Electrochemistry in gas phase

ELECTROCHEMICAL GAS SENSING

In both the literature and industry, there are various examples of gas detection devices which use electrochemical sensors, resistive metal oxide based sensors, catalytic or even piezoelectric sensors. The growing interest in these microsensors, for many applications is due to several reasons. Among others, we can cite low production costs aided by the development of microtechnologies. This allows us to reduce the size of components and therefore produce a large number of sensors on one silicon wafer. As such, with the emergence of micro and nano technologies, we are seeing an ever increasing development of miniature, portable and “intelligent” devices integrating sensor(s), its supply, processing electronics and other elements. These are therefore termed as integrated electronic noses.

Producing these new devices involves micro and nano technologies as well as new techniques for integrating new sensing materials which are often nanostructures or even new micro-production or assembly methods. This allows the industry to respond to the needs of the market such as low production costs, the lowest possible energy consumption, good stability, reproducibility, reliability and increased portability for embedded systems or sensor networks.

In our team, to go through in these interests, thanks to our know-how in micro-nanotechnology, gas sensor activities are currently focused on the development of semi-conducting microsensors, with moderate cost and low consumption in order to develop an integrated electronic nose for different applications as environment, health, transport, home automation, agro-industry and/or still defence.

Their realization leans on :

• the development of new technological processes (new materials, new structures, new designs of single and multisensor platforms),
• integration of various sensing materials (semiconductors, metal oxides, spinel oxides, ferrites),
• multiphysical simulations,
• electrical and thermal characterizations
• signal processing with dedicated electronic circuits.

Metal-oxides chemical micro-sensors are still the best candidates to meet this demand at industrial level: they are highly sensitive to many gases, with fast response times, and their production cost could be very low. As it is well known, their main drawback is a lack of selectivity.

Since 2009, our research work has consisted of developing a multi gas sensor array based on conductivity detection on a silicon micromachined chip with different sensitive layers to selectively detect several gases in a mixture.

Most important developments have been focused on :

• Stable microhotplates for high operating temperatures (around 600°C)
• integration process to deposit various sensitive materials. Different technics are investigated (PVD, Inkjet, screen printing) to answer different needs. A flexible method for depositing quickly and at low costs several sensitive layers (ZnO, CuO and SnO₂) on a single cell structure has been developed with industrial inkjet printer. An example of this multi sensor platform is shown in figure 1.

Figure 1:  schematic view of the micro sensor array and its realisation.

In parallel, we proceeded to develop a decision-making system, including two main elements: the development of an optimized working dynamic profile to control heater and sensitive resistors in order to improve stability, sensitivity, and above all selectivity thanks to appropriate data multivariate analysis. Thanks to this approach, it has therefore been possible to selectively detect few “popular” target gases (alone and mixed) at low concentrations (NO₂-0.2ppm, C₂H₄O-2ppm, NH₃-5ppm and CO-100ppm) which is still not possible with actual commercial MEMS gas sensors.

MAIN PROJECTS

Few projects are in progress to use these new integrated electronic noses for different applications. A strong collaboration with chemist laboratories (LCC-CNRS, CIRIMAT) for new sensing materials allows us to meet strong demand in several fields of application with ALPHAMOS and RENAULT for instance. In this frame, a new patent concerning a new multistack structure has been deposited in 2011 and published in December 2012.

Concerning the development of wireless sensor networks, MICA team is involved in two different projects related to two different approaches. The first one consists in using the technology of multisensor array previously described combined with a specific working protocole and data treatment embedded in a micro controller and associated with an RF chip module. In that case, we should optimise all of the different parts (sensor technology, working principle and data acquisition and treatment) to realize a low consumption wireless gas sensor.

The second way is about new transduction principle using radiofrequency (RF) electrical function in order to provide powerless sensors. This new research started in 2007, in collaboration with the LAAS-MINC team. Now these studies are focused on autonomous wireless sensors network. We have therefore proposed a new RF transduction for detecting gas which is based on changing the permittivity of a metal oxide (used as a resonator) by the phenomenon of dielectric relaxation in the presence of gas which therefore causes a shift in frequency at the hyperfrequency filter. The principle of transduction developed is based on modification, by the size being measured, in a resonator’s resonant frequency. Several types of resonators can therefore be imagined: planar resonators in coplanary or microstrip technology or even dielectric resonators. In our case, we have used a sensor as a variable element in a filter where the characteristic frequency is read with as high a quality factor as possible in order to have the best level of sensitivity.

Figure 2: Photos of the first gas sensors with electromagnetic transduction

The demonstrator shown in fig.2 is based on Titanium dioxide dielectric resonator operating with whispering-gallery modes (WGM). Gas vapours adsorption modifies its dielectric permittivity and then the variation of resonant frequencies of high-Q WGM in the millimeter-wave frequency range. After a full wave electromagnetic simulation that demonstrate the transduction principle, we validated experimentally in a first hand, the strong deviation of the resonant frequencies in presence of ethanol and isopropanol vapours, and in a second hand, the possibility to detect these variations with a 3 meters-remote FMCW-Radar and antenna connected to this passive sensor.

Main Publications :

- “Tuning the Bias Sensing Layer: A New Way to Greatly Improve Metal-Oxide Gas Sensors Selectivity” N.DUFOUR, A.CHAPELLE, C.TALHI, F.BLANC, B.FRANC, P.MENINI, K.AGUIR, International Conference on Sensing Technology ( ICST ) 3-5 dec2013, Wellington (New-Zealand),  Rapport LAAS n°13357

- “Wireless sensing and identification based on radar cross section variability measurement of passive electromagnetic sensors”, H.Aubert, F.Chebila, M. M.Jatlaoui, T.T.Thai, H.Hallil, A.Traille, S.Bouaziz, A.Rifai, P.Pons, P.Menini, M.M.Tentzeris, Annals of Telecommunications, Vol.68, N°7-8, pp.425-435, August 2013.

- “3D stationary and temporal electro-thermal simulations of metal oxide gas sensor based on a high temperature and low power consumption micro-heater structure using COMSOL”, N. Dufour, C. Wartelle, P. Menini. International COMSOL Conference 2012, Milan (Italie), 10-12 october 2012,

- "A computational chemist approach to gas sensors: Modeling the response of SnO2 to CO, O2, and H2O Gases”, A. Hemeryck, J.M. Ducéré, A. Estève, M. Djafari Rouhani, G. Landa, C. Tropis, P.Menini, A.Maisonnat , P. Fau and B.Chaudret, Journal of Computational Chemistry ; vol.33 (2012), 247-258, 12p.

- “Benzene monitoring by micro-machined sensors with SnO2 layer obtained using micro-droplet deposition technique”,  B. Ghaddab, F. Berger, J.B. Sanchez, P. Menini, C. Mavon, P. Yoboue, Sensors and Actuators B: Chemical, Volume 152, Issue 1, 20 February 2011, Pages 68-72

- “Performances Of A New Generation Of Metal Oxide Gas Sensor Based On Nanostructured-Sno2 And On High Operating Temperature Microhotplate”, P. Yoboue, Ph. Ménini, C. Tropis, P. Fau, André Maisonnat. European Conference MME, Toulouse (France) September 2009.

- “Feasibility of Passive Gas Sensor based on Whispering Gallery Modes and its RADAR Interrogation: theoretical and experimental investigations”, H. Hallil, F. Chebila, P. Ménini and H. Aubert, Sensors & Transducers Journal, Vol. 116, Issue 5, May 2010, pp. 38-48

-“Manufacturability of gas sensor with ZnO nanoparticles suspension deposited by ink jet printing”,     V. Conedera, P. Yoboue , F. Mesnilgrente, N. Fabre and P. Menini, SPIE2010 MEMS-NEMS, 23-26/01/2010, San Francisco, EU.

- “Improvement Of Micromachined SnO₂ Gas Sensors Selectivity By Optimised Dynamic Temperature Operating Mode”, F. Parret, P. Menini, A. Martinez, K. Soulantica, A. Maisonnat , B. Chaudret. Sensors and Actuators B 118 (2006) 276.

- “CO response of a nanostructured SnO2 Gas sensor doped with palladium and platinum”, P.Menini , F.Parret , M.Guerrero , K.Soulantica , L.Erades , A.Maisonnat , B.Chaudret ,LAAS N°03477, 20p, Sensors and Actuators B: Chemical, Issues 1-2, Vol.103, pp.111-114, sept. 2004

PATENT :

A. Gaudon, F. Loubet, P. Menini, C.H. Shim

Chemoresistor type gas sensor having a multi-storey architecture

patent 11305707.9-2204 -  ALPHA MOS , LAAS-CNRS - 12/12/2012

AWARD :

C. TALHI, F. BLANC, C. GANIBAL, P. MENINI, N. DUFOUR, A. CHAPELLE, "Banc de test de capteurs de gaz innovants au LAAS", Best article in "Instrumentation/Electronic test", NIDAYS 11/02/2014

Contact :

Philippe MENINI