17th International Meeting on Chemical Sensors - IMCS 2018 560 Tin Oxide Gas Sensor on Tin Oxide Microheater for Methane Sensing Maryam Moalaghi 1 , Mohsen Gharesi 1 , Alireza Ranjkesh 1 1 Electronic Materials Laboratory, Electrical Engineering Department, K.N. Toosi University of Technology, Tehran, 16317-14191, Iran. mohsengharesi@email.kntu.ac.ir Abstract: Despite the ever increasing demand for methane detection in residential and industrial locations, the common tin oxide-based methane sensors fail to satisfy the quality requirements for long-term operation in harsh environs. Particularly, the RuO2 microheaters utilized in these sensors deteriorate in reducing atmospheres and cannot provide the high temperatures required for methane detection in a long-time period. Here, we disclose a tin oxide gas sensor complete on a tin oxide microheater which can stably operate at temperatures as high as 850 °C. Both components are produced by ultrasonic spray pyrolysis of tin chloride solution on alternative sites of an alumina chip. Thermally stable electrical contacts are formed by diffusion bonding of gold wire segments onto the SnO2 films. The response of the fabricated sensor to different methane concentrations is examined at operation temperatures in the 500-850 °C range. The device can detect 50 ppm of methane in normal atmosphere with a response time of 10 s, demonstrating suitability of the introduced sensor for online leakage detection applications. Key words: Gas sensor, Microheater, Tin oxide, Spray pyrolysis, Electrical contact. Introduction The explosive nature of methane and its global warming issues have made detecting natural gas leakages important. Among the available leakage detection technologies, online leakage monitoring by chemoresistive gas sensors (CGSs) is advantageous as it provides a facile and economical route to safety. However, providing a stable means of supplying the elevated temperatures required for methane sensing is yet a technological challenge. RuO2 microheaters commonly utilized in the CGS structures are susceptible to reducing atmospheres and their long-term operating temperature is limited to 400 °C [1, 2]. On the contrary, SnO2 microheaters operate durably at temperatures as high as 900 °C [1, 3]. SnO2 is also the base material of gas sensitive elements and its employment as microheater material reduces the total production costs. Here, a CGS is introduced in which both the sensing element and the microheater are SnO2 films produced by ultrasonic spray pyrolysis (USP) deposition. The films’ microstructure and thickness are engineered so that the sensing element resistively responds to the composition of the surrounding atmosphere while the microheater is insensitive to that. Experimental The USP system utilized for tin oxide deposition was described elsewhere [1]. The sensing element is composed of SnO2 nanoparticles produced by 1-minute spraying of a 0.05 M ethanolic solution of SnCl2.2H2O on an alumina chip heated to 320 °C. The heating element is a 10 μm thick tin oxide layer USP-deposited at 420 °C on the backside of the alumina substrate using a 0.2 M solution of the same precursor [1]. The sample is then annealed at 900 °C in air for 1 h to stabilize the deposits. Electrical contacts to both the sensing element and the microheater are formed by diffusion bonding of gold wire segments to the SnO2 films. The method has been proved to provide ohmic electrical contacts with fine thermal and mechanical stabilities [3]. Photograph and SEM images of a sample sensor are given in Fig. 1. Results and Discussion The sensor resistance reduces in reaction to the presence of methane gas in the surrounding atmosphere. The sensor response, defined as DOI 10.5162/IMCS2018/P1GS.22