Available online at www.sciencedirect.com Sensors and Actuators B 132 (2008) 568–575 Integrated interface circuit with multiplexed input and digital output for a 5 × 5 SnO 2 thick film gas-sensor matrix M. Grassi a,∗ , P. Malcovati a , L. Francioso b , P. Siciliano b , A. Baschirotto c a Department of Electrical Engineering, University of Pavia, via Ferrata, 27100 Pavia, Italy b CNR-IMM Institute for Microelectronics and Microsystems, via Monteroni,73100 Lecce, Italy c Department of Physics, University of Milano-Bicocca, Piazza della Scienza, 20126 Milano, Italy Available online 4 December 2007 Abstract This paper presents the design and experimental results for a 5 × 5 tin-oxide gas-sensor array system with particular focus on the employed multiplexed-analog-input 0.35 m CMOS interface circuit chip. This interface circuit reads the electrical signal of all the elements of the array in time sharing by means of a solid-state selector, actually exploiting a row-column query technique and provides digital output to a dedicated LabView TM Software. The proposed system shows very promising properties in terms of data redundancy in order to improve the signal-to-noise- ratio in electronic nosing and for future studies about the influence of gas consumption rate over the metal oxide surface for a 2D array. Sensors fabrication details, electronic interface performance characterization and chemical measurements results are also reported for completeness. © 2007 Elsevier B.V. All rights reserved. Keywords: Metal oxide sensor array; Micro-fabrication technology; Integrated interface; ASIC 1. Introduction Micro-fabricated gas sensors arrays are employed in several applications, like environmental and air-quality monitoring or homeland safety and industrial control. Recently, especially in view of worldwide legislative initiatives aimed to the reduc- tion of pollution and of exposure to dangerous gases, portable systems for gas sensing are becoming quite important and both manufacturers and research consortia [1] are pushing in the direction of stressing the performance (especially in terms of dynamic range for exploiting novel gas recognition algo- rithms), minimizing size, power consumption and cost of the systems. Metal oxide-based (SnO 2 , WO 3 , In 2 O 3 , etc.) gas sensors operating principle is related with chemiadsorption and charge transfer processes between the gas molecules and the MOX film, which causes a simple electrical resistance variation of the gas sensing element. Therefore, they are characterized by a real resistive electrical behavior [2,3]. ∗ Corresponding author. Tel.: +39 0382 985226. E-mail address: marco.grassi@unipv.it (M. Grassi). This paper presents design and experimental characterization of a 5 × 5 tin-oxide gas-sensor array system, including fabrica- tion, metal oxide sensitive film deposition, and design of the experimental setup required to read-out a large number of sen- sors [4]. The development of the transducers with the electrical interconnections necessary to address the considered number of sensors has been carried out with a strong interaction with the design of the read-out circuitry. One main task, in order to achieve a successful integration of a large number of sensor spots on the transducing platform, is the production and integration of many identical devices. At present, the expertise, available within authors’ institutions, allows a selective deposition of spe- cific thick sensitive films deposited on standard dielectric layers, such as silicon dioxide or silicon nitride. Eventually an investigation about the compatibility of etching processes with the electrical connections deposition step will be needed as well. The 2D MOX array used in this work, involves a5 × 5 complete metal oxide sensor array with an integrate heater/thermometer on the backside, and a row-column reading layout, as depicted in Fig. 1. This structure allows experimental investigation about interplay between diffusion and consump- tion rates over a two-dimensional array of metal oxides gas sensors as well as the verification of the high-dynamic-range 0925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2007.11.045