Microfabricated ultrasonic transducers and related apparatus and methods

• US 10,175,206 B2
• Filed: 08/29/2017
• Issued: 01/08/2019
• Est. Priority Date: 07/14/2014
• Status: Active Grant

• Current Assignee: BFLY Operations, Inc. (Butterfly Network, Inc.)
• Original Assignee: Butterfly Network, Inc.
• Inventors: Rothberg, Jonathan M., Alie, Susan A., Fife, Keith G., Sanchez, Nevada J., Ralston, Tyler S.
• Primary Examiner(s): Kim, Su C
• Application Number:
  US15/689,863
• Publication Number:
  US 20180003678A1
• Time in Patent Office: 497 Days
• CPC Class Codes: A61B 8/4483 characterised by features of the ultrasound transducer
• CPC Class Codes: B06B 1/0292 Electrostatic transducers, e.g. electret-type
• CPC Class Codes: B81B 2201/0271 Resonators; ultrasonic resonators
• CPC Class Codes: B81B 7/007 Interconnections between the MEMS and external electrical signals
• CPC Class Codes: B81C 1/00238 Joining a substrate with an electronic processing unit and a substrate with a micromechanical structure
• CPC Class Codes: B81C 1/00301 Connecting electric signal lines from the MEMS device with external electrical signal lines, e.g. through vias
• CPC Class Codes: B81C 2201/019 Bonding or gluing multiple substrate layers
• CPC Class Codes: B81C 2203/036 Fusion bonding
• CPC Class Codes: B81C 2203/0792 Forming interconnections between the electronic processing unit and the micromechanical structure
• CPC Class Codes: G01N 29/2406 Electrostatic or capacitive probes, e.g. electret or cMUT-probes
• CPC Class Codes: H01L 2224/4813 Connecting within a semiconductor or solid-state body, i.e. fly wire, bridge wire
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/146 Mixed devices
• CPC Class Codes: H01L 2924/1461 MEMS

Abstract

Micromachined ultrasonic transducers integrated with complementary metal oxide semiconductor (CMOS) substrates are described, as well as methods of fabricating such devices. Fabrication may involve two separate wafer bonding steps. Wafer bonding may be used to fabricate sealed cavities in a substrate. Wafer bonding may also be used to bond the substrate to another substrate, such as a CMOS wafer. At least the second wafer bonding may be performed at a low temperature.

Claims

1. An ultrasound device, comprising:

a first substrate having a capacitive micromachined ultrasonic transducer (CMUT) flush with a top surface of the first substrate, the CMUT comprising a cavity and a silicon layer at least partially sealing the cavity;

a node disposed on the silicon layer;

a second substrate having an integrated circuit formed therein, the second substrate bonded to the first substrate;

a bond pad disposed on the second substrate and electrically connected to the integrated circuit; and

a conductive path disposed between the node and the bond pad, wherein the conductive path is external to the first and second substrates.

2. The ultrasound device of claim 1, wherein the conductive path comprises a wire bond.

3. The ultrasound device of claim 1, wherein the conductive path comprises a conductive material that is deposited between the node and the bond pad.

4. The ultrasound device of claim 1, further comprising a region of the first substrate that has been etched away and in which the bond pad is located.

5. The ultrasound device of claim 1, wherein the silicon layer is doped.

6. The ultrasound device of claim 5, wherein the silicon layer is doped with a doping concentration greater than approximately 10¹⁵ dopants/cm3.

7. The ultrasound device of claim 1, wherein a bond between the first substrate and the second substrate comprises a thermocompression bond or a silicide bond.

8. The ultrasound device of claim 1, wherein the first substrate and the second substrate comprise wafers.

9. The ultrasound device of claim 1, wherein the first substrate comprises first and second wafers, and wherein at least one of the first and second wafers comprises a bulk silicon wafer having a doped portion.

10. A method of electrically contacting a capacitive micromachined ultrasonic transducer (CMUT) in an ultrasound device, the method comprising:

providing an ultrasound device comprising;

a first substrate having a CMUT flush with a top surface of the first substrate, the CMUT comprising a cavity and a silicon layer at least partially sealing the cavity;

a node disposed on the silicon layer;

a second substrate having an integrated circuit formed therein, the second substrate bonded to the first substrate; and

a bond pad disposed on the second substrate and electrically connected to the integrated circuit; and

forming a conductive path between the node and the bond pad, wherein the conductive path is external to the first and second substrates.

11. The method of claim 10, wherein forming the conductive path between the node and the bond pad comprises forming a wire bond between the node and the bond pad.

12. The method of claim 10, wherein forming the conductive path between the node and the bond pad comprises depositing a conductive material between the node and the bond pad.

13. The method of claim 10, wherein the ultrasound device further comprises a region of the first substrate that has been etched away and in which the bond pad is located.

14. The method of claim 10, wherein the silicon layer is doped.

15. The method of claim 10, wherein a bond between the first substrate and the second substrate comprises a thermocompression bond or a silicide bond.

16. The method of claim 10, wherein the first substrate and the second substrate comprise wafers.

17. The method of claim 10, wherein the first substrate comprises first and second wafers, and wherein at least one of the first and second wafers comprises a bulk silicon wafer having a doped portion.

18. The method of claim 10, wherein providing the ultrasound device comprises:

forming the CMUT in the first substrate;

forming the node on the silicon layer of the CMUT;

bonding the second substrate having the integrated circuit formed therein to the first substrate; and

forming the bond pad on the second substrate.

19. An ultrasound device, comprising:

a first substrate having a capacitive micromachined ultrasonic transducer (CMUT), the CMUT comprising a cavity and a silicon layer directly sealing the cavity;

a node disposed on the silicon layer;

a second substrate having an integrated circuit formed therein, the second substrate bonded to the first substrate;

a bond pad disposed on the second substrate and electrically connected to the integrated circuit; and

a conductive path disposed between the node and the bond pad, wherein the conductive path is external to the first and second substrates.

20. The ultrasound device of claim 19, wherein the conductive path comprises a wire bond.