Carbon nanotube gas sensor array for multiplex analyte discrimination

The lack of selectivity toward a particular analyte has always been the primary concern regarding CNT-based gas sensors. For that reason, in here we present a gas discrimination strategy that focuses on the electrode-CNT junction. The junction is shown to play a key role in the sensing mechanism. Resistive gas sensors based on horizontal CNT arrays have been fabricated using various designs and different top-contacting metals: Pt, Pd and Au. Arrays of devices have been exposed to a series of gases to monitor their resistive response. It was found for our system that the sensor response does not significantly change as a function of the device design or the available CNT sensing area in between the anchoring electrodes. On the contrary, responses to gases are observed to be specific to each sensor electrode metal. Exposure of locally passivated devices (for which distinct areas have been covered) to NO2, H-2 and NH3 highlights different sensing mechanisms for each gas. Multiplex gas discrimination for room temperature can be achieved by strategically choosing the right metal/CNT combination in a complete sensor system. (C) 2014 Elsevier B.V. All rights reserved

High-yield, in-situ fabrication and integration of horizontal carbon nanotube arrays at the wafer scale for robust ammonia sensors

This paper reports the successful experimental demonstration of the localized growth of horizontal, dense carbon nanotube (CNT) arrays in situ and at the wafer scale. The selectivity and directionality of the CNT catalytic growth process along with the adequate design and fabrication of the catalyst support enables the direct integration of nanotubes arrays into heterogeneous devices. This novel CNT integration method is developed to manufacture conductance based gas sensors for ammonia detection and is demonstrated to produce a yield above 90% at the wafer scale. Owing to its flexibility, the integration process can be useful for a wide range of applications and complies with industrial requirements in terms of manufacturability and yield, requirements for the acceptance of CNTs as alternate materials. A state-of-the-art CNT array resistivity of 1.75 x 10(-5) m has been found from the CNT characterization. When exposed to low NH3 concentrations, the CNT sensors show good repeatability, long-term stability, and high design robustness and tackle the reproducibility challenge for CNT devices. Individual device calibration is not needed. The ammonia adsorption isotherm on the sensor is well fitted by Freundlich equation. The extrapolated detection limit is about 1 ppm. The dependence of the sensitivity with temperature indicates that ammonia sensing is likely to involve an endothermic process. Finally, relative humidity cross sensitivity has been found to have no adverse effect on the ammonia response enabling NH3 monitoring in ambient conditions. (C) 2014 Elsevier Ltd. All rights reserved

Tunable MEMS capacitors using vertical carbon nanotube arrays grown on metal lines

In this work, tunable MEMS capacitors are realized using a vertically grown carbon nanotube array. The vertical CNT array forms an effective CNT membrane, which can be electrostatically actuated like the conventional metal plates used in MEMS capacitors. The CNT membrane is grown on titanium nitride metal lines, with a Al/Fe bi-layer as buffer layer and catalyst material respectively, using chemical vapor deposition process. Two different anchor configurations are investigated. A maximum capacitance of 400 fF and maximum tunability of 5.8% is extracted from the S-parameter measurements. Using the tunable MEMS vertical array capacitor a voltage controlled oscillator (VCO) is demonstrated showing promise for integrating CNTs for communications applications