Printed semiconducting gas sensors

Whilst printed films are currently used in varied devices across a wide range of fields, research into their development and properties is increasingly uncovering even greater potential. Printed films provides comprehensive coverage of the most significant recent developments in printed films and their applications. Materials and properties of printed films are the focus of part one, beginning with a review of the concepts, technologies and materials involved in their production and use. Printed films as electrical components and silicon metallization for solar cells are discussed, as are conduction mechanisms in printed film resistors, and thick films in packaging and microelectronics. Part two goes on to review the varied applications of printed films in devices. Printed resistive sensors are considered, as is the role of printed films in capacitive, piezoelectric and pyroelectric sensors, mechanical micro-systems and gas sensors. The applications of printed films in biosensors, actuators, heater elements, varistors and polymer solar cells are then explored, followed by a review of screen printing for the fabrication of solid oxide fuel cells, and laser printed micro- and meso-scale power generating devices

THE ROLE OF NANOSTRUCTURE IN GAS SENSING

This work aimed to analyze the role of nanostructure in gas sensing. For this purpose, as functional material, a TixSn1-xO2 system has been chosen because of the wide difference in grain dimension obtained by varying the stoichiometry (0.1<x<0.9) of the synthesised powders. The role of nanostructured grains has been investigated both for large specific surface offered and for the influence in reducing the surface charge density; a special model in this respect has been reviewed, discussing about the characteristic length below which a material can be properly considered as nanostructure

AC measurements and modeling of WO3 thick film gas sensors

PolycrystallineWO3 films were fabricated through thick film technology. Stimulated temperature measurements showed that the intergranular Schottky barrier is not high enough to apply the depletion approximation to evaluate the fundamental parameters related to the sensing properties. Therefore, a semi-analytical approach to the Poisson’s equation with the complete charge density was chosen. As a result, we could estimate the dependence on frequency of both apparent permittivity and depletion region width by impedance spectroscopy

Monitoring of ethylene for agro-alimentary applications and compensation of humidity effects

We used SnO2 gas sensors for monitoring ethylene in the range of interest for fruit ripening. The effect of atmospheric humidity on the sensor conductance and response towards ethylene was quantitatively measured. An algorithm for humidity compensation of the sensor’s response was developed and applied to experimental data. The results of our analysis proved useful for the application of chemoresistive sensors for agro-alimentary monitoring

(Ti,Sn)O2 Nanopowders: Functional Properties for Gas Sensing

Great attention has been recently given to mixed metal oxides and solid solutions being promising candidates for gas sensing devices due the superior performances showed in comparison of their single-oxides counterparts [1]. This work focuses on the synthesis and the characterisation of TixSn1-xO2 (0.1 < x < 0.9, step 0.2) n-type semiconductor nanopowders and their sintered thick films. All materials were obtained via Symplectic Gel Coprecipitation (SGC) of stoichiometric Sn(4+) and Ti(4+) hydroalcoholic solutions and further calcination of the resulting xerogels. Calcination was performed at 550, 650, 850 or 1050°C, while the sintering of the film was carried out at 650, 750 or 850°C for 1h. Both type of thermal treatment were done under air flow conditions. The authors attempted to join advantages of SnO2, i.e. high sensitivity, and TiO2, i.e. gas response less affected by humidity than SnO2, and, possibly, to dump their disadvantages, i.e. poor selectivity for SnO2 , high resistivity and exaggerated grain growth for TiO2

Comparison between titania thick films obtained through sol-gel and hydrotermal synthetic processes

Titania films were obtained through two synthetic processes, a traditional sol\u2013gel method and a hydrothermal route. In SG synthesis, thermal decomposition of the precursor in oven at 400 \ub0C for 2 h led to pure anatase TiO2; in HY synthesis, instead, crystalline anatase grains were obtained in autoclave at 200 \ub0C for 1 h. To investigate the microstructural evolution of SG and HY titania with temperature, each powder was annealed at 650, 750, 850 \ub0C for 1 h and subjected to XRD analysis. Surprisingly, HY titania, contrary to SG, maintained the anatase phase, up to 850 \ub0C, without any introduction of foreign elements. The sensing layers, obtained from as grown powders, were fired at 650, 750 or 850 \ub0C and tested vs. methane and carbon monoxide. Both types of films fired at 850 \ub0C yield insignificant responses to both CO and CH4, demonstrating the lack of influence of the crystalline phase on the gas response. Moreover, as regards the films fired at 650 and 750 \ub0C, the gas responses are higher for SG than for HY samples, despite larger particle size

Semiconductor gas sensors for environmental monitoring

Atmospheric pollution is still a topical problem in most European cities; it injures human health and greatly damages monuments and historical buildings. Atmospheric pollution control is today performed by means of traditional analytical techniques, which are expensive and require cumbersome devices. Thereby, low cost, portable and versatile equipment is an issue. Recently developments in the European legislation have caused a general change in the management of air quality assessment, making proposable the use of reliable solid state gas sensors. This work aims to analyze the most important semiconductor oxides for gas sensing. Aspects, such as the role of nanostructures to improve gas sensor performance, addition of catalysts and/or dopants to obtain a better selectivity, theoretical models to justify the size-dependent behaviour of the gas response of nanocrystalline oxides will be described. Array of these sensors, assembled in small remotely controlled monitoring units, have been used for on-field tests. The results of a long term field trial, performed locating several units closely to conventional monitoring stations, will be reported, as well as the experiments aimed to evaluate the concentrations of the same pollutants at different heights. These experiments are crucial to investigate air quality inside buildings, since the pollution of the outdoor air is one of the main factors affecting the indoor atmosphere