CMUT device manufacturing method, CMUT device and apparatus
Disclosed is a method of manufacturing a capacitive micro-machined ultrasonic transducer (CMUT) device comprising a first electrode ( 112 ) on a substrate ( 110 ) and a second electrode ( 122 ) embedded in an electrically insulating membrane, the first electrode and the membrane being separated by a cavity ( 130 ) formed by the removal of a sacrificial material ( 116 ) in between the first electrode and the membrane, the method comprising forming a membrane portion ( 22 ) on the second electrode and a further membrane portion ( 24 ) extending from the membrane portion towards the substrate alongside the sacrificial material, wherein the respective thicknesses the membrane portion and the further membrane portion exceed the thickness of the sacrificial material prior to forming said cavity. A CMUT device manufactured in accordance with this method and an apparatus comprising such a CMUT device are also disclosed.
1. A capacitive micro-machined ultrasonic transducer (CMUT) device comprising a first electrode on a substrate and a second electrode embedded in an electrically insulating membrane, the first electrode and the membrane being separated by a cavity, wherein the membrane comprises a single layer membrane portion on the second electrode and a further membrane portion extending from the single layer membrane portion towards the substrate alongside the cavity, wherein the single layer membrane portion and the further membrane portion each have a thickness exceeding a height of the cavity by at least a factor five.
2. The CMUT device of claim 1 , wherein the single layer membrane portion and the further membrane portion each have a thickness exceeding the height of the cavity by at least a factor ten.
3. The CMUT device of claim 1 , wherein the thickness of said further membrane portion exceeds the thickness of the single layer membrane portion.
4. The CMUT device of claim 3 , further comprising a ring of an electrically insulating material on the further membrane portion, wherein said single layer membrane portion is at least partially exposed inside said ring.
5. The CMUT device of claim 1 , further comprising a protrusion of a sealing material extending from the cavity.
6. The CMUT device of claim 5 , wherein the sealing material is a metal such as aluminium or a metal alloy such as an aluminium-based alloy.
7. An apparatus comprising the CMUT device of claim 1 .
8. The CMUT device of claim 1 , wherein the cavity comprises a first circular portion and a plurality of protrusions extending outward from the first circular portion.
9. The CMUT device of claim 8 , wherein a height of each of the plurality of protrusions is less than a height of the first circular portion.
10. The CMUT device of claim 5 , wherein the protrusion of the sealing material comprises a sealing plug formed within an access that extends through the membrane into the cavity.
11. The CMUT device of claim 10 , wherein the cavity comprises a first circular portion and a plurality of protrusions extending outward from the first circular portion, wherein the access extends through the membrane into at least one of the protrusions.
12. The CMUT device of claim 1 , further comprising a ring of an electrically insulating material on the further membrane portion, wherein said single layer membrane portion is at least partially exposed inside said ring.
13. The CMUT device of claim 1 , further comprising a dielectric layer deposited over the first electrode and the substrate.
14. The CMUT device of claim 13 , wherein a portion of the further membrane portion contacts the dielectric layer.