Microfabricated ultrasonic transducer having individual cells with electrically isolated electrode sections
An ultrasonic transducer includes a membrane, a bottom electrode, and a plurality of cavities disposed between the membrane and the bottom electrode, each of the plurality of cavities corresponding to an individual transducer cell. Portions of the bottom electrode corresponding to each individual transducer cell are electrically isolated from one another. Each portion of the bottom electrode corresponds to each individual transducer that cell further includes a first bottom electrode portion and a second bottom electrode portion, the first and second bottom electrode portions electrically isolated from one another.
1. An apparatus, comprising:
an ultrasonic transducer cell comprising:
a membrane;
a bottom electrode comprising:
a first bottom electrode portion;
a second bottom electrode portion; and
one or more trench isolation regions disposed within the bottom electrode and configured to electrically isolate the first and second bottom electrode portions of the bottom electrode from one another; and
a cavity disposed between the membrane and the bottom electrode.
2. The apparatus of claim 1 , wherein the first and second bottom electrode portions are separately electrically addressable from one another.
3. The apparatus of claim 1 , wherein the first bottom electrode portion comprises an inner bottom electrode with respect to a diameter of the ultrasonic transducer cell, and the second bottom electrode portion comprises an outer bottom electrode with respect to the diameter of the ultrasonic transducer cell.
4. The apparatus of claim 1 , wherein:
one of the first bottom electrode portion and the second bottom electrode portion is configured to perform a transmit function of the apparatus; and
the other of the first bottom electrode portion and the second bottom electrode portion is configured to perform a receive function of the apparatus.
5. The apparatus of claim 4 , wherein the apparatus is configured to perform the transmit and receive functions simultaneously.
6. The apparatus of claim 1 , further comprising a CMOS substrate electrically coupled to the ultrasonic transducer cell, wherein:
the CMOS substrate comprises metallization; and
the first and second bottom electrode portions are disposed between the metallization and the cavity.
7. The apparatus of claim 1 , wherein the first and second bottom electrode portions are horizontally adjacent.
8. The apparatus of claim 1 , wherein the one or more trench isolation regions are disposed within a footprint of the cavity.
9. The apparatus of claim 1 , further comprising a CMOS substrate electrically coupled to the ultrasonic transducer cell, wherein:
multiple electrical contacts electrically couple the bottom electrode to the CMOS substrate.
10. The apparatus of claim 9 , wherein:
the multiple electrical contacts comprise a first electrical contact and a second electrical contact;
the first electrical contact is electrically coupled to the first bottom electrode portion; and
the second electrical contact is electrically coupled to the second bottom electrode portion.
11. The apparatus of claim 1 , wherein the one or more trench isolation regions protrude into the cavity.
12. A method, comprising:
forming a cavity in a first side of a first substrate;
defining a first bottom electrode portion and a second bottom electrode portion in the first substrate underneath the cavity by forming at least one isolation trench in the first side of the first substrate;
sealing the cavity by bonding a second substrate to the first substrate; and
forming a membrane from the second substrate, wherein the membrane, the first and second bottom electrode portions, and the cavity define at least part of an ultrasonic transducer cell for which the cavity is disposed between the membrane and the first and second bottom electrode portions.
13. The method of claim 12 , wherein the first substrate comprises a silicon material, and wherein forming the at least one isolation trench in the first side of the first substrate comprises:
forming an insulating layer over the first side of the first substrate, including the cavity;
etching though the insulating layer and into the silicon material to define the at least one isolation trench; and
filling the at least one isolation trench with one or more insulating materials.
14. The method of claim 13 , wherein the insulating layer and the one or more insulating materials comprise oxide.
15. The method of claim 13 , wherein filling the at least one isolation trench with one or more insulating materials comprises filling the at least one isolation trench with one or more insulating materials comprising thermal oxide and undoped polysilicon.
16. The method of claim 12 , wherein defining a first bottom electrode portion and a second bottom electrode portion in the first substrate underneath the cavity by forming at least one isolation trench in the first side of the first substrate comprises disposing the at least one isolation trench within a footprint of the cavity.
17. The method of claim 12 , further comprising electrically isolating the first and second bottom electrode portions from each other.
18. The method of claim 17 , wherein electrically isolating the first and second bottom electrode portions from each other comprises filling the at least one isolation trench with an insulating material.
19. The method of claim 17 , wherein electrically isolating the first and second bottom electrode portions from each other comprises reducing a thickness of the first substrate.
20. The method of claim 12 , wherein defining a first bottom electrode portion and a second bottom electrode portion in the first substrate underneath the cavity by forming at least one isolation trench in the first side of the first substrate comprises electrically isolating the first bottom electrode portion and second bottom electrode portion from each other.
21. The method of claim 12 , wherein defining a first bottom electrode portion and a second bottom electrode portion comprises defining the first bottom electrode portion as an inner bottom electrode with respect to a diameter of the ultrasonic transducer cell, and the second bottom electrode portion as an outer bottom electrode with respect to the diameter of the ultrasonic transducer cell.
22. The method of claim 12 , wherein defining a first bottom electrode portion and a second bottom electrode portion in the first substrate underneath the cavity comprises defining the first and second bottom electrode portions as horizontally adjacent to each other.
23. The method of claim 12 , wherein defining a first bottom electrode portion and a second bottom electrode portion in the first substrate underneath the cavity by forming at least one isolation trench comprises forming the at least one isolation trench to protrude into the cavity.