Acoustic transducer and method of making the same

Abstract

The present invention provides an transducer and a method of making the same. The transducer is comprised of a plurality of transducer cells, and conductive interconnects between the cells. Each transducer cell contains a bottom electrode formed on a layer of insulator material, a lower insulating film portion formed over the bottom electrode, a middle insulating film portion that includes an air/vacuum void region, and an upper insulating film portion that includes a top electrode formed within a portion of the upper insulating film portion. A first layer of interconnects electrically connect the bottom electrodes of each transducer cell and a second layer of interconnects electrically connect the top electrodes of each transducer cell. The top and bottom layers of interconnects are patterned to avoid overlap between them, thus reducing the parasitic capacitance. Further, as noted, the top electrode is preferably formed within the upper insulating film portion, closer to the air/vacuum void than to the top surface of the insulating film, to increase the electric field for a given voltage. Still furthermore, the electrodes within each transducer cell are preferably formed to have dimensions that are smaller than the overall surface area of the membrane that they excite.

I claim:  
     
         1 . A transducer comprising: 
 a supporting substrate;    at least two transducer cells formed on the substrate, each transducer cell including:    a first electrode formed over the substrate;    an insulating film formed over the first electrode and including a void region therein; and    a second electrode disposed at least substantially parallel to the first electrode and formed over at least a portion of the insulating film such that the void region is disposed between the first electrode and the second electrode;    a first interconnect that electrically connects the first electrodes of each of the at least two transducer cells; and    a second interconnect that electrically connects the second electrodes of each of the at least two transducer cells, wherein the first and second interconnect do not substantially overlap.    
     
     
         2 . The transducer of    claim 1    further including an insulator material disposed between the substrate and the transducer cells.  
     
     
         3 . The transducer of    claim 2    wherein the substrate is silicon, the insulator material is silicon oxide and the insulating film is silicon nitride.  
     
     
         4 . The transducer of    claim 2    wherein there is no overlap of the first and second interconnects at areas which do not overlap the void regions.  
     
     
         5 . The transducer of    claim 1    wherein the second electrode is formed within the insulating film.  
     
     
         6 . The transducer of    claim 5    wherein the first and second interconnects are formed on the same conductor layer as the first and second electrodes, respectively.  
     
     
         7 . The transducer of    claim 6    wherein the first and second electrodes each have a surface area that is smaller than a surface area of the corresponding void region.  
     
     
         8 . The transducer of    claim 7    wherein the first and second interconnects are formed on the same conductor layer as the first and second electrodes, respectively.  
     
     
         9 . The transducer of    claim 1    wherein the first and second interconnects are formed on the same conductor layer as the first and second electrodes, respectively.  
     
     
         10 . The transducer of    claim 1    wherein the first and second electrodes each have a surface area that is smaller than a surface area of the corresponding void region.  
     
     
         11 . The transducer of    claim 1    wherein the first and second electrodes and the first and second interconnects are made of aluminum.  
     
     
         12 . The transducer of    claim 1    wherein the first and second electrodes and the first and second interconnects are made of copper.  
     
     
         13 . The transducer of    claim 1    wherein the first and second electrodes and the first and second interconnects are made of tungsten.  
     
     
         14 . An transducer comprising: 
 a supporting substrate; and    a transducer cell formed on the substrate, said transducer cell including: 
 a first electrode formed over the substrate;  
 an insulating film formed over the first electrode and including a void region therein; and  
 a second electrode disposed at least substantially parallel to the first electrode and formed within the insulating film such that the void region is disposed between the first electrode and the second electrode, and the thickness of the insulating film is greater than the spacing between the first and second electrode.  
   
     
     
         15 . The transducer of    claim 14    further including an insulator material disposed between the substrate and the transducer cell.  
     
     
         16 . The transducer of    claim 14    wherein the insulating film is silicon nitride.  
     
     
         17 . The transducer of    claim 14    wherein the the first and second electrodes each have a surface area that is smaller than a surface area of the corresponding void region.  
     
     
         18 . A method of manufacturing a transducer comprising: 
 depositing a first conductive layer on a substrate;    etching the first conductive layer to form at least two first electrodes and a first interconnect electrically connecting the at least two first electrodes;    depositing a first insulating film layer of insulator material on the etched conductor;    depositing a sacrificial layer over the first insulating film;    etching the sacrificial layer to create at least two sacrificial portions, each in substantial alignment with and overlapping one of the two first electrodes;    depositing a second insulating film layer of insulator material over the etched sacrificial layer;    depositing a second conductive layer over the second insulating film layer;    etching the second conductive layer to form at least two second electrode that overlap and substantially align with the first electrodes, and a second interconnect electrically connecting the two second electrodes, wherein the second interconnect does not overlap the first interconnect; and    removing the sacrificial portions to form corresponding void areas.    
     
     
         19 . The method of    claim 18    wherein further comprising the step of depositing a third insulating film layer of insulator material over the etched second conductive layer.  
     
     
         20 . The method of    claim 19    wherein the step of removing takes place after the step of depositing the second insulating film layer.  
     
     
         21 . The method of    claim 18    wherein: 
 the step of creating the sacrificial layer further creates a sacrificial pathway connected to the at least two sacrificial portions; and  
 the step of removing the sacrificial portions includes the steps of: 
 creating a via hole in the second insulating film layer to the sacrificial pathway; and  
 etching the sacrificial pathway and the at least two sacrificial portions.  
 
 
     
     
         22 . The method of    claim 18    wherein the steps of depositing the first and second conductive layers deposit aluminum.  
     
     
         23 . The method of    claim 22    wherein the step of depositing the sacrificial layer deposits aluminum.  
     
     
         24 . The method of    claim 18    wherein the steps of depositing the first and second conductive layers deposit copper.  
     
     
         25 . The method of    claim 18    wherein the steps of depositing the first and second conductive layers deposit tungsten.  
     
     
         26 . The method of    claim 18    wherein the steps of depositing the first and second insulating film layers deposit silicon nitride using plasma-enhanced chemical vapor deposition.  
     
     
         27 . The method of    claim 18    wherein the step of depositing the sacrificial layer deposits a low temperature oxide.  
     
     
         28 . The method of    claim 19    wherein the step of depositing the sacrificial layer deposits aluminum.  
     
     
         29 . The method of    claim 18    wherein the step of etching the sacrificial layer creates the at least two sacrificial portions such that each sacrificial portion has a surface area that is larger than the corresponding first electrode.  
     
     
         30 . The method of    claim 18    wherein a plurality of transducers are simultaneously formed in an array.