The demand for flexible substrates in the electronics industry and medicine has highlighted the importance of applicable printing techniques on these materials. Neural prosthetics interfacing with soft tissues and tight packaging requirements in the high-frequency electronics field require application-specific fabrication methodologies for printing conductors on or embedded in flexible substrates. The purpose of this dissertation is to introduce novel fabrication techniques for printing metal patterns on silicone elastomers. In pursuing this goal, two applications in the biomedical and antennas fields are given. These applications require printing of metals on silicone elastomers and the requirements of these applications are met with application-specific microfabrication processes. The initial project involves printing microwave structures on PDMS-ceramic composites. These structures include transmission lines, a patch antenna and a feeding pattern for a GPS antenna. The second work requires the fabrication of a microelectrode array for recording neural signals from the brain cortex surface. Microfabrication techniques have been developed for the device fabrications.
In the first application, a novel technique for direct printing of patterned conducting geometries on silicone-based, flexible polymer composites is presented. Specifically, micro-texturing is applied on the polymer composite surface followed by evaporation of a buffer titanium layer and a seed layer of copper. Electroplating is also applied as a final step to increase conductor layer thickness to accommodate polymer layer bending while maintaining good RF conductivity. The printed examples include 5 mm wide copper microstrip lines on polymer composite substrates. These printed microstrip lines demonstrated very low sheet resistivity of 0.1 ohm per square for frequencies up to several GHz. They were also shown to maintain low resistance during large bending deformations. To investigate RF performance, a patch antenna was also printed on a polymer-ceramic composite and shown to perform as predicted. Apart from patch antenna, a more complex patterned microwave structure that is a hybrid feeding structure of a GPS antenna has been fabricated. The performance evaluation of this hybrid feeding is in accordance with the simulated results and demonstrates the working fabrication process.
In the second application, the neural microelectrode has been fabricated based on a silicone elastomer substrate with an array of three-dimensional platinum contacts as the recording sites. Platinum contacts are exposed on the elastomer surface and these recording sites are embedded in elastomer, forming a robust three-dimensional structure suitable for surface recording. This robust yet flexible device is fabricated with microfabrication techniques including evaporation, photolithography, wet etching, electroplating and welding. Cytocompatibility of the device was tested with mouse fibroblasts and mouse forebrain neurons. The cell viability results verify the cytocompatibility of the fabricated device. The electrical characteristics of the electrodes were demonstrated with impedance measurements.