Benjamin Y. Park

Electrical Properties and Shrinkage of Carbonized Photoresist Films and the Implications for Carbon Microelectromechanical Systems Devices in Conductive Media

Recent advances in fabricating 3D micro- and nanostructures using carbon microelectromechanical systems, or C-MEMS, has opened up a wide variety of new and exciting applications. The development of 3D C-MEMS has been catapulted forward by the use of transparent, high-viscosity resists such as SU-8. The electrical characteristics and shrinkage of various thickness carbon films derived from SU-8 and AZ P4620 are quantified and discussed in the context of the decomposition and carbonization mechanisms of epoxy and phenolic resins. Measurements obtained reveal a thickness dependence of the resistivity at lower carbonization temperatures but not much dependence at 1000°C. Possible explanations for this low-temperature thickness dependence are given. The electrical characteristics of carbon films obtained from both types of photoresists carbonized at 1000°C are very similar to that of glassy carbon. Simulations have been carried out to demonstrate the importance of the carbon resistivity for C-MEMS devices when used in conductive media. A method for simple optimization and verification of C-MEMS device designs for use in conductive media is introduced.

A Case for Fractal Electrodes in Electrochemical Applications

Fractal electrode designs are proposed for electrochemical devices. A zeroth-order approximation fractal model is analyzed and basic insights into the scaling laws of the electrical properties and the surface-to-area ratio are derived. Fractal electrodes can minimize internal resistance while maximizing surface-to-volume ratios. Recent carbon microelectromechanical systems CMEMS techniques show great promise for use in the fabrication of fractal electrodes for electrochemical applications. Preliminary results showing carbon fractal electrodes fabricated using C-MEMS techniques are presented.

Introduction to microfabrication techniques.

The advent of photolithography literally brought about the integrated circuit (IC) revolution of the latter part of the twentieth century. Almost all electronic devices that we use today have one or more ICs inside. Improving lithography techniques led to smaller and smaller transistors, which translated into faster and more efficient computing machines. Photolithography also powered the advent of MicroElectroMechanical Systems (MEMS), which are now starting to become more and more diverse in commercial products from mechanical to biomedical devices, helping to change the way people perceive the applicability of IC technology. In this chapter, we examine basic photolithography techniques and their uses in soft lithography and MEMS.

Design and fabrication of an ac-electro-osmosis micropump with 3D high-aspect-ratio electrodes using only SU-8

Lab-on-a-chip devices require integrated pumping and fluid control in microchannels. A recently developed mechanism that can produce fluid flow is an integrated ac-electro-osmosis micropump. However, like most electrokinetic pumps, ac-electro-osmotic pumps are incapable of handling backpressure as the pumping force mechanism acts on the surface of the fluid rather than the bulk. This paper presents a novel 3D electrode structure designed to overcome this limitation. The electrodes are fabricated using carbon-MEMS technology based on the pyrolysis of the photo-patternable polymer SU-8. The novel ac-electro-osmosis micropump shows an increase in the flow velocity compared to planar electrodes.

Carbon as a MEMS material: micro and nanofabrication of pyrolysed photoresist carbon

Carbon, like Si, is an attractive and very versatile engineering material and is available in more structural varieties than Si. Carbon materials are already in use in a wide variety of applications because of their widely differing crystalline structures and properties, which enable very different physical, chemical, mechanical, thermal and electrical uses. Carbon-based Microelectromechanical Systems (MEMS) and Nanoelectromechanical Systems (NEMS), with sizes ranging from millimetre to nanometre, can provide solutions, alone or in combination with Si and other materials for microelectronics, nanoelectronics, sensors, miniaturised power systems, etc. In this review, Carbon-MEMS (C-MEMS) and Carbon-NEMS (C-NEMS) technology based on pyrolysis of patterned photoresist is reviewed. The fabrication process and the most promising applications are introduced.

Fabrication of polydimethylsiloxane microfluidics using SU-8 molds.

We detail the widely prevalent technique of polydimethylsiloxane (PDMS) molding using SU-8 for creating microfluidic chambers and channels. Although other techniques such as injection molding are more apt for mass manufacturing and cost-effective, PDMS molding is used almost exclusively for rapid prototyping in corporate and research environments because of its simplicity and fast turnaround time.

Fabrication of microelectrodes using the lift-off technique.

The lift-off technique is one of the most prevalent methods for fabricating microelectrodes on a flat surface (e.g., a silicon [Si] wafer). It represents an alternative for metal-etching techniques that often utilize hazardous chemicals in order to define a pattern. This chapter presents an example of patterning gold electrodes on an Si wafer.

Fractal Carbon-MEMS Electrodes: Theory and Preliminary Fabrication

Fractal electrode designs are proposed for electrochemical devices. A zeroth-order approximation fractal model is analyzed and basic insights into the scaling laws of the electrical properties and the surface-to-area ratio are derived. Fractal electrodes can minimize internal resistance while maximizing surface to volume ratios. Recent C-MEMS techniques show great promise for use in the fabrication of fractal electrodes for electrochemical applications. Preliminary results showing carbon fractal electrodes fabricated using C-MEMS techniques are presented.

Novel dielectrophoretic filtration methods and designs

A dielectrophoretic oil filter concept utilizing three-dimensional electrode geometries for electric and flow field shaping is introduced. Dielectrophoretic separation systems that incorporate planar microelectrodes cannot effectively filter large amounts of fluids because the dielectrophoretic force rapidly decays as the distance from the electrodes increases. 3D electrode designs for flow-through dielectrophoretic separation/concentration/filtration systems are advantageous because 1) The 3D electrodes extend the electric field within the fluid. 2) The electrodes can be designed so that the velocity field as well as the electric field is shaped for maximum efficiency. and 3) Filtration of particles that are too small to be physically filtered is possible. Three novel electrode designs that are not based on 2D electrode designs are introduced. Initial experimental results from particle count analysis that suggest that a reduction of up to 90% of particulate contaminants could be achieved are presented (It is important to note that the standard deviation was large due to the small number of particles within view and the uneven distribution of particles within the oil).