A 256-Element Spiral CMUT Array with Integrated Analog Front End and Transmit Beamforming Circuits

MEMS-based Capacitive Micromachined Ultrasonic Transducer (CMUT) technology enables the development of advanced transducer-electronics integrated multi-chip modules (MCM) for medical imaging applications. In this paper, we present the design, fabrication and characterization of a 256-element CMUT spiral array integrated with a 256-channel analog front end (AFE) ASIC featuring highvoltage unipolar pulsers, low-noise amplifiers and a programmable transmit beamformer. The spiral array, designed to perform volumetric beam steering at 7 MHz, is characterized by a density-tapered layout of 220μm -wide hexagonal elements distributed over a quasi-circular area of 10 mm diameter. The CMUT and the AFE were co-designed, fabricated and interconnected through an acoustically optimized 3-D packaging method. The resulting MCM was electromechanically and acoustically characterized, demonstrating the potential of the proposed approach for integrated 2-D CMUT array fabrication.