Effect of thickness of thin film SnO 2 based LPG sensors
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Effect of thickness of thin film SnO2 based LPG sensors
Divya Haridas1,2, K. Sreenivas1 and Vinay Gupta1 1 Dept. of Physics and Astrophysics,University of Delhi, Delhi, India 2 Keshav Mahavidyalaya, Pitampura, University of Delhi, India
ABSTRACT This paper reports the response characteristics of rf-sputtered SnO2 thin films (of varying thickness) for LPG detection. To monitor and precisely measure leakages, the development of a reliable LPG sensor with improved sensitivity is crucial in preventing fatal accidents. In the present study, thin film of SnO2 is used as the sensing element for LPG sensor. The thickness of a thin film is a very important parameter and determines their main operating characteristics, such as sensor response, rate of response, and working temperature. In the present study, thickness of SnO2 film is varied between 30 nm to 180 nm. The structure, composition and optical properties of SnO2 thin films have been examined by XRD, SEM, AFM and UV-Vis. The crystallite size for 90 nm thin film (for (110) plane) is found to be the smallest ~4-5 nm. Sensor ⎛ Ra − Rg ⎞ ⎟⎟ × 100%) increases with thickness of the sensing film, with a highest response ( S = ⎜⎜ ⎝ Ra ⎠ sensor response (~67%) observed for 90 nm thin film and thereafter it decreases. The structural and optical properties clearly support the observed enhanced sensor response for 90 nm thin film. INTRODUCTION Environmental pollution and accidental leakages of explosive gases have become a great cause of concern. The usage of liquefied petroleum gas (LPG) as cooking gas has extensively increased in the domestic and industrial sites and thus accidental explosion due to its leakages has sharply increased. Therefore it is highly desirable to develop an efficient LPG sensor. Initially sintered ceramics [1] have been used as gas sensing materials but later semiconducting metal oxide thin films has attracted a lot of attention because they possess high surface to volume ratio, which helps in enhancing the sensor response towards any gas as gas sensing is a surface phenomenon. Among a variety of semiconducting metal oxides, tin oxide (SnO2) is the most preferred material for gas sensor application because of its enhanced ability to adsorb oxygen on its surface. Structure of the sensing SnO2 material is one of the main factors in determining the gas sensing properties. In particular, the size of crystallites forming the gas sensitive layer determines both the absolute gas sensitivity and the signal stability during gas exposure [1,2]. As a result till now, the nature of a large number of effects, experimentally observed in thin film gas sensors, are slowly becoming understood. Still most of the research is focused on using gas sensors of single thickness and thereby neglecting the effect of thickness of the sensing material on the sensing response [3]. Very few attempts have been made in analyzing the influence of film thickness on sensing performance [4]. In the present article we will try to analyze the
influence of the film thickness on the gas se
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