Patent Publication Number: US-11646718-B2

Title: Acoustic wave resonator, RF filter circuit device and system

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority to and is a continuation of the following application: U.S. patent application Ser. No. 17/667,336, filed Feb. 8, 2022, which is a continuation of U.S. patent application Ser. No. 17/558,147, filed Dec. 21, 2021, which is a continuation of U.S. patent application Ser. No. 17/306,132, filed May 3, 2021; which is a continuation-in-part application of U.S. patent application Ser. No. 16/828,675, filed Mar. 24, 2020, which is a continuation-in-part application of U.S. patent application Ser. No. 16/707,885, filed Dec. 9, 2019; which is a continuation-in-part application of U.S. patent application Ser. No. 16/290,703, filed Mar. 1, 2019, now U.S. Pat. No. 10,979,026; which is a continuation-in-part application of U.S. patent application Ser. No. 16/175,650, filed Oct. 30, 2018, now U.S. Pat. No. 10,979,025; which is a continuation-in-part application of U.S. patent application Ser. No. 16/019,267, filed Jun. 26, 2018, now U.S. Pat. No. 10,979,022; which is a continuation-in-part application of U.S. patent application Ser. No. 15/784,919, filed Oct. 16, 2017, now U.S. Pat. No. 10,355,659; which is a continuation-in-part application of U.S. patent application Ser. No. 15/068,510, filed Mar. 11, 2016, now U.S. Pat. No. 10,217,930. This application also claims priority to and is a continuation-in-part application of U.S. patent application Ser. No. 16/514,717, filed Jul. 17, 2019, now U.S. Pat. No. 11,418,169; which is a continuation-in-part application of U.S. patent application Ser. No. 16/290,703, filed Mar. 1, 2019, now U.S. Pat. No. 10,979,026; which is a continuation-in-part application of U.S. patent application Ser. No. 16/175,650, filed Oct. 30, 2018, now U.S. Pat. No. 10,979,025; which is a continuation-in-part application of U.S. patent application Ser. No. 16/019,267, filed Jun. 26, 2018, now U.S. Pat. No. 10,979,022; which is a continuation-in-part application of U.S. patent application Ser. No. 15/784,919, filed Oct. 16, 2017, now U.S. Pat. No. 10,355,659; which is a continuation-in-part application of U.S. patent application Ser. No. 15/068,510, filed Mar. 11, 2016, now U.S. Pat. No. 10,217,930. This application also claims priority to and is a continuation-in-part application of U.S. patent application Ser. No. 16/541,076, filed Aug. 14, 2019; which is a continuation-in-part application of U.S. patent application Ser. No. 16/290,703, filed Mar. 1, 2019, now U.S. Pat. No. 10,979,026; which is a continuation-in-part application of U.S. patent application Ser. No. 16/175,650, filed Oct. 30, 2018, now U.S. Pat. No. 10,979,025; which is a continuation-in-part application of U.S. patent application Ser. No. 16/019,267, filed Jun. 26, 2018, now U.S. Pat. No. 10,979,022; which is a continuation-in-part application of U.S. patent application Ser. No. 15/784,919, filed Oct. 16, 2017, now U.S. Pat. No. 10,355,659; which is a continuation-in-part application of U.S. patent application Ser. No. 15/068,510, filed Mar. 11, 2016, now U.S. Pat. No. 10,217,930. This application also claims priority to and is a continuation-in-part application of U.S. patent application Ser. No. 16/391,191, filed Apr. 22, 2019; which is a continuation-in-part application of U.S. patent application Ser. No. 16/290,703, filed Mar. 1, 2019, now U.S. Pat. No. 10,979,026; which is a continuation-in-part application of U.S. patent application Ser. No. 16/175,650, filed Oct. 30, 2018, now U.S. Pat. No. 10,979,025; which is a continuation-in-part application of U.S. patent application Ser. No. 16/019,267, filed Jun. 26, 2018, now U.S. Pat. No. 10,979,022; which is a continuation-in-part application of U.S. patent application Ser. No. 15/784,919, filed Oct. 16, 2017, now U.S. Pat. No. 10,355,659; which is a continuation-in-part application of U.S. patent application Ser. No. 15/068,510, filed Mar. 11, 2016, now U.S. Pat. No. 10,217,930. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to electronic devices. More particularly, the present invention provides techniques related to a method of manufacture and a structure for bulk acoustic wave resonator devices, single crystal bulk acoustic wave resonator devices, single crystal filter and resonator devices, and the like. Merely by way of example, the invention has been applied to a single crystal resonator device for a communication device, mobile device, computing device, among others. 
     Mobile telecommunication devices have been successfully deployed world-wide. Over a billion mobile devices, including cell phones and smartphones, were manufactured in a single year and unit volume continues to increase year-over-year. With ramp of 4G/LTE in about 2012, and explosion of mobile data traffic, data rich content is driving the growth of the smartphone segment—which is expected to reach 2B per annum within the next few years. Coexistence of new and legacy standards and thirst for higher data rate requirements is driving RF complexity in smartphones. Unfortunately, limitations exist with conventional RF technology that is problematic, and may lead to drawbacks in the future. 
     With 4G LTE and 5G growing more popular by the day, wireless data communication demands high performance RF filters with frequencies around 5 GHz and higher. Bulk acoustic wave resonators (BAWR) using crystalline piezoelectric thin films are leading candidates for meeting such demands. Current BAWRs using polycrystalline piezoelectric thin films are adequate for bulk acoustic wave (BAW) filters operating at frequencies ranging from 1 to 3 GHz; however, the quality of the polycrystalline piezoelectric films degrades quickly as the thicknesses decrease below around 0.5 um, which is required for resonators and filters operating at frequencies around 5 GHz and above. Single crystalline or epitaxial piezoelectric thin films grown on compatible crystalline substrates exhibit good crystalline quality and high piezoelectric performance even down to very thin thicknesses, e.g., 0.4 um. Even so, there are challenges to using and transferring single crystal piezoelectric thin films in the manufacture of BAWR and BAW filters. 
     From the above, it is seen that techniques for improving methods of manufacture and structures for acoustic resonator devices are highly desirable. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the present invention, techniques generally related to electronic devices are provided. More particularly, the present invention provides techniques related to a method of manufacture and structure for bulk acoustic wave resonator devices, single crystal resonator devices, single crystal filter and resonator devices, and the like. Merely by way of example, the invention has been applied to a single crystal resonator device for a communication device, mobile device, computing device, among others. 
     In an example the present invention provides an RF filter circuit device in a ladder configuration. The device includes a plurality of resonator devices, and a plurality of shunt configuration resonators. Each of the plurality of resonator devices includes a capacitor device including a substrate member having a cavity region and an upper surface region contiguous with a first opening of the cavity region. Each of the plurality of resonator devices also includes a bottom electrode configured within a portion of the cavity region, a piezoelectric material configured overlying the upper surface region and the bottom electrode, a top electrode configured overlying the piezoelectric material and overlying the bottom electrode, and an insulating material overlying the top electrode and configured with a thickness to tune the resonator. The plurality of resonator devices is configured in a serial configuration, while the plurality of shunt configuration resonators is configured in a parallel configuration such that one of the plurality of shunt configuration resonators is coupled to the serial configuration following each of the plurality of resonator devices. As used, the terms “top” and “bottom” are not terms in reference to a direction of gravity. Rather, these terms are used in reference to each other in context of the present device and related circuits. 
     In a specific example, the piezoelectric materials are each essentially a single crystal aluminum nitride (AlN) bearing material or aluminum scandium nitride (AlScN) bearing material, a single crystal gallium nitride (GaN) bearing material or gallium aluminum nitride (GaAlN) bearing material, or the like. In another specific embodiment, these piezoelectric materials each comprise a polycrystalline aluminum nitride (AlN) bearing material or aluminum scandium nitride (AlScN) bearing material, or a polycrystalline gallium nitride (GaN) bearing material or gallium aluminum nitride (GaAlN) bearing material, or the like. In a specific example, each of the insulating materials comprises a silicon nitride bearing material or an oxide bearing material configured with a silicon nitride material an oxide bearing material. 
     In an example the present invention provides an RF filter circuit device in a lattice configuration. The device includes a plurality of top resonator devices, a plurality of bottom resonator devices, and a plurality of shunt configuration resonators. Each of the plurality of top and bottom resonator devices includes a capacitor device including a substrate member having a cavity region and an upper surface region contiguous with a first opening of the cavity region. Each of the plurality of top and bottom resonator devices also includes a bottom electrode configured within a portion of the cavity region, a piezoelectric material configured overlying the upper surface region and the bottom electrode, a top electrode configured overlying the piezoelectric material and overlying the bottom electrode, and an insulating material overlying the top electrode and configured with a thickness to tune the resonator. The plurality of top resonator devices is configured in a top serial configuration and the plurality of bottom resonator devices is configured in a bottom serial configuration. Further, the plurality of shunt configuration resonators is configured in a cross-coupled configuration such that a pair of the plurality of shunt configuration resonators is cross-coupled between the top serial configuration and the bottom serial configuration and between one of the plurality of top resonator devices and one of the plurality of the bottom resonator devices. 
     In a specific example, the device further includes a first balun coupled to the differential input port and a second balun coupled to the differential output port. The device can further include an inductor device coupled between the differential input and output ports In a specific example, this device also includes a plurality of inductor devices, wherein the plurality of inductor devices are configured such that one of the plurality of inductor devices is coupled between the differential input port, one of the plurality of inductor devices is coupled between the differential output port, and one of the plurality of inductor devices is coupled to the top serial configuration and the bottom serial configuration between each cross-coupled pair of the plurality of shunt configuration resonators. The details described above in reference to the ladder configuration can also apply to this lattice configuration. Of course, there can be other variations, modifications, and alternatives. 
     One or more benefits are achieved over pre-existing techniques using the invention. In particular, the present device can be manufactured in a relatively simple and cost effective manner while using conventional materials and/or methods according to one of ordinary skill in the art. The present device provides an ultra-small form factor RF resonator filter with high rejection, high power rating, and low insertion loss. Such filters or resonators can be implemented in an RF filter device, an RF filter system, or the like. Depending upon the embodiment, one or more of these benefits may be achieved. 
     A further understanding of the nature and advantages of the invention may be realized by reference to the latter portions of the specification and attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more fully understand the present invention, reference is made to the accompanying drawings. Understanding that these drawings are not to be considered limitations in the scope of the invention, the presently described embodiments and the presently understood best mode of the invention are described with additional detail through use of the accompanying drawings in which: 
         FIG.  1 A  is a simplified diagram illustrating an acoustic resonator device having topside interconnections according to an example of the present invention. 
         FIG.  1 B  is a simplified diagram illustrating an acoustic resonator device having bottom-side interconnections according to an example of the present invention. 
         FIG.  1 C  is a simplified diagram illustrating an acoustic resonator device having interposer/cap-free structure interconnections according to an example of the present invention. 
         FIG.  1 D  is a simplified diagram illustrating an acoustic resonator device having interposer/cap-free structure interconnections with a shared backside trench according to an example of the present invention. 
         FIGS.  2  and  3    are simplified diagrams illustrating steps for a method of manufacture for an acoustic resonator device according to an example of the present invention. 
         FIG.  4 A  is a simplified diagram illustrating a step for a method creating a topside micro-trench according to an example of the present invention. 
         FIGS.  4 B and  4 C  are simplified diagrams illustrating alternative methods for conducting the method step of forming a topside micro-trench as described in  FIG.  4 A . 
         FIGS.  4 D and  4 E  are simplified diagrams illustrating an alternative method for conducting the method step of forming a topside micro-trench as described in  FIG.  4 A . 
         FIGS.  5  to  8    are simplified diagrams illustrating steps for a method of manufacture for an acoustic resonator device according to an example of the present invention. 
         FIG.  9 A  is a simplified diagram illustrating a method step for forming backside trenches according to an example of the present invention. 
         FIGS.  9 B and  9 C  are simplified diagrams illustrating an alternative method for conducting the method step of forming backside trenches, as described in  FIG.  9 A , and simultaneously singulating a seed substrate according to an embodiment of the present invention. 
         FIG.  10    is a simplified diagram illustrating a method step forming backside metallization and electrical interconnections between top and bottom sides of a resonator according to an example of the present invention. 
         FIGS.  11 A and  11 B  are simplified diagrams illustrating alternative steps for a method of manufacture for an acoustic resonator device according to an example of the present invention. 
         FIGS.  12 A to  12 E  are simplified diagrams illustrating steps for a method of manufacture for an acoustic resonator device using a blind via interposer according to an example of the present invention. 
         FIG.  13    is a simplified diagram illustrating a step for a method of manufacture for an acoustic resonator device according to an example of the present invention. 
         FIGS.  14 A to  14 G  are simplified diagrams illustrating method steps for a cap wafer process for an acoustic resonator device according to an example of the present invention. 
         FIGS.  15 A- 15 E  are simplified diagrams illustrating method steps for making an acoustic resonator device with shared backside trench, which can be implemented in both interposer/cap and interposer free versions, according to examples of the present invention. 
         FIGS.  16 A- 16 C  through  FIGS.  31 A- 31 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. 
         FIGS.  32 A- 32 C  through  FIGS.  46 A- 46 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a cavity bond transfer process for single crystal acoustic resonator devices according to an example of the present invention. 
         FIGS.  47 A- 47 C  though  FIGS.  59 A- 59 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a solidly mounted transfer process for single crystal acoustic resonator devices according to an example of the present invention. 
         FIG.  60    is a simplified diagram illustrating filter pass-band requirements in a radio frequency spectrum according to an example of the present invention. 
         FIG.  61    is a simplified diagram illustrating an overview of key markets that are applications for acoustic wave RF filters according to an example of the present invention. 
         FIG.  62 A- 62 G  are simplified diagrams illustrating application areas and frequency spectrums for RF filters according to examples of the present invention. 
         FIGS.  63 A- 63 C  are simplified diagrams illustrating cross-sectional views of resonator devices according to various examples of the present invention. 
         FIGS.  64 A- 64 C  are simplified circuit diagrams illustrating representative lattice and ladder configurations for acoustic filter designs according to examples of the present invention. 
         FIGS.  65 A- 65 B  are simplified diagrams illustrating packing approaches according to various examples of the present invention. 
         FIGS.  66 A- 66 B  are simplified diagrams illustrating packing approaches according to examples of the present invention. 
         FIG.  67 A  is a simplified circuit diagram illustrating a 2-port BAW RF filter circuit according to an example of the present invention. 
         FIG.  67 B  is a simplified circuit block diagram illustrating a 2-chip configuration according to an example of the present invention. 
         FIG.  67 C  is a simplified circuit diagram illustrating a 4-port BAW Triplexer circuit according to an example of the present invention. 
         FIGS.  68 A- 68 K  are simplified tables of filter parameters according to various examples of the present invention. 
         FIGS.  69 A- 69 J  are simplified graphs representing insertion loss over frequency for various RF resonator filter circuits according examples of the present invention. 
         FIGS.  70 A- 70 J  are simplified graphs representing insertion loss over frequency for various RF resonator filter circuits according examples of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the present invention, techniques generally related to electronic devices are provided. More particularly, the present invention provides techniques related to a method of manufacture and structure for bulk acoustic wave resonator devices, single crystal resonator devices, single crystal filter and resonator devices, and the like. Merely by way of example, the invention has been applied to a single crystal resonator device for a communication device, mobile device, computing device, among others. 
       FIG.  1 A  is a simplified diagram illustrating an acoustic resonator device  101  having topside interconnections according to an example of the present invention. As shown, device  101  includes a thinned seed substrate  112  with an overlying single crystal piezoelectric layer  120 , which has a micro-via  129 . The micro-via  129  can include a topside micro-trench  121 , a topside metal plug  146 , a backside trench  114 , and a backside metal plug  147 . Although device  101  is depicted with a single micro-via  129 , device  101  may have multiple micro-vias. A topside metal electrode  130  is formed overlying the piezoelectric layer  120 . A top cap structure is bonded to the piezoelectric layer  120 . This top cap structure includes an interposer substrate  119  with one or more through-vias  151  that are connected to one or more top bond pads  143 , one or more bond pads  144 , and topside metal  145  with topside metal plug  146 . Solder balls  170  are electrically coupled to the one or more top bond pads  143 . 
     The thinned substrate  112  has the first and second backside trenches  113 ,  114 . A backside metal electrode  131  is formed underlying a portion of the thinned seed substrate  112 , the first backside trench  113 , and the topside metal electrode  130 . The backside metal plug  147  is formed underlying a portion of the thinned seed substrate  112 , the second backside trench  114 , and the topside metal  145 . This backside metal plug  147  is electrically coupled to the topside metal plug  146  and the backside metal electrode  131 . A backside cap structure  161  is bonded to the thinned seed substrate  112 , underlying the first and second backside trenches  113 ,  114 . Further details relating to the method of manufacture of this device will be discussed starting from  FIG.  2   . 
       FIG.  1 B  is a simplified diagram illustrating an acoustic resonator device  102  having backside interconnections according to an example of the present invention. As shown, device  101  includes a thinned seed substrate  112  with an overlying piezoelectric layer  120 , which has a micro-via  129 . The micro-via  129  can include a topside micro-trench  121 , a topside metal plug  146 , a backside trench  114 , and a backside metal plug  147 . Although device  102  is depicted with a single micro-via  129 , device  102  may have multiple micro-vias. A topside metal electrode  130  is formed overlying the piezoelectric layer  120 . A top cap structure is bonded to the piezoelectric layer  120 . This top cap structure  119  includes bond pads which are connected to one or more bond pads  144  and topside metal  145  on piezoelectric layer  120 . The topside metal  145  includes a topside metal plug  146 . 
     The thinned substrate  112  has the first and second backside trenches  113 ,  114 . A backside metal electrode  131  is formed underlying a portion of the thinned seed substrate  112 , the first backside trench  113 , and the topside metal electrode  130 . A backside metal plug  147  is formed underlying a portion of the thinned seed substrate  112 , the second backside trench  114 , and the topside metal plug  146 . This backside metal plug  147  is electrically coupled to the topside metal plug  146 . A backside cap structure  162  is bonded to the thinned seed substrate  112 , underlying the first and second backside trenches. One or more backside bond pads ( 171 ,  172 , and  173 ) are formed within one or more portions of the backside cap structure  162 . Solder balls  170  are electrically coupled to the one or more backside bond pads  171 - 173 . Further details relating to the method of manufacture of this device will be discussed starting from  FIG.  14 A . 
       FIG.  1 C  is a simplified diagram illustrating an acoustic resonator device having interposer/cap-free structure interconnections according to an example of the present invention. As shown, device  103  includes a thinned seed substrate  112  with an overlying single crystal piezoelectric layer  120 , which has a micro-via  129 . The micro-via  129  can include a topside micro-trench  121 , a topside metal plug  146 , a backside trench  114 , and a backside metal plug  147 . Although device  103  is depicted with a single micro-via  129 , device  103  may have multiple micro-vias. A topside metal electrode  130  is formed overlying the piezoelectric layer  120 . The thinned substrate  112  has the first and second backside trenches  113 ,  114 . A backside metal electrode  131  is formed underlying a portion of the thinned seed substrate  112 , the first backside trench  113 , and the topside metal electrode  130 . A backside metal plug  147  is formed underlying a portion of the thinned seed substrate  112 , the second backside trench  114 , and the topside metal  145 . This backside metal plug  147  is electrically coupled to the topside metal plug  146  and the backside metal electrode  131 . Further details relating to the method of manufacture of this device will be discussed starting from  FIG.  2   . 
       FIG.  1 D  is a simplified diagram illustrating an acoustic resonator device having interposer/cap-free structure interconnections with a shared backside trench according to an example of the present invention. As shown, device  104  includes a thinned seed substrate  112  with an overlying single crystal piezoelectric layer  120 , which has a micro-via  129 . The micro-via  129  can include a topside micro-trench  121 , a topside metal plug  146 , and a backside metal  147 . Although device  104  is depicted with a single micro-via  129 , device  104  may have multiple micro-vias. A topside metal electrode  130  is formed overlying the piezoelectric layer  120 . The thinned substrate  112  has a first backside trench  113 . A backside metal electrode  131  is formed underlying a portion of the thinned seed substrate  112 , the first backside trench  113 , and the topside metal electrode  130 . A backside metal  147  is formed underlying a portion of the thinned seed substrate  112 , the second backside trench  114 , and the topside metal  145 . This backside metal  147  is electrically coupled to the topside metal plug  146  and the backside metal electrode  131 . Further details relating to the method of manufacture of this device will be discussed starting from  FIG.  2   . 
       FIGS.  2  and  3    are simplified diagrams illustrating steps for a method of manufacture for an acoustic resonator device according to an example of the present invention. This method illustrates the process for fabricating an acoustic resonator device similar to that shown in  FIG.  1 A .  FIG.  2    can represent a method step of providing a partially processed piezoelectric substrate. As shown, device  102  includes a seed substrate  110  with a piezoelectric layer  120  formed overlying. In a specific example, the seed substrate can include silicon, silicon carbide, aluminum oxide, or single crystal aluminum gallium nitride materials, or the like. The piezoelectric layer  120  can include a piezoelectric single crystal layer or a thin film piezoelectric single crystal layer. 
       FIG.  3    can represent a method step of forming a top side metallization or top resonator metal electrode  130 . In a specific example, the topside metal electrode  130  can include a molybdenum, aluminum, ruthenium, or titanium material, or the like and combinations thereof. This layer can be deposited and patterned on top of the piezoelectric layer by a lift-off process, a wet etching process, a dry etching process, a metal printing process, a metal laminating process, or the like. The lift-off process can include a sequential process of lithographic patterning, metal deposition, and lift-off steps to produce the topside metal layer. The wet/dry etching processes can includes sequential processes of metal deposition, lithographic patterning, metal deposition, and metal etching steps to produce the topside metal layer. Those of ordinary skill in the art will recognize other variations, modifications, and alternatives. 
       FIG.  4 A  is a simplified diagram illustrating a step for a method of manufacture for an acoustic resonator device  401  according to an example of the present invention. This figure can represent a method step of forming one or more topside micro-trenches  121  within a portion of the piezoelectric layer  120 . This topside micro-trench  121  can serve as the main interconnect junction between the top and bottom sides of the acoustic membrane, which will be developed in later method steps. In an example, the topside micro-trench  121  is extends all the way through the piezoelectric layer  120  and stops in the seed substrate  110 . This topside micro-trench  121  can be formed through a dry etching process, a laser drilling process, or the like.  FIGS.  4 B and  4 C  describe these options in more detail. 
       FIGS.  4 B and  4 C  are simplified diagrams illustrating alternative methods for conducting the method step as described in  FIG.  4 A . As shown,  FIG.  4 B  represents a method step of using a laser drill, which can quickly and accurately form the topside micro-trench  121  in the piezoelectric layer  120 . In an example, the laser drill can be used to form nominal 50 um holes or holes between 10 um and 500 um in diameter, through the piezoelectric layer  120  and stop in the seed substrate  110  below the interface between layers  120  and  110 . A protective layer  122  can be formed overlying the piezoelectric layer  120  and the topside metal electrode  130 . This protective layer  122  can serve to protect the device from laser debris and to provide a mask for the etching of the topside micro-via  121 . In a specific example, the laser drill can be an  11 W high power diode-pumped UV laser, or the like. This mask  122  can be subsequently removed before proceeding to other steps. The mask may also be omitted from the laser drilling process, and air flow can be used to remove laser debris. 
       FIG.  4 C  can represent a method step of using a dry etching process to form the topside micro-trench  121  in the piezoelectric layer  120 . As shown, a lithographic masking layer  123  can be forming overlying the piezoelectric layer  120  and the topside metal electrode  130 . The topside micro-trench  121  can be formed by exposure to plasma, or the like. 
       FIGS.  4 D and  4 E  are simplified diagrams illustrating an alternative method for conducting the method step as described in  FIG.  4 A . These figures can represent the method step of manufacturing multiple acoustic resonator devices simultaneously. In  FIG.  4 D , two devices are shown on Die #1 and Die #2, respectively.  FIG.  4 E  shows the process of forming a micro-via  121  on each of these dies while also etching a scribe line  124  or dicing line. In an example, the etching of the scribe line  124  singulates and relieves stress in the piezoelectric single crystal layer  120 . 
       FIGS.  5  to  8    are simplified diagrams illustrating steps for a method of manufacture for an acoustic resonator device according to an example of the present invention.  FIG.  5    can represent the method step of forming one or more bond pads  140  and forming a topside metal  141  electrically coupled to at least one of the bond pads  140 . The topside metal  141  can include a topside metal plug  146  formed within the topside micro-trench  121 . In a specific example, the topside metal plug  146  fills the topside micro-trench  121  to form a topside portion of a micro-via. 
     In an example, the bond pads  140  and the topside metal  141  can include a gold material or other interconnect metal material depending upon the application of the device. These metal materials can be formed by a lift-off process, a wet etching process, a dry etching process, a screen-printing process, an electroplating process, a metal printing process, or the like. In a specific example, the deposited metal materials can also serve as bond pads for a cap structure, which will be described below. 
       FIG.  6    can represent a method step for preparing the acoustic resonator device for bonding, which can be a hermetic bonding. As shown, a top cap structure is positioned above the partially processed acoustic resonator device as described in the previous figures. The top cap structure can be formed using an interposer substrate  119  in two configurations: fully processed interposer version  601  (through glass via) and partially processed interposer version  602  (blind via version). In the  601  version, the interposer substrate  119  includes through-via structures  151  that extend through the interposer substrate  119  and are electrically coupled to bottom bond pads  142  and top bond pads  143 . In the  602  version, the interposer substrate  119  includes blind via structures  152  that only extend through a portion of the interposer substrate  119  from the bottom side. These blind via structures  152  are also electrically coupled to bottom bond pads  142 . In a specific example, the interposer substrate can include a silicon, glass, smart-glass, or other like material. 
       FIG.  7    can represent a method step of bonding the top cap structure to the partially processed acoustic resonator device. As shown, the interposer substrate  119  is bonded to the piezoelectric layer by the bond pads ( 140 ,  142 ) and the topside metal  141 , which are now denoted as bond pad  144  and topside metal  145 . This bonding process can be done using a compression bond method or the like.  FIG.  8    can represent a method step of thinning the seed substrate  110 , which is now denoted as thinned seed substrate  111 . This substrate thinning process can include grinding and etching processes or the like. In a specific example, this process can include a wafer backgrinding process followed by stress removal, which can involve dry etching, CMP polishing, or annealing processes. 
       FIG.  9 A  is a simplified diagram illustrating a step for a method of manufacture for an acoustic resonator device  901  according to an example of the present invention.  FIG.  9 A  can represent a method step for forming backside trenches  113  and  114  to allow access to the piezoelectric layer from the backside of the thinned seed substrate  111 . In an example, the first backside trench  113  can be formed within the thinned seed substrate  111  and underlying the topside metal electrode  130 . The second backside trench  114  can be formed within the thinned seed substrate  111  and underlying the topside micro-trench  121  and topside metal plug  146 . This substrate is now denoted thinned substrate  112 . In a specific example, these trenches  113  and  114  can be formed using deep reactive ion etching (DRIE) processes, Bosch processes, or the like. The size, shape, and number of the trenches may vary with the design of the acoustic resonator device. In various examples, the first backside trench may be formed with a trench shape similar to a shape of the topside metal electrode or a shape of the backside metal electrode. The first backside trench may also be formed with a trench shape that is different from both a shape of the topside metal electrode and the backside metal electrode. 
       FIGS.  9 B and  9 C  are simplified diagrams illustrating an alternative method for conducting the method step as described in  FIG.  9 A . Like  FIGS.  4 D and  4 E , these figures can represent the method step of manufacturing multiple acoustic resonator devices simultaneously. In  FIG.  9 B , two devices with cap structures are shown on Die #1 and Die #2, respectively.  FIG.  9 C  shows the process of forming backside trenches ( 113 ,  114 ) on each of these dies while also etching a scribe line  115  or dicing line. In an example, the etching of the scribe line  115  provides an optional way to singulate the backside wafer  112 . 
       FIG.  10    is a simplified diagram illustrating a step for a method of manufacture for an acoustic resonator device  1000  according to an example of the present invention. This figure can represent a method step of forming a backside metal electrode  131  and a backside metal plug  147  within the backside trenches of the thinned seed substrate  112 . In an example, the backside metal electrode  131  can be formed underlying one or more portions of the thinned substrate  112 , within the first backside trench  113 , and underlying the topside metal electrode  130 . This process completes the resonator structure within the acoustic resonator device. The backside metal plug  147  can be formed underlying one or more portions of the thinned substrate  112 , within the second backside trench  114 , and underlying the topside micro-trench  121 . The backside metal plug  147  can be electrically coupled to the topside metal plug  146  and the backside metal electrode  131 . In a specific example, the backside metal electrode  130  can include a molybdenum, aluminum, ruthenium, or titanium material, or the like and combinations thereof. The backside metal plug can include a gold material, low resistivity interconnect metals, electrode metals, or the like. These layers can be deposited using the deposition methods described previously. 
       FIGS.  11 A and  11 B  are simplified diagrams illustrating alternative steps for a method of manufacture for an acoustic resonator device according to an example of the present invention. These figures show methods of bonding a backside cap structure underlying the thinned seed substrate  112 . In  FIG.  11 A , the backside cap structure is a dry film cap  161 , which can include a permanent photo-imageable dry film such as a solder mask, polyimide, or the like. Bonding this cap structure can be cost-effective and reliable, but may not produce a hermetic seal. In  FIG.  11 B , the backside cap structure is a substrate  162 , which can include a silicon, glass, or other like material. Bonding this substrate can provide a hermetic seal, but may cost more and require additional processes. Depending upon application, either of these backside cap structures can be bonded underlying the first and second backside vias. 
       FIGS.  12 A to  12 E  are simplified diagrams illustrating steps for a method of manufacture for an acoustic resonator device according to an example of the present invention. More specifically, these figures describe additional steps for processing the blind via interposer “ 602 ” version of the top cap structure.  FIG.  12 A  shows an acoustic resonator device  1201  with blind vias  152  in the top cap structure. In  FIG.  12 B , the interposer substrate  119  is thinned, which forms a thinned interposer substrate  118 , to expose the blind vias  152 . This thinning process can be a combination of a grinding process and etching process as described for the thinning of the seed substrate. In  FIG.  12 C , a redistribution layer (RDL) process and metallization process can be applied to create top cap bond pads  160  that are formed overlying the blind vias  152  and are electrically coupled to the blind vias  152 . As shown in  FIG.  12 D , a ball grid array (BGA) process can be applied to form solder balls  170  overlying and electrically coupled to the top cap bond pads  160 . This process leaves the acoustic resonator device ready for wire bonding  171 , as shown in  FIG.  12 E . 
       FIG.  13    is a simplified diagram illustrating a step for a method of manufacture for an acoustic resonator device according to an example of the present invention. As shown, device  1300  includes two fully processed acoustic resonator devices that are ready to singulation to create separate devices. In an example, the die singulation process can be done using a wafer dicing saw process, a laser cut singulation process, or other processes and combinations thereof. 
       FIGS.  14 A to  14 G  are simplified diagrams illustrating steps for a method of manufacture for an acoustic resonator device according to an example of the present invention. This method illustrates the process for fabricating an acoustic resonator device similar to that shown in  FIG.  1 B . The method for this example of an acoustic resonator can go through similar steps as described in  FIGS.  1 - 5   .  FIG.  14 A  shows where this method differs from that described previously. Here, the top cap structure substrate  119  and only includes one layer of metallization with one or more bottom bond pads  142 . Compared to  FIG.  6   , there are no via structures in the top cap structure because the interconnections will be formed on the bottom side of the acoustic resonator device. 
       FIGS.  14 B to  14 F  depict method steps similar to those described in the first process flow.  FIG.  14 B  can represent a method step of bonding the top cap structure to the piezoelectric layer  120  through the bond pads ( 140 ,  142 ) and the topside metal  141 , now denoted as bond pads  144  and topside metal  145  with topside metal plug  146 .  FIG.  14 C  can represent a method step of thinning the seed substrate  110 , which forms a thinned seed substrate  111 , similar to that described in  FIG.  8   .  FIG.  14 D  can represent a method step of forming first and second backside trenches, similar to that described in  FIG.  9 A .  FIG.  14 E  can represent a method step of forming a backside metal electrode  131  and a backside metal plug  147 , similar to that described in  FIG.  10   .  FIG.  14 F  can represent a method step of bonding a backside cap structure  162 , similar to that described in  FIGS.  11 A and  11 B . 
       FIG.  14 G  shows another step that differs from the previously described process flow. Here, the backside bond pads  171 ,  172 , and  173  are formed within the backside cap structure  162 . In an example, these backside bond pads  171 - 173  can be formed through a masking, etching, and metal deposition processes similar to those used to form the other metal materials. A BGA process can be applied to form solder balls  170  in contact with these backside bond pads  171 - 173 , which prepares the acoustic resonator device  1407  for wire bonding. 
       FIGS.  15 A to  15 E  are simplified diagrams illustrating steps for a method of manufacture for an acoustic resonator device according to an example of the present invention. This method illustrates the process for fabricating an acoustic resonator device similar to that shown in  FIG.  1 B . The method for this example can go through similar steps as described in  FIG.  1 - 5   .  FIG.  15 A  shows where this method differs from that described previously. A temporary carrier  218  with a layer of temporary adhesive  217  is attached to the substrate. In a specific example, the temporary carrier  218  can include a glass wafer, a silicon wafer, or other wafer and the like. 
       FIGS.  15 B to  15 F  depict method steps similar to those described in the first process flow.  FIG.  15 B  can represent a method step of thinning the seed substrate  110 , which forms a thinned substrate  111 , similar to that described in  FIG.  8   . In a specific example, the thinning of the seed substrate  110  can include a back side grinding process followed by a stress removal process. The stress removal process can include a dry etch, a Chemical Mechanical Planarization (CMP), and annealing processes. 
       FIG.  15 C  can represent a method step of forming a shared backside trench  113 , similar to the techniques described in  FIG.  9 A . The main difference is that the shared backside trench is configured underlying both topside metal electrode  130 , topside micro-trench  121 , and topside metal plug  146 . In an example, the shared backside trench  113  is a backside resonator cavity that can vary in size, shape (all possible geometric shapes), and side wall profile (tapered convex, tapered concave, or right angle). In a specific example, the forming of the shared backside trench  113  can include a litho-etch process, which can include a back-to-front alignment and dry etch of the backside substrate  111 . The piezoelectric layer  120  can serve as an etch stop layer for the forming of the shared backside trench  113 . 
       FIG.  15 D  can represent a method step of forming a backside metal electrode  131  and a backside metal  147 , similar to that described in  FIG.  10   . In an example, the forming of the backside metal electrode  131  can include a deposition and patterning of metal materials within the shared backside trench  113 . Here, the backside metal  131  serves as an electrode and the backside plug/connect metal  147  within the micro-via  121 . The thickness, shape, and type of metal can vary as a function of the resonator/filter design. As an example, the backside electrode  131  and via plug metal  147  can be different metals. In a specific example, these backside metals  131 ,  147  can either be deposited and patterned on the surface of the piezoelectric layer  120  or rerouted to the backside of the substrate  112 . In an example, the backside metal electrode may be patterned such that it is configured within the boundaries of the shared backside trench such that the backside metal electrode does not come in contact with one or more side-walls of the seed substrate created during the forming of the shared backside trench. 
       FIG.  15 E  can represent a method step of bonding a backside cap structure  162 , similar to that described in  FIGS.  11 A and  11 B , following a de-bonding of the temporary carrier  218  and cleaning of the topside of the device to remove the temporary adhesive  217 . Those of ordinary skill in the art will recognize other variations, modifications, and alternatives of the methods steps described previously. 
     As used herein, the term “substrate” can mean the bulk substrate or can include overlying growth structures such as an aluminum, gallium, or ternary compound of aluminum and gallium and nitrogen containing epitaxial region, or functional regions, combinations, and the like. 
     One or more benefits are achieved over pre-existing techniques using the invention. In particular, the present device can be manufactured in a relatively simple and cost effective manner while using conventional materials and/or methods according to one of ordinary skill in the art. Using the present method, one can create a reliable single crystal based acoustic resonator using multiple ways of three-dimensional stacking through a wafer level process. Such filters or resonators can be implemented in an RF filter device, an RF filter system, or the like. Depending upon the embodiment, one or more of these benefits may be achieved. Of course, there can be other variations, modifications, and alternatives. 
     With 4G LTE and 5G growing more popular by the day, wireless data communication demands high performance RF filters with frequencies around 5 GHz and higher. Bulk acoustic wave resonators (BAWR), widely used in such filters operating at frequencies around 3 GHz and lower, are leading candidates for meeting such demands. Current bulk acoustic wave resonators use polycrystalline piezoelectric AlN thin films where each grain&#39;s c-axis is aligned perpendicular to the film&#39;s surface to allow high piezoelectric performance whereas the grains&#39; a- or b-axis are randomly distributed. This peculiar grain distribution works well when the piezoelectric film&#39;s thickness is around 1 um and above, which is the perfect thickness for bulk acoustic wave (BAW) filters operating at frequencies ranging from 1 to 3 GHz. However, the quality of the polycrystalline piezoelectric films degrades quickly as the thicknesses decrease below around 0.5 um, which is required for resonators and filters operating at frequencies around 5 GHz and above. 
     Single crystalline or epitaxial piezoelectric thin films grown on compatible crystalline substrates exhibit good crystalline quality and high piezoelectric performance even down to very thin thicknesses, e.g., 0.4 um. The present invention provides manufacturing processes and structures for high quality bulk acoustic wave resonators with single crystalline or epitaxial piezoelectric thin films for high frequency BAW filter applications. 
     BAWRs require a piezoelectric material, e.g., AlN, in crystalline form, i.e., polycrystalline or single crystalline. The quality of the film heavy depends on the chemical, crystalline, or topographical quality of the layer on which the film is grown. In conventional BAWR processes (including film bulk acoustic resonator (FBAR) or solidly mounted resonator (SMR) geometry), the piezoelectric film is grown on a patterned bottom electrode, which is usually made of molybdenum (Mo), tungsten (W), or ruthenium (Ru). The surface geometry of the patterned bottom electrode significantly influences the crystalline orientation and crystalline quality of the piezoelectric film, requiring complicated modification of the structure. 
     Thus, the present invention uses single crystalline piezoelectric films and thin film transfer processes to produce a BAWR with enhanced ultimate quality factor and electro-mechanical coupling for RF filters. Such methods and structures facilitate methods of manufacturing and structures for RF filters using single crystalline or epitaxial piezoelectric films to meet the growing demands of contemporary data communication. 
     In an example, the present invention provides transfer structures and processes for acoustic resonator devices, which provides a flat, high-quality, single-crystal piezoelectric film for superior acoustic wave control and high Q in high frequency. As described above, polycrystalline piezoelectric layers limit Q in high frequency. Also, growing epitaxial piezoelectric layers on patterned electrodes affects the crystalline orientation of the piezoelectric layer, which limits the ability to have tight boundary control of the resulting resonators. 
     Embodiments of the present invention, as further described below, can overcome these limitations and exhibit improved performance and cost-efficiency. 
       FIGS.  16 A- 16 C  through  FIGS.  31 A- 31 C  illustrate a method of fabrication for an acoustic resonator device using a transfer structure with a sacrificial layer. In these figure series described below, the “A” figures show simplified diagrams illustrating top cross-sectional views of single crystal resonator devices according to various embodiments of the present invention. The “B” figures show simplified diagrams illustrating lengthwise cross-sectional views of the same devices in the “A” figures. Similarly, the “C” figures show simplified diagrams illustrating widthwise cross-sectional views of the same devices in the “A” figures. In some cases, certain features are omitted to highlight other features and the relationships between such features. Those of ordinary skill in the art will recognize variations, modifications, and alternatives to the examples shown in these figure series. 
       FIGS.  16 A- 16 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a piezoelectric film  1620  overlying a growth substrate  1610 . In an example, the growth substrate  1610  can include silicon (S), silicon carbide (SiC), or other like materials. The piezoelectric film  1620  can be an epitaxial film including aluminum nitride (AlN), gallium nitride (GaN), or other like materials. Additionally, this piezoelectric substrate can be subjected to a thickness trim. 
       FIGS.  17 A- 17 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a first electrode  1710  overlying the surface region of the piezoelectric film  1620 . In an example, the first electrode  1710  can include molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials. In a specific example, the first electrode  1710  can be subjected to a dry etch with a slope. As an example, the slope can be about 60 degrees. 
       FIGS.  18 A- 18 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a first passivation layer  1810  overlying the first electrode  1710  and the piezoelectric film  1620 . In an example, the first passivation layer  1810  can include silicon nitride (SiN), silicon oxide (SiO), or other like materials. In a specific example, the first passivation layer  1810  can have a thickness ranging from about 50 nm to about 100 nm. 
       FIGS.  19 A- 19 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a sacrificial layer  1910  overlying a portion of the first electrode  1810  and a portion of the piezoelectric film  1620 . In an example, the sacrificial layer  1910  can include polycrystalline silicon (poly-Si), amorphous silicon (a-Si), or other like materials. In a specific example, this sacrificial layer  1910  can be subjected to a dry etch with a slope and be deposited with a thickness of about 1 um. Further, phosphorous doped SiO 2  (PSG) can be used as the sacrificial layer with different combinations of support layer (e.g., SiN). 
       FIGS.  20 A- 20 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a support layer  2010  overlying the sacrificial layer  1910 , the first electrode  1710 , and the piezoelectric film  1620 . As shown in  FIG.  20 B , portions of a surface of support member  2010  define a cavity region  90  within which at least a portion of first electrode  1710  is located. In an example, the support layer  2010  can include silicon dioxide (SiO2), silicon nitride (SiN), or other like materials. In a specific example, this support layer  2010  can be deposited with a thickness of about 2-3 um. As described above, other support layers (e.g., SiNx) can be used in the case of a PSG sacrificial layer. 
       FIGS.  21 A- 21 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of polishing the support layer  2010  to form a polished support layer  2011 . In an example, the polishing process can include a chemical-mechanical planarization process or the like. 
       FIGS.  22 A- 22 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate flipping the device and physically coupling overlying the support layer  2011  overlying a bond substrate  2210 . In an example, the bond substrate  2210  can include a bonding support layer  2220  (SiO 2  or like material) overlying a substrate having silicon (Si), sapphire (Al 2 O 3 ), silicon dioxide (SiO 2 ), silicon carbide (SiC), or other like materials. In a specific embodiment, the bonding support layer  2220  of the bond substrate  2210  is physically coupled to the polished support layer  2011 . Further, the physical coupling process can include a room temperature bonding process following by a 300 degree Celsius annealing process. 
       FIGS.  23 A- 23 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of removing the growth substrate  1610  or otherwise the transfer of the piezoelectric film  1620 . In an example, the removal process can include a grinding process, a blanket etching process, a film transfer process, an ion implantation transfer process, a laser crack transfer process, or the like and combinations thereof. 
       FIGS.  24 A- 24 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming an electrode contact via  2410  within the piezoelectric film  1620  (becoming piezoelectric film  1621 ) overlying the first electrode  1710  and forming one or more release holes  2420  within the piezoelectric film  1620  and the first passivation layer  1810  overlying the sacrificial layer  1910 . The via forming processes can include various types of etching processes. 
       FIGS.  25 A- 25 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a second electrode  2510  overlying the piezoelectric film  1621 . In an example, the formation of the second electrode  2510  includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching the second electrode  2510  to form an electrode cavity  2511  and to remove portion  2511  from the second electrode to form a top metal  2520 . Further, the top metal  2520  is physically coupled to the first electrode  1720  through electrode contact via  2410 . 
       FIGS.  26 A- 26 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a first contact metal  2610  overlying a portion of the second electrode  2510  and a portion of the piezoelectric film  1621 , and forming a second contact metal  2611  overlying a portion of the top metal  2520  and a portion of the piezoelectric film  1621 . In an example, the first and second contact metals can include gold (Au), aluminum (Al), copper (Cu), nickel (Ni), aluminum bronze (AlCu), or related alloys of these materials or other like materials. 
       FIGS.  27 A- 27 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a second passivation layer  2710  overlying the second electrode  2510 , the top metal  2520 , and the piezoelectric film  1621 . In an example, the second passivation layer  2710  can include silicon nitride (SiN), silicon oxide (SiO), or other like materials. In a specific example, the second passivation layer  2710  can have a thickness ranging from about 50 nm to about 100 nm. 
       FIGS.  28 A- 28 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of removing the sacrificial layer  1910  to form an air cavity  2810 . In an example, the removal process can include a poly-Si etch or an a-Si etch, or the like. Portions of the support member  2011  surface define cavity region  90  within which at least a portion of first electrode  1710  is located. As shown in  FIG.  28 B , first electrode  1710  is located in cavity region  90  such that the surface of the support member  2011  defining cavity region  90  is contiguous with an upper surface of the electrode  1710 . First passivation layer  1810  when present can be considered as a portion of support member  5011 . 
       FIGS.  29 A- 29 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the second electrode  2510  and the top metal  2520  to form a processed second electrode  2910  and a processed top metal  2920 . This step can follow the formation of second electrode  2510  and top metal  2520 . In an example, the processing of these two components includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching (e.g., dry etch or the like) this material to form the processed second electrode  2910  with an electrode cavity  2912  and the processed top metal  2920 . The processed top metal  2920  remains separated from the processed second electrode  2910  by the removal of portion  2911 . In a specific example, the processed second electrode  2910  is characterized by the addition of an energy confinement structure configured on the processed second electrode  2910  to increase Q. As shown in  FIG.  29 B , portions of the support member  2011  surface define cavity region  90  within which at least a portion of first electrode  1710  is located. 
       FIGS.  30 A- 30 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the first electrode  1710  to form a processed first electrode  2310 . This step can follow the formation of first electrode  1710 . In an example, the processing of these two components includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching (e.g., dry etch or the like) this material to form the processed first electrode  3010  with an electrode cavity, similar to the processed second electrode  2910 . Air cavity  2811  shows the change in cavity shape due to the processed first electrode  3010 . In a specific example, the processed first electrode  3010  is characterized by the addition of an energy confinement structure configured on the processed second electrode  3010  to increase Q. As shown in  FIG.  30 B , portions of the support member  2012  surface define cavity region  90  within which at least a portion of first electrode  3010  is located. 
       FIGS.  31 A- 31 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the first electrode  1710 , to form a processed first electrode  3010 , and the second electrode  2510 /top metal  2520  to form a processed second electrode  2910 /processed top metal  2920 .  FIG.  31 B  shows portions of the support member  2012  surface defining cavity region  90  within which at least a portion of first electrode  3010  is located. These steps can follow the formation of each respective electrode, as described for  FIGS.  29 A- 29 C and  30 A- 30 C . Those of ordinary skill in the art will recognize other variations, modifications, and alternatives. 
       FIGS.  32 A- 32 C  through  FIGS.  46 A- 46 C  illustrate a method of fabrication for an acoustic resonator device using a transfer structure without sacrificial layer. In these figure series described below, the “A” figures show simplified diagrams illustrating top cross-sectional views of single crystal resonator devices according to various embodiments of the present invention. The “B” figures show simplified diagrams illustrating lengthwise cross-sectional views of the same devices in the “A” figures. Similarly, the “C” figures show simplified diagrams illustrating widthwise cross-sectional views of the same devices in the “A” figures. In some cases, certain features are omitted to highlight other features and the relationships between such features. Those of ordinary skill in the art will recognize variations, modifications, and alternatives to the examples shown in these figure series. 
       FIGS.  32 A- 32 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a piezoelectric film  3220  overlying a growth substrate  3210 . In an example, the growth substrate  3210  can include silicon (S), silicon carbide (SiC), or other like materials. The piezoelectric film  3220  can be an epitaxial film including aluminum nitride (AlN), gallium nitride (GaN), or other like materials. Additionally, this piezoelectric substrate can be subjected to a thickness trim. 
       FIGS.  33 A- 33 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a first electrode  3310  overlying the surface region of the piezoelectric film  3220 . In an example, the first electrode  3310  can include molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials. In a specific example, the first electrode  3310  can be subjected to a dry etch with a slope. As an example, the slope can be about 60 degrees. 
       FIGS.  34 A- 34 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a first passivation layer  3410  overlying the first electrode  3310  and the piezoelectric film  3220 . In an example, the first passivation layer  3410  can include silicon nitride (SiN), silicon oxide (SiO), or other like materials. In a specific example, the first passivation layer  3410  can have a thickness ranging from about 50 nm to about 100 nm. 
       FIGS.  35 A- 35 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a support layer  3510  overlying the first electrode  3310 , and the piezoelectric film  3220 . In an example, the support layer  3510  can include silicon dioxide (SiO 2 ), silicon nitride (SiN), or other like materials. In a specific example, this support layer  3510  can be deposited with a thickness of about 2-3 um. As described above, other support layers (e.g., SiN) can be used in the case of a PSG sacrificial layer. 
       FIGS.  36 A- 36 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the optional method step of processing the support layer  3510  (to form support layer  3511 ) in region  3610 . In an example, the processing can include a partial etch of the support layer  3510  to create a flat bond surface. In a specific example, the processing can include a cavity region. In other examples, this step can be replaced with a polishing process such as a chemical-mechanical planarization process or the like. 
       FIGS.  37 A- 37 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming an air cavity  3710  within a portion of the support layer  3511  (to form support layer  3512 ). In an example, the cavity formation can include an etching process that stops at the first passivation layer  3410 . 
       FIGS.  38 A- 38 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming one or more cavity vent holes  3810  within a portion of the piezoelectric film  3220  through the first passivation layer  3410 . In an example, the cavity vent holes  3810  connect to the air cavity  3710 . 
       FIGS.  39 A- 39 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate flipping the device and physically coupling overlying the support layer  3512  overlying a bond substrate  3910 . In an example, the bond substrate  3910  can include a bonding support layer  3920  (SiO 2  or like material) overlying a substrate having silicon (Si), sapphire (Al 2 O 3 ), silicon dioxide (SiO 2 ), silicon carbide (SiC), or other like materials. In a specific embodiment, the bonding support layer  3920  of the bond substrate  3910  is physically coupled to the polished support layer  3512 . Further, the physical coupling process can include a room temperature bonding process following by a 300 degree Celsius annealing process. 
       FIGS.  40 A- 40 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of removing the growth substrate  3210  or otherwise the transfer of the piezoelectric film  3220 . In an example, the removal process can include a grinding process, a blanket etching process, a film transfer process, an ion implantation transfer process, a laser crack transfer process, or the like and combinations thereof. 
       FIGS.  41 A- 41 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming an electrode contact via  4110  within the piezoelectric film  3220  overlying the first electrode  3310 . The via forming processes can include various types of etching processes. 
       FIGS.  42 A- 42 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a second electrode  4210  overlying the piezoelectric film  3220 . In an example, the formation of the second electrode  4210  includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching the second electrode  4210  to form an electrode cavity  4211  and to remove portion  4211  from the second electrode to form a top metal  4220 . Further, the top metal  4220  is physically coupled to the first electrode  3310  through electrode contact via  4110 . 
       FIGS.  43 A- 43 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a first contact metal  4310  overlying a portion of the second electrode  4210  and a portion of the piezoelectric film  3220 , and forming a second contact metal  4311  overlying a portion of the top metal  4220  and a portion of the piezoelectric film  3220 . In an example, the first and second contact metals can include gold (Au), aluminum (Al), copper (Cu), nickel (Ni), aluminum bronze (AlCu), or other like materials. This figure also shows the method step of forming a second passivation layer  4320  overlying the second electrode  4210 , the top metal  4220 , and the piezoelectric film  3220 . In an example, the second passivation layer  4320  can include silicon nitride (SiN), silicon oxide (SiO), or other like materials. In a specific example, the second passivation layer  4320  can have a thickness ranging from about 50 nm to about 100 nm. 
       FIGS.  44 A- 44 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the second electrode  4210  and the top metal  4220  to form a processed second electrode  4410  and a processed top metal  4420 . This step can follow the formation of second electrode  4210  and top metal  4220 . In an example, the processing of these two components includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching (e.g., dry etch or the like) this material to form the processed second electrode  4410  with an electrode cavity  4412  and the processed top metal  4420 . The processed top metal  4420  remains separated from the processed second electrode  4410  by the removal of portion  4411 . In a specific example, the processed second electrode  4410  is characterized by the addition of an energy confinement structure configured on the processed second electrode  4410  to increase Q. 
       FIGS.  45 A- 45 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the first electrode  3310  to form a processed first electrode  4510 . This step can follow the formation of first electrode  3310 . In an example, the processing of these two components includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching (e.g., dry etch or the like) this material to form the processed first electrode  4510  with an electrode cavity, similar to the processed second electrode  4410 . Air cavity  3711  shows the change in cavity shape due to the processed first electrode  4510 . In a specific example, the processed first electrode  4510  is characterized by the addition of an energy confinement structure configured on the processed second electrode  4510  to increase Q. 
       FIGS.  46 A- 46 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process using a sacrificial layer for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the first electrode  3310 , to form a processed first electrode  4510 , and the second electrode  4210 /top metal  4220  to form a processed second electrode  4410 /processed top metal  4420 . These steps can follow the formation of each respective electrode, as described for  FIGS.  44 A- 44 C and  45 A- 45 C . Those of ordinary skill in the art will recognize other variations, modifications, and alternatives. 
       FIGS.  47 A- 47 C  through  FIGS.  59 A- 59 C  illustrate a method of fabrication for an acoustic resonator device using a transfer structure with a multilayer mirror structure. In these figure series described below, the “A” figures show simplified diagrams illustrating top cross-sectional views of single crystal resonator devices according to various embodiments of the present invention. The “B” figures show simplified diagrams illustrating lengthwise cross-sectional views of the same devices in the “A” figures. Similarly, the “C” figures show simplified diagrams illustrating widthwise cross-sectional views of the same devices in the “A” figures. In some cases, certain features are omitted to highlight other features and the relationships between such features. Those of ordinary skill in the art will recognize variations, modifications, and alternatives to the examples shown in these figure series. 
       FIGS.  47 A- 47 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a piezoelectric film  4720  overlying a growth substrate  4710 . In an example, the growth substrate  4710  can include silicon (S), silicon carbide (SiC), or other like materials. The piezoelectric film  4720  can be an epitaxial film including aluminum nitride (AlN), gallium nitride (GaN), or other like materials. Additionally, this piezoelectric substrate can be subjected to a thickness trim. 
       FIGS.  48 A- 48 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a first electrode  4810  overlying the surface region of the piezoelectric film  4720 . In an example, the first electrode  4810  can include molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials. In a specific example, the first electrode  4810  can be subjected to a dry etch with a slope. As an example, the slope can be about 60 degrees. 
       FIGS.  49 A- 49 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a multilayer mirror or reflector structure. In an example, the multilayer mirror includes at least one pair of layers with a low impedance layer  4910  and a high impedance layer  4920 . In  FIGS.  49 A- 49 C , two pairs of low/high impedance layers are shown (low:  4910  and  4911 ; high:  4920  and  4921 ). In an example, the mirror/reflector area can be larger than the resonator area and can encompass the resonator area. In a specific embodiment, each layer thickness is about ¼ of the wavelength of an acoustic wave at a targeting frequency. The layers can be deposited in sequence and be etched afterwards, or each layer can be deposited and etched individually. In another example, the first electrode  4810  can be patterned after the mirror structure is patterned. 
       FIGS.  50 A- 50 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. Referring to  FIG.  50 B , portions of a surface of support member  5010  define a cavity region  90  within which at least a portion of first electrode  4810  is located. As shown, these figures illustrate the method step of forming a support layer  5010  overlying the mirror structure (layers  4910 ,  4911 ,  4920 , and  4921 ), the first electrode  4810 , and the piezoelectric film  4720 . In an example, the support layer  5010  can include silicon dioxide (SiO2), silicon nitride (SiN), or other like materials. In a specific example, this support layer  5010  can be deposited with a thickness of about 2-3 um. As described above, other support layers (e.g., SiNx) can be used. 
       FIGS.  51 A- 51 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of polishing the support layer  5010  to form a polished support layer  5011 . In an example, the polishing process can include a chemical-mechanical planarization process or the like. 
       FIGS.  52 A- 52 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate flipping the device and physically coupling overlying the support layer  5011  overlying a bond substrate  5210 . In an example, the bond substrate  5210  can include a bonding support layer  5220  (SiO 2  or like material) overlying a substrate having silicon (Si), sapphire (Al 2 O 3 ), silicon dioxide (SiO 2 ), silicon carbide (SiC), or other like materials. In a specific embodiment, the bonding support layer  5220  of the bond substrate  5210  is physically coupled to the polished support layer  5011 . Further, the physical coupling process can include a room temperature bonding process following by a 300 degree Celsius annealing process. 
       FIGS.  53 A- 53 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of removing the growth substrate  4710  or otherwise the transfer of the piezoelectric film  4720 . In an example, the removal process can include a grinding process, a blanket etching process, a film transfer process, an ion implantation transfer process, a laser crack transfer process, or the like and combinations thereof. 
       FIGS.  54 A- 54 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming an electrode contact via  5410  within the piezoelectric film  4720  overlying the first electrode  4810 . The via forming processes can include various types of etching processes. 
       FIGS.  55 A- 55 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a second electrode  5510  overlying the piezoelectric film  4720 . In an example, the formation of the second electrode  5510  includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching the second electrode  5510  to form an electrode cavity  5511  and to remove portion  5511  from the second electrode to form a top metal  5520 . Further, the top metal  5520  is physically coupled to the first electrode  5520  through electrode contact via  5410 . 
       FIGS.  56 A- 56 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to an example of the present invention. As shown, these figures illustrate the method step of forming a first contact metal  5610  overlying a portion of the second electrode  5510  and a portion of the piezoelectric film  4720 , and forming a second contact metal  5611  overlying a portion of the top metal  5520  and a portion of the piezoelectric film  4720 . In an example, the first and second contact metals can include gold (Au), aluminum (Al), copper (Cu), nickel (Ni), aluminum bronze (AlCu), or other like materials. This figure also shows the method step of forming a second passivation layer  5620  overlying the second electrode  5510 , the top metal  5520 , and the piezoelectric film  4720 . In an example, the second passivation layer  5620  can include silicon nitride (SiN), silicon oxide (SiOx), or other like materials. In a specific example, the second passivation layer  5620  can have a thickness ranging from about 50 nm to about 100 nm. Portions of the support member  5011  surface define cavity region  90  within which at least a portion of first electrode  4810  is located. As shown in  FIG.  56 B , first electrode  4810  is located in cavity region  90  such that the surface of the support member  5011  defining cavity region  90  is contiguous with an upper surface of the electrode  4810 . A passivation layer when present can be considered as a portion of support member  5011 . 
       FIGS.  57 A- 57 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the second electrode  5510  and the top metal  5520  to form a processed second electrode  5710  and a processed top metal  5720 . This step can follow the formation of second electrode  5710  and top metal  5720 . In an example, the processing of these two components includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching (e.g., dry etch or the like) this material to form the processed second electrode  5410  with an electrode cavity  5712  and the processed top metal  5720 . The processed top metal  5720  remains separated from the processed second electrode  5710  by the removal of portion  5711 . In a specific example, this processing gives the second electrode and the top metal greater thickness while creating the electrode cavity  5712 . In a specific example, the processed second electrode  5710  is characterized by the addition of an energy confinement structure configured on the processed second electrode  5710  to increase Q. As shown in  FIG.  57 B , portions of the support member  5011  surface define cavity region  90  within which at least a portion of first electrode  4810  is located. 
       FIGS.  58 A- 58 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the first electrode  4810  to form a processed first electrode  5810 . This step can follow the formation of first electrode  4810 . In an example, the processing of these two components includes depositing molybdenum (Mo), ruthenium (Ru), tungsten (W), or other like materials; and then etching (e.g., dry etch or the like) this material to form the processed first electrode  5810  with an electrode cavity, similar to the processed second electrode  5710 . Compared to the two previous examples, there is no air cavity. In a specific example, the processed first electrode  5810  is characterized by the addition of an energy confinement structure configured on the processed second electrode  5810  to increase Q. As shown in  FIG.  58 B , portions of the support member  5011  surface define cavity region  90  within which at least a portion of first electrode  5810  is located. 
       FIGS.  59 A- 59 C  are simplified diagrams illustrating various cross-sectional views of a single crystal acoustic resonator device and of method steps for a transfer process with a multilayer mirror for single crystal acoustic resonator devices according to another example of the present invention. As shown, these figures illustrate the method step of processing the first electrode  4810 , to form a processed first electrode  5810 , and the second electrode  5510 /top metal  5520  to form a processed second electrode  5710 /processed top metal  5720 .  FIG.  59 B  shows portions of the support member  5011  surface defining cavity region  90  within which at least a portion of first electrode  5810  is located. These steps can follow the formation of each respective electrode, as described for  FIGS.  57 A- 57 C and  58 A- 58 C . Those of ordinary skill in the art will recognize other variations, modifications, and alternatives. 
     In each of the preceding examples relating to transfer processes, energy confinement structures can be formed on the first electrode, second electrode, or both. In an example, these energy confinement structures are mass loaded areas surrounding the resonator area. The resonator area is the area where the first electrode, the piezoelectric layer, and the second electrode overlap. The larger mass load in the energy confinement structures lowers a cut-off frequency of the resonator. The cut-off frequency is the lower or upper limit of the frequency at which the acoustic wave can propagate in a direction parallel to the surface of the piezoelectric film. Therefore, the cut-off frequency is the resonance frequency in which the wave is travelling along the thickness direction and thus is determined by the total stack structure of the resonator along the vertical direction. In piezoelectric films (e.g., AlN), acoustic waves with lower frequency than the cut-off frequency can propagate in a parallel direction along the surface of the film, i.e., the acoustic wave exhibits a high-band-cut-off type dispersion characteristic. In this case, the mass loaded area surrounding the resonator provides a barrier preventing the acoustic wave from propagating outside the resonator. By doing so, this feature increases the quality factor of the resonator and improves the performance of the resonator and, consequently, the filter. 
     In addition, the top single crystalline piezoelectric layer can be replaced by a polycrystalline piezoelectric film. In such films, the lower part that is close to the interface with the substrate has poor crystalline quality with smaller grain sizes and a wider distribution of the piezoelectric polarization orientation than the upper part of the film close to the surface. This is due to the polycrystalline growth of the piezoelectric film, i.e., the nucleation and initial film have random crystalline orientations. Considering AlN as a piezoelectric material, the growth rate along the c-axis or the polarization orientation is higher than other crystalline orientations that increase the proportion of the grains with the c-axis perpendicular to the growth surface as the film grows thicker. In a typical polycrystalline AlN film with about a 1 um thickness, the upper part of the film close to the surface has better crystalline quality and better alignment in terms of piezoelectric polarization. By using the thin film transfer process contemplated in the present invention, it is possible to use the upper portion of the polycrystalline film in high frequency BAW resonators with very thin piezoelectric films. This can be done by removing a portion of the piezoelectric layer during the growth substrate removal process. Of course, there can be other variations, modifications, and alternatives. 
     In an example, the present invention provides a high-performance, ultra-small pass-band Bulk Acoustic Wave (BAW) Radio Frequency (RF) filter circuit. Embodiments of this circuit device can configured for various passband frequencies depending upon application. Further details of example application bands are shown in  FIG.  60   . 
       FIG.  60    is a simplified diagram illustrating filter pass-band requirements in a radio frequency spectrum according to an example of the present invention. As shown, the frequency spectrum  6000  shows a range from about 3.0 GHz to about 7.0 GHz. Here, a first application band (3.3 GHz-4.2 GHz)  6010  is configured for 5G n77 applications. This band includes a 5G n78 sub-band (3.3 GHz-3.8 GHz)  6011 , which includes further LTE sub-bands (3.4 GHz-3.6 GHz)  6012 , B43(3.6 GHz-3.8 GHz)  6013 , and CRBS B48/49(3.55 GHz-3.7 GHz)  6014 . A second application band  6020  (4.4 GHz-5.0 GHz) is configured for 5G n79 applications. Those of ordinary skill in the art will recognize other variations, modifications, and alternatives. 
     A third application band  6030 , labeled (5.15 GHz-5.925), can be configured for the 5.5 GHz Wi-Fi and 5G applications. In an example, this band can include a B252 sub-band (5.15 GHz-5.25 GHz)  6031 , a B255 sub-band (5.735 GHz-5850 GHz)  6032 , and a B47 sub-band (5.855 GHz-5.925 GHz)  6033 . These sub-bands can be configured alongside a UNIT-1 band (5.15 GHz-5.25 GHz)  6034 , a UNII-2A band (5.25 GHz-5.33 GHz)  6035 , a UNII-2C band (5.49 GHz-5.735 GHz)  6036 , a UNII-3 band (5.725 GHz-5.835 GHz)  6037 , and a UNIT-4 band (5.85 GHz-5.925 GHz)  6038 . These bands can coexist with additional bands configured following the third application band  6030  for other applications. In an example, there can be a UNII-5 band (5.925 GHz-6.425 GHz)  6040 , a UNII-6 band (6.425 GHz-6.525 GHz)  6050 , a UNII-7 band (6.525 GHz-6875 GHz)  6060 , and a UNII-8 band (6.875 GHz-7.125 GHz)  6070 . Of course, there can be other variations, modifications, and alternatives. 
     In an embodiment, the present filter utilizes high purity piezoelectric XBAW technology as described in the previous figures. This filter provides low insertion loss across U-NII-1, U-NII-2A, U-NII-3 bands and meets the stringent rejection requirements enabling coexistence with U-NII-5, U-NII-6, U-NII-7, and U-NII-8 bands, as shown in  FIG.  60   . The high-power rating satisfies the demanding power requirements of the latest Wi-Fi standards. 
       FIG.  61    is a simplified diagram illustrating an overview of key markets that are applications for acoustic wave RF filters according to an example of the present invention. The application chart  6100  for BAW RF filters shows mobile devices, smartphones, automobiles, Wi-Fi tri-band routers, tri-band mobile devices, tri-band smartphones, integrated cable modems, Wi-Fi tri-band access points, LTE-U/LAA small cells, and the like. 
       FIG.  62 A  is a simplified diagram illustrating application areas for 5.2 GHz and 5.6 GHz RF filters in Tri-Band Wi-Fi radios according to examples of the present invention. As shown, RF filters used by communication devices  6210  can be configured for specific applications at three separate bands of operation. In a specific example, application area  6211  operates at 2.4 GHz and includes computing and mobile devices, application area  6212  operates at 5.2 GHz and includes television and display devices, and application area  6213  operates at 5.6 GHz and includes video game console and handheld devices. Those of ordinary skill in the art will recognize other variations, modifications, and alternatives. 
       FIG.  62 B  is a simplified diagram illustrating a frequency spectrum  6202  for 5.2 GHz RF filters in mobile applications according to examples of the present invention. As shown, RF filters used by communication devices can be configured for specific applications at a specific band of operation. In a specific example, a mobile application area can be designated at the frequency range between 5150 MHz and 5350 MHz, which the 5.2 GHz RF filter can configure as the pass-band. The other frequency ranges (600 MHz to 2700 MHz, 3300 MHz to 4200 MHz, 4400 MHz to 5000 MHz, and 5470 MHz to 10000 MHz) are rejected. 
       FIG.  62 C  is a simplified diagram illustrating a frequency spectrum  6203  for 4.4-5 GHz RF filters in mobile applications according to examples of the present invention. As shown, RF filters used by communication devices can be configured for specific applications at a specific band of operation. In a specific example, a mobile application area can be designated at the frequency range between 4400 MHz and 5000 MHz, which the 4.4-5 GHz RF filter can configure as the pass-band. The other frequency ranges (600 MHz to 1000 MHz, 1700 MHz to 2700 MHz, 3400 MHz to 4200 MHz, and 5150 MHz to 10000 MHz) are rejected. 
       FIG.  62 D  is a simplified diagram illustrating a frequency spectrum  6204  for 5.5 GHz RF filters in mobile applications according to examples of the present invention. As shown, RF filters used by communication devices can be configured for specific applications at a specific band of operation. In a specific example, a mobile application area can be designated at the frequency range between 5150 MHz and 5850 MHz, which the 5.5 GHz RF filter can configured as the pass-band. The other frequency ranges (600 MHz to 2700 MHz, 3300 MHz to 4200 MHz, 4400 MHz to 5000 MHz, and 5900 MHz to 10000 MHz) are rejected. 
       FIG.  62 E  is a simplified diagram illustrating a frequency spectrum  6205  for Wi-Fi/5G RF triplexers in mobile applications according to examples of the present invention. As shown, RF filters used by communication devices can be configured for specific applications at specific bands (or multiple bands) of operation. In a specific example, a mobile application area can be designated at three frequency ranges using the three filters configured in the triplexer. The three pass-band frequency bands of the three filters can include the range between 4400 MHz and 5000 MHz, the range between 5150 MHz and 5350 MHz, and the range between 5470 MHz and 5855 MHz. In another example, the three pass-band frequency bands of the three filters can include the range between 4400 MHz and 5000 MHz, the range between 5130 MHz and 5170 MHz, and the range between 5470 and 5835 MHz. 
       FIG.  62 F  is a simplified diagram illustrating a frequency spectrum  6206  for 2.6 GHz RF filters in mobile applications according to examples of the present invention. As shown, RF filters used by communication devices can be configured for specific applications at a specific band of operation. In a specific example, a mobile application area can be designated at the frequency range between 2515 MHz and 5675 MHz, which the 2.6 GHz RF filter can configured as the pass-band. The other frequency ranges (600 MHz to 1000 MHz, 1785 MHz to 2472 MHz, 334200 MHz to 4200 MHz, and 4400 MHz to 5000 MHz) are rejected. 
       FIG.  62 G  is a simplified diagram illustrating a frequency spectrum  6207  for 3.55-3.7 GHz RF filters in mobile applications according to examples of the present invention. As shown in diagram  6200 , RF filters used by communication devices can be configured for specific applications at a specific band of operation. In a specific example, a mobile application area can be designated at the frequency range between 3550 MHz and 3700 MHz, which the 3.55-3.7 GHz RF filter can configure as the pass-band. The other frequency ranges (600 MHz to 1000 MHz, 1785 MHz to 2690 MHz, 4400 MHz to 5000 MHz, and 5150 MHz to 5850 MHz) are rejected. Those of ordinary skill in the art will recognize other variations, modifications, and alternatives to the frequency spectrums discussed previous. 
     The present invention includes resonator and RF filter devices using both textured polycrystalline materials (deposited using PVD methods) and single crystal piezoelectric materials (grown using CVD technique upon a seed substrate). Various substrates can be used for fabricating the acoustic devices, such silicon substrates of various crystallographic orientations and the like. Additionally, the present method can use sapphire substrates, silicon carbide substrates, gallium nitride (GaN) bulk substrates, or aluminum nitride (AlN) bulk substrates. The present method can also use GaN templates, AlN templates, and Al x Ga 1-x N templates (where x varies between 0.0 and 1.0). These substrates and templates can have polar, non-polar, or semi-polar crystallographic orientations. Further the piezoelectric materials deposed on the substrate can include allows selected from at least one of the following: AlN, AlGaN, MgHfAlN, GaN, InN, InGaN, AlInN, AlInGaN, ScAlN, ScAlGaN, ScGaN, ScN, BAlN, BAlScN, and BN. 
     The resonator and filter devices may employ process technologies including but not limited to Solidly-Mounted Resonator (SMR), Film Bulk Acoustic Resonator (FBAR), or XBAW technology. Representative cross-sections are shown below in  FIGS.  63 A- 63 C . For clarification, the terms “top” and “bottom” used in the present specification are not generally terms in reference of a direction of gravity. Rather, the terms “top” and “bottom” are used in reference to each other in the context of the present device and related circuits. Those of ordinary skill in the art will recognize other variations, modifications, and alternatives. 
     In an example, the piezoelectric layer ranges between 0.1 and 2.0 um and is optimized to produce optimal combination of resistive and acoustic losses. The thickness of the top and bottom electrodes can range between 250 Å and 2500 Å and the metal consists of a refractory metal with high acoustic velocity and low resistivity. In a specific example, the resonators can be “passivated” with a dielectric (not shown in  FIGS.  63 A- 63 C ) consisting of a nitride and or an oxide and whose range is between 100 Å and 2000 Å. In this case, the dielectric layer is used to adjust resonator resonance frequency. Extra care is taken to reduce the metal resistivity between adjacent resonators on a metal layer called the interconnect metal. The thickness of the interconnect metal can range between 500 Å and 5 um. The resonators contain at least one air cavity interface in the case of SMRs and two air cavity interfaces in the case of FBARs and XBAWs. In an example, the shape of the resonators can be selected from asymmetrical shapes including ellipses, rectangles, and polygons, and the like. Further, the resonators contain reflecting features near the resonator edge on one or both sides of the resonator. 
       FIGS.  63 A- 63 C  are simplified diagrams illustrating cross-sectional views of resonator devices according to various examples of the present invention. More particularly, device  6301  of  FIG.  63 A  shows a BAW resonator device including an SMR,  FIG.  63 B  shows a BAW resonator device including an FBAR, and  FIG.  63 C  shows a BAW resonator device with a high purity XBAW. As shown in SMR device  6301 , a reflector device  6320  is configured overlying a substrate member  6310 . The reflector device  6320  can be a Bragg reflector or the like. A bottom electrode  6330  is configured overlying the reflector device  6320 . A polycrystalline piezoelectric layer  6340  is configured overlying the bottom electrode  6330 . Further, a top electrode  6350  is configured overlying the polycrystalline layer  6340 . As shown in the FBAR device  6302 , the layered structure including the bottom electrode  6330 , the polycrystalline layer  6340 , and the top electrode  6350  remains the same. The substrate member  6311  includes an air cavity  6312 , and a dielectric layer is formed overlying the substrate member  6311  and covering the air cavity  6312 . As shown in XBAW device  6303 , the substrate member  6311  also contains an air cavity  6312 , but the bottom electrode  6330  is formed within a region of the air cavity  6312 . A high purity piezoelectric layer  6341  is formed overlying the substrate member  6311 , the air cavity  6312 , and the bottom electrode  6341 . Further, a top electrode  6350  is formed overlying a portion of the high purity piezoelectric layer  6341 . This high purity piezoelectric layer  6341  can include piezoelectric materials as described throughout this specification. These resonators can be scaled and configured into circuit configurations shown in  FIGS.  64 A- 64 C . 
     The RF filter circuit can comprise various circuit topologies, including modified lattice (“I”)  6401 , lattice (“II”)  6402 , and ladder (“III”)  6403  circuit configurations, as shown in  FIGS.  64 A,  64 B, and  64 C , respectively. These figures are representative lattice and ladder diagrams for acoustic filter designs including resonators and other passive components. The lattice and modified lattice configurations include differential input ports  6410  and differential output ports  6450 , while the ladder configuration includes a single-ended input port  6411  and a single-ended output port  6450 . In the lattice configurations, nodes are denoted by top nodes (t1-t3) and bottom nodes (b1-b3), while in the ladder configuration the nodes are denoted as one set of nodes (n1-n4). The series resonator elements (in cases I, II, and III) are shown with white center elements  6421 - 6424  and the shunt resonator elements have darkened center circuit elements  6431 - 6434 . The series elements resonance frequency is higher than the shunt elements resonance frequency in order to form the filter skirt at the pass-band frequency. The inductors  6441 - 6443  shown in the modified lattice circuit diagram ( FIG.  64 A ) and any other matching elements can be included either on-chip (in proximity to the resonator elements) or off-chip (nearby to the resonator chip) and can be used to adjust frequency pass-band and/or matching of impedance (to achieve the return loss specification) for the filter circuit. The filter circuit contains resonators with at least two resonance frequencies. The center of the pass-band frequency can be adjusted by a trimming step (using an ion milling technique or other like technique) and the shape the filter skirt can be adjusted by trimming individual resonator elements (to vary the resonance frequency of one or more elements) in the circuit. 
     In an example, the present invention provides an RF filter circuit device using a ladder configuration including a plurality of resonator devices and a plurality of shunt configuration resonator devices. Each of the plurality of resonator devices includes at least a capacitor device, a bottom electrode, a piezoelectric material, a top electrode, and an insulating material configured in accordance to any of the resonator examples described previously. The plurality of resonator devices is configured in a serial configuration, while the plurality of shunt configuration resonators is configured in a parallel configuration such that one of the plurality of shunt configuration resonators is coupled to the serial configuration following each of the plurality of resonator devices. 
     In an example, the RF filter circuit device in a ladder configuration can also be described as follows. The device can include an input port, a first node coupled to the input port, a first resonator coupled between the first node and the input port. A second node is coupled to the first node and a second resonator is coupled between the first node and the second node. A third node is coupled to the second node and a third resonator is coupled between the second node and the third node. A fourth node is coupled to the third node and a fourth resonator is coupled between the third node and the output port. Further, an output port is coupled to the fourth node. Those of ordinary skill in the art will recognize other variations, modifications, and alternatives. 
     Each of the first, second, third, and fourth resonators can include a capacitor device. Each such capacitor device can include a substrate member, which has a cavity region and an upper surface region contiguous with an opening in the first cavity region. Each capacitor device can include a bottom electrode within a portion of the cavity region and a piezoelectric material overlying the upper surface region and the bottom electrode. Also, each capacitor device can include a top electrode overlying the piezoelectric material and the bottom electrode, as well as an insulating material overlying the top electrode and configured with a thickness to tune the resonator. 
     The device also includes a serial configuration includes the input port, the first node, the first resonator, the second node, the second resonator, the third node, the third resonator, the fourth resonator, the fourth node, and the output port. A separate shunt configuration resonator is coupled to each of the first, second, third, fourth nodes. A parallel configuration includes the first, second, third, and fourth shunt configuration resonators. Further, a circuit response can be configured between the input port and the output port and configured from the serial configuration and the parallel configuration to achieve a transmission loss from one or more configured pass-band. 
     In an example, the pass-band has a characteristic frequency centered around 5.2 GHz and having a bandwidth from 5.170 GHz to 5.330 GHz such that the characteristic frequency centered around 5.2 GHz is tuned from a lower frequency ranging from about 4 GHz to 5.1 GHz. 
     In an example, the pass-band has a characteristic frequency centered around 5.6 GHz and having a bandwidth from 5.490 GHz to 5.835 GHz such that the characteristic frequency centered around 5.6 GHz is tuned from a lower frequency ranging from about 4.8 GHz to 5.5 GHz. 
     In an example, the pass-band has a characteristic frequency centered around 5.8875 GHz and having a bandwidth from 5.85 GHz to 5.925 GHz such that the characteristic frequency centered around 5.8875 GHz is tuned from a lower frequency ranging from about 5 GHz to 5.7 GHz. 
     In an example, the pass-band has a characteristic frequency centered around 4.7 GHz and having a bandwidth from 4.4 GHz to 5.0 GHz such that the characteristic frequency centered around 4.7 GHz is tuned from a lower frequency ranging from about 4 GHz to 5.1 GHz. 
     In an example, the pass-band has a characteristic frequency centered around 5.5025 GHz and having a bandwidth from 5.170 GHz to 5.835 GHz such that the characteristic frequency centered around 5.5025 GHz is tuned from a lower frequency ranging from about 4.7 GHz to 5.4 GHz. 
     In an example, the one or more configured pass-bands includes three pass-bands collectively having a characteristic frequency centered around 5.1275 GHz and having a collective bandwidth from 4.400 GHz to 5.855 GHz such that the characteristic frequency centered around 5.1275 GHz is tuned from a lower frequency ranging from about 4.0 GHz to 5.5 GHz. 
     In an example, the pass-band has a characteristic frequency centered around 2.595 GHz and having a bandwidth from 2.515 GHz to 2.675 GHz such that the characteristic frequency centered around 2.595 GHz is tuned from a lower frequency ranging from about 2.0 GHz to 2.5 GHz. 
     In an example, the pass-band has a characteristic frequency centered around 3.625 GHz and having a bandwidth from 3.55 GHz to 3.7 GHz such that the characteristic frequency centered around 3.625 GHz is tuned from a lower frequency ranging from about 2.9 GHz to 3.5 GHz. Those of ordinary skill in the art will recognize other variations, modifications, or alternatives. 
     In an example, the piezoelectric materials can include single crystal materials, polycrystalline materials, or combinations thereof and the like. The piezoelectric materials can also include a substantially single crystal material that exhibits certain polycrystalline qualities, i.e., an essentially single crystal material. In a specific example, the first, second, third, and fourth piezoelectric materials are each essentially a single crystal aluminum nitride (AlN) bearing material or aluminum scandium nitride (AlScN) bearing material, a single crystal gallium nitride (GaN) bearing material or gallium aluminum nitride (GaAlN) bearing material, a magnesium hafnium aluminum nitride (MgHfAlN) material, or the like. In other specific examples, these piezoelectric materials each comprise a polycrystalline aluminum nitride (AlN) bearing material or aluminum scandium nitride (AlScN) bearing material, or a polycrystalline gallium nitride (GaN) bearing material or gallium aluminum nitride (GaAlN) bearing material, a magnesium hafnium aluminum nitride (MgHfAlN) material, or the like. In other examples, the piezoelectric materials can include aluminum gallium nitride (Al x Ga 1-x N) material or an aluminum scandium nitride (Al x Sc 1-x N) material characterized by a composition of 0≤X&lt;1.0. As discussed previously, the thicknesses of the piezoelectric materials can vary, and in some cases can be greater than 250 nm. 
     In a specific example, the piezoelectric material can be configured as a layer characterized by an x-ray diffraction (XRD) rocking curve full width at half maximum ranging from 0 degrees to 2 degrees. The x-ray rocking curve FWHM parameter can depend on the combination of materials used for the piezoelectric layer and the substrate, as well as the thickness of these materials. Further, an FWHM profile is used to characterize material properties and surface integrity features, and is an indicator of crystal quality/purity. The acoustic resonator devices using single crystal materials exhibit a lower FWHM compared to devices using polycrystalline material, i.e., single crystal materials have a higher crystal quality or crystal purity. 
     In a specific example, the serial configuration forms a resonance profile and an anti-resonance profile. The parallel configuration also forms a resonance profile and an anti-resonance profile. These profiles are such that the resonance profile from the serial configuration is off-set with the anti-resonance profile of the parallel configuration to form the pass-band. 
     In a specific example, the pass-band is characterized by a band edge on each side of the pass-band and having an amplitude difference ranging from 10 dB to 60 dB. The pass-band has a pair of band edges; each of which has a transition region from the pass-band to a stop band such that the transition region is no greater than 250 MHz. In another example, pass-band can include a pair of band edges and each of these band edges can have a transition region from the pass-band to a stop band such that the transition region ranges from 5 MHz to 250 MHz. Further, the pass-band can be characterized by an amplitude variation of less than 1.0 dB. 
     In a specific example, each of the first, second, third, and fourth insulating materials comprises a silicon nitride bearing material or an oxide bearing material configured with a silicon nitride material an oxide bearing material. 
     In a specific example, the present device can be configured as a bulk acoustic wave (BAW) filter device. Each of the first, second, third, and fourth resonators can be a BAW resonator. Similarly, each of the first, second, third, and fourth shunt resonators can be BAW resonators. The present device can further include one or more additional resonator devices numbered from N to M, where N is four and M is twenty. Similarly, the present device can further include one or more additional shunt resonator devices numbered from N to M, where N is four and M is twenty. In other examples, the present device can include a plurality of resonator devices configured with a plurality of shunt resonator devices in a ladder configuration, a lattice configuration, or other configuration as previously described. 
     In an example, the present invention provides an RF filter circuit device using a lattice configuration including a plurality of top resonator devices, a plurality of bottom resonator devices, and a plurality of shunt configuration resonator devices. Similar to the ladder configuration RF filter circuit, each of the plurality of top and bottom resonator devices includes at least a capacitor device, a bottom electrode, a piezoelectric material, a top electrode, and an insulating material configured in accordance to any of the resonator examples described previously. The plurality of top resonator devices is configured in a top serial configuration and the plurality of bottom resonator devices is configured in a bottom serial configuration. Further, the plurality of shunt configuration resonators is configured in a cross-coupled configuration such that a pair of the plurality of shunt configuration resonators is cross-coupled between the top serial configuration and the bottom serial configuration and between one of the plurality of top resonator devices and one of the plurality of the bottom resonator devices. In a specific example, this device also includes a plurality of inductor devices, wherein the plurality of inductor devices are configured such that one of the plurality of inductor devices is coupled between the differential input port, one of the plurality of inductor devices is coupled between the differential output port, and one of the plurality of inductor devices is coupled to the top serial configuration and the bottom serial configuration between each cross-coupled pair of the plurality of shunt configuration resonators. 
     In an example, the RF circuit device in a lattice configuration can also be described as follows. The device can include a differential input port, a top serial configuration, a bottom serial configuration, a first lattice configuration, a second lattice configuration, and a differential output port. The top serial configuration can include a first top node, a second top node, and a third top node. A first top resonator can be coupled between the first top node and the second top node, while a second top resonator can be coupled between the second top node and the third top node. Similarly, the bottom serial configuration can include a first bottom node, a second bottom node, and a third bottom node. A first bottom resonator can be coupled between the first bottom node and the second bottom node, while a second bottom resonator can be coupled between the second bottom node and the third bottom node. 
     In an example, the first lattice configuration includes a first shunt resonator cross-coupled with a second shunt resonator and coupled between the first top resonator of the top serial configuration and the first bottom resonator of the bottom serial configuration. Similarly, the second lattice configuration can include a first shunt resonator cross-coupled with a second shunt resonator and coupled between the second top resonator of the top serial configuration and the second bottom resonator of the bottom serial configuration. The top serial configuration and the bottom serial configuration can each be coupled to both the differential input port and the differential output port. 
     In a specific example, the device further includes a first balun coupled to the differential input port and a second balun coupled to the differential output port. The device can further include an inductor device coupled between the differential input and output ports. In a specific example, the device can further include a first inductor device coupled between the first top node of the top serial configuration and the first bottom node of the bottom serial configuration; a second inductor device coupled between the second top node of the top serial configuration and the second bottom node of the bottom serial configuration; and a third inductor device coupled between the third top node of the top serial configuration and the third bottom node of the bottom serial configuration. 
     For a typical k-squared (K 2  eff) of 6.5% to 7%, the modified lattice configuration can be used with the three helper inductors to achieve the 360 MHz passband which equates to 6.3% fractional bandwidth (equal to the passband divided by the center frequency). The challenge with the modified lattice and lattice architectures is the differential input and output, which can be adapted to a single-ended architecture by incorporation of baluns on the input and output. For a single-ended 5.6 GHz RF filter using the modified lattice architecture, the design requires three inductors plus two baluns. 
     The standard lattice configuration with K 2  eff of the piezoelectric material at 6.5% to 7% is inadequate for meeting the bandwidth and suffers from poor return loss in the passband. Further, the design also requires two baluns for single-ended operation. Alternatively, higher K 2  eff piezo-materials can be used with the lattice configuration to meet the filter requirements. 
     The ladder configuration offers the benefit of being single-ended, but again the K 2  eff of the piezoelectric material at 6.5% to 7% is inadequate to achieve passband without degradation of insertion loss and return loss in the center of the band. Incorporating higher K 2  eff piezoelectric materials (greated than 8.5% is required) or helper inductors can be used to achieve the bandwidth and return loss performance. Alternatively, helper inductors can be used, but may require a higher number of helper inductors compared to the modified lattice configuration. 
     A summary of the design methodology for the three circuit configuration (to achieve a single-ended 5.6 GHz RF filter) is provided below: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Summary of design methodology for a 5.6 GHz RF Filter. 
               
            
           
           
               
               
               
               
            
               
                 5.6 GHz RF Filter 
                   
                   
                   
               
               
                 Design Summary 
                 Modified Lattice 
                 Lattice 
                 Ladder 
               
               
                   
               
               
                 Piezo Material 
                 K 2  eff: 6.5% to 7% OK 
                 Need K 2  eff &gt; 8.5% 
                 Need K 2  eff &gt; 8.5% 
               
               
                 Helper Inductors 
                 Yes, 3 min. 
                 Not if higher K 2  eff 
                 Not if higher K 2  eff 
               
               
                 Baluns 
                 Yes, 2 req&#39;d 
                 Yes, 2 req&#39;d 
                 None 
               
               
                 Design challenges 
                 # of external passives 
                 Trade b/t K 2  eff &amp; Q 
                 Trade b/t K 2  eff &amp; Q 
               
               
                   
               
            
           
         
       
     
     The packaging approach includes but is not limited to wafer level packaging (WLP), WLP-plus-cap wafer approach, flip-chip, chip and bond wire, as shown in  FIGS.  65 A,  65 B,  66 A and  66 B . One or more RF filter chips and one or more filter bands can be packaged within the same housing configuration. Each RF filter band within the package can include one or more resonator filter chips and passive elements (capacitors, inductors) can be used to tailor the bandwidth and frequency spectrum characteristic. For a 5G-Wi-Fi system application, a package configuration including 5 RF filter bands, including the n77, n78, n79, and a 5.17-5.835 GHz (U-NII-1, U-NII-2A, UNII-2C and U-NII-3) bandpass solutions is capable using BAW RF filter technology. For a Tri-Band Wi-Fi system application, a package configuration including 3 RF filter bands, including the 2.4-2.5 GHz, 5.17-5.835 GHz and 5.925-7.125 GHz bandpass solutions is capable using BAW RF filter technology. The 2.4-2.5 GHz filter solution can be either surface acoustic wave (SAW) or BAW, whereas the 5.17-5.835 GHz and 5.925-7.125 GHz bands are likely BAW given the high frequency capability of BAW. 
       FIG.  65 A  is a simplified diagram illustrating a packing approach according to an example of the present invention. As shown, device  6501  is packaged using a conventional die bond of an RF filter die  6510  to the base  6520  of a package and metal bond wires  6530  to the RF filter chip from the circuit interface  6540 . 
       FIG.  65 B  is as simplified diagram illustrating a packing approach according to an example of the present invention. As shown, device  6502  is packaged using a flip-mount wafer level package (WLP) showing the RF filter silicon die  6510  mounted to the circuit interface  6540  using copper pillars  6531  or other high-conductivity interconnects. 
       FIGS.  66 A- 66 B  are simplified diagrams illustrating packing approaches according to examples of the present invention. In  FIG.  66 A , device  6601  shows an alternate version of a WLP utilizing a BAW RF filter circuit MEMS device  6631  and a substrate  6611  to a cap wafer  6641 . In an example, the cap wafer  6641  may include thru-silicon-vias (TSVs) to electrically connect the RF filter MEMS device  6631  to the topside of the cap wafer (not shown in the figure). The cap wafer  6641  can be coupled to a dielectric layer  6621  overlying the substrate  6611  and sealed by sealing material  6651 . 
     In  FIG.  66 B , device  6602  shows another version of a WLP bonding a processed BAW substrate  6612  to a cap layer  6642 . As discussed previously, the cap wafer  6642  may include thru-silicon vias (TSVs)  6632  spatially configured through a dielectric layer  6622  to electrically connect the BAW resonator within the BAW substrate  6612  to the topside of the cap wafer. Similar to the device of  FIG.  66 A , the cap wafer  6642  can be coupled to a dielectric layer overlying the BAW substrate  6612  and sealed by sealing material  6652 . Of course, there can be other variations, modifications, and alternatives. 
     In various examples, the present filter can have certain features. The die configuration can be less than 2 m×2 m×0.5 mm; in a specific example, the die configuration is typically less than 1 m×1 m×0.2 mm. The packaged device has an ultra-small form factor, such as a 1.1 m×0.9 m×0.3 mm for a WLP approach, shown in  FIGS.  65 B,  66 A, and  66 B . A larger form factor, such as a 2 m×2.5 m×0.9 mm, is available using a wire bond approach, shown in  FIG.  65 A , for higher power applications. In a specific example, the device is configured with a single-ended 50-Ohm antenna, and transmitter/receiver (Tx/Rx) ports. The high rejection of the device enables coexistence with adjacent Wi-Fi UNIT and 5G bands. The device is also be characterized by a high power rating (maximum power handling capability greater than +27 dBm or 0.5 Watt), a low insertion loss pass-band filter with less than 3.0 dB transmission loss, and performance over a temperature range from −40 degrees Celsius to +95 degrees Celsius. Further, in a specific example, the device is RoHS (Restriction of Hazardous Substances) compliant and uses Pb-free (lead-free) packaging. 
       FIG.  67 A  is a simplified circuit diagram illustrating a 2-port BAW RF filter circuit according to an example of the present invention. As shown, circuit  6701  includes a first port (“Port 1”)  6711 , a second port (“Port 2”)  6730 , and a filter  6710 . The first port represents a connection from a transmitter (TX) or received (RX) to the filter  6710  and the second port represents a filter connection from the filter  6710  to an antenna (ANT). 
       FIG.  67 B  is a simplified circuit block diagram illustrating a 2-chip configuration according to an example of the present invention. As shown, diagram  6702  includes a first chip  6721  and a second chip  6722 . The first chip  6721  contains a notch circuit and the second chip  6722  includes a filter circuit, such as those in  FIGS.  64 A- 64 C . For a typical k-squared (K 2  eff) of 6.5% to 7% for AlN, a ladder configuration (1-chip) or notch plus ladder (2-chip) configuration is useful. The notch filter is a useful addition to the ladder in order to achieve appropriate attenuation at the right edge of the U-NII-3 band. The filter pass-band is 75 MHz, which equates to a small 1.7% fractional bandwidth (equal to the pass-band divided by the center frequency) and can be achieved with a smaller K 2  eff. 
     The challenge with such a high K 2  eff is that the resonators must either be loaded with parallel capacitance (undesirable size) or the piezoelectric material thickness must be reduced (high capacitance per unit area; manufacturing concerns due to thin piezoelectric) to achieve filter skirt performance. In the case where a notch filter (3-element pi-configuration) is used, the K 2  eff of the notch configuration is not sensitive to the pass-band requirement and the piezo thickness does not have to be adjusted to reduce K 2  eff. However, the filter pass-band skirt is determined by the ladder configured chip and hence the piezo of the ladder chip must be thinned to achieve lower K 2  eff for the small fractional bandwidth filter. In summary, for high K 2  eff piezo materials, either a 1-chip ladder can be deployed with a thin piezoelectric or a 2-chip ladder plus notch design can be deployed with one thick and one thin piezo material stack, as shown in Table 1 below. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Material thicknesses for a 2-chip configuration with an AIN 
               
               
                 narrow notch band chip. 
               
            
           
           
               
               
               
            
               
                   
                 Narrow Notch Band Chip 
                 Ladder Filter Chip 
               
               
                   
               
            
           
           
               
               
               
            
               
                 FM1 Thickness (A) 
                 1100 
                 1822 
               
               
                 FM2 Thickness (A) 
                 1548 
                 1822 
               
               
                 FM3 Thickness (A) 
                 1077 
                 95 
               
               
                 BM Thickness 
                 900 
                 — 
               
               
                 AIN (A) 
                 3300 
                 1545 
               
               
                   
               
            
           
         
       
     
     In another example, the present invention can use a lower e33 material, such as AlGaN, which has approximately 25% lower K 2  eff. Because the K 2  eff is more optimal for the small bandwidth, a thicker and more manufacturable piezo material can be used to achieve the desired specification. For a typical-squared (K 2  eff) of 4.5% to 4.8% for AlGaN, a ladder configuration (1-chip) or notch plus ladder (2-chip) configuration is still useful. By deploying AlGaN, thick piezo materials can be used for both the notch and the filter chip designs, as shown in Table 2 below. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Material thicknesses for a 2-chip configuration with an AlGaN 
               
               
                 narrow notch band chip. 
               
            
           
           
               
               
               
            
               
                   
                 Narrow Notch Band Chip 
                 Ladder Filter Chip 
               
               
                   
               
            
           
           
               
               
               
            
               
                 FM1 Thickness (A) 
                 1100 
                 1270 
               
               
                 FM2 Thickness (A) 
                 1260 
                 1270 
               
               
                 FM3 Thickness (A) 
                 1100 
                 95 
               
               
                 BM Thickness 
                 900 
                 — 
               
               
                 AlGaN (A) 
                 3250 
                 3300 
               
               
                   
               
            
           
         
       
     
       FIG.  67 C  is a simplified circuit diagram illustrating a 4-port BAW Triplexer circuit according to an example of the present invention. As shown, circuit  6703  includes a first port (“Port 1”)  6711 , a second port (“Port 2”)  6712 , and a third port (“Port 3”)  6713 . These port represents a connection from a transmitter (TX) or receiver (RX) to the Triplexer, shown by filters  6731 - 6733 . The antenna port  6730  represents a filter connection from the Triplexer  6731 - 6733  to an antenna (ANT). 
       FIGS.  68 A- 68 K  are simplified tables of filter parameters according to various examples of the present invention. The circuit parameters are provided along with the specification units, minimum, typical and maximum specification values. As shown in  FIG.  68 A , table  6801  includes electrical specifications for a 5.2 GHz Wi-Fi RF resonator filter circuit. 
     In  FIG.  68 B , table  6802  includes electrical specifications for a 5.6 GHz Wi-Fi RF resonator filter circuit according to an example of the present invention. In a specific example, the IEEE-802.11a channel plan for Wi-Fi uses UNII-2C and UNII-3, 5490 MHz up to 5835 MHz. 
     In  FIG.  68 C , table  6803  includes electrical specifications for a 5.9 GHz RF resonator filter circuit according to an example of the present invention. 
     In  FIG.  68 D , table  6804  includes electrical specifications for a 5.2 GHz Wi-Fi CAWR RF resonator filter circuit according to an example of the present invention. 
     In  FIG.  68 E , table  6805  includes electrical specifications for a 4.4-5 GHz (5G band) n79 RF resonator filter circuit according to an example of the present invention. 
     In  FIG.  68 F , table  6806  includes electrical specifications for a 5.5 GHz Wi-Fi 5G CAWR RF resonator filter circuit according to an example of the present invention. 
     In  FIG.  68 G , table  6807  includes electrical specifications for a 5G n79 Wi-Fi Triplexer circuit according to an example of the present invention. 
     In  FIG.  68 H , table  6808  includes electrical specifications for a 5G n41 2.6 GHz RF resonator filter circuit according to an example of the present invention. 
     In  FIG.  68 I , table  6809  includes electrical specifications for a 5.5 GHz CAWR RF resonator filter circuit according to an example of the present invention. 
     In  FIG.  68 J , table  6810  includes electrical specifications for a 4.5G 3.55-3.7 GHz RF resonator filter circuit according to an example of the present invention. 
     In  FIG.  68 K , table  6811  includes electrical specifications for a 5.5 GHz CAWR RF resonator filter circuit. 
       FIGS.  69 A- 69 J  are simplified graphs representing insertion loss over frequency for various RF resonator filter circuits according examples of the present invention. In some of these graphs, the modeled curve is the transmission loss (s21) predicted from a linear simulation tool incorporation non-linear, full 3-dimensional (3D) electromagnetic (EM) simulation. The measured curve is the s21 measured from scattering parameters (s-parameters) taken from a network analyzer test system. The vertical axis plots the transmission gain, S21 (in dB), and the horizontal axis is the stimulus frequency (in GHz). 
     In  FIG.  69 A , graph  6901  represents a narrowband measured ( 6911 ) vs. modeled ( 6912 ) response for 5.2 GHz RF filter using a ladder RF filter circuit configuration. 
     In  FIG.  69 B , graph  6902  represents transmission loss ( 6912 ) vs. return loss ( 6921 ) for a narrowband modeled response for a 5.6 GHz RF filter using a ladder RF filter circuit configuration. 
     In  FIG.  69 C , graph  6903  represents transmission loss ( 6912 ) vs. return loss ( 6921 ) for a narrowband modeled response for a 5.9 GHz RF filter using a modified lattice RF filter circuit configuration. 
     In  FIG.  69 D , graph  6904  represents transmission loss ( 6912 ) vs. return loss ( 6921 ) for a narrowband modeled response for a 4.4-5 GHz n79 RF filter using a ladder RF filter configuration. 
     In  FIG.  69 E , graph  6905  represents a modeled narrowband response  6912  for a 5.5 GHz RF filter using a ladder RF filter configuration. 
     In  FIG.  69 F , graph  6906  represents a narrowband response  6931 - 6933  for a 5G Wi-Fi Triplexer compared to a modeled response using a ladder RF filter configuration. 
     In  FIG.  69 G , graph  6907  represents a modeled narrowband response  6912  for a 2.6 GHz RF filter compared to a modeled response using a ladder RF filter configuration. 
     In  FIG.  69 H , graph  6908  represents a modeled narrowband response  6912  for a 5.5 GHz RF filter using a ladder RF filter configuration. 
     In  FIG.  69 I , graph  6909  represents a modeled narrowband response  6912  for a 3.55-3.7 GHz RF filter using a ladder RF filter configuration. 
     In  FIG.  69 J , graph  6910  represents a modeled narrowband response  6912  for a 5.5 GHz RF filter using a ladder RF filter configuration. 
       FIGS.  70 A- 70 J  are simplified graphs representing insertion loss over frequency for various RF resonator filter circuits according examples of the present invention. In some of these graphs, the modeled curve is the transmission loss (s21) predicted from a linear simulation tool incorporation non-linear, full 3-dimensional (3D) electromagnetic (EM) simulation. The measured curve is the s21 measured from scattering parameters (s-parameters) taken from a network analyzer test system. The vertical axis plots the transmission gain, S21 (in dB), and the horizontal axis is the stimulus frequency (in GHz). 
     In  FIG.  70 A , graph  7000  represents a wideband modeled response transmission loss ( 7012 ) vs. return loss ( 7021 ) for a 5.6 GHz RF filter using a modified lattice RF filter circuit configuration. 
     In  FIG.  70 B , graph  7002  represents a wideband modeled response transmission loss ( 7012 ) vs. return loss ( 7021 ) for a 5.9 GHz RF filter using a modified lattice RF filter circuit configuration. 
     In  FIG.  70 C , graph  7003  represents a lumped wideband modeled response  7012  for a 5.2 GHz RF filter. 
     In  FIG.  70 D , graph  7004  represents a wideband modeled response transmission loss ( 7012 ) vs. return loss ( 7021 ) for a 4.4-5 GHz n79 RF filter using a ladder RF filter configuration. 
     In  FIG.  70 E , graph  7005  represents a wideband modeled response  7012  for a 5.5 GHz RF filter compared to a modeled response using a ladder RF filter configuration. 
     In  FIG.  70 F , graph  7006  represents a triplexer wideband response  7031 - 7033  for a 5G Triplexer circuit using a ladder RF filter configuration. 
     In  FIG.  70 G , graph  7007  represents a wideband modeled response  7012  for a 2.6 GHz RF filter compared using a ladder RF filter configuration. 
     In  FIG.  70 H , graph  7008  represents a wideband modeled response  7012  for a 5.5 GHz RF filter compared to a modeled response using a ladder RF filter configuration. 
     In  FIG.  70 I , graph  7009  represents a wideband modeled response  7012  for a 3.55-3.7 GHz RF filter using a ladder RF filter configuration. 
     In  FIG.  70 J , graph  7010  represents a wideband modeled response  7012  for a 5.5 GHz RF filter using a ladder RF filter configuration. 
     While the above is a full description of the specific embodiments, various modifications, alternative constructions and equivalents may be used. As an example, the packaged device can include any combination of elements described above, as well as outside of the present specification. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.