Thin-film piezoelectric resonator, band-pass filter and method of making thin-film piezoelectric resonator

Abstract

A thin-film piezo-resonator includes a silicon substrate and a resonator assembly. The substrate is formed with a cavity or through-hole which is opened in the upper and the lower surfaces of the substrate. The resonator assembly, disposed at a location corresponding to the cavity, is composed of a first electrode contacting the upper surface of the substrate, a piezoelectric layer formed on the first electrode and a second electrode formed on the piezoelectric layer. The cavity has a side surface extending in a substantially perpendicular direction to the first surface.

1 . A thin-film piezo-resonator comprising: 
 a substrate having a first surface and a second surface opposite to said first surface, the substrate being formed with a cavity that has a first opening in said first surface and a second opening in said second surface; and    a resonator assembly including an exciter composed of a first electrode contacting said first surface, a piezoelectric layer on the first electrode and a second electrode on the piezoelectric layer, the assembly being disposed at a location corresponding to the cavity;    wherein the cavity includes a side surface extending in a substantially perpendicular direction to said first surface.    
     
     
         2 . The resonator according to  claim 1 , wherein the first electrode comprises a uniaxially oriented single-layer conductive member or uniaxially oriented multi-layer conductive member.  
     
     
         3 . The resonator according to  claim 2 , wherein the piezoelectric layer is uniaxially oriented.  
     
     
         4 . The resonator according to  claim 1 , wherein the substrate is a (111)-cut silicon substrate, said first surface and said second surface each being a (111) surface.  
     
     
         5 . The resonator according to  claim 4 , wherein the first electrode comprises a single conductive layer containing either one of (111)-uniaxially oriented Al and (111)-uniaxially oriented Cu.  
     
     
         6 . The resonator according to  claim 4 , wherein the first electrode comprises a stack of uniaxially oriented conductive layers including a first conductive layer held in contact with said first surface, the first conductive layer containing either one of (111)-uniaxially oriented Al and (111)-uniaxially oriented Cu.  
     
     
         7 . The resonator according to  claim 4 , wherein the first electrode has a two-layer structure comprising a first conductive layer and a second conductive layer, the first conductive layer held in contact with said first surface and containing either one of (111)-uniaxially oriented Al and (111)-uniaxially oriented Cu, the second conductive layer containing (110)-uniaxially oriented Mo.  
     
     
         8 . The resonator according to  claim 4 , wherein the piezoelectric layer is made of either one of (002)-uniaxially oriented AlN and (002)-uniaxially oriented ZnO.  
     
     
         9 . The resonator according to  claim 1 , further comprising a cover substrate bonded to said second surface of the substrate so as to close the cavity.  
     
     
         10 . The resonator according to  claim 1 , wherein each of the first and the second openings has a circular or oval configuration.  
     
     
         11 . The resonator according to  claim 1 , wherein each of the first electrode and the piezoelectric layer includes a portion exposed to the cavity.  
     
     
         12 . The resonator according to  claim 11 , wherein the exposed portion of the first electrode and the exposed portion of the piezoelectric layer are made of a material which is not etched by a fluorine gas.  
     
     
         13 . A thin-film piezo-resonator comprising: 
 a (111)-cut silicon substrate;    a first electrode formed on the substrate and containing either one of Al and Cu;    a piezoelectric layer formed on the first electrode and containing either one of AlN and ZnO; and    a second electrode formed on the piezoelectric layer;    wherein the silicon substrate includes a first surface which is a (111) surface, the first electrode being held in contact with said first surface.    
     
     
         14 . A thin-film piezo-resonator comprising: 
 a substrate having a first surface and a second surface opposite to said first surface, the substrate being formed with a cavity that has a first opening in said first surface; and    a resonator assembly including a first electrode contacting said first surface, a piezoelectric layer on the first electrode and a second electrode on the piezoelectric layer, the assembly being disposed at a location corresponding to the cavity;    wherein each of the first electrode and the piezoelectric layer includes a portion exposed to the cavity.    
     
     
         15 . The resonator according to  claim 1 , wherein the first and the second electrodes comprise first and second exciter portions, respectively, that define the exciter, the first opening being greater in area than the exciter portions by a factor of 1˜2.25.  
     
     
         16 . The resonator according to  claim 15 , wherein the first exciter portion and the second exciter portion are substantially identical in shape.  
     
     
         17 . The resonator according to  claim 15 , wherein each of the first and the second exciter portions is at least partially circular or oval.  
     
     
         18 . A filter comprising: 
 a substrate having a first surface and a second surface opposite to said first surface, the substrate being formed with a plurality of cavities spaced from each other;    a first electrode pattern held in contact with said first surface;    a piezoelectric layer on the first electrode pattern;    a second electrode pattern on the piezoelectric layer; and    a plurality of resonator assemblies provided by a combination of the first electrode pattern, the piezoelectric layer and the second electrode pattern, each of the resonator assemblies corresponding in position to one of the cavities;    wherein each of the cavities has a side surface extending in a substantially perpendicular direction to said first surface.    
     
     
         19 . The filter according to  claim 18 , wherein each of the cavities includes a first opening in said first surface and a second opening in said second surface, a distance between adjoining first openings being no greater than 420 μm.  
     
     
         20 . The filter according to  claim 18 , wherein said plurality of resonator assemblies include a first group of resonator assemblies connected in series and a second group of resonator assemblies connected in parallel.  
     
     
         21 . The filter according to  claim 18 , wherein the first electrode pattern and the piezoelectric layer are exposed to one of the cavities.  
     
     
         22 . A filter comprising: 
 a substrate having a first surface and a second surface opposite to said first surface, the substrate being formed with a plurality of cavities each including a first opening in said first surface and a second opening in said second surface;    a first electrode pattern held in contact with said first surface;    a piezoelectric layer on the first electrode pattern;    a second electrode pattern on the piezoelectric layer; and    a plurality of exciters provided by a combination of the first electrode pattern, the piezoelectric layer and the second electrode pattern, each of the exciters corresponding in position to one of the cavities;    wherein the first electrode pattern and the piezoelectric layer each include a portion exposed to one of the cavities.    
     
     
         23 . The filter according to  claim 22 , wherein the exposed portions of the first electrode pattern and the piezoelectric layer are made of a material which is not etched by a fluorine gas.  
     
     
         24 . The filter according to  claim 22 , wherein each of the exciters is defined by a first exciter portion and a second exciter portion contained respectively in the first electrode pattern and the second electrode pattern, the first exciter portion and the second exciter portion being substantially identical in shape.  
     
     
         25 . The filter according to  claim 24 , wherein the first opening of the cavity corresponding to said each exciter is greater in area than the exciter portions by a factor of 1˜2.25.  
     
     
         26 . The filter according to  claim 22 , wherein the first and the second openings of each cavity are circular or oval.  
     
     
         27 . A method of making a thin-film piezo-resonator comprising steps of: 
 preparing a substrate including a first surface and a second surface opposite to said first surface;    forming a resonator assembly which includes a first electrode held in contact with said first surface, a piezoelectric layer formed on the first electrode and a second electrode formed on the piezoelectric layer; and    forming a cavity by dry-etching the substrate, the cavity being disposed at a location corresponding to the resonator assembly, the cavity being opened in said first surface and said second surface;    wherein the cavity includes a side surface extending in a substantially perpendicular direction to said first surface.    
     
     
         28 . The method according to  claim 27 , wherein the dry etching is Deep-RIE.  
     
     
         29 . The method according to  claim 27 , further comprising the step of bonding a cover substrate to said second surface so as to close the cavity.  
     
     
         30 . The method according to  claim 27 , wherein a groove for dividing the substrate is also formed by etching at the cavity-forming step.  
     
     
         31 . A method of making a thin-film piezo-resonator comprising steps of: 
 preparing a substrate including a first surface and a second surface opposite to said first surface;    forming a resonator assembly which includes a first electrode held in contact with said first surface, a piezoelectric layer formed on the first electrode and a second electrode formed on the piezoelectric layer; and    forming a cavity by dry-etching the substrate, the cavity being disposed at a location corresponding to the resonator assembly, the cavity being opened in said first surface and said second surface;    wherein the first electrode and the piezoelectric layer are partially exposed to the cavity at the cavity-forming step.