Two-dimensional array transducers using hybrid connection technology
We previously described 2-D array transducers consisting of 16 x 16 = 256 PZT-5H elements operating at 2.5 MHz fabricated by hand wiring. Element spacing is 0.5 mm x 0.5 mm. There are severe difficulties in electrical connnection to such elements which are less than one ultrasound wavelength on a side. To solve this problem, we have now developed a new connection technique, a multi-layer ceramic (MLC) connector (thick-film hybrid microelectronic technology) consisting of 20 thick films of alumina and screen printed metallization with customized inter-connections between the layers called vias. Ten ground layers are inleaved between ten signal layers to reduce electrical cross-talk. A λ/4 mis-matching layer of conductive epoxy is bonded between each PZT element and the silver metal pad of the MLC connector to provide a low impedance backing. In the current configuration, a 16 × 16 transducer array, 0.6 mm element spacing, is expanded to a 16 × 16 grid of connector pins at a standard spacing of 2.5 mm. Vector impedance, sensitivity and bandwidth are all in good agreement between conventional fabrication versus the MLC connector, but interelement cross-talk improved by 10 dB. Hybrid microelectronic circuit technology shows promise for solving the fabrication problems of 2.-D array transducers of over a thousand elements at frequencies exceeding 5 MHz.
