Base for piezoelectric device and piezoelectric device

Abstract

To provide a base with a novel structure for a piezoelectric device.SOLUTION: A base 10 includes a first substrate 11 formed of glass or crystal, a mount pad 11b for a piezoelectric element that is provided on a first surface 11a of the first substrate, a contact hole 11d and a contact hole wire 11e that are provided in the first substrate and communicate with a second surface 11c on the side opposite to the first surface from the mount pad, a first metal film 11f provided in a region including a peripheral region of the contact hole on the second surface, a second substrate 13 formed of the same material as the first substrate, a second metal film 13b provided on a surface of the second substrate on the first substrate side and forming inter-metal junction together with the first metal film, a leading wire 13e, a castellation 13f, and an external mount terminal 13g.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a base for a piezoelectric device and a piezoelectric device using the base. [Background technology]

[0002] Piezoelectric devices require a container to contain the piezoelectric element. For this reason, various containers are used or researched for quartz devices, which are a type of piezoelectric device, such as metal containers, ceramic containers, and containers made of glass or quartz. Surface-mount containers are widely used, especially for mass-produced quartz devices, as there is a high demand for surface-mount containers.

[0003] A typical example of a surface-mount type container suitable for mass production is a ceramic container. Specifically, it is a container in which a ceramic base is joined to a metal or ceramic lid. The ceramic base is typically formed by integrally firing a bottom plate made of a ceramic material and having a rectangular shape in a plan view, and a bank portion made of a ceramic material laminated on the bottom plate (see, for example, paragraph 26, FIG. 1, etc. of Patent Document 1).

[0004] As an example of a container using quartz crystal and glass, for example, as disclosed in Patent Document 2, there is a container having a structure in which a quartz crystal structure in which a quartz crystal vibrating piece and an outer frame are integrally formed, a glass upper plate, and a glass lower plate are bonded together by anodic bonding (Summary, Figures 1 and 3 of Patent Document 2, etc.).

[0005] Another example of a glass container is a container having a structure in which a lid and a base made of borosilicate glass are directly bonded to each other, as disclosed in Patent Document 3 (paragraphs 18 and 32, FIG. 1(b), etc., of Patent Document 3).

[0006] As an example of a quartz container, for example, as disclosed in Patent Document 4, there is a container having a structure formed by bonding a lid wafer, a piezoelectric wafer, and a base wafer made of quartz wafers with a bonding material or by direct bonding, and then dicing this into individual piezoelectric devices (paragraphs 72, 75, 76, Figures 8 and 9, etc. of Patent Document 4). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2007-274071 A [Patent Document 2] JP 2000-68780 A [Patent Document 3] JP 2014-192644 A [Patent Document 4] JP 2015-33035 A Summary of the Invention [Problem to be solved by the invention]

[0008] Among the various containers described above, the most excellent at present is one that uses a ceramic base. However, as piezoelectric devices become thinner and smaller, it can be said that ceramic bases have limitations in terms of structure, precision, and cost. Therefore, a base with a new structure that can replace ceramic bases and surpass the conventional containers that use glass and / or quartz is desired. The present invention has been made in consideration of the above-mentioned points, and therefore an object of the present application is to provide a base having a novel structure for a piezoelectric device, and a piezoelectric device using the same. [Means for solving the problem]

[0009] In order to achieve this object, the base for a piezoelectric device of the present invention is characterized by comprising a first substrate made of glass or quartz, a mounting pad for a piezoelectric element provided on a first surface of the first substrate, a contact hole and a contact hole wiring provided on the first substrate and extending from the mounting pad to a second surface opposite the first surface, a first metal film provided in an area including the surrounding area of ​​the contact hole on the second surface, a second substrate made of the same material as the first substrate and bonded to the first substrate by metal-to-metal bonding, a second metal film provided on a third surface of the second substrate which is the surface facing the first substrate and which forms the metal-to-metal bond together with the first metal film, wiring extending from the contact hole wiring via the third surface and a side surface of the second substrate to a fourth surface of the second substrate which is the surface opposite the third surface, castellations provided on the side surfaces for the wiring, and an external mounting terminal provided on the fourth surface and connected to the wiring.

[0010] a piezoelectric device according to the present invention includes a base including: a first substrate made of glass or quartz; a mounting pad for a piezoelectric element provided on a first surface of the first substrate; a contact hole and a contact hole wiring provided on the first substrate and extending from the mounting pad to a second surface opposite the first surface; a first metal film provided in a region including a peripheral region of the contact hole on the second surface; a second substrate made of the same material as the first substrate and bonded to the first substrate by metal-to-metal bonding; a second metal film provided on a third surface of the second substrate which is a surface of the second substrate facing the first substrate and which constitutes the metal-to-metal bonding together with the first metal film; the piezoelectric element connected and fixed to the mounting pad by a conductive member; and and a lid member that is joined to the base and seals the piezoelectric element.

[0011] According to the base of the present invention, a base for a piezoelectric device is constructed with a structure in which a first substrate and a second substrate made of glass or quartz are laminated by intermetallic bonding. Moreover, a base is realized in which a mounting pad for a piezoelectric element is connected to an external mounting terminal by a contact hole wiring provided on the first substrate and a lead wiring using castellation provided on the second substrate. Moreover, since the periphery of the contact hole is surrounded by intermetallic bonding of the first metal film and the second metal film, the contact hole region, which is likely to become a bottleneck in reducing airtightness, is sealed by intermetallic bonding. Moreover, since the first substrate and the second substrate are made of the same material, they have the same physical properties such as the thermal expansion coefficient. Therefore, even if the first and second substrates are made of glass or quartz, a base that ensures airtightness can be realized. Furthermore, since both glass and quartz crystal can be processed by photolithography, they can be processed with relatively high precision, and the material costs of both are relatively low, making it possible to realize a highly accurate and inexpensive base. Furthermore, according to the piezoelectric device of the present invention, a novel piezoelectric device can be realized using a base having the above-mentioned novel structure. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram for explaining a base 10 according to the first embodiment. [Diagram 2] 5A to 5C are diagrams for explaining an example of a method for manufacturing a base according to the present invention. [Diagram 3] 1 is a diagram illustrating a piezoelectric device 40 according to a first embodiment. [Figure 4] 11 is a diagram illustrating a base 10x and a piezoelectric device 70 according to a second embodiment. FIG. [Diagram 5] FIG. 1 is a diagram for particularly explaining castellations and external mounting terminals. [Figure 6] FIG. 2 is a diagram particularly for explaining a contact hole. [Figure 7] FIG. 11 is a diagram for explaining modified examples of the planar shapes of the first metal film and the second metal film in particular. [Figure 8] FIG. 2 is a diagram for explaining a preferred structural example when wiring is routed on a first substrate. [Figure 9] 13A and 13B are diagrams for explaining a modified example of the base of the second embodiment. [Figure 10] 4A to 4C are diagrams for explaining specific configuration examples of a first metal film and a second metal film. [Figure 11] 11A to 11C are diagrams for explaining a preferred structural example when a seal pattern is provided. [Figure 12] 1A and 1B are diagrams for explaining an example of a structure preferable for reducing the joining pressure when performing intermetallic joining. [Figure 13] FIG. 13 is a view continuing from FIG. 12 for explaining a preferred structural example for reducing the joining pressure when performing intermetallic joining. [Figure 14] 4A to 4C are diagrams illustrating a preferred example of the structure of the surface of the first substrate on which piezoelectric elements are mounted. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the base and piezoelectric device of the present invention will be described with reference to the drawings. Note that each drawing used in the description is merely a schematic illustration to the extent that the present invention can be understood. In addition, in each drawing used in the description, similar components are indicated by the same numbers, and their description may be omitted. Furthermore, the shapes, dimensions, materials, etc. described in the following examples are merely preferred examples within the scope of the present invention. Therefore, the present invention is not limited to the following embodiments.

[0014] 1. Base of the first embodiment 1(A) and (B) are diagrams for explaining a base 10 according to a first embodiment. In particular, Fig. 1(A) is a perspective view of the base 10, and Fig. 1(B) is an exploded perspective view showing the base 10 divided into a first substrate 11 and a second substrate 13. The base 10 of the embodiment comprises a first substrate 11 made of glass or quartz, a mounting pad 11b for a piezoelectric element provided on a first surface 11a of the first substrate 11, a contact hole 11d and contact hole wiring 11e provided on the first substrate 11 and leading from the mounting pad 11b to a second surface 11c which is the opposite surface 11a to the first surface 11a, a first metal film 11f provided in an area including the surrounding area of ​​the contact hole 11d on the second surface 11c, an insulating area 11g, and a seal pattern 11h. Further, the base 10 includes a second substrate 13 made of the same material as the first substrate 11 and bonded to the first substrate 11 by intermetallic bonding, a second metal film 13b provided on a third surface 13a of the second substrate 13 facing the first substrate 11 and forming an intermetallic bond together with the first metal film 11f, i.e., bonded to the first metal film 11f, a wiring 13e extending from the contact hole wiring 11e through the third surface 13a and a side surface 13c of the second substrate 13 to a fourth surface 13d of the second substrate 13 opposite to the third surface 13a, a castellation 13f provided on the side surface 13c for the wiring 13e, and an external mounting terminal 13g (see FIG. 3) provided on the fourth surface 13d and connected to the wiring. Specific examples of each of the above-mentioned components will be described below.

[0015] In this example, the first substrate 11 has a rectangular planar shape. In the case of quartz crystal, the specific material of the first substrate 11 is preferably a Z-cut plate or an AT-cut plate. Both the Z-cut plate and the AT-cut plate of quartz crystal are mass-produced substrates for use in quartz crystal resonators, and therefore are advantageous in terms of cost. In addition, in the case of glass, any suitable glass such as soda glass may be used.

[0016] The mounting pad 11b is connected and fixed to the piezoelectric element 50 (see FIG. 3) by a conductive adhesive or the like. The mounting pad 11b is provided at any location on the first surface 11a of the first substrate 11, with a shape corresponding to the mounting structure of the piezoelectric element. In this example, since a structure in which the piezoelectric element is cantilevered is illustrated, the mounting pads 11b are provided in two locations near one side of the first substrate 11 and spaced apart from each other in a direction along the one side. More specifically, as will be described later with reference to FIG. 3, the piezoelectric element 50 (see FIG. 3) mounted on the first substrate is rectangular in plan view, and the mounting pads 11b are provided at two locations on the first substrate corresponding to both ends on one side of the rectangular piezoelectric element 50 and along the one side. The planar shape of the mounting pad 11b can be any shape, such as a square, a round, or an elliptical shape. The mounting pad 11b can be made of any suitable metal film, for example, a laminate film of a chromium film and a gold film.

[0017] The contact holes 11d and the contact hole wiring 11e communicate from the first surface 11a to the second surface 11c of the first substrate 11, and can be formed on the first substrate 11 by using, for example, photolithography, etching, and film formation techniques. The contact hole wiring 11e can be made of, for example, the same material as that of the mounting pad 11b.

[0018] The first metal film 11f is one of the members for bonding the first substrate 11 and the second substrate 13 by intermetallic bonding, and also serves as one of the sealing members for ensuring airtightness of the contact holes 11d. Therefore, in this example, the first metal film 11f is composed of three parts: a first part 11f1 having a planar shape surrounding one of the two contact holes 11d, a second part 11f2 having a planar shape surrounding the other of the two contact holes 11d, and a third part 11f3 covering the remaining area. The above three parts 11f1, 11f2, and 11f3 of the first metal film 11f need to be electrically isolated from each other, and are therefore separated by an insulating region 11g in which the metal film is removed. However, in order to increase the area of ​​intermetallic bonding with the second metal film 13b described later, it is preferable to minimize the area of ​​the insulating region 11g. The second metal film 13b provided on the second substrate 13 is the other member for bonding the first substrate 11 and the second substrate 13 by metal-to-metal bonding, and also serves as the other sealing member for ensuring airtightness of the contact hole 11d. Therefore, the second metal film 13b is composed of three parts corresponding to the three parts 11f1, 11f2, and 11f3 of the first metal film 11f, and these three parts are separated by an insulating region 13h. It is preferable that the area of ​​this insulating region 13h is as small as possible, similar to the insulating region 11g.

[0019] Here, the materials of the first metal film 11f and the second metal film 13b will be described with reference to Figures 10(A) to 10(C). These figures are cross-sectional views of a structure of the first substrate 11 (or the second substrate 13) and the first metal film 11f (or the second metal film 13b). Each of the first metal film 11f and the second metal film 13b can be made of any suitable metal film capable of performing intermetallic bonding. For example, it can be made of a laminated film of a chromium film 80a and a gold film 80b, which are laminated in this order from the first substrate side (FIG. 10(A)). In this way, the first metal film 11f and the second metal film 13b cooperate to generate intermetallic bonding between the gold films, thereby enabling intermetallic bonding between the first substrate 11 and the second substrate 13. More preferably, as shown in Fig. 10(B), each of the first metal film 11f and the second metal film 13b is preferably made of a three-layer laminate film consisting of a chromium film 80a as an undercoat film, a nickel film or nickel-tungsten alloy film 80c as an intermediate film, and a gold film 80b as an upper layer film. The configuration with a nickel film or nickel-tungsten alloy film as an intermediate film can prevent the chromium film as an undercoat film from diffusing into the gold film as an upper layer film, so that intermetallic bonding by the first metal film and the second metal film can be performed better. In addition, it is considered that this three-layer laminate film can prevent the diffusion of chromium into the gold film over time. More preferably, as shown in Fig. 10(C), each of the first metal film 11f and the second metal film 13b is a five-layered metal film having a laminated film consisting of a titanium film 80d and a gold film 80e laminated on the titanium film 80d on the gold film 80b, which is the upper layer of the three-layered metal film. Even if nickel or a nickel-tungsten alloy is provided, chromium may diffuse into the gold film, but the titanium film can prevent the diffusion of chromium into the top gold film, thereby achieving better intermetallic bonding. It is considered that this five-layered laminated film can also better prevent the diffusion of chromium into gold over time.

[0020] The seal pattern 11h (FIG. 1) is for joining a lid member 60 (see FIG. 3) to be described later to the base 10. The base 10 of this embodiment shows an example in which the lid member is joined to the base by a solder material, such as a gold-tin alloy. Therefore, the seal pattern 11h is made of any suitable material that is easy to join with gold-tin. The seal pattern 11h is provided with a predetermined width along the edge of the first substrate 11. In providing the seal pattern 11h on the first surface 11a of the first substrate 11, it is preferable to provide a recess 11ha having a depth d (see FIG. 11(B)) equal to the thickness of the seal pattern 11h in the region of the first surface 11a of the first substrate 11 where the seal pattern 11h is to be provided, as shown in FIGS. 11(A) and (B), and provide the seal pattern 11h in this recess 11ha. When realizing a low-profile piezoelectric device, the thickness of the seal pattern 11h itself may be an obstacle to low-profile design, but if the seal pattern 11h is embedded in the recess 11ha as in this preferred example, it is possible to prevent the thickness of the piezoelectric device from increasing due to the thickness of the seal pattern 11h. FIG. 11(B) is a schematic cross-sectional view of the base 10 taken along the line PP in FIG. 11(A).

[0021] The second substrate 13 is bonded to the first substrate 11 by intermetallic bonding between the first metal film and the second metal film. The second substrate 13 is made of the same material as the first substrate 11 and has substantially the same planar shape. However, the planar shape of the second substrate 13 is slightly different from that of the first substrate 11 in that castellations 13f are provided. The castellations 13f will be described later.

[0022] The lead wiring 13e is a wiring that extends from the contact hole wiring 11e to the fourth surface 13d via the third surface 13a and the side surface 13c of the second substrate 13. However, the lead wiring 13e is formed using a part of the first metal film 11f and the second metal film 13b. Specifically, the lead wiring between the first substrate 11 and the second substrate 13 is formed of the first portion 11f1 and the second portion 11f2 of the first metal film and the second metal film 13b (13e) facing them. Note that the portion of the lead wiring 13e that extends from the side surface 13c of the second substrate 13 to the external mounting terminal 13g is formed of a metal film that is continuous with the second metal film 13b.

[0023] The castellation 13f is for routing the lead wiring 13e to the external mounting terminal 13g. The castellation 13f is a notch-like shape that is slightly recessed from the edge of the second substrate to the center on each of two opposing sides of the third substrate. The details will be described later with reference to FIG. 2, but the castellation 13f can be formed by providing a hole that is elongated in a plan view in a wafer for forming the second substrate 13, and dividing the wafer into the second substrates with a dicing saw or the like. Note that, although the number of castellations is two in the illustrated example, there may be three or more.

[0024] The external mounting terminals 13g are provided on the fourth surface 13d and connected to the above-mentioned lead wiring 13e. The external mounting terminals 13g are terminals used when mounting the piezoelectric device (see FIG. 3) manufactured using the base 10 of the present invention to various electronic devices. In this example, four terminals are shown as the external mounting terminals 13g, but the number of terminals is not limited to this. In this case, two of the four terminals are non-connected (NC). In cases where the piezoelectric device has an earth structure, these non-connected terminals can also be used as earth terminals.

[0025] 2. Example of Base 10 manufacturing method Next, in order to deepen understanding of the base of the present invention, an example of a method for manufacturing the base 10 of the first embodiment will be described. Figures 2(A) to (D) are diagrams for explaining this example of the manufacturing method. In order to form the first substrate 11, a quartz wafer 20x is prepared, and the first substrate 11, i.e., mounting pads 11b, contact holes 11d, contact hole wiring 11e, and first metal film 11f, are formed in a matrix on the wafer 20x by known photolithography, film formation, and etching techniques (FIG. 2(A)). Moreover, in order to form the second substrate 13, a quartz wafer 20y is prepared, and a second metal film 13b, holes 20z for castellation, etc. are formed on the wafer 20y by known photolithography, film formation, and etching techniques (Figure 2(B)).

[0026] Next, the wafer 20x and the wafer 20y are stacked in a predetermined positional relationship, and are heated in a low-pressure atmosphere in a vacuum chamber and pressurized with a predetermined force (FIG. 2(C)). This process causes the first metal film 11f and the second metal film 13b to bond with each other, so that the wafer 20x and the wafer 20y are bonded together, and therefore the first substrate 11 and the second substrate 13 are bonded together (FIG. 2(D)). Next, the bonded wafer is diced along predetermined lines, for example, by a dicing saw, to obtain the base 10 of the first embodiment.

[0027] The first substrate 11 and the second substrate 13 are bonded by intermetallic bonding between the first metal film 11f and the second metal film 13b. At this time, a predetermined pressure is applied to the first substrate 11 and the second substrate 13 from the opposite side to the bonding surface. If this pressure can be made as low as possible, the cost of the bonding device and the manufacturing throughput can be reduced. Therefore, as described below with reference to Figs. 12 and 13, the second surface 11c of the first substrate 11 and / or the third surface 13a of the second substrate 13 may be provided with a plurality of convex regions 90 for concentrating the bonding force applied from the outside to the first substrate 11 and the second substrate 13 when performing intermetallic bonding. An example is shown in Figs. 12(A) to 12(C).

[0028] First, Fig. 12(A) shows an example in which the regions corresponding to insulating region 11g of first substrate 11 and insulating region 13h of second substrate 13 are respectively concave, and the portions of first substrate 11 and second substrate 13 other than insulating regions 11g and 13h are ultimately convex, thereby forming convex region 90. Figs. 12(B) and (C) are cross-sectional views taken along lines PP and QQ in Fig. 12(A), respectively, and these cross-sectional views clearly show convex region 90. Fig. 13(A) shows an example in which the regions corresponding to the insulating region 11g of the first substrate 11 and the insulating region 13h of the second substrate 13 are each made concave, and some other regions are also made concave, resulting in the first substrate 11 and the second substrate 13 being made convex other than the concave regions, thereby forming a convex region 90. In the perspective view shown in Fig. 13(A), a convex region 90a provided other than the vicinity of the insulating regions 11g and 13h is clearly shown. In addition, Fig. 13(B) is a cross-sectional view taken along the line RR in Fig. 13(A), and in this cross-sectional view, the convex regions 90, 90a are clearly shown. In the above example, the convex regions 90, 90a are provided on both the mutually opposing surfaces of the first substrate 11 and the second substrate 13, but the convex regions 90, 90a may be provided on only one of the opposing surfaces of the first substrate 11 and the second substrate 13. The ratio of the area of ​​the convex regions 90, 90a to the area of ​​the substrate of the first substrate 11 or the second substrate 13 is determined in consideration of the reliability of the intermetallic bonding and the reduction in the pressing force. Although not limited thereto, the ratio of the area of ​​the convex regions 90, 90a to the area of ​​the substrate of the first substrate 11 or the second substrate 13 is preferably selected from the range of 20 to 50%.

[0029] 3. Piezoelectric device according to the first embodiment Next, a piezoelectric device 40 according to a first embodiment will be described. Fig. 3(A) is an exploded perspective view for explaining the piezoelectric device 40 according to the first embodiment, and Fig. 3(B) is a cross-sectional view of a cover member 60 taken along line PP in Fig. 3(A). The piezoelectric device 40 of the first embodiment includes the base 10 of the first embodiment described above, a quartz crystal vibrating piece 50 as a piezoelectric element, and a cover member 60. Although there is no particular limitation, the quartz crystal vibrating piece 50 is typically an AT-cut quartz crystal piece. In this case, the quartz crystal vibrating piece 50 as a piezoelectric element includes an AT-cut quartz crystal piece 50a and excitation electrodes 50b provided on the front and back sides of the AT-cut quartz crystal piece 50a. In this case, the lid member 60 has a cap-like structure including a recess 60a capable of containing the quartz crystal vibrating piece 50 and a bank portion 60b provided around the recess 60a. The quartz crystal vibrating piece 50 is connected and fixed to the mounting pad 11b by a conductive adhesive (not shown) at the position of the lead wire led out from the excitation electrode 50b. After the quartz crystal vibrating piece 50 has been mounted on the mounting pads 11b, the cover member 60 is bonded to the base 10, in this example with gold-tin, to seal the quartz crystal vibrating piece 50. For sealing, the sealed space is preferably in a reduced pressure atmosphere, a nitrogen atmosphere, or an inert gas atmosphere. From the viewpoint of cost and ease of manufacture, it is preferable that the cover member 60 is made of metal. Any suitable metal material may be used for the cover member 60, but the following materials are preferable in consideration of the linear expansion coefficients of the first and second substrates.

[0030] When the first substrate 11 and the second substrate 13 are each made of quartz, the linear expansion coefficient of quartz (ppm / °C) is 11.4 when parallel to the optical axis and 19.5 when perpendicular to the optical axis at a temperature of about 500K (Kelvin) (Science Chronology, published on November 27, 2015). The reason why the linear expansion coefficient is around 500K is that the temperature at which the lid member 60 is sealed to the first substrate 11 is often selected from a range of temperatures of about 400K to 600K, and it is good to consider the linear expansion coefficient at such a temperature. In this case, the metal material constituting the lid member 60 is preferably a material that exhibits a linear expansion coefficient close to that of quartz, and thus, for example, copper (linear expansion coefficient around the above temperature is 18.3, according to the Science Chronology) or nickel (linear expansion coefficient around the above temperature is 15.3, according to the Science Chronology). When the cover member 60 is made of copper, it is preferable to plate the surface with nickel in order to improve corrosion resistance. Furthermore, when first substrate 11 and second substrate 13 are each made of glass, it is preferable to make cover member 60 from Kovar (linear expansion coefficient of approximately 6), which is known to have a linear expansion coefficient close to that of glass.

[0031] 4. Base and Piezoelectric Device of Second Embodiment Next, the base 10x and the piezoelectric device 70 according to the second embodiment will be described with reference to Fig. 4. Fig. 4(A) is an exploded perspective view for explaining the base 10x and the piezoelectric device 70 according to the second embodiment, and Fig. 4(B) is a cross-sectional view of the piezoelectric device 70 taken along line QQ in Fig. 4(A). The base 10x of the second embodiment differs from the base 10 of the first embodiment in that a recess 10y that contains a piezoelectric element is provided in the first substrate 11. The piezoelectric device 70 of the second embodiment differs from the piezoelectric device 40 of the first embodiment in that the cover member 60x is flat due to the use of the base 10x. In this example, for example, a seal pattern 11h is provided on the bank portion around the recess 11y of the first substrate 11, and the flat cover member 60x can be bonded to the first substrate 11 by, for example, a gold-tin alloy. In this case, the lid member 60x is preferably made of metal like the lid member 60, and is preferably made of metal taking into consideration the linear expansion coefficients of the first and second substrates. That is, for example, for the reasons described above, a lid member made of copper, nickel or kovar is preferable.

[0032] 5. Other embodiments 5-1.Castellation structure Fig. 5 is a diagram illustrating a preferred example of the castellation 13f. In particular, Fig. 5(A) and (B) are plan views of the first substrate 11 and the second substrate 13, and Fig. 5(C) to (E) are enlarged views showing preferred examples of the castellation. First, as shown in Fig. 5(A), it is preferable to provide a notch 11i for viewing the castellation 13f from above in a portion of the first substrate 11 that corresponds to the castellation 13f provided on the second substrate 13. When mounting a piezoelectric device on a substrate of an electronic device, the quality of the soldering of the mounting solder is often checked by checking whether the solder reaches the castellation 13f. The notch 11i makes this check easy. 5(C) to (E) are structural examples for reducing damage to the piezoelectric device caused by the shape of the castellations 13f. 5(C) is an example in which the castellation 13f is provided with an R-shaped portion 13x on the central side of the second substrate 13. By providing the R-shaped portion 13x, damage to the portion of the castellation 13f on the central side of the second substrate 13 can be easily reduced. 5(D) is an example in which a convex portion 13y is provided on the corner side of the second substrate 13 of the castellation 13f, where a part of the second substrate 13 remains in a convex shape. When the convex portion 13y is provided, intermetallic bonding is also generated between the first metal film and the second metal film in the convex portion 13y, so that the strength of the piezoelectric device at the corner of the piezoelectric device can be increased. The example shown in FIG. 5(E) is a structural example in which both the R-shaped portion 13x and the convex portion 13y are provided to obtain the advantages of both.

[0033] 5-2. Contact hole structure Fig. 6 is a diagram illustrating a preferred example of contact hole 11d. In particular, Fig. 6(A) is a plan view showing the relationship between contact hole 11d and first substrate 11, Figs. 6(B) to (D) are enlarged views showing a preferred planar shape and arrangement direction of contact hole 11d in Fig. 6(A), and Fig. 6(E) is a plan view and a cross-sectional view along line RR showing a preferred example of the positional relationship of contact hole 11d on the front and back of first substrate 11. When the first substrate 11 is made of a quartz substrate, because quartz is a crystalline material, when forming the contact holes, anisotropy occurs in the etching solution due to the crystal axes of the quartz, and the contact holes may not open as desired. In such cases, the desired contact hole wiring may not be formed, leading to an increase in wiring resistance. To avoid this, it may be a good idea to devise the shape of the contact holes in the direction where etching is difficult. The example in Figure 6(B) is an example of a contact hole that is elongated in a direction that is difficult to etch. The example in Figure 6(C) is an example of a contact hole that is elongated in a direction that is difficult to etch. The example in Figure 6(D) is an example of a contact hole that is elongated in a plan view in a direction that is difficult to etch. The longitudinal direction of the elongated hole or elongated triangular shape can be any direction taking into consideration the etching direction (Figure 6(D)). Furthermore, due to the etching anisotropy of quartz crystal described above, the direction in which etching predominantly proceeds may not be the thickness direction of the first substrate 11, but may be an oblique direction at a certain angle to the thickness direction. FIG. 6(E) shows an example of a countermeasure. In this example, the opening of an etching-resistant mask for forming the contact hole 11d is shifted by a dimension L on the front and back of the first substrate 11, and etching is performed. In this way, the contact hole wiring can be formed by utilizing the inclined surface of the inner surface of the contact hole 11d, and therefore improvement in wiring resistance can be expected. Note that the shift dimension D is not limited to this, but is preferably set to a dimension selected from the range of one-third to one-half the diameter of the contact hole 11d, for example.

[0034] 5-3. Planar shapes of the first metal film and the second metal film When forming the base 10 of the present invention, the first and second substrates are heated and pressurized under reduced pressure while in contact with each other, so that the first metal film 11f and the second metal film 13b form an intermetallic bond. Therefore, it is preferable to remove as much air as possible between the first and second substrates. FIG. 7 is a diagram for explaining a structure example for this purpose. That is, this is an example in which the planar shapes of the insulating region 11g of the first substrate and the insulating region 13h of the second substrate each have many curved and / or straight line portions so that air can escape as easily as possible when the two substrates are in contact with each other. This is preferable because it is easier to remove air between the substrates when the two substrates are in contact with each other and vacuumed, compared to the case where this is not done.

[0035] 5-4. When wiring is provided on the first board 8(A) and 8(B) are a plan view and a cross-sectional view along line MM showing a preferred example of a case in which wiring 11j extending from mounting pad 11b of first substrate 11 to another location on first substrate 11 is provided. There is also a strong demand for low-profile piezoelectric devices, and in that case, the height of the wiring 11j is also considered to be a problem. Therefore, in the example of Fig. 8, a recess 11k for embedding the wiring 11j is provided in the region of the first substrate 11 where the wiring 11j is provided. The depth of the recess 11k is set to a value that allows the wiring 11j to be embedded and ensures the strength of the first substrate 11. Specifically, the depth of the recess 11k is preferably set to a value selected from the range of 10 µm to about one-fourth the thickness of the first substrate 11.

[0036] 5-5. When a recess for a piezoelectric element is provided on the first substrate As already described with reference to FIG. 4, in the base 10x and the piezoelectric device 70 of the second embodiment, the first surface side of the first substrate 11 is provided with a recess 10y for the piezoelectric element 50. Therefore, a bank portion 10z (see FIG. 4) is generated around the recess 10y, i.e., on the edge of the first substrate 11. On the other hand, in the case of the piezoelectric device 70, it may be modularized by resin molding together with other electronic components, and the piezoelectric device 70 may be damaged by pressure during molding. Therefore, as one means for avoiding this, the bank portion 10z may be structured to have increased rigidity, for example by protruding like an eave toward the center side of the first substrate 11, as shown in FIG. 9(A). From another point of view, the demand for a thinner piezoelectric device having a recess 10y for the piezoelectric element 20 may be increasing, and the thickness of the first substrate and / or the second substrate may be required to be thinner. For example, when a demand for a thinner first substrate 11 is made as shown in FIG. 9(B), it is necessary to ensure the bonding strength with the second substrate 13 even in the state where the recess 10y is provided. As a preferred structural example in this case, it is preferable to provide a tapered portion 10t at the inside corner between the recess 10y and the bank portion 10z as shown in FIG. 9(B). This is because the area of ​​the thick portion of the first substrate increases in the bonding structure between the first substrate and the second substrate by providing the tapered portion 10t, and therefore the bonding strength between the two substrates can be improved compared to the case where the tapered portion is not provided.

[0037] 5-6. About the pillow when mounting the piezoelectric element on the first board In a typical piezoelectric device, as described with reference to Fig. 3, the quartz crystal vibrating piece 50 serving as a piezoelectric element has a rectangular shape in a plan view. Furthermore, the mounting pads 11b are often provided in two places on the first substrate corresponding to both ends along one side of the piezoelectric element 50. That is, the piezoelectric element 50 is often mounted in a cantilevered manner. In the case of cantilever support, when mounting the piezoelectric element 50 on the first substrate, the tip of the piezoelectric element may bow and come into contact with the first substrate, which may lead to deterioration of the characteristics of the piezoelectric device. In order to avoid this, for example, as described using Figure 14, it is preferable to have a first convex portion 11m formed integrally with the first substrate 11 on the side of the center of the piezoelectric element 50 (Figure 14 (B)) in two areas where mounting pads 11b are provided on the first surface 11a of the first substrate 11, and to have a second convex portion 11n formed integrally with the first substrate in an area facing the tip side of the piezoelectric element 50 on the first surface 11a of the first substrate 11. The height h1 of the first protrusion 11m and the height h2 of the second protrusion 11n are set to a height that can prevent bowing of the tip of the piezoelectric element 50. Although not limited to this, the height h1 of the first protrusion 11m is about 0.8 to 1.2 times, and preferably about the same as, the height of the mounting pad 11b, and the height h2 of the second protrusion 11n is about 0.8 to 1.5 times, and preferably about the same as or higher than the height of the mounting pad 11b. According to this configuration, the first convex portion and the second convex portion can prevent the tip of the piezoelectric element from bowing. The first and second convex portions can be easily formed integrally with the first substrate 11 by processing the first substrate 11 using photolithography and wet etching techniques. Furthermore, the top surfaces of the first and second convex portions manufactured by such a method are unlikely to be sharp, so there is little risk of damaging the piezoelectric element 50 even if it comes into contact with them. [Explanation of symbols]

[0038] 10: Base of the first embodiment 10x: Base of the second embodiment 10y: Recess (recess for mounting piezoelectric element) 10z: Bank 11: 1st board 11a: 1st side 11b: Mounting pad 11c: Second surface 11d: Contact hole 11e: Contact hole wiring 11f, 11f1, 11f2, 11f3: First metal film 11g: Insulation area 11h: Seal pattern 11ha: Recess for seal pattern 11i: Notch 11j: Wiring 11k: Recess (recess for embedding wiring) 11m: First convex part 11n: Second convex part 13: second substrate 13a: third surface 13b: Second metal film 13c: Side surface 13d: 4th side 13e: Wiring 13f: Castellation 13g: External mounting terminal 13h: Insulation area 40: Piezoelectric device according to the first embodiment 50: Piezoelectric element (quartz crystal vibrating piece) 60,60x: Lid material 70: Piezoelectric device according to the second embodiment 80a: Chromium film 80b: Gold film 80c: Nickel film or nickel-dum alloy film 80d: Titanium film 80e: Gold film

Claims

1. 1. A base for a piezoelectric device, comprising: a first substrate made of glass or quartz; a mounting pad for a piezoelectric element provided on a first surface of the first substrate; a contact hole and a contact hole wiring provided on the first substrate, the contact hole and the contact hole wiring extending from the mounting pad to a second surface opposite to the first surface; a first metal film provided on the second surface in a region including a peripheral region of the contact hole; a second substrate made of the same material as the first substrate and joined to the first substrate by metal-to-metal bonding; a second metal film provided on a third surface of the second substrate, the third surface being a surface of the second substrate facing the first substrate, and constituting the intermetallic bond together with the first metal film; a lead-out wiring extending from the contact hole wiring through the third surface and a side surface of the second substrate to a fourth surface of the second substrate, the fourth surface being the surface opposite to the third surface; A castellation is provided on the side surface for the wiring; an external mounting terminal provided on the fourth surface and connected to the lead wiring; A base comprising:

2. The base according to claim 1 , wherein the first substrate is a flat plate and is provided with a seal pattern for sealing along an edge of the first substrate.

3. 3. The base according to claim 2, wherein a recess having a depth equal to a thickness of the seal pattern is provided in an area of ​​the first substrate where the seal pattern is to be provided, and the seal pattern is provided within the recess.

4. The base according to claim 1 , wherein the first substrate has a recess for accommodating the piezoelectric element and a bank portion around the recess.

5. 5. The base according to claim 4, further comprising a tapered portion at an inside corner between said recess and said bank portion.

6. The first substrate is rectangular in plan view, the mounting pads are provided in two locations near one side of the first substrate and spaced apart from each other in a direction along the one side; A base as described in any one of claims 1 to 5, characterized in that it has a first convex portion formed integrally with the first substrate on a first surface of the first substrate, beside the two mounting pads and on the side toward the center of the first surface, and a second convex portion formed integrally with the first substrate in an area on the other side opposite the one side of the first surface of the first substrate, facing one end of a piezoelectric element to be mounted on the base.

7. The base according to any one of claims 1 to 6, characterized in that each of the first metal film and the second metal film is a laminated film of a chromium film as a base film, a nickel film or a nickel-tungsten alloy film as an intermediate film, and a gold film as an upper layer film.

8. The base according to claim 7, wherein each of the first metal film and the second metal film comprises a laminate film on the upper layer film, the laminate film being made of a titanium film and a gold film laminated on the titanium film.

9. the contact holes are two contact holes, a first contact hole and a second contact hole, each of the first metal film and the second metal film includes a first portion surrounding the first contact hole in a planar manner, a second portion surrounding the second contact hole in a planar manner, and a third portion covering the remaining area; The base according to any one of claims 1 to 8, further comprising an insulating region for insulating the first portion, the second portion and the third portion from each other.

10. A base as described in claim 9, characterized in that the insulating region is a recessed region provided between the first portion, the second portion and the third portion of the second surface of the first substrate and / or the third surface of the second substrate.

11. The base according to any one of claims 1 to 10, wherein each of the first substrate and the second substrate is made of a quartz AT plate or a quartz Z plate.

12. A piezoelectric device comprising: a base according to any one of claims 1 to 11; a piezoelectric element connected and fixed to the mounting pad by a conductive member; and a lid member joined to the base and sealing the piezoelectric element.

13. Each of the first substrate and the second substrate is made of a quartz AT plate or a quartz Z plate, 13. The piezoelectric device according to claim 12, wherein the cover member is made of copper or nickel.

14. 14. The piezoelectric device according to claim 13, wherein the copper cover member has a nickel-plated layer on a surface thereof.

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