A 128×128 ultrasonic transducer hybrid array

Ultrasonic imaging in the low MHz frequency range with large, dense arrays presents many design and fabrication challenges. Conventional ultrasound systems use micro-coaxial cable to connect the array to the front end electronics. While coax technology has improved dramatically in the past decade, interconnecting 16384 array elements with separate wires remains a formidable challenge. In addition to this practical issue, the capacitance of a long coaxial cable (~40 pF/m) is much larger than that of a typical 2D array element (<1 pF), creating a voltage divider that severely reduces the signal-to-noise ratio of the channel. A 2D composite piezoelectric receiver array bonded directly to four large custom integrated circuits is described. This 128×128 (16384 total) element Transducer Hybrid Array (THA) of 200 μm unit cell spacing is intended for a 3D real-time imaging system for medical and underwater applications. By reducing the interconnect length to less than 20 μm, cable capacitance is no longer a problem. Massively parallel, on-chip signal processing enables true real-time three-dimensional imaging. Favorable tradeoffs using composite piezoelectric materials, enabled by this high-density flip-chip interconnection technology are discussed