Patent Publication Number: US-2021184643-A1

Title: Film bulk acoustic resonator and fabrication method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of PCT Patent Application No. PCT/CN2020/099741, filed on Jul. 1, 2020, which claims priority to Chinese patent application No. 201910657440.7, filed on Jul. 19, 2019, the entirety of all of which is incorporated herein by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure generally relates to the field of semiconductor manufacturing, and more particularly, relates to a film bulk acoustic resonator and its fabrication method. 
     BACKGROUND 
     Radio frequency filters are required in radio frequency (RF) communications, such as mobile phone communication. Each radio frequency filter may transmit its required frequency and limit all other frequencies. With the development of mobile communication technology, the quantity of mobile data transmission has increased rapidly. Therefore, under the premise that frequency resources are limited and as few mobile communication devices as possible should be used, increasing the transmission power of wireless power transmission equipment, such as wireless base stations, micro base stations or repeaters, must be considered; meanwhile, it also indicates that the filter power requirement in the front-end circuits of mobile communication equipment has continuously increased. 
     Currently, high-power filters in equipment such as wireless base stations are mainly cavity filters with power reaching hundreds of watts, but the sizes of such filters are extremely large. Dielectric filters, which may have the average power reaching more than 5 watts, may also be used in certain equipment, but the sizes of the filters are also extremely large. Such two types of filters cannot be integrated into the RF front-end chips due to their large sizes. 
     As MEMS technology has been well developed, filters composed of bulk acoustic resonators may effectively overcome the defects of the above-mentioned two types of filters. Film Bulk Acoustic Resonators (FBAR), a hot spot in the market, have various advantages such as high operation frequency, small insertion loss, high Q value, high withstand power, and small size, which may meet the urgent needs of high-frequency and miniaturized RF filters in the RF transceiver front ends of electronic systems, such as communications, radars, and the like. 
     The core structure of the film bulk acoustic resonator is a stacked structure (“sandwich” structure) composed of an upper electrode—a piezoelectric film layer—a lower electrode. Its working principle is described as the following. The inverse piezoelectric effect of the piezoelectric film layer is used to convert electrical energy into mechanical energy; the mechanical vibration excites acoustic waves in the film for transmission; finally, the acoustic signal is converted into an electrical signal output through the piezoelectric effect. The most important feature of the resonator is to ensure that the energy of the acoustic wave is limited to the piezoelectric film layer in addition to ensuring the piezoelectric performance of the piezoelectric film layer. Therefore, a cavity is provided below the region of the lower electrode of the film bulk acoustic resonator facing the upper electrode. 
     The film bulk acoustic resonator may be fabricated on a substrate material through a deposition process. After the stacked structure composed of the upper electrode, the piezoelectric film layer and the lower electrode is formed, a cavity needs to be formed under the stacked structure, which makes the fabrication of the film bulk acoustic resonator relatively difficult. An existing technology illustrated in  FIGS. 1A-1E  may be described as the following. A trench  110 ′ may be first formed on a substrate  100 , as shown in  FIG. 1A ; then, a sacrificial layer material may be filled in the trench  110 ′, and the surfaces of the substrate  100  and the sacrificial layer material may be planarized by a chemical mechanical polishing (CMP) process to form a sacrificial layer  101 , as shown in  FIG. 1B ; next, a first electrode  102 , a piezoelectric film layer  103 , and a second electrode  104  may be sequentially deposited on the surfaces of the planarized substrate  100  and the sacrificial layer  101 , as shown in  FIG. 1C ; then, the piezoelectric film layer  103  and the second electrode  104  may be patterned, and only the piezoelectric film layer  103  and the second electrode  104  above the sacrificial layer  101  may be retained, as shown in  FIG. 1D ; next, a plurality of through holes  120  may be disposed at the first electrode  102  which is above the sacrificial layer  101  and not covered by the piezoelectric film layer  103  and the second electrode  104 , as shown in  FIG. 1D ; finally, the formed device may be placed in a chemical reagent which etches away the material of the sacrificial layer through the through holes  120  to release the sacrificial layer  101  to form a cavity  110 , thereby realizing the floating arrangement of the film bulk acoustic resonator, as shown in  FIG. 1E . 
     However, the above-mentioned method still has a plurality of shortcomings. For example, when the CMP process is performed on the substrate  100  and the sacrificial material using the above-mentioned method, small recessions may be formed in the region of the sacrificial layer  101  due to the difference in polishing rates, which may affect the subsequent growth uniformity of the piezoelectric layer  103 , and eventually affect the performance of the film bulk resonator. Moreover, the method needs the fabrication of the sacrificial layer  101 ; and during the releasing process of the sacrificial layer  101 , the related film of the film bulk acoustic resonator is easily broken. Furthermore, if the sacrificial layer  101  is not released completely to have certain impurity residuals, it may greatly reduce the Q value of the film bulk acoustic resonator and affect the quality of the film bulk acoustic resonator. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     One aspect of the present disclosure provides a method for fabricating a film bulk acoustic resonator, including:
         providing a first substrate, and sequentially forming a first electrode layer, a piezoelectric material layer, and a second electrode layer, on the first substrate;   forming a support layer on the second electrode layer and forming a cavity with a top opening in the support layer, where the cavity passes through the support layer;   providing a second substrate and bonding the second substrate with the support layer;   removing the first substrate; and   patterning the first electrode layer, the piezoelectric material layer, and the second electrode layer to form a first electrode, a piezoelectric layer, and a second electrode.       

     Another aspect of the present disclosure provides a film bulk acoustic resonator, including:
         a second substrate;   a support layer bonded on the second substrate, where a cavity, passing through the support layer, is disposed in the support layer; and   a second electrode, a piezoelectric layer, and a first electrode which are sequentially disposed on the support layer.       

     Other aspects of the present disclosure can be understood by those skilled in the art in light of the description, the claims, and the drawings of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to clearly explain the technical solutions in the embodiments of the present disclosure or the existing technology, the drawings that need to be used in the description of the embodiments or the existing technology are illustrated hereinafter. Obviously, the drawings in the following description are merely some embodiments of the present disclosure. For those skilled in the art, other drawings can be obtained based on such drawings without creative work. 
         FIGS. 1A-1E  illustrate structural schematics corresponding to certain stages of a fabrication method of a film bulk acoustic resonator; 
         FIG. 2  illustrates a flowchart of a fabrication method of a film bulk acoustic resonator according to various embodiments of the present disclosure; and 
         FIGS. 3A-3K  illustrate structural schematics corresponding to certain stages of a fabrication method of a film bulk acoustic resonator according to various embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A film bulk acoustic resonator and a fabrication method of film bulk acoustic resonator in the present disclosure may be further described in detail with reference to the accompanying drawings and specific embodiments hereinafter. The advantages and features of the present disclosure may be more apparent according to the following description and the accompanying drawings. However, it should be noted that the concept of the technical solution of the present disclosure may be implemented in various different forms and may not be limited to specific embodiments set forth herein. The accompanying drawings may be all in simplified forms and non-precise scales and may be merely for convenience and clarity of the purpose of the embodiments of the present disclosure. 
     The terms “first”, “second” and the like in the specification and the claims may be used to distinguish similar elements and may be not necessarily used to describe a particular order or chronological order. It should be understood that the used terms may be substituted, as appropriate. For example, the embodiments described herein of the present disclosure may be enabled to operate in other sequences than sequences described or illustrated herein. Similarly, if the method described herein comprise a series of steps, the order of the steps presented herein may not be necessarily the only order in which the steps may be performed, and some of the steps may be omitted and/or other steps, which are not described herein, may be added to the method. If components in one of the drawings are same as components in other drawings, although the components may be easily recognized in all drawings, in order to make the description of the drawings clearer, labels of all the same components may not be marked in each figure in the present specification. 
     Various embodiments of the present disclosure provide a fabrication method of a film bulk acoustic resonator. For example, as shown in  FIG. 2 , an exemplary fabrication method of a film bulk acoustic resonator may include the following:
         S 01 , providing a first substrate and sequentially forming a first electrode layer, a piezoelectric material layer, and a second electrode layer on the first substrate;   S 02 , forming a support layer on the second electrode layer and forming a cavity with a top opening in the support layer, where the cavity passes through the support layer;   S 03 , providing a second substrate and bonding the second substrate with the support layer;   S 04 , removing the first substrate; and   S 05 , patterning the first electrode layer, the piezoelectric material layer, and the second electrode layer to form a first electrode, a piezoelectric layer, and a second electrode.       

       FIGS. 3A-3K  illustrate structural schematics corresponding to certain stages of the fabrication method of the film bulk acoustic resonator according to various embodiments of the present disclosure. The fabrication method of the film bulk acoustic resonator provided in one embodiment is described in detail with reference to  FIG. 2  and  FIGS. 3A-3K  hereinafter. 
     As shown in  FIG. 3A , a first substrate  200  may first be provided. The first substrate  200  may be any suitable substrate known to those skilled in the art. For example, the first substrate  200  may be at least one of the materials mentioned below: silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbon (SiC), silicon germanium (SiGeC), indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP) or other III/V compound semiconductors. The first substrate may also be a multilayer structure composed of above-mentioned semiconductors; or silicon-on-insulator (SOI), silicon-on-insulator (SSOI), silicon-germanium-on-insulator (S—SiGeOI), silicon germanium-on-insulator (SiGeOI), and germanium-on-insulator (GeOI); or double side polished wafers (DSP), a ceramic substrate such as alumina, a quartz or glass substrate, and the like. 
     Optionally, as shown in  FIG. 3B , a release layer  201  may be formed on the first substrate  200 . The release layer  201  may prevent the piezoelectric stacked layer structure of the film bulk acoustic resonator formed subsequently from affecting the first substrate  200 ; meanwhile, in the subsequent removal process of the first substrate  200 , the first substrate  200  may be separated from the piezoelectric stacked layer structure formed subsequently by the manner of etching the release layer  201 , which is beneficial for rapid removing the first substrate  200  and improving the manufacturing efficiency of the process. The release layer is made of a material including a dielectric material, a light solidification adhesive, a thermally melt adhesive, a laser release material, or a combination thereof. For example, the material of the release layer  201  may include silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), aluminum oxide (Al 2 O 3 ), and aluminum nitride (AlN). The release layer  201  may be formed by a process including chemical vapor deposition, magnetron sputtering, evaporation, and the like. In one embodiment, the first substrate  200  may be a silicon wafer; and the material of the release layer  201  may be silicon dioxide (SiO 2 ). 
     Next, as shown in  FIG. 3C , a piezoelectric stacked layer structure may be formed on the release layer  201 ; and the piezoelectric stacked layer structure may include a first electrode layer  202 ′, a piezoelectric material layer  203 ′, and a second electrode layer  204 ′, where the piezoelectric material layer  203 ′ may be located between the first electrode layer  202 ′ and the second electrode layer  204 ′; and the first electrode layer  202 ′ and the second electrode layer  204 ′ may be disposed oppositely. The first electrode layer  202 ′ may be used as an input electrode or an output electrode which receives or provides electrical signals such as radio frequency (RF) signals. For example, when the second electrode layer  204 ′ is used as the input electrode, the first electrode layer  202 ′ may be used as the output electrode; when the second electrode layer  204 ′ is used as the output electrode, the first electrode layer  202 ′ may be used as the input electrode; and the piezoelectric material layer  203 ′ may convert the electrical signal inputted through the first electrode layer  202 ′ or the second electrode layer  204 ′ into the bulk acoustic wave. For example, the piezoelectric material layer  203 ′ may convert the electrical signal into bulk acoustic wave through physical vibration. 
     The first electrode layer  202 ′ and the second electrode layer  204 ′ may be made of any suitable conductive materials or semiconductor materials known in the existing technology, where the conductive material may be a metal material with conductive properties, such as one metal or a stacked layer of the following metals including molybdenum (Mo), aluminum (Al), copper (Cu), tungsten (W), tantalum (Ta), platinum (Pt), ruthenium (Ru), rhodium (Rh), iridium (Ir), chromium (Cr), titanium (Ti), gold (Au), osmium (Os), rhenium (Re), palladium (Pd), and the like; and the semiconductor material may be, for example, Si, Ge, SiGe, SiC, SiGeC, and the like. The first electrode layer  202 ′ and the second electrode layer  204 ′ may be formed by a physical vapor deposition process or a chemical vapor deposition process such as magnetron sputtering, evaporation, and the like. The piezoelectric material layer  203 ′ may also be called a piezoelectric resonance layer or a piezoelectric resonance part. The material of the piezoelectric material layer  203 ′ may be one or a combination of piezoelectric materials with wurtzite crystal structure, including aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), lithium niobate (LiNbO 3 ), quartz (Quartz), potassium niobate (KNbO 3 ), lithium tantalate (LiTaO 3 ), and the like. When the piezoelectric material layer  203 ′ includes aluminum nitride (AlN), the piezoelectric material layer  203 ′ may also include rare earth metals, such as at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). Moreover, when the piezoelectric material layer  203 ′ includes aluminum nitride (AlN), the piezoelectric material layer  203 ′ may also include transition metals, such as at least one of zirconium (Zr), titanium (Ti), manganese (Mn), and hafnium (Hf). The piezoelectric material layer  203 ′ may be deposited by any suitable process known to those skilled in the art, such as chemical vapor deposition, physical vapor deposition, or atomic layer deposition. Preferably, in one embodiment, the first electrode layer  202 ′ and the second electrode layer  204 ′ may be made of metallic molybdenum (Mo); and the piezoelectric material layer  203 ′ may be made of aluminum nitride (AlN). 
     The shapes of the first electrode layer  202 ′, the piezoelectric material layer  203 ′, and the second electrode layer  204 ′ may be same or different, and the areas of the first electrode layer  202 ′, the piezoelectric material layer  203 ′, and the second electrode layer  204 ′ may be same or different. In one embodiment, the shapes and areas of the first electrode layer  202 ′, the piezoelectric material layer  203 ′, and the second electrode layer  204 ′ are same, where the shapes may all be polygonal, such as square. 
     Before forming the first electrode layer  202 ′, a seed layer (not shown in  FIG. 3C ) may be formed on the release layer  201 . The seed layer may be formed between the release layer  201  and the first electrode layer  202 ′. The seed layer may guide the crystal orientation of the first electrode layer  202 ′ (the piezoelectric material layer  203 ′ and the second electrode layer  204 ′) subsequently formed, which is convenient for the piezoelectric stacked layer structure formed subsequently to grow along a specific crystal orientation, thereby ensuring the uniformity of the piezoelectric layer. The material of the seed layer may be aluminum nitride (AlN). In addition to AlN, the seed layer may also be formed by a metal or a dielectric material having a hexagonal close packed (HCP) structure. For example, the seed layer may also be formed by metal titanium (Ti). 
     Next, as shown in  FIG. 3D , step S 02  may be performed to form a support layer  206  over the second electrode layer  204 ′ and to form a cavity  210  with a top opening in the support layer  206 , where the cavity  210  passes through the support layer  206 . For example, the support layer  206  may be first formed by a chemical deposition process. The material of the support layer  206  may be, for example, one or a combination of silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), aluminum oxide (Al 2 O 3 ), and aluminum nitride (AlN). The material of the support layer  206  in one embodiment may be silicon dioxide (SiO 2 ). Then, the support layer  206  may be etched by an etching process to form an opening  210 ′ to expose a portion of the second electrode layer  204 ′. The etching process may be a wet etching process or a dry etching process; and the dry etching process may be preferably used. The dry etching processes may include, but may not be limited to, reactive ion etching (RIE), ion beam etching, plasma etching, or laser cutting. The depth and shape of the opening  210 ′ may depend on the depth and shape of the cavity required by the bulk acoustic resonator to be fabricated; and the thickness of the cavity in the film bulk acoustic resonator is related to the resonance frequency. Therefore, the depth of the opening  210 ′, that is, the thickness of the support layer  206 , may be set according to the required resonance frequency of the film bulk acoustic resonator. Exemplarily, the depth of the opening  210 ′ may be about 0.5 micrometer to about 3 micrometers, for example, 1 micrometer or 2 micrometers or 3 micrometers. The shape of the bottom surface of the opening  210 ′ may be a rectangle or a polygon other than a rectangle, such as a pentagon, a hexagon, an octagon, and the like, and may also be a circle or an ellipse. The sidewall of the opening  210 ′ may be inclined or vertical. In one embodiment, the bottom surface of the opening  210 ′ may be a rectangle, and an obtuse angle may be formed between the side wall and the bottom surface (the shape of the longitudinal section of the opening  210 ′ (the section along the thickness direction of the substrate) is an inverted trapezoid). In other embodiments of the present disclosure, the longitudinal cross-sectional shape of the opening  210 ′ may also be a spherical crown with a wide top and a narrow bottom, that is, the longitudinal cross-section may be U-shaped. 
     In one embodiment, before forming the support layer  206 , an etch stop layer  205  may be further formed on the second electrode layer  204 ′. The material of the etch stop layer  205  may include, but may not be limited to, silicon nitride (Si 3 N 4 ) and silicon oxynitride (SiON). The etch stop layer  205  has a lower etch rate compared with the support layer  206  formed subsequently, which may prevent over-etching when the support layer  206  is subsequently etched to form the opening, thereby protecting the surface of the second electrode layer  204 ′ under the etch stop layer  205  from being damaged. 
     Next, as shown in  FIG. 3F , step S 03  may be performed to provide a second substrate  300  and to bond the second substrate  300  with the support layer  206 . The second substrate  300  and the second electrode  204  may form the cavity  210  at the opening  210 ′ of the support layer  206 . The second substrate  300  may be any suitable substrate known to those skilled in the art. For example, the second substrate  300  may be at least one of the materials mentioned below: silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbon (SiC), silicon germanium (SiGeC), indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP) or other III/V compound semiconductors. The second substrate  300  may also be a multilayer structure composed of such semiconductors; or silicon-on-insulator (SOI), silicon-on-insulator (SSOI), silicon-germanium-on-insulator (S—SiGeOI), silicon germanium-on-insulator (SiGeOI), and germanium-on-insulator (GeOI); or double side polished wafers (DSP), a ceramic substrate such as alumina, a quartz or glass substrate, and the like. The bonding of the second substrate  300  and the support layer  206  may be implemented by thermocompression bonding. In order to increase the bonding capability between the support layer  206  and the second substrate  300 , a bonding layer may be disposed on the side of the support layer  206  for the thermocompression bonding. The bonding layer may be, for example, a silicon dioxide layer. In other embodiments of the present disclosure, other bonding manners may also be used for bonding. The second substrate  300  and the support layer  206  may be bonded into a single piece by dry film bonding. For example, a dry film layer may be disposed on the side of the second substrate  300  for bonding the dry film, and the second substrate  300  may be bonded to the support layer  206  through the dry film. After the bonding process is completed, the above-mentioned film bulk acoustic resonator after bonding may be turned over to obtain the structure shown in  FIG. 3G . 
     Next, as shown in  FIG. 3H , step S 04  may be performed to remove the first substrate  200 . The first substrate  200  may be removed through a thinning process, a thermal release process, and a peeling process. For example, the release layer  201  may be made of a material including a dielectric material; and the release layer  201  and the first substrate  200  may be removed by the thinning process, such as mechanical polishing; the release layer  201  may be a light solidification adhesive, and the light solidification adhesive may be removed by a chemical agent to remove the first substrate  200 ; the release layer may be a thermally melt adhesive, and the thermally melt adhesive may lose its viscosity through a thermal release process to remove the first substrate  200 . In other embodiments of the present disclosure, the first substrate  200  may also be removed by other manners, which are not listed in detail herein. 
     Next, as shown in  FIG. 3I , step S 05  may be performed to pattern the first electrode layer  202 ′, the piezoelectric material layer  203 ′, and the second electrode layer  204 ′ to form a first electrode  202 , a piezoelectric layer  203  and the second electrode  204 . The overlapped region of the first electrode  202 , the piezoelectric layer  203  and the second electrode  204  along the vertical direction (i.e., the thickness direction) may be at least partially located above the cavity  210 . 
     After the patterning step, the second electrode  204  may not only cover the opening of the cavity  210  but also extend and cover a portion of the support layer  206  around the opening  210 ′ (for example, directly cover the surface of the etch stop layer  205  above the support layer  206 ). That is, the second electrode  204  may not only completely enclose the cavity  210  but also adjoin the support layer  206 . The portion of the second electrode  204  that adjoins the support layer  206  may be a closed loop structure formed by surrounding the opening of the cavity  210  for one turn. In other embodiments of the present disclosure, the second electrode  204  may be coplanar with the edge of the support layer  206 . 
     After patterning the first electrode layer  202 ′, the piezoelectric material layer  203 ′, and the second electrode layer  204 ′, the shapes of the first electrode  202  and the piezoelectric layer  203  formed may be same as or different from the shape of the second electrode  204 ; and the top-view shape may be pentagons or other polygons, such as quadrangles, hexagons, heptagons, or octagons. In one embodiment, after the patterning step, the first electrode  202  and the piezoelectric layer  203  may be completely overlapped with a same area, and the area of the second electrode  204  may be greater than the area of the opening of the cavity  210 . 
     For example, the first electrode layer  202 ′, the piezoelectric material layer  203 ′, and the second electrode layer  204 ′ may be patterned through photolithography and etching processes. Exemplarily, the electrode pattern of the first electrode  202  may be defined by a photolithography process, and the shape of the first electrode  202  may be formed by a dry etching process or a wet etching process. Then, using the first electrode  202  as a mask, the piezoelectric material layer  203 ′ may be etched using a dry etching process or a wet etching process, as shown in  FIG. 3I . Next, the electrode pattern of the second electrode  204  may be defined by a photolithography process, and the shape of the second electrode  204  may be formed by a dry etching process or a wet etching process, as shown in  FIG. 3J . The patterned first electrode  202 , the piezoelectric layer  203 , and the second electrode  204  may have an overlapped region along the vertical direction. Therefore, after the first electrode  202  and the second electrode  204  are applied with a voltage, an electric field may be formed between such two electrodes, and the electric field may facilitate the piezoelectric layer  203  to generate mechanical vibrations. Moreover, the overlapped region may be at least partially located above the cavity  210 , and a portion of the second electrode  204  above the cavity  210  may be exposed. That is, the overlapped region, along the thickness direction, of the first electrode  202 , the piezoelectric layer  203 , and the second electrode  204  located above the cavity  210  may be an active working region (effective working region) of the bulk acoustic resonator. Such arrangement may relatively reduce the dissipation of acoustic wave energy and improve the quality factor of the bulk acoustic resonator. 
     Moreover, after patterning the first electrode layer  202 ′, the piezoelectric material layer  203 ′, and the second electrode layer  204 ′ to form the first electrode  202 , the piezoelectric layer  203 , and the second electrode  204 , the method for fabricating the film bulk acoustic resonator provided by the present disclosure may further include forming a passivation layer  207 . The passivation layer  207  may cover the first electrode  202 , the piezoelectric layer  203 , and the second electrode  204 , and further cover the support layer  206 . Passivation layer openings may be formed in the passivation layer  207  above the support layer  206  and in the passivation layer  207  above the second electrode  204 , respectively, where a part of the passivation layer openings may expose the second electrode  204 , and another part of the passivation layer openings may expose the second electrode  202 . A first soldering pad  208   a  and a second soldering pad  208   b,  which are electrically connected to the first electrode  202  and the second electrode  204 , may be respectively formed at the passivation layer openings, as shown in  FIG. 3K . For example, the passivation layer  207  may be formed by chemical deposition or thermal oxidation. The material of the passivation layer  207  may be silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), silicon oxynitride (SiON), aluminum nitride (AlN), aluminum oxide (Al 2 O 3 ), and the like. Then, the passivation layer  207  may be etched to form the passivation layer openings on the first electrode  202  and the second electrode  204  as electrode lead-out windows. Finally, a conductive material such as metal may be filled in the passivation layer openings to form the first soldering pad  208   a  and the second soldering pad  208   b  which are electrically connected to the first electrode  202  and the second electrode  204 , respectively, thereby further realizing the connection between the electrodes of the film bulk acoustic resonator and an external power supply device. The material of each of the first soldering pad  208   a  and the second soldering pad  208   b  may be a composite structure formed by one or a combination of aluminum (Al), copper (Cu), gold (Au), titanium (Ti), nickel (Ni), silver (Ag), tungsten (W) and the like. Preferably, in one embodiment, the first soldering pad  208   a  and the second soldering pad  208   b  may be aluminum soldering pads; and the first soldering pad  208   a  and the second soldering pad  208   b  may be located on two sides of the cavity  210 , respectively. 
     In the above-mentioned etching steps, the etching manners may include, but may not be limited to, a wet etching technology, an inductively coupled plasma (ICP) etching process, a reactive ion etching (RIE) process, and the like. The deposition manners may include, but may not be limited to, a chemical vapor deposition process, a magnetron sputtering process, an electrochemical deposition process, an atomic layer deposition (ALD) process, a molecular beam epitaxy (MBE) process, and the like. 
     The embodiments of the present disclosure also provide a film bulk acoustic resonator, which is fabricated by using the above-mentioned fabrication method of the film bulk acoustic resonator. As shown in  FIG. 3K , the film bulk acoustic resonator may include:
         the second substrate  300 ;   the support layer  206  disposed on the second substrate  300 , where the support layer  206  may be bonded to the second substrate  300 , and the cavity  210 , passing through the support layer  206 , may be disposed in the support layer  206 ; and   the second electrode  204 , the piezoelectric layer  203 , and the first electrode  202  sequentially disposed on the support layer  206 .       

     The cavity  210  may be disposed in the support layer  206  below the overlapped region, along the thickness direction, of the first electrode  202 , the piezoelectric layer  203 , and the second electrode  204 . The second electrode  204  may cover the opening of the cavity  210  and a portion of the support layer  206  around the opening. The portion of the second electrode  204  that adjoins the support layer  206  may a closed loop structure formed by surrounding the opening of the cavity  210  for one turn. In other embodiments of the present disclosure, the second electrode  204  may be coplanar with the edge of the support layer  206 . 
     The second substrate  300  may be any suitable substrate known to those skilled in the art. For example, the second substrate  300  may be at least one of the materials mentioned below: silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbon (SiC), silicon germanium (SiGeC), indium arsenide (InAs), Gallium arsenide (GaAs), indium phosphide (InP) or other III/V compound semiconductors. The second substrate  300  may be a multilayer structure composed of such semiconductors; or silicon-on-insulator (SOI), silicon-on-insulator (SSOI), silicon-germanium-on-insulator (S—SiGeOI), silicon germanium-on-insulator (SiGeOI), and germanium-on-insulator (GeOI); or double side polished wafers (DSP), a ceramic substrate such as alumina, a quartz or glass substrate, and the like. In one embodiment, the first electrode  202  and the second electrode  204  may be made of metal molybdenum (Mo), and the piezoelectric layer  203  may be made of aluminum nitride (AlN). The material of the support layer  206  may be, for example, one or a combination of silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), aluminum oxide (Al 2 O 3 ) and aluminum nitride (AlN). Preferably, the material of the support layer  206  may be silicon dioxide (SiO 2 ). 
     Optionally, the areas of the first electrode  202  and the piezoelectric layer  203  may be equal and completely overlapped, and the area of the second electrode  204  may be greater than the area of the opening of the cavity  210 . The overlapped region, along the thickness direction, of the first electrode  202 , the piezoelectric layer  203 , and the second electrode  204  located above the cavity  210  may be an active working region (effective working region) of the bulk acoustic resonator. Such arrangement may relatively reduce the dissipation of acoustic wave energy and improve the quality factor of the bulk acoustic resonator. 
     The support layer  206  may be bonded to the second substrate  300  by a thermocompression bonding manner or a dry film bonding manner. Using the thermocompression bonding manner, a bonding layer may be disposed on a side of the support layer for bonding with the second substrate by the thermocompression bonding. Using the dry film bonding manner, a dry film layer may be disposed on a side of the second substrate for bonding with the support layer by the dry film bonding. 
     Optionally, the etch stop layer  205  may be disposed between the second electrode  204  and the support layer  206 . Furthermore, the etch stop layer  205  and the second electrode  204 , having a same shape and a same area, may be completely overlapped with each other. The material of the etch stop layer  205  may include, but may not be limited to, silicon nitride (Si 3 N 4 ) and silicon oxynitride (SiON). 
     Optionally, the film bulk acoustic resonator may further include the passivation layer  207 . The passivation layer  207  may cover the first electrode  202 , the piezoelectric layer  203 , the second electrode  204 , and the support layer  206 . 
     Optionally, passivation layer openings, different from the cavity  210 , may be respectively formed in the passivation layer  207  above the support layer  206  and in the passivation layer  207  above the second electrode  204 . The film bulk acoustic resonator may further include at least two soldering pads. The soldering pads, disposed at the passivation layer  207 , may be electrically connected to the first electrode  202  and the second electrode  204  respectively through the openings of the passivation layer  207 . For example, the first soldering pad  208   a  may be electrically connected to the first electrode  202 , and the second soldering pad  208   b  may be electrically connected to the second electrode  204 . Preferably, the first soldering pad  208   a  and the second soldering pad  208   b  may be located on two sides of the cavity  210 , respectively. 
     From the above-mentioned embodiments, it can be seen that the technical solutions provided by the present disclosure may achieve at least the following beneficial effects. 
     The present disclosure provides the film bulk acoustic resonator and its fabrication method. The first electrode layer, the piezoelectric material layer, and the second electrode layer may be sequentially formed on the first substrate. Then, the support layer may be formed on the second electrode layer and the cavity with the top opening may be formed in the support layer, where the cavity passes through the support layer. Next, the second substrate may be bonded with the support layer, and the first substrate may be removed; and the first electrode layer, the piezoelectric material layer, and the second electrode layer may be patterned to form the first electrode, the piezoelectric layer, and the second electrode, such that the overlapped region of the first electrode, the piezoelectric layer, and the second electrode along the thickness direction may be directly above the cavity. The cavity structure of the film bulk acoustic filter may be realized through the etching support layer and the bonding process, which avoids the influence of slight fluctuations between different media caused by the CMP process on the uniformity of the piezoelectric layer and avoids the influence on the performance of the film bulk acoustic wave filter due to incompletely dissolving the sacrificial layer. 
     It should be noted that each embodiment in present specification may be described in a related manner, and the same or similar parts between the various embodiments may be referred to each other. Each embodiment may focus on the differences from other embodiments. Particularly, as for the structural embodiments, since it is basically similar to the method embodiments, the description may be relatively simple, and related parts may refer to the partial description of the method embodiments. 
     The above-mentioned description may merely the description of preferred embodiments of the present disclosure and may not limit the scope of the present disclosure in any way. Any changes or modifications made by those skilled in the art in the field of the present disclosure according to the above-mentioned description shall fall within the protection scope of the claims.