| Two types of low-temperature, electrosynthesized nanocomposite materials for MEMS applications are developed, including nickel-nanoparticle composite and conductive-polymer-nanotube composite. In the nickel nanocomposite work, low temperature, stress-free, wafer-level fabrication via both an electroless nickel and an electrolytic nickel deposition process have been demonstrated, with the addition of uniformly dispersed nanoparticles of either cordierite (diameter ≈100 nm ∼ 5 mum) or diamond (diameter ∼4nm). The as-deposited electroless nickel-cordiente films exhibit better thermal compatibility with silicon, compared to pure nickel with measured coefficient of thermal expansion of 17.34 ppm/°K and 26.69 ppm/°K, respectively. Stress-temperature measurement of electroless nickel-cordierite composite also confirms that thermally-induced residual stress decreases with the incorporation of cordiente. Finally, by adding various concentrations of nanodiamond particles into an electrolytic nickel matrix, it is found that higher diamond concentrations render the film to be more compressively stressed.; Conductive polymer-based nanocomposite represents a unique class of sensing material due to its responsiveness to external stimulants and its compatibility with MEMS fabrication technology via a one-step, selective on-chip deposition process at room temperature. Doped polypyrrole (PPy) and its nanocomposite variant synthesized by incorporating multi-walled carbon nanotube, have been successfully demonstrated as biochemical sensing materials. A two-terminal, micro-gap chemiresistor architecture is proposed for sensing applications by bridging the gap using either dodecylbenzenesulfonate (DBS)-doped PPy or PPy-carbon nanotube nanocomposites that are responsive to hydrogen peroxide and glucose concentration, respectively. The humidity- and temperature-dependent responses of the conductivity of PPy were characterized experimentally, with the results showing that the conductivity of PPy decreases due to the insertion of water molecules into the polymer matrix as a secondary dopant, and increases due to the presence of oxidizing agent such as hydrogen peroxide. The oxidant sensing effect is employed in the design of a glucose oxidase encapsulating, doped PPy-carbon nanotube nanocomposite glucose sensor. This new micro-gap sensor architecture obviates the need for reference electrode and electron mediators, via measuring the direct, reversible, oxidation-reduction induced conductivity change. Experimentally, glucose oxidase-laden, doped PPy is tested to be sensitive to glucose concentration between 0--10 mM and the incorporation of multi-walled carbon nanotube extends the detection ceiling to 20mM, which covers the physiologically important range of 0--20 mM for diabetics. |
