Electric charge fill to the insulator film with the contact to the cavity subordinate surface of the membrane underside is controlled, when projection of the insulator film which extends to the cavity section is arranged, ideal projection arrangement structure in order to control the decrease of rise of the drive voltage of CMUT and reception sensitivity and the ultrasonic diagnostic device which uses that are offered. As for ultrasonic transducer of this invention, in order to form the cavity section on the lower part insulator film and the said lower part insulator film which were formed on the 1st electrode and the said 1st electrode, the 2nd electrode which was formed on the upper insulator film and the said upper insulator film which are provided and, it had, projection was formed by the aforementioned cavity section side to the aforementioned lower part insulator film or the aforementioned upper insulator film, the aforementioned 1st electrode which is suitable to the position where the aforementioned projection was formed or, it features that the open part is formed in the 2nd electrode.メンブレン下面の空洞部下面への接触による絶縁膜への電荷注入を抑制し、空洞部に突き出た絶縁膜の突起を配置する場合に、CMUTの駆動電圧の上昇や、受信感度の低下を抑制するための好適な突起配置構造と、それを用いた超音波診断装置を提供する。本発明の超音波トランスデューサは、第1電極と、該第1電極上に形成された下部絶縁膜と、該下部絶縁膜上に空洞部を形成するように設けられた上部絶縁膜と、該上部絶縁膜上に形成された第2電極と、を備え、前記下部絶縁膜又は前記上部絶縁膜には前記空洞部側に突起が形成され、前記突起の形成された位置に相当する前記第1電極又は第2電極には、開口部が形成されていることを特徴とする。
