Film bulk acoustic wave resonator, film bulk acoustic wave resonator filter and method of manufacturing film bulk acoustic wave resonator

Abstract

The present invention provides a film bulk acoustic wave resonator (FBAR) filter that can keep the Q factor high. The FBAR filter comprises a first FBAR with a first resonant frequency and a second FBAR with a second resonant frequency, formed on a same substrate. The FBAR filter has such a structure that a first underlayer is formed between the substrate and a first bottom electrode layer and a second underlayer is formed between the substrate and a second bottom electrode layer, the first underlayer thickness being different from the second underlayer thickness.

1 . A film bulk acoustic wave resonator comprising: 
 a substrate having a cavity;    an underlayer formed on said substrate to cover said cavity;    a bottom electrode layer formed on top of said underlayer;    a piezoelectric layer formed on top of said bottom electrode layer; and    a top electrode layer formed on top of said piezoelectric layer,    wherein said resonator's resonant frequency can be adjusted, depending on the thickness of said underlayer over said cavity.    
   
   
       2 . The film bulk acoustic wave resonator according to  claim 1 , 
 wherein at least either of said bottom electrode layer and said top electrode layer is made of a material which consists chiefly of at least one of the following:    molybdenum and tungsten.    
   
   
       3 . The film bulk acoustic wave resonator according to claim 
 wherein said underlayer is made of a material which consists chiefly of at least one of the following: silicon oxide, silicon nitride, alumina, aluminum nitride, and silicon carbide.    
   
   
       4 . A film bulk acoustic wave resonator filter including a plurality of film bulk acoustic wave resonators comprising: 
 a substrate having a plurality of cavities;    an underlayer formed on said substrate to cover said cavities;    a bottom electrode layer formed on top of said underlayer;    a piezoelectric layer formed on top of said bottom electrode layer; and    a top electrode layer formed on top of said piezoelectric layer,    wherein the underlayer thickness in a first region where a first resonator out of said plurality of resonators is formed differs from the underlayer thickness in a second region where a second resonator out of said plurality of resonators is formed.    
   
   
       5 . The film bulk acoustic wave resonator filter according to  claim 4 , 
 wherein at least either of said bottom electrode layer and said top electrode layer is made of a material which consists chiefly of at least one of the following: molybdenum and tungsten.    
   
   
       6 . The film bulk acoustic wave resonator filter according to  claim 4 , 
 wherein said underlayer is made of a material which consists chiefly of at least one of the following: silicon oxide, silicon nitride, alumina, aluminum nitride, and silicon carbide.    
   
   
       7 . A transmitting and receiving filter complex including a plurality of film bulk acoustic wave resonators comprising: 
 a substrate having a plurality of cavities;    an underlayer formed on said substrate to cover said cavities;    a bottom electrode layer formed on top of said underlayer;    a piezoelectric layer formed on top of said bottom electrode layer; and    a top electrode layer formed on top of said piezoelectric layer,    wherein said plurality of resonators' resonant frequencies can be adjusted, depending on the thickness of said underlayer over said cavities,    wherein a first resonator out of said plurality of resonators and a second resonator out of said plurality of resonators constitute a transmitting filter and a third resonator out of said plurality of resonators and a fourth resonator out of said plurality of resonators constitute a receiving filter, and    wherein the underlayer thickness in a first region where said first resonator is formed, the underlayer thickness in a second region where said second resonator is formed, the underlayer thickness in a third region where said third resonator is formed, and the underlayer thickness in a fourth region where said fourth resonator is formed differ one another.    
   
   
       8 . The transmitting and receiving filter complex according to  claim 7 , 
 wherein at least either of said bottom electrode layer and said top electrode layer is made of a material which consists chiefly of at least one of the following:    molybdenum and tungsten.    
   
   
       9 . The transmitting and receiving filter complex according to  claim 7 , 
 wherein said underlayer is made of a material which consists chiefly of at least one of the following: silicon oxide, silicon nitride, alumina, aluminum nitride, and silicon carbide.    
   
   
       10 . A method of manufacturing a film bulk acoustic wave resonator filter comprising a plurality of film bulk acoustic wave resonators on a single substrate, comprising steps of: 
 forming a trench with a depth on said single substrate, the depth corresponding to a difference between a first resonator's resonant frequency and a second resonator's resonant frequency out of said plurality of resonators; and    depositing an underlayer over said single substrate.    
   
   
       11 . The method of manufacturing the film bulk acoustic wave resonator filter according to  claim 10 , further comprising steps of: 
 smoothing to make said underlayer surface in a first region where said first resonator is formed substantially flush with said underlayer surface in a second region where said second resonator is formed    depositing a bottom electrode layer over the surface and patterning said bottom electrode layer, thereby forming a first bottom electrode layer on top of the underlayer in said first region and a second bottom electrode layer on top of the underlayer in said second region;    depositing a piezoelectric layer over the surface;    depositing a top electrode layer over the surface and patterning said top electrode layer, thereby forming a first top electrode layer on top of the piezoelectric layer in said first region and a second top electrode layer on top of the piezoelectric layer in said second region; and    from the back side of said single substrate, forming a first cavity in said first region and a second cavity in said second region by trenching,    wherein said step of depositing said underlayer over said single substrate deposits said underlayer over said single substrate in which said trench has been formed.    
   
   
       12 . The method of manufacturing the film bulk acoustic wave resonator filter according to  claim 10 , further comprising steps of: 
 depositing a bottom electrode layer over the surface and patterning said bottom electrode layer, thereby forming a first bottom electrode layer on top of the underlayer in said first region and a second bottom electrode layer on top of said underlayer in said second region where said second resonator is formed;    depositing a piezoelectric layer over the surface;    depositing a top electrode layer over the surface and patterning said top electrode layer, thereby forming said first region's top electrode layer and said second region's top electrode layer; and    from the back side of said single substrate, forming a first cavity in said first region and a second cavity in said second region by trenching,    wherein said film bulk acoustic wave resonator filter comprises the plurality of resonators with different underlayer thicknesses on said single substrate, and    wherein said step of forming the trench forms the trench in said underlayer in the first region where said first resonator is formed.