Ultrasonic transducer, method of producing same, and ultrasonic probe using same

Abstract

Disclosed is an art for a capacitive micromachined ultrasonic transducer (CMUT), which suppresses deformation in a cavity, non-uniformity in the thickness of an insulating film enclosing the cavity, and deterioration in the flatness of the surface profile of a membrane, even when the bottom electrode of the ultrasonic transducer is electrically connected from the bottom of the bottom electrode. The ultrasonic transducer is provided with: a bottom electrode ( 306 ); an electric connection part ( 304 ) which is connected to the bottom electrode from the bottom of the bottom electrode; a first insulating film which is formed so as to cover the bottom electrode; a cavity ( 308 ) which is formed on the first insulating film so as to overlap the bottom electrode when seen from above; a second insulating film which is formed so as to cover the cavity ( 308 ); and a top electrode ( 310 ) which is formed on the second insulating film so as to overlap the cavity ( 308 ) when seen from above. The electric connection part ( 304 ) to the bottom electrode ( 306 ) is positioned so as to not overlap the cavity ( 308 ) when seen from above.

1 . An ultrasonic transducer comprising:
 (a) a bottom electrode;   (b) an electric connection part that is connected to the bottom electrode from a lower surface of the bottom electrode;   (c) a first insulating film that is formed so as to cover the bottom electrode;   (d) a cavity that is formed on the first insulating film so as to overlap the bottom electrode when seen from above;   (e) a second insulating film that is formed so as to cover the cavity; and   (f) a top electrode that is formed on the second insulating film so as to overlap the cavity when seen from above, the ultrasonic transducer wherein   (g) the electric connection part is positioned where the electric connection part does not overlap the cavity when seen from above.   
     
     
         2 . An ultrasonic transducer comprising:
 (a) a plurality of bottom electrodes;   (b) a plurality of electric connection parts that is connected to the plurality of bottom electrodes from respective lower surfaces of the plurality of bottom electrodes;   (c) a first insulating film that is formed so as to cover the plurality of bottom electrodes;   (d) a plurality of cavities that is formed on the first insulating film so as to overlap the plurality of bottom electrodes when seen from above;   (e) a second insulating film that is formed so as to cover the plurality of cavities; and   (f) a plurality of top electrodes that is formed on the second insulating film so as to overlap the plurality of cavities when seen from above, the ultrasonic transducer wherein   (g) the plurality of electric connection parts is positioned where the plurality of electric connection parts do not overlap the plurality of cavities when seen from above.   
     
     
         3 . The ultrasonic transducer according to  claim 1 , further comprising:
 (h) a semiconductor substrate;   (i) a wiring that is formed on the semiconductor substrate; and   (j) a third insulating film that is formed so as to cover the wiring, the ultrasonic transducer wherein   (k) the other end of the electric connection part is connected to the wiring through an opening of the third insulating film.   
     
     
         4 . The ultrasonic transducer according to  claim 3 , further comprising:
 (l) a second electric connection part, the ultrasonic transducer wherein   (m) one end of the second electric connection part is connected to the top electrode through the opening of the third insulating film, and the other end of the second electric connection part is connected to the wiring formed on the semiconductor substrate.   
     
     
         5 . The ultrasonic transducer according to  claim 2 , further comprising:
 (h) a semiconductor substrate;   (i) a wiring that is formed on the semiconductor substrate; and   (j) a third insulating film that is formed so as to cover the wiring, the ultrasonic transducer wherein   (k) the other end of the electric connection part is connected to the wiring through an opening of the third insulating film.   
     
     
         6 . The ultrasonic transducer according to  claim 5 , further comprising:
 (l) a second electric connection part, the ultrasonic transducer wherein   (m) one end of the second electric connection part is connected to the to electrode through the opening of the third insulating film, and the other end of the second electric connection part is connected to the wiring formed on the semiconductor substrate.   
     
     
         7 . An ultrasonic probe using the ultrasonic transducer according to  claim 1 . 
     
     
         8 . An ultrasonic probe using the ultrasonic transducer according to  claim 2 . 
     
     
         9 . An ultrasonic probe using the ultrasonic transducer according to  claim 3 . 
     
     
         10 . An ultrasonic probe using the ultrasonic transducer according to  claim 4 . 
     
     
         11 . An ultrasonic probe using the ultrasonic transducer according to  claim 5 . 
     
     
         12 . An ultrasonic probe using the ultrasonic transducer according to  claim 6 . 
     
     
         13 . A method of producing an ultrasonic transducer, the method comprising the steps of:
 (a) forming a wiring;   (b) forming a first insulating film that covers the wiring;   (c) flattening the first insulating film;   (d) forming, in the first insulating film, a first opening that reaches the wiring;   (e) forming an electric connection part by embedding a conductive film into the first opening;   (f) forming a bottom electrode on the electric connection part;   (g) forming a second insulating film so as to cover the bottom electrode;   (h) forming a sacrifice layer on the first insulating film at a position where the sacrifice layer overlaps the bottom electrode, but does not overlap the electric connection part when seen form above;   (i) forming a third insulating film so as to cover the sacrifice layer;   (j) forming a top electrode on the third insulating film so as to overlap the sacrifice layer when seen from above;   (k) forming a fourth insulating film that covers the top electrode and the third insulating film;   (l) forming a second opening that penetrates the third insulating film and the fourth insulating film to reach the sacrifice layer;   (m) forming a cavity by removing the sacrifice layer using the second opening; and   (n) sealing the cavity by forming a fifth insulating film so as to cover the opening that reaches the second insulating film and the sacrifice layer.   
     
     
         14 . The method of producing an ultrasonic transducer according to  claim 13 , wherein
 the step of forming the electric connection part by embedding the conductive film into the first opening and the step of forming the bottom electrode on the electric connection part are performed in one step.   
     
     
         15 . The method of producing an ultrasonic transducer according to  claim 13 , wherein
 the step of forming the wiring is to form the wiring on a semiconductor substrate.