Fabrication of functional devices using soft lithography and unconventional micropatterning

In this thesis, I present part of our work in the fabrication of functional devices using soft lithography, and also describe unconventional micropatterning techniques involving photographic films. Soft lithography is a set of techniques that are complementary to photolithography, but not limited to planar patterning. It offers the capability of generating micro and nanostructures to a larger community than that familiar with conventional fabrication facilities.; The first part of this thesis (chapter 1–4) focuses on the fabrication of microelectronic and micromagnetic devices. These successful demonstrations establish the compatibility of soft lithography with multilayer fabrication of functional devices, and open the door for the further development in these areas.; Chapter 1 and 2 describe the use of microtransfer molding (μTM), micromolding in capillaries (MIMIC), and microcontact (μCP) for fabricating Schottky diodes and half-wave rectifier circuits. The fabrication processes involve multiple soft lithography steps and address the registrations between different layer of structures. Room temperature characteristics of these devices resemble those of diodes and rectifiers fabricated by photolithography.; Chapter 3 and 4 demonstrate the fabrication of micromagnetic systems. In chapter 3, a one-dimensional bead motor is reported. Based on current-carrying wire systems, the bead motor can trap and transfer magnetic beads suspended in aqueous solutions. Chapter 4 shows a microfiltration system that uses arrays of nickel posts positioned in a polydimethylsiloxane (PDMS) microfluidic channel as the filtering elements. Turning on or off the magnetic field that is localized by these nickel posts can trap or release magnetic beads flowing by.; The second part of this thesis (chapter 5–7) focuses on the development of unconventional microfabrication. The major objective underlying this work is to explore the simplest and most broadly available techniques that we could identify for forming patterns with features useful in functional microstructures.; Chapter 5 and 6 describe the use of photographic films (microfiche and slide film) and transparencies printed using different printers as photomasks in the fabrication of PDMS stamps/molds for soft lithography. In chapter 6, we also compare different methods of generating microstructures using facilities readily and inexpensively available to chemistry and biology laboratories. Among the films and transparencies investigated, microfiche carries the highest resolution. It can generate structures as small as ∼10 μm in lateral dimensions.; Chapter 7 shows a new rapid prototyping process for the fabrication of metallic microstructures using silver halide-based photographic film. The whole process, which involves photographic development and electrochemical deposition, only takes ∼2 hours, starting from a computer design file. It can generate electrically continuous structures with the smallest dimension of ∼30 μm in the plane of the film. The resulting structures—either supported on the film backing, or freed from it—are appropriate for use as passive, structural materials such as wire frames or meshes, and can also be used in microfluidic, microanalytical, and microelectromechanical systems (MEMS).