Patent ID: 8421170

Claim:
A method for microfabrication of a capacitive micromachined ultrasonic transducer (CMUT) containing at least one CMUT cell comprising the steps preparing a substrate by preparing a first electrode layer on a substrate, preferably by doping of the surface of said substrate; forming cavity walls on said first electrode by depositing and then etching a cavity wall material; preparing a membrane by preparing or obtaining of diamond layer coated on a substrate; forming and polishing an intermediate layer on the diamond layer; assembling the membrane on the substrate such that the intermediate layer is facing cavities, by plasma-activated direct wafer bonding between the intermediate layer and the cavity walls; removing the substrate of the diamond layer; and forming at least one first electrode connection; wherein said intermediate layer is of a material with high chemical affinity towards the cavity wall material, the surface roughness of said intermediate layer is decreased by polishing to below 0.5 nm, and the thickness of said intermediate layer after polishing is determined such that the behavior of the membrane is determined by the diamond layer.