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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Cracks and holes observed at the CMUT membrane after handling-layer removal: (a) linear array; (b) dual ring array; and (c) SEM image of holes on the ring array CMUT surface after handling layer removing.