Microfabrication of electrode patterns for high-frequency ultrasound transducer arrays

Abstract

High-frequency ultrasound is needed for medical imaging with high spatial resolution. A key issue in the development of ultrasound imaging arrays to operate at high frequencies (≥30 MHz) is the need for photolithographic patterning of array electrodes. To achieve this directly on 1-3 piezocomposite, the material requires not only planar, parallel, and smooth surfaces, but also an epoxy composite filler that is resistant to chemicals, heat, and vacuum. This paper reports, first, on the surface finishing of 1-3 piezocomposite materials by lapping and polishing. Excellent surface flatness has been obtained, with an average surface roughness of materials as low as 3 nm and step heights between ceramic/polymer of ∼80 nm. Subsequently, high-frequency array elements were patterned directly on top of these surfaces using a photolithography process. A 30-MHz linear array electrode pattern with 50-μm element pitch has been patterned on the lapped and polished surface of a high-frequency 1-3 piezocomposite. Excellent electrode edge definition and electrical contact to the composite were obtained. The composite has been lapped to a final thickness of ∼55 μm. Good adhesion of electrodes on the piezocomposite has been achieved and electrical impedance measurements have demonstrated their basic functionality. The array was then packaged, and acoustic pulse-echo measurements were performed. These results demonstrate that direct patterning of electrodes by photolithography on 1-3 piezocomposite is feasible for fabrication of high-frequency ultrasound arrays. Furthermore, this method is more conducive to mass production than other reported array fabrication techniques.

Experimental investigation of the rheological behaviors of polypropylene in a capillary flow

“…The rheological characterization of polymer melts plays an important role in quality control, process design, simulation, and troubleshooting applications. Recently, the application of and research into the microscopic behaviors of polymeric melts have attracted attention because of the development of microelectromechanical systems, and the demand for the molding of polymeric parts with micrometric structures has especially increased . Viscosity is a crucial rheological parameter of polymers; it is closely related to the flow properties of the polymer melt.…”

“…Recently, the application of and research into the microscopic behaviors of polymeric melts have attracted attention because of the development of microelectromechanical systems, and the demand for the molding of polymeric parts with micrometric structures has especially increased. [1][2][3][4][5] Viscosity is a crucial rheological parameter of polymers; it is closely related to the flow properties of the polymer melt. Studies have confirmed that the viscosity of polymer melts in a microcapillary is different from that in a conventional one, and it is affected on different levels by factors such as the geometry characteristics, wall slip, molecular structure, shear rate, and even the heat-transfer behavior.…”

Temperature-Dependent Properties of a 1–3 Connectivity Piezoelectric Ceramic–Polymer Composite

“…Comparing with monolithic 0.90Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) ceramics, the 1-3 composites show advantages of higher piezoelectric constants g h , higher value of k t , flexible processing in manufacturing, and relatively low impendence Z which leads to better material performance in matching with human tissue and water (Dyaz and Castillero 2001;Wang et al 2008). At present, methods developed for processing finescale 1-3 piezoelectric composites include dice-and-fill (Xu et al 2012), injection molding (Leslie, Gentilman, and Pham 1993), viscous-polymer processing (VPP) (Abrar et al 2004;Bernassau et al 2012), among which dice-and-fill is the uppermost process because of its mature technique and easy setup preparation. On the other hand, in the VPP, the size and shape of fibers can be changed flexibly as well as the distribution in the composites, therefore the prepared 1-3 composites have advantages in optimizing the material properties to meet various requirements for different applications (Bowen and Stevens 2006).…”

Optimization and characterisation of bonding of piezoelectric transducers using anisotropic conductive adhesive

“…Moreover, in the case of transducers integrated into needles, the medical requirement of small gauges (G16 or above) prohibits wire bonding interconnect above a certain array size. The lack of suitable integration technology limited many earlier attempts at ultrasound transducers array in a needle to single element transducer [2] or using unsuitable packaging solutions [3].…”