Bulk acoustic wave resonator and preparation method thereof

Abstract

The invention provides a bulk acoustic wave resonator structure and a preparation method thereof.The bulk acoustic wave resonator structure comprises a substrate, a piezoelectric layer, a first load layer, a first electrode layer, a dielectric layer, a second load layer and a second electrode layer, and the dielectric layer, the substrate and the first electrode layer define a cavity structure to limit the longitudinal wave propagation range; the upper surface and the lower surface of the piezoelectric layer are respectively provided with the first load layer and the second load layer, so that the transverse wave propagation is effectively inhibited, the parasitic mode is reduced, the quality factor of the resonator is obviously improved, and the insertion loss is reduced. The dielectric layer is formed and planarized, the dielectric layer and the substrate are bonded through the opening to form the cavity, after the middle substrate is removed, the second load layer and the second electrode layer are formed on the other face of the piezoelectric layer, the electrical leading-out structure is completed, and compared with a traditional sacrificial layer release process, the method has the advantages that generation of bevel angle steps is avoided, and device loss is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a bulk acoustic wave resonator and a preparation method thereof. Background Art

[0002] Currently, wireless data transmission requires RF filters with an operating frequency of 5 GHz or higher for 5G communications. Acoustic resonators that can meet 5G communication requirements include surface acoustic wave (SAW) resonators and bulk acoustic wave (BAW) resonators. BAW resonators have a Q value (quality factor) of over 4000 and an operating frequency band of 100 MHz to 20 GHz. BAW resonators are widely used in the communications field due to their advantages such as high operating frequency, low insertion loss, high frequency selectivity, high power capacity, and strong anti-static ability.

[0003] However, BAW resonators still face key performance bottlenecks in practical applications. Specifically, the impedance characteristics of BAW resonators exhibit significant ripples in the frequency bands between the series resonant frequency and the parallel resonant frequency, as well as above the parallel resonant frequency. This phenomenon stems from the non-completely ideal structure of the BAW resonator. Therefore, when excited by an electrical signal, most of the sound waves in the BAW resonator propagate longitudinally. However, due to the existence of the boundary conditions of the BAW resonator (for example, the high-low impedance mismatch boundary where the electrode and the air are in contact), some transverse waves will propagate during operation. These transverse waves are also called transverse standing waves. The existence of these transverse standing waves weakens the quality factor (Q value) of the BAW resonator to a certain extent, thereby increasing the insertion loss (Insertion Loss) of the filter composed of multi-stage BAW resonators. In addition, the energy dissipation caused by the transverse standing waves will also limit the suppression ability of the filter outside the passband, thereby affecting the overall signal-to-noise ratio of the communication system. Therefore, it is crucial to improve the Q value by changing the device structure. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the object of the present invention is to provide a bulk acoustic wave resonator and a method for preparing the same, so as to solve the problem in the prior art that, due to the non-completely ideal structure of the bulk acoustic wave resonator, there is partial shear wave propagation in the working state, which in turn leads to a weakening of the quality factor of the bulk acoustic wave resonator and the resulting increase in the insertion loss of the filter.

[0005] To achieve the above-mentioned and other related objectives, the present invention provides a bulk acoustic wave resonator, comprising:

[0006] substrate;

[0007] a piezoelectric layer located above the substrate;

[0008] a first load layer, located on the lower surface of the piezoelectric layer;

[0009] a first electrode layer, located on the lower surface of the piezoelectric layer and covering the first load layer;

[0010] a dielectric layer located between the substrate and the piezoelectric layer, and between the first electrode layer and the substrate, wherein a cavity structure penetrating the dielectric layer is formed in the dielectric layer, and the cavity structure partially exposes the first electrode layer;

[0011] a second load layer, located on the upper surface of the piezoelectric layer, wherein the horizontal projections of the first load layer and the second load layer are both located within the horizontal projection of the cavity structure;

[0012] a second electrode layer, located on the upper surface of the piezoelectric layer and covering the second load layer;

[0013] an electrical lead-out structure, penetrating the piezoelectric layer and contacting and connecting with the first electrode layer, the electrical lead-out structure comprising a through hole penetrating the piezoelectric layer and exposing the first electrode layer, and a first lead-out electrode at least filling the through hole;

[0014] The second extraction electrode is in contact with and connected to the second electrode layer; wherein the horizontal projections of the first extraction electrode and the second extraction electrode do not overlap with the horizontal projection of the cavity structure.

[0015] Optionally, the piezoelectric layer includes a piezoelectric material layer or a ferroelectric material layer or a stack of a piezoelectric material layer and a ferroelectric material layer.

[0016] Furthermore, the piezoelectric material layer includes an AlN layer, an Al x Ga 1-x N layer, Al 1-y Sc y One or more layers selected from the group consisting of an N layer, a LiNbO3 layer, a ZnO layer, a PZT layer, a PbTiO3 layer, and a Ga2O3 layer, wherein 0≤x≤1, 0≤y≤1, and the thickness of a single layer of the piezoelectric material layer is not less than 0.01 μm, and the thickness of the piezoelectric layer is not greater than 2 μm.

[0017] Furthermore, the ferroelectric material layer includes Sc x Al 1-x One or more layers of N layer, BST layer, PZT layer and PbTiO3 layer, wherein 0≤x≤1, and the thickness of the single layer of the ferroelectric material layer is not less than 0.01μm, and the thickness of the piezoelectric layer is not more than 2μm.

[0018] Optionally, the material of the first electrode layer includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf, and the material of the second electrode layer includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf, and the thickness of the first electrode layer and the second electrode layer is not greater than 0.3 μm.

[0019] Optionally, a first adhesion layer is provided between the first load layer and the first electrode layer, a second adhesion layer is provided between the second load layer and the second electrode layer, and materials of both the first adhesion layer and the second adhesion layer include Ti.

[0020] Optionally, the cross-sectional shape of the first load layer is annular, and the cross-sectional shape of the second load layer is annular.

[0021] Optionally, the material of the first load layer includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, SiO2, AlN and Al2O3, and the material of the second load layer includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, SiO2, AlN and Al2O3.

[0022] The present invention also provides a method for preparing a bulk acoustic wave resonator, characterized in that the preparation method comprises:

[0023] providing an intermediate substrate;

[0024] forming a piezoelectric layer on the intermediate substrate, wherein the piezoelectric layer has a first surface and a second surface opposite to each other, and the first surface is away from the intermediate substrate;

[0025] forming a patterned first load layer on the first surface of the piezoelectric layer;

[0026] forming a patterned first electrode layer on the first surface of the piezoelectric layer and on the first load layer, wherein the first electrode layer covers the first load layer;

[0027] forming a dielectric layer covering the first electrode layer and the first surface of the piezoelectric layer, and performing a planarization process on the surface of the dielectric layer;

[0028] forming a first opening penetrating the dielectric layer and exposing the first electrode layer, wherein a horizontal projection of the first load layer is located within a horizontal projection of the first opening;

[0029] Providing a substrate, and bonding the substrate to the dielectric layer to form a cavity structure;

[0030] removing the intermediate substrate;

[0031] forming a patterned second load layer on the second surface of the piezoelectric layer, wherein a horizontal projection of the second load layer is located within a horizontal projection of the cavity structure;

[0032] forming a patterned second electrode layer on the second surface of the piezoelectric layer and on the second load layer, wherein the second electrode layer covers the second load layer;

[0033] An electrical lead-out structure is formed that passes through the piezoelectric layer and is in contact with the first electrode layer. The electrical lead-out structure includes a through hole that passes through the piezoelectric layer and exposes the first electrode layer, and a first lead-out electrode that at least fills the through hole, and a second lead-out electrode that is in contact with the second electrode layer is formed; wherein the horizontal projections of the first lead-out electrode and the second lead-out electrode do not overlap with the horizontal projection of the cavity structure.

[0034] Optionally, the material of the intermediate substrate includes one of Si, SiC, Ge and sapphire; the material of the substrate includes one of Si, SiC, Ge and sapphire.

[0035] As described above, the bulk acoustic wave resonator and the preparation method thereof of the present invention have the following beneficial effects: the bulk acoustic wave resonator includes a substrate, a piezoelectric layer, a first load layer, a first electrode layer, a dielectric layer, a second load layer, and a second electrode layer, wherein the dielectric layer, the substrate, and the first electrode layer enclose a cavity structure, which effectively limits the propagation range of longitudinal waves. At the same time, the first load layer and the second load layer are respectively arranged on the upper and lower surfaces of the piezoelectric layer, and the horizontal projections of the two load layers are both located within the projection of the cavity structure, thereby achieving effective suppression of transverse waves and reducing the generation of parasitic modes, thereby significantly improving the quality factor of the resonator, enhancing its frequency selectivity and stability, and reducing insertion loss. The present invention discloses a method for preparing a bulk acoustic wave resonator. The method comprises providing an intermediate substrate, forming a piezoelectric layer on the intermediate substrate, patterning a first load layer and a first electrode layer, forming a dielectric layer and flattening it, forming an opening through the dielectric layer, and bonding the dielectric layer to the substrate to form a cavity structure. The intermediate substrate is then removed, and a second load layer and a second electrode layer are formed on the other side of the piezoelectric layer, and an electrical lead structure is formed. Compared with a conventional sacrificial layer release process, the method for preparing a bulk acoustic wave resonator proposed in the present invention does not produce a piezoelectric layer with angled steps, thereby reducing the loss of the prepared device and preventing an increase in the insertion loss of a filter composed of multi-stage bulk acoustic wave resonators. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1It is a schematic diagram of the cross-sectional structure of a bulk acoustic wave resonator in the prior art that cannot suppress shear waves.

[0037] Figure 2 It is a schematic cross-sectional structural diagram of a BAW resonator with a top load layer in the prior art.

[0038] Figure 3 It is a schematic diagram showing the cross-sectional structure of the bulk acoustic wave resonator of the present invention.

[0039] Figure 4 It is a schematic flow chart of the method for preparing a bulk acoustic wave resonator according to the present invention.

[0040] Figures 5 to 16 It shows a schematic cross-sectional structure diagram of each step in preparing a bulk acoustic wave resonator according to the present invention.

[0041] Figure 17 Shown are impedance distribution curves corresponding to three types of BAW resonators (a BAW resonator in the prior art that cannot suppress shear waves, a BAW resonator in the prior art with a top load layer, and the BAW resonator of the present invention).

[0042] Figure 18 Shown are impedance phase curves corresponding to three types of BAW resonators (a BAW resonator in the prior art that cannot suppress shear waves, a BAW resonator in the prior art with a top load layer, and the BAW resonator of the present invention).

[0043] Figure 19 The diagram shows the effect of different widths of the first load layer and the second load layer on the quality factor of the BAW resonator of the present invention.

[0044] Component number description

[0045] 10 Intermediate substrate

[0046] 11 Piezoelectric layer

[0047] 111 Page 1

[0048] 112 Page 2

[0049] 12 First load layer

[0050] 13. First electrode layer

[0051] 14 Dielectric layer

[0052] 141 First Opening

[0053] 142 Cavity Structure

[0054] 15 substrate

[0055] 16 Second load layer

[0056] 17 Second electrode layer

[0057] 18 through holes

[0058] 19 First extraction electrode

[0059] 20 Electrical lead structure

[0060] 21 Second extraction electrode

[0061] 31 substrate

[0062] 32 bottom electrode

[0063] 33 Piezoelectric film

[0064] 34 Top electrode

[0065] 35 cavity

[0066] 36 Top load layer

[0067] Steps S1 to S11 DETAILED DESCRIPTION

[0068] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0069] See also Figures 1 to 19 It should be noted that the diagrams provided in this embodiment are merely schematic illustrations of the basic concept of the present invention. Therefore, the diagrams only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0070] This embodiment provides a bulk acoustic wave resonator, such as Figure 3 As shown, the bulk acoustic wave resonator includes:

[0071] substrate 15;

[0072] a piezoelectric layer 11 located above the substrate 15;

[0073] A first load layer 12, located on the lower surface of the piezoelectric layer 11;

[0074] A first electrode layer 13 is located on the lower surface of the piezoelectric layer 11 and covers the first load layer 12;

[0075] a dielectric layer 14 located between the substrate 15 and the piezoelectric layer 11 and between the first electrode layer 13 and the substrate 15 , wherein a cavity structure 142 penetrating the dielectric layer 14 is formed in the dielectric layer 14 , and the cavity structure 142 partially exposes the first electrode layer 13 ;

[0076] A second load layer 16 is located on the upper surface of the piezoelectric layer 11 , and the horizontal projections of the first load layer 12 and the second load layer 16 are both located within the horizontal projection of the cavity structure 142 ;

[0077] a second electrode layer 17 , located on the upper surface of the piezoelectric layer 11 and covering the second load layer 16 ;

[0078] an electrical lead-out structure 20 penetrating the piezoelectric layer 11 and contacting and connecting with the first electrode layer 13 , the electrical lead-out structure 20 comprising a through hole 18 penetrating the piezoelectric layer 11 and exposing the first electrode layer 13 , and a first lead-out electrode 19 at least filling the through hole 18 ;

[0079] The second extraction electrode 21 is in contact with and connected to the second electrode layer 17 . The horizontal projections of the first extraction electrode 19 and the second extraction electrode 21 do not overlap with the horizontal projection of the cavity structure 142 .

[0080] The bulk acoustic wave resonator of this embodiment includes a substrate, a piezoelectric layer, a first load layer, a first electrode layer, a dielectric layer, a second load layer, and a second electrode layer. The dielectric layer, the substrate, and the first electrode layer enclose a cavity structure, which effectively limits the propagation range of longitudinal waves. At the same time, the first load layer and the second load layer are respectively arranged on the upper and lower surfaces of the piezoelectric layer, and the horizontal projections of these two load layers are both located within the projection of the cavity structure, thereby achieving effective suppression of shear waves and reducing the generation of parasitic modes, thereby significantly improving the quality factor of the resonator, enhancing its frequency selectivity and stability, and reducing insertion loss.

[0081] As an example, the piezoelectric layer 11 includes a piezoelectric material layer or a ferroelectric material layer or a stack of a piezoelectric material layer and a ferroelectric material layer, which can provide different operating frequencies and application scenarios for flexible design options, and no excessive restrictions are imposed here.

[0082] As a further example, the piezoelectric material layer includes an aluminum nitride (AlN) layer, a gallium aluminum nitride (Al x Ga 1-x N) layer, scandium aluminum nitride (Al 1-y Sc yN) layer, lithium niobate (LiNbO3) layer, zinc oxide (ZnO) layer, lead zirconium titanate (PZT) layer, lead titanate (PbTiO3) layer and gallium oxide (Ga2O3) layer or a stack of two or more layers. In this embodiment, an AlN layer is preferably used, wherein 0≤x≤1, 0≤y≤1, and the thickness of a single layer of the piezoelectric material layer is not less than 0.01μm, and the thickness of the piezoelectric layer is not more than 2μm.

[0083] As a further example, the ferroelectric material layer includes scandium aluminum nitride (Sc x Al 1-x N) layer, barium titanate (BST) layer, PZT layer and PbTiO3 layer or a stack of two or more layers. In this embodiment, Sc x Al 1-x N layers, wherein 0≤x≤1, and the thickness of a single ferroelectric material layer is not less than 0.01 μm, and the thickness of the piezoelectric layer is not greater than 2 μm.

[0084] As an example, the material of the first electrode layer 13 includes one or more of gold (Au), silver (Ag), ruthenium (Ru), tungsten (W), molybdenum (Mo), iridium (Ir), aluminum (Al), platinum (Pt), niobium (Nb) and hafnium (Hf), and the material of the second electrode layer 17 includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf. The thickness of the first electrode layer 13 and the second electrode layer 17 is not greater than 0.3 μm. The materials of the first electrode layer 13 and the second electrode layer 17, as well as the thickness of the first electrode layer 13 and the second electrode layer 17 can be flexibly designed and selected according to actual needs, and no excessive restrictions are imposed here.

[0085] As a preferred example, a first adhesion layer (not shown) is provided between the first load layer 12 and the first electrode layer 13, and a second adhesion layer (not shown) is provided between the second load layer 16 and the second electrode layer 17. The materials of the first adhesion layer and the second adhesion layer both include titanium (Ti) to enhance the bonding strength between the first load layer 12 and the first electrode layer 13 and the bonding strength between the second load layer 16 and the second electrode layer 17.

[0086] As an example, the cross-sectional shape of the first load layer 12 is a circular ring, and the cross-sectional shape of the second load layer 16 is a circular ring, which further effectively suppresses the transverse waves, so that the sound waves mainly propagate in the longitudinal direction, thereby improving the propagation directionality of the sound waves, reducing the diffusion and loss of energy in the lateral direction, and improving the quality factor of the resonator.

[0087] As an example, the material of the first load layer 12 includes one or more of gold (Au), silver (Ag), ruthenium (Ru), tungsten (W), molybdenum (Mo), iridium (Ir), aluminum (Al), platinum (Pt), niobium (Nb), hafnium (Hf), silicon dioxide (SiO2), aluminum nitride (AlN) and aluminum oxide (Al2O3), and the material of the second load layer 16 includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, SiO2, AlN and Al2O3. The materials of the first load layer 12 and the second load layer 16 can be flexibly designed and selected based on factors such as the acoustic properties and mechanical stability of the materials, combined with actual needs, and no excessive restrictions are imposed here.

[0088] This embodiment also provides a method for preparing a bulk acoustic wave resonator, which is used to prepare the above-mentioned bulk acoustic wave resonator, but is not limited thereto. Other suitable preparation methods can also be used. The above content can be quoted in full here, and will not be repeated below for the purpose of brevity. Figure 4 As shown, the preparation method comprises:

[0089] S1, providing an intermediate substrate;

[0090] S2, forming a piezoelectric layer on the intermediate substrate, wherein the piezoelectric layer has a first surface and a second surface opposite to each other, and the first surface is away from the intermediate substrate;

[0091] S3, forming a patterned first load layer on the first surface of the piezoelectric layer;

[0092] S4, forming a patterned first electrode layer on the first surface of the piezoelectric layer and on the first load layer, wherein the first electrode layer covers the first load layer;

[0093] S5, forming a dielectric layer covering the first electrode layer and the first surface of the piezoelectric layer, and performing a planarization process on the surface of the dielectric layer;

[0094] S6, forming a first opening penetrating the dielectric layer and exposing the first electrode layer, wherein a horizontal projection of the first load layer is located within a horizontal projection of the first opening;

[0095] S7, providing a substrate, and bonding the substrate to the dielectric layer to form a cavity structure;

[0096] S8, removing the intermediate substrate;

[0097] S9, forming a patterned second load layer on the second surface of the piezoelectric layer, wherein a horizontal projection of the second load layer is located within a horizontal projection of the cavity structure;

[0098] S10, forming a patterned second electrode layer on the second surface of the piezoelectric layer and on the second load layer, wherein the second electrode layer covers the second load layer;

[0099] S11, forming an electrical lead-out structure that passes through the piezoelectric layer and is in contact with the first electrode layer, the electrical lead-out structure including a through hole that passes through the piezoelectric layer and exposes the first electrode layer and a first lead-out electrode that at least fills the through hole, and forming a second lead-out electrode that is in contact with the second electrode layer; wherein the horizontal projections of the first lead-out electrode and the second lead-out electrode do not overlap with the horizontal projection of the cavity structure.

[0100] The method for preparing a BAW resonator of this embodiment, through specific process steps, includes providing an intermediate substrate, forming a piezoelectric layer on the intermediate substrate, patterning a first load layer and a first electrode layer, forming a dielectric layer and flattening it, forming an opening through the dielectric layer, and bonding it to the substrate to form a cavity structure. The intermediate substrate is then removed, and a second load layer and a second electrode layer are formed on the other side of the piezoelectric layer, along with an electrical lead-out structure. Compared with the traditional sacrificial layer release process, the method for preparing a BAW resonator proposed in this embodiment does not produce a piezoelectric layer with angled steps, thereby reducing the loss of the prepared device and preventing increased insertion loss of a filter composed of multi-stage BAW resonators. In addition, by forming the first load layer and the second load layer structure, shear waves are suppressed, and the quality factor of the BAW resonator is improved, thereby enhancing its performance and reliability, meeting the demand for high-performance filters in fields such as high-frequency wireless communications.

[0101] The method for preparing the bulk acoustic wave resonator of this embodiment will be described in detail below with reference to the specific drawings.

[0102] like Figure 5 As shown, step S1 is first performed to provide an intermediate substrate 10 .

[0103] As an example, the material of the intermediate substrate 10 includes one of silicon (Si), silicon carbide (SiC), germanium (Ge) and sapphire, but the material of the intermediate substrate 10 is not limited to the above materials and can be selected according to actual needs. In this embodiment, Si substrate is preferably used. The specific shape and size of the intermediate substrate 10 can be selected according to actual needs and are not excessively restricted here.

[0104] like Figure 6 As shown, step S2 is then performed to form a piezoelectric layer 11 on the intermediate substrate 10 . The piezoelectric layer 11 has a first surface 111 and a second surface 112 opposite to each other, and the first surface 111 is away from the intermediate substrate 10 .

[0105] like Figure 7As shown, step S3 is then performed to form a patterned first load layer 12 on the first surface 111 of the piezoelectric layer 11 .

[0106] like Figure 8 As shown, step S4 is then performed to form a patterned first electrode layer 13 on the first surface 111 of the piezoelectric layer 11 and on the first load layer 12 . The first electrode layer 13 covers the first load layer 12 .

[0107] like Figure 9 and Figure 10 As shown, step S5 is then performed to form a dielectric layer 14 covering the first electrode layer 13 and the first surface 111 of the piezoelectric layer 11 , and the surface of the dielectric layer 14 is planarized.

[0108] As an example, a chemical mechanical polishing process can be used to planarize the surface of the dielectric layer 14 away from the first electrode layer 13. In other embodiments, a spin coating process can also be used to form the dielectric layer 24 to directly achieve the required flat surface requirements, thereby eliminating the need for surface polishing and thinning steps, thereby simplifying the process and reducing costs.

[0109] like Figure 11 As shown, step S6 is then performed to form a first opening 141 penetrating the dielectric layer 14 and exposing the first electrode layer 13 , and the horizontal projection of the first load layer 12 is located within the horizontal projection of the first opening 141 .

[0110] like Figure 12 As shown, step S7 is then performed to provide a substrate 15 , and the substrate 15 is bonded to the dielectric layer 14 to form a cavity structure 142 .

[0111] It should be noted here that if Figure 12 As shown, the structure obtained in step S6 needs to be inverted so that the dielectric layer 14 and the substrate 15 can be bonded and fixed, and the substrate 15, the first dielectric layer 14 and the first electrode layer 13 after bonding form the cavity structure 142.

[0112] Compared with the traditional cavity release process, the piezoelectric layer 11 is first formed on the intermediate substrate 10, and then the substrate 15 is bonded and the intermediate substrate 10 is removed. No piezoelectric layer with angled steps will be generated, thereby making the prepared device loss smaller and not causing an increase in the insertion loss of the filter composed of a multi-stage bulk acoustic wave resonator.

[0113] As an example, the material of the substrate 15 includes one of Si, SiC, Ge and sapphire, but the material of the substrate 15 is not limited to the above materials and can be selected according to actual needs.

[0114] like Figure 13 As shown, step S8 is then performed to remove the intermediate substrate 10.

[0115] like Figure 14 As shown, step S9 is then performed to form a patterned second load layer 16 on the second surface 112 of the piezoelectric layer 11 , wherein the horizontal projection of the second load layer 16 is located within the horizontal projection of the cavity structure 142 .

[0116] In this embodiment, based on considerations of better process implementation and convenient simulation, the width and thickness of the first load layer 12 and the second load layer 16 are the same. However, in other embodiments, the width and thickness of the first load layer 12 and the second load layer 16 may also be different, which is not limited here.

[0117] like Figure 15 As shown, step S10 is then performed to form a patterned second electrode layer 17 on the second surface 112 of the piezoelectric layer 11 and on the second load layer 16 . The second electrode layer 17 covers the second load layer 16 .

[0118] like Figure 16 As shown, step S11 is then performed to form an electrical lead-out structure 20 that penetrates the piezoelectric layer 11 and is in contact with the first electrode layer 13. The electrical lead-out structure 20 includes a through hole 18 that penetrates the piezoelectric layer 11 and exposes the first electrode layer 13 and a first lead-out electrode 19 that at least fills the through hole 18, and forms a second lead-out electrode 21 that is in contact with the second electrode layer 17; wherein the horizontal projections of the first lead-out electrode 19 and the second lead-out electrode 21 do not overlap with the horizontal projection of the cavity structure 142.

[0119] Furthermore, as a preferred example, the through hole 18 is formed first, and then the first lead-out electrode 19 and the second lead-out electrode 21 are formed simultaneously, so as to simplify the preparation process and improve production efficiency.

[0120] like Figure 17 As shown, it shows the impedance distribution curves corresponding to the three types of BAW resonators, such as Figure 18 As shown, it shows the impedance phase curves corresponding to the three types of BAW resonators, where W0 corresponds to Figure 1The bulk acoustic wave resonator shown in the prior art is unable to suppress shear waves and includes a substrate 31, a bottom electrode 32, a piezoelectric film 33, a top electrode 34 and a cavity 35; W1 corresponds to Figure 2 The BAW resonator with a top load layer 36 in the prior art shown includes a substrate 31, a bottom electrode 32, a piezoelectric film 33, a top electrode 34, a cavity 35 and a top load layer 36; W2 corresponds to the BAW resonator with the first load layer 12 and the second load layer 16 in the embodiment of the present invention.

[0121] like Figure 17 and Figure 18 As shown in the figure, below the series resonant frequency (fs), between the series resonant frequency (fs) and the parallel resonant frequency (fp), and above the parallel resonant frequency (fp), W0 has ripples, which means there are transverse waves. The presence of transverse waves will weaken the quality factor of the resonator to a certain extent. The BAW resonator without a load layer can suppress the transverse waves by adding a load layer, but introducing only the top load layer will also introduce new transverse waves (corresponding to Figure 17 and Figure 18 The series resonant frequency (fs) of the W1 curve in FIG is reflected below, and W1 will introduce an obvious peak at around 4.5 GHz), but the BAW resonator with the first load layer 12 and the second load layer 16 will suppress the peak and further weaken the ripple amplitude at the series resonant frequency.

[0122] Compared to the region of the BAW resonator of this embodiment where the load layer 12 and the second load layer 16 are formed, the region where the load layer 12 and the second load layer 16 are formed has a greater structural thickness. Therefore, the resonant frequency of the piezoelectric layer in the region where the load layer 12 and the second load layer 16 are formed is slightly lower than the resonant frequency of the active region where the load layer is not formed. As a result, additional parasitic modes are introduced below the series resonant frequency (fs). By introducing the load layer 12 and the second load layer 16, the BAW resonator of this embodiment further increases the structural thickness of the region where the load layer 12 and the second load layer 16 are formed, thereby adjusting the resonant frequency of the parasitic mode to a lower level, away from the series resonant frequency, and better matching the requirements of a specific operating frequency band.

[0123] Furthermore, this embodiment takes the first load layer 12 and the second load layer 16 as an example of having the same width and thickness for simulation, and Figure 19 The influence of the change of the width of the load layer (the first load layer 12 and the second load layer 16) on the quality factor of the bulk acoustic wave resonator is shown in FIG. Figure 19It can be seen that as the widths of the first load layer 12 and the second load layer 16 increase, the quality factor of the BAW resonator shows a trend of first decreasing, then increasing, and finally decreasing. In particular, when the widths of the first load layer 12 and the second load layer 16 exceed 1.4 μm, the quality factor of the BAW resonator reaches a maximum value. As the widths of the first load layer 12 and the second load layer 16 continue to increase, the quality factor of the BAW resonator decreases. Therefore, by reasonably selecting the width and thickness of the first load layer 12 and the second load layer 16, better suppression of shear waves can be achieved, while simultaneously improving the quality factor of the BAW resonator.

[0124] In summary, the bulk acoustic wave resonator and preparation method thereof of the present invention include a substrate, a piezoelectric layer, a first load layer, a first electrode layer, a dielectric layer, a second load layer, and a second electrode layer, wherein the dielectric layer, the substrate, and the first electrode layer enclose a cavity structure, which effectively limits the propagation range of longitudinal waves. At the same time, the first load layer and the second load layer are respectively arranged on the upper and lower surfaces of the piezoelectric layer, and the horizontal projections of the two load layers are both located within the projection of the cavity structure, thereby achieving effective suppression of shear waves and reducing the generation of parasitic modes, thereby significantly improving the quality factor of the resonator, enhancing its frequency selectivity and stability, and reducing insertion loss. The present invention's method for fabricating a BAW resonator includes providing an intermediate substrate, forming a piezoelectric layer on the intermediate substrate, patterning a first load layer and a first electrode layer, forming and flattening a dielectric layer, forming an opening through the dielectric layer, and bonding the dielectric layer to the substrate to form a cavity structure. The intermediate substrate is then removed, and a second load layer and a second electrode layer are formed on the other side of the piezoelectric layer, along with an electrical lead structure. Compared to conventional sacrificial layer release processes, the present invention's BAW resonator fabrication method avoids the production of piezoelectric layers with angled steps, resulting in lower device losses and preventing increased insertion loss in filters comprised of multi-stage BAW resonators. Therefore, the present invention effectively overcomes the shortcomings of existing technologies and possesses high industrial value.

[0125] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A bulk acoustic wave resonator, characterized in that: The bulk acoustic wave resonator comprises: substrate; a piezoelectric layer located above the substrate; a first load layer, located on the lower surface of the piezoelectric layer; a first electrode layer, located on the lower surface of the piezoelectric layer and covering the first load layer; a dielectric layer located between the substrate and the piezoelectric layer, and between the first electrode layer and the substrate, wherein a cavity structure penetrating the dielectric layer is formed in the dielectric layer, and the cavity structure partially exposes the first electrode layer; a second load layer, located on the upper surface of the piezoelectric layer, wherein the horizontal projections of the first load layer and the second load layer are both located within the horizontal projection of the cavity structure; a second electrode layer, located on the upper surface of the piezoelectric layer and covering the second load layer; an electrical lead-out structure, penetrating the piezoelectric layer and contacting and connecting with the first electrode layer, the electrical lead-out structure comprising a through hole penetrating the piezoelectric layer and exposing the first electrode layer, and a first lead-out electrode at least filling the through hole; The second extraction electrode is in contact with and connected to the second electrode layer; wherein the horizontal projections of the first extraction electrode and the second extraction electrode do not overlap with the horizontal projection of the cavity structure.

2. The bulk acoustic wave resonator according to claim 1, wherein: The piezoelectric layer includes a piezoelectric material layer or a ferroelectric material layer or a stacked layer consisting of a piezoelectric material layer and a ferroelectric material layer.

3. The bulk acoustic wave resonator according to claim 2, wherein: The piezoelectric material layer includes an AlN layer, an Al x Ga 1-x N layer, Al 1-y Sc y One or more layers selected from the group consisting of an N layer, a LiNbO3 layer, a ZnO layer, a PZT layer, a PbTiO3 layer, and a Ga2O3 layer, wherein 0≤x≤1, 0≤y≤1, and the thickness of a single layer of the piezoelectric material layer is not less than 0.01 μm, and the thickness of the piezoelectric layer is not greater than 2 μm.

4. The bulk acoustic wave resonator according to claim 2, wherein: The ferroelectric material layer includes Sc x Al 1-x One or more layers of N layer, BST layer, PZT layer and PbTiO3 layer, wherein 0≤x≤1, and the thickness of the single layer of the ferroelectric material layer is not less than 0.01μm, and the thickness of the piezoelectric layer is not more than 2μm.

5. The bulk acoustic wave resonator according to claim 1, wherein: The material of the first electrode layer includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf, and the material of the second electrode layer includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb and Hf. The thickness of the first electrode layer and the second electrode layer is not more than 0.3 μm.

6. The bulk acoustic wave resonator according to claim 1, wherein: A first adhesion layer is provided between the first load layer and the first electrode layer, and a second adhesion layer is provided between the second load layer and the second electrode layer. Materials of the first adhesion layer and the second adhesion layer both include Ti.

7. The bulk acoustic wave resonator according to claim 1, wherein: The cross-sectional shape of the first support layer is annular, and the cross-sectional shape of the second support layer is annular.

8. The bulk acoustic wave resonator according to claim 1, wherein: The material of the first load layer includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, SiO2, AlN and Al2O3, and the material of the second load layer includes one or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, Hf, SiO2, AlN and Al2O3.

9. A method for preparing a bulk acoustic wave resonator, characterized in that: The preparation method comprises: providing an intermediate substrate; forming a piezoelectric layer on the intermediate substrate, wherein the piezoelectric layer has a first surface and a second surface opposite to each other, and the first surface is away from the intermediate substrate; forming a patterned first load layer on the first surface of the piezoelectric layer; forming a patterned first electrode layer on the first surface of the piezoelectric layer and on the first load layer, wherein the first electrode layer covers the first load layer; forming a dielectric layer covering the first electrode layer and the first surface of the piezoelectric layer, and performing a planarization process on the surface of the dielectric layer; forming a first opening penetrating the dielectric layer and exposing the first electrode layer, wherein a horizontal projection of the first load layer is located within a horizontal projection of the first opening; Providing a substrate, and bonding the substrate to the dielectric layer to form a cavity structure; removing the intermediate substrate; forming a patterned second load layer on the second surface of the piezoelectric layer, wherein a horizontal projection of the second load layer is located within a horizontal projection of the cavity structure; forming a patterned second electrode layer on the second surface of the piezoelectric layer and on the second load layer, wherein the second electrode layer covers the second load layer; An electrical lead-out structure is formed that passes through the piezoelectric layer and is in contact with the first electrode layer. The electrical lead-out structure includes a through hole that passes through the piezoelectric layer and exposes the first electrode layer, and a first lead-out electrode that at least fills the through hole, and a second lead-out electrode that is in contact with the second electrode layer is formed; wherein the horizontal projections of the first lead-out electrode and the second lead-out electrode do not overlap with the horizontal projection of the cavity structure.

10. The method for preparing a bulk acoustic wave resonator according to claim 9, wherein: The material of the intermediate substrate includes one of Si, SiC, Ge and sapphire; the material of the substrate includes one of Si, SiC, Ge and sapphire.

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