A MEMS T/R switch embedded in CMUT structure for ultrasound imaging frontends

This paper describes a novel MEMS transmit/ receive (T/R) switch that could be embedded in the general structure of a capacitive micromachined ultrasonic transducer (CMUT). A MEMS switch and a CMUT element were fabricated side by side using an anodic-bonding-based fabrication process. The plates of the CMUT and the membrane-type switch were formed at the same step by anodic bonding. A single switch was tested in air for preliminary characterization. Vacuum-sealing of the switch cell was confirmed by an atmospheric deflection measurement. The switch was then biased at 59-V DC voltage and turned on and off by applying a 1-kHz, 5-Vpp square wave to the control terminal while a 1-MHz, 300-mVpp sinusoidal signal was applied at the RF input. The signal measured at the RF output demonstrates the basic switching behavior with a switch series resistance of 124 ?. This work is important for the ultrasound imaging system efficiency and could significantly ease the high-voltage requirements of frontend circuits.