Piezoelectric thin film resonator and manufacturing method thereof

Abstract

A piezoelectric thin film resonator which can reduce variations in resonant frequency and resonant resistance by uniformly planarizing a structural film, and a method of manufacturing the piezoelectric thin film resonator. The piezoelectric thin film resonator has a substrate having at least one flat major surface; a dielectric film having two support portions supported by the major surface of the substrate and a floating portion which is connected to the support portions and which is disposed over the major surface of the substrate with an airspace layer provided therebetween; and a vibration portion which is formed of a pair of electrodes and a piezoelectric thin film provided therebetween and which is provided on the floating portion of the dielectric film at a side opposite to the airspace layer. A surface of the dielectric film at a side opposite to the substrate is planarized by a plasma treatment using an inert gas or a gas containing an element forming a dielectric film.

1 . A piezoelectric thin film resonator comprising: 
 a substrate having at least one flat major surface;    a dielectric film having two support portions supported by the major surface of the substrate and a floating portion connected to the support portions and disposed over the major surface of the substrate with an airspace layer provided therebetween; and    a vibration portion comprising a pair of electrodes and a piezoelectric thin film provided therebetween, the vibration portion being provided on the floating portion of the dielectric film at a position opposite to the airspace layer,    wherein a surface of the dielectric film opposite to the substrate is plasma treatment planarized using an inert gas or a gas containing an element forming the dielectric film.    
   
   
       2 . The piezoelectric thin film resonator according to  claim 1 , wherein the dielectric film comprises a material selected from the group consisting of Si 3 N 4 , SiO 2 , and Al 2 O 3 .  
   
   
       3 . A method for manufacturing piezoelectric thin film resonators, the method comprising: 
 forming sacrifice layer patterns on an upper surface of a mother substrate;    forming a dielectric film on the sacrifice layer patterns;    processing a surface of the dielectric film by a plasma treatment;    forming vibration portions on the dielectric film, the vibration portions each being composed of two excitation electrodes and a piezoelectric thin film provided therebetween;    etching the sacrifice layers; and    cutting the mother substrate into separate piezoelectric thin film resonators.    
   
   
       4 . The method for manufacturing a piezoelectric thin film, according to  claim 3 , 
 wherein the step of processing the surface of the dielectric film comprises:    fitting the mother substrate provided with the dielectric film formed thereon to a substrate plate;    placing the mother substrate in a sputtering chamber;    supplying a gas in the sputtering chamber; and    performing sputtering etching of the surface of the dielectric film with plasma of the gas generated by supplying an RF voltage to the substrate plate while the substrate plate is electrically floated from the sputtering chamber.    
   
   
       5 . The method for manufacturing a piezoelectric thin film, according to  claim 4 , wherein the gas is an inert gas selected from the group consisting of Ar and He.  
   
   
       6 . The method for manufacturing a piezoelectric thin film, according to  claim 4 , wherein the gas is a gas comprising an element forming the dielectric film.  
   
   
       7 . The method for manufacturing a piezoelectric thin film, according to  claim 6 , wherein the dielectric film is formed of SiO 2  or Al 2 O 3 , and oxygen is used as the gas.  
   
   
       8 . The method for manufacturing a piezoelectric thin film, according to  claim 6 , wherein the dielectric film is formed of Si 3 N 4 , and nitrogen is used as the gas.