Two-Dimensional Array Transducers Using Thick Film Connection Technology

Abstract

Two-dimensional array ultrasound transducers have been previously developed in our laboratory by hand wiring 16 × 16 arrays of PZT-5H elements operating at 2.5 MHz with element spacing of 0.5 mm × 0.5 mm. There are severe difficulties in electrical connection to such elements which are less than one ultrasound wavelength on a side. To solve this problem, a new connection technique has been developed by combining a conductive λ /4 mismatching layer with a multi-layer ceramic (MLC) connector (thick-film microelectronic technology). The connector consists of 20 thick films of alumina and screen printed metallization with customized interconnections between the layers called vias. Ten ground layers are interleaved between ten signal layers to reduce electrical cross talk. A λ/4 mismatching layer of conductive epoxy is bonded between each PZT element and the silver metal pad of the MLC connector to provide an effective 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, bandwidth, interelement uniformity, and cross talk are all in good agreement with arrays of conventional fabrication. However, an array with MLC connector can be fabricated more quickly independent of the number of elements. Thick-film microelectronic circuit technology shows promise for solving the fabrication problems of 2-D array transducers of over a thousand elements at frequencies approaching 10 MHz. © 1993 IEEE