Piezoelectric element and method for manufacturing the same

Abstract

Provided is a piezoelectric element and a method for manufacturing the same, which improves the crystal impedance of a piezoelectric element including an AT-cut crystal sheet having a quadrangular shape, and a side intersecting a Z' axis of the crystal includes a prescribed first side, a second side, and a third side. The crystal sheet is fixed to a container by a conductive adhesive at a first side, which is a side of the crystal sheet that touches the -X side of the X axis of the crystal, of two sides parallel to the Z' axis. When the dimension of a linear portion of a second side, which is opposite the first side, along the Z' axis is represented as W1, and the dimension of the AT-cut crystal sheet along the Z' axis is represented as W0, W1 / W0 is 0.91 or more. The two sides of the linear portion of the second side along the Z' axis are substantially right-angled corners connected to the side of the crystal sheet along the X axis of the crystal.

Description

Technical Field

[0001] This invention relates to a crystal oscillator, a crystal oscillator including a crystal oscillator, and a piezoelectric element such as a crystal oscillator using a temperature sensor such as a thermistor or a PN diode, and a method for manufacturing the same. Background Technology

[0002] To further miniaturize crystal oscillators, a type of piezoelectric element, photolithography and wet etching techniques were used in the fabrication of crystal oscillators.

[0003] In, for example, Patent Document 1 of the applicant of this application, a crystal oscillator manufactured using the aforementioned technology is described. Specifically, as shown in Figure 1 of Patent Document 1, a crystal oscillator using an AT-cut crystal wafer is described, in which at least one of the three surfaces—the first surface, the third surface, and the third surface—forms a side surface that intersects the Z' axis of the crystallization axis of the crystal.

[0004] According to the crystal oscillator, compared with the past, unwanted vibrations other than the original vibration of the AT-cut crystal oscillator can be suppressed. Therefore, compared with the past, the impedance of the crystal oscillator, i.e., crystal impedance (hereinafter also referred to as CI (Crystal Impedance)), can be improved.

[0005] [Existing technical documents]

[0006] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2016-197778 Summary of the Invention

[0008] [The problem the invention aims to solve]

[0009] The piezoelectric element disclosed in Patent Document 1 can improve CI, but in the continued research of the inventors of this application, as shown below, it has been determined that there is room for further improvement of CI.

[0010] The piezoelectric element disclosed in Patent Document 1 includes a crystal wafer having a defined first to third surface. However, to obtain the defined first to third surfaces, a process of etching the crystal wafer for a long time is employed. Therefore, when the front end side of the crystal wafer is viewed in a plane, that is, the side of the crystal wafer opposite to the side supported by the conductive adhesive, the area from the center of the front end toward the two corners is extensively etched into a roughly triangular shape, and the planar area of ​​the crystal wafer is correspondingly reduced (see Comparative Example 1 described later). Figure 6 In the case of AT-cut crystal wafers, if it is assumed that CI is easier to optimize when the area of ​​the crystal wafer plane is large, then there is room for improvement in the piezoelectric element disclosed in Patent Document 1.

[0011] Furthermore, it has been determined that whether the front end of the crystal sheet is set as the positive or negative side of the crystallization axis (X-axis) results in differences in the shape of the front end, thus causing differences in the CI of the piezoelectric element. Therefore, there is room for improvement in this regard.

[0012] This application is made in view of these aspects, and therefore, the object of this application is to provide a piezoelectric element that can alleviate the aforementioned problems and a method for manufacturing the same.

[0013] [Technical means to solve the problem]

[0014] To achieve the aforementioned objective, the piezoelectric element according to the present invention comprises an AT-cut crystal wafer, a conductive adhesive, and a container. The AT-cut crystal wafer uses the X-Z' plane, represented by the crystallographic axis of the crystal, as its main surface. Its planar shape is quadrilateral, and at least one of its three surfaces (first to third) intersects the Z' axis of the crystallographic axis in this order. The AT-cut crystal wafer, on the side of the first side parallel to the Z' axis, is connected by the... The piezoelectric element is connected and fixed to the container by a conductive adhesive. When the dimension of the straight portion along the Z' axis of the second side opposite to the first side is represented as W1, and the dimension of the AT-cut crystal wafer along the Z' axis is represented as W0, W1 / W0 is 0.91 or more. The two sides of the straight portion form corners that are approximately right angles to the side of the AT-cut crystal wafer along the X-axis of the crystal. The side of the first side is the -X side on the X-axis of the crystallization axis of the crystal, and the side of the second side is the +X side on the X-axis.

[0015] Here, the approximately right-angled corner mentioned in this invention application ideally refers to a true right angle. However, in the manufacturing process of AT-cut crystal wafers, when using photolithography and wet etching, due to the anisotropy of the etching rate caused by the anisotropy of the crystal relative to the crystallographic axis of the crystal etchant, the approximately right-angled corner may not actually be a right angle. For example, it may become a structure as shown in (1), or a structure as shown in (2), or a structure that includes both (1) and (2). Therefore, in carrying out the present invention, the approximately right-angled corner is specifically preferably a structure as shown in (1) and / or (2).

[0016] (1) The structure is as follows: the two sides of the straight section of the second side along the Z' axis become approximately right angles θa and θb of the second side and the side of the AT-cut crystal sheet along the X-axis of the crystal, which are 90° to 115°.

[0017] (2) The structure is as follows: the two sides of the straight section of the second side along the Z' axis are represented by a chamfered C, with a dimension of C1 along the Z' axis, a dimension of C2 along the X axis that is greater than C1, and a corner of approximately right angle C2 / C1 of 2.7 to 4.3.

[0018] If the structure is as described in (1) and / or (2), then as can be seen from the embodiments described later, the characteristics of CI can be improved and the manufacturing process is also easier.

[0019] In implementing this invention, it is preferable that the second side of the AT-cut crystal wafer is a tapered portion that thins along the X-axis and toward the second side. According to this structure, unwanted patterns of the crystal along the X-direction can be reduced.

[0020] In implementing this invention, preferably, the first surface is a surface that rotates the main surface by 4° ± 3.5° with the X-axis of the crystal as the rotation axis, the second surface is a surface that rotates the main surface by -57° ± 5° with the X-axis of the crystal as the rotation axis, and the third surface is a surface that rotates the main surface by -42° ± 5° with the X-axis of the crystal as the rotation axis. According to this structure, as described in Patent Document 1, unwanted patterns of the crystal along the Z' direction can be reduced.

[0021] Furthermore, according to the invention of the piezoelectric element manufacturing method of this application, when the piezoelectric element of this application described above is manufactured using photolithography and wet etching techniques, the process includes:

[0022] The process of forming an etch-resistant mask on a crystal wafer with the fourth mask portion being the +X side of the crystal's X-axis, wherein the etch-resistant mask is an etch-resistant mask for wet etching and includes: a first mask portion forming a matrix of the pattern of the AT-cut crystal wafer; a second mask portion extending between the matrix along a direction corresponding to the Z' axis to form a pattern for forming crossbars arranged sequentially along the X-axis; a third mask portion forming a bridging pattern for holding the AT-cut crystal wafer in the crossbars after wet etching; and a fourth mask portion having a predetermined width W, disposed between the corner of the second side of the pattern of the AT-cut crystal wafer and the third mask portion, causing the crystal at this location to disappear when the second etching process is completed;

[0023] The crystal wafer with the etch-resistant mask is immersed in a hydrofluoric acid-based wet etching solution for a specified time in a first etching process.

[0024] The process of removing the first mask portion and the fourth mask portion from the crystal wafer from which the first etching has been completed;

[0025] The second etching process involves immersing a crystal wafer, from which the first and fourth mask portions have been removed, in a hydrofluoric acid-based wet etching solution for a specified time.

[0026] The process of forming excitation electrodes on a crystal wafer after the second etching process has been completed;

[0027] The process of monolithizing the AT-cut crystal wafer from a crystal wafer from which the formation of the excitation electrodes has been completed; and

[0028] The process of connecting and fixing the monolithized AT-cut crystal wafers to the container.

[0029] [The effects of the invention]

[0030] According to the invention of the piezoelectric element of this application, in a piezoelectric element using an AT-cut crystal wafer with a predetermined first to third surface intersecting the Z' axis of the crystal, the edge of the front end side of the crystal wafer has a predetermined amount of straight line portion and the corners are approximately right angles. Therefore, the planar area of ​​the crystal wafer is increased, thus providing a piezoelectric element with improved CI compared to the past. Furthermore, since the front end side of the crystal wafer is set as the +X side of the crystal's X-axis, a piezoelectric element with reduced shape unevenness at the front end of the crystal wafer can be achieved compared to the case where the front end side of the crystal wafer is set as the -X side of the crystal's X-axis (see the embodiments below for details). Therefore, CI can be further improved.

[0031] Furthermore, according to the invention of the piezoelectric element manufacturing method of this application, after forming the crystal wafer using an etch-resistant mask including a defined first to fourth mask portion, a first etching is performed on the crystal wafer. Subsequently, a second etching is performed with the first and fourth mask portions removed. Therefore, during the second etching, although the portion of the crystal wafer from which the fourth mask portion has been removed gradually disappears, it does not disappear until the corner of the crystal wafer's front end disappears. Moreover, the portion that becomes the bridging pattern side, i.e., the front end side of the crystal wafer, becomes the + side of the crystal's X-axis, thus easily manufacturing a crystal wafer with the front end side being the +X side. Therefore, it is possible to prevent a reduction in the planar area of ​​the front end side of the crystal wafer and easily manufacture a crystal wafer including the desired side surface having a first to third surface and with the front end being the +X side. Attached Figure Description

[0032] Figure 1A , Figure 1B This is an explanatory diagram of the piezoelectric element 10 according to the embodiment.

[0033] Figure 2A , Figure 2B , Figure 2C , Figure 2DThis is an explanatory diagram of the AT-cut crystal wafer 20 included in the piezoelectric element 10 of the embodiment.

[0034] Figure 3A , Figure 3B It is an AT-cut crystal wafer 20 along the Z' axis of the crystal (along... Figure 2A Explanation diagram of the IIC-IIC line cross section. Figure 3C , Figure 3D It is an AT-cut crystal wafer 20 along the X-axis of the crystal (along... Figure 2A Explanatory diagram of the cross section (IIB-IIB line).

[0035] Figure 4A , Figure 4B , Figure 4C This is a diagram illustrating the main parts of the manufacturing method of the piezoelectric element 10 according to the embodiment.

[0036] Figure 5A , Figure 5B The manufacturing method of the piezoelectric element 10 in the embodiment is immediately following Figure 4B The following is an explanatory diagram.

[0037] Figure 6 This is an explanatory diagram of Comparative Example 1, and a plan view illustrating the AT-cut wafer 50 when the corner shape of the front end side of the crystal wafer is not considered.

[0038] Figure 7A , Figure 7B This is a graph illustrating the difference in CI distribution when paying attention to the corner of the front end of the crystal plate (Example 1) and when not paying attention to the corner of the front end of the crystal plate (Comparative Example 1).

[0039] Figure 8A , Figure 8B These are explanatory diagrams for Example 2 and Comparative Example 2, showing the case where the front end of the crystal sheet is set to the +X side of the crystal's X-axis. Figure 8A ), and when set to the -X side of the X-axis ( Figure 8B Metal microscope photographs of each crystal slice.

[0040] Figure 9A , Figure 9B These are explanatory diagrams for Example 2 and Comparative Example 2, and are for when the front end of the crystal sheet is set as the +X side of the crystal's X-axis ( Figure 9A ), and when set to the -X side of the X-axis ( Figure 9B A diagram comparing the size distribution of the front cone-shaped portion of each crystal slice.

[0041] Figure 10A , Figure 10B These are explanatory diagrams for Example 2 and Comparative Example 2, and are for when the front end of the crystal sheet is set as the +X side of the crystal's X-axis ( Figure 10A), and when set to the -X side of the X-axis ( Figure 10B A graph comparing the CI distribution of each piezoelectric element.

[0042] [Explanation of Symbols]

[0043] 10: Piezoelectric element of the embodiment

[0044] 20: Crystal wafer of the embodiment (AT-cut crystal wafer)

[0045] 20a: First side

[0046] 20b: Second side

[0047] 20c: First page

[0048] 20d: Second side

[0049] 20e: Third face

[0050] 20f: Main surface

[0051] 20g: Fourth side

[0052] 20h: Fifth page

[0053] 20i: The Sixth Page

[0054] 20j: Page 7

[0055] 20k: The Eighth Side

[0056] 20m: Ninth side

[0057] 20t: Conical part (front conical part)

[0058] 20u: Conical part (posterior conical part)

[0059] 20x, 20y: Approximately right angles

[0060] 20z: The edge of the crystal sheet along the X-axis of the crystal.

[0061] 20w: Crystal wafer

[0062] 21: Excitation electrode

[0063] 23: Lead-out electrode

[0064] 30: Container

[0065] 30a: concave part

[0066] 30b: Support pad

[0067] 30c: External mounting terminal

[0068] 33: Conductive adhesives

[0069] 35: Cover component

[0070] 40: Etching-resistant mask

[0071] 40a: First mask section

[0072] 40b: Second mask section

[0073] 40c: Third mask section

[0074] 40d: Fourth mask section

[0075] 50: Comparative Example 1 crystal wafer (AT-cut crystal wafer)

[0076] 60: Crystal sheet of Comparative Example 2

[0077] 60t: Conical front end

[0078] IB-IB, IIB-IIB, IIC-IIC: lines

[0079] C: Size

[0080] C1, C2: Dimensions of approximately right-angled corners based on the C-shaped chamfer.

[0081] L0: The length of the crystal sheet along the X-axis of the crystal.

[0082] M, N, R: Partial

[0083] O: Center point

[0084] P1: Central

[0085] R1, R2: Regions

[0086] T: Thickness

[0087] W: Specified width

[0088] W1: The dimension of the straight section along the Z' axis of the crystal on the second side of the crystal sheet.

[0089] W0: The dimension of the crystal sheet along the Z' axis of the crystal.

[0090] X, Y', Z': Axes (coordinate axes)

[0091] θ1~θ6, θa, θb: angle

[0092] ΔX: Dimension Detailed Implementation

[0093] Hereinafter, embodiments of the piezoelectric element and its manufacturing method according to the present invention will be described with reference to the accompanying drawings. Furthermore, the drawings used for description are only schematic representations to the extent that these inventions can be understood. Additionally, in the drawings used for description, the same numbers are used to denote the same components, and there are instances where their descriptions are omitted. Furthermore, the shapes, sizes, materials, etc., described in the following description are merely suitable examples within the scope of the present invention. Therefore, the present invention is not limited to the embodiments described below.

[0094] 1. Description of piezoelectric elements

[0095] First, refer to Figures 1A to 3D The piezoelectric element 10 of the embodiment will be described here. Figure 1A This is a top view of the piezoelectric element 10. Figure 1B It is along Figure 1A A cross-sectional view of the piezoelectric element 10 of the IB-IB line. Furthermore, in Figure 1A in, omit Figure 1B The illustration includes the cover member 35. Additionally, Figure 2A This is a top view of the AT-cut crystal wafer 20 included in the piezoelectric element 10 of the embodiment. Figure 2B It is along Figure 2A A cross-sectional view of crystal slice 20 along line IIB-IIB. Figure 2C It is along Figure 2A A cross-sectional view of crystal wafer 20 with the IIC-IIC line in the image. Figure 2D It is Figure 2A The image is a magnified view of the front end of the crystal plate 20. Additionally, Figure 3A This is a diagram illustrating the side view of the AT-cut crystal wafer 20 that intersects the Z' axis of the crystal. Figure 3B It is Figure 3A The N part in the diagram is shown in magnified form. Additionally, Figure 3C It is Figure 2B The image shown is an enlarged view of the +X side of the cross-section. Figure 3D yes Figure 2B The image shown is an enlarged view of the -X side of the cross-section. Furthermore, Figure 2A , Figure 2B , Figure 2C , Figure 2D or Figure 3A , Figure 3B , Figure 3C , Figure 3D The coordinate axes X, Y', and Z' shown represent the crystallization axes of the crystals in the AT-cut crystal wafer 20 (hereinafter, sometimes simply referred to as crystal wafer 20).

[0096] The crystal wafer 20 in this embodiment is an AT-cut crystal wafer with a rectangular planar shape, its long side being parallel to the X-axis of the crystal and its short side being parallel to the Z'-axis of the crystal.

[0097] The crystal wafer 20 includes an excitation electrode 21 and a lead-out electrode 23 on its two main surfaces. The lead-out electrode 23 extends from the excitation electrode 21 near both ends of a first side 20a, which is an edge of the crystal wafer 20. The first side 20a is the -X side of the crystal along the X-axis of the crystal wafer 20, and the second side 20b, facing the first side 20a, is the +X side of the crystal along the X-axis of the crystal wafer 20.

[0098] like Figure 1A and Figure 1B As shown, the crystal sheet 20 is installed within the recess 30a of the container 30. Specifically, the crystal sheet 20 is fixed to the support pad 30b of the container 30 near its first side 20a and along both ends of the first side 20a by a conductive adhesive 33. Therefore, the crystal sheet 20 is cantilevered in the container 30 on the first side 20a, i.e., on the -X side of the X-axis of the crystal sheet 20, and the +X side of the X-axis of the crystal sheet 20 becomes the free end.

[0099] The container 30 can be, for example, made of ceramic. On the bottom surface of the outer side of the container 30, an external mounting terminal 30c for connecting the piezoelectric element 10 to other electronic devices is provided. The support pad 30b is connected to the external mounting terminal 30c via a via (not shown) wiring or the like.

[0100] Additionally, a suitable cover member 35 is engaged with the embankment of the surrounding recess 30a of the container 30 to seal the crystal sheet 20 inside the container 30.

[0101] Furthermore, in the crystal wafer 20, when the dimension of the straight portion of the second side 20b facing the first side 20a along the Z' axis is represented as W1, and the dimension of the crystal wafer 20 along the Z' axis is represented as W0, W1 / W0 is 0.91 or more, and the two sides of the straight portion become: corner 20x and corner 20y that are approximately right angles to the side 20z of the AT-cut crystal wafer along the X-axis of the crystal.

[0102] Here, the approximately right-angled corners 20x and 20y are ideally true right angles, but due to the effects of etching anisotropy, as already explained, they become approximately right angles that differ slightly from true right angles. Specifically, as... Figure 1A , Figure 2DAs shown, the two sides of the straight section of dimension W1 form approximately right-angled corners, having angles θa and θb formed by the second side 20b and the side 20z of the AT-cut crystal wafer along the X-axis of the crystal. According to the embodiments described later, especially Embodiment 2, the angles θa and θb are preferably 90° to 115°. The length of the AT-cut crystal wafer along the X-axis of the crystal is L0.

[0103] Alternatively, the two sides of the straight portion of dimension W1 become: a corner, represented by the chamfer C, with a dimension of C1 along the Z' axis, a dimension of C2 along the X axis greater than C1, and C2 / C1 being a roughly right angle within a specified range. According to the embodiments described later, especially embodiment 2, the specified C2 / C1 is preferably 2.7 to 4.3.

[0104] Furthermore, θa and θb mentioned above can be the same angle or different angles. Additionally, C2 / C1 at the approximately right angles on the left and right sides can be the same or different.

[0105] Here, θa, θb, C1, C2, and W1 refer to the specified width W of the fourth pattern as described in the manufacturing method described later (refer to...). Figure 4C The value of W1 / W0 varies depending on factors such as the etching time of the crystal wafer using a hydrofluoric acid-based etchant. Preferably, W1 / W0 is 1 or close to 1. Therefore, the value of the specified width W of the fourth pattern, or the etching time of the crystal wafer using a hydrofluoric acid-based etchant, is preferably set to be close to 1. The closer W1 / W0 is to 1, the closer θa and θb are to right angles, and the closer C1 and C2 are to zero.

[0106] In addition, the side surfaces (Z' planes) of the crystal sheet 20 that intersect the Z' axis of the crystal are as follows: Figure 3A , Figure 3B As shown, the surface includes three surfaces: the first surface 20c, the second surface 20d, and the third surface 20e. Moreover, the first surface 20c is the surface that intersects with the main surface 20f of the crystal sheet 20, and is the surface that rotates the main surface 20f by θ1 with the X-axis of the crystal as the rotation axis.

[0107] Furthermore, the first surface 20c, the second surface 20d, and the third surface 20e intersect in this order. The second surface 20d is equivalent to rotating the main surface 20f by θ2 using the crystal's X-axis as the rotation axis, and the third surface 20e is equivalent to rotating the main surface 20f by θ3 using the crystal's X-axis as the rotation axis. Moreover, the two side surfaces are point-symmetric with respect to the center point O of the crystal sheet.

[0108] Furthermore, based on the applicant's experiments, it is known that the angles θ1, θ2, and θ3 are preferably the following angles: θ1 = 4° ± 3.5°, θ2 = -57° ± 5°, θ3 = -42° ± 5°, and more preferably θ1 = 4° ± 3°, θ2 = -57° ± 3°, θ3 = -42° ± 3°.

[0109] In having the use of the above Figure 3A , Figure 3B , Figure 3C , Figure 3D In the case of the crystal sheet with the sides described, the sides have a unique mouth shape, which can attenuate unwanted vibrations propagating in the Z' direction, thus contributing to the improvement of the characteristics of the piezoelectric element.

[0110] Furthermore, the aforementioned structure is described in the applicant's Japanese Patent Application Publication No. 2016-197778, therefore, its detailed description is omitted here.

[0111] In addition, in crystal sheet 20, especially as Figure 2B , Figure 3C As shown, the second side 20b (refer to) Figure 2A The side of the crystal becomes a thin, tapered portion 20t (also called the front tapered portion 20t) along the X-axis of the crystal and towards the second side 20b. More specifically, as Figure 3C As shown, the conical portion 20t comprises four surfaces: the fourth surface 20g, the fifth surface 20h, the sixth surface 20i, and the seventh surface 20j. The fourth surface 20g and the seventh surface 20j are symmetrical about the X-axis, and the fifth surface 20h and the sixth surface 20i are also symmetrical about the X-axis. Furthermore, the angle θ4 formed by the fourth surface 20g or the seventh surface 20j and the main surface 20f of the crystal sheet 20 is θ4 = 4° ± 5°, preferably θ4 = 4° ± 3°; the angle θ5 formed by the fifth surface 20h or the sixth surface 20i and the main surface 20f of the crystal sheet 20 is θ5 = 27° ± 5°, preferably θ5 = 27° ± 3°.

[0112] On the other hand, such as Figure 3D As shown, the end of the crystal sheet 20 on the -X side is such that it is along the X-axis of the crystal and toward the first side 20a (refer to...). Figure 2A The thin-walled conical portion 20u (also called the rear conical portion 20u) comprises two surfaces: an eighth surface 20k and a ninth surface 20m. The eighth surface 20k and the ninth surface 20m are symmetrical about the X-axis. Furthermore, the angle θ6 formed by the eighth surface 20k or the ninth surface 20m and the main surface 20f of the crystal sheet 20 is θ6 = 17° ± 5°, preferably θ6 = 17° ± 3°.

[0113] 2. Explanation of the manufacturing method of piezoelectric elements

[0114] Next, refer to Figures 4A to 4C , Figure 5A , Figure 5B A preferred method for manufacturing the piezoelectric element 10 according to the embodiment will be described. Furthermore, Figures 4A to 4C This diagram illustrates the main parts of the process for manufacturing the crystal wafer 20 used in the piezoelectric element 10. In particular, Figure 4A This is a planar diagram illustrating a 20W crystal wafer in an intermediate state. Figure 4B This diagram illustrates the state in which an etch-resistant mask 40 is formed on the crystal wafer, and it shows... Figure 4A The M part in the diagram is an enlarged representation of the plan view. Figure 4C This diagram illustrates a method for making the corners 20x and 20y on the front end side of the crystal sheet 20 approximately right angles. Figure 4B The R part in the diagram is enlarged to represent a planar view. Additionally, Figure 5A , Figure 5B This indicates that the process has been changed from... Figure 4B A diagram showing the state of progress.

[0115] In the manufacturing method of this application, the crystal wafer 20 is manufactured by photolithography and wet etching techniques.

[0116] Specifically, an etch-resistant mask 40 is used to manufacture the wafer 20, wherein the etch-resistant mask 40 is an etch-resistant mask 40 for wet etching (see reference). Figure 4B The device comprises: a first mask portion 40a, which forms a matrix pattern of the AT-cut crystal wafer 20; a second mask portion 40b, which extends between the matrices along a direction corresponding to the Z' axis to form a pattern for forming crossbars arranged sequentially along the X-axis; a third mask portion 40c, which forms a bridging pattern for holding the AT-cut crystal wafer in the crossbars after the wet etching; and a fourth mask portion 40d, having a predetermined width W, disposed between the corner of the second side (front end side) of the AT-cut crystal wafer and the third mask portion, causing the crystal at that location to disappear when the wet etching is completed. Furthermore, the fourth mask portion 40d is disposed between the two corner portions of the first mask portion 40a corresponding to the front end side of the crystal wafer, i.e., the +X side of the crystal of the crystal wafer 20 along the X-axis, and the second mask portion 40b.

[0117] Specifically, an etch-resistant metal film can be formed on the front surface of the back of the crystal wafer 20w, a photoresist can be coated on its surface, and the photoresist can be exposed using photomasks for forming the first to fourth mask portions. Afterward, the metal film can be selectively removed to form the etch-resistant mask 40. However, the etch-resistant mask 40 is formed on the crystal wafer 20w such that the fourth mask portion 40d is on the +X side of the crystal's X-axis.

[0118] Furthermore, the width W of the fourth mask portion 40d along the Z' axis of the crystal (refer to...) Figure 4C The width is set as follows (refer to the embodiment, etc.), which is the width of the crystal portion under the fourth mask 40d that disappears after the second etching process described later.

[0119] Next, a first etching process is performed, in which the crystal wafer with the etch-resistant mask 40 is immersed in a hydrofluoric acid-based wet etching solution for a specified time. The first etching process is used to form the shape of the crystal wafer 20.

[0120] Next, the first mask portion 40a and the fourth mask portion 40d are removed from the crystal wafer after the first etching process has been completed. Furthermore, in this embodiment, the third mask portion 40c is also removed. This mask portion processing can be performed using well-known photolithography techniques. However, if the size of the third mask portion 40c is small, it may be left as a residue without removal.

[0121] After the etching-resistant mask is processed, the crystal portion covered by the first mask portion, the second mask portion, and the third mask portion is exposed (see reference). Figure 5A ).

[0122] Next, a second etching process is performed, in which the crystal wafer, with the first, second, and third mask portions removed, is immersed in a hydrofluoric acid-based wet etching solution for a predetermined time. This second etching process is used to adjust the frequency of the crystal wafer 20 and to form predetermined first to third surfaces on the sides of the crystal wafer 20 that intersect the Z' axis of the crystal. The crystal portion exposed by the removal of the fourth mask portion 40d disappears during the second etching because its width W is set to a predetermined width. Therefore, the two corners 20x and 20y of the side of the crystal wafer 20 that is not fixed to the container, i.e., the second side 20b, appear as corners for the first time around the end of the second etching. Thus, even after wet etching, corners 20x and 20y are approximately right angles, and the portion of the second side 20b between corners 20x and 20y is straight.

[0123] After the second etching process is completed, excitation electrodes and lead-out electrodes are formed on the crystal wafer. From the crystal wafer from which the excitation electrodes and the like have been formed, the AT-cut crystal wafer is monolithized. The monolithized crystal wafer is fixed to the container 30 (see reference) at the -X side end using a conductive adhesive. Figure 1A , Figure 1B Then, with the container in a specified environment, the container is sealed using a lid member, thereby manufacturing the piezoelectric element 10 of the present invention.

[0124] 3. Examples and Comparative Examples

[0125] To enhance understanding of the present invention, several embodiments and comparative examples are shown below.

[0126] 3-1. Example 1, Comparative Example 1: Experiment on the planar shape of the front end side of the crystal sheet

[0127] First, in order to investigate the effect of the planar shape of the front end of the crystal wafer on the characteristics of the piezoelectric element, the following Example 1 and Comparative Example 1 were carried out.

[0128] As a piezoelectric element of Example 1, multiple AT-cut crystal wafers with an oscillation frequency of 27.12MHz, an X size of approximately 870μm, and a Z' size of approximately 640μm are manufactured using the manufacturing method described above. These wafers are then mounted in a container, and the container is sealed using a lid member to manufacture multiple piezoelectric elements of Example 1.

[0129] Furthermore, in the piezoelectric element of Comparative Example 1, when manufacturing the crystal wafer, a method without a fourth mask portion 40d (see reference) is used. Figure 4B Using an etch-resistant mask, multiple crystal wafers of Comparative Example 1 with the same frequency, X-size, and Z'-size as Example 1 are manufactured. These wafers are then mounted in a container, and the container is sealed using a lid member to manufacture multiple piezoelectric elements of Comparative Example 1.

[0130] However, in manufacturing the crystal wafers of Example 1 and Comparative Example 1, the following changes were made to the manufacturing method described above. Specifically, an etch-resistant mask was configured on the crystal wafer with the -X side of the crystal's X-axis as the front end of the crystal wafer. Furthermore, when fixing the crystal wafer to the container, the positive side of the crystal's X-axis was fixed to the container using a conductive adhesive. This is because it is believed that using this crystal axis configuration and fixing position eliminates the influence of the corner shape of the front end of the crystal wafer, which will be described later, making it easier to judge only the influence of the corner shape.

[0131] Figure 6 This is a plan view of the crystal wafer 50 manufactured as Comparative Example 1. In the crystal wafer 50 of Comparative Example 1, when viewed on a plane, its front end side, that is, the side of the crystal wafer opposite to the side supported by the conductive adhesive, is etched into approximately triangular shapes in regions R1 and R2 from the center P1 at the front end toward the two corners, and the area of ​​the crystal wafer is reduced accordingly.

[0132] On the other hand, the straight portion of the second side 20b of the crystal wafer used in Example 1 is large, and the two sides of the straight portion are approximately right angles (see reference). Figure 8B That is, the crystal slice of Example 1 appears more rectangular when viewed on a plane.

[0133] For the multiple crystal plates used in Example 1, the approximate right angle of the front end side (equivalent to) was measured using a measuring microscope. Figure 1A , Figure 1B , Figure 2A , Figure 2B , Figure 2C , Figure 2D The angles θa and θb of the angles 20x and 20y (refer to...) Figure 1A , Figure 1B , Figure 2A , Figure 2B , Figure 2C , Figure 2D The results show that angles θa and θb are in the range of 85 to 90 degrees, and W1 is in the range of 605 μm to 632 μm. Furthermore, the target size for the Z' dimension near the center of the crystal sheet, i.e., dimension W0, is 640 μm; however, actual measurements show it to be in the range of 638 μm to 650 μm. Therefore, when calculating W1 / W0 based on the measured values ​​of W1 and W0, the lower limit is 605 / 650 ≈ 0.93, and the upper limit is 632 / 638 ≈ 0.99. Thus, in the sample of Example 1, W1 / W0 can be said to be 0.93 to 0.99. Most samples are 0.96 to 0.99.

[0134] Furthermore, for the two corners of the front ends of the plurality of crystal wafers 50 used in Example 1 and the plurality of crystal wafers 50 used in Comparative Example 1, the C-dimension based on the C-bevel angle was measured using a tool microscope (see reference). Figure 6 (The C-size is shown). As a result, in the case of the crystal wafer of Example 1, the C-size is 10 μm to 18 μm, all of which are less than 20 μm. On the other hand, in the case of the crystal wafer 50 of Comparative Example 1, the C-size is 70 μm to 95 μm, which is 7 to 9 times larger than that of Example 1.

[0135] Furthermore, the dimensions of the straight portion at the front end of the crystal sheet 50 in Comparative Example 1 were measured and found to be small, approximately 130 μm to 160 μm. Moreover, the straight portion has a sloping shoulder shape extending from its end towards the corner of the crystal sheet.

[0136] In addition, the electrical characteristics of the piezoelectric elements of Example 1 and Comparative Example 1 were measured by CI. Figure 7A This is a diagram showing the distribution of CI in the piezoelectric element of Example 1. Figure 7B This is a graph showing the distribution of CI in the piezoelectric element of Comparative Example 1. In each graph, CI (Ω) is used on the horizontal axis and frequency on the vertical axis. The number of samples was 12 in each graph.

[0137] In the CI distribution of the piezoelectric element of Example 1, the average value is 83.5 Ω and the standard deviation is 6.6 Ω. In the CI distribution of the piezoelectric element of Comparative Example 1, the average value is 123.6 Ω and the standard deviation is 13.0 Ω. Example 1 is superior in terms of the average CI value of 40.1 Ω and the standard deviation of 6.4 Ω.

[0138] Based on the CI measurement results of Example 1 and Comparative Example 1, it can be seen that when the straight portion of the front edge of the crystal sheet is large and the two corners are approximately right angles, CI can be improved compared to cases where this is not the case.

[0139] 3-2. Example 2, Comparative Example 2: Experiment with the front end of the crystal slice set as the +X side

[0140] Next, in order to investigate the influence of setting the front end of the crystal sheet to the +X side of the crystal's X-axis versus setting it to the -X side on the characteristics of the piezoelectric element, the following Example 2 and Comparative Example 2 were implemented.

[0141] As a piezoelectric element of Example 2, multiple crystal sheets 20 with an oscillation frequency of 40 MHz, an X size of approximately 750 μm, and a Z' size of approximately 520 μm were manufactured using the manufacturing method described above. Then, these crystal sheets were fixed to a container with a conductive adhesive at the -X side end of the crystal, thereby manufacturing multiple piezoelectric elements 10 of Example 2.

[0142] Furthermore, as a piezoelectric element of Comparative Example 2, when manufacturing the crystal wafer using the aforementioned manufacturing method, unlike Example 2, an etch-resistant mask was arranged on the crystal wafer with the -X side of the crystal's X-axis as the front end of the crystal wafer to manufacture multiple crystal wafers of Comparative Example 2 with the same frequency, X-size, and Z'-size as those of Example 2. Then, these crystal wafers were fixed to a container with a conductive adhesive at the +X side end of the crystal, thereby manufacturing multiple piezoelectric elements of Comparative Example 2.

[0143] Figure 8A The photographs of the crystal slide 20 in Example 2 were taken using a metal microscope. Figure 8B The photographs were taken using a metal microscope of the crystal slide 60 in Comparative Example 2. The differences at the front ends of the crystal slides are particularly clear when the two photographs are compared.

[0144] Therefore, firstly, the dimensions W0 of the central portion of the crystal wafer 20 of Example 2 along the Z' axis and the dimension W1 of the straight portion of the second side 20b are measured, as well as the dimensions of the two corner portions 20x and 20y on both sides of the straight portion. Figure 2DThe angles θa and θb are shown, as well as the dimensions C1 of the first C-bevel and C2 of the second C-bevel at corner 20x. A total of 22 samples were measured. The results are shown in Table 1, including the mean avg, standard deviation σ, maximum value Max, minimum value Min, avg+3σ, and avg-3σ.

[0145] According to Table 1, in the sample of Example 1, the avg-3σ of W1 is 480.6, and the avg+3σ of W0 is 524.6, therefore (avg-3σ of W1) / (avg+3σ of W0) = 480.6 / 524.6 = 0.916. Furthermore, the avg+3σ of W1 is 498.9, and the avg-3σ of W0 is 520.1, therefore (avg+3σ of W1) / (avg-3σ of W0) = 498.9 / 520.1 = 0.959. Therefore, in Example 2, the W1 / W0 ratio, which is an indicator of the perpendicularity of the approximately right-angled corners 20x and 20y, is 0.916 to 0.959, so it can be said that the worst-case scenario for W1 / W0 is 0.916, or 0.91.

[0146] Furthermore, according to Table 1, in the sample of Example 2, for the angles θa and θb at the approximately right-angled corners 20x and 20y, the largest angle farthest from the right angle is 114.7°, which is located in the avg+3σ column. That is, approximately 115°.

[0147] Furthermore, according to Table 1, in the sample of Example 2, the avg+3σ of dimension C1 is 15.4, and the avg-3σ of dimension C2 is 42.7, therefore (avg-3σ of dimension C2) / (avg+3σ of dimension C1) = 42.7 / 15.4 = 2.77. Additionally, the avg-3σ of dimension C1 is 12.2, and the avg+3σ of dimension C2 is 52.5, therefore (avg+3σ of dimension C2) / (avg-3σ of dimension C1) = 52.5 / 12.2 = 4.30. Therefore, in Example 2, C2 / C1, as an indicator of the perpendicularity of the approximately right-angled corners 20x and 20y, can be considered to be between 2.77 and 4.30. Furthermore, considering ±3σ, the actual C1 at this time is between 12.2 and 15.4, approximately 16 μm or less. In addition, considering ±3σ, the actual C2 is 42.7 to 52.5, which is below 53 μm.

[0148] [Table 1]

[0149]

[0150] Next, the crystal wafer 20 of Example 2 and the crystal wafer 60 of Comparative Example 2 were measured (refer to...). Figure 8BThe dimensions ΔX of the conical tip of each specimen were measured. 120 specimens were measured for both Example 2 and Comparative Example 2. The measurement results are shown in Table 2, including the mean avg, standard deviation σ, maximum value Max, minimum value Min, avg+3σ, and avg-3σ. Additionally, in... Figure 9A , Figure 9B A histogram of the measurement results is shown. Figure 9A This is a histogram of the dimensions of the front cone-shaped portion of Embodiment 2. Figure 9B This is a histogram of the dimensions of the front tapered portion of Comparative Example 2. In each graph, the dimensions (μm) of the front tapered portion are used on the horizontal axis, and the number of portions is used on the vertical axis.

[0151] According to Table 2, the average value of the dimension ΔX along the X-axis of the front cone portion 20t of the crystal wafer 20 in Example 2 is 113.2 μm, with a standard deviation of 0.19. The average value of the dimension ΔX along the X-axis of the front cone portion 60t of the crystal wafer 60 in Comparative Example 2 is 61 μm, with a standard deviation of 0.97. The difference between the dimension ΔX of the front cone portion 20t of the crystal wafer 20 in Example 2 and the dimension ΔX of the front cone portion 60t of the crystal wafer 60 in Comparative Example 2 is due to the anisotropy of the crystal axis relative to the etchant, but it should be noted that the standard deviation is different. The standard deviation of the dimension along the X-axis of the front cone portion 60t of the crystal wafer 60 in Comparative Example 2 is 0.97 / 0.19 = 5.1, which is a value that has deteriorated by a factor of 5.1. In the case of a crystal oscillator, a predetermined shape can be ensured, and the small non-uniformity of the predetermined shape can optimize the absolute value or non-uniformity of the characteristics. Furthermore, in the design of crystal oscillators, to reduce the influence of the fixing part relative to the container on the crystal plate, the vibrating part is usually offset towards the front end of the crystal plate. Therefore, uneven shape of the front end of the crystal plate can easily affect the vibrating part, so it is preferable that the uneven shape of the front end of the crystal plate is small. In this regard, it is preferable to set the front end of the crystal plate as the -X side of the crystal, as in this invention. Moreover, combined with a structure in which the corners of the front end of the crystal plate are set to approximately right angles, it can help improve the characteristics of the piezoelectric element.

[0152] Furthermore, in the case of crystal wafer 20 of Example 2, avg+3σ = 113.8 μm and avg-3σ = 112.7 μm in Table 2. Moreover, the thickness T of crystal wafer 20 in Example 2 is 36.9 μm; therefore, if the value of avg±3σ is normalized using the thickness T of crystal wafer 20, it is 3.053 to 3.083. That is, ΔX / T is approximately 3.05 to 3.09.

[0153] [Table 2]

[0154] avg 61.0 113.2 σ 0.97 0.19 Max. 62.8 113.7 Min. 58.9 112.7 avg+3σ 63.9 113.8 avg-3σ 58.1 112.7

[0155] Unit: μm

[0156] In addition, to demonstrate the advantage of setting the front end of the crystal sheet as the -X side of the crystal, the piezoelectric element of Example 2 was measured ( Figure 1A , Figure 1B The piezoelectric element with the structure shown is compared with the piezoelectric element of Comparative Example 2. The sample size is 580 for each.

[0157] Figure 10A This is a diagram showing the distribution of CI in the piezoelectric element of Example 2. Figure 10B This is a graph showing the distribution of CI in the piezoelectric element of Comparative Example 2. In each graph, CI (Ω) is used on the horizontal axis and the number of elements is used on the vertical axis.

[0158] In the CI distribution of the piezoelectric element of Example 2, the average value was 32.4 Ω and the standard deviation was 3.2 Ω. In the CI distribution of the piezoelectric element of Comparative Example 2, the average value was 38.4 Ω and the standard deviation was 7.1 Ω. Compared with Comparative Example 2, Example 2 is superior by 6 Ω in terms of the average CI and by 3.9 Ω in terms of the standard deviation. Based on the results, it can be understood that setting the front end side of the crystal wafer as the -X side of the crystal is preferable.

[0159] Furthermore, since the front end of the crystal wafer is set as the -X side of the crystal, in the wafer state (refer to...) Figure 4B In this configuration, the crystal sheet is connected to the crossbar with its +X side end attached. It is also understood that, compared to the case where the crystal sheet is connected to the crossbar with its -X side end attached, the case where the crystal sheet is connected to the crossbar with its +X side end attached reduces the likelihood of burrs or other defects at the folding point when individual crystal sheets are folded from the wafer. From this perspective, it is also understood that it is preferable to set the front end of the crystal sheet as the -X side and fix the crystal sheet to the container with its +X side end.

[0160] According to the various embodiments and comparative examples, it is desirable for the two corners 20x and 20y on the front end side of the crystal sheet 20 to be approximately right angles, which would be true right angles. However, when the front end of the crystal sheet is set as the +X side of the crystal, according to the results of Embodiment 2, it can be confirmed that when the two corners 20x and 20y are expressed in terms of C-size (C-bevel), having a first C-size portion with a size of C1 along the Z' axis of the crystal and a second C-size portion with a size of C2 along the X-axis of the crystal and larger than the first C-size portion, and if the corners with C2 / C1 being 2.7 to 4.3, is preferred for improving CI. However, it is certainly better if the C1 and C2 sizes are close to zero.

[0161] Furthermore, even if the angles θa and θb of the two corners 20x and 20y are 115° away from right angles, CI improvement can still be achieved. Therefore, for approximately right-angled corners, the angles θa and θb are at least 90° to 115°, thus CI improvement can be achieved. Additionally, if W1 / W0 is 0.916 or higher, i.e., W1 / W0 is 0.91 or higher, CI improvement can be achieved.

[0162] Furthermore, in the case of AT-cut crystal wafers, even with different frequencies or sizes, ratios such as W1 / W0 or C2 / C1 are generally effective in improving characteristics. Therefore, in the embodiments, the effects of the present invention were confirmed using crystal wafers of two different frequencies and sizes, but it is believed that the present invention can also be applied to crystal wafers of other frequencies and sizes. The more miniaturized crystal wafers become, the more the present invention can contribute.

[0163] In addition, the container used is not limited to the examples described above. For example, the present invention can also be applied to piezoelectric elements with other structures, such as piezoelectric elements using containers that include a flat base and a cap-shaped cover member with a recess for receiving crystal sheets.

Claims

1. A piezoelectric element, characterized in that, include: AT-cut crystal wafers; Conductive adhesives; as well as container, The AT-cut crystal sheet uses the X-Z' plane, represented by the crystallization axis of the crystal, as its main surface. It has a quadrilateral shape and utilizes a first, second, and third surface to form at least one side intersecting the Z' axis of the crystallization axis. These three surfaces intersect in this order. The AT-cut crystal sheet is connected and fixed to the container via a conductive adhesive on the first side of the two sides parallel to the Z' axis. When the dimension of the straight section along the Z' axis of the second side facing the first side is denoted as W1, and the dimension of the AT-cut crystal wafer along the Z' axis is denoted as W0, W1 / W0 is 0.91 or greater, and the two sides of the straight section form corners that are approximately right angles to the sides of the AT-cut crystal wafer along the X-axis of the crystal. The first side is the -X side on the X-axis of the crystallization axis, and the second side is the +X side on the X-axis. The two sides of the straight section along the Z' axis of the second side are: The term C-bevel indicates a corner with a dimension of C1 along the Z' axis, a dimension of C2 along the X axis that is greater than C1, and a ratio of C2 / C1 that is approximately a right angle of 2.7 to 4.

3.

2. The piezoelectric element according to claim 1, characterized in that, The two sides of the straight section along the Z' axis of the second side become: The angles θa and θb formed by the second side and the side of the AT-cut crystal wafer along the X-axis of the crystal are approximately right angles of 90° to 115°.

3. The piezoelectric element according to claim 1 or 2, characterized in that, The second side of the AT-cut crystal wafer becomes: A thin, tapered portion along the X-axis and toward the second side.

4. The piezoelectric element according to claim 3, characterized in that, When the dimension of the conical portion along the X-axis is expressed as ΔX and the thickness of the AT-cut crystal wafer is expressed as T, ΔX / T is 3.05 to 3.

09.

5. The piezoelectric element according to claim 3, characterized in that, The conical portion comprises four faces.

6. The piezoelectric element according to claim 1 or 2, characterized in that, The first surface is equivalent to rotating the main surface by 4° ± 3.5° using the X-axis of the crystal as the rotation axis. The second surface is equivalent to rotating the main surface by -57°±5° using the X-axis of the crystal as the rotation axis. The third surface is equivalent to rotating the main surface by -42°±5° using the X-axis of the crystal as the rotation axis.

7. A method for manufacturing a piezoelectric element, characterized in that, When using photolithography and wet etching techniques to manufacture the piezoelectric element as described in any one of claims 1 to 6, the process includes: The process of forming an etch-resistant mask on a crystal wafer with the fourth mask portion being the +X side of the crystal's X-axis, wherein the etch-resistant mask is an etch-resistant mask for wet etching and includes: a first mask portion forming a matrix of patterns of the AT-cut crystal wafer; a second mask portion extending between the matrix along a direction corresponding to the Z' axis to form a pattern for forming crossbars arranged sequentially along the X-axis; a third mask portion forming a bridging pattern for holding the AT-cut crystal wafer in the crossbars after wet etching; and a fourth mask portion having a predetermined width W, disposed between the corner of the AT-cut crystal wafer on the second side and the third mask portion, causing the crystal at this location to disappear when the second etching process is completed; The crystal wafer with the etch-resistant mask is immersed in a hydrofluoric acid-based wet etching solution for a specified time in a first etching process. The process of removing the first mask portion and the fourth mask portion from the crystal wafer from which the first etching process has been completed; The second etching process involves immersing a crystal wafer, from which the first and fourth mask portions have been removed, in a hydrofluoric acid-based wet etching solution for a specified time. The process of forming excitation electrodes on a crystal wafer after the second etching process has been completed; The process of monolithizing the AT-cut crystal wafer from a crystal wafer from which the formation of the excitation electrodes has been completed; and The process of connecting and fixing the monolithized AT-cut crystal wafers to a container.

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