Two-dimensional arrays for medical ultrasound using multilayer flexible circuit interconnection

Abstract

The development of 2-D array transducers has received much recent interest. Unfortunately, fabrication of high density 2-D arrays is difficult due to the large number of electrical interconnections which must be made to the back side of the elements. A typical array operating at 2.2 MHz may have 256 or more connections within a 16.4 mm circular footprint. Interconnection becomes even more challenging as operating frequencies increase. To solve this problem, we have developed a multilayer flexible (MLF) circuit interconnect consisting of a polyimide dielectric with inter-laminar vias routing signals vertically and etched metal traces routing signals horizontally. A transducer is fabricated from an MLF by bonding a PZT chip to its surface and dicing the chip into individual elements, with the saw kerf extending partially into the top polyimide layer to ensure physical and electrical isolation of the elements. The KLM model was used to compare the performance of an MLF 2-D array to a conventional hand wired 2-D array. MLF and wire guide transducers were fabricated, each with 256 active elements, 0.4 mm interelement spacing, and 2.2 MHz center frequency. Vector impedance, pulse length, bandwidth, angular response, and cross-coupling were found to be comparable in both types of arrays. Using the MLF, however, fabrication time was reduced dramatically. More importantly, MLF technology may be used to increase 2-D array connection density beyond the limitations of current of hand wired fabrication techniques. Thus MLF circuits provide a means for the interconnection of current and future high frequency 2-D arrays.

Characterizing cellular morphology by photoacoustic spectrum analysis with an ultra-broadband optical ultrasonic detector

“…Detecting high-frequency ultrasound signals (e.g., ~hundreds of MHz) usually requires carefully manufactured transducers with thin and fragile piezoelectric elements. Besides, due to the resonance effect in the piezoelectric part, these transducers usually have maximum responses at a high frequency, and therefore, a reduced response at the low frequency regime [18][19][20].…”

Hybrid multi/single layer array transducers for increased signal-to-noise ratio

“…14, the proposed transducer assembly is shown with the IC transmitters and Preamplifiers. The single and multi-layer hybrid ceramic is bonded to a polyimide flexible circuit connector [17]. This is used in place of conventional wire guides [14], and it is similar in design and concept to the thick film, multi-layer alumina connectors previously designed and tested at Duke [18].…”

Volumetric ultrasound system for left ventricle motion imaging

“…Second, the design of high density 2D array transducers involves interconnecting a large number of elements to the back side of the array. These electrical interconnections still remain the major difficulty in spite of progress made in the circuit interconnection techniques and in the choice of various material parameters [30]- [34]. The close proximity of the elements induces electrical cross-coupling that reduces the gain for large steering angles, and the spacing between the elements must be precise in order to limit the occurrence of unwanted grating lobes in the array response.…”