Bulk acoustic wave resonator

Abstract

The present invention supports the implementation of structures for bulk acoustic wave resonators that can increase piezoelectric coupling and suppress parasitic modes. The grooves between the electrodes of the disclosed digital to analog converter (IDT) reduce the generation of parasitic modes and prevent the propagation of the parasitic modes and the resonance accumulation of the amplitude of the parasitic modes. In addition, the grooves between the disclosed IDT electrodes suppress a high order mode in a horizontal direction and increase the resonant-anti-resonant frequency gap of the bulk acoustic wave resonator.

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of bulk acoustic wave devices, and more specifically, to a bulk acoustic resonator configured to increase piezoelectric coupling and suppress spurious modes, and related electronic devices. BACKGROUND

[0002] Acoustic resonator devices utilize a thin piezoelectric layer of sub-micron thickness as the resonator material. Examples include bulk acoustic resonators (BARs), such as horizontally-excited bulk acoustic resonators (XBARs) or vertically-excited bulk acoustic resonators (FBARs, YBARs). At least in some cases, such conventional acoustic resonator devices can suffer from some drawbacks.

[0003] For example, in the case of a YBAR, a floating metal layer can be added under the crystal film, creating a vertical electric field with the top interdigital transducer (IDT) layer. The uniformly distributed vertical electric field excites a resonance in the piezoelectric thin film.

[0004] However, these devices use a fragile sub-micron piezoelectric thin film suspended over a cavity for acoustic isolation. At least in some cases, the manufacturing process required for such devices can be difficult because the bottom side of the thin film needs to be opened. Furthermore, these devices can be fragile due to the very thin film. In addition, these devices can have poor power handling characteristics due to the low thermal conductivity of the thin lithium niobate (LN) film.

[0005] On the other hand, while a YBAR that is firmly mounted on a high acoustic velocity substrate can provide a robust device structure and good power handling capability compared to a YBAR structure with a suspended thin film, various spurious modes have been found in the vicinity of the resonance and anti-resonance frequency range in a YBAR on a solid substrate, which interfere with the main resonant mode and complicate the resonator and filter design. The piezoelectric coupling can also be reduced due to the firm bottom substrate, providing a smaller coupling factor than the ideal coupling factor for sub-6 GHz filter designs.

[0006] Finally, if the period (pitch) between the electrodes in a YBAR is large, bulk acoustic waves are generated into the high acoustic velocity substrate, resulting in severe degradation of resonator performance due to energy loss.

[0007] Therefore, at least in some cases, a solution that can suppress unwanted spurious modes and improve piezoelectric coupling can be desirable. SUMMARY

[0008] This summary is provided to introduce a selection of concepts, in a simplified form, that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.

[0009] It is an object of the present invention to make a bulk acoustic wave resonator configured to increase the piezoelectric coupling and suppress spurious modes. The above and other objects are achieved by the features of the independent claims. Further implementation forms are evident from the dependent claims, the description and the drawings.

[0010] According to a first aspect, there is provided a bulk acoustic wave resonator having a resonance frequency F R . The bulk acoustic wave resonator comprises a support substrate. The bulk acoustic wave resonator further comprises a bulk substrate layer arranged on the support substrate. The bulk substrate layer has a first thickness and a speed of sound V sub . The bulk acoustic wave resonator further comprises a dielectric layer arranged on the bulk substrate layer. The dielectric layer has a second thickness and a first acoustic impedance. The bulk acoustic wave resonator further comprises a metal layer arranged on the dielectric layer. The metal layer has a third thickness and a second acoustic impedance. The second acoustic impedance is higher than the first acoustic impedance. The bulk acoustic wave resonator further comprises a piezoelectric plate having a fourth thickness substantially equal to half a wavelength of a shear acoustic wave propagating in the thickness direction in the piezoelectric plate. The piezoelectric plate has a front surface and a back surface, the back surface being attached to the metal layer. The first thickness is at least ten times the fourth thickness. The bulk acoustic wave resonator further comprises an interdigital transducer (IDT) arrangement comprising a first set of electrodes connected to a first busbar and a second set of electrodes connected to a second busbar. The electrodes in the first and second sets of electrodes are arranged on the front surface of the piezoelectric plate one after another in an electrode pitch p alternately and periodically. The bulk acoustic resonator further comprises a set of recesses arranged periodically on the front surface of the piezoelectric plate between the electrodes in the first and second sets of electrodes. Each recess in the set of recesses extends in a direction parallel to the electrodes in the first and second sets of electrodes, and each recess in the set of recesses is at least partly sunken into the piezoelectric plate. The invention can be used in a structure of a bulk acoustic wave resonator which is capable of increasing the piezoelectric coupling and suppressing spurious modes. The disclosed recesses between the electrodes reduce the generation of spurious modes and prevent the propagation of spurious modes and the resonance accumulation of amplitudes. Furthermore, the disclosed recesses between the electrodes suppress high order modes in the horizontal direction.

[0011] In an implementation form of the first aspect, the inter-electrode distance p between the first electrode and the electrodes of the second set of electrodes satisfies the condition . This implementation form can avoid the generation of bulk waves in a high acoustic velocity substrate.

[0012] In an implementation form of the first aspect, a sidewall of each recess of the set of recesses drops into the piezoelectric plate perpendicular to a plane of the front surface of the piezoelectric plate. This implementation form can further increase the piezoelectric coupling by making the piezoelectric material under the electrodes more free to vibrate.

[0013] In an implementation form of the first aspect, a sidewall of each recess of the set of recesses drops into the piezoelectric plate with an inclination angle with respect to a plane of the front surface of the piezoelectric plate. This implementation form can further increase the piezoelectric coupling by optimizing the inclination angle.

[0014] In an implementation form of the first aspect, the inclination angle is in a range of 70 degrees to 90 degrees. This implementation form can further increase the piezoelectric coupling.

[0015] In an implementation form of the first aspect, a depth of each recess of the set of recesses is in a range of 30% to 100% of the fourth thickness. This implementation form can further increase the piezoelectric coupling.

[0016] In an implementation form of the first aspect, the third thickness is substantially equal to a quarter of an acoustic wavelength of a shear acoustic wave propagating in the metal layer at the resonance frequency F R of the shear acoustic wave propagating in the metal layer. This implementation form helps to further increase the piezoelectric coupling by reducing the portion of acoustic energy penetrating into the dielectric layer and further into the bulk substrate layer.

[0017] In an implementation form of the first aspect, the metal layer comprises at least one of tungsten, molybdenum or platinum. This implementation form helps to further increase the piezoelectric coupling by reducing the portion of acoustic energy penetrating into the bulk substrate layer.

[0018] In an implementation form of the first aspect, the IDT arrangement is configured in an in-plane orientation on the front surface of the piezoelectric plate to minimize the coupling coefficients k 11 2 , k 31 2 and k 35 2 , and to maximize the coupling coefficient k 34 2 . This implementation form can further increase the suppression of the parasitic modes. Minimizing k 112 and k 31 2 helps to suppress S0 mode, minimizing k 35 2 helps to suppress A1 mode. For the main resonance SH1 mode, keeping k 34 2 as high as possible, helps to achieve a larger piezoelectric coupling.

[0019] In an implementation form of the first aspect, the piezoelectric plate comprises at least one of lithium niobate or lithium tantalate with a crystal orientation of X-cut or Y-cut. This implementation form helps to increase the coupling by optimal selection of piezoelectric material, crystal cut and propagation direction.

[0020] In an implementation form of the first aspect, the second thickness is substantially equal to a quarter of the acoustic wavelength of the bulk acoustic wave propagating in the dielectric layer at the resonance frequency F R In an implementation form of the first aspect, the second thickness is substantially equal to a quarter of the acoustic wavelength of the bulk acoustic wave propagating in the dielectric layer at the resonance frequency F

[0021] In an implementation form of the first aspect, the bulk substrate layer comprises at least one of silicon carbide (SiC) (polytype crystal structure 4H-SiC, 6H-SiC or 3C-SiC), boron nitride (BN) or diamond. This implementation form helps to further increase the piezoelectric coupling, proving the isolation of the in-layer vibrations and their exponential decay into the substrate when observing the above-mentioned pitch limitation.

[0022] In an implementation form of the first aspect, the bulk substrate layer has a crystal orientation for increasing the shear acoustic wave velocity V sub This implementation form helps to increase the energy leakage cutoff frequency. This implementation form also helps to increase the applicable pitch values, thus reducing the photolithography resolution requirements. This implementation form helps to further increase the piezoelectric coupling, proving the isolation of the in-layer vibrations and their exponential decay into the substrate when observing the above-mentioned pitch limitation.

[0023] In an implementation form of the first aspect, the bulk acoustic wave resonator further comprises a wall edge reflector arranged outside each outermost electrode of at least one of the first set of electrodes or the second set of electrodes. This implementation form helps to improve the quality factor Q around the anti-resonance frequency by better reflecting and confining the acoustic energy within the resonator area.

[0024] According to a second aspect, an electronic device is provided. The electronic device comprises the bulk acoustic resonator according to the first aspect, which is electrically connectable through the first bus bar and the second bus bar. The present invention can be used in the structure of the bulk acoustic resonator, which is capable of increasing the piezoelectric coupling and suppressing the spurious modes. The disclosed grooves between the electrodes reduce the generation of the spurious modes and prevent the propagation of the spurious modes and the resonance accumulation of the amplitude. Furthermore, the disclosed grooves between the electrodes suppress the high order modes along the horizontal direction.

[0025] In an implementation form of the second aspect, the bulk acoustic resonator is comprised in a radio frequency filter. This implementation form facilitates the use of the bulk acoustic resonator for radio frequency filter applications.

[0026] Many accompanying features will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, and so, are more readily understood. BRIEF DESCRIPTION OF DRAWINGS

[0027] The exemplary embodiments will be described in detail below with reference to the following drawings:

[0028] FIG. 1A Perspective view of a bulk acoustic resonator provided for embodiments of the present invention;

[0029] FIG. 1B Cross-sectional view of a bulk acoustic resonator provided for embodiments of the present invention;

[0030] FIGS. 2A-2C Diagram of a groove provided for embodiments of the present invention;

[0031] FIG. 3 Diagram of a wall edge reflector provided for embodiments of the present invention;

[0032] FIG. 4 Block diagram of an electronic device provided for embodiments of the present invention;

[0033] FIG. 5 Influence of the propagation direction is shown;

[0034] FIG. 6 Dependence of the piezoelectric coupling on the groove wall inclination is shown;

[0035] FIG. 7 Dependence of the piezoelectric coupling on the groove depth is shown.

[0036] In the following, the same reference signs refer to the same or at least functionally equivalent features. DETAILED DESCRIPTION

[0037] In the following description, reference is made to the accompanying drawings, which form part of the invention and illustrate, by way of description, specific aspects to which the invention may be applied. It will be understood that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the invention. Therefore, the following detailed description should not be construed in a limiting sense, as the scope of the invention is defined by the appended claims.

[0038] For example, it should be understood that the disclosure relating to the described method also applies to the apparatus or system corresponding to performing the method, and vice versa. For example, if specific method steps are described, the corresponding apparatus may include units that perform the described method steps, even if such units are not explicitly described or shown in the drawings. On the other hand, for example, if a particular apparatus is described based on functional units, the corresponding method may include steps that perform the described functions, even if such steps are not explicitly described or shown in the drawings. Furthermore, it should be understood that features of the various exemplary aspects described herein can be combined with each other unless otherwise explicitly stated.

[0039] As will be discussed in more detail below, at least some of the disclosed embodiments can support the implementation of a structure for a bulk acoustic resonator that can increase piezoelectric coupling and suppress parasitic modes.

[0040] Next, based on FIG. 1A and FIG. 1B , FIGS. 2A-2C and FIG. 3 Describe a frequency F R An exemplary embodiment of the bulk acoustic resonator 100. Some features of the described device are optional features that provide other advantages.

[0041] FIG. 1A This is a perspective view of the bulk acoustic resonator 100. FIG. 1B A cross-sectional view of the bulk acoustic resonator 100. FIGS. 2A-2C A diagram showing an exemplary embodiment of the disclosed groove 110. FIG. 3 This is a diagram illustrating an exemplary embodiment of the wall edge reflector 112. For clarity, in... FIG. 1A The groove 110 is not shown. It should be noted that, although only two IDT electrodes are shown for clarity, the bulk acoustic resonator structure may include, for example, hundreds of electrodes.

[0042] The bulk acoustic resonator 100 includes a support substrate 101.

[0043] The bulk acoustic wave resonator 100 further includes a bulk substrate layer 102 disposed on a support substrate 101. The bulk substrate layer 102 has a first thickness and a sound velocity V. subFor example, the bulk substrate 102 may include at least one of silicon carbide (SiC) (polymorphic crystal structures 4H-SiC, 6H-SiC, or 3C-SiC), boron nitride (BN), or diamond. The bulk substrate 102 may have high resistance (high resistivity, non-conductive).

[0044] In at least some embodiments, the bulk substrate layer 102 may have a crystal orientation for increasing, for example, the shear acoustic velocity V in a direction parallel to the interface. sub The displacement is parallel to electrodes 106 and 108, causing the wave to sweep across the interface.

[0045] The bulk acoustic resonator 100 further includes a dielectric layer 103 disposed on a bulk substrate layer 102. The dielectric layer 103 has a second thickness and a first acoustic impedance. For example, the second thickness may be substantially equal to the resonant frequency F. R A quarter of the wavelength of a bulk acoustic wave propagating in dielectric layer 103 in a direction perpendicular to the layer, wherein the displacement is parallel to electrodes 106 and 108.

[0046] The bulk acoustic wave resonator 100 also includes a metal layer 104 disposed on the dielectric layer 103. For example, the metal layer 104 may include at least one of tungsten, molybdenum or platinum.

[0047] The metal layer 104 has a third thickness and a second acoustic impedance. The second acoustic impedance is higher than the first acoustic impedance. For example, the third thickness can be substantially equal to the thickness at the resonant frequency F. R The shear acoustic wave propagating in the metal layer 104 in a direction perpendicular to the layer has a wavelength of one-quarter of the acoustic wavelength, wherein the displacement is parallel to the electrodes 106 and 108.

[0048] In at least some embodiments, the metal layer 104 may include a metal having two conductive adhesive layers, one on each side. The material of the adhesive layers may include at least one of, for example, titanium (Ti) or chromium (Cr).

[0049] The bulk acoustic resonator 100 further includes a piezoelectric plate 105 having a fourth thickness substantially equal to half the wavelength of a shear acoustic wave propagating in the thickness direction of the piezoelectric plate 105 in a direction perpendicular to the layer, wherein the displacement is parallel to the electrodes 106, 108. For example, the piezoelectric plate 105 comprises at least one of lithium niobate or lithium tantalate with an X-cut or Y-cut crystal orientation.

[0050] The piezoelectric plate 105 has a front surface and a rear surface, with the rear surface attached to the metal layer 104. The first thickness is at least ten times the fourth thickness.

[0051] The bulk acoustic wave resonator 100 also includes an interdigital transducer (IDT) device comprising a first set of electrodes 106 connected to a first bus 107 and a second set of electrodes 108 connected to a second bus 109. The electrodes in the first set of electrodes 106 and the second set of electrodes 108 are arranged alternately and periodically one after another on the front surface of the piezoelectric plate 105 with an electrode spacing p.

[0052] In at least some embodiments, the bottom electrode / metal layer 104 may not overlap with the top bus regions 107 and 109, thereby helping to eliminate the potentially large capacitance and small resistance due to the overlap of the top and bottom electrodes in the bus regions, and thus improving coupling and Q factor.

[0053] At least in some embodiments, the electrode spacing p between the electrodes in the first group of electrodes 106 and the second group of electrodes 108 can satisfy the condition This condition helps prevent bulk acoustic wave radiation from entering the bulk substrate layer 102, thereby increasing the Q factor of the bulk acoustic wave resonator 100. In at least some embodiments, the propagation direction and vibration direction of the acoustic wave can be determined by the vibration mode at the resonant frequency in the piezoelectric plate 105.

[0054] In at least some embodiments, the IDT device can be configured in an in-plane orientation on the front surface of the piezoelectric plate 105 to minimize the coupling coefficient k. 11 2 k 31 2 and k 35 2 and maximizing the coupling coefficient k 34 2 .

[0055] FIG. 5 Figure 500 shows that the chosen propagation direction (in this example, the third Euler angle, 30° or 34.4°) can help reduce parasitic A1 patterns at least in some cases.

[0056] The bulk acoustic resonator 100 also includes a set of grooves 110 on the front surface of the piezoelectric plate 105, these grooves being periodically arranged between the electrodes in the first set of electrodes 106 and the second set of electrodes 108. Each groove in the set of grooves 110 extends in a direction parallel to the electrodes in the first set of electrodes 106 and the second set of electrodes 108, and each groove in the set of grooves 110 at least partially descends into the piezoelectric plate 105. For example, at least some of the grooves 110 may be fabricated by etching.

[0057] In at least some embodiments, the sidewall 111 of each of the set of grooves 110 may descend into the piezoelectric plate 105 perpendicular to the plane of the front surface of the piezoelectric plate 105.

[0058] Alternatively, the sidewall 111 of each of the grooves 110 may descend into the piezoelectric plate 105 at an angle relative to the plane of the front surface of the piezoelectric plate 105. For example, the angle may be in the range of 70 to 90 degrees, thereby allowing more piezoelectric material to participate in vibration generation without being too strongly coupled to the bulk substrate layer 102. In one embodiment, the angle may be 80 to 85 degrees.

[0059] FIG. 6 Figure 600 shows that the optimal tilt angle (for obtaining the strongest piezoelectric coupling) can be approximately 80° in at least some cases.

[0060] In at least some embodiments, the depth of each groove in a set of grooves 110 can be in the range of 30% to 100% of the fourth thickness.

[0061] FIG. 7 Figure 700 shows that, in at least some cases, piezoelectric coupling can grow deeper grooves.

[0062] In at least some embodiments, the bulk acoustic resonator 100 may further include a wall-edge reflector 112 disposed outside each outermost electrode 108F, 108L of at least one set of electrodes in the first set of electrodes 106 or the second set of electrodes 108. For example, the wall-edge reflector 112 may be disposed at a distance b from the middle of the outermost electrode 108F, such that b = p / 2, as shown. FIG. 3 As shown. The same situation can also be applied to the outermost electrode 108L ( FIG. 3 (Not shown in the image).

[0063] In at least some embodiments, the wall-edge reflector 112 can prevent waves from escaping from the bulk acoustic resonator 100 to the outside, thereby improving the Q factor, especially near the anti-resonant frequency. In at least some cases, such escape can produce admittance oscillations, which can be detrimental to the use of the bulk acoustic resonator 100.

[0064] FIG. 4This is a block diagram of an electronic device 400 provided in an embodiment of the present invention. The electronic device 400 includes a bulk acoustic wave resonator 100 as described above, which can be electrically connected via a first bus 107 and a second bus 109. The electronic device 400 may also include a radio frequency (RF) filter 401. More specifically, in at least some embodiments, one or more of the bulk acoustic wave resonators 100 may be included in the RF filter 401.

[0065] Any ranges or device values ​​given herein may be extended or modified without losing the desired effect. Furthermore, unless expressly prohibited, any embodiment may be combined with another embodiment.

[0066] Although the subject matter has been described in language specific to structural features and / or actions, it should be understood that the subject matter defined in the claims is not necessarily limited to the specific features or actions described above. In fact, the specific features and actions described above are disclosed as examples of implementing the claims, and other equivalent features and actions are intended to fall within the scope of the claims.

[0067] It should be understood that the above benefits and advantages may relate to one embodiment or several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It is further understood that a reference to "a" may refer to one or more of those items.

[0068] Without losing the desired effect, aspects of any of the above embodiments can be combined with aspects of any other described embodiments to form other embodiments.

[0069] As used herein, the term "comprising" means including the identified method, block, or element, but such blocks or elements are not included in an exclusive list, and the method or apparatus may include other blocks or elements.

[0070] It should be understood that the above description is given by way of example only, and various modifications can be made by those skilled in the art. The above description, examples, and data provide a complete description of the structure and use of exemplary embodiments. Although various embodiments have been described above with some degree of specificity or with reference to one or more individual embodiments, those skilled in the art can make various modifications to the disclosed embodiments without departing from the spirit or scope of this specification.

Claims

1. A type of atom with resonant frequency F R The bulk acoustic resonator (100) is characterized by, include: Support substrate (101); A bulk substrate layer (102) is disposed on the supporting substrate (101), the bulk substrate layer (102) having a first thickness and a sound velocity V. sub ; A dielectric layer (103) is disposed on the bulk substrate layer (102), the dielectric layer (103) having a second thickness and a first acoustic impedance; A metal layer (104) is disposed on the dielectric layer (103), the metal layer (104) having a third thickness and a second acoustic impedance, the second acoustic impedance being higher than the first acoustic impedance; The piezoelectric plate (105) has a fourth thickness that is substantially equal to half the wavelength of a shear sound wave propagating in the thickness direction in the piezoelectric plate (105), the piezoelectric plate (105) having a front surface and a rear surface, the rear surface being attached to the metal layer (104), and the first thickness being at least ten times the fourth thickness. An interdigital transducer (IDT) device includes a first set of electrodes (106) connected to a first bus (107) and a second set of electrodes (108) connected to a second bus (109), wherein the electrodes in the first set of electrodes (106) and the second set of electrodes (108) are arranged one after another alternately and periodically at an electrode spacing p on the front surface of the piezoelectric plate (105); The bulk acoustic resonator (100) further includes a set of grooves (110) arranged periodically on the front surface of the piezoelectric plate (105) between the electrodes of the first set of electrodes (106) and the second set of electrodes (108). Each groove in the set of grooves (110) extends in a direction parallel to the electrodes of the first set of electrodes (106) and the second set of electrodes (108) and descends at least partially into the piezoelectric plate (105).

2. The bulk acoustic resonator (100) according to claim 1, characterized in that, The electrode spacing p between the electrodes in the first group of electrodes (106) and the second group of electrodes (108) satisfies the condition .

3. The bulk acoustic resonator (100) according to claim 1 or 2, characterized in that, The sidewall (111) of each of the set of grooves (110) descends into the piezoelectric plate (105) perpendicular to the plane of the front surface of the piezoelectric plate (105).

4. The bulk acoustic resonator (100) according to claim 1 or 2, characterized in that, The sidewall (111) of each of the set of grooves (110) descends into the piezoelectric plate (105) at an inclined angle relative to the plane of the front surface of the piezoelectric plate (105).

5. The bulk acoustic resonator (100) according to claim 4, characterized in that, The tilt angle is in the range of 70 to 90 degrees.

6. The bulk acoustic resonator (100) according to any one of claims 1 to 5, characterized in that, The depth of each groove in the set of grooves (110) is in the range of 30% to 100% of the fourth thickness.

7. The bulk acoustic resonator (100) according to any one of claims 1 to 6, characterized in that, The third thickness is substantially equal to the resonant frequency F. R The shear wave propagating in the metal layer (104) has a wavelength of one-quarter of the acoustic wavelength.

8. The bulk acoustic resonator (100) according to claim 7, characterized in that, The metal layer (104) includes at least one of tungsten, molybdenum or platinum.

9. The bulk acoustic resonator (100) according to any one of claims 1 to 8, characterized in that, The IDT device is configured in-plane orientation on the front surface of the piezoelectric plate (105) to minimize the coupling coefficient k. 11 2 k 31 2 and k 35 2 and maximizing the coupling coefficient k 34 2 .

10. The bulk acoustic resonator (100) according to any one of claims 1 to 9, characterized in that, The piezoelectric plate (105) includes at least one of lithium niobate or lithium tantalate with a crystal orientation of X-cut or Y-cut.

11. The bulk acoustic resonator (100) according to any one of claims 1 to 10, characterized in that, The second thickness is substantially equal to the resonant frequency F. R The bulk acoustic wave propagating in the dielectric layer (103) has a wavelength of one-quarter of the acoustic wavelength.

12. The bulk acoustic resonator (100) according to any one of claims 1 to 11, characterized in that, The bulk substrate layer (102) includes at least one of silicon carbide (SiC), polymorphic crystal structure 4H-SiC, 6H-SiC or 3C-SiC, boron nitride (BN) or diamond.

13. The bulk acoustic resonator (100) according to claim 12, characterized in that, The bulk substrate layer (102) has features for increasing the shear acoustic velocity V. sub Crystal orientation.

14. The bulk acoustic resonator (100) according to any one of claims 1 to 13, characterized in that, It also includes a wall edge reflector (112) arranged outside each outermost electrode (108F, 108L) of at least one group of electrodes in the first group of electrodes (106) or the second group of electrodes (108).

15. An electronic device (400), characterized in that, Includes a bulk acoustic resonator (100) according to any one of the preceding claims, the bulk acoustic resonator (100) being electrically connected via the first bus (107) and the second bus (109).

16. The electronic device (400) according to claim 15, characterized in that, The bulk acoustic resonator (100) is included in the radio frequency filter (401).

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