A novel 6 × 6 element MEMS capacitive ultrasonic transducer with multiple moving membranes for high performance imaging applications

A 6 × 6 element multiple moving membrane capacitive micromachined ultrasonic transducer (M3-CMUT) array has been developed for air-coupled detection purposes in the low megahertz frequency range. Unlike conventional capacitive MEMS transducers, the developed transducer array employs a novel cell configuration where more than one flexible membrane contributes in the transducer signal transmission and detection. In this structure, a stack of two vibrating membranes is suspended over a fixed grounded bottom electrode. The transducer array has been fabricated through employing a MEMS sacrificial technique, with the top and middle membrane radii of 65 and 42 μm, respectively. The electrical, optical and acoustic evaluation results of this transducer array are presented in this paper. It is shown that using this configuration, the amplitude of membrane displacement is increased which enhances the transducer power output and sensitivity for a given bias condition. The experimental results demonstrate that this transducer array structure can be highly beneficial in high performance imaging application systems.