This paper presents a high performance capacitive micromachined ultrasound sensor (CMUS) with a large fractional bandwidth (FB) ∼113 % and a low bias voltage of 5 V in an immersion testing of an ultrasonic sensor. The thin polysilicon for the CMOS gate was utilized as a sacrificial layer and the multiple layers of metal and dielectric for the CMOS electric interconnects were used as the structural layer to decrease the effective gap, which resulted in a lower bias voltage, between two electrodes. An etching ditch design to release the CMUS membrane was demonstrated successfully to increase the sensor yield in the post CMOS MEMS processing. To further improve the sensitivity of the CMUS, our ASIC was integrated with the CMUS and a great sensitivity of 45dB was obtained.
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