Sensors and Actuators B 115 (2006) 396–402 Inﬂuence of electrodes ageing on the properties of the gas sensors based on SnO 2 Simonetta Capone a , Mauro Epifani a , Luca Francioso a , Saulius Kaciulis b , Alessio Mezzi b , Pietro Siciliano a , Antonella M. Taurino a,∗ a CNR, IMM Lecce, Via Arnesano, 73100 Lecce, Italy b CNR, ISMN Roma, Via Salaria, Km 29,300, C.P. 10, 00016 Monterotondo Stazione, Roma, Italy Received 28 June 2005; accepted 3 October 2005 Available online 3 November 2005 Abstract Undoped and doped microsensors, based on tin oxide, have been prepared by the sol–gel deposition technique. The inﬂuence of the ageing of the Ti/Au interdigitated electrical contacts on the responses of the samples has been investigated. In particular, in this paper, are reported the responses of different sensors towards some gases and vapours, discussing the reproducibility, repeatability and the baseline drift during the measurements. SEM and XPS analyses of the samples were performed before and after the working period. The sensors showed a little drift, probably due to the ageing of the electrical contacts that was observed also in the SEM images. Obtained XPS results are in good agreement with SEM images. © 2005 Elsevier B.V. All rights reserved. Keywords: Drift; Ageing; Interdigitated electrical contacts; XPS; SEM 1. Introduction It is a common knowledge that an important goal for the development of metal oxide based semiconductor gas sensors is to improve their stability and reliability. In fact, the lack of sta- bility and reliability in the responses of these semiconductor gas sensors make prohibitive their use as measuring devices. More- over, when the sensors are used in array conﬁguration for elec- tronic nose application, the lack of stability and reliability of the single sensors deteriorates the performance of the whole device. Great efforts have been made with the aim to determine and improve the parameters that contribute to the electrical conductivity and inﬂuence the electrical response of the sen- sors. Several phenomena can be considered as the causes of instability: the dependence of the sensor conductance on the ambient atmosphere conditions, the changes in the morphology of the sensitive layer (change in size, number and distribution of grains and intergranular boundaries), the change in the electronic properties of the sensing layer, temperature and humidity inﬂu- ence, irreversible reaction with chemical species in the ambient, ∗ Corresponding author. Tel.: +39 0832 422509; fax: +39 0832 422552. E-mail address: antonella.taurino@le.imm.cnr.it (A.M. Taurino). modiﬁcation of sensor heating element, modiﬁcation of the elec- trodes. All these factors can lead to the ageing and drift of the sensors and consequently to the performance variable during the time [1,2]. The time-dependent behaviour of semiconductor gas sensors can be classiﬁed into three time domains: (i) the rise time of the sensors after a sudden concentration change; (ii) the short- term drift after switching on; (iii) the long-term drift. It is quite plausible that the shortest time constant is correlated with the gas detection process of the semiconductor gas sensor: the reaching of the equilibrium state of oxygen content at the sensing layer under the inﬂuence of a gas. The short-term drift is correlated with a relaxation process in the material after the heating up. The long-term drift is correlated with materials degradation and as a consequence the deterioration of some components of the device after a certain pre-ageing period [3]. Thus, in order to improve the sensors stability and the relia- bility each time domain has to be studied and all the factors that can inﬂuence the behaviour of the sensors should be considered. In fact, concerning the dependence of the conductance from the ambient atmosphere, there have been made many attempts to ﬁnd methods to calibrate the sensors, usually based on empir- ical observation depending on the particular sensing layer and gasses involved in the detection process [4]. Moreover, by pre- 0925-4005/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2005.10.001