pH sensitive capacitive detectors based on localized nanowire arrays : nanotechnology & device integration routes

(eng) “Small” and “Sensitive” are two essential properties hard to reconcile in the sensors manufacturing. The challenge is to appropriately manipulate and localize novel nanostructures, to act as potential performance enhancers for low-scale devices fabrication. The aim of this work was to develop and characterize a highly-sensitive capacitive sensor achieved by increasing its active surface using large arrays of localized vertically-aligned nanowires. First, the macro-, micro- and nano-technologies used in the fabrication of the device were detailed, discussed and evaluated. The methods were carefully tailored to the standard silicon technology. Large arrays of metallic nanowires of controlled geometries were nicely localized on top of substrate pre-patterned micro-strips. The supported alumina template was a key element for designing, controlling and tuning the nanowires geometry. To probe the boosted performance, a pH sensor was fabricated by functionalizing the nano-brushes with polyaniline as an electrochemical transducer. Second, electrical modeling methodologies were coupled with frequency based measurements, in order to evaluate the impedance, capacitive and resistive performances of the device. The results demonstrated that the presence of the vertically-aligned nanowires increased the sensitivity of the element with up to two orders of magnitude. The investigations conducted toward the potential integration of the nanostructured element as silicon based detecting chip. Finally, a real-time stand-alone detector was designed, having as active sensing core the nanostructured element previously fabricated and characterized. The proposed solution is very promising and amiable to miniaturization offering great perspectives and enhanced sensing capabilities. The proof-of-concept was probed in the end by implementing an improved sensing core that demonstrates the nanoscale possibility for wireless in-situ capacitive bio-detection and monitoring.