Investigation of residual stress influence on CMUT in standard CMOS process

Residual stress will be generated in capacitive micromachined ultrasonic transducer (CMUT) during standard CMOS fabrication process, which has great effect on the CMUT performance, such as collapse voltage, resonant frequency, transformer ratio, sensitivity and bandwidth. To meet the requirements of design and improvements of fabrication process, sufficient considerations for the effects of residual stresses on the performances of CMUT should be taken. The finite element simulation methods (FEM) are used to investigate the influences of residual stresses on the performance of CMUT in this paper. The results show that the residual tensile stress is beneficial to the collapse voltage, sensitivity and the maximum output sound pressure, and the residual compressive stress is beneficial to the stiffness, transformer ratio, the maximum output sound pressure and output voltage.