Quartz crystal oscillator, its manufacturing method, and intermediate wafer for quartz crystal oscillator

Abstract

To provide a crystal oscillator with a novel structure having a through-hole that is preferable to conduct the front and back sides of a crystal piece.SOLUTION: A crystal oscillator 10 includes a crystal piece 11, a container 13 that accommodates the crystal piece, a conductive adhesive 15 that connects and fixes the crystal piece to the container, a through-hole 17, and electrodes (excitation electrode 11a and wiring electrode 11b) provided on one surface of the crystal piece, on an inner wall of the through-hole, and on the other surface of the crystal piece. The through-hole 17 is provided on a portion of a connecting and fixing area 11c of the crystal piece, penetrating the front and back sides of the crystal piece, and having on the inner wall a surface on which the crystallinity of the crystal is vanished. The through-hole 17 is formed using a picosecond laser or a femtosecond laser, which is a short pulse laser.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a quartz crystal resonator characterized by a structure in which a quartz crystal blank is adhesively fixed to a container with a conductive adhesive, a method for manufacturing the same, and an intermediate wafer for the quartz crystal resonator. [Background technology]

[0002] Most quartz crystal units available today are SMD type. Therefore, when fixing a quartz crystal blank to a case, one of the two main surfaces of the quartz crystal blank faces the adhesive pad on the case, and a predetermined portion of that main surface is electrically and mechanically connected to the adhesive pad with a conductive adhesive.

[0003] On the other hand, since the crystal blank has excitation electrodes on both sides, the excitation electrodes on the side opposite the bonding pads must be routed to the bonding pads, which is generally done via the side of the crystal blank. When an excitation electrode is routed from one surface of a crystal blank to the other via the side surface of the crystal blank, the electrode is prone to breakage at the edge of the crystal blank, which is the boundary between the main surface and the side surface of the crystal blank. One way to reduce this disconnection is to create a through hole from one side of the crystal piece to the other, as shown in Patent Document 1, and use this through hole to ensure electrical conductivity between the front and back (Patent Documents 1, 3, 5, paragraph 83, etc.). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-191579 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 does not provide any specific description of the specific structure of the through-hole, particularly the internal shape in the depth direction. It also does not provide any description of the method for manufacturing the through-hole. While photolithography and wet etching techniques are conceivable as methods for manufacturing through-holes in quartz crystal pieces, when this method is used to form through-holes in quartz crystal pieces, the opening and interior of the through-hole are affected by the crystal planes resulting from the crystallinity of the quartz crystal, resulting in a complex structure inside the through-hole consisting of multiple crystal planes. Therefore, it is difficult to form through-holes in a state where a conductive material such as an electrode film can be easily formed inside the through-hole. That is, depending on the structure of the through-hole, the objective of achieving electrical continuity between the front and back of the crystal blank may not be achieved, and there is room for improvement in the structure of the through-hole and its manufacturing method. The inventors of the present application have also conducted extensive research into the structure of the through holes for achieving electrical continuity between the front and back of the crystal blank, and the manufacturing method thereof. This application has been made in consideration of the above points, and therefore, the object of this application is to provide a quartz crystal resonator with a novel structure having a preferable through hole for providing electrical conductivity between the front and back of the quartz crystal blank, a manufacturing method that can easily form this structure, and an intermediate wafer for forming the quartz crystal resonator. [Means for solving the problem]

[0006] In order to achieve this object, the quartz crystal resonator of this application comprises a quartz crystal piece, a container for accommodating the quartz crystal piece, a conductive adhesive for connecting and fixing the quartz crystal piece to the container, and a through-hole that is provided in a portion of the connection and fixing area of ​​the quartz crystal piece and penetrates the front and back of the quartz crystal piece, The through hole has an inner wall formed of a surface of quartz crystal that has lost its crystallinity; and electrodes provided on one surface of the crystal blank, on the inner wall of the through-hole, and across the other surface of the crystal blank.

[0007] Here, the surface from which the crystallinity of the quartz crystal has been eliminated refers to a surface that is different from the surface formed by photolithography and wet etching using a hydrofluoric acid-based etchant, in which the quartz crystal surface remains on part or all of the inner wall and bottom surface of the recess. Specifically, a surface in which the crystallinity of the quartz crystal has been eliminated is a surface in which linear traces extending in the depth direction from the surface of the quartz crystal blank are aligned in the circumferential direction of the inner wall of the through-hole, resulting in minute irregularities caused by these aligned linear traces (see the SEM photograph in Figure 2(A)). Such a surface can be formed by a manufacturing method using a short-pulse laser, such as a picosecond laser or femtosecond laser, which is another invention of the present application.

[0008] In carrying out the invention of this quartz crystal resonator, it is preferable that the cross-sectional shape of the through hole taken along the thickness direction of the quartz crystal blank is a funnel shape that tapers from the first surface side to the opposite second surface side of the quartz crystal blank (see Figure 1(C)). Furthermore, when implementing the invention of this quartz crystal resonator, the cross-sectional shape of the through hole cut along the thickness direction of the quartz crystal element may be a so-called hourglass shape, in which the opening decreases midway through the thickness direction of the quartz crystal element and then expands (see FIG. 2(B)). Such a funnel-like or hourglass-like shape makes it easy to coat the inside of the through-hole with a film for forming an electrode.

[0009] According to another invention of this application, a method for manufacturing a quartz crystal resonator, when manufacturing a quartz crystal resonator having a structure in which a quartz crystal blank is fixed to a container with a conductive adhesive, forming a through-hole penetrating the quartz crystal blank by using a short-pulse laser in a portion of the area of ​​the quartz crystal blank that is to be fixed with a conductive adhesive; forming a metal film for forming electrodes of a quartz crystal unit on the quartz crystal element having the through-holes formed therein so as to cover the inside of the through-holes; forming a photoresist on the crystal piece on which the metal film is formed so as to cover the inside of the through-hole; a step of exposing and developing the photoresist to form a resist pattern for forming an electrode; and a step of selectively removing the metal film exposed from the resist pattern to form an electrode that also covers the inside of the through hole. The present invention is characterized by comprising: [Effects of the Invention]

[0010] According to the quartz crystal resonator of this application, a portion of the region of the quartz crystal blank connected to the container includes a through-hole penetrating the quartz crystal blank and having a surface on its inner wall that has been decrystallized, and electrodes provided on one side of the quartz crystal blank, on the inner wall of the through-hole, and across the other side of the quartz crystal blank. This results in a quartz crystal resonator with a quartz crystal blank with a structure in which the quartz crystal blank has no crystal surface within the through-hole. Furthermore, the excitation electrode on the side opposite the container is routed to the container side through the through-hole and connected to the bonding pad, resulting in a quartz crystal resonator. However, if a quartz crystal surface is present within the through-hole, the crystal surface is due to the anisotropy of the crystal, which often reduces the aperture ratio of the through-hole, thereby adversely affecting the purpose of routing the electrode through the through-hole. In contrast, in the present invention, the through-hole has a side surface that has been decrystallized, allowing for a higher aperture ratio of the through-hole compared to a case in which a crystalline surface is present. Therefore, the electrodes provided on one side of the crystal blank, on the inner wall of the through hole, and across the other side of the crystal blank are effectively formed within the through hole, ensuring reliable conductivity between the front and back of the crystal blank. Furthermore, according to the method for manufacturing a quartz crystal unit of this application, through-holes that penetrate the front and back of a quartz crystal blank are formed using a short-pulse laser, making it possible to easily form through-holes with surfaces that eliminate the crystallinity of the quartz crystal. Furthermore, through-holes with surfaces that eliminate the crystallinity of the quartz crystal tend to have a higher aperture ratio and have inner walls that are highly coatable with metal films or photoresists compared to through-holes with surfaces that retain the crystallinity of the quartz crystal. Therefore, it is easy to coat the inside of the through-holes with metal films or photoresists for forming electrodes on the quartz crystal unit, making it possible to form desired electrodes within the through-holes. [Brief explanation of the drawings]

[0011] [Figure 1]1A to 1D are explanatory diagrams of a quartz crystal resonator 10 according to an embodiment. [Figure 2] 1(A) to 1(C) are diagrams illustrating some specific examples of through-holes according to the present invention. [Figure 3] 1A and 1B are process diagrams illustrating an embodiment of a manufacturing method. [Figure 4] 4(A) and 4(B) are process diagrams following FIG. 3 for explaining an embodiment of the manufacturing method. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the inventions of this application will be described with reference to the drawings. Note that the drawings used for the description are merely schematic illustrations to the extent that the inventions can be understood. Furthermore, in the drawings used for the description, similar components are designated by the same numbers, and their description may be omitted. Furthermore, the shapes, materials, manufacturing methods, etc. described in the following embodiments are merely preferred examples within the scope of the present invention. Therefore, the present invention is not limited to the following embodiments.

[0013] 1. Crystal unit embodiment A quartz crystal resonator 10 according to an embodiment will be described with reference to Fig. 1. Figs. 1A to 1D are explanatory diagrams of the quartz crystal resonator 10 according to an embodiment. In particular, Fig. 1A is a top view thereof, Fig. 1B is a top view focusing on the quartz crystal blank 11, Fig. 1C is a cross-sectional view taken along line P-P in Fig. 1B, and Fig. 1D is a top view of part Q in Fig. 1C as viewed from above the quartz crystal blank 11 (in the direction indicated by R in the figure). The quartz crystal resonator 10 of this embodiment includes a quartz crystal blank 11, a container 13 that houses the quartz crystal blank 11, a conductive adhesive 15 that connects and fixes the quartz crystal blank 11 to the container 13, and a through-hole 17 that is provided in a portion of the connection and fixation area 11c (see FIG. 1(B)) of the quartz crystal blank 11 with the conductive adhesive 15, and has an inner wall that is a surface where the crystallinity of the quartz crystal has been eliminated. Each of the constituent components will be described in detail below.

[0014] In this example, the crystal blank 11 is an AT-cut crystal blank. The crystal blank 11 includes an excitation electrode 11a, an extraction electrode 11b, and a through-hole 17 (described in detail below), which is a feature of the present invention. The excitation electrode 11a is provided in a predetermined area on each of the front and back principal surfaces of the crystal blank 11 and is made of any suitable metal film. The extraction electrode 11b is routed from each of the excitation electrodes 11a on both principal surfaces of the crystal blank 11 through the through-hole 17 to the other side of the crystal blank 11, in this example, one end of the crystal blank. In other words, the excitation electrode on the side opposite the container is routed to the container side via the electrode in the through-hole 17. Note that a routing structure via the sidewall of the crystal blank may also be used to route the excitation electrodes between the front and back of the crystal blank.

[0015] In this example, the container 13 includes a recess 13a that accommodates the crystal blank 11, a bank portion 13b that defines the recess 13a, and an adhesive pad 13c. In this example, the adhesive pad 13c is located on the bottom surface of the recess 13a, in an area corresponding to the extraction electrode 11b of the crystal blank 11. The adhesive pad 13c is connected to an external connection terminal (not shown) on the back surface of the container 13 via via wiring or castellation wiring (neither is shown). The crystal blank 11 is electrically and mechanically connected and fixed to the adhesive pad 13c at the position of the extraction electrode 11b with a conductive adhesive 15. In other words, the crystal blank 11 is cantilevered by the container 13. A lid member (not shown) is bonded to the top surface of bank portion 13b of container 13, sealing crystal blank 11 in container 13. Note that the bonding between container 13 and lid member is performed by any suitable method depending on the sealing method. Container 13 can be made of, for example, a ceramic package. The conductive adhesive 15 can be made of any suitable material, but in this example it is a silicone-based conductive adhesive.

[0016] Next, a specific structural example of the through hole 17, which is a feature of the present invention, will be described. This description will be made with reference to FIG. 2 in addition to FIG. 1. FIG. 2(A) is an SEM (electron microscope) photograph of a cross section of the crystal blank 11 near the connection and fixing region 11C in the thickness direction of the crystal blank 11. Also, FIGS. 2(B) and 2(C) are diagrams showing other examples of through holes, and are cross-sectional views at the same position as FIG. 2(A). Note that the dimensions shown in the SEM photograph in FIG. 2(A) are example dimensions during prototype processing using a short-pulse laser. Through-hole 17 is a through-hole for providing an electrode that connects the front and back of crystal blank 11, and furthermore, is a through-hole whose inner wall is a surface 17a where the crystallinity of the crystal has been eliminated. In this example, surface 17a is formed by linear traces that extend in the depth direction from the surface of crystal blank 11 and are aligned in the circumferential direction of the inner wall of through-hole 17, creating minute irregularities in surface 17a. Such a surface can be easily formed by a manufacturing method using a short-pulse laser, which is another invention of the present application (details will be described later).

[0017] As shown in FIGS. 1(C) and 2(A), the through-hole 17 in this embodiment has a funnel-like shape when viewed in a cross section along the thickness direction of the quartz element, tapering from the first surface side of the quartz element toward the second surface side, which is the opposite surface. This shape is preferable because it facilitates coating the inner wall of the through-hole with a metal film for forming an electrode when forming the metal film on the inner wall of the through-hole by, for example, sputtering, and also facilitates coating the inner wall of the through-hole with a photoresist. The size of the through-hole 17 is determined taking into consideration the ease of coating with a metal film or resist film. While not limited thereto, it is preferable that the diameter of the larger opening side of the through-hole 17 (the upper opening in FIG. 2(A)) be, for example, 20 to 50 μm, and the diameter of the smaller opening side of the through-hole 17 (the lower opening in FIG. 2(A)) be, for example, 10 to 30 μm.

[0018] In addition, the through-hole may be a so-called hourglass-shaped through-hole 17x (see FIG. 2(B)) whose shape when viewed in a cross section along the thickness direction of the crystal piece has a reduced opening ratio in the middle of the thickness direction of the crystal piece and then expands. Also in this example, when forming a metal film for electrode formation on the inner wall of the through-hole by, for example, sputtering method, etc., metal particles are likely to enter the through-hole from both sides of the crystal piece, so it is easy to coat the metal film, and further, it is easy to coat the inner wall of the through-hole with photoresist, which is preferable. When forming the through-hole 17x having an hourglass-shaped cross-sectional shape, the depths d1, d2 (see FIG. 2(B)) from the front and back of the crystal piece to the narrowed portion of the through-hole 17x are preferably about the same, that is, a structure that narrows near the center of the thickness of the crystal piece 11 is preferable. However, cases where d1>d2 or d1<d2 may also be acceptable. Also, as shown in FIG. 2(C), the through-hole may be a through-hole 17y having substantially the same thickness across the front and back of the crystal piece 11. However, in the case of this through-hole 17y, it is difficult to coat the inner wall of the through-hole with a metal film or a resist in the same way as in the cases of FIGS. 2(A) and (B). In each example of FIG. 2, the through-hole was one for each of the two excitation electrodes having opposite potentials, but the through-hole may be provided in two or more.

[0019] The planar shape of the through-hole 17 can be arbitrary, but considering the coverage of the electrode film at the opening of the through-hole, etc., the opening of the through-hole is preferably circular or elliptical. In the crystal oscillator 10 of this invention, conduction between the front and back of the crystal piece can be achieved by a predetermined through-hole and the electrode in the through-hole, so the reliability of electrode routing is increased compared to the case where the electrode is routed through the side wall of the crystal piece without using the through-hole 17.

[0020] 1. Embodiment of the manufacturing method Next, an embodiment of the manufacturing method of the present invention will be described with reference to Figures 3 and 4. Figures 3 and 4 are both manufacturing process diagrams showing the main parts of the manufacturing method of the embodiment. Note that since it is preferable to manufacture the quartz crystal resonator 10 of the present invention from a large quartz crystal wafer using a process that employs photolithography and film formation techniques, this embodiment will describe such an example. First, an AT-cut quartz crystal wafer 110 of a predetermined thickness and size is prepared for manufacturing the quartz crystal unit 10 (FIG. 3(A)). Then, using a well-known method, a large number of intermediates 11x for the quartz crystal unit 10 are formed in a matrix on the quartz crystal wafer 110, each intermediate having the outer shape of the quartz crystal blank 11 and before the formation of the excitation electrodes. Next, a part of the connection and fixing region 11c of the intermediate body 11x of each vibrator of the quartz crystal wafer 110, which is bonded with a conductive adhesive, is irradiated with short-pulse laser light 21a from a laser device, for example, a short-pulse laser device 21, to form a through-hole 17. The laser device 21 is equipped with a galvanometer mirror (not shown) and can scan the connection and fixing region 11c with the laser light 21a in any shape, so that a through-hole 17 of any planar shape can be formed. In addition, the size of the through-hole 17 can be adjusted by setting the power and / or number of scans of the laser light 21a to predetermined conditions (see FIG. 3(A)). The through-hole 17 formed by the laser in this way has an inner wall and a bottom surface made of quartz crystal. The result The surface becomes one in which the crystallinity has been eliminated, that is, a finely uneven surface with many linear traces lined up. When forming through-holes 17x having an hourglass-shaped cross section as shown in FIG. 2B in the quartz-crystal wafer 110, laser light can be irradiated from both sides of the quartz-crystal wafer 110.

[0021] After the through-holes 17 have been formed, a metal film 11m for forming the excitation electrodes 11a and extraction electrodes 11b is formed over the entire surface of the quartz-crystal wafer 110 using a well-known film-forming technique, such as sputtering, to obtain the metal-film-formed quartz-crystal wafer 112 (FIG. 3(B)). As shown in FIG. 4(A), the metal film 11m coats not only both surfaces of the quartz-crystal wafer 112 but also the inner walls of the through-holes 17. In the case of the through-holes 17 of this embodiment, the metal film 11m can coat the through-holes 17 as desired due to the effect of the micro-irregularities resulting from the loss of crystal crystallinity and the funnel-shaped cross section. Next, the entire surface of the quartz-crystal wafer 112 and the inside of the through-holes 17 are coated with photoresist 23 (FIG. 4(A)). In the case of the through-holes 17 of this embodiment, the above-described side surface condition and funnel-shaped cross section allow the photoresist 23 to coat the through-holes 17 as desired. Next, the photoresist 23 is exposed and developed to form a resist pattern (not shown) for forming electrodes, and then the metal film 11m exposed from the resist pattern is selectively removed to form the electrodes that also cover the inside of the through-holes, i.e., the excitation electrodes 11a and extraction electrodes 11b. The quartz crystal wafer 112 shown in Figure 4(B) corresponds to an intermediate wafer for quartz crystal resonators. Thereafter, the crystal wafer 112 is cut into individual crystal unit intermediates 11y by a known method, and each individual crystal unit intermediate is bonded and fixed to the container 13 (see FIG. 1) by a conductive adhesive. After the conductive adhesive has hardened, the frequency of the crystal blank 11 is adjusted, and the container 13 is sealed with a lid member (not shown), thereby forming the crystal resonator 10 shown in FIG. 1(A). According to this manufacturing method, the through hole 17 is formed using a short-pulse laser, so that the inner wall and bottom surface of the through hole are surfaces where the crystallinity of the quartz has been removed, and it is possible to easily form a through hole having a shape that makes it easy to coat the inside of the through hole with a metal film or photoresist for forming an electrode.

[0022] While the above embodiment illustrates an example in which an AT-cut crystal blank is used as the crystal blank, the crystal blank may be a crystal blank other than an AT-cut crystal blank, such as a tuning-fork crystal blank or an SC-cut crystal blank, which is a so-called two-rotation crystal blank. Furthermore, while the example illustrates an example in which the extraction electrodes 11b are extended from the excitation electrodes 11a on both main surfaces of the crystal blank 11 to the both end regions of one side of the crystal blank 11, i.e., a shape corresponding to cantilever support, the present invention can also be applied to adhesive structures with two-point fixation and four-point fixation at both ends. Furthermore, while the example illustrates a structure in which the container 13 has a recess 13a, the present invention can also be applied to a crystal resonator in which the container is flat and the lid member is cap-shaped with a recess for accommodating the crystal blank. [Explanation of symbols]

[0023] 10: Crystal resonator of an embodiment; 11: Crystal blank; 11a: Excitation electrode, 11b: Extraction electrode, 11c: connection fixing area; 13: container; 13a: recessed portion, 13b: bank portion, 13c: adhesive pad; 15: conductive adhesive; 17: Through hole, 17a: Crystal The result Surface with no crystallinity 21: laser device; 21a: laser light; 23: Photoresist 110: Quartz wafer 112: Quartz crystal wafer (intermediate wafer for quartz crystal oscillator), 11x, 11y: Intermediate crystal oscillator 11m: Metal film for electrode formation

Claims

1. A quartz crystal resonator comprising: a quartz crystal blank; a container for accommodating the quartz crystal blank; a conductive adhesive for connecting and fixing a connection and fixing region of the quartz crystal blank to the container; and a through hole provided in a portion of the connection and fixing region of the quartz crystal blank, penetrating the front and back of the quartz crystal blank, The through hole has an inner wall on which the crystallinity of the quartz crystal has been eliminated, and linear traces extending in the depth direction from the surface of the quartz crystal piece are aligned in the circumferential direction of the inner wall, and a surface on which minute irregularities are generated by these aligned linear traces; and electrodes provided on one surface of the quartz crystal blank, on the inner wall of the through hole, and across the other surface of the quartz crystal blank.

2. 2. The quartz crystal unit according to claim 1, wherein the cross-sectional shape of the through hole taken along the thickness direction of the quartz crystal piece is a funnel shape tapering from a first surface side of the quartz crystal piece toward a second surface side, which is the opposite surface.

3. 2. The quartz crystal unit according to claim 1, wherein the through hole has a cross-sectional shape taken along the thickness direction of the quartz crystal piece, the cross-sectional shape being an hourglass shape in which the opening decreases midway along the thickness direction of the quartz crystal piece and then expands.

4. When manufacturing a quartz crystal unit having a structure in which a quartz crystal blank is fixed to a container with a conductive adhesive, a step of forming a through hole penetrating the quartz element in a portion of the area of ​​the quartz element to be fixed with a conductive adhesive by using a short pulse laser, the through hole having an inner wall surface where the crystallinity of the quartz has been eliminated, linear traces progressing in the depth direction from the surface of the quartz element are aligned in the circumferential direction of the inner wall, and the aligned linear traces create a surface where minute irregularities are generated; forming a metal film for forming electrodes of a quartz crystal unit on the quartz crystal element having the through-holes formed therein so as to cover the inside of the through-holes; forming a photoresist on the crystal piece on which the metal film is formed so as to cover the inside of the through-hole; a step of exposing and developing the photoresist to form a resist pattern for forming an electrode; and a step of selectively removing the metal film exposed from the resist pattern to form an electrode that also covers the inside of the through hole. A method for manufacturing a quartz crystal resonator, comprising:

5. In an intermediate wafer for crystal resonators, which has a large number of crystal pieces arranged in a matrix, the intermediate wafer is used to form crystal resonators. A through hole penetrating the front and back of the quartz crystal blank in a portion of the area connected and fixed to the container by a conductive adhesive, the through hole having an inner wall where the crystallinity of the quartz crystal has been eliminated, linear traces extending in the depth direction from the surface of the quartz crystal blank are aligned in the circumferential direction of the inner wall, and the aligned linear traces create minute irregularities on the surface; an electrode provided on one surface of the quartz crystal blank, on the inner wall of the through hole, and across the other surface of the quartz crystal blank;

6. 6. The intermediate wafer for quartz crystal resonators according to claim 5, wherein the cross-sectional shape of the through-hole taken along the thickness direction of the quartz crystal piece is a funnel-like shape tapering from the first surface side of the quartz crystal piece toward the second surface side, which is the opposite surface.

7. 6. The intermediate wafer for quartz crystal resonators according to claim 5, wherein the through-holes have an hourglass-shaped cross section cut along the thickness direction of the quartz crystal piece, the opening narrowing midway through the thickness direction of the quartz crystal piece and then widening thereafter.

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