Acoustic mirror structure for a bulk acoustic wave structure and method for fabricating same

Abstract

According to one embodiment of the invention, an acoustic mirror structure situated in a bulk acoustic wave structure includes a number of alternating low acoustic impedance and high acoustic impedance layers situated on a substrate. Each high acoustic impedance layer includes a first mole percent of a primary metal and a second mole percent of a secondary metal, where the first mole percent of the primary metal is greater than the second mole percent of the secondary metal, and where the secondary metal causes each high acoustic impedance layer to have increased resistivity. According to this exemplary embodiment, the second mole percent of the secondary metal can cause only a minimal decrease in density of each high acoustic impedance layer. The increased resistivity of each high acoustic impedance layer can cause a reduction in electrical loss in the bulk acoustic wave structure.

1 - 8 . (canceled) 
     
     
         9 . A method for fabricating an acoustic mirror structure in a bulk acoustic wave structure, said method comprising steps of:
 depositing a plurality of alternating low acoustic impedance and high acoustic impedance layers on a substrate;   wherein each of said high acoustic impedance layers comprises a first mole percent of a primary metal and a second mole percent of a secondary metal, wherein said first mole percent of said primary metal is greater than said second mole percent of said secondary metal, wherein said secondary metal is selected to cause each of said high acoustic impedance layers to have an increase in resistivity.   
     
     
         10 . The method of  claim 9  wherein said second mole percent of said secondary metal does not cause a substantial decrease in density of each of said high acoustic impedance layers. 
     
     
         11 . The method of  claim 9  wherein said primary metal comprises tungsten. 
     
     
         12 . The method of  claim 11  wherein said secondary metal comprises titanium. 
     
     
         13 . The method of  claim 12  wherein said first mole percent is approximately 70 mole percent and said second mole percent is approximately 30 mole percent. 
     
     
         14 . The method of  claim 12  wherein said secondary metal causes said resistivity of each of said high acoustic impedance layers to increase by a factor of approximately five. 
     
     
         15 . The method of  claim 9  wherein said increase in said resistivity of each of said high acoustic impedance layers causes a reduction in electrical loss in said bulk acoustic wave structure. 
     
     
         16 . A method for fabricating an acoustic mirror structure in a bulk acoustic wave structure, said method comprising steps of:
 depositing a plurality of alternating low acoustic impedance and high acoustic impedance layers on a substrate, each of said high acoustic impedance layers comprising a metal;   wherein said step of depositing said plurality of alternating low acoustic impedance and high acoustic impedance layers comprises depositing each of said high acoustic impedance layers so as to increase a resistivity thereof while preventing a substantial decrease in a density of each of said high acoustic impedance layers.   
     
     
         17 . The method of  claim 16  wherein each of said high acoustic impedance layers is deposited by adding an impurity to a deposition process, wherein said impurity causes said resistivity of each of said high acoustic impedance layers to increase while preventing a substantial decrease in said density of each of said high acoustic impedance layers. 
     
     
         18 . The method of  claim 17  wherein said impurity comprises oxygen. 
     
     
         19 . The method of  claim 17  wherein said impurity comprises nitrogen. 
     
     
         20 . The method of  claim 16  wherein each of said high acoustic impedance layers is deposited by adjusting at least one process parameter in a deposition process so as to cause said resistivity of each of said high acoustic impedance layers to increase while pretending a substantial decrease in said density of each of said high acoustic impedance layers. 
     
     
         21 . The method of  claim 20  wherein said adjusting said at least one process parameter in said deposition process comprises increasing deposition power. 
     
     
         22 . The method of  claim 16  wherein said metal comprises tungsten. 
     
     
         23 . The method of  claim 16  wherein said increase in said resistivity of each of said high acoustic impedance layers causes a reduction in electrical loss in said bulk acoustic wave structure. 
     
     
         24 . A method for forming an acoustic mirror structure, said method comprising:
 forming a plurality of low acoustic impedance and high acoustic impedance layers situated on a substrate;   wherein at least one of said high acoustic impedance layers comprises a first mole percent of a primary metal and a second mole percent of a secondary metal, wherein said secondary metal causes said at least one of said high acoustic impedance layers to have increased resistivity.   
     
     
         25 . The method of  claim 24  wherein said second mole percent of said secondary metal does not cause a substantial decrease in density of at least one of said plurality of acoustic impedance layers. 
     
     
         26 . The method of  claim 24  wherein said increased resistivity of said at least one of said high acoustic impedance layers causes a reduction in electrical loss. 
     
     
         27 . The method of  claim 24  wherein said primary metal comprises tungsten, and said secondary metal comprises titanium. 
     
     
         28 . The method of  claim 24  wherein said secondary metal increases said resistivity of said at least one of said high acoustic impedance layers by a factor of approximately five.