Low Cost Integrated Sensors Utilizing Patterned Nano-Structured Titania Arrays Fabricated Using a Simple Process
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Low Cost Integrated Sensors Utilizing Patterned Nano-Structured Titania Arrays Fabricated Using a Simple Process Zuruzi Abu Samah1, Andrei Kolmakov2, Martin Moskovits2 and Noel C. MacDonald1 1 Materials Department and echanical and Environmental Engineering Department, University of California at Santa Barbara, California, CA 93106. 2 Chemistry and Biochemistry Department, University of California at Santa Barbara, CA 93106.
ABSTRACT Using a novel low-temperature process, we demonstrate the facile integration of crack-free nanostructured titania (NST) as sensing elements in microsystems. Unlike conventional sol-gel methods, NST layers of interconnected nano-walls and nano-wires were formed by reacting Ti surfaces with aqueous hydrogen peroxide solution. Cracks were observed in NST layers formed on blanket Ti films but absent on arrays of patterned Ti pads below a threshold dimension. Analyses using TEM, high resolution SEM, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal that NST consists of anatase TiO2 nano-crystals. NST pads were found able to detect oxygen gas of a few ppm. NST pad arrays were integrated on rigid and flexible substrates with potential applications in low cost and wearable sensing systems.
INTRODUCTION Nanostructures of various material systems are excellent candidates for ultrasensitive and highly miniaturized sensors. Recent studies have focused on discrete nanostructures such as nano-tubes [1], nanowires [2] and mesowire arrays [3]. However, difficulties in locating and manipulating nanostructures limit their implementation in practical systems. To address this issue, novel methods have been proposed such as fluidic-assisted alignment coupled with surface patterning technique [4], fabrication of silicon nanowires from silicon-on-insulator substrates [5] and electrochemical deposition of polymers and palladium [6,7]. We propose a new concept of using micrometer scale features of sponge-like structures consisting of interconnected nanoscale walls or wires. These structures would possess the ultra-sensitivity of nanostructures coupled with ease of processing of micrometer scale features amenable for implementation into devices. In this report, we demonstrate the concept using titanium dioxide (TiO2) as a model material system and a novel fabrication technique. We use a facile technique to integrate NST arrays into microsystems devices by reacting prepatterned Ti surfaces with hydrogen peroxide solution. Other workers had reported aqueous oxidation of Ti powders, unpatterned bulk Ti foils by hydrogen peroxide solution [8,9]. However, these prior works largely focused on biomedical applications and NST layers formed have high crack density that made them unsuitable for device applications. The technique that we have developed eliminates crack formation in micrometer-scale NST pads. In addition, this process has high process yield and is compatible with current manufacturing practices and, hence, is a promising method towards implementing NST as a platform for sen
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