Bulk acoustic wave resonator, filter and duplexer and methods of making same

Abstract

A resonator having a membrane formed of a piezoelectric layer sandwiched between first and second electrode is suspended above a cavity formed from the back surface of the support structure. In one embodiment, the cavity walls are substantially perpendicular to the back surface. In another embodiment, the first electrode is formed in the cavity such that it is electrically connected to an electrode on the back surface of the support structure. In yet another embodiment, the cavity is formed via an etch through via holes in the back surface of the support structure, which leads to greater flexibility in designing a method of manufacture while reducing the need for alignment relative to other designs.

1 . A method of manufacturing a resonator, comprising the steps of:
 patterning a first electrode on a first surface of a support structure;   patterning a piezoelectric layer on said support structure to overlap said first electrode;   patterning a second electrode on said piezoelectric layer, wherein said first electrode, said piezoelectric layer and said second electrode form a membrane structure; and   forming, from a second surface of said support structure opposite to said first surface, a parallel walled via hole acting as a cavity under said membrane structure.   
   
   
       2 . A method in accordance with  claim 1 , further comprising the step of:
 thinning said support structure at a location of said membrane structure and prior to forming said parallel walled via hole.   
   
   
       3 . A method in accordance with  claim 1 , wherein said step of forming said parallel walled via hole includes a Reactive Ion Etching (RIE) process. 
   
   
       4 . A method of manufacturing a resonator, comprising the steps of:
 patterning a piezoelectric layer on a first surface of a support structure;   patterning a second electrode on said piezoelectric layer;   forming, from a second surface of said support structure opposite to said first surface, a cavity under said piezoelectric layer; and   patterning a first electrode in said cavity to extend on said piezoelectric layer, across at least part of a wall of said cavity and on said second surface of said support structure, wherein said first electrode, said piezoelectric layer and said second electrode form a membrane structure.   
   
   
       5 . A method in accordance with  claim 4 , wherein said cavity is a parallel walled via hole and further comprising the step of thinning said support structure at a location of said membrane structure and prior to forming said parallel walled via hole. 
   
   
       6 . A method in accordance with  claim 4 , wherein said step of forming said parallel walled via hole includes a Reactive Ion Etching (RIE) process. 
   
   
       7 . A method of manufacturing a resonator, comprising the steps of:
 patterning a first electrode on a first surface of a support structure;   patterning a piezoelectric layer on said support structure to overlap said first electrode;   patterning a second electrode on said piezoelectric layer, wherein said first electrode, said piezoelectric layer and said second electrode form a membrane structure;   forming, from a second surface of said support structure opposite to said first surface, a via hole under said membrane structure; and   removing a portion of said support structure to form a cavity under said membrane structure by introducing an etching agent through said via hole.   
   
   
       8 . A method in accordance with  claim 7 , further comprising the step of:
 forming a depression in said support structure prior to forming said first electrode; and   filling said depression with a sacrificial material to be part of said support structure, wherein said first electrode is formed on said sacrificial material and said removing step includes removing said sacrificial material to form said cavity under said membrane structure by introducing an etching agent through said via hole.   
   
   
       9 . A method in accordance with  claim 7 , further comprising the step of:
 forming at least one etch stop layer in said support structure to delimit said cavity.   
   
   
       10 . A method in accordance with  claim 7 , wherein said step of forming said parallel walled via hole includes a Reactive Ion Etching (RIE) process.