Surface acoustic wave filter, balanced type circuit, and communication apparatus

Abstract

A surface acoustic wave filter including a piezoelectric substrate, IDT electrodes which are formed on the piezoelectric substrate and are connected to balanced type terminals. Further, IDT electrodes are formed on the piezoelectric substrate and are connected to an unbalanced type terminal, connection electrodes of connecting the IDT electrodes, the IDT electrodes IDT electrodes to the balanced type terminals or the unbalanced type terminal, and a dielectric thin film formed between the piezoelectric substrate and the IDT electrodes, the IDT electrodes, the connection electrodes.

1 . A surface acoustic wave filter, comprising: 
 a piezoelectric substrate,    a first IDT electrode formed on the piezoelectric substrate.    a second IDT electrode formed on the piezoelectric substrate    a first connection electrode connected to the first IDT electrode,    a second connection electrode connected to the second IDT electrode, and    a dielectric thin film formed between the piezoelectric substrate and at least one of the first connection electrode and the second connection electrode but not formed between the piezoelectric substrate, and the first IDT electrode and the second IDT electrode.    
   
   
       2 . The surface acoustic wave filter according to  claim 1 , wherein the dielectric thin film comprises silicon nitride or silicon oxide.  
   
   
       3 . The surface acoustic wave filter according to  claim 1 , wherein the piezoelectric substrate comprises lithium tantalate or lithium niobate.  
   
   
       4 . The surface acoustic wave filter according to  claim 1 , wherein the dielectric thin film is smaller in effective relative dielectric constant than the piezoelectric substrate.  
   
   
       5 . The surface acoustic wave filter according to  claim 4 , wherein the dielectric thin film has a piezoelectric property.  
   
   
       6 . The surface acoustic wave filter according to  claim 4 , wherein the piezoelectric substrate has an effective relative dielectric constant of about 40 or more.  
   
   
       7 . A communication apparatus, comprising: 
 transmitting and receiving means of performing transmission and/or reception, and    a surface acoustic wave filter according to  claim 1 , performing filtering on a transmission signal for transmission and/or a reception signal for reception.    
   
   
       8 . A method for fabricating a surface acoustic wave filter, comprising: 
 a first step of forming a first connection electrode connected to a first IDT electrode formed on a piezoelectric substrate,    a second step of forming a second connection electrode connected to a second IDT electrode formed on the piezoelectric substrate, and    a third step of forming a dielectric thin film,    wherein the dielectric thin film is formed between the piezoelectric substrate and at least one of the first connection electrode and the second connection electrode, but is not formed between the piezoelectric substrate, and the first IDT electrode and the second IDT electrode.