Method for manufacturing ultrasonic transducer, ultrasonic transducer, and distance measuring equipment

A method for manufacturing an ultrasonic transducer, comprising:

• preparing a first SOI substrate including a first silicon film, a second silicon film, and an intermediate silicon oxide film sandwiched between the first silicon film and the second silicon film;
• forming a piezoelectric element on the first silicon film of the first SOI substrate;
• forming a diaphragm of the first silicon film by etching the second silicon film and the intermediate silicon oxide film of the first SOI substrate;
• connecting a silicon substrate to the second silicon film;
• and
• forming an opening and a gap in an acoustically resonant structure including the first SOI substrate and the silicon substrate, and also causing the diaphragm and the acoustically resonant structure to match in resonant frequency, so as to amplify a sonic wave of vibration of the diaphragm,
• wherein
• the step of forming a diaphragm includes forming a first support of the second silicon film, and
• the step of causing the diaphragm and the acoustically resonant structure to match in resonant frequency includes forming a trench in the silicon substrate to form a movable plate and a second support connected to the first support, and also causing the movable plate to be movable relative to the second support to change the gap in volume to cause the diaphragm and the acoustically resonant structure to match in resonant frequency.