Ultrasound transducer devices and methods for fabricating ultrasound transducer devices
Aspects of the technology described herein relate to ultrasound transducer devices including capacitive micromachined ultrasonic transducers (CMUTs) and methods for forming CMUTs in ultrasound transducer devices. Some embodiments include forming a cavity of a CMUT by forming a first layer of insulating material on a first substrate, forming a second layer of insulating material on the first layer of insulating material, and then etching a cavity in the second insulating material. A second substrate may be bonded to the first substrate to seal the cavity. The first layer of insulating material may include, for example, aluminum oxide. The first substrate may include integrated circuitry. Some embodiments include forming through-silicon vias (TSVs) in the first substrate prior to forming the first and second insulating layers (TSV-Middle process) or subsequent to bonding the first and second substrates (TSV-Last process).
1. A method of fabricating an ultrasound transducer device, comprising:
forming first and second insulating layers on a third insulating layer of a first integrated circuit substrate;
forming a first cavity in the second insulating layer by etching the second insulating layer down to the first insulating layer; and
bonding a second substrate to the first integrated circuit substrate to seal the first cavity, wherein
the first insulating layer serves as an etch stop layer for the etching.
2. A method of fabricating an ultrasound transducer device, comprising:
forming first, second, and third insulating layers on a first integrated circuit substrate, with a first cavity in the second insulating layer; and
bonding a second substrate to the first integrated circuit substrate to seal the first cavity, wherein
the first insulating layer is formed on the third insulating layer.
3. The method of claim 2 , wherein
the first insulating layer comprises aluminum oxide.
4. The method of claim 2 , wherein
the second insulating layer comprises silicon oxide.
5. The method of claim 4 , wherein
the second substrate comprises a silicon oxide layer, and
the bonding of the second substrate to the first integrated circuit substrate comprises forming a silicon oxide-silicon oxide bond between the silicon oxide layer on the second substrate and the second insulating layer on the first integrated circuit substrate.
6. The method of claim 2 , further comprising
forming a fourth insulating layer on the second substrate, wherein the fourth insulating layer comprises aluminum oxide.
7. The method of claim 6 , wherein
the second insulating layer comprises silicon oxide, and
the bonding of the second substrate to the first integrated circuit substrate comprises forming an aluminum oxide-silicon oxide bond between the fourth insulating layer on the second substrate and the second insulating layer on the first integrated circuit substrate.
8. The method of claim 6 , further comprising:
forming a fifth insulating layer on the fourth insulating layer on the second substrate; and
forming a second cavity in the fifth insulating layer.
9. The method of claim 8 , wherein
the fifth insulating layer comprises silicon oxide.
10. The method of claim 9 , wherein
the bonding of the second substrate to the first integrated circuit substrate comprises forming a silicon oxide-silicon oxide bond between the fifth insulating layer on the second substrate and the second insulating layer on the first integrated circuit substrate.
11. The method of claim 8 , wherein
the bonding of the second substrate to the first integrated circuit substrate comprises aligning the first cavity with the second cavity.
12. The method of claim 2 , wherein
the third insulating layer comprises silicon oxide.
13. The method of claim 2 , wherein
the second substrate comprises a silicon-on-insulator (SOI) substrate.
14. The method of claim 2 , wherein
a thickness of the first insulating layer is between approximately 0.005 microns to 0.100 microns.
15. The method of claim 2 , further comprising
forming a self-assembled monolayer (SAM) on the first insulating layer within the first cavity.
16. The method of claim 2 , wherein
the forming of the first insulating layer comprises using atomic layer deposition (ALD).
17. The method of claim 2 , wherein
the forming of the second insulating layer comprises using atomic layer deposition (ALD).
18. A method of fabricating an ultrasound transducer device, comprising:
forming first and second insulating layers on a first integrated circuit substrate, with a first cavity in the second insulating layer;
bonding a second substrate to the first integrated circuit substrate to seal the first cavity; and
forming a through-silicon via (TSV) in the first integrated circuit substrate using a TSV-Middle process prior to forming the first and second insulating layers.
19. A method of fabricating an ultrasound transducer device, comprising:
forming first and second insulating layers on a first integrated circuit substrate, with a first cavity in the second insulating layer;
bonding a second substrate to the first integrated circuit substrate to seal the first cavity; and
forming a through-silicon via (TSV) in the first integrated circuit substrate using a TSV-Last process subsequent to bonding the second substrate to the first integrated circuit substrate.