WO2020125351A1

WO2020125351A1 - Filter unit with improved support structure, filter and electronic device

Info

Publication number: WO2020125351A1
Application number: PCT/CN2019/121081
Authority: WO
Inventors: 杨清瑞; 庞慰; 张孟伦
Original assignee: 天津大学; 诺思(天津)微系统有限责任公司
Priority date: 2018-12-18
Filing date: 2019-11-26
Publication date: 2020-06-25
Also published as: CN111342810A; CN111342810B

Abstract

The present invention relates to a filter unit, comprising: a functional substrate arranged with a cavity; and a functional means arranged at the functional substrate and comprising a plurality of bulk acoustic wave resonators, wherein the plurality of resonators share a piezoelectric layer, and each resonator is provided with a top electrode and a bottom electrode arranged at two sides of the corresponding portion of the shared piezoelectric layer, and the top electrode, the bottom electrode and the shared piezoelectric layer form a sandwich structure, and each resonator constitutes a sub-sandwich structure; the sub-sandwich structure and a cavity-type acoustic lens arranged therebelow form an effective area corresponding to the resonator, and the cavity-type acoustic lens is part of the cavity; and the sandwich structure is supported by the cavity, and the cavity-type acoustic lenses of at least two resonators are in communication with each other. The present invention also relates to a filter and an electronic device with the filter.

Description

Filter unit, filter and electronic equipment with improved support structure

Technical field

Embodiments of the present invention relate to the semiconductor field, and in particular, to a filter unit, a filter with the filter unit, and an electronic device with the filter unit or filter.

Background technique

Generally, a conventional filter composed of several individual acoustic wave resonators has a top-view structure as shown in FIG. 1a. Along the line AA' in FIG. 1a, a cross-sectional structure as shown in FIG. 1B can be obtained.

The filters shown in FIGS. 1a and 1b include several individual acoustic wave resonators, and the specific structure of each resonator includes a substrate P100; a cavity-type acoustic mirror P200 (P210, P220) embedded on the surface of the substrate; The bottom electrode P300 (P310, P320) covering part of the base surface; the piezoelectric layer film P400 covering the bottom electrode and part of the substrate surface, and P400 is shared by multiple resonators; the top electrode P500 (P510, P520) above the piezoelectric layer ). The overlapping part of the piezoelectric layer and the acoustic mirror, bottom electrode, and top electrode of each resonator in the lateral direction defines the effective acoustic region of the resonator (P600, P610, and P620).

If the bottom electrode, the piezoelectric layer and the top electrode are completely removed from FIGS. 1a and 1b, the substrate structure with cavities shown in FIGS. 1c and 1d can be obtained.

Since the thickness of each film layer constituting the filter is only on the order of micrometers, the film is easily deformed by the influence of stress. The distortion of the sandwich structure will seriously reduce the Q value of the resonator constituting the filter, thereby seriously affecting the performance of the filter. Therefore, traditional bulk acoustic wave filters with cavity-type acoustic mirrors usually use the base of a discrete cavity structure: that is, each resonator in the filter has its own independent cavity.

The advantage of this structure is that a supporting structure (P110 in Figure 1c) can be formed below the resonators, thereby enhancing the stability of the overall structure of the filter.

However, the drawback of this structure is that under ideal conditions, when the resonator is operating, the energy conversion only occurs in the effective acoustic region. However, in practice, the energy of the resonator is always inevitably dissipated outside the effective acoustic region and passes through the support structure on the substrate that contacts the bottom electrode and the piezoelectric layer (P110 and P120 in Figure 1c) Further escape into the substrate (as shown by arrows EL100, EL110, EL120 and EL130 in Fig. 1b). This structure will cause significant energy loss, and eventually cause the Q value to decline severely and cause the filter performance to deteriorate.

Summary of the invention

In order to alleviate or solve at least one aspect of using the above problems in the prior art, the present invention is proposed.

According to an aspect of an embodiment of the present invention, a filter unit is proposed, including:

A functional base with a cavity; and

A functional device, which is provided on the functional substrate and includes a plurality of bulk acoustic wave resonators, the plurality of resonators share a piezoelectric layer, and each resonator has a top electrode and a bottom provided on both sides of a corresponding portion of the shared piezoelectric layer Electrodes, the top electrode, the bottom electrode and the common piezoelectric layer form a sandwich structure, and each resonator constitutes a sub-sandwich structure,

among them:

The sub-sandwich structure and the cavity-type acoustic mirror underneath form an effective area of the corresponding resonator, and the cavity-type acoustic mirror is a part of the cavity;

The sandwich structure is supported by the cavity and cavity-type acoustic mirrors of at least two resonators communicate with each other.

In one embodiment, the sandwich structure is supported only by the edge of the cavity.

Further, the cavity has a substantially rectangular shape; the sandwich structure is supported by two opposite edges of the cavity.

Optionally, the two opposite edges simultaneously support the bottom electrode and the piezoelectric layer of the outermost resonator.

Optionally, the functional device has electrode pins for the resonator; the piezoelectric layer is located between and spaced apart from the two opposite edges; and the sandwich structure is provided by the The electrode pins at the two opposite edges are supported on the two opposite edges.

Optionally, two sides of the piezoelectric layer are respectively supported on the two opposite edges.

Optionally, the sandwich structure is supported by opposite edges of the cavity; and in a top view of the filter unit, there is a gap between at least a part of the edge of the sandwich structure and the edge of the cavity.

In another embodiment, the sandwich structure is supported only by a plurality of supporting protrusions provided in the cavity.

Optionally, the plurality of support protrusions includes at least one island-shaped support protrusion spaced apart from the edge of the cavity.

Optionally, the resonator is a polygonal resonator; and the island-shaped support protrusion is used to support an apex portion of the polygonal resonator. Further, each island-shaped supporting protrusion is used to simultaneously support the apex portions of multiple resonators.

Optionally, the resonator is a polygonal resonator; and the island-shaped support protrusion is used to support the side portion of the resonator. Further, each island-shaped supporting protrusion is used to simultaneously support a plurality of side portions of the resonator.

Optionally, the plurality of support protrusions includes at least one peninsula-shaped support protrusion from the edge of the cavity to the cavity radially inward.

In yet another embodiment, the sandwich structure is supported only by support bar ribs connected between the edges of the cavity.

In another embodiment, the sandwich structure is composed of an edge of the cavity, at least one support protrusion provided in the cavity, an electrode pin of the resonator, and a support bar rib connected between the edges of the cavity At least two structural supports.

Optionally, in the above filter unit, all resonators are provided on the functional substrate, and the filter unit has a packaging substrate opposite to the functional substrate; and the sum of the areas of the effective areas of all resonators is not greater than the 1/2 of the area of one surface of the functional substrate; or the area where the functional area where the functional device is located is projected vertically onto the packaging substrate is not larger than 2/3 of the surface area of the packaging substrate.

Optionally, in the above filter unit, the piezoelectric layer is doped with one or more of the following elements: scandium, yttrium, magnesium, titanium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, Gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium; and the atomic fraction of doping elements ranges from 1% to 40%. Optionally, the piezoelectric layer is an aluminum nitride piezoelectric layer, a zinc oxide piezoelectric layer, a lithium niobate piezoelectric layer, or a lead titanium zirconate piezoelectric layer.

Optionally, in the above filter unit, the atomic fraction of the doping element ranges from 3% to 20%.

An embodiment of the present invention also relates to a functional substrate for a filter, provided with a cavity, wherein: the cavity is provided with a plurality of support protrusions that are independent of each other, and the support protrusions are suitable for supporting filter functional devices Or there is no supporting structure for supporting the functional device in the cavity.

Embodiments of the present invention also relate to a filter, including: the filter unit according to the above or the above functional base.

Embodiments of the present invention also relate to an electronic device, including the above filter unit or the above filter.

BRIEF DESCRIPTION

The following description and drawings can better help to understand these and other features and advantages in the various embodiments disclosed in the present invention. The same reference numerals in the figures always denote the same parts, among which:

FIG. 1a is a schematic plan view of a filter unit composed of a plurality of bulk acoustic wave resonators in the prior art;

Figure 1b is a schematic cross-sectional view taken along line AA' in Figure 1a;

FIG. 1c is a schematic top view of the functional base of the filter unit in FIG. 1a;

FIG. 1d is a schematic perspective view of the functional base of the filter unit in FIG. 1a;

2 is a schematic top view of a functional substrate of a filter unit according to an exemplary embodiment of the present invention;

3 is a schematic top view of a functional base of a filter unit according to an exemplary embodiment of the present invention;

4a is a schematic top view of a functional substrate of a filter unit according to an exemplary embodiment of the present invention;

4b is a schematic cross-sectional view of a filter unit using the functional substrate in FIG. 4a according to an exemplary embodiment of the present invention, which shows the supporting state of the sandwich structure;

4c is an exemplary schematic diagram of the support edge of the cavity of the functional substrate in FIG. 4a after further moving outward;

4d is a schematic cross-sectional view of a filter unit using the functional substrate in FIG. 4c according to another exemplary embodiment of the present invention, which shows the supporting state of the sandwich structure;

4e is a schematic cross-sectional view of a filter unit using the functional substrate in FIG. 4c according to another exemplary embodiment of the present invention, which shows the supporting state of the sandwich structure;

5 is a schematic top view of a functional base of a filter unit according to an exemplary embodiment of the present invention;

6 is a schematic diagram of a sandwich structure of a bulk acoustic wave resonator; and

7 is a graph showing the relationship between the electromechanical coupling coefficient Nkt and the ratio r of a bulk acoustic wave resonator.

detailed description

The technical solutions of the present invention will be further specifically described below through the embodiments and the accompanying drawings. In the description, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the drawings is intended to explain the general inventive concept of the present invention, and should not be construed as a limitation of the present invention.

The present invention will be exemplarily described below with reference to the drawings.

FIG. 2 is a schematic top view of a functional substrate of a filter unit according to an exemplary embodiment of the present invention A100.

In order to facilitate the display and description of the functional base structure, the acoustic structure of the filter in the upper part of the base in Embodiment A100 is omitted in FIG. 2.

The filter unit in Embodiment A100 includes the functional substrate 100. The cavity structure of the functional substrate 100 includes a cavity edge 120, and a number of island-shaped support structures 110 located in the cavity. Among them, the island-shaped support structure 110 is used to support the apex portion of the polygonal resonator, where the dotted line portion shows the removed portion relative to the conventional structure of FIG. 1c. Each island-shaped supporting protrusion can simultaneously support the apex portions of multiple resonators.

Compared with the conventional structure, the embodiment A100 reduces the support structure in contact with the resonator. For example, in the case where only the four support structures 110 in FIG. 2 are in contact with the acoustic structure of the resonator, only these four islands exist The leakage channel formed by the support structure. Therefore, the solution of Example A100 reduces the energy leakage into the functional substrate.

When the sandwich structure is placed on the cavity, the sandwich structure may be supported only by the four support structures 110 in FIG. 2, or may be supported by the edge 120 of the cavity together with the four support structures 110.

FIG. 3 is a schematic top view of a functional substrate of a filter unit according to an exemplary embodiment of the present invention A200.

In order to facilitate the display and description of the base structure, the acoustic structure of the filter located above the functional base in Embodiment A200 is omitted in FIG. 3.

The filter unit in the embodiment A200 includes the substrate 200. The cavity structure of the substrate 200 includes a cavity edge 220 and a number of island-shaped support structures 210 located in the cavity. Among them, the island-shaped support structure 210 is used to support the side portion of the polygonal resonator (ie, the portion between the vertices of the resonator), where the dotted portion shows the portion removed relative to the conventional structure of FIG. 1c. Each island-shaped supporting protrusion may simultaneously support a plurality of side portions of the resonator.

Compared with the conventional structure, the embodiment A200 reduces the support structure in contact with the resonator, thereby reducing the energy leakage into the functional substrate.

Although not shown, the supporting protrusion may protrude from the edge of the cavity toward the inside of the cavity (ie, protrude radially inward). This solution can also be combined with the support protrusion in FIG. 3 or FIG. 2.

In the case where, for example, the supporting protrusions of FIG. 2 or FIG. 3 are used, all of the cavity-type acoustic mirrors of the nine resonators are in communication with each other.

In the solutions shown in FIGS. 2 and 3, the support structure is a plurality of separate protrusions. However, as shown in FIG. 2, two longitudinal support ribs or two lateral support ribs in FIG. 2 may be provided. In this case, for example, if there are two longitudinal support ribs, the nine resonators are divided into three columns, and each column includes three, and the cavity-type acoustic mirrors of the three resonators in each column communicate with each other.

4a is a schematic top view of a functional substrate of a filter unit according to an exemplary embodiment of the present invention A300. 4b is a schematic cross-sectional view of a filter unit using the functional substrate in FIG. 4a according to an exemplary embodiment of the present invention, which shows a supporting state of a sandwich structure.

When the area of the resonator is small enough (the rigidity is strong enough), all the supporting structures in the cavity on the surface of the functional substrate 300 can be removed. The dashed line in the cavity of the embodiment A300 shown in FIG. 4a represents the portion removed with respect to the conventional structure of FIG. 1c. As shown in the region 330 in FIG. 4b, in the embodiment A300, only the cavity edge 320 is used to support the bottom electrode and the piezoelectric layer of the outermost resonator.

Fig. 4c is an exemplary schematic diagram of the support edge of the cavity of the functional substrate in Fig. 4a after further moving outward. The functional substrate 400, the cavity support edge 410 (dashed line) in FIG. 4b, and the new support edge 420 are shown in FIG. 4c.

FIG. 4d is a schematic cross-sectional view of a filter unit using the functional substrate in FIG. 4c according to another exemplary embodiment of the present invention, which shows the supporting state of the sandwich structure. In FIG. 4d, it can be seen that both ends of the piezoelectric layer of the sandwich structure are supported by the edge of the cavity, as shown by the support region 430 in FIG. 4d.

FIG. 4e is a schematic cross-sectional view of a filter unit using the functional substrate in FIG. 4c according to another exemplary embodiment of the present invention, which shows the supporting state of the sandwich structure. In FIG. 4e, the two sides of the sandwich structure are supported on the support edge of the cavity via the electrode pins 450 of the resonator, and the support area 440 shows the specific support situation. It should be pointed out that Figure 4d and Figure 4e can also be combined.

As can be seen from FIGS. 4a-4e, the sandwich structure of the filter unit can be supported only by the edge of the cavity, and no protrusions or ribs for supporting the sandwich structure are provided inside the cavity at all.

In the example of FIGS. 4a-4e, the cavity is substantially rectangular, and the two opposite edges of the cavity support the sandwich structure, however, the present invention is not limited thereto. The cavity can have other shapes based on actual needs, and even a substantially rectangular cavity can be sandwiched by more sides. When the sandwich structure is supported by the opposite edges of the cavity, in a plan view of the filter unit, at least a part of the edges of the sandwich structure may also have a gap between the edges of the cavity.

In an alternative embodiment, as shown in FIG. 5, the support structure 92 provided in the cavity 92 has some missing support ribs compared to the prior art (FIG. 1 c ), as shown by the dotted line in FIG. 5.

Although not shown, the solutions of FIGS. 2 and 3, the solutions of FIGS. 4a-4e and the solution of FIG. 5 can be used in combination with each other.

Based on the above, the present invention proposes a filter unit, including:

A functional substrate (for example, 100 in FIG. 2) provided with a cavity (for example, a space enclosed by the edge 120 in FIG. 2); and

A functional device, which is provided on the functional substrate and includes a plurality of bulk acoustic resonators (see, for example, FIG. 1b, except that the supporting structure of the sandwich structure is replaced by the structure shown in FIGS. 2 to 4e of the present invention), A plurality of resonators share a piezoelectric layer (for example, see P400 in FIG. 1b), and each resonator has a top electrode (for example, P500 in FIG. 1b) and a bottom electrode provided on both sides of a corresponding portion of the common piezoelectric layer ( For example, P300 in FIG. 1b), the top electrode, the bottom electrode, and the common piezoelectric layer form a sandwich structure, and each resonator forms a sub-sandwich structure. It should be noted that the resonator structure shown in FIG. 1b is also applicable In the embodiment shown in FIGS. 2 to 4e of the present invention,

among them:

It should be noted that at least two cavity-type acoustic mirrors here communicate with each other indicating that the two cavity-type acoustic mirrors are not closed independent sub-cavities. It is precisely because the cavity-type acoustic mirror is not a closed independent subspace, so, for example, the support bar rib in FIG. 1c is in a disconnected state, and the disconnection directly leads to a reduction in the contact area of the support bar rib and the acoustic structure, thereby reducing The energy loss dissipated into the functional substrate.

The filter unit adopts, for example, the technical solutions of FIG. 2 to FIG. 4e, which can be implemented in the case of the size of the current resonator, or can be implemented in the case of reducing the size of the current resonator. For the latter case, the present invention proposes a solution to reduce the size of the resonator by reducing the area of the effective area of the resonator. Reducing the size of the resonator can directly increase the rigidity of the sandwich structure of the filter. In the case where the rigidity of the sandwich structure is increased, even if the corresponding supporting structure is reduced or eliminated in the cavity, the sandwich structure of the resonator will not be severely deformed to lower the Q value of the resonator.

Specifically, in one embodiment, a bulk acoustic wave resonator (having a piezoelectric layer, a bottom electrode, and a top electrode), by incorporating an impurity element in a piezoelectric layer such as an aluminum nitride (AlN) piezoelectric layer, makes the resonator The area of the effective area is reduced, making the size of the resonator smaller.

The principle of using element doping to reduce the area of the effective area of the bulk acoustic wave resonator is specifically described below with reference to FIGS. 6-7.

Electromechanical coupling coefficient (Nkt) is one of the important performance indicators of bulk acoustic wave resonators. This performance parameter is closely related to the following factors: (1) the proportion of the impurity elements incorporated into the piezoelectric film; and (2) the electrode layer and The thickness ratio of the piezoelectric layer.

The sandwich structure of the bulk acoustic wave resonator shown in FIG. 6 includes a top electrode TE having a thickness t, a bottom electrode BE, and a piezoelectric layer PZ having a thickness d. Define scale here

For a specific undoped resonator, the relationship between the normalized electromechanical coupling coefficient Nkt and the ratio r can be described by the characteristic curve C0 shown in FIG. 7.

As shown in FIG. 7, when the piezoelectric layer of the resonator is doped, the characteristic curve C0 moves upward to form a curve C1. If the electromechanical coupling coefficient of the resonator with the thickness ratio r ₀ is Nkt ₀ before undoping, then the coefficient increases to Nkt ₁ after doping.

Generally, the electromechanical coupling coefficient is limited by the technical specifications of the filter's relative bandwidth and roll-off characteristics, so it needs to remain unchanged. Therefore, in the case of doping, the electromechanical coupling coefficient needs to be restored to the undoped level by adjusting the ratio r. Note that curve C1 has a maximum value, so there are two ways to adjust the ratio r, which can reduce the ratio r from r ₀ to r ₂ or increase to r ₁ . However, since reducing r means that the electrode layer becomes thinner and the resistance increases, which causes the device loss to increase, the ratio r to r ₁ is selected to be increased.

On the other hand, the frequency f of the resonator is constrained by the technical specifications of the filter center frequency and needs to be fixed. The frequency f has the following simplified relationship with the overall thickness of the sandwich structure:

Where D is the equivalent total thickness of the electrode material (Mo) to the piezoelectric material, specifically D = 2tv ₁ /v ₂ + d, where v ₂ is the longitudinal wave sound velocity in the electrode material and v ₁ is the piezoelectric material Medium longitudinal wave sound velocity. Taking formula (1) into formula (2), we can get:

Since the sound velocity v ₁ due to doping decreases, and at the same time, r increases, then if the frequency f is not required to change, then the thickness d of the piezoelectric layer should decrease.

In addition, there is a technical requirement for the impedance of the resonator (50 ohms), and the impedance Z and the thickness d of the piezoelectric layer are related by the following formula:

Where ε is the dielectric constant of the piezoelectric material, A is the effective area of the resonator, and j is the imaginary unit representing the phase.

When the impedance Z is required to be constant, if the thickness d of the piezoelectric layer becomes smaller, the effective area A must also become smaller.

Based on the above, it is possible to reduce the thickness d of the piezoelectric layer by adding an impurity element to the piezoelectric layer, thereby reducing the effective area A of the resonator.

In an embodiment, the piezoelectric layer is doped with one or more of the following elements: scandium, yttrium, magnesium, titanium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium , Holmium, erbium, thulium, ytterbium, lutetium; and the atomic fraction of the doping element ranges from 1% to 40%, further, from 3% to 20%. The specific atomic fraction may be 1%, 3%, 6%, 20%, 30%, 40%, etc.

The piezoelectric layer may be an aluminum nitride piezoelectric layer, a zinc oxide piezoelectric layer, a lithium niobate piezoelectric layer, or a titanium zirconate piezoelectric layer.

In the present invention, the materials of the top electrode and the bottom electrode may be selected but not limited to: molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a combination of the above metals or alloys thereof.

The use of the above doping technical solution greatly reduces the area of the resonator, which in turn can reduce the size of the sandwich structure of the filter (resonator as the core device of the filter), thereby improving the rigidity of the sandwich structure.

Correspondingly, the present invention also proposes a functional substrate for a filter provided with a cavity, wherein: the cavity is provided with a plurality of support protrusions independent of each other, and the support protrusions are suitable for supporting the filter function Device (for example, see the embodiments of FIGS. 2 and 3); or there is no supporting structure for supporting the functional device in the cavity (for example, see the embodiments of FIGS. 4a-4e).

In an alternative embodiment, all resonators are provided on the functional substrate; and the sum of the effective area areas of all resonators is not greater than 2/3 of the area of one surface of the functional substrate. Further, 1/2. It should be noted that the area of the surface of the functional substrate here is the entire area of one surface (including the area where the via and the functional device are located).

Correspondingly, the invention also relates to a filter, including the above-mentioned filter unit.

The invention also relates to an electronic device, including the above-mentioned filter unit or filter or functional substrate. It should be noted that the electronic devices here include but are not limited to intermediate products such as radio frequency front-ends, filter amplification modules, and terminal products such as mobile phones, WIFI, and drones.

Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that these embodiments can be changed without departing from the principle and spirit of the present invention. The appended claims and their equivalents are limited.

Claims

A filter unit, including:

A functional base with a cavity; and

A functional device, which is provided on the functional substrate and includes a plurality of bulk acoustic wave resonators, the plurality of resonators share a piezoelectric layer, and each resonator has a top electrode and a bottom provided on both sides of a corresponding portion of the shared piezoelectric layer Electrodes, the top electrode, the bottom electrode and the common piezoelectric layer form a sandwich structure, and each resonator constitutes a sub-sandwich structure,

among them:

The sub-sandwich structure and the cavity-type acoustic mirror underneath form an effective area of the corresponding resonator, and the cavity-type acoustic mirror is a part of the cavity;

The sandwich structure is supported by the cavity and cavity-type acoustic mirrors of at least two resonators communicate with each other.
The filter unit according to claim 1, wherein:

The sandwich structure is only supported by the edge of the cavity.
The filter unit according to claim 2, wherein:

The cavity is substantially rectangular in shape;

The sandwich structure is supported by two opposite edges of the cavity.
The filter unit according to claim 3, wherein:

The two opposite edges simultaneously support the bottom electrode and the piezoelectric layer of the outermost resonator.
The filter unit according to claim 3 or 4, wherein:

The functional device has electrode pins for the resonator;

The piezoelectric layer is located between and spaced from the two opposing edges; and

The sandwich structure is supported on the two opposite edges by electrode pins provided at the two opposite edges, respectively.
The filter unit according to claim 3, wherein:

Two sides of the piezoelectric layer are respectively supported on the two opposite edges.
The filter unit according to claim 2, wherein:

The sandwich structure is supported by opposite edges of the cavity; and

In a top view of the filter unit, there is a gap between at least a part of the edge of the sandwich structure and the edge of the cavity.
The filter unit according to claim 1, wherein:

The sandwich structure is only supported by a plurality of supporting protrusions provided in the cavity.
The filter unit according to claim 8, wherein:

The plurality of support protrusions includes at least one island-shaped support protrusion spaced apart from the edge of the cavity.
The filter unit according to claim 9, wherein:

The resonator is a polygonal resonator; and

The island-shaped support protrusion is used to support the vertex portion of the polygonal resonator.
The filter unit according to claim 10, wherein:

Each island-shaped supporting protrusion is used to simultaneously support the apex portions of multiple resonators.
The filter unit according to claim 9, wherein:

The resonator is a polygonal resonator; and

The island-shaped supporting protrusion is used to support the side portion of the resonator.
The filter unit according to claim 12, wherein:

Each island-shaped supporting protrusion serves to simultaneously support a plurality of side portions of the resonator.
The filter unit according to any one of claims 8 to 13, wherein:

The plurality of support protrusions includes at least one peninsula-shaped support protrusion from the edge of the cavity to the cavity radially inward.
The filter unit according to claim 1, wherein:

The sandwich structure is only supported by the support bar ribs connected between the edges of the cavity.
The filter unit according to claim 1, wherein:

The sandwich structure is supported by at least two structures among the edge of the cavity, at least one supporting protrusion provided in the cavity, the electrode pin of the resonator, and the support bar rib connected between the edges of the cavity.
The filter unit according to any one of claims 1-16, wherein:

All resonators are provided on the functional substrate, and the filter unit has a packaging substrate opposite to the functional substrate; and

The sum of the effective areas of all resonators is not greater than 1/2 of the area of one surface of the functional substrate; or the area of the functional area where the functional device is located is projected vertically onto the packaging substrate is not greater than 2/3 of the area of the surface of the packaging substrate.
The filter unit according to any one of claims 1-17, wherein:

The piezoelectric layer is doped with one or more of the following elements: scandium, yttrium, magnesium, titanium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, Thulium, Ytterbium, Lutetium; and

The atomic fraction of the doping element ranges from 1% to 40%.
The filter unit according to claim 18, wherein:

The piezoelectric layer is an aluminum nitride piezoelectric layer, a zinc oxide piezoelectric layer, a lithium niobate piezoelectric layer, or a lead titanium zirconate piezoelectric layer.
The filter unit according to claim 18 or 19, wherein:

The atomic fraction of the doping element ranges from 3% to 20%.
A functional base for a filter, provided with a cavity, in which:

A plurality of support protrusions independent of each other are provided in the cavity, the support protrusions are suitable for supporting the filter functional device; or

There is no supporting structure for supporting the functional device in the cavity.
A filter, including:

The filter unit according to any one of claims 1-20 or the functional substrate according to claim 21.
An electronic device comprising the filter unit according to any one of claims 1-20 or the filter according to claim 22.