In this paper, we reports the development of a miniaturized capacitive ultrasonic sensor with a Parylene diaphragm using a micromachining technique. Since the polymer diaphragm is flexible and nonbrittle, good sensitivity and durability are expected. Moreover, Parylene has good complementary metal oxide semiconductor (CMOS) compatibility, since it can be deposited at room temperature. Practical sensor devices were fabricated, and their performance was characterized. They can receive an impulsive ultrasonic pulse transmitted by a spark discharge with an open-circuit sensitivity of 0.3 mV/Pa. A well-damped waveform was obtained by setting appropriate acoustic holes. The ranging system using this sensor can detect distances up to 1 m with an error of less than 1 mm. The developed sensor can receive ultrasound from a wide area. The wide directivity could be effective for realizing the omni-directional characteristics of the future arrayed sensor, which contains many of the developed sensors.

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