Capacitive ultrasonic transducer and method of fabricating the same

Abstract

A capacitive ultrasonic transducer and method of fabricating the same are disclosed, whereas the capacitive ultrasonic transducer is a stacking of multiple metal layers. The fabrication method of the invention is characterized in that: the structure and cavity of excitation are formed by lithographing and etching the sacrificial layer and other stacking layers, whereas the sacrificial layer and the other stacking layer are made of metal, and moreover, a protective bulk is formed on the capacitive ultrasonic transducer by a means of metal depositing. It is noted that not only the structure of capacitive ultrasonic transducer of the invention has a bulk for protection, which is different to that of a conventional capacitive ultrasonic transducer, but also the method of fabricating the same can do without the steps of electrode formation, high-temperature processing and annealing, which enable the method to have simplified process and thus cost less than that of conventional methods. The capacitive ultrasonic transducer can be integrated into a variety of integrated circuit that enables the same to be vastly implemented in consumer electronic products, and products of bio-medical science and other engineering fields.

1 . A capacitive ultrasonic transducer, comprising: 
 an assembly of supporting frames, being formed on a substrate; and    a metal layer, being formed on top of the assembly;    wherein at least a cavity is formed by the enclosure of the metal layer, the assembly of supporting frames and the substrate.    
   
   
       2 . The capacitive ultrasonic transducer of  claim 1 , wherein at least a bulk is being formed on the metal layer at a position corresponding to each supporting frame.  
   
   
       3 . The capacitive ultrasonic transducer of  claim 2 , wherein the bulk is made of nickel.  
   
   
       4 . The capacitive ultrasonic transducer of  claim 1 , wherein each supporting frame is made of a metal.  
   
   
       5 . The capacitive ultrasonic transducer of  claim 4 , wherein the metal is nickel.  
   
   
       6 . The capacitive ultrasonic transducer of  claim 1 , wherein the metal layer is made of nickel.  
   
   
       7 . A capacitive ultrasonic transducer, comprising: 
 an assembly of supporting frames, being formed on a substrate;    a metal layer, being formed on top of the assembly; and    at least a bulk, each being formed on the metal layer at a position corresponding to each supporting frame;    wherein at least a cavity is formed by the enclosure of the metal layer, the assembly of supporting frames and the substrate.    
   
   
       8 . The capacitive ultrasonic transducer of  claim 7 , wherein the bulk is made of nickel.  
   
   
       9 . The capacitive ultrasonic transducer of  claim 7 , wherein each supporting frame is made of a metal.  
   
   
       10 . The capacitive ultrasonic transducer of  claim 9 , wherein the metal is nickel.  
   
   
       11 . The capacitive ultrasonic transducer of  claim 7 , wherein the metal layer is made of nickel.  
   
   
       12 . A method for fabricating a capacitive ultrasonic transducer, comprising steps of: 
 (a) forming an insulating layer on a substrate;    (b) forming a first structure on the insulating layer by a means of electrochemical deposition while enabling the first structure to be configured with an assembly of supporting frames and the material of a sacrificial layer filling each space enclosed by each supporting frame by the depositing of the sacrificial layer on the assembly of supporting frames;    (c) polishing the surface of the first structure for enabling the assembly of supporting frames and the deposited sacrificial layer to coplanar;    (d) forming a first metal layer on the first structure by a means of electrochemical deposition;    (e) polishing the first metal layer until a specific thickness of the same is achieved; and    (f) removing the sacrificial layer.    
   
   
       13 . The method of  claim 12 , wherein the step (b) of forming the first structure in the fabrication method further comprises steps of: 
 (b1) forming a layer of photo resist on the insulating layer;    (b2) removing a portion of the photo resist layer to form at least a cavity thereby;    (b3) forming a sacrificial layer on the partially removed photo resist layer while enabling each cavity to be filled by the sacrificial layer;    (b4) polishing the surface of the sacrificial layer for enabling the remaining photo resist layer and the sacrificial layer to coplanar;    (b5) removing the remaining photo resist layer so as to form hollows in the sacrificial layer; and    (b6) depositing a layer of a second metal on the sacrificial layer by a means of electrochemical deposition while filling the hollows with the second metal to form the assembly of supporting frames.    
   
   
       14 . The method of  claim 13 , the method further comprising a step of: 
 (g) forming a layer of a third metal on the first metal layer for enabling at least a protective bulk to be formed at a position corresponding to each supporting frames of the assembly in a posterior process.    
   
   
       15 . The method of  claim 14 , wherein the first metal layer, the second metal layer and the third metal layer are all made of nickel.  
   
   
       16 . The method of  claim 12 , wherein the step (b) of forming the first structure in the fabrication method further comprises steps of: 
 (b1′) forming a layer of photo resist on the insulating layer;    (b2′) removing a portion of the photo resist layer to create hollows for forming the assembly of supporting frames therein in a later step;    (b3′) depositing a layer of a second metal on the hollowed photo resist layer by a means of electrochemical deposition while filling the hollows with the second metal to form the assembly of supporting frames;    (b4′) polishing the surface of the second metal layer for enabling the remaining photo resist layer and the second metal layer to coplanar and thus completing the formation of the assembly of supporting frames;    (b5′) removing the remaining photo resist layer to form at least a cavity; and    (b6′) depositing the sacrificial layer by a means of electrochemical deposition while filling each cavity therewith.    
   
   
       17 . The method of  claim 16 , the method further comprising a step of: 
 (g) forming a layer of a third metal on the first metal layer for enabling at least a protective bulk to be formed at a position corresponding to each supporting frames of the assembly in a posterior process.    
   
   
       18 . The method of  claim 17 , wherein the first metal layer, the second metal layer and the third metal layer are all made of nickel.  
   
   
       19 . The method of  claim 12 , the method further comprising a step of: 
 (g) forming a layer of a third metal on the first metal layer for enabling at least a protective bulk to be formed at a position corresponding to each supporting frames of the assembly in a posterior process.    
   
   
       20 . The method of  claim 19 , wherein the first metal layer and the third metal layer are made of nickel.  
   
   
       21 . The method of  claim 12 , wherein each supporting frame is made of a metal.  
   
   
       22 . The method of  claim 21 , wherein the metal is nickel.  
   
   
       23 . The method of  claim 12 , wherein the sacrificial layer is made of copper.  
   
   
       24 . The method of  claim 1 , wherein the step (f) of removing the sacrificial layer in the above fabrication method further comprises the steps of: 
 (f1) etching the first metal layer to form a plurality of apertures thereon while enabling each aperture to be channeled to the corresponding sacrificial layer.    
   
   
       25 . The method of  claim 24 , wherein the plural apertures are going to be filled by a posterior process being performed after the step (f1).  
   
   
       26 . The method of  claim 12 , wherein the removing of the sacrificial layer is performed by a means of wet etching