Synthesis of Tin Oxide Thin Films by Pulsed Laser Deposition Using SnO 2 Targets
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Synthesis of Tin Oxide Thin Films by Pulsed Laser Deposition Using SnO2 Targets Yoshiaki Suda, Hiroharu Kawasaki, Kazuya Doi, Jun Nanba Department of Electrical Engineering, Sasebo National College of Technology, Okishin 1-1, Sasebo, Nagasaki, 857-1193, Japan Kenji Wada Department of Chemistry and Biotechnology, Sasebo National College of Technology, Okishin 1-1, Sasebo, Nagasaki, 857-1193, Japan Kenji Ebihara, Tamiko Ohshima Department of Electrical and Computer Engineering, Kumamoto University, Kurokami 2-39-1, Kumamoto, 860-0862, Japan ABSTRACT Tin oxide (SnO2) thin films have been grown on Si (100) and Al2O3 substrates by pulsed Nd:YAG (532nm) and KrF excimer (248 nm) laser deposition methods using SnO2 targets. X-ray diffraction measurement showed that the almost amorphous microstructure transformed into a crystalline SnO2 phase and preferred orientation varied from (101) to (110) on Si (100) with increasing oxygen gas pressure. This result suggests that oxygen gas pressure affects the phase formation, crystalline structure and preferred orientation of the films. Gas sensing properties of SnO2 thin films by PLD method were also investigated over the temperature range 300 – 600°C, using 0.31vol%H2 as a test gas. The oxygen gas pressure results in a notable change in gas sensing properties of SnO2 thin films. INTRODUCTION Tin oxide (SnO2) has long been utilized as a gas sensing material, because it shows an electric conductivity change in contact with flammable gases, e.g. hydro-carbons (CHx), hydrogen (H2), etc and deoxidizable gases, e.g. nitrogen oxide (NOx) etc [1-3]. SnO2 gas sensors have been produced in forms of thick films, ceramics and thin films. Among those, thin film sensor seems to be more promising to improve the sensor performance as well as compatible with semiconductor technology for making small-integrated gas sensors [4]. Therefore, many studies have been reported on SnO2 film gas sensors formed by various techniques such as sputtering [5-12], chemical vapor deposition [13, 14], spray pyrolysis [13, 15] and evaporation [16, 17]. Ogawa et al. showed that spongy films formed by plasma assisted gas evaporation had high gas sensitivity [16]. Miyoshi and Onisawa investigated the structure of sputtered SnO2 films deposited under different pressures and showed that the film density decreased as the pressure increased [18]. But they did not report on the gas sensing properties. Yamamoto et al. showed that sensitivity of the SnO2 films deposited by sputtering method was strongly related to the film crystallinity [19]. They also showed that the high sensitive SnO2 films had the sharp peak of SnO2 (110). Very few papers have been published on SnO2 film gas sensors synthesized by pulsed laser deposition (PLD) method. PLD method has become a widely used technique for the deposition of thin films during the past few years due to the advantages of a simple system setup, a wide ranging deposition conditions, the possibility of using many kinds of materials and a high instantaneous deposition rate. Especially,
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