Piezoelectric device

Abstract

Provided is a piezoelectric device having an improved resonance characteristic. This piezoelectric device comprises: a piezoelectric layer having a thickness in a first direction; a first electrode provided on one side of the piezoelectric layer in the first direction; a second electrode provided on the other side of the piezoelectric layer in the first direction; an insulating layer provided on one side of the piezoelectric layer in the first direction and partially located between the piezoelectric layer and the second electrode; and a frame electrode provided on one side of the second electrode in the first direction. The frame electrode is provided along the outer periphery of an excitation region so as to surround the excitation region. The insulating layer overlaps a part of the outer periphery of the first electrode, a part of the outer periphery of the second electrode, and a part of the outer periphery of the frame electrode in plan view in the first direction. There are two different positions on the inner periphery of the frame electrode, and the distances between the respective positions and the outer periphery of the first electrode in a direction orthogonal to the first direction and / or the widths of the frame electrode at the respective positions are different from each other.

Description

Piezoelectric device

[0001] The present invention relates to a piezoelectric device.

[0002] Patent Document 1 discloses a bulk acoustic wave resonator including: a first raised frame (frame electrode) provided on a functional electrode and formed of a metal; and a second raised frame (insulating layer) provided between the functional electrode and a piezoelectric layer and formed of an oxide.

[0003] Japanese Unexamined Patent Application Publication No. 2022-186649

[0004] In such a resonator, the width of the frame electrode that contributes to excitation between electrodes may differ from the design due to manufacturing variations, which may lead to degradation of resonance characteristics.

[0005] An object of the present invention is to provide a piezoelectric device capable of improving resonance characteristics.

[0006] A piezoelectric device according to one aspect includes: a piezoelectric layer having a thickness in a first direction; a first electrode provided on one side of the piezoelectric layer in the first direction; a second electrode provided on the other side of the piezoelectric layer in the first direction; an insulating layer provided on one side of the piezoelectric layer in the first direction, a part of which is located between the piezoelectric layer and the second electrode; and a frame electrode provided on one side of the second electrode in the first direction. A region that overlaps the piezoelectric layer, the first electrode, and the second electrode when viewed in plan in the first direction and does not overlap the insulating layer when viewed in plan in the first direction is defined as an excitation region. The frame electrode is provided along an outer periphery of the excitation region so as to surround the excitation region. The insulating layer overlaps a part of an outer periphery of the first electrode, a part of an outer periphery of the second electrode, and a part of an outer periphery of the frame electrode when viewed in plan in the first direction. There are two different positions on an inner periphery of the frame electrode, wherein at least one of a distance between the position and the outer periphery of the first electrode in a direction orthogonal to the first direction and a width of the frame electrode at the position is different from each other between the two positions.

[0007] According to the piezoelectric device of the present invention, resonance characteristics can be improved.

[0008] Figure 1 is a plan view showing a piezoelectric device according to the first embodiment. Figure 2 is a diagram showing the configuration y3 on the second main surface of the piezoelectric layer of the piezoelectric device according to the first embodiment. Figure 3 is a cross-sectional view along the line III-III' in Figure 1. Figure 4 is an enlarged view of Figure 1 showing the configuration of the upper electrode, lower electrode, and frame electrode. Figure 5 is a cross-sectional view along the line V-V' in Figure 1. Figure 6 is a cross-sectional view illustrating a method for manufacturing the piezoelectric device according to the first embodiment. Figure 7 is a plan view showing a piezoelectric device according to the second embodiment. Figure 8 is a diagram showing the configuration on the second main surface of the piezoelectric layer of the piezoelectric device according to the second embodiment. Figure 9 is a cross-sectional view along the line IX-IX' in Figure 7. Figure 10 is an enlarged view of Figure 7 showing the configuration of the upper electrode, lower electrode, and frame electrode. Figure 11 is a cross-sectional view along the line XI-XI' in Figure 7. Figure 12 is a plan view showing a piezoelectric device according to the third embodiment. Figure 13 is a diagram showing the configuration on the second main surface of the piezoelectric layer of the piezoelectric device according to the third embodiment. Figure 14 is a cross-sectional view along the line XIV-XIV' in Figure 12. Figure 15 is an enlarged view of Figure 12 showing the configuration of the upper electrode, lower electrode, and frame electrode. Figure 16 is a cross-sectional view along the line XVI-XVI' in Figure 12. Figure 17 is a diagram showing the configuration of the second main surface of the piezoelectric layer of the piezoelectric device according to the fourth embodiment.

[0009] Embodiments of the present disclosure will be described in detail below with reference to the drawings. However, these embodiments do not limit the present disclosure. Each embodiment described in this disclosure is illustrative, and partial substitution or combination of configurations is possible between different embodiments. In modifications and subsequent embodiments, descriptions of matters common to the first embodiment will be omitted, and only the differences will be described. In particular, similar effects and benefits due to similar configurations will not be mentioned sequentially for each embodiment.

[0010] (First Embodiment) Figure 1 is a plan view showing a piezoelectric device according to the first embodiment. Figure 2 is a diagram showing the configuration of the second main surface of the piezoelectric layer of the piezoelectric device according to the first embodiment. In Figure 2, for explanatory purposes, the lower electrode 32, frame electrode 33, lead wiring 35, and insulating layer 36 provided on the second main surface 20b of the piezoelectric layer 20 are shown in a plan view, and the frame electrode 33, which is provided so as to overlap the lower electrode 32, is shown separately. Figure 3 is a cross-sectional view along the line III-III' in Figure 1. The piezoelectric device 10 according to the first embodiment is a resonator that utilizes the bulk wave of the sliding vibration mode, i.e., a BAW (Bulk Acoustic Wave) element.

[0011] As shown in Figures 1 to 3, the piezoelectric device 10 includes a support member 13, a piezoelectric layer 20, an upper electrode 31, a lower electrode 32, a frame electrode 33, lead wires 34 and 35, an insulating layer 36, and connecting electrodes 41 and 42. As shown in Figure 3, the piezoelectric layer 20 is laminated on the support member 13. On top of the piezoelectric layer 20, the upper electrode 31 and lead wires 34, and connecting electrodes 41 and 42 are laminated in that order. Below the piezoelectric layer 20, the insulating layer 36, lower electrode 32 and lead wires 35, and frame electrode 33 are laminated in that order.

[0012] In the following description, the thickness direction of the piezoelectric layer 20 will be referred to as the Z direction, the direction perpendicular to the Z direction as the X direction, and the direction perpendicular to both the Z and X directions as the Y direction. The Z direction is an example of the "first direction" in this disclosure. In embodiments of this disclosure, the direction from the second main surface 20b toward the first main surface 20a within the Z direction may be described as up, and the direction from the first main surface 20a toward the second main surface 20b within the Z direction may be described as down. The X and Y directions are directions parallel to the surface of the piezoelectric layer 20 (first main surface 20a), respectively.

[0013] The support member 13 is provided facing the second main surface 20b of the piezoelectric layer 20. The support member 13 comprises a support substrate 11 and an intermediate layer 12. The support substrate 11 is made of silicon (Si), quartz, or the like. The intermediate layer 12 is provided between the support substrate 11 and the piezoelectric layer 20. The intermediate layer 12 is formed of an insulating material such as silicon oxide. However, the support member 13 may also be configured without the intermediate layer 12, with the piezoelectric layer 20 provided on the support substrate 11. That is, the piezoelectric layer 20 is joined to the support substrate 11 directly or via the intermediate layer 12 (insulating layer).

[0014] A recess 14 (cavity) is formed on the surface of the support member 13 (intermediate layer 12) facing the second main surface 20b of the piezoelectric layer 20. The recess 14 is provided so as to overlap with the excitation region of the resonator, which is formed by the overlapping of the piezoelectric layer 20, the upper electrode 31, and the lower electrode 32, when viewed in plan in the Z direction. In the example in Figure 3, the recess 14 is provided on the piezoelectric layer 20 side of the intermediate layer 12. This reduces the energy loss of the bulk wave during excitation, resulting in good resonance characteristics. The shape of the recess 14 when viewed in plan in the Z direction is magnifying glass-like, that is, a circular shape with a portion extending along the Y direction, but this is merely an example and is not limited to this; it may also be elliptical, rectangular, or other shapes.

[0015] In the first embodiment, the piezoelectric layer 20 has etching holes 20h. The etching holes 20h are located in a position that overlaps with the recess 14 when viewed in plan in the Z direction, and penetrate the piezoelectric layer 20 in the Z direction. In the example of Figure 2, the etching holes 20h are located at the tip of the portion of the recess 14 that extends along the Y direction when viewed in plan in the Z direction, but this is merely one example.

[0016] The piezoelectric layer 20 is a flat plate-shaped layer having a first main surface 20a and a second main surface 20b opposite to the first main surface 20a. The piezoelectric layer 20 is made of lithium niobate (LiNbO ３ ) or lithium tantalate (LiTaO) ３The substrate is made of a single crystal of ). The piezoelectric layer 20 is not limited to this, and aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), etc. may be used. The thickness of the piezoelectric layer 20 is not particularly limited, but it is preferably 1 μm or less.

[0017] The upper electrode 31 is provided on the piezoelectric layer 20 (first main surface 20a). The lower electrode 32 is provided below the piezoelectric layer 20 (second main surface 20b). In the first embodiment, the upper electrode 31 is an example of the "first electrode" of the present disclosure, and the lower electrode 32 is an example of the "second electrode" of the present disclosure. As shown in Figures 1 and 2, when viewed in plan in the Z direction, the upper electrode 31 and the lower electrode 32 overlap in the region that overlaps with the recess 14. In other words, when viewed in plan in the Z direction, in the region that overlaps with the recess 14, the piezoelectric layer 20 is positioned between the upper electrode 31 and the lower electrode 32 in the Z direction. As a result, bulk waves propagate between the upper electrode 31 and the lower electrode 32.

[0018] The names upper electrode 31 and lower electrode 32 are used solely for the purpose of defining the parts and do not limit the spatial arrangement and position in the piezoelectric device according to this disclosure.

[0019] The lead wire 34 is provided in the same layer as the upper electrode 31 and is connected to one side of the upper electrode 31 in the X direction. The lead wire 34 extends in one direction in the X direction from the region overlapping with the recess 14 and is connected to a different connecting electrode 41 than the upper electrode 31. The lead wire 35 is provided in the same layer as the lower electrode 32 and is connected to the other side of the lower electrode 32 in the X direction. The lead wire 35 extends from the region overlapping with the recess 14 to the side opposite to the lead wire 34 and is connected to the connecting electrode 42 through an opening OP formed in the piezoelectric layer 20. In the first embodiment, the lead wire 34 is an example of the "first lead wire" of this disclosure, and the lead wire 35 is an example of the "second lead wire" of this disclosure.

[0020] The upper electrode 31 and the lower electrode 32 are formed from conductive materials such as aluminum (Al), platinum (Pt), gold (Au), copper (Cu), molybdenum (Mo), tungsten (W), titanium (Ti), chromium (Cr), ruthenium (Ru), tantalum (Ta), and iridium (Ir), or from an alloy containing at least one of these materials. The upper electrode 31 and the lower electrode 32 may also be laminated films containing these materials. Furthermore, there may be an adhesion layer of Ti, NiCr, etc., between the support member 13 (intermediate layer 12). The lead wire 34 is formed from the same material as the upper electrode 31. The lead wire 35 is formed from the same material as the lower electrode 32. However, the lead wires 34 and 35 may be made from different materials than the upper electrode 31 and the lower electrode 32.

[0021] As shown in Figure 2, the insulating layer 36 is provided on the second main surface 20b of the piezoelectric layer 20. A portion of the insulating layer 36 is provided between the lower electrode 32 and the piezoelectric layer 20 in the Z direction. The insulating layer 36 is made of an insulator such as silicon dioxide or silicon nitride. With the insulating layer 36 in place, the portion 321 of the lower electrode 32 that overlaps with the insulating layer 36 when viewed in plan in the Z direction, and the portion of the upper electrode 31 above the portion 321, no longer contribute to excitation.

[0022] As shown in Figure 2, the frame electrode 33 is provided below the lower electrode 32 (on the side opposite to the piezoelectric layer 20 side). The frame electrode 33 is made of the same material as the lower electrode 32. However, the frame electrode 33 may be made of a different material than the upper electrode 31 and the lower electrode 32.

[0023] The piezoelectric device 10 according to the first embodiment is a film-bulk acoustic resonator (FBAR). Specifically, a recess 14 (cavity) is formed in the support member 13 (intermediate layer 12) in the portion overlapping with the excitation region, and the piezoelectric layer 20, upper electrode 31, and lower electrode 32 have a membrane structure. However, the piezoelectric device 10 is not limited to this, and may be a solidly mounted acoustic resonator (SMR) in which multiple low-impedance layers and high-impedance layers are stacked instead of the recess 14 (cavity).

[0024] Next, with reference to Figures 4 and 5, the configurations of the upper electrode 31, lower electrode 32, frame electrode 33, and insulating layer 36 will be described in more detail. Figure 4 is an enlarged view of Figure 1 showing the configurations of the upper electrode, lower electrode, and frame electrode. Figure 5 is a cross-sectional view along the line V-V' in Figure 1.

[0025] In this disclosure, the excitation region C is sometimes described as the region in which the piezoelectric layer 20, the upper electrode 31, and the lower electrode 32 overlap when viewed in plan in the Z direction, but do not overlap with the insulating layer 36. That is, the excitation region C is the region of the upper electrode 31 and the lower electrode 32 that contributes to excitation. In the first embodiment, the excitation region C is a circular region centered on point C1 when viewed in plan in the Z direction. In Figure 4, the excitation region C is shown as the region enclosed by a dashed line.

[0026] In this disclosure, the direction perpendicular to the Z direction and toward the geometric centroid (point C1) of the excitation region C may be described as "inside," and the direction perpendicular to the Z direction and toward the geometric centroid (point C1) of the excitation region C may be described as "outside." That is, "inside" refers to the side closer to the geometric centroid of the excitation region C, and "outside" refers to the side farther from the geometric centroid of the excitation region C. Furthermore, "inner circumference" refers to the inner periphery, and "outer circumference" refers to the outer periphery.

[0027] In the examples shown in Figures 1 and 4, the shape of the upper electrode 31 is a combination of semicircles with different radii. More specifically, the upper electrode 31 is a combination of a semicircle with a larger radius on the side of the lead wiring 34 in the X direction and a semicircle with a smaller radius on the opposite side of the lead wiring 34 in the X direction. Here, the semicircles of the upper electrode 31 all have point C1 as their center.

[0028] In the examples shown in Figures 1, 2, and 4, the shape of the lower electrode 32 is circular. The radius of the lower electrode 32 is larger than the radius of the semicircle on the X-direction lead wiring 34 side of the upper electrode 31. Preferably, the radius of the lower electrode 32 is larger than the radius of the semicircle on the X-direction lead wiring 34 side of the upper electrode 31 by a range of 0.5 μm to 5.0 μm.

[0029] In the examples in Figures 1 and 4, the radius of the semicircle on the side of the upper electrode 31 opposite to the X-direction lead wiring 34 is smaller than the radius of the circle of the lower electrode 32. Also, in the examples in Figures 1 and 4, the radius of the semicircle on the X-direction lead wiring 34 side of the upper electrode 31 is smaller than the radius of the circle of the lower electrode 32.

[0030] In the example in Figure 2, the shape of the insulating layer 36 is an arch that curves toward the lead wiring 34 in the X direction. In Figures 2 and 4, the area where the insulating layer 36 is located is indicated by hatching. More specifically, the shape of the insulating layer 36 is a semicircular ring with point C1 as the center of the circle. In the examples in Figures 2 and 4, the radius of the inner arc (inner circumference 36a) of the insulating layer 36 is equal to the radius of the semicircle on the side of the upper electrode 31 opposite to the lead wiring 34 in the X direction. Also, the radius of the outer arc of the insulating layer 36 is larger than the radius of the circle of the lower electrode 32.

[0031] As shown in Figure 4, the frame electrode 33 is provided along the outer circumference of the excitation region C so as to surround the excitation region C. This suppresses leakage of the waves excited in the excitation region C and improves the resonance characteristics. In this disclosure, "provided along the outer circumference of the excitation region C" means that, when viewed in plan in the Z direction, the frame electrode 33 is provided so as to overlap with the outer circumference of the excitation region C, the frame electrode 33 is provided in contact with the outer circumference of the excitation region C, and the frame electrode 33 is provided slightly inward from the outer circumference of the excitation region C at a predetermined distance.

[0032] In the example shown in Figure 4, the frame electrode 33 is provided along the outer circumference of the lower electrode 32. In this disclosure, "provided along the outer circumference of the lower electrode 32 (second electrode)" means that, when viewed in plan in the Z direction, the frame electrode 33 is provided so as to overlap with the outer circumference 32a of the lower electrode 32; the frame electrode 33 is provided in contact with the outer circumference 32a of the lower electrode 32; and the frame electrode 33 is provided slightly inward from the outer circumference 32a of the lower electrode 32 at a predetermined distance.

[0033] As shown in Figures 2 and 4, in the first embodiment, the width D1 of the frame electrode 33 in the first outer peripheral region A1, viewed in plan in the Z direction, is the same as the width D2 of the frame electrode 33 in the second outer peripheral region A2. In this disclosure, the width of the frame electrode 33 refers to the distance between the inner circumference 33a and the outer circumference 33b of the frame electrode 33 in a direction perpendicular to the Z direction. In the examples of Figures 2 and 4, the shape of the frame electrode 33 is annular. In Figures 2 and 4, the area occupied by the frame electrode 33 is shown by hatching. More specifically, the shape of the frame electrode 33 is annular with point C1 as the center of the circle. In the examples of Figures 2 and 4, the radius of the inner arc (inner circumference 33a) of the frame electrode 33 is smaller than the radius of the semicircle on the side opposite to the lead wiring 34 side in the X direction of the upper electrode 31. Furthermore, the radius of the outer arc (outer circumference 33b) of the frame electrode 33 is smaller than the radius of the semicircle of the lower electrode 32, and larger than the radius of the semicircle on the X-direction lead wiring 34 side of the upper electrode 31.

[0034] As shown in Figures 2, 3, and 5, in the first embodiment, the insulating layer 36 overlaps with a portion of one side in the X direction of the outer circumference of the upper electrode 31, lower electrode 32, and frame electrode 33 when viewed in plan in the Z direction. As a result, the outer circumference of the excitation region C is determined by the dimensions of the inner circumference of the insulating layer 36, thereby suppressing variations in the shape and size of the excitation region C during the manufacturing of the piezoelectric device 10 and improving the resonance characteristics.

[0035] As shown in Figures 4 and 5, in the first embodiment, the distances B1 and B2 between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 in the direction perpendicular to the Z direction differ depending on the position of the inner circumference 33a of the frame electrode 33. In other words, there are two different positions on the inner circumference 33a of the frame electrode 33, where the distances B1 and B2 between the position of the inner circumference 33a of the frame electrode 33 and the outer circumference of the first electrode in the direction perpendicular to the first direction are different. The distances B1 and B2 will be described in more detail below.

[0036] In the following description, the outer peripheral region is defined as the region that overlaps with at least one of the upper electrode 31, lower electrode 32, and frame electrode 33 when viewed in plan in the Z direction, and is located outside the inner circumference of the frame electrode 33. In the first embodiment, the outer peripheral region is the region that overlaps with the frame electrode 33 when viewed in plan in the Z direction. Furthermore, the first outer peripheral region A1 is defined as the region within the outer peripheral region where, when viewed in plan in the Z direction, there are no lead wires 34 and 35 outside the inner circumference 33a of the frame electrode 33, and there is no insulating layer 36 outside the inner circumference 33a of the frame electrode 33. Furthermore, the second outer peripheral region A2 is defined as the region within the outer peripheral region where, when viewed in plan in the Z direction, there are no lead wires 34 and 35 outside the inner circumference 33a of the frame electrode 33, and there is an insulating layer 36 outside the inner circumference of the frame electrode 33.

[0037] As shown in Figure 5, in the first embodiment, in the first outer peripheral region A1, the distance B1 in the direction perpendicular to the Z direction between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 when viewed in the Z direction is smaller than the distance B2 in the direction perpendicular to the Z direction between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 when viewed in the Z direction is smaller than the distance B2 in the direction perpendicular to the Z direction between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 when viewed in the Z direction is.

[0038] This makes it possible to make the widths E1 and E2 of the portion of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction equal in the first outer peripheral region A1 and the second outer peripheral region A2. In other words, the width E1 of the portion of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction in the first outer peripheral region A1 equal to the width E2 of the portion of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction in the second outer peripheral region A2. Therefore, the width of the portion of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction can be kept constant. This makes it possible to keep the width of the frame electrode 33 that contributes to the excitation of the upper electrode 31 and the lower electrode 32 constant, regardless of the manufacturing limit of the width of the frame electrode 33 itself, and improve the resonance characteristics.

[0039] Although a piezoelectric device according to the first embodiment has been described above, the piezoelectric device according to the first embodiment is not limited to the example shown in Figures 1 to 5. For example, the shape of the lower electrode 32 may be a combination of semicircles with different radii. More specifically, the lower electrode 32 has a shape that combines a semicircle with a smaller radius on the side of the lead wiring 35 in the X direction and a semicircle with a larger radius on the side opposite to the lead wiring 35 in the X direction. Here, the semicircles of the upper electrode 31 all have point C1 as the center of the circle. When the shape of the lower electrode 32 is a combination of semicircles with different radii, the radius of the inner arc (inner circumference 36a) of the insulating layer 36 is equal to the radius of the semicircle of the lower electrode 32 on the side of the lead wiring 35 in the X direction and the radius of the semicircle of the upper electrode 31 on the side opposite to the lead wiring 34 in the X direction. Also, the radius of the outer arc of the insulating layer 36 is greater than the radius of the semicircle of the lower electrode 32 on the side opposite to the lead wiring 35 in the X direction. If the shape of the lower electrode 32 is a combination of semicircles with different radii, the radius of the inner arc (inner circumference 33a) of the frame electrode 33 is smaller than the radius of the semicircle on the X-direction lead wiring 35 side of the lower electrode 32 and the radius of the semicircle on the opposite side of the X-direction lead wiring 34 side of the upper electrode 31. Also, the radius of the outer arc (outer circumference 33b) of the frame electrode 33 is the same as the radius of the semicircle on the opposite side of the X-direction lead wiring 35 side of the lower electrode 32.

[0040] (Manufacturing Method) An example of a method for manufacturing a piezoelectric device according to the first embodiment will be described below. Figure 6 is a cross-sectional view illustrating the method for manufacturing a piezoelectric device according to the first embodiment. The method for manufacturing a piezoelectric device according to the first embodiment includes a piezoelectric layer formation step, a lower electrode formation step, a sacrificial layer formation step, an intermediate layer formation step, a support substrate bonding step, a fabricated substrate removal step, an upper electrode formation step, and a sacrificial layer removal step.

[0041] In the piezoelectric layer forming step (step S1), the piezoelectric layer 20 is formed. Specifically, a piezoelectric single crystal substrate is bonded to a production substrate S, and the piezoelectric single crystal substrate is thinned to form the piezoelectric layer 20. The production substrate S is a substrate made of silicon, a quartz substrate or the like. A bonding method for the piezoelectric single crystal substrate is selected from direct bonding, plasma activation bonding, atomic diffusion bonding, and the like. Thinning of the piezoelectric single crystal substrate is performed by grinding and polishing processing such as grinding or chemical mechanical polishing (CMP: Chemical Mechanical Polishing), but the method is not limited thereto, and a method of forming a damaged layer by ion implantation into the piezoelectric single crystal substrate and peeling off the formed damaged layer may also be combined.

[0042] In the lower electrode forming step (step S2), an insulating layer 36, a lower electrode 32, an extraction wiring 35, and a frame electrode 33 are sequentially formed on a second main surface 20b of the piezoelectric layer 20. The insulating layer 36, the lower electrode 32, the extraction wiring 35, and the frame electrode 33 can be formed, for example, by a vapor deposition lift-off method using photolithography.

[0043] In the sacrifice layer forming step (step S3), a sacrifice layer 14S is formed on the second main surface 20b of the piezoelectric layer 20 so as to cover the insulating layer 36, the lower electrode 32, and the frame electrode 33. The sacrifice layer 14S is formed, for example, by a sputtering method. The sacrifice layer 14S is made of, for example, zinc oxide (ZnO).

[0044] In the intermediate layer forming step (step S4), an intermediate layer 12 is formed on the second main surface 20b of the piezoelectric layer 20 so as to cover the sacrifice layer 14S. The intermediate layer 12 is formed, for example, by a sputtering method. A main surface of the intermediate layer opposite to the piezoelectric layer 20 is preferably planarized by CMP or the like for a bonding step described later.

[0045] In the support substrate bonding step (step S5), a support substrate 11 is bonded to the intermediate layer 12. A bonding method can be selected from, for example, direct bonding, plasma activation bonding, atomic diffusion bonding, and the like.

[0046] In the production substrate removal step (step S6), the production substrate S is removed from the piezoelectric layer 20. For the removal of the production substrate S, grinding, cutting and polishing processing by CMP, wet etching, or the like can be used.

[0047] In the upper electrode formation step (step S7), the upper electrode 31, the lead-out wiring 34, and the connection electrodes 41 and 42 are formed in order. Similarly to the lower electrode formation step, the upper electrode 31, the lead-out wiring 34, and the connection electrodes 41 and 42 can be produced by, for example, a vapor deposition lift-off method using photolithography. Further, the connection electrode 42 is formed such that the piezoelectric layer 20 on the lead-out wiring 35 is etched in advance by a method such as reactive ion etching (RIE: Reactive Ion Etching) to provide an opening OP, whereby the lead-out wiring 35 and the connection electrode 42 are connected to each other.

[0048] In the sacrificial layer removal step (step S8), the sacrificial layer 14S is removed. The removal of the sacrificial layer 14S is performed using wet etching or the like. More specifically, an etching hole 20h is formed in the piezoelectric layer 20 by RIE or the like, and an etching solution is injected through the formed etching hole 20h, thereby etching the sacrificial layer 14S.

[0049] Through the above steps, the piezoelectric device 10 according to the first embodiment can be manufactured. Note that the manufacturing method of the piezoelectric device 10 described above is not limited to the above.

[0050] (Second Embodiment) FIG. 7 is a plan view showing a piezoelectric device according to a second embodiment. FIG. 8 is a diagram showing a configuration on the second main surface of the piezoelectric layer of the piezoelectric device according to the second embodiment. In FIG. 8, a region where the insulating layer 36 is provided is indicated by hatching. FIG. 9 is a cross-sectional view taken along the line IX-IX' in FIG. 7. FIG. 10 is an enlarged view of FIG. 7 showing the configuration of the upper electrode, the lower electrode and the frame electrode. In FIG. 10, the excitation region C is indicated by a region surrounded by an alternate long and short dash line. FIG. 11 is a cross-sectional view taken along the line XI-XI' in FIG. 7.

[0051] As shown in Figures 7, 8, and 10, the piezoelectric device 10 according to the second embodiment differs from the first embodiment in that the shape of the upper electrode 31 is circular and the width of the frame electrode 33 varies depending on the position of the inner circumference 33a of the frame electrode 33.

[0052] In the examples of Figures 7 and 10, the shape of the upper electrode 31 is a circle with point C1 as its center. In the examples of Figures 7 and 10, the radius of the circle of the upper electrode 31 is smaller than the radius of the circle of the lower electrode 32.

[0053] In the examples shown in Figures 8 and 10, the radius of the inner arc (inner circumference 36a) of the insulating layer 36 is smaller than the radius of the circle of the upper electrode 31.

[0054] In the examples of Figures 8 and 10, the frame electrode 33 has a shape that combines semicircular rings with different outer peripheries. In Figure 10, the area occupied by the frame electrode 33 is shown with hatching. More specifically, the frame electrode 33 has a shape that combines a semicircular ring with a larger outer radius on the side of the insulating layer 36 in the X direction, and a semicircular ring with a smaller outer radius on the side opposite to the insulating layer 36 in the X direction. The shape and radius of the inner circumference 33a of the frame electrode 33 are the same as in the first embodiment. Here, in all cases, the semicircular rings of the frame electrode 33 have point C1 as the center of the circle. In the examples of Figures 8 and 10, the radius of the outer arc of the frame electrode 33 on the side of the insulating layer 36 in the X direction is smaller than the radius of the lower electrode 32 and larger than the radius of the upper electrode 31. The radius of the outer arc of the frame electrode 33 on the side opposite to the insulating layer 36 in the X direction is smaller than the radius of the upper electrode 31 and equal to the radius of the inner arc (inner circumference 36a) of the insulating layer 36. As shown in Figures 10 and 11, in the second embodiment, in the first outer peripheral region A1, the distance B1 in the direction perpendicular to the Z direction between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 when viewed in the Z direction is the same as the distance B2 in the direction perpendicular to the Z direction between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 when viewed in the Z direction in the second outer peripheral region A2.

[0055] As shown in Figures 8 and 10, in the second embodiment, the widths D1 and D2 of the frame electrode 33 differ depending on the position of the inner circumference 33a of the frame electrode 33. In other words, there are two different positions on the inner circumference 33a of the frame electrode 33, where the widths D1 and D2 of the frame electrode 33 at the inner circumference 33a of the frame electrode 33 are different from each other.

[0056] As shown in Figure 11, in the second embodiment, the width D1 of the frame electrode 33 in the first outer peripheral region A1, viewed in plan in the Z direction, is smaller than the width D2 of the frame electrode 33 in the second outer peripheral region A2.

[0057] This makes it possible to make the widths E1 and E2 of the portion of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction equal in the first outer peripheral region A1 and the second outer peripheral region A2. In other words, the width E1 of the portion of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction in the first outer peripheral region A1 equal to the width E2 of the portion of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction in the second outer peripheral region A2. Therefore, the width of the portion of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction can be kept constant. This makes it possible to keep the width of the frame electrode 33 that contributes to the excitation of the upper electrode 31 and the lower electrode 32 constant, regardless of the manufacturing limit of the width of the frame electrode 33 itself, and improve the resonance characteristics.

[0058] Although a piezoelectric device according to the second embodiment has been described above, the piezoelectric device according to the second embodiment is not limited to the examples shown in Figures 7 to 11. For example, the shape of the lower electrode 32 may be a combination of semicircles with different radii. More specifically, the lower electrode 32 has a shape that combines a semicircle with a smaller radius on the side of the lead wiring 35 in the X direction and a semicircle with a larger radius on the side opposite to the lead wiring 35 in the X direction. Here, the semicircles of the upper electrode 31 all have point C1 as their center. When the shape of the lower electrode 32 is a combination of semicircles with different radii, the radius of the circle of the upper electrode 31 is larger than the radius of the semicircle of the lower electrode 32 on the side of the lead wiring 35 in the X direction, and smaller than the radius of the semicircle of the lower electrode 32 on the side opposite to the lead wiring 35 in the X direction. If the shape of the lower electrode 32 is a combination of semicircles with different radii, the radius of the inner arc (inner circumference 36a) of the insulating layer 36 is equal to the radius of the semicircle on the X-direction lead wiring 35 side of the lower electrode 32, and smaller than the radius of the circle of the upper electrode 31. If the shape of the lower electrode 32 is a combination of semicircles with different radii, the radius of the outer arc of the frame electrode 33 on the X-direction insulating layer 36 side is the same as the radius of the semicircle on the side of the lower electrode 32 opposite to the X-direction lead wiring 35 side, and the radius of the outer arc of the frame electrode 33 on the side of the X-direction insulating layer 36 opposite to the X-direction lead wiring 35 side is the same as the radius of the semicircle on the X-direction lead wiring 35 side of the lower electrode 32. That is, in the example of Figure 10, the outer circumference 33b of the frame electrode 33 coincides with the outer circumference 32a of the lower electrode 32 when viewed in plan in the Z direction.

[0059] (Third Embodiment) Figure 12 is a plan view showing a piezoelectric device according to the third embodiment. Figure 13 is a diagram showing the configuration of the piezoelectric layer on the second main surface of the piezoelectric device according to the third embodiment. In Figure 13, the region where the insulating layer 36 is located is shown by hatching. Figure 14 is a cross-sectional view along the line XIV-XIV' in Figure 12. Figure 15 is an enlarged view of Figure 12 showing the configuration of the upper electrode, lower electrode and frame electrode. In Figure 15, the excitation region C is shown as a region enclosed by a dashed line. Figure 16 is a cross-sectional view along the line XVI-XVI' in Figure 12.

[0060] As shown in Figures 12, 13, and 15, the piezoelectric device 10 according to the third embodiment differs from the first embodiment in that the width of the frame electrode 33 varies depending on the position of the inner circumference 33a of the frame electrode 33, and differs from the second embodiment in that the shape of the upper electrode 31 is not circular.

[0061] In the examples shown in Figures 12 and 15, the shape of the upper electrode 31 is a combination of semicircles with different radii, similar to the first embodiment. That is, the upper electrode 31 has a shape that combines a semicircle with a larger radius on the side of the lead wiring 34 in the X direction and a semicircle with a smaller radius on the side opposite to the lead wiring 34 in the X direction. Here, the semicircles of the upper electrode 31 all have point C1 as their center.

[0062] In the examples shown in Figures 12 and 15, the radius of the semicircle on the side of the upper electrode 31 opposite to the X-direction lead wiring 34, and the radius of the semicircle on the X-direction lead wiring 34 side of the upper electrode 31, are smaller than the radius of the semicircle on the X-direction lead wiring 35 side of the lower electrode 32.

[0063] In the examples of Figures 13 and 15, the radius of the inner arc (inner circumference 36a) of the insulating layer 36 is smaller than the radius of the lower electrode 32 and the radius of the semicircle on the X-direction lead wiring 34 side of the upper electrode 31, and equal to the radius of the semicircle on the opposite side of the X-direction lead wiring 34 side of the upper electrode 31.

[0064] In the examples of Figures 13 and 15, the shape of the frame electrode 33 is a combination of semicircular rings with different outer circumferences, similar to the second embodiment. In Figure 15, the area occupied by the frame electrode 33 is shown with hatching. In the examples of Figures 12 and 15, the radius of the outer arc of the frame electrode 33 on the insulating layer 36 side in the X direction is smaller than the radius of the lower electrode 32 and larger than the radius of the semicircle on the lead wiring 34 side of the upper electrode 31 in the X direction. The radius of the outer arc of the frame electrode 33 on the side opposite to the insulating layer 36 side in the X direction is smaller than the radius of the upper electrode 31 and equal to the radius of the semicircle on the side opposite to the lead wiring 34 side of the upper electrode 31 in the X direction and the radius of the inner arc (inner circumference 36a) of the insulating layer 36.

[0065] As shown in Figures 15 and 16, in the third embodiment, when viewed from above in the Z direction, the distances B1 and B2 between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 in a direction perpendicular to the Z direction differ depending on the position of the inner circumference 33a of the frame electrode 33.

[0066] As shown in Figure 16, in the third embodiment, in the first outer peripheral region A1 viewed in the Z direction, the distance B1 in the direction perpendicular to the Z direction between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 is smaller than the distance B2 in the second outer peripheral region A2 viewed in the Z direction between the inner circumference 33a of the frame electrode 33 and the outer circumference 31a of the upper electrode 31 in the direction perpendicular to the Z direction.

[0067] As shown in Figures 13 and 15, in the third embodiment, the widths D1 and D2 of the frame electrode 33 differ depending on the position of the inner circumference 33a of the frame electrode 33.

[0068] As shown in Figure 16, in the third embodiment, the width D1 of the frame electrode 33 in the first outer peripheral region A1, viewed in plan in the Z direction, is smaller than the width D2 of the frame electrode 33 in the first outer peripheral region A1.

[0069] This makes it possible to make the widths E1 and E2 of the frame electrode 33 that overlap with the excitation region C when viewed in plan in the Z direction equal in the first outer peripheral region A1 and the second outer peripheral region A2. In other words, the width E1 of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction in the first outer peripheral region A1 equal to the width E1 of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction in the second outer peripheral region A2. Therefore, the width of the frame electrode 33 that overlaps with the excitation region C when viewed in plan in the Z direction can be kept constant. This makes it possible to keep the width of the frame electrode 33 that contributes to the excitation of the upper electrode 31 and the lower electrode 32 constant, regardless of the manufacturing limit of the width of the frame electrode 33 itself, and improve the resonance characteristics.

[0070] Although a piezoelectric device according to the third embodiment has been described above, the piezoelectric device according to the third embodiment is not limited to the examples shown in Figures 12 to 16. For example, the shape of the lower electrode 32 may be a combination of semicircles with different radii. When the shape of the lower electrode 32 is a combination of semicircles with different radii, the lower electrode 32 has a shape that combines, for example, a semicircle with a smaller radius on the side of the lead wiring 35 in the X direction and a semicircle with a larger radius on the side opposite to the lead wiring 35 in the X direction. Here, all semicircles of the upper electrode 31 have point C1 as the center of the circle. The radius is the same as that of the semicircle of the lower electrode 32 on the side of the lead wiring 35 in the X direction. Also, the radius of the semicircle of the upper electrode 31 on the side of the lead wiring 34 in the X direction is smaller than the radius of the semicircle of the lower electrode 32 on the side opposite to the lead wiring 35 in the X direction. If the shape of the lower electrode 32 is a combination of semicircles with different radii, the radius of the inner arc (inner circumference 36a) of the insulating layer 36 is equal to the radius of the semicircle on the X-direction lead wiring 35 side of the lower electrode 32 and the radius of the semicircle on the opposite side of the X-direction lead wiring 34 side of the upper electrode 31.

[0071] (Fourth Embodiment) Figure 17 is a diagram showing the configuration of the second main surface of the piezoelectric layer of the piezoelectric device according to the fourth embodiment. As shown in Figure 17, the piezoelectric device according to the fourth embodiment differs from the second embodiment in that the shape of the outer circumference 33b of the frame electrode 33 is a convex closed curve.

[0072] In this disclosure, the shape of the outer circumference 33b of the frame electrode 33 is described as a convex closed curve when viewed in plan in the Z direction, and a line segment is drawn connecting any two points on the outer circumference 33b of the frame electrode 33, and the entire line segment never extends beyond the outer circumference 33b. As a result, in the fourth embodiment, the width of the outer circumference 33b of the frame electrode 33 changes smoothly. This suppresses unwanted waves generated at locations where the width of the frame electrode 33 changes significantly, thereby further improving the resonance characteristics.

[0073] In the example shown in Figure 17, the shape of the frame electrode 33 is such that the width of the frame electrode 33 decreases smoothly in the semicircular ring opposite to the insulating layer 36 side in the X direction. Here, the shape and radius of the inner circumference 33a of the frame electrode 33 and the outer circumference 33b of the semicircular ring on the insulating layer 36 side in the X direction are the same as in the second embodiment.

[0074] The embodiments described above are provided to facilitate understanding of the present invention and are not intended to limit its interpretation. The present invention may be modified or improved without departing from its spirit, and equivalents thereof are also included.

[0075] For example, in the embodiments described above, the first electrode is the upper electrode 31 and the second electrode is the lower electrode 32, but the invention is not limited to this, and the first electrode may be the lower electrode and the second electrode may be the upper electrode.

[0076] 10 Piezoelectric device 11 Support substrate 12 Intermediate layer 13 Support member 14 Recess 20 Piezoelectric layer 20a First main surface 20b Second main surface 31 Upper electrode 32 Lower electrode 33 Frame electrode 34, 35 Lead-out wiring 36 Insulating layer A1 First outer region A2 Second outer region

Claims

1. A piezoelectric layer having thickness in a first direction; a first electrode provided on one side of the piezoelectric layer in the first direction; a second electrode provided on the other side of the piezoelectric layer in the first direction; an insulating layer provided on one side of the piezoelectric layer in the first direction, with a portion of it located between the piezoelectric layer and the second electrode; and a frame electrode provided on one side of the second electrode in the first direction, wherein the region superimposed on the piezoelectric layer, the first electrode and the second electrode when viewed in plan in the first direction, and not superimposed on the insulating layer when viewed in plan in the first direction, is defined as the excitation region, the frame electrode is provided along the outer circumference of the excitation region so as to surround the excitation region, and the insulating layer superimposed on a portion of the outer circumference of the first electrode, a portion of the outer circumference of the second electrode and a portion of the outer circumference of the frame electrode when viewed in plan in the first direction. A piezoelectric device having two different positions on the inner circumference of the frame electrode, where at least one of the distance between the position and the outer circumference of the first electrode in a direction perpendicular to the first direction, and the width of the frame electrode at the position, is different from each other.

2. Further comprising: a first lead wire connected to the first electrode; and a second lead wire connected to the second electrode, wherein, when viewed in plan in the first direction, the region that overlaps with at least one of the first electrode, the second electrode, and the frame electrode, and which is outside the inner circumference of the frame electrode, is defined as the outer peripheral region; of the outer peripheral region, when viewed in plan in the first direction, the region where the first lead wire and the second lead wire are not located outside the inner circumference of the frame electrode, and where the insulating layer is not located outside the inner circumference of the frame electrode, is defined as the first outer peripheral region; and of the outer peripheral region, when viewed in plan in the first direction, the region where the first lead wire and the second lead wire are not located outside the inner circumference of the frame electrode, and where the insulating layer is located outside the inner circumference of the frame electrode, is defined as the second outer peripheral region. The piezoelectric device according to claim 1, wherein in the first outer peripheral region, the distance between the inner circumference of the frame electrode, the outer circumference of the first electrode, and the direction perpendicular to the first direction when viewed in plan in the first direction is smaller than the distance between the inner circumference of the frame electrode, the outer circumference of the first electrode, and the direction perpendicular to the first direction when viewed in plan in the first direction in the second outer peripheral region.

3. A piezoelectric device according to claim 1, further comprising: a first lead wire connected to the first electrode; and a second lead wire connected to the second electrode, wherein, when viewed in plan in the first direction, the region that overlaps with at least one of the first electrode, the second electrode, and the frame electrode, and is located outside the inner circumference of the frame electrode, is defined as the outer peripheral region; of the outer peripheral region, when viewed in plan in the first direction, the region where the first lead wire and the second lead wire are not located outside the inner circumference of the frame electrode, and where the insulating layer is not located outside the inner circumference of the frame electrode, is defined as the first outer peripheral region; of the outer peripheral region, when viewed in plan in the first direction, the region where the first lead wire and the second lead wire are not located outside the inner circumference of the frame electrode, and where the insulating layer is located outside the inner circumference of the frame electrode, is defined as the second outer peripheral region, wherein the width of the frame electrode in the first outer peripheral region is smaller than the width of the frame electrode in the second outer peripheral region.

4. The piezoelectric device according to claim 2 or 3, wherein the width of the portion of the frame electrode that overlaps with the excitation region when viewed in plan in the first direction is equal in the first outer peripheral region and the second outer peripheral region.

5. The piezoelectric device according to any one of claims 1 to 4, wherein, when viewed in plan in the first direction, the shape of the outer circumference of the frame electrode is a convex closed curve.

6. The piezoelectric device according to any one of claims 1 to 5, further comprising a support member provided on the other side of the piezoelectric layer in the first direction.

7. The piezoelectric device according to any one of claims 1 to 6, wherein the width of the portion of the frame electrode that overlaps with the excitation region when viewed in plan in the first direction is constant.

8. The piezoelectric device according to any one of claims 1 to 7, wherein the piezoelectric layer comprises lithium niobate or lithium tantalate.

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