JP2018050211A - Piezoelectric vibration element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent disconnection and peeling of extraction electrodes in a piezoelectric vibration element including a piezoelectric element plate that is reduced in thickness from a center part toward peripheral parts.SOLUTION: A piezoelectric vibration element 10 comprises: a piezoelectric element plate 20 that is reduced in thickness from a center part 23 toward peripheral parts 241 to 244; excitation elements 311 and 312 that apply a voltage to the piezoelectric element plate 20; external connection electrodes 321 and 322 that are electrically connected to the outside; an extraction electrode 331 that electrically connects the excitation electrode 311 and external connection electrode 321; and an extraction electrode 332 that electrically connects the excitation electrode 312 and external connection electrode 322. The extraction electrodes 331 and 332 have shapes sandwiched by an inside line 34 of a center part 23 side and an outside line 35 of each of peripheral parts 241, 242, and 244 sides, and the inside line is a curve protruding from the center part 23 toward each of the peripheral parts 241, 242, and 244.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piezoelectric vibration element used for an electronic component such as a piezoelectric device, and more particularly to a piezoelectric vibration element having a piezoelectric base plate that becomes thinner from a central part to a peripheral part.

  In order to reduce the crystal impedance, a piezoelectric vibration element is known in which the shape of the piezoelectric element plate is reduced from the central part to the peripheral part (see, for example, Patent Documents 1 and 2). An example of this type of piezoelectric vibration element will be described as Related Art 1.

  3 shows a piezoelectric vibration element according to Related Technique 1, FIG. 3 [A] is a plan view, FIG. 3 [B] is a cross-sectional view taken along line IIIb-IIIb in FIG. 3 [A], and FIG. A sectional view taken along line IIIc-IIIc in FIG. 3A, and FIG. 3D is a rear view. Hereinafter, description will be given based on these drawings.

  The piezoelectric vibration element 70 includes a rectangular piezoelectric element plate 80 having a first main surface 81 and a second main surface 82 that are in a front-back relationship, excitation electrodes 911 and 912 that apply a voltage to the piezoelectric element plate 80, and externally. External connection electrodes 921 and 922 that are electrically connected, lead electrodes 931 that electrically connect the excitation electrodes 911 and the external connection electrodes 921, and leads that electrically connect the excitation electrodes 912 and the external connection electrodes 922 An electrode 932. The piezoelectric element plate 80 is subjected to processing (bevel processing) in which the thickness t becomes thinner from the central portion 83 to the peripheral portions 841 to 844. Accordingly, the four corners of the piezoelectric element plate 80 are rounded. When the piezoelectric element plate 80 has such a shape, vibration energy is confined in the central portion 83 of the piezoelectric element plate 80, so that the crystal impedance can be lowered.

JP 2013-034176 A JP 2006-072937 A

  The extraction electrode 931 connects the excitation electrode 911 and the external connection electrode 921 in a straight line. That is, since the extraction electrode 931 extends in the longitudinal direction of the piezoelectric element plate 80 and the external connection electrode 921 extends in the short direction of the piezoelectric element plate 80, the vicinity of the joint 941 between the extraction electrode 931 and the external connection electrode 921 is It is a right angle. In the vicinity of the joint 941, since the outer shape of the piezoelectric element plate 80 has an arc shape, the width of the extraction electrode 931 becomes narrow, and there is a possibility that the extraction electrode 931 may be disconnected or peeled off. As for the extraction electrode 932, the extraction electrode 932 may be disconnected or peeled off in the vicinity of the joint 942.

  Accordingly, an object of the present invention is to improve yield and reliability of a piezoelectric vibration element having a piezoelectric element plate that becomes thinner from the central part to the peripheral part by preventing disconnection and peeling of the extraction electrode. .

The piezoelectric vibration element according to the present invention is
A rectangular piezoelectric element whose thickness decreases as it goes from the central part to the peripheral part,
An excitation electrode provided at the center and applying a voltage to the piezoelectric element plate;
An external connection electrode provided on the peripheral edge side and electrically connected to the outside;
An extraction electrode provided on the peripheral edge side and electrically connecting the excitation electrode and the external connection electrode;
A piezoelectric vibration element comprising:
The extraction electrode has a shape sandwiched between an inner line on the central side and an outer line on the peripheral side.
The inner line is a curve that protrudes from the central part side to the peripheral part side,
It is characterized by that.

  According to the present invention, in the piezoelectric vibration element having the piezoelectric element plate that becomes thinner from the central part to the peripheral part, the lead electrode for connecting the excitation electrode and the external connection electrode protrudes from the central part side to the peripheral part side. By being curved, it is possible to prevent the width of the extraction electrode from being reduced in the vicinity of the joint between the extraction electrode and the external connection electrode, so that disconnection and peeling of the extraction electrode can be prevented.

FIG. 1A is a plan view, FIG. 1B is a cross-sectional view taken along line Ib-Ib in FIG. 1A, and FIG. 1C is FIG. 1A. A sectional view taken along line Ic-Ic and FIG. 1D is a rear view. 2A is a partially enlarged view of FIG. 1A, and FIG. 2B is a cross-sectional view showing a piezoelectric device using the piezoelectric vibration element of the first embodiment. FIG. 3A is a plan view, FIG. 3B is a cross-sectional view along line IIIb-IIIb in FIG. 3A, and FIG. 3C is in FIG. 3A. IIIc-IIIc sectional view, FIG. 3D is a rear view.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the accompanying drawings. In the present specification and drawings, the same reference numerals are used for substantially the same components. The shapes depicted in the drawings are drawn so as to be easily understood by those skilled in the art, and thus do not necessarily match the actual dimensions and ratios.

  1A and 1B show a piezoelectric vibration element of Embodiment 1, FIG. 1A is a plan view, FIG. 1B is a cross-sectional view taken along line Ib-Ib in FIG. 1A, and FIG. FIG. 1A is a cross-sectional view taken along line Ic-Ic in FIG. FIG. 2A is a partially enlarged view of FIG. Hereinafter, description will be given based on these drawings.

  As shown in FIG. 1, the piezoelectric vibration element 10 according to the first embodiment is provided on a rectangular piezoelectric element plate 20 whose thickness t decreases from the central part 23 toward the peripheral parts 241 to 244, and the central part 23. In addition, excitation electrodes 311 and 312 for applying a voltage to the piezoelectric element plate 20, external connection electrodes 321 and 322 provided on the peripheral edge 241 side and electrically connected to the outside, and provided on the peripheral edge 244 side and an excitation electrode 311 and a lead electrode 331 that electrically connects the external connection electrode 321, and a lead electrode 332 that is provided on the peripheral edge 242 side and electrically connects the excitation electrode 312 and the external connection electrode 322. . The piezoelectric element plate 20 has a first main surface 21 and a second main surface 22 that are in a front-back relationship.

  As shown in FIG. 2A, the extraction electrode 331 has a shape sandwiched between an inner line 34 on the central portion 23 side and an outer line 35 on the peripheral edge portions 241, 244 side, and the inner line 34 has a central portion. It is a curve that protrudes from the 23 side toward the peripheral portions 241 and 244. Further, the outer line 35 as well as the inner line 34 may be curves that protrude from the central part 23 side to the peripheral edge parts 241 and 244 side.

  The piezoelectric element plate 20 may be configured such that the four vertices 251 to 254 of the quadrangle are arcuate, and the inner line 34, the outer line 35, and the apex 251 are concentric arcs. In this case, if the radius from the center O to the vertex 251 is R1, the radius from the center O to the outer line 35 is R2, and the radius from the center O to the inner line 34 is R3, then R1> R2> R3. The vertices 251 to 254 are included in the peripheral portions 241 to 244, that is, a part of the peripheral portions 241 to 244.

  The curves of the inner line 34 and the outer line 35 may be lines connecting portions of the same thickness t in the piezoelectric element plate 20. In other words, the extraction electrode 331 may be formed in accordance with a curve connecting portions having the same thickness t on the first main surface 21 of the piezoelectric element plate 20. For example, when the inner line 34, the outer line 35, and the vertex 251 are concentric arcs, the curves of the inner line 34 and the outer line 35 are lines that connect portions of the piezoelectric element plate 20 having the same thickness t.

  The lead electrode 331 has been mainly described above, but the lead electrode 332 is the same as the lead electrode 331. As long as the inner line 34 and the outer line 35 are curves that protrude from the central part 23 side to the peripheral edge parts 241 and 244 side, in addition to the arc shape, any one such as an elliptical arc shape, a parabola shape, a hyperbola shape, a quadratic curve shape, etc. Such a shape may be used. The term “curve” here refers mathematically to a “smooth curve” that does not have a cusp (vertex), in other words, a curve that can be differentiated at any point on the curve, ie, “differentiable”. "Curve".

  Next, the configuration of the piezoelectric vibration element 10 will be described in more detail.

  The piezoelectric vibration element 10 according to the first embodiment is a thickness shear crystal vibration element. The piezoelectric element plate 20 has a thin strip shape made of a crystal piece of an AT cut plate. More specifically, the piezoelectric element plate 20 is cut out along a plane obtained by rotating the XZ plane by 35.25 degrees (35 degrees 15 minutes) about the X axis in crystal axes X, Y, and Z orthogonal to each other. The X-axis direction is the longitudinal direction (length direction), the Z′-axis direction is the short direction (width direction), and the Y′-axis direction is the thickness t direction.

  Examples of dimensions of the piezoelectric element plate 20 are as follows. The length is 2.2 mm, the width is 1.5 mm, the thickness t of the central portion 23 is 0.21 mm, and the radius R1 is 0.5 mm. At this time, the frequency of the main vibration is 8 MHz (low frequency band).

  The inner surface shape of the processing container used in the barrel processing is transferred to the first main surface 21 and the second main surface 22 and the apexes 251 to 254 of the piezoelectric element plate 20. Therefore, the piezoelectric element plate 20 is processed into a shape in which the thickness t gradually decreases from the substantially flat central portion 23 toward the peripheral portions 241 to 244.

  The excitation electrode 311, the external connection electrode 321 and the extraction electrode 331, and the excitation electrode 312, the external connection electrode 322 and the extraction electrode 332 are electrically insulated from each other. The excitation electrode 311 is provided on the first main surface 21, and is connected to the external connection electrode 321 by the extraction electrode 331 on the first main surface 21. The external connection electrode 321 extends from the first main surface 21 to the second main surface 22 across the vertex 251. The excitation electrode 312 is provided on the second main surface 22, and is connected to the external connection electrode 322 by the extraction electrode 332 on the second main surface 22. The external connection electrode 322 extends from the second main surface 22 to the first main surface 21 across the vertex 252. The excitation electrode 311 and the excitation electrode 312 are both squares having the same area, and face each other with the piezoelectric element plate 20 sandwiched in the thickness t direction. In other words, the excitation electrodes 311 and 312 are provided in the central portion 23, the external connection electrodes 321 and 322 are provided on the vertexes 251 and 252 side, and the extraction electrodes 331 and 332 are provided on the peripheral edge portions 244 and 242 side.

  The material of the excitation electrodes 311 and 312, the external connection electrodes 321 and 322, and the extraction electrodes 331 and 332 is, for example, a laminated film of underlying chromium (Cr) and surface gold (Au). This laminated film is formed on the first main surface 21 and the second main surface 22 by sputtering or vapor deposition, and is patterned on each electrode by photolithography and etching.

  Next, the piezoelectric device 40 using the piezoelectric vibration element 10 will be described with reference to FIG.

  The piezoelectric device 40 includes a piezoelectric vibration element 10, an element mounting member 50 that mounts the piezoelectric vibration element 10 on the inner surface 51, and a lid member 60 that seals the piezoelectric vibration element 10 together with the element mounting member 50. A child. The element mounting member 50 has an inner surface 51 and an outer surface 52 that are in a front-back relationship, and the piezoelectric vibration element 10 is mounted on the inner surface 51. The lid member 60 forms a recessed space 41 that houses the piezoelectric vibration element 10 together with the element mounting member 50. The two element pads 53 are provided on the inner surface 51 of the element mounting member 50, and are electrically and mechanically connected to the two element pads 53 via the conductive adhesive 54, respectively. 10 is fixed in a cantilever shape. That is, in the piezoelectric device 40, the element mounting member 50 and the lid member 60 are bonded to each other by a glass sealing material or a brazing material (both not shown) in a state where the piezoelectric vibration element 10 is mounted on the element mounting member 50. The piezoelectric vibration element 10 is hermetically sealed in the recess space 41. This will be described in more detail below.

  The element mounting member 50 includes an inner surface 51 and an outer surface 52 that are in a front-back relationship, a recessed space 41 and two element pads 53 provided on the inner surface 51 side, and four external connection terminals 57 provided on the outer surface 52 side. And having. The element pad 53 and the external connection terminal 57 are electrically connected. The element mounting member 50 is made of, for example, laminated ceramics and a metal frame, and includes a substrate portion 55 and a frame portion 56. The frame portion 56 is provided in an annular shape along the periphery on the inner surface 51 side of the substrate portion 55. In other words, the element mounting member 50 is provided with the element pad 53 on the inner surface 51 side which is the bottom surface of the recessed space 41, and the external connection terminal 57 on the outer surface 52 side which is the opposite side of the inner surface 51.

  The element pad 53 is made of a conductor obtained by applying gold plating or the like to a metallization such as tungsten, and is provided at a position facing the external connection electrodes 321 and 322 of the piezoelectric vibration element 10. The external connection electrode 321 is formed by a conductive adhesive 54. , 322 are electrically connected. External connection terminals 57 are provided on the projecting end surfaces at the four corners of the outer surface 52. Examples of the external connection terminal 57 include a frequency control terminal, a ground terminal, an output terminal, and a power supply voltage terminal. The element pad 53 and the external connection terminal 57 are electrically connected to each other by an internal wiring (not shown).

  The conductive adhesive 54 is made of, for example, silver paste and has fluidity before curing. More specifically, the conductive adhesive 54 contains conductive powder as a conductive filler in a binder such as a silicone resin.

  The lid member 60 is overlaid on the upper end of the frame portion 56 of the element mounting member 50 and seals the recessed space 41. The lid member 60 is made of a metal such as Kovar, and is a rectangular flat plate. In other words, the lid member 60 is joined to the element mounting member 50 with a sealing material or the like to form a hermetically sealed concave space 41. The recessed space 41 is formed on the element mounting member 50 side in the first embodiment, but may be formed on the lid member 60 side.

  Next, the operation and effect of the piezoelectric vibration element 10 will be described.

  (1) In the first embodiment, the extraction electrode 331 has a shape sandwiched between the inner line 34 on the central part 23 side and the outer line 35 on the peripheral edge parts 241 and 244 side, and the inner line 34 extends from the central part 23 side. It is a curve that protrudes toward the peripheral edge portions 241 and 244. The same applies to the extraction electrode 332. Therefore, according to the first embodiment, the excitation electrodes 311 and 312 and the external connection electrodes 321 and 322 are provided in the piezoelectric vibration element 10 having the piezoelectric element plate 20 that becomes thinner from the central portion 23 toward the peripheral portions 241 to 244. In the vicinity of the joint between the extraction electrodes 331 and 332 and the external connection electrodes 321 and 322, the extraction electrodes 331 and 332 to be connected have a curved shape that protrudes from the central portion 23 side to the peripheral edge portions 241, 242, and 244 side. Since it is possible to suppress the width w (FIG. 2A) of the extraction electrodes 331 and 332 from being narrowed, disconnection and peeling of the extraction electrodes 331 and 332 can be prevented. Here, the width w of the extraction electrodes 331 and 332 is the distance between the inner line 34 and the outer line 35, that is, the dimension of the extraction electrodes 331 and 332 in the direction orthogonal to the current passing through the extraction electrodes 331 and 332. .

  (2) When both the inner line 34 and the outer line 35 are curves that protrude from the central portion 23 side toward the peripheral edge portions 241, 244, the width w of the extraction electrodes 331, 332 is substantially constant. For this reason, the width w of the extraction electrodes 331 and 332 can be suppressed not only from being narrowed but also from being widened, so that the influence on the frequency characteristics of the piezoelectric vibration element 10 can be eliminated. This is because an unnecessary voltage is applied to the piezoelectric element plate 20 when the width w of the extraction electrodes 331 and 332 is increased.

  (3) When the four vertices 251 to 254 of the piezoelectric element plate 20 are arcuate and the inner line 34, the outer line 35, and the apex 251 are concentric arcs, the width w (= R2) of the extraction electrodes 331 and 332 -R3) is completely constant. For this reason, the width w of the extraction electrodes 331 and 332 can be reliably suppressed not only from being narrowed but also from being widened, so that the influence on the frequency characteristics of the piezoelectric vibration element 10 can be completely eliminated.

  (4) When the curve of the inner line 34 and the outer line 35 is a line that connects the portions having the same thickness t in the piezoelectric element plate 20, disconnection and peeling of the extraction electrodes 331 and 332 can be further prevented. This is what the inventors have clarified experimentally, and the reason is considered as follows. The extraction electrodes 331 and 332 are formed on the first main surface 21 and the second main surface 22 by sputtering or vapor deposition, and are patterned by photolithography and etching. Even if this film formation and patterning are performed uniformly on a flat surface, they tend to be non-uniform on curved surfaces and inclined surfaces on which the extraction electrodes 331 and 332 are formed. That is, the adhesion force of the electrode film changes according to the thickness t of the piezoelectric element plate 20. For this reason, when the inner line and the outer line at the side edges of the electrode film are formed longitudinally at different thicknesses t, disconnection or peeling is likely to occur from a portion having a weak adhesion.

  The present invention can be used for a piezoelectric vibration element using piezoelectric ceramics such as lithium niobate and lithium tantalate as a piezoelectric material in addition to the above-described quartz.

<Embodiment 1>
DESCRIPTION OF SYMBOLS 10 Piezoelectric vibration element 20 Piezoelectric base plate 21 1st main surface 22 2nd main surface 23 Center part 241,242,243,244 Peripheral part 251,252,253,254 Apex 311,312 Excitation electrode 321,322 External connection electrode 331 , 332 Lead electrode 34 Inner line 35 Outer line 40 Piezoelectric device 41 Recessed space 50 Element mounting member 51 Inner surface 52 Outer surface 53 Element pad 54 Conductive adhesive 55 Substrate portion 56 Frame portion 57 External connection terminal 60 Lid member O center R1, R2, R3 radius t thickness w width <Related technology 1>
70 Piezoelectric vibrating element 80 Piezoelectric element plate 81 First main surface 82 Second main surface 83 Central portion 841, 842, 843, 844 Peripheral portion 911, 912 Excitation electrode 921, 922 External connection electrode 931, 932 Lead electrode 941, 942 Connection Eye

Claims (4)

A rectangular piezoelectric element whose thickness decreases as it goes from the central part to the peripheral part,
An excitation electrode provided at the center and applying a voltage to the piezoelectric element plate;
An external connection electrode provided on the peripheral edge side and electrically connected to the outside;
An extraction electrode provided on the peripheral edge side and electrically connecting the excitation electrode and the external connection electrode;
A piezoelectric vibration element comprising:
The extraction electrode has a shape sandwiched between an inner line on the central side and an outer line on the peripheral side.
The inner line is a curve that protrudes from the central part side to the peripheral part side,
The piezoelectric vibration element characterized by the above-mentioned. The outer line as well as the inner line is a curve that protrudes from the central part side to the peripheral part side,
The piezoelectric vibration element according to claim 1. The piezoelectric element plate has an arc shape at the four vertices of the square, and the inner line, the outer line, and the vertices are concentric arcs.
The piezoelectric vibration element according to claim 2. The curve is a line connecting the same thickness portions in the piezoelectric element plate,
The piezoelectric vibration element as described in any one of Claims 1 thru | or 3.

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