CN117639708B

CN117639708B - Bulk acoustic wave resonator, filter and electronic equipment

Info

Publication number: CN117639708B
Application number: CN202310025414.9A
Authority: CN
Inventors: 万晨庚
Original assignee: Beijing Xinxi Semiconductor Technology Co ltd
Current assignee: Beijing Xinxi Semiconductor Technology Co ltd
Priority date: 2023-01-09
Filing date: 2023-01-09
Publication date: 2024-08-09
Anticipated expiration: 2043-01-09
Also published as: CN117639708A

Abstract

The present disclosure relates to a bulk acoustic wave resonator, a filter, and an electronic device. The bulk acoustic wave resonator includes: a piezoelectric material layer, wherein the piezoelectric material layer is flat; a first electrode layer disposed on a first side of the piezoelectric material layer; a second electrode layer disposed on a second side of the piezoelectric material layer opposite the first side; and a frame portion formed on a side of at least one of the first electrode layer and the second electrode layer, which is away from the piezoelectric material layer, wherein the frame portion includes a first step portion and a second step portion located inside the first step portion, and a first height of the first step portion from the piezoelectric material layer is different from a second height of the second step portion from the piezoelectric material layer.

Description

Bulk acoustic wave resonator, filter and electronic equipment

Technical Field

The disclosure relates to the technical field of electronic devices, and in particular relates to a bulk acoustic wave resonator, a filter and electronic equipment.

Background

Bulk acoustic wave resonators or film bulk acoustic wave resonators (FBARs) are receiving increasing attention as one of the core devices of Radio Frequency (RF) front ends. Bulk acoustic wave resonators offer great advantages over, for example, surface Acoustic Wave (SAW) devices in high power applications. In the bulk acoustic wave resonator, a longitudinal wave propagation mode of the bulk acoustic wave is adopted, so that better conversion of acoustic wave energy can be achieved by utilizing excellent piezoelectric properties of materials such as AlN. In addition, the bulk acoustic wave resonator also has high bandwidth, excellent roll-off and other performances, so that the current requirement on radio frequency performance can be well met.

However, in bulk acoustic wave resonators, there is often a certain defect due to factors such as the piezoelectric material and electrode material not being perfect single crystals of perfect Z-axis crystal orientation, which will cause coupling out of the transverse wave during propagation of the longitudinal wave. Without limiting this, lateral leakage of energy will occur, degrading the quality factor (Q value) of the resonator. Accordingly, there is a need for improvements in bulk acoustic wave resonators.

Disclosure of Invention

It is an object of the present disclosure to propose a bulk acoustic wave resonator, a filter and an electronic device to improve its performance and reliability.

According to a first aspect of the present disclosure, there is provided a bulk acoustic wave resonator comprising:

A piezoelectric material layer, wherein the piezoelectric material layer is flat;

A first electrode layer disposed on a first side of the piezoelectric material layer;

a second electrode layer disposed on a second side of the piezoelectric material layer opposite the first side; and

And a frame portion formed on at least one of the first electrode layer and the second electrode layer, wherein the frame portion is configured to protrude toward a side away from the piezoelectric material layer with respect to at least one of the first electrode layer and the second electrode layer, the frame portion includes a first step portion and a second step portion located inside the first step portion, and a first height of the first step portion from the piezoelectric material layer is different from a second height of the second step portion from the piezoelectric material layer.

In some embodiments, the first height of the first step is greater than the second height of the second step.

In some embodiments, the first height of the first step is less than the second height of the second step.

In some embodiments, the height difference between adjacent steps in the frame portion is 1nm-1 μm; and/or

The height difference between the step portion having the lowest height in the frame portion and the first electrode layer or the second electrode layer adjacent to the step portion having the lowest height is 1nm to 1 μm.

In some embodiments, at least one longitudinal edge of the first step is angled 15-80 ° relative to a plane parallel to the layer of piezoelectric material; and/or

At least one longitudinal edge of the second step is angled between 15 and 80 degrees relative to a plane parallel to the layer of piezoelectric material.

In some embodiments, the frame portion is configured to be formed of a stepped material disposed on a side of at least one of the first electrode layer and the second electrode layer remote from the piezoelectric material layer.

In some embodiments, the frame portion is configured to be formed by a protrusion of at least one of the first electrode layer and the second electrode layer on a side away from the piezoelectric material layer, wherein a step material is configured to be disposed between the at least one of the first electrode layer and the second electrode layer and the piezoelectric material layer such that the side of the at least one of the first electrode layer and the second electrode layer away from the piezoelectric material layer protrudes to form the protrusion.

In some embodiments, the step material is the same as an electrode material of at least one of the first electrode layer and the second electrode layer.

In some embodiments, the frame portion is configured to be formed by a protrusion of at least one of the first electrode layer and the second electrode layer on a side remote from the piezoelectric material layer, wherein the protrusion is formed by etching a portion of an electrode material forming at least one of the first electrode layer and the second electrode layer.

In some embodiments, the bulk acoustic wave resonator further comprises:

A support portion, wherein the support portion is disposed on a first side of the first electrode layer away from the piezoelectric material layer, and a cavity is formed on a first side of a portion of the first electrode layer that is not in contact with the support portion, or the support portion is disposed on a second side of the second electrode layer away from the piezoelectric material layer, and a cavity is formed on a second side of a portion of the second electrode layer that is not in contact with the support portion;

Wherein at least a part of the overlapping region of the cavity, the first electrode layer, the piezoelectric material layer and the second electrode layer forms an effective region of the bulk acoustic wave resonator, and the frame portion is located in the effective region.

In some embodiments, the frame portion is disposed along at least a portion of an edge of the active area.

In some embodiments, the frame portion is disposed around an edge of the active area.

In some embodiments, a first width between an outer edge of the first step distal from the center of the active area and an inner edge proximal to the center of the active area is different at least two different locations along the edge of the active area; and/or

At least two different locations along the edge of the active area, a second width between an outer edge of the second step away from the center of the active area and an inner edge near the center of the active area is different.

In some embodiments, a first width between an outer edge of the first step distal from the center of the active area and an inner edge proximal to the center of the active area is a constant width; and/or

A second width between an outer edge of the second step portion distant from the center of the effective area and an inner edge near the center of the effective area is a constant width.

In some embodiments, a first width between an outer edge of the first step away from the center of the active area and an inner edge of the second step near the center of the active area is equal to a second width between an outer edge of the second step away from the center of the active area and an inner edge near the center of the active area.

In some embodiments, a first width between an outer edge of the first step distal from the center of the active area and an inner edge proximal to the center of the active area is less than or equal to 10 μm; and/or

A second width between an outer edge of the second step portion away from the center of the effective region and an inner edge near the center of the effective region is less than or equal to 10 μm.

In some embodiments, at least one frame portion and the support portion are located on opposite sides of the layer of piezoelectric material, respectively.

In some embodiments, the first electrode layer has a first electrode slot formed therein; and/or

And a second electrode groove is formed in the second electrode layer.

In some embodiments, the first electrode slot is disposed along a portion of an edge of the active area and the second electrode slot is disposed along a remaining portion of the edge of the active area.

In some embodiments, the first electrode slot is disposed around an edge of the active area; or (b)

The second electrode groove is arranged around the edge of the effective area.

In some embodiments, at least a portion of an outer edge of the frame portion remote from the center of the active area is aligned with a corresponding portion of an inner edge of the first electrode slot proximate to the center of the active area in a longitudinal direction perpendicular to a plane in which the layer of piezoelectric material lies; and/or

At least a portion of an outer edge of the frame portion remote from the center of the active area is aligned with a corresponding portion of an inner edge of the second electrode slot near the center of the active area in the longitudinal direction.

In some embodiments, at least one frame portion is adjacent to the first electrode slot, and both the at least one frame portion and the first electrode slot are disposed on a first side of the layer of piezoelectric material; and/or

At least one frame portion is adjacent to the second electrode slot, and the at least one frame portion and the second electrode slot are both disposed on a second side of the layer of piezoelectric material.

In some embodiments, a projection of a connection side of the frame portion onto a plane parallel to the piezoelectric material layer extends beyond the active area, wherein the connection side is a side of an outer edge of the frame portion that is not contiguous with any of the first electrode slot and the second electrode slot.

In some embodiments, in an overlapping region of the cavity, the first electrode layer, the piezoelectric material layer, and the second electrode layer, a region between an inner edge of the support portion near a center of the effective region and an outer edge of the first electrode groove away from the center of the effective region is formed as a first buffer region, and the effective region is located inside the first buffer region; and/or

In the overlapping region of the cavity, the first electrode layer, the piezoelectric material layer, and the second electrode layer, a region between an inner edge of the support portion and an outer edge of the second electrode groove is formed as a second buffer region, and the effective region is located inside the second buffer region.

In some embodiments, a third width between an outer edge of the first buffer region distal from the center of the active region and an inner edge proximal to the center of the active region is less than or equal to 10 μm; and/or

A fourth width between an outer edge of the second buffer region distal from the center of the active region and an inner edge proximal to the center of the active region is less than or equal to 10 μm.

In some embodiments, at least a portion of an outer edge of the first electrode layer distal from a center of the active area is a corresponding portion of an edge of the active area; and/or

At least a portion of an outer edge of the second electrode layer remote from a center of the active region serves as a corresponding portion of an edge of the active region.

In some embodiments, the frame portion includes three or more stepped portions, wherein two adjacent stepped portions are different in height from the piezoelectric material layer.

In some embodiments, the bulk acoustic wave resonator further comprises:

and a protective layer covering a portion of at least one of the first electrode layer and the second electrode layer where the frame portion is not provided and a side of the frame portion away from the piezoelectric material layer.

According to a second aspect of the present disclosure, a filter is presented, the filter comprising a bulk acoustic wave resonator as described above.

According to a third aspect of the present disclosure, an electronic device is presented, comprising a bulk acoustic wave resonator as described above or a filter as described above.

Other features of the present disclosure and its advantages will become apparent from the following detailed description of exemplary embodiments of the disclosure, which proceeds with reference to the accompanying drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the principles of the disclosure.

The disclosure may be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 (a) shows a partial schematic structure of a bulk acoustic wave resonator;

fig. 1 (b) shows a partial schematic structure of another bulk acoustic wave resonator;

Fig. 1 (c) shows the result of comparing the maximum stress value in a bulk acoustic wave resonator with a non-pure flat piezoelectric material layer and the maximum stress value in a bulk acoustic wave resonator with a pure flat piezoelectric material layer obtained by simulation;

fig. 2 shows a schematic plan view of a bulk acoustic wave resonator according to a first embodiment of the present disclosure;

FIG. 3 shows a schematic cross-sectional view of a bulk acoustic wave resonator taken along AA' in FIG. 2;

fig. 4 shows a schematic cross-sectional view of a bulk acoustic wave resonator according to a second embodiment of the present disclosure;

fig. 5 shows a schematic cross-sectional view of a bulk acoustic wave resonator according to a third embodiment of the present disclosure;

fig. 6 shows a schematic cross-sectional view of a bulk acoustic wave resonator according to a fourth embodiment of the present disclosure;

fig. 7 shows a schematic cross-sectional view of a bulk acoustic wave resonator according to a fifth embodiment of the present disclosure;

fig. 8 shows a schematic cross-sectional view of a bulk acoustic wave resonator according to a sixth embodiment of the present disclosure;

Fig. 9 shows a schematic cross-sectional view of a bulk acoustic wave resonator according to a seventh embodiment of the present disclosure;

fig. 10 shows a schematic cross-sectional view of a bulk acoustic wave resonator according to an eighth embodiment of the present disclosure;

fig. 11 shows the variation of the performance of the bulk acoustic wave resonator with the width of the step in a specific example.

Note that in the embodiments described below, the same reference numerals are used in common between different drawings to denote the same parts or parts having the same functions, and a repetitive description thereof may be omitted. In this specification, like reference numerals and letters are used to designate like items, and thus once an item is defined in one drawing, no further discussion thereof is necessary in subsequent drawings.

For ease of understanding, the positions, dimensions, ranges, etc. of the respective structures shown in the drawings and the like may not represent actual positions, dimensions, ranges, etc. Accordingly, the disclosed invention is not limited to the disclosed positions, dimensions, ranges, etc. as illustrated in the drawings. Moreover, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components.

Detailed Description

Various exemplary embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. It should be noted that: the relative arrangement of the components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present disclosure unless it is specifically stated otherwise.

The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. That is, the various techniques, methods, and apparatus herein are shown by way of example to illustrate different embodiments in the present disclosure and are not intended to be limiting. Those skilled in the art will appreciate that they are merely illustrative of exemplary ways in which the invention may be practiced, and not exhaustive.

Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but should be considered part of the specification where appropriate.

In the bulk acoustic wave resonator, the conversion of acoustic wave energy can be well realized by adopting a longitudinal wave propagation mode of the bulk acoustic wave. Bulk acoustic wave resonators have high power, high bandwidth, and excellent roll-off properties compared to other types of resonators, and thus play a great role in various applications.

In a bulk acoustic wave resonator, as shown in fig. 1 (a), each of the structural layers may be formed sequentially in the order from bottom to top. Specifically, the substrate 110 'may be etched first to form the cavity 111', and the cavity 111 'is filled with a releasable material, then the patterned first electrode layer 120', the piezoelectric material layer 130', and the second electrode layer 140' are sequentially prepared on the substrate 110 'with the releasable material, and finally the releasable material is removed to release the cavity 111'. In such a process, it is necessary to perform patterning or the like on the layer located below before the preparation of the layer located above can be continued. It can be seen that the first electrode material used to form the first electrode layer 120' needs to be subjected to etching or the like before the piezoelectric material layer 130' is deposited to form the patterned first electrode layer 120'. Thus, during deposition of the piezoelectric material layer 130', it will be necessary to etch the interface 121' longitudinally across the first electrode layer 120', such that the piezoelectric material layer 130' cannot be a purely planar, flat layer. This will result in a discontinuity of the piezoelectric material layer 130 'grown along the Z-axis at the longitudinal etched interface 121', a certain deformation of its crystal lattice, which in turn will result in a degradation of the film growth quality of the piezoelectric material layer 130', and a degradation of the quality factor of the resonator, and in addition will result in a larger step in the piezoelectric material layer 130' at the longitudinal etched interface 121 'at the connection side of the first electrode layer 120', so that stress concentration of the film layer will easily occur here. In a specific example, as shown in fig. 1 (c), in such a bulk acoustic wave resonator having a non-pure flat piezoelectric material layer, the maximum stress obtained through simulation may be as high as 6.99GPa, which is disadvantageous for the improvement of the device reliability, especially in the case of high power application, such a structure easily causes the breakage of the film layer.

In order to solve the above-described problems, the present disclosure proposes a bulk acoustic wave resonator whose performance is improved while ensuring the reliability of the bulk acoustic wave resonator by providing a flat piezoelectric material layer and a frame portion therein. In some embodiments of the present disclosure, as shown in fig. 2 to 10, the bulk acoustic wave resonator may include a piezoelectric material layer 130, a first electrode layer 120, a second electrode layer 140, and a frame portion 150.

The piezoelectric material layer 130 may be flat. In other words, there is no level difference in the piezoelectric material layer 130. In order to form such a pure flat piezoelectric material layer 130, it is required that the upper surface of the carrier for carrying the piezoelectric material layer 130 is flat during the deposition of the piezoelectric material layer 130, in which there is no structure in which there is a height difference in the longitudinal direction, such as the longitudinal etched interface shown in fig. 1 (a). In a specific example, if the first electrode layer 120', the piezoelectric material layer 130', and the second electrode layer 140' shown in fig. 1 (a) are each changed to be a flat layer of Cheng Chunping, i.e., as shown in fig. 1 (b), the maximum stress value obtained through simulation can be reduced to 3.39GPa, i.e., the maximum stress value of the resonator can be reduced by about 51.5%, thereby helping to improve the uniformity of the bulk acoustic wave resonator, and thus, having great benefits for power improvement of the resonator.

The piezoelectric material used to form the piezoelectric material layer 130 may be selected as desired. For example, the piezoelectric material may include at least one of the following materials: single crystal piezoelectric material, polycrystalline piezoelectric material and rare earth element doped material containing the above materials in a certain atomic ratio. Specifically, the single crystal piezoelectric material may include at least one of single crystal aluminum nitride, single crystal gallium nitride, single crystal lithium niobate, single crystal lead zirconate titanate (PZT), single crystal potassium niobate, single crystal quartz thin film, single crystal lithium tantalate, and the like; the polycrystalline piezoelectric material may include at least one of polycrystalline aluminum nitride, zinc oxide, PZT, and the like; and rare earth element doped materials containing the above materials in a certain atomic ratio may include doped aluminum nitride and the like, in which at least one rare earth element is contained, 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.

The first electrode layer 120 may be disposed on a first side of the piezoelectric material layer 130, and the second electrode layer 140 may be disposed on a second side of the piezoelectric material layer 130 opposite the first side. The first electrode material used to form the first electrode layer 120 may be the same as or different from the second electrode material used to form the second electrode layer 140, and both the first electrode material and the second electrode material are conductive materials. For example, the first electrode material or the second electrode material may be at least one selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, and the like, or the first electrode material or the second electrode material may be a composite of the above metals, an alloy thereof, or the like.

The frame portion 150 may be formed on at least one of the first electrode layer 120 and the second electrode layer 140, and the frame portion 150 may be configured to protrude toward a side remote from the piezoelectric material layer 130 with respect to at least one of the first electrode layer 120 and the second electrode layer 140. For example, as shown in fig. 3 to 7, the frame portion 150 is formed on a second side of the second electrode layer 140 away from the piezoelectric material layer 130; as shown in fig. 8 to 10, the frame portion 150 may also be formed on a first side of the first electrode layer 120 away from the piezoelectric material layer 130 and a second side of the second electrode layer 140 away from the piezoelectric material layer 130, respectively; furthermore, it is understood that the frame portion may also be formed only on the first side of the first electrode layer remote from the piezoelectric material layer.

Further, as shown in fig. 2 to 10, the frame part 150 may include a first step part 151 and a second step part 152 located inside the first step part 151, the first step part 151 and the second step part 152 each have a height greater than that of the central region of the resonator, and the first step part 151 is spaced apart from the piezoelectric material layer 130 by a first height different from the second step part 152. In some preferred embodiments, the first height of the first step 151 may be greater than the second height of the second step 152, i.e., the height of the frame 150 increases gradually from the center to the edge of the bulk acoustic wave resonator. Or in other embodiments, the first height of the first step 151 may be smaller than the second height of the second step 152, i.e., the height of the frame 150 gradually decreases from the center to the edge of the bulk acoustic wave resonator. Further, in the frame portion 150, a first height difference between two adjacent stepped portions may be the same as or different from a second height difference between the lowest stepped portion and the electrode layer adjacent to the lowest stepped portion. In some embodiments, the first and/or second height differences may be in the range of 1nm-1 μm. For example, in the first embodiment shown in fig. 3, a first height difference of the upper surface of the first step portion 151 with respect to the upper surface of the second step portion 152 may be in the range of 1nm to 1 μm, and a second height difference of the upper surface of the second step portion 152 with respect to the upper surface of the second electrode layer 140 may be in the range of 1nm to 1 μm.

In some embodiments, the frame portion may include more (e.g., three, four, or five, etc.) steps, each step having a height greater than the height of the central region of the resonator, and wherein two steps adjacent to each other have different heights. For example, the heights of the respective step portions included in the frame portion may be gradually increased from the center to the edge of the bulk acoustic wave resonator. Or the height of each step portion included in the frame portion may be gradually reduced from the center to the edge of the bulk acoustic wave resonator. Or from the center to the edge of the bulk acoustic wave resonator, the heights of the steps contained in the frame part can be gradually increased and then gradually decreased, or gradually decreased and then gradually increased, or alternatively, the heights of the two adjacent step parts can be different. In this context, the features of the bulk acoustic wave resonator will be described in detail taking the example of the frame portion having two stepped portions, however it will be appreciated that the skilled person can apply these features also to frame portions having more stepped portions, without limitation. The purpose of the frame portion is to thicken the region of the bulk acoustic wave resonator near the edge so that the acoustic impedance in this region is greater than the acoustic impedance in the central region of the bulk acoustic wave resonator, the difference in impedance causing the transverse wave to return into the resonator there, thereby reducing leakage of energy. In the embodiments of the present disclosure, by providing the frame portion including at least two stepped portions, the acoustic impedance difference interface can be further increased, thereby suppressing the lateral energy leakage.

In some embodiments, as shown in fig. 3, 4, and 7-10, the frame portion 150 may be configured to be formed of a stepped material disposed on a side of at least one of the first electrode layer 120 and the second electrode layer 140 remote from the piezoelectric material layer 130. In other words, the frame portion may be formed by depositing a step material on the side of the respective electrode layer remote from the piezoelectric material layer. In this case, the corresponding electrode layer may be formed first, and then the step material may be deposited. In a specific example, a portion of the step material having a certain thickness may be deposited in the region where the first step 151 is located, and then another portion of the step material having a certain thickness may be deposited in the region where both the first step 151 and the second step 152 are located, so that the height of the finally formed first step 151 may be made greater than the height of the second step 152. In another specific example, it is also possible to directly deposit a step material having a thickness corresponding to the first height of the first step 151 in the region where the first step 151 is located, and to directly deposit a step material having a thickness corresponding to the second height of the second step 152 in the region where the second step 152 is located.

In other embodiments, as shown in fig. 5 and 6, the frame portion 150 may be configured to be formed by a protrusion of at least one of the first electrode layer 120 and the second electrode layer 140 on a side remote from the piezoelectric material layer 130. Here, the step material may be configured to be disposed between at least one of the first electrode layer 120 and the second electrode layer 140 and the piezoelectric material layer 130 such that a side of the at least one of the first electrode layer 120 and the second electrode layer 140, which is remote from the piezoelectric material layer 130, protrudes to form a protrusion. In other words, the frame portion may be formed by applying a step material between the respective electrode layers and the piezoelectric material layer, so that the respective electrode layers are padded with the step material to form a convex portion that protrudes toward a side away from the piezoelectric material layer. In this case, the step material may be deposited first, and then the corresponding electrode layer may be formed. Similarly, in a specific example, a portion of the step material having a certain thickness may be formed in the region where the first step 151 is located, and then another portion of the step material having a certain thickness may be formed in the region where both the first step 151 and the second step 152 are located, so that the height of the finally formed first step 151 may be made greater than the height of the second step 152. In another specific example, it is also possible to directly form a step material having a thickness corresponding to the first height of the first step 151 in the region where the first step 151 is located, and to directly form a step material having a thickness corresponding to the second height of the second step 152 in the region where the second step 152 is located.

Under the condition that the step material is the same as the electrode material, compared with the preparation mode of firstly forming the electrode layer and then depositing the step material, the preparation mode of firstly depositing the step material and then forming the electrode layer has great advantages. This is because when etching the step material to form a desired structure, a piezoelectric material different from it is located under the step material, which allows a larger selectivity during etching, thereby contributing to higher process accuracy.

As described above, in some embodiments, the step material may be the same as the electrode material of at least one of the first electrode layer and the second electrode layer. However, in other embodiments, the step material may also be a different material than the electrode material. For example, the step material may be at least one selected from molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, and the like, or the step material may be a composite of the above metals or an alloy thereof, and the like.

In still other embodiments, the frame portion may be configured to be formed by a protrusion of at least one of the first electrode layer and the second electrode layer on a side remote from the piezoelectric material layer, wherein the protrusion may be formed by etching a portion of the electrode material forming the at least one of the first electrode layer and the second electrode layer. In other words, the frame portion and the electrode layer adjacent to the frame portion may be integrally formed together from an electrode material, and a desired shape of the electrode layer and the frame portion is formed in the electrode material by an etching process. Specifically, the electrode material may be deposited first such that the thickness of the deposited electrode material is at least the sum of the thickness of the electrode layer and the maximum thickness of the frame portion, and then regions of the electrode material layer corresponding to the positions of the electrode layer and the lower step portion of the frame portion are etched to remove part of the electrode material in these regions, thereby forming the desired electrode layer and frame portion shape. For example, the electrode layer and the region corresponding to the lower step portion may be etched first, so that the portion of the electrode material layer that is not etched forms the higher step portion, and then the region corresponding to the electrode layer is etched, thereby constructing the height difference between the electrode layer and the lower step portion. Or the electrode layer and the region corresponding to the lower step portion may be etched respectively to remove the electrode material of the corresponding thickness, thereby forming the electrode layer having the lowest thickness, the lower step portion having the middle thickness, and the higher step portion having the highest thickness. There may be no obvious interface between the adjacent electrode layers and the frame portion prepared in this way, contributing to an improvement in the performance of the bulk acoustic wave resonator.

In addition, in either of the above-described forms of the frame portion, the longitudinal edges of the step portion are not generally absolutely perpendicular to a plane parallel to the piezoelectric material layer due to restrictions of process conditions or the like. In particular, in the case of depositing the step material before forming the electrode layer, in order to avoid breakage of the deposited electrode material or the like caused by the vertical or substantially vertical longitudinal edges of the step material, as shown in fig. 5 and 6, the angle of at least one longitudinal edge of the first step 151 with respect to the plane parallel to the piezoelectric material layer may be 15 to 80 °. Similarly, at least one longitudinal edge of the second step 152 may be angled 15-80 ° with respect to a plane parallel to the layer of piezoelectric material. It will be appreciated that in other embodiments, the angle between at least one longitudinal edge of the step portion and the plane parallel to the piezoelectric material layer may be in the range of 15 ° to 80 ° to avoid the corresponding film layer from breaking, thereby improving the reliability of the bulk acoustic wave resonator.

In some embodiments, as shown in fig. 3 and 5 to 9, the bulk acoustic wave resonator may further include a support portion 110, the support portion 110 may be disposed on a first side of the first electrode layer 120 remote from the piezoelectric material layer 130, and the cavity 111 is formed on a first side of a portion of the first electrode layer 120 not in contact with the support portion 110. Or as shown in fig. 4, the support part 110 may be disposed on a second side of the second electrode layer 140 away from the piezoelectric material layer 130, and the cavity 111 is formed on a second side of a portion of the second electrode layer 140 not in contact with the support part 110.

To create such a support 110 and cavity 111 and to make the layer of piezoelectric material 130 flat, in one embodiment a temporary substrate may be provided first, on which at least a part of the structural layer of the bulk acoustic wave resonator is formed in sequence, wherein upon depositing the layer of piezoelectric material the previously deposited structure should all be flat, without a step in the longitudinal direction, then the support material is deposited and etched on the formed structural layer to form the support 110, finally the whole structure is flipped upside down, the support 110 is bonded to another substrate provided, and the temporary substrate is removed to form the bulk acoustic wave resonator or to proceed with the preparation of other structural layers in the bulk acoustic wave resonator. In another embodiment, the cavity may be formed by directly etching the substrate, and at least a portion of the substrate that is not etched may be used as the support portion. It is noted, however, that in such embodiments, it is also necessary to ensure that the structure deposited before this is flat, without a step in the longitudinal direction, when depositing the layer of piezoelectric material, so as to ensure that the deposited layer of piezoelectric material is flat. In some embodiments, the material used to form the support 110 may be selected from at least one of monocrystalline silicon, polycrystalline silicon, silicon oxide, silicon nitride, gallium arsenide, sapphire, quartz, silicon carbide, silicon On Insulator (SOI), and organic support materials, among others.

The cavity 111 formed may act as an acoustic mirror. In some preferred embodiments, the cavity 111 may be an enclosed cavity isolated from the outside, filled with a gas such as air, which is generally more reliable. Or in other embodiments cavity 111 may be an open cavity. Accordingly, at least a part of the region of the overlapping region of the cavity 111, the first electrode layer 120, the piezoelectric material layer 130, and the second electrode layer 140 may form an effective region 191 of the bulk acoustic wave resonator. In some embodiments, as shown in fig. 2-10, the frame portion 150 may be located within the active region 191 of the bulk acoustic wave resonator.

Furthermore, in some embodiments, as shown in fig. 3 and 5 to 10, at least one frame portion 150 may be disposed on the electrode layer on a side remote from the support portion 110, or at least one frame portion 150 and the support portion 110 may be respectively located on opposite sides of the piezoelectric material layer 130 to suppress leakage of lateral energy. Or in other embodiments, as shown in fig. 2, at least one frame portion 150 may be disposed on the same side of the piezoelectric material layer 130 as the support portion 110.

In some embodiments, as shown in fig. 2, the projection of the active region 191 onto a plane parallel to the piezoelectric material layer may be a convex polygon with no two sides of the convex polygon parallel to help suppress lateral leakage of energy. In some embodiments, for the frame portion on the electrode layer on each side, it may be disposed along at least a portion of the edge of the active area 191, for example, the frame portion 150 may be disposed along one or more sides of the convex pentagon shown in fig. 2. In other embodiments, the frame portion 150 may also be disposed around the entire edge of the active area.

In this context, the shortest distance between the outer edge of each step, which is distant from the center of the effective area, and the inner edge, which is close to the center of the effective area, may be defined as the width or effective width of this step. Further, the total width of the frame portion may be the sum of the widths of all the step portions included therein. For example, in the specific example shown in fig. 3, the first width of the first step portion 151 may be d1 or d4, the second width of the second step portion 152 may be d2 or d3, and the total width of the frame portion 150 may be d1+d2 or d3+d4. In some embodiments, the first width of the first step may be different at least two different locations along the edge of the active area. For example, the first width d1 of the first stepped portion 151 at one position shown in fig. 3 to 10 may not be equal to the first width d4 thereof at another position. Similarly, the second width of the second step may be different at least two different locations along the edge of the active area. For example, the second width d2 of the second stepped portion 152 shown in fig. 3 to 10 at one position may not be equal to the second width d3 thereof at another position. Or in other embodiments, the first width of the first step may be a constant width, as shown in fig. 3 to 10, in which case d1=d4 is satisfied. Similarly, the second width of the second step portion may be a constant width, as shown in fig. 3 to 10, in which case d2=d3 is satisfied. Further, in some embodiments, the first width of the first step may be equal to the second width of the second step, in particular, at each corresponding location along the edge of the active area. For example, in the embodiments shown in fig. 3 to 10, d1=d2 and d3=d4.

According to the result of the simulation, the performance of the bulk acoustic wave resonator will vary with the variation of the width of the frame portion (the convex structure), as shown in fig. 11, in the case where the width of the frame portion is below the threshold width, the performance of the bulk acoustic wave resonator varies like a periodicity with the increase of the width of the frame portion; in the case where the width of the frame portion is equal to or greater than the threshold width, the performance of the bulk acoustic wave resonator decreases as the width of the frame portion increases. For example, in the case where the frame portion has a single step portion (single-layer convex structure), when the width of the frame portion is about 3 μm or 4.5 μm, the bulk acoustic wave resonator has a large parallel resonance point resistance (Rp) and thus has a good performance. In addition, as described in the exemplary embodiments of the present disclosure, in the case where the frame portion has two stepped portions (double-layered convex structure), when the width (d1+d2 or d3+d4) of the frame portion is about 3 μm or 4.5 μm, the bulk acoustic wave resonator also has a large parallel resonance point impedance (Rp), and thus has better performance. Further, as shown in fig. 11, when the width of the single-layer bump structure and the total width of the double-layer bump structure are equal, the resonator having the double-layer bump structure can have a larger parallel resonance point resistance Rp, i.e., the preparation of the frame portion having at least two stepped portions contributes to further improvement in the performance of the bulk acoustic wave resonator. In general, the first width of the first step portion may be less than or equal to 10 μm. Similarly, the second width of the second step may be less than or equal to 10 μm.

In some embodiments, as shown in fig. 3, 4, 6, 8 and 9, a first electrode groove 121 may be formed in the first electrode layer 120. Similarly, as shown in fig. 3, 4, 6, 7, 8 and 9, a second electrode groove 141 may be formed in the second electrode layer 140.

Wherein the first electrode groove 121 (shown as a dotted line box in fig. 2) may be disposed along a portion of the edge of the effective region 191, and the second electrode groove 141 (shown as a dotted line box in fig. 2) may be disposed along the remaining portion of the edge of the effective region 191. In other words, the projection of the first electrode groove 121 on a plane parallel to the piezoelectric material layer and the projection of the second electrode groove 141 on a plane parallel to the piezoelectric material layer jointly encircle the effective area 191, as shown for example in fig. 2, 3, 4, 6, 8 and 9. In other embodiments, the first electrode slot may be disposed around the entire edge of the active area; or the second electrode groove 141 may be disposed around the entire edge of the active region, as shown in fig. 7, for example. The first electrode groove and the second electrode groove may separate the first electrode layer and the second electrode layer, respectively, to help define an active area of the bulk acoustic wave resonator, wherein the active area is located inside an inner edge of the first electrode groove and the second electrode groove. The first electrode groove and the second electrode groove make acoustic impedance mismatch by bringing the end surfaces of the respective first electrode layer and second electrode layer into contact with air, thereby contributing to suppression of transverse wave leakage.

Further, in some embodiments, as shown in fig. 3,4, 6, 7, 8, and 9, at least a portion of an outer edge of the frame portion 150 away from the center of the effective region 191 may be aligned with a corresponding portion of an inner edge of the first electrode groove 121 near the center of the effective region 191 in a longitudinal direction perpendicular to a plane in which the piezoelectric material layer is located. Similarly, at least a portion of the outer edge of the frame portion 150 away from the center of the effective region 191 may be aligned with a corresponding portion of the inner edge of the second electrode groove 141 near the center of the effective region 191 in the longitudinal direction. For example, in the embodiment shown in fig. 3, one outer edge 153 of the frame portion 150 is aligned with the inner edge 142 of the second electrode slot 141, and the other outer edge 154 of the frame portion 150 is aligned with the inner edge 122 of the first electrode slot 121. Such an arrangement helps to further suppress lateral leakage in the bulk acoustic wave resonator to improve the performance of the bulk acoustic wave resonator.

In some embodiments, at least one frame portion may be adjacent to the first electrode slot, and both the at least one frame portion and the first electrode slot are disposed on a first side of the layer of piezoelectric material. Similarly, at least one frame portion may be adjacent to the second electrode slot, and both the at least one frame portion and the second electrode slot are disposed on the second side of the layer of piezoelectric material. In the particular embodiment shown in fig. 7, the frame portion 150 is disposed on a second side of the layer of piezoelectric material 130 and is adjacent to the second electrode slot 141. In the embodiment shown in fig. 8, frame portions 150 are provided on the first side and the second side of the piezoelectric material layer 130, respectively, and each frame portion 150 is adjacent to the first electrode groove 121 or the second electrode groove 141 on the same side thereof, respectively.

In some embodiments, as shown in fig. 5 and 6, the projection of the connection side 155 of the frame portion 150 onto a plane parallel to the piezoelectric material layer 130 may extend beyond the effective region 191 to effectively reduce the resistance of the series resonance point of the resonator. Wherein the connection side 155 is a side of the outer edge of the frame part 150 that is not adjacent to any one of the first electrode groove 121 and the second electrode groove 141, specifically, on the first electrode layer side, the first connection side and the first electrode groove of the frame part on the first electrode layer side may be disposed along different portions of the edge of the effective area, respectively, and the first connection side and the first electrode groove together encircle the entire edge of the effective area; similarly, on the second electrode layer side, the second connection side of the frame portion on the second electrode layer side and the second electrode groove may be disposed along different portions of the edge of the effective region, respectively, and the second connection side and the second electrode groove may collectively surround the entire edge of the effective region.

In order to prevent abrupt changes in the vibration state of the resonator at the edge of the acoustic mirror, a buffer region may also be provided in the bulk acoustic wave resonator. Specifically, as shown in fig. 3, 4, 6, 7,8, and 9, in the overlapping region of the cavity 111, the first electrode layer 120, the piezoelectric material layer 130, and the second electrode layer 140, a region between an inner edge of the support part 110 near the center of the effective region and an outer edge of the first electrode groove 121 away from the center of the effective region may be formed as a first buffer region 192, and the effective region 191 is located inside the first buffer region 192; similarly, in the region where the cavity 111, the first electrode layer 120, the piezoelectric material layer 130, and the second electrode layer 140 overlap, a region between the inner edge of the support part 110 and the outer edge of the second electrode groove may be formed as a second buffer region 193, and the effective region 191 is located inside the second buffer region 193. In the embodiment shown in fig. 4, the first buffer region 192 is formed between the inner edge 112 of the support part 110 and the outer edge 123 of the first electrode groove 121, and the second buffer region 193 is formed between the inner edge 113 of the support part 110 and the outer edge 143 of the second electrode groove 141.

In some embodiments, as shown in fig. 3, 4, 6, 7, 8, and 9, a third width d5 between an outer edge of the first buffer region 192, which is far from the center of the effective region, and an inner edge, which is near the center of the effective region, may be less than or equal to 10 μm. Similarly, a fourth width d0 between an outer edge of the second buffer area distant from the center of the effective area and an inner edge near the center of the effective area may be less than or equal to 10 μm. Further, the width of the buffer region may be different at least two different positions along the edge of the effective region, or the width of the buffer region may be a constant width, similar to the width of the step. Further, the third width of the first buffer area and the fourth width of the second buffer area may be equal or unequal.

In some embodiments, as shown in fig. 10, at least a portion of an outer edge of the first electrode layer 120 remote from the center of the active region serves as a corresponding portion of an edge of the active region. Similarly, at least a portion of the outer edge of the second electrode layer 140 away from the center of the active region serves as a corresponding portion of the edge of the active region. Here, all electrode material located outside the outer edge of the electrode layer may be removed by, for example, etching. Further, in some embodiments, a portion of the edge of the active region may be formed by a corresponding portion of the outer edge of the first electrode layer 120, while the remaining portion of the edge of the active region may be formed by a corresponding portion of the outer edge of the second electrode layer 140. In other words, the effective region may not be defined between the electrode grooves, or the effective region may not be surrounded by the electrode grooves etched in the electrode layer, but the electrode material except for the side of the electrode layer corresponding to the edge of the effective region may be entirely etched away, so that the etched boundary of the electrode layer can serve as the boundary of the effective region of the resonator.

In some embodiments, as shown in fig. 3 to 10, the bulk acoustic wave resonator may further include a protective layer 160, and the protective layer 160 may cover a second side of the portion of the second electrode layer 140 where the frame portion 150 is not disposed, which is remote from the piezoelectric material layer 130, and may also cover a second side of the frame portion 150 located on the second electrode layer 140, which is remote from the piezoelectric material layer 130, to repair and protect the second electrode layer 140 and the frame portion 150 that may exist thereon. Similarly, in other embodiments, the protective layer may overlie the first side of the portion of the first electrode layer where the frame portion is not disposed away from the piezoelectric material layer, and may also overlie the first side of the frame portion located on the first electrode layer away from the piezoelectric material layer to repair and protect the first electrode layer and the frame portion that may be present thereon. The material of the protective layer 160 may be at least one selected from aluminum nitride, silicon oxide, and the like.

In the bulk acoustic wave resonator, the flat piezoelectric material layer is arranged, so that stress concentration caused by the introduction of a level difference in the piezoelectric material layer is avoided, and the integrity and reliability of the device structure are guaranteed. On the basis, the frame part comprising at least two step parts is arranged, so that leakage of transverse wave energy is restrained, and the quality factor, the working power and the like of the bulk acoustic wave resonator are improved.

According to another aspect of the present disclosure, there is also provided a filter, which may include a bulk acoustic wave resonator as described above. The filter can filter out interference, noise and the like outside the target frequency spectrum so as to improve the signal selectivity and meet the requirements of a radio frequency system and the like on the signal to noise ratio.

According to yet another aspect of the present disclosure, an electronic device is also presented, which may comprise a bulk acoustic wave resonator or filter as described above. In some embodiments, the electronic device may be various wireless communication terminals, such as communication devices like cell phones.

In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values.

The words "front," "back," "top," "bottom," "over," "under," and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the disclosure described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

As used herein, the word "exemplary" means "serving as an example, instance, or illustration," and not as a "model" to be replicated accurately. Any implementation described herein by way of example is not necessarily to be construed as preferred or advantageous over other implementations. Furthermore, this disclosure is not limited by any expressed or implied theory presented in the preceding technical field, background, brief summary or the detailed description.

As used herein, the term "substantially" is intended to encompass any minor variation due to design or manufacturing imperfections, tolerances of the device or element, environmental effects and/or other factors. The word "substantially" also allows for differences from perfect or ideal situations due to parasitics, noise, and other practical considerations that may be present in a practical implementation.

The foregoing description may indicate elements or nodes or features that are "connected" or "coupled" together. As used herein, unless expressly stated otherwise, "connected" means that one element/node/feature is directly connected (or in direct communication) electrically, mechanically, logically, or otherwise with another element/node/feature. Similarly, unless expressly stated otherwise, "coupled" means that one element/node/feature may be directly or indirectly joined to another element/node/feature in a mechanical, electrical, logical, or other manner to permit interactions, even though not directly connected. That is, "coupled" is intended to encompass both direct and indirect coupling of elements or other features, including connections utilizing one or more intermediate elements.

It will be further understood that the terms "comprises" and/or "comprising," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components, and/or groups thereof.

Those skilled in the art will recognize that the boundaries between the above described operations are merely illustrative. The operations may be combined into a single operation, the single operation may be distributed among additional operations, and the operations may be performed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in other various embodiments. Other modifications, variations, and alternatives are also possible. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

Although some specific embodiments of the present disclosure have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present disclosure. The embodiments disclosed herein may be combined in any desired manner without departing from the spirit and scope of the present disclosure. Those skilled in the art will also appreciate that various modifications might be made to the embodiments without departing from the scope and spirit of the present disclosure. The scope of the present disclosure is defined by the appended claims.

Claims

1. A bulk acoustic wave resonator, the bulk acoustic wave resonator comprising:

The piezoelectric material layer is flat and has no step difference in the longitudinal direction perpendicular to the plane of the piezoelectric material layer;

The first electrode layer is arranged on the first side of the piezoelectric material layer, and a first electrode groove is formed in the first electrode layer;

The second electrode layer is arranged on a second side, opposite to the first side, of the piezoelectric material layer, and a second electrode groove is formed in the second electrode layer;

A support portion provided on a side of one of the first electrode layer and the second electrode layer away from the piezoelectric material layer, and a cavity is formed on a side of a portion of the one electrode layer that is not in contact with the support portion; and

A frame portion formed on at least one of the first electrode layer and the second electrode layer, wherein the frame portion is configured to be formed by a protruding portion of the at least one of the first electrode layer and the second electrode layer on a side away from the piezoelectric material layer, the frame portion including a first step portion and a second step portion located inside the first step portion, a first height of the first step portion from the piezoelectric material layer being different from a second height of the second step portion from the piezoelectric material layer, there being no gap between the frame portion and a corresponding one of the first electrode layer and the second electrode layer on which the frame portion is formed, and the frame portion and a corresponding one of the first electrode layer and the second electrode layer on which the frame portion is formed being integrally formed by an electrode material such that there is no interface between the frame portion and the corresponding one of the first electrode layer and the second electrode layer on which the frame portion is formed;

Wherein at least a part of the overlapping region of the cavity, the first electrode layer, the piezoelectric material layer and the second electrode layer forms an effective region of the bulk acoustic wave resonator, and a projection of a connection side of the frame portion on a plane parallel to the piezoelectric material layer extends beyond the effective region, wherein the connection side is a side of an outer edge of the frame portion not adjacent to any one of the first electrode groove and the second electrode groove.

2. The bulk acoustic wave resonator according to claim 1, characterized in that the first height of the first step is greater than the second height of the second step.

3. The bulk acoustic wave resonator according to claim 1, characterized in that the first height of the first step is smaller than the second height of the second step.

4. The bulk acoustic wave resonator according to claim 1, characterized in that the height difference between adjacent step portions in the frame portion is 1 nm-1 μm; and/or

The height difference between the step portion having the lowest height in the frame portion and the first electrode layer or the second electrode layer adjacent to the step portion having the lowest height is 1 nm-1 μm.

5. The bulk acoustic wave resonator according to claim 1, characterized in that at least one longitudinal edge of the first step is angled between 15-80 ° with respect to a plane parallel to the layer of piezoelectric material; and/or

6. The bulk acoustic wave resonator according to claim 1, characterized in that the protruding portion is formed by etching a portion of an electrode material forming at least one of the first electrode layer and the second electrode layer.

7. The bulk acoustic resonator according to claim 1, characterized in that the frame portion is arranged along at least a part of the edge of the active area.

8. The bulk acoustic resonator according to claim 1, characterized in that the frame portion is arranged around the edge of the active area.

9. The bulk acoustic wave resonator according to claim 1, characterized in that at least two different positions along the edge of the active area, a first width between an outer edge of the first step away from the center of the active area and an inner edge near the center of the active area is different; and/or

10. The bulk acoustic wave resonator according to claim 1, characterized in that a first width between an outer edge of the first step portion distant from the center of the effective region and an inner edge near the center of the effective region is a constant width; and/or

11. The bulk acoustic wave resonator according to claim 1, characterized in that a first width between an outer edge of the first step portion remote from the center of the active area and an inner edge near the center of the active area is equal to a second width between an outer edge of the second step portion remote from the center of the active area and an inner edge near the center of the active area.

12. The bulk acoustic wave resonator according to claim 1, characterized in that a first width between an outer edge of the first step portion distant from the center of the effective area and an inner edge near the center of the effective area is less than or equal to 10 μm; and/or

A second width between an outer edge of the second step portion away from the center of the effective area and an inner edge near the center of the effective area is less than or equal to 10 [ mu ] m.

13. The bulk acoustic resonator according to claim 1, characterized in that at least one frame portion and the support portion are located on opposite sides of the layer of piezoelectric material, respectively.

14. The bulk acoustic wave resonator of claim 1, wherein the first electrode slot is disposed along a portion of an edge of the active region and the second electrode slot is disposed along a remaining portion of the edge of the active region.

15. The bulk acoustic wave resonator according to claim 1, characterized in that the first electrode slot is arranged around an edge of the active area; or (b)

The second electrode groove is arranged around the edge of the effective area.

16. The bulk acoustic resonator according to claim 1, characterized in that at least a portion of an outer edge of the frame portion remote from the center of the active area is aligned with a corresponding portion of an inner edge of the first electrode groove near the center of the active area in a longitudinal direction perpendicular to a plane in which the piezoelectric material layer lies; and/or

17. The bulk acoustic wave resonator of claim 1, wherein at least one frame portion is adjacent to the first electrode slot, and wherein the at least one frame portion and the first electrode slot are both disposed on a first side of the layer of piezoelectric material; and/or

18. The bulk acoustic wave resonator according to claim 1, characterized in that, in an overlapping region of the cavity, the first electrode layer, the piezoelectric material layer, and the second electrode layer, a region between an inner edge of the support portion near a center of the effective region and an outer edge of the first electrode groove away from the center of the effective region is formed as a first buffer region, and the effective region is located inside the first buffer region; and/or

19. The bulk acoustic wave resonator according to claim 18, characterized in that a third width between an outer edge of the first buffer region distant from the center of the active region and an inner edge near the center of the active region is less than or equal to 10 μm; and/or

A fourth width between an outer edge of the second buffer region away from the center of the active region and an inner edge near the center of the active region is less than or equal to 10 [ mu ] m.

20. The bulk acoustic wave resonator according to claim 1, characterized in that at least a portion of an outer edge of the first electrode layer remote from the center of the active area is taken as a corresponding portion of an edge of the active area; and/or

21. The bulk acoustic resonator according to claim 1, characterized in that the frame portion comprises three or more step portions, wherein two adjacent step portions differ in height from the piezoelectric material layer.

22. The bulk acoustic wave resonator according to claim 1, characterized in that it further comprises:

23. A filter comprising a bulk acoustic wave resonator according to any of claims 1 to 22.

24. An electronic device comprising a bulk acoustic wave resonator according to any of claims 1 to 22 or a filter according to claim 23.