  CMUT technology was invented and has been widely researched on silicon
substrates. In recent years, fabrication of CMUT on glass substrates has raised
significant interests because a number of advantages it can offer. First,
parasitic capacitance could be easily reduced since glass is an insulating
material. Second, insulation steps required in the silicon-based CMUT
fabrication process could be avoided, leading to a reduced fabrication
complexity. Third, anodic bonding can be used when the substrate is
borosilicate glass, which is a low-temperature bonding technique and has a high
tolerance to bonding surface area and roughness in addition to the advantages
of silicon wafer bonding. Moreover, glass transparency can enable novel
applications beyond pulse-echo ultrasound medical imaging and enlarge the
potential markets of CMUTs.
