Polysilicon on Quartz Substrate for Silicide Based Row-Column CMUTs

This paper presents a new type of insulating substrate, polysilicon-on-quartz (POOQ), that can be used for wafer bonded capacitive micromachined ultrasonic transducers (CMUTs). The substrate is based on a quartz handle wafer on which a device layer of polysilicon is deposited. The polysilicon is polished to an average surface roughness below 0.2 nm which allows for wafer bonding. Fusion bonding of such wafers is successfully performed at 950 °C which opens up for new CMUT device designs including the use of silicides for low resistance large scale row-column addressed (RCA) ultrasound transducers.