CMOS ultrasonic transducers and related apparatus and methods
CMOS Ultrasonic Transducers and processes for making such devices are described. The processes may include forming cavities on a first wafer and bonding the first wafer to a second wafer. The second wafer may be processed to form a membrane for the cavities. Electrical access to the cavities may be provided.
1. A method, comprising:
forming a cavity on a top region of a complementary metal oxide semiconductor (CMOS) substrate, the cavity surrounded by a sidewall, the CMOS substrate comprising a first surface proximate the cavity and a second surface distal the cavity;
disposing a membrane over the sidewall of the cavity to substantially seal the cavity;
forming a first electrical contact on a top side of the membrane, wherein the top side of the membrane is disposed distal the cavity;
forming a second electrical contact proximate the first surface and on the top region of the CMOS substrate;
forming an opening through the membrane and extending to the second electrical contact, the opening having a first dimension at the membrane and a second dimension at the second electrical contact, the first dimension being larger than the second dimension; and
depositing a conductive material into the opening to cover sidewalls of the opening and to connect the second electrical contact to the first electrical contact,
wherein the membrane and the first electrical contact are doped with substantially a same dopant.
2. The method of claim 1 , wherein the first electrical contact and the second electrical contact comprise a metal.
3. The method of claim 1 , wherein the first electrical contact and the second electrical contact comprise aluminum.
4. The method of claim 1 , further comprising forming an interface layer between the first electrical contact and the top side of the membrane.
5. The method of claim 1 , wherein the first electrical contact is common to two or more membranes of two or more cavities.
6. The method of claim 1 , wherein forming the second electrical contact comprises etching the CMOS substrate to expose the second electrical contact.
7. The method of claim 1 , further comprising forming a third electrical contact on the CMOS substrate, wherein the third electrical contact is electrically coupled to a substrate electrode disposed on an opposite side of the cavity from the membrane, with the cavity between the substrate electrode and the membrane.
8. The method of claim 1 , wherein the CMOS substrate comprises processing circuitry configured to:
actuate the membrane to transmit an ultrasound wave; and
detect a received ultrasound wave based on vibration of the membrane.
9. An ultrasound structure, comprising:
a complementary metal-oxide-semiconductor (CMOS) substrate having a cavity formed in a top region thereof, the cavity surrounded by a sidewall, the CMOS substrate comprising a first surface proximate the cavity and a second surface distal the cavity;
a membrane disposed over the sidewall of the cavity to substantially seal the cavity;
a first electrical contact on a top side of the membrane, wherein the top side of the membrane is disposed distal to the cavity; and
a second electrical contact proximate the first surface and on the top region of the CMOS substrate; wherein
an opening passing through the membrane and extending to the second electrical contact, the opening having a first dimension at the membrane and a second dimension at the second electrical contact, the first dimension being larger than the second dimension; and
a conductive material deposited into the opening and covering sidewalls of the opening, the conductive material configured to connect the second electrical contact and the first electrical contact,
wherein the membrane and the first electrical contact are doped with substantially a same dopant.
10. The ultrasound structure of claim 9 , wherein the first electrical contact and the second electrical contact comprise a metal.
11. The ultrasound structure of claim 9 , wherein the first electrical contact and the second electrical contact comprise aluminum.
12. The ultrasound structure of claim 9 , further comprising an interface layer between the first electrical contact and the top side of the membrane.
13. The ultrasound structure of claim 9 , wherein the first electrical contact is common to two or more membranes of two or more cavities.
14. The ultrasound structure of claim 9 , further comprising a third electrical contact on the CMOS substrate, wherein the third electrical contact is electrically coupled to a substrate electrode disposed on an opposite side of the cavity from the membrane, with the cavity between the substrate electrode and the membrane.
15. The ultrasound structure of claim 9 , wherein the CMOS substrate comprises processing circuitry configured to:
actuate the membrane to transmit an ultrasound wave; and
detect a received ultrasound wave based on vibration of the membrane.
16. The ultrasound structure of claim 9 , wherein the ultrasound structure is included as part of at least one paddle of two opposed paddles used for ultrasound imaging.