Transversely-excited film bulk acoustic resonator using pre-formed cavities

Abstract

Acoustic resonator devices, filter devices, and methods of making acoustic resonator devices and filter devices. An acoustic resonator device includes a substrate with a cavity and an alignment pattern in a surface of the substrate. The cavity and the alignment pattern have a same depth. A back surface of a piezoelectric plate is attached to the surface of the substrate. A portion of the piezoelectric plate that spans the cavity forms a diaphragm. An interdigital transducer (IDT) is on a front surface of the piezoelectric plate. Interleaved fingers of the IDT are on the diaphragm.

It is claimed: 
     
         1 . An acoustic resonator comprising:
 a substrate including a base and an intermediate layer, wherein a cavity and an alignment pattern each extend into at least the intermediate layer of the substrate;   at least one piezoelectric plate supported by the substrate and including a diaphragm that spans the cavity; and   an interdigital transducer (IDT) at a surface of the at least one piezoelectric plate and including a plurality of interleaved fingers on the diaphragm.   
     
     
         2 . The acoustic resonator of  claim 1 , wherein the cavity and the alignment pattern have a same depth extending into the substrate. 
     
     
         3 . The acoustic resonator of  claim 1 , wherein the at least one piezoelectric plate is directly connected to the intermediate layer of the substrate. 
     
     
         4 . The acoustic resonator of  claim 1 , wherein the IDT and the at least one piezoelectric plate are configured such that a radio frequency signal applied to the IDT excites a primary acoustic mode in the diaphragm. 
     
     
         5 . The acoustic resonator of  claim 1 , wherein the alignment pattern is a trench configured to facilitate alignment of the at least one piezoelectric plate and the interleaved fingers. 
     
     
         6 . The acoustic resonator of  claim 1 , wherein the base of the substrate comprises Si and the intermediate layer of the substrate comprises SiO 2 . 
     
     
         7 . The acoustic resonator of  claim 1 , further comprising:
 a front-side dielectric layer on a front surface of the at least one piezoelectric plate; and   a back-side dielectric layer on a back surface of the at least one piezoelectric plate that is opposite the front surface of the at least one piezoelectric plate.   
     
     
         8 . The acoustic resonator of  claim 1 , wherein the alignment pattern comprises a plurality of alignment patterns positioned at a perimeter of the substrate and the cavity is positioned internal to the plurality of alignment patterns relative to a lateral direction of the surface of the at least one piezoelectric plate. 
     
     
         9 . A filter device comprising:
 a substrate including a base and an intermediate layer, wherein a plurality of cavities and at least one alignment pattern each extend into at least the intermediate layer of the substrate;   at least one piezoelectric plate supported by the substrate, the at least one piezoelectric plate including a plurality of diaphragms that span the plurality of cavities, respectively; and   a conductor pattern at a surface of the at least one piezoelectric plate, the conductor pattern comprising a plurality of interdigital transducers (IDTs) of a respective plurality of acoustic resonators, wherein interleaved fingers of each of the plurality of IDTs are on a respective diaphragm of the plurality of diaphragms.   
     
     
         10 . The filter device of  claim 9 , wherein the plurality of cavities and the alignment pattern all have a same depth extending into the substrate. 
     
     
         11 . The filter device of  claim 9 , wherein the at least one piezoelectric plate is directly connected to the intermediate layer of the substrate. 
     
     
         12 . The filter device of  claim 9 , wherein the plurality of IDTs and the at least one piezoelectric plate are each configured such that a radio frequency signal applied to each IDT excites a primary acoustic mode in the respective diaphragm of the plurality of diaphragms. 
     
     
         13 . The filter device of  claim 9 , wherein the alignment pattern is a trench configured to facilitate alignment of the at least one piezoelectric plate and the interleaved fingers. 
     
     
         14 . The filter device of  claim 9 , wherein the base of the substrate comprises Si and the intermediate layer of the substrate comprises SiO 2 . 
     
     
         15 . The filter device of  claim 9 , further comprising:
 a front-side dielectric layer on a front surface of the at least one piezoelectric plate; and   a back-side dielectric layer on a back surface of the at least one piezoelectric plate that is opposite the front surface of the at least one piezoelectric plate.   
     
     
         16 . The filter device of  claim 9 , wherein the alignment pattern comprises a plurality of alignment patterns positioned at a perimeter of the substrate and the plurality of cavities are positioned internal to the plurality of alignment patterns relative to a lateral direction of the surface of the at least one piezoelectric plate. 
     
     
         17 . An acoustic resonator comprising:
 a substrate including a cavity and an alignment pattern that each extend into at least a portion of the substrate;   at least one piezoelectric plate supported by the substrate and including a diaphragm that spans the cavity; and   an interdigital transducer (IDT) at a surface of the at least one piezoelectric plate and including a plurality of interleaved fingers on the diaphragm.   
     
     
         18 . The acoustic resonator of  claim 17 , wherein the cavity and the alignment pattern have a same depth extending into the substrate. 
     
     
         19 . The acoustic resonator of  claim 17 , wherein the substrate includes a base and an intermediate layer, such that the cavity and the alignment pattern each extend into at least the intermediate layer of the substrate. 
     
     
         20 . The acoustic resonator of  claim 19 , wherein the base of the substrate comprises Si and the intermediate layer of the substrate comprises SiO 2 .