Development of MEMS fabrication for transparent and flexible capacitive micromachined ultrasonic transducer (CMUT)

Abstract

This thesis reports the process of making transparent and flexible Capacitive Micromachined Ultrasonic Transducer (CMUT) using polymer. CMUT is widely used in medical ultrasound imaging because it can be manufactured with the desired type of micro-array by MEMS fabrication. However, conventionally used CMUT fabrication is difficult to make transparent and flexible because silicon is rigid and opaque. In this work, a new MEMS fabrication was developed using polymer CPI and SU-8 instead of silicon and transparent electrode ITO and AgNW. Also, we proposed a hybrid membrane with ITO between SU-8 to improve the low output pressure of polymer-based CMUT. The FEM simulation shows that the device has a resonance frequency of 4.78 MHz, pull-in voltage of 68.188V, and an output pressure of more than twice as high as that of the polymer-only membrane. The completed device has a ROC of less than 1.3 mm and transmittance of 60 – 80% in the visible range. This study is the first of the transparent and flexible CMUTs to perform ultrasound imaging and has higher transmittance than conventional transparent CMUTs.