Bulk acoustic wave resonator, manufacturing method thereof, filter, and electronic device

Abstract

The present application relates to a bulk acoustic wave resonator and a manufacturing method thereof. The bulk acoustic wave resonator includes: a substrate; a piezoelectric layer; an acoustic mirror; a bottom electrode; and a top electrode, wherein: the piezoelectric layer is a single-crystal piezoelectric layer; a mass loading layer is provided on at least the lower side of the piezoelectric layer. The present application also relates to a filter and an electronic device.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the field of semiconductor, and in particular to a bulk acoustic wave resonator and a manufacturing method thereof, a filter comprising the bulk acoustic wave resonator, and an electronic device comprising the bulk acoustic wave resonator or the filter. BACKGROUND

[0002] With the increasing development of 5G communication technology, the requirements for communication frequency bands are becoming higher and higher. The traditional radio frequency filter cannot meet the requirements of high frequency communication due to the limitations of structure and performance. As a new type of MEMS device, the film bulk acoustic resonator (FBAR) has the advantages of small size, light weight, low insertion loss, wide frequency band and high quality factor, which well adapts to the upgrading of wireless communication systems, and makes the FBAR technology one of the research hotspots in the field of communication.

[0003] The main structure of the film bulk acoustic resonator is a "sandwich" structure composed of an electrode-piezoelectric film-electrode, that is, a layer of piezoelectric material is sandwiched between two metal electrode layers. By inputting a sinusoidal signal between the two electrodes, the FBAR converts the input electrical signal into mechanical resonance by using the inverse piezoelectric effect, and then converts the mechanical resonance into an electrical signal output by using the piezoelectric effect.

[0004] Currently, the process characteristics of the conventional polycrystalline FBAR resonator limit the quality load layer to be prepared above the piezoelectric layer, and the main reasons are as follows: 1. The current AlN-based FBAR is prepared by deposition, and the stress of the AlN itself is relatively large; 2. Since there is a step difference after etching the bottom electrode, the AlN with large stress is prone to breakage at the step difference. At this time, if a quality load layer is added between the bottom electrode and the piezoelectric layer, it will further increase the risk of AlN breakage, thereby causing electrostatic discharge (ESD) risk. Based on the above conditions, the FBAR prepared by deposition cannot well prepare a quality load layer on the bottom electrode, so there are big problems.

[0005] Currently, the quality load layer is generally only provided above the piezoelectric layer, and this structure will increase the non-uniformity of the resonator in the thickness direction, making the second-order intermodulation (IMD) nonlinearity of the resonator more serious.

[0006] In addition, the preparation of the quality load layer only above the piezoelectric layer also makes the frequency adjustment range of the resonator smaller.

[0007] The current polycrystalline AlN-based FBAR cannot eliminate the nonlinearity in the thickness direction due to the above reasons, so the filter has a large second-order intermodulation, which can usually be solved by the resonator splitting method, but this will increase the area of the filter, so the preparation of the quality load layer on the upper and lower sides has a great influence on the performance of the filter. SUMMARY

[0008] To alleviate or solve at least one aspect of the above problems in the prior art, the present application is proposed.

[0009] According to one aspect of an embodiment of the present application, a bulk acoustic wave resonator is proposed, comprising:

[0010] a substrate;

[0011] a piezoelectric layer supported on the substrate;

[0012] an acoustic mirror disposed between the substrate and the piezoelectric layer;

[0013] a bottom electrode disposed on a lower side of the piezoelectric layer; and

[0014] a top electrode disposed on an upper side of the piezoelectric layer,

[0015] wherein:

[0016] a mass loading layer is further disposed on at least the lower side of the piezoelectric layer.

[0017] According to another aspect of the present application, a method of manufacturing the aforementioned bulk acoustic wave resonator is also provided, comprising:

[0018] Step 1: providing a POI substrate, the POI substrate comprising an auxiliary substrate, an insulating layer disposed on the auxiliary substrate, and a single-crystal piezoelectric layer disposed on the insulating layer, a side of the piezoelectric layer facing away from the insulating layer being a first side of the piezoelectric layer;

[0019] Step 2: forming a bottom electrode of the resonator on the first side of the single-crystal piezoelectric layer;

[0020] Step 3: forming a support layer and an acoustic mirror material layer for forming an acoustic mirror of the resonator, the support layer defining a boundary of the acoustic mirror material layer, and a side of the support layer being in contact with the first side of the piezoelectric layer;

[0021] Step 4: disposing a functional substrate, the functional substrate being bonded to another side of the support layer opposite to the side;

[0022] Step 5: removing the auxiliary substrate and at least a portion of the insulating layer to at least expose a second side of the piezoelectric layer corresponding to an active area of the resonator, the first side and the second side being opposite in a thickness direction of the piezoelectric layer;

[0023] Step 6: forming a top electrode of the resonator on the second side of the piezoelectric layer,

[0024] wherein:

[0025] Step 2 further comprises forming a first mass loading layer on the first side of the piezoelectric layer.

[0026] According to another aspect of the present application, there is also provided a filter including the aforementioned bulk acoustic resonator.

[0027] According to another aspect of the present application, there is also provided an electronic device including the aforementioned bulk acoustic resonator or filter. BRIEF DESCRIPTION OF DRAWINGS

[0028] The following description with the accompanying drawings can better help understand these and other features and advantages of the various embodiments disclosed by the present application, in which the same reference numerals are always used to designate the same components throughout the various drawings:

[0029] Figure 1 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application;

[0030] Figure 2 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application, showing a piezoelectric layer and electrodes and mass load layers positioned on both sides of the piezoelectric layer; Figure 1 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application, showing a piezoelectric layer and electrodes and mass load layers positioned on both sides of the piezoelectric layer;

[0031] Figure 3 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application, showing a piezoelectric layer and electrodes and mass load layers positioned on both sides of the piezoelectric layer; Figure 1 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application, showing a piezoelectric layer and electrodes and mass load layers positioned on both sides of the piezoelectric layer;

[0032] Figure 4 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application, showing a piezoelectric layer and electrodes and mass load layers positioned on both sides of the piezoelectric layer; Figure 1 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application, showing a piezoelectric layer and electrodes and mass load layers positioned on both sides of the piezoelectric layer;

[0033] Figures 5A-5I An exemplary manufacturing process of a bulk acoustic resonator in Figure 1 is shown;

[0034] Figure 6 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application, in which the position of the mass load layer is different from that shown in Figure 1 ;

[0035] Figure 7 A cross-sectional view of a bulk acoustic resonator according to an exemplary embodiment of the present application, in which the mass load layer is provided only on the lower side of the piezoelectric layer. DETAILED DESCRIPTION

[0036] The technical solutions of the present application are further specifically explained below by examples in combination with the drawings. In the description, the same or similar reference signs indicate the same or similar components. The following description of the embodiments of the present application with reference to the drawings is intended to explain the general inventive concept of the present application, and should not be understood as a limitation of the present application. The following description of the embodiments of the present application is only a part of the embodiments, and not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0037] First, the reference signs in the drawings of the present application are explained as follows:

[0038] 110: auxiliary substrate, which can be made of single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

[0039] 111: functional substrate, which can be made of single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

[0040] 112: packaging substrate, which can be made of single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc.

[0041] 120: insulating layer, which can be made of silicon dioxide and its doped materials, silicon nitride, silicon carbide, sapphire, etc.

[0042] 130: single crystal piezoelectric layer, which can be made of single crystal aluminum nitride, single crystal gallium nitride, single crystal lithium niobate, single crystal lead zirconate titanate, single crystal potassium niobate, single crystal quartz film, or single crystal lithium tantalate, etc., and can further contain rare earth element doped materials of certain atomic ratio of the above-mentioned materials, for example, doped aluminum nitride containing at least one rare earth element such as scandium (Sc), yttrium (Y), magnesium (Mg), titanium (Ti), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). In further embodiments, the single crystal piezoelectric layer is a single crystal lithium niobate piezoelectric layer or a single crystal lithium tantalate piezoelectric layer.

[0043] 141: bottom electrode, which can be made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite of the above metals or an alloy thereof, etc.

[0044] 142: top electrode, which can be made of molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite of the above metals or an alloy thereof, etc. The materials of the top electrode and the bottom electrode are generally the same, but can also be different.

[0045] 152: Sacrificial material layer, which can be SiO2, SiN, or other dielectric material and its doped materials.

[0046] 151: Support layer, which can be copper, gold, or other metal or alloy thereof, or SiN, SiO2, or other dielectric material. As those skilled in the art can understand, in the present application, if the sacrificial material layer 152 is used to form an acoustic mirror cavity, the material of the support layer 151 and the material of the sacrificial material layer 152 need to have a certain etching selectivity.

[0047] 161: First encapsulation layer, which can be a bonding material layer, which can be copper, gold, or other metal or alloy thereof, or SiN, SiO2, or other dielectric material.

[0048] 162: Second encapsulation layer, which can be a bonding material layer, which can be copper, gold, or other metal or alloy thereof, or SiN, SiO2, or other dielectric material. In one embodiment of the present application, the first encapsulation layer 161 and the second encapsulation layer 162 are bonded to each other to combine the encapsulation substrate 112 and the piezoelectric layer 130 with each other.

[0049] 170: Acoustic mirror, which can be a cavity, or a Bragg reflector, or other equivalent form. In the embodiment shown in the present application, it is a cavity.

[0050] 180: Mask layer, which can be photoresist or SiO2, or other hard mask.

[0051] 201: First mass loading layer, which can be the same material as the bottom electrode, or different from the bottom electrode. The material of the first mass loading layer can also be a non-metallic material, such as silicon dioxide or metal oxide. The first mass loading layer can be disposed between the piezoelectric layer and the bottom electrode, or in the bottom electrode, or on the side of the bottom electrode away from the piezoelectric layer.

[0052] 202: Second mass loading layer, which can be the same material as the top electrode, or different from the top electrode. The material of the second mass loading layer can also be a non-metallic material, such as silicon dioxide or metal oxide. The second mass loading layer can be disposed between the piezoelectric layer and the top electrode, or in the top electrode, or on the side of the top electrode away from the piezoelectric layer. The material of the first mass loading layer 201 and the second mass loading layer 202 can be the same or different.

[0053] Figure 1 Cross-sectional view of a bulk acoustic wave resonator according to an exemplary embodiment of the present application.

[0054] As Figure 1As shown, the bulk acoustic wave resonator includes a substrate 111, a piezoelectric layer 130, an acoustic mirror 170, a bottom electrode 141 and a top electrode 142. As shown in the figure, the bottom electrode 141 is disposed on the lower side of the piezoelectric layer 130, and the top electrode 142 is disposed on the upper side of the piezoelectric layer 130. Figure 1 As shown, in the illustrated embodiment, a first mass load layer 201 and a second mass load layer 202 are respectively disposed on the lower side and the upper side of the piezoelectric layer 130.

[0055] Therefore, in the illustrated embodiment, the performance of the resonator can be improved by adjusting the thickness of the first mass load layer 201 and the second mass load layer 202. Figure 1 In the illustrated embodiment, the present application can adjust the series resonance frequency Fs of the resonator in a wider range, and can better adjust the symmetry of the resonator in the thickness direction, thereby facilitating the maximum elimination of the second-order intermodulation.

[0056] As shown in the figure, in the illustrated embodiment, the first mass load layer 201 is disposed on the lower side of the bottom electrode 141, i.e., the bottom electrode 141 is sandwiched between the first mass load layer 201 and the piezoelectric layer 130. The second mass load layer 202 is disposed on the upper side of the top electrode 142, i.e., the top electrode 142 is sandwiched between the second mass load layer 202 and the piezoelectric layer 130. Figure 1 As shown in the figure, in the illustrated embodiment, the first mass load layer 201 is disposed on the lower side of the bottom electrode 141, i.e., the bottom electrode 141 is sandwiched between the first mass load layer 201 and the piezoelectric layer 130. The second mass load layer 202 is disposed on the upper side of the top electrode 142, i.e., the top electrode 142 is sandwiched between the second mass load layer 202 and the piezoelectric layer 130.

[0057] Figure 2 As shown in the figure, in the illustrated embodiment, the first mass load layer 201 is disposed on the lower side of the bottom electrode 141, i.e., the bottom electrode 141 is sandwiched between the first mass load layer 201 and the piezoelectric layer 130. The second mass load layer 202 is disposed on the upper side of the top electrode 142, i.e., the top electrode 142 is sandwiched between the second mass load layer 202 and the piezoelectric layer 130.

[0058] Figure 1 As shown in the figure, in the illustrated embodiment, the first mass load layer 201 is disposed on the lower side of the bottom electrode 141, i.e., the bottom electrode 141 is sandwiched between the first mass load layer 201 and the piezoelectric layer 130. The second mass load layer 202 is disposed on the upper side of the top electrode 142, i.e., the top electrode 142 is sandwiched between the second mass load layer 202 and the piezoelectric layer 130. Figure 1 As shown in the figure, in the illustrated embodiment, the first mass load layer 201 is disposed on the lower side of the bottom electrode 141, i.e., the bottom electrode 141 is sandwiched between the first mass load layer 201 and the piezoelectric layer 130. The second mass load layer 202 is disposed on the upper side of the top electrode 142, i.e., the top electrode 142 is sandwiched between the second mass load layer 202 and the piezoelectric layer 130.

[0059] In the illustrated embodiment, the thickness symmetry of the bulk acoustic wave resonator can be adjusted by adjusting the thickness of the first mass load layer 201 and the thickness of the second mass load layer 202, so that the structures on the upper and lower sides of the piezoelectric layer 130 of the resonator are substantially symmetrical, which is beneficial to reduce or eliminate the second-order intermodulation and improve the performance of the resonator. Figure 2 Figure 1 In the illustrated embodiment, the thickness symmetry of the bulk acoustic wave resonator can be adjusted by adjusting the thickness of the first mass load layer 201 and the thickness of the second mass load layer 202, so that the structures on the upper and lower sides of the piezoelectric layer 130 of the resonator are substantially symmetrical, which is beneficial to reduce or eliminate the second-order intermodulation and improve the performance of the resonator.

[0060] In the illustrated embodiment, the thickness symmetry of the bulk acoustic wave resonator can be adjusted by adjusting the thickness of the first mass load layer 201 and the thickness of the second mass load layer 202, so that the structures on the upper and lower sides of the piezoelectric layer 130 of the resonator are substantially symmetrical, which is beneficial to reduce or eliminate the second-order intermodulation and improve the performance of the resonator. Figure 1 2 ​​​As shown, the materials of the first mass loading layer 201 and the second mass loading layer 202 are the same as the materials of the bottom electrode 141 and the top electrode 142, and in addition, the bulk acoustic wave resonator satisfies the following relationship: 0.5≤(d1+d2) / (d3+d4)≤1.5 (relationship 1),

[0061] wherein d1 is the thickness of the top electrode 142, d2 is the thickness of the second mass loading layer 202, d3 is the thickness of the bottom electrode 141, and d4 is the thickness of the first mass loading layer 201. The above value of (d1+d2) / (d3+d4) is advantageous to make the value of (d1+d2) and the value of (d3+d4) not too different from each other, so as to reduce or eliminate the second-order intermodulation.

[0062] In further embodiments, the range of the aforementioned thickness ratio (d1+d2) / (d3+d4) can also be: 0.95≤(d1+d2) / (d3+d4)≤1.05 (relationship 2). In this way, the thickness symmetry of the bulk acoustic wave resonator can be further improved, which is further advantageous to reduce or eliminate the second-order intermodulation and improve the performance of the resonator.

[0063] It should be further noted that when the frequency of the resonator is low or the frequencies of different resonators need to be large, if only one mass loading layer is provided, the thickness of the mass loading layer needs to be large, and the thickness uniformity of the mass loading layer with large thickness is poor. In Figure 2 and Figure 3 In the embodiments shown, the mass loading layer is divided into two layers arranged above and below, which is advantageous to improve the thickness uniformity of the mass loading layer. In the exemplary embodiments of the present application, the thicknesses of the first mass loading layer 201 and the second mass loading layer 202 are not greater than

[0064] In order to improve the Q value and other performances of the bulk acoustic wave resonator, a recess structure, a protrusion structure, a bridge wing structure, etc. are usually provided on one side of the piezoelectric layer 130, but these structures will increase the asymmetry of the bulk acoustic wave resonator in the thickness direction. The mass loading layer is provided on both sides of the resonator, which is advantageous to balance the symmetry or reduce the asymmetry of the resonator in the thickness direction.

[0065] In an exemplary embodiment of the present invention, the materials of the first mass load layer 201 and the second mass load layer 202 are the same as the materials of the bottom electrode 141 and the top electrode 142. In this case, the symmetry of the film layer can be controlled simply by controlling or improving the thickness using the aforementioned relation 1 or relation 2. However, when the materials of the first mass load layer 201 and the second mass load layer 202 are different from the materials of the bottom electrode 141 and the top electrode 142, this can be achieved by controlling the number of acoustic wave cycles propagating vertically in the piezoelectric layer 130 (for example, by using relation 3 mentioned below; for example, when the value of t1 / t2 in this relation is 1, it is assumed that the number of acoustic wave cycles propagating vertically is the same, and by setting this relation 3, the difference in the number of acoustic wave cycles propagating vertically in the piezoelectric layer 130 can be controlled). The following will refer to... Figure 3 This section explains in detail how to control the difference in the number of sound wave cycles propagating above and below the piezoelectric layer 130.

[0066] Figure 1 For another exemplary embodiment of the present invention, the following is shown Figure 3 A variation of the bulk acoustic resonator shown depicts a piezoelectric layer and electrodes and a mass load layer located on either side of the piezoelectric layer. Figure 3 In the illustrated variation, the materials of the first mass loading layer 201 and the second mass loading layer 202 are different from the materials of the bottom electrode 141 and the top electrode 142. This causes the propagation speed of sound waves of the same frequency in the first mass loading layer 201 and the second mass loading layer 202 to differ from their propagation speed in the bottom electrode 141 and the top electrode 142. Figure 1 In the embodiment shown, in order to control the number of sound wave cycles propagating above and below the piezoelectric layer 130, the bulk acoustic resonator should satisfy the following relationship:

[0067] 0.5≤t1 / t2≤1.5 (Equation 3)

[0068] Where t1 = d0 / V0 + d1 / V1 + d2 / V2, t2 = d0 / V0 + d3 / V3 + d4 / V4, d0 is half the thickness of the piezoelectric layer, d1 is the thickness of the top electrode, d2 is the thickness of the second mass load layer, d3 is the thickness of the bottom electrode, d4 is the thickness of the first mass load layer 201, V0 is the sound velocity of the sound wave in the piezoelectric layer 130, V1 is the sound velocity of the sound wave in the top electrode 142, V2 is the sound velocity of the sound wave in the second mass load layer 202, V3 is the sound velocity of the sound wave in the bottom electrode 141, and V4 is the sound velocity of the sound wave in the first mass load layer 201.

[0069] In a further embodiment, t1 / t2 is in the range of: 0.95≤t1 / t2≤1.05 (relation 4). In this way, it is further facilitated to reduce the difference in the number of acoustic wave cycles for the acoustic wave propagating up and down the piezoelectric layer 130.

[0070] In embodiments of the application, the thickness of the first mass load layer 201 can be the same as the thickness of the second mass load layer 202 (see for example Figure 2 , Figure 3 and Figure 4 ), or different (see for example Figure 1 mentioned later).

[0071] As shown in Figure 1 , in the illustrated embodiment, the piezoelectric layer 130 is a single crystal lithium carbonate piezoelectric layer or a single crystal lithium niobate piezoelectric layer.

[0072] In embodiments of the application, the single crystal piezoelectric layer 130 is a pure flat film layer, i.e. the top and bottom surfaces of the piezoelectric layer 130 are flat surfaces perpendicular to the thickness direction of the piezoelectric layer 130.

[0073] As shown in Figure 1 , in the illustrated embodiment, the bulk acoustic wave resonator further comprises a support layer 151 disposed between the substrate 111 and the piezoelectric layer 130, the support layer 151 supporting the piezoelectric layer 130 on the substrate 111. In the embodiment shown in Figure 1 , the acoustic mirror is in the form of a cavity, and the boundaries of the cavity in the lateral direction are defined by the support layer 151, as shown in Figure 1 , the bottom electrode 141 and the first mass load layer 201 are within the acoustic mirror cavity. In Figure 1 , the lower side of the acoustic mirror cavity is defined by the upper side of the substrate 111, but although not shown, the lower side of the acoustic mirror cavity can also be defined by the support layer 151, in which case the acoustic mirror cavity is a recessed portion recessed into the support layer 151.

[0074] In an optional embodiment, as shown in Figure 1 , the piezoelectric layer 130 is a flat piezoelectric layer, and the piezoelectric layer 130 is substantially parallel to the substrate 111.

[0075] As shown in Figure 1 , in the illustrated embodiment, the bulk acoustic wave resonator further comprises a packaging structure, the packaging structure comprising a packaging substrate 112 and packaging layers (161 and 162) disposed between the packaging substrate 112 and the piezoelectric layer 130, the packaging substrate 112, the piezoelectric layer 130 and the packaging layers defining a containing cavity, the top electrode 142 and the second mass load layer 202 being in the containing cavity. As shown in Figure 1 , the packaging layers comprise a first packaging layer 161 and a second packaging layer 162.

[0076] like Figures 5A-5I As shown in the illustrated embodiment, when the first encapsulation layer and the second encapsulation layer are bonded together, by providing the first encapsulation layer 161 and the second encapsulation layer 162, an appropriate bonding material can be selected based on the material of the encapsulation substrate 112 and the material of the piezoelectric layer 130.

[0077] Figure 1 An example is shown Figures 5A-5I The manufacturing process of the bulk acoustic resonator is described below. (Refer to Appendix...) Figure 1 Detailed description Figure 5A The manufacturing process of a bulk acoustic resonator.

[0078] First, such as Figure 5A As shown, a POI substrate is provided, which includes a substrate 110, an insulating layer 120 disposed on the substrate 110, and a single crystal piezoelectric layer 130 disposed on the insulating layer 120.

[0079] like Figure 5B As shown, a bottom electrode 141 is then formed on the first side (i.e., the lower surface of the piezoelectric layer 130) of the single-crystal piezoelectric layer 130. For example, an electrode metal layer can be deposited on the first side of the single-crystal piezoelectric layer 130 and the metal layer can be patterned to form the bottom electrode 141.

[0080] Second, such as Figure 5B As shown, a first mass loading layer 201 is formed on the bottom electrode 141. The first mass loading layer 201 can be formed on the outer surface of the bottom electrode 141 in any suitable manner, for example, by deposition or sputtering.

[0081] In an optional embodiment, an electrode material layer for the bottom electrode and a material layer for the first mass load can be sequentially deposited on the first side of the piezoelectric layer 130. Then, the mass load material layer is patterned to form the first mass load layer, and the electrode material layer is patterned to form the bottom electrode 141. In an optional embodiment, the electrode material layer for the bottom electrode and the material layer for the first mass load layer can be formed first, and then the bottom electrode 141 and the first mass load layer 201 can be formed in one step.

[0082] All of the above can be formed Figure 5C The structure shown.

[0083] Third, such as Figure 5B As shown, in Figure 5CIn the structure shown, a sacrificial material layer 152 and a support layer 151 are formed on the first side of the single-crystal piezoelectric layer 130. For example, the support layer 151 can be formed first on the first side of the single-crystal piezoelectric layer 130, then the support layer 151 can be etched to obtain a cavity constituting the acoustic mirror 170, and finally the cavity can be filled with sacrificial material to form the sacrificial material layer 152. Figure 5C As shown, the surface of the support layer 151 can be made flush with the surface of the sacrificial material layer 152 by, for example, CMP (chemical mechanical polishing). Alternatively, the sacrificial material layer 152 can be formed first, and then the support layer 151 can be formed.

[0084] exist Figure 5B In the illustrated embodiment, the surface of the sacrificial material layer 152 is flush with the surface of the support layer 151, but the invention is not limited thereto. As mentioned earlier, it is possible to first... Figure 5D The structure shown deposits and patterns sacrificial material to form a sacrificial material layer 152, and then deposits and patterns a support material that can cover the entire sacrificial material layer 152. The surface of the support layer 151 is then smoothed by, for example, CMP (chemical mechanical polishing), but the sacrificial material layer 152 is covered by the support layer 151.

[0085] Fourth, provide a base 111, and as... Figure 5C As shown, Figure 5D The resulting structure is bonded to the substrate 111, that is, the substrate 111 is bonded to the support layer 151. This bonding can be a bonding method or any other method that can bond the substrate 111 to the support layer 151.

[0086] Fifth, Figure 5E The structural flip, and such Figure 5F As shown, the substrate 110 and insulating layer 120 of the POI substrate are removed. Although not shown, a portion of the insulating layer 120 may be retained in the non-effective region of the resonator. The substrate 110 and insulating layer 120 can provide temporary support and protection for the single-crystal piezoelectric layer 130 during the aforementioned manufacturing process, preventing damage to the piezoelectric layer 130.

[0087] Sixth, such as Figure 5G As shown, a top electrode 142 is formed on the second side (i.e., the upper surface of the piezoelectric layer 130) of the single-crystal piezoelectric layer 130. For example, a metal layer can be deposited on the top surface of the single-crystal piezoelectric layer 130 and patterned into the top electrode 142.

[0088] Seventh, such as Figure 5H As shown, a second mass-loaded layer 202 is formed on the top electrode 142. The second mass-loaded layer 202 can be formed on the outer surface of the top electrode 142 in any suitable manner, for example, by deposition or sputtering.

[0089] Similarly, it is understood that, in an optional embodiment, the electrode material layer of the top electrode and the material layer of the second mass load can be deposited sequentially on the second side of the piezoelectric layer 130 first, then the mass load material layer is patterned to form the second mass load layer, and then the electrode material layer is patterned to form the top electrode 142. In an optional embodiment, the electrode material layer for the top electrode and the material layer for the second mass load layer can also be formed first, and then the top electrode 142 and the second mass load layer 202 can be formed in one step.

[0090] Eighth, such as Figure 5I As shown, the sacrificial material layer 152 is removed using an etchant to obtain the acoustic mirror 170.

[0091] Ninth, such as Figure 2 As shown, an encapsulation structure is formed on the second side of the single-crystal piezoelectric layer 130 to encapsulate the top electrode 142 and the second mass load layer 202 in a cavity defined by the encapsulation structure.

[0092] exist Figure 3 and Figure 4 In the illustrated embodiment, the thickness of the bottom electrode 141 is the same as or approximately the same as the thickness of the top electrode 142. However, when different products are fabricated on a substrate, the thicknesses of the bottom and top electrodes may differ significantly depending on the electromechanical coupling coefficient and resonant frequency requirements of the resonator. In such cases, a mass loading layer is needed to adjust the symmetry between the film layers, as will be discussed below. Figure 4 Let me explain the situation in detail.

[0093] Figure 1 For another exemplary embodiment of the present invention, the following is shown Figure 4 A variation of the bulk acoustic resonator shown depicts a piezoelectric layer and electrodes and a mass load layer located on either side of the piezoelectric layer. Figure 4 In the illustrated embodiment, the thickness of the bottom electrode 141 is much greater than the thickness of the top electrode 142, resulting in a significant difference in thickness between the bottom electrode 141 and the top electrode 142. Therefore, in Figure 6 In the embodiment shown, the balance of the resonator needs to be adjusted by adjusting the thickness of the first mass load layer 201 and the second mass load layer 202 so that the mass load effects on the upper and lower sides of the piezoelectric layer 130 are the same or similar.

[0094] Figure 1 This is a cross-sectional schematic diagram of a bulk acoustic resonator according to another exemplary embodiment of the present invention, wherein the mass load layer is disposed at a position relative to... Figure 6 The differences are shown. Figure 1 The bulk acoustic resonator of the embodiment shown is Figure 6The first embodiment of the bulk acoustic wave resonator shown differs in the positions where the first mass load layer 201 and the second mass load layer 202 are provided.

[0095] As shown in the drawing, in the illustrated embodiment, the first mass load layer 201 is provided on the upper side of the bottom electrode 141, i.e., the first mass load layer 201 is sandwiched between the bottom electrode 141 and the piezoelectric layer 130. The second mass load layer 202 is provided on the lower side of the top electrode 142, i.e., the second mass load layer 202 is sandwiched between the top electrode 142 and the piezoelectric layer 130. Figure 6

[0096] The other structures of the bulk acoustic wave resonator of the illustrated embodiment and the manufacturing method thereof are substantially the same as those of the bulk acoustic wave resonator shown in Figure 1 Figure 7

[0097] Figure 7 A cross-sectional view of a bulk acoustic wave resonator according to still another exemplary embodiment of the present application. As shown in the drawing, in the illustrated embodiment, the bulk acoustic wave resonator is provided with a mass load layer 201 only on the lower side of the piezoelectric layer 130, and is not provided with any mass load layer on the upper side of the piezoelectric layer 130. Figure 7

[0098] As shown in the drawing, in the illustrated embodiment, the mass load layer 201 on the lower side of the piezoelectric layer 130 is provided on the lower side of the bottom electrode 141, i.e., the bottom electrode 141 is sandwiched between the mass load layer 201 and the piezoelectric layer 130. Figure 7

[0099] However, the present application is not limited to the embodiment shown, for example, the mass load layer 201 can also be provided on the upper side of the bottom electrode 141, i.e., the mass load layer 201 is sandwiched between the bottom electrode 141 and the piezoelectric layer 130. Figure 1

[0100] Although not shown, in another exemplary embodiment of the present application, the mass load layer 201 can also be made in the bottom electrode 141.

[0101] As can be understood by those skilled in the art, the bulk acoustic wave resonator according to the present application can be used to form a filter or other semiconductor device.

[0102] Although embodiments of the present application have been shown and described with respect to the drawings, it should be understood that various changes, modifications and substitutions can be made therein without departing from the principles and spirit of the application, for example, in Figure 6 and ​ ​​​​​In the illustrated embodiment, the first mass load layer 201 and the second mass load layer 202 can be formed inside the bottom electrode 141 and the top electrode 142, respectively.

[0103] In the foregoing example embodiment of the present application, since the mass load layer is provided on at least one of the two sides of the piezoelectric layer, the present application can adjust the series resonance frequency Fs of the resonator and the symmetry of the resonator in the thickness direction by adjusting the thickness of the mass load layer.

[0104] In the present application, upper and lower are relative to the bottom surface of the substrate of the resonator, and for a component, the side close to the bottom surface is the lower side, and the side away from the bottom surface is the upper side. In the present application, the substrate here is the device substrate of the resonator.

[0105] In the present application, inner and outer are relative to the center of the effective area (the effective area is composed of the overlapping area of the piezoelectric layer, the top electrode, the bottom electrode and the acoustic mirror in the thickness direction of the resonator) of the resonator (i.e. the center of the effective area) in the lateral direction or the radial direction, and for a component, the side or end close to the center of the effective area is the inner side or end, and the side or end away from the center of the effective area is the outer side or end. For a reference position, the inner side of the position means between the position and the center of the effective area in the lateral direction or the radial direction, and the outer side of the position means further away from the center of the effective area than the position in the lateral direction or the radial direction.

[0106] As those skilled in the art can understand, the bulk acoustic wave resonator according to the present application can be used to form a filter or an electronic device.

[0107] Based on the above, the present application proposes the following technical solutions:

[0108] 1. A bulk acoustic wave resonator, comprising:

[0109] a substrate;

[0110] a piezoelectric layer;

[0111] an acoustic mirror;

[0112] a bottom electrode; and

[0113] a top electrode,

[0114] wherein:

[0115] the piezoelectric layer is a single crystal piezoelectric layer;

[0116] a mass load layer is provided on at least the lower side of the piezoelectric layer.

[0117] 2. The bulk acoustic wave resonator according to 1, wherein:

[0118] A mass load layer is provided only on the lower side of the piezoelectric layer.

[0119] 3. The bulk acoustic wave resonator according to 2, wherein:

[0120] The mass load layer is provided between the piezoelectric layer and the corresponding electrode, or in the corresponding electrode, or on the side of the corresponding electrode away from the piezoelectric layer.

[0121] 4. The bulk acoustic wave resonator according to 1, wherein:

[0122] First and second mass load layers are provided on the lower and upper sides of the piezoelectric layer, respectively.

[0123] 5. The bulk acoustic wave resonator according to 4, wherein:

[0124] The bulk acoustic wave resonator satisfies the following relationship:

[0125] 0.5 < t1 / t2 < 1.5,

[0126] wherein t1 = d0 / V0 + d1 / V1 + d2 / V2, t2 = d0 / V0 + d3 / V3 + d4 / V4, d0 is half the thickness of the piezoelectric layer, d1 is the thickness of the top electrode, d2 is the thickness of the second mass load layer, d3 is the thickness of the bottom electrode, d4 is the thickness of the first mass load layer, V0 is the speed of sound of acoustic waves in the piezoelectric layer, V1 is the speed of sound of acoustic waves in the top electrode, V2 is the speed of sound of acoustic waves in the second mass load layer, V3 is the speed of sound of acoustic waves in the bottom electrode, and V4 is the speed of sound of acoustic waves in the first mass load layer.

[0127] 6. The bulk acoustic wave resonator according to 5, wherein:

[0128] The bulk acoustic wave resonator satisfies the following relationship: 0.95 < t1 / t2 < 1.05.

[0129] 7. The bulk acoustic wave resonator according to 5, wherein:

[0130] The materials of the first and second mass load layers are the same as the materials of the bottom and top electrodes.

[0131] 8. The bulk acoustic wave resonator according to 7, wherein:

[0132] The bulk acoustic wave resonator satisfies the following relationship:

[0133] 0.5 ≤ (d1 + d2) / (d3 + d4) ≤ 1.5, where d1 is the thickness of the top electrode, d2 is the thickness of the second mass loading layer, d3 is the thickness of the bottom electrode, and d4 is the thickness of the first mass loading layer.

[0134] 9. The bulk acoustic wave resonator of claim 8, wherein:

[0135] The bulk acoustic wave resonator satisfies the following relationship: 0.95 ≤ (d1 + d2) / (d3 + d4) ≤ 1.05.

[0136] 10. The bulk acoustic wave resonator of claim 5, wherein:

[0137] The materials of the first and second mass loading layers are different from the materials of the bottom and top electrodes.

[0138] 11. The bulk acoustic wave resonator of claim 4, wherein:

[0139] The thickness of the first mass loading layer is the same as the thickness of the second mass loading layer; or

[0140] The thickness of the first mass loading layer is different from the thickness of the second mass loading layer.

[0141] 12. The bulk acoustic wave resonator of claim 4, wherein:

[0142] The thickness of the first and second mass loading layers is less than the thickness of the bottom and top electrodes; or

[0143] The thickness of the first and second mass loading layers is not greater than or

[0144] The thickness of the bottom electrode is different from the thickness of the top electrode, and the thickness of the first and second mass loading layers are different from each other.

[0145] 13. The bulk acoustic wave resonator of claim 1, further comprising:

[0146] a support layer disposed between the substrate and the piezoelectric layer.

[0147] 14. The bulk acoustic wave resonator of claim 13, wherein:

[0148] The piezoelectric layer is a flat piezoelectric layer, and the piezoelectric layer is substantially parallel to the substrate.

[0149] 15. The bulk acoustic wave resonator of any one of claims 1-14, further comprising:

[0150] A package structure includes a package substrate and a package layer disposed between the package substrate and the piezoelectric layer, the package substrate, the piezoelectric layer and the package layer defining a receiving cavity, the top electrode being in the receiving cavity.

[0151] 16. A bulk acoustic wave resonator, comprising:

[0152] a first substrate and a second substrate;

[0153] a first support layer and a second support layer;

[0154] a piezoelectric layer, the first support layer being disposed between the first substrate and a first side of the piezoelectric layer to form a first cavity between the piezoelectric layer and the first substrate, the second support layer being disposed between the second substrate and a second side of the piezoelectric layer opposite to the first side to form a second cavity;

[0155] a first electrode and a second electrode disposed on the first side and the second side of the piezoelectric layer respectively, at least a portion of the first electrode being located in the first cavity, at least a portion of the second electrode being located in the second cavity,

[0156] wherein:

[0157] the piezoelectric layer is a single-crystal piezoelectric layer;

[0158] a mass loading layer is disposed on at least one of the first side and the second side of the piezoelectric layer.

[0159] 17. A method of manufacturing a bulk acoustic wave resonator, comprising:

[0160] Step 1: providing a POI substrate, the POI substrate including an auxiliary substrate, an insulating layer disposed on the auxiliary substrate, and a single-crystal piezoelectric layer disposed on the insulating layer, a side of the piezoelectric layer facing away from the insulating layer being a first side of the piezoelectric layer;

[0161] Step 2: forming a bottom electrode of the resonator on the first side of the single-crystal piezoelectric layer;

[0162] Step 3: forming a support layer and an acoustic mirror material layer for forming an acoustic mirror of the resonator, the support layer defining a boundary of the acoustic mirror material layer, and a side of the support layer being in contact with the first side of the piezoelectric layer;

[0163] Step 4: disposing a functional substrate to the other side of the support layer opposite to the side;

[0164] Step 5: removing the auxiliary substrate and at least a portion of the insulating layer to expose at least a second side of the piezoelectric layer corresponding to an active area of the resonator, the first side and the second side being opposite in a thickness direction of the piezoelectric layer;

[0165] Step 6: forming a top electrode of the resonator on the second side of the piezoelectric layer,

[0166] wherein:

[0167] Step 2 further comprises forming a first mass loading layer on the first side of the piezoelectric layer.

[0168] 18. The method of 17, wherein:

[0169] the acoustic mirror is an acoustic mirror cavity, the layer of acoustic mirror material is a layer of sacrificial material, the method further comprising the step of removing the layer of sacrificial material to form the acoustic mirror cavity.

[0170] 19. The method of 17, further comprising, after the step 6:

[0171] Step 7: providing a packaging substrate;

[0172] Step 8: providing a packaging layer between the second side of the piezoelectric layer and a side of the packaging substrate;

[0173] Step 9: causing the packaging substrate and the second side of the piezoelectric layer to engage with each other to define a containment cavity between the packaging substrate, the second side of the piezoelectric layer and the packaging layer, the top electrode being in the containment cavity.

[0174] 20. The method of 19, wherein:

[0175] the support layer and / or the packaging layer is a layer of bonding material.

[0176] 21. The method of 17, wherein:

[0177] Step 2 comprises the step of forming a first mass loading layer and Step 6 comprises the step of forming a second mass loading layer;

[0178] the method comprises the step of selecting the thicknesses of the first mass loading layer, the second mass loading layer, the top electrode and the bottom electrode to satisfy the following relationship:

[0179] 0.5 < ti / t2 < 1.5,

[0180] wherein t1 = d0 / V0 + d1 / V1 + d2 / V2, t2 = d0 / V0 + d3 / V3 + d4 / V4, d0 is half of the thickness of the piezoelectric layer, d1 is the thickness of the top electrode, d2 is the thickness of the second mass loading layer, d3 is the thickness of the bottom electrode, d4 is the thickness of the first mass loading layer, V0 is the sound velocity of the acoustic wave in the piezoelectric layer, V1 is the sound velocity of the acoustic wave in the top electrode, V2 is the sound velocity of the acoustic wave in the second mass loading layer, V3 is the sound velocity of the acoustic wave in the bottom electrode, and V4 is the sound velocity of the acoustic wave in the first mass loading layer.

[0181] 22. The method of 21, wherein:

[0182] the first and second mass loading layers are of the same material as the bottom and top electrodes;

[0183] the method further comprises the step of selecting the thicknesses of the first mass loading layer, the second mass loading layer, the top electrode and the bottom electrode to satisfy the following relationship:

[0184] 0.5 ≤ (d1 + d2) / (d3 + d4) ≤ 1.5, wherein d1 is the thickness of the top electrode, d2 is the thickness of the second mass loading layer, d3 is the thickness of the bottom electrode, and d4 is the thickness of the first mass loading layer.

[0185] 23. The method of 21 or 22, wherein:

[0186] the first mass loading layer covers the bottom electrode and the second mass loading layer covers the top electrode.

[0187] 24. A filter comprising the bulk acoustic wave resonator of any one of 1-16.

[0188] 25. An electronic device comprising the bulk acoustic wave resonator of any one of 1-16 or the filter of 24.

[0189] Here, the electronic device includes, but is not limited to, radio frequency front-ends, filter amplification modules, and other intermediate products, as well as mobile phones, WIFI, drones, and other terminal products.

[0190] Although embodiments of the present application have been shown and described, it is to be understood that various modifications can be made to these embodiments without departing from the principles and spirit of the application, the scope of which is to be determined by the appended claims and their equivalents.

Claims

1. A bulk acoustic wave resonator, comprising: a substrate; a piezoelectric layer; an acoustic mirror; a bottom electrode; and a top electrode, wherein: the piezoelectric layer is a single-crystal piezoelectric layer; a mass loading layer is provided on at least the lower side of the piezoelectric layer; the acoustic mirror is an acoustic mirror cavity, and the bottom electrode and the mass loading layer on the lower side of the piezoelectric layer are located in the cavity. 2.The bulk acoustic wave resonator according to claim 1, wherein: a mass loading layer is provided only on the lower side of the piezoelectric layer. 3.The bulk acoustic wave resonator according to claim 2, wherein: the mass loading layer is provided between the piezoelectric layer and the corresponding electrode, or in the corresponding electrode, or on the side of the corresponding electrode away from the piezoelectric layer. 4.The bulk acoustic wave resonator according to claim 1, wherein: a first mass loading layer and a second mass loading layer are provided on the lower side and the upper side of the piezoelectric layer, respectively. 5.The bulk acoustic wave resonator according to claim 4, wherein: the bulk acoustic wave resonator satisfies the following relationship: 0.5≤t1 / t2≤1.5, wherein t1=d0 / V0+d1 / V1+d2 / V2, t2=d0 / V0+d3 / V3+d4 / V4, d0 is half of the thickness of the piezoelectric layer, d1 is the thickness of the top electrode, d2 is the thickness of the second mass loading layer, d3 is the thickness of the bottom electrode, d4 is the thickness of the first mass loading layer, V0 is the acoustic velocity of acoustic wave in the piezoelectric layer, V1 is the acoustic velocity of acoustic wave in the top electrode, V2 is the acoustic velocity of acoustic wave in the second mass loading layer, V3 is the acoustic velocity of acoustic wave in the bottom electrode, and V4 is the acoustic velocity of acoustic wave in the first mass loading layer. 6.The bulk acoustic wave resonator according to claim 5, wherein: the bulk acoustic wave resonator satisfies the following relationship: 0.95≤t1 / t2≤1.

05. 7.The bulk acoustic wave resonator according to claim 5, wherein: the materials of the first mass loading layer and the second mass loading layer are the same as the materials of the bottom electrode and the top electrode. 8.The bulk acoustic wave resonator according to claim 7, wherein: the bulk acoustic wave resonator satisfies the following relationship: 0.5≤(d1+d2) / (d3+d4)≤1.5, wherein d1 is the thickness of the top electrode, d2 is the thickness of the second mass loading layer, d3 is the thickness of the bottom electrode, and d4 is the thickness of the first mass loading layer. 9.The bulk acoustic wave resonator according to claim 8, wherein: the bulk acoustic wave resonator satisfies the following relationship: 0.95≤(d1+d2) / (d3+d4)≤1.

05. 10.The bulk acoustic wave resonator according to claim 5, wherein: the materials of the first mass loading layer and the second mass loading layer are different from the materials of the bottom electrode and the top electrode. 11.The bulk acoustic wave resonator according to claim 4, wherein: the thickness of the first mass loading layer is the same as the thickness of the second mass loading layer; or the thickness of the first mass loading layer is different from the thickness of the second mass loading layer. 12.The bulk acoustic wave resonator according to claim 4, wherein: ​ The thickness of the first mass loading layer and the second mass loading layer is less than the thickness of the bottom electrode and the top electrode; or a thickness of the first mass loading layer and the second mass loading layer is not greater than or The thickness of the bottom electrode is different from the thickness of the top electrode, and the thickness of the first mass loading layer and the second mass loading layer are different from each other.

13. The bulk acoustic wave resonator of claim 1, further comprising: a support layer disposed between the substrate and the piezoelectric layer.

14. The bulk acoustic wave resonator of claim 13, wherein: the piezoelectric layer is a flat piezoelectric layer, and the piezoelectric layer is parallel to the substrate.

15. The bulk acoustic wave resonator of any one of claims 1-14, further comprising: a package structure, the package structure comprising a package substrate and a package layer disposed between the package substrate and the piezoelectric layer, the package substrate, the piezoelectric layer and the package layer defining a containment cavity, the top electrode being in the containment cavity.

16. A bulk acoustic wave resonator, comprising: a first substrate and a second substrate; a first support layer and a second support layer; a piezoelectric layer, the first support layer being disposed between the first substrate and a first side of the piezoelectric layer to form a first cavity between the piezoelectric layer and the first substrate, the second support layer being disposed between the second substrate and a second side of the piezoelectric layer opposite to the first side to form a second cavity; a first electrode and a second electrode, respectively disposed on the first side and the second side of the piezoelectric layer, at least a portion of the first electrode being in the first cavity, at least a portion of the second electrode being in the second cavity, wherein: the piezoelectric layer is a single-crystal piezoelectric layer; a mass loading layer is disposed on at least one of the first side and the second side of the piezoelectric layer, the first electrode and the mass loading layer being in the first cavity or the second cavity.

17. A method of manufacturing a bulk acoustic wave resonator, comprising: Step 1: providing a POI substrate, the POI substrate comprising an auxiliary substrate, an insulating layer disposed on the auxiliary substrate, and a single-crystal piezoelectric layer disposed on the insulating layer, a side of the piezoelectric layer facing away from the insulating layer being a first side of the piezoelectric layer; Step 2: forming a bottom electrode of the resonator on the first side of the single-crystal piezoelectric layer; Step 3: forming a support layer and an acoustic mirror material layer for forming an acoustic mirror of the resonator, the support layer defining a boundary of the acoustic mirror material layer, and a side of the support layer being in contact with the first side of the piezoelectric layer; Step 4: disposing a functional substrate, the functional substrate being bonded to another side of the support layer opposite to the side; Step 5: removing the auxiliary substrate and at least a portion of the insulating layer to expose at least a second side of the piezoelectric layer corresponding to an active area of the resonator, the first side and the second side being opposite in a thickness direction of the piezoelectric layer; Step 6: forming a top electrode of the resonator on the second side of the piezoelectric layer, wherein: Step 2 further comprises forming a first mass loading layer on the first side of the piezoelectric layer; the acoustic mirror is an acoustic mirror cavity, the acoustic mirror material layer is a sacrificial material layer, and the method further comprises a step of removing the sacrificial material layer to form the acoustic mirror cavity.

18. The method of claim 17, after the step 6, the method further comprises: Step 7: providing a packaging substrate; Step 8: disposing a packaging layer between the second side of the piezoelectric layer and a side of the packaging substrate; Step 9: causing the packaging substrate and the second side of the piezoelectric layer to engage with each other to define a containing cavity between the packaging substrate, the second side of the piezoelectric layer and the packaging layer, the top electrode being in the containing cavity.

19. The method of claim 18, wherein: the support layer and / or the packaging layer is a layer of a bonding material.

20. The method of claim 17, wherein: Step 2 comprises a step of forming a first mass load layer, and Step 6 comprises a step of forming a second mass load layer; the method comprises a step of selecting thicknesses of the first mass load layer, the second mass load layer, the top electrode and the bottom electrode to satisfy the following relationship: 0.5 < t1 / t2 < 1.5, wherein t1 = d0 / V0 + d1 / V1 + d2 / V2, t2 = d0 / V0 + d3 / V3 + d4 / V4, d0 is half of the thickness of the piezoelectric layer, d1 is the thickness of the top electrode, d2 is the thickness of the second mass load layer, d3 is the thickness of the bottom electrode, d4 is the thickness of the first mass load layer, V0 is the speed of sound of acoustic wave in the piezoelectric layer, V1 is the speed of sound of acoustic wave in the top electrode, V2 is the speed of sound of acoustic wave in the second mass load layer, V3 is the speed of sound of acoustic wave in the bottom electrode, and V4 is the speed of sound of acoustic wave in the first mass load layer.

21. The method of claim 20, wherein: the materials of the first mass load layer and the second mass load layer are the same as the materials of the bottom electrode and the top electrode; the method further comprises a step of selecting thicknesses of the first mass load layer, the second mass load layer, the top electrode and the bottom electrode to satisfy the following relationship: 0.5 < (d1 + d2) / (d3 + d4) < 1.5, wherein d1 is the thickness of the top electrode, d2 is the thickness of the second mass load layer, d3 is the thickness of the bottom electrode, and d4 is the thickness of the first mass load layer.

22. The method of claim 20 or 21, wherein: the first mass load layer covers the bottom electrode, and the second mass load layer covers the top electrode.

23. A filter comprising the bulk acoustic wave resonator of any one of claims 1-16.

24. An electronic device comprising the bulk acoustic wave resonator of any one of claims 1-16, or the filter of claim 23. ​

Images