Abstract
This work presents a capacitive ultrasonic sensor chip fabricated by the CMOS-MEMS technology. The unique feature of this work is integrating the circuit and the sensor on the same chip, which can efficiently reduce the parasitic capacitance. This work used the TSMC 0.18-μm 1P6M CMOS process, for fabrication, in which the MIM capacitors are used as our sensing structure. The thin CTM layer is used as the sacrificial layer in order to reduce the air cavity thickness for achieving higher sensitivity than our previous work. The structure is successfully released by wet etching and sealed by 2-μm silicon dioxide. The fabricated capacitive ultrasonic sensor is tested in water. The microstructure has an 80-μm diameter. The measured resonant frequency, band width and sensitivity are 5.8 MHz, 2.2 MHz, and 249.1 (mV_pp)⁄(MPa/V), respectively, which are better than the previous devices fabricated in the TSMC 0.35-μm 2P4M CMOS process .