Electrode structure of crystal oscillator, crystal oscillator and crystal oscillator

Abstract

The present invention provides an electrode structure of a crystal oscillator for reducing CI value of a crystal without performing a precise crystal sheet processing. The electrode structure of a crystal oscillator (1) of the present invention has exciting electrodes (21, 22) disposed at least at the center of the main surfaces (11, 12) of a crystal sheet (10). The exciting electrodes (21, 22) have a structure in which vibration energy for thickness shear vibration of the crystal sheet (10) is concentrated in a central region of the crystal sheet (10).

Description

Technical Field

[0001] This invention relates to an electrode structure for a crystal oscillator, a crystal oscillator, and a crystal oscillator. Background Technology

[0002] In recent years, the miniaturization, weight reduction, and multifunctionality of various devices equipped with crystal oscillators have been continuously developing. As a result, the crystal oscillators used in these devices need to meet the requirements of miniaturization and high performance. When miniaturizing the crystal oscillator, the size of the crystal chip used in the crystal oscillator and the area of ​​the excitation electrodes arranged on the crystal chip also need to be reduced. As a result, the equivalent series resistance (CI: Crystal Impedance) of the crystal oscillator (crystal chip) increases. Furthermore, the main oscillation is also susceptible to the influence of secondary vibrations such as anharmonics. Therefore, when mounting the crystal chip on a housing, the conditions for the adhesive to suppress the influence of secondary vibrations (e.g., the application position and amount of adhesive) become stringent, easily leading to problems such as decreased yield during mass production.

[0003] Prior to this, techniques for manufacturing miniaturized and high-performance crystal oscillators by precisely machining the shape of the sides of the crystal wafer have also been proposed (for example, see Patent Document 1).

[0004] In the technology disclosed in Patent Document 1, the axial directions of the crystal wafer are adjusted, and two crystal surfaces are formed on the side of the crystal wafer along the -X-axis direction and six (or four) crystal surfaces are formed on the side of the crystal wafer along the +X-axis direction during wet etching. As a result, secondary vibrations are suppressed, and the CI value of the vibrating wafer is reduced. However, to form the desired crystal surfaces, this technology requires precise control of the mask pattern formation and the etching amount of the crystal wafer thickness at the μm level during the photolithography process, and requires multiple steps. Therefore, maintaining high productivity without reducing the yield between each step is extremely difficult in this technology.

[0005] Existing technical documents

[0006] Patent documents:

[0007] Patent Document 1: Japanese Patent Application Publication No. 2014-027505 Summary of the Invention

[0008] The problem the invention aims to solve

[0009] The purpose of this invention is to provide an electrode structure, a crystal oscillator, and a crystal oscillator that can reduce the CI value of a crystal without the need for precise crystal wafer processing.

[0010] Solution for solving the problem

[0011] The electrode structure of the crystal oscillator, the crystal oscillator and the crystal oscillator of the present invention have an excitation electrode disposed at least at the center of the main surface of the crystal wafer, the excitation electrode having a structure that concentrates the vibrational energy of the thickness shear vibration of the crystal wafer into the central region of the crystal wafer.

[0012] Invention Effects

[0013] According to the present invention, the CI value can be reduced without the need for precision crystal wafer processing. Attached Figure Description

[0014] Figure 1 (a) is a schematic top view illustrating an embodiment of the crystal oscillator of the present invention. Figure 1 (b) is along Figure 1 A schematic cross-sectional view of the crystal oscillator (a) taken along line AA.

[0015] Figure 2 It is shown Figure 1 A graph illustrating the relationship between the area ratio of the electrodes in a crystal oscillator and the CI value.

[0016] Figure 3 (a) is shown in Figure 1 The chart shows the simulation results of the admittance circle diagram when the excitation electrode in the crystal oscillator has a single-layer structure. Figure 3 (b) is a graph showing the simulation results of the admittance circle diagram when the excitation electrode has a 2-layer structure in the crystal wafer.

[0017] Figure 4 It shows that applying it to Figure 1 A graph showing the magnitude of the crystal displacement along the length of the crystal plate when the voltage on the crystal plate of the crystal oscillator is constant.

[0018] Figure 5 This is a schematic cross-sectional view illustrating an embodiment of the crystal oscillator of the present invention.

[0019] Figure 6 This is a schematic cross-sectional view illustrating another embodiment of the crystal oscillator of the present invention. Figure 6 (a) shows a plate-type crystal sheet. Figure 6 (b) shows a beveled crystal plate. Figure 6 (c) shows a crystal sheet of the reverse mesa type.

[0020] Figure 7 This is a schematic cross-sectional view illustrating yet another embodiment of the crystal oscillator of the present invention. Figure 7 (a) shows a structure in which the outer edge and the central part of the electrode have the same thickness. Figure 7(b) shows a structure in which a large-mass metal film at the center of the electrode is covered by a small-mass metal film. Figure 7 (c) shows a structure in which the thickness of the outer edge of the electrode is greater than the thickness of the central part of the electrode. Detailed Implementation

[0021] Hereinafter, embodiments of the electrode structure (hereinafter referred to as "this structure"), crystal oscillator, and crystal oscillator of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals are used to label the same parts, and repeated descriptions are omitted.

[0022] Crystal oscillator

[0023] First, embodiments of the crystal oscillator and the structure of the present invention will be described.

[0024] Figure 1 (a) is a schematic top view illustrating an embodiment of the crystal oscillator of the present invention. Figure 1 (b) is along Figure 1 A schematic cross-sectional view of the crystal oscillator (a) taken along line AA. Figure 1 (a) For ease of explanation, the cover 50 described later is indicated by a dashed line.

[0025] The crystal oscillator 1 is mounted on a predetermined oscillation circuit, thereby generating a signal with a predetermined oscillation frequency based on an applied voltage (hereinafter referred to as "applied voltage"). The crystal oscillator 1 is, for example, a surface-mount (SMD) type crystal oscillator. The crystal oscillator 1 includes a crystal chip 10, electrodes 20, conductive adhesive 30, a housing 40, and a cover 50.

[0026] The crystal wafer 10 is excited at a predetermined frequency based on an applied voltage. The crystal wafer 10 is, for example, an AT-cut crystal wafer. Since AT cutting is a well-known technique, its description is omitted. The crystal wafer 10 is rectangular in top view and plate-like in side view. The crystal wafer 10 has a first main surface 11 ( Figure 1 (b) the side surface of the paper) and the second main surface 12 ( Figure 1 (b) The lower side of the paper surface). In this embodiment, the length direction of the crystal sheet 10 is along the X-axis direction of the crystal, and the width direction of the crystal sheet 10 is along the Z' axis of the crystal (an axis inclined at 35.15° from the Z-axis of the crystal). The direction perpendicular to the two main surfaces 11 and 12 of the crystal sheet 10 is along the Y' axis of the crystal oscillator (an axis inclined at 35.15° from the Y-axis of the crystal).

[0027] The first main surface 11 has an outer edge 111 and a central portion 112 located inside the outer edge 111 when viewed from above. The central portion 112 protrudes upward from the outer edge 111 in a rectangular shape. The second main surface 12 has an outer edge 121 and a central portion 122 located inside the outer edge 121 when viewed from above. The central portion 122 protrudes downward from the outer edge 121 in a rectangular shape. That is, the crystal wafer 10 has a mesa-shaped structure in which the central portions 112 and 122 of the two main surfaces 11 and 12 are thicker than the outer edges 111 and 121.

[0028] Electrode 20 applies a predetermined voltage to crystal plate 10. The structure of electrode 20 (i.e., this structure) will be described later.

[0029] Conductive adhesive 30 electrically connects the pair of connecting electrodes 212a and 222a (described later) to the electrode pads 412 of the housing 40 (described later). As a result, the crystal chip 10 is mechanically fixed inside the housing 40.

[0030] The housing 40 houses the crystal sheet 10 having the structure described later. The housing 40 is a sintered body made of ceramic layers such as alumina. The housing 40 is a known housing (encapsulation) for a crystal oscillator. The housing 40 is rectangular in top view and is box-shaped with an opening at the top. The housing 40 includes an electrode 41 and a stepped portion 42.

[0031] Electrode 41 includes an external electrode 411 disposed on the lower surface of the bottom of housing 40 and a pair of electrode pads 412 disposed on the upper surface of the bottom (step portion 42) of housing 40. Step portion 42 is disposed on the upper surface of the bottom of one short side of housing 40.

[0032] The cover 50 provides an airtight seal to the opening at the top of the housing 40. The cover 50 may be made of metal, for example.

[0033] Electrode structure of crystal oscillator

[0034] Next, the structure will be explained.

[0035] The electrode 20 includes a first main surface electrode 21 disposed on the first main surface 11 and a second main surface electrode 22 disposed on the second main surface 12.

[0036] The first main surface electrode 21 includes a first excitation electrode 211 and a first lead-out electrode 212. The first excitation electrode 211 applies an applied voltage to the crystal wafer 10. The first excitation electrode 211 includes a first electrode portion 211a and a second electrode portion 211b.

[0037] A first electrode portion 211a is disposed on the central portion 112 of the first main surface 11. In a top view, the first electrode portion 211a has an area smaller than that of the central portion 112 and is disposed inside the central portion 112. A second electrode portion 211b is stacked on top of the first electrode portion 211a. In a top view, the second electrode portion 211b has an area smaller than that of the first electrode portion 211a and is disposed inside the first electrode portion 211a. That is, the first excitation electrode 211 has a two-layer structure consisting of two electrode portions 211a and 211b stacked in a manner that successively decreases in area.

[0038] The angle between the end face (side face) of the first electrode portion 211a and the central portion 112 of the first main surface 11 is, for example, 30° to 90°. The angle between the end face (side face) of the second electrode portion 211b and the first electrode portion 211a is, for example, 30° to 90°. Here, the first electrode portion 211a is substantially parallel to the central portion 112 of the first main surface 11. In other words, the angle between the end face of each of the plurality of electrode portions 211a, 211b and a virtual plane parallel to the first main surface 11 is 30° to 90°. Here, the angle of the end face is measured physically, for example, by a probe, or optically using transmitted light.

[0039] Here, the outer edge of the first excitation electrode 211 (the region in the first electrode portion 211a where the second electrode portion 211b is not stacked) constitutes the outer edge of the electrode according to the present invention. On the other hand, the region inside the outer edge of the electrode (the region where the first electrode portion 211a and the second electrode portion 211b are stacked) in top view constitutes the central portion of the electrode according to the present invention. The outer edge of the electrode is composed of the first electrode portion 211a, and the central portion of the electrode is composed of the first electrode portion 211a and the second electrode portion 211b. That is, the central portion of the electrode is thicker than the outer edge of the electrode.

[0040] The first lead-out electrode 212 transmits the applied voltage to the first excitation electrode 211. The first lead-out electrode 212 is connected to the first excitation electrode 211 and is disposed on the first main surface 11 such that it extends from the central portion 112 to the outer edge portion 111 on a short side of the crystal wafer 10. A portion of the first lead-out electrode 212 extending (disposed) to the outer edge portion 111 constitutes a connecting electrode 212a connected to the conductive adhesive 30. The first lead-out electrode 212 and the first electrode portion 211a are integrally formed.

[0041] The first lead-out electrode 212 and the first electrode portion 211a include a base metal film disposed on the first main surface 11 and a metal film disposed on the base metal film. The second electrode portion 211b includes a base metal film disposed on the first electrode portion 211a and a metal film disposed on the base metal film. In this embodiment, the base metal film is a Cr film and the metal film is an Au film.

[0042] The second main surface electrode 22 includes a second excitation electrode 221 and a second lead-out electrode 222. The second excitation electrode 221 applies an applied voltage to the crystal wafer 10. The second excitation electrode 221 includes a first electrode portion 221a and a second electrode portion 221b.

[0043] The first electrode portion 221a is disposed on the central portion 122 of the second main surface 12. In top view, the first electrode portion 221a has an area smaller than that of the central portion 122 and is disposed inside the central portion 122. The second electrode portion 221b is stacked on top of the first electrode portion 221a. In top view, the second electrode portion 221b has an area smaller than that of the first electrode portion 221a and is disposed inside the first electrode portion 221a. That is, the second excitation electrode 221 has a two-layer structure consisting of two electrode portions 221a and 221b stacked in a manner where their areas decrease sequentially. In this embodiment, the second excitation electrode 221 has a structure symmetrical to the first excitation electrode 211, separated by the crystal plate 10.

[0044] The angle between the end face (side face) of the first electrode portion 221a and the central portion 122 of the second main surface 12 is, for example, 30° to 90°. The angle between the end face (side face) of the second electrode portion 221b and the first electrode portion 221a is, for example, 30° to 90°. Here, the first electrode portion 221a is substantially parallel to the central portion 122 of the second main surface 12. In other words, the angle between the end face of each of the plurality of electrode portions 221a, 221b and the virtual plane parallel to the second main surface 12 is 30° to 90°.

[0045] Here, the outer edge of the second excitation electrode 221 (the region in the first electrode region 221a where the second electrode region 221b is not stacked) constitutes the outer edge of the electrode according to the present invention. On the other hand, the region inside the outer edge of the electrode (the region where the first electrode region 221a and the second electrode region 221b are stacked) in top view constitutes the central portion of the electrode according to the present invention. The outer edge of the electrode is composed of the first electrode region 221a, and the central portion of the electrode is composed of the first electrode region 221a and the second electrode region 221b. That is, the central portion of the electrode is thicker than the outer edge of the electrode.

[0046] The second lead-out electrode 222 transmits the applied voltage to the second excitation electrode 221. The second lead-out electrode 222 is connected to the second excitation electrode 221 and is disposed on the second main surface 12 such that it extends from the central portion 122 to the outer edge portion 121 on one short side of the crystal wafer 10. A portion of the second lead-out electrode 222 extending (disposed) to the outer edge portion 121 constitutes a connecting electrode 222a connected to the conductive adhesive 30. The second lead-out electrode 222 is integrally formed with the first electrode portion 221a.

[0047] The second lead-out electrode 222 and the first electrode portion 221a include a base metal film disposed on the second main surface 12 and a metal film disposed on the base metal film. The second electrode portion 221b includes a base metal film disposed on the first electrode portion 221a and a metal film disposed on the base metal film. In this embodiment, the base metal film is a Cr film and the metal film is an Au film.

[0048] The first main surface electrode 21 and the second main surface electrode 22 are formed, for example, by a photolithography process. That is, for example, after forming two layers of base metal film and metal film on the wafer 10 by vapor deposition or the like, the upper metal film and the base metal film are removed by etching while the second electrode portions 211b and 221b are masked with a photoresist. Then, while the first electrode portions 211a and 221a, the first lead-out electrode 212 and the second lead-out electrode 222 are masked, the lower metal film and the base metal film are removed by etching.

[0049] It should be noted that, after the first electrode portion, the first lead-out electrode, and the second lead-out electrode are formed, the substrate metal film and the metal film on the upper side can be deposited by vapor deposition while the portion other than the second electrode portion is masked by photoresist. In this case, the substrate metal film and the metal film other than the second electrode portion are removed together with the photoresist.

[0050] Alternatively, after the first electrode portion, the first lead-out electrode, and the second lead-out electrode are formed, the substrate metal film and the metal film on the upper side can be deposited by vapor deposition while the portion other than the second electrode portion is covered by a metal mask or the like.

[0051] Figure 2 This is a graph showing an example of the relationship between the electrode area ratio and the CI value when the area of ​​the second electrode portion 211b is varied while the area of ​​the first electrode portion 211a is fixed.

[0052] The horizontal axis of this graph represents the area ratio of the second electrode portion 211b to the area of ​​the first electrode portion 211a (area of ​​the second electrode portion 211b / area of ​​the first electrode portion 211a). The vertical axis of this graph represents the CI value. Figure 2 As shown, the CI value decreases between approximately 83% and 95% of the area ratio, and decreases significantly, especially between approximately 83% and 90% of the area ratio.

[0053] Figure 3 (a) is a graph showing the simulation results of the admittance circle diagram when the excitation electrode has a single-layer structure in a crystal wafer equivalent to the crystal wafer 10 of this embodiment. Figure 3 (b) is a graph showing the simulation results of the admittance circle plot in this embodiment (the excitation electrode has a 2-layer structure).

[0054] like Figure 3As shown, the CI value (approximately 10Ω) when the excitation electrode has a 2-layer structure is significantly lower than the CI value (approximately 70Ω) when the excitation electrode has a 1-layer structure.

[0055] Figure 4 It is a graph showing the magnitude of the displacement of the crystal chip 10 in the length direction of the crystal chip 10 when the voltage applied to the crystal chip 10 is kept constant.

[0056] The horizontal axis of this graph represents the position of crystal plate 10 along its length (the X-axis direction of the crystal's axis). The vertical axis represents the magnitude of the displacement along the X-axis. "L1" in this graph represents the displacement when the excitation electrode has a single-layer structure, and "L2" represents the displacement when the excitation electrode has a two-layer structure. Here, the magnitude of the displacement along the vertical axis can be expressed as admittance Y. The relationship between admittance Y and impedance Z, "Y = 1 / Z", holds. That is, when the displacement X increases, the impedance Z (i.e., the CI value) decreases.

[0057] like Figure 4 As shown, the displacement when the excitation electrode has a two-layer structure is approximately 2 to 3 times that when the excitation electrode has a one-layer structure. In particular, the difference in displacement between the two structures increases as it moves from the ends towards the center in the X-axis direction. This indicates that the vibrational energy of the main vibration is concentrated in the central region of the crystal plate 10 (the region between the central portions 112 and 122 of the two main surfaces 11 and 12), and this energy is confined to the central region.

[0058] Thus, since the first excitation electrode 211 and the second excitation electrode 221 each have a two-layer structure with a smaller area as they become the upper layer, the vibrational energy of the main vibration is concentrated in the central region of the crystal sheet 10, and this vibrational energy is confined to the central region. As a result, the equivalent series resistance (CI: Crystal Impedance) of the crystal sheet 10 is reduced.

[0059] Crystal oscillator

[0060] Next, embodiments of the crystal oscillator of the present invention will be described. In the embodiments described below, descriptions of components that are the same as those in the previously described embodiments will be omitted.

[0061] Figure 5 This is a schematic cross-sectional view illustrating an embodiment of the crystal oscillator of the present invention.

[0062] Crystal oscillator 100 is, for example, a temperature-compensated crystal oscillator (TCXO). Crystal oscillator 100 is, for example, an SMD (surface mount device) crystal oscillator. Crystal oscillator 100 includes the aforementioned crystal chip 10, electrode 20, conductive adhesive 30, cover 50, housing 40A, and circuit 60A.

[0063] The housing 40A houses the crystal chip 10 and the circuit 60A. The housing 40A is a sintered body made of laminated ceramic layers such as alumina. The housing 40A is a known housing (encapsulation) for crystal oscillators. The housing 40A is rectangular in shape when viewed from above and is box-shaped with an opening at the top. The housing 40A includes electrodes (not shown), a stepped portion 42, and a circuit receiving portion 43A.

[0064] The circuit receiving part 43A houses the circuit 60A. The circuit receiving part 43A is located at the center of the bottom of the housing 40A.

[0065] Circuit 60A controls the oscillation frequency of crystal chip 10 (crystal oscillator 1). Circuit 60A is, for example, a known temperature compensation circuit.

[0066] Summarize

[0067] According to the embodiments described above, in this structure, the first excitation electrode 211 and the second excitation electrode 221 each have a two-layer structure whose area decreases as they become the upper layer. Therefore, this structure concentrates the vibrational energy of the main vibration in the central region of the crystal wafer 10, confining the vibrational energy to the central region. As a result, the CI value of the crystal wafer 10 is reduced. Thus, this structure, the crystal oscillator 1 having this structure, and the crystal oscillator 100 can reduce the CI value without the need for precise processing of the crystal wafer 10.

[0068] Furthermore, by reducing the CI value, the absolute value of the deviation of the CI value becomes smaller. For example, an average CI value increased by 50% relative to an average CI value of 100Ω is 150Ω, while an average CI value increased by 50% relative to an average CI value of 10Ω is 15Ω. Similarly, for example, an average CI value increased by 50Ω relative to a CI value of 100Ω is 150Ω, while an average CI value increased by 50Ω relative to a CI value of 10Ω is 60Ω. Thus, even if the CI value deviates, it is easier for the CI value to fall within the standard range. As a result, the productivity (yield) of both the crystal oscillator 1 and the crystal oscillator 100 with this structure is improved. Additionally, in this case, by reducing the CI value according to the present invention, the etching amount of the outer edges 111 and 121 of the crystal wafer 10 is reduced. As a result, the productivity (yield) of the crystal wafer 10 is improved.

[0069] Furthermore, according to the embodiments described above, by confining the vibrational energy of the main vibration to the central region of the crystal wafer 10, the influence of the combined vibration on the ends of the crystal wafer 10, i.e., the outer edge 111 of the crystal wafer 10 where the connecting electrodes 212a and 222a are arranged, can be suppressed. Therefore, the influence of the conductive adhesive 30 on the main vibration is suppressed. As a result, the productivity (yield) of both the crystal oscillator 1 and the crystal oscillator 100 having this structure is improved.

[0070] Furthermore, according to the embodiments described above, the crystal oscillator 100 using the crystal oscillator 1 with this structure can perform low-excitation operation when assembled into the oscillation circuit, which helps to stabilize the oscillation.

[0071] other

[0072] It should be noted that the crystal wafer in this invention can be excited by thickness shear vibration as the main vibration, and the cutting of the crystal wafer in this invention is not limited to AT cutting. That is, for example, the crystal wafer in this invention can also be cut by BT cutting, SC cutting, or IT cutting.

[0073] Furthermore, the crystal wafer in this invention is not limited to a mesa type. That is, for example, the crystal wafer in this invention can have any of the following structures: flat, beveled, reverse mesa, convex, or plano-convex. In this case, by reducing the CI value of this invention, the amount of bevel is reduced in the beveled type, and the amount of etching in the central recess of the crystal wafer is reduced in the reverse mesa type. As a result, the productivity (yield) of the crystal wafer is improved.

[0074] Figure 6 (a)~ Figure 6 (c) is a schematic cross-sectional view illustrating another embodiment of the crystal oscillator of the present invention. For ease of explanation, only cross-sections of the crystal plate and the electrodes are shown in this figure. Figure 6 (a) shows a plate-type crystal sheet. Figure 6 (b) shows a beveled crystal plate. Figure 6 (c) shows a crystal sheet of the reverse mesa type.

[0075] Furthermore, the length of the long side (side along the X-axis) of each crystal sheet in this invention is preferably 2 mm or less. According to this structure, this structure reduces the CI value more effectively than other structures (e.g., crystal sheet shape, electrode thickness, position, etc.). That is, in this structure, the smaller the crystal sheet, the more effectively the CI value can be reduced compared to other structures.

[0076] In addition, the crystal wafers in this invention can be formed in batches by photolithography, or they can be formed individually by grinding, cutting, surface etching and other methods.

[0077] In addition, the crystal in this invention can be excited in the fundamental frequency mode or in the high-order (3rd or 5th) harmonic mode.

[0078] Furthermore, the first and second excitation electrodes in this invention can each be composed of multiple electrode portions stacked on two main surfaces with progressively smaller areas, and are not limited to a two-layer structure. That is, for example, the first and second excitation electrodes in this invention may each have a third electrode portion stacked on the second electrode portion and having an area smaller than that of the second electrode portion. Additionally, for example, the number of layers in the first excitation electrode may differ from the number of layers in the second excitation electrode.

[0079] Furthermore, the second excitation electrode in this invention may also have an asymmetrical structure with respect to the first excitation electrode separated by a crystal plate. That is, for example, the second excitation electrode in this invention may also be offset relative to the first excitation electrode in the X-axis direction and / or Z'-axis direction when viewed from above.

[0080] Furthermore, the first electrode portion and the second electrode portion in this invention can also be integrally formed. That is, for example, the first electrode portion and the second electrode portion in this invention can also be composed of a single base metal film and a metal film. In this case, the outer edge portion of the electrode can also be formed, for example, by removing the outer edge portion of the single metal film.

[0081] Furthermore, the thickness of the first electrode portion and the thickness of the second electrode portion in this invention can be the same or different. Here, the thickness of each electrode portion is calculated, for example, based on the frequency of the crystal wafer before and after vapor deposition. Additionally, the thickness of each electrode portion can be physically measured using a probe, or optically measured using transmitted light.

[0082] Furthermore, the substrate metal film in this invention can be any metal film having an affinity for both the crystal wafer and the metal film, and is not limited to a Cr film. That is, for example, the substrate metal film in this invention may also contain at least one metal selected from Cr, Ni, or W.

[0083] Furthermore, the metal film in this invention is not limited to an Au film, as long as it can supply an applied voltage capable of exciting the crystal. That is, for example, the metal film in this invention may also contain at least one metal selected from Au, Ag, Cu, Al, W, Ni, or Mg.

[0084] Furthermore, the first and second excitation electrodes in this invention can also be composed of an outer edge and a central portion, respectively. The central portion, viewed from above, is located in a region closer to the inner edge than the outer edge and contains a metal with a greater mass than the metal constituting the outer edge. For example, the outer edge can be composed of an Ag or Al film, while the central portion can be composed of an Au film. In this structure, the mass of the central portion in one axial direction (e.g., the X-axis direction) is greater than the mass of the outer edge. Therefore, the thickness of the central portion can be the same as or thinner than the outer edge. Additionally, for example, a large-mass metal film (e.g., an Au film) can be covered by a small-mass metal film (e.g., an Al film) in the central portion. Due to the mass effect of the central portion, these structures, similar to the two-layer structures described above, concentrate the vibrational energy of the main vibration in the central region of the crystal sheet 10, confining this vibrational energy to the central region.

[0085] Figure 7 (a)~ Figure 7 (c) is a schematic cross-sectional view illustrating yet another embodiment of the crystal oscillator of the present invention. For ease of explanation, only cross-sections of the crystal plate and electrodes are shown in this figure. The electrodes, which are highlighted in black, are made of a metal with a much higher mass than the blank electrode. Figure 7 (a) shows a structure in which the outer edge and the central part of the electrode have the same thickness. Figure 7 (b) shows a structure in which a large-mass metal film at the center of the electrode is covered by a small-mass metal film. Figure 7 (c) shows a structure in which the thickness of the outer edge of the electrode is greater than the thickness of the central part of the electrode.

[0086] In addition, the end faces of each electrode portion of the present invention may also be curved surfaces.

[0087] In addition, when viewed from above, one of the four sides of the second electrode of the present invention may coincide with one of the four sides of the first electrode.

[0088] Furthermore, the crystal oscillator of the present invention is not limited to a temperature-compensated crystal oscillator. That is, for example, the crystal oscillator of the present invention may also be a voltage-controlled crystal oscillator (VCXO), a crystal oscillator with a temperature-controlled bath (OCXO), or a packaged crystal oscillator (SPXO).

[0089] Explanation of reference numerals in the attached figures

[0090] 1: Crystal oscillator

[0091] 10: Crystal sheet

[0092] 11: First primary surface

[0093] 12: Second primary surface

[0094] 21: First main surface electrode

[0095] 211: First excitation electrode

[0096] 211a: First electrode section

[0097] 211b: Second electrode section

[0098] 22: Second main surface electrode

[0099] 221: Second excitation electrode

[0100] 221a: First electrode section

[0101] 221b: Second electrode section

[0102] 100: Crystal oscillator.

Claims

1. An electrode structure for a crystal oscillator, characterized in that, It has an excitation electrode disposed at least at the center of the main surface of the crystal wafer, which is rectangular in shape when viewed from above. The excitation electrode includes: An outer edge of an electrode portion, which is composed of a first electrode portion disposed on the main surface and rectangular in plan view; and The central portion of the electrode, which, when viewed from above, is the region inward from the outer edge of the electrode, is composed of a portion of the first electrode portion and a second electrode portion stacked on the portion of the first electrode portion, and is rectangular in shape. The first electrode portion is composed of a metal film and a substrate metal film. The metal film functions as the excitation electrode, and the substrate metal film functions as a substrate disposed between the metal film and the crystal wafer. The second electrode portion is composed of a metal film, which functions as the excitation electrode. The first area of ​​the excitation electrode is divided by the outer edge of the outer edge of the electrode and is smaller than the area of ​​the main surface. The second area of ​​the central portion of the electrode is smaller than the first area. The mass per unit area of ​​the central portion of the electrode is greater than the mass per unit area of ​​the outer edge portion of the electrode. The CI curve, which shows the relationship between the area ratio of the second area relative to the first area and the CI value of the crystal sheet, includes the first and second minimum points where the CI value reaches its minimum. The area ratio corresponding to the second bottom point is less than the area ratio corresponding to the first bottom point. The first area and the second area are set according to the area ratio corresponding to the second bottom point.

2. The electrode structure of the crystal oscillator according to claim 1, characterized in that, The CI value of the second bottom point is not greater than the CI value of the first bottom point.

3. The electrode structure of the crystal oscillator according to claim 2, characterized in that, The CI value at the second bottom point is less than the CI value at the first bottom point.

4. The electrode structure of the crystal oscillator according to any one of claims 1 to 3, characterized in that, The first bottom point exists within the range where the area ratio is not less than 90% and less than 100%. The second bottom point exists within the range where the area ratio is not less than 80% and less than 90%.

5. The electrode structure of the crystal oscillator according to claim 1, characterized in that, The angle between the end face of the first electrode portion and the second electrode portion and the virtual plane parallel to the main surface is 30° to 90°.

6. The electrode structure of the crystal oscillator according to claim 5, characterized in that, The metal film of the first electrode portion and the metal film of the second electrode portion are respectively composed of at least one metal selected from Au, Ag, Cu, Al, W, Ni or Mg.

7. The electrode structure of the crystal oscillator according to claim 6, characterized in that, The metal film constituting the second electrode portion is made of the same metal as the metal film constituting the first electrode portion.

8. The electrode structure of the crystal oscillator according to claim 6, characterized in that, The substrate metal film contains at least one metal selected from Cr, Ni, or W.

9. The electrode structure of the crystal oscillator according to any one of claims 1 to 3, characterized in that, The central portion of the electrode contains metal, which has a greater mass than the metal constituting the outer edge of the electrode.

10. The electrode structure of the crystal oscillator according to claim 9, characterized in that, The thickness of the outer edge of the electrode is the same as the thickness of the central part of the electrode.

11. The electrode structure of the crystal oscillator according to claim 9, characterized in that, The thickness of the outer edge of the electrode is greater than the thickness of the central part of the electrode.

12. A crystal oscillator, characterized in that, have: Crystal sheets; and An excitation electrode is disposed at least at the center of the main surface of the crystal wafer. The excitation electrode has the electrode structure described in any one of claims 1 to 11.

13. The crystal oscillator according to claim 12, characterized in that, The crystal sheet is excited by thickness shear vibration as the dominant vibration.

14. The crystal oscillator according to claim 12, characterized in that, The crystal sheet comprises: First primary surface; as well as The second primary surface is the surface opposite to the first primary surface. The excitation electrode includes: A first excitation electrode is disposed on the first main surface; as well as The second excitation electrode is disposed on the second main surface. The first excitation electrode has a structure that is symmetrical to the second excitation electrode across the crystal plate.

15. The crystal oscillator according to claim 12, characterized in that, The crystal sheet comprises: First primary surface; as well as The second primary surface is the surface opposite to the first primary surface. The excitation electrode includes: A first excitation electrode is disposed on the first main surface; as well as The second excitation electrode is disposed on the second main surface. The first excitation electrode has an asymmetrical structure with respect to the second excitation electrode separated by the crystal plate.

16. The crystal oscillator according to claim 12, characterized in that, The crystal sheet, when viewed from above, is roughly rectangular with a long side of less than 2 mm.

17. The crystal oscillator according to claim 12, characterized in that, The crystal plate is excited by any one of the following vibration modes: fundamental mode, third harmonic mode, and fifth harmonic mode.

18. The crystal oscillator according to claim 12, characterized in that, The crystal wafer has any one of the following structures: flat, inclined, mesa, reverse mesa, convex, or plano-convex.

19. A crystal oscillator, characterized in that, have: Crystal oscillator; and The circuit controls the oscillation frequency of the crystal oscillator. The crystal oscillator is the crystal oscillator according to claim 12.

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