A method of forming an ultrasonic transducer device involves depositing a first layer on a substrate, depositing a second layer on the first layer, patterning the second layer at a region corresponding to a location of a transducer cavity, depositing a third layer that refills regions created by patterning the second layer, planarizing the third layer to a top surface of the second layer, removing the second layer, conformally depositing a fourth layer over the first layer and the third layer, defining the transducer cavity in a support layer formed over the fourth layer; and bonding a membrane to the support layer.