A wideband PVDF-on-silicon ultrasonic transducer array with microspheres embedded low melting temperature alloy backing.

A PVDF-based 8-element ultrasound transducer array (1 mm x 1 mm element size with an inter-element spacing of 1 mm) on a silicon carrier substrate is fabricated and characterized. To improve the performance of the transducer, new CMOS-compatible fabrication technologies are introduced. These include: (1) adhesive micro-contact printing on non-radiating areas, and (2) glass microspheres (7-20 microm in diameter) embedded low melting temperature alloy (LMA) for backside electrical connection. The first improvement removes the adverse effects of adhesive layer (e.g., lower sensitivity) between the PVDF and backside contact while the second one improves the pulse-echo signal quality by eliminating reflections at the backing/water interface. The fabricated array elements are tested in a water tank and their pulse-echo response are recorded. The central frequency of each element is 25 MHz with a 100% measured 6-dB bandwidth (60% 3-dB bandwidth).