Single chip CMUT arrays with integrated CMOS electronics: Fabrication process development and experimental results

One of the most important promises of capacitive micromachined ultrasonic transducer (CMUT) technology is integration with electronics. This approach maximizes transducer sensitivity by minimizing parasitic capacitances and ultimately improves the signal to noise ratio. Additionally, due to physical size limitations required for catheter based imaging devices, optimization of area occurs when the CMUTs are fabricated directly above the associated electronics. Here, we describe successful fabrication of CMUTs on custom designed CMOS electronics from a commercial IC foundry. This is achieved by modifying a low temperature micromachining process by adding one additional mask and developing a sloped wall dry etching step on isolation oxide layer for metal interconnect. Experiments show that both the CMUT and the integrated CMOS electronics are functional, resulting combination generating pulse-echo response suitable for ultrasound imaging.