Abstract
This study proposed a 4 × 4 capacitive ultrasonic sensor chip produced by CMOS-MEMS process technology. By using the sensing circuit placed at the bottom of the sensor structure, the routing interconnect is reduced, so is the parasitic capacitance. It had a better signal-to-noise-ratio, but also improved the efficiency of area utilization. The structures were released through wet etching (Metal 3), and sealed by using the Parylene. Nine membranes, each with an inner diameter of 60 μm, formed a single detection unit with the area of 280 μm × 280 μm and the capacitance value of 312.2 fF. The sensor array is composed of 16 (4 × 4) sensors with a total area of about 1120 μm × 1120 μm. The experimental results show that the 4 × 4 sensor array can successfully receive the signals of 5 MHz ultrasound in the water, outputs of hundreds of mV can be measured under appropriate measurement conditions. 2D large-aperture arrays were emulated by 2D mechanical scanning of a single sensing element or 16 (4 × 4) sensing elements. The 3D photoacoustic images of a carbon fiber and a hair were successfully produced.