AbstractsEngineering

Direct-write technologies, a subset of the rapid prototyping, have been applied for many applications including electronics, photonics and biomedical engineering. Among them, MicropenTM is a promising technique, providing precision deposition of materials with various viscosities, on-line design changes and writing on nonplanar substrates. The objective of this project was to directly write two- and three-dimensional novel structures by MicropenTM for potential optical and transducer applications. First, to gain a basic understanding of MicropenTM operation, poly(methyl methacrylate) (PMMA) solutions were developed as a model system. The effects of solution rheological properties on deposition conditions were investigated. Secondly, PMMA/SiO2 hybrids were developed using sol-gel process. The effects of organic/inorganic ratios on thermal stability, microstructure and optical properties were studied. The solution with 80 wt% PMMA loading was chosen to deposit lines for optical applications. Another application was the direct-write of lead zirconate titanate (PZT) thick films (6-70 µm) for MEMS or high frequency medical imaging applications. Pastes consisting of 15-30 vol% ceramic loading in a sol-gel solution were prepared for the deposition of films on various substrates. The PZT sol was used as a binder as well as to achieve low temperature heat treatment of the films. Using the 15 vol% paste with a 250-µm pen tip, a four-layer film was deposited on a silicon substrate. This 16-µm film with 1 cm2 area had K of 870, tanδ of 4.1%, Pr of 12.2 µC/cm2 and Ec of 27 kV/cm. Furthermore, MicropenTM was utilized for the direct-write of ceramic skeletal structures to develop PZT ceramic/polymer composites with 2-2 connectivity for medical ultrasound transducers. Ceramic/binder based pastes were developed as writing materials. The 35 vol% paste exhibited shear thinning with a viscosity of 45 Pa•s at lower shear rate and 3 Pa•s at higher shear rate. Using a 100-µm pen tip, the fabricated composite with ~360 µm height had resonance frequencies of ~4 MHz, and electromechanical properties of K=650, tanδ=2.1%, kt=0.60 and d33=210 pC/N. Finally, composites with linear and Gaussian volume fraction gradients were fabricated by MicropenTM. Their vibration amplitude profiles showed maximum output at center with gradual decreasing towards edge of the composites.