Incremental tuning process for electrical resonators based on mechanical motion

Abstract

The present invention is a method for adjusting the resonant frequency of a mechanical resonator whose frequency is dependent on the overall resonator thickness. Alternating selective etching is used to remove distinct adjustment layers from a top electrode. One of the electrodes is structured with a plurality of stacked adjustment layers, each of which has distinct etching properties from any adjacent adjustment layers. Also as part of the same invention is a resonator structure in which at least one electrode has a plurality of stacked layers of a material having different etching properties from any adjacent adjustment layers, and each layer has a thickness corresponding to a calculated frequency increment in the resonant frequency of the resonator.

1 . A mechanical resonator comprising a first electrode a transducer and a second electrode wherein the second electrode comprises a conductive layer and a plurality of distinct stacked adjustment layers, each of said adjustment layers having distinct etching properties from any adjacent adjustment layers.  
     
     
         2 . A mechanical resonator according to  claim 1  wherein said resonator has a resonant frequency that is a function of said resonator thickness and wherein the stacked adjustment layers each have a thickness such that removal of an adjustment layer increases the resonant frequency by a known increment.  
     
     
         3 . A mechanical resonator according to  claim 2  wherein said adjustment layer thickness is a same thickness for all adjustment layers.  
     
     
         4 . A mechanical resonator according to  claim 2  wherein said adjustment layer thickness is different for different adjustment layers such different being a function of the material and process used for depositing and etching such material.  
     
     
         5 . A mechanical resonator according to  claim 2  wherein said first electrode is a bottom electrode over a supporting substrate.  
     
     
         6 . A method for manufacturing a mechanical resonator comprising using alternating selective etching to remove distinct adjustment layers from an electrode comprising a plurality of stacked adjustment layers, each of said adjustment layers having distinct etching properties from any adjacent adjustment layers.  
     
     
         7 . A method of manufacturing a mechanical resonator having a desired resonant frequency comprising: 
 forming a first electrode;    forming a transducer layer over said first electrode;    forming a second electrode having a plurality of discreet layers of known thickness, each of said discreet layers having etching properties different from at least one other of said discreet layers;    sequentially etching a calculated number of said discreet layers thereby incrementally reducing said resonator overall thickness by a known amount to adjust said resonator resonant frequency to a desired resonant frequency.    
     
     
         8 . The method according to  claim 7  wherein the thickness of each of the discreet layers is calculated to represent a selected frequency increment of the resonant frequency.  
     
     
         9 . The method according to  claim 7  wherein the step of forming the second electrode discreet layers further comprises: 
 forming a first conductive electrode layer having a thickness calculated to produce a resonator having a first resonant frequency that is higher than the desired resonant frequency;  
 calculating a desired thickness for an adjustment layer such that when said adjustment layer is placed over said first conductive layer the resonant frequency of the resonator is reduced by a selected frequency increment;  
 forming a plurality of adjustment layers over said conductive layer sufficient to produce a second electrode thickness such that the resonant frequency of the resonator is below said desired resonant frequency, each of said adjustment layers having etching properties different from the etching properties of any adjacent adjustment layers;  
 measuring an actual resonant frequency of the resonator and calculating a number of adjustment layers to be removed to incrementally adjust the actual resonator frequency to the desired resonant frequency; and  
 sequentially selectively etching said calculated number of adjustment layers to adjust the resonator resonant frequency to said desired frequency.  
 
     
     
         10 . The method according to  claim 9  wherein said adjustment layers are alternating layers of two materials having distinct etching properties.  
     
     
         11 . The method according to  claim 9  wherein the etching is a wet etching process.  
     
     
         12 . The method according to  claim 9  wherein there are at least two resonators electrically connected and wherein the step of forming said adjustment layers comprises forming a first plurality of stacked alternating adjustment layers having first and second etching properties on one of said at least two resonators, and forming a second plurality of stacked alternating adjustment layers having third and fourth etching properties, and alternatively selectively etching said first and said second pluralities of alternating stacked layers to remove said calculated number of adjustment layers to adjust the resonator resonant frequency to a different desired frequency for each of said at least two resonators.