Patent ID: 8324006

Claim:
A method of forming capacitive micromachined ultrasonic transducer (CMUT) elements comprising: Providing a first semiconductor-on-insulator (SOI) structure; wherein the first SOI structure includes a handle wafer, an active layer and a buried layer therebetween; and forming an oxide layer over the active layer of the first SOI structure by means of: growing a pad oxide layer over the active layer; depositing a nitride layer over the pad oxide layer; masking and etching the nitride layer defining the locations of the CMUT elements; providing a local oxidation of silicon (LOCOS) in the areas of exposed pad oxide, wherein the LOCOS oxide is substantially thicker than the pad oxide and extends above the pad oxide; removing the nitride layer; forming isolation trenches in the active layer of the first (SOI) structure to electrically isolate multiple portions of the active layer of the first SOI structure from each other; bonding a second SOI structure to the LOCOS areas on the active layer side of the first SOI structure; wherein the bonding of the first and second SOI structures forms multiple cavities between the adjacent thicker LOCOS portions of the oxide layer and the first and second SOI structures; wherein the second SOI structure includes a second handle wafer, a second buried layer and a second active layer consisting of membrane material; removing portions of the second SOI structure to leave a membrane bonded to the first SOI structure LOCOS areas, wherein multiple cavities are located between the membrane and the oxide layer of the first SOI structure, forming multiple (CMUT) elements using the isolated portions of the SOI structure, each CMUT element formed in one of the isolated portions of the SOI structure and comprising multiple CMUT cells; forming electrical connections to the CMUT elements through a second side of the SOI structure; and forming an additional CMUT element that includes a contact hole from the first side of the first SOI structure to the second side of the first SOI structure, the contact hole associated with an electrically conductive path from the first side of the SOI structure to the second side of the SOI structure.