Transversely-excited film bulk acoustic resonator

Abstract

Acoustic resonator devices and filters are disclosed. A piezoelectric plate is attached to a substrate, a portion of the piezoelectric plate forming a diaphragm spanning a cavity in the substrate. A first conductor pattern is formed on a surface of the piezoelectric plate. The first conductor pattern includes interleaved fingers of an interdigital transducer disposed on the diaphragm, and a first plurality of contact pads. A second conductor pattern is formed on a surface of a base, the second conductor pattern including a second plurality of contact pads. Each pad of the first plurality of contact pads is directly bonded to a respective pad of the second plurality of contact pads. A ring-shaped seal is form between a perimeter of the piezoelectric plate and a perimeter of the base.

It is claimed: 
     
         1 . A method of fabricating an acoustic resonator device, comprising:
 fabricating an acoustic resonator chip, comprising:
 bonding a back surface of a piezoelectric plate to a substrate; 
 forming a cavity in the substrate such that a portion of the piezoelectric plate forms a diaphragm spanning the cavity; and 
 forming a first conductor pattern as one or more conductor layers on a front surface of the single-crystal piezoelectric plate, the first conductor pattern including:
 an interdigital transducer (IDT), interleaved fingers of the IDT are disposed on the diaphragm, and 
 a first plurality of contact pads; 
 
   forming a second conductor pattern on a back surface of a base, the second conductor pattern including:
 a second plurality of contact pads; 
   attaching the back surface of the base to the front surface of the piezoelectric plate by directly bonding each contact pad of the first plurality of contact pads to a respective contact pads of the second plurality of contact pads; and   forming a ring-shaped seal between a perimeter of the piezoelectric plate and a perimeter of the base.   
     
     
         2 . The method of  claim 1 , wherein
 the cavity is a hole passing through a thickness of the substrate, and   the method further comprises bonding a cap to a back surface of the substrate.   
     
     
         3 . The method of  claim 1 , wherein
 the first conductor pattern further includes a first conductor ring about the perimeter of the piezoelectric plate,   the second conductor pattern further includes a second conductor ring about the perimeter of the base, and   forming a ring-shaped seal comprises directly bonding the first conductor ring to the second conductor ring.   
     
     
         4 . The method of  claim 1 , wherein forming a ring-shaped seal further comprises:
 applying a ring of adhesive material around one or both of a perimeter of the piezoelectric plate and a perimeter of the base; and   curing the adhesive material after or concurrent with directly bonding the first plurality of contact pads to the second plurality of contact pads.   
     
     
         5 . The method of  claim 1 , wherein
 the method further comprises forming vias to connect the second plurality of contact pads to a third plurality of contact pads formed on the front surface of the base.   
     
     
         6 . The method of  claim 1 , further comprising:
 prior to attaching the base to the piezoelectric plate, forming a recess in the back surface of the base, the recess located in an area of the back surface of the base that will face the diaphragm.   
     
     
         7 . The method of  claim 6 , wherein forming a recess in the back surface of the base further comprises:
 forming a recess having a depth such that, after attaching the base to the piezoelectric plate, a distance from a bottom of the recess to the diaphragm is greater than or equal to 15 microns and less than or equal to 100 microns.   
     
     
         8 . The method of  claim 1 , wherein
 the acoustic resonator device is a bandpass filter;   forming a cavity in the substrate comprises forming a plurality of cavities such that a plurality of portions of the piezoelectric plate form a corresponding plurality of diaphragms spanning respective cavities of the plurality of cavities; and   the first conductor pattern includes a plurality of IDTs, interleaved fingers of each IDT disposed on a respective diaphragm of the plurality of diaphragms.   
     
     
         9 . The method of  claim 1 , wherein
 the method further comprises forming vias to connect the second plurality of contact pads to a third plurality of contact pads formed on the front surface of the base; and   wherein the base is silicon and the vias are through-silicon-vias (TSVs).   
     
     
         10 . The method of  claim 1 , wherein the IDT and piezoelectric plate are configured such that a radio frequency signal applied to the IDT excites a bulk shear acoustic wave in the diaphragm. 
     
     
         11 . A method of fabricating an acoustic resonator device, comprising:
 fabricating an acoustic resonator chip, comprising:
 bonding a back surface of a piezoelectric plate to a substrate; 
 forming a cavity in the substrate such that a portion of the piezoelectric plate forms a diaphragm spanning the cavity; and 
 forming a first conductor pattern as one or more conductor layers on a front surface of the single-crystal piezoelectric plate, the first conductor pattern including:
 an interdigitated transducer (IDT) comprising two bus bars and interleaved fingers, the interleaved fingers of the IDT disposed on the diaphragm, 
 the piezoelectric plate and IDT configured so that a radio frequency or microwave signal applied between the two busbars excites a bulk shear acoustic wave within the diaphragm; and 
 a first plurality of contact pads; 
 
   forming a second conductor pattern on a back surface of a base of an interposer, the second conductor pattern including:
 a second plurality of contact pads; 
   attaching the back surface of the base to the front surface of the piezoelectric plate by directly bonding each contact pad of the first plurality of contact pads to a respective contact pads of the second plurality of contact pads; and   forming a ring-shaped seal between a perimeter of the piezoelectric plate and a perimeter of the base.   
     
     
         12 . The method of  claim 11 , wherein
 the first conductor pattern further includes a first conductor ring about the perimeter of the piezoelectric plate,   the second conductor pattern further includes a second conductor ring about the perimeter of the base, and   forming a ring-shaped seal comprises directly bonding the first conductor ring to the second conductor ring.   
     
     
         13 . The method of  claim 11 , wherein
 the interposer further comprises through-silicon-vias (TSVs) connecting the second plurality of contact pads to a third plurality of contact pads formed on the front surface of the base; and   the base is silicon.   
     
     
         14 . The method of  claim 11 , further comprising:
 prior to attaching the base to the piezoelectric plate, forming a recess in the back surface of the base, the recess located in an area of the back surface of the base that will face the diaphragm; and   wherein forming a recess in the back surface of the base further comprises forming a recess having a depth such that, after attaching the base to the piezoelectric plate, a distance from a bottom of the recess to the diaphragm is greater than or equal to 15 microns and less than or equal to 100 microns.   
     
     
         15 . The method of  claim 11 , wherein
 the acoustic resonator device is a bandpass filter;   forming a cavity in the substrate comprises forming a plurality of cavities such that a plurality of portions of the piezoelectric plate form a corresponding plurality of diaphragms spanning respective cavities of the plurality of cavities; and   the first conductor pattern includes a plurality of IDTs, interleaved fingers of each IDT disposed on a respective diaphragm of the plurality of diaphragms.   
     
     
         16 . A method of fabricating a filter device, comprising:
 fabricating an acoustic resonator chip, comprising:
 bonding a back surface of a piezoelectric plate to a substrate; 
 forming one or more cavities in the substrate such that a portion of the piezoelectric plate forms a diaphragm spanning the cavities; and 
 forming a conductor pattern on a front surface of the single-crystal piezoelectric plate, the conductor pattern including:
 a plurality of interdigitated transducer (IDTs) of a respective plurality of resonators and a first plurality of contact pads; wherein 
 interleaved fingers of each of the plurality of IDTs are disposed on respective portions of the piezoelectric plate suspended over the one or more cavities; 
 
 depositing a first thickness of a first dielectric layer between the fingers of the IDT of a first resonator of a respective plurality of resonators; and 
 depositing a second thickness of a second dielectric layer between the fingers of the IDT of a second resonator of a respective plurality of resonators; and 
   forming a second conductor pattern on a back surface of a base of an interposer, the second conductor pattern including:
 a second plurality of contact pads; and 
   attaching the back surface of the base to the front surface of the piezoelectric plate by directly bonding each contact pad of the first plurality of contact pads to a respective contact pads of the second plurality of contact pads; and   forming a ring-shaped seal between a perimeter of the piezoelectric plate and a perimeter of the base.   
     
     
         17 . The method of  claim 16 , wherein the plurality of resonators includes at least five resonators, each resonator having:
 a recess in the base facing the diaphragm; and   a distance from a bottom of the recess to the diaphragm is greater than or equal to 15 microns and less than or equal to 100 microns.   
     
     
         18 . The method of  claim 16 , wherein
 all of the plurality of IDTs are configured to excite shear acoustic waves in the piezoelectric plate in response to respective radio frequency signals applied to each IDT;   the interposer further comprises through-silicon-vias (TSVs) connecting the second plurality of contact pads to a third plurality of contact pads formed on the front surface of the base; and   the base is silicon.