Development, Characterization, and Performance Enhancement of CMOS-MEMS Dual-Gap Capacitive Transducers

This study proposes a platform for designing microelectromechanical system (MEMS) capacitive transducers, utilizing conventional 0.18 µm 1-Poly-6-Metal complementary metal-oxide-semiconductor (CMOS) technology to realize dual transduction gap sizes. As capacitive transducers, different transduction gap sizes come with their respective advantages and disadvantages, often requiring designers to make tradeoffs among various performance metrics. The proposed CMOS-MEMS platform provides two transduction gap sizes on a single chip, demonstrating excellent circuit integration capabilities. This design is based on partial etching technology applied to the back-end-of-line metal layers, and uses a titanium nitride antireflective coating as the electrode, enabling the simultaneous fabrication of 125 and 450 nm transduction gaps without damaging the integrated circuits. In addition, the study proposes a dc bias inversion technique to enhance the transmission performance of ultrasonic transducers, which is validated through ultrasonic water tank experiments.