Bulk acoustic wave resonator

Abstract

A bulk acoustic wave (BAW) resonator includes: an acoustic reflector disposed in a substrate; a lower electrode disposed over the acoustic reflector; a piezoelectric layer disposed over the lower electrode; and an upper electrode disposed over the piezoelectric layer. A contacting overlap of the lower electrode, the piezoelectric layer and the upper electrode over the acoustic reflector comprising an active area of the BAW resonator. An opening exists in the upper electrode in a region of the BAW resonator susceptible to unacceptable overheating.

1 . A bulk acoustic wave (BAW) resonator, comprising:
 an acoustic reflector disposed in a substrate;   a lower electrode disposed over the acoustic reflector;   a piezoelectric layer disposed over the lower electrode; and   an upper electrode disposed over the piezoelectric layer, a contacting overlap of the lower electrode, the piezoelectric layer, and the upper electrode over the acoustic reflector comprising an active area of the BAW resonator, wherein an opening exists in the upper electrode in a region of the BAW resonator susceptible to unacceptable overheating.   
     
     
         2 . The BAW resonator as claimed in  claim 1 , wherein the opening does not extend into the piezoelectric layer. 
     
     
         3 . The BAW resonator as claimed in  claim 1 , wherein the opening exists substantially in a central portion of the upper electrode. 
     
     
         4 . The BAW resonator as claimed in  claim 1 , wherein the acoustic reflector is a cavity provided in the substrate. 
     
     
         5 . The BAW resonator as claimed in  claim 1 , wherein the acoustic reflector comprises alternating low acoustic impedance and high acoustic impedance layers. 
     
     
         6 . The BAW resonator as claimed in  claim 1 , wherein the opening has a substantially circular shape. 
     
     
         7 . The BAW resonator as claimed in  claim 1 , wherein the opening has a substantially hexagonal shape. 
     
     
         8 . The BAW resonator as claimed in  claim 1 , wherein the active area is increased by an areal dimension substantially equal to an areal dimension of the opening, and the BAW resonator has substantially the same electrical impedance as a known BAW resonator having substantially the same size active area as the BAW resonator. 
     
     
         9 . The BAW resonator as claimed in  claim 1 , further comprising a passivation layer disposed over the upper electrode, wherein the opening extends through the passivation layer. 
     
     
         10 . The BAW resonator as claimed in  claim 1 , wherein the region has an areal dimension, and the opening is substantially located in the region, and has the areal dimension. 
     
     
         11 . A BAW resonator as claimed in  claim 1 , wherein the piezoelectric layer comprises aluminum nitride (AlN) doped with scandium (Sc). 
     
     
         12 . The BAW resonator as claimed in  claim 1 , wherein a center of the opening is located at a greatest distance from an anchor point of the BAW resonator. 
     
     
         13 . An electrical filter, comprising:
 a series bulk acoustic wave (BAW) resonator connected to a shunt BAW resonator, the series BAW resonator comprising:   an acoustic reflector disposed in a substrate;   a lower electrode disposed over the acoustic reflector;   a piezoelectric layer disposed over the lower electrode; and   an upper electrode disposed over the piezoelectric layer, a contacting overlap of the lower electrode, the piezoelectric layer, and the upper electrode over the acoustic reflector comprising an active area of the series BAW resonator, wherein an opening exists in the upper electrode in a region of the series BAW resonator susceptible to unacceptable overheating.   
     
     
         14 . The electrical filter as claimed in  claim 13 , wherein the opening does not extend into the piezoelectric layer. 
     
     
         15 . The electrical filter as claimed in  claim 13 , wherein the opening exists substantially in a central portion of the upper electrode. 
     
     
         16 . The electrical filter as claimed in  claim 13 , wherein the acoustic reflector is a cavity provided in the substrate. 
     
     
         17 . The electrical filter as claimed in  claim 13 , wherein the acoustic reflector comprises alternating low acoustic impedance and high acoustic impedance layers. 
     
     
         18 .- 25 . (canceled) 
     
     
         26 . An acoustic resonator, comprising:
 a substrate;   a first electrode disposed over the substrate;   a piezoelectric layer disposed over the first electrode;   a second electrode disposed over the piezoelectric layer,   an acoustic reflector disposed below the first electrode, wherein   a contacting overlap of the first electrode, the piezoelectric layer, and the second electrode over the acoustic reflector corresponds to an active area of the acoustic resonator, and   the second electrode having an opening that extends completely through the second electrode; and   a frame element disposed over the second electrode, wherein the frame element is disposed adjacent to a perimeter of the active area of the acoustic resonator.   
     
     
         27 . The acoustic resonator of  claim 26 , wherein the frame element comprises a metal material. 
     
     
         28 . The acoustic resonator of  claim 26 , wherein the frame element comprises a dielectric material. 
     
     
         29 . The acoustic resonator of  claim 26 , wherein the frame element is provided on at least one side of the second electrode. 
     
     
         30 . The acoustic resonator of  claim 29 , wherein the second electrode further comprises a cantilevered portion provided on at least one side of the second electrode. 
     
     
         31 . The acoustic resonator of  claim 26 , wherein the second electrode further comprises a cantilevered portion provided on at least one side of the second electrode. 
     
     
         32 . The acoustic resonator of  claim 26 , wherein the acoustic reflector is a cavity disposed in the substrate. 
     
     
         33 . The acoustic resonator of  claim 26 , wherein the acoustic reflector is a Bragg reflector disposed in the substrate.