A CMOS MEMS capacitive ultrasonic sensor array for three-dimensional photoacoustic imaging

Three dimensional (3-D) photoacoustic imaging is demonstrated in this study by using a 4 × 4 CMOS (complementary metal oxide semiconductor) micromachined capacitive ultrasonic sensor array. The sensing membranes are fabricated by a post-CMOS metal etch and sealed by parylene with a measured resonant frequency between 3 to 5.1 MHz. The area of a single detection unit is 280 × 280 μm². A large 2-D aperture was emulated by 2-D mechanical scanning of the array with a scanning step of 1.12 mm. The measured -6-dB spatial resolutions were 381 μm in axial and 1.3 mm in lateral, respectively, at a depth of ~2.1 cm. The 3-D photoacoustic image of a hair phantom was successfully produced.