Design of high-frequency broadband CMUT arrays

In this work we demonstrate a high-frequency (29-MHz) broadband (100% FBW) CMUT 1D array. The devices are fabricated using anodic bonding with only three photolithography steps. We also discuss the design guidelines for high-frequency broadband CMUTs using the simulations. A high fill factor and a thin plate are important for the broadband design. Small cell size is required for the increased center frequency. To improve the transducer sensitivity and to keep the collapse voltage low, the gap height should be small and a high-k dielectric insulation layer should be employed. The fabrication steps we report in this paper have good potential to meet the high-frequency broadband CMUT design requirements. So far we have demonstrated that we can define a 50-nm gap, bond to a post as narrow as 2 μm, and pattern a high-k dielectric layer on the bottom electrode.