation electrodes, lead-out electrodes, and connection electrodes can be formed integrally. Figure 3 In the example shown, each electrode of the pair of electrodes of the crystal resonating element 10 has a lower layer 21 and an upper layer 22.

[0070] The lower layer 21 is in contact with the wafer 11 and is disposed between the wafer 11 and the upper layer 22. The lower layer 21 is made of a material with higher adhesion to the wafer 11 than the material of the upper layer 22, and contains chromium (Cr) as the main component. The lower layer 21 is, for example, a chromium film formed on the surface of the wafer 11 by sputtering.

[0071] The upper layer 22 is disposed on the side opposite to the crystal resonating element 10 of the lower layer 21. For example, the thickness of the upper layer 22 is greater than the thickness of the lower layer 21. The upper layer 22 is disposed of a material with higher chemical stability than the material of the lower layer 21, containing gold (Au) as the main component. The upper layer 22 is, for example, a gold film formed on the surface of the lower layer 21 by sputtering. Figure 3 As shown, the thickness of the upper layer 22 of the first excitation electrode 14a is greater than the thickness of the upper layer 22 of the second excitation electrode 14b. Furthermore, the central portion of the XZ′ plane of the upper layer 22 of the first excitation electrode 14a is ground more extensively than the periphery by ion milling for frequency adjustment, as described later. That is, a concave shape is formed in the central portion of the XZ′ plane on the surface of the first excitation electrode 14a. It should be noted that by increasing the extent of ion milling, the thickness of the upper layer 22 of the first excitation electrode 14a can be made more uniform.

[0072] Here, if a chromium oxide film is formed on the upper layer of the excitation electrode as described in Patent Document 1, oxidation will not continue, and the frequency should not change. However, in reality, the frequency changes after a subsequent heating process. Therefore, the inventors focused on the chromium compound present on the surface of the upper layer 22 of the first excitation electrode 14a. When the surface of the upper layer 22 is imaged using FE-SEM (Field Emission-Scanning Electron Microscope), as... Figure 4 As shown, on the surface of the upper layer 22, the surface portions 26 of multiple gold grains 23 are exposed, and chromium compounds 27 surround them in a mesh shape.

[0073] More specifically, such as Figure 5 As shown, the upper layer 22 is a polycrystalline material composed of multiple grains 23. The grain boundaries 24 of each grain 23 serve as diffusion paths for chromium diffusing from the lower layer 21. Each grain 23 has an interface portion 25 located near the grain boundary 24 and a surface portion 26 surrounded by the interface portion 25. In the first excitation electrode 14a, the interface portion 25 is higher than the surface portion 26. Furthermore, the interface portion 25 is covered by a chromium compound 27. Therefore, as... Figure 4 As shown, the surface of the first excitation electrode 14a is composed of a mesh-shaped chromium compound 27 and a surface portion 26 of a plurality of grains 23 surrounded by the chromium compound 27. It should be noted that the chromium compound 27 is a compound in which chromium in the lower layer 21 diffuses through the grain boundaries of the upper layer 22 and is oxidized on the surface of the upper layer 22, and is chromium oxide or its hydrate.

[0074] The inventors speculate that the frequency change in subsequent heating processes is due to the newly diffused chromium from the grain boundary 24 causing the chromium compound 27 to rise, and the chromium exposed near the interface 25 to oxidize. Since the grain boundary 24 acts as a diffusion path for chromium, it is preferable that each of the plurality of grains 23 has a large grain size to inhibit chromium diffusion and thus prevent the formation of the chromium compound 27. That is, if the grain size of each of the plurality of grains 23 increases, the grain boundary 24 becomes narrower, thereby suppressing chromium diffusion.

[0075] More specifically, when the area fraction of multiple grains 23 is 35% to 60%, chromium diffusion can be suppressed. Here, as... Figure 4As shown, when viewed from below along the surface of the first excitation electrode 14a, the interface portion 25 of each of the plurality of grains 23 is covered by chromium compound 27. Therefore, the area of ​​the plurality of grains 23 on the surface of the first excitation electrode 14a is the sum of the areas of the plurality of surface portions 26. That is, when viewed from above, if the sum of the areas of the plurality of surface portions 26 in a certain unit area is denoted as Sa, the area of ​​chromium compound 27 is denoted as Sc, and the area ratio of the plurality of grains 23 is denoted as Rau, then Rau = Sa / (Sa + Sc), satisfying 0.4 ≤ Rau ≤ 0.6.

[0076] It should be noted that Sa and Sc are calculated based on an 800×1200 pixel image obtained by photographing the area near the center of the surface of the first excitation electrode 14a using FE-SEM at 50,000x magnification. One pixel is equivalent to 1.984375nm. 2 The area is such that Sa or Sc can be calculated by multiplying it by the number of pixels of the image constituting the surface portion 26 or the interface portion 25.

[0077] The area of ​​the grain 23 relative to 50% of the cumulative frequency is preferably 1200 nm. 2 That's all. In other words, the area Sp50 of the surface portion 26 with a cumulative frequency of 50% preferably satisfies 1200 nm. 2 ≤Sp50. More preferably, the area of ​​the grain 23 relative to 80% of the cumulative frequency is 4400 nm. 2 That's all. In other words, the area Sp80 of the surface portion 26, which accounts for 80% of the cumulative frequency, preferably satisfies 4400 nm. 2 ≤Sp80.

[0078] On the surface of the first excitation electrode 14a, the ratio of chromium atoms to gold atoms (Cr / Au) is preferably less than 0.38. The atomic ratio is determined, for example, by quantitative analysis using XPS (X-ray photoelectron spectroscopy).

[0079] Next, refer to Figures 6-9 The manufacturing method of crystal oscillator 1 is explained. Figure 6 This is a flowchart that roughly illustrates the manufacturing method of the crystal oscillator according to the first embodiment. Figure 7 This is a simplified cross-sectional view of the first excitation electrode before ion milling. Figure 8 This is a cross-sectional view that roughly represents the variation of the first excitation electrode based on ion milling. Figure 9 It is a cross-sectional view that roughly represents the changes in the first excitation electrode based on annealing.

[0080] First, prepare the crystal wafer (S10).

[0081] In this process, a crystal substrate is cut from the artificial crystal using the XZ′ plane as the main plane. A portion of the crystal substrate is removed using wet etching with photolithography, forming the outline of the crystal wafer 11 as seen from above the XZ′ plane. Next, a portion corresponding to the peripheral portions 18 and 19 of the crystal wafer 11 is removed using wet etching, forming a two-sided mesa structure. It should be noted that the manufacturing method of the crystal wafer 11 is not limited to wet etching. The crystal wafer 11 can be monolithically produced by cutting the crystal substrate, or the monolithically produced crystal wafer 11 can be beveled.

[0082] Next, a pair of electrodes, each containing an electrode sandwiching a wafer 11, is formed by sputtering methods such as magnetron sputtering.

[0083] This process includes a preheating step S20, a lower film layer 21 forming step S30, and an upper film layer 22 forming step S40.

[0084] The inventors conducted in-depth research and found that in order to increase the average grain size of the grains 23 in the upper layer 22, not only the film formation temperature is important, but also the temperature management of preheating is crucial. Specifically, in the preheating process S20, the wafer 11 needs to be preheated to 100°C to 300°C. If the temperature of the wafer 11 is below 100°C, the average grain size of the grains 23 in the upper layer 22 becomes smaller, and chromium diffusion is easier. Even if the annealing described later leads to grain growth, it cannot ensure sufficient grain growth. If the temperature of the wafer 11 is above 300°C, chromium diffusion outweighs the suppression of chromium diffusion by grain growth, resulting in an increased amount of chromium protruding on the surface of the excitation electrode. When the lower layer 21 setting process S30 and the upper layer 22 setting process S40 are patterned films using metal masks, the metal mask has a large heat capacity, making it difficult to raise the temperature of the wafer 11 in the film formation chamber. Therefore, preheating is performed in the front chamber of the film formation chamber.

[0085] Step S30, which sets the lower layer 21, and step S40, which sets the upper layer 22, are patterned films using a metal mask via sputtering. In step S30, chromium is used as a sputtering target, and chromium is deposited on the surface of a preheated wafer 11 to form the lower layer 21 of the film electrode pattern. The thickness of the lower layer 21 is, for example, 5 nm. In step S40, gold is used as a sputtering target, and gold is deposited on the surface of the lower layer 21 to form the upper layer 22 of the film electrode pattern. Figure 7 As shown, multiple grains 23 grow columnarly from the lower layer 21. Chromium diffuses to the grain boundaries 24 and the surfaces of the grains 23. At this time, the thickness of the upper layer 22 on the upper surface 11A side of the wafer 11 is, for example, 140 nm. In order to increase the adjustment margin based on the frequency of ion milling described later, the upper layer 22 is set to have a greater thickness on the upper surface 11A side of the wafer 11 than on the lower surface 11B side.

[0086] It should be noted that preheating can be performed in the film formation chamber, either during the formation of at least one of the lower layer 21 and the upper layer 22, or between the formation of the lower layer 21 and the upper layer 22. The process of setting electrodes on the surface of the wafer 11 is not limited to patterned film formation. Alternatively, after the lower layer 21 and upper layer 22 are formed on the entire surface of the wafer 11, a portion of the lower layer 21 and upper layer 22 can be removed by etching to form an electrode pattern. The film formation method for the lower layer 21 and upper layer 22 is not limited to sputtering; various vapor deposition methods such as PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) can be appropriately selected. Furthermore, the lower layer 21 and upper layer 22 can be formed using film formation methods other than vapor phase growth methods such as printing and plating.

[0087] Next, a crystal resonant element 10 is mounted on the base component 30 (S50).

[0088] First, a paste-like resin composition, serving as the material for the first conductive retaining member 36a and the second conductive retaining member 36b, is coated onto the first and second electrode pads 33a and 33b of the base component 30. Next, the crystal vibrating element 10 is placed on the resin composition, allowing the resin composition to cure and form the first conductive retaining member 36a and the second conductive retaining member 36b. It should be noted that the resin composition of the first conductive retaining member 36a and the second conductive retaining member 36b can be pre-coated onto the crystal vibrating element 10.

[0089] Next, ion milling (S60) is performed.

[0090] like Figure 8 As shown, at least a portion of the surface of the first excitation electrode 14a is irradiated with an ion beam BM, removing a portion of the upper layer 22. This changes the mass of the excitation portion 17 of the crystal resonator 10, adjusting the frequency of the crystal resonator 10. That is, step S60 corresponds to a frequency adjustment step. While applying voltage to the first excitation electrode 14a and the second excitation electrode 14b and monitoring the frequency, the first excitation electrode 14a is removed, gradually increasing its frequency to the target frequency.

[0091] The removal rate of gold based on ion beam BM is greater than that of chromium. Therefore, at the end of process S60, due to the influence of chromium diffusing along the grain boundary 24, the interface portion 25 is raised above the surface portion 26.

[0092] Next, annealing (S70) will be performed.

[0093] The annealing temperature is, for example, 200°C. Lattice defects formed in the multiple grains 23 by ion milling are reduced by annealing, and the multiple grains 23 recrystallize. Furthermore, the recrystallized multiple grains 23 undergo grain growth, or as... Figure 9 The adjacent grains 23 are fused, thereby increasing the individual grain size of each grain 23 and reducing the number of grains per unit area. As a result, a first excitation electrode 14a with a surface area ratio of more than 35% of the multiple grains 23 can be obtained.

[0094] (Evaluation of frequency stability and surface structure)

[0095] Next, the effects of preheating on frequency stability and the evaluation results regarding changes in surface structure are explained. For samples without preheating, samples preheated to 100°C, samples preheated to 200°C, and samples preheated to 250°C, the frequency deviation of the sealed crystal vibrating element 10 was measured at the junction of the base component 30 and the cover component 40. FE-SEM-based image analysis and XPS-based compositional analysis were performed on the surface of the first excitation electrode 14a after annealing and before sealing, under the same modified preheating conditions.

[0096] Figure 10 This graph shows the relationship between the frequency deviation after sealing and the film formation conditions. The horizontal axis represents the temperature of the wafer before film formation and excitation of the electrode (hereinafter referred to as "initial temperature"), and the vertical axis represents the normalized frequency deviation. An initial temperature of 20°C represents the manufacturing condition without preheating (hereinafter referred to as "no preheating"). Initial temperatures of 100°C, 150°C, 200°C, and 250°C are equivalent to preheating temperatures (hereinafter referred to as "preheating temperatures"). Ten crystal oscillators with their frequencies adjusted to 40 kHz before sealing were prepared under each manufacturing condition. After sealing, they were placed in an environment of 25 ± 1°C and 30–60% RH for 24 hours, and the frequency deviation was measured to determine the deviation. The frequency deviation is normalized to 1 by the frequency deviation of the crystal oscillator at the initial temperature of 20°C. That is, the value obtained by dividing the frequency deviation of the crystal oscillator at each initial temperature by the frequency deviation of the crystal oscillator at the initial temperature of 20°C is used as the vertical axis.

[0097] The frequency deviations at initial temperatures of 100℃, 150℃, 200℃, and 250℃ were improved compared to the frequency deviation at an initial temperature of 20℃. Specifically, compared to the frequency deviation without preheating, the frequency deviation at a preheating temperature of 100℃ was improved by approximately 80%, at 150℃ by approximately 65%, at 200℃ by approximately 60%, and at 250℃ by approximately 40%. This is attributed to the reduced grain boundaries of the upper gold layer, which suppresses chromium diffusion and reduces the mass change of the first excitation electrode caused by the oxidation of diffused chromium.

[0098] Figure 11 This is a diagram showing an FE-SEM image obtained by photographing the surface of the first excitation electrode. Figure 11 This section shows FE-SEM images of two samples fabricated under film-forming conditions with initial temperatures of 20°C, 100°C, 150°C, 200°C, and 250°C. The FE-SEM images were obtained by magnifying the area near the center and end of the first excitation electrode at 50,000x magnification. The displayed 800×1200 pixel image corresponds to a size of 1.6μm × 2.4μm = 3.744μm. 2 The area.

[0099] In each image, the bright areas represent gold, and the dark areas represent chromium compounds. It can be seen that as the preheating temperature increases, the area of ​​the bright areas increases, and the area of ​​each bright area surrounded by the dark areas also increases. To quantitatively evaluate this, the bright areas representing gold and the dark areas representing chromium compounds were numerically analyzed using image analysis. The results are explained below.

[0100] Figure 12 It is a table representing the area ratio of multiple grains. Figure 12 This represents the area percentage (%) of multiple grains obtained by analyzing FE-SEM images of samples manufactured under film-forming conditions with initial temperatures of 20°C, 100°C, 150°C, 200°C, and 250°C. Specifically, the area percentage column indicates the area percentage of gold occupying the surface of the first excitation electrode at each initial temperature, and the average column represents the average of the gold area percentages calculated from multiple samples. Figure 12 The "area ratio" in the text is, for example, Figure 11 The proportion of bright areas in the image will Figure 11 The value is calculated by multiplying the number of gold-containing grains per unit area (the number of bright areas surrounded by dark areas) by the average area of ​​the grain, and then dividing by the unit area. The number of samples at initial temperatures of 20°C and 100°C is 2, and the number of samples at initial temperatures of 150°C, 200°C, and 250°C is 4.

[0101] At an initial temperature of 20°C, the area fraction of gold is 30.2% and 32.2%, both less than 35%, with an average of 31.2%. Furthermore, the higher the initial temperature, the higher the area fraction. Specifically, at an initial temperature of 100°C, the area fractions are 38.6% and 42.3%, with an average of 40.5%. At an initial temperature of 150°C, the area fractions are 42.1%, 43.2%, 46.9%, and 46.4%, with an average of 44.7%. At an initial temperature of 200°C, the area fractions are 42.6%, 43.6%, 46.9%, and 47.4%, with an average of 45.1%. At an initial temperature of 250°C, the area fractions are 47.2%, 44.6%, 45.7%, and 45.7%, with an average of 45.8%. That is, as... Figure 10 As shown, at a preheating temperature of 100°C where frequency deviation is improved, the gold area fraction of each sample is at least 35%, and the average area fraction is at least 40%. Furthermore, at a preheating temperature of 150°C where frequency deviation is improved, the gold area fraction of each sample is at least 42%, and the average area fraction is at least 44%. Furthermore, at a preheating temperature of 200°C where frequency deviation is improved, the gold area fraction of each sample is at least 42%, and the average area fraction is at least 45%. Furthermore, at a preheating temperature of 250°C where frequency deviation is improved, the gold area fraction of each sample is at least 44%, and the average area fraction is at least 45%.

[0102] Figure 13 This is a graph showing the relationship between the area ratio of gold on the surface of the first excitation electrode and the film formation conditions. Figure 13 In the figure, the horizontal axis represents the film formation conditions (initial temperature), and the vertical axis represents the area ratio of multiple grains in the region of the first excitation electrode where ion milling is performed, i.e., the area ratio of gold (Au area ratio).

[0103] As the initial temperature increases, the area fraction of gold increases, and its deviation decreases. The area fraction of gold is approximately 30% at an initial temperature of 20°C, but increases to approximately 40% at an initial temperature of 100°C, and to approximately 45% at an initial temperature of 150°C. The rate of increase in the area fraction of gold relative to the initial temperature changes around 150°C. Specifically, the rate of increase in the area fraction of gold at initial temperatures of 150°C to 250°C is smaller than the rate of increase at initial temperatures above 20°C but below 150°C. This is presumably because gold crystal growth is sufficient at preheating temperatures above 150°C. Therefore, a preheating temperature of 100°C or higher is preferred, and 150°C or higher is more preferred.

[0104] Figure 14 It is a table representing the atomic composition of the surface of the first excitation electrode. Figure 14This represents the atomic composition of the surface of two samples manufactured under film-forming conditions with initial temperatures of 20°C, 100°C, 200°C, and 250°C, based on XPS quantitative analysis (equipment used: ULVAC-PHI PHI5000 VersaProbeIII, X-ray irradiation: Alkα rays). Figure 14 In this context, "C" represents the percentage of carbon atoms, "O" represents the percentage of oxygen atoms, "Si" represents the percentage of silicon atoms, "Cr" represents the percentage of chromium atoms, and "Au" represents the percentage of gold atoms, each in units of atomic%. Additionally, "Cr / Au" represents the ratio of the percentage of Cr atoms to the percentage of Au atoms.

[0105] As the initial temperature increases, "Cr" decreases, "Au" increases, and the "Cr / Au" ratio decreases. At an initial temperature of 20°C (without preheating), the "Cr / Au" ratio is 0.55 and 0.63; at an initial temperature of 100°C, it is 0.40 and 0.38; at an initial temperature of 200°C, it is 0.35 and 0.32; and at an initial temperature of 250°C, it is 0.31 and 0.31. Therefore, from the viewpoint of reducing frequency deviation, a "Cr / Au" ratio of 0.40 or less is preferred, more preferably 0.35 or less, and even more preferably 0.31 or less.

[0106] Figure 15 This is a graph showing the relationship between the cumulative frequency and area of ​​multiple grains on the surface of the first excitation electrode. The horizontal axis represents the cumulative frequency of the surface portion 26, and the vertical axis represents the area of ​​the surface portion 26 at each cumulative frequency. The evaluation results of the sample without preheating are depicted with a rhombus, the evaluation results of the sample preheated to an initial temperature of 100°C are depicted with a quadrilateral, the evaluation results of the sample preheated to an initial temperature of 200°C are depicted with a triangle, and the evaluation results of the sample preheated to an initial temperature of 250°C are depicted with a cross.

[0107] The area Sp50 of the surface portion 26 relative to 50% of the cumulative frequency increases with increasing preheating temperature; the higher the preheating temperature, the smaller the change in Sp50 (Sp50 / ΔT) relative to the temperature change (ΔT). The same applies to the area Sp80 of the surface portion 26 relative to 80% of the cumulative frequency. A reduction in frequency deviation was confirmed in samples satisfying at least one of Sp50 ≥ 1200 and Sp80 ≥ 4400.

[0108] The following describes some or all of the embodiments of the present invention and their effects. It should be noted that the present invention is not limited to the following description.

[0109] According to one aspect of the present invention, a crystal oscillator comprises: a crystal resonating element having a pair of electrodes comprising mutually opposing electrodes, and a holder for housing the crystal resonating element; at least one of the pairs of electrodes has an upper layer comprising gold and a lower layer comprising chromium disposed between the crystal wafer and the upper layer, the surface of the at least one electrode having a plurality of grains made of gold and a chromium compound formed along the grain boundaries of the plurality of grains, and the area ratio of the plurality of grains is 35% to 60% when viewed from above the surface of the at least one electrode.

[0110] If the area ratio of multiple grains is 35% or more, chromium exposure due to diffusion can be suppressed, thus reducing frequency variation after sealing. Therefore, a crystal oscillator with reduced initial frequency deviation and improved frequency stability can be provided. Furthermore, even in high humidity environments, mass changes in the excitation electrode can be suppressed, thereby reducing frequency variation over time. It should be noted that if the preheating temperature is increased to achieve an area ratio of multiple grains greater than 60%, chromium diffusion is more effective than the suppression of chromium diffusion by gold grain growth, resulting in an increased chromium content in the upper layer. Conversely, if the area ratio of multiple grains is 60% or less, damage to the conductivity retention component and changes in the piezoelectric properties of the crystal wafer due to preheating can be suppressed.

[0111] In one approach, the ratio of chromium atoms to gold atoms on the surface of at least one electrode is less than 0.38.

[0112] As one embodiment of this invention, the area of ​​the grain with a cumulative frequency of 50% is 1200 nm. 2 The above. Further preferred is a grain area of ​​4400 nm relative to 80% of the cumulative frequency. 2 above.

[0113] As one method, the retainer has: a base member for retaining the crystal vibrating element, a cover member forming an internal space between the base member and the cover member for receiving the crystal vibrating element, and a connecting member for joining the base member and the cover member; the connecting member comprises a resin material.

[0114] Using a resin-based sealant reduces manufacturing costs compared to using a metal seal, but reduces airtightness. Consequently, chromium exposed to moisture oxidizes and forms hydrates, easily causing frequency variations due to changes in the mass of the excitation electrode. However, according to this embodiment, even with a resin seal, frequency variations can be suppressed.

[0115] In one manner, in at least one electrode, multiple grains have grain boundaries that are more raised than the surrounding grains.

[0116] As another aspect of the present invention, a method for manufacturing a crystal oscillator includes: a step of preparing a crystal wafer, a step of setting a pair of electrodes comprising electrodes that sandwich each other and are opposed to each other, a step of mounting a crystal oscillating element on a base member using a conductive retaining member, and a step of joining a cover member to the base member using a joining member; the step of setting a pair of electrodes includes: a step of preheating the crystal wafer to 100°C to 300°C, a step of setting a lower layer comprising chromium on the preheated crystal wafer, and a step of setting an upper layer comprising gold on the lower layer.

[0117] As a further method, it includes a process of removing a portion of the electrode on the side opposite to the base component of a pair of electrodes to adjust the frequency of the crystal resonator, and a process of annealing the pair of electrodes.

[0118] The embodiments of the present invention are not limited to crystal oscillators, but can also be applied to piezoelectric oscillators. An example of a piezoelectric resonator unit is a crystal oscillator unit incorporating a crystal resonator element. The crystal resonator element utilizes a crystal wafer as a piezoelectric plate excited by the piezoelectric effect, but the piezoelectric plate can also be formed from any piezoelectric material such as a piezoelectric single crystal, piezoelectric ceramic, piezoelectric thin film, or piezoelectric polymer film. As an example, lithium niobate (LiNbO3) can be cited as a piezoelectric single crystal. Similarly, piezoelectric ceramics can include barium titanate (BaTiO3), lead titanate (PbTiO3), and lead zirconate titanate (Pb(Zr)). x Ti 1－x )O3; PZT), aluminum nitride (AlN), lithium niobate (LiNbO3), lithium metaniobate (LiNb2O6), bismuth titanate (Bi4Ti3O) 12 Lithium tantalate (LiTaO3), lithium tetraborate (Li2B4O7), lanthanum gallium silicate (La3Ga5SiO3) 14 Examples of piezoelectric materials include tantalum pentoxide (Ta₂O₅) and others. Examples of piezoelectric thin films include those formed by sputtering or other methods to deposit the aforementioned piezoelectric ceramics onto substrates such as quartz or sapphire. Examples of piezoelectric polymer films include polylactic acid (PLA), polyvinylidene fluoride (PVDF), or vinylidene fluoride / trifluoroethylene (VDF / TrFE) copolymers. These various piezoelectric materials can be stacked together or laminated onto other components.

[0119] The embodiments of the present invention can be appropriately applied without particular limitation to any device that uses the piezoelectric effect to convert electromechanical energy, such as a timing device, a sound generator, an oscillator, or a load sensor.

[0120] As explained above, according to one aspect of the present invention, it is possible to provide a piezoelectric oscillator with improved frequency stability and a method for manufacturing the same.

[0121] It should be noted that the embodiments described above are for the purpose of facilitating understanding of the present invention and are not intended to limit the interpretation of the present invention. The present invention can be modified / improved without departing from its spirit, and its equivalents are also included in the present invention. That is, any technical solution obtained by those skilled in the art through appropriate design modifications to the various embodiments, as long as it possesses the features of the present invention, is also included within the scope of the present invention. For example, the elements, configurations, materials, conditions, shapes, dimensions, etc., of each embodiment are not limited to the examples shown and can be appropriately modified. For example, the vibration element and oscillator of the present invention can be used in timing devices or load sensors. Furthermore, the elements of each embodiment can be combined as long as it is technically possible, and any technical solution obtained by combining them, as long as it contains the features of the present invention, is also included within the scope of the present invention.

[0122] Symbol Explanation

[0123] 1… Crystal oscillator,

[0124] 10… Crystal Vibrating Element,

[0125] 11…crystal wafers,

[0126] 14a, 14b… excitation electrodes,

[0127] Electrodes 15a, 15b… are drawn out.

[0128] 16a, 16b… connect electrodes,

[0129] 21…lower level,

[0130] 22… Upper level,

[0131] 23… grains,

[0132] 24…grain boundary,

[0133] 25…Interface Department,

[0134] 26… Surface portion,

[0135] 27…chromium compounds,

[0136] 30…basic components,

[0137] 40… Cover components,

[0138] 50…jointing components

Claims

1. A piezoelectric oscillator, comprising: A piezoelectric vibrating element has a piezoelectric plate and a pair of electrodes comprising electrodes facing each other and sandwiching the piezoelectric plate. A retainer for housing the piezoelectric vibrating element; At least one of the pair of electrodes has an upper layer comprising gold and a lower layer comprising chromium disposed between the piezoelectric sheet and the upper layer. The surface of the at least one electrode has a plurality of gold grains and chromium compounds formed along the grain boundaries of the plurality of grains. When viewed from above, the surface of the at least one electrode has an area ratio of 35% to 60% for the plurality of grains.

2. The piezoelectric oscillator according to claim 1, wherein, On the surface of the at least one electrode, the ratio of chromium atoms to gold atoms is less than 0.

38.

3. The piezoelectric oscillator according to claim 1, wherein, The area of ​​the grain relative to 50% of the cumulative frequency is 1200 nm. 2 above.

4. The piezoelectric vibrator according to claim 2, wherein, The area of ​​the grain relative to 50% of the cumulative frequency is 1200 nm. 2 above.

5. The piezoelectric vibrator according to claim 3, wherein, The average area of ​​the grain relative to 80% of the cumulative frequency is 4400 nm. 2 above.

6. The piezoelectric vibrator according to claim 4, wherein, The average area of ​​the grain relative to 80% of the cumulative frequency is 4400 nm. 2 above.

7. The piezoelectric oscillator according to any one of claims 1 to 6, wherein, The retainer has: a base member for retaining the piezoelectric vibrating element, a cover member forming an internal space between the base member and the cover member for receiving the piezoelectric vibrating element, and a connecting member for engaging the base member and the cover member; The joining member comprises a resin material.

8. The piezoelectric oscillator according to any one of claims 1 to 6, wherein, In the at least one electrode, the plurality of grains have grain boundaries that are more raised than the surrounding grains.

9. The piezoelectric oscillator according to any one of claims 1 to 6, wherein, The piezoelectric vibrating element is a crystal vibrating element.

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