Bulk acoustic wave resonator, filter and electronic device with concave and air wing structure

Abstract

The present invention relates to a bulk acoustic wave resonator, comprising: a substrate; an acoustic mirror; a bottom electrode, arranged above the substrate; a top electrode; and a piezoelectric layer, arranged above the bottom electrode and between the bottom electrode and the top electrode, wherein: the overlapping area of ​​the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode in the thickness direction of the resonator constitutes the effective area of ​​the resonator; one side of the top electrode has an electrode connection portion, and the other side has an air wing structure; and the piezoelectric layer is provided with a recessed structure, and the recessed structure has an inner edge and an outer edge. The present invention also relates to a filter having the above resonator, and an electronic device having the above resonator or filter.

Description

Technical Field

[0001] Embodiments of the present invention relate to the semiconductor field, and in particular, to a bulk acoustic wave resonator with a recess and an air wing structure, a filter having the resonator, and an electronic device having the resonator or the filter. Background Art

[0002] In recent years, semiconductor devices based on silicon materials, especially integrated circuit chips, have achieved rapid development and have firmly occupied the mainstream position in the industry. Thin film bulk wave resonators made by longitudinal resonance of piezoelectric thin films in the thickness direction have become a feasible alternative to surface acoustic wave devices and quartz crystal resonators in wireless communication systems.

[0003] like Figure 1 As shown, a film bulk acoustic resonator (FBAR) includes: a substrate P00, an acoustic reflection structure P10 (which may be a cavity, a Bragg reflection layer, or other equivalent structures) located on or embedded in the substrate, a bottom electrode P20 located on the acoustic reflection structure P10 and the substrate P00, a piezoelectric layer film P30 covering the bottom electrode P20 and the upper surface of the substrate P00, and a top electrode P40 located on the piezoelectric layer, etc., wherein the overlapping area of ​​the acoustic reflection structure P10, the bottom electrode P20, the piezoelectric layer P30, and the top electrode P40 in the thickness direction constitutes an effective acoustic area AR of the resonator, and the top electrode, the piezoelectric layer, and the bottom electrode constitute a sandwich structure.

[0004] When the BAW resonator is in an ideal working state, only piston mode sound waves propagate in the sandwich structure, and the energy of this vibration mode is confined within the effective acoustic region AR. However, in reality, in the sandwich structure of the resonator, there are not only piston mode vibrations but also transversely propagating vibration modes, and the energy of the latter will dissipate in the transverse direction from the piezoelectric layer in the sandwich structure to the piezoelectric layer and other structures outside the sandwich structure (the part composed of the electrodes and the piezoelectric layer within the AR) (indicated by the arrow PE), resulting in a decrease in the quality factor (Q value) of the resonator, thereby deteriorating the performance of the resonator. Summary of the invention

[0005] In order to alleviate or solve the above problems in the prior art, the present invention is proposed.

[0006] According to one aspect of an embodiment of the present invention, a bulk acoustic wave resonator is provided, comprising:

[0007] substrate;

[0008] Acoustic mirror;

[0009] A bottom electrode disposed above the substrate;

[0010] a top electrode; and

[0011] a piezoelectric layer disposed above the bottom electrode and between the bottom electrode and the top electrode,

[0012] in:

[0013] The overlapping area of ​​the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode in the thickness direction of the resonator constitutes the effective area of ​​the resonator;

[0014] The top electrode has an electrode connection portion on one side and an air wing structure on the other side; and

[0015] The piezoelectric layer is provided with a concave structure, and the concave structure has an inner edge and an outer edge.

[0016] Optionally, in a vertical projection, the recessed structure is located on the inner side of an edge of the acoustic mirror.

[0017] Optionally, in a vertical projection, an inner edge of the recessed structure coincides with an edge of the air wing structure.

[0018] Optionally, in vertical projection, the edge of the air wing structure is located between the inner edge and the outer edge of the recessed structure, or the outer edge of the recessed structure coincides with the edge of the air wing structure, or the recessed structure is located between the edge of the air wing structure and the edge of the top electrode, or the inner edge of the recessed structure coincides with the edge of the top electrode. Further optionally, in vertical projection, the radial distance X between the inner edge of the recessed structure and the edge of the top electrode is not greater than 10μm. In vertical projection, the radial distance X between the recessed structure and the edge of the top electrode may be: 0-10μm, further, 0μm≤X≤1μm, or 2.5μm≤X≤4.5μm, or 6μm≤X≤8μm. Further optionally, the gap height of the air wing structure is 0.02μm-0.5μm.

[0019] Optionally, in a vertical projection, the edge of the top electrode is located between the inner edge and the outer edge of the recessed structure; or the outer edge of the recessed structure coincides with the edge of the top electrode; or the outer edge of the recessed structure is located on the inner side of the edge of the top electrode.

[0020] Optionally, the recessed structure includes a recessed portion. The recessed portion may be a stepped recessed portion.

[0021] Optionally, the recessed structure has at least two recesses. The at least two recesses may be spaced apart from each other in a radial direction.

[0022] Optionally, in a vertical projection, an outer edge of the recessed structure is located inside an edge of the bottom electrode.

[0023] Optionally, in a vertical projection, an outer edge of the recessed structure is located inside an edge of the acoustic mirror.

[0024] Optionally, the electrode connecting portion is formed with a bridge portion; and the recessed structure is a shaped recessed structure.

[0025] Optionally, the width of the recessed structure ranges from 0.5 μm to 4 μm, or one quarter of the wavelength of the S1 mode Lamb wave at the parallel resonant frequency or an odd multiple thereof; and the depth of the recessed structure ranges from 0.02 μm to 0.5 μm, or 5% to 100% of the thickness of the piezoelectric layer, further, 10% to 40%.

[0026] An embodiment of the present invention further relates to a filter, comprising the above-mentioned BAW resonator.

[0027] An embodiment of the present invention also relates to an electronic device, comprising the above-mentioned filter or the above-mentioned resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following description and accompanying drawings may better help understand these and other features and advantages of various embodiments disclosed by the present invention, in which the same reference numerals always represent the same components, wherein:

[0029] Figure 1 is a cross-sectional schematic diagram of a bulk acoustic wave resonator in the prior art;

[0030] Figure 2 is a schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;

[0031] Figure 2A A schematic diagram for exemplifying the sound wave reflection effect of the concave structure;

[0032] Figures 3A to 3H Along Figure 2 A partial cross-sectional view of a left portion of the boundary S1 cut along A1-A2 in FIG. 1 according to an exemplary embodiment of the present invention;

[0033] Figures 4A to 4H Along Figure 2 A partial cross-sectional view of a right portion of the boundary S2 cut along A1-A2 in FIG. 1 according to an exemplary embodiment of the present invention;

[0034] Figure 5 A schematic diagram for explaining the technical effect of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention;

[0035] Figure 6is a schematic structural diagram of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention, wherein the width of the recessed structure is D1, the depth is H1, and the radial distance between the inner edge of the recessed structure and the edge of the top electrode is X1;

[0036] Figure 7 Graph showing the relationship between the parallel resonant impedance (Rp) and the radial distance X between the recessed structure and the edge of the top electrode;

[0037] Figure 8 is the dispersion curve of the S1 mode at the parallel resonant frequency of the BAW resonator. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further specifically described below by examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0039] The bulk acoustic wave resonator with a piezoelectric layer having a recessed structure according to an embodiment of the present invention will be described below by way of example with reference to the accompanying drawings.

[0040] Figure 2 A schematic top view of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention is given as follows: Figure 2 As shown, the resonator includes a substrate 00, a bottom electrode 20 located on the substrate, a piezoelectric layer 30 located on the bottom electrode and the substrate, a recessed structure 31 (the channel portion shown in the shaded portion) located on the upper surface of the piezoelectric layer, a top electrode 40 located on the piezoelectric layer, and a pin (i.e., an electrode connecting portion) 43 of the top electrode.

[0041] Figure 2 The acoustic reflection structure (acoustic mirror) located on the upper surface of the substrate and the pins of the bottom electrode are not shown.

[0042] Refer to the following Figure 2A The function of the concave structure is illustrated as follows. Figure 2A As shown, the upper surface of the piezoelectric layer 30 has a concave structure 31, which forms two boundaries of B1 and B2 with mismatched acoustic impedance in the piezoelectric layer. When the sound wave propagates laterally from the effective acoustic area (not shown in the figure) located on the right side of B1 to the B1 or B2 area, it will be reflected back to the effective area of ​​the resonator, thereby reducing energy leakage.

[0043] The embodiments of the present invention accordingly propose the following technical solutions: Figure 2 , 3A to 3H as well as 4A to 4H As shown:

[0044] A bulk acoustic wave resonator, comprising:

[0045] Base 00;

[0046] Acoustic mirror 10;

[0047] A bottom electrode 20 is disposed above the substrate 00;

[0048] A top electrode 40; and

[0049] The piezoelectric layer 30 is disposed above the bottom electrode and between the bottom electrode and the top electrode.

[0050] in:

[0051] The overlapping area of ​​the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode in the thickness direction of the resonator constitutes the effective area AR of the resonator (see Figure 1 );

[0052] One side of the top electrode has an electrode connection portion 43 (see Figure 2 ), and the other side has an air wing structure (see, for example Figure 3A , the air wing structure has boundaries D1 and T1, boundary T1 also constituting the edge of the top electrode); and

[0053] The piezoelectric layer is provided with a recessed structure 31 , and the recessed structure 31 has an inner edge (a side of the recessed structure close to the effective area) and an outer edge (a side of the recessed structure away from the effective area).

[0054] Figure 5 Schematic diagram for explaining the technical effect of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention. Figure 5 As shown, in the present invention, when the resonator is working, the reflection structure A formed by the air wing and the reflection structure B formed by the recessed structure not only vibrate respectively, but also can respectively transfer part of the sound wave energy (Q A and Q B ) is reflected back to the effective area of ​​the resonator. At the same time, due to the strong acoustic coupling between the reflective structure A and the structure B, the mutual influence between the two eventually leads to a resonance similar to that of a tuning fork. When properly matched together, the two structures form a coupled structure and also reflect another energy Q A+B , then the total reflected energy Q = Q A +Q B +Q A+B Greater than Q A +Q B The Q value improvement effect of the combination of the air wing and the concave is higher than the simple superposition of the sound wave reflection effect of the suspension wing and the concave.

[0055] Therefore, in the present invention, not only can the recessed structure and the air wing structure respectively reflect the sound waves that propagate laterally beyond the boundary T1 back into the sandwich area, but the recessed structure and the air wing structure also jointly form a tuning fork-like structure, which can further reflect the sound waves and reduce energy leakage, thereby improving the Q value.

[0056] In the present invention, the material of the substrate 00 may be selected from but is not limited to: single crystal silicon, gallium arsenide, quartz, sapphire, silicon carbide, etc.

[0057] In the present invention, the materials of the electrodes 20 and 40 may be selected from but are not limited to: molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or a composite of the above metals or an alloy thereof.

[0058] In the present invention, the material of the piezoelectric layer 30 may be selected from but not limited to: aluminum nitride, zinc oxide, lead zirconate titanate (PZT), lithium niobate, etc. Optionally, a certain proportion of rare earth element impurities may be added to the material.

[0059] In the present invention, the piezoelectric layer is a thin film with a thickness of less than 10 microns, has a single crystal or polycrystalline microstructure, and can be made by sputtering or deposition process.

[0060] In the present invention, the acoustic mirror 10 is not limited to the acoustic mirror structure shown in the example.

[0061] Figure 3A For along Figure 2 A partial cross-sectional view of the left portion of the boundary S1 according to an exemplary embodiment of the present invention taken along line A1 - A2 in FIG.

[0062] Figure 3A In the structure, the acoustic mirror (or acoustic reflection structure) 10 is located on the upper surface of the substrate 00 and has a left boundary C1, the top electrode 40 has a left boundary T1, and a recessed structure 31 is embedded in the upper surface of the piezoelectric layer 30, and the recessed structure is a rectangle ABCD. It should be noted that the shape of the recessed structure 31 is not limited thereto, and based on actual applications or actual manufacturing processes, it can be, for example, an inverted trapezoidal cross section.

[0063] The recessed structure 31 has a width W30 and a depth H30. Figure 3A In the figure, the right side CD (inner edge) of the recessed structure 31 coincides with the boundary D1 of the air wing structure.

[0064] The width W30 of the recessed structure (see Figure 3A ) has a value range of 0.5 μm to 4 μm, further 1 to 3 μm, and in addition to the above endpoint values, can also be 2 μm; or one quarter of the wavelength of the S1 mode Lamb wave at the parallel resonant frequency or an odd multiple thereof.

[0065] The depth of the recessed structure H30 (see Figure 3A ) ranges from 0.02 microns to 0.5 microns, further from 0.1 microns to 0.3 microns, and in addition to the above endpoint values, it can also be 0.2 microns.

[0066] In the present invention, the depth of the recessed structure is the maximum depth of the recessed structure; and the width of the recessed structure is the width of the top opening of the recessed structure.

[0067] The following is a brief description of the S1 mode Lamb wave wavelength λ at the parallel resonant frequency of the resonator. When the BAW resonator is working, a large number of vibrations will be generated in the sandwich structure. If these vibrations are plotted as dispersion curves according to the relationship between their frequency (f) and wave number (k), curves of multiple modes can be obtained, one of which is called the S1 mode (the curves of the other modes are not shown in the figure). Figure 8 ), which has Figure 8 The dispersion curve is shown in the shape of the horizontal axis, where the horizontal axis is the wave number and the vertical axis is the vibration frequency. The vibration frequency is the parallel resonance frequency f p When the corresponding wave number is k p , and the wavelength λ of the S1 mode is defined as follows:

[0068] exist Figure 3A In the embodiment, the inner edge of the recessed structure coincides with the edge D1 of the air wing structure; however, the recessed structure may also be located at other positions.

[0069] like Figure 3B As shown, in vertical projection, the edge of the air wing structure is located within the recessed structure.

[0070] like Figure 3C As shown, in vertical projection, the outer edge of the recessed structure coincides with the edge of the air wing structure.

[0071] like Figure 3D As shown, in vertical projection, the recessed structure is located between the edge of the air wing structure and the edge of the top electrode.

[0072] like Figure 3E As shown, in a vertical projection, the inner edge of the recessed structure coincides with the edge of the top electrode.

[0073] like Figure 3F As shown, in a vertical projection, the edge of the top electrode is located between the inner edge and the outer edge of the recessed structure.

[0074] like Figure 3G As shown, in a vertical projection, the outer edge of the recessed structure coincides with the edge of the top electrode.

[0075] like Figure 3HAs shown, in a vertical projection, the outer edge of the recessed structure is located inside the edge of the top electrode.

[0076] Furthermore, although not shown, in a vertical projection, the inner edge of the recessed structure may be located outside the edge D1 of the air wing structure.

[0077] In addition, although not shown, the recessed structure may be filled with other materials, and the filling material may be a non-metal such as silicon dioxide, silicon carbide, silicon nitride, etc., or a metal such as titanium, molybdenum, magnesium, aluminum, etc.

[0078] The influence of the distance between the recessed structure and the edge of the top electrode on the Q value of the resonator is described below. Figure 6 : is a schematic diagram of the structure of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention, wherein the width of the recessed structure is D1, the depth is H1, the distance between the inner edge of the recessed structure and the edge of the top electrode is X1, Figure 7 A graph showing the relationship between the parallel resonant impedance (Rp) and the radial distance X1 between the recessed structure and the edge of the top electrode is shown.

[0079] exist Figure 7 In the example, X1 changes from 0 to 7 microns, with each change step of 0.5 microns. The other two parameters D and H are fixed to two groups. Each time X1 changes, D1 and H1 remain unchanged. Specifically, Figure 5 The following three sets of change data are shown:

[0080] (1) D = 1um, H = 1000A, parallel resonant impedance Rp1 changes with X1.

[0081] (2) D = 1um, H = 3000A, parallel resonant impedance Rp2 changes with X1.

[0082] Comparing the above data with the known parallel resonant impedance Rp0 of a resonator without a recessed structure and plotting the result, we can obtain Figure 7 The curve graph shown (the higher the Rp value, the higher the Q value of the resonator and the better the performance).

[0083] Depend on Figure 7 The results show that the performance of the resonator with a recessed structure in terms of Q value is higher than that of the traditional resonator without a recessed structure in most ranges of X. In addition, in some ranges of X, the recessed structure can significantly improve the Q value of the resonator, such as at X1 = 0 microns and around X1 = 3.5 microns.

[0084] In view of the above, in the embodiment of the present invention, X1 is not greater than 10 micrometers, and further ranges from 0 μm ≤ X1 ≤ 1 μm, or 2.5 μm ≤ X1 ≤ 4.5 μm, or 6 μm ≤ X1 ≤ 8 μm. Accordingly, the gap height of the air wing structure is 0.02 μm-0.5 μm.

[0085] It should be noted that the recessed structure is not limited to being disposed on the upper side of the piezoelectric layer (such as Figure 3B ), may also be disposed on the lower side of the piezoelectric layer, or between the upper and lower sides, or penetrate the piezoelectric layer in the thickness direction of the resonator (e.g., similarly, see Figure 4F The recessed structure 31).

[0086] In addition, the recessed structure may also be a stepped recessed structure (for example, similarly, see Figure 4G Specifically, the recessed structure 31 has components with different depths. The stepped recess not only increases the number of acoustic impedance mismatching boundaries, but also enriches the reflection wavelength.

[0087] exist Figures 3A to 3H In the example of FIG. 1 , the recessed structure is a single recessed structure, but the present invention is not limited thereto. The recessed structure may also include at least two recesses (for example, similarly, see Figure 4H The two recesses may be spaced apart from each other by a distance in the radial direction. It should be noted that the widths of the two recesses may be the same or different; in addition, the depths of the two recesses may also be different.

[0088] Figure 4A For along Figure 2 A partial cross-sectional view of the right side of the boundary S2 obtained by sectioning along A1-A2 in FIG. 1 according to an exemplary embodiment of the present invention. As shown in the figure, the electrode connecting portion 43 is formed with a bridge portion (i.e., the arched portion in the figure); and the recessed structure 31 is an annular recessed structure passing through the electrode connecting portion 43 (see Figure 2 the ring shape in the figure).

[0089] like Figure 4A As shown, the acoustic mirror 10 has a right boundary C2, the top electrode 40 has a right boundary T2, the top electrode has an electrode connection structure (i.e., a pin) 43, the electrode connection structure 43 has an arched bridge structure, and the upper surface of the piezoelectric layer 30 is provided with a recessed structure 31. Figure 4A In the vertical projection, the edge or boundary T2 of the top electrode is located between the inner edge and the outer edge of the recessed structure. However, the recessed structure may also be located at other positions.

[0090] The left edge of the recessed structure 31 (the inner edge of the recessed structure) coincides with the boundary C2.

[0091] like Figure 4B As shown, in the vertical projection, the outer edge of the recessed structure coincides with the edge of the top electrode.

[0092] like Figure 4C As shown, in the vertical projection, the outer edge of the recessed structure is on the inner side of the edge of the top electrode.

[0093] like Figure 4D As shown, in the vertical projection, the inner edge of the recessed structure coincides with the edge of the top electrode.

[0094] like Figure 4E As shown, in vertical projection, the recessed structure is located between the edge of the top electrode and the edge of the acoustic mirror.

[0095] In addition, although not shown, the inner edge of the recessed structure may be located outside the edge of the acoustic mirror.

[0096] See also Figure 3A-3H In an optional embodiment, in a vertical projection, the outer edge of the recessed structure is located inside the edge of the bottom electrode.

[0097] In an optional embodiment, the outer edge of the recessed structure is located inside the edge of the bottom electrode.

[0098] Optionally, in a vertical projection, an outer edge of the recessed structure is located inside an edge of the acoustic mirror.

[0099] In an embodiment of the present invention, the width of the recessed structure ranges from 0.5 μm to 4 μm, or is one quarter of the wavelength of the S1 mode Lamb wave at the parallel resonant frequency or an odd multiple thereof; and the depth of the recessed structure ranges from 0.02 μm to 0.5 μm.

[0100] In the present invention, the expression "vertical projection" is used, as shown in the attached Figure 3A As shown, it should be understood that the projection is made in the thickness direction of the resonator, for example, Figure 3A In the embodiment, the dotted lines or boundaries C1 and T1 can also be considered as vertical projection lines. The "coincidence" in the present invention means being on the same vertical projection line, or substantially on the same vertical projection line. The "edge" in the present invention means the outermost edge or the innermost edge of the corresponding component.

[0101] Although not shown, an embodiment of the present invention also relates to a filter including the above-mentioned BAW resonator.

[0102] An embodiment of the present invention also relates to an electronic device, comprising the above-mentioned resonator or the above-mentioned filter.

[0103] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bulk acoustic wave resonator, comprising: substrate; Acoustic mirror; A bottom electrode disposed above the substrate; Top electrode; and a piezoelectric layer disposed above the bottom electrode and between the bottom electrode and the top electrode, in: The overlapping area of ​​the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode in the thickness direction of the resonator constitutes the effective area of ​​the resonator; The top electrode has an electrode connection portion on one side and an air wing structure on the other side; The piezoelectric layer is provided with a concave structure, wherein the concave structure has an inner edge and an outer edge; On the side where the non-electrode connection portion of the top electrode is located, in vertical projection, the outer edge of the recessed structure is located on the inner side of the edge of the acoustic mirror, and the inner edge of the recessed structure is located on the outer side of the edge of the top electrode and is spaced a certain distance apart.

2. The resonator according to claim 1, wherein: On the side where the non-electrode connection portion of the top electrode is located, in a vertical projection, the inner edge of the recessed structure coincides with the edge of the air wing structure.

3. The resonator of claim 1, wherein: On the side where the non-electrode connecting portion of the top electrode is located, in a vertical projection, the edge of the air wing structure is located between the inner edge and the outer edge of the recessed structure, or the outer edge of the recessed structure coincides with the edge of the air wing structure, or the recessed structure is located between the edge of the air wing structure and the edge of the top electrode.

4. The resonator of claim 2, wherein: On the side where the non-electrode connection portion of the top electrode is located, in a vertical projection, a radial distance X between an inner edge of the recessed structure and an edge of the top electrode is not greater than 10 μm.

5. The resonator of claim 4, wherein: On the side where the non-electrode connection portion of the top electrode is located, in a vertical projection, a radial distance X between the recessed structure and an edge of the top electrode is: 0 μm≤X≤1 μm, or 2.5 μm≤X≤4.5 μm, or 6 μm≤X≤8 μm.

6. The resonator of claim 5, wherein: The air wing structure has a void height of 0.02 μm-0.5 μm.

7. The resonator of claim 1, wherein: The recessed structure includes a recess.

8. The resonator of claim 7, wherein: The depression is a stepped depression.

9. The resonator of claim 1, wherein: The recessed structure has at least two recesses.

10. The resonator of claim 9, wherein: The at least two recesses are spaced apart from each other in the radial direction.

11. The resonator of claim 1 , wherein: The electrode connecting portion is formed with a bridge portion; and The recessed structure is an annular recessed structure.

12. The resonator according to any one of claims 1 to 11, wherein: The width of the concave structure is in the range of 0.5 μm to 4 μm, or one quarter of the wavelength of the S1 mode Lamb wave at the parallel resonant frequency or an odd multiple thereof; and The depth of the concave structure ranges from 0.02 μm to 0.5 μm, or 5% to 100% of the thickness of the piezoelectric layer.

13. The resonator of claim 12, wherein: The depth of the concave structure ranges from 10% to 40% of the thickness of the piezoelectric layer.

14. A filter comprising the BAW resonator according to any one of claims 1 to 13.

15. An electronic device comprising the filter according to claim 14 or the resonator according to any one of claims 1 to 13.

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