A recently introduced set up of capacitive micromachined ultrasonic transducers (cMUT) combines a conductive membrane above a structured sacrificial layer [1]. All previous approaches either require an additional metallic electrode [2], [3] or do not possess a structured sacrificial layer [4] and, consequently, may make exact adjustment of the membrane dimensions difficult. The present set ups are especially suited for the fabrication of cMUT with gap heights ranging between 50 nm and 2 m between the electrodes. Large gaps are a prerequisite to enabling sufficient deflections of the membrane and, therewith, to generating high pressure gradients. On the other hand, small gap sizes are desirable for detecting weak ultrasonic sources. This paper focuses on the fabrication process of cMUT to realize electrode separation above 500 nm and, in addition, on the manufacturing of cMUT with gaps below 500 nm. The successful realization has been proven by some basic experimental investigations. Finally, the fundamental equations of a frequently chosen simulation model are documented, as a number of ambiguities exist in the common literature.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.