Coupling nanowire chemiresistors with MEMS microhotplate gas sensing platforms

Abstract

Recent advances in nanotechnology have yielded materials and structures that offer great potential for improving the sensitivity, selectivity, stability, and speed of next-generation chemical gas sensors. To fabricate practical devices, the "bottom-up" approach of producing nanoscale sensing elements must be integrated with the "top-down" methodology currently dominating microtechnology. In this letter, the authors illustrate this approach by coupling a single-crystal SnO 2 nanowire sensing element with a microhotplate gas sensor platform. The sensing results obtained using this prototype sensor demonstrate encouraging performance aspects including reduced operating temperature, reduced power consumption, good stability, and enhanced sensitivity.

Copper (II) oxide nanowires for p-type conductometric NH3 sensing

“…In our case, the α value is higher than the obtained with individual SnO 2 nanowires with diameter about 100 nm obtained following an equivalent procedure (α ≈ 0.07) [17]. SnO 2 devices fabricated with alternative methodologies showed different α values highlighting the strong influence in this parameter of changes in the device processing [33].…”

“…Previous works on individual SnO 2 nanowires demonstrated that the relationship given in eq.9 is followed by very similar device configurations and gas measurements [33]. In practise, α is a parameter dependent on the experimental conditions and the intrinsic properties of the metal oxide, such as the material quality and the diameter in the case of nanowires [28][29][30].…”

“…In practise, α is a parameter dependent on the experimental conditions and the intrinsic properties of the metal oxide, such as the material quality and the diameter in the case of nanowires [28][29][30]. From the validity of this model in individual nanowires three conclusions are implied [26,33]: (i) the resistance change induced by the analyte is ascribable to the width modulation of the conduction channel due to the formation of a depleted region beside the surface, (ii) the ionosorbed oxygen at the metal oxide plays a key role in the sensing mechanism, and (iii) the concentration of the tested analyte is significant lower that the total oxygen species at the surface. Three devices followed the power law reported in eq.9 (inset of Fig.5a), with the exponent close to α ≈ 0.4.…”

Metal Oxide-Based Nanostructures

“…It was established that Joule self-heating of NWs operated under a passing electric current can be applied for NW-based gas sensors. Meier et al ( 2007a, b ) and Hernandez-Ramirez et al ( 2007a, b ) have shown that sensors based on individual NWs with selfheating can be fabricated with power consumption of only a few tens of microwatts, much less than that required for thin-fi lm sensors mounted on microhotplates, which usually require milliwatts to work in continuous mode. Moreover, Prades et al ( 2008 ) have demonstrated that the response of the sensors to 0.5 ppm NO 2 without a heater ( I m = 10 nA) was the absolute equivalent to that with a heater ( T = 175 °C) (see Fig.…”

Microstructural Control of Mesoporous SnO2 Powders and Their H2 Sensing Properties

“…(2) Among various sensor materials, SnO 2 is an ideal and important material for semiconductor-type gas sensors. (3) Therefore, various types of nanostructured SnO 2 such as nanoparticles, (4) nanowires, (4,6,7) nanobelts (4) and nanorods (4,8) have been prepared as gas-sensor materials by a general sol-gel technique, (9,10) a hydrothermal or solvothermal method, (9) or some physical vapor deposition methods (11,12) because they have provided a promising way towards miniaturized ultrasensitive gas sensors. (9) Recently, mesoporous SnO 2 (m-SnO 2 ) powder has also been prepared by employing the self-assembly of n-cetylpyridinium chroride as a template and Na 2 SnO 3 as a tin source, and thermal stabilizing by a treatment in an aqueous phosphoric acid solution.…”