Processing Soft Materials for Integrated Photonic and Macroelectronic Components and Devices
Speaker: Candice Tsai
Series: Final Public Orals
Location: Engineering Quadrangle J401
Date/Time: Monday, January 10, 2011, 10:30 a.m. - 12:30 p.m.
Incorporating soft materials into micro-fabrication processes opens up new functionalities for fabricated devices, but requires unique processing routes. This thesis presents our development of integrated photonic and macroelectronic structures through novel processing innovations that unite disparate inorganic/organic, and soft/rigid materials systems.
For the integrated photonic system, we focus our efforts on chalcogenide glasses, dielectric materials that exhibit a variety of optical properties that make them desirable for near- and mid-infrared communications and sensing applications. However, processing limitations for these relatively fragile materials have made the direct integration of waveguides with sources or detectors challenging. Here we demonstrate the viability of several additive methods for patterning chalcogenide glass waveguides from solution. In particular, we focus on two complementary soft lithography methods. The first, micro-molding in capillaries (MIMIC), is shown to fabricate multi-mode As2S3 waveguides which are directly integrated with quantum cascade lasers (QCLs). In a second method, we demonstrate the ability of micro-transfer molding (µTM), to produce arrays of single mode rib waveguides over large areas while maintaining low surface and edge roughness. These methods form a suite of processes that can be applied to chalcogenide solutions to create a diverse array of mid-IR photonic structures ranging from less than 5 to 10’s of µm in dimension. Optical characterization, including measurement of waveguide loss by cut-back, is carried out in the mid-IR using QCLs. In addition, materials characterization of the chalcogenide glass structures is carried out to determine loss mechanisms and optimize processing.
While we use soft polymeric materials to pattern chalcogenide glasses, we also employ them as substrate material for stretchable electronic systems, which comprise a new class of flexible macroelectronics. These devices must undergo elastic deformation to large strain (>10%), for applications in which electronics are conformally shaped around surfaces of arbitrary shape, like many biological surfaces. We develop strategies for processing stretchable metallic electrodes and study the mechanism of their stretchability via careful observation of thin film micro-structures. Our macroelectronic work culminates in fabrication of stretchable microelectrode arrays that interface with brain tissue, laying the groundwork for future development of advanced bio-electronic interfaces.