Piezoelectric element and method for manufacturing the same

Abstract

A piezoelectric element with improved crystal impedance and a manufacturing method thereof are provided. The piezoelectric element includes an AT-cut crystal sheet. The planar shape of the AT-cut crystal sheet is a quadrilateral shape. A side intersecting a Z' axis of the crystal has a prescribed first surface, a second surface, and a third surface. The crystal sheet includes, in order, a first surface in which a main surface is rotated by 4°±3.5° with respect to an X axis of the crystal as a rotation axis, a second surface in which the main surface is rotated by -57°±5° with respect to the X axis of the crystal as the rotation axis, and a third surface in which the main surface is rotated by -42°±5° with respect to the X axis of the crystal as the rotation axis. The crystal sheet is fixed to a container by a conductive adhesive on a first side of two sides parallel to the Z' axis. Two corners on a second side of the crystal sheet opposite the first side each become an angle of 85 degrees to 90 degrees when viewed from above. A ratio W1 / W0 of a dimension W1 of a linear portion of a front end of the crystal sheet to a width dimension W0 of the crystal sheet is 0.96 or more.

Description

Technical Field

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

[0002] To further miniaturize crystal oscillators, which are a type of piezoelectric element, photolithography and wet etching techniques are used.

[0003] In, for example, Patent Document 1, which is related to the applicant of this application, a piezoelectric element using the aforementioned technology is described. Specifically, as shown in Figure 1 of Patent Document 1, a piezoelectric element having an AT-cut crystal sheet is disclosed. The AT-cut crystal sheet is an AT-cut crystal sheet in which at least one side intersects the Z' axis of the crystallization axis of the crystal using three surfaces: a first surface, a third surface, and a third surface. The first surface is a surface in which the X-Z' surface (main surface) represented by the crystallization axis of the crystal sheet is rotated by 4° ± 3.5° using the X-axis of the crystal as the rotation axis; the second surface is a surface in which the main surface is rotated by -57° ± 5° using the X-axis of the crystal as the rotation axis; and the third surface is a surface in which the main surface is rotated by -42° ± 5° using the X-axis of the crystal as the rotation axis.

[0004] According to the piezoelectric element, compared with the past, unnecessary vibrations other than the original vibration of the AT-cut crystal oscillator can be suppressed. Therefore, compared with the past, the impedance of the oscillator, i.e. the 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 is a piezoelectric element that can improve CI (Cleanliness), but in the research of the inventors of this application, it has been determined that further improvements in CI can be achieved. That is, the piezoelectric element disclosed in Patent Document 1 is a piezoelectric element comprising a crystal wafer having a defined first to third surface, but in order to obtain the defined first to third surfaces, a process of etching the crystal wafer for a long time is adopted. Therefore, when the front end side of the crystal wafer, that is, the side of the crystal wafer opposite to the side supported by the conductive adhesive, is viewed in a plane, the area from the center of the front end toward the two corners is etched into a roughly triangular shape, and the area of ​​the crystal wafer is correspondingly reduced (see the comparative example or... described later). Figure 6 , Figure 7B In the case of AT-cut crystal wafers, if the area of ​​the crystal wafer's plane is large, it is easier to achieve good CI, and there is room for improvement in the piezoelectric element disclosed in Patent Document 1.

[0010] This application was made in view of this point of view, and therefore, the purpose of this application is to provide a piezoelectric element that can reduce the aforementioned problems and a method for manufacturing the same.

[0011] [Technical means to solve the problem]

[0012] To achieve the aforementioned objective, according to the invention of the piezoelectric element of this application, a piezoelectric element is proposed, comprising: a container; and an AT-cut crystal wafer, wherein the AT-cut crystal wafer uses the X-Z' plane represented by the crystallization axis of the crystal as the main surface, the planar shape of the AT-cut crystal wafer is quadrilateral, and the AT-cut crystal wafer utilizes three surfaces—a first surface and a third surface—to form at least one side surface intersecting the Z' axis of the crystallization axis of the crystal, the first surface and the third surface intersecting in this order. 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; and the third surface is equivalent to rotating the main surface by -42°±5° using the X-axis of the crystal as the rotation axis. The AT-cut crystal sheet is connected and fixed to the container by a conductive adhesive on the first side of the two sides parallel to the Z' axis. In the piezoelectric element, the two corners of the AT-cut crystal sheet on the second side opposite to the first side are approximately right angles when viewed from above.

[0013] When implementing the present invention, the approximately right angle, in terms of the angle at which the two sides constituting the corner intersect, is preferably an angle in the range of 85 degrees to 90 degrees, and more preferably an angle in the range of 87 degrees to 90 degrees.

[0014] Furthermore, when implementing the present invention, it is preferable that the second side is a straight line between the two corners.

[0015] Furthermore, when the length of the straight portion of the second side is set as W1 and the width dimension of the AT-cut crystal wafer along the Z' axis is set as W0, it is preferable that W1 / W0 is 0.90 or more, more preferably that W1 / W0 is 0.93 or more, and even more preferably that W1 / W0 is 0.96 or more.

[0016] Furthermore, when implementing the present invention, if the approximate right angle is defined by the expression of the C-shaped chamfer of the two corners, it is preferable that the C-size is 20 μm or less.

[0017] Furthermore, according to the invention of the piezoelectric element manufacturing method of this application, when the piezoelectric element of this application is manufactured using photolithography and wet etching techniques, the process includes:

[0018] The step of forming an etch-resistant mask on a crystal wafer, wherein the etch-resistant mask is an etch-resistant mask used in the wet etching, has: a first mask portion that forms the pattern of the AT-cut crystal wafer into a matrix shape; a second mask portion that extends between the matrices along a direction corresponding to the Z' axis to form a frame-forming pattern arranged sequentially along the X-axis; a third mask portion that forms a bridging pattern for holding the AT-cut crystal wafer in the frame after the 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 step is completed;

[0019] The crystal wafer with the etch-resistant mask formed thereon is immersed in a hydrofluoric acid-based wet etching solution for a specified time in the first etching step.

[0020] The step of removing the first mask portion and the fourth mask portion from the crystal wafer from which the first etching step has been completed;

[0021] The second etching step involves immersing the crystal wafer, from which the first mask portion and the fourth mask portion have been removed, in a hydrofluoric acid-based wet etching solution for a specified time.

[0022] The step of forming excitation electrodes on the crystal wafer after the second etching step has been completed;

[0023] The step of monolithizing the AT-cut crystal wafer from the crystal wafer from which the formation of the excitation electrodes has been completed; and

[0024] The step of connecting and fixing the monolithized AT-cut crystal wafers to the container.

[0025] Furthermore, in the etching mask processing step performed before the second etching step, the second mask portion (the mask portion for pattern formation of the frame) is left intact, while the third mask portion (the mask portion for forming the bridging pattern) can be left intact or removed, depending on the size of the bridging pattern. That is, if the bridging pattern is large, even if the third mask portion is removed, the bridging will remain after the second etching step, so the third mask portion can also be removed. Conversely, if the bridging pattern is small, the third mask portion can be left intact without removal, thus protecting the conforming portion of the wafer in a way that the bridging does not disappear in the second etching step.

[0026] [The effects of the invention]

[0027] According to the invention of the piezoelectric element of this application, regarding the piezoelectric element using an AT-cut crystal wafer with a defined first to third surface on the side intersecting the Z' axis of the crystal, by leaving the corner of the front end intact, the planar area of ​​the crystal wafer is increased, thereby providing a piezoelectric element with improved CI compared to the past.

[0028] Furthermore, according to the invention of the piezoelectric element manufacturing method of this application, after forming the crystal wafer using an etch-resistant mask having a defined first to fourth mask portion, the crystal wafer is subjected to a first etching. 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 leading edge of the crystal wafer. Thus, the reduction of the planar area on the leading edge side of the crystal wafer can be prevented, and a crystal wafer containing the desired side surfaces having a first to third surface can be easily manufactured. Attached Figure Description

[0029] Figure 1A , Figure 1B This is an explanatory diagram of the piezoelectric element 10 according to the embodiment.

[0030] Figures 2A to 2C This is an explanatory diagram of the AT-cut crystal wafer 20 included in the piezoelectric element 10 of the embodiment.

[0031] Figure 3A , Figure 3B This is an explanatory diagram of the AT-cut crystal wafer 20, particularly the side intersecting the Z' axis.

[0032] 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.

[0033] Figure 5A , Figure 5BThe manufacturing method of the piezoelectric element 10 in the embodiment is immediately following Figure 4B The following is an explanatory diagram.

[0034] Figure 6 This is an explanatory diagram for a comparative example.

[0035] Figure 7A This is a scanning electron microscope (SEM) image of the crystal slice in the embodiment, viewed from above. Figure 7B This is a SEM image of the crystal slice of the comparative example viewed from above.

[0036] Figure 8A This is a characteristic diagram showing the CI distribution of the piezoelectric element in the embodiment. Figure 8B This is a characteristic diagram showing the CI distribution of the piezoelectric element in the comparative example.

[0037] [Explanation of Symbols]

[0038] 10: Piezoelectric element of the embodiment

[0039] 20: Crystal wafer of the embodiment

[0040] 20a: First side

[0041] 20b: Second side

[0042] 20c: First page

[0043] 20d: Second side

[0044] 20e: Third face

[0045] 20f: Main page

[0046] 20x, 20y: Corner

[0047] 20z: Long side

[0048] 20w: Crystal wafer

[0049] 21: Excitation electrode

[0050] 23: Lead-out electrode

[0051] 30: Container

[0052] 30a: concave part

[0053] 30b: Support pad

[0054] 30c: External mounting terminal

[0055] 33: Conductive adhesives

[0056] 35: Cover component

[0057] 40: Etching-resistant mask

[0058] 40a: First mask section

[0059] 40b: Second mask section

[0060] 40c: Third mask section

[0061] 40d: Fourth mask section

[0062] 120: Comparative piezoelectric element

[0063] C: The C dimension is used to describe the C-shaped chamfer.

[0064] M, N, R: Partial

[0065] O: Center point

[0066] P1: Center of the front end

[0067] R1, R2: Regions

[0068] W: Size

[0069] W0: Width dimension

[0070] W1: Length

[0071] X, Y', Z': Axes (coordinate axes)

[0072] θ1, θ2, θ3, θx, θy: angle Detailed Implementation

[0073] 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. Also, 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 following embodiments.

[0074] 1. Description of piezoelectric elements

[0075] First, refer to Figures 1A to 3B 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. Additionally, in Figure 1A in, omit Figure 1B The illustration shows the cover member 35 included in the piezoelectric element 10. Additionally, Figure 2AThis 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 along the IIC-IIC line. 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 2A 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).

[0076] The crystal wafer 20 in this embodiment is an AT-cut crystal wafer as described below: the planar shape of the crystal wafer 20 is rectangular, and the long side of the crystal wafer 20 is parallel to the X-axis of the crystal, and the short side of the crystal wafer 20 is parallel to the Z' axis of the crystal.

[0077] The crystal wafer 20 has 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 toward the vicinity of both ends of a first side 20a, which is an edge of the crystal wafer 20.

[0078] like Figure 1A As shown, the crystal sheet 20 is mounted 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, for example, by means of a conductive adhesive 33. Thus, the crystal sheet 20 is cantilevered and held within the container 30 on the first side 20a.

[0079] 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 is provided for connecting the piezoelectric element 10 to other electronic devices. The support pad 30b is connected to the external mounting terminal 30c via a via (not shown) wiring.

[0080] Additionally, a suitable cover member 35 is joined to the embankment surrounding the recess 30a of the container 30 to seal the crystal sheet 20 inside the container 30.

[0081] Furthermore, in the crystal sheet 20, the side surface that intersects the Z' axis of the crystal has the following structure.

[0082] Each side (Z' plane) of crystal sheet 20 that intersects the Z' axis of the crystal, such as Figure 3A , Figure 3BAs shown, the structure comprises a side surface including a first surface 20c, a second surface 20d, and a third surface 20e. Furthermore, the first surface 20c is the surface that intersects with the main surface 20f of the crystal sheet 20, and is equivalent to rotating the main surface 20f by θ1 using the X-axis of the crystal as the rotation axis.

[0083] Furthermore, in the crystal sheet 20, the first surface 20c, the second surface 20d, and the third surface 20e intersect in this order. The second surface 20d is the surface in which the principal surface 20f is rotated by θ2 using the crystal's X-axis as the rotation axis, and the third surface 20e is the surface in which the principal surface 20f is rotated 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.

[0084] 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°.

[0085] In having the use of the above Figure 3A and Figure 3B In the case of the crystal sheet with the described side surface, the side surface becomes a unique mouth shape, which can attenuate unnecessary vibrations propagating in the Z' direction, thus contributing to the improvement of the characteristics of the piezoelectric element. Furthermore, this structure is described in Japanese Patent Application Publication No. 2016-197778, which is related to the applicant; therefore, its detailed description is omitted here.

[0086] Additionally, the cross-section of crystal sheet 20 along the X-axis of the crystal (the cross-section along line IIB-IIB) is as follows: Figure 2B As shown, the two ends along the X-axis are convex in shape.

[0087] Furthermore, as a feature of the present invention, when the crystal sheet 20 is viewed from above, the two corners 20x and 20y on the second side 20b of the crystal sheet 20 are approximately right angles.

[0088] Specifically, such as Figure 1A , Figure 2AAs shown, when viewed from above, the angle θx, which is the intersection of the shorter side (the second side 20b) of the two sides constituting corner 20x and the longer side 20z of crystal plate 20, and the angle θy, which is the intersection of the shorter side (the second side 20b) of the two sides constituting corner 20y and the longer side 20z of crystal plate 20, are preferably in the range of 85 degrees to 90 degrees, and more preferably in the range of 87 degrees to 90 degrees. With such angles, the CI of the piezoelectric element 10 can be improved compared to cases where these angles are not present (for details, please refer to the embodiments described later).

[0089] In addition, angles θx and θy can be the same or different, typically differing slightly due to the anisotropy of the crystallization axis.

[0090] Furthermore, regarding the approximate right angles of the two corners 20x and 20y, from the viewpoint of the C-dimension of the two corners, it can be less than 20 μm. If this C-dimension is used, the CI of the piezoelectric element 10 can be improved compared to cases where this C-dimension is not used (for details, please refer to the embodiments described later).

[0091] Furthermore, the second side 20b of the crystal sheet 20 becomes a straight line between the two corners 20x and 20y. When the length of the straight portion of the second side 20b is set as W1, and the width dimension of the crystal sheet 20 along the Z' direction, i.e., the width dimension near the center of the crystal sheet 20, is set as W0, it is preferable that W1 / W0 is 0.93 or more, and more preferably that W1 / W0 is 0.96 or more. However, the maximum value of W1 / W0 is only 1. If the value of W1 / W0 is set within the aforementioned range, the CI of the piezoelectric element 10 can be improved compared to the case where it is not set within the aforementioned range (for details, please refer to the embodiments described later).

[0092] Furthermore, the length W1 of the straight section is based on the dimension W of the fourth pattern described in the manufacturing method below (refer to...). Figure 4C The value of W1 / W0 varies depending on the etching time of the crystal wafer using a hydrofluoric acid-based etchant. Preferably, W1 / W0 is 1 or close to 1, so the value of the fourth pattern size W, or the etching time of the crystal wafer using a hydrofluoric acid-based etchant, can be set such that W1 / W0 is close to 1.

[0093] 2. Explanation of the manufacturing method of piezoelectric elements

[0094] Then, referring 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 steps involved in 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 of the crystal plate 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 steps have been changed from... Figure 4B A diagram showing the state of progress.

[0095] In the manufacturing method of this application, the crystal wafer 20 is manufactured by photolithography and wet etching techniques.

[0096] Specifically, the step of forming an etch-resistant mask 40 on a crystal wafer 20w is utilized, wherein the etch-resistant mask 40 is an etch-resistant mask 40 for wet etching (see reference). Figure 4B The device includes: 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 frame-forming pattern arranged sequentially along the X direction; a third mask portion 40c, which forms a bridging pattern for holding the AT-cut crystal wafer in the frame after the wet etching; and a fourth mask portion 40d, having a predetermined width W, disposed between the corner of the second side of the AT-cut crystal wafer and the third mask portion, which causes the crystal at the location to disappear when the wet etching is completed. Here, the fourth mask portion 40d is disposed between the portions of the first mask portion 40a corresponding to the two corners of the front end side of the crystal wafer and the second mask portion 40b.

[0097] Specifically, an etch-resistant metal film can be formed on the front side of the back of the crystal wafer 20w, a photoresist can be coated on its surface, the photoresist can be exposed using photomasks for forming the first to fourth mask portions, and then the metal film can be selectively removed to form the etch-resistant mask 40.

[0098] Additionally, 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 (please refer to the embodiments described later, etc.), the specified width is: the width by which the crystal portion under the fourth mask portion 40d disappears after the second etching step described later.

[0099] Next, a first etching step is performed to form a crystal wafer with an etch-resistant mask 40, which is then immersed in a hydrofluoric acid-based wet etching solution for a specified time. This first etching step is used to form the shape of the crystal wafer 20.

[0100] Subsequently, the first mask portion 40a and the fourth mask portion 40d are removed from the crystal wafer after the first etching has been completed. Additionally, in this embodiment, the third mask portion 40c is also removed. This mask portion can be processed using well-known photolithography techniques. However, as explained, if the size of the third mask portion 40c is small, it is preferable not to remove it and leave it as a residue.

[0101] Once the etching-resistant processing is complete, the crystal portion covered by the first mask, second mask, and third mask is exposed (see reference). Figure 5A ).

[0102] Next, a second etching step 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 specified time. The second etching step involves adjusting the frequency of the crystal wafer 20 and forming specified first to third surfaces on the side of the crystal wafer 20 that intersects the Z' axis of the crystallization axis. 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 specified width. Therefore, the two corners 20x and 20y of the second side 20b of the crystal wafer 20, which are not fixed to the container side, appear as corners for the first time around the end of the second etching. Thus, even after wet etching, corners 20x and 20y become approximately right angles, and the portion of the second side 20b between corners 20x and 20y becomes a straight line.

[0103] Excitation electrodes and lead-out electrodes are formed on the crystal wafer where the second etching step has been completed. The AT-cut crystal wafer is then monolithized from the crystal wafer where the formation of the excitation electrodes, etc., has been completed. The monolithized crystal wafer is then fixed in container 30 (see reference) using a conductive adhesive. Figure 1A and Figure 1B Subsequently, under conditions where the container is in a specified environment, the container is sealed using a lid member, thereby manufacturing the piezoelectric element of the present invention.

[0104] 3. Examples and Comparative Examples

[0105] Then, referring to Figure 6 , Figure 7A and Figure 7B , Figure 8A and Figure 8B The embodiments and comparative examples are described below.

[0106] As an example of a piezoelectric element, multiple crystal wafers with an oscillation frequency of 27.12 MHz, an X size of approximately 870 μm, and a Z' size of approximately 640 μm are manufactured using the manufacturing method described above. These crystal wafers are then mounted in a container, and the container is sealed using a lid member to manufacture the piezoelectric element of multiple embodiments.

[0107] Furthermore, as a comparative example, the piezoelectric element is manufactured using a process that does not have a fourth mask portion 40d (see reference). Figure 4B The etch-resistant mask is used to manufacture multiple comparative example crystal wafers with the same frequency, X size, and Z' size as the embodiment described above. These wafers are then mounted in a container, and the container is sealed using a cover member to manufacture multiple comparative example piezoelectric elements.

[0108] Figure 6 This is a plan view showing the crystal plate 120 used in the comparative example. Figure 7A This is a SEM image of the crystal wafer 20 used in the embodiment, viewed from above. Figure 7B This is a SEM image of the crystal plate 120 used in the comparative example, viewed from above.

[0109] according to Figure 6 and Figure 7B It can be seen that when the front end side of the crystal wafer 120 used in the comparative example is viewed in a plane, that is, the side of the crystal wafer opposite to the side supported by the conductive adhesive, the regions R1 and R2 from the center P1 of the front end toward the two corners are etched into approximately triangular shapes, and the area of ​​the crystal wafer is reduced accordingly.

[0110] On the other hand, according to Figure 7A As can be seen, the two corners 20x and 20y on the front end side of the crystal sheet 20 used in the embodiment are approximately right angles, and the two corners 20x and 20y are in a straight line. That is, it can be seen that the crystal sheet 20 is indeed a rectangular crystal sheet when viewed in a plane.

[0111] For the multiple crystal plates 20 used in the embodiment, the angles θx and θy of the two corners 20x and 20y were measured using a measuring microscope (refer to...). Figure 1A , Figure 1B , Figures 2A to 2CThe results show that angles θx and θy are in the range of 85 to 90 degrees, and W1 is in the range of 605 μm to 632 μm. On the other hand, the target value for the Z' dimension near the center of the crystal wafer, i.e., the width W0, is 640 μm, but actual measurements show it to be in the range of 638 μm to 650 μm. Therefore, if W1 / W0 is estimated 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 actual products, W1 / W0 can be said to be 0.93 to 0.99, with most values ​​being 0.96 to 0.99.

[0112] Furthermore, the C-dimension, based on the C-bevel angle, was measured at two corners of the front ends of each of the plurality of crystal wafers 20 used in the embodiment and the plurality of crystal wafers 120 used in the comparative example, using a measuring microscope. That is, the C-dimension was measured using a measuring microscope. Figure 7A , Figure 7B The C-size of the corners in the SEM images shown is expressed as a C-bevel. As a result, in the case of crystal wafer 20 of the embodiment, the C-size is 10μm to 18μm, both of which are less than 20μm. On the other hand, in the case of crystal wafer 120 of the comparative example, the C-size is 70μm to 95μm, which is 7 to 9 times larger than that of the embodiment.

[0113] Furthermore, the dimensions of the straight portion at the front end of the comparative example crystal sheet 120 were measured and found to be small, approximately 130 μm to 160 μm. Moreover, the straight portion forms a sloping shoulder shape towards the corner of the crystal sheet.

[0114] Furthermore, the CI was measured based on the electrical characteristics of the piezoelectric elements used in the embodiments and comparative examples. The CI distribution of the piezoelectric elements in the embodiments is shown below. Figure 8A The CI distribution of the piezoelectric element in the comparative example is shown in... Figure 8B All graphs use CI (Ω) on the horizontal axis and frequency on the vertical axis. The sample size is 12 for each graph.

[0115] In the piezoelectric element of the embodiment, the average CI distribution is 83.5 Ω, and the standard deviation is 6.6 Ω. In the piezoelectric element of the comparative example, the average CI distribution is 123.6 Ω, and the standard deviation is 13.0 Ω. The embodiment is superior by 40.1 Ω in terms of the average CI and by 6.4 Ω in terms of the standard deviation. Based on these results, it can be seen that the piezoelectric element of the present invention is superior to that of the past.

[0116] Based on the CI measurement results, it can be seen that if the two corners on the front end side of the crystal sheet described in this invention are approximately right angles, CI improvement can be achieved. Specifically, it can be seen that if the angles θx and θy of the two corners on the front end side of the crystal sheet, or the ratio W1 / W0 of the width of the straight portion of the crystal sheet on the front end side to the width near the center of the crystal sheet, or the C dimension is within the aforementioned range, then it is preferable for improving CI.

[0117] 4. Other implementation methods

[0118] The embodiments of various inventions concerning piezoelectric elements and their manufacturing methods have been described above, but the present invention is not limited to the examples described. For example, the container used is not limited to the examples described; for example, the present invention can also be applied to piezoelectric elements with other structures, such as piezoelectric elements using containers comprising: a flat base plate and a cap-shaped cover member having a recess for receiving a crystal wafer. Furthermore, the applicable frequency or the size of the crystal wafer is not limited to the examples described. The more miniaturization of the crystal wafer progresses, the greater the contribution of the present invention.

Claims

1. A piezoelectric element, characterized in that, include: container; as well as AT-cut crystal wafers, among which, The AT-cut crystal wafer uses the X-Z' plane, represented by the crystallization axis of the crystal, as the principal plane. The planar shape of the main surface of the AT-cut crystal wafer is quadrilateral. The AT-cut crystal wafer utilizes three surfaces—the first to the third—to form at least one side that intersects the Z' axis of the crystallization axis of the crystal, with the first to the third surfaces intersecting in this order. The first face is equivalent to rotating the main face by 4° ± 3.5° using the X-axis of the crystal as the rotation axis. The second face is equivalent to rotating the main face 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. The AT-cut crystal wafer is connected and fixed to the container on the first side of the two sides parallel to the Z' axis using a conductive adhesive. The AT-cut crystal wafer has two corners formed by the quadrilateral shape on the side facing the second side opposite to the first side, and the second side is a straight line between the two corners. The two corners, in terms of the C-dimension as expressed by C-bevel, are corners with a diameter of 10 μm to 20 μm or less. When the length of the straight section is set as W1 and the width of the AT-cut crystal wafer along the Z' axis is set as W0, W1 / W0 is 0.93 to 0.

99.

2. The piezoelectric element according to claim 1, characterized in that, The ratio of W1 to W0 is 0.96 to 0.

99.

3. The piezoelectric element according to claim 1 or 2, characterized in that, The AT-cut crystal wafer is a rectangular AT-cut crystal wafer in a top view where the first and second sides are set as short sides and the side along the X-axis of the crystal is set as a long side.

4. A method for manufacturing a piezoelectric element, comprising using photolithography and wet etching techniques to manufacture the piezoelectric element as described in any one of claims 1 to 3, characterized in that, include: The steps for providing crystal wafers; The step of forming an etch-resistant mask on the crystal wafer, wherein the etch-resistant mask is an etch-resistant mask used in the wet etching process, having: The first mask portion forms the pattern of the AT-cut crystal wafer into a matrix shape; The second mask portion extends between the matrices along a direction corresponding to the Z' axis to form a pattern for forming a frame arranged sequentially along the X-axis. The third mask portion forms a bridging pattern for holding the AT-cut wafer in the frame after the wet etching; and The fourth mask portion, having a specified width W, is disposed between the corner portion on the side of the second edge of the AT-cut crystal wafer and the third mask portion; The crystal wafer with the etch-resistant mask formed thereon is immersed in a hydrofluoric acid-based wet etching solution for a specified time in a first etching step. The step of removing the first mask portion and the fourth mask portion from the crystal wafer from which the first etching step has been completed; The crystal wafer, after the removal of the first mask portion and the fourth mask portion, is immersed in a hydrofluoric acid-based wet etching solution for a specified time in a second etching step. The crystal portion of the crystal wafer exposed by the removal of the fourth mask portion will disappear in the second etching step. The step of forming excitation electrodes on the crystal wafer after the second etching step has been completed; The step of monolithizing the AT-cut crystal wafer from the crystal wafer from which the formation of the excitation electrodes has been completed; and The step of connecting and fixing the monolithized AT-cut crystal wafers to the container.

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