Method for manufacturing ultrasonic transducer, ultrasonic transducer, and distance measuring equipment
A method for manufacturing an ultrasonic transducer comprises the following steps: 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 is prepared. A piezoelectric element is formed on the first silicon film of the first SOI substrate. The second silicon film is etched to form a diaphragm. A silicon substrate is connected to the second silicon film. An opening and a gap are formed in an acoustically resonant structure including the first SOI substrate and the silicon substrate and the diaphragm and the acoustically resonant structure are also matched in resonant frequency so as to amplify vibration of a sonic wave of the diaphragm.
1 . 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.
2 . The method for manufacturing an ultrasonic transducer according to claim 1 , wherein the step of causing the diaphragm and the acoustically resonant structure to match in resonant frequency includes fixing the movable plate to the second support while the diaphragm and the acoustically resonant structure are matched in resonant frequency.
3 . The method for manufacturing an ultrasonic transducer according to claim 1 , wherein
the silicon substrate is a second SOI substrate,
the second SOI substrate includes an SOI active layer, an SOI support layer, and an SOI intermediate silicon oxide film sandwiched between the SOI active layer and the SOI support layer, and
the step of causing the diaphragm and the acoustically resonant structure to match in resonant frequency includes etching the SOI active layer, the SOI support layer, and the SOI intermediate silicon oxide film to form the movable plate of the SOI active layer.
4 . The method for manufacturing an ultrasonic transducer according to claim 1 , wherein the step of causing the diaphragm and the acoustically resonant structure to match in resonant frequency includes forming a beam in the silicon substrate to interconnect the movable plate and the second support.
5 . The method for manufacturing an ultrasonic transducer according to claim 1 , wherein the step of causing the diaphragm and the acoustically resonant structure to match in resonant frequency includes causing the movable plate to be movable relative to the second support by electrostatic attraction of a jig electrode.
6 . The method for manufacturing an ultrasonic transducer according to claim 5 , wherein
the silicon substrate is a second SOI substrate,
the second SOI substrate includes an SOI support layer, and
the jig electrode is disposed on the SOI support layer.
7 . The method for manufacturing an ultrasonic transducer according to claim 1 , wherein the step of causing the diaphragm and the acoustically resonant structure to match in resonant frequency includes changing the opening in length to cause the diaphragm and the acoustically resonant structure to match in resonant frequency.
8 . The method for manufacturing an ultrasonic transducer according to claim 1 , wherein the step of causing the diaphragm and the acoustically resonant structure to match in resonant frequency includes changing the opening in area to cause the diaphragm and the acoustically resonant structure to match in resonant frequency.
9 . An ultrasonic transducer comprising:
an acoustically resonant structure including a first support and a diaphragm composed of an SOI substrate, and a second support and a movable plate composed of a silicon substrate; and
a piezoelectric element attached to the acoustically resonant structure,
the diaphragm composed of the SOI substrate being connected to the first support,
the second support composed of the silicon substrate being connected to the first support on a side opposite to the diaphragm with respect to the first support,
the movable plate composed of the silicon substrate being connected to the second support so as to face the diaphragm,
the piezoelectric element being connected to the diaphragm of the acoustically resonant structure,
the movable plate having an opening,
the opening being in communication with a gap surrounded by the first support, the diaphragm, the second support, and the movable plate,
the opening and the gap being formed to cause the diaphragm and the acoustically resonant structure to match in resonant frequency.
10 . Distance measuring equipment comprising the ultrasonic transducer according to claim 9 .