Ultrasonic transducer and method of manufacturing the same

1. An ultrasonic transducer comprising:

a conductive substrate;

a support which is disposed on the conductive substrate and includes cavities;

a membrane which is disposed on the support to cover the cavities;

a via hole penetrating the conductive substrate and the membrane;

a first electrode layer which is disposed on an inner wall and a top portion of the via hole, the first electrode layer having a top surface at a same height as a top surface of the membrane;

a second electrode layer which is disposed on a bottom surface of the conductive substrate to be spaced apart from the first electrode layer;

a top electrode which is disposed to contact the top surface of the first electrode layer on the top surface of the membrane; and

a pad substrate which is disposed below the conductive substrate and has formed thereon bonding pads electrically connected to the first and second electrode layers.

2. The ultrasonic transducer of claim 1 , wherein an element separation line penetrates through the membrane and the top electrode.

3. The ultrasonic transducer of claim 2 , wherein the inner wall of the via hole and an inner wall of the element separation line contacting the top electrode have rounded shapes.

4. The ultrasonic transducer of claim 2 , wherein:

the membrane comprises silicon; and

the support comprises silicon oxide.

5. The ultrasonic transducer of claim 4 , wherein the silicon oxide is formed on an inner wall of the element separation line.

6. The ultrasonic transducer of claim 1 , wherein an insulation material is formed on the inner wall of the via hole.

7. The ultrasonic transducer of claim 1 , wherein an upper insulation layer and a lower insulation layer are respectively formed on a top surface and a bottom surface of the conductive substrate.

8. The ultrasonic transducer of claim 7 , wherein the lower insulation layer is patterned such that the second electrode layer contacts the bottom surface of the conductive substrate.

9. The ultrasonic transducer of claim 1 , wherein the bonding pads are disposed on a top surface of the pad substrate and comprise a first upper pad and a second upper pad that are respectively bonded to the first electrode layer and the second electrode layer.

10. The ultrasonic transducer of claim 9 , wherein:

the first and second electrode layers comprise at least one of Au and Cu; and

the first and second upper pads comprise at least one from among Au, Cu, and Sn.

11. The ultrasonic transducer of claim 9 , wherein the bonding pads further comprise first and second lower pads which are disposed on a bottom surface of the pad substrate and are electrically connected to the first and second upper pads.

12. The ultrasonic transducer of claim 9 , wherein an eutectic alloy is formed due to eutectic bonding at an interface between the first electrode layer and the first upper pad and an interface between the second electrode layer and the second upper pad.

13. An ultrasonic transducer comprising:

a conductive substrate;

a membrane formed on the conductive substrate;

a via hole formed in the conductive substrate and the membrane, the via hole defining an internal surface area and an opening;

an electrode layer comprising a first portion covering the internal surface area and a second portion covering the opening; and

an electrode disposed on the second portion,

wherein the electrode layer has a top surface at a same height as a top surface of the membrane,

wherein the via hole is formed such that the internal surface area is curved away from the electrode layer at a boundary of the first and second portions to form a notch into which the electrode is formed, to thereby increase a surface area at which the electrode contacts the electrode layer.

14. The ultrasonic transducer according to claim 13 , wherein the ultrasonic transducer comprises a capacitive micromachined ultrasonic transducer (CMUT).