Complementary metal oxide semiconductor (CMOS) ultrasonic transducers and methods for forming the same
Complementary metal oxide semiconductor (CMOS) ultrasonic transducers (CUTs) and methods for forming CUTs are described. The CUTs may include monolithically integrated ultrasonic transducers and integrated circuits for operating in connection with the transducers. The CUTs may be used in ultrasound devices such as ultrasound imaging devices and/or high intensity focused ultrasound (HIFU) devices.
1. An apparatus, comprising:
a semiconductor wafer having a complementary metal oxide semiconductor (CMOS) integrated circuit;
an electrode;
an insulating material having a cavity formed at least partially therein;
a conductive membrane contacting the insulating material, sealing the cavity and having a first side proximate the cavity and a second side distal the cavity, wherein the electrode, cavity, and conductive membrane together define, at least in part, an ultrasonic transducer, with the cavity being between the electrode and the conductive membrane;
a conductive contact coupling the electrode to the CMOS integrated circuit; and
a conductive plug embedded in the insulating material and terminating on the first side of the conductive membrane proximate the cavity without extending through the conductive membrane such that a surface of the conductive plug forms at least part of a bonding interface between the first side of the conductive membrane and the insulating material, the conductive plug electrically connecting the conductive membrane to the CMOS integrated circuit,
wherein the electrode and the conductive plug are electrically isolated from each other, and
wherein the apparatus lacks an electrode that is on the second side of the conductive membrane and that overlies the cavity.
2. The apparatus of claim 1 , wherein the insulating material, the electrode, and the conductive plug are on the semiconductor wafer.
3. The apparatus of claim 2 , wherein the conductive membrane comprises doped silicon.
4. The apparatus of claim 3 , wherein the doped silicon is single crystal silicon.
5. The apparatus of claim 3 , wherein the doped silicon is polysilicon.
6. The apparatus of claim 3 , wherein the doped silicon is amorphous silicon.
7. The apparatus of claim 3 , wherein the conductive plug comprises tungsten.
8. The apparatus of claim 2 , wherein the insulating material defines a sidewall of the cavity.
9. The apparatus of claim 8 , wherein the electrode is at least partially within the insulating material.
10. The apparatus of claim 2 , wherein the cavity has a depth between 0.1 microns and 10 microns and a width between 20 microns and 100 microns, and wherein the conductive membrane has a thickness less than 30 microns.
11. The apparatus of claim 1 , wherein the conductive membrane comprises doped silicon.
12. The apparatus of claim 11 , wherein the doped silicon is single crystal silicon.
13. The apparatus of claim 11 , wherein the doped silicon is polysilicon.
14. The apparatus of claim 11 , wherein the doped silicon is amorphous silicon.
15. The apparatus of claim 11 , wherein the conductive plug comprises tungsten.
16. The apparatus of claim 1 , wherein the insulating material defines a sidewall of the cavity.
17. The apparatus of claim 1 , wherein a width of the electrode is smaller than a width of the cavity.
18. The apparatus of claim 1 , wherein the cavity has a depth between 0.1 microns and 10 microns and a width between 20 microns and 100 microns, and wherein the conductive membrane has a thickness less than 30 microns.