Microfabricated lab-on-a-chip devices employing a fully integrated electrochemical (EC) detection system have been developed and evaluated. Both capillary electrophoresis (CE) channels and all CE/EC electrodes were incorporated directly onto glass substrates via traditional microfabrication techniques, including photolithographic patterning, wet chemical etching, DC sputtering, and thermal wafer bonding. Unlike analogous CE/EC devices previously reported, no external electrodes were required, and critical electrode characteristics, including size, shape, and placement on the microchip, were established absolutely by the photolithography process. For the model analytes dopamine and catechol, detection limits in the 4-5 microM range (approximately 200 amol injected) were obtained with the Pt EC electrodes employed here, and devices gave stable analytical performance over months of usage.

A scalable and rather inexpensive solution to producing microanalytical systems with "on-chip" three-dimensional (3D) microelectrodes is presented in this study, along with applicability to practical electrochemical (EC) detection scenarios such as preconcentration and interferant removal. This technique to create high-aspect-ratio (as much as 4:1) gold microstructures in constrained areas involved the modification of stud bump geometry with microfabricated silicon molds via an optimized combination of temperature, pressure, and time. The microelectrodes that resulted consisted of an array of square pillars approximately 18 microm tall and 20 microm wide on each side, placed at the end of a microfabricated electrophoresis channel. This technique increased the active surface area of the microelectrodes by as much as a factor of 50, while mass transfer and, consequently, preconcentration collection efficiencies were increased to approximately 100%, compared to approximately 30% efficiency for planar nonmodified microelectrodes (samples that were used included the neurotransmitters dopamine and catechol). The 3D microelectrodes were used both in a stand-alone configuration, for direct EC detection of model catecholamine analytes, and, more interestingly, in dual electrode configurations for EC sample processing prior to detection downstream at a second planar electrode. In particular, the 3D electrodes were shown to be capable of performing coulometry or complete (100%) redox conversion of analyte species over a wide range of concentrations, from 4.3 microM to 4.4 mM, in either plug-flow or continuous-flow formats.

The use of anisotropic conductive film (ACF) and stud bumping to form interconnects between die and substrates is one variation of current flip chip technologies with potential applications to MEMS devices. The key concerns associated with ACF are its long-term mechanical stability and consistent electrical performance. During this study a process methodology was developed for using ACF interconnections on MEMS devices by investigating key electrical parameters, and a practical example was investigated by packaging a pressure sensor using ACF flip chip techniques. Results of process development and contact resistance measurements using glass substrates and the anisotropic conductive film Sony FP1526 are discussed and analyzed. All required processing steps, such as stud bumping, application of ACF and thermocompression bonding of the die and substrate, were carried out using a digital wire bonder and a bench-top flip chip system. FP1526 yielded an average contact resistance of 10.23 mΩ, a stray capacitance measurement of 10 femtofarad and less than 0.1% change in contact resistance after being encapsulated in parylene C and being immersed in DI water for 72 h. Finally, the performance of an ACF-packaged MEMS piezoresistive pressure sensor was compared to that of a conventional wire-bonded device and showed a significant improvement in temperature stability (<0.34% deviation in offset voltage) with essentially no change in sensitivity.

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