Low temperature process for CMUT fabrication with wafer bonding technique

We present the successful fabrication of capacitive micromachined ultrasonic transducers (CMUTs) based on low temperature wafer bonding (<;400°C). Such a fabrication process enables the direct integration of CMUTs on top of IC substrates, and requires only two additional lithography steps for fabricating the complete CMUT. Our approach benefits from both the integrated electronics and the well-controlled performance of CMUTs with single-crystal silicon plates. The yield of the CMUTs is almost 100%, and the standard deviation of resonance frequency in air is less than 1% in the whole 4 inch wafer.