CN217741692U - Bulk acoustic wave resonant structure and acoustic wave device - Google Patents

Abstract

The embodiment of the present disclosure provides a bulk acoustic wave resonance structure, including: a substrate; the reflecting structure, the first electrode, the piezoelectric layer and the second electrode are sequentially positioned on the substrate; wherein, the overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the reflecting structure on the substrate is a first overlapping area; a first convex structure located on a side of the piezoelectric layer or the second electrode opposite to the substrate; wherein an orthographic projection of the first raised structure on the substrate at least partially overlaps the first overlapping region; the second protruding structure is at least partially positioned on one side of the second electrode, which is relatively far away from the substrate; wherein an orthographic projection of the second raised structure on the substrate at least partially overlaps an orthographic projection of the first raised structure on the substrate; and the frequency trimming layer covers the surface of the second electrode, the piezoelectric layer, the first convex structure and the second convex structure which is relatively far away from the substrate.

Description

Bulk acoustic wave resonant structure and acoustic wave device

Technical Field

The present disclosure relates to the field of semiconductor technologies, and in particular, to a bulk acoustic wave resonator structure and an acoustic wave device.

Background

In a widely used communication apparatus such as a mobile phone, an acoustic wave device using an acoustic wave is generally included as a filter of the communication apparatus. As examples of the Acoustic Wave device, there are a device using a Surface Acoustic Wave (SAW), a device using a Bulk Acoustic Wave (BAW), or the like. The performance of the acoustic wave device affects the communication performance of the communication apparatus.

With the development of communication technology, how to improve the performance of acoustic wave devices while following the trend of integration and miniaturization of communication devices becomes an urgent problem to be solved.

SUMMERY OF THE UTILITY MODEL

According to a first aspect of embodiments of the present disclosure, there is provided a bulk acoustic wave resonant structure, including:

a substrate;

the reflecting structure, the first electrode, the piezoelectric layer and the second electrode are sequentially positioned on the substrate; wherein, the overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the reflecting structure on the substrate is a first overlapping area;

the first convex structure is positioned on one side, relatively far away from the substrate, of the piezoelectric layer or the second electrode; wherein the first raised structure at least partially overlaps the first overlap region in an orthographic projection of the substrate for reflecting transverse shear waves within the first overlap region;

the second protruding structure is at least partially positioned on one side of the second electrode, which is relatively far away from the substrate; wherein an orthographic projection of the second convex structure on the substrate at least partially overlaps an orthographic projection of the first convex structure on the substrate, for reflecting transverse shear waves in the first overlapping region;

and the frequency trimming layer covers the surfaces, far away from the substrate, of the second electrode, the piezoelectric layer, the first convex structure and the second convex structure.

According to a second aspect of the embodiments of the present disclosure, there is provided an acoustic wave device including the bulk acoustic wave resonant structure according to the above embodiments.

In the bulk acoustic wave resonance structure provided by the embodiment of the disclosure, on one hand, a first convex structure is additionally arranged, and the first convex structure is positioned on one side of the piezoelectric layer or the second electrode, which is relatively far away from the substrate; the projection overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the reflecting structure on the substrate is a first overlapping area, and the orthographic projection of the first protruding structure on the substrate at least partially overlaps with the first overlapping area. It can be understood that, in the embodiment of the present disclosure, a first protruding structure is disposed in the resonant structure corresponding to the first overlapping region, the first protruding structure is configured to reflect the transverse shear wave in the first overlapping region, and the transverse shear wave can be attenuated by the first protruding structure, so that energy is concentrated on the longitudinal wave in the first overlapping region, and the effects of suppressing the transverse parasitic mode (i.e., suppressing the parasitic resonance) and increasing the Quality Factor (Q value) are achieved.

On the other hand, the second convex structure is at least partially positioned on the side of the second electrode opposite to the substrate, and the orthographic projection of the second convex structure on the substrate is at least partially overlapped with the orthographic projection of the first convex structure on the substrate. It will be appreciated that the second raised structure is at least partially longitudinally stacked on the second electrode, and the second raised structure forms a mass-loading structure, so that when a transverse shear wave propagates to the second raised structure, the transverse shear wave propagating to the region can be reflected, reducing acoustic energy leakage, and thereby increasing the Q of the bulk acoustic wave resonant structure.

In the embodiment of the disclosure, a first protrusion structure and a second protrusion structure are additionally arranged in the bulk acoustic wave resonance structure. Transverse shear waves are attenuated through the first protruding structures and the second protruding structures, and acoustic wave energy leakage is reduced, so that the Q value of the bulk acoustic wave resonant structure is improved.

Drawings

FIG. 1 is a first schematic diagram illustrating a bulk acoustic wave resonant structure in partial cross-section in a direction perpendicular to a substrate, according to an exemplary embodiment;

FIG. 2a is a second schematic diagram illustrating a partial cross-section of a bulk acoustic wave resonant structure in a direction perpendicular to a substrate, in accordance with an exemplary embodiment;

FIG. 2b is a graphical illustration of experimental results of a bulk acoustic wave resonant structure shown in accordance with an exemplary embodiment;

FIG. 3 is a third schematic diagram illustrating a bulk acoustic wave resonant structure in partial cross-section in a direction perpendicular to a substrate, in accordance with an exemplary embodiment;

FIG. 4 is a schematic top view of a second bump structure in a bulk acoustic wave resonant structure according to an exemplary embodiment;

FIG. 5 is a fourth schematic diagram illustrating a partial cross-section of a bulk acoustic wave resonant structure in a direction perpendicular to a substrate, in accordance with an exemplary embodiment;

FIG. 6 is a fifth schematic diagram illustrating a partial cross-section of a bulk acoustic wave resonant structure in a direction perpendicular to a substrate in accordance with an exemplary embodiment;

FIG. 7 is a sixth schematic diagram illustrating a partial cross-section of a bulk acoustic wave resonant structure in a direction perpendicular to a substrate, in accordance with an exemplary embodiment;

FIG. 8 is a seventh schematic diagram illustrating a partial cross-section of a bulk acoustic wave resonant structure in a direction perpendicular to a substrate, in accordance with an exemplary embodiment;

FIG. 9 is an eighth schematic diagram illustrating a partial cross-section of a bulk acoustic wave resonant structure in a direction perpendicular to a substrate in accordance with an exemplary embodiment;

FIG. 10 is a ninth schematic diagram illustrating a partial cross-section of a bulk acoustic wave resonant structure in a direction perpendicular to a substrate in accordance with an exemplary embodiment;

fig. 11 is a first flowchart illustrating a method of fabricating a bulk acoustic wave resonant structure according to an exemplary embodiment;

fig. 12a to 12n are process cross-sectional views schematically illustrating a method of manufacturing a bulk acoustic wave resonant structure according to an exemplary embodiment;

fig. 13 is a schematic cross-sectional view of a closed ring-shaped first bump structure during a method of manufacturing a bulk acoustic wave resonant structure according to an exemplary embodiment;

fig. 14 is a second flowchart illustrating a method of fabricating a bulk acoustic wave resonant structure according to an exemplary embodiment.

Detailed Description

The technical solution of the present disclosure is further described in detail below with reference to the drawings and specific embodiments of the specification.

In the embodiments of the present disclosure, the terms "first", "second", and the like are used for distinguishing similar objects, and are not used for describing a particular order or sequence.

In the disclosed embodiments, the term "a is in contact with B" includes the case where a is in direct contact with B, or the case where A, B has other components interposed therebetween and a is in contact with B indirectly.

In embodiments of the present disclosure, the term "layer" refers to a portion of material that includes a region having a thickness. A layer may extend over the entirety of the underlying or overlying structure or may have an extent that is less than the extent of the underlying or overlying structure. Furthermore, a layer may be a region of a homogeneous or heterogeneous continuous structure having a thickness less than the thickness of the continuous structure. For example, a layer may be located between the top and bottom surfaces of the continuous structure, or a layer may be between any horizontal pair at the top and bottom surfaces of the continuous structure. The layers may extend horizontally, vertically and/or along inclined surfaces. Also, a layer may include multiple sublayers.

It is to be understood that the meaning of "on … …", "above … …" and "above … …" in this disclosure should be read in the broadest manner such that "on … …" not only means that it is "on" something without intervening features or layers therebetween (i.e., directly on something), but also includes the meaning of "on" something "with intervening features or layers therebetween.

In recent years, the exponential growth of mobile data and the huge demand of emerging consumer electronics have driven the rapid development of the wireless communication technology industry, the use demand of terminal equipment is also increasingly complicated and multifunctional, the continuous richness of the functions of the terminal equipment means the integration and further miniaturization of internal chips, and the requirement for an important structure in a receiving and transmitting module of the terminal equipment, namely a radio frequency front end, is new. In view of the development process of the mobile network, each time a new communication protocol generated by a new generation of mobile network update promotes the upgrade of the radio frequency device module to be configured, and the number of filter components is further increased.

The resonators include dielectric resonators, surface Acoustic Wave (SAW) resonators, and bulk Acoustic Wave resonators. The larger power capacity of the dielectric resonator is the advantage of the technology, but the larger volume of the dielectric resonator cannot well meet the development of chip miniaturization and integration, and in addition, the frequency difference between different frequency bands in the mobile communication field is smaller and smaller at present, which puts higher requirements on the signal selectivity of the filter, so that the device needs to have a higher quality factor (Q value).

The surface acoustic wave resonator has been widely used in commercial products due to its high operating frequency, low phase noise, high Q value, low insertion loss, and simple fabrication process below 2 GHz. However, with the development of 5G communication, the surface acoustic wave resonator has a limitation in its application to the field of high frequency communication due to the size limitation of the interdigital electrode.

The resonant frequency of a Bulk Acoustic Wave (BAW) depends on the thickness of a material, and can be much higher than the operating frequency of a SAW device, and the size of the BAW is reduced along with the increase of the frequency, so that the BAW has the advantage of smaller volume, and plays an important role in the communication field, wherein a Film Bulk Acoustic Resonator (FBAR) is used as a branch of the BAW, and as the development of the communication technology is greatly improved, the related filter, duplexer and the like have been commercially and massively applied in the high-frequency communication field.

There are many parameters that measure the performance of FBAR devices, and the main parameter includes the electromechanical coupling coefficient (K) _t ² ) Quality factor (Q value), etc. To more systematically characterize these two key parameters of the FBAR, the product of the two can be defined as the Figure of Merit (FOM) of the FBAR. Wherein, the greater the figure of merit, the greater theThe FBAR filter is better in frequency selectivity, and the lower the insertion loss, the better the edge roll-off effect.

In the related art, when electric power is applied to upper and lower electrodes of a bulk acoustic wave resonator, piezoelectric layers located in the upper and lower electrodes generate an acoustic wave due to a piezoelectric effect. In addition to longitudinal waves, transverse shear waves (transverse shear waves may also be referred to as lateral waves or shear waves) are generated within the piezoelectric layer. The presence of transverse shear waves affects the energy of the primary longitudinal wave, which results in loss of energy and degrades the Q-value of the bulk acoustic wave resonator.

For example, in a mobile terminal, there is a case where a plurality of frequency bands are used simultaneously, which requires a steeper skirt and a smaller insertion loss of a filter or a duplexer in the mobile terminal. The performance of the filter is determined by the wave resonators constituting it, and increasing the Q value of the resonators enables steep skirts and small insertion loss. In addition, too large a parasitic resonance of the resonator may also adversely affect the performance of the filter or duplexer.

In view of the above, how to reduce the parasitic resonance of the bulk acoustic wave resonator and increase the Q value of the bulk acoustic wave resonator is an urgent problem to be solved.

Fig. 1 is a schematic partial cross-sectional view of a bulk acoustic wave resonant structure 100 in a direction perpendicular to a substrate, according to an exemplary embodiment. Referring to fig. 1, the bulk acoustic wave resonant structure 100 includes:

a substrate 101;

a reflective structure 102, a first electrode 103, a piezoelectric layer 104 and a second electrode 105, which are sequentially located on the substrate; wherein, the overlapping area of the orthographic projection of the first electrode 103 on the substrate 101 and the orthographic projection of the reflecting structure 102 on the substrate 101 is a first overlapping area;

a first bump structure 106 on a side of the piezoelectric layer 104 or the second electrode 105 opposite to the substrate 101; wherein the orthographic projection of the first convex structure 106 on the substrate 101 at least partially overlaps the first overlapping region for reflecting the transverse shear wave in the first overlapping region;

a second raised structure 107 at least partially located on a side of the second electrode 105 opposite to the substrate 101; wherein the orthographic projection of the second convex structure 107 on the substrate 101 at least partially overlaps the orthographic projection of the first convex structure 106 on the substrate, for reflecting the transverse shear wave in the first overlapping region;

and the frequency trimming layer 108 covers the surface, far away from the substrate, of the second electrode 105, the piezoelectric layer 104, the first convex structure 106 and the second convex structure 107.

It should be noted that, in order to intuitively describe the positions of the first bump structure 106 and the second bump structure 107, the bulk acoustic wave resonator structure 100 (fig. 1) is a partial cross-sectional schematic diagram highlighting the first bump structure 106 and the second bump structure 107. Here, the bulk acoustic wave resonant structure shown in fig. 1 is only one example of the embodiment of the present disclosure, and is not used to limit the features of the bulk acoustic wave resonant structure in the embodiment of the present disclosure, and other examples of the bulk acoustic wave resonant structure of the embodiment of the present disclosure are also shown in the following embodiments. Here, fig. 1 shows that the first bump structure 106 is located on a side of the piezoelectric layer 104 relatively far from the substrate 101.

In practical applications, the constituent material of the substrate 101 may include silicon (Si), germanium (Ge), and the like.

The first electrode 103 may be referred to as a lower electrode, and correspondingly, the second electrode 105 may be referred to as an upper electrode, through which electric power may be applied to the bulk acoustic wave resonance structure 100. The first electrode 103 and the second electrode 105 may be the same in composition material, and the composition material may include: and a conductive material made of a conductive metal such as aluminum (Al), molybdenum (Mo), ruthenium (Ru), iridium (Ir), or platinum (Pt), or an alloy of the conductive metals.

The piezoelectric layer 104 can be used for generating vibration according to the inverse piezoelectric characteristic, and converting the electric signal loaded on the first electrode 103 and the second electrode 105 into an acoustic signal, so as to realize conversion from electric energy to mechanical energy.

In practical applications, the composition of the piezoelectric layer 104 may include: a material having piezoelectric properties. For example, aluminum nitride, zinc oxide, lithium tantalate, lead zirconate titanate, barium titanate, or the like. The constituent material of the piezoelectric layer 104 may also include a material having piezoelectric properties by doping. The doping can be of a transition metal or a rare metal, for example scandium-doped aluminum nitride or the like.

Here, the reflective structure 102 is used to reflect the acoustic wave signal. When the acoustic wave signal generated by the piezoelectric layer 104 propagates toward the reflective structure 102, the acoustic wave signal may be totally reflected at the interface where the first electrode 103 and the reflective structure 102 contact, so that the acoustic wave signal is reflected back into the piezoelectric layer 104. Thus, the energy of the acoustic wave signal generated by the piezoelectric layer 104 can be localized in the piezoelectric layer 104, which can reduce the energy loss of the acoustic wave signal and improve the quality of the acoustic wave signal transmitted by the bulk acoustic wave resonant structure.

It should be noted that the bulk acoustic wave resonant structure shown in fig. 1 provides only one example for the present disclosure, and in practical applications, the bulk acoustic wave resonant structure may be specifically divided into: a first type of cavity Film Bulk Acoustic Wave Resonator (FBAR), a second type of cavity FBAR, a Solid-state assembled Resonator (SMR), and the like. The scheme provided by the embodiment of the disclosure can be suitable for the different types of bulk acoustic wave resonant structures.

Here, when the bulk acoustic wave resonator structure 100 includes the first type cavity FBAR, the reflective structure 102 includes a first electrode 103 protruding upward and forming a first cavity between the surface of the substrate 101. When the bulk acoustic wave resonator structure 100 includes the second cavity type FBAR, the reflective structure 102 includes a second cavity formed between the surface of the substrate 101 recessed downward and the first electrode 103.

In practical applications, an overlapping region of the orthographic projection of the first electrode 103 on the substrate 101 and the orthographic projection of the reflective structure 102 on the substrate 101 is a first overlapping region (S1 shown in fig. 2 a), and the orthographic projection of the first protruding structure 106 on the substrate 101 at least partially overlaps the first overlapping region.

It can be understood that, in the embodiment of the present disclosure, the first raised structure 106 is disposed near the edge of the first overlapping region, and the first raised structure 106 is configured to reflect the transverse shear wave in the first overlapping region, so that the energy is concentrated on the longitudinal wave in the first overlapping region, thereby achieving the effects of suppressing the transverse parasitic mode (i.e., suppressing the parasitic resonance) and increasing the quality factor (Q value).

In practical applications, the second protruding structures 107 are at least partially located on a side of the second electrode 105 opposite to the substrate 101, the second protruding structures 107 are located above the first protruding structures 106, and an orthographic projection of the second protruding structures 107 on the substrate 101 at least partially overlaps an orthographic projection of the first protruding structures 106 on the substrate.

Here, the positional relationship in which the second convex structure 107 is at least partially located on the side of the second electrode 105 relatively far from the substrate 101 may include the following, and the second convex structure 107 may include a first portion and a second portion, the first: the first part is positioned between the second electrode 105 and the frequency modification layer 108, and the second part is positioned between the first convex structure 106 and the frequency modification layer 108; and the second method comprises the following steps: the first portion and the second portion are both located between the second electrode 105 and the frequency modifying layer 108.

It is understood that the positional relationship of the second electrode 105 and the second bump structure 107 includes a vertical configuration of stacking up and down. That is, the second electrode 105 and the second bump structure 107 are not of a same layer structure, and the second electrode 105 and the second bump structure 107 are not formed in the same step process.

Specifically, in this embodiment, the second protrusion 107 is at least partially overlapped on the second electrode 105 in the longitudinal direction, and the second protrusion 107 forms a mass loading structure. When a shear wave propagates to a longitudinal region where the second bump structure 107 overlaps the second electrode 105, an acoustic wave propagating to the region can be reflected, reducing acoustic wave energy leakage, thereby improving the Q value of the bulk acoustic wave resonant structure.

According to the test result, only the first protruding structure or only the second protruding structure is added in the bulk acoustic wave resonant structure, and the Q value of the improved bulk acoustic wave resonant structure can be improved by 10-20%. The first protruding structure and the second protruding structure are preferably added in the bulk acoustic wave resonant structure, and at the moment, the Q value of the bulk acoustic wave resonant structure can be improved by 30% -40%.

In the embodiment of the disclosure, a first protrusion structure and a second protrusion structure are additionally arranged in the bulk acoustic wave resonance structure. The first convex structure and the second convex structure can inhibit the leakage of transverse shear waves, and the Q value of the bulk acoustic wave resonance structure can be obviously improved.

In some embodiments, referring to fig. 2a, the first raised structure 106, is located only between the piezoelectric layer 104 and the second electrode 105; wherein the orthographic projection of the first raised structure 106 on the substrate 101 falls within the first overlap region;

a second raised structure 107 located only on a surface of the second electrode 105 relatively distant from the substrate 101; wherein the orthographic projection of the second raised structure 107 on the substrate 101 falls within the first overlap region.

Exemplarily, the positional relationship in which the first convex structure 106 is located only between the piezoelectric layer 104 and the second electrode 105 includes the following cases: referring to fig. 2a, the lower surface (the side relatively close to the substrate 101) of the first bump structure 106 is attached to the side of the piezoelectric layer 104 relatively far from the substrate 101, and the upper surface (the side relatively far from the substrate 101) of the first bump structure 106, the left side wall and the right side wall of the first bump structure 106 are attached to the second electrode 105.

Here, the positional relationship in which the second projection structure 107 is located only on the surface of the second electrode 105 relatively distant from the substrate 101 includes the following cases: referring to fig. 2a, the lower surface (the side relatively close to the substrate 101) of the second protruding structure 107 is attached to the side of the second electrode 105 relatively far from the substrate 101, and the upper surface (the side relatively far from the substrate 101) of the second protruding structure 107, the left sidewall and the right sidewall of the second protruding structure 107 are attached to the frequency modification layer 108.

Exemplarily, referring to fig. 2a, the second overlap region may include an overlap region (S as shown in fig. 2 a) of an orthographic projection of the reflective structure 102 on the substrate 101, an orthographic projection of the first electrode layer 103 on the substrate 101, an orthographic projection of the piezoelectric layer 104 on the substrate 101, and an orthographic projection of the second electrode layer 105 on the substrate 101.

Here, taking the fact that the area of the first overlapping area (S1 as shown in fig. 2 a) is larger than the area of the second overlapping area (S as shown in fig. 2 a), the relationship between the first overlapping area and the second overlapping area can be determined according to the actual size of the reflective structure 102, the first electrode layer 103, the piezoelectric layer 104, and the second electrode layer 105 in practical applications.

Research shows that the variation trend of the Q value of the bulk acoustic wave resonance structure under different resonance areas comprises the following steps: the smaller the resonance area, the more parasitic resonances and the lower the Q value. Therefore, in order to improve the performance of the bulk acoustic wave resonant structure, the resonance area should be increased as much as possible. Here, the resonance area includes an area of the second overlap region.

In the present embodiment, an orthogonal projection of the first protruding structure 106 on the substrate 101 and an orthogonal projection of the second protruding structure 107 on the substrate 101 are both located within the second overlap region. Referring to fig. 2a, the first bump structure 106 and the second bump structure 107 are located in a non-resonance region S2, and the second overlapping region S is divided into a primary resonance region S3 and a secondary resonance region S4 except for the non-resonance region S2. It is understood that, on the premise that the area of the second electrode layer 105 is not changed, the first bump structure 106 may adjust the resonance area of the primary resonance region S3. Specifically, during the movement of the first protrusion 106 along the first direction (the direction pointing from the primary resonance region S3 to the secondary resonance region S4 and parallel to the substrate 101), the larger the resonance area of the primary resonance region S3 is, the better the Q value of the bulk acoustic wave resonance structure can be increased.

In the embodiment of the disclosure, the orthographic projection of the first protruding structure 106 on the substrate 101 and the orthographic projection of the second protruding structure 107 on the substrate 101 are both located in the first overlapping region, and the orthographic projection of the first protruding structure 106 on the substrate 101 and the orthographic projection of the second protruding structure 107 on the substrate 101 are both located in the second overlapping region, so that the lateral leakage of the acoustic wave can be better suppressed, the acoustic loss caused by the lateral shear wave is reduced, and the Q value of the bulk acoustic wave resonant structure is improved.

In some embodiments, referring to fig. 2a, the orthographic projection of the second raised structure 107 on the substrate 101 falls within the orthographic projection of the first raised structure 106 on the substrate 101.

The first protruding structure 106 and the second protruding structure 107 with different line widths are tested, and the variation trend of the Q value of the bulk acoustic wave resonant structure under different resonant areas is obtained. Referring to fig. 2B, B45 denotes that the line width of the first bump structure 106 is 4.5 μm, F25 denotes that the line width of the second bump structure 107 is 2.5 μm, B25+ F45 denotes a resonant structure including the line width of the first bump structure 106 of 2.5 μm and the line width of the second bump structure 107 of 4.5 μm, B25 denotes that the resonant structure of the first bump structure 106 of 2.5 μm, and Normal denotes that the resonant structure is not provided with the first bump structure 106 and the second bump structure 107; the line width includes a bottom surface width of the first protruding structure 106 or the second protruding structure 107 on a side relatively close to the substrate 101.

Referring to fig. 2B, as the resonance area is gradually increased, the Q value (e.g., Q in fig. 2B) of the bulk acoustic wave resonance structure (i.e., B45+ F25) including the first bump structure 106 having a line width of 4.5 μm and the second bump structure 107 having a line width of 2.5 μm _p Or Q _max ) Larger than the Q value (Q in FIG. 2B) of a bulk acoustic wave resonator structure (i.e., B25+ F45) including a first bump structure 106 having a line width of 2.5 μm and a second bump structure 107 having a line width of 4.5 μm _p Or Q _max )。

Therefore, according to the influence of the line widths of the first and second convex structures 106 and 107 under different resonance areas on the Q value, in order to further improve the Q value of the bulk acoustic wave resonance structure, it is preferable that the orthographic projection of the second convex structure 107 on the substrate 101 falls within the orthographic projection of the first convex structure 106 on the substrate 101.

In the embodiment of the disclosure, the orthographic projection of the second convex structure 107 on the substrate 101 falls into the orthographic projection of the first convex structure 106 on the substrate 101, so that the lateral leakage of the acoustic wave can be better suppressed, the acoustic loss caused by the lateral shear wave can be reduced, and the Q value of the bulk acoustic wave resonant structure can be further improved.

In some embodiments, referring to fig. 3, an overlapping area of an orthographic projection of the first electrode 103 on the substrate 101, an orthographic projection of the piezoelectric layer 104 on the substrate 101, and an orthographic projection of the second electrode 105 on the substrate 101 is a second overlapping area;

the first raised structure 106 at least partially overlaps the second overlap region in an orthographic projection of the substrate 101;

the second electrode 105 includes: a third convex structure, which is convex towards the direction far away from the substrate 101 and is located at the edge of the second electrode 105, wherein a first end of the third convex structure is in contact with the piezoelectric layer 104, and a second end of the third convex structure is only located between the frequency correction layer 108 and the first convex structure 106; the first end and the second end of the third bulge structure are opposite ends;

the first protruding structure 106 is away from the side edge of the second end of the third protruding structure, and has a preset distance L with the second end of the third protruding structure; wherein the preset distance L is greater than 0 and less than or equal to 10 μm.

Here, the second overlap region includes a region S as illustrated in fig. 3.

In the present embodiment, the orthographic projection of the first protruding structure 106 on the substrate 101 at least partially overlaps the region S, which may include the following cases: the overlapping region of the orthographic projection of the first raised structure 106 on the substrate 101 and the region S includes a region where the preset distance L is located (as shown in fig. 3), or the orthographic projection of the first raised structure 106 on the substrate 101 falls within the region S (not shown).

Referring to fig. 3, the portion where the first protrusion structure 106 is located is a non-resonance region, a preset distance L is provided between the first protrusion structure 106 and the second end of the third protrusion structure, and the preset distance L is adjusted to enable the first protrusion structure 106 to be close to the edge of the second electrode 105 (i.e., the second end of the third protrusion structure), so that the area of the resonance region on the left side of the first protrusion structure 106 can be increased, and the Q value of the bulk acoustic wave resonance structure can be better improved.

As shown in fig. 1, the second electrode 105 includes: and a third convex structure convex in a direction away from the substrate 101. The second raised structure 107 is located on a third raised structure having a slope in a direction away from the substrate 101, and the second raised structure 107 extends upward along the slope.

In another embodiment, as shown in fig. 2a and 3, the second electrode 105 includes: and a third bump structure, wherein the second bump structure 107 is located on the third bump structure, the frequency trimming layer 108 may extend upward along the slopes of the third bump structure and the second bump structure 107, and the second bump structure 107 may also extend upward along the slope of the third bump structure (not shown). Here, the preset distance L is greater than 0, and the preset distance is less than or equal to 10 μm is just one example of the present embodiment. The preset distance may be set according to a specific size of the bulk acoustic wave resonant structure.

In the embodiment of the present disclosure, by making the first protrusion 106 as close to the edge of the second electrode 105 as possible, the lateral leakage of the acoustic wave can be better suppressed, and the acoustic loss caused by the lateral shear wave is reduced, thereby further improving the Q value of the bulk acoustic wave resonant structure.

In some embodiments, referring to fig. 4, the second protrusion structure 107 is provided in a ring shape.

It should be noted that, in order to intuitively describe that the second convex structure 107 is configured in a ring shape, the schematic top view (fig. 4) is a schematic top view of the bulk acoustic wave resonant structure 100 (fig. 1) with other resonant structures omitted, and only the second convex structure 107 and the piezoelectric layer 104 are shown in a top view. In addition, the shape of the second protrusion structure 107 shown in fig. 4 is only one example of the embodiment of the present disclosure, and is not used to limit the shape of the second protrusion structure 107 in the embodiment of the present disclosure.

For example, the second protrusion structure 107 may be provided in a fan-shaped ring shape (refer to fig. 4), and the second protrusion structure 107 may also be provided in a circular ring shape, an elliptical ring shape, a polygonal ring shape, or the like.

In the present embodiment, the second protrusion structure 107 encloses a closed ring shape or a ring shape with a gap in a front projection of the substrate 101. Here, it is preferable that the second protrusion 107 forms a closed ring shape in the front projection of the substrate 101, and the closed ring shape is better capable of reducing the lateral leakage of the acoustic wave than a ring shape having a gap (i.e., an unclosed shape).

Here, the shape of the orthographic projection of the second convex structure 107 on the substrate 101 and the orthographic projection of the first convex structure 106 on the substrate 101 may be the same or different. It is preferable that the orthographic projection of the second convex structure 107 on the substrate 101 and the orthographic projection of the second convex structure 107 on the substrate 101 have the same shape, and it should be understood that when the orthographic projection of the first convex structure 106 on the substrate 101 is a closed ring shape, and the orthographic projection of the second convex structure 107 on the substrate 101 is a closed ring shape, it is more advantageous to reduce the lateral leakage of the acoustic wave.

In some embodiments, referring to fig. 4, the outer profile of the second raised structure 107 may comprise a closed shape, the closed shape comprising an arc and two or more straight lines. Here, the outer contour can be understood with reference to fig. 4, that is, the outer edge shape of the second projection structure 107 as viewed from a top view.

It should be noted that the outer contour shape of the second bump structure 107 is similar to the outer contour shape of the first electrode 103 or the second electrode 105. In practical applications, the second protruding structures 107 under the frequency correction layer 108 cannot be directly observed from the top view shown in fig. 4, and here, in order to show the shapes of the second protruding structures 107 more clearly, the frequency correction layer 108 is omitted and the second protruding structures 107 are shown in a perspective view.

In practical applications, the orthographic projection of the outer contour of the second bump structure 107 on the substrate 101 falls within the orthographic projection of the outer contour of the second electrode 105 on the substrate 101, so as to ensure that the acoustic energy is confined within the second overlapping region. It can be understood that, when the outer contour of the second protruding structure 107 is a closed line segment with a uniform width, the shape of the second protruding structure is better, and the energy of the sound wave can be better limited in the second overlapping area.

The outer contour of the first bump structure 106 can refer to the above description of the outer contour of the second bump structure 107, and is not described herein again.

In the embodiment of the present disclosure, the second protruding structures 107 preferably form a closed ring in the orthographic projection of the substrate 101, and compared with a ring with a gap, the closed ring can better reduce the lateral leakage of the acoustic wave, reduce the acoustic loss caused by the lateral shear wave, and further improve the Q value of the bulk acoustic wave resonant structure.

In some embodiments, referring to fig. 5 and 6, a first raised structure 106 is located at least partially between the piezoelectric layer 104 and the second electrode 105; wherein the content of the first and second substances,

the orthographic projection of the first end of the first convex structure 106 on the substrate 101 falls into the overlapping region of the orthographic projection of the first electrode 103 on the substrate 101 and the orthographic projection of the second electrode 105 on the substrate 101; the orthographic projection of the second end of the first convex structure 106 on the substrate 101 falls within the orthographic projection of the reflective structure 102 on the substrate 101; wherein the first end and the second end of the first protrusion structure 106 are opposite ends.

Exemplarily, the position relationship that the first convex structure 106 is at least partially located between the piezoelectric layer 104 and the second electrode 105 may include the following, and the first convex structure 106 may include a third portion and a fourth portion, the first: a third part is located between the piezoelectric layer 104 and the second electrode 105, and a fourth part is located between the piezoelectric layer 104 and the frequency modifying layer 108 (refer to fig. 5 and 6); and the second method comprises the following steps: the third and fourth sections are both located between the piezoelectric layer 104 and the second electrode 105 (not shown).

Here, the sidewalls of the reflective structure 102 are processed to be slope-shaped, and the sidewalls of the reflective structure 102 may also include other shapes. Compared with the case that the side wall of the reflective structure 102 is right-angled (i.e., the side wall of the reflective structure 102 is perpendicular to the surface of the substrate 101), the side wall of the reflective structure 102 in the embodiment of the disclosure is sloped, so that other layers above the reflective structure 102 have better adhesion and continuity on the side wall of the reflective structure 102, the probability of fracture of other layers is reduced, and the stability of the bulk acoustic wave resonant structure is improved.

Specifically, as shown in fig. 5, when the third portion of the first convex structure 106 is located between the piezoelectric layer 104 and the second electrode 105, and the fourth portion is located between the piezoelectric layer 104 and the frequency modifying layer 108, the orthographic projection of the second end of the first convex structure 106 on the substrate 101 falls within the orthographic projection of the reflective structure 102 on the substrate 101, and the fourth portion of the first convex structure 106 has a slope P. As shown in fig. 6, the orthographic projection of the second end of the first convex structure 106 on the substrate 101 falls into a region outside the orthographic projection of the reflective structure 102 on the substrate 101, and the fourth portion of the first convex structure 106 has two slopes P.

Illustratively, according to the experimental results, the Q value of the bulk acoustic wave resonant structure shown in fig. 6 is larger than that of the bulk acoustic wave resonant structure shown in fig. 5.

In the actual process flow for manufacturing the bulk acoustic wave resonator structure, the material deposited at the slope P during the formation of the first protruding structure 106 may be less than that at the flat portion, the continuity of the constituent material of the first protruding structure formed at the slope P is poor, and the problem of stress concentration at the slope P after other layers are subsequently deposited on the first protruding structure 106 may be caused, and the stress concentration may cause cracks or even fractures in the first protruding structure 106, thereby affecting the performance of the bulk acoustic wave resonator structure, and therefore, it is preferable that the first protruding structure 106 has a slope. Compared to the case that the fourth portion of the first bump structure 106 in the bulk acoustic wave resonator structure shown in fig. 6 has two slopes P, the fourth portion of the first bump structure 106 in the bulk acoustic wave resonator structure shown in fig. 5 has only one slope P, and the bulk acoustic wave resonator structure shown in fig. 5 is preferable.

In the embodiment of the disclosure, the first protruding structure 106 is introduced at the inner edge of the second overlapping region, so as to better reduce the lateral leakage of the acoustic wave and reduce the acoustic loss caused by the lateral shear wave, thereby further improving the Q value of the bulk acoustic wave resonant structure.

In some embodiments, referring to fig. 7 and 8, the first raised structure 106 is located only between the piezoelectric layer 104 and the frequency shaping layer 108; wherein the content of the first and second substances,

the orthographic projection of the first ends of the first convex structures 106 on the substrate 101 falls into the orthographic projection of the first electrode 103 on the substrate 101, the orthographic projection of the first ends of the first convex structures 106 on the substrate 101 falls into a region outside the orthographic projection of the second electrode 105 on the substrate 101, and the orthographic projection of the second ends of the first convex structures 106 on the substrate 101 falls into the orthographic projection of the reflecting structure 102 on the substrate 101; wherein the first end and the second end of the first protrusion structure 106 are opposite ends.

Here, the positional relationship in which the first convex structure 106 is located only between the piezoelectric layer 104 and the frequency-modifying layer 108 includes the following cases: referring to fig. 7 and 8, the lower surface (the side relatively close to the substrate 101) of the first bump structure 106 is attached to the side of the piezoelectric layer 104 relatively far from the substrate 101, and the upper surface (the side relatively far from the substrate 101) of the first bump structure 106, the left side wall and the right side wall of the first bump structure 106 are attached to the frequency correction layer 108.

Specifically, as shown in fig. 7, the second end of the first protruding structure 106 falls within the orthographic projection of the reflective structure 102 on the substrate 101, and the first protruding structure 106 has a slope P. As shown in fig. 8, the orthographic projection of the second end of the first convex structure 106 on the substrate 101 falls into a region outside the orthographic projection of the reflective structure 102 on the substrate 101, and the first convex structure 106 has two slopes P.

In practical applications, it can be found from experimental results that the Q value of the bulk acoustic wave resonant structure shown in fig. 8 is greater than that of the bulk acoustic wave resonant structure shown in fig. 7, and compared with the bulk acoustic wave resonant structure shown in fig. 8 in which the first bump structure 106 has two slopes P, the bulk acoustic wave resonant structure shown in fig. 7 in which the first bump structure 106 has only one slope P is preferred to be the bulk acoustic wave resonant structure shown in fig. 7.

In the embodiment of the present disclosure, the first protruding structure 106 is introduced near the edge of the second overlapping region to reduce lateral leakage of the acoustic wave and reduce acoustic loss caused by lateral shear wave, thereby further improving the Q value of the bulk acoustic wave resonant structure.

In some embodiments, referring to fig. 9, the first raised structure 106 is located only between the piezoelectric layer 104 and the frequency shaping layer 108; wherein the content of the first and second substances,

the orthographic projection of the first convex structure 106 on the substrate 101 falls within the orthographic projection of the first electrode 103 on the substrate 101, and the orthographic projection of the first convex structure 106 on the substrate 101 falls in a region outside the orthographic projection of the second electrode 105 on the substrate 101.

Specifically, the positional relationship in which the first convex structure 106 is located only between the piezoelectric layer 104 and the frequency-modifying layer 108 includes the following cases: referring to fig. 9, a lower surface (a side relatively close to the substrate 101) of the first convex structure 106 is attached to a side of the piezoelectric layer 104 relatively far from the substrate 101, and an upper surface (a side relatively far from the substrate 101) of the first convex structure 106, and left and right sidewalls of the first convex structure 106 are attached to the frequency correction layer 108.

As shown in fig. 9, the first convex structure 106 is disposed between the piezoelectric layer 104 and the frequency correction layer 108, the first convex structure 106 is not in contact with the second electrode 105, and the first convex structure 106 is close to the second overlap region. In the embodiment of the present disclosure, the first protruding structure 106 is introduced near the edge of the second overlapping region to reduce lateral leakage of the acoustic wave and reduce acoustic loss caused by lateral shear wave, thereby further improving the Q value of the bulk acoustic wave resonant structure. In practical applications, according to experimental results, the Q value of the bulk acoustic wave resonant structure shown in fig. 7 or 8 is larger than that of the bulk acoustic wave resonant structure shown in fig. 9, and the bulk acoustic wave resonant structure shown in fig. 7 or 8 is preferred to that shown in fig. 9.

In some embodiments, referring to fig. 10, a first raised structure 106 is at least partially located between the second electrode 105 and the frequency shaping layer 108; wherein the content of the first and second substances,

the projection overlapping area of the orthographic projection of the first electrode 103 on the substrate 101, the orthographic projection of the piezoelectric layer 104 on the substrate 101 and the orthographic projection of the second electrode 105 on the substrate 101 is a second overlapping area;

the orthographic projection of the first convex structure 106 on the substrate 101 comprises a first projection part and a second projection part; wherein the first projection portion is located within the second overlap region and the second projection portion is located outside the second overlap region.

Illustratively, the positional relationship that the first bump structures 106 are at least partially located between the second electrode 105 and the frequency modifying layer 108 may include the following cases: as shown in fig. 10, the first bump structure 106 may include a third portion between the second electrode 105 and the frequency modifying layer 108, and a fourth portion between the piezoelectric layer 104 and the frequency modifying layer 108.

Here, the second overlapping area includes a region S as shown in fig. 10.

As shown in fig. 10, the first protruding structure 106 is disposed between the second electrode 105 and the frequency modifying layer 108, and the first protruding structure 106 is partially located in the second overlapping region and partially located outside the second overlapping region in the orthogonal projection of the substrate 101.

In the embodiment of the disclosure, the first protruding structure 106 is introduced at the edge of the second overlapping region, so that the lateral leakage of the acoustic wave can be better reduced, and the acoustic loss caused by the lateral shear wave can be reduced, thereby further improving the Q value of the bulk acoustic wave resonant structure.

In some embodiments, the thickness of the first raised structure 106 comprises 10nm to 500nm.

Here, the thickness of the first convex structure 106 includes a length of the first convex structure 106 in a direction perpendicular to the substrate surface.

In the embodiment of the present disclosure, the thicknesses of the first protrusion structures 106 may be set to be 100nm, 200nm, 300nm, and 400nm for tests, as shown in table 1, table 1 is a Q value measured after the bulk acoustic wave resonance structures with the thicknesses of 100nm, 200nm, 300nm, and 400nm of the first protrusion structures 106 are respectively set for tests, according to a test result, it is shown that an excessively large or excessively small thickness of the first protrusion structures 106 may cause poor resonance performance of the bulk acoustic wave resonance structures, and preferably, the thickness of the first protrusion structures 106 includes 200nm.

TABLE 1

Thickness of	100nm	200nm	300nm	400nm
					Q	1339	1350	1342	1267

Illustratively, the thickness of the first bump structure 106 may also be varied according to the actual design size of the bulk acoustic wave resonator structure, for example, the thickness of the first bump structure 106 may be set to 10nm to 500nm.

In the embodiment of the present disclosure, it is preferable that the thickness of the first protrusion structure 106 includes 200nm, which is more beneficial to the resonance performance of the bulk acoustic wave resonance structure, and is more beneficial to improve the quality of the acoustic wave signal transmitted by the bulk acoustic wave resonance structure.

In some embodiments, the line width of the first bump structures 106 includes 1 μm to 5 μm.

Here, the line width of the first bump structure 106 includes a bottom surface width of a side of the first bump structure 106 relatively close to the substrate.

The line widths of the first bump structures 106 are set to be 2.5 μm, 3 μm, 4 μm, and 5 μm for the test, and referring to table 2, as shown in table 2, the Q values measured after the test of the bulk acoustic wave resonant structures respectively set to be 2.5 μm, 3 μm, 4 μm, and 5 μm for the line widths of the first bump structures 106 are shown in table 2, according to the test results, as the line width of the first bump structure 106 gradually increases, the Q value of the bulk acoustic wave resonant structure gradually increases, but the number of parasitic resonances of the bulk acoustic wave resonant structure increases exponentially. Therefore, the resonance performance of the bulk acoustic wave resonant structure is considered comprehensively according to the Q value and the number of parasitic resonances, and according to the test results, the number of parasitic resonances of the bulk acoustic wave resonant structure is the smallest when the line width of the first bump structure 106 is 2.5 μm, and the line width of the first bump structure 106 is preferably 2.5 μm. The line width length of the first bump structure 106 may also be changed according to the actual design size of the bulk acoustic wave resonator structure, which is not limited by the embodiment.

TABLE 2

Line width	2.5μm	3μm	4μm	5μm
					Q	1286	1347	1360	1473

In the embodiment of the present disclosure, the line width of the first bump structure 106 is preferably 2.5 μm, which is more beneficial to the resonance performance of the bulk acoustic wave resonance structure, and is more beneficial to improving the quality of the acoustic wave signal transmitted by the bulk acoustic wave resonance structure.

In some embodiments, the sidewalls of the first raised structures 106 have an oblique angle with respect to the surface of the substrate 101, including an oblique angle of 10 ° to 80 °.

Illustratively, the inclination angle of the sidewall of the first protruding structure 106 with respect to the surface of the substrate 101 may include 10 ° to 80 °, and may also be performed according to the design size of the bulk acoustic wave resonant structure.

In the embodiment of the present disclosure, the sidewall of the first protruding structure 106 is processed into a slope, so that other structural layers above the first protruding structure 106, for example, the second electrode 105 or the frequency modification layer 108, have better adhesion and continuity on the sidewall of the first protruding structure 106, the probability of fracture of the second electrode 105 or the frequency modification layer 108 is reduced, and the stability of the bulk acoustic wave resonant structure is improved.

In some embodiments, the material of the first raised structure 106 comprises air or a functional material for reflecting sound waves, wherein the acoustic impedance of the functional material is less than or equal to the acoustic impedance of air.

In practical applications, the first bump structures 106 may include vacuum gaps, and may also be other gas medium gaps. When the material of the first raised structure 106 includes air, a portion of the edge of the piezoelectric layer 104 can be exposed to the air, thereby effectively suppressing the transverse wave. The first raised structure 106 may also be a functional material with low acoustic impedance, such as silicon carbide (SiC), silicon dioxide (SiO) ₂ ) And the like.

In the embodiment of the disclosure, the first protrusion structure 106 can reduce the leakage of the transverse wave, and improve the Q value of the bulk acoustic wave resonant structure. Preferably, the material of the first bump structure 106 includes air, which is more favorable for improving the quality of the acoustic wave signal transmitted by the bulk acoustic wave resonator structure.

In some embodiments, the material of the second bump structure 107 is the same as the material of the second electrode 105.

In practical applications, the second bump structure 107 may be made of a metal material or a dielectric material, and the metal material may includeAluminum (Al), molybdenum (Mo), etc., and the dielectric material may include silicon carbide (SiC), silicon dioxide (SiO) ₂ ) And the like. In other cases, materials having low acoustic loss and high acoustic impedance such as tungsten (W), platinum (Pt), ruthenium (Ru), iridium (Ir), zinc oxide (ZnO), and the like may also be selected.

The positional relationship of the second electrode 105 and the second bump structure 107 includes a vertical configuration of stacking up and down. Preferably, the second electrode 105 and the second bump structure 107 may be the same material, for example, molybdenum (Mo). In this way, the second protrusion structure 107 can increase the thickness of the conductor of the second electrode 105, and when a current with a high frequency passes through the second electrode 105, it can be considered that the current flows through the conductor after the thickening, which is equivalent to the increase of the conductor cross section, the effective resistance is reduced, and the ohmic loss is reduced. Therefore, the Q value of the bulk acoustic wave resonant structure can be improved without reducing the electromechanical coupling coefficient.

In the embodiment of the disclosure, the second protruding structure is preferably made of the same material as the second electrode, so that the thickness of the conductor of the second electrode can be increased, the effective resistance is reduced, the ohmic loss is reduced, and the quality of the sound wave signal transmitted by the bulk acoustic wave resonance structure is improved.

In some embodiments, the reflective structure 102 comprises a cavity or a bragg reflective structure; the Bragg reflection structure comprises two dielectric materials with different acoustic impedances which are arranged in a laminated mode.

In some embodiments, when the bulk acoustic wave resonator structure 100 includes a first cavity type FBAR, the reflective structure 102 includes a first electrode 103 protruding upward and forming a first cavity between the surface of the substrate 101.

In some embodiments, when the bulk acoustic wave resonator structure 100 includes the second cavity-type FBAR, the reflective structure 102 includes a second cavity formed between the surface of the substrate 101 and the first electrode 103 recessed downward.

In some embodiments, when the bulk acoustic wave resonant structure 100 includes an SMR resonant structure, the reflective structure 102 includes two dielectric materials having different acoustic impedances that are stacked, for example, a first dielectric layer and a second dielectric layer that are alternately stacked.

Illustratively, the acoustic impedance of the first dielectric layer may be greater than the acoustic impedance of the second dielectric layer. At this time, the composition material of the first dielectric layer may include: molybdenum or tungsten; the composition material of the second dielectric layer may include: silicon dioxide.

Illustratively, the acoustic impedance of the first dielectric layer may be less than the acoustic impedance of the second dielectric layer. At this time, the first dielectric layer composition material may include: silicon dioxide; the composition material of the second dielectric layer may include: molybdenum or tungsten.

In the embodiment of the disclosure, the reflective structure 102 may include a cavity or a bragg reflective structure, and the reflective structure 102 is used for implementing reflection of an acoustic wave, where the acoustic wave is reflected back to the resonant cavity, so that energy of an acoustic signal generated by the piezoelectric layer 104 can be localized in the piezoelectric layer 104, energy loss of the acoustic signal can be reduced, and quality of the acoustic signal transmitted by the bulk acoustic wave resonant structure can be improved.

Embodiments of the present disclosure provide an acoustic wave device including the bulk acoustic wave resonant structure according to the above embodiments.

In the embodiments of the present disclosure, for specific description of the bulk acoustic wave resonant structure in the acoustic wave device, reference may be made to the bulk acoustic wave resonant structure in the foregoing embodiments, and details are not repeated here.

Fig. 11 is a first flowchart illustrating a method of manufacturing a bulk acoustic wave resonant structure according to an exemplary embodiment. Based on the bulk acoustic wave resonant structure, an embodiment of the present disclosure provides a method for manufacturing a bulk acoustic wave resonant structure, as shown in fig. 11, including:

step S10: providing a substrate;

step S20: forming a sacrificial layer on the surface of the substrate;

step S30: forming a first electrode covering the sacrificial layer and extending to the surface of the substrate; the projection overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the sacrificial layer on the substrate is a first overlapping area;

step S40: forming a piezoelectric layer on a side of the first electrode opposite to the substrate;

step S50: forming a first convex structure on one side of the piezoelectric layer, which is relatively far away from the substrate; wherein the orthographic projection of the first convex structure on the substrate is at least partially overlapped with the first overlapping region, and is used for reflecting transverse shear waves in the first overlapping region;

step S60: forming a second electrode on a side of the piezoelectric layer opposite to the substrate;

step S70: forming a second convex structure on the surface of the second electrode opposite to the substrate; wherein the orthographic projection of the second convex structure on the substrate at least partially overlaps the orthographic projection of the first convex structure on the substrate, and is used for reflecting the transverse shear wave in the first overlapping region;

step S80: forming a frequency trimming layer covering the second electrode, the piezoelectric layer, the first convex structure and the second convex structure on one side of the piezoelectric layer, which is relatively far away from the substrate;

step S90: at least one etch hole is formed through the frequency shaping layer and the piezoelectric layer, and the sacrificial layer is released through the etch hole to form the reflective structure.

The manufacturing methods of the substrate, the reflective structure, the first electrode, the piezoelectric layer, and the second electrode are well known in the related art and will only be briefly described here. The materials of the substrate, the first electrode, the piezoelectric layer, and the second electrode may refer to the description of the embodiments in the bulk acoustic wave resonant structure, which is not repeated herein.

Fig. 12a to 12n are process cross-sectional views illustrating a method of manufacturing a bulk acoustic wave resonant structure according to an exemplary embodiment. Referring to fig. 12a and 12b, steps S10 to S20 are performed, and in some embodiments, a sacrificial layer 102a is deposited on the substrate 101, the sacrificial layer 102a may be formed over the substrate 101, and the sacrificial layer 102a protrudes from the upper surface of the substrate 101.

The method further comprises the following steps: the sacrificial layer 102a is etched to form a sacrificial layer 102a ', and the sacrificial layer 102a' may be removed in a subsequent process to form an upper cavity type reflective structure 102 (refer to fig. 12n below).

Referring to fig. 12c and 12d, step S30 is performed, and in some embodiments, forming the first electrode 103 covering the sacrificial layer 102a' and extending to the surface of the substrate 101 includes: a first electrode material 103a is formed covering the sacrificial layer 102a' and extending to the surface of the substrate 101, and the first electrode material 103a is patterned to form a first electrode 103.

Referring to fig. 12e, step S40 is performed, and in some embodiments, referring to fig. 12f, the method further comprises: the piezoelectric layer 104 is etched to reveal a portion of the first electrode 103.

Referring to fig. 12g and 12h, step S50 is performed, and in some embodiments, a first bump structure material 106a is formed covering the piezoelectric layer 104 and extending to the surface of the first electrode 103, and the first bump structure material 106a is patterned to form a first bump structure 106. Here, description is made with respect to forming the first bump structure 106 between the piezoelectric layer 104 and the second electrode 105. The first raised structure material 106a may include air, silicon carbide (SiC), silicon dioxide (SiO) ₂ ) And the like.

Here, the first bump structure 106 is described as an annular bump structure having a gap (i.e., not closed), wherein a tangential direction of the cross-sectional views shown in fig. 12h to 12n is a direction along the gap between the first bump structure 106 and the first bump structure 106.

In another embodiment, as shown in FIG. 13, the first raised structure 106 may also be provided as a closed annular raised structure. Specifically, a first projection structure material 106a covering the piezoelectric layer 104 and extending to the surface of the first electrode 103 is formed, and the first projection structure material 106a is patterned to form a first projection structure 106 of a closed ring shape, as shown in a cross-sectional view of fig. 13, showing a first portion, a second portion, a third portion, and a fourth portion of the first projection structure 106.

Here, it is preferable to form the first convex structure 106 in a closed ring shape, and the first convex structure 106 in a closed ring shape can reduce the lateral leakage of the acoustic wave better than a ring shape having a gap (i.e., an unclosed shape).

Note that when the material of the first convex structure 106 includes air, the first convex structure 106 composed of a silicon oxide material is formed between the piezoelectric layer 104 and the second electrode 105. The etching holes penetrate through the frequency modification layer 108 until the surface of the first bump structure 106 (composed of silicon dioxide material) is exposed, and the silicon dioxide material is removed by using the etching holes to release an etchant, so as to form the air-type first bump structure 106.

Referring to fig. 12i to 12k, step S60 is performed, a second electrode material 105a is formed covering the piezoelectric layer 104 and extending to the surfaces of the first bump structures 106 and the first electrodes 103, and the second electrode material 105a is patterned to form second electrodes 105b.

In some embodiments, referring to fig. 12k, the method further comprises: the second electrode 105b is thinned to form the second electrode 105. Through the attenuate, can further reduce bulk acoustic wave resonant structure's thickness and volume, be favorable to bulk acoustic wave resonant structure's miniaturization and integration.

Fig. 12a to 12n do not show the second bump structure, and the process of forming the second bump structure refers to the process of forming the first bump structure 106, and the second bump structure is formed on the surface of the second electrode relatively far from the substrate, and the arrangement position of the second bump structure is determined according to the orthographic projection of the first bump structure on the substrate, so that the orthographic projection of the second bump structure on the substrate at least partially overlaps with the orthographic projection of the first bump structure on the substrate.

Referring to fig. 12l and 12m, step S80 is performed, and in some embodiments, a frequency modification material layer 108a covering the second electrode, the piezoelectric layer, the first convex structure and the second convex structure is formed, and the frequency modification material layer 108a is patterned to form the frequency modification layer 108.

The method further comprises the following steps: conductive structures 109 are formed. Specifically, referring to fig. 12m, a portion of the first electrode 103 is exposed during the process of forming the frequency modifying layer 108, and conductive materials are deposited at a first end and a second end of the exposed first electrode 103, respectively, to form a conductive structure 109; wherein the first end and the second end of the first electrode 103 are opposite ends.

Referring to fig. 12n, step S90 is performed to form an etch hole EH through which the sacrificial layer 102a' is released to form the reflective structure 102.

Exemplarily, referring to fig. 12n, the sacrificial layer 102a' is removed using an etch hole EH to release an etchant; the etching hole EH may penetrate through the frequency modification layer 108, the piezoelectric layer 104 and the sacrificial layer 102a' to expose the surface of the substrate 101.

In some embodiments, the etch hole EH may only penetrate through the frequency modification layer 108 and the piezoelectric layer 104 to expose the surface of the sacrificial layer 102a ', i.e., the etch hole EH may not penetrate through the sacrificial layer 102a'.

Illustratively, the constituent materials of the sacrificial layer 102a' may include: phosphosilicate glass (PSG), silicon dioxide, or the like. For example, the sacrificial layer 102a' may be silicon dioxide, and Silane (SiH) may be used ₄ ) With oxygen (O) ₂ ) As a reaction gas, a sacrificial layer 102a' is formed on the first surface of the substrate 101 by a chemical vapor deposition process.

Illustratively, the sacrificial layer 102a 'may be removed by injecting an etchant into the etching hole EH by selecting a suitable etchant, so that the etchant contacts the exposed sacrificial layer 102a' and chemically reacts to generate a liquid product or a gaseous product.

Specifically, when the constituent material of the sacrificial layer 102a 'is silicon dioxide, a wet etching process may be used to remove the sacrificial layer 102a' by using Hydrogen Fluoride (HF) as an etchant. After the hydrogen fluoride reacts with the sacrificial layer 102a' exposed through the etching hole EH, gaseous silicon fluoride (SiF) is generated ₄ ) And liquid water.

In the embodiment of the disclosure, a first protruding structure and a second protruding structure are additionally arranged in the process of preparing the bulk acoustic wave resonance structure. Transverse shear waves are attenuated through the first protruding structures and the second protruding structures, acoustic wave energy leakage is reduced, and therefore the Q value of the bulk acoustic wave resonance structure is improved.

Fig. 14 is a second flowchart illustrating a method of fabricating a bulk acoustic wave resonant structure according to an exemplary embodiment. Based on the bulk acoustic wave resonant structure, an embodiment of the present disclosure provides a method for manufacturing a bulk acoustic wave resonant structure, as shown in fig. 14, including:

step S100: providing a substrate;

step S200: forming a sacrificial layer on the surface of the substrate;

step S300: forming a first electrode covering the sacrificial layer and extending to the surface of the substrate; the overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the sacrificial layer on the substrate is a first overlapping area;

step S400: forming a piezoelectric layer on a side of the first electrode opposite to the substrate;

step S500: forming a second electrode on a side of the piezoelectric layer opposite to the substrate;

step S600: forming a first protruding structure on one side of the second electrode, which is relatively far away from the substrate; wherein the orthographic projection of the first convex structure on the substrate at least partially overlaps the first overlapping region, and is used for reflecting transverse shear waves in the first overlapping region;

step S700: forming a second protruding structure on one side of the first protruding structure, which is relatively far away from the substrate; wherein the orthographic projection of the second convex structure on the substrate at least partially overlaps the orthographic projection of the first convex structure on the substrate, and is used for reflecting the transverse shear wave in the first overlapping region;

step S800: forming a frequency trimming layer covering the second electrode, the piezoelectric layer, the first convex structure and the second convex structure on one side of the piezoelectric layer, which is relatively far away from the substrate;

step S900: at least one etch hole is formed through the frequency shaping layer and the piezoelectric layer, and the sacrificial layer is released through the etch hole to form the reflective structure.

Here, the description is made with the first convex structure 106 formed between the second electrode 105 and the frequency correction layer 108. In some embodiments, step S600 is performed to form a first raised structure material covering the surface of the second electrode 105, and the first raised structure material is patterned to form the first raised structure 106. Forming a second raised structure material covering the surface of the first raised structure 106 and patterning the second raised structure material to form a second raised structure 107; wherein an orthographic projection of the second raised structure 107 on the substrate 101 at least partially overlaps an orthographic projection of the first raised structure 106 on the substrate 101.

It should be noted that, for the specific processes of forming the substrate 101, the reflective structure 102, the first electrode 103, the piezoelectric layer 104, the second electrode 105, and the frequency correction layer 108 in steps S100 to S900, reference is made to the description in the first flowchart, and details are not repeated here.

Taking as an example that the reflection structure 102 includes two dielectric materials with different acoustic impedances, when the bulk acoustic wave resonance structure includes an SMR resonance structure, the method for manufacturing the bulk acoustic wave resonance structure is shown in this example, and includes the following steps:

the method comprises the following steps: providing a substrate;

step two: forming a first dielectric layer and a second dielectric layer which are alternately stacked on the surface of the substrate to form a reflecting structure; the acoustic impedance of the first dielectric layer is different from that of the second dielectric layer;

step three: forming a first electrode covering the reflection structure and extending to the surface of the substrate; the projection overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the reflecting structure on the substrate is a first overlapping area;

step four: forming a piezoelectric layer on a side of the first electrode opposite to the substrate;

step five: forming a first bump structure on a side of the piezoelectric layer opposite to the substrate; wherein the orthographic projection of the first convex structure on the substrate at least partially overlaps the first overlapping region, and is used for reflecting transverse shear waves in the first overlapping region;

step six: forming a second electrode on a side of the piezoelectric layer opposite to the substrate;

step seven: forming a second convex structure on the surface of the second electrode opposite to the substrate; wherein the orthographic projection of the second convex structure on the substrate at least partially overlaps the orthographic projection of the first convex structure on the substrate, and is used for reflecting the transverse shear wave in the first overlapping region;

step eight: and forming a frequency trimming layer covering the second electrode, the piezoelectric layer, the first convex structure and the second convex structure on the side of the piezoelectric layer, which is relatively far away from the substrate.

In this embodiment, a plurality of first dielectric layers and second dielectric layers alternately stacked are formed on the surface of the substrate 101 to form the reflective structure 102. It should be noted that the first dielectric layers and the second dielectric layers that are alternately stacked do not need to be removed in a subsequent process.

Illustratively, the acoustic impedance of the first dielectric layer may be greater than the acoustic impedance of the second dielectric layer. At this time, the composition material of the first dielectric layer may include: molybdenum or tungsten; the composition material of the second dielectric layer may include: silicon dioxide.

Illustratively, the acoustic impedance of the first dielectric layer may be less than the acoustic impedance of the second dielectric layer. At this time, the first dielectric layer composition material may include: silicon dioxide; the composition material of the second dielectric layer may include: molybdenum or tungsten.

It should be noted that, for the specific process of forming the substrate, the reflective structure, the first electrode, the piezoelectric layer, the second electrode, the frequency correction layer, the first bump structure, and the second bump structure in the first to eighth steps, reference is made to the description in the first flowchart, and details are not repeated here.

Taking as an example that the reflection structure 102 includes two dielectric materials with different acoustic impedances, when the bulk acoustic wave resonant structure includes an SMR resonant structure, the method for manufacturing the bulk acoustic wave resonant structure is shown in this example, and includes the following steps:

the method comprises the following steps: providing a substrate;

step two: forming a first dielectric layer and a second dielectric layer which are alternately stacked on the surface of the substrate to form a reflecting structure; the acoustic impedance of the first dielectric layer is different from that of the second dielectric layer;

step three: forming a first electrode covering the reflective structure and extending to the surface of the substrate; the projection overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the reflecting structure on the substrate is a first overlapping area;

step four: forming a piezoelectric layer on a side of the first electrode opposite to the substrate;

step five: forming a second electrode on a side of the piezoelectric layer opposite to the substrate;

step six: forming a first protruding structure on one side of the second electrode, which is relatively far away from the substrate; wherein the orthographic projection of the first convex structure on the substrate at least partially overlaps the first overlapping region, and is used for reflecting transverse shear waves in the first overlapping region;

step seven: forming a second protruding structure on one side of the first protruding structure, which is relatively far away from the substrate; wherein the orthographic projection of the second convex structure on the substrate at least partially overlaps the orthographic projection of the first convex structure on the substrate, and is used for reflecting the transverse shear wave in the first overlapping region;

step eight: and forming a frequency trimming layer covering the second electrode, the piezoelectric layer, the first convex structure and the second convex structure on the side of the piezoelectric layer, which is relatively far away from the substrate.

In the present embodiment, first dielectric layers and second dielectric layers alternately stacked are formed on the surface of the substrate 101 to form the reflective structure 102. It should be noted that the first dielectric layers and the second dielectric layers that are alternately stacked do not need to be removed in a subsequent process.

It should be noted that, for the specific process of forming the substrate, the reflective structure, the first electrode, the piezoelectric layer, the second electrode, the frequency correction layer, the first protrusion structure, and the second protrusion structure in the first to eighth steps, reference is made to the description in the second schematic flow chart, and details are not repeated here.

Taking the case that the bulk acoustic wave resonant structure includes the second cavity type FBAR, and the reflective structure 102 includes the second cavity formed between the downward depression of the surface of the substrate 101 and the first electrode 103, this example shows a method for manufacturing the bulk acoustic wave resonant structure, which includes the following steps:

the method comprises the following steps: providing a substrate, and forming a groove on the surface of the substrate;

step two: forming a second sacrificial layer filling the groove;

step three: forming a first electrode covering the second sacrificial layer and extending to the surface of the substrate; the orthographic projection of the first electrode on the substrate and the orthographic projection of the second sacrificial layer on the substrate are overlapped in a first overlapping area;

step four: forming a piezoelectric layer on a side of the first electrode opposite to the substrate;

step five: forming a first bump structure on a side of the piezoelectric layer opposite to the substrate; wherein the orthographic projection of the first convex structure on the substrate at least partially overlaps the first overlapping region, and is used for reflecting transverse shear waves in the first overlapping region;

step six: forming a second electrode on a side of the piezoelectric layer opposite to the substrate;

step seven: forming a second convex structure on the surface of the second electrode opposite to the substrate; wherein the orthographic projection of the second convex structure on the substrate at least partially overlaps the orthographic projection of the first convex structure on the substrate, and is used for reflecting the transverse shear wave in the first overlapping region;

step eight: forming a frequency trimming layer covering the second electrode, the piezoelectric layer, the first convex structure and the second convex structure on one side of the piezoelectric layer, which is relatively far away from the substrate;

step nine: at least one etch hole is formed through the frequency shaping layer and the piezoelectric layer, and the second sacrificial layer is released through the etch hole to form the reflective structure.

In some embodiments, a second sacrificial layer may be formed in the substrate, the second sacrificial layer being recessed into the upper surface of the substrate, and the second sacrificial layer may be removed during subsequent processing to form a recessed cavity type reflective structure (not shown). In practical applications, the composition material of the second sacrificial layer includes, but is not limited to, silicon oxide.

Illustratively, etching the upper surface of the substrate to form a recess in the upper surface; forming a second sacrificial layer filling the groove; wherein the upper surface of the substrate comprises a surface for forming resonant structures such as the first electrode, the piezoelectric layer and the second electrode.

And removing the second sacrificial layer, and forming a second cavity between the first electrode and the upper surface of the substrate based on the appearance of the second sacrificial layer to form the reflecting structure. The specific way of removing the second sacrificial layer can refer to the description of removing the sacrificial layer 102a' in the first flow chart.

It should be noted that, for the specific processes of forming the substrate, the first electrode, the piezoelectric layer, the second electrode, and the frequency correction layer in the first to ninth steps, reference is made to the description in the first flowchart, and details are not repeated here.

Taking the case that the bulk acoustic wave resonant structure includes the second cavity type FBAR, and the reflective structure 102 includes the second cavity formed between the downward depression of the surface of the substrate 101 and the first electrode 103, this example shows a method for manufacturing the bulk acoustic wave resonant structure, which includes the following steps:

the method comprises the following steps: providing a substrate, and forming a groove on the surface of the substrate;

step two: forming a second sacrificial layer filling the groove;

step three: forming a first electrode covering the second sacrificial layer and extending to the surface of the substrate; the projection overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the second sacrificial layer on the substrate is a first overlapping area;

step four: forming a piezoelectric layer on a side of the first electrode opposite to the substrate;

step five: forming a second electrode on a side of the piezoelectric layer opposite to the substrate;

step six: forming a first protruding structure on one side of the second electrode, which is relatively far away from the substrate; wherein the orthographic projection of the first convex structure on the substrate at least partially overlaps the first overlapping region, and is used for reflecting transverse shear waves in the first overlapping region;

step seven: forming a second protruding structure on one side, relatively far away from the substrate, of the first protruding structure; wherein the orthographic projection of the second convex structure on the substrate at least partially overlaps the orthographic projection of the first convex structure on the substrate, and is used for reflecting the transverse shear wave in the first overlapping region;

step eight: forming a frequency trimming layer covering the second electrode, the piezoelectric layer, the first convex structure and the second convex structure on one side of the piezoelectric layer, which is relatively far away from the substrate;

step nine: at least one etch hole is formed through the frequency shaping layer and the piezoelectric layer, and the second sacrificial layer is released through the etch hole to form the reflective structure.

In some embodiments, a second sacrificial layer may be formed in the substrate, the second sacrificial layer being recessed downward into the upper surface of the substrate, and the second sacrificial layer may be removed during subsequent processing to form a recessed cavity type reflective structure (not shown). In practical applications, the composition material of the second sacrificial layer includes, but is not limited to, silicon oxide.

The specific way of removing the second sacrificial layer can refer to the description of removing the sacrificial layer 102a' in the first flow chart.

It should be noted that, for the specific processes of forming the substrate, the reflective structure, the first electrode, the piezoelectric layer, the second electrode, the frequency correction layer, the first protrusion structure, and the second protrusion structure in the steps one to nine, reference is made to the description in the second flowchart, and details are not repeated here.

The above description is only for the specific embodiments of the present disclosure, but the scope of the present disclosure is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the present disclosure, and shall cover the scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.

Claims (16)

1. A bulk acoustic wave resonant structure, comprising:

a substrate;

the reflecting structure, the first electrode, the piezoelectric layer and the second electrode are sequentially positioned on the substrate; wherein an overlapping area of the orthographic projection of the first electrode on the substrate and the orthographic projection of the reflecting structure on the substrate is a first overlapping area;

a first convex structure located on a side of the piezoelectric layer or the second electrode opposite to the substrate; wherein the first raised structure at least partially overlaps the first overlap region in an orthographic projection of the substrate for reflecting transverse shear waves within the first overlap region;

the second protruding structure is at least partially positioned on one side of the second electrode, which is relatively far away from the substrate; wherein an orthographic projection of the second convex structure on the substrate at least partially overlaps an orthographic projection of the first convex structure on the substrate, for reflecting transverse shear waves in the first overlapping region;

and the frequency trimming layer covers the surface of the second electrode, the piezoelectric layer, the first convex structure and the second convex structure which is relatively far away from the substrate.

2. The bulk acoustic wave resonant structure of claim 1,

the first convex structure is only positioned between the piezoelectric layer and the second electrode; wherein an orthographic projection of the first raised structure on the substrate falls within the first overlap region;

the second protruding structures are only located on the surface, relatively far away from the substrate, of the second electrode; wherein an orthographic projection of the second raised structure on the substrate falls within the first overlap region.

3. The bulk acoustic wave resonant structure of claim 2, wherein an orthographic projection of the second raised structure on the substrate falls within an orthographic projection of the first raised structure on the substrate.

4. The bulk acoustic wave resonator structure of claim 2, wherein an overlapping area of an orthographic projection of the first electrode on the substrate, an orthographic projection of the piezoelectric layer on the substrate, and an orthographic projection of the second electrode on the substrate is a second overlapping area;

the first protruding structure at least partially overlaps the second overlapping region in an orthographic projection of the substrate;

the second electrode includes: a third protruding structure protruding in a direction away from the substrate and located at an edge of the second electrode, wherein a first end of the third protruding structure is in contact with the piezoelectric layer, and a second end of the third protruding structure is located only between the frequency correction layer and the first protruding structure; wherein the first end and the second end of the third bump structure are opposite ends;

the side edge of the first protruding structure, which is relatively far away from the second end of the third protruding structure, has a preset distance with the second end of the third protruding structure; wherein the preset distance is greater than 0 and less than or equal to 10 μm.

5. The bulk acoustic wave resonant structure of claim 1, wherein the second raised structure is provided in a ring shape.

6. The bulk acoustic wave resonator structure of claim 1, wherein the first raised structure is located at least partially between the piezoelectric layer and the second electrode; wherein the content of the first and second substances,

the orthographic projection of the first end of the first protruding structure on the substrate falls into the overlapping region of the orthographic projection of the first electrode on the substrate and the orthographic projection of the second electrode on the substrate; the orthographic projection of the second end of the first convex structure on the substrate falls into the orthographic projection of the reflecting structure on the substrate; wherein the first end and the second end of the first protrusion structure are opposite ends.

7. The bulk acoustic wave resonant structure of claim 1, wherein the first raised structure is located only between the piezoelectric layer and the frequency shaping layer; wherein the content of the first and second substances,

the orthographic projection of the first end of the first protruding structure on the substrate falls into the orthographic projection of the first electrode on the substrate, the orthographic projection of the first end of the first protruding structure on the substrate falls into an area outside the orthographic projection of the second electrode on the substrate, and the orthographic projection of the second end of the first protruding structure on the substrate falls into the orthographic projection of the reflecting structure on the substrate; wherein the first end and the second end of the first protrusion structure are opposite ends.

8. The bulk acoustic wave resonant structure of claim 1, wherein the first raised structure is located only between the piezoelectric layer and the frequency shaping layer; wherein, the first and the second end of the pipe are connected with each other,

the orthographic projection of the first protruding structure on the substrate falls into the orthographic projection of the first electrode on the substrate, and the orthographic projection of the first protruding structure on the substrate falls into an area outside the orthographic projection of the second electrode on the substrate.

9. The bulk acoustic wave resonator structure of claim 1, wherein the first bump structure is located at least partially between the second electrode and the frequency shaping layer; wherein, the first and the second end of the pipe are connected with each other,

the projection overlapping area of the orthographic projection of the first electrode on the substrate, the orthographic projection of the piezoelectric layer on the substrate and the orthographic projection of the second electrode on the substrate is a second overlapping area;

the orthographic projection of the first convex structure on the substrate comprises a first projection part and a second projection part; wherein the first projected portion is located within the second overlap region and the second projected portion is located outside the second overlap region.

10. The bulk acoustic wave resonant structure according to claim 1, wherein a thickness of the first bump structure comprises 10nm to 500nm.

11. The bulk acoustic wave resonant structure of claim 1, wherein the line width of the first bump structure comprises 1 μ ι η to 5 μ ι η.

12. The bulk acoustic wave resonator structure of claim 1, wherein the sidewalls of the first protrusion structure have an inclination angle with respect to the substrate surface, the inclination angle comprising 10 ° to 80 °.

13. The bulk acoustic wave resonant structure of claim 1, wherein the material of the first raised structure comprises air or a functional material for reflecting acoustic waves, wherein the acoustic impedance of the functional material is less than or equal to the acoustic impedance of air.

14. The bulk acoustic wave resonator structure of claim 1, wherein the material of the second bump structure is the same as the material of the second electrode.

15. The bulk acoustic wave resonant structure of claim 1, wherein the reflective structure comprises a cavity or a bragg reflective structure; the Bragg reflection structure comprises two dielectric materials which are arranged in a laminated mode and have different acoustic impedances.

16. An acoustic wave device characterized by comprising the bulk acoustic wave resonant structure according to any one of claims 1 to 15.

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