阅读说明：本技术 单晶体声波谐振器及其制造方法、滤波器及电子设备 (Single crystal bulk acoustic wave resonator, method for manufacturing the same, filter, and electronic device ) 是由 张孟伦 庞慰 牛鹏飞 于 2020-12-31 设计创作，主要内容包括：本发明涉及一种体声波谐振器及其制造方法。该谐振器包括：基底；声学镜；底电极；顶电极；和单晶压电层,设置在底电极与顶电极之间,其中：声学镜、底电极、压电层和顶电极在谐振器的厚度方向上的重合区域构成谐振器的有效区域；压电层的下表面与基底的上表面之间设置有支撑结构,压电层与基底大体平行布置；且在有效区域之外,所述压电层的上表面的至少一部分设置有绝缘层。本发明还涉及一种体声波谐振器组件、一种滤波器以及一种电子设备。(The present invention relates to a bulk acoustic wave resonator and a method of manufacturing the same. The resonator includes: a substrate; an acoustic mirror; a bottom electrode; a top electrode; and a single crystal piezoelectric layer disposed between the bottom electrode and the top electrode, wherein: the superposition area of the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode in the thickness direction of the resonator forms the effective area of the resonator; a support structure is arranged between the lower surface of the piezoelectric layer and the upper surface of the substrate, and the piezoelectric layer and the substrate are arranged in a substantially parallel manner; and outside the active area, at least a portion of an upper surface of the piezoelectric layer is provided with an insulating layer. The invention also relates to a bulk acoustic wave resonator assembly, a filter and an electronic device.)

1. A bulk acoustic wave resonator comprising:

a substrate;

an acoustic mirror;

a bottom electrode;

a top electrode; and

a single crystal piezoelectric layer disposed between the bottom electrode and the top electrode,

wherein:

the superposition area of the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode in the thickness direction of the resonator forms the effective area of the resonator;

a support structure is disposed between a lower surface of the piezoelectric layer and an upper surface of the base, the piezoelectric layer being disposed substantially parallel to the base.

2. The resonator of claim 1, wherein:

outside the active area, at least a portion of an upper surface of the piezoelectric layer is provided with an insulating layer.

3. The resonator of claim 2, wherein:

the insulating layer is provided at least between a lower surface of the top electrode and an upper surface of the piezoelectric layer in a region corresponding to a portion of the top electrode outside the active region.

4. The resonator of claim 3, wherein:

the insulating layer is arranged between the lower surface of the electrode connecting end of the top electrode and the upper surface of the piezoelectric layer.

5. The resonator of claim 2, wherein:

at least a portion of a surface of the upper surface of the piezoelectric layer not covered by the top electrode is provided with an insulating layer.

6. The resonator of claim 5, wherein:

and at the position of the piezoelectric layer where the through hole is not formed, the part of the upper surface of the piezoelectric layer which is not covered by the top electrode is provided with an insulating layer.

7. The resonator of claim 6, wherein:

the through holes comprise first through holes, and the electrode connecting structure is electrically connected with the electrode connecting end of the bottom electrode through the first through holes; and/or

The acoustic mirror is an acoustic mirror cavity, and the through hole comprises a second through hole which is communicated with the acoustic mirror cavity and is used as a release hole.

8. The resonator of claim 1, wherein:

the acoustic mirror is an acoustic mirror cavity that is shaped to be recessed into the support layer, and a lower boundary of the acoustic mirror cavity is defined by the support layer.

9. The resonator of any of claims 1-8, wherein:

the piezoelectric layer is a lithium niobate piezoelectric layer or a lithium tantalate piezoelectric layer.

10. A method of manufacturing a bulk acoustic wave resonator, the bulk acoustic wave resonator comprising a substrate; an acoustic mirror; a bottom electrode; a top electrode; and a piezoelectric layer disposed between the bottom electrode and the top electrode, the method comprising:

step 1: providing a POI wafer comprising a substrate, a single crystal piezoelectric layer, and an insulating layer disposed between a first side of the single crystal piezoelectric layer and the substrate;

step 2: forming a bottom electrode on a second side of the piezoelectric layer of the POI wafer opposite the first side;

and step 3: providing an intermediate layer consisting of an acoustic mirror layer and a support layer, wherein the intermediate layer covers the second side of the piezoelectric layer and the bottom electrode, and one side of the intermediate layer, which is far away from the substrate, is a flat surface;

and 4, step 4: bonding the substrate to the intermediate layer at the flat side of the intermediate layer;

and 5: removing the substrate and the insulating layer, wherein at least a part of the insulating layer is removed to expose the first side of the piezoelectric layer, and the insulating layer corresponding to the effective area of the resonator on the first side of the piezoelectric layer is removed;

step 6: a top electrode and an electrode connection structure are disposed on a first side of the piezoelectric layer.

11. The method of claim 10, wherein:

step 5 includes step 5A: removing the entire substrate; and removing at least a portion of the insulating layer, the insulating layer acting as a barrier to the removal of the substrate during the removal of the entire substrate.

12. The method of claim 10, wherein:

step 5 includes step 5B: forming a plurality of release holes in a substrate; and releasing the insulating layer via the plurality of release holes.

13. The method of claim 12, wherein:

at least part of the release holes are arranged outside the area of the resonator.

14. The method of claim 10, wherein:

in step 5, all of the insulating layer is removed.

15. The method of claim 10, wherein:

in step 5, at least a portion of the upper surface of the piezoelectric layer is left with the insulating layer outside the active area of the resonator.

16. The method of claim 15, wherein:

such that the insulating layer remains between the lower surface of the top electrode and the upper surface of the piezoelectric layer in an area corresponding to a portion of the top electrode outside the active area.

17. The method of claim 16, wherein:

so that the insulating layer remains between the lower surface of the electrode connection end of the top electrode and the upper surface of the piezoelectric layer.

18. The method of claim 10, wherein:

such that at least a portion of the surface of the upper surface of the piezoelectric layer not covered by the top electrode remains with the insulating layer.

19. The method of claim 18, wherein:

the method further comprises the steps of: providing a through hole in the piezoelectric layer;

so that the insulating layer remains on the portion of the upper surface of the piezoelectric layer not covered with the top electrode at a position where the through hole is not provided on the piezoelectric layer.

20. The method of claim 10, wherein:

the acoustic mirror is an acoustic mirror cavity, the acoustic mirror layer is a sacrificial material layer, and the step 3 includes: step 3A: forming a sacrificial material layer covering only a part of the bottom electrode or covering a part of the non-electrode connecting end of the bottom electrode and a part of the piezoelectric layer; and step 3B: providing a support material layer covering the sacrificial material layer, the bottom electrode and the piezoelectric layer, and flattening the support material layer to form the support layer; or

The acoustic mirror is a non-Bragg reflection layer, the acoustic mirror layer is a Bragg reflection layer, and the step 3 comprises the following steps: and step 3C: forming an unmelted grating reflective layer covering only a portion of the bottom electrode; and step 3D: a layer of support material is provided overlying the bragg reflector layer, the bottom electrode, and the piezoelectric layer such that the layer of support material is planarized to form the support layer.

21. The method of claim 20, wherein:

in step 3B or step 3D, the side of the support layer facing away from the substrate is made to constitute the flat surface, or the side of the support layer facing away from the substrate is made flush with the side of the acoustic mirror layer facing away from the substrate so as to collectively constitute the flat surface.

22. The method of claim 10, wherein:

the acoustic mirror is an acoustic mirror cavity, the acoustic mirror layer is a sacrificial material layer, and the step 3 includes: and step 3E: providing a layer of support material covering the bottom electrode and the piezoelectric layer, and planarizing the layer of support material; and step 3F: removing a portion of the support material at a location of the layer of support material corresponding to the acoustic mirror to form an acoustic mirror cavity and a support layer; or

The acoustic mirror is a non-Bragg reflection layer, the acoustic mirror layer is a Bragg reflection layer, and the step 3 comprises the following steps: step 3H: providing a layer of support material covering the bottom electrode and the piezoelectric layer, and planarizing the layer of support material; step 3I: removing a portion of the support material at a location of the layer of support material corresponding to the acoustic mirror to form a cavity and a support layer; step 3J: and forming a Bragg reflection layer in the cavity.

23. The method of claim 22, wherein:

the method comprises the following steps of 3G: after step 3F, filling a sacrificial material in the acoustic mirror cavity and allowing the filled sacrificial material layer and the support layer to define the flat face together;

the method further comprises the steps of: providing a release through hole in the piezoelectric layer, and releasing the sacrificial material layer based on the release through hole.

24. A method of manufacturing a bulk acoustic wave resonator, comprising the steps of:

providing a POI wafer comprising a substrate, a single crystal piezoelectric layer, and an insulating layer disposed between a first side of the single crystal piezoelectric layer and the substrate;

and removing the substrate and at least one part of the insulating layer, wherein the insulating layer is used as a barrier layer for protecting the piezoelectric layer in the process of removing the substrate, the at least one part of the insulating layer is removed to expose the piezoelectric layer, and the insulating layer of the piezoelectric layer corresponding to the effective area of the resonator is removed.

25. The method of claim 24, wherein:

all of the insulating layer is removed.

26. The method of claim 24, wherein:

such that the insulating layer remains between the top electrode and the piezoelectric layer in a region corresponding to a portion of the top electrode of the resonator outside the active area.

27. The method of any one of claims 10-26, wherein:

the single crystal piezoelectric layer is a lithium niobate piezoelectric layer or a lithium tantalate piezoelectric layer.

28. A filter comprising a bulk acoustic wave resonator according to any one of claims 1-9.

29. An electronic device comprising a filter according to claim 28, or a bulk acoustic wave resonator according to any of claims 1-9.

Technical Field

Embodiments of the present invention relate to the field of semiconductors, and in particular, to a single crystal acoustic wave resonator, a method of manufacturing the same, a filter having the same, and an electronic device.

Background

Electronic devices have been widely used as basic elements of electronic equipment, and their application ranges include mobile phones, automobiles, home electric appliances, and the like. In addition, technologies such as artificial intelligence, internet of things, 5G communication and the like which will change the world in the future still need to rely on electronic devices as a foundation.

Film Bulk Acoustic Resonator (FBAR, also called Bulk Acoustic Resonator, BAW for short) is playing an important role in the communication field as an important member of piezoelectric devices, especially FBAR filters have an increasingly large market share in the field of radio frequency filters, FBARs have excellent characteristics of small size, high resonant frequency, high quality factor, large power capacity, good roll-off effect and the like, the filters gradually replace traditional Surface Acoustic Wave (SAW) filters and ceramic filters, play a great role in the radio frequency field of wireless communication, and the advantage of high sensitivity can also be applied to sensing fields of biology, physics, medicine and the like.

The structural main body of the film bulk acoustic resonator is a sandwich structure consisting of a bottom electrode, a piezoelectric film or a piezoelectric layer and a top electrode, namely a layer of piezoelectric material is sandwiched between two metal electrode layers. By inputting a sinusoidal signal between the two electrodes, the FBAR converts the input electrical signal into mechanical resonance using the inverse piezoelectric effect, and converts the mechanical resonance into an electrical signal for output using the piezoelectric effect.

Due to the limitations of the manufacturing process, for example, the existence of the non-electrode connecting end of the bottom electrode, the piezoelectric layer of the bulk acoustic wave resonator is not a flat structure, which is not favorable for improving the performance of the resonator.

The prior art has proposed that the piezoelectric layer is a single crystal piezoelectric layer having a flat characteristic, so that the problem caused by the presence of the stepped portion of the piezoelectric layer can be overcome. However, in the manufacturing process of the bulk acoustic wave resonator based on the single crystal piezoelectric layer, there is a case that the piezoelectric layer is easily damaged in the process of removing the auxiliary base.

Disclosure of Invention

The present invention has been made to mitigate or solve at least one of the above-mentioned problems in the prior art.

According to an aspect of an embodiment of the present invention, there is provided a bulk acoustic wave resonator including:

a substrate;

an acoustic mirror;

a bottom electrode;

a top electrode; and

a single crystal piezoelectric layer disposed between the bottom electrode and the top electrode,

wherein:

the superposition area of the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode in the thickness direction of the resonator forms the effective area of the resonator;

a support structure is disposed between a lower surface of the piezoelectric layer and an upper surface of the base, the piezoelectric layer being disposed substantially parallel to the base.

Further optionally, at least a portion of an upper surface of the piezoelectric layer is provided with an insulating layer outside the active area.

The invention also relates to a method of manufacturing a bulk acoustic wave resonator comprising a substrate; an acoustic mirror; a bottom electrode; a top electrode; and a piezoelectric layer disposed between the bottom electrode and the top electrode, the method comprising:

step 1: providing a POI wafer comprising a substrate, a single crystal piezoelectric layer, and an insulating layer disposed between a first side of the single crystal piezoelectric layer and the substrate;

step 2: forming a bottom electrode on a second side of the piezoelectric layer of the POI wafer opposite the first side;

and step 3: providing an intermediate layer consisting of an acoustic mirror layer and a support layer, wherein the intermediate layer covers the second side of the piezoelectric layer and the bottom electrode, and one side of the intermediate layer, which is far away from the substrate, is a flat surface;

and 4, step 4: bonding the substrate to the intermediate layer at the flat side of the intermediate layer;

and 5: removing the substrate and the insulating layer, wherein at least a part of the insulating layer is removed to expose the first side of the piezoelectric layer, and the insulating layer corresponding to the effective area of the resonator on the first side of the piezoelectric layer is removed;

step 6: a top electrode and an electrode connection structure are disposed on a first side of the piezoelectric layer.

An embodiment of the present invention also relates to a method for manufacturing a bulk acoustic wave resonator, including the steps of:

providing a POI wafer comprising a substrate, a single crystal piezoelectric layer, and an insulating layer disposed between a first side of the single crystal piezoelectric layer and the substrate;

and removing the substrate and at least one part of the insulating layer, wherein the insulating layer is used as a barrier layer for protecting the piezoelectric layer in the process of removing the substrate, the at least one part of the insulating layer is removed to expose the piezoelectric layer, and the insulating layer of the piezoelectric layer corresponding to the effective area of the resonator is removed.

Embodiments of the present invention also relate to a filter comprising the bulk acoustic wave resonator described above.

Embodiments of the invention also relate to an electronic device comprising a filter as described above or a resonator as described above.

Drawings

These and other features and advantages of the various embodiments of the disclosed invention will be better understood from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate like parts throughout, and in which:

1A-1C are, respectively, a top view illustration, a schematic cross-sectional view along line AA in FIG. 1A, and a schematic cross-sectional view along line BB in FIG. 1A of a bulk acoustic wave resonator in accordance with an exemplary embodiment of the present invention;

2A-2C through 18A-18C are a series of diagrams illustrating exemplary fabrication processes of the bulk acoustic wave resonator shown in FIGS. 1A-1C, wherein A corresponds to a top view schematic, B corresponds to a schematic cross-sectional view of line AA, and C corresponds to a schematic cross-sectional view of line BB;

fig. 19A to 19C and fig. 20A to 20C are a series of diagrams exemplarily showing a manufacturing process of a bulk acoustic wave resonator according to another exemplary embodiment of the present invention which is different from that shown in fig. 2A to 2C up to fig. 18A to 18C, wherein a corresponds to a schematic top view, B corresponds to a schematic cross-sectional view of line AA, and C corresponds to a schematic cross-sectional view of line BB;

fig. 21A to 21C and fig. 24A to 24C are a series of diagrams exemplarily showing a manufacturing process of a bulk acoustic wave resonator according to still another exemplary embodiment of the present invention which is different from that shown in fig. 2A to 2C up to fig. 18A to 18C, wherein a corresponds to a schematic top view, B corresponds to a schematic cross-sectional view of line AA, and C corresponds to a schematic cross-sectional view of line BB;

fig. 25A-25C are schematic top views, schematic cross-sectional views along line AA in fig. 25A, and schematic cross-sectional views along line BB in fig. 25A, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention, showing a remaining insulating layer between an electrode connection end of a top electrode and a piezoelectric layer;

fig. 26A to 26C are schematic diagrams illustrating a partial removal of an insulating layer in a manufacturing process of the bulk acoustic wave resonator illustrated in fig. 25A to 25C, wherein a corresponds to a schematic top view, B corresponds to a schematic cross-sectional view of line AA, and C corresponds to a schematic cross-sectional view of line BB, and when the insulating layer is removed, the insulating layer between the electrode connection end of the top electrode and the piezoelectric layer remains;

27A-27C are schematic top views, schematic cross-sectional views along line AA in FIG. 27A, and schematic cross-sectional views along line BB in FIG. 27A, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention showing an upper surface of a piezoelectric layer with a remaining insulating layer outside an electrode deposition area on an upper side of the piezoelectric layer;

fig. 28A to 28C are schematic diagrams illustrating a partial removal of an insulating layer in the process of manufacturing the bulk acoustic wave resonator illustrated in fig. 27A to 27C, where fig. 28A corresponds to a schematic top view, fig. 28B corresponds to a schematic cross-sectional view of line AA in fig. 28A, and fig. 28C corresponds to a schematic cross-sectional view of line BB in fig. 28A, and when the insulating layer is removed, the insulating layer is left outside an electrode deposition region on the upper side of the piezoelectric layer.

Detailed Description

The technical scheme of the invention is further specifically described by the following embodiments and the accompanying drawings. In the specification, the same or similar reference numerals denote 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 general inventive concept of the present invention and should not be construed as limiting the invention. Some, but not all embodiments of the invention are described. All other embodiments that can be derived by one of ordinary skill in the art from the embodiments given herein are intended to be within the scope of the present invention.

In the present invention, a bulk acoustic wave resonator is fabricated based on a POI (single crystal piezoelectric layer on Insulator) substrate. The POI wafer includes an auxiliary substrate, a single crystal piezoelectric layer, and an insulating layer disposed between the single crystal piezoelectric layer and the auxiliary substrate.

As mentioned later, the insulating layer can better protect the single crystal piezoelectric film (i.e. the single crystal piezoelectric layer) during the transfer process of the resonator, so that the damage to the single crystal piezoelectric film during the subsequent process of removing the auxiliary substrate can be reduced or even avoided, and the surface damage to the piezoelectric film can be reduced or even avoided, so as to obtain the bulk acoustic wave resonator with excellent performance.

In addition, the existence of the insulating layer is also beneficial to diversification of an auxiliary substrate removing scheme, and the device processing technology is simplified.

Embodiments of the present invention will be specifically described below with reference to fig. 1A to 1C through fig. 18A to 18C.

The reference numerals in the drawings of the present invention are exemplarily illustrated as follows:

100: the auxiliary substrate is made of silicon, silicon carbide, sapphire, silicon dioxide or other silicon-based materials.

101: a release hole penetrating the substrate 100.

110: the insulating layer functions as an electrical insulator, and is, for example, silicon dioxide, silicon nitride, silicon carbide, sapphire, or the like.

111: an insulating layer, which functions to protect the piezoelectric layer or to separate the electrode connection terminal from the piezoelectric layer, such as silicon dioxide, silicon nitride, silicon carbide, sapphire, etc., may be a part of the insulating layer 110.

120: a single crystal piezoelectric layer, which may be made of single crystal aluminum nitride, single crystal gallium nitride, single crystal lithium niobate, single crystal lead zirconate titanate, single crystal potassium niobate, single crystal quartz film, or single crystal lithium tantalate, and may further include an atomic ratio of rare earth element doped material of the above materials, for example, doped aluminum nitride, which contains at least one rare earth element, such as scandium (Sc), yttrium (Y), magnesium (Mg), titanium (Ti), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and the like.

121: and the release hole is used for releasing the sacrificial layer material in the acoustic mirror cavity.

122: vias or electrical connection holes, in particular embodiments, are used to deposit conductive material to bring the bottom electrode 131 out to be coplanar with the top electrode 181.

130: the bottom electrode film layer is made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or their composite or their alloy.

131: the bottom electrode is formed by patterning a bottom electrode film layer, for example.

140: the sacrificial material film may be polysilicon, amorphous silicon, silicon dioxide, phosphorus doped silicon dioxide (PSG), zinc oxide, magnesium oxide, polymer, and the like.

141: the sacrificial material layer includes a cavity region 142 corresponding to the cavity of the acoustic mirror formed after release and a channel region for forming a release channel of the sacrificial material after release.

142: the release of the sacrificial material layer 141 forms the cavity region of the acoustic mirror cavity.

143: the acoustic mirror can be a cavity, and a Bragg reflection layer and other equivalent forms can also be adopted. The embodiment of the invention shown uses a cavity.

150: the supporting material layer can be made of aluminum nitride, silicon nitride, polysilicon, silicon dioxide, amorphous silicon, boron-doped silicon dioxide and other silicon-based materials

151: and the support layer is formed by flattening the support material layer.

160. a bonding layer, which may be silicon dioxide or other silicon-based material, may be used to bond the support layer to the transfer substrate, and this material may be omitted. The bonding layer may also be an adhesive tape or the like.

170: the substrate is made of silicon, silicon carbide, sapphire, silicon dioxide or other silicon-based materials.

180: the top electrode film layer is made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or their composite or their alloy. The material of the top electrode film layer may be the same as or different from the material of the bottom electrode film layer.

181: the top electrode is formed by patterning a top electrode film layer, for example.

182: the material of the bottom electrode electric connection part can be selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium or the compound of the above metals or the alloy thereof, and the like. The material of the bottom electrode electrical connection portion 182 may be the same as or different from that of the top electrode film layer.

Fig. 1A to 1C are a top view, a schematic cross-sectional view along line AA in fig. 1A, and a schematic cross-sectional view along line BB in fig. 1A, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention.

Fig. 2A to 2C through fig. 18A to 18C illustrate a series of diagrams of a manufacturing process of the bulk acoustic wave resonator shown in fig. 1A to 1C, in all of which a corresponds to a schematic top view, B corresponds to a schematic cross-sectional view of line AA, and C corresponds to a schematic cross-sectional view of line BB.

Fig. 2A-2C show a POI wafer. As shown in fig. 2, the POI wafer includes an auxiliary substrate 100, an insulating layer 110, and a single crystal piezoelectric layer 120, which may be a piezoelectric single crystal thin film such as lithium niobate, lithium tantalate, quartz, etc., as already mentioned above.

The crystal orientation of the piezoelectric single crystal film in the POI wafer is various and is not limited by the growth conditions of the piezoelectric thin film, so that the piezoelectric single crystal film with special crystal orientation can be selected according to the requirement to manufacture resonators and filters with various performances.

FIGS. 2A-2C correspond to step 1: a POI wafer is provided that includes an auxiliary substrate 100, a single crystal piezoelectric layer 120, and an insulating layer 110 disposed between a first side of the single crystal piezoelectric layer and the substrate.

Fig. 3A to 3C and fig. 4A to 4C exemplarily show a process of depositing an electrode film layer on a surface of a piezoelectric single crystal thin film and forming a pattern of a bottom electrode. Fig. 3A to 3C are respectively a schematic top view, a schematic cross-sectional view along line AA in fig. 3A, and a schematic cross-sectional view along line BB in fig. 3A of a bulk acoustic wave resonator. Fig. 4A to 4C are a schematic top view, a schematic cross-sectional view along line AA in fig. 4A, and a schematic cross-sectional view along line BB in fig. 4A, respectively, of a bulk acoustic wave resonator.

A uniform electrode film 130 can be first deposited on the piezoelectric layer 120, as shown in fig. 3A-3C; the patterned bottom electrode 131 is then formed by wet or dry etching, as shown in fig. 4A-4C).

Alternatively, the pattern of the bottom electrode may be directly formed by a lift-off process (lift-off) or a printing process.

The bottom electrode active area shown in fig. 4A-4C is elliptical, but may also be polygonal, such as circular, square, pentagonal, hexagonal, etc.

FIGS. 3A-3C and FIGS. 4A-4C correspond to step 2: a bottom electrode 131 is formed on a second side of the piezoelectric layer 120 of the POI wafer opposite the first side.

Figures 5A-5C and 6A-6D illustrate the process of depositing a film layer 140 of sacrificial material and patterning the layer 141 of sacrificial material on the bottom electrode 131 and the single crystal piezoelectric layer 120. Fig. 5A to 5C are respectively a schematic top view, a schematic cross-sectional view along the line AA in fig. 5A, and a schematic cross-sectional view along the line BB in fig. 5A of a bulk acoustic wave resonator. Fig. 6A to 6D are respectively a schematic top view, a schematic cross-sectional view along the line AA in fig. 6A, a schematic cross-sectional view along the line BB in fig. 6A, and a schematic cross-sectional view along the line AA' in fig. 6A of a bulk acoustic wave resonator.

The patterned sacrificial material layer 141 may be formed by first depositing a uniform sacrificial material film layer 140 on the bottom electrode 131 and the piezoelectric single crystal thin film as shown in fig. 5A to 5C, and then forming the patterned sacrificial material layer 141 by wet or dry etching as shown in fig. 6A to 6D.

In fig. 6A to 6D, the sacrificial material layer 141 (corresponding to the acoustic mirror cavity) covers only a part of the bottom electrode 131 (at this time, as shown in fig. 18B, the non-electrode connecting end of the bottom electrode 131 is caused to be covered by the support layer 151 mentioned later), but the present invention is not limited thereto, and the sacrificial material layer 141 may cover both a part of the bottom electrode 131 and a part of the piezoelectric layer at the non-electrode connecting end of the bottom electrode 131 (at this time, although not shown, the non-electrode connecting end of the bottom electrode 131 is caused to be within the acoustic mirror cavity and not covered by the support layer 151).

The sacrificial material layer 141 of fig. 6C and 6D includes a cavity region 142 corresponding to the cavity of the acoustic mirror formed after release and a channel region for the release channel of the sacrificial material formed after release.

Fig. 7A-7C and 8A-8C illustrate the process of depositing and planarizing a layer of support material on the single crystal piezoelectric layer 120, the bottom electrode 131, and the layer of sacrificial material 141. The thickness of the support material layer 150 is greater than the thickness of the bottom electrode 131. The polished support layer 151 is formed by a polishing process such as CMP (chemical mechanical polishing).

FIGS. 5A-5C, FIGS. 6A-6D, FIGS. 7A-7C, and FIGS. 8A-8C correspond to step 3: an intermediate layer consisting of an acoustic mirror layer (i.e., a layer for forming an acoustic mirror) and a support layer 151 is provided, the intermediate layer covering the second side of the piezoelectric layer 120 and the bottom electrode 131, and a side of the intermediate layer remote from the auxiliary substrate 100 being a flat surface. More specifically, in fig. 5A-5C, fig. 6A-6D, fig. 7A-7C, and fig. 8A-8C, step 3 includes: step 3A: forming a sacrificial material layer 141, the sacrificial material layer 141 covering only a portion of the bottom electrode 131 or a portion of the non-electrode connecting end of the bottom electrode 131 and a portion of the piezoelectric layer 120; and step 3B: a support material layer 150 is provided covering the sacrificial material layer 141, the bottom electrode 131 and the piezoelectric layer 120 such that the support material layer 150 is planarized to form the support layer 151.

More specifically, in step 3B described above, the side of the support layer 151 away from the substrate 100 is made the flat surface. However, the present invention is not limited thereto, and as shown in fig. 19A to 19C, for example, the support material layer 150 may also be ground and polished until the side of the support layer 151 away from the substrate 100 is made flush with the side of the sacrificial material layer 141 away from the substrate 100 to collectively constitute the flat surface.

As will be understood by those skilled in the art, the acoustic mirror may also employ a bragg reflector, and in this case, step 3 includes: and step 3C: forming a non-Lag reflective layer covering only a portion of the bottom electrode; and step 3D: a layer of support material overlying the bragg reflector layer, the bottom electrode, and the piezoelectric layer is disposed such that the layer of support material is planarized to form the support layer.

More specifically, in the above step 3D, the side of the support layer 151 away from the substrate 100 is made to constitute the flat surface. However, the present invention is not limited thereto, and the support material layer 150 may be polished until the side of the support layer 151 away from the substrate 100 is flush with the side of the bragg reflection layer away from the substrate 100 to collectively constitute the flat surface.

Fig. 9A to 9C and fig. 10A to 10C illustrate a process of bonding the support layer 151 with the substrate 170. Fig. 9A to 9C are respectively a schematic top view, a schematic cross-sectional view along the line AA in fig. 9A, and a schematic cross-sectional view along the line BB in fig. 9A of a bulk acoustic wave resonator. Fig. 10A to 10C are a schematic top view, a schematic cross-sectional view along line AA in fig. 10A, and a schematic cross-sectional view along line BB in fig. 10A, respectively, of a bulk acoustic wave resonator.

As shown in fig. 9A to 9C, the flat surface of the support layer 151 is provided with a bonding layer 160, and as shown in fig. 10A to 10C, a substrate 170 is bonded to the support layer 151 via the bonding layer 160.

The substrate 170 and the support layer 151 may be physically or chemically bonded, and the material of the bonding layer 160 may be on the substrate 170 or the support layer 151, or on both surfaces.

The substrate 170 and the support layer 151 may be directly bonded without a bonding layer, and a chemical bond may be formed between the substrate 170 and the support layer 151, or a physical bond may be formed by intermolecular force when the surface is polished to have extremely low surface roughness.

Fig. 9A to 9C and fig. 10A to 10C correspond to step 4: the substrate 170 is bonded to the intermediate layer (containing the support layer and the sacrificial material layer) at its planar side.

Fig. 11A-11D to 13A-13C are processes of device inversion, removal of the substrate 100 and the insulating layer 110. Fig. 11A to 11C are respectively a schematic top view, a schematic cross-sectional view along the line AA in fig. 11A, and a schematic cross-sectional view along the line BB in fig. 11A of the bulk acoustic wave resonator, and fig. 11D is a schematic diagram of a removal manner different from fig. 11B. Fig. 12A to 12C are a schematic top view, a schematic cross-sectional view along the line AA in fig. 12A, and a schematic cross-sectional view along the line BB in fig. 12A, respectively, of a bulk acoustic wave resonator. Fig. 13A to 13C are a schematic plan view, a schematic cross-sectional view along line AA in fig. 13A, and a schematic cross-sectional view along line BB in fig. 13A, respectively, of a bulk acoustic wave resonator.

The etching processes of the auxiliary substrate 100 and the insulating layer 110 (barrier layer) are different, for example, the auxiliary substrate 100 is silicon, the insulating layer 110 is silicon dioxide, the insulating layer 110 can function as a stop layer or a barrier layer in the process of removing the auxiliary substrate 100, the removing process of the insulating layer 110 is mild, and damage to the other surface of the piezoelectric single crystal thin film in the process of removing the auxiliary substrate 100 is reduced or even avoided.

The piezoelectric single crystal thin film surface release process may be implemented by removing the substrate 100 entirely and removing the insulating layer 110 entirely, for example, see fig. 11B, 12B, and 13B.

In an alternative embodiment, as shown in fig. 11D, due to the existence of the insulating layer 110 as a barrier layer, the piezoelectric single crystal thin film surface release process may employ first forming release holes 101 on the substrate 100, and then releasing the insulating layer 110 material through the release holes. If the process of forming the release holes 101 on the substrate 100 does not cause any damage to the insulating layer 110 and the single crystal piezoelectric layer 120, the release holes may be arranged in any region; if the insulating layer 110 and the single crystal piezoelectric layer 120 are damaged, a release hole can be formed in an out-of-band area (such as a scribe lane) of the resonator or a filter formed by the resonator, so that the device processing process is simple.

The process of removing the entire substrate 100 or forming the release hole may be grinding, lapping, polishing, wet or dry etching, laser ablation, or the like, or a combination thereof.

The overall removal process of the insulating layer 110 may use grinding, lapping, polishing, wet or dry etching, laser ablation, or other related processes or a combination of these processes.

After the insulating layer 110 is removed, if the surface of the piezoelectric single crystal thin film has partial damage, particularly, the effective region of the resonator or the filter formed of the resonator has damage, the surface of the piezoelectric thin film may be polished through a polishing process.

Fig. 11A to 11D to fig. 13A to 13C correspond to step 5: the substrate and the insulating layer are removed, at least a portion of the insulating layer is removed to expose the first side of the piezoelectric layer, and the insulating layer of the first side of the piezoelectric layer corresponding to the active area of the resonator is removed.

Fig. 14A to 14C and fig. 15A to 15C show a process of depositing a top electrode film on the release surface of the piezoelectric single crystal film or piezoelectric layer 120 and patterning the top electrode. Fig. 14A to 14C are respectively a schematic top view, a schematic cross-sectional view along the line AA in fig. 14A, and a schematic cross-sectional view along the line BB in fig. 14A of a bulk acoustic wave resonator. Fig. 15A to 15C are a schematic top view, a schematic cross-sectional view along the line AA in fig. 15A, and a schematic cross-sectional view along the line BB in fig. 15A, respectively, of a bulk acoustic wave resonator.

The top electrode may be formed by first depositing a uniform electrode film layer 180 (as shown in fig. 14A-14C) and then forming a patterned top electrode 181 (as shown in fig. 15A-15C) by means of wet or dry etching.

The top electrode may be directly patterned by a lift-off process (lift-off) or a printing process.

The active area of the top electrode shown in fig. 15A is oval, but may be polygonal such as circular, square, pentagonal, hexagonal, etc., which is required to conform to the shape of the bottom electrode.

Fig. 16A to 16C and fig. 17A to 17C show a process of forming a release hole of a sacrificial material layer, a connection hole of a bottom electrode connection part on a piezoelectric layer, and forming an electrical connection pattern. Fig. 16A to 16C are respectively a schematic top view, a schematic cross-sectional view along the line AA in fig. 16A, and a schematic cross-sectional view along the line BB in fig. 16A of a bulk acoustic wave resonator. Fig. 17A to 17C are a schematic top view, a schematic cross-sectional view along the line AA in fig. 17A, and a schematic cross-sectional view along the line BB in fig. 17A, respectively, of a bulk acoustic wave resonator.

The release holes 121 (shown in fig. 16A-16C) and the electrical connection holes 122 (shown in fig. 16A-16C) for forming the sacrificial material layer may be implemented by a related process such as wet or dry etching, laser ablation, or a combination thereof.

Forming the electrical connection pattern or bottom electrode electrical connection 182 can be done by first depositing a uniform conductive film layer and then forming a patterned bottom electrode electrical connection by wet or dry etching, or by lift-off or printing processes, etc. (as shown in fig. 17A-17C).

The process of forming the release hole 121 of the sacrificial material layer, the electrical connection hole 122 of the bottom electrode (fig. 16A-16C and fig. 17A-17C), and the bottom electrode electrical connection 182 and the top electrode (fig. 14A-14C and fig. 15A-15C) can be interchanged.

Fig. 18A-18C illustrate the process of releasing the sacrificial material layer 143 to form the acoustic mirror cavity 143. Fig. 18A to 18C are respectively a schematic top view, a schematic cross-sectional view along the line AA in fig. 18A, and a schematic cross-sectional view along the line BB in fig. 18A of a bulk acoustic wave resonator.

The sacrificial material layer 141 may be removed by wet or dry methods to form the acoustic mirror cavity 143, thereby obtaining the resonator structure shown in fig. 1A-1C.

In the above embodiment, the sacrificial material layer 141 is formed first and then the support layer 151 is formed after the bottom electrode 131 is formed, but the present invention is not limited thereto and the sacrificial material layer 141 may be formed after the support material layer is formed. Fig. 21A-21C to 24A-24C illustrate such an embodiment according to the present invention.

After the bottom electrode 131 is formed, a support material layer 150 may be grown first (see fig. 21A to 21C) and planarized to form a support layer 151 (see fig. 22A to 22C). Next, the support layer 151 is etched to form a cavity, a sacrificial material is grown to fill the cavity to form a sacrificial material layer 141, the surface is ground and polished to a level where no sacrificial material is present except for the cavity (as shown in fig. 23A to 23C), and then the same or similar steps as in the above-described processes of fig. 2A to 2C to 18A to 18C are performed to bond the device to the substrate 170, remove the substrate 100 and the insulating layer 110, form the top electrode, and release the sacrificial material layer 141 to form the acoustic mirror cavity, thereby forming the resonator.

In addition, after the cavity is formed on the support layer 151, the resonator may be formed by directly bonding the device to the base, removing the substrate and the insulating layer, forming the top electrode, and the like in the same or similar steps as in the above-described processes of fig. 2A to 2C to 18A to 18C, without filling the sacrificial material. This processing step can form release holes on the piezoelectric layer 120 before the substrate 100 is removed, so that the two sides of the piezoelectric layer are connected, thereby preventing the single crystal piezoelectric film from cracking due to the difference of pressures on the two sides during the subsequent processing.

Based on the above, the invention provides a method for manufacturing a bulk acoustic wave resonator, which comprises the following steps:

providing a POI wafer comprising a substrate, a single crystal piezoelectric layer, and an insulating layer disposed between a first side of the single crystal piezoelectric layer and the substrate;

and removing the substrate and at least one part of the insulating layer, wherein the insulating layer is used as a barrier layer for protecting the piezoelectric layer in the process of removing the substrate, the at least one part of the insulating layer is removed to expose the piezoelectric layer, and the insulating layer of the piezoelectric layer corresponding to the effective area of the resonator is removed.

In the above embodiment, the insulating layer 110 is completely removed in the process of releasing the first side of the piezoelectric layer 120 to set the top electrode. However, the present invention is not limited thereto, in other words, in the present invention, only a portion of the insulating layer may be removed to expose the first side of the piezoelectric layer 120, and the insulating layer of the first side of the piezoelectric layer corresponding to the effective area of the resonator is removed.

Fig. 25A-25C are schematic top views, schematic cross-sectional views along line AA in fig. 25A, and schematic cross-sectional views along line BB in fig. 25A, respectively, of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention, showing a remaining insulating layer 111 (which is a portion of the insulating layer 110) between the electrode connection end of the top electrode and the piezoelectric layer. As can be appreciated, the insulating layer 110 within the active area of the resonator is removed. Since the insulating layer 111 may be disposed between the electrode connection end of the top electrode and the piezoelectric layer 120, it is advantageous to reduce an edge parasitic electric field of the resonator, thereby improving the performance of the resonator.

Fig. 26A to 26C are schematic diagrams illustrating a partial removal of the insulating layer 110 during the fabrication of the bulk acoustic wave resonator in fig. 25A to 25C according to an exemplary embodiment of the present invention, wherein fig. 26A corresponds to a schematic top view, fig. 26B corresponds to a schematic cross-sectional view along line AA in fig. 26A, and fig. 26C corresponds to a schematic cross-sectional view along line BB in fig. 26A, and when the insulating layer 110 is removed, a portion of the insulating layer 110 in the electrode deposition area on the upper side of the piezoelectric layer 120 remains to be formed as the insulating layer 111.

Fig. 27A to 27C are respectively a schematic top view, a schematic cross-sectional view along line AA in fig. 27A, and a schematic cross-sectional view along line BB in fig. 27A of a bulk acoustic wave resonator according to an exemplary embodiment of the present invention, in which the upper surface of the piezoelectric layer (excluding the electrical connection hole or the release hole) is shown with the insulating layer 111 remaining outside the electrode deposition area on the upper side of the piezoelectric layer 120. The insulating layer 111 here may function as a protective layer.

Fig. 28A to 28C schematically illustrate a schematic diagram of partially removing an insulating layer in the process of manufacturing the bulk acoustic wave resonator illustrated in fig. 27A to 27C, where fig. 28A corresponds to a schematic top view, fig. 28B corresponds to a schematic cross-sectional diagram taken along line AA in fig. 28A, and fig. 28C corresponds to a schematic cross-sectional diagram taken along line BB in fig. 28A, and when the insulating layer is removed, the insulating layer outside the electrode deposition region on the upper side of the piezoelectric layer remains to form the insulating layer 111.

In the present invention, the upper and lower are with respect to the bottom surface of the base of the resonator, and with respect to one component, the side thereof close to the bottom surface is the lower side, and the side thereof far from the bottom surface is the upper side.

In the present invention, the inner and outer are in the lateral direction or the radial direction with respect to the center of the effective area (i.e., the effective area center) of the resonator (the overlapping area of the piezoelectric layer, the top electrode, the bottom electrode, and the acoustic mirror in the thickness direction of the resonator constitutes the effective area), one side or one end of a member close to the effective area center is the inner side or the inner end, and one side or one end of the member away from the effective area center is the outer side or the outer end. For a reference position, being inside of the position means being between the position and the center of the effective area in the lateral or radial direction, and being outside of the position means being further away from the center of the effective area than the position in the lateral or radial direction.

As can be appreciated by those skilled in the art, the bulk acoustic wave resonator according to the present invention may be used to form a filter or an electronic device.

Based on the above, the invention provides the following technical scheme:

1. a bulk acoustic wave resonator comprising:

a substrate;

an acoustic mirror;

a bottom electrode;

a top electrode; and

a single crystal piezoelectric layer disposed between the bottom electrode and the top electrode,

wherein:

the superposition area of the acoustic mirror, the bottom electrode, the piezoelectric layer and the top electrode in the thickness direction of the resonator forms the effective area of the resonator;

a support structure is disposed between a lower surface of the piezoelectric layer and an upper surface of the base, the piezoelectric layer being disposed substantially parallel to the base.

2. The resonator of claim 1, wherein:

outside the active area, at least a portion of an upper surface of the piezoelectric layer is provided with an insulating layer.

3. The resonator of claim 2, wherein:

the insulating layer is provided at least between a lower surface of the top electrode and an upper surface of the piezoelectric layer in a region corresponding to a portion of the top electrode outside the active region.

4. The resonator of claim 3, wherein:

the insulating layer is arranged between the lower surface of the electrode connecting end of the top electrode and the upper surface of the piezoelectric layer.

5. The resonator of claim 2, wherein:

at least a portion of a surface of the upper surface of the piezoelectric layer not covered by the top electrode is provided with an insulating layer.

6. The resonator of claim 5, wherein:

and at the position of the piezoelectric layer where the through hole is not formed, the part of the upper surface of the piezoelectric layer, which is not covered by the top electrode, is provided with an insulating layer.

7. The resonator of claim 6, wherein:

the through holes comprise first through holes, and the electrode connecting structure is electrically connected with the electrode connecting end of the bottom electrode through the first through holes; and/or

The acoustic mirror is an acoustic mirror cavity, and the through hole comprises a second through hole which is communicated with the acoustic mirror cavity and is used as a release hole.

8. The resonator of claim 1, wherein:

the acoustic mirror is an acoustic mirror cavity that is shaped to be recessed into the support layer, and a lower boundary of the acoustic mirror cavity is defined by the support layer.

9. The resonator of any of claims 1-8, wherein:

the piezoelectric layer is a lithium niobate piezoelectric layer or a lithium tantalate piezoelectric layer.

10. A method of manufacturing a bulk acoustic wave resonator, the bulk acoustic wave resonator comprising a substrate; an acoustic mirror; a bottom electrode; a top electrode; and a piezoelectric layer disposed between the bottom electrode and the top electrode, the method comprising:

step 1: providing a POI wafer comprising a substrate, a single crystal piezoelectric layer, and an insulating layer disposed between a first side of the single crystal piezoelectric layer and the substrate;

step 2: forming a bottom electrode on a second side of the piezoelectric layer of the POI wafer opposite the first side;

and step 3: providing an intermediate layer consisting of an acoustic mirror layer and a support layer, wherein the intermediate layer covers the second side of the piezoelectric layer and the bottom electrode, and one side of the intermediate layer, which is far away from the substrate, is a flat surface;

and 4, step 4: bonding the substrate to the intermediate layer at the flat side of the intermediate layer;

and 5: removing the substrate and the insulating layer, wherein at least a part of the insulating layer is removed to expose the first side of the piezoelectric layer, and the insulating layer corresponding to the effective area of the resonator on the first side of the piezoelectric layer is removed;

step 6: a top electrode and an electrode connection structure are disposed on a first side of the piezoelectric layer.

11. The method of claim 10, wherein:

step 5 includes step 5A: removing the entire substrate; and removing at least a portion of the insulating layer, the insulating layer acting as a barrier to the removal of the substrate during the removal of the entire substrate.

12. The method of claim 10, wherein:

step 5 includes step 5B: forming a plurality of release holes in a substrate; and releasing the insulating layer through the plurality of release holes.

13. The method of claim 12, wherein:

at least part of the release holes are arranged outside the area of the resonator.

14. The method of claim 10, wherein:

in step 5, all of the insulating layer is removed.

15. The method of claim 10, wherein:

in step 5, at least a portion of the upper surface of the piezoelectric layer is left with the insulating layer outside the active area of the resonator.

16. The method of claim 15, wherein:

such that the insulating layer remains between the lower surface of the top electrode and the upper surface of the piezoelectric layer in an area corresponding to a portion of the top electrode outside the active area.

17. The method of claim 16, wherein:

so that the insulating layer remains between the lower surface of the electrode connection end of the top electrode and the upper surface of the piezoelectric layer.

18. The method of claim 10, wherein:

such that at least a portion of the surface of the upper surface of the piezoelectric layer not covered by the top electrode remains with the insulating layer.

19. The method of 18, wherein:

the method further comprises the steps of: providing a through hole in the piezoelectric layer;

so that the insulating layer remains on a portion of the upper surface of the piezoelectric layer not covered by the top electrode at a position where the through hole is not provided on the piezoelectric layer.

20. The method of claim 10, wherein:

the acoustic mirror is an acoustic mirror cavity, the acoustic mirror layer is a sacrificial material layer, and the step 3 includes: step 3A: forming a sacrificial material layer covering only a part of the bottom electrode or covering a part of the non-electrode connecting end of the bottom electrode and a part of the piezoelectric layer; and step 3B: providing a support material layer covering the sacrificial material layer, the bottom electrode and the piezoelectric layer, and flattening the support material layer to form the support layer; or

The acoustic mirror is a non-Bragg reflection layer, the acoustic mirror layer is a Bragg reflection layer, and the step 3 comprises the following steps: and step 3C: forming an unmelted grating reflective layer covering only a portion of the bottom electrode; and step 3D: a layer of support material is provided overlying the bragg reflector layer, the bottom electrode, and the piezoelectric layer such that the layer of support material is planarized to form the support layer.

21. The method of 20, wherein:

in step 3B or step 3D, the side of the support layer facing away from the substrate is made to constitute the flat surface, or the side of the support layer facing away from the substrate is made flush with the side of the acoustic mirror layer facing away from the substrate so as to collectively constitute the flat surface.

22. The method of claim 10, wherein:

the acoustic mirror is an acoustic mirror cavity, the acoustic mirror layer is a sacrificial material layer, and the step 3 includes: step 3E: providing a layer of support material covering the bottom electrode and the piezoelectric layer, and planarizing the layer of support material; and step 3F: removing a portion of the support material at a location of the layer of support material corresponding to the acoustic mirror to form an acoustic mirror cavity and a support layer; or

The acoustic mirror is a non-Bragg reflection layer, the acoustic mirror layer is a Bragg reflection layer, and the step 3 comprises the following steps: step 3H: providing a layer of support material covering the bottom electrode and the piezoelectric layer, and planarizing the layer of support material; step 3I: removing a portion of the support material at a location of the layer of support material corresponding to the acoustic mirror to form a cavity and a support layer; step 3J: and forming a Bragg reflection layer in the cavity.

23. The method of claim 22, wherein:

the method comprises the following steps of 3G: after step 3F, filling a sacrificial material in the acoustic mirror cavity and allowing the filled sacrificial material layer and the support layer to define the flat face together;

the method further comprises the steps of: providing a release via in the piezoelectric layer, and releasing the sacrificial material layer based on the release via.

24. A method of manufacturing a bulk acoustic wave resonator, comprising the steps of:

providing a POI wafer comprising a substrate, a single crystal piezoelectric layer, and an insulating layer disposed between a first side of the single crystal piezoelectric layer and the substrate;

and removing the substrate and at least one part of the insulating layer, wherein the insulating layer is used as a barrier layer for protecting the piezoelectric layer in the process of removing the substrate, the at least one part of the insulating layer is removed to expose the piezoelectric layer, and the insulating layer of the piezoelectric layer corresponding to the effective area of the resonator is removed.

25. The method of claim 24, wherein:

all of the insulating layer is removed.

26. The method of claim 24, wherein:

such that the insulating layer remains between the top electrode and the piezoelectric layer in a region corresponding to a portion of the top electrode of the resonator outside the active area.

27. The method of any one of claims 10-26, wherein:

the single crystal piezoelectric layer is a lithium niobate piezoelectric layer or a lithium tantalate piezoelectric layer.

28. A filter comprising a bulk acoustic wave resonator according to any one of claims 1-9.

29. An electronic device comprising the filter according to 28, or the bulk acoustic wave resonator according to any one of claims 1-9.

The electronic device includes, but is not limited to, intermediate products such as a radio frequency front end and a filtering and amplifying module, and terminal products such as a mobile phone, a WIFI and an unmanned aerial vehicle.

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