JP2007208845A - Piezoelectric resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric resonator capable of attenuating an unnecessary vibration mode laterally propagated in a piezoelectric film, an upper electrode, a lower electrode, and a resonator holding member. <P>SOLUTION: The piezoelectric resonator has a piezoelectric film 11 and a resonator main body section including the upper electrode 12 and lower electrode 13 formed opposite each other across the piezoelectric film 11. The resonator main body section has a resonance region 21 where the upper electrode 12 and lower electrode 13 are both formed and a sound reflection region 22 which excludes the resonance region 21 of the resonator main body section 20 and where projection and recess shapes which are periodically arranged are formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a resonator using a piezoelectric body, and more particularly to a resonator used for a high frequency filter or the like.

  In recent years, with the widespread use of mobile phones worldwide, small and high-performance high-frequency filters are required. As a small and high-performance filter, a filter using a piezoelectric resonator such as a thin film bulk acoustic resonator (FBAR) has attracted attention.

  The piezoelectric resonator uses vibration in the thickness (longitudinal) direction of a piezoelectric film sandwiched between an upper electrode and a lower electrode. On the other hand, since transverse vibration parallel to the electrode surface is also excited, there are a plurality of transverse propagation modes. The transverse propagation mode is an unnecessary vibration mode, which propagates in parallel with the electrode surface and interferes with the longitudinal vibration to generate spurious. In the case of a device such as a filter in which a plurality of piezoelectric resonators are arranged adjacent to each other, unnecessary vibration mode interference occurs between adjacent piezoelectric resonators, and therefore the unnecessary vibration mode causes spurious. The spurious attributed to this lateral propagation mode degrades the frequency characteristics of the piezoelectric resonator.

  As a method of attenuating the unnecessary vibration mode that propagates in the lateral direction, it is conceivable to separate the resonators so that the unnecessary vibration mode does not propagate in the lateral direction. However, in this method, it is necessary to separate a plurality of resonators once formed integrally on a substrate by etching, and the number of processes is greatly increased. In addition, it is necessary to take into account the etching margin between adjacent resonators, leading to an increase in chip area.

As a method that does not require etching, Patent Document 1 discloses a method of providing an acoustic attenuation region that is a portion having low crystallinity in a part of a piezoelectric film. According to this method, it is possible to attenuate the lateral unnecessary vibration mode propagating through the piezoelectric film.
JP 2005-110230 A

  However, the conventional piezoelectric resonator has a problem that the unnecessary vibration mode propagating in the lateral direction is not sufficiently attenuated because the acoustic attenuation region is provided by lowering the crystallinity of the piezoelectric film. Further, although the unnecessary vibration mode propagating in the lateral direction through the piezoelectric film can be attenuated, there is a problem that the unnecessary vibration mode propagating in the lateral direction through the electrode or resonator holding member cannot be attenuated.

  The present invention solves the above-described conventional problems and makes it possible to realize a piezoelectric resonator capable of attenuating an unnecessary vibration mode that propagates in the lateral direction through the piezoelectric film, the upper electrode, the lower electrode, and the resonator holding member. Objective.

  In order to achieve the above-mentioned object, the present invention is configured such that the piezoelectric resonator includes an acoustic reflection region in which a periodic uneven shape is formed.

  Specifically, a first piezoelectric resonator according to the present invention includes a resonator main body including a piezoelectric film, and an upper electrode and a lower electrode that are formed to face each other with the piezoelectric film interposed therebetween. The main body part is a resonance area where both the upper electrode and the lower electrode are formed, and an acoustic reflection area which is a part excluding the resonance area of the resonator main body part and where a periodic uneven shape is formed. It is characterized by having.

  According to the first piezoelectric resonator, the acoustic reflection region has an acoustic reflection region that is a portion in which irregularities arranged periodically are formed. Since the acoustic reflection region is a portion where the average acoustic impedance density of the material with respect to the sound wave is different, it is possible to reflect the sound wave having a wavelength determined by the period of the uneven shape. Thereby, it becomes possible to attenuate the unnecessary vibration mode propagating in the lateral direction through the resonator body.

  In the first piezoelectric resonator, the concavo-convex portion preferably forms a sonic crystal in the acoustic reflection region. By making the acoustic reflection region a sonic crystal in which the portions that reflect sound waves are regularly arranged, the unnecessary vibration mode can be surely attenuated in the acoustic reflection region.

  In the first piezoelectric resonator, the concavo-convex shape is formed by a plurality of convex portions formed on the piezoelectric film, and the outer periphery of one of the plurality of convex portions and the other adjacent to the one convex portion. It is preferable that the distance from the outer periphery of the convex portion is shorter than the wavelength of the sound wave set as the operating frequency of the resonator body. The uneven shape is formed by a plurality of recesses formed in the piezoelectric film, and the interval between the outer periphery of one of the plurality of recesses and the outer periphery of another recess adjacent to the one recess is resonant. It may be shorter than the wavelength of the sound wave set as the operating frequency of the main body. By adopting such a configuration, it is possible to attenuate only the unnecessary vibration mode without affecting the sound wave of the operating frequency of the resonator body.

  In the first piezoelectric resonator, it is preferable that at least a part of the plurality of recesses is formed so as to penetrate the piezoelectric film.

  The first piezoelectric resonator further includes a substrate having a cavity portion and holding the lower electrode in the resonator body portion, and at least a part of the plurality of recesses penetrates the piezoelectric film and is deeper than the upper surface of the substrate. The position is preferably reached. By adopting such a configuration, an unnecessary vibration mode propagating through the substrate can also be attenuated. Further, the substrate further includes a substrate for holding the lower electrode in the resonator main body, and a cavity portion is formed between the substrate and the resonator main body in the resonance region, and at least some of the plurality of recesses are piezoelectric films. And may reach a position deeper than the upper surface of the substrate. Furthermore, the substrate further includes a holding member that is formed on the substrate and holds the lower electrode in the resonator main body, and at least a part of the plurality of recesses penetrates the piezoelectric film and is deeper than the upper surface of the holding member. The position may be reached.

  In the first piezoelectric resonator, the first thin film and the second thin film having a higher acoustic impedance than the first thin film are laminated, and the lower electrode in the resonator main body is formed. Preferably, an acoustic mirror layer is further provided, and at least a part of the plurality of recesses penetrates the piezoelectric film and reaches a position deeper than the upper surface of the acoustic mirror layer. By adopting such a configuration, the resonance region is not supported by the peripheral portion and does not float in the air, so that the mechanical strength can be improved. .

  In this case, it is preferable that at least some of the plurality of recesses reach a position deeper than the interface between the first thin film and the second thin film formed on the uppermost portion of the acoustic mirror layer. By setting it as such a structure, formation of a recessed part becomes easy.

  In this case, the plane dimension of the acoustic mirror layer is larger than the plane dimension of the resonator body, and the plurality of recesses are also formed in a region around the portion of the acoustic mirror layer where the resonator body is held. Preferably it is. By adopting such a configuration, an acoustic reflection region is also formed in the acoustic mirror layer itself, so that it is possible to reliably attenuate unnecessary vibration modes that propagate in the lateral direction through the acoustic mirror layer.

  In the first piezoelectric resonator, it is preferable that the resonator main body has a plurality of resonance regions and a plurality of acoustic reflection regions, and the formation periods of the concave portions in the respective acoustic reflection regions are different from each other. By adopting such a configuration, it is possible to realize a piezoelectric resonator in which unnecessary vibration modes hardly propagate to adjacent resonance regions. In this case, the filter preferably includes the first piezoelectric resonator.

  The second piezoelectric resonator according to the present invention is an acoustic device in which a first thin film formed on a substrate and a second thin film having a higher acoustic impedance than the first thin film are alternately laminated. A mirror layer and a resonator main body held on the acoustic mirror layer and having a piezoelectric film and an upper electrode and a lower electrode formed opposite to each other with the piezoelectric film interposed therebetween, and the acoustic mirror layer includes: An outer periphery of one of the plurality of recesses and an outer periphery of another recess adjacent to the one recess having a plurality of recesses formed in a region around the portion where the acoustic resonator main body is held Is shorter than the wavelength of the sound wave set as the operating frequency of the resonator body.

  According to the second piezoelectric resonator, the acoustic mirror layer has a plurality of recesses formed in a region around the portion where the acoustic resonator main body is held, so that the acoustic mirror layer has an acoustic reflection region. It is formed. Therefore, since the unnecessary vibration mode propagating in the lateral direction through the acoustic mirror layer can be attenuated, a piezoelectric resonator with less spurious generation can be realized.

  In the second piezoelectric resonator, the concave portion is preferably formed in a region including a portion where the acoustic resonator main body portion of the acoustic mirror layer is held. By adopting such a configuration, it is possible to reflect the propagation of sound waves in the lateral direction not only in the support area around the resonator area but also in the area inside the resonator. It becomes.

  In the second piezoelectric resonator, a material having a lower acoustic impedance than that of the first thin film is preferably embedded in the recess. By setting it as such a structure, since the acoustic impedance in an acoustic mirror layer can be changed, it becomes possible to reflect the sound wave of a horizontal direction more effectively. In addition, since the upper surface of the acoustic mirror layer can be flattened, the piezoelectric resonator main body can be easily formed.

  A third piezoelectric resonator according to the present invention is an acoustic device in which first thin films formed on a substrate and second thin films having a higher acoustic impedance than the first thin films are alternately stacked. A mirror layer and a resonator main body held on the acoustic mirror layer and having a piezoelectric film and an upper electrode and a lower electrode formed opposite to each other with the piezoelectric film interposed therebetween, At least one of the plurality of hole portions penetrating vertically is periodically formed in at least one of them, and the outer periphery of one of the plurality of hole portions and the other adjacent to the one hole portion. The distance from the outer periphery of the hole is shorter than the wavelength of the sound wave set as the operating frequency of the resonator body.

  According to the third piezoelectric resonator, in at least one of the first thin films, a plurality of holes penetrating vertically are periodically formed, and one hole of the plurality of holes is formed. Since the distance between the outer periphery of the part and the outer periphery of the other hole adjacent to the one hole is shorter than the wavelength of the sound wave set as the operating frequency of the resonator body, the acoustic mirror layer has an acoustic reflection region. It is formed. Therefore, since the unnecessary vibration mode propagating in the lateral direction through the acoustic mirror layer can be attenuated, a piezoelectric resonator with less spurious generation can be realized.

  In the third piezoelectric resonator, a material having a lower acoustic impedance than that of the first thin film is preferably embedded in the hole. By adopting such a configuration, it becomes easy to form the acoustic mirror layer and to form the acoustic resonator main body on the acoustic mirror layer.

  In the second and third piezoelectric resonators, it is preferable that a plurality of resonator main bodies are held on the acoustic mirror layer. The filter preferably includes a third piezoelectric resonator.

  The piezoelectric resonator according to the present invention can realize a piezoelectric resonator capable of attenuating an unnecessary vibration mode that propagates in the lateral direction through the piezoelectric film, the upper electrode, the lower electrode, and the resonator holding member.

(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings. 1A and 1B show a piezoelectric resonator according to the first embodiment. FIG. 1A shows a planar configuration, and FIG. 1B shows a cross-sectional configuration taken along line Ib-Ib in FIG. Show. In FIG. 1, only the resonator main body is shown, and the actual resonator is held on a substrate on which the resonator main body is formed with a cavity or an acoustic mirror.

  As shown in FIG. 1, the piezoelectric resonator of this embodiment includes a resonator main body 20 including a piezoelectric film 11 and an upper electrode 12 and a lower electrode 13 that are formed to face each other with the piezoelectric film 11 interposed therebetween. ing. The portion of the resonator main body 20 where the upper electrode 12 and the lower electrode 13 of the piezoelectric film 11 are formed is a resonance region 21 that confines sound wave vibration in the thickness direction (longitudinal direction) of the piezoelectric film. In the piezoelectric resonator of the present embodiment, an acoustic reflection region 22 is formed around the resonance region 21.

  In the acoustic reflection region 22, a plurality of recesses 14 are formed in the piezoelectric film 11. In FIG. 1, the recess 14 penetrates the piezoelectric film 11, but it does not necessarily have to penetrate. The interval d between the outer peripheries of the recesses 14 is shorter than the wavelength of the sound wave set as the operating frequency of the resonator. For example, when the operating frequency of the resonator is 2 GHz, it may be 2.5 μm to 5 μm.

  By forming the plurality of recesses 14 at such intervals, the average density of the piezoelectric film 11 with respect to the sound wave changes in the acoustic reflection region 22. That is, the acoustic reflection region 22 is a sonic crystal in which sound wave scattering portions are regularly formed. Therefore, only the resonance mode having the frequency set by the interval between the recesses 14 can be reflected by the recesses 14. As a result, the occurrence of spurious due to the unnecessary vibration mode in the lateral direction can be suppressed. In addition, when a plurality of pairs of upper and lower electrodes are formed on a single piezoelectric film, and a plurality of resonator main bodies are integrally formed, unnecessary vibration modes of the resonator main bodies interfere with each other. Thus, it is possible to suppress the occurrence of spurious.

  The piezoelectric film 11 may be formed using an appropriate piezoelectric material such as aluminum nitride (AlN) or zinc oxide (ZnO). The recess 14 may be formed by, for example, forming a mask on the piezoelectric film 11 using photolithography and then performing dry etching using a chlorine (Cl) or fluorine (F) etchant. The upper electrode 12 and the lower electrode 13 may be formed using a known appropriate material such as molybdenum (Mo) or tungsten (W). Moreover, you may use a laminated body and a mixture.

  Although FIG. 1 shows an example in which the lower electrode 13 is formed in a part of the acoustic reflection region 22, the upper electrode 12 may be formed instead of the lower electrode 13 or together with the lower electrode 13. . Further, when the upper electrode 12 or the lower electrode 12 is formed, the recess 14 may penetrate the upper electrode 12 or the lower electrode 13. In this way, when the plurality of resonator main body portions 20 are integrally formed and the adjacent resonator main body portions 20 share the upper electrode 12 or the lower electrode 13, they propagate through the upper electrode 12 or the lower electrode 13. The unnecessary vibration mode can be attenuated.

  In the present embodiment, the concave portion 14 is formed in the acoustic reflection region 22, but a plurality of convex portions may be formed by electron beam evaporation or the like.

(Second Embodiment)
The second embodiment of the present invention will be described below with reference to the drawings. FIG. 2 shows a cross-sectional configuration of the piezoelectric resonator according to the second embodiment. In FIG. 2, the same components as those of FIG.

  As shown in FIG. 2, in the piezoelectric resonator of this embodiment, the resonator body 20 is held on a substrate 41 on which a cavity 42 is formed. The cavity portion 42 is formed below the resonance region 21 of the resonator body 20, and the region excluding the resonance region 21 is held by the substrate 41. A plurality of recesses 14 are formed in at least a part of the portion of the piezoelectric film 11 held by the substrate 41. In the piezoelectric resonator of the present embodiment, the concave portion 14 penetrates the piezoelectric film 11 and reaches a position deeper than the upper surface of the substrate 11. Therefore, not only the unnecessary vibration mode that propagates in the lateral direction through the piezoelectric film 11 but also the unnecessary vibration mode that propagates in the lateral direction through the substrate 41 can be attenuated.

  In FIG. 2, the recess 14 does not penetrate the substrate 41, but may be formed so as to penetrate the substrate 41. Further, the concave portion 14 may be formed in a region of the substrate 41 where the piezoelectric film 11 is not held.

(Third embodiment)
The third embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a cross-sectional configuration of the piezoelectric resonator according to the third embodiment. In FIG. 3, the same components as those in FIG.

  As shown in FIG. 3, in the piezoelectric resonator according to this embodiment, the resonator body 20 is held on the substrate 41, and the substrate 41 and the lower electrode are disposed below the resonance region 21 of the resonator body 20. 13 is formed with a cavity 43. The cavity 43 may be formed by a method using a known sacrificial layer.

  A region excluding the resonance region 21 of the resonator body 20 is held by the substrate 41, and a plurality of recesses 14 are formed in at least a part of the portion of the piezoelectric film 11 held by the substrate 41. In the piezoelectric resonator of the present embodiment, the concave portion 14 penetrates the piezoelectric film 11 and reaches a position deeper than the upper surface of the substrate 11. Therefore, not only the unnecessary vibration mode that propagates in the lateral direction through the piezoelectric film 11 but also the unnecessary vibration mode that propagates in the lateral direction through the substrate 41 can be attenuated.

(Fourth embodiment)
The fourth embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows a cross-sectional configuration of the piezoelectric resonator according to the fourth embodiment. In FIG. 4, the same components as those of FIG.

  As shown in FIG. 4, in the piezoelectric resonator according to this embodiment, the resonator body 20 is held on the substrate 41 with a holding part 45 interposed. Thereby, a cavity 44 is formed between the substrate 41 and the lower electrode 13 below the resonance region 21 of the resonator body 20.

  A region excluding the resonance region 21 of the resonator body 20 is held by the substrate 41, and a plurality of recesses 14 are formed in at least a part of the portion of the piezoelectric film 11 held by the substrate 41. In the piezoelectric resonator of the present embodiment, the concave portion 14 penetrates the piezoelectric film 11 and reaches a position deeper than the upper surface of the holding portion 45. Therefore, the unnecessary vibration mode propagating to the substrate 41 via the holding portion 45 can be attenuated.

  The same configuration can be applied to a resonator main body in which a plurality of pairs of upper and lower electrodes are formed with one piezoelectric film interposed therebetween.

(Fifth embodiment)
Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings. 5A and 5B show a piezoelectric resonator according to the fifth embodiment, where FIG. 5A shows a planar configuration, and FIG. 5B shows a cross-sectional configuration taken along line Vb-Vb in FIG. Yes. In FIG. 5, the same components as those of FIG.

  As shown in FIG. 5, the piezoelectric resonator of the present embodiment is formed on the acoustic mirror layer 33 in which the resonator body 20 including the piezoelectric film 11, the upper electrode 12, and the lower electrode 13 is held on the substrate 31. Has been. Since the resonator main body 20 is held by the acoustic mirror 32, unlike the case where a cavity is provided under the resonator main body 20, the resonance region 21 does not have a structure that floats in the air, so mechanical strength is improved. And resistance to physical destruction is improved.

The acoustic mirror layer 33 is formed by laminating a plurality of pairs of the first thin film 33A and the second thin film 33B. The first thin film 33A may be formed using silicon (Si), silicon oxide (SiO ₂ ), silicon nitride (SiN), or the like with low acoustic impedance. The second thin film 33B may be formed using molybdenum (Mo), hafnium oxide (HfO), or the like that has a higher acoustic impedance than the first thin film 33A. In FIG. 5, in the acoustic mirror layer 33, the number of laminations of the first thin film 33A and the second thin film 33B is three cycles, but the number of laminations may be larger.

  In the piezoelectric resonator of the present embodiment, at least a part of the concave portion 14 penetrates the piezoelectric film 11 and reaches a position deeper than the upper surface of the acoustic mirror layer 33. Since the concave 14 is also formed on the acoustic mirror layer 33 that holds the piezoelectric film, not only an unnecessary vibration mode that propagates in the piezoelectric film 11 in the lateral direction but also an unnecessary vibration mode that propagates in the acoustic mirror layer 33 in the lateral direction. Can be attenuated.

  In general, the acoustic reflection characteristics of the mirror layer are determined by the ratio of acoustic impedance. When viewed from the piezoelectric film 11 side, the sound waves propagated to the first pair of first thin film 33A and the second thin film 33B are the first pair of second thin film 33B and the second pair of first thin film 33A. Only the sound waves that could not be reflected at the interface between the first pair of second thin films 33B and the second pair of first thin films 33A approach the state of free reflection at the interface with the second pair of first thin films. Propagated to 33A and the second thin film 33B. Therefore, although there is a variation depending on the material of the acoustic mirror layer 33, generally about 80% of sound waves are reflected at the interface between the first pair of second thin films 33B and the second pair of first thin films 33A.

  Therefore, as shown in FIG. 6, the depth of the recess 14 is shallower than the interface between the first pair of second thin films 33B and the second pair of first thin films 33A when viewed from the piezoelectric film 11 side. However, most of the unnecessary vibration modes can be attenuated. The etching process can be simplified by reducing the depth of the recess 14.

  As shown in FIG. 7, in the case where the resonator body 20 is composed only of the resonance region 21, the influence of the unnecessary vibration mode propagating in the lateral direction through the piezoelectric film 11 may be almost ignored. The recess 14 may be formed only in the mirror layer 33.

(Sixth embodiment)
The sixth embodiment of the present invention will be described below with reference to the drawings. 8A and 8B show a piezoelectric resonator according to the sixth embodiment, where FIG. 8A shows a planar configuration, and FIG. 8B shows a cross-sectional configuration taken along line VIIIb-VIIIb in FIG. 8, the same components as those in FIG.

  As shown in FIG. 8, in the piezoelectric resonator of this embodiment, the uppermost first thin film 33 </ b> A of the acoustic mirror layer 33 has a hole 15 that penetrates vertically. The holes 15 are periodically formed in the same manner as the recesses 14 in the first embodiment.

  In the piezoelectric resonator of this embodiment, the recess 14 is not formed in the resonator main body 20, but the hole 15 is formed in the entire first thin film 33 </ b> A including the resonance region 21. Thereby, since it becomes possible to block the sound wave propagating through the mirror layer in the lateral direction, it is possible to suppress the generation of the unnecessary vibration mode.

  Further, the upper surface of the acoustic mirror layer 33 may be flattened by embedding a material having a lower acoustic impedance than that of the first thin film 33 </ b> A in the hole 15. By flattening the upper surface of the acoustic mirror layer 33, the resonator body 20 can be easily formed on the acoustic mirror layer 33.

  The low acoustic impedance material may be embedded in the recess 14 by, for example, a spin-on-glass method in which a liquid glass material or the like is spin-coated and heat-treated. An organic material may be spin coated.

  FIG. 9 shows a modification of the piezoelectric resonator of the present embodiment. As shown in this modification, the hole 15 may be formed in the lower first thin film 33A instead of the uppermost first thin film 33A. Even in such a configuration, since it is possible to cut off the sound wave propagating in the lateral direction through the mirror layer, it is possible to suppress the generation of unnecessary vibration modes. Also in this case, if the low impedance material is embedded in the hole 15, the acoustic mirror layer 33 can be easily stacked. Further, the holes 15 may be formed in a plurality of layers.

  The piezoelectric resonator of the present invention can realize a piezoelectric resonator capable of attenuating an unnecessary vibration mode that propagates in the lateral direction through the piezoelectric film, the upper electrode, the lower electrode, and the resonator holding member. In particular, it is useful as a resonator used for a high frequency filter or the like.

(A) And (b) shows the piezoelectric resonator which concerns on the 1st Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the Ib-Ib line | wire of (a). . It is sectional drawing which shows the piezoelectric resonator which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows the piezoelectric resonator which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows the piezoelectric resonator which concerns on the 4th Embodiment of this invention. (A) And (b) shows the piezoelectric resonator which concerns on the 5th Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the Vb-Vb line | wire of (a). . It is sectional drawing which shows the modification of the piezoelectric resonator which concerns on the 5th Embodiment of this invention. It is sectional drawing which shows the modification of the piezoelectric resonator which concerns on the 5th Embodiment of this invention. (A) And (b) shows the piezoelectric resonator which concerns on the 6th Embodiment of this invention, (a) is a top view, (b) is sectional drawing in the VIIIb-VIIIb line | wire of (a). . It is sectional drawing which shows the modification of the piezoelectric resonator which concerns on the 6th Embodiment of this invention.

Explanation of symbols

11 Piezoelectric film 12 Upper electrode 13 Lower electrode 14 Recess 15 Hole 20 Resonator main body 21 Resonance region 22 Acoustic reflection region 33 Acoustic mirror layer 33A First thin film 33B Second thin film 41 Substrate 42 Cavity unit 43 Cavity unit 45 Support Element

Claims (20)

A resonator main body including a piezoelectric film, and an upper electrode and a lower electrode formed to face each other with the piezoelectric film interposed therebetween;
The resonator body has a resonance region where both the upper electrode and the lower electrode are formed, and a portion excluding the resonance region of the resonator body, and a periodic uneven shape is formed. A piezoelectric resonator having an acoustic reflection region as a portion.   The piezoelectric resonator according to claim 1, wherein the concavo-convex portion forms a sonic crystal in the acoustic reflection region. The uneven shape is formed by a plurality of convex portions formed on the piezoelectric film,
The distance between the outer periphery of one of the plurality of convex portions and the outer periphery of another convex portion adjacent to the one convex portion is based on the wavelength of the sound wave set as the operating frequency of the resonator body portion. The piezoelectric resonator according to claim 1, wherein the piezoelectric resonator is short. The uneven shape is formed by a plurality of recesses formed in the piezoelectric film,
The interval between the outer periphery of one of the plurality of recesses and the outer periphery of another recess adjacent to the one recess is shorter than the wavelength of the sound wave set as the operating frequency of the resonator body. The piezoelectric resonator according to claim 1 or 2, characterized in that:   The piezoelectric resonator according to claim 4, wherein at least some of the plurality of recesses are formed so as to penetrate the piezoelectric film. A substrate having a cavity and holding the lower electrode in the resonator body;
The piezoelectric resonator according to claim 5, wherein at least a part of the plurality of concave portions penetrates the piezoelectric film and reaches a position deeper than an upper surface of the substrate. A substrate for holding the lower electrode in the resonator main body;
In the resonance region, a cavity is formed between the substrate and the resonator body,
The piezoelectric resonator according to claim 5, wherein at least a part of the plurality of concave portions penetrates the piezoelectric film and reaches a position deeper than an upper surface of the substrate. A substrate,
A holding member formed on the substrate and holding the lower electrode in the resonator body,
6. The piezoelectric resonator according to claim 5, wherein at least a part of the plurality of recesses penetrates the piezoelectric film and reaches a position deeper than an upper surface of the holding member. An acoustic mirror formed on a substrate, wherein the first thin film and a second thin film having a higher acoustic impedance than the first thin film are laminated, and holding the lower electrode in the resonator body Further comprising a layer,
6. The piezoelectric resonator according to claim 5, wherein at least a part of the plurality of recesses penetrates the piezoelectric film and reaches a position deeper than an upper surface of the acoustic mirror layer.   The at least part of the plurality of recesses reaches a position deeper than an interface between the first thin film and the second thin film formed on the uppermost part of the acoustic mirror layer. 9. The piezoelectric resonator according to 9. The plane dimension of the acoustic mirror layer is larger than the plane dimension of the resonator body.
11. The piezoelectric resonator according to claim 9, wherein the plurality of concave portions are also formed in a region around a portion of the acoustic mirror layer where the resonator main body portion is held. The resonator body has a plurality of resonance regions and a plurality of acoustic reflection regions,
The piezoelectric resonator according to any one of claims 1 to 11, wherein the formation periods of the recesses in the acoustic reflection regions are different from each other.   A filter comprising the piezoelectric resonator according to claim 12. An acoustic mirror layer formed by alternately laminating a first thin film and a second thin film having a higher acoustic impedance than the first thin film formed on the substrate;
A resonator main body that is held on the acoustic mirror layer and includes a piezoelectric film and an upper electrode and a lower electrode that are formed to face each other with the piezoelectric film interposed therebetween;
The acoustic mirror layer has a plurality of concave portions formed periodically in a region around a portion where the acoustic resonator main body is held,
The interval between the outer periphery of one of the plurality of recesses and the outer periphery of another recess adjacent to the one recess is shorter than the wavelength of the sound wave set as the operating frequency of the resonator body. A characteristic piezoelectric resonator.   15. The piezoelectric resonator according to claim 14, wherein the recess is formed in a region including a portion of the acoustic mirror layer where the acoustic resonator main body is held.   16. The piezoelectric resonator according to claim 14, wherein a material having a lower acoustic impedance than that of the first thin film is embedded in the recess. An acoustic mirror layer formed by alternately laminating a first thin film and a second thin film having a higher acoustic impedance than the first thin film formed on the substrate;
A resonator main body that is held on the acoustic mirror layer and includes a piezoelectric film and an upper electrode and a lower electrode that are formed to face each other with the piezoelectric film interposed therebetween;
In at least one of the first thin films, a plurality of holes penetrating vertically are periodically formed,
The distance between the outer periphery of one of the plurality of holes and the outer periphery of the other hole adjacent to the one hole is based on the wavelength of the sound wave set as the operating frequency of the resonator body. A piezoelectric resonator characterized by being short.   The piezoelectric resonator according to claim 17, wherein a material having a lower acoustic impedance than that of the first thin film is embedded in the hole.   The piezoelectric resonator according to any one of claims 14 to 18, wherein a plurality of the resonator main body portions are held on the acoustic mirror layer. A filter comprising the piezoelectric resonator according to claim 19.

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